Síntese e caracterização do catalisador KF/suporte e sua aplicação no processo de transesterificação em condições pressurizadas

Abstract

Biodiesel is considered a substitute for fossil diesel. It is commonly produced by the process of transesterification of vegetable oil and animal fats, through homogeneous alkaline catalysis. Although this route presents high yields in fatty acid esters, disadvantages such as saponification reaction and biodiesel purification steps are observed. In this context, the use of heterogeneous catalyst in the process of obtaining biodiesel, such as those containing potassium fluoride in their composition, has been explored. Therefore, a catalyst based on waste glass particles and potassium fluoride was synthetized and used the continuous production of ethyl esters under pressurized conditions. Catalyst synthesis conditions were evaluated from the central composite rotational design, varying the mass ratio of potassium fluoride, waste glass particles, calcination temperature for the variable responses of ethyl ester content and potassium leaching. The best catalyst synthesis condition, in the evaluated ranges, was identified as 50 % potassium fluoride in relation to the support calcined at 500 °C. This catalyst provided 69 % ethyl esters and 8 % potassium leaching. Transesterification reactions were carried out in a continuous flow reactor under pressurized conditions, in which the operational conditions of the transesterification reaction were evaluated. The highest fatty acid ethyl esters (FAEE) content (~99 %) were obtained under conditions of 250 °C; 20 MPa; mass ratio oil: ethanol 1:2; 2,5 g of de catalyst with a residence time of 30 min. The catalyst produced under the optimized conditions was characterized in order to verify the efficiency of the chemical treatment of potassium fluoride in the waste glass particles. In this sense, Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy, laser induced-breakdown spectroscopy (LIBS) and powder X-ray diffraction (PDRX) analysis helped to determine the functional groups, structural, elemental composition, and active sites that favor catalytic activity. In addition, a basicity of 1.54 mmol g-1 was observed in the catalyst produced under optimized conditions, and the basicity basic strength changed from H_-<6.8 to 9.8<H_-<11.0 after chemical treatment of waste glass particles with potassium fluoride.