Pore subnano-environment engineering of organosilica membranes for highly selective propylene/propane separation

Membrane-based separation techniques are responsible for great advances in the separation of propylene/propane mixtures. In this study, bis(triethoxysilyl)acetylene (BTESA) was selected as the precursor in the fabrication of organosilica membranes for use in propylene/propane separation. We proposed an effective strategy to finely engineer the pore subnano-environment of BTESA membranes for highly selective propylene/propane separation via controlling the calcination temperatures. Measurement of the surface energy, the ²⁹Si-NMR spectra, and the gas sorption isotherms clearly indicated that low-temperature calcined BTESA materials with a greater number of silanol groups showed an enhanced affinity to propylene molecules. BTESA membranes calcined at 150 °C featured a promisingly high C₃H₆/C₃H₈ selectivity of 52 and a C₃H₆ permeance of 1.7 ✕ 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ at 50 °C. These values were approximate to those reported for ZIF-8 membranes and higher than the standards for commercialization. The high level of C₃H₆/C₃H₈ separation performance was believed to be accounted by the synergetic effects of both controlled pore size and enhanced affinity to propylene molecules. Moreover, compared with traditional organosilica membranes that were calcined at ~350 °C, low-temperature calcination (150 °C) for BTESA membranes efficiently reduced the energy consumption and fabrication cost.