The effects of additive on the gas separation performance of asymmetric membrane for CO2 separation

摘要

Polymeric membrane gas separation process is an emerging technology for CO2 capture from power plants. For improving the gas transfer properties and sustainability of the membranes, blending selected polymer materials in the membrane fabrication process has been widely investigated for dense film membrane. However, such a strategy has not been fully explored on asymmetric membranes, which are used in the majority of commercial membrane products. With this regard, a thorough investigation was carried out in this study to understand the effect of additives in the polymeric membrane fabrication process and to evaluate its influence on gas separation performance of both asymmetric flat sheet and hollow fiber membranes. In this study, polyethylene glycol (PEG) and PEG-PDMS (polydimethylsiloxane) copolymer were selected as the additives based on their performance in enhancing the CO2 separation performance in dense film membranes as well as their function in modifying the phase inversion during membrane formation process which consequently influence the membrane structure and the thickness of the skin layer. Therefore, the investigation in this study contributes to the knowledge in ascertain the effect of two types of additive in the structure and gas separation performance of asymmetric membranes.Compared with the pure PPE membranes, the CO2 permeances of the membranes containing 40 wt% PEG and 40 wt% PEG-PDMS of total polymer content were 5 and 2 times higher respectively without a loss of selectivity. Significant improvement in selectivity was also observed for the blended membranes with lower concentrations of additive. Matrimid® 5218 hollow fibers with 0 to 12 wt% additive (PEG or PEG-PDMS copolymer) fabricated with phase inversion technique were also evaluated in gas transport properties in relation to the membrane morphology and surface composition. Changes in membrane structure, particularly the skin layer of the hollow fiber were observed in hollow fibers with both additives. In particular, the aggregation of PEG-PDMS copolymer towards to fiber out surface was observed which contributed in the improvement in CO2/N2 selectivity.