Study On The Law Of Olefin Saturation And Octane Loss In FCC Gasoline Hydrodesulfurization Process

In china,fluid catalytic cracking(FCC)gasoline,which represents 75% of the total gasoline pool,is the most important sulfur and olefins contributor in gasoline products,up to 85%.So the key to decrease the sulfur content of motor gasoline is to remove the sulfur compounds in FCC gasoline.The hydrodesulfurization(HDS)technology,which is the most frequently used method,can effectively reduce the sulfur content of FCC gasoline.But the octane number loss in this process is lager.It is difficult to have a balance between the desulfurization and the octane number.It is found that the octane number loss in HDS process was led by the olefin hydrogenation.And it concluded that the crux of the matter is to study the relationship between the olefins and octane number loss.In this paper,three kinds of FCC gasoline fraction and heavy fraction were selected,and were analyzed by the gas chromatographic.The octane number was calculated by the calculation model on the gas chromatographic result.The transformation of olefins in this paper was based on the olefins reaction which was happened to HDS process.The study was analyzed from several aspects which involve carbon number,structure,content and degree of difficulty of hydrogenation,and the result was shown in the follow.1)The research result about the FCC gasoline fraction: i)The influence of olefins hydrogenation: Under the same saturation rate the RON loss caused by the C6~C8 olefins conversion was larger than that led by the conversion C5,C9 and C10 olefins.However,as the olefins' conversion is 100%,the biggest RON loss was caused by the C5/C6 olefins' conversion,which was followed by the C7/C8/C9 and C10.ii)The influence of olefins divided by the molecular structures was also studied,and the result showed that the octane number loss led by the normal olefins(n-olefins)hydrogenation was larger than that caused by iso-olefins' hydrogenation.Therefore,the isomerization of n-olefin was an effective method to decrease the RON loss.iii)the hydrodesulfurization experiment of the full fraction FCC gasoline were carried out,and it could be found that the hydrogenation of C5~C7 olefins caused the largest RON loss.The reactivity of olefins in the HDS was also analyzed,and showed that the hydrogenation activity of C8 olefins was the lowest.2)The research result about the FCC gasoline fraction: i)The influence of olefins hydrogenation: Under the same saturation rate the RON loss caused by the C8 olefins conversion was larger than that lead by the conversions of C7,C9,C10 and C11 olefins;ii)The hydrogenation of C10/C11 i-olefins was benefit for the gasoline octane number;iii)The hydrodesulfurization experiment was also carried out,and found that there is a negative correlation between the hydrogenation activity and the carbon number in olefins.3)The calculation formula for RON loss was established,which was based on the invention result,and it was validated by HDS experiments.The result shows that the formula prediction error is less than 0.5 units.However,limited by the calculation module of octane number,the formula was only applied to the gasoline which had the similar hydrocarbon components.