Study On Catalytic Pyrolysis Of Heavy Naphtha To Olefin

Ethylene and propylene and other olefins are very important basic chemical rawmaterials, whose demands are increasing, With that of propylene more remarkablethan ethylene. The traditional steam thermal pyrolysis method for olefin has someshortcomings, including high reaction temperature, narrow source for raw materialsand reluctant product distribution adjustment. Similarly, the disadvantages, i.e.gasoline and diesel as the main production and low olefin yield, exist in thetechnology to produce more olefin in fluid catalytic cracking unit. However, catalyticpyrolysis owns the advantages of deep pyrolysis and high olefin yield just as steamthermal pyrolysis does and low reaction temperature and various raw sources just ascatalytic cracking does, which could overcome what were mentioned above. Hence,the research has the extremely vital significance on saving energy and satisfyingincreasing olefin demand. It is reported that the study about middle heavy naphthafractions is few. Therefore, pyrolysis properties on the catalyst and somecorresponding study were investigated in this paper in order to broaden the range ofraw sources.Firstly, catalytic pyrolysis reaction, with heavy naphtha as feed and HZSM-5ascatalyst, was carried out in the modified fixed bed micro-reactor and effects oftemperature and Si/Al ratio on olefin yield were investigated. The results revealed thatthe heavy naphtha is good source to product olefin by catalytic pyrolysis. The totalolefin yield could go up to30%-37%under580℃-660℃and low Si/Al ratioconditions. The yield of propylene exceeds that of ethylene at the lower temperatureand the reverse is true at higher. In addition, the olefin yield achieved the maximumvalue and stability of catalyst is good, which could be used as the carrier of othermodified materials to improve the catalyst properties.Secondly, based on composition analysis of feed, reasonable probe componentswere screened in order to comprehensive study the catalytic pyrolysis properties ofdifferent types of hydrocarbon. Meanwhile, thermal pyrolysis properties of heavynaphtha were studied under the same conditions above. The results indicated thatolefin yield of each probe components order in turn: heptane, octane> hexane> ethylcyclohexane> isooctane and reaction activity: n-paraffin, naphthenes>iso-paraffin when HZSM-5with Si/Al50was used. In addition, compared withtraditional thermal pyrolysis, the pyrolysis temperature was200℃lower in thecatalytic pyrolysis in order to obtain the same olefin yield. The productiondistributions by the two methods were different and propylene yield by the farmermethod is higher than that by the latter.Finally, effect of Hβ molecular sieve catalyst on the catalytic pyrolysis propertiesof heavy naphtha was evaluated. Molecular shape and size of probe components andproducts were simulated in order to observe how shape-selective properties of sievecatalyst depend on its bore diameter and molecular shape and size. What’s more, themodification of catalyst was preliminarily discussed. It is demonstrated that HZSM-5with smaller pore diameter was better fit to be used as carrier. The expression withthree-dimensional conformation and size of hydrocarbon was more exact. Theminimum cross section of iso-paraffin is larger than that of n-paraffin. The increase ofiso-paraffin went against olefin yield. Catalyst was synthesized by incipient wetnessimpregnation and modified by Silver nitrate and copper nitrate, whose aromatizationand coke were serious and olefin yield was low.