Hydrocracking Tail Oil Polycondensation Reaction And Mesophase Pitch Formation Process Research

This research aimed to prepare the mesophase pitch from hydrocacking tail oil by direct heat-treatment reaction,the reaction temperature and time were optimized.In order to study the generating process of mesophase,the properties of the mesophase pitch were characterized.This article also covered using two additional methods of preparing mesophase from the same oil,the mechanism of two-stage process and co-carbonization process were primarily studied.The optimum conditions of direct carbonization of hydrocracking oil was at the temperature of 455℃ and reaction pressure of 6 MPa for 10 h.The optical textures of mesophase pitch were large domain,and the softening point was 213℃ under this conditions.The preparation of carbonaceous mesophase follows the free radical mechanism and can be described by the first-order reaction kinetics equation.Reaction temperature and time have a great effect on the optical textures,softening point and the generating process of mesophase pitch.In the formation process of mesophase pitch,mesocarbon microbeads appeared,grew up,fused into mosaic texture mesophase,finally the large domain texture mesophase pitches were obtained;at the same time,the components of product converted as follows: n-Heptane Solubles(HS)→ n-Heptane Insolubles-Toluene Solubles(HI-TS)→Toluene Insolubles(TI).The optimum conditions of two-stage process of hydrocracking oil was at the temperature of 470℃ and reaction pressure of 6 MPa for 2 h in the first stage,and at the temperature of 455℃ and reaction pressure of 4 MPa for 6 h in the second stage.The optical textures of mesophase pitch were large domain,and softening point was lower than the direct carbonization one.Through the characterization of the product which produced under different conditions,we found pretreatment can effectively accelerate the reaction,reduce the number of alkyls.Product yield and softening point increased with the increasement of pretreatment temperature and the prolongation of time.The optimum conditions of co-carbonization process of hydrocracking oil was at the temperature of 455℃ and reaction pressure of 6 MPa for 10 h with 5 wt% DAO as additive.The optical textures of mesophase pitch were large domain,and the softening point was 194℃ under this conditions.On the one hand,dealkylation reaction can induce the reaction of free radicals which due to the added of DAO.Structure group analysis indicates DAO contains more and longer alkyl side chain than HTO.The join of DAO,bring more alkyl side chain to the mesophase pitch,it increase the average molecular layer spacing.