Study On Formation Process And Mechanism Of Primary Mesophase By Polycondensation From Aromatics-rich Heavy Oil

Based on the preparation of mesophase pitch from hydrocracking tail(HCTO-2)oil by one-step thermal polycondensation,the production process was optimized to solve the carbonization problem easily occurring in the process of one-step thermal polycondensation.The mesophase pitch was prepared by low temperature high pressure-low pressure two-stage method,solvent treatment method and vacuum distillation method.The performance characterization of mesophase asphalt products and the formation process of mesophase structure were studied.The effects of reaction temperature,pressure and time on the formation of mesophase asphalt were studied.The formation mechanism of primary mesophase was preliminarily discussed.The primary mesophase pitch with high content of mesophase was prepared by the two-stage process of high pressure and low pressure at low temperature.The tail oil was divided into raw materials.The reaction temperature was 430 ?,the initial reaction pressure was 4 MPa,the reaction time was 6 h,and the reaction pressure was released to atmospheric pressure for 5 h.The reaction mechanism of mesophase pitch prepared by high pressure and low pressure two-stage method at low temperature follows the continuous reaction mechanism of free radicals.The change of pressure and the selection of pressure changing time point have influence on the reaction rate of the system,the optical structure and softening point of the mesophase asphalt products,and the formation process of the mesophase asphalt.The product system of primary mesophase pitch was treated by vacuum distillation,under the conditions of reaction temperature 430 ?,pre-reaction pressure4 MPa,reaction time 6 h,and then release pressure to atmospheric pressure for 5 h,the mesophase with large basin-type optical structure could be prepared.It was found that the primary mesophase pitch was concentrated by vacuum distillation,the yield of carbonization was greatly reduced,the content of mesophase was increased,and the softening point and toluene insoluble(TI)were also increased.The product system of primary mesophase pitch was treated by solvent.Under the conditions of reaction temperature 430 ?,pre-reaction pressure 4 MPa,reaction time 6 h,and then release pressure to atmospheric pressure for 5 h,the mesophase pitch with large basin-type optical structure can be treated,and the softening point gradually increases.It is found that the process of pressure swing thermal polycondensation is an organic combination of pyrolysis and thermal polycondensation.The change of components in the system follows the path of n-heptane soluble(HS)? n-heptane insoluble-toluene soluble(HI-TS)? toluene insoluble-pyridine soluble(TI-PS)? pyridine insoluble(PI).The content of mesophase with large basin-type optical structure and softening point increase gradually.