Refined coal pitch is a recognized precursor to produce high-quality needle coke with its higher aromaticity, lower ash content, and a relatively narrow distribution of molecular weight. The aromatic index (f a) of refined coal pitch is one of the key roles in the production of high-quality needle coke. In order to a detailed study on the effects of f a on the microstructure and properties of needle coke, 9 kinds of refined coal pitches with varied f a were used as the raw materials to produce needle coke in this study. Briefly, 1H NMR was used to calculate the f a of each refined coal pitch. Polarizing microscope, scanning electron microscopy, microstrength tester, X-ray diffraction, Raman spectrum, and curve-fitted methods have been used to quantitatively examine the microstructure and microstrength of each needle coke. The results have shown that the refined coal pitch with the f a of 0.95–0.98 was the best precursor to produce high-quality needle coke.

Refined coal tar pitch is considered as a promising material for the production of needle coke owing to its excellent physical–chemical properties. It was generally accepted that the basic properties of refined coal pitch played a vital role in affecting the resulting quality of the derived needle coke during the delayed coking process. Our previous research showed that an f a of 0.95–0.98 of refined coal pitch was optimal and produced needle coke of the highest quality. What is more, we found that the contents of β resin in refined pitch were also important to the properties (microstructure, microstrength, and true density) of the derived needle coke. Therefore, the effects of the contents of β resin on the properties of needle coke were investigated thoroughly, and eight types of refined coal pitch (the f a range from 0.9621 to 0.9725) with varied contents of β resin were employed as the precursors of needle coke. The techniques of proton nuclear magnetic resonance and gel permeation chromatography were utilized to determine the f a and molecular weight of each refined coal pitch, respectively. Microstructures (optical microstructure and surface morphology) have been analyzed by polarizing microscopy and scanning electron microscopy, separately. X-ray diffraction, Raman spectra, and curve-fitting enabled the quantitative examination of the microcrystalline structure. What is more, the microstrength and true density of each needle coke have also been examined in this study. It was concluded that a β resin content of 13–16% in the refined coal pitch achieved the best results and was optimal for needle coke production.

High-temperature coal tar pitch is often used to produce high-quality needle coke. Its basic properties [such as f a value, β resin, and quinoline insoluble (QI) content] significantly affect the quality of the resulting needle coke. Refined pitch with f a and β-resin values in the 0.95–0.98 and 13–16% ranges, respectively, is considered an excellent raw material for this purpose. The influence of QI content on the characteristics of coal-based needle coke is still not fully clarified in the literature. To analyze how QI content affects coal-based needle coke properties, this work used 10 different kinds of coal tar pitch (refined from the same source) with different QI contents for the needle coke production. We thoroughly analyzed optical microstructure and crystalline sizes, surface morphology and microstrength, true density, and coefficient of thermal expansion (CTE) of the resulting products. The high-temperature coal tar pitch with the QI content of <0.8% was a preferable raw material to obtain superior needle coke; it possessed higher density and microstrength, lower CTE, and graphitized more easily than cokes with other parameters.

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Refined polymerized pitch (RPP) is a by-product from the production of mesocarbon microbeads (MCMB). In order to understand the effects of an air oxidation treatment on the microstructure of the synthesized pitch coke, oxidized and polymerized pitch (prepared by oxidation in air with RPP as the raw material) has been used as the raw material to produce pitch coke. The microstructure of as-prepared pitch coke was determined using optical microscopy, scanning electron microscopy, XRD, and Raman spectroscopy and was combined with a curve-fitting method. The true density and micro-strength of each pitch coke was also investigated in this study. The results showed that the oxidation of RPP in air caused a mosaic structure with amorphous carbon in the derived pitch coke. In addition, the micro-strength of the derived pitch coke improved from 65% to 77%, and the amorphous carbon content also increased from 10.41% to 14.59% after the air oxidation treatment. Therefore, the air oxidation treatment of RPP took place before liquid-carbonization and was a feasible method for the production of hard carbon. K E Y W O R D S micro-strength, microstructure, Oxidized polymerized pitch, pitch coke, true density 1 | INTRODUCTION As a type of polycyclic aromatic carbonaceous compounds with excellent physical and chemical properties, coal pitch has attracted more attention in varied fields such as: metallurgy, the chemical industry, machining, and construction. 1-4 In recent years, the efficient and high value-added utilization of coal pitch has been a common research topic. 5-8 Coal pitch is usually divided into four categories in literature: high-temperature coal

Medium–low temperature coal tar pitch (MLP) is a type of aromatic carbonaceous material obtained by the low temperature distillation of low rank coal, and is considered as a desirable raw material for the production of artificial carbon/graphite material. The thermal conversion behaviors of MLP during the liquid‐phase carbonization process were analyzed in detail in this study. Further, the changes of molecular structure and carbon microcrystalline structure of MLP and liquid‐phase carbonization products derived from it were quantitatively investigated by optical microscopy, fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, and curve‐fitting method. Results showed that both branched chain and the contents of C=O functional groups in the MLP played a key role in the reaction reactivity. Moreover, temperature of 450 °C was found to be a rapid changing temperature point on the enhancement of thermal conversion of MLP. The stacking height (Lc), parallel layers (N), average number of aromatic rings in each layer (n), ratio of ‘impurity’ structure (RI), ratio of amorphous carbon structure (RAC), ratio of graphite carbon structure (RGC), and ratio of defects graphite carbon structure (RDGC) exhibited a significant change with the improvement of liquid‐phase carbonization temperature.

Needle coke was recognized as one of the most important precursor to produce ultra‐high power graphite electrode, commercial anode materials for lithium‐ion battery, and special graphite materials. It was generally accepted that the microstructure of needle coke has been acted as a key role on the quality of its derived graphite materials. In this work, four kinds of green needle cokes (coal‐based green needle coke and petroleum‐based green needle coke) have been used as the raw materials to investigate the changes of micro‐structure during the calcination process. The micro‐structure of needle cokes at different calcination temperature has been detailed characterized by X‐ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM), and transmission electron microscopy (TEM), respectively. Briefly, the size of carbon crystalline (Lc), the content of graphite carbon (IG/IAll), and the content of regular carbon microcrystals (Ig) in coal‐based needle coke were higher than petroleum‐based needle coke when the calcinations temperature was below 1500°C. What's more, the calcinations temperature of 1400°C is the characteristic temperature of the transition of carbon microcrystalline. In other words, the coal‐based needle coke was easier to graphitization than petroleum‐based needle coke.

Four types of spinnable pitches (MP‐N‐A, MP‐A, MP‐A‐H, and MP‐A‐N) for general‐purpose carbon fiber have been prepared under certain conditions with the refined pitch as the raw materials. Fourier transform infrared spectrum and solid‐state nuclear magnetic resonance spectra combined with curve‐fitting analysis have been used to characterize the average molecular structure (Iar, CH3/CH2, SAR, and SHFG) of spinnable pitches. Thermogravimetric analyses and polarizing microscope have been used to observe the thermal stability and the microstructure of spinnable pitches, respectively. The X‐ray diffraction combined with curve‐fitting analysis have showed that, the stacking heights (Lc) of these four kinds of spinnable pitches were 2.21, 1.78, 1.79, and 1.76 nm, respectively. The parallel layers (N) of each spinnable pitch were 7.30, 6.02, 6.06, and 5.97. What is more, the numbers of aromatic ring in each layer (n) were 17.03, 11.61, 11.75, and 11.41. Finally, the scanning electron microscopy has been used to characterize the surface morphology of carbon fibers which obtained by each spinnable pitches. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47880.