Fabrication variables affecting the structure and properties of supported carbon molecular sieve membranes for hydrogen separation

A high molecular weight polyimide (Matrimid) was used as a precursor for fabricating supported carbon molecular sieve membranes without crack formation at 550–700 °C pyrolysis temperature. A one-step polymer (polyimide) coating method as precursor of carbon layer was used without needing a prior modification of a TiO2 macroporous support. The following fabrication variables were optimized and studied to determine their effect on the carbon structure: polymeric solution concentration, solvent extraction, heating rate and pyrolysis temperature. Two techniques (Thermogravimetric analysis and Raman spectroscopy) were used to determine these effects on final carbon structure. Likewise, the effect of the support was also reported as an additional and important variable in the design of supported carbon membranes. Atomic force microscopy and differential scanning calorimetry quantified the degree of influence. Pure gas permeation tests were performed using CH4, CO, CO2 and H2. The presence of a molecular sieving mechanism was confirmed after defects were plugged with PDMS solution at 12 wt%. Gas selectivities higher than Knudsen theoretical values were reached with membranes obtained over 650 °C, showing as best values 4.46, 4.70 and 10.62 for H2/N2, H2/CO and H2/CH4 ratio, respectively. Permeance values were over 9.82×10−9 mol/(m2 Pa s)during pure hydrogen permeation tests.