Improving Selectivity of Nanoporous Carbons for Gas Separation

Many potential applications exist for nanoporous carbon (NPC) membranes in industrial gas separations including air separation, refining syngas, separating landfill gas, and recovering hydrogen from hydrocarbons. The size selective nature of carbon, its chemical inertness, and its high temperature and pressure stability make carbon membranes promising candidates for gas separations. Given that carbon materials are mechanically fragile, supported carbon membranes are attractive for the fabrication of more robust membrane separation units. Thus, previous work has been done to explore the optimization of the permselectivity of NPC membranes on porous stainless steel supports. This work continues the approach of improving NPC membranes by enhancing single gas selectivity. NPC membranes with improved selectivity for oxygen over nitrogen were fabricated on nanofiller modified porous stainless steel supports by two different methods. In the first method, the NPC precursor, polyfurfuryl alcohol was synthesized at various temperatures to vary the molecular weight of the precursor. In the second method, silver was used in various weight fractions as a dopant in the membrane. NPC membranes were synthesized as a function of the synthesis conditions of the polyfurfuryl alcohol precursor. The performance of the NPC membrane was optimized at a polymerization temperature of 15ºC where O2/N2 selectivity and permeance values were 8.7 and 0.12(mol/sec/m2) x 105 respectively. This is most likely a result of optimal chain length and amount of cross-linking. Silver, which has an affinity for oxygen adsorption, was doped into the carbon matrix in an effort to increase the O2/N2 selectivity. Silver nanoparticles were incorporated into the membrane at various weight fractions and permeation testing was carried out as a function of silver loading. O2/N2 selectivity was increased by a factor of approxamately 2 when silver nanoparticle concentration reached 10% by weight in the NPC membrane.