Study On Reaction Behaviors And Coke Formation Inhibition Of Tahe Atmospheric Residue Visbreaking

This thesis focuses on thermal visbreaking of Tahe atmospheric residue?THAR?to investigate the influence of reaction conditions on the properties of visbroken oils and the coke yield of visbreaking.The structural composition of heavy oil and the molecular composition of heteroatomic compounds before and after the reaction are analyzed.The effects of solvent to oil ratio,reaction pressure and catalyst type on the coke yield are studied in the hydrogen donor method and supercritical fluid disperation method of inhibiting coke formation respectively.After thermal visbreaking of THAR,the viscosity and average molecular weight are reduced,the<350°C light distillate content and the carbon residue value are increased,the H/C atomic ratio and S,O element content are reduced,but the N element content is increased.After the reaction,the aromatic carbon ratio and naphthenic carbon ratio are increased,but the alkyl carbon ratio,the total ring number,the aromatic ring number,the naphthenic ring number,and the average chain length parameter are reduced,which indicates that the quality of the visbroken oil has been improved to a certain degree.At the same reaction temperature,with the increase of reaction time,the coke yield of visbreaking shows a growth trend.The rapid growth of the coke yield occurs when the reaction time at low temperature is longer,indicating that there is a coke induction period.A large amount of coke can be produced at high temperature even if the reaction time is short,indicating that high temperature promotes the condensation reaction.The reduction of heavy oil viscosity comes at the expense of coke formation.When the same viscosity reduction is achieved,the reaction conditions of low temperature-long time are more favorable to reduce the generation of coke than the reaction conditions of high temperature-short time.Carboxylic acid materials which have poor thermal stabilities mainly account for the O₂ compounds in the THAR.The O₂ compounds can be removed completely at the higher reaction severity.Therefore the visbreaking reaction has a certain deacid effect.N₁O₂ compounds may take the reaction of alkyl side chain cracking,and carboxylic acid materials within N₁O₂ compounds can be removed in the process of visbreaking.Alkaline N₁ compounds may take the reaction of alkyl side chain cracking.Alkaline N₁S₁ compounds may also take the reaction of alkyl side chain cracking accompanied by the breaking of C-S bonds.Therefore the visbreaking reaction has a certain desulfurization effect.In the hydrogen donor method of inhibiting coke formation,the hydrogen donor can only achieve the best hydrogen-dominating effect when the liquid phase is completely presented under the pressure condition.The effect of coke inhibition becomes more and more obvious with the increase of additive amount of the hydrogen donor.The addition of catalyst naphthenate or oleic acid has a certain catalytic effect on hydrogen catalysis,which can further inhibit coke formation of visbreaking.In the supercritical fluid dispersion method of inhibiting coke formation,toluene solvent under the condition of low pressure is not obvious.Under the condition of high pressure,the supercritical toluene has a very strong ability to dissolve heavy oil,so that the macromolecular radicals of heavy oil originally aggregated together are better diluted and dispersed,which can significantly inhibit the cccurance of the condensation coking reaction.Increasing the additive amount of supercritical toluene properly can inhibit coke formation more effectively.But when the additive amount of supercritical toluene is too much,it may promote coke formation of visbeaking reversely.