(24e) Modeling Analysis of Non-Isothermal Water-Gas Shift Reaction in CO2 Perm-Selective Dual-Phase Membrane Reactor

A CO₂ perm-selective water-gas shift membrane reactor offers the ability to enrich syngas streams with molecular hydrogen while promoting CO₂ capture for sequestration purposes. A dual-phase membrane is constructed from a porous samarium-doped ceria (SDC) membrane which is impregnated with a 43.5/31.5/25 mol% Li₂CO₃/Na₂CO₃/K₂CO₃ eutectic mixture with a melting point of 400⁰C. Transmembrane CO₂ permeation is limited by oxide anion diffusion in the SDC phase, and an empirical relationship for the transmembrane flux of CO₂ has been determined within a limited temperature range.  This work is focused on non-isothermal modeling of catalyst-free water gas shift reaction in the dual-phase membrane reactor with CO₂ removal at high temperatures.  The membrane surface induced homogeneous water gas shift reaction kinetics was determined by comparing differential reactor model with experimental data.  The results show an activation energy and pre-exponential constant of 90.2 kJ/mol and 1047 m³/mol-s respectively.  Concurrent and countercurrent models of shell-tube membrane reactors under non-ideal and non-isothermal conditions were developed in Matlab2013b on a basis of the Peng-Robinson equation of state.  Effects of membrane characteristics and operation conditions on the water gas shift reaction and CO2 capture were analyzed by the models.   The non-isothermal model shows that a membrane reactor requires 6.8 times less membrane surface area than estimated by a single-point extrapolation of the isothermal, ideal case.  Subsequently, the use of an accurate thermodynamic model is proposed for all membrane reactor designs which incorporate significant reaction enthalpy.