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Diamine modification of P84 polyimide membranes for pervaporation dehydration of isopropanol



The effectiveness of chemical crosslinking modification of P84 copolyimide membranes using diamine compounds for pervaporation dehydration has been investigated, and the scheme to enhance separation performance of asymmetric polyimide membranes has been developed. Two diamine crosslinking agents, p-xylenediamine and ethylenediamine (EDA), were used in this study for both dense and asymmetric P84 membranes. Experimental results suggest that the crosslinking reaction induced by EDA is much faster than that by p-xylenediamine because the former has a smaller and linear structure than that of the latter. However, membranes crosslinked by p-xylenediamine are thermally more stable than those by EDA. Membranes modified by p-xylenediamine or EDA have increased hydrophilicity. An increase in the degree of crosslinking reaction initially results in an increase in separation factor with the compensation of lower flux for pervaporation dehydration of isopropanol (IPA). However, a further increase in the degree of crosslinking reaction may swell up the polymeric chains because of the hydrophilic nature of these diamine compounds, thus resulting in low separation performance. It is found that post treatment after crosslinking reaction can significantly enhance as well as tailor membrane performance because of the formation of charge transfer complexes (CTCs) and the enhanced degree of crosslinking reaction. A low-temperature heat treatment may develop pervaporation membranes with high flux and medium separation factor, whereas a high-temperature heat treatment may produce membranes with high separation factor with medium flux. © 2006 American Institute of Chemical Engineers AIChE J, 2006