Liu Jinchang,Shen Chenyang,Liu Qin,Li Yaping,Wang Tong,An Xiaoya,Liang Dingcheng,Xie Qiang
Coal liquefaction residue (CLR) has a high content of carbon and organic substances. However, sulfur and inorganics pose a challenge for the high-value-added utilization of CLR. In this work, general-purpose carbon fiber was successfully prepared by the new method of chlorination–dechlorination using CLR as raw material and benzyl chloride as chlorinating agent. The effect of benzyl chloride addition amount on the property of isotropic pitch precursor and the performance of general-purpose carbon fiber were investigated. The results showed that the as-prepared pitch precursors were dominated by carbon elements and contained small numbers of hydrogen, oxygen, nitrogen, and sulfur. The characteristic peaks generated from chlorine elements were observed in both FTIR and XPS spectra. The peaks at the wavenumbers of 1490 cm −1 and 696 cm −1 corresponded to the vibration of C–Cl bond, and a tiny Cl 2p peak located at 200.0 eV was observed by reducing the noise of XPS spectra. It indicates that the trace chlorine remains in the as-synthesized isotropic pitch precursor even after undergoing dechlorination. The molecular compositions of isotropic pitches were mainly polyaromatic hydrocarbons, and the chlorination–dechlorination promotes the oligomerization of polyaromatic hydrocarbons to form dimers and trimers. Therefore, the polycondensed degree and carbon aromaticity were improved. It is known from 13 C NMR analysis that the effect of chlorine–dechlorination makes the molecular structure of pitches transform more linear, thus enhancing their spinnability. In addition, the higher the amount of benzyl chloride added, the better the property of isotropic pitch was. The pitch of BC-30 and BC-40 showed excellent spinnability, stabilized property, and carbonized property compared to other pitches. The morphology of obtained carbon fiber was homogeneous and smooth without defects in surface and section. The as-prepared general-purpose carbon fiber demonstrated good tensile strength up to 1220 MPa with an average diameter of 8.5 μm. Graphical abstract
The carbonaceous pitch derived from coal liquefaction residue was controllably synthesized from the molecular dimension with a novel method, chlorination–dechlorination. The factors affecting the qualities of chlorination–dechlorination derived pitch, including chlorine ratios, were studied. The qualities of the pitches prepared with chlorination–dechlorination and the conventional thermal condensation method are compared. The carbons in the prepared carbonaceous pitch mainly exist in aromatic structures, which are oligomerized to transform dimers and trimers by chlorination–dechlorination. The C/H ratio, average molecular weight, and carbon aromaticity are increased by chlorination–dechlorination. According to the result of the simulation, the hydrogen atoms on the side chain of aromatic compounds are easier to be mono-substituted by chlorine atoms during chlorination, and then the substituting chlorine atoms connect with other hydrogen atoms to form to escape out of the reactor in the formation of hydrogen chloride during dechlorination , making the aromatic compounds oligomerize with each other. Thus, the conclusion that the chlorinated pitch has a more linear and cross-linking molecular structure is demonstrated, which is also confirmed by the results of 13 C NMR. The pitch precursors exhibit better thermal stability and thermochemical property even when the softening point has been raised to around 230 ℃ owing to the linear and cross-linking molecular structure. In addition, the pitches synthesized by the method of chlorination–dechlorination shows a more homogeneous state, while the pitch produced by thermal condensation contains a small number of powdery coke particles, and they also possess more excellent spinnability and appropriate viscosity for the process of melt-spinning. Chlorination–dechlorination can be used to achieve the controllable synthesis of the carbonaceous pitch from the molecular dimension. The properties of derived pitches are better as the addition of chlorine increases.
危险品化学品经营许可证（带存储）