Practical designs of membrane contactors and their performances in CO2/CH4 separation

Porous polypropylene (PP) hollow fiber membrane contactors operated by either single absorption processes or combined absorption/desorption processes using water have been investigated for use in the production of biomethane from simulated biogas. To observe the effect of operating parameters on the membrane contactors, the connection of modules, flow rates, and operating pressures were tuned. For CO2/CH4 separation, operations using single absorption processes produced a good yield (85%) of high purity CH4 (97%). Connections in series containing two absorption modules facilitated CO2 absorption due to an increase in contact area at the liquid-gas interface. In the combined absorption/desorption processes, CH4 was recovered in 75% yield and 98% purity using two 1″ absorption modules and four 2″ desorption modules connected in series. Although the results were somewhat poorer than those of the single absorption processes due to limits in desorption performance, the combined process provided the potential for producing renewable methane as a fuel for vehicles. Furthermore, for the single absorption processes, the PP hollow fiber membrane contactor was operated continuously, while the membrane used in the combined absorption/desorption processes required periodic maintenance to maintain an acceptable performance.