Reaction Performance Of Naphthenic-based Asphaltenes During Hydroliquefaciton Decomposition Process

The molecular weight of asphaltene is the largest in petroleum.Besides,its polarity is the strongest.Its complex colloid system brings many difficulties to heavy oil processing.To this end,the research group proposed a technology,HLDC.Hydrogen donor solvent could achieve efficient conversion of asphaltenes and solve the engineering and operational problems caused by large amounts of carbon residue.This thesis mainly investigates during HLDC process,the changes of asphaltenes of naphthenic base with the highest content of naphthenic hydrocarbon and aromatic hydrocarbon,highest viscosity,highest relative density.Firstly,the stability of the asphaltene colloidal system has been studied in order to predict the feasibility of HLDC and guide the selection of the reaction conditions to increase the asphaltene conversion rate.Five different types of asphaltenes and four different types of hydrogen donor solvents were selected to calculate the solubility parameters of the disperse phase(asphaltene)and the dispersion medium(maltene)and investigate the differences between them.Results indicate that the main reason for phase separation is the reduction of the mutual solubility of the two phases.The difference between the two phases is determined by a variety of factors,including: structure,properties of two phases and reaction condition.The solubility parameter of asphaltene with low H/C atomic ratio,high aromatic carbon ratio,high content of sulfur and nitrogen is the highest.The solubility parameter of dispersion medium with aromatic hydrocarbon is the highest,which has the best compatibility with asphaltene.The colloidal system is more stable.The higher reaction temperature and the lower pressure,the lower stability of the system.Increasing the reaction pressure can prevent asphaltene from phase separating due to the high reaction temperature.In the system of Venezuela asphaltene with high solubitliy parameter and dispersion medium FEO-5,temperature and pressure range of asphaltene precipitation was determined by calculation.Results show that asphaltenes precipitate within the reaction temperature 350~480 °C and the reaction pressure 5~35 MPa,which can guide the choice of reaction conditions in the actual reaction.S separation value and Flory-Huggins thermodynamic model were adopted to analyze the stability of the colloidal system during HLDC process.The results show that with the increase of the amount of FEO-5,the system gradually becomes stable.The S value decreased from 13% to 7.5% and the coke yield decreased from 3.27% to 1.33%.This indicates that hydrogen donor solvent can maintain the stability of the colloidal system for converting asphaltene efficiently.Secondly,the changes of Venezuela asphaltene during HLDC process were carried out.According to the calculation of the previous solubility parameter,the hydrogen donor solvent FEO-5 and the catalytic cracking recovery oil 430~450 °C(HCO-5)were choosed,which are highly compatible with the Venezuela asphaltene.FEO-5 compare with HCO-5 and select a better one.Then,the effect of reaction conditions on products distribution was investigated.The results show that,compared with HCO-5,FEO-5 is more suitable hydrogen donor solvent for the converting of Venezuela asphaltenes.The increase of reaction temperature and reaction time promote the conversion of asphaltenes efficiently,but excessively high temperature and long time will lead to the increase of coke yield.The increase of the reaction hydrogen pressure is favorable for the hydrogen donor solvent to provide more active hydrogen free radicals for the asphaltenes and inhibit the cracking of the hydrogen donor solvent itself.This trend is also similar to the influence of the reaction pressure on the stability of the colloidal system.The accession of the catalyst can make the coke yield decrease,however,the quantity of catalyst does not have strong impact on the asphaltene conversion rate.Considering comprehensively,the optimal reaction conditions are 390 °C,5 h,6 MPa,solvent ratio 5:1,the quantity of catalyst 500 ?g/g.Asphaltene conversion rate reaches as high as 74.6% and coke yield reduces to 4.61%..Finally,the transfer path of active hydrogen free radicals during HLDC process was analyzed to determine the hydrogenation path of heteroatom groups and polycyclic aromatic hydrocarbons in asphaltenes,and the way of ? bond opening in asphaltenes.Compounds which are similar to asphaltenes were selected,including pyrene,quinolone,indole,and benzothiophene.GC-MS was used to analyze the products distribution of the above compounds.The results indicate that in the absence of catalyst,the hydrogen donor solvent can release the active hydrogen free radicals and hydrogenate the heteroatom compounds.The heteroatom-containing heterocycle can be further cracked or heteroatoms can even be removed.FT-ICR MS was applied to predict the changes of the heteroatom compounds of the asphaltenes and maltene.FT-ICR MS and GC-MS were used to speculate hydrogenation path of polycyclic aromatic hydrocarbons and heteroatom groups of asphaltenes.Under the role of heat,asphaltenes undergo the cleavage of alkyl side chains.The aromatic rings or heterocycles then undergo hydrogenation saturation and continue to crack and enter into the soluble fraction.The partial cracked macromolecular radicals are combined with each other as a secondary asphaltene component in the system.Meanwhile,dehydrogenation reaction leads to the remaining asphaltene becoming coke.Transmission electron microscope(TEM)and X-ray diffraction(XRD)were used to observe and analysis the nanoaggregate of asphaltene.The results show that with the progress of the reaction,the stacking degree of asphaltene aromatic plate is weakened,and the stacking height of the unit sheets reduces from 2.86 nm to 2.39 nm.Its number reduces from 9 to 7.It shows that the active hydrogen free radicals provided by hydrogen donor solvent and aromatic fused rings,fused-heterocycles form new complex compounds,which weakens the charge transfer between the aromatic plates of the asphaltene.Under the role of heat,part of the nanoaggregate can be dissociated and the aromatic plates of the asphaltene are opened.In conclusion,HLDC process is conducive to the efficient conversion of asphaltenes of naphthenic base and to maintain the stability of the colloidal system.