One of the main problems of microalgae lipids is their high content of free fatty acids (FFAs), which creates problems of soap formation during homogeneous alkali transesterification. The main purpose of this study was to test heterogeneous catalysts to transform the FFAs from a oil (oleic acid + canola oil) used as a model and from microalgae lipids (Scenedesmus obliquus and Chlorella protothecoides) into biodiesel. Under the conditions tested (temperature: 120 degrees C, autogenous pressure, reaction time: 60 min, methanol to lipid ratio: 0.57 mL/g and 2.5 wt% Amberlyst-15 relative to microalgae lipids), Chlorella protothecoides lipids allowed to reach a higher conversion (84%) compared to Scenedesmus obliquus lipids (34%). However, the study showed that both microalgae lipids suffered from mass transfer limitations, due to impurities, because FFAs conversions higher than 90% were obtained with the model oils (20-33 wt% FFAs in canola oil). Despite the fact that the FFAs from both microalgae were suitable to produce biodiesel, further studies must be made on alkali transesterification of the remaining lipids still present in microalgae biodiesel and on crude lipid purification in order to limit the mass transfer problems. (C) 2016 Elsevier B.V. All rights reserved.