Modelagem cinética e termodinâmica da transesterificação de óleo de soja degomado catalisada por Zr/CaO

Abstract

Biodiesel presents itself as an alternative with less environmental impact in relation to mineral diesel. The incorporation of larger portions of biodiesel into diesel of fossil origin represents a significant reduction in the emission of air pollutants. The application of heterogeneous catalysis to transesterification reactions has as main objective the reduction of process costs, which is favored by the greater ease of recovery and recycling potential presented. The use of ethanol as a reagent has advantages such as lower toxicity and production of a fuel with a higher cetane number and better lubricity, in addition to having consolidated production in Brazil. A bibliographic review was carried out investigating the application of heterogeneous catalysts for the transesterification of soybean oil. The research was applied in the database of Science Direct searching for research articles written in English, with the keywords biodiesel AND transesterification and (“heterogeneous catalyst” OR “heterogeneous catalysis”) AND soybean oil, within the period from 2015 to 2019. This work presents an investigation of the use of zirconium impregnated calcium oxide in the production of biodiesel from ethyl transesterification of degummed soybean oil. The catalyst was prepared using a wet impregnation method, containing 15 wt % of Zr and calcined at 700 ° C. The transesterification reactions were conducted in a batch reactor with an ethanol reflux system. Temperatures between 60°C and 90°C, quantities of ethanol in molar ratio between 15: 1 and 27: 1 in relation to oil, and reaction time up to 6h were investigated. The samples were filtered to remove the catalyst, the excess ethanol was evaporated and the resulting mixture was centrifuged to separate the upper layer containing biodiesel and acylglycerols from the glycerol. The samples were analyzed on HPLC-UV to quantify the acylglycerols and determine the yield. To investigate the effects of the reaction parameters, a second order linear empirical model was adjusted based on a Box-Behnken experimental design. It was considered a kinetic model composed of three consecutive reversible reactions, in which for high values of excess alcohol, the reactions can be described as Pseudo first order in the direction of product formation and second order for the reverse reaction. From the experimentally obtained concentrations of acylglycerols over time, for a 60°C – 90°C temperature range, 4 parameters were adjusted for each reaction: 𝐴, 𝐸𝑎, ΔH0 e ΔS0. Within the range of parameters evaluated, the yield has a direct correlation with temperature and reaction time and an inverse correlation with MR. It was possible to accurately describe the process using a proposed model.