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 13C 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.

Carbonaceous pitch; coal liquefaction residue; chlorination–dechlorination; synthesis; molecular dimension