Role of Catalyst in Hydrogenation of Coal

Abstract

Coal liquefaction has been performed in the absence and in the presence of catalyst such as iron, tungsten or molybdenum oxides, and the characteristic role of each catalyst in the reaction has been discussed. Taiheiyo-Coal of 80g, tetralin solvent of 100g and catalyst of lOg were put into a 500ml stainless steel autoclave and were heated at 400°C for 2hr under hydrogen pressure. The total pressure was maintained at 220kg/cm2 by means of introducing hydrogen gas through a pressure controller during the reaction.The 86% of coal was converted in non-catalytic reaction to toluene-soluble materials, while conversion of 93% was obtained in the reaction with each catalyst of calcined hematite and red mud and conversion of 100% with each catalyst of sulfided hematite, red mud, nickel-tungsten-alumina, nickel-molybdenum-alumina and cobaltmolybdenum-alumina.The liquefied product separated into distillate fraction (-410°C), oil fraction (undistillable and heptane-soluble) and asphaltene fraction (heptane-insoluble and toluene-soluble). The yield and properties of each fraction were significantly depended on the catalyst. In case that either calcined-or sulfided-hematite or red mud catalyst was used, coal conversion increased but the yield of asphaltene was also rather high, which indicates that the secondary cracking of asphaltene produced is difficult to proceed with iron-type catalysts. On the other hand, high value of coal conversion, and low yield of asphaltene were obtained with either molybdenum or tungsten catalyst, which indicates that the secondary cracking of asphaltene is promoted on these catalysts. Further cracking of oil fraction to distillate fraction is found to be rather difficult with any of the catalyst used in this study.The degree of dehydrogenation of solvent was calculated from the value of naphthalene/ (naphthalene+tetralin) in the distillate fraction after reaction. The lowest value of it was obtained when sulfided irontype catalyst was used. The role of catalyst in coal liquefaction has been discussed.