2020-10-25T19:51:02Zhttp://edoc.mpg.de/ac_p_oai.ploai:edoc.mpg.de:137352005-11-0719:91
Abstraction based supervisory controller synthesis for high order monotone continuous systems
Moor, T.
Raisch, J.
Abstraction based approaches to hybrid control systems synthesis have so far been mostly limited to problems with low- order linear continuous dynamics. In this paper, results from the theory of monotone dynamical systems are used to efficiently compute discrete abstractions for a class of nonlinear models. Furthermore, a situation is investigated where the high-dimensional plant state converges to a low- dimensional manifold; in the proposed approach the computational effort is governed by the dimension of the low- order manifold without neglecting the high-order dynamics. Results are applied to synthesize a discrete event controller for the automatic start-up of a nonlinear distillation column model of order 42.
Springer-Verlag Berlin
2002
InBook
http://edoc.mpg.de/13735
urn:ISSN:0170-8643
Modelling, analysis, and design of hybrid systems, 247-265 (2002)
en
oai:edoc.mpg.de:137362003-08-1419:92
Application of gradients in the simulated moving bed process
Antos, D.
Seidel-Morgenstern, A.
simulated moving bed chromatography; step gradients
In the last decade the simulated moving bed (SMB) process was implemented successfully in the pharmaceutical industry to perform difficult separations of valued added products. Mainly liquid solvent mixtures with adjusted but constant composition were applied as the mobile phases (isocratic operation). Only recently the potential of modulating the solvent strength during the process was realised (gradient operation). The purpose of this paper is to present the results of studying a two-step gradient SMB process using a weaker solvent to introduce the feed and a stronger solvent for efficient adsorbent regeneration. A mathematical model for the simulation of this process was proposed and solved numerically. Systematic calculations were performed in order to identify suitable operating conditions as a function of averaged desorbent concentrations taking into account the locally changing nonlinear adsorption equilibria. Based on the predictions and on preliminary experimental investigations devoted to determine the required model parameters the separation of a mixture of two cycloketons using normal-phase silica was designed. A two- step gradient SMB process was applied using pure n-hexane as the weak solvent in the feed stream and pure ethyl acetate as the strong solvent in the desorbent stream. The achieved purities and concentrations in the raffinate and extract streams confirmed the potential of the gradient technique applied. In agreement with the theoretical results a significant improvement in the process performance compared to the common isocratic SMB separation was found. (C) 2001 Elsevier Science Ltd. All rights reserved.
2001
Article
http://edoc.mpg.de/13736
urn:ISSN:0009-2509
Chemical Engineering Science, v.56, 6667-6682 (2001)
en
oai:edoc.mpg.de:137372004-03-1719:90
Current status of and recent developments in the direct methanol fuel cell
Schultz, T.
Zhou, S.
Sundmacher, K.
The direct methanol fuel cell (DMFC) has been discussed recently as an interesting option for a fuel-cell-based mobile power supply system in the power range from a few watts to several hundred kilowatts. In contrast to the favoured hydrogen-fed fuel cell systems (e.g. the polymer electrolyte membrane fuel cell, PEMFC), the DMFC has some significant advantages. It uses a fuel which is, compared to hydrogen, easy to handle and to distribute. It also comprises a fairly simple system design compared to systems utilising liquid fuels (like methanol) to produce hydrogen from them by steam reforming or partial oxidation to filially feed a standard PEMFC. Nevertheless. many severe problems still exist for the DMFC, hindering its competitiveness as an option to hydrogen-fed fuel cells. This work reviews the major research activities concerned with the DMFC by highlighting the problems (slow kinetics of the anodic methanol oxidation, methanol permeation through the membrane, carbon dioxide evolution at the anode) and their possible solutions. Special attention is devoted to the steady state and dynamic simulation of these fuel cell systems.
2001
Article
http://edoc.mpg.de/13737
urn:ISSN:0930-7516
Chemical Engineering & Technology, v.24, 1223-1233 (2001)
en
oai:edoc.mpg.de:137382004-03-1719:91
Discrete supervisory control of hybrid systems based on l- complete approximations
Moor, T.
Raisch, J.
O'Young, S.
hybrid systems; supervisory control; behavioral approach; l- complete approximations
The topic of this paper is the synthesis of discrete supervisory control for hybrid systems Sigma with discrete external signals. Such systems are in general neither l- complete nor can they be represented by finite state machines. Our solution to the control problem is as follows: we find the strongest l-complete approximation (abstraction) Sigma (l) for Sigma, represent it by a finite state machine, and investigate the control problem for the approximation. If a solution exists on the approximation level, we synthesize the maximally permissive supervisor for Sigma (l). We show that it also solves the control problem for the underlying hybrid system Sigma. If no solution exists, approximation accuracy can be increased by computing the strongest k-complete abstraction Sigma (k), k > l. The basic ideas regarding the approximation step are explained within the framework of Willems' behavioral systems theory. Implementation issues are treated in a state space framework, and the main results are interpreted from a traditional control engineering point of view.
2002
Article
http://edoc.mpg.de/13738
urn:ISSN:0924-6703
Discrete Event Dynamic Systems-Theory and Applications, v.12, 83-107 (2002)
en
oai:edoc.mpg.de:137392012-03-2919:90
Residue curve maps for reactive distillation systems with liquid-phase splitting
Qi, Z. W.
Kolah, A.
Sundmacher, K.
residue curves; reaction kinetics; phase splitting; reactive distillation; bifurcation analysis; reactive azeotrope
A model has been developed to study the effects of chemical kinetics on the residue curve maps (RCM) for reactive distillation systems with liquid phase splitting. In the model, chemical reaction can occur in both or only one of the two liquid phases. The heating policy V/V-0 = H/H-0 is applied so that the kinetic effect can be described by a single parameter, the Damkohler number Da. The effects of reaction kinetics on pseudohomogeneous and heterogeneous mixtures have been compared. The properties of their RCMs are the same outside, but are fully different inside the liquid-liquid (L-L) region if they have different chemical equilibrium curves. Inside the L-L region, the chemical equilibrium curve coincides to a unique reactive liquid-liquid tie line in case that the pseudohomogeneous chemical equilibrium curve intersects with the L-L envelope. When the reaction occurs in only one of the two liquid phases, the residue curves inside the L-L region are strongly affected by the L-L. envelope, especially at high Da. In the present paper, first an illustrative arbitrary reaction system, and then the reaction of cyclohexene with water to cyclohexanol are analysed with respect to their RCMs. (C) 2002 Elsevier Science Ltd. All rights reserved.
2002
Article
http://edoc.mpg.de/13739
Chemical Engineering Science, v.57, 163-178 (2002)
en
oai:edoc.mpg.de:137432004-03-1819:92
Two-step solvent gradients in simulated moving bed chromatography - Numerical study for linear equilibria
Antos, D.
Seidel-Morgenstern, A.
gradient elution; simulated moving bed chromatography; true moving beds; adsorption isotherms; mathematical modelling
The application of gradients in simulated moving bed (SMB) chromatography has recently attracted interest as a method for further improving the performance of this continuous separation process. One possible implementation of gradients consists in setting the solvent strength in the desorbent stream higher than that in the feed stream. As a result, the components to be separated are more retained in the zones upstream of the feed position and more easily eluted in the zones downstream of the feed position. If a liquid mobile phase is used, gradients can be created by, dosing different solvents into the feed and desorbent ports. In a closed-loop gradient SMB arrangement the solvent strength within the unit will depend on the two feed compositions and on the characteristic flow-rates of the process. In this work an equilibrium stage model describing a true moving bed process is used to analyze, numerically the main features of a two-step gradient SMB process. The adsorption isotherms are assumed to be always linear under isocratic conditions. The relevant Henry constants depend in a nonlinear manner on the composition of the solvent. Based on numerical simulations the impact of the two inlet solvent compositions is demonstrated in terms of the size and shape of regions of applicable flow-rates. Different strategies of designing the process are discussed and compared with respect to maximizing productivities and minimizing desorbent requirements. (C) 2002 Elsevier Science BV All rights reserved.
2002
Article
http://edoc.mpg.de/13743
urn:ISSN:0021-9673
Journal of Chromatography A, v.944, 77-91 (2002)
en
oai:edoc.mpg.de:137472004-03-1719:92
Impact of adsorption isotherm parameters on the performances of enantioseparation using simulated moving bed chromatography
Kaspereit, M.
Jandera, P.
Skavrada, M.
Seidel-Morgenstern, A.
adsorption isotherms; enantiomer separation; simulated moving bed chromatography; preparative chromatography; mandelic acid
Often there are several chromatographic systems, i.e., combinations of mobile and stationary phases, available to solve a certain separation problem. Essential differences of these chromatographic systems are the separation factors and the efficiencies. For preparative applications in addition also the column saturation capacities and solubility limits are of importance. The impact of all these parameters appears to be rather well understood for conventional overloaded elution chromatography using a single column. In the last years the continuous simulated moving bed (SMB) process was increasingly used as a powerful alternative to batch elution since increased productivities and reduced solvent consumptions could be realised. However, the selection of suitable chromatographic systems is more, sophisticated for this process. In this paper five different chromatographic systems capable of separating the enantiomers of mandelic acid are compared based on the achievable productivities using SMB chromatography. For these five systems the adsorption isotherms have been determined experimentally. Subsequently, an analysis of the SMB process was performed numerically using a well-established model. (C) 2002 Elsevier Science B.V. All rights reserved.
2002
Article
http://edoc.mpg.de/13747
urn:ISSN:0021-9673
Journal of Chromatography A, v.944, 249-262 (2002)
en
oai:edoc.mpg.de:137492004-03-1719:94
Calculability analysis in underdetermined metabolic networks illustrated by a model of the central metabolism in purple nonsulfur bacteria
Klamt, S.
Schuster, S.
Gilles, E. D.
metabolic flux analysis; metabolite balancing; calculability; observability; underdetermined systems; stoichiometric analysis; purple nonsulfur bacteria; photosynthetic bacteria
Metabolite balancing has turned out to be a powerful computational tool in metabolic engineering. However, the linear equation systems occurring in this analysis are often underdetermined. If it is difficult or impossible to find the missing constraints, it is nevertheless feasible in some cases to determine the values of a subset of the unknown rates. Here, a procedure for finding out which reaction rates can be uniquely calculated in underdetermined metabolic networks and computing these rates is given. The method is based on the null space to the stoichiometry matrix corresponding to the reactions with unknown rates. It is shown that this method is considerably easier to handle than an algorithm given previously (Van der Heijden et al, 1994a). Furthermore, a useful elementary representation of the null space is presented which is closely related with the elementary flux modes. This unique representation is central to a more general approach to observability/calculability analysis. In particular, it allows one to find, in an easy way, those sets of measurable rates that enable a calculation of a certain unknown rate. Besides, rates which are never calculable by metabolite balancing may be easily detected by this method. The applicability of these methods is illustrated by a model of the central metabolism in purple nonsulfur bacteria. The photoheterotrophic growth of these representatives of anoxygenic photosynthetic bacteria is stoichiometrically analyzed. Interesting metabolic constraints caused by the necessary balancing of NAD(P)H can be detected in a highly underdetermined system. This is, to our knowledge, the first application of stoichiometric analysis to the metabolic network in this bacteria group using metabolite balancing techniques. A new software tool, the FluxAnalyzer, is introduced. It allows quantitative and structural analysis of metabolic networks in a graphical user interface. (C) 2002 John Wiley Sons, Inc.
2002
Article
http://edoc.mpg.de/13749
urn:ISSN:0006-3592
Biotechnology and Bioengineering, v.77, 734-751 (2002)
en
oai:edoc.mpg.de:137502004-03-1719:92
Binary and ternary phase diagrams of two enantiomers in solvent systems
Lorenz, H.
Seidel-Morgenstern, A.
phase diagram; DSC; solubility; enantiomers; mandelic acid
The binary phase diagram of the mandelic acid enantiomers and the binary and ternary phase diagrams of the same enantiomer(s) and water are studied as a typical enantiomeric system. The results of the experimental work performed are presented in detail and discussed both with regard to the applicability of different methods for solubility measurement and their importance for crystallization based enantioseparation. It will be shown that, in addition to classical methods differential scanning calorimetry (DSC) can be applied successfully for solubility determination. From the obtained phase diagram various possibilities of gaining pure mandelic acid enantiomers from aqueous solutions are derived. The particular role of the eutectic composition in the enantiomeric system is emphasized. (C) 2002 Elsevier Science B.V. All rights reserved.
2002
Article
http://edoc.mpg.de/13750
urn:ISSN:0040-6031
Thermochimica Acta, v.382, 129-142 (2002)
en
oai:edoc.mpg.de:137512004-02-2719:94
The organization of metabolic reaction networks - II. Signal processing in hierarchical structured functional units
Kremling, A.
Gilles, E. D.
Based on the analysis of molecular interactions of proteins with DNA binding sites, a new approach to developing mathematical models describing gene expression is introduced. Detection of hierarchical structures in metabolic networks can be used to decompose complex reaction schemes. This will be achieved by assigning each regulator protein to one level in the hierarchy. Signals are then transduced from the top level to the lower level, but not vice versa. The method is shown by a simple example with two interacting proteins. A comparison of simulation results shows good agreement between a model taking all interactions into account and a model developed with the new approach. Finally, the method is applied to the crpA modulon in Escherichia coli, which controls uptake and metabolism for a number of carbohydrates. Here, RNA polymerase represents the top level, CrpA the second level, and the lactose-specific repressor LacI the lowest level, respectively. Besides the lactose operon, the method is applied to the adenylate cyclase gene and the gene for the regulator CrpA. (C) 2001 Academic Press.
2001
Article
http://edoc.mpg.de/13751
urn:ISSN:1096-7176
Metabolic Engineering, v.3, 138-150 (2001)
en
oai:edoc.mpg.de:137532004-02-0919:94
The organization of metabolic reaction networks. III. Application for diauxic growth on glucose and lactose
Kremling, A.
Bettenbrock, K.
Laube, B.
Jahreis, K.
Lengeler, J. W.
Gilles, E. D.
A mathematical model to describe carbon catabolite repression in Escherichia coli is developed and in part validated. The model is aggregated from two functional units describing glucose and lactose transport and degradation. Both units are members of the erp modulon and are under control of a global signal transduction system which calculates the signals that turn on or off gene expression for the specific enzymes. Using isogenic mutant strains, our model is validated by a set of experiments. In these experiments, substrate composition of the preculture and of the experimental culture are varied in order to stimulate the system in different ways. With the obtained measurements (three states in the liquid phase and one intracellular component) a part of the model parameters could be estimated. Therefore all experiments could be sufficiently described with a single set of parameters. (C) 2001 Academic Press.
2001
Article
http://edoc.mpg.de/13753
urn:ISSN:1096-7176
Metabolic Engineering, v.3, 362-379 (2001)
en
oai:edoc.mpg.de:137592004-03-1819:94
Use of network analysis of metabolic systems in bioengineering
Schuster, S.
Klamt, S.
Weckwerth, W.
Moldenhauer, F.
Pfeiffer, T.
Basic ideas and recent developments in network analysis of metabolic systems and various applications of this analysis in bioengineering are reviewed. Central concepts are the null- space to the stoichiometry matrix and the elementary flux modes. The applicability of elementary-modes analysis in biotechnology is illustrated by the synthesis of the cyclooctadepsipeptides PF1022 in the fungus Mycelia sterilia. Network analysis is also useful in metabolic flux analysis. In particular, a procedure for finding out which reaction rates can be uniquely calculated in underdetermined reaction networks is outlined. The concept of 'enzyme subsets' is explained and its use for analysing genetic regulation is demonstrated. In particular, the correlation between expression data concerning the diauxic shift in yeast and the enzyme subsets in yeast metabolism is discussed.
2002
Article
http://edoc.mpg.de/13759
urn:ISSN:1615-7591
Bioprocess and Biosystems Engineering, v.24, 363-372 (2002)
en
oai:edoc.mpg.de:137662004-03-1719:94
Computational modeling of the dynamics of the MAP kinase cascade activated by surface and internalized EGF receptors
Schöberl, B.
Eichler-Jonsson, C.
Gilles, E. D.
Müller, G.
We present a computational model that offers an integrated quantitative, dynamic, and topological representation of intracellular signal networks, based on known components of epidermal growth factor (EGF) receptor signal pathways. The model provides insight into signal-response relationships between the binding of EGF to its receptor at the cell surface and the activation of downstream proteins in the signaling cascade. It shows that EGF-induced responses are remarkably stable over a 100-fold range of ligand concentration and that the critical parameter in determining signal efficacy is the initial velocity of receptor activation. The predictions of the model agree well with experimental analysis of the effect of EGF on two downstream responses, phosphorylation of ERK-1/2 and expression of the target gene, c-fos.
2002
Article
http://edoc.mpg.de/13766
urn:ISSN:1087-0156
Nature Biotechnology, v.20, 370-375 (2002)
en
oai:edoc.mpg.de:137682012-03-2919:90
Reactive separation of isobutene from C4 crack fractions by catalytic distillation processes
Qi, Z. W.
Sundmacher, K.
Stein, E.
Kienle, A.
Kolah, A.
reactive distillation; reactive separation; MTBE; C4 olefins; multiple steady states
Reactive distillation is a hybrid process where chemical reaction and distillative separation are performed in a single equipment. Even though reactive distillation could increase the selectivity of the desired product by the selective reaction this is not always true as shown in this work. A study on the MTBE reaction system using two coupled reactive distillation columns to separate a C4 crack mixture is carried out, where methanol acts as reactive entrainer and MTBE is the intermediate product. In the first column, isobutene and methanol react to form MTBE hence separating the inert C4 component, while in the second column MTBE splits back to methanol and isobutene. Methanol is recycled back to the MTBE formation column and isobutene is obtained as a product. This coupled process with direct recycle of methanol is possible only if no side reactions occur. When the side reactions are taken into account, byproducts such as diisobutene, dimethyl ether and water will be produced so that higher purity methanol can not be obtained at the bottom of the splitting column. The outlet of the splitting column must be firstly separated rather than being recycled directly to the formation column. Moreover, an attempt has been made to show how the selectivity of the desired product isobutene can be critically influenced by the operating parameters such as the reflux ratio. If the reflux ratio increases, a high quantity of diisobutene and dimethyl ether will be obtained which seriously affects the selectivity of isobutene. The influence of operating parameters is investigated by using a continuation method, which shows that bifurcation behavior can appear in both MTBE formation and decomposition process. (C) 2002 Elsevier Science B.V. All rights reserved.
2002
Article
http://edoc.mpg.de/13768
Separation and Purification Technology, v.26, 147-163 (2002)
en
oai:edoc.mpg.de:137702007-10-2619:92
Analysis of a discontinuously operated chromatographic reactor
Falk, T.
Seidel-Morgenstern, A.
reaction engineering; chromatographic reactor; kinetics; adsorption; ion exchange resins; methyl formate
The principle of a discontinuously operated chromatographic reactor was studied experimentally and theoretically. The heterogeneously catalysed hydrolysis of methyl formate was chosen as a model reaction. An acidic ion exchange resin was used as catalyst and adsorbent. The relevant adsorption equilibrium constants were available from a previous study. In this work the reaction rates were quantified on the basis of batch reactor experiments. Subsequently, systematic experiments were carried out using a fixed bed. The influence of temperature, residence time, feed concentration and cycle time on the reactor performance was studied. It was attempted to analyse the observations using a simplified pseudo-homogeneous cell model. Since the model was found to be capable of describing the reactor behaviour over a wide parameter range, it was applied to perform extensive parametric calculations. Besides the achievable conversion other objective functions such as recoveries and production rates were also analysed. From the results obtained a few generally applicable rules to evaluate the potential of discontinuously operated chromatographic reactors could be derived.
2002
Article
http://edoc.mpg.de/13770
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 1599-1606 (2002)
en
oai:edoc.mpg.de:137712004-03-1719:92
Influence of stagnant zones on transient and asymptotic dispersion in macroscopically homogeneous porous media
Kandhai, D.
Hlushkou, D.
Hoekstra, A. G.
Sloot, P. M. A.
Van As, H.
Tallarek, U.
The role of stagnant zones in hydrodynamic dispersion is studied for creeping flow through a fixed bed of spherical permeable particles, covering several orders of characteristic time and length scales associated with fluid transport. Numerical simulations employ a hierarchical model to cope with the different temporal and spatial scales, showing good agreement with our experimental results on diffusion-limited mass transfer, transient, and asymptotic longitudinal dispersion. These data demonstrate that intraparticle liquid holdup in macroscopically homogeneous porous media clearly dominates over contributions caused by the intrinsic flow field heterogeneity and boundary-layer mass transfer.
2002
Article
http://edoc.mpg.de/13771
urn:ISSN:0031-9007
Physical Review Letters, v.88, 234501 (2002)
en
oai:edoc.mpg.de:137742003-08-1319:93
Adaption of a fragment analysis technique to an automated high- throughput multicapillary electrophoresis device for the precise qualitative and quantitative characterization of microbial communities
Trotha, R.
Reichl, U.
Thies, F. L.
Sperling, D.
Koenig, W.
Koenig, B.
biodiversity; fragment analysis; multicapillary electrophoresis; ribosomal deoxyribonucleic acid
The analysis of microbial communities is of increasing importance in life sciences and bioengineering. Traditional techniques of investigations like culture or cloning methods suffer from many disadvantages. They are unable to give a complete qualitative and quantitative view of the total amount of microorganisms themselves, their interactions among each other and with their environment. Obviously, the determination of static or dynamic balances among microorganisms is of fast growing interest. The generation of species specific and fluorescently labeled 16S ribosomal DNA (rDNA) fragments by the terminal restriction fragment length polymorphism (T-RFLP) technique is a suitable tool to overcome the problems other methods have. For the separation of these fragments polyacrylamide gel sequencers are preferred as compared to capillary sequencers using linear polymers until now because of their higher electrophoretic resolution and therefore sizing accuracy. But modern capillary sequencers, especially multicapillary sequencers, offer an advanced grade of automation and an increased throughput necessary for the investigation of complex communities in long-time studies. Therefore, we adapted a T-RFLP technique to an automated high- throughput multicapillary electrophoresis device (ABI 3100 Genetic Analysis(R)) with regard to a precise qualitative and quantitative characterization of microbial communities.
2002
Article
http://edoc.mpg.de/13774
urn:ISSN:0173-0835
Electrophoresis, v.23, 1070-1079 (2002)
en
oai:edoc.mpg.de:137762004-03-1719:90
Pollution prevention through solvent selection and waste minimization
Krewer, U.
Liauw, M. A.
Ramakrishna, M.
Babu, M. H.
Raghavan, K. V.
To prevent pollution in chemical manufacturing processes, concepts respectively for solvent selection and waste minimization have been developed and improved. The first concept selects solvents for a given process that exhibit good environmental behavior in addition to good performance. For the performance test, relative and absolute solubility calculations of solvent-solute combinations are performed, and reactivity is estimated. The acceptable solvents are tested for important environmental characteristics such as global warming, ozone depletion, risk of fire and explosion, BOD5, and toxicity. Estimations of the risk of fire and explosion were made by implementing a model for solvent storage in the calculation of Dow's F&E index. The second concept helps minimize waste during manufacturing. Steinbach's concept of the balance yield BA is slightly varied and set into software. Both concepts are applied via software to manufacturing processes for NMSM. They identify the solvent DMSO as the most suitable solvent for the new process and highlight the most productive process, as well as the weak points of each process.
2002
Article
http://edoc.mpg.de/13776
urn:ISSN:0888-5885
Industrial & Engineering Chemistry Research, v.41, 4534-4542 (2002)
en
oai:edoc.mpg.de:137782004-03-1719:92
Continuous step gradient elution for preparative separations
Antos, D.
Seidel-Morgenstern, A.
preparative chromatography; continuous overloaded step gradient elution
A continuous step gradient elution process is suggested using several columns fixed in parallel to a multifunctional valve. The positions of the columns are changed in a periodic manner by shifting the valve at discrete times. Thus, the inlet streams into a certain column can be modulated in each time interval. Through one port, the feed is supplied whereas through the next port, eluent with increasing modifier concentration is dosed. In this work, the principle was studied for a normal-phase high-performance liquid chromatography system using the separation of a binary mixture of two cycloketones as an example. In these experiments, four columns were used. The feed stream was introduced in a relatively weak solvent and then three gradient steps using stronger solvents followed. In order to study the concept quantitatively, a mathematical model describing the column dynamics was developed. In preliminary experiments, the most relevant thermodynamic and kinetic parameters of the chromatographic system have been determined. In particular, the dependence of the adsorption isotherms on the mobile phase composition was analyzed. The influence of extra column volumes on the process performance was also considered. Four gradient elution experiments were carried out varying the shape of the step gradients. Besides a modulation of the eluent composition, flow rate gradients have also been considered. In the experiments performed, the separation process turned out to be stable and reproducible. The experimental results were compared with the model predictions. Due to the relatively good agreement found, the model can be applied to design the step gradient process and to evaluate its potential compared to conventional isocratic elution.
2002
Article
http://edoc.mpg.de/13778
urn:ISSN:0149-6395
Separation Science and Technology, v.37, 1469-1487 (2002)
en
oai:edoc.mpg.de:137802004-03-1719:90
Synthesis of cylohexanol by three-phase reactive distillation: influence of kinetics on phase equilibria
Steyer, F.
Qi, Z. W.
Sundmacher, K.
reactive distillation; residue curve maps; multiphase reactors; phase equilibria; reactive separation
A reactive distillation process is being suggested for the production of the commercially interesting intermediate cyclohexanol from cyclohexene and water, which avoids some of the drawbacks of the conventional liquid-phase cyclohexane oxidation process, especially with respect to operational safety. This reactive distillation process has its own intricate challenges due to the fact that reaction, distillative separation and liquid-phase splitting occur simultaneously. The interaction of these three phenomena is studied using residue curve maps for both, model simulations and experimental data. Based on the fixed point analysis of the residue curves, a novel process is proposed for the reactive separation of cyclohexene/cyclohexane mixtures which is difficult to be carried out by conventional distillation due to very close boiling temperatures. (C) 2002 Elsevier Science Ltd. All rights reserved.
2002
Article
http://edoc.mpg.de/13780
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 1511-1520 (2002)
en
oai:edoc.mpg.de:137822004-03-1719:92
Enantiomeric mandelic acid system-melting point phase diagram and solubility in water
Lorenz, H.
Sapoundjiev, D.
Seidel-Morgenstern, A.
A systematic study of the binary melting point phase diagram and ternary solubility phase diagram of the enantiomeric mandelic acid species in water has been undertaken. The melting point phase diagram of the system (+)-/(-)-mandelic acid was determined by means of thermal analysis. In agreement with previous observations mandelic acid was found to belong to the compound forming systems. The solubilities of three fixed enantiomeric mixtures in water (pure enantiomer, racemic, and eutectic compositions) were measured in the temperature range between 0 degreesC and > 90 degreesC. The results revealed that the solubility is strongly affected by temperature in a medium- temperature range. The ideal solubility curves of the three enantiomeric mixtures were calculated and the activity coefficients derived. An empirical three-step model is suggested to describe these activity coefficients.
2002
Article
http://edoc.mpg.de/13782
urn:ISSN:0021-9568
Journal of Chemical and Engineering Data, v.47, 1280-1284 (2002)
en
oai:edoc.mpg.de:137852004-03-1719:92
Solubility measurement using differential scanning calorimetry
Mohan, R.
Lorenz, H.
Myerson, A. S.
The measurement of solubility in microsamples employing a differential scanning calorimeter (DSC) has been evaluated for several aqueous and nonaqueous systems substance A in acetonitrile, (RS) mandelic acid, (S) mandelic acid, adipic acid, diphenhydramine HCl, alpha glycine, and terephthalic acid in water, (RS)-mandelic acid and beta succinic acid in ethanol and methanol, and adipic acid in ethanol. This technique requires samples in the range of milligrams and can be used at high temperatures and pressures. Results show that the solubility data of most compounds studied using this technique are within 5% of solubility data obtained from the literature. Factors that influence solubility measurement by DSC were examined along with methods to minimize associated errors.
2002
Article
http://edoc.mpg.de/13785
urn:ISSN:0888-5885
Industrial & Engineering Chemistry Research, v.41, 4854-4862 (2002)
en
oai:edoc.mpg.de:137892004-03-1719:94
Combinatorial complexity of pathway analysis in metabolic networks
Klamt, S.
Stelling, J.
combinatorial complexity in metabolic networks; elementary flux modes; metabolic pathway analysis; structural network analysis
Elementary flux mode analysis is a promising approach for a pathway-oriented perspective of metabolic networks. However, in larger networks it is hampered by the combinatorial explosion of possible routes. In this work we give some estimations on the combinatorial complexity including theoretical upper bounds for the number of elementary flux modes in a network of a given size. In a case study, we computed the elementary modes in the central metabolism of Escherichia coli while utilizing four different substrates. Interestingly, although the number of modes occurring in this complex network can exceed half a million, it is still far below the upper bound. Hence, to a certain extent, pathway analysis of central catabolism is feasible to assess network properties such as flexibility and functionality.
2002
Article
http://edoc.mpg.de/13789
urn:ISSN:0301-4851
Molecular Biology Reports, v.29, 233-236 (2002)
en
oai:edoc.mpg.de:137902004-03-1719:94
Calculating as many fluxes as possible in underdetermined metabolic networks
Klamt, S.
Schuster, S.
A frequently occurring problem in Metabolic Flux Analysis is that the linear equation systems are underdetermined. A procedure for determining which reaction velocities can be calculated in underdetermined metabolic systems from measured rates and computing these velocities is given. The method is based on the null-space matrix to the stoichiometry matrix corresponding to the reactions with unknown velocities. Moreover, an elementary representation of the null-space is presented. This representation enables one to find those sets of measurable velocities that allow calculation of a certain non-measurable rate. The approach is illustrated by an example from monosaccharide metabolism.
2002
Article
http://edoc.mpg.de/13790
urn:ISSN:0301-4851
Molecular Biology Reports, v.29, 243-248 (2002)
en
oai:edoc.mpg.de:137912004-03-1719:94
Metabolic network structure determines key aspects of functionality and regulation
Stelling, J.
Klamt, S.
Bettenbrock, K.
Schuster, S.
Gilles, E. D.
The relationship between structure, function and regulation in complex cellular networks is a still largely open question(1- 3). Systems biology aims to explain this relationship by combining experimental and theoretical approaches(4). Current theories have various strengths and shortcomings in providing an integrated, predictive description of cellular networks. Specifically, dynamic mathematical modelling of large-scale networks meets difficulties because the necessary mechanistic detail and kinetic parameters are rarely available. In contrast, structure-oriented analyses only require network topology, which is well known in many cases. Previous approaches of this type focus on network robustness(5) or metabolic phenotype(2,6), but do not give predictions on cellular regulation. Here, we devise a theoretical method for simultaneously predicting key aspects of network functionality, robustness and gene regulation from network structure alone. This is achieved by determining and analysing the non- decomposable pathways able to operate coherently at steady state (elementary flux modes). We use the example of Escherichia coli central metabolism to illustrate the method.
2002
Article
http://edoc.mpg.de/13791
urn:ISSN:0028-0836
Nature, v.420, 190-193 (2002)
en
oai:edoc.mpg.de:137932012-03-2919:90
Bifurcation analysis of reactive distillation systems with liquid-phase splitting
Qi, Z. W.
Sundmacher, K.
bifurcation; phase splitting; reactive distillation; singular point; pinch point; reactive azeotrope
The bifurcations are studied in simple reactive distillation processes, where liquid-phase splitting can happen, and the chemical reaction can occur in both or only one of the two liquid phases. Due to the different basic singular points and different chemical equilibrium curves, the bifurcations in the heterogeneous system are identical outside but fully different inside the liquid-liquid region compared to those in the pseudohomogeneous chemical equilibrium curve system. The bifurcations are also different inside the liquid-liquid region when the chemical reaction takes place in only one of the two liquid phases. There are potential singular point curves which are connected by the basic singular points in the corresponding nonreactive system. All the singular point bifurcations with respect to the normalized Damkohler number D and all the pinch point bifurcations with respect to the chemical equilibrium constant K follow these potential singular point curves. The analysis reveals that there exist critical values of the parameters D and K, at which the properties of the singular points change.
2002
Article
http://edoc.mpg.de/13793
Computers & Chemical Engineering, v.26, 1459-1471 (2002)
en
oai:edoc.mpg.de:137962007-10-2619:94
A network theory for the structured modelling of chemical processes
Mangold, M.
Motz, S.
Gilles, E. D.
systematic modelling; computer aided modelling; mathematical modelling; spatially distributed systems; population balances; dynamic simulation; process control
A structuring methodology for dynamic models of chemical engineering processes is presented. The main ideas of the methodology were outlined in a previous publication for the class of well-mixed systems. In this contribution, the methodology is extended to spatially distributed systems and to particulate processes. Furthermore, the structuring principle is used to make a conceptual link between the macroscopic world of process simulation and the microscopic world of molecular simulation. It is shown that a uniform structuring principle can be applied to the modularisation of most classes of chemical engineering models. The structuring principle can be used as a theoretical framework for the implementation of modular families of chemical engineering models in modem computer aided modelling tools.
2002
Article
http://edoc.mpg.de/13796
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 4099-4116 (2002)
en
oai:edoc.mpg.de:137982004-03-1819:89
Yield effects in single and coupled nonlinear thermokinetic reaction systems
Zeyer, K. P.
Mangold, M.
Shah, S.
Kienle, A.
Gilles, E. D.
coupling; thermokinetic systems; oscillations; yield; optimization
The influence of nonlinear dynamic effects on yield is considered for consecutive-parallel reaction schemes in a single phase CSTR. In the first part, the behavior of a single uncoupled reactor is investigated. Emphasis is on the reaction dynamics and the yield of the intermediate ethanal using continuation and optimization techniques. We characterize regions of periodic, complex periodic, and chaotic oscillations. The chaotic region is reached by type III intermittency. In all cases, the global optimum yield of the intermediate is a steady state, which is unstable or stable due to the location of the stability boundary. It is found that autonomous periodic operation is only locally better than steady state operation. In the second part, different types of mass and energy coupling between two reactors are studied. The results obtained for a simple consecutive parallel reaction scheme are validated by a more detailed model of the ethanol oxidation by hydrogen peroxide under iron(III) catalysis, which can be described by an extended consecutive-parallel reaction scheme. Analogies are found with respect to the dynamics and the yield of the intermediate.
2002
Article
http://edoc.mpg.de/13798
urn:ISSN:0942-9352
Zeitschrift für Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, v.216, 403-433 (2002)
en
oai:edoc.mpg.de:138012012-03-2819:89
A numerical bifurcation analysis of nonlinear oscillations in crystallization processes
Pathath, P. K.
Kienle, A.
crystallization; modeling; population balance; bifurcation; stability; nonlinear dynamics
The main aim of this work is the theoretical prediction and analysis of the nonlinear behavior of crystallization processes. As a first step towards the theoretical analysis a fairly simple population balance model including fines dissolution and classified product removal has been considered. By means of numerical bifurcation and stability analysis, regions in the parameter space of the operating conditions and the physical properties with periodic behavior have been predicted. Due to the simplicity of the underlying model the results are only of qualitative nature. Future work will focus on a quantitative prediction of the nonlinear behavior with more detailed models and an experimental verification.
2002
Article
http://edoc.mpg.de/13801
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 4391-4399 (2002)
en
oai:edoc.mpg.de:138032007-10-2619:91
Population balance modelling and H-infinity-controller design for a crystallization process
Vollmer, U.
Raisch, J.
crystallization; population balance; process control; infinite- dimensional system; robust control
In this paper we consider the robustly stabilizing control of a 10001 draft tube baffled crystallizer. When operated at high fines dissolution rates, the crystallizer exhibits sustained oscillations. A detailed population balance model for the process can be found in the literature. Based on this detailed model we develop a simpler population balance model. This, in turn, permits the derivation of an irrational transfer function from manipulated to measured variable. An H-infinity mixed sensitivity minimization problem is formulated and solved using an infinite-dimensional version of H-infinity theory. Two different controllers are designed and compared in simulation studies.
2002
Article
http://edoc.mpg.de/13803
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 4401-4414 (2002)
en
oai:edoc.mpg.de:138042004-05-1819:90
Conceptual design aspects of reactive distillation processes for ideal binary mixtures
Sundmacher, K.
Qi, Z. W.
reactive distillation; conceptual design; recycle systems; hybrid columns; isomerisation
A comparative study on the conceptual design of reactive distillation process configurations is presented, considering the reversible reaction A(1) double left right arrowA(2) in an ideal binary mixture as simple model system. The analysed flow schemes are a reactor-distillation column sequence with an external recycle loop, the same recycle system with a prereactor, a nonreactive distillation column on top of a reactive reboiler, a fully reactive distillation column, and a hybrid distillation column combining a reactive and a nonreactive section. For these configurations, the design aspects are discussed in terms of the most important operating parameters, kinetic parameters and design parameters. (C) 2003 Elsevier Science B.V. All rights reserved.
2003
Article
http://edoc.mpg.de/13804
urn:ISSN:0255-2701
Chemical Engineering and Processing, v.42, 191-200 (2003)
en
oai:edoc.mpg.de:138062004-06-2219:94
FluxAnalyzer : exploring structure, pathways, and flux distributions in metabolic networks on interactive flux maps
Klamt, S.
Stelling, J.
Ginkel, M.
Gilles, E. D.
Motivation: The analysis of structure, pathways and flux distributions in metabolic networks has become an important approach for understanding the functionality of metabolic systems. The need of a user-friendly platform for stoichiometric modeling of metabolic networks in silico is evident. Results: The FluxAnalyzer is a package for MATLAB(R) and facilitates integrated pathway and flux analysis for metabolic networks within a graphical user interface. Arbitrary metabolic network models can be composed by instances of four types of network elements. The abstract network model is linked with network graphics leading to interactive flux maps which allow for user input and display of calculation results within a network visualization. Therein, a large and powerful collection of tools and algorithms can be applied interactively including metabolic flux analysis, flux optimization, detection of topological features and pathway analysis by elementary flux modes or extreme pathways. The FluxAnalyzer has been applied and tested for complex networks with more than 500 000 elementary modes. Some aspects of the combinatorial complexity of pathway analysis in metabolic networks are discussed. Availability: Upon request from the corresponding author. Free for academic users (license agreement). Special contracts are available for industrial corporations. Supplementary information: http://www.mpi-magdeburg.mpg.de/projects/fluxanalyzer Contact: klamt@mpi-magdeburg.mpg.de.
2003
Article
http://edoc.mpg.de/13806
urn:ISSN:1367-4803
Bioinformatics, v.19, 261-269 (2003)
en
oai:edoc.mpg.de:138082005-07-2119:92
Mathematical modelling of adsorption and transport processes in capillary electrochromatography : open-tubular geometry
Paces, M.
Kosek, J.
Marek, M.
Tallarek, U.
Seidel-Morgenstern, A.
adsorption; capillary electrochromatography; coupled transports; electrical double layer; electroosmosis; electrophoresis; nonlinear effects
A mathematical modelling approach for open-tubular capillary electrochromatography is presented. The spatially one- dimensional model takes into account (i) a coupling of (non)linear adsorption of positively or negatively charged analyte molecules (at a negatively charged capillary inner surface) with the equilibrium electrokinetics at this solid- liquid interface, (ii) mobile phase transport by electroosmosis and pressure-driven flow, as well as (iii) transport of species by electrophoresis and molecular diffusion. Under these conditions the local zeta-potential and electroosmotic mobility become a function of the concentration of the charged analyte. The resulting inhomogeneity of electroosmotic flow through the capillary produces a compensating pore pressure as requirement for incompressible mobile phase flow (i.e., for constant volumetric flow along the capillary). The results of the simulations are discussed in view of the surface-to-volume ratio of the capillary lumen, the analyte concentration (in combination with a Langmuir isotherm for the adsorption process), and buffer effects.
2003
Article
http://edoc.mpg.de/13808
urn:ISSN:0173-0835
Electrophoresis, v.24, 380-389 (2003)
en
oai:edoc.mpg.de:138092004-03-1719:89
Improving simulated moving bed processes by cyclic modulation of the feed concentration
Schramm, H.
Kaspereit, M.
Kienle, A.
Seidel-Morgenstern, A.
A new mode of operation for simulated moving bed chromatographic processes is presented. While conventional SMB processes are operated with constant feed concentration, a modulation of the feed concentration during the switching cycles is introduced in the new mode of operation. Thereby the performance compared to the conventional SMB process is improved significantly. The productivity and the product concentration is increased. Simultaneously, the solvent consumption is decreased.
2002
Article
http://edoc.mpg.de/13809
urn:ISSN:0930-7516
Chemical Engineering & Technology, v.25, 1151-1155 (2002)
en
oai:edoc.mpg.de:138102012-04-2319:89
Stochastic resonance in a thermokinetic reaction system
Zeyer, K. P.
Münster, A. F.
Gilles, E. D.
We present numerical simulations of the counterintuitive effect of stochastic resonance in a model of a thermokinetic chemical oscillator. Small periodic perturbations are amplified by stochastic or deterministically chaotic parameter fluctuations giving way to large temperature oscillations. Stochastic resonance is characterized by various means, among them Fourier transforms, probability distribution functions and interspike histograms.
2002
Article
http://edoc.mpg.de/13810
Physical Chemistry Chemical Physics, v.4, 5988-5994 (2002)
en
oai:edoc.mpg.de:138112004-07-2619:89
Particulate processes: a special issue of chemical engineering science
Gilles, E. D.
Kienle, A.
2002
Article
http://edoc.mpg.de/13811
urn:ISSN:0009-2509
Chemical Engineering Science, v.57, 4255-4255 (2002)
en
oai:edoc.mpg.de:138122007-10-2619:90
Molten carbonate fuel cell (MCFC) with internal reforming : model-based analysis of cell dynamics
Heidebrecht, P.
Sundmacher, K.
mathematical modelling; nonlinear dynamics; transient response; molten carbonate fuel cell; potential field
A transient mathematical model for a single counter-flow cell of a molten carbonate fuel cell has been developed. The model is based on the description of physical phenomena related to the concentration, temperature and potential field within the gas and the solid phases. Simplifications like plug flow and constant pressure in the gas phase as well as a lumped solid phase for energy balance are used. The rate expressions for the electrochemical reactions include mass transport resistances. The potential field is described by a set of algebraic equations allowing for the calculation of a spatially distributed potential field. Some results of the model are presented using the example of a stepwise change in load demand. The results include the steady states of the system as well as the transient functions of concentrations, temperatures, current densities and cell voltage. Due to the general notation of this model in dimensionless form it can easily be extended to describe cross-flow 2D cells as well as 3D stacks.
2003
Article
http://edoc.mpg.de/13812
urn:ISSN:0009-2509
Chemical Engineering Science, v.58, 1029-1036 (2003)
en
oai:edoc.mpg.de:138152004-09-1019:94
The systems biology markup language (SBML) : a medium for representation and exchange of biochemical network models
Hucka, M.
Finney, A.
Sauro, H. M.
Bolouri, H.
Doyle, J. C.
Kitano, H.
Arkin, A. P.
Bornstein, B. J.
Bray, D.
Cornish-Bowden, A.
Cuellar, A. A.
Dronov, S.
Gilles, E. D.
Ginkel, M.
Gor, V.
Goryanin, I. I.
Hedley, W. J.
Hodgman, T. C.
Hofmeyr, J. H.
Hunter, P. J.
Juty, N. S.
Kasberger, J. L.
Kremling, A.
Kummer, U.
Le Novere, N.
Loew, L. M.
Lucio, D.
Mendes, P.
Minch, E.
Mjolsness, E. D.
Nakayama, Y.
Nelson, M. R.
Nielsen, P. F.
Sakurada, T.
Schaff, J. C.
Shapiro, B. E.
Shimizu, T. S.
Spence, H. D.
Stelling, J.
Takahashi, K.
Tomita, M.
Wagner, J.
Wang, J.
Motivation: Molecular biotechnology now makes it possible to build elaborate systems models, but the systems biology community needs information standards if models are to be shared, evaluated and developed cooperatively. Results: We summarize the Systems Biology Markup Language (SBML) Level 1, a free, open, XML-based format for representing biochemical reaction networks. SBML is a software-independent language for describing models common to research in many areas of computational biology, including cell signaling pathways, metabolic pathways, gene regulation, and others.
2003
Article
http://edoc.mpg.de/13815
urn:ISSN:1367-4803
Bioinformatics, v.19, 524-531 (2003)
en
oai:edoc.mpg.de:138162007-10-2619:92
Linear two-step gradient counter-current chromatography : analysis based on a recursive solution of an equilibrium stage model
Beltscheva, D.
Hugo, P.
Seidel-Morgenstern, A.
counter-current chromatography; gradient elution; adsorption isotherms; equilibrium stage model; mathematical modeling; preparative chromatography
The implementation of gradients in continuously operated chromatographic counter-current processes has recently attracted considerable interest as a method to improve the performance of this effective separation method. If liquid mobile phases are applied it is advantageous to set the solvent strength in the desorbent stream higher than that in the feed stream. As a consequence, the components to be separated are more retained in the adsorption zones and more easily eluted in the desorption zones. Due to the additional degrees of freedom the design and the optimization of such a two-step gradient counter-current process is difficult. In this paper a steady state equilibrium stage model is used to simulate the process under linear conditions. A simple solution of the underlying model equations is presented capable to describe efficiently the unit for large stage numbers typically encountered in chromatographic columns. Due to the rapidity of the algorithm developed a broad range of operating conditions can be evaluated systematically for different types of gradients. The impact of (a) the functional dependence of the adsorption equilibrium constants on the solvent composition, (b) the number of equilibrium stages and (c) the specification of purity requirements is illustrated and discussed based on results of parametric calculations. The results achieved emphasize the potential of two-step gradient counter-current chromatography.
2003
Article
http://edoc.mpg.de/13816
urn:ISSN:0021-9673
Journal of Chromatography A, v.989, 31-45 (2003)
en
oai:edoc.mpg.de:138172007-10-2619:89
Steady-state multiplicity in bioreactors : bifurcation analysis of cybernetic models
Namjoshi, A.
Kienle, A.
Ramkrishna, D.
cybernetic modeling; multiplicity; bifurcation analysis; mammalian bioreactors
Biological systems have an additional level of complexity compared to other chemical systems because of the effects of metabolic regulation, a defining feature of biosystems. Metabolic regulation in the form of control of enzyme synthesis and activity leads to non-linear behavior in bioreactors. Mathematical models that take into account these control mechanisms can be very successful in capturing the peculiarities of bioreactors such as multiple steady states and periodic phenomena. Cybemetic models model the expression and activation of enzymes by the use of cybernetic control variables and have been used to explain multiplicities in hybridoma reactors. In particular Namjoshi et al. (Biotechnol. BioEng. (2002), accepted) have been able to predict the transition from batch and fed batch to continuous culture in hybridoma experiments (Biotechnol. BioEng. 67(l) (2000) 25). The resulting multiple steady states vary widely in cell mass and waste metabolites. The model captures this multiplicity and its bifurcation analysis his revealed additional steady-state branches, three unstable and one stable. The stability of the additional steady state (steady state 4) was confirmed by dynamic simulations using fed-batch strategy prior to initiation of continuous operation. Steady state 4, in view of its close proximity to steady state 3, appears to have little practical significance. The likelihood of additional steady states that may be significantly different can, however not be ignored. Thus, it seems possible to envisage other states of metabolic activity, displaying alternative flux distributions that could lead to steady states notably different from those already determined. Calculation of the most singular point of the system herein is rendered difficult by both its size and possession of non-differentiable variables. The bifurcation analysis reveals the steady-state behavior under a range of operating conditions and can be used to plan optimum bioreactor operation.
2003
Article
http://edoc.mpg.de/13817
urn:ISSN:0009-2509
Chemical Engineering Science, v.58, 793-800 (2003)
en
oai:edoc.mpg.de:138202004-05-1819:94
Two approaches for metabolic pathway analysis?
Klamt, S.
Stelling, J.
Metabolic pathway analysis is becoming increasingly important for assessing inherent network properties in (reconstructed) biochemical reaction networks. Of the two most promising concepts for pathway analysis, one relies on elementary flux modes and the other on extreme pathways. These concepts are closely related because extreme pathways are a subset of elementary modes. Here, the common features, differences and applicability of these concepts are discussed. Assessing metabolic systems by the set of extreme pathways can, in general, give misleading results owing to the exclusion of possibly important routes. However, in certain network topologies, the sets of elementary modes and extreme pathways coincide. This is quite often the case in realistic applications. In our opinion, the unification of both approaches into one common framework for metabolic pathway analysis is necessary and achievable.
2003
Article
http://edoc.mpg.de/13820
urn:ISSN:0167-7799
Trends in Biotechnology, v.21, 64-69 (2003)
en
oai:edoc.mpg.de:345742004-02-1819:90
Dynamic Modeling and Simulation of a Countercurrent Molten Carbonate Fuel Cell (MCFC) with Internal Reforming
Heidebrecht, P.
Sundmacher, K.
A dynamic mathematical model for a countercurrent MCFC with direct internal methane reforming is introduced. It allows for the simulation of the gas phase compositions and flows, the temperatures in gas and solid phases, the cell voltage, and the current density distribution. This state space model is fully formulated in terms of dimensionless parameter groups, which are derived from the underlying physical and chemical phenomena. The model assumptions and equations are outlined in detail and a numerical solution strategy is proposed. The model is used to predict the current-voltage curve as well as the dynamic cell response to a stepwise load change.
2002
Article
http://edoc.mpg.de/34574
Fuel Cells, v.2, 166-180 (2002)
oai:edoc.mpg.de:345752012-04-2319:92
Numerical simulation and measurement of liquid holdup in biporous media containing discrete stagnant zones
Kandhai, D.
Tallarek, U.
Hlushkou, D.
Hoekstra, A. G.
Sloot, P. M. A.
Van As, H.
We have studied hydrodynamic dispersion in single-phase incompressible liquid flow through a fixed bed made of spherical, permeable (porous) particles. The observed behaviour was contrasted with the corresponding fluid dynamics in a random packing of impermeable (non-porous) spheres with an interparticle void fraction of 0.37. Experimental data were obtained in the laminar flow regime by pulsed field gradient nuclear magnetic resonance and were complemented by numerical simulations employing a hierarchical transport model with a discrete (lattice Boltzmann) interparticle flow field. Finite-size effects in the simulation associated with the spatial discretization of support particles or dimension and boundaries of the bed were minimized and the simulation results are in reasonable agreement with experiment.
2002
Article
http://edoc.mpg.de/34575
Philosophical Transactions of the Royal Society of London A, v.360, 521-534 (2002)
oai:edoc.mpg.de:346862012-03-2619:93
Validation of a T-RFLP Technique for the Precise Qualitative and Quantitative Characterization of Microbioal Communities by Using an Automated High Throughput Multi-Capillary Electrophoresis Device
Trotha, R.
Reichl, U.
Koenig, W.
Koenig, B.
Background: The analysis of microbial communities is of importance in many cases of life sciences and bioengineering. Traditional techniques of investigations like culture or cloning methods are characterized by many disadvantages. They are by and large unable to give a total qualitative and quantitative view of the total amount of microorganisms themselves, their interactions among each other and with their environment. Method: We generated species specfic and fluorescently labeled 16S rRNA gene fragments by the T-RFLP technique. For this purpose bacterial DNA of clinically important microorganisms of different genome sizes (P. aeruginosa, Campylobacter jejuni, Staphylococcus aureus, Staphylococcus epidermidis, Klebsiella pneumoniae, Burkholderia cepacia, Mycobacterium avium, Stenotrophomonas maltophilia, Alcaligenes xylosoxidans) were amplified by PCR using FAM-labeled 8-27f primer and unlabeled 1507-1492r primer (E. coli 16S rRNA);, using 8-27f and 1507-1492r. The amplfied DNA was digested with the restriction enzyme Hha I. For the separation of these fragments we validated a T-RFLP technique to an automated high throughput multi-capillary electrophoresis device (ABI 3100 Genetic Analysis?) with regard to a precise qualitative and quantitative characterization of microbial communities. We constructed a single stranded ROX labeled sizing standard up to for accurate sizing up to 780bp. The differences from the nominal size was less than half a base pair. Additionally we generated an internal quantification standard and investigated the minimal detectable concentration. The standard error was less than 3
2002
Conference-Paper
http://edoc.mpg.de/34686
Abstracts of the General Meeting of the American Society for Microbiology, 323 (2002)
oai:edoc.mpg.de:346902003-07-3119:92
Auslegung der Regenerationszonen des SMB-Verfahrens
Kaspereit, M.
Seidel-Morgenstern, A.
2002
Article
http://edoc.mpg.de/34690
Chemie-Ingenieur-Technik, v.74, 591-592 (2002)
oai:edoc.mpg.de:347182005-11-0919:91
Application of virtual reference direct control design in rehabilitation engineering
Previdi, F.
Schauer, T.
Savaresi, S. M.
This paper deals with design of feedback controllers for kneejoint movement of paraplegics using Functional Electrical Stimulation (FES) of the paralysed quadriceps muscle group. The controller design approach, Virtual Reference Feedback Tuning (VRFT), is directly based on open loop measured data and fits the controller in such a way that the closed-loop meets a model reference objective. The use of this strategy, avoiding the modelling step, significantly reduces the time required for controller design and considerably simplifies the rehabilitation protocols. Linear and nonlinear controllers have been designed and experimentally tested, preliminary on a healthy subject and finally on a paraplegic patient. It is shown that the control design is effective in controlling the leg position and rejecting disturbances and it could be successfully used in a rehabilitation protocol.
2002
Conference-Paper
http://edoc.mpg.de/34718
3. Wismarer Automatisierungssymposium (2002)
oai:edoc.mpg.de:347192004-02-1819:90
Reactive separation of iso-butene from C4 crack fractions via catalytic distillation processes
Qi, Z.
Sundmacher, K.
Stein, E.
Kienle, A.
In the C4 Olefins from steam cracking and fluid catalytic cracking there are several components. For the downstream processes, high purity isobutene or high purity C4s with very low isobutene content is required which is economically not feasible by a conventional distillation scheme because of the very close boiling points of the components. The schemes of the coupled reactive distillations is investigated to separate the closely boiling point C4s with isobutene and 1-butane as representatives. The undesired side reactions may play a major role. Based on systematic process simulations, the influence of the different operating parameters is investigated and the new reactive distillation flow scheme is suggested to obtain high purity isobutene and 1-butane.
DGMK
2002
Conference-Paper
http://edoc.mpg.de/34719
urn:ISBN:3-931850-98-6
G. Emig et al.: Proceedings of the DGMK-Conference, DGMK, 187-194 (2002)
oai:edoc.mpg.de:347272005-11-0719:91
Controller design for an oscillatory DTB crystallizer based on a population balance model
Vollmer, U.
Raisch, J.
In industrial crystallization, fines dissolution is used to improve crystalsize distribution (CSD) properties. Intense fines dissolution may lead to undesirable oscillations. Therefore, a controller design based on a population balance model is proposed. A late lumping approach is used where the controller design is based on an irrational transfer function resulting from the linearized population balance. The resulting irrational controller transfer function is then approximated by a rational one. The effectiveness of the controller is demonstrated in simulations. The proposed feedback control enables the use of high fines dissolution rates and hence the improvement of CSD properties.
AIDIC
2002
Conference-Paper
http://edoc.mpg.de/34727
urn:ISBN:88-900775-0-6
Chianese, A.: 15th International Symposium on Industrial Crystallization, September, 15 - 18, Sorrento, Italy, AIDIC, 1233-1239 (2002)
oai:edoc.mpg.de:347282003-07-3119:90
Simulation einer Tieftemperaturkolonne für ein IGCC-Kraftwerk
Hanke, R.
Hannemann, F.
Sundmacher, K.
2002
Article
http://edoc.mpg.de/34728
Chemie-Ingenieur-Technik, v.74, 1109-1113 (2002)
oai:edoc.mpg.de:347312005-11-1219:91
Regelung der Trittgeschwindigkeit beim Liegedreiradfahren von Querschnittgelähmten
Schauer, T.
Hunt, K. J.
Negard, N.-O.
Fraser, M. H.
Stewart, W.
Dieser Beitrag befasst sich mit dem Aufbau und der Regelung von Liegedreirädern für querschnittgelähmte Personen. Der Antrieb erfolgt dabei durch elektrische Stimulation der motorisch gelähmten Beinmuskulatur. Kommerziell erhältliche Dreiräder wurden speziell für diesen Zweck instrumentiert, um sie sowohl stationär in Form eines Ergometers als auch mobil für Freizeitzwecke verwenden zu können. Zur optimalen Regelung der Trittgeschwindigkeit wird in diesem Aufsatz ein neuer Ansatz vorgestellt. Ergebnisse mit querschnittgelähmten Probanden werden präsentiert. - This work deals with the design and feedback control of recumbent tricycles for paraplegic subjects propelled by their paralysed legs using electrical stimulation. Commercially available tricycles were instrumented in such a way that the systems can be either used as a stationary ergometer or as mobile device for recreational use. A new method for optimal cadence control is described. Results with paraplegic subjects are given.
2002
Article
http://edoc.mpg.de/34731
at - Automatisierungstechnik, v.50, 271-278 (2002)
oai:edoc.mpg.de:347322005-11-0719:91
Robust nonlinear control of knee-joint angle: A simulation study
Negard, N.-O.
Schauer, T.
Raisch, J.
The aim of this work was to design a robust nonlinear controller for the knee-joint angle by means of Functional Electrical Stimulation (FES). It is well known that a good mechanical model of the body segments can be obtained by first principles and simple pendulum tests, while it is hard to obtain a good of the lectrically elicited muscle contractions for control purposes due to time-variant and nonlinear properties of the muscles combined with limited measurements. For this reason only a linear model with uncertainty bounds is identified. A nonlinear control design approach is performed based on Lyapunov techniques, where uncertainty terms in the model, especially in the actuator dynamics, are dominated with the intention to make the controller robust. This design approach is highly attractive as it can easily be extended to multivariate systems with many body segments and muscle groups, and it allows nonlinear models of the muscle contraction dynamics to be incorporated into the control design. A simulation study of the controller is carried out using a physiologically based model of the muscle contraction dynamics as a substitution of the real plant. Robustness and performance of the designed controller, also with respect to the discrete time implementation and an unmodelled time delay are discussed.
2002
Conference-Paper
http://edoc.mpg.de/34732
3. Wismarer Automatisierungssymposium (2002)
oai:edoc.mpg.de:347332005-11-0919:91
Graybox-modelling of electrically stimulated musculoskeletal systems in paraplegia
Schauer, T.
Previdi, F.
Negard, N.-O.
Raisch, J.
In this paper, a new approach for estimating a nonlinear model of the electrically stimulated quadriceps muscle group under non-isometric conditions is investigated. In order to identify the muscle dynamics (stimulation pulse width-active knee moment relation) from discrete-time angle measurements only, a hybrid model structure is postulated for the shank-quadriceps dynamics. The model consists of a relatively well known time-invariant passive component and an uncertain time-variant active component. Rigid body dynamics, described by the Equation of Motion (EoM), and passive joint properties form the time-variant part. The actuator, i.e. the electrically stimulated muscle group, represents the uncertain time-varying section. A recursive algorithm is outlined for identifying online the stimulated quadriceps muscle group. The algorithm requires EoM and passive joint characteristics to be known a priori. The muscle dynamics represents the product of a continuous-time nonlinear activation dynamics and an nonlinear static contraction function described by a Normalised Radial Basis Function (NRBF) network which has knee-joint angle and angular velocity as input arguments. An Extended Kalman Filter (EKF) approach is chosen to estimate muscle dynamics parameters and to obtain full state estimates of the shank-quadriceps dynamics simultaneously.
2002
Conference-Paper
http://edoc.mpg.de/34733
3. Wismarer Automatisierungssymposium (2002)
oai:edoc.mpg.de:347342005-11-0719:91
Strategic refinements in abstraction based supervisory control of hybrid systems
Moor, T.
Davoren, J. M.
Raisch, J.
2002
Conference-Paper
http://edoc.mpg.de/34734
urn:ISBN:0-7695-1683-1
Silva, M.: Proceedings/ 6th International Workshop on Discrete Event Systems, 329-334 (2002)
oai:edoc.mpg.de:347422003-07-3119:92
Integrierte Prozesse in der Verfahrenstechnik
Schmidt-Traub, H.
Emig, G.
Hoffmann, U.
Marquardt, W.
Seidel-Morgenstern, A.
Wiley-VCH
2002
InBook
http://edoc.mpg.de/34742
urn:ISBN:3-527-27054-X
Deutsche Forschungsgemeinschaft: Perspektiven der Forschung und ihrer Förderung: Aufgaben und Finanzierung 2002-2006, 442-457 (2002)
oai:edoc.mpg.de:349002004-02-1819:94
Development, analysis and validation of population models for continuous and batch crystallizers
Gerstlauer, A.
Motz, S.
Mitrovic, A.
Gilles, E. D.
This contribution deals with the derivation of mathematical models for continuous and batch crystallizers based on the population balance approach. Detailed kinetic expressions for primary nucleation, crystal growth and attrition are incorporated into the models. The proper mathematical formulation of these phenomena as well as their incorporation into the population balance are discussed. Subsequently, system theoretical properties (e.g. the differential index of the resulting differential-algebraic equation system) of the derived models are analysed. Finally, the models for the continuous and the batch crystallizer are validated by comparison to measurements of temperature, supersaturation and particle size distribution.
2002
Article
http://edoc.mpg.de/34900
Chemical Engineering Science, v.57, 4311-4327 (2002)
oai:edoc.mpg.de:349042012-04-2319:92
Electroosmotic Flow Phenomena in Packed Capillaries: From the Interstitial Velocities to Intraparticle and Boundary Layer Mass Transfer
Tallarek, U.
Rapp, E.
Seidel-Morgenstern, A.
Van Ass, H.
Pulsed field gradient nuclear magnetic resonance studies of electrokinetic flow through a 250 m i.d. cylindrical fused-silica capillary packed with spherical porous particles (dp = 41 m) have revealed the following phenomena and parameters: (i) An electrokinetic wall effect exists due to a mismatch of zeta-potentials associated with the capillary inner wall and the particles surface. It results in a transcolumn velocity profile which depends on the column-to-particle diameter ratio and causes additional longitudinal dispersion. (ii) Compared to the ressure-driven flow through the porous medium, the intraparticle mass transfer rate constant is significantly increased under the influence of a potential gradient. This increase also depends on the buffer concentration via electric double layer overlap. (iii) Fluid molecules in the porous particles remain diffusion-limited in the presence of a pressure gradient. By contrast, intraparticle Peclet numbers above unity have been measured for electroosmotic flow and were found to increase with the applied potential difference. (iv) Interparticle resistance to mass transfer appears to vanish on the pore scale when electric double layers are small compared to the relevant pore dimension.
2002
Article
http://edoc.mpg.de/34904
Journal of Physical Chemistry B, v.106, 12709-12721 (2002)
oai:edoc.mpg.de:349082012-04-2319:92
Fluid dynamics in monolithic adsorbents: Phenomenological approach to equivalent particle
Tallarek, U.
Leinweber, F.
Seidel-Morgenstern, A.
Due to the complex, often sponge-like structure of monolithic adsorbents it is diffcult to define appropriate constituent units that characterize the hydrodynamics of the material, or to determine relevant shape and size distribution factors comparable to those for spherical particles in (particulate) fixed beds. Based on a phenomenological analysis to the friction factor (Reynolds number relation and the longitudinal dispersivity - Peclet number dependence for random sphere packings) we derive characteristic lengths (i. e., equivalent particle dimensions) for a monolith with regard to its hydraulic permeability and dispersion originating in stagnant zones. Equivalence to the hydrodynamic behavior in "reference" sphere packings is established by dimensionless scaling of the respective data for the monolithic structure. This phenomenological apprach, which is simply based on liquid flow and stagnation in a porous medium, can successfully relate hydrodynamic properties of the monolith to that of particulate beds.
2002
Article
http://edoc.mpg.de/34908
Chemical Engineering & Technology, v.25, 1177-1181 (2002)
oai:edoc.mpg.de:349132004-02-1819:92
Adsorption from solvent mixtures with varying composition
Gueorguieva, L.
Beltcheva, D.
Antos, D.
Seidel-Morgenstern, A.
To achieve a desired separation using adsorption processes usually two distinct steps are needed (adsorption/regeneration). Thus, certain operating conditions are changed periodically. During the two half periods usually the operating conditions are kept constant (isocratic operation). A potential for improvement is offered if during the process operating parameters are altered systematically. To realize such gradient concepts several operating parameters might be modulated depending on the type of process. Possible parameters are e. g. temperature, flowrate, ionic strength and pH. In this paper we consider liquid chromatographic separations under the influence of forced solvent composition gradients.
IK International, Ltd.
2002
Conference-Paper
http://edoc.mpg.de/34913
K. Kaneko et al.: Fundamentals of Adsorption 7, IK International, Ltd., 1070-1077 (2002)
oai:edoc.mpg.de:349242003-07-3019:89oai:edoc.mpg.de:349472004-02-1819:94oai:edoc.mpg.de:349502004-02-1819:92
Determination of particle size distribution from online laser backscattering measurements
Mahoney, A.
Lorenz, H.
Perlberg, H.
Seidel-Morgenstern, A.
The modeling of particle dynamics requires accurate measurements of evolving particle size distributions. One technique for obtaining these dynamic measurements is through the use of chord length distributions obtained from laser backscattering. A model that captures the interactions between the measuring probe and the particle size distribution is proposed here. The interactions are determined not through first-principle modeling, but rather through an inverse problem approach that creates the model directly from a reference particle measurement technique. Once this calibration is performed, evolving particle size distributions can be measured dynamically online. An example system of glass beads in water is examined and some features and drawbacks of the technique are identified.
AIDIC: Assoziazione Italiana Ingegniere di Chimica
2002
Conference-Paper
http://edoc.mpg.de/34950
urn:ISBN:88-900775-0-6
Chianese, A.: Proceedings of the 15th International Symposium in Industrial Crystallization, AIDIC: Assoziazione Italiana Ingegniere di Chimica, 197-202 (2002)
oai:edoc.mpg.de:349522004-02-1819:92
Determination of crystallization relevant data for enantioseparation purposes
Perlberg, A.
Lorenz, H.
Seidel-Morgenstern, A.
For the chiral ternary system of the enantiomers of mandelic acid in water, the metastable zone width was determined for different enantiomentric compositions. Furthermore, an acoustic inline concentration measurement technique was
tested concerning its applicability in chiral systems and compared with conventional offline density measurements. First result of enantioselective batch-crystallization experiments are repesented and the applicability of different in and offline methods is verified.
AIDIC: Assoziazione Italiana Ingegniere di Chimica
2002
Conference-Paper
http://edoc.mpg.de/34952
urn:ISBN:88-900775-0-6
Chianese, A.: Proceedings of the 15th International Symposium in Industrial Crystallization, AIDIC: Assoziazione Italiana Ingegniere di Chimica, 173-178 (2002)
oai:edoc.mpg.de:349542004-02-1819:92
Study of solubility equilibria in chiral systems
Lorenz, H.
Sapoundjiev, D.
Seidel-Morgenstern, A.
The ternary solubility equilibria in various systems of two enantiomers in solvents were studied applying different measurement techniques. The resulting ternary phase diagrams are presented and the possibility of obtaining pure enantiomers is discussed. The effect of different solvents on the solubility is studied for the example of mandelic acid. The real solution behavior is quantified by activity coeffcients derived from known thermadynamic relations. A simple empirical 3-step model describing the temperature dependence of the activity coefficients allows to calculate the mandelic acid solubility in the entire temperature range. Finally, a new method for solubility determination will be suggested.
AIDIC: Assoziazione Italiana di Ingegneria Chimica
2002
Conference-Paper
http://edoc.mpg.de/34954
urn:ISBN:88-900775-0-6
Chianese, A.: Proceedings of the 15th International Symposium in Industrial Crystallization, AIDIC: Assoziazione Italiana di Ingegneria Chimica, 167-172 (2002)
oai:edoc.mpg.de:349572003-07-3119:92
Coupling of chromatography and crystallisation for efficient enantioseparation
Kaspereit, M.
Lorenz, H.
Seidel-Morgenstern, A.
2002
Conference-Paper
http://edoc.mpg.de/34957
Proceedings of the 14th International Symposium on Chirality (ISCD-14), 120 (2002)
oai:edoc.mpg.de:349722003-07-3119:90oai:edoc.mpg.de:349842003-07-3119:94oai:edoc.mpg.de:349862005-11-0719:91
Hierarchical control in a behavioural framework
Raisch, J.
Itigin, A.
Moor, T.
This contribution presents some ideas on the synthesis of hierarchical control systems. Hierarchical control is an attempt to handle complex problems by decomposing them into smaller subproblems and reassembling their solutions in a hierarchical structure. A systematic approach to this topic clearly requires a mathematical guarantee that the resulting system of interacting controller units does indeed solve the underlying complex problem. We will argue that behavioural systems theory represents a neat conceptual framework where this can be achieved.
Institute of Control Enginering, Technical University of Szczecin
2002
Conference-Paper
http://edoc.mpg.de/34986
urn:ISBN:88764-66-7
Proceedings MMAR 2002, Institute of Control Enginering, Technical University of Szczecin (2002)
oai:edoc.mpg.de:349882003-07-3019:94oai:edoc.mpg.de:349942005-11-0719:91
Sliding-mode control of knee-joint angle: experimental results
Schauer, T.
Holderbaum, W.
Hunt, K. J.
The aim of this work was to experimentally validate a sliding-mode controller for the problem of knee-joint angle tracking. The robust controller was designed on the assumption that only a simplified mechanical model is available but not a detailed description of the muscle dynamics. Experiments with an intact subject have been successfully carried out. Performance limitations of this control method due to the effects of sampling and muscle time delay are reported.
Institut Republike Slovenije za rehabilitacijo
2002
Conference-Paper
http://edoc.mpg.de/34994
Karcnik, T.: 7th Annual Conference of the International Functional Electrical StimulationSociety (IFESS2002), Institut Republike Slovenije za rehabilitacijo, 316-318 (2002)
oai:edoc.mpg.de:349962005-11-0719:91
A pilot study of lower-limb FES cycling in paraplegia
Hunt, K. J.
Schauer, T.
Negard, N.-O.
Fraser, M. H.
Stewart, W.
The aim of this work was to develop the engineering methods and apparatus for FES cycling, and to achieve regular periods of mobile FES cycling over significant distances with paraplegic subjects. The study utilised a commercial recumbent tricycle, which was instrumented for stimulation control. Three subjects with a complete spinal cord lesion at level T7-T10 were recruited for the study. After four months of participation in the study the subjects were able to cycle outdoors for distances of up to 3km in a single session. The subjects are also able to cycle continuously and reliably on an indoor cycle trainer for periods of up to 1 h. We conclude that mobile FES cycling over useful distances outdoors is a realistic option for the paraplegic population, even with a low intensity training regime. Future work will involve FES cycling exercise tests to document changes in cardio-pulmonary fitness in SCI subjects.
Institut Republike Slovenije za rehabilitacijo
2002
Conference-Paper
http://edoc.mpg.de/34996
Karcnik, T.: 7th Annual Conference of the International Functional Electrical Stimulation Society (IFESS 2002), Institut Republike Slovenije za rehabilitacijo, 350-352 (2002)
oai:edoc.mpg.de:349972005-11-0719:91
FES-Cycling with electric motor assist
Hunt, K. J.
Stone, B.
Negard, N.-O.
Schauer, T.
Fraser, H. M.
The aim of this study was to develop and test feedback control strategies for integration of electric motor assist and functional electrical stimulation for paraplegic cycling. An integrated two-loop feedback control strategy is proposed, in which the electric motor is driven to provide feedback control of cycling speed, and the cyclist’s leg power is controlled by automatic variation of stimulation intensity. Representative experimental results are presented for one complete-lesion paraplegic subject. The results show accurate feedback control of: cycle cadence; leg power; and external disturbance rejection. We conclude that the addition of electric motor assist, with an integrated feedback control strategy, can compensate for external disturbances, it can greatly increase the overall power output and thereby significantly extend the range of operation, and it can provide optimal operating conditions for the stimulated muscles.
2002
Conference-Paper
http://edoc.mpg.de/34997
1st FESnet Conference, 7-9 (2002)
oai:edoc.mpg.de:350012004-02-1719:89
Nonlinear dynamics and control of reactive distillation processes
Kienle, A.
In some cases reactive distillation is very economical compared to a conventional process design, where reaction and separation are carried out in different processing units. Typical examples are esterification and etherification processes. Consequently, there has been a lot of interest in this type of integrated process during the last years. Emphasis has been on steady state modeling, on development of new processes and on process design. Still, comparably little work has been done on dynamics and control of reactive distillation processes, although these processes can sometimes show an intricate nonlinear dynamic behavior including multiplicities and instabilities. Reliable prediction and understanding of these phenomena is a necessary prerequisite for better process design and control. The objective of this contribution is to give an overview of the present knowledge on dynamics and control of reactive distillation processes with emphasis on the authors work in this field. The outline of the contribution is the following: First, focus is on open loop dynamics of reactive distillation processes involving-multiplicities, self-sustained oscillations and spatio temporal pattern formation also termed as nonlinear wave propagation. Different sources for nonlinear behaviour are systematically identified and implications for process operation and process control are discussed. The second part is concerned with control of continuously operated reactive distillation columns. Emphasis is on inferential control schemes, where the desired product purities are inferred from temperature measurements.
Czech Society for Chemical Engineering (CSCHI)
2002
Conference-Paper
http://edoc.mpg.de/35001
urn:ISBN:80-86059-33-2
Novosad, J.: 15th International Congress of Chemical and Process Engineering CHISA 2002, Czech Society for Chemical Engineering (CSCHI) (2002)
oai:edoc.mpg.de:350032003-07-2819:94
Applying metabolic pathway analysis to make good use of methanol
Schuster, S.
Klamt, S.
Comment article - no abstract available.
2002
Article
http://edoc.mpg.de/35003
Trends in Biotechnology, v.20, 322 (2002)
oai:edoc.mpg.de:350132004-02-1719:89
Steady state multiplicity in bioreactors: bifurcation analysis of cybernetic models
Namjoshi, A.
Kienle, A.
Ramkrishna, D.
Biological systems have an additional level of complexity compared to other chemical systems because of the effects of metabolic regulation. Such regulation in the form of control of enzyme synthesis and activity leads to nonlinear behavior in bioreactors. Mathematical models that take into account these control mechanisms can be very successful in capturing the peculiarities of bioreactors such as multiple steady states and periodic phenomena. Cybernetic models, which are extremely suitable for this task model expression and activation of enzymes by the use of cybernetic control variables and have been used to explain multiplicities in hybridoma reactors. In particular, the cybernetic model of Namjoshi et al. (2002) has been able to predict the transition from batch and fed-batch to continuous culture in hybridoma experiments of Europa et al. The multiple steady states that result, vary widely in the concentration of cell mass and waste metabolites. The model captures the multiplicity of steady states for the hybridoma reactors. The bifurcation analysis of such models reveals the steady state behavior under a range of operating conditions and can be used to plan bioreactor operation to get the desired staedy states for maximum productivity.
2002
Conference-Paper
http://edoc.mpg.de/35013
17th Symposium on Chemical Reaction Engineering ISCRE 17 (2002)
oai:edoc.mpg.de:350152004-06-3019:89
Dynamic plantwide modelling, flowsheet simulation and nonlinear analysis of an industrial production plant
Waschler, R.
Kienle, A.
Anoprienko, A.
Osipova, T.
A detailed dynamic model of the Monsanto process for the production of acetic acid is presented. The nonlinear behaviour of the process is investigated and implications different control structures have on its dynamic behaviour are pointed out.
2002
Conference-Paper
http://edoc.mpg.de/35015
Grievink, J.; van Schijndel, J.: European Symposium on Computer Aided Process Engineering - 12 - ESCAPE-12, 583-588 (2002)
oai:edoc.mpg.de:350162004-09-0619:94
Control-key to better understanding biological systems
Gilles, E. D.
Biological cells use very effcient and hierarchically structured regulations to control their metabolism and to adapt it to variations in the environmental conditions. Only these regulations prevent the potential chaos of thousands of individual reactions occurring in a cell. To understand the functioning of these regulations and the complexity of their interactions mathematical modelling on the basis of a detailed biomolecular description of cellular functional units is not only helpful but necessary. This modelling process can be supported by a modelling concept interconnecting elementary modelling objects assigned to elementary biomolecular building blocks. This correspondence allows for biological transparency and facilitates interdisciplinary co-operation between biology and system sciences as an important precondition to enable a deeper understanding of regulatory processes. The important role regulation plays in cellular biological systems is demonstrated by means of two typical functional units, the catabolite repression in E. coli and the cell cycle regulation in Saccharomyces cerevisiae. These two examples show both the typical hierarchical structure and the high effciency of regulatory processes in cells.
2002
Article
http://edoc.mpg.de/35016
Automatisierungstechnik, v.50, 7-17 (2002)
oai:edoc.mpg.de:350182004-09-0619:89
Nonlinear Analysis of gPROMS Models Using DIVA as via a CAPE ESO interface
Mangold, M.
Mohl, K. D.
Grüner, S.
Kienle, A.
Gilles, E. D.
The CAPE ESO interface of the process simulator gPROMS is used to pass model information to numerical methods contained in the simulation environment DIVA. By the interface, algorithms for the continuation of stable and unstable steady states and periodic solutions can be applied directly to gPROMS models. The use of the interface is illustrated by a detailed nonlinear model of an industrial distillation column.
2002
Conference-Paper
http://edoc.mpg.de/35018
urn:ISBN:0-444-51109-1
Grievink, J.; van Schijndel, J.: European Symposium on Computer Aided Process Engineering - 12, 919-924 (2002)
oai:edoc.mpg.de:350252004-02-1719:92
Measurement and modeling of the equilibrium behavior of the Tröger's base enantiomers on an amylose-based chiral stationary phase
Mihlbachler, K.
Kaczmarski, K.
Seidel-Morgenstern, A.
Guiochon, G.
The binary isotherms of the two enantiomers of Tröger’s base were measured on a system made of pure 2-propanol as the mobile phase and of Chiralpak AD, a chiral stationary phase (CSP) based on amylose tri-(3,5-dimethylphenyl carbamate). The experimental data were acquired using both frontal analysis and the perturbation method. The results obtained are most unusual. The adsorption of the more-retained (-)-enantiomer is not competitive: the amount adsorbed onto the CSP at equilibrium with a constant concentration of the (-)-enantiomer is independent of the concentration of the (+)-enantiomer. On the other hand, the adsorption of the less-retained enantiomer is cooperative: the amount of this (+)-enantiomer adsorbed by the CSP at equilibrium with a constant concentration of this enantiomer increases with increasing concentration of the (-)-enantiomer. Such a phenomenon has hardly ever been reported. A model equation is proposed that account well for all these isotherm data.
2002
Article
http://edoc.mpg.de/35025
Journal of Chromatography A, v.955, 35-52 (2002)
oai:edoc.mpg.de:350392004-09-0619:94
Analysis of the dynamics of the Escherichia coli glucose PTS in different time windows
Sauter, T.
Kremling, A.
Bettenbrock, K.
Fischer, S.
Gilles, E. D.
The analysis of metabolic pathways with mathematical models contributes to the better understanding of the behaviour of metabolic processes. In this paper, the analysis of the glucose phosphotransferase system in Escherichia coli is presented. It is shown that dynamic processes cover a broad time span from some milliseconds to several hours. This is shown by simulation as well as by experimental studies.
AKA-Verl.-Ges.
2002
Conference-Paper
http://edoc.mpg.de/35039
urn:ISBN:3-89838-030-0
Polani, D.; Kim, J.; Martinetz, T.: Abstracting and synthesizing the principles of living systems: Proceedings of the Fifth German Workshop on Artificial Life, AKA-Verl.-Ges., 33-42 (2002)
oai:edoc.mpg.de:350472003-07-2919:92
Coupling chromatographic separation and crystallisation of enantiomers
Lorenz, H.
Perlberg, A.
Kaspereit, M.
Gedicke, K.
Sapoundjiev, D.
Seidel-Morgenstern, A.
Abstract
2002
Conference-Paper
http://edoc.mpg.de/35047
Proceedings of the 15th International Symposium on Preparative/Process Chromatography (Prep 2002), L-206 (2002)
oai:edoc.mpg.de:350502004-02-1619:92
Coupling of simulated moving bed technology and crystallization to separate enantiomers
Kaspereit, M.
Lorenz, H.
Seidel-Morgenstern, A.
The separation of enantiomers is a diffcult task and important in the pharmaceutical industry. Often only with chromatographic methods the required high purity can be reached. In the last years the powerful simulated moving bed (SMB) process was applied successfully to separate a broad spectrum of racemic mixtures. However, chromatographic processes must still be considered as an expensive separation technology. Alternatively enantioseparation is often feasible by crystallization provided a certain enrichment has been achieved. In this work the combination of the two mentioned concepts is discussed.
IK International Ltd.
2002
InBook
http://edoc.mpg.de/35050
Fundamentals of adsorption 7, 101-108 (2002)
oai:edoc.mpg.de:350762004-02-1719:92
Effect of the homogeneity of the column set on the performance of a simulated moving bed unit. Part II: Experimental study
Mihlbachler, K.
Jupke, A.
Seidel-Morgenstern, A.
Schmidt-Traub, H.
Guiochon, G.
Previous studies of the simulated moving bed (SMB) process assume identical characteristics of all the columns incorporated in a given unit. Due to the practical impossibility to manufacture identical columns, numerical applications of the theory to modeling and optimization use for each of the needed column parameter the average value for the entire column set. In this study, the effects of these simplifications on the actual productivity of the SMB process are evaluated by making exact calculations, i.e., by taking the differences in the porosity values into account. We apply a revised set of separation conditions previously introduced and derived from the eqiuilibrium theory. Earlier theoretical results are compared to experimental results obtained in the study of the enantiomeric separation of Troger‘s base on Chiralpak AD. Due to the non Langmuirian character of the adsorption isotherms of these two compounds on the packing material used, the separation area cannot be determined analytically. As an alternative, a reliable numerical algorithm was used to scan a wider region and to define the separation area. The form of this area depends on the applied porosity values. A UV detector and a laser polarimeter located at one node of the SMB monitor on-line the internal concentration profiles. Excellent agreement between the calculated and the experimentally determined concentration profiles was obtained under nonlinear conditions. The influence of column-to-column variations on the performance of the SMB process was found to be more significant under nonlinear than under linear conditions.
2002
Article
http://edoc.mpg.de/35076
Journal of Chromatography A, v.944, 3-22 (2002)
oai:edoc.mpg.de:351092003-07-3119:92
Investigating gasification processes of solid fuels by in-situ gaspotentiometric probe
Schotte, E.
Lorenz, H.
Rau, H.
2002
Conference-Paper
http://edoc.mpg.de/35109
Proceedings of the Energy Forum 2002, 87-92 (2002)
oai:edoc.mpg.de:351112005-11-0719:91
Discrete approximation and control of high-order nonlinear continuous systems
Moor, T.
Raisch, J.
Itigin, A.
2002
Conference-Paper
http://edoc.mpg.de/35111
Proceedings of the 15th IFAC World Congress on Automatic Control (2002)
oai:edoc.mpg.de:351122003-07-3019:91oai:edoc.mpg.de:351152005-11-0719:91
Think continuous, act discrete: des techniques for continuous systems
Moor, T.
Raisch, J.
Instituto Superior Tecnico
2002
Conference-Paper
http://edoc.mpg.de/35115
Proceedings of the 10th Mediterranean Conference on Control and Automation, Instituto Superior Tecnico (2002)
oai:edoc.mpg.de:351182005-11-0719:91
Discrete models for hybrid systems
Lunze, J.
Raisch, J.
This contribution provides an introduction to the topic of discrete models for hybrid systems. It motivates the use of discrete approximations of hybrid or purely continuous dynamics and comments on two complementary approaches. The article explains the core property of any suitable approximation and describes its major implications.
Springer
2002
InBook
http://edoc.mpg.de/35118
urn:ISBN:3-540-43812-2
Modelling, analysis, and design of hybrid systems, 67-80 (2002)
oai:edoc.mpg.de:351242003-07-3019:90oai:edoc.mpg.de:351392004-09-0619:94
FluxAnalyzer : a graphical user interface for stoichiometric and quantitative analysis of metabolic networks
Klamt, S.
Kremling, A.
Gilles, E. D.
Metabolic Flux Analysis has turned out to be a powerful approach for studying and engineering metabolic networks. Nevertheless, there seems to be a lack of a comprehensive software platform where all computational routines for metabolite balancing and stoichiometric analysis can be used in a convenient way. Therefore, the FluxAnalyzer, a programming package for MATLAB, was developed. The interactive software allows a menu-driven use of various procedures within a graphical user interface, where the metabolic networks under investigation and the results of calculations are visualized in flux maps. Arbitrary networks can be defined symbolically. The FluxAnalyzer is used in current projects at our institute and its application for flux analysis of cell cultures in an industrial process is planned.
Published for the International Federation of Automatic Control by Pergamon
2002
InBook
http://edoc.mpg.de/35139
urn:ISBN:0-08-043681-1
Computer applications in biotechnology 2001 (CAB8): Modelling, monitoring and control of biotechnological processes, 119-124 (2002)
oai:edoc.mpg.de:351462004-07-2619:94
Integrating Workbench for Modeling and Numerical Analysis of Cellular Systems
Kremling, A.
Ginkel, M.
Gilles, E. D.
With increasing knowledge in biology and improved measurement methods it becomes possible to build detailed models of the cells interior. In this contribution a computer framework is described which allows to build modular structured metabolic models using a abstract and general modeling methodology. With this methodology reusable modeling entities are introduced which lead to the development of modeling knowledge-bases. Therefore the modeling tool ProMot is introduced. For the numerical analysis and identification of the resulting models the simulation environment DIVA is described. For the management of the resulting data from measurements and simulations on different models management and visualization facilities are necessary which are available in the MATLAB tool CellView. The described tools are the first steps towards an integrated computer-based modeling, simulation and visualization environment.
2002
Conference-Paper
http://edoc.mpg.de/35146
Dochain, D.; Perrier, M.: Proc. 8th International Conference on Computer Applications in Biotechnology, 85-90 (2002)
oai:edoc.mpg.de:351482005-03-1719:95
Mathematical Model of Virus Replication in Animal Cells
Möhler, L.
Flockerzi, D.
Reichl, U.
2002
Article
http://edoc.mpg.de/35148
Chemie-Ingenieur-Technik, v.74, 661-662 (2002)
oai:edoc.mpg.de:351492013-02-0119:93
Analysis of cell growth, virus replication and medium composition in equine influenza vaccine production
Genzel, Y.
Reichl, U.
2002
Article
http://edoc.mpg.de/35149
Chemie-Ingenieur-Technik, v.74, 673-674 (2002)
oai:edoc.mpg.de:622362004-01-3019:92
Analysis of discontinuously operated chromatographic reactors
Falk, T.
Seidel-Morgenstern, A.
DECHEMA
2001
Conference-Paper
http://edoc.mpg.de/62236
ECCE - 3rd European Congress on Chemical Engineeging (ECCE-3), DECHEMA (2001)
oai:edoc.mpg.de:622402012-04-1219:92
Attempt to quantify the coupling of SMB and fractional crystallisation for enantioseparation
Lorenz, H.
Sheehan, P.
Seidel-Morgenstern, A.
Elsevier
2001
Conference-Paper
http://edoc.mpg.de/62240
Guichon, G.: International Symposium on Preparative and Process Chromatography, Elsevier, 40 (2001)
oai:edoc.mpg.de:622412004-01-3019:92
Investigation of mass transfer through inorganic membranes with several layers
Thomas, S.
Schäfer, R
Caro, J.
Seidel-Morgenstern, A.
Elsevier
2001
Conference-Paper
http://edoc.mpg.de/62241
Santamaria, J.: Catalysis in membrane reactors: proceedings of the 4th International Conference on Catalysis in Membrane Reactors, Elsevier, 175-176 (2001)
oai:edoc.mpg.de:622452004-09-0619:94
Towards a Virtual Biological Laboratory
Stelling, J.
Kremling, A.
Ginkel, M.
Bettenbrock, K.
Gilles, E. D.
For a system-level understanding of living cells, a quantitative representation of these systems involving mathematical models and corresponding computer tools is required. Our approach focuses on a modeling concept which relies upon modular structuring of cellular systems focusing strongly on the biomolecular structure of these systems. Mathematical submodels for functional units comprising metabolism and regulation can be aggregated in a hierarchical way to obtain more complex modules. In the Virtual Biological Laboratory, the process modeling tool ProMoT contains an object-oriented knowledge base with reusable modeling entities and enables a purely symbolical model development process via a graphical user interface. The simulation environment Diva then uses the model library for dynamic simulation, parameter estimation and model analysis. Two examples of models of complex regulatory networks in Escherichia coli and in Saccharomyces cerevisiae are given to demonstrate the usefulness of this approach. It can provide a framework for straightforward development of virtual representations for cellular systems.
MIT Press
2001
InBook
http://edoc.mpg.de/62245
urn:ISBN:0-262-11266-3
Foundations of systems biology, 189-212 (2001)
oai:edoc.mpg.de:622462004-02-1619:92
Selectivity improvement with stagewise adjusted membrane properties
Thomas, S.
Seidel-Morgenstern, A.
Elsevier
2001
Conference-Paper
http://edoc.mpg.de/62246
Santamaria J.: Catalysis in membrane reactors: proceedings of the 4th International Conference on Catalysis in Membrane Reactors, Elsevier, 29-30 (2001)
oai:edoc.mpg.de:623892004-02-1619:93
Sedimentation effects in hollow fiber bioreactors
Sankarnarayan, R.
Nayak, D. P.
Patkar, A.
The fluid dynamics of hollow fibre bioreactors was studied using residence time distribution (RTD) and protein polarisation experiments. Small differences in the densities of tracer protein solution and carrier liquid resulted in broad RTDs with long tails due to settling of tracer solution near the upstream extracapillary space (ECS) port. Moreover, module orientation and ECS flow direction had a significant influence on the observed RTDs. After matching the densities of the tracer and the carrier fluid, the tracer moved through the ECS as a dispersed plug. The reactor orientation and flow direction did not influence RTDs in these density-matched experiments. The reactor orientation had a dramatic effect on protein polarisation in the ECS.
2001
Article
http://edoc.mpg.de/62389
Chemical Engineering Communications, v.185, 237-246 (2001)
oai:edoc.mpg.de:623992004-06-3019:93
Development of bioprocess concepts on vaccine production : influenza virus as an example
Genzel, Y.
Voges, L.
Reichl, U.
Kluwer Acad. Publ.
2001
Conference-Paper
http://edoc.mpg.de/62399
urn:ISBN:1-402-00264-5
Lindner-Olsson, E.; Chatzissavidou, N.; Luellau, E.: Animal cell technology : from target to market ; proceedings of the 17 ESACT meeting, Kluwer Acad. Publ., 344-346 (2001)
oai:edoc.mpg.de:624102004-09-0619:94
Inland-ECDIS chart validation and correction using radar image processing technics
Driescher, A.
Saez, L.
Gilles, E. D.
One of the most promising developments in inland navigation are electronic chart based navigation systems. Emerging from the ECDIS standard used in see navigation the Inland-ECDIS standard provides a well-accepted foundation for electronic navigation systems. Meanwhile, industrial vendors start equipping vessels with the first navigation systems and authorities are releasing first river chart series based on the provisional Inland-ECDIS standard. Until now, the process of validating Inland-ECDIS charts is mainly done by feedback from skippers using this charts in there navigation system. While minor problems like missing or misplaced navigation marks can easily be handled by standard chart editing software, more elaborated issues concerning malfunctions in radar overlays due to errors in radar conspicuous objects are not addressed in standard tools. However, correct handling of radar overlays is a corner stone for save and reliable navigation and therefor a need for easy verification arise, leading to a powerful radar image post processing system. The paper will present the standard features implemented in a commercial navigation system that are relevant to chart verification and correction. Based on the mechanisms provided in this system, a radar image post processing algorithm is discussed that can produce overlay pictures for use in ECDIS-chart editors. Although the algorithm is primarily tuned for chart verification it turned out to be even as powerful for automated chart production in areas where traditional charts are not available. The paper will handle the following topics in more detail:- The radar overlay mechanism required by the Inland-ECDIS standard. - Sensor requirements for data acquisition and processing in navigation systems.- Typical features found in commercial systems and there application to chart validation. - Chart production errors and there consequences for navigation systems. - Radar image post-processing by merging image sequences by Bays estimation. - Integration and image handling in commercial ECDIS chart editors. - Examples for data verification and chart production.
Secretariat of National Organising Comittee of EIWN 2001
2001
Conference-Paper
http://edoc.mpg.de/62410
urn:ISBN:963-420-693-X
Hadhazi, D.; Simongati, G.: Proceedings of the European Inland Waterway Navigation Conference, Secretariat of National Organising Comittee of EIWN 2001, keine Paginierung (2001)
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