Desenvolvimento e otimização de métodos para determinação de ésteres metílicos e acidez em amostras de biodiesel, por técnicas cromatográfica e de eletromigração

Abstract

Biodiesel has attracted attention mainly for environmental subjects. This biofuel might reduce carbon dioxide emissions by 78% when compared to conventional diesel and presents better lubricating properties; greater point of combustion, making its transport and storage safer. According to the chemical standpoint, biodiesel is a mixture of esters formed from the transesterification reaction of triglycerides present in oils and fats, or from the esterification of fatty acids extracted from microorganisms with short chain alcohol (usually methanol or ethanol) in the presence of a basic (NaOH and KOH), acid (HCl and H2SO4) or enzymatic catalysts. Within this context, the development and optimization of increasingly efficient and rapid analytical methodologies for both biodiesel quality control and its raw materials become necessary. In the present work, samples of biodiesel were synthesized, via basic and acid catalysis, from different commercially obtained vegetable oils. For the determination of major fatty acid methyl esters in biodiesel samples, fast gas chromatography with flame ionization detector, “Fast GC-FID”, was used through a capillary column containing a stationary phase of ionic liquid under isothermal conditions of temperature. The method was successfully applied in the monitoring of transesterification reactions of basic catalysts and acids of vegetable oils such as soybean, canola, corn, sunflower and those used in the frying process. On the other hand, the determination of acidity in biodiesel samples was mediated through a method developed and optimized by capillary electrophoresis, with indirect ultraviolet detection at 224 nm. The investigative step for the preparation of the samples, which was configured as crucial to the success of the analyzes was carried out with the aid of a complete 32 factorial design, through the variation of the factors mass and the agitation time. The capillary electrophoresis method was satisfactory, since there were no significant differences, at the 95% level, when compared with the official methodology by potentiometric titration.