Method for preparing high cetane number biodiesel through hydrogen backflow grease hydrogenation

The invention relates to the field of renewable energy and specifically relates to a method for preparing high cetane number biodiesel through hydrogen backflow grease hydrogenation. The method comprises the following steps: (1) under hydrogen existence, biological renewable grease contacts a hydrotreating catalyst to perform a first section of hydrotreating to obtain refined oil; (2) under the hydrogen existence, the refined oil contacts an isomerism catalyst to perform a second section of hydroisomerization pour point depressing treatment, and then distillation and separation are performed to obtain biodiesel; in the step (1), the hydrotreating conditions are that hydrogen partial pressure is 5.0 to 8.0MPa, a volume ratio of hydrogen to oil is (500 to 1) to (800 to 1), a liquid time massspace velocity is 0.5h to 3h, and a reaction temperature is 320 to 400 DEG C; in the step (2), the conditions of the second section of the hydroisomerization pour point depressing treatmentare that hydrogen partial