Catalytic performance of bulk and Al₂O₃-supported molybdenum oxide for the production of biodiesel from oil with high free fatty acids content

Non-edible vegetable oils are characterized by high contents of free fatty acids (FFAs) that prevent from using the conventional basic catalysts for the production of biodiesel. In this work, solid acid catalysts are used for the simultaneous esterification and transesterification with methanol of the FFAs and triglycerides contained in sunflower oil acidified with oleic acid. Molybdenum oxide (MoO₃), which has been seldom considered as a catalyst for the production of biodiesel, was used in bulk and alumina-supported forms. Results showed that bulk MoO3 is very active for both transesterification and esterification reactions, but it suffered from severe molybdenum leaching in the reaction medium. When supported on Al₂O₃, the MoO₃ performance improved in terms of active phase utilization and stability though molybdenum leaching remained significant. The improvement of catalytic performance was ascribed to the establishment of MoO₃Al₂O₃ interactions that favored the anchorage of molybdenum to the support and the formation of new strong acidic centers, although this effect was offset by a decrease of specific surface area. It is concluded that the development of stable catalysts based on MoO₃ offers an attractive route for the valorization of oils with high FFAs content.
Financial support from Spanish Ministerio de Ciencia, Innovación y Universidades, and the European Regional Development Fund (ERDF/FEDER) (grant RTI2018-096294-B-C31) is gratefully acknowledged. L.M.G. thanks Banco de Santander and Universidad Pública de Navarra for their financial support under 'Programa de Intensificación de la Investigación 2018' initiative. JL is a Serra Húnter Fellow and is grateful to ICREA Academia program and 2017 SGR 128.