Microwave-driven oleic acid esterification over chlorosulfonic acid-treated hydroxyapatite: synergism for intensified biodiesel production

Abstract

O. Subsequently, the catalytic activity of HAP-S1 was evaluated in oleic acid esterification under microwave irradiation, resulting in a yield of up to 87% under optimized conditions of 10 wt% of catalyst to oleic acid weight, 10 : 1 methanol to oleic acid molar ratio, and 40 min reaction duration under microwave irradiation at 150 °C. The activity of HAP-S1 was attributed to the active S[double bond, length as m-dash]O and S-O-H functional groups, and a possible mechanism of acid-catalyzed esterification is proposed. The catalyst was also tested in the transesterification reaction of rapeseed oil, achieving a conversion of 40.2% after 60 min reaction duration under microwave irradiation. Furthermore, the catalyst was evaluated in a two-step esterification reaction to investigate its activity towards acidified feedstocks. Results showed that after two successive runs, acidity was reduced by 79.6% with a total FAME yield of 40.13%. The obtained results indicate that this catalyst, being an acid catalyst, is more suitable for direct esterification.