A carbon–silica–zirconia ceramic membrane with CO2 flow-switching behaviour promising versatile high-temperature H2/CO2 separation

Abstract

Many researchers regard silica, silica-based and zeolite membranes as the agents that will accomplish H₂ separation. These membranes are expected to be productive in various mixture systems and under very high temperatures. This work reports the successful fabrication of a composite carbon–SiO₂–ZrO₂ ceramic membrane with a unique pressure-induced switching of CO₂ flows that allows versatile H₂/CO₂ separation at elevated temperatures. TG-MS, DTG-TGA, FT-IR, CP-MAS-¹³C-NMR, and TEM provide corroborative evidence of the carbonization of starting material SiO₂–ZrO₂-acetylacetonate into C–SiO₂–ZrO₂. The resultant C–SiO₂–ZrO₂ displayed significant hysteresis in the CO₂ adsorption isotherm at a temperature well above the critical temperature of CO₂ (31 °C), which indicates structural conformation. Furthermore, single-gas permeation measurements showing upstream pressures of 200 and 500 kPa reveal different permeation values for CO₂ at 300 °C. In separating a H₂/CO₂ mixture at 50 and 300 °C under upstream pressures of 200 and 500 kPa, respectively, the flow of H₂ permeance reduces as the concentration of CO₂ increases in the feed side at 50 °C (1.14 × 10⁻⁸ down to 3.9 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹ at 200 kPa). The pressure-induced surface flow of CO₂ at 300 °C and 500 kPa, however, reduces the hindrance to H₂ flow and results in H₂/CO₂ selectivity of ∼20–30 for all CO₂ concentrations, which is on a par with molecular sieving membranes. This novel C–SiO₂–ZrO₂ material shows promise for many interesting applications.