Preparation Of Spinnable Pitch From Petroleum Residues

High performance pitch-based carbon fibers are widely used in aerospace and military industries because of their unique properties such as high thermal conductivity,high electrical conductivity,high strength,high modulus,high temperature resistance,corrosion resistance,impact resistance and coefficient of thermal expansion close to zero.The petroleum residue is a raw material for the preparation of spinnable pitch because of its high H/C atomic ratio and the presence of abundant alkyl side chains in the molecules.In the first part of this work,the preparation of mesophase pitch and its carbon fiber from fcc oil slurry were investigated,and the molecular structure of the fcc oil slurry showed that it is a suitable raw material for the preparation of high quality mesophase pitch.The effects of different reaction temperatures,reaction times and system pressures on the formation of mesophase pitch were investigated by a two-step thermal polycondensation method.The characterization of polarized microscope,softening point,IR,TG,fraction content and XRD showed that:increasing the reaction temperature would enhance the activity of thermal polycondensation;the extension of the reaction time would enhance thermal polycondensation to proceed continuously;increasing the pressure of the system would hinder the progress of thermal polycondensation.Polycondensed product has a high mesophase content of nearly 100%,large domain and long flow co-existing optical texture and a suitable softening point of 309℃prepared at a reaction temperature of 420℃,a reaction time of 7 h and a system pressure of 1 MPa.The mesophase pitch has the best spinnability,and the mesophase pitch-based carbon fiber preliminarily obtained after pre-oxidation and carbonization has a radial structure with a tensile strength of about 1.17 GPa and a thermal conductivity of about 683.5 W·m^-1·K^-1,exhibiting relatively excellent mechanical and thermal conductivity properties.In the second part,the preparations of general-purpose grade pitch and its carbon fibers from ethylene tar were investigated.Based on the explorations of fraction analysis and the molecular model calculation,it is reasonable to believe that ethylene tar is suitable for the preparation of isotropic high softening point pitch.First,by the investigation of reaction temperature from preparation process,it is found that the reaction temperature can not exceed410℃,otherwise it is easy to produce a large amount of mesophase pitch.Further making the blowing port below the liquid surface is beneficial for the efficient removal of small molecules in ethylene tar.The effects of blowing time and blowing pressure on the formation of pitch were investigated,and the results showed that high quality spinnable pitch with isotropic content of higher than 97%and softening point of 268℃can be obtained under the conditions of 2 h blowing and 0.08 MPa blowing pressure.Thus the general-purpose pitch carbon fiber obtained after pre-oxidation and carbonization possesses the tensile strength of about 541.0 MPa and the thermal conductivity of 22.0 W·m^-1·K^-1;Under the condition of blowing time of 1.75 h and blowing pressure of 0.1 MPa,high quality spinnable pitch with isotropic content of higher than 95%and softening point of 277℃can be obtained,and the general grade pitch carbon fiber has a tensile strength of about 442.1 MPa and a thermal conductivity of about 19.7 W·m^-1·K^-1,proving the feasibility of preparing high softening point pitch and its carbon fibers using ethylene tar as the precursor.