Objective The second-generation biodiesel is produced through technological transformation of idle hydrogenation units to increase the application proportion of green, low-carbon and clean fuels, and practice the national strategy of carbon peaking and carbon neutralization.

Methods According to the current situation of the existing idle 0.3 Mt/a coal tar hydrogenation unit in a petrochemical company, the original key equipment and high-pressure equipment are maintained as much as possible to avoid problems such as long-term manufacturing and procurement of equipment. After comprehensive consideration of multiple factors, it was decided to transform reactor 1 into expanded-bed reactor, reactor 2 was still a fixed-bed reactor, and the reactor internals and process flow were adaptively transformed. After the transformation of the unit, the process flow was the combined process flow of expanded-bed/fixed-bed hydrogenation.

Results After the implementation of the transformation, the unit produced qualified second-generation biodiesel, the temperature rise of the expanded-bed reactor was gentle, the pressure drop in the reactor bed was stable, which effectively protected the fixed-bed reactor, reduced the severity of the unit operation and prolonged the unit operation cycle.

Conclusions The second-generation biodiesel produced by transforming the idle fixed-bed hydrogenation unit into the expanded-bed/fixed-bed hydrogenation combined process meets the requirements of product standards. The unit transformation has the advantages of small quantities, short transformation cycle, less investment and quick effect. It has good industrial promotion value for the transformation of similar units at home and abroad.