固定化脂肪酶催化高酸废油脂酯交换生产生物柴油

Transesterification of Waste Oil with High Acid Value to Biodiesel Catalyzed by Immobilized Lipase

探讨了固定化脂肪酶NOVOZYM 435催化高酸废油脂与乙酸甲酯酯交换生产生物柴油.NOVOZYM 435能催化高酸废油脂与乙酸甲酯的酯交换反应,反应24 H后甲酯产率为77.5%,但该值大大低于以精制玉米油为原料时的甲酯产率(86.2%).系统研究了反应体系中的水、游离脂肪酸和乙酸对反应的影响.当反应体系中的水含量低于0.05%时,水对酶反应速率和甲酯产率影响甚小,而水含量高于0.05%时,酶反应速率和甲酯产率随着水含量的增加而降低.游离脂肪酸对反应有较大影响,甲酯产率随着游离脂肪酸含量的增加而急剧下降.乙酸甲酯与游离脂肪酸反应产生的副产物乙酸是导致甲酯产率显著下降的原因.在反应体系中添加适量(油重的10%)的有机碱三羟甲基氨基甲烷或三乙胺可有效提高酶促高酸废油脂的酯交换反应速率和甲酯产率,使反应12 H后的甲酯产率分别达到85.9%和80.8%;碱的加入还提高了酶的操作稳定性,添加有机碱三羟甲基氨基甲烷或三乙胺可使反应10批次后NOVOZYM 435的相对酶活力分别由对照值86%提高到97%和93%.

The transesterification of waste oil with high acid value and methyl acetate to biodiesel catalyzed by the immobilized lipase Novozym 435 was explored. Novozym 435 can catalyze this reaction, and the methyl ester （ME） yield reaches 77.5% after reaction for 24 h, which is much lower than that （86.2%） using refined corn oil as the raw material. The effects of water, free fatty acid, and acetic acid in the reaction system on the reaction were systematically studied. Water has little influence on the reaction when its content is lower than 0.05 %, while above this value both the ME yield and the reaction rate decrease with increasing water content. Free fatty acid influences the reaction greatly, and the ME yield drops sharply with increasing free fatty acid concentration. Acetic acid, the by-product formed in the transesterification of free fatty acid with methyl acetate, is responsible for the decrease of ME yield. The addition Of organic bases such as trihydroxymethyi aminomethane and triethylamine at a concentration of 10 % based on the oil mass to the reaction system can not only speed up the reaction, but improve the ME yield as well, with ME yields being 85.9% and 80.8%, respectively, after reaction for 12 h. The operational stability of Novozym 435 is improved markedly by the addition of bases. Adding trihydroxymethyl aminomethane and triethylamine to the reaction system leads to a retention of 97 % and 93 % of the original activity of Novozym 435, respectively, after operation of 10 batches, while the control is only 86 %.