Investigation on the Esterification of Fatty Acids Catalyzed by the H₃PW₁₂O₄₀ heteropolyacid

• Published in: Journal of the American Oil Chemists' Society 2008-06, Vol.85 (6), p.555-560
• Main Authors: Cardoso, Abiney L, Augusti, Rodinei, Silva, Márcio J. da
• Format: Article
• Language: English
• Subjects: Agriculture; Biodiesel; Biological and medical sciences; Biomaterials; Biotechnology; Catalytic esterification; Chemistry; Chemistry and Materials Science; esterification; Fat industries; Food industries; Food Science; Free fatty acids; Fundamental and applied biological sciences. Psychology; Heteropolyacids; Industrial Chemistry/Chemical Engineering; Original Paper; renewable energy sources
• ISSN: 0003-021X; 1558-9331
• DOI: 10.1007/s11746-008-1231-0

In this work, the H₃PW₁₂O₄₀ heteropolyacid (HPW) was employed as a homogeneous catalyst to promote the efficient esterification (ethanolysis) of a number of saturated and unsaturated fatty acids (myristic, palmitic, stearic, oleic, and linoleic) under mild reaction conditions. HPW showed a similar activity to those observed for p-toluene sulfonic acid (PTSA) and sulfuric acid (H₂SO₄), the other acidic catalysts we compared them with in this study. In the HPW-catalyzed esterification of stearic acid, the addition of water caused a remarkable decrease in the ethyl stearate yields. On the other hand, the increase in the HPW concentration (up to a maximum value) promoted a proportional improvement in the oleic acid to ethyl oleate conversion. Kinetic measurements using oleic acid as a prototype substrate revealed that the esterification reactions catalyzed by HPW, H₂SO₄, and PTSA are of first-order in relation to the fatty acid concentration. Finally, the catalytic activity of HPW remained unaltered even after several recovery/reutilization cycles whereas the tungsten content in the final product (biodiesel produced by the HPW-catalyzed esterification of oleic acid) was found to be at an acceptably low level (0.0095 mg of W per g of biodiesel).