Study On The Technology Of Coking Naphtha Catalytic Pyrolysis

In China, with the rapid development of delayed coking, the production of CN has beenincreasing continuously. However, there is no efficient and reasonable routes to process CNwhich could bring remarkable economic benefits to the refinery. Compared withhydrotreating, upgrading CN by catalytic pyrolysis has a number of advantages, such asconvenience in operation, less investment and quick gains. But this route also has somedisadvantages. To our disappointment, little work has been done on the research of CNcatalytic pyrolysis process and the development of matching technologies.In this study, the influence of basic reaction conditions on the CN cracking wasinvestigated in detail as well as types of zeolitic catalyst firstly. Then the reaction rules of CNcracking alone and combined cracking with CGO both in single-diameter riser andchanging-diameter riser were studied respectively. On the basis of previous study, thetechnology of CN and CGO catalytic pyrolysis combinatorially had been developedsuccessfully.Lengthening residence time was beneficial to the increase of conversion and light olefinyield. When the residence time became longer, the content of n-paraffin, naphthene and olefindecreased while the content of i-paraffin and aromatic increased. As reaction temperature andC/O ratio went up, the conversion of CN increased faster and faster. Meanwhile, yield ofethylene increased gradually. The content of aromatic and calculated octane number increasedobviously with reaction temperature and C/O ratio becoming higher. Comparative study onthe catalysts indicated that, catalytic pyrolysis catalyst had advantages on the conversion andlight olefin yield.Compared with single-diameter riser, CN was conversed more sufficiently in thechanging-diameter riser, and the quality of the gasoline product was better, but the yield andselectivity of light olefins were lower because of too much secondary reactions. Theconversions of CN were55.42wt.%and68.58wt.%respectively when the residence time were1.24s and2.68s in the changing-diameter riser, which were5.36and12.54percenthigher than in single-diameter riser respectively. In order to obtain higher conversion andlight olefin yield at the same time, the structure of changing-diameter riser should beoptimized.For the combining feeding of CN and CGO, when the ratio of CN increased, the contentof propylene and butene in LPG decreased, and so did the content of olefin and aromatic ingasoline, but the content of n-paraffin increased rapidly. For combination technology, theconversion of CN and the yield and selectivity of light olefins in the changing-diameter riserwere all higher than those in the single-diameter riser. In addition, when the changing-diameter riser was used, the content of olefin and i-paraffin in gasoline product was lowerwith higher content of aromatic. However, high CN ratio was suitable for neither of these tworisers.Compared with the result of CGO catalytic pyrolysis alone, combination technology ofCGO and CN catalytic pyrolysis had obvious advantages on improving CGO conversion,upgrading gasoline quality and increasing the yield of light olefins. So we can make theconclusion that CN play an synergistic and stimulative role to the CGO catalytic pyrolysis incombination technology.