Mixed matrix composite membranes based on Pebax and nano-amorphous MIP-202 for CO2 separation

Abstract

Membrane-based separation technology for carbon capture has received increasing attention in the world due to low energy consumption, investment and operating cost. However, the simultaneous improvement in selectivity and permeance has faced large challenge for mixed matrix membranes owing to limited affinity sites and transport channels. Herein, the nano-scale MIP-202 (SM-202) was first prepared by inhibited Ostwald ripening strategy during crystal growth, and then nano-scale amorphous MIP-202 (ASM-202) was prepared by thermal chemical reaction. Subsequently, mixed matrix composite membranes (MMCMs) were developed by using ASM-202 as a filler and polyether-block-amide (Pebax) as a polymer matrix, and the hydrophilicity-modified polysulfone ultrafiltration membrane (mPSf) was utilized as a porous support. It is observed that ASM-202 possessed good miscibility with Pebax polymer chains as a result of hydrogen bonds between two phases. Thus, the as-obtained MMCMs showed outstanding CO2 separation performance (CO2 permeance: 936 GPU; CO2/N2 selectivity: 52), which were enhanced by 138 % and 108 % over that of the pristine Pebax membrane, as well as 15.3 % and 13.0 % over that of MMCMs incorporating with SM-202, respectively. The improvement in gas separation performance can be explained by the reason that the nano-scale ASM-202 with large specific surface area afforded more unsaturated metal sites and nitrogen-doped structure, thus improving the CO2 affinity in membranes. Moreover, the loose amorphous structure of ASM-202 provides more transport passageways, which enhanced the diffusion rate of gas molecules through the membranes. Besides, resultant MMCMs maintained great stability for over 360 h using the CO2/N2 mixed gas as feed gas, whose average CO2 permeance and CO2/N2 selectivity fluctuated at 880 GPU and 47.