Low severity lignite liquefaction: temperature programming to 350 °C in an inorganic solvent system

Abstract High conversions of Indian Head lignite into THF-soluble products can now be achieved using a temperature programming technique. Various temperature programmes using times up to 60 min and temperatures from 300 °C to 350 °C were used to liquefy Indian Head lignite. The inorganic solvent system H 2 SH 2 O was used in conjunction with CO, H 2 and pyrrhotite as the liquefaction medium. Programming the temperature produced higher THF-, toluene- and cyclohexane-soluble yields than the use of comparable isothermal temperatures. The temperature programme design was based upon data from electron spin resonance, thermal gravimetric analysis and differential scanning calorimetry. The maximum 60 min conversions obtained using temperature programming, to a final temperature of 350 °C were 95% THF-, 52% toluene-and 37% cyclohexane-soluble materials. Comparable isothermal yields with the reactor temperature at 350 °C were 78%, 36% and 31%, respectively. Therefore, enhanced liquefaction yields can be obtained by selectively programming the reactor temperature, presumably because of matching the free-radical generation rate with that of hydrogen donation.