Study On The Adsorption Separation Of Naphtha In Double-columns Fixed-beds

Separating the naphtha based on the strategy of molecular scale management is an important way to have a better use of naphtha. Based on the adsorption separation of naphtha in MSFA, this article built the double-columns fixed-beds and carried out the studies on the adsorption separation of normal alkanes from naphtha using5A molecular sieves as absorbent in double-column fixed-beds. The performance of cracking desorption oil to make ethylene and reforming raffinate oilto make aromatics were compared. After5adsorption/desorption circles, the adsorption separation process reached dynamic equilibrium. The optimal conditions for the adsorption/desorption circle process were an operation temperature of270℃, a naphtha feed space velocity of90.1h-1, a switch time of30minutes, using N2as desorption gas and a space velocity of127.5h-1, an intermediate oil cutting time of2minutes. The most dealing quality of naphtha in the device was8.05g naphtha/100gMS·h.The normal alkanes content of raffinate oilwas2.99%, and the normal alkanes content of the desorption oil was95.18%. After setting Cutting Middle Oil Loop process, the normal alkanes content in the raffinate oil was3.42%and the potential aromatic content was12.14%higher than that of the raw naphtha. The normal alkanes content of the desorption oil was96.61%and the ethylene yield was15.08%higher compared with the feed naphtha. With a high cutting ratio, the n-alkanes content of desorption oil can reach99.22%. The activity of molecular sieves can still stay in94.76%after850circles.This article has studied the influence of different hydrocarbons on the adsorption of n-alkanes on5A molecular sieves. The aromatics have a worst influence on the adsorption process of n-alkanes. Using LRC model to predict the adsorption capacity of n-alkanes on5A molecular sieves, it has a rather small error.The coke oxidation regeneration process in fixed bed was also studied in this paper. The optimal conditions for the oxidation of cokes and the regeneration of molecular sieves was obtained:using high pure air as regeneration gas and a velocity of127.5h-1, a regeneration temperature of325～350℃and a regeneration time of4～5h. The activity of molecular sieves can be recovered to94.59%. After12times oxidation regeneration process, the activity of molecular sieves can still reach91.68%.