Low Temperature Naphthenic Acid Corrosion Study

Abstract The aim of this work is to define the corrosiveness of naphthenic acids and to examine a non-phosphorus corrosion inhibitor for low temperature (~ 200°C) naphthenic acid corrosion. Corrosiveness of NA is a function of their molecular weight (boiling point), and temperature. Corrosiveness of seven pure NA, twelve aliphatic and two aromatic organic acids, and fractions of NA distilled from industrial NA mixtures of three suppliers “F”, “A”, and “M”, was examined at their boiling points and at 195°C. Corrosion rates of carbon steel in contact with boiling aliphatic organic acids were 12 to 90 mm/year, but in pure boiling NA were 100 to 400 mm/year. Two aliphatic organic acids, heptanoic and nonanoic, showed corrosiveness similar to pure NA with corrosion rates 179 and 195 mm/year, respectively. Two aromatic hydrocinnamic (benzenepropanoic) and 6-phenylhexanoic acids showed extremely high corrosiveness in carbon steel: 646 and 638 mm/year respectively. The corrosiveness of the fractions from “F”, “A”, and “M” showed a maximum at about 300°C. Correlation between total acid number (TAN) and corrosiveness of NA fractions was not found. An industrial sulfur-based corrosion inhibitor showed lower efficiency (80 to 85%) than the phosphorus inhibitor (94 to 99%) and did not deteriorate catalyst activity and fuel quality.