Kinetic model of biodiesel production catalyzed by free liquid lipase from Thermomyces lanuginosus

Conversion of plant oil to biodiesel was investigated using liquid lipase from Thermomyces lanuginosus. Presence of 2-3% water was necessary to preserve the enzymatic activity under methanolysis (3 x 0.5 equivalents of MeOH added in steps). Several individual reaction blocks were investigated and became the individual segments of the full kinetic scheme. Additional reaction schemes were introduced to imitate changing solubility/surface area of the reactants in aqueous and organic phases. The relevant rate constants were evaluated and included into a mathematical model. The experimental results and computer modeling showed that conversion of oil to 92-97% of biodiesel is feasible at 1% enzyme load (24 h, 35 degrees C) using the feedstocks containing 2-20% of water, 0-10% of glycerol, 0-20% of free fatty acids (F). The enzyme can be collected in a narrow white layer settled between biodiesel and glycerol-water phases, containing also F and monoglycerides (M). The lipase can be then reused after compensation for 5-10% loss of the enzyme. The main contaminants in the produced biodiesel are F (2-6%) and M (1-3%). Monoglycerides decrease below 0.2% if methanolysis is continued after separation of glycerol, while the level of F slightly increases. Major amounts of F and M are removed after brief mixing of biodiesel with alkali (2-5% of 5 M NaOH) and centrifugation. The obtained product is within the specification limits, which makes application of liquid lipase a perspective method for a large scale production of biodiesel. (C) 2016 Elsevier B.V. All rights reserved.