Produção de acetinas: emprego de catalisadores à base de Sn(IV) e desenvolvimento e validação de metodologia analítica por GC-FID

Abstract

The challenges inherent to fossil fuels have enhanced the interest in biodiesel as a biofuel, because it is renewable and less harmful to the environment. However, its production route (transesterification) generates about 10% in volume of glycerol as a co-product. In order to add value to this co-product, this work proposes to evaluate the acetylation of glycerol (GLI) with acetic acid (AA), for the first time, with Sn(IV) based catalysts aiming to obtain monoacetin (MA), diacetin (DA) and triacetin (TA), which present vast industrial application, making it an attractive technological route. Moreover, in order to promote the expansion of analytical methods for the characterization of these chemical inputs, a GC-FID based methodology was developed and validated for the determination of glycerol acetates. The reaction tests with catalysts Bu2SnCl2, Me2SnCl2, BuSnCl3, Bu2SnLau2, BuSnO(OH), Bu2SnO, showed that BuSnCl3 presented the best performance, with full conversion of GLI and expressive selectivity to acetins (25.7, 43.5 and 30.8% for MA, DA and TA, respectively) under mild reaction conditions (80 °C, molar ratio AA:GLI of 4:1 with 3 h of reaction). These observations were evidenced by the kinetic study of the reactions under different temperatures (40, 80 and 120 °C) and molar ratios of the reactants (AA:GLI - 3:1, 4:1 and 6:1). The determination of activation energy (Ea), showed that without catalyst, Ea = 23.9 kJ mol-1 and with BuSnCl3, Ea =14.3 kJ mol-1, demonstrating the potential performance of Sn(IV) species in this route. The GC-FID method developed with an apolar column (RTX-5MS - 30 m x 0.25 mm x 0.25μm) was completed with total run time of 3.3 min, demonstrating time and cost savings. The validation process initially evaluated the selectivity of the method, in which solvent and sample chromatogram comparisons did not demonstrate the presence of interferents in the retention times of the peaks of interest; the analytical curves presented R ≥ 0.9982 and from their parameters the LOD and LOQ were determined, which resulted in ≤ 0.0007 g mL-1 and ≤ 0.0022 g mL-1 values; the precision of the method, evaluated through repeatability and reproducibility, resulted in ≤ 3,3% coefficient of variation values; the recovery tests carried out by the fortification of a reaction sample with the analytical standards at 3 concentration levels resulted in recoveries from 80.81% to 101.60%; and with changes in sample preparation (different solvents and injection volumes), the method showed to be robust. All parameters evaluated proved to be within the adopted criteria, and finally the validated methodology was applied to real samples of pure and biodiesel residual glycerol (with and without catalyst), and it proved to be efficient. Thus, the results generated in this Thesis have shown to be highly viable alternatives for industrial application of glycerol transformation into products with higher added value, besides providing a validated methodology for quantitative determination of the reaction products.