微酸强化超临界甲醇法连续化合成生物柴油

Weak acid intensification for continuous synthesis of biodiesel by supercritical methanol method

超临界甲醇法合成生物柴油的苛刻反应条件制约其大规模工业化。加入微量酸可提高反应速率,降低苛刻的反应条件,且不会带来后续分离问题。实验在温度270—360℃,压力9—15 MPa,停留时间300—1 300 s,醇油摩尔比(20∶1)—(40∶1)的条件下,研究了加入油酸、硬脂酸和微量磷酸对过程的强化,并进行了比较。结果表明:磷酸是最佳的酸性催化剂,在磷酸催化的条件下,最佳反应条件为温度300℃、压力13 MPa、停留时间700 s、醇油摩尔比30∶1,磷酸加入量为使大豆油酸价为15 mg/g(以每g大豆油KOH质量计)的加入量。在此条件下,脂肪酸甲酯的收率达到95%以上。

The severe condition of supercritical methanol restricts the large-scale industrialization of biodiesel synthesis. Weak acid can increase the reaction rates, reduce the severe reaction conditions and has no follow-up separation problems. The investigation was carried out in a tubular reactor, under the conditions of temperature 270-360℃, pressure 9-15 MPa, residence time 300-1 300 s, mole ratio of methanol to oil （20 ： 1 ） -（40 ： 1 ）. The effects of adding oleic acid, stearic acid and phosphoric acid on intensifying the process were investigated, and a comparison of each other was given. The results indicate that the phosphoric acid is the best catalyst among those three acids. Under the condition of phosphoric acid catalysis, the optimal reaction conditions are as follows： temperature 300℃, pressure 13 MPa, residence time 700 s, mole ratio of methanol to soybean oil 30： 1, and the dosage of phosphoric acid is in such an amount that makes the soybean oil acidity be 15 mg/g （ as per gram of soybean oil KOH mass）. FAME yield can reach 95%.