Produção de biocombustíveis avançados pelo processo de hidrodesoxigenação utilizando bio óleos e óleos alimentares usados

Abstract

The increasing demand for sustainable alternatives to fossil fuels has driven research into the production of advanced biofuels. This study investigates the hydrodeoxygenation process for the valorization of eucalyptus bio-oil and waste cooking oils (WCO), using CoMo catalyst with the aim of optimizing the reaction conditions to maximize the yield of hydrocarbons suitable for use as transport fuels. The experimental work evaluated the influence of temperature, initial H₂ pressure, and feedstock composition on the production of hydrocarbons, utilizing a fractional factorial design approach. To this end, a factorial matrix was constructed that integrates individual coefficients (main effects of temperature, initial H₂ pressure, and feedstock composition), interaction coefficients (combined effects of the factors), and quadratic coefficients. The study proposes five scenarios for constructing this matrix, culminating in the selection of a scenario composed of eight coefficients, which demonstrated the greatest influence on the yield of the solid, gaseous, and organic liquid phases. The investigation into the effect of temperature involved reactions conducted at 300°C and 440°C, with initial hydrogen pressures of 0,09 MPa and 1,1 MPa. The results demonstrated that higher temperatures favored the formation of gaseous products due to increased thermal cracking and decarboxylation reactions, while the yields of the liquid phase decreased. The best yield of n-alkanes was obtained at 440°C using only WCO, reaching 30,5% (v/v), with n-C17 and n-C15 as the predominant hydrocarbons. However, an increase in oxygenated compounds was observed when bio-oil was used, indicating a lower efficiency in oxygen removal. The effect of hydrogen pressure was studied through experiments at 0,09 MPa and 1,1 MPa, while keeping the temperature and residence time constant. The findings confirmed that higher hydrogen pressures increased the efficiency of hydrodeoxygenation, significantly reducing the content of oxygenated compounds in the liquid phase and enhancing the yield of saturated hydrocarbons. The highest yield of n-alkanes was achieved at 440°C with WCO, with concentrations ranging between 12– 12,8% (v/v) in the C5–C10 range (compounds characteristic of petrol) and between 17,7–19,4% (v/v) in the C11–C20 range (compounds characteristic of diesel). The greater availability of H₂ favored decarbonization over decarboxylation, resulting in lower CO₂ formation and a higher production of CO in the gaseous phase. Conversely, lower pressures promoted coke formation due to the increased polymerization of oxygenated compounds. The effect of feedstock composition was examined by analyzing the use of bio-oil, WCO, and 50:50 mixtures under conditions of 400°C and 0,55 MPa, with the aim of investigating the synergy between the two types of feedstocks. However, the presence of bio-oil in the mixture led to increased coke formation, adversely affecting catalyst efficiency and hydrocarbon yield. The application of more severe conditions (440°C and 1,1 MPa) resulted in a significant increase in polycyclic aromatic hydrocarbons, indicating that these conditions favored aromatization reactions over the saturation of hydrocarbons. The results demonstrate that the reaction conditions play a crucial role in defining the composition of the biofuel, with both temperature and hydrogen pressure directly influencing the efficiency of oxygen removal, the distribution of products, and the balance between liquid and gaseous yields. This study highlights that the conversion of WCO is more efficient than that of bio-oil due to its lower oxygen content, while the incorporation of bio-oil increases the production of aromatic and solid by-products, thereby reducing process efficiency. The 50:50 mixture provided a compromise between product yield and hydrocarbon quality.