Molecular Structure And Catalytic Processing Of FCC HCO

Directly recycling the FCC HCO,which owns hight content of tri-and tetra-ring aromatic,to the FCC riser will increase the processing load of the device as well as high dry gas and coke yield,on the other hand,reduce the light oil yield caused by the increasing hydrogen transfer reaction.In order to overcome this drawback,a combined hydrogenation and FCC was employed.The HCO was continuously subjected to hydrogenation and FCC.The hard converting components,i.e.,tri-and tetra-ring aromatic,was converted to easily cracking components,i.e.,naphthene or naphthenic aromatic hydrocarbons,in hydrogenation process.Then the hydrogenated HCO?HHCO?owing easily cracking components was undergoing FCC.After the combined hydrogenation and FCC,the conversion of FCC HCO and light oil yield were enhanced at the same the octane number of gasoline was also increased.To achieve this goal,the following reseaches were done in the this work:proton nuclear magnetic resonance and GC-MS were used to analyze the molecular structure of FCC HCO and HHCO;model compounds were used to study the catalytic cracking law of key components in HHCO;the industrial equilibrium-catalyst which can high selectively cracking the cycloalkane ring structure was screened,at the same time,the optimal conditions for HHCO cracking process was obtained;The effect of hydrogenation depths on HHCO reaction performance was investigated;An eight-lumped kinetic model for catalytic cracking of HHCO was established.From the analysis of molecular structure parameters of FCC HCO and HHCO based on the B-L method,it can be seen that the aromatic carbon ratio of HCO decreased from0.46 to 0.25,and the carbon content of naphthenics increased from 0.24 to 0.29.The alkane carbon rate increased from 0.30 to 0.46,the total number of rings dropped from3.01 to 2.05,the number of aromatic rings decreased from 1.80 to 0.67,while the number of cycloalkane rings increased from 1.21 to 1.38.This shows that the FCC HCO in the hydrogenation process mainly occurred of aromatic ring saturation reaction,but some cycloalkane also occurred ring-opening cracking.GC-MS was used to analyze the hydrocarbon compositions of HCO and HHCO,the content of total aromatics in HCO is as high as 67.8%,and the content of tricyclic and tetracyclic aromatics accounts for 55.16%of the total aromatics.In HHCO,monocyclic aromatics,naphthenics and naphthenic aromatics are the main components.Therefore,hydrogenation favors the catalytic cracking of HCO.Tetralin,decalin and 9,10-dihydroanthracene were used as model compounds to study their transformation laws.The experimental results showed that both enhancing reaction temperature and catalyst to oil mass ratio can promote the conversion and selectivity of open ring cracking products.At the same time,With the decrease of aromatic rings,the optimum catalyst to oil mass ratio can be reduced appropriately,which indicates that the catalytic cracking efficiency of HCO can be improved by hydrogenation.By studying the hydrogen transfer law of naphthenes and olefins on the naphthenic structure of aromatics,it can be summed up that mixing HHCO with heavy raw material oil into a catalytic cracking unit,polycyclic aromatic hydrocarbons and olefins in heavy raw material oil will undergo a severe hydrogen transfer reaction with naphthenic hydrocarbons and naphthenic aromatics in HHCO,which will transform HHCO to to aromatics again,and cause the selectivity of cracking products to decrease.Therefore,this paper proposes that HHCO will be added into the catalytic cracking unit alone to improve the cracking efficiency.In this study,three industrial catalysts were selected,and YH-HHCO was used as the feed for exploring the FCC reaction performance.USY type industrial balancer-2 is the best catalyst for YH-HHCO catalytic cracking with higher YH-HHCO ring-opening reaction selectivity,and prolific gasoline,lower dry gas and coke yield.The optimal reaction conditions for YH-HHCO catalytic cracking using this catalyst were:reaction temperature 530°C,catalyst to oil mass ratio 9 and weight hourly space velocity 15 h^-1,and residence time 3 s.At this optimal conditions,the yield of gasoline increase by 11.39%compared with YH-HCO.By investigating the effect of hydrogenation depth on the catalytic cracking performance of YH-HCO,the results indicates that the conversion rate of YH-HCO and the yield of gasoline both increase with increasing the hydrogenation depth.Nevertheless,the gasoline yield start to decrease when the HHCO density is 0.9424g/cm³,caused by the enhanced cracking reaction during the HCO hydrogenation.Therefore,in order to increase the conversion of YH-HCO and produce more gasoline with high octane number,the preferable density of the HHCO is 0.9424 g/cm³.Comparied YH-HCO with high tetra-ring aromatics JN-HCO:JN-HCO and YH-HCO have similar laws and the preferably density for JN-HCO is 0.9623 g/cm³.Therefore,the catalytic cracking conversion and gasoline yield can be both increased by selective hydrogenation of HCO.Based on the above studies,combined with the catalytic cracking reaction mechanism and raw material characteristics,HHCO were divided into three lumps:paraffins,naphthenes and aromatics,and the products were divided into five lumps:heavy oil,diesel,gasoline,liquefied gas,dry gas and coke.Therefore,including eight lumps kinetic model were built.Marquardt calculation method and MATLAB software were used to solve the kinetic parameters and verify the model.Compared with the traditional kinetic parameters of heavy oil catalytic cracking,the 25 rate constants calculated from this model are larger,and lower activation energy?ranging from 33 to 94 kJ/mol?.At the same time,the paraffins are more likely to generate liquefied gas,while the naphthenes are more easily to generate diesel and gasoline,and the rate constant of generating gasoline from naphtenes is obviously higher than that from aromatics.It has been proved that the HCO is easier to be lightened by using the combination of hydrogenation and catalytic cracking,as a results of increasing the gasoline yield.By verifying the results of the model,the relative error between the calculated value and the experimental value of the main product is within 10%,indicating the model can accurately predict the product distribution of HHCO catalytic cracking.The kinetic model can provide a theoretical guidance for the development and optimization of the combined process.