Synthesis Of Organic Polysulfides Corrosion Inhibitor And Study Of The Corrosion Mitigation Performance

The corrosion caused by naphthenic acids is the most difficult problem in high acid value crude oil refining and there are many ways to inhibit the corrosion such as mixing the crude oil with lower acid crude oils, using corrosion resistant material and adding corrosion inhibitors, in which the corrosion inhibitors is convenient, economical and effective way. Organic polysulfides are one kind of effective corrosion inhibitors to resist the corrosion caused by naphthenic acids. Polysulfides were synthesized by the reaction of alkenes and sulfur, in which ammonia was the catalyst. The polysulfides were characterized by elemental analysis, infrared spectrum, GC/MS and DTA-TG. The performances of the corrosion inhibitor were studied by ferrous powder method and dynamic weight-loss method.Ferrous powder method was used to determine the corrosion rate by determining the concentration of ferric ion in oil of corrosion. The effect of pH, color development time and amount of buffer solution to the concentration of ferric ion were investigated. The preferable results could be obtained, while the pH and the color development time were 4-6 and 30min. The results of iron content in the oil of corrosion showed that dodecyl mercaptan could inhibit the corrosion of naphthenic acid. The results of iron content were consistent with that obtained from atomic absorption spectrophotometry, which the relative deviation was below 3.5%.Cyclohexene polysulfides were prepared with cyclohexene and sulfur by the catalysis of ammonia. The results showed that the yield of the polysulfides could be achieved 92.6%, when the molar ratio of cyclohexene to sulfur and to ammonia, reaction temperature and reaction time were 1:1.9:0.32, 165℃and 4h repectively. When cyclohexene was instead of octylene, the appropriate molar ratio of octylene/sulfur/ammonia was 0.73:0.19:0.32, reaction temperature was 165℃and the reaction time was 4h, in which the yields of octylene polysulfides were 98%.When the molar ratio of cyclohexene to sulfur is 1:2.5, the GC/MS analysis of cyclohexene polysulfides showed that the contents of the polysulfides were 86.19%, in which the percentage of (C6H11)2S, (C6H11)2S2 and (C6H11)2S3 were 57.75%, 21.24% and 7.20%, respectively, and the others were cyclohexyl mercaptans. When the mol ratio of cyclohexene and sulfur is 1:2.5, the contents of the polysulfides were 59.51%, in which the percentage of (C6H11)2S, (C6H11)2S2 and (C6H11)2S3 were 13.56%, 18.23% and 27.72%, respectively, and the others were cyclohexyl mercaptans. The x in (C6H11)2Sx was increased with increasing sulfur in the reaction. The DTA-TG analysis of cyclohexene polysulfides and octene polysulfides indicated that the polysulfides were easy to decompose at high temperature.The anti-corrosion rate increased when cyclohexene polysulfides mixed with Tributyl phosphate. The anti-corrosion rate reached 98.72% when the corrosion inhibitors concentration was 320.95 g·g-1 (the molar content of sulfur is 30.35%) in the corrosive oil with acid number 10mgKOH·g-1. The anti-corrosion rate reached 99.97% when the corrosion inhibitors concentration was 87.91 g·g-1 in the corrosive oil with acid number 1mgKOH·g-1. The anti-corrosion rate reaches 100% when the corrosion inhibitors concentration was 256.76 g·g-1 in the corrosive oil with acid number 3mgKOH·g-1.