Kinetic study of esterification of rapeseed oil contained in waste activated bleaching earth using Candida rugosa lipase in organic solvent system

The effect of activated bleaching earth (ABE) from the oil processing industry on the production of fatty acid alkyl esters (FAMEs) by the lipase-catalyzed alcoholysis of waste plant oil with methanol in an organic solvent system was investigated. When ABE was added to a reaction mixture, the FAME formation rate improved nine-fold over the mixtures that did not contain ABE. The optimum ratio of ABE to ABE and rapeseed oil was 0.7 for the esterification of the rapeseed oil, where the lipase activity remained high without inactivation. The methanol was adsorbed onto the ABE and the equilibrium concentration (S) in the reaction mixture was represented as a function of ABE (m) and the initial methanol concentrations (Si) as follows: S=0.16m−1.76⋅Si2.17. In the case of the increase in the ABE concentration in the reaction mixture, the initial FAME formation rate increased rapidly until 1.8 mM/min and remained at a high rate regardless of the increase in the initial methanol concentration. The inhibition kinetics are summarized as a function of methanol on the conditions of the sufficient existence of rapeseed oil and lipase as follow: v=vmKs+S+S2Ki, where v, Ks and Ki denote the initial FAME formation rate, the Michaelis-Menten constant and the methanol inhibition constant, respectively. Subscript 'm' denotes the maximum. The kinetic parameters, vm, Ks and Ki, were determined to be 2.9 mM/min, 0.09 mM and 0.98 mM, respectively. These results indicate that the presence of ABE relieves the inhibitory effect of methanol on the enzyme because of the adsorption of methanol by ABE.