Optimization of rapeseed oil fatty acid esterification with methanol in the presence of sulfuric acid

The interest in biodiesel production from low cost feedstocks is still increasing. Such feedstocks usually contain large amounts of free fatty acids, which make the currently employed base catalysts inefficient, thereby promoting the use of acid catalysts. Due to the high activity and low cost, sulfuric acid could become the most widely used acid catalyst for biodiesel production. Research undertaken so far using sulfuric acid for esterification of fatty acids has shown that the products obtained fail to meet the requirements of the standard EN 14214. This paper describes a systematic study of rapeseed oil fatty acids esterification in order to obtain a product complying with the standard EN 14214. The influence of sulfuric acid concentrations (0.1-3.0%), methanol molar ratios (1:1-20:1) and reaction time (0-360 min) was evaluated. Finally, a two-stage esterification process was developed, where in optimal conditions esterification yield of 97.8% and ester content of 99.6% were achieved.