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Schlagwörter:
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Zusammenfassung:
In order to promote the industrial application of chromatographic reactors there is a need in further systematic studies1. Recently, an approach using simultaneously an extension of the equilibrium theory2 and a rate model3 was applied successfully to improve understanding and to perform a feasibility and design study of reactive chromatographic processes. The results of this theory can be conveniently presented in the hodograph space. It was shown that some reactions (e.g. reactions of the type A -> B + C) can reach total conversion and total separation, whereas the component separation for other reactions (e.g. reactions of the type 2A -> B + C) can be limited by reactive azeotropy4. The theoretical predictions were confirmed by experimental results for the heterogeneously catalyzed hydrolysis reactions of methyl formate (MF) and methyl acetate (MA) at a temperature of 25 °C. Fig. 1 shows as an example a hodograph plot for the hydrolysis of MF. In Fig. 2 are shown dependencies of MF conversion and product separation as a function of column length. Fig. 3 represents experimental data for a certain column length which allows (in agreement with the expectation, Fig. 2) to reach total conversion and total separation. It is of interest and the topic of this contribution how such ester hydrolysis reactions can be performed in the chromatographic reactor at other temperatures.
To continue and extent the previous work2-4 systematic experiments for the hydrolysis of methyl formate, ethyl formate, methyl acetate and ethyl acetate were carried out at 35, 45 and 55 °C under diluted conditions using the strongly acidic ion-exchange resin DOWEX 50W-X8 as the catalyst and adsorbent. The following essential parameters depend on temperature: reaction rate constants, chemical equilibrium constants and distribution equilibrium constants of the components involved. Up to now, the parameters summarized in Tables 1 and 2 have been determined. These parameters follow expected trends (except the distribution equilibrium constants of the alcohols). On the basis of the determined parameters the effects of temperature on the performance of fixed-bed chromatographic reactors can be predicted. Using the theory validated at 25 °C required column lengths and performance criteria will be evaluated in the whole temperature range covered. Finally, conclusions regarding optimized temperatures will be made for the four different reactions.
References
(1) T. Aida and P. L. Silveston, Cyclic Seperating Reactors, Blackwell Publishing, Oxford, 2005.
(2) S. Grüner, A. Kienle, Chem. Eng. Sci. 59 (2004) 901.
(3) Phong T. Mai, Tien D. Vu, Ky X. Mai, A. Seidel-Morgenstern, Ind. Eng. Chem. Res. 43 (2004) 4691.
(4) T. D. Vu, A. Seidel-Morgenstern, S. Grüner, and A. Kienle, Ind. Eng. Chem. Res. 44 (2005) 9565.
