Phenols and Thiophenols in Petroleum Products by Spectrophotometry

This method is for determining phenols and thiophenols in gasoline, refinery caustics and crude cresylic acids derived from refinery caustics. In this method, the term "phenols" refers to mixtures of phenol, cresols, xylenols and other phenolic compounds that are typically found in these samples. Similarly, "thiophenols" refers to the analogous sulfur compounds. The method can be applied to higher boiling petroleum fractions such as kerosines and diesel oils, but the results are biased low and thus results by this method for such fractions are considered semi-quantitative.

The presence of high concentrations of thiophenols will interfere with the determination of phenols while high concentrations of alkyl mercaptans will interfere with the determination of thiophenols. A specific determination for phenols can be made after removal of both thiophenols and mercaptans by extraction. The quantitation range for phenols is 0.01 to 0.5 mass-% in gasoline, 0.01 to 40 mass-% in refinery caustic, and 0.1 to 10 mass-% in crude cresylic acids. The lower quantitation limit for thiophenols in gasoline is 0.002 mass-%. Due to the possibility of oxidation of the sulfur-containing compounds, prompt analysis after sampling is required to obtain correct results.