Improved hydrogen selectivity of Surface Modified Graphite (SMG) membranes: Permeation experiments and characterisation by micro-Raman spectroscopy and XPS

Abstract

Permeation experiments on Surface Modified Graphite (SMG) membranes showed an improved mixed gas separation factor α (H2/CO2) of 9.2 (+80%) and α (H2/H2O) of 10.2 (+70%) compared with the pristine graphite membranes with α (H2/CO2) of 5.1 and α (H2/H2O) of 6.0. The surface modification was obtained by the treatment with different silanes at 140°C, for 2h under reflux and continuous stirring in an argon atmosphere. The dried powders were pressed to discs and evaluated for the ternary feed mixture (41vol.‐% H2/41vol.‐% CO2/18vol.‐% H2O). XPS analysis of the membrane surface revealed sp2 and sp3 hybridisation states, carbonyl, carboxyl groups and CFx bonds for the pristine and SMG membranes. Spatially resolved micro-focused Raman spectroscopy showed that the improved separation performance correlates with a specific modification of the G and D1 modes of the pristine graphite surface for each functionalisation carried out. Therefore, the improved performances result from the specific chemical and physical interactions of H2, CO2 and H2O with the applied defect modifications of the SMG membranes.