Evaluating the gas permeation properties and hydrothermal stability of organosilica membranes under different hydrosilylation conditions

Abstract

Organosilica membranes were fabricated under controlled sol-preparation conditions such as the ratio of triethoxysilane (TRIES) and vinyltrimethoxysilane (VTMS) and the hydrosilylation temperature. The single-gas permeation properties and hydrothermal stability of organosilica membranes were evaluated to clarify the relationship between hydrothermal stability and organosilica structure. Pt-catalyzed and thermally cured hydrosilylation was applied to evaluate the effect that hydrosilylation temperature exerts on the properties of membranes. Organosilica membranes (Pt-catalyzed hydrosilylation at 40°C) showed H2 permeance of approximately 10−6molm−2s−1Pa−1 with H2 selectivity (H2/CH4:15, H2/CF4:950) at 500°C, and were stable under an oxidative atmosphere at 500°C. The organosilica network size derived by thermal curing at 500°C was smaller than that by Pt-catalyzed hydrosilylation, even though the units (Si–C–C–Si, Si–O–Si) were the same. Hydrosilylation reactivity derived by thermal curing (500°C, N2) strongly depended on the TRIES/VTMS (=H/V) ratio in the SQ sol, and an H/V ratio of 1.25 showed a higher level of hydrosilylation reactivity. Its hydrothermal stability was better than that of amorphous silica membranes, due to the incorporation of Si–(CH2)2–Si units in the networks via hydrosilylation, based on the decreased ratio of He and H2 permeance, the He/H2 permeance ratio, and the activation energy before/after steam treatment.