(300d) Multi-Scale (Pellet-Reactor Scale) Membrane Reactor Modeling and Simulation: High Temperature and High Pressure Water-Gas Shift Reaction

Karagoz, S., UCLA
Manousiouthakis, V., University of California Los Angeles, Los Angeles
Tsotsis, T., University of Southern California
The objective of this work is to develop a mathematical model and simulation of the Membrane Reactor (MR) in order to carry out the water gas shift (WGS) reaction. MR subsystems integrate reaction and separation in a single unit, with the aim of attaining increased process efficiency, and process compactness. In the MR, a membrane that is selective to hydrogen is used to enhance the WGS reactionâ??s kinetic rate, and to possibly overcome equilibrium conversion limitations imposed by thermodynamics.

The MR system is composed of a reaction zone packed with catalyst pellets, and a permeation zone, where the reaction products permeate. For the reaction zone (classic packed bed reactor), after completing a single-pellet isothermal/non-isothermal steady-state, stand-alone simulations, we couple our model with an isothermal/non-isothermal steady-state packed-bed reactor model to form a hybrid multi-scale reactor model. The catalyst pellet simulation is repeatedly carried out along the reactor bed length (yielding the effectiveness factor along the reactor length for the locally prevailing reaction conditions), and is coupled with a 1-D (axial) reactor model that captures species transport/reaction along the reactor length. Finally, classic packed bed reactor is coupled with a permeation zone to create full membrane reactor (MR) system.

The velocity and speciesâ?? concentration profiles along the reactor length are captured by momentum/species transport models accounting for convection/reaction /diffusion mechanisms. In the derivation of the modelâ??s equations, the Reynolds Transport Theorem was applied separately to each of the domains; the pelletâ??s domain, the reactorâ??s domain and the permeationâ??s domain. The rigorous Maxwell Stefan and dusty gas models are applied to describe mass diffusion fluxes. The effectiveness factors are calculated along the membrane reactor. Finally, performances of the classic packed bed reactor and the membrane reactor are compared.