Hydrothermal liquefaction experiments were carried out in a batch stainless steel reactor (GSHA-0.5) equipped with a magnetic stirrer. The reactor was provided by Xintai Chemical Machinery Co., Ltd. (Weihai, China) with a volume capacity of 500 mL and designed to a maximum temperature and pressure of 723 K and 30 MPa, respectively. In a typical run, firstly, a certain amount of rice husk, ethanol and catalyst (if needed) mixture were loaded into the reactor. Secondly, the vessel was sealed and heated to the specified temperature by an external electric furnace. The temperature inside the reactor was monitored using a inner thermocouple and controlled by a proportional integral derivative module. Heating
time was about 50–60 min. Then the temperature was maintained for 20 min. The reactants were agitated vertically at 75 rpm. After the desired reaction time was elapsed, the autoclave was cooled down to room temperature by cool water. Cooling time was about one hour.