Fabrication of Carbon Molecular Sieve Membranes Supported on a Novel Porous Carbon Fiber

Carbon molecular sieve (CMS) membranes are inorganic membranes that can be easily prepared to separate gas components based on their molecular sizes. Supported CMS membranes are commonly fabricated by coating a precursor on a porous support followed by pyrolysis under inert conditions. However, the current availability of suitable porous supports is limited. Recently, a new porous carbon fiber (PCF), which can potentially be used as a support, has been prepared for commercialization. Thus, we herein report the preparation of CMS membranes supported on this new PCF using wood tar as the precursor. More specifically, the CMS membrane was formed on the outer surface of the PCF by dip-coating the wood tar solution (40, 60, 70, or 80 wt%) followed by pyrolysis at 600 degrees C. For comparison, CMS membranes supported on commercially available porous ceramic tubes (NA3) were also prepared under the same conditions. The morphologies of the CMS membranes were characterized by scanning electron microscopy. It was found that for both supports, the CMS membranes derived from the 70 wt% wood tar solution exhibited the optimum results for H-2 separation, although the PCF-supported CMS membranes exhibited a higher gas permeance and selectivity than the NA3-supported membranes. Furthermore, a thinner layer of dense carbon was formed on the PCF than on the NA3 support. Overall, this study demonstrated that PCF can be used for supported CMS membranes, wherein the PCF-supported CMS membrane derived from the 70 wt% wood tar solution and pyrolyzed at 600 degrees C exhibited the highest H-2 selectivity among the various membranes obtained over the pyrolysis temperature range of 500-700 degrees C. This membrane exhibited moderate H-2/N-2 and H-2/CH4 selectivities of 155 and 340, respectively, with a H-2 permeance of 86 GPU. Finally, our results show that wood tar is an attractive raw material for the preparation of CMS membrane precursors.