An Integrated Process Of Biodiesel Production And PUFAs-rich Triglyceride Preparation From Microalgae Oil

It has been calculated with mathematic model that the most potential substituent of traditional diesel is the biodiesel produced from microalgae, which has also been considered as a potential source of polyunsaturated fatty acids(PUFAs). Microalgae with considerable PUFAs content may be used for both biodiesel production and PUFAs enrichment so as to improve its economic effect. To do this, in this paper, an integrated process of biodiesel production and PUFAs-rich triglycerides enrichment was systematically investigated. First, alkali- and lipase-catalyzed transesterifications were respectively studied and optimized; then molecular distillation was employed to separate PUFAs from the fatty acid ethyl esters(FAEEs). Based on the derivative, the parameters of PUFAs-rich triglyceride preparation were optimized by response surface method(RSM). The main results were listed bellow:(1) In the alkali-catalyzed transesterification, the optimal conditions were Na OH dosage 1.0%, molar ratio of ethanol to oil 10.0:1, temperature 75.0 °C and reaction time 2.0 h, with FAEE yield of 96.03%. The lipase-catalyzed transesterification in solvent-free system was optimized by RSM, and the optimal conditions were Novozym 435 dosage 6.0%, molar ratio of ethanol to oil 4.0:1, temperature 44.7 °C and reaction duration 17.6 h, with FAEE yield of 94.86%. Lipase-catalyzed transesterification is more suitable for this process due to its mild reaction conditions and less post-treatment procedures.(2) The optimal conditions of molecular distillation were temperature 90 °C and rotating speed 150 rpm. Under the optimal conditions, the heavy phase yield was 43.79%, the main fatty acid composition was C18:1(4.36%), C18:2(2.02%), C20:5(1.54%), C22:5(22.39%) and C22:6(58.96%). Docosapentenoic acid(DPA) and docosahexaenoic acid(DHA) ethyl ester content in the heavy phase was 81.35%, the recovery rate of DPA and DHA ethyl ester was 87.20%. The light phase yield was 56.21%, the main fatty acid composition was C14:0(15.56%), C16:0(35.80%), C16:1(2.76%), C18:1(17.30%), C18:2(9.33%), C18:3(2.16%), C22:5(2.80%), C22:6(6.50%), could be used as biodiesel.(3) The synthesis of PUFAs-rich triglyceride was optimized by single factor and RSM, the optimal conditions were Novozym 435 lipase dosage 3.1%, mole ratio of FAEEs to glycerol 3.1:1, temperature 61.3 °C, reaction time 24.0 h, with the glyceride yield of 96.96%. After removal of FAEEs, the product consisted of tricylglycerol(TAG, 71.74%), 1,3-diacylglycerol(1,3-DAG, 23.26%), 1,2-diacylglycerol(1,2-DAG, 4.75%), and monoacylglycerol(MAG, 0.10%).(4) In the whole process of transesterification and PUFAs-rich triglyceride preperation, the final biodiesel yield was 56.07%, and the main fatty acid composition was C14:0(15.56%), C16:0(35.80%), C16:1(2.76%), C18:1(17.30%), C18:2(9.33%), C18:3(2.16%), C22:5(2.80%), C22:6(6.50%). The glyceride yield was 43.04%, and the content of DPA and DHA in the final product was 83.93%, 2.2 folds of that in raw microalgae oil, the whole recovery rate of DPA and DHA was 85.80%.