Method for Isolation and Detection of Ketones Formed from High-Temperature Naphthenic Acid Corrosion

Corrosion control at refineries remains a challenge because the mechanism of naphthenic acid (NAP) corrosion is still not fully understood. The rate of NAP corrosion does not correlate with acidity (as measured by total acid number); therefore, it has been suggested that a subset of NAP in petroleum fractions may be more corrosive than others. Because the primary corrosion product (iron naphthenates) may thermally decompose to ketones at corrosion temperatures (250–400 °C), ketones in corrosion fluids could potentially be used to implicate specific problematic acids in corrosion tests. To that end, we have developed a method for isolating and characterizing ketones in corrosion test solutions. Ketones from tests on palmitic and 4-cyclohexyl pentanoic acids (C16H32O2and C11H20O2) have been successfully isolated with a strong anion exchange solid-phase separation. Gas chromatography/mass spectrometry identifies ketones formed as a result of model acid corrosion. Fourier transform ion cyclotron resonance mass spectrometry further confirms the detection of these ketones and structurally confirms ketones by use of a commercially available reagent that targets ketones and aldehydes. Additional oxygen species generated in the corrosion test likely result from reactions between dissolved atmospheric oxygen and the mineral oil matrix. With this method now validated, it can be applied in future studies of more complex acid mixtures to determine any structural specificity in naphthenic acid corrosion.