High performance purification process of methyl and ethyl esters produced by transesterification

Abstract

The aim of this work is the obtention of high quality methyl and ethyl esters, particularly in those cases in which conventional purification procedures fail such as in the production of ethylesters or in the case of methylesters obtained from high acidity raw materials, e.g. in the range 1–4%. Three different methodologies were employed, according to the soap content of the crude biodiesel: (a) one washing step with a CO2 saturated solution; (b) two consecutive washing steps with CO2 saturated solutions; (c) first neutral washing using a small volume of water and a subsequent washing with a CO2 saturated solution. These procedures were compared with the classical method that uses a first acid washing followed by a neutral one. The washings with CO2 saturated solutions showed excellent performance, giving a final product with quality parameters similar to the ones obtained with conventional methods (washing with HCl solution). It was demonstrated that the utilization of a first neutral washing to purify biodiesel with high soap content is highly efficient since it abates a high percentage of these soaps without generating phase separation or problems of emulsion formation. Furthermore, this acid solution (water saturated with CO2) is less corrosive than the solutions normally used (hydrochloric, sulfuric, phosphoric, or citric acid). It was found that in order to decrease the sterol glucosides deposition in the final biodiesel, the combination of longer washing times and centrifugal separation was very effective in reducing these contaminants in the final product.