ENZYMATIC BIODIESEL SYNTHESIS FROM ACID OIL USING A LIPASE MIXTURE

The conventional biodiesel production process has some disadvantages. It is necessary to use refined vegetable oils with low free fatty acids (FFAs) content. An alternative route is to use low-cost acid oils in an enzymatic process. The use of lipases allows simultaneous esterification of FFAs and transesterification of triglycerides present in raw material forming alkyl esters. The aim of this work was to study the production of biodiesel using soybean oils with different acid contents (Acid Value of 8.5, 50, 90) and ethanol catalyzed by commercial immobilized lipases (Novozym 435, Lipozyme RM IM and Lipozyme TL IM). A significant decrease of acid value was observed mainly with Novozym 435 and Lipozyme RM IM. The use of a mixture of two immobilized lipases was also investigated to decrease catalyst cost and increase the amount of ester produced. The three commercial immobilized lipases were mixed in a dual system and tested for biodiesel synthesis from acid oil (AV of 8.5, 50 and 90). A positive synergistic effect occurred mainly for Lipozyme TL IM (1,3-specific lipase) and Novozym 435 (non-specific lipase) blend. The ester content doubled when this lipase mixture was used in ethanolysis of acid oil with AV of 90.传统生物柴油的常规生产工艺存在诸多弊端，必须使用游离脂肪酸（free fatty acids, FFAs）含量较低的精炼植物油。一种可行的替代路线是在酶法工艺中采用低成本酸化油。脂肪酶（lipase）的应用可同步实现原料中游离脂肪酸的酯化反应与甘油三酯的转酯化反应，生成烷基酯。本研究旨在探究以酸值（Acid Value, AV）分别为8.5、50、90的大豆油为原料，结合商业化固定化脂肪酶（诺维信435 (Novozym 435)、Lipozyme RM IM及Lipozyme TL IM）催化乙醇解制备生物柴油的工艺。研究结果显示，诺维信435与Lipozyme RM IM可显著降低原料的酸值。为降低催化剂成本并提升酯产物收率，本研究同时考察了双固定化脂肪酶复配体系的应用效果。将三种商业化固定化脂肪酶以二元复配形式组合，用于以酸值AV为8.5、50及90的酸化油为原料的生物柴油合成反应。结果表明，Lipozyme TL IM（1,3-特异性脂肪酶）与诺维信435（非特异性脂肪酶）的复配体系展现出显著的协同增效效果。当采用该脂肪酶复配体系催化酸值AV为90的酸化油乙醇解反应时，酯产物含量提升了一倍。