In a direct coal liquefaction process, in addition to the liquefaction condition, the distillation condition of the liquid product is an important factor to develop the process because it strongly affects the properties and yields of the distillate and bottom. Therefore, this paper investigates the effects of the vacuum distillation temperature on the yields and properties of the bottom and distillate, using the liquid products obtained from the primary hydrogenation section of the two-stage Victorian brown coal liquefaction (BCL) process with various feed solvents.
When recycled distillate (b. p.180-420°C) was used as a feed solvent, almost all of the n-hexane solubles (HS) in the heavy product were distillable up to a temperature of ca.315°C at 10 mmHg. As a result, the distillate yield increased with the temperature. However, the preasphaltenes also increased gradually with the temperature. On the other hand, when the solvent containing a bottom derived from primary and/or secondary hydrogenation was used as a feed solvent, the HS in the bottom remained at the same temperature (315°C), and the amount of preasphaltenes was constant. These differences were explained by the fact that the HS and asphaltenes derived from the bottom-containing solvent were more hydrogenated and stabilized, and their molecular weight was larger than that derived from the distillate solvent. It is also found that the viscosity of the bottom from the bottom-containing solvent was higher than that from the distillate solvent.
