Kinetic and technological aspects of butyloleate production in the presence of metal oxides

Abstract

The kinetic regularity of reaction between oleic acid and butan-1-ol in the presence of zinc, nickel (II), iron (II), and copper (II) oxides were investigated under stationary conditions. It was found that at 383 K zinc oxide is the most active catalyst among other oxides. The rate of esterification reaction in the presence of other metal oxides is lower and approximately the same. It was shown that the kinetic equation of esterification reaction has the first order for oleic acid (at a content of 0.25 % mass of the heterogeneous catalyst in the reaction mixture and 7.6–8.0 times molar excess of alcohol). The effective rate constants for a quasi-homogeneous kinetic model of esterification reaction catalyzed by zinc and nickel (II) oxides at different temperatures are determined. The constants are used to calculate the activation energy and pre-exponential factor. It was shown that the quasi-homogeneous model of the reaction between oleic acid and butan-1-ol satisfactorily describes the esterification process under non-stationary conditions. The conversion values of oleic acid calculated according to the kinetic parameters and its values determined experimentally under non-stationary conditions for 360 min of the reaction were 80.0 and 75.9 % for zinc oxide catalysis and 53.7 and 47.5% in the presence nickel (II) oxide, respectively. The obtained data allow calculating the duration of the esterification process required to achieve a given oleic acid conversion under appropriate temperature conditions. It was found that zinc and copper (II) oxides interact with oleic acid during the reaction and form the corresponding salts. Using conductometry, it was found that the electrical conductivity of the reaction mixture increases by 6.1 and 1.6 times compared to the model mixture of reagents without catalysts, provided that the reaction is catalyzed with copper (II) oxide and zinc oxide, respectively. It is assumed that in presence of these oxides heterogeneous and homogeneous catalytic esterification of oleic acid by butan-1-ol occurs simultaneously. It is indicated that one of the limiting factors for the use of metal oxides as catalysts for the transesterification of triglycerides by lower aliphatic alcohols is the content of free fatty acids in the oil.