New Indicators for Determination of Acid Number in Diesel Fuel Containing Biodiesel

Abstract

A simple and green visual method for determination of Total Acid Number (TAN) is proposed for analysis of different engine fuels, especially biodiesel, its raw materials and blends with petroleum fuels. Two 4-hydroxystyryl N-octylpyridinium bromides dyes: 4-[-2-(4-hydroxy-3-methoxyphenyl) ethenyl]-1-octylpyridinium bromide and 4-[-2-(4-hydroxy-3,5-dymethylphenyl) ethenyl]-1-octylpyridinium bromide were used as indicators. Determination of TAN in butanol medium in the presence of 10−5–10−4 mol/L of the indicator have shown a high color contrast. Well-marked transition from pale yellow to blue/violet merocyanine form provides for determination of more than 0.01 mg/g of free fatty acids and more strong acids with RSD 1–5%. For the vast majority of samples, the value of the acid numbers found by the proposed method is in good agreement with the data obtained according to the standard ASTM D664-11 method. The optimal conditions for analysis of TAN in diesel samples were found. Particular attention is paid to the FTIR-spectrometric determination of biodiesel content in commercial diesel fuel samples. The content of biodiesel with a characteristic peak in the region that is responsible for the carbonyl group (1730–1750 cm−1) can be seen on the IR spectra