Producing a carbon fiber precursor by supercritical fluid extraction

Abstract

Abstract Supercritical fluid extraction is being investigated for the production of mesophase 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 °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 °C and 70 bar using a solvent-to-feed ratio of 3:1. This material was spun into 10 μm-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.