17-38: Enzyme-catalyzed production of biodiesel from waste cooking oil

Biodiesel is commonly produced by alkaline catalysis, which requires high-purity oils. However, low-quality oil can be used as feedstock to produce biodiesel by enzyme-catalyzed transesterification. In this work, waste cooking oil was evaluated as feedstock for fatty acid ethyl ester (FAEE) production. The raw material was mainly composed by palmitic (13.65%), oleic (30.19%) and linoleic (38.22%) acids. Free acid content (1.33±0.01 mgKOH/g) showed that the waste cooking oil was inappropriate for alkaline-catalyzed transesterification because saponification reaction could occur. Molar ratio oil:ethanol, mass ratio enzyme:oil and temperature were the investigated variables.  Immobilized lipases from Candida antarctica (CALB), Pseudomonas fluorescens (LPF) and Thermomyces lanuginosa (LTL) were evaluated. Microwave-assisted heating was also compared to conventional one. The yields of transesterification catalyzed by CALB were 2.5 and 3.5-fold higher than those catalyzed at the same conditions by LPF and LTL, respectively. After 24h FAEE yield of 65.35±0.02% was achieved when CALB-catalyzed ethanolysis was carried out under 40^oC, 1:7 molar ratio oil:ethanol, and 10% mass ratio enzyme:oil. Similar yield (61.4±3.1%) was achieved with LTL-catalyzed ethanolysis at 25^oC. The most significant factor affecting the yield of FAEE was the heating pattern. FAEE-yield of almost 75% was achieved after 6h of transesterification catalyzed by CALB (1:7 molar ratio oil:ethanol, 10% mass ratio enzyme:oil, 40^oC) in a microwave reactor. The high viscosity of waste cooking oil (62.39±4.61 cP) was greatly reduced after enzyme-catalyzed ethanolysis. This study showed that waste cooking oil can be used as feedstock for enzymatic production of biodiesel.

Financial support: FAPESP (Project 2011/23194-0) and ANP-PRH-44.