Polycondensation Characteristics Of Hydrogenation Tail Oil Aromatic-rich Components At Low Pressure And Formation Mechanism Of Mesophase Structure

In this paper,mesophase pitch is prepared from HCTO-2 by low pressure-normal pressure method,low pressure-gas stripping method and low pressure-vacuum method.Control reaction pressure does not exceed 4MPa,gradually increase the degree of removal of light components in the reaction system by means of atmospheric pressure,nitrogen stripping and vacuuming,optimization of production process conditions for mesophase pitch.The effect of the removal of light components in the reaction system at low pressure on the formation of mesophase pitch were investigated emphatically.Besides,the formation mechanism of mesophase was discussed preliminarily by combining with the change of light component content during the reaction.Using low pressure-normal pressure method,control reaction temperature of 440°C,low pressure section pressure of 3MPa,reaction time of 6h,and subsequent release pressure of 0.1 MPa and continuous reaction for 5 hours can obtain large basin-type optical structure mesophase pitch.Under this condition,the carbon yield can reach 74.26% and the softening point is 158°C.The existence of low pressure section is beneficial to the formation of mesocarbon microbeads,the presence of light components can increase the fluidity of the system in the early stage of the reaction and conducive to large number of active free radicals involved in the reaction,at the same time,the presence of a large number of small molecular hydrocarbons can effectively inhibit the occurrence of excessive carbonization.On the basis of sufficiently generating mesocarbon microbeads,the removal of the light components increases the viscosity of the system,facilitating the insertion between the fragrant sheets and the longitudinal stacking.High quality mesophase pitch with large basin-type optical structure were prepared by low pressure-vacuum method.The optimal condition of low pressure-gas stripping method is control reaction temperature of 440°C,low pressure section pressure of 3MPa,reaction time of 6h,and then under blowing nitrogen for 5 h.Through this method,Carbon yield decreased to 71.76% and softening point rises to162°C.The results of product softening point,carbon residue,component content and elemental analysis data shows the degree of polycondensation of the product is slightly deepened under gas stripping.Small molecular substances are quickly discharged outside the system with a nitrogen gas stream,at the same time,the decrease in vapor pressure of the small molecule above the liquid reaction system leads to more alkyl or cycloalkyl side chain breaks,the viscosity of the reaction system is further increased and the steric hindrance between the aromatic sheets is reduced.It is benefit for the formation of mesophase pitch with better orientation in the middle and late stages of the reaction.Control reaction temperature of 440°C,low pressure section pressure of 3MPa,reaction time of 6h,and subsequent release pressure of 0.1 MPa and continuous reaction for 2 hours,The product under this condition is used as the precursor of the vacuum experiment,then,using this precursor to be raw materials with the conditions of reaction temperature of 310°C,The vacuum degree is 0.06 MPa soaking 30 min or the vacuum degree is 0.08 MPa soaking 60 min.Under the two conditions,the carbon yield is significantly decreased to 56.68% and 51.33%,respectively and softening point is rising sharply to 271°C and 265°C respectively.The light components were removed more thoroughly in the middle and later stages by vacuum extraction,It significantly reduces the time required for the middle and late stages of the reaction.The vacuum temperature is essential for promoting the thermal cracking reaction and preventing the liquid phase reaction system from bumping.However,the probability of excessive carbonization of the product is greatly increased with the extension of the vacuum time at a lower vacuum degree.