Utilization of used palm oil for lipase-based biodiesel production

Abstract

This study aimed to salvage used frying palm oil for lipase base-biodiesel production and to determine if polycyclic aromatic hydrocarbons (PAHs) formed in used frying palm oil affected the production. Chicken breast was repeatedly fried at 170°C for 15 minutes for 21 cycles. The color of the used oil became 56 folds darker than that of the refined palm oil and with 10 % higher viscosity. While water content remained similar, fatty acid composition was changed in that unsaturated fatty acid increased by 4% in used oil. By HPLC and GC-MS analysis, PAHs formed in used oil were detected and identified as naphthalene. The amount of naphthalene increased in each frying cycle and reached 0.16 ppm in the 21st frying cycle. When used frying palm oil was utilized for transesterification for biodiesel production catalyzed by immobilized lipase, Lipozyme RM IM and Novozym 435. PAHs accumulated in the oil exhibited adverse effect to the immobilized enzyme catalyst. It was found that naphthalene adsorbed onto Lipozyme RM IM and Novozym 435 upto 1.96 and 1.93 µmole per gram immobilized lipase, respectively. Further investigation showed that in the presence of naphthalene and benzo[a]pyrene, hydrolytic activity of Lipozyme RM IM was decreased by 77-80%, while that of Novozym 435 was decreased by 54-82%, respectively. Besides catalytic efficiency of the enzyme, there are several factors involving biodiesel production. Different types of methanolysis clearly yielded different %FAME conversion. When one-step methanolysis, three-step methanolysis and continuous-flow methanolysis were used, %FAME conversion using Lipozyme RM IM was 20.19, 38.96, and 39.89, respectively, while it was 48.0%, 52.0%, and 43.3% when Novozym 435 was used. Water content (0, 5, 10, 15% v/v), dosage of immobilized lipase (5, 10, 20%w/v), and reaction temperature (40°C, 50°C and 60°C) affected %FAME conversion differently when the reaction was catalyzed by Lipozyme RM IM and Novozym 435. The optimum production condition using 20% (w/v) Lipozyme RM IM were as followed: 1:4 molar ratio of used frying palm oil to methanol, with continuous-flow methanolysis at 60°C without water. With 24 hour reaction time, the maximum yield of FAME conversion was 52.1 %. On the other hand, the optimum production condition catalyzed by 20% (w/v). Novozym 435 were as followed: 1:3 molar ratio of used frying palm oil to methanol with continuous-flow methanolysis at 60°C without water. After 24 hour reaction time, the maximum yield of FAME conversion was 40.0%.