PDMS/PEI Composite Membranes Modified With Porous Materials For Gas Separation

When using polymeric membranes for gas separation, an upper limit was found by Robeson which suggested that a trade-off existing between permeability and selectivity. While the inorganic membranes which have properties lying far beyond the limit cannot be produced large-scalely in industry for the lack of technology. In view of that the mixed matrix membrane combining the advantages of both sides has emerged.ZSM-5 molecular sieve and metal organic frameworks Cu3(BTC)2 both possess regular pore size and relatively large porosity, and many researches have shown that adding them into polymeric membranes have improved the overall separation properties of the membranes.For the first stage, PDMS/PEI composite membrane consisting of ZSM-5 molecular sieve was prepared. The composite membrane showed the best separation performance with 20% ZSM-5 loading. The CO2/CH4 selectivity was 4.7, and O2/N2 was 3.1. High pressure was beneficial for selectivity and permeability. But the SEM figures showed that the combination of ZSM-5 molecular sieve and PDMS was not compact, and ZSM-5 molecular sieve cannot be dispersed evenly in PDMS.In the following experiment, by using a couple agnet, the particle surface of ZSM-5 molecular sieve was modified. Experimental results and SEM figures both proved:ZSM-5 molecular sieve could be dispersed more evenly in the polymer, and better interface morphology was formed. Compared with the composite membrane loaded with unmodified molecular sieve, the composite membrane filled with surface-modification ZSM-5 molecular sieve showed better performance:When using OTES as coupling agnent for modification, the CO2/CH4 selective could reach at 5.36, O2/N2 at 3.6. At the same time, the higher pressure was helpful to improve the gas separation and permeable performance of composite membrane.In the former experiment, it suggested that 5A ZSM-5 molecular sieve ddin’t match PDMS. PDMS has good permeability but filling ZSM-5 molecular sieve would reduce the permeable performance of composite membrane for gas permeability. Metal organic frameworks Cu3(BTC)2 had been proven to be a material with both high selectivity and permeability, so in the following experiment composite membrane loaded with Cu3(BTC)2 was prepared. The results showed that the composite membrane with 20% Cu3(BTC)2 loading has the best separation effect. The selectivity of CO2/CH4 was 5.56, which was better than before The increase of stress was beneficial for composite membrane separation and permeability.At last, the composite membrane with 20% ZSM-5 molecular sieve loading and the composite membrane with 20% Cu3(BTC)2 loading were used for CO2/CH4 mixture gas system experiment, raw material gas pressure CO2 concentration in the feed gas and retention gas flux were considered to be the relevant factor to influence the performance of composite membrane. The results showed that the two kinds of composite membrane present differently, for Cu3(BTC)2 filling composite membrane, high pressure, low CO2 concentration was beneficial for the separation of the gas; For filling ZSM-5 molecular sieve composite membrane, lower pressure and higher of CO2 concentration was conducive to the gas separation. Low flux of retention gas was good for composite membrane.