Low-temperature cross-linking fabrication of sub-nanoporous SiC-based membranes for application to the pervaporation removal of methanol

Abstract

Separating azeotropic organic-organic mixtures using membranes is of great importance in the chemical and petrochemical industries, but remains extremely challenging because membranes must be able to withstand harsh working conditions while providing adequate permselectivity. Silicon carbide (SiC)-based membranes have attracted a great deal of interest due to their high level of structural stability, mechanical strength, and corrosion resistance. Herein is an account of the first study focused on a systematic investigation into the physicochemical and pore structural variations of polycarbosilane (PCS)-derived SiC-based membranes under different air-curing and pyrolysis temperatures. Air curing for cross-linking behavior was found to occur at temperatures as low as 150 °C, and the completion of polymer-to-ceramic conversion for PCS was observed at 750 °C. In addition, the pore structure and surface properties (hydrophilicity/hydrophobicity) of PCS membranes could be tuned by the pyrolysis temperature. PCS membranes derived from air curing at a temperature as low as 150 °C possessed sub-nanopores that ranged from 0.5 to 0.66 nm depending on the pyrolysis temperature. The formation of these sub-nanopores was attributed to sparsely cross-linked networks. Subsequently, the pervaporation (PV) performance of methanol/methyl acetate, methanol/toluene, and methanol/methyl tert-butyl ether were evaluated and discussed with respect to any effects of different pore sizes of the membranes and operating parameters. The most outstanding separation performance emerged from SiC-based membranes with a pore size of 0.50 nm that were air-cured at 150 °C and then pyrolyzed at 750 °C. The impressive PV separation capability was attributed to the surface hydrophilicity, suitable pore size, and high quality of the SiC-based membranes. Furthermore, the PV performance correlated well with single-gas permeation, suggesting that PV performance could be predicted based on single-gas permeation. The developed SiC-based membranes have excellent separation performance and are a promising candidate for the PV separation of MeOH from organic mixture systems.