Controllable Synthesis of a Carbonaceous Pitch from Molecular Dimension by a Novel Method of Chlorination-Dechlorination

Coal pitch was recognized as an important raw material to produce artificial carbon/graphite materials. The pyrolytic process was the essential process during the production of artificial carbon/graphite materials, and the pyrolytic behaviors of coal pitch acted a key role on the quality of derived carbon materials. In order to detailed study on the pyrolytic behaviors of coal pitch, four kinds of coal pitches named as medium coal tar pitch (MP, a kind of high-temperature coal pitch), medium-low temperature coal pitch (MLP), coal direct liquefaction pitch (CLP), and coal pyrolytic extraction (CPE) were used as raw materials, and FTIR, TG/DTG-FTIR combined with curve-fitted method have been used to determine the pyrolysis characteristics of coal pitches. The microstructure of pyrolysis products from different coal pitches has been analyzed by optical microscope, X-ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM) and N2-adsorption and desorption (BET method), respectively. What's more, the micro-strength and resistance of pyrolytic products have been also investigated in this study. In fact, the CLP has the highest aromaticity, and the content of graphite carbon microcrystalline (IG/IAll), the size of carbon microcrystalline (Lc), the specific area (SBET), the micro-strength, and resistance of its' pyrolytic products were 13.22%, 1.94 nm, 2.909 m2/g, 65%, and 5.22 Ω, respectively. In other words, the molecular structure of coal pitch has key effects on the pyrolysis characteristics of coal pitch, and the aromaticity of coal pitch also has an significant influence on the carbon crystalline, micro-strength, and resistance of pyrolytic products. The higher aromaticity of coal pitch always meant for the higher content of graphite carbon crystalline and a lower resistance. 

Differences of the pyrolytic behaviors and pyrolysis products of coal pitch from different sources

Chlorination–dechlorination of coal liquefaction residue using benzyl chloride for general-purpose carbon fiber synthesis

Pitch-based carbon fiber, as one of the important engineering materials, has been widely used in aerospace, defense, sports, and other fields. In the long production process of pitch-based carbon fiber, the property of pitch precursor is significant for the mechanical performance of obtained carbon fiber. Thus, it is crucial to improve the property of pitch precursor by efficient means. Halogenation–dehalogenation is a newly developed method for the controllable synthesis of a pitch precursor from the molecular dimension, including fluorination–defluorination, chlorination–dechlorination, and bromination–debromination. This work reviewed the mechanism and application, as well as the advantages and disadvantages of each halogenation–dehalogenation method.

Mechanism and application of halogenation–dehalogenation in the development of pitch-based carbon fiber: A review

Tetrahydrofuran (THF) extract of coal tar pitch (CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fibre through bromination–dehydrobromination. The feasibility and effectiveness of synthesising an isotropic pitch precursor derived from THF-soluble (CTP-THFs) is demonstrated in this study. The results show that CTP-THFs contains more light components than CTP; CTP-THFs and CTP monomer proportions were 62.52% and 45.32%, respectively. However, based on comparisons of CTP-THFsBr0 and CTPBr0 characterisations, CTP-THFs exhibits better polycondensation than CTP. Bromination–dehydrobromination promotes polycondensation of pitch precursors, leading to greater carbon aromaticity in CTP-THFsBr5, CTP-THFsBr10, and CTP-THFsBr15 than that in CTP-THFsBr0 and CTPBr0. CTP-THFsBr5 and CTP-THFsBr10 have excellent spinnability even with softening points as high as 230 °C. The peri-condensed carbon and carbon aromaticity of CTP-THFsBr5 and CTP-THFsBr10 are high owing to the higher degree of polycondensation; however, they still possess a more linear molecular structure. The as-prepared carbon fibre exhibits homogeneity and uniformity, and the mechanical performance is comparable with that of commercial general-purpose carbon fibre products. 

Tinghao Fang

Papers

Preparation of pitch precursor with excellent spinnability for general-purpose carbon fibre using coal tar pitch as raw material