Membrane modules for CO2 capture based on PVDF hollow fibers with ionic liquids immobilized

Hollow fiber membrane contactors with ionic liquids are promising alternatives to traditional spray towers and amines for carbon dioxide absorption. Ionic liquids have emerged as new alternative solvents because of their zero emission features compared with amines. The aim of this work was to compare fibers based on PVDF and different additives, as well as fibers including two different ionic liquids. On the one hand, 1-ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO4] presents physical absorption, and on the other hand, 1-ethyl-3-methylimidazolium acetate [emim][Ac] presents chemical absorption. To compare the fibers under study, the thickness of the composite fiber was examined using scanning electron microscopy (SEM). The mechanical properties and the bubble point were also evaluated. Permeability tests were conducted, and the gas permeation of the composite hollow fibers was measured using pure CO2. Laboratory-made stainless steel modules were used for the tests. All of the above tests were performed with the fibers in both wet and dry conditions. It was determined that the fibers with the ionic liquid immobilized would be promising for CO2 capture because the CO2 permeance significantly increased. Namely, D+[emim][EtSO4] achieved a 43% increase compared with the fibers without the addition of the ionic liquid, resulting in a CO2 permeance value of 57040 NL/(h m2 bar), which is higher than the values reported in the literature for PVDF. Moreover, the overall mass transfer coefficient for CO2 capture using the D+[emim][Ac] fibers also presented highly competitive values.