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ID: 111990.0, MPI für Dynamik komplexer technischer Systeme / Process Synthesis and Process Dynamics
Optimization of a reactor network for ethylene glycol synthesis : an algorithmic approach
Authors:Stein, E.; Kienle, A.; Esparta, A. R.; Mohl, K. D.; Gilles, E. D.
Date of Publication (YYYY-MM-DD):1999
Title of Journal:Computers and Chemical Engineering
Issue / Number:Suppl.
Start Page:S903
End Page:S906
Review Status:not specified
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:This contribution is concerned with reactor network synthesis for the production of ethylene glycol by hydration of ethylene oxide, which is an industrially relevant process. This reaction is not only very fast and strongly exothermic but also higher glycols are formed as by products. Starting point of the study is a general reactor network serving as a superstructure. The system consists of two different kinds of units: a reaction-condensation unit with chemical reaction in the liquid phase and simultaneous vaporization as well as condensation, and different mixer/splitters. Usually, reactor network synthesis is concerned with rather simple isothermal reactions in homogeneous liquid or gasphase. Instead, here a rigorous
non-isothermal two-phase model with a liquid and a vapor phase is developed. Chemical reaction and mass separation by vaporization is included. In principle, the synthesis problem is solved on the phase level [4]. This approach allows the combination of the unit operations reaction and separation in various ways. In particular, the resulting superstructure includes two processes, which have been treated previously. The first is the conventional process for the production of ethylene glycol which consists of a reactor followed by a separation sequence with a water recycle [6]. The second is a reactive distillation column recently proposed in [3]. The latter is also used to validate the reactor network model. Moreover, completely new two-phase reactor separator structures are synthesized. Recently, Mehta and Kokossis presented a similar approach for the synthesis of novel reactor designs [5]. The general superstructure is optimized by means of NLP techniques in the optimization tool GAMS [1]. Starting with a detailed examination of a single reaction-condensation unit a better understanding of the physical and chemical processes is obtained with emphasis on interaction between chemical reaction and separation. In the next step a network containing two reaction-condensation units is investigated. It turns out that the principle of the conventional process, spatial separation of reaction and mass separation, is an optimal structure. Finally, networks with up to eleven reaction-condensation units are considered, corresponding to the reactive distillation column presented by Ciric and coworkers [3]. Completely new structures for the production of ethylene glycolare synthesized and compared with the structure of the column with respect to the energy costs. It turns out that the structure equivalent to the column represents a local optimum for the isobaric network considered here in a first step. Further improvements can be achieved by the feeding strategy and by varying the pressure from unit to unit. However, due to the strongly nonlinear reactor network model and its enormous number of degrees of freedom no claims of globality of optima found can be made. To overcome these limitations of local optimizers and to find new structures for ethylene glycol synthesis to chastic optimization algorithms are considered [2]. [1] A. Brooke, D. Kendrick and A. Meeraus: GAMS A user’s guide, release 2.25. The Scientific Press, San Francisco, 1992. [2] M.F. Cardoso, R.L. Salcedo, S.F. de Azevedo and D. Barbosa: A simulated an nealing approach to the solution of MINLP problems. Comp. Chem. Engng, 21(12):1349-1364, 1997. [3] A.R. Ciric and D. Gu: Synthesis of nonequilibrium reactive distillation processes by MINLP optimization. AIChE Journal, 40:1479-1487, 1994. [4] E.D. Gilles: Network theory for chemical processes. Chem. Engng. Technol., 21(2):121-132, 1998. [5] V.L. Mehta and A. Kokossis: Development of novel multiphase reactors using a systematic design framework. Comp. Chem. Engng, 21, Suppl.:S325-S330, 1997. [6] Ullmann’s encyclopedia of industrial chemistry, Vol. A 10, Chap. Ethylene Glycol. VCH Verlagsgesellschaft mbH, Weinheim, 1990.
External Publication Status:published
Document Type:Article
Communicated by:Achim Kienle
Affiliations:MPI für Dynamik komplexer technischer Systeme/Process Synthesis and Process Dynamics
MPI für Dynamik komplexer technischer Systeme/Systems Biology
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