Descarboxilação fotocatalítica de ácidos graxos para produção de biocombustíveis drop-in

Abstract

The growing concern about the progression of global warming effects caused by greenhouse gas emissions (GHG) over the years has sparked interest in diversifying the energy matrix. In this context, there has been an increased demand to produce drop-in biofuels, chemically identical to fossil fuels, to reduce dependence on non-renewable resources and mitigate CO2 emissions. To create a mixture of renewable hydrocarbons compatible with engine structures, the biomass used needs to undergo deoxygenation processes, such as thermo-catalytic ones. However, existing methodologies have some operational limitations such as high temperatures, high hydrogen gas pressures, and the need for specific reactors. In this sense, the present work proposes the development of a selective photocatalytic method for deoxygenating fatty acids from vegetable oils at room temperature, in a metal-free process without the use of hydrogen gas, employing an organic photocatalyst. The reaction was optimized for lauric acid (C12:0), found in various vegetable oils, yielding up to 80% conversion to alkanes with trace amounts of corresponding aldehyde and alcohol. The reactions were monitored by GC-MS and GC-FID, and the parameters evaluated included photocatalyst, hydrogen transfer agent, base, stoichiometry, solvent, reaction concentration, light source, and reaction time. In control experiments, the atmosphere played a crucial role. The use of oxygen gas promoted the formation of oxygenated products, while the use of inert gases favored alkane production. Subsequently, the reaction scope was expanded to include other pure fatty acids, resulting in a reduced proportion of oxygenated products and the formation of hydrocarbons in the range of aviation bio-kerosene and green diesel, with conversions ranging from 30% to 90%. Finally, the photocatalytic system proved highly efficient when applied to a mixture of fatty acids obtained from Licuri oil hydrolysis, yielding a mixture of alkanes (C9-C17) with a conversion rate of >90%. The analysis of the operational cost of the process determined that the expenditure associated with the energy required for the execution of a reaction is R$ 11.90. Thus, this new method emerges as a viable alternative to existing deoxygenation processes, enabling the production of drop-in biofuels gently with selective formation of Cn-1 hydrocarbons.