Effect of long-term operation on the performance of polypropylene and polyvinylidene fluoride membrane contactors for CO2 absorption

Abstract

The reduction of CO2 emission to the atmosphere is necessary with regard to the global warming mitigation. Gas absorption membrane (GAM) contactor for CO2 capture is an emerging technology and exhibits great advantages compared to conventional chemical CO2 absorption processes. In this study, to better understand the GAM process, especially its long-term performance for CO2 absorption, both polypropylene (PP) and polyvinylidene fluoride (PVDF) hollow fiber membrane contactors were investigated for a 30-day operation period. The CO2 flux and recovery declined with time for both PP and PVDF membrane systems and the situation was worse for PVDF membrane. Analysis of mass transfer resistance based on Wilson plot method suggested that after long-term operation the resistance for CO2 intramembrane transport increased by 160% and 290% for PP and PVDF membrane systems, respectively. The significant increase in the membrane mass transfer resistance means the membrane has been wetted.The contact angle measurements indicated that the membrane hydrophobicity declined significantly for PP and PVDF after 30days of operation. Scanning electron microscope and the overall membrane porosity analysis proved that the change of the membrane pore structure were responsible for the deterioration. After long-term contacting with MEA solution, physical or chemical dissolving of membrane surface occurred for both PP and PVDF. Some pinholes appeared on the outer surface of the PVDF membrane after use for 3days, and both their number and size significantly increased after 30days; however, in the case of PP membrane, the pores changed from originally a long and narrow shape to oval, and the pore size also became uneven. Therefore, the variation in physical and chemical membrane properties during the long-term run should be paid attention to in order to comprehensively evaluate the GAM contactor for CO2 absorption.