Supercritical reactive extraction for Jatropha curcas L seed was demonstrated to be a viable process for biodiesel production process with high yield and the elimination of separate extraction step. However, because the solid seeds were reacted directly and susceptible to impurities contamination such as water and free fatty acid (FFA), it was important to determine their effects to the extraction efficiency and FAME (fatty acid methyl ester) yield in supercritical reactive extraction. In this study, varying amounts of water (0-40 wt.%) and FFA (0-30 wt.%) were added to the supercritical reactive extraction process performed at 300 degrees C, 30 min effective reaction time, 10 MPa and 5.0 ml/g methanol to solid ratio. It was found that the supercritical reactive extraction process had a higher tolerance limit for impurities than the nonsupercritical acid-catalyzed in situ transesterification process. The former was able to withstand up to 30 wt.% of water or FFA without significantly affecting the extraction efficiency and FAME content. A time variation study on the water content showed that the forward hydrolysis of triglyceride molecules to FFA led to a higher reaction rate. Furthermore, the re-hydrolysis reaction of methyl esters to FFA would also occur under a high concentration of methyl esters and water content. A thermal stability study demonstrated that there was no obvious ester decomposition for the process at or below 300 C for a reaction time not exceeding 30 min. (C) 2014 Elsevier Ltd. All rights reserved.