Production of biodiesel via ethanolysis of waste cooking oil using immobilised lipase

This study reports the lipase-catalysed ethanolysis of waste cooking oil (cottonseed) in batch reactors at temperatures between 297 and 348 K, spanning sub- and supra-stoichiometric initial ethanol to oil molar ratios (1 <= beta <= 9). Lipase from Candida antarctica, supported on macroporous acrylic resin (Novozym 435) was employed as catalyst. Optimum reactant ratio was found to be beta = 3, with rapid decline in rate observed on either side of this value. A kinetic model based on the Ping-Pong Bi Bi mechanism incorporating inhibition by both substrate and ethanol as well as the effect of temperature was developed and adequately described the rate data. A transition in apparent activation energy, from 50.0 +/- 3.2 kJ mol(-1) to 17.3 +/- 0.2 kJ mol(-1), attributed to both kinetic factors and thermal denaturation, occurred at 320 K. Transient water concentration profiles exhibited pronounced oscillatory behaviour as the reaction approached equilibrium, symptomatic of the role of water as an allosteric regulator of lipase. (C) 2012 Elsevier B.V. All rights reserved.