Research On The Synergistic Effect Of Corrosion Inhibition Between Nitrogen-containing Heterocyclic Compounds And Sulfur-containing Compounds

The serious destroy of equipment and pipelines in oilfield development and operation caused by CO2 corrosion.Corrosion inhibitors are widely used in petrochemical,machinery,transportation and other fields to protect the metal materials due to low dosage and cost,effective and easy to operation.However,the single corrosion inhibitor is ineffective for the complex environment.Therefore,the research on the synergistic corrosion inhibitors has become an inevitable trend.However,at present,there is rarely research to clear explain the synergistic mechanism between different corrosion inhibitors,and the influence of complex environment on the performance of synergistic inhibitors.This paper selected nitrogen-containing heterocyclic compounds and sulfur-containing compounds as inhibitors,used the weight loss and electrochemical method to study inhibition performance of for one-component inhibitor,bicomponent inhibitors and three-component inhibitor,and combined with theoretical computational chemistry,X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM)to study the mechanism of synergistic inhibition in-depth.The main results are as follows:1.Selected pyridine and three pyridine derivatives with different methyl groups and quinoline to quaternized as nitrogen-containing heterocyclic compounds,thiourea(TU)and mercaptoethanol(TZ)as sulfur-containing compounds.Single corrosion inhibition performance was evaluated.The results show that the nitrogen-containing compound of pyridine with a concentration of 2×10-4 mol/L at 60? had poor inhibition efficiency on Q235 carbon steel in a CO2-saturated 3.5%NaCl solution,while quinoline and its quaternary ammonium salt and the sulfur-containing compound had positive inhibition when used alone.2.The nitrogen-containing heterocyclic compounds of pyridine mixed with two kinds of sulfur-containing compounds by molar ratio 1:1 and evaluate the performance of the bicomponent inhibitors.The results show that the nitrogen-containing heterocyclic compounds after quaternization had significant synergistic effect with sulfur-containing compounds,and the methylation position of the nitrogen-containing heterocyclic compound affected synergistic effect,and the type of sulfur-containing compound was slight.4-methylpyridine quaternary ammonium salt(4-PQ)had the best synergistic effect with sulfur-containing compounds,and mainly affects the anode process of corrosion.3.The effects of different molar ratios on synergistic effect of bicomponent inhibitors 4-PQ and sulfur compounds were studied.The results show the performance of bicomponent inhibitors with a total concentration of 2×10-4 mol/L at 60? was affected by the molar ratio in the following order:3:1>5:1>1:1>1:5>1:3(4-PQ:TZ or TU).At the molar ratio of 1:3 or 1:5,the corrosion inhibition behavior of the mixed corrosion inhibitors was similar to the single TZ or TU,because the large number of sulfur-containing compounds decreased the chance of 4-PQ molecules accessing the metal surface.The synergistic corrosion inhibition effect between 4-PQ and sulfur-containing compounds increased with the increase of the content of 4-PQ in the mixed corrosion inhibitors,but the corrosion inhibition effect decreased after the molar ratio reached 3:1.In addition,the synergistic corrosion inhibition performance of nitrogen-containing heterocyclic compounds of quinoline and sulfur-containing compound was better than pyridine under 3:1,which indicates that the heterocyclic number had a strong influence on synergistic effect.4.Three-component inhibitor system of pyridine(PQ),quinoline(QQ)and sulfur compounds was built,and test the synergistic effect of three-component inhibitor by weight loss and polarization curves method.The results show three-component inhibitor has a better synergistic effect with the total concentration of 5×10-5 mol/L at 60?,when the molar ratio of the nitrogen-containing compound to the sulfur compound was 3:1(PQ:QQ:TU=1.5:1.5:1),the inhibition efficient was over 95%.5.The synergistic mechanism of bicomponent inhibitors and three-component inhibitors was studied by periodic linear polarization,electrochemical impedance tests,SEM,XPS,and quantum chemical calculations and molecular dynamics simulations.The results show that there was adsorption sequence between the corrosion inhibitors in the mixture.For bicomponent inhibitors,the two molecules are plane-adsorbed on the metal surface,the large-volume pyridine derivatives compound molecules have a priority to adsorb on the metal surface,while the small sulfur-containing compounds molecules fill in vacancies,and at a suitable molar ratio,a dense protective film is formed on the metal surface to protect.It is the same adsorption order as three-component inhibitors.Finally,the three-component inhibitors were applied in the actual environment,and the effect of water cut on the synergistic effect was studied.It was found the great influence between the proportion of corrosion inhibitor and water cut.Adjusting the proportion of mixed inhibitors for different environments had greatly practical significance.