In this work, the transesterification reaction of refined and crude oils was studied. The reaction was carried
out using methanol, with the aim of studying the effect of different catalysts, such as sodium and potassium
hydroxides and methoxides, all of them in the same molar concentration. The saponification is an important
side-reaction in this system, and was carefully analyzed in order to compare the yields and the rate of soaps
formation with each catalyst. Significant differences among them have been found. The catalyst and soaps
distribution between the biodiesel and the glycerine phases was also determined. It was found that a very
important fraction of the hydroxides, both sodium and potassium, are consumed by the saponification reaction,
thus decreasing the final acyl-glycerides conversion. Carrying out the reaction in two steps, it was
found that not improvement was obtained regarding the catalyst consumption and soap formation, what
indicates that the water fed to the system and the water formed by free fatty acid neutralization, determine
these values independently of the reaction strategy followed in the process.
The importance of this study is that in medium and small scale plants, the biodiesel production is often
carried out with crude oils, and consequently, the selection of the catalyst that minimizes soap formation
and its solubility in the biodiesel phase, is an important issue