Otimização multivariada dos parâmetros do processo de produção de ésteres etílicos e modelagem cinética da reação de esterificação via catálise heterogênea utilizando óleo não comestível da polpa de macaúba, resina macroporosa de troca iônica e rota etílica

Abstract

Macauba pulp oil fruit has been exploited for the production of biodiesel because it comes from a raw material of low cost, inedible and high potential in oil. Its fruits capacity to generate different co-products favors the residues minimization in oil extraction and added value to the production chain. Furthermore, the macauba palm has a perennial culture, which exhibits high resistance to pests and can to grow in low rainfall areas. However, macauba oil has a high acid content, which requires alternative production processes such as homogeneous or heterogeneous acid esterification, hydrocracking, and thermal cracking. Hence, the production of ethyl esters was explored using macauba oil, ethanol and ion exchange resin. The system was conducted in batch through heterogeneous catalysis, which different types of macroporous ion exchange resins were evaluated with low and high acidity oils. The exploitation of this second type of oil (80.6% wt. acid content) is innovative, because previously reported works aimed the care in the collect and storage of the fruit with purpose that the oils did not reach high acidity. Although, this research focuses in the process development that adapts the oil characteristics, according to the industrial situation, besides oil refinement process are expensive. Among the resins tested: Purolite A500 / 2788, Amberlyst A26OH and Purolite CT275, the last presented the best performance and was selected to proceed with the exploration and optimization of the process. The investigation of the variables influence in the system was evaluated through Fractional Factorial Design 2IV4-1 and optimized by the Central Composite Design. In this step, a conversion of free fatty acids (FFA) obtained was higher than 80%. This could be increased for other variables variation such as: increase in reaction time, which was done in the kinetic study whose results reached average values FFA conversion of 93%. Moreover, it was also evaluated the reaction kinetic modeling by the pseudo-homogeneous (PH) first and second order models. The PH second order model was better suited to the experimental data, and the kinetic parameters could be estimated. The proposed model explained the experimental results with precision between 96 to 98%. The high value of the activation energy (Ea = 44 kJ / mol) ratified the hypothesis that the kinetics of the reaction be controlled only in the first 9 hours by the reaction that occurs in the catalytic surface, not limited by internal diffusion and external mass transfer. The main catalytic products were composed of esters, namely oleic acid ethyl ester, palmitic acid ethyl ester, linoleic acid ethyl ester, and palmitoleic acid ethyl ester. Furthermore, the catalyst was structurally stable after 10 reaction cycles even without any further treatment between cycles. Therefore, the esterification process proposed herein is a viable alternative to convert nonedible oils with high FFA, e.g. macauba pulp oil, into biodiesel; through a viable and sustainable eco-friendly process