Study On Distribution, Type And Pyrolysis Of Petroleum Acids From High Acid Crude Oil Of CNOOC

Acid value of most crude oil of CNOOC is high. The petroleum acid corrodes theprocessing devices severely, threatening the safety of production and stability of operation inplant. Therefore, the study of the composition, regularity of distribution and pyrolysisbehavior of petroleum acids in CNOOC high-acid crude oil and methods of preventingcorrosion is the basis of corrosion prevention.The thesis mainly studied CNOOC high-acid crude oil. The research, first, separatedCNOOC high-acid crude oil by True Boiling Point Distillation, and analyzed acidsdistribution in each distillate; second, isolated acids from different distillates by the extractionwith aqueous ammonia alcoholic solution and studied the composition and chemical structureof these petroleum acids in detail by use of IR, EA and GC/MS; third, studied the pyrolysisbehavior of petroleum acid by examining the effect of pyrolysis time and pyrolysistemperature on the acid value of crude oil. The result of the research has directive significanceto the corrosion prevention of every device and each part of a plant.By analyzing acids distribution in each fraction of SZ36-1、QHD32-6and PL19-3, thestudy concluded that acid values of these three oils were all over2.0mgKOH/g, indicatingthat all the three oils were high-acid oil. Acid values were relatively higher in the300~465℃distillates of SZ36-1, the400~450℃distillates of QHD32-6and diesel and lubricating oildistillates of PL19-3whose naphthenic acid mainly existed in middle distillates.As the material of asphalt, SZ36-1oil was mined and processed in a large amount. Thisthesis studied the composition and chemical structure of naphthenic acids in differentdistillates of SZ36-1oil. The results indicated that these naphthenic acids were mainly mano-,bi-and tri-cyclic naphthenic acids, and contained less aromatic ring; as the distillates becameheavier, average molecular weight of the naphthenic acid was larger and chemical structuresof the petroleum acids were increasingly complex.Pyrolysis of petroleum acids did not substantially occur in the temperature less than350℃. After the temperature reached360℃, the pyrolysis of petroleum acids partiallyoccurred and as the temperature increased, the pyrolysis of petroleum acids speeded up. Whenthe temperature reached440℃, petroleum acids almost completely decomposed. Thepyrolysis time was a major factor that affected pyrolysis of petroleum acid in high-acid oil.With the increase of the pyrolysis time, the acid value of SZ36-1oil significantly reduced;after thermal cracking, the acid value of the180~250℃distillates increased, indicating thatcarbon-oxygen bond cleavage in the petroleum acid in heavy components did not take place entirely in cracking process. Carbon-carbon bond cleavage occurred in part of the petroleumacids and generated small molecule petroleum acids which were more corrosive.The thesis studied many methods of corrosion prevention, assessed performance of theinhibiter in laboratory, applied the inhibiter to industrial devices, and got satisfying effect.Meanwhile, the use of material upgrades and corrosion online monitoring ensured the securityof high-acid oil process.