Effect of hydrogenation of liquefied heavy oil on direct coal liquefaction

•DCL result of liquefied oil is dependent on its boiling range and composition.•Hydrogenation of liquefied heavy oil help to improve its hydrogen donating ability.•A new method to prepare recycle solvent by hydrogenation of heavy oil is proposed.

The effect of hydrotreatment of liquefied heavy oil on direct coal liquefaction (DCL) was studied by hydrogenating the liquefied heavy oil (initial boiling point greater than 320 °C) in a 30 ml continuous hydrogenation apparatus at operating conditions of pressure (P) 13-19 MPa, temperature (T) 360-400 °C, liquid space velocity (LHSV) 0.6-1.4 h−1. After hydrogenation, the properties and hydrocarbon composition of liquefied heavy oil were regulated, leading to the enhancement of hydrogen donating ability and 5.6% increase in oil yield of DCL as compared with non-hydrogenated raw oil. Based on the results, a new method of preparing recycle solvent for direct coal liquefaction by mixing hydrogenated heavy oil and un-hydrogenated middle oil in a suitable proportion was proposed, which has been verified to be effective and efficient to increase oil yield.