PDMS membrane incorporated by zeolites with tunable pore chemistry for dimethyl carbonate/methanol azeotropic mixture separation

The separation of organic-organic azeotropic mixtures is important in the petrochemical, agrochemical, and pharmaceutical industries, which is energy-intensive by using the current distillation technology. Pervaporation process is energy-efficient for azeotropic separation, while lacks of high-performing membrane materials. In this work, to realize efficient separation of dimethyl carbonate/methanol azeotropic mixtures, a benchmarked membrane, polydimethylsiloxane (PDMS), was incorporated by zeolites with tunable pore chemistry. Specifically, MFI-type zeolite was grafted by alkyl chains with different carbon numbers (C₁, C₄, C₈), thereby providing tunable transport channels for organic molecules. Based on systematic characterizations (e.g., sorption and LF-NMR) and permeation test, we found that the organophilic alkyl chain can trap organic molecules into the zeolitic pores while may also hinder the organic diffusion through the zeolite due to the steric hindrance effect. The PDMS mixed-matrix membrane (MMM) with optimized C₁-grafted MFI loading as high as 50 wt% exhibited separation factor of 3.6, and permeation flux of 11.5 kg m⁻² h⁻¹ for 30 wt% DMC-methanol azeotropic mixture at 40 °C. With slightly higher separation factor, the flux of PDMS MMM is 1.5-fold higher than that of the pure PDMS membrane. This work highlights the critical role of filler pore chemistry on the solution-diffusion transport and thus performance enhancement of MMM.