New inhibitors for preventing naphthenic acid corrosion

The aim of this work is to define the inhibitive properties of tannic acid; the high-density alcohols 1,2-propanediol and glycerol; the heavy vacuum gas oil (HVGO) fraction distilled from the acidic crude oil "AL" at 370-520°C; and high molecular weight residues remaining after distillation of various commercially available naphthenic acid (NA) mixtures at 1 atmosphere having a final boiling point of above 300°C, for preventing low temperature (∼ 200°C) naphthenic acid corrosion (NAC). The substances investigated significantly inhibited the NAC of pure iron and carbon steels C1010 and A516Gr70 in acidic corrosive kerosene. Tannic acid can be used alone as a powder at concentrations > 10 ppm or dissolved in 1,2-propanediol or a mixture of the latter with isopropyl alcohol with efficiency > 90%. The solvent 1,2-propanediol alone at concentrations 25 to 50 ppm showed efficiency of 90%. Glycerol alone at 50 ppm showed efficiency of 100%. The HVGO fraction distilled from the acidic crude oil "AI" at 370-520°C, at 50 ppm showed efficiency of 96%. Corrosiveness of different fractions of NA, distilled every 10°C from industrial NA mixtures of four suppliers "F", "A", "M", and "K", was examined on carbon steel at their boiling points and at 195°C. Corrosion rates of carbon steel increased with increasing boiling points of different fractions, but significantly decreased above 300°C. High molecular weight residues, remaining after distillation of NA mixtures at 1 atm and having a boiling point above 300°C (NA "F", "A", and "M"), and 320"C (NA "K"), acted as corrosion inhibitors. At concentrations of 200 ppm (NA "F", "A", and "M") their efficiency was 88 to 93%, and 50 ppm NA "K" resulted in 94% efficiency.