AbstractThe free fatty acids in waste oil with high acid value were removed and transformed into fatty acid methyl esters by the extraction-reaction coupled process. The de-acidification efficiency and esterification conversion in the extraction-reaction coupled process were studied and compared with those in the stand-alone extraction process and the esterification process, respectively. Compared with cross-current batch extraction, the de-acidification efficiency of the extraction-reaction coupled process was equivalent to that of seven equilibrium stages in the conditions of the oil/methanol mass ratio of 1:1 at 60 oC. Compared with the esterification process, the esterification conversion of the coupled process was 90.3%, which is much larger than 46% in the esterification process at the reaction time of 32 minutes. Based on these findings, it is suggested that the extraction-reaction coupled process is a very effective and promising method for biodiesel production from oils having high acid value.