Quantification of detergent-dispersant additives in gasoline by thermogravimetry

Although additized gasoline has been commercially available in Brazil for many years, the national regulatory agency, Agencia Nacional de Petroleo, Biocombustivel e Gas Natural, has not published any reference method for the quantitative analysis of the detergent-dispersant additives present in such gasoline. The issue is hampered by the fact that the exact composition of the additives is unknown: they are sold as packages and their composition is treated as a trade secret by their manufacturers. In this study, a quantification method is proposed that only uses thermogravimetry, preceded merely by the pre-concentration of the additives by standard atmospheric distillation. The distillation residues from seven samples of gasoline additized with additive A at nominal concentrations from 100 to 5000 mg kg(-1) were analyzed, as were regular gasoline (without additive - blank), pure additives, and 15 samples of additized gasoline acquired at filling stations. By calculating the additive concentration ratio from the atmospheric distillation process and the mass loss relating to the main active components of the additives by thermogravimetry, it was possible to quantify the detergent-dispersant additives present in the gasoline samples, with a mean relative error of up to 11.2%. The proposed method is simpler and less costly than any other method encountered in the literature and the results indicate that it is potentially adequate for the analysis of any additized gasoline, irrespective of the additives contained in the package, and could be adopted by fuel quality control laboratories.