| In this paper,the modification of coal tar pitch as carbon precursor is investigated. Firstly,we design the molecular structure for coal tar pitch,and modify industrial medium-temperature coal tar pitch with divinylbenzene (DVB) and p-methyl benzaldehyde (PMB) in the presence of p-toluene sulfonic acid (PTS),the modification mechanism of which is studied. Secondly,we study the relation among modification process,properties and fractions of modified coal tar pitch. Finally,we also study thermal decomposition,rheological behavior and mesophase transformation behavior of the modified coal tar pitch,respectively.We put forward a model for coal tar pitch with high carbon yield and low viscosity by molecular structure design. The molecule of coal tar pitch is supposed to be hydrocarbon with condensed rings which has higher aromaticity and condensation. Otherwise,it should have cycloalkane structure,some side chain substituting group and good order of the molecular structure.The molecular structure of modified coal tar pitch is studied using Fourier transform infra-red (FT-IR) and 'H nuclear magnetic resonance ('H-NMR) spectroscopy technologies. The results show that coal tar pitch can happen electrophilic substithtion reaction with DVB or PMB with help of PTS,which makes the molecular weight of coal tar pitch larger. Moreover,cationic polymerization of DVB also can happen in the condition.Scanning electron microscope (SEM) is used to observe the shape of modified coal tar pitch. There are many chain fibers in the coal tar pitch modified with DVB at initial stages. A great deal of small spheres,which form under the action of whipping,are found in the modified coal tar pitch with increase of modification degree. There are also many chain fibers in the coal tar pitch modified with PMB. The fibers grow with increase of modification degree,finally form bundles which present even distributing and good linearity.An overall study is made in the relation among modification process,properties and fractions of modified coal tar pitch. The results show that modification process,such as reaction temperature,greatly influences the properties and fractions. The properties of coal tar pitch modified with DVB are listed as follows:(l).Carbon yield is 53.4%-71.2%;(2).Softening point is 89 - 151.0;(3).Density tested at room temperature is 1.305g/cm3-1.358g/cm3. The properties (carbon yield,softening point,density) of coaltar pitch modified with PMB are 54.3%-67.6%,84.6C-131.0 and 1.306g/cm3-1.342g/cm3,respectively. The content of TI-PS,which dissolves in pyridine but toluene,keeps a value from 16.0% to 19.0%. However,Toluene soluble substances (TS) have good linearity relation with the properties of coal tar pitch,i.e.,carbon yield,softening point and density tested at room temperature. Pyridine insoluble substances (PI) have good linearity relation with these properties,too.The thermal decomposition behaviors of the modified coal tar pitches are studied using thermogravimetric analysis (TGA) and Kissinger expressions. The results show that the thermal decompsoition reaction of coal tar pitch modified with DVB proceeds in one-step,the energy of activation (Ea) of which is 218.31 kJ/mol. Pre-exponential factor InA is 37.68 s-1,and reaction order n is 1.04. However,the thermal decompsoition reaction of coal tar pitch modified with PMB is more complicated,the energy of activation (Ea) of which is 180.91 kJ/mol. Pre-exponential factor InA is 31.75 s-1,and reaction order n is 1.11.A viscometer is applied to study the rheological behaviors of modified coal tar pitches. The modified coal tar pitches behaves in non-Newton fluid. The viscous flow activation energy of modified coal tar pitches markedly increases with rise of TS content,and pre-exponential factor A decreases. The results also show that the viscousity can be controlled by adjusting modification process in order to meet different requirements.The optical texture of resultant semicokes of modified coal tar pitch is characterized by reflected polarized-light mi...
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