Removal From Gas Streams Using a Carbon Fiber Composite Molecular Sieve

A novel adsorbent carbon monolith has been developed at Oak Ridge National Laboratory. The monolith is fabricated from isotropic-pitch-derived carbon fibers and powdered phenolic resin via a slurry molding process. The resultant green-form is dried, cured, and carbonized to convert the phenolic resin to carbon, and then activated to develop a connected network of micropores within the carbon fibers and resin-derived carbon binder. The monolith is also macroporous, exhibiting large (>50 μm) pores between the fibers. The resultant open structure allows the free flow of fluids through the monoliths such that gases can reach the micropores where they may be selectively adsorbed. This novel adsorbent has been named a “carbon fiber composite molecular sieve” (CFCMS). Several separations have been demonstrated such as the separation of hydrogen from experimental gas mixtures containing H2 and H2S or H2 and CO2; the separation of CO2 from CH4; the separation of CO2 from air; and the separation of CO2, CO, H2S, and H2O from a variety of proprietary gas mixtures. The CFCMS is being investigated as a CO2 separation and capture device in carbon mitigation strategies for natural gas processing, fuel cells, and gas turbines. The monolithic material is rigid and strong, resistant to attrition and dusting, and because of its continuous carbon skeletal structure, electrically conductive. An adsorbed gas may be quickly and efficiently desorbed by the passage of an electric current, thereby allowing for a low-energy, electrical-swing separation system. It is possible to regenerate the carbon monoliths in the absence of a temperature increase, potentially reducing swing cycle times and improving separation efficiency. The structure and properties of the adsorbent CFCMS monoliths are reported. Some information on the experimental apparatus is provided. Breakthrough plots and performance data for CO2 separation and capture are presented, and the electrical swing adsorption process is discussed.