Esterificação catalítica de ácido acético e glicerol para a produção de aditivos de combustível

Abstract

Biodiesel production through the transesterification route is on the rise, as a result, glycerol, a low-cost by-product of biodiesel, has become more saturated in the international market. A potential solution to this drawback could involve glycerol valorization, by its transformation into acetyl glycerides, by direct acetylation with acetic acid. Among the synthesized acetyl glycerides, triacylglyceride (TAG) have been labeled as potential high-quality liquid bio-additive to enhance fuel properties and could be adopted as surrogates for the tertiary alkyl ethers. However, glycerol acetylation is a slow reaction and hence the use of catalysts is necessary. Homogeneous catalysts are usually used, but they are difficult to be removed and toxic. Thus, heterogeneous catalysts arise as an alternative, due to being safer and easier to be removed. In this study, four different heterogeneous catalysts were evaluated in the glycerol acetylation: Nb2O5, NbOPO4, Al2O3, and HZSM-5. Catalysts were characterized by XRD, FTIR and N2 adsorption. The catalytic tests were carried out for 360 min in a batch reactor at 120 ºC, with varying catalyst loading and using acetic acid to glycerol molar ratios of 2:1, 4:1, and 6:1. An experimental planning was performed to evaluate operational condition effects in the reaction with the best catalyst. NbOPO4 performed the best for all the catalytic tests. With acetic acid to glycerol molar ratio of 6:1, NbOPO4 showed the total conversion of glycerol within 120 min reaction and the combined DAG and TAG selectivity of 70.93%. Furthermore, glycerol conversion and products selectivity are greatly influenced by the reaction temperature and the molar ratio of acetic acid to glycerol. Higher temperatures and molar ratios promote better glycerol conversion and higher TAG selectivity, reaching 100% glycerol conversion and 27,89% TAG selectivity when the reaction temperature is 120 ºC and the molar ratio is 6:1. Lastly, NbOPO4 is a promising alternative for glycerol valorization through acetylation.