Variables affecting homogeneous acid catalyst recoverability and reuse after esterification of concentrated omega-9 polyunsaturated fatty acids in vegetable oil triglycerides

Global concerns regarding greenhouse gas emissions combined with soaring oil prices have driven the search for renewable diesel fuels derived from either virgin or waste vegetable oils, dubbed “bio-diesels”. A key challenge in the emerging bio-diesel industry is cost-effective pre-treatment of
waste vegetable oils to reduce free-fatty acid content prior to transesterification. This article reports, for the first time, recoverability and reusability of hydrochloric and sulfuric acid catalysts for efficient pre-treatment of waste cooking oils for subsequent conversion to bio-diesels. Esterification of omega-9 polyunsaturated fatty acids, particularly 18:2,18:3 linoleic acid with methanol and a homogenous acid catalyst was investigated over a range of fatty acid concentrations. It was determined that greater than 95% by weight of each catalyst was recovered after esterification under all conditions investigated. When recovered methanol was used, containing recovered catalyst and water, it was determined that hydrochloric acid catalyzed esterification exhibits a higher tolerance to water accumulation. After sulfuric acid was recovered and re-used, the observed rate constant decreased more than 50% to a value comparable to that observed for hydrochloric acid at more than three times the water concentration.