Efeito do pH da carga reacional na reforma em fase líquida do sorbitol em catalisador Pt-Re suportado em carbono

Abstract

With global economic growth and the huge concern about the quality of life in society and the planet, it is necessary to search for new technologies for power generation, making use of renewable natural resources efficiently. Regarded as one of the 12 most promising building block chemicals to be used in future biorefineries, sorbitol is an alternative to generate higher value added products such as liquid fuels, syngas, light alkanes and chemical inputs. Thus, this study aimed at contributing to a better understanding of the reforming reaction in liquid phase of sorbitol at high pressures using metal catalysts. The starting point was the reduction of the catalyst, which used a temperature ramp starting at room temperature until it reaches 400 ° C over a period of 10 hours, kept at this temperature for 2 hours and 15 minutes for decreasing the reaction temperature. Were used hydrogen stream flow equal to 30 ml.min-1 in the absence of pressure. For the reaction, were used a feeding solution of 20% sorbitol in water at pH 6,5, 10 and 3, a flow of argon, used as a carrier gas of 10 ml.min-1, temperatures of 250 and 265 ° C and pressures of 42 and 54 bar respectively, keeping the reaction system to a bar above the bubble point. The reduction profile of the catalyst 10%Pt/C showed the presence of two major distinct peaks, indicating the possibility of formation of species more easily reducible. The reduction profile of the catalyst 10%Re/C showed low hydrogen consumption, indicating that rhenium was partially reduced. Since the bimetallic catalyst 10%PtRe(1:1)/C was modified to reduce their profile after the addition of rhenium, indicating a strong interaction between the atoms of Pt and Re. CO chemisorption experiments show that the addition of rhenium increased the dispersion of platinum, resulting in the formation of alloy catalyst for Pt-Re/C. Observing the results of catalytic tests in pH 6,5 can be concluded that for the same conditions of temperature, pressure, WHSV and maintaining the pH of the solution supply around 6.5, the bimetallic catalyst 10%PtRe(1:1)/C has a much higher yield in the conversion of sorbitol monometallic catalysts compared to 10%Pt/C and 10%Re/C. In tests with pH10, it was observed that the conversion, both globally and gas was higher than that obtained in the tests compared with neutral pH tests at the same temperature. The study also found a significant hydrogen yield, especially compared to the values obtained in tests with pH 6,5, which can be justified by the addition of KOH solution supply. Already in the tests with pH 3, there was a decrease in both the overall conversion in the gas phase and with decreasing temperature as occurred in the tests with pH 6,5 and 10. It also showed a low income for all temperatures studied. The increase in space velocity causes a decrease in conversion at all pHs studied, which indicates the occurrence of a kinetic regime in the reaction system. At pH 6.5 the formation was mainly CO2, ethane, propane and butane in the gas phase and 1,4-Sorbitan in the liquid phase. Increasing the pH led to greater selectivity to CO2 propane and ethane, as well as an increase in hydrogen yield, indicating reactions of APDH. Under acid conditions, there was an increase in selectivity of the liquid phase, mainly producing isosorbide, 1,4-sorbitan and 1,4-Mannitan, denoting the occurrence of dehydration reactions.