Study On Catalytic Cracking Performance Of Aromatics From Coker Gas Oil

In recent years, due to the deterioration of crude oil, delayed coking technology has become the main force for treating heavy oil. As a result, a great deal of coker gas oil(CGO) has been produced and needed to be processed. Generally, CGO with high aromatic content is converted by fluid catalytic cracking(FCC) technology in refineries. However,the aromatics in CGO are difficult to crack, and tend to generate slurry and coke through dehydrogenation condensation reactions. Therefore, this study is aimed at investigating the cracking performance of the aromatics in CGO and proposing a reasonable FCC processing technology.In this work, furfural was used as extraction solvent to extract coker gas oil, the high-aromatic-content extract oil and low-aromatic-content raffinate oil were obtained respectively. GC-MS technology was further used to characterize aromatics inside the extract oil, and the results indicated that these aromatics in CGO can be divided into two categories: one is naphthenic aromatics, the other is poly-aromatics. And two-ring, three-ring and four-ring aromatics with short side chains dominated, meanwhile, a lot of benzothiophene compounds were also included.Afterwards, the extract oil and raffinate oil were mixed in different proportions to get CGO samples with different aromatic contents. Under the same conditions, catalytic cracking performance of these samples were carried out in a FCC pilot unit, the results demonstrated that the feed conversion decreased sharply with increasing aromatic content, meanwhile the intensities of thermal cracking, dehydrogenation condensation and monomolecular cracking reactions all increased greatly, consequently deteriorating the product distribution. With the increase of aromatic content in CGO, more aromatics were distributed into the gasoline and diesel fractions. However, due to the enhanced cracking and dealkylation reactions of two-ring and three-ring aromatics, both the selectivity and yield of diesel increased remarkably, which indicated that the aromatics in CGO had a great potential to produce diesel.Furthermore, tetralin and decalin were used as model compounds to investigate the ring-openning reaction of naphthenic aromatics. Although the conversion was lower, ZSM-5 zeolite exhibited a better naphthenic ring-openning setectivity than USY zeolite due to lower hydrogen transfer activity. And decalin has a better cracking performance than tetralin, which indicated that the higher hydrogen content, the better cracking performance for aromatics.Two stage riser catalytic cracking technology was efficient in converting CGO with high aromatic content. The conversion and the total liquid yield are up to 84.02 wt.% and 76.59 wt.% respectively. Because of the low hydrogen transfer activity of TMP commercial equilibrium catalyst, both the ring-opening reaction of the naphthenic aromatics and the dealkylation reaction of poly-aromatics in CGO were enhanced. In addition, the yields of gasoline and diesel were enhanced, and the condensation reaction of aromatics was inhibited effectively.