Produção de biodiesel utilizando óxido de cálcio e zirconato de sódio livre e suportado em materiais poliméricos

Abstract

Biodiesel is commonly produced by the transesterification reaction of oils or fats, in the presence of an alcohol of short chain and a catalyst. The development of suitable heterogeneous catalysts is important in order to propose alternative processes that are economically viable for biodiesel production as well as to facilitate the purification steps. In this research, two different catalysts (calcium oxide, CaO, and sodium zirconate, Na2ZrO3) were evaluated for biodiesel production in their free form and also supported on polymeric materials. Moreover, different reactor configurations were evaluated: reactor with magnetic stirring (MS), with recycle (RL) and with ultrasonic agitation (US). For the assays with CaO, the obtained reaction yield was approximately the same (80% of Fatty Acid Methyl Esther - FAME) in the three proposed reactor configurations. The reusability of CaO was evaluated in the ultrasonic reactor, but the results were not satisfactory for more than the first reaction cycle due to the catalyst deactivation. Moreover, the polymers evaluated to support CaO did no resist the reaction conditions. The catalyst Na2ZrO3 was evaluated in its free form and also supported in poly (vinyl alcohol) (PVA) and in reactors with magnetic stirring and with ultrasonic agitations. The obtained kinetic profile showed that, in the beginning, the reaction is slower in the ultrasonic reactor than in the reactor with magnetic stirring. However, at the end, both reactor configurations reached the same yield. A composite central planning was carried out to evaluate the optimal conditions of methanol:oil molar ration and catalyst loading (%) when using the free and supported catalysts and in the magnetic stirring and ultrasonic reactor. The answer was evaluated in terms of %FAME and viscosity. Reactions were performed at a fixed temperature and time (55°C and 6 h). Different answers were obtained for the different reactor configurations. For the free catalyst in the reactor with magnetic stirring, great values of %FAME and low values of viscosity are obtained in the central region of the composite central planning. For the free catalyst in the ultrasonic reactor, the best values are obtained at higher values of methanol:oil molar ratio and at the central region of the catalyst loading. For the supported catalyst in the reactor with magnetic stirring, the best values are obtained in the region of 5 to 7% of catalyst loading and methanol:oil molar ratio of 10:1 to 30:1. For the supported catalyst in the ultrasonic reactor, the best values are obtained at higher methanol:oil molar ratios, but at lower catalyst loadings. These results are associated with the mass transfers related to the different degree of agitation in both reactors and to the accessibility to active sites of the catalyst. The catalyst reuse was evaluated in five sequential baths without intermediated washings with solvents. For both reactor configurations, the Na2ZrO3 presented suitable stability. Results showed that the heterogeneous catalysis is a viable alternative for biodiesel production. Moreover, the utilization of a supported catalyst is feasible due to the easier catalyst recovery. The ultrasonic assisted reactor is also a suitable alternative.