Effect of phase separation temperature on ester yields from ethanolysis of rapeseed oil in the presence of NaOH and KOH as catalysts

The effects of phase separation temperatures (5–90 °C) on losses of higher fatty acid (C16 and C18) ethyl esters in the glycerol phase were investigated. Losses of ethyl esters produced from ethanolysis of rapeseed oil were 30–60% higher when NaOH rather than KOH was used as homogeneous catalyst. The losses decreased with an increase in separation temperature, resulting in an increase in the yield of the ester phase. The concentration of impurities (e.g. alkali metals, free glycerol and glycerides) in the ester phase increased with increasing separation temperature due reversible transesterification and reciprocal solubility of the compounds. Carbonates formed during neutralization of the catalysts are also transesterification catalysts and they cause reverse reaction. The ethyl ester bound in the glycerol phase during NaOH-mediated catalysis can be extracted by heating the separated glycerol phase to 60–90 °C. The ester yield is increasing with increasing separation temperature, however with decreasing quality.