Study of biodiesel production from animal fats with high free fatty acid content

► Biodiesel was obtained from animal fats with high free fatty acids. ► By acid-transesterification with H2SO4, 48 h of reaction were needed. ► H2SO4 and p-TsOH esterification decreased free fatty acids from fats less than 0.5%. ► 97.3% ester content was obtained by basic-transesterification of esterified fats. ► Most of biodiesel properties were well within EN 14214.