Studies On A Process For Demercaptaning Of Fluid Catalytic Cracked Naphtha (FCCN) In Combination With Hydrotreating Technonogy

A process for demercaptaning of SPC (Shanghai Petrochemical Company) produced fluid catalytic cracked naphtha (FCCN) in combination with a hydrotreating technonogy was studied. This process can be used in the production of low sulfur clean fuel meeting the standard of the National Ⅲ or Ⅳ. The results of fractionation with the true boiling point distillation unit showed that sulfur content in FCCN increases with the increase of distillate boiling point. Mercaptans (thiols) are mainly concentrated in the light fractions (LCN) below 80～100℃ and thiophenes in the heavy fractions (HCN) over 80～100℃. The olefin content of SPC’s FCCN decreases with the increase of distillate boiling point. Olefins are concentrated in LCN and aromatics concentrated in HCN. Olefins in LCN are the group with high octane number.Mercaptans in LCN of SPC’s FCCN were removed by caustic extraction. The laboratory results showed that the contents of mercaptan sulfurs in LCN1 (below 80℃) and LCN2 (below 100℃) could be reduced to about 5μg/g by caustic extraction at a temperature range of room temperature to 40℃, a volume ratio of oil to 5% to 50% alkaline liquor in the range of 1/1 to 15/1. The olefin contents and octane numbers were basically no change, the doctor tests and copper corrosion tests were qualified, and the product yields were near 100%. The alkaline liquors were regenerated through oxidation under a temperature range of 40 to 80 ℃ with a catalyst addition rate over 10μg/g. The disulfides in regenerated alkaline liquors were extracted by petroleum ether and the alkaline liquors could be reused.Recombinant mercaptans formed during the selective hydrodesulfurization of HCN were stable and hard to be removed. The oxidation removal of these stable mercaptans with different catalysts and promoters was studied in the laboratory. The test results showed that anion-pair-based catalyst combining with a complex-based promoter exhibited higher oxidation activity and stability than a conventional catalyst combining with a conventional promoter; with said catalyst combination the contents of mercaptan sulfurs in hydrotreated HCN feeds (varies from 30～50μg/g) could stably reduced to below 5μg/g during a 1000h fixed-bed run.Based on the improvements in the conventional caustic extraction and cobalt phthalocyanine oxidation processes, two combined processes for reducing sulfur content of SPC’s FCCN were proposed, such as a sweetening process for treating the mixture of LCN and the hydrotreated HCN; a combined process of caustic extracting LCN and followed by sweetening the mixture of extracted LCN and the hydrotreated HCN. The commercial feasibility of these combined processes was discussed for the production of low sulfur clean fuel reaching the standard of the National III or IV. The test results showed that the gasoline sulfur content could meet the requirements of the National Light Vehicle Exhaust Standard III or IV by applying these combined processes flexibly. The contents of mercaptan sulfurs in FCCN feeds could be reduced stably to less than 5μg/g with a complex-based promoter combination if no addition of anion-pair-based catalyst.