Promoted propylene/nitrogen separation by direct incorporating 2-methylimidazole into PDMS membranes

Polymeric membrane separations have been used for hydrocarbon recovery in some polyolefin plants due to the low energy consumption and easy operation, but the relatively low separation factor and hydrocarbon permeance block their ways to popularization. In this study, membranes with high propylene permeance and sufficient separation factor for propylene/nitrogen separation were prepared by direct incorporating 2-methylimidazole (MIM) into polydimethylsiloxane (PDMS), which manifested simultaneous promotion of separation factor and propylene permeance. Interestingly, MIM simultaneously acted in promoting the crosslinking process of PDMS and tetraethyl orthosilicate. A series of tests and characterizations were conducted to investigate the microstructure, morphology, thermal property, and mass transfer property of the membranes. The gas separation performance of the MIM-incorporated PDMS membrane with a separation factor of 20.2 and propylene permeance of 440.9 GPU outperformed many other propylene-selective membranes reported in the literature. Molecular dynamics simulations revealed that MIM had a preferential affinity for propylene rather than nitrogen, which was similar to PDMS, but the propylene-affinity of MIM was significantly higher than that of PDMS, accounting for the promoted separation of propylene/nitrogen upon the incorporation of MIM. The MIM-incorporated PDMS membranes with readily available, cheap materials and straightforward manufacturing procedures should be a promising alternative for hydrocarbon recovery. It is also enlightening for the study and design of membrane materials for gas separation.