High-performance carbon molecular sieve membranes for hydrogen purification and pervaporation dehydration of organic solvents

Abstract

Ultrathin (∼200 nm) and defect-free carbon molecular sieve (CMS) membranes were successfully fabricated on the inner surface of hierarchically structured porous supports (γ-Al₂O₃ layer coated α-Al₂O₃ tubes) via pyrolysis of a polyimide precursor at 700 °C. The chemical structure of the carbonized samples was examined in detail by means of Raman spectroscopy and X-ray photoelectron spectroscopy. From these studies, it was found that the carbonized samples consist of graphitic carbon layers containing sp³-type defects. The synthesized CMS membranes showed an unprecedentedly high H₂ permeance of up to 1.1 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and ideal separation factors of 24, 130 and 228 for H₂/CO₂, H₂/N₂ and H₂/CH₄, respectively at 200 °C. Furthermore, outstanding separation factors of 791 and 1946 with a water flux of about 0.5 kg m⁻² h⁻¹ were obtained at 70 °C for the pervaporation of 10 wt% water-containing binary mixtures of methanol and ethanol, respectively. These results unambiguously show that the carbon membranes developed in this work possess the potential for high-temperature hydrogen purification and dewatering of organic solvents.