Esterification of free fatty acids using water-tolerable Amberlyst as a heterogeneous catalyst.

To produce biodiesel from high free fatty acid (FFA) oils, the esterification characteristics of two kinds of heterogeneous acid catalysts, Amberlyst 15 and Amberlyst BD20, were compared. When the FFA contents of oils were 50.0 and 99.8 wt%, the activity of Amberlyst 15 gradually decreased with recycling, whereas the activity of Amberlyst BD20 was maintained during recycling. The activity of Amberlyst 15 was inhibited by the water produced during the esterification process, but the activity of Amberlyst BD20 was not similarly affected by water. In images obtained with a scanning electron microscope (SEM), many pores were seen within the Amberlyst 15 catalyst, whereas Amberlyst BD20 showed few pores. Despite the fact that the pores of the catalyst play a role in increasing the number of active sites, Amberlyst BD20, which had fewer pores, was deemed to have more desirable performance in reducing the inhibition by water of the esterification of high FFA oils.