Esterification of enzymatically treated macaw palm oil catalyzed by heteropolyacid supported onto Nb₂O₅

Abstract

An approach to producing biodiesel is the esterification of free fatty acids with an acyl acceptor. Free fatty acids can be produced through the hydrolysis of acylglycerols and represent a somewhat challenging feedstock for the production of biodiesel due to slower kinetics and the production of water in the reaction. The purpose of this work was to demonstrate the feasibility of a Keggin-structured heteropolyacid, H₃PW₁₂O₄₀ (HPW) supported onto Nb₂O₅ to be used as a catalyst for the reaction of free fatty acids with ethanol to produce ethyl esters that comply with biodiesel norm values. The use of heteropolyacids as heterogeneous catalysts may present advantageous operational benefits, including the tolerance to residual water present in the medium and the potential for reusability. The catalyst was prepared via impregnation of HPW onto Nb₂O₅ and was characterized in terms of acidity and surface properties. The enzymatic hydrolysis of macaw palm oil yielded a feedstock containing a free fatty acid content greater than 93%. The hydrolysate was assessed as a reactant for the esterification reaction, evaluating temperature, molar ratio, and catalyst amount, leading to optimal conversions greater than 99% with viscosity and density within the regulatory limits for biodiesel. The use of heterogeneous acid catalysts, such as HPW/Nb₂O₅, represents a potentially feasible alternative to unlocking the potential of working with challenging feedstocks as oil hydrolysates.

Keywords:

• Biodiesel
• heteropolyacid
• niobia
• esterification
• macaw palm oil

Acknowledgements

The authors would like to acknowledge the unaccountable and caring dedication of Dr. Heizir F. De Castro (in memoriam) to the development of this work. Authors are also thankful to FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) for grants #2016/10636-8 and #2020/15513-7, and to CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), finance code 001.

Disclosure statement

No potential conflict of interest was reported by the authors.