Effects Of Acidic Species In Petroleum On Corrosion Inhibitor Performance

Crude oils with a high content of acid cause serious corrosion to equipment and pipelines during transportation and processing.To relieve corrosion,adding corrosion-inhibitor is one of the most convenient and fastest methods to implement anti-corrosion.In order to explore the protection methods for different petroleum acid,Mannich-base-type corrosion inhibitors MLPP,MLMBT,and MLMB were synthesized,whose molecular structures and purity were determined by nuclear magnetic resonance and FTIR.A static corrosion test was used to study the effects of single petroleum acid simulated oils,mixed petroleum acid simulated oils,trace water,and the amounts of inhibitors on the corrosion inhibition performance.The surface of test pieces was analyzed by the corrosion morphology,scanning electron microscope,energy spectrum analysis,and Raman spectroscopy.The inhibitor MLMBT has good corrosion inhibition for various petroleum acid simulated oils,which is less affected by the water content in the simulated oil.But the corrosion inhibition decreases dramatically when the amount of MLMBT is reduced.The inhibitor MLMB shows so excellent corrosion inhibition for various types of petroleum acid simulated oils free from water that the inhibition rate for the triacid simulated oil can still reach 99%when the addition amount is as low as 0.01%.The corrosion inhibition of MLMB for the water-containing simulated oil decreased significantly.The inhibitor MLPP has poor corrosion inhibition ability for single acid simulated oil and water-containing simulated oil but the inhibition rate for triacid simulated oil reaches 85.8%.The surface of the metal is strongly adsorbed by nitrogen and oxygen atoms,which contain unshared electron pairs,in the morpholine rings in three inhibitors.The thiadiazole structure and benzotriazole structure were introduced into MLBMT and MLMB respectively combined with morpholine structure.The reason why the inhibitions of MLMBT and MLMB are better than MLPP is that abundant unshared electron pairs in these molecules of MLMBT and MLMB reinforce the adsorption on the metal surface.The hydrophilic characteristic of MLMB,which is caused by more nitrogen atoms in benzotriazole,make MLMB far less effective in water-containing simulated oils.