Avaliação da produção de biodiesel por transesterificação com catalisadores homogêneos e heterogêneos

Abstract

The increasing demand for renewable fuels with lower environmental impact has driven research focused on optimizing sustainable routes for biodiesel production, with the transesterification of vegetable oils standing out as an alternative to fossil fuels. In this context, the present study aimed to optimize biodiesel production from soybean oil using sodium hydroxide (NaOH) as a homogeneous catalyst, as well as to evaluate the catalytic performance of alternative metal oxides obtained from the recovery of metals present in spent batteries. The work sought to integrate reaction performance, experimental feasibility, and green chemistry principles. In the first stage, a 23 factorial experimental design was applied to evaluate the influence of temperature, reaction time, and NaOH concentration on mass yield and acidity index. Statistical analysis revealed that catalyst concentration was the most significant factor, directly affecting triglyceride conversion and soap formation. The optimal conditions identified (50 oC, 0.5 h, and 0.5 wt% NaOH) resulted in a yield of 94.9% and an acidity index of 0.28 mg KOH/g. Thermoanalytical and spectroscopic analyses confirmed the chemical conversion, evidenced by the difference in thermal profiles between soybean oil and biodiesel and by the presence of characteristic methyl ester bands in the FTIR spectra. In the subsequent stage, cobalt, copper, and zinc oxides, as well as ZnMn2O4, were recovered through hydrometallurgical processes and applied as heterogeneous catalysts. The transesterification assays showed the highest yield for CuO (74.5%), followed by CoO (64.3%) and ZnMn2O4 (64.5%), while ZnO (55.6%) obtained from alkaline batteries presented the lowest performance, possibly due to lower surface area and reduced accessibility of active sites. Physicochemical analyses indicated partial conversion for all oxides, confirming ester formation. Although the efficiency of the metal oxide catalysts was lower than that of NaOH, the results demonstrate the potential of these materials as sustainable alternatives, particularly due to their reusability, reduced environmental impact, and valorization of electronic waste. It is concluded that the use of catalysts derived from batteries is a promising route for sustainable biodiesel production, and further optimization of operational parameters, is recommended to enhance catalytic activity.