Performance comparison of different membrane micro-channel reactors for methanol production from biogas and hydrogen

Abstract

In order to integrate simultaneous methanol production with biogas upgrading in a single unit, the computational fluid dynamics (CFD) models of a triple pipe tubular membrane reactor (TMR) and a planar membrane micro-structured reactor (MMR) were established via COMSOL Multiphysics 5.3a and compared their effect on reactor performance under predetermined condition. For the conceptual design of these reactors, the channel inside the reactors can be divided into three parts; biogas channel (BC), reaction channel (RC) and sweep gas channel (SC). The CO2 in biogas entering into BC is separated through CO2 selective membrane to produce methanol inside RC. Afterwards, water occurred from the reactions in RC diffuses through water selective membrane to SC in order to shift the reactions to move forward as well as improve methanol production rate. The methanol yield, factor of CO2 and water permeation of MMR provides 28.88, 99.24 and 89.64% which are higher than TMR 18.92, 65.79 and 77.16 %, respectively. In addition, the surface to volume ratio of MMR providing high both heat and mass transfer rate is a key factor affecting to the performance of reactor. For MMR, the operating and design parameters were also investigated. The mass flow ratio of BC to RC (gas flow rate in biogas channel) and WHSV in reaction channel are able to significantly influence to the reactor performance. From the studied ranges, the optimal condition includes inlet temperature of 508.15 K, pressure of 50 bar, WHSV of 20 h-1, BC:RC ratio of 0.5, SC:RC ratio of 4, reactor length of 75 mm and width of 0.5 mm.