Effect of Hydrotreatment of Various Heavy Oils as Solvent for Coal Liquefaction

The correlation between the properties of vehicle solvents and the yield of distillable oil products from the liquefaction of Japanese subbituminous coal using tar sand bitumen, shale oil, coal liquid, anthracene oil, and their hydrotreated oils as vehicle oil was investigated. Experiments were carried out in a 500-mL autoclave at 420-450 °C under 160-200 kg/cm² (gauge) hydrogen pressure using red mud-sulfur as a catalyst. In some cases, hydrotreatment of solvents and liquefied heavy products was also carried out in the same autoclave at 390 or 420 °C using Ni-Mo type catalyst. The yields of distillable oil calculated on a daf feed basis from coal liquefaction using untreated heavy solvents were fairly low at about 65-75 wt % with the exception of tar sand bitumen which showed 55 wt %. The distillable oil yields increased up to 80 wt % with hydrotreatment to a level comparable with coal-derived solvent with the additional hydrotreatment of the liquefied products. To obtain a higher yield of distillable oil, prehydrotreatment of tar sand bitumen is very important. On the other hand, hydrotreatment of the liquefied product is very effective in the case of shale oil and coal-derived solvent. The oil yields calculated on the basis of the reactivity of solvent without coal under the same conditions also improved with hydrotreatment. Distillation characteristics and structural analyses of solvents are discussed in detail with yields of gas, oil, and SRC.