Synthesis Of Thiazolines As High Temperature Corrosion Inhibitor And Study Of The Anti-corrosion Performance

Recently, rapid development of the petroleum industry promotes the exploitation and refining of acidic crude oil. High-temperature naphthenic acid corrosion of distillation units is one of the major corrosion problems in worldwide oil refineries. There are many ways to inhibit the corrosion, in which the use of inhibitor is one of the most practical, economical, convenient methods for protecting metal against corrosion. Thiazoline compounds containing N, S hetero atoms and unsaturated double bonds have been considered as extremely effective organic corrosion inhibitors components, which can offer active electrons or vacant orbital to donate or accept electrons. Therefore, a series of thiazoline corrosion inhibitors were synthesized from alkyl-ketones, element sulfur with ammonia using xylene as solvent. With 2,2-pentamethylene-4,5-tetramethylene-1,3-thiazoline synthesized by cyclohexanone and element sulfur, the effects of reaction time, reaction temperature, the mole ratio of element sulfur and cyclohexanone and the adding amount of xylene solvent were also discussed. The optimal conditions were as follows: no adding xylene solvent, maintaining ammonia, n(element sulfur):n(cyclohexanone) 0.875:1, controlling reaction temperature at 50℃, for 2 hours. The yield was up to 88.9%. The structures were characterized by the means of element analysis, infrared spectra analysis and GC/MS analysis.The optimal synthetic technological conditions of 2,2-pentamethylene-4,5-tetramethylene-1,3-thiazoline were applied to synthetic thiazoline process with butanone, sec-octyl ketone as raw material. The yields of thiazoline synthesized by butanone, sec-octyl ketone are 89.2% and 72.2%, respectively.Static weight-loss method was used to investigate the effect of phosphorous inhibitor with different substituent groups and thiazoline inhibitor with different substituent groups on the anti-corrosion performance to A3 steel. The results showed that the anti-corrosion performance of the phosphite is better than phosphate with same alkyl group; the anti-corrosion performance of phosphate inhibitor decreased with the increase of molecular weight; the anti-corrosion effect of thiazoline synthesized from butanone was best, trimethyl phosphate best in phosphorous inhibitors, respectively. The corrosion inhibitor of thiazoline synthesized from butanone combined with trimethyl phosphate was applied to a vacuum distillates of Shtar Science & Technology Group. The anti-corrosion rate was up to 100% when the corrosion inhibitor concentration was 205μg·g^-1 in the corrosive oil with acid number 3mgKOH·g^-1. The characteristic parameters of thiazolines were studied by B3LYP of Density Functional Theory. Through the calculation of the molecular frontier orbital energy, mulliken atomic charge and number of transferred electrons ( N) etc, this paper analyzed systematically the characteristic parameters of the reaction activity and selectivity of thiazolines. Quantum chemical calculations were conducted and also to provide molecular-level understanding of the observed experimental behaviour.