Kinetics of transesterification of soybean oil

Abstract

Transesterification of soybean oil with methanol was investigated. Three stepwise and reversible reacttons are believed to occur. The effect of variations in mixing intensity (Reynolds number = 3,100 to 12,400) and temperature (30 to 70'CJ on the rate oireaction were studied while the molar ratio of alcohol to triglycerol (6:l) and the concentration of catalyst (0.20 wt% based on soybean oil) were held constant. The variations in mixing intensity appear to effect the reaction parallel to the variations in temperature. A reaction mechanism consisting of an initial mass transfer-controlled region followed by a kinetically controlled region is proposed. The experimental data for the latter region appear to be a good fit into a second-order kinetic mechanism. The reaction rate constants and the activation energies were determined for all the forward and reverse reactions. lAOCS 74,1457-1463 (1997).KEY WORDS: Biodiesel, kinetics, methyl esters, mixing, renewable fuels, soybean oil, transesterification. triglycerides.Over the last few years. fatty acid methyl esters have assumed importance as research has intensified on the utilization of vegetable oils and animal fats derivatives for liquid fuels, known as biodiesel. Fatty acid methyl esters are products of the transesterification of fats and oils with alcohols in the presence of an acid or an alkaline catalyst. Three consecutive and reversible reactions are believed to occur ( l ) . Mono-(MG) and diglycerides (DG) are the intermediates formed in these reactions.The variables affecting the transesterification process (also called alcoholysis) have been intensively investigated as widening industrial uses were found for esters (2-6). Molar ratio of alcohol to vegetable oil, type of catalyst, temperature, and presence of impurities such as free fatty acids and moisture are among the variables that have been studied.There are a number of kinetic studies in the literature on the transesterification of esters with alcohol. However, only a few of these studies deal with vegetable oils and fatty esters. The studies on the transesterification kinetics for nonfatty esters include: the determination of the reaction rate constants, the equilibrium constant, and the activation energy for the acid-catalyzed reaction of butanol with ethyl acetate (7) and ethanol with butyl acetate (8). .4 review by Sridharan and Mathai (9) on the transesterification reactions involving alco--To whom correspondence should be addressed. E-&. houreddini@unI.edu.holysis, acidolysis, vinyl interchange, and ester-ester inrerchange contains many of the reported studies.The transesterification kinetics for vegetable oils and fatty esters has been reported in a few studies. Dufek and coworkers (10) studied the acid-catalyzed esterification and transesterification of 9(1O)-carboxystearic acid and its mono-and dimethyl esters and reported unequal chemical reactivity for different carboxyl and carboxymethyl groups. Freedman and conorkers ( l ) investigated both acid-and alkaline-catalyzed transester...

On-line monitoring of the transesterification reaction carried out in microreactors using near infrared spectroscopy

“…According to previous works [35], the use of high ethanol to oil molar ratio results in greater ester formation in a shorter time. As shown in Fig.…”

Production of biodiesel by transesterification of refined soybean oil

“…They suggested that hydroxide concentration could be increased up to 1. wt%, resulting in 95% methyl ester after 15 min. Using 1% sodium hydroxide in this present study, ~98% methyl ester was produced in 3 h. Noureddini and Zhu (1997) recommended a 6:1 molar ratio of alcohol to soybean oil which was adopted in this work and a reaction temperature near the boiling point of the alcohol (60 o C for methanol). Optimal conversion of soybean oil to methyl ester was also established under these conditions in this work.…”

“…A 6:1 molar ratio of alcohol to soybean oil and a reaction temperature near the boiling point of the alcohol (e.g. 60 o C for methanol) were recommended (Noureddini and Zhu, 1997). After the transesterification reaction, different separation techniques to purify the biodiesel product from the other products were investigated by Karaosmanoğlu et al (1996).…”

Monitoring of Biodiesel Transesterification Process Using Impedance Measurement

“…As two phases is not immiscible caused poor diffusion between the phases it has a result in a reaction rate. When methyl esters are formed, it will become a mutual solvent for reactants [9], and boost the reaction as explain by steep increase in capacitance value. When the catalyst and reactance is decrease consumed by the process, the reaction rate has slow before it reached steady state.…”