In this work, the biodiesel production process by transesterification of sunflower oil was investigated using tetramethyl ammonium hydroxide (TMAH) as catalyst. The reaction conditions, such as catalyst concentration, temperature and reaction time were optimized in order to obtain a product that fulfills the quality requirements of international standards. It was found that the optimum reaction conditions were: temperature 60 degrees C, 1.76 wt% TMAH catalyst and 2 h reaction time. High amount of soaps were formed when using this catalyst. Therefore, an alternative purification methodology was used, especially useful for samples with high soaps content. This procedure consists of a first extraction stage using neutral water, which efficiently remove soaps. TMAH increases the solubility of mono and di-glycerides in the glycerine phase, thus decreasing their concentration in the biodiesel phase. Consequently, for a given production of mono-and di-glycerides, lower amount of these compounds were found in the final biodiesel product, being this an important advantage of this catalyst. (C) 2013 Elsevier Ltd. All rights reserved.