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          Institute: MPI für Dynamik komplexer technischer Systeme     Collection: Physical and Chemical Process Engineering     Display Documents

ID: 62982.0, MPI für Dynamik komplexer technischer Systeme / Physical and Chemical Process Engineering
New concepts for the production of high-purity isobutene in coupled reactive distillation columns
Authors:Stein, E.; Kienle, A.; Kolah, A.; Qi, Z.; Sundmacher, K.; Mohl, K. D.
Place of Publication:Frankfurt am Main
Date of Publication (YYYY-MM-DD):2001
Title of Proceedings:3rd European Congress on Chemical Engineering (ECCE-3)
Sequence Number:6-5
Physical Description:CD-ROM
Name of Conference/Meeting:3rd European Congress on Chemical Engineering (ECCE-3)
Place of Conference/Meeting:Nürnberg, Germany
(Start) Date of Conference/Meeting
End Date of Conference/Meeting 
Review Status:not specified
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:Isobutene is an important starting material for many industrial syntheses. It is produced by either steam cracking of naphtha or fluid catalytic cracking of gas oil, obtaining a mixture of C4 hydrocarbons for both routes. The separation of the isomers isobutene and 1-butene by distillationis economically not feasible due to a 1 K difference of the normal boiling points. However, it is possible to separate them utilizing the difference in reactivities with a reactive entrainer such as methanol. In a first step methanol reacts with isobutene to form methyltert-butyl ether (MTBE), thereby facilitating theremoval of the inert component 1-butene. In a second step MTBE is decomposed back to isobutene and methanol, recycling the latter to the first process step. Recently, Trotta and Miracca [1] presented this process with a liquid-phase reactor for MTBE synthesis, a gas-phasereactor for MTBE decomposition and several distillation columns for the separation task. In contrast, in this paper it is demonstrated that the production of high-purity isobutene via MTBE formation and decomposition can also be carried out in coupled reactive distillation columns. The process integration comes along with a more complex behavior demanding a profound investigation of the system. The advantages of this process areobvious: The number of process units is reduced and the decomposition of MTBE is performed in the liquid phase. Virtually no methanol and MTBE is lost from the process as a waste stream, leading to an environment friendly process. The synthesis of MTBE was investigated theoretically and experimentally by various research groups during the last decade. Interesting features like multiple steady states and a complex dynamic behavior were demonstrated. Hardly any literature seems to be available on the regeneration of isobutene and methanol from MTBE making use of reactive distillation. This presentation outlines the following studies: Conceptual design with the help of reactive residue curve maps [2,3] the knowledge of non-reactive azeotropes and a separation boundary, attainable product regions are identified. It is shown that the separation boundary can be crossed by the simultaneous chemical reaction resulting in a feasible design for the decomposition of MTBE to pure isobutene and methanol. Feasibility of the conceptual design by simulation studies a rigorous tray-by-tray model of a reactive distillation column [4] is used to simulate the steady state behavior of the separate columns as well as the coupled column system. In a first step only the main reaction is considered. It is shown that 1-butene can be obtained with high-purity as the distillate of the MTBE formation column where as pure isobutene leaves the system as the distillate of the MTBE decomposition column. In a second step the important side reactions are taken into account, too. It is shown that the products are still obtained in high purity but the design of the process has to be changed considerably. Different design alternatives are presented and compared. [1] Trotta, R. and Miracca, I. (1997) Case history: Synthesis and decomposition of MTBE.Catal. Today, 34(3-4):447-455. [2] Barbosa, D. and Doherty, M.F. (1988) The influence of equilibrium chemical reactions on vapour-liquid phase diagrams. Chem. Eng. Sci., 43(3):529-540. [3] Thiel, Ch., Sundmacher, K. and Hoffmann,U. (1997) Residue curve maps for heterogeneously catalysed reactive distillation of fuel ethers MTBE and TAME. Chem. Eng. Sci., 52(6):993-1005. [4] Mohl, K.D., Kienle, A., Gilles, E.D., Rapmund, P., Sundmacher, K. and Hoffmann,U. (1999) Steady-state multiplicities in reactive distillation columns for the production of fuel ethers MTBE and TAME: theoretical analysis and experimental verification. Chem. Eng. Sci., 54:1029-1043.
External Publication Status:published
Document Type:Conference-Paper
Communicated by:Kai Sundmacher
Affiliations:MPI für Dynamik komplexer technischer Systeme/Physical and Chemical Process Engineering
MPI für Dynamik komplexer technischer Systeme/Process Synthesis and Process Dynamics
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