Study On The Oil-Soluble Corrosion Inhibitor Used In H₂S/CO₂ System

Hydrogen sulfide and carbon dioxide result in serious corrosion to the drilling equipment and gas pipelines. They always make the pipelines thinner or perforated, and even lead to hydrogen embrittlement and stress corrosion cracking, which easily cause severe accidents, economic losses and even injury and death. So it is imperative to take some measures to slow down or prevent corrosion.The using of corrosion inhibitors can effectively inhibite the corrosions. Oil-soluble corrosion inhibitors have better performance than the water-soluble corrosion inhibitors due to their better and longer adsorption on the metal surface.In this paper, seven imidazolines were synthesized by different saturated fatty acids with 6 to 18 carbon chain and diethylenetriamine. The relationships between fatty acid carbon chain length and inhibitive performance of imidazolines were studied by static weight loss test and electrochemical methods. The results showed that it had a better oil-soluble and inhibitive perfoemance when the carbon chain length of corrosion was 10. Activative alumina was proved to be the best catalysts after comparing the inhibitive perfoemance of oleic imidazolines synthesized by using different catalysts and dehydrating agent. After evaluating a series of industrial fatty acid imidazoline through the static weight loss test, several good imidazoline corrosion inhibitors such as D2,1# IM180,1# 4420180,0924,0131 etc. were selected and evaluated in dynamic autoclave.A series of 1# acid imidazoline derivatives were synthesized by modifying end-groups. Comparing inhibitive performance of 1# 4420180 and 1# 4420120 showed that derivative synthesized at 180℃was better than it at 120℃. After several evaluation comparasion, the 0924 was suggested to be the best inhibitor under the autoclave test environment at 3.6MPa,600r/min, and 60℃. Its corrosion inhibitive perfoemance was better than foreign corrosion inhibitors CI-545 and ME-805 as its corrosive rate was only 0.0025mm/a. Adhering to the principle of "lower corrosion rate and less pitting ", oil-soluble corrosion inhibitors were compounded with water-soluble corrosion inhibitor such as quinoline, imidazoline quaternary ammonium salts and surface active agent. It was proved OP-15 can effectively reduce the occurrence of pitting in dynamic autoclave test.Characterized by IR spectral indicated that the synthesis product was a mixture of imidazoline and amide. The polarization curves show that the imidazolines greatly reduces the corrosion current density, and made the corrosion potential move to the corrective direction. The anode polarization curves indicated that imidazoline is an anodic inhibitor.