(145d) Effect of Naphthenic Acid Structure on Corrosion

This work investigates the effect of the type of side chain attached to the acid on the acid corrosivity towards carbon steel. Three acid mixtures with a comparable carbon number range were selected for this study: two containing predominantly acyclic structures (A and B) and one containing a predominantly cyclic type structures (C). Structural information for these acid mixtures was obtained initially by liquid chromatography/mass spectroscopy. In the temperature range of 425-500 F, A and B acid mixtures showed comparable corrosion rates (32 mpy at 425 and 55 mpy at 500 F). However, C acid mixture showed significantly higher corrosion rates (42 mpy at 425 F and 87 mpy at 500 F). It is presently unclear why the cyclic structures are more corrosive. No evidence for excessive thermal breakdown or volatilization was seen in any of the three acid mixtures under the conditions studied. Presently, the overall TAN and the temperature have disproportionate effects on the corrosion rate, and structure appears at best to be a secondary effect.