Producing a Carbon Fiber Precursor by Supercritical Fluid Extraction

摘要

Supercritical fluid extraction is being investigated for the production ofmesophase pitch, a liquid crystalline precursor for the manufacture of high-performance carbon fibers. A continuous-flow apparatus is being used to fractionate an isotropic petroleum pitch feedstock with supercritical toluene at temperatures to 400 deg C and pressures to 200 bar. This pitch was separated into isotropic and liquid crystalline, or mesophase, portions in a region of liquid-liquid equilibrium. Since the phases are opaque, an electrical impedance technique was used to monitor the location of the liquid-liquid interface. A 100% mesophase pitch was produced at 340 deg C and 70 bar using a solvent-to-feed ratio of 3:1. This material wa spin into 10 micrometer diameter fibers which were oxidized, carbonized and tested for physical properties. The final fibers exhibit tensile strengths and moduli comparable to the best pitch-based fibers currently available. With these fiber properties and the continuous nature of this process, supercritical extraction is an attractive alternative to existing pitch treatment processes.