Analysis of heat effects in a membrane reactor for the WGSR

M.E. ADROVER; E. LÓPEZ; D.O. BORIO; M. PEDERNERA

México

Congreso; Mexican Congress on Chemical Reaction Engineering (MCCRE 2008); 2008

The Water Gas Shift Reaction (WGSR) is a reversible and moderately exothermic reactionwidely used in industry. In ammonia plants, two adiabatic reactors at different temperature levelsare disposed in series (HTS and LTS) to reach high CO conversions. In smaller scaleapplications, such as fuel processing for PEM fuel cells, the WGSR reactor is instaleddownstream the reformer to increase the H2 production rate and purify the process stream. Inthese designs, the WGSR is carried out in a single adiabatic reactor at intermediate temperature[1]. However, the chemical equilibrium limitations make neccesary to introduce anotherpurification stage (e.g., CO PrOx) to reach the specified CO content for the fuel cell (<10 ppm).An attractive alternative to the Fixed Bed Reactor (FBR) is the Membrane Reactor (MR). Adense membrane (e.g., Pd supported on a porous substrate) is used to shift the equilibrium bymeans of selective and continuous permeation of one of the reaction products (e.g., H2) [2]. Theadvantages of the MR to carry out equilibrium limited reactions have been demonstrated bydifferent authors [3-5]. In most of the literature contributions the heat effects are neglected andthe MR operation is supposed to be isothermal. This common modeling assumption agrees withthe temperature measurements inside the reactor at laboratory scale, due to the high ratiosbetween heat-transfer area and reactor volume. However, this condition may not be true forhigher process scales, e.g.: several membrane tubes installed in parallel within a shell where asweep gas is circulated.In this article, the operation of a non-isothermal MR for the WGSR is simulated and comparedwith that of a FBR.