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Zusammenfassung:
During the last two decades intensive study is being done on inorganic membrane reactors in order to improve yield and selectivity of the oxidative dehydrogenation reactions. A number of recent research have reported that the use of the membrane reactors in selective oxidation reactions can result in improving selectivity of desired intermediates and suppressing the deep oxidation (Reyes et al.(1993), Tonkovich et al(1995)). Membrane reactors are promising candidates to improve the reactor performance limited by the reaction kinetic or thermodynamics using the concept of distributed educt dosing. The application of this concept would be beneficial, including dehydrogenations, synthesis gas production and esterifications.
In heterogeneous catalyzed partial oxidation systems, the product selectivity can be enhanced when the order of the reaction in oxygen for the formation of target product is lower than that of the formation of undesired product. Hence a decrease in oxygen concentration favors product selectivity (Santamaria et al. (1995,1999)). A packed bed membrane reactor combines both axial feed of reactant and distributive oxygen feeding through the membrane with low axial back mixing in the catalyst bed.
Simplified 1D models are state of the art and widely-used for the simulation of packed bed membrane bed reactors (PBMR) (Varma et al.(2002a,b). Only fewer studies were oriented on two dimensional description (Kürten et al.(2004)) . However this detailed models seems to be needed to be able predict and understand governing effects in the PBMR.
In our study we have considered oxidative dehydrogenation of ethane on a VOx/γ-Al2O3 catalyst as model reaction. (Klose et al. (2003)).
One objective of this thesis is to implement a one dimensional, pseudo-homogeneous membrane reactor model to study the effect of varying flow rates, dosed oxygen amounts, and especially the influence of tube/shell ratio on the ethane conversion and ethylene selectivity.
Another objective of this study was the investigation of the PBMR using two dimensional pseudo homogenous reactor models. The commercial software package FEMLABTM3.1 is used as a promising simulation tool.
With the implemented two dimensional models following effects are studied in detail:
- Axial and radial distribution of the oxidant, the effects of interparticle mass transfer limitations on the reactor performance
- Study of radial and axial velocity profiles,
- Influence of temperature on the product distribution
- The possibilities of a model simplification, considering heat, mass and momentum transfer in the boundary conditions
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A.L.Y. Tonkovich, Jennifer L. Zilka, Daniel M. Jimenez, Gary L. Roberts and John L. COX: Experimental investigations of inorganic membrane reactors: A Distributed feed approach for partial oxidation reactions. Chem. Eng. Sci. 51, 789-806
(1995)
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A.Varma, V.Diakov: Reactant distribution by inert membrane enhances packed bed reactor stability. Chem. Eng. Sci. 57, 1099-1105 (2002)
A.Varma, V. Diakov, B. Blackwell: Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model. Chem. Eng. Sci. 57, 1563 – 1569 (2002)
Ulrich Kürten, M. van Sint Annaland, J. A. M. Kuipers: Oxygen Distribution in Packed Bed Membrane Reactors for Partial Oxidation Systems and its Effect on Product Selectivity. Ind. Eng. Chem. Res. 43, 4753-4760 (2004)
F. Klose , T. Wolff, S. Thomas, and A. Seidel Morgenstern: Concentration and residence time effects in packed bed membrane reactors. Catalysis Today 82, 25-40 (2003)
