Refining Of Heavy Oils And Study On Stability Of Their Mesophases

Heavy oils are process by-products widely available from petroleum processingand coal coking, advanced carbon materials with high commercial values have beenproduced from properly refined heavy oils, for example, pitch-based carbon fiber andso on. Mesophase pitches prepared from properly refined heavy oils have stabilityproblems such as breaking fiber in the spinning process, which seriously affects theperformance improvement of pitch-based carbon fibers. The heavy oils used formesophase pitches production generally need to have high concentration of aromatichydrocarbons. Therefore, purification and refining processes are required in order toremove unfavorable substances from heavy oil feedstock, including solid particles,wax and heteroatom compounds. The main content of this paper is to remove paraffinwax fractions from heavy oil feedstock and to research the spinning stability problemsof mesophase pitches.In this paper, three different samples of heavy oil were selected for solventdewax, using butanone as solvent with solvent and heavy oil ratio(mass ratio) at1.5and3. A high-speed refrigerated centrifuge was used for solid and liquid separation attemperatures of10℃,5℃,0℃,-5℃.The experimental results show that:concentrationof aromatic hydrocarbons of heavy oil had been increased after the centrifugation. Atthe same solvent and heavy oil ratio, the temperature of centrifugal separation waslower, the result of heavy oil dewaxing was better. When heavy oil contains morewaxes, more solvent conducive to dewaxing of heavy oil.Structure characterizations of original heavy oil samples and their fractions wereperformed, using proton and carbon-13nuclear magnetic resonance (1H-NMR,13C-NMR), the experimental results indicated that: After the centrifugation, thearomatic hydrocarbons and the fatty wax fractions in the heavy oil had been separated.The solvent dewax was very effective. Additionally attempt was made to examinestructural parameters of original samples of heavy oil and separated fractions by usingBrown-Ladner (B-L) model with data from NMR and elemental analysis. Thestructural parameters were aromatic carbon ratio(fA), the aromatic ring system insteadof the neighboring carbon ratio(σ) and the condensation of the aromatic ringsystem(HAU/CA). the structural parameters results indicated that: the fAof heavy oilS03was largest, and the fAof heavy oil S01was minimum. Research the group components, phase stability, rheological stability, and thethermal stability of the mesophase pitches in the spinning process by determinatingthe group components and using polarized light microscopy, capillary rheometer, andintegrated thermal analyzer. The research results show that: The changes of the groupcomponents of mesophase pitches in the spinning process indicated that the content ofQuinoline insoluble of mesophase pitch had increased and the content of solublemesophase had decreaaed in the spinning process. Part of the fibrous streamlinedstructure of the anisotropic mesophase pitch changed into the mosaic structure. Themesophase pitch produced isotropic component. Separation and stratification occurredbetween the anisotropic component and isotropic component. The holes appeared inthe spinning process affected the stability of mesophase pitch. The mixture of the twocomponents reduced the temperatures of the softening point and flow point, whichcaused fiber breaking in the spinning process. The smooth curve after the flow pointin the displacement-temperature curve of the mesophase pitch became not smooth,which indicated that the mixture of the two components affected rheological stabilityof mesophase pitch. The starting weight lost temperature of heavy oil and naphthalenebased mesophase pitches were both above410℃, and their carbon yield were bothmore than70%, whick indicated that their TG rates were both relatively small, theyboth had good thermal stability.