Production of biodiesel by esterification of oleic acid with ethanol over organophosphonic acid-functionalized silica

► A novel catalyst organophosphonic acid-functionalized silica SG-T-P was developed. ► Esterification of free fatty acid oleic acid with ethanol was catalyzed by SG-T-P. ► Effects of various experimental conditions in esterification reactions were studied. ► The biodiesel production process optimization was carried out by RSM. ► SG-T-P can absorb water in reaction mixture at the same time.