Sol–gel preparation of polymethylsilsesquioxane aerogel membranes for CO2 absorption fluxes in membrane contactors

The hydrophobic membrane in a membrane contactor serves as the interface between gaseous mixtures that contain CO2 and an aqueous amine solution. This hydrophobic membrane prevents the amine solution from passing through and wetting the membrane; however, gaseous CO2 can enter the membrane pores and be absorbed by the amine. In this study, hydrophobic polymethylsilsesquioxane (PMSQ) aerogels were coated successfully via a sol–gel process onto an Al2O3 membrane support using methyltrimethoxysilane (MTMS) precursors. We examined the effects of the NH4OH concentration and the molar ratio of EtOH2nd (ethanol adding in second step of sol–gel processes) and MTMS on this sol–gel process for membrane preparation. In addition, we investigated the CO2 absorption fluxes obtained using these aerogel membranes. The PMSQ aerogel membranes prepared with 17% NH4OH and a 1:1 M ratio of EtOH2nd to MTMS exhibited the highest CO2 absorption flux of 1.2 mmole/m2 s. Furthermore, the as-prepared PMSQ aerogel membranes can be used continuously to absorb CO2 for at least 4 days, and they can be reused in three consecutive cycles of CO2 absorption. The results of this study demonstrated that these as-prepared PMSQ aerogel membranes are not only durable but also reusable. Thus, these as-prepared PMSQ aerogel membranes show promise for use in membrane contactors for CO2 absorption.