A CFD study on the performance of CO2 methanation in a water-permeable membrane reactor system

CO2 hydrogenation is one of the important routes for CO2 utilization to address the global warming issue, which has aroused much attention in recent years. A novel water-permeable membrane reactor has been proposed to promote the conversion of CO2 methanation with in situ removal of H2O. However, existing research studies mainly focused on the overall performance and hardly discussed the detailed behavior of water-permeation and methanation inside the membrane reactor, which is crucial for the development of membrane reactors. The main objective of this work is to study the interplay of water permeation and methanation within the membrane reactor, and recommend the appropriate membrane properties and optimal operation conditions. In this regard, a two-dimensional CFD simulation model is built up, and its accuracy is verified by comparison with the literature data. The distribution of the reactant/product species and H2O permeation flux is well presented, and the effects of GHSV, H2O permeance and CO2/H2 permeation selectivity are also investigated. Our results show that the match of methanation reaction rate and H2O permeation rate is crucial. At GHSV of 0.051 s−1, the membrane with a H2O permeance of 7.85 × 10−8 mol m−2 s−1 Pa−1 is capable of removing nearly 90% of H2O produced, leading to an 8.3% increase in CO2 conversion. However, a H2O permeance of magnitude order of 1 × 10−7 mol m−2 s−1 Pa−1 is a prerequisite to provide a significant increase in CO2 conversion at GHSV higher than 0.51 s−1. Besides, it is important to keep H2 and CO2 permeation selectivity lower than 0.1 to avoid the negative effect.