Synthesis and Property Evaluation of New Double Quaternary Ammonium Salt as Corrosion Inhibitor

Four kinds of double quaternary ammonium salt corrosion inhibitors-1,2-diullotropine ethane bromide, 1,4-diullotropine butane bromide, 1,6-diullotropine hexane bromide, 1,8-diullotropine octane bromide-were synthesized using urotropine and dihalogenated hydrocarbon as raw materials by quaternary ammonium reaction. The corrosion inhibition performance of double quaternary ammonium salt corrosion inhibitors to QT-800 steel in 15% (mass fraction) HCl was studied by weight-loss method and electrochemical method, the mechanism of corrosion inhibitors was analyzed by quantum chemical calculation, and the surface after corrosion was analyzed by electron scanning microscopy. The results show that the corrosion inhibition performance of double quaternary ammonium salts increased with the increase of carbon chain length of corrosion inhibitor molecule. 1,8-diullotropine octane bromide showed the best corrosion inhibition among four corrosion inhibitors, which had a corrosion rate lower than 4 g/(m²·h) when its dosage was in the range of 0.7%-1.0% (mass fraction). 1,8-diullotropine octane bromide was a mixed inhibitor that inhibits both anodic reaction and cathodic reaction. The energy gaps of the corrosion inhibitor molecules and their adsorption energy on the surface of iron increased with the increase of carbon chain length of corrosion inhibitor, and the adsorption energy was much greater than that of water molecule. So the corrosion inhibitor molecules could adsorb on the surface of QT-800 steel and inhibited pitting corrosion.