Pitch Precursor Research Articles

Optimizing Aromaticity for Graphitization.

The increasing graphite demand for energy storage confronts a significant hurdle: a dwindling supply of high-quality precursors. This study introduces a simple additive upgradation strategy, exploring the potential of waste plastics and lower-quality aliphatic pitches to improve scant high-aromaticity pitch precursors by providing donatable hydrogen. The results indicate not only that high-quality aromatic pitches can accommodate waste plastics and lower-quality aliphatic pitches but also that their synergistic composition leads to improved graphitic quality and a uniform crystalline phase in the heat-treated products. Optimal aromaticity values have been investigated through a graphitization study of diverse pitch samples. Additionally, the effectiveness of quinoline insoluble removal as a subtractive strategy on crystallite sizes after graphitization was investigated, and remarkable improvements were observed in the crystallite sizes of the graphitized product.

Self-template synthesis of pitch-based hierarchical porous carbon for high performance supercapacitor in aqueous and ionic liquid electrolytes

Pitch-based hierarchical porous carbons (PHPCs) have been fabricated by means of self-templated method that is adopting metal oxides and metallic salts impurities originate from coal tar pitch (CTP) precursor serve as in-situ hard template along with KOH activation. The porosity properties of PHPCs are significantly influenced by the mass ratio of KOH to pitch. The micro-morphology, hierarchical porosity constituted of co-existing micro-/meso-/macropores, specific surface area, surface elementary composition and electrochemical properties have been comprehensively investigated. It is shown that the high specific surface area (2479 m2 g-1), lay-stacked microstructure, hierarchical porosity characteristic and considerable oxygen-containing functional groups (4.51 a.t %) that synergistically facilitate the electrochemical performance of PHPCs. The electrochemical measurements results exhibit that the gravimetric capacitance for the optimal sample PHPCs-4 is as high as 317 F g-1 at a current density of 0.2 A g-1, with retention of 213 F g-1 even at 10 A g-1 in a three-electrode configuration. In a two-electrode device, the PHPCs-4 based symmetric supercapacitor cell exhibits a specific capacitance of 245 F g-1 at 0.1 A g-1, along with a good rate capability of 75.5% (185 F g-1 at 10 A g-1) and a considerable energy density of 8.51Wh kg-1 at a power density of 50 W kg-1. When tested in EMIMBF4 ionic liquid electrolyte at a cell voltage of 3.5 V, the assembled symmetric supercapacitor cell demonstrates a high energy density of 77 Wh kg-1 at a power density of 175 W kg-1, maintaining 65.3 Wh kg-1 at a current density of 1 A g-1, and 32.1 Wh kg-1 at a high power density of 17500 W kg-1. Furthermore, the specific capacitance of the PHPCs-4 based symmetric supercapacitor retains nearly 100% of its initial value over 5000 cycles in 6M KOH aqueous electrolyte and 91.4 % after 2500 cycles in EMIMBF4 ionic liquid electrolyte. This strategy exploits a novel approach to synthesizing hierarchical porous carbons from coal tar pitch using a self-templating method, offering potential benefits for various applications.

Synthesis of spinnable isotropic pitch from low-softening-point coal tar pitch via Blanc bromomethylation-dehydrobromination towards carbon fibers with enhanced mechanical properties

Blanc bromomethylation-dehydrobromination is proposed to synthesize isotropic pitches with superior spinnability, utilizing refined coal tar pitch as the feedstock. This strategy involves introducing bromomethyl functional groups into pitch molecules through the Blanc bromomethylation reaction. In the subsequent process of dehydrobromination, methylene bridges generate between neighboring aromatic molecules. The pitch precursor prepared by this method not only displays an increased level of oligomerization and pitch yield, but also exhibits a more linear molecular structure compared with that produced through purely thermal polycondensation. The enhanced linear molecular configuration contributes to the improved spinnability of the pitch precursor and the oxidation reactivity of its derived fiber. Furthermore, the tensile strength of the resulting carbon fibers rises with an elevation in the amount of polyoxymethylene, and it exhibits the trend of an initial growth followed by a subsequent decrease as the stabilization temperature escalates. The carbon fibers obtained from the pitch prepared through thermal polycondensation present a low Young’s modulus of 24 GPa and a low tensile strength measuring of 456 MPa. In contrast, carbon fibers derived from the pitch synthesized via Blanc bromomethylation-dehydrobromination exhibit superior mechanical performance, offering Young’s modulus and tensile strength of 58 GPa and 1210 MPa, separately.

Investigating the structure, dynamics, and phase behaviour of polycyclic aromatic hydrocarbons derived from coal tar pitch: (I) temperature dependence

Carbon fiber (CF) is regarded as a “wonder material” in modern era for its several advantageous technological applications. It justifiably boasts of its light weight and high tensile strength. Unfortunately, the increased raw material cost of PAN-based CF restricts the horizon of its applications with an otherwise enormous potential. To this end, coal tar derived pitch is rich in poly aromatic hydrocarbons (PAHs) and can be a cheaper, promising source of precursors for CF manufacturing. Thus, herein, we have performed molecular dynamics (MD) simulation of several coal tar PAHs (varying in molecular weight and aromaticity) at various temperatures with an aim to enrich the current state of understanding on some intriguing precursor behaviours. This leads to the findings that low molecular weight precursors are most suited to form isotropic phase (random arrangement), whereas high molecular weight precursors are best suited to develop mesophase (ordered arrangement). Softening point of the precursors generally elevates with increase in molecular weight, but it is also affected by the phase of the system. The phase transition of pitch precursors from solid to liquid is not abrupt; rather, we discover a temperature range of phase coexistence that broadens as molecular weight increases.

Enhancing spinnability and properties of carbon fibers through modification of isotropic coal tar pitch precursor

Producing general-purpose carbon fibers (GPCFs) with excellent properties using an economical raw material such as coal tar pitch (CTP) holds significant importance. To synthesize carbon fibers, the spinnability of precursor material plays an important role. However, the CTP impedes flowability during the spinning process due to possessing high molecular weight complex aromatic structures. To address this limitation, CTP was blended with varying proportions of petroleum pitch (5, 10 and 20 %) and spinnability and flow behavior were analyzed using Rheology measurements. The distinct constitutional properties of petroleum pitch also contributed to alterations in both the stabilization and carbonization processes. Carbon fibers produced from 10PP showed the highest tensile strength and modulus of ∼784 MPa and ∼47 GPa, respectively. The impact of oxidative and carbonization treatments on the resultant microstructural and mechanical properties of carbon fibers was thoroughly examined using various techniques such as FTIR, XPS, XRD, SEM, Raman and UTM. The results showed that the composition of petroleum pitch influenced the stabilization of fibers which eventually affected the carbonization process and resultant properties of carbon fibers. This study offers an understanding of the connection between the precursor's composition, stabilization conditions, and mechanical properties of the resultant carbon fibers.

The electrochemical effects of pitch stabilization for supercapacitor-grade activated carbon precursors

Petroleum pitch (PP) is a by-product generated during the petroleum refining process, characterized by its high carbon content, tunable structure, and cost-effectiveness. These attributes have spurred extensive research into its potential as a carbon material. In this study, we prepared both untreated PP and oxidative stabilized PP (sPP) to explore the influence of pitch structural modifications on physical and electrochemical properties following carbonization and activation. Stabilizing the pitch above its softening point introduced oxygen functional groups on the surface, reaching levels of up to 19.6 at.%. These structural changes concurrently reduced aromaticity while increasing the coking value. Two types of activated carbons suitable for supercapacitors were derived from these distinct pitches, and their energy storage capacities were correlated with precursor pitch structural properties. The sPP-derived activated carbon exhibited a remarkable gravimetric specific capacitance of 39.6 F g−1, owing to its high specific surface area of 2508 m2 g−1. Conversely, PP-derived activated carbon exhibited a relatively lower specific surface area of 1122 m2 g−1. However, it demonstrated an increased electrode density and shallow ion intercalation within its graphitic structure, resulting in a notable volumetric capacitance of 26.0 F cc−1. This research not only sheds light on the electrochemical effects of pitch stabilization but also provides a foundation for the development of high-performance activated carbon materials through tailored modifications to the PP structure.

Preparation of Silicon Oxide-Carbon Composite with Tailored Electrochemical Properties for Anode in Lithium-Ion Batteries

For high-efficiency and high-stability lithium ion batteries, a silicon oxide-based carbon composite has been developed as an anode material. To minimize structural defects (cracking and pulverization) due to volumetric contraction/expansion during charge/discharge, silicon oxide (SiOx) is adopted. A pitch—a carbon precursor—is introduced to the surface of SiOx using the mechanofusion method. The introduced pitch precursor can be readily transformed into a carbon layer through stabilization and carbonization processes, resulting in SiOx@C. This carbon layer plays a crucial role in buffering the volume expansion of SiOx during lithiation/delithiation processes, enhancing electrical conductivity, and preventing direct contact with the electrolyte. In order to improve the capacity and cycle stability of SiOx, the electrochemical performances of SiOx@C composites are comparatively analyzed according to the mixing ratio of SiOx and pitch, as well as the loading amount in the anode material. Compared to pristine SiOx, the SiOx@C composite prepared through the optimization of the experimental conditions exhibits approximately 1.6 and 1.8 times higher discharge capacity and initial coulombic efficiency, respectively. In addition, it shows excellent capacity retention and cycle stability, even after more than 300 charge and discharge tests.

Polyarylacetylene as a novel graphitizable precursor for fabricating high-density C/C composite via ultra-high pressure impregnation and carbonization

High-density carbon/carbon (C/C) composite plays a critical role in the aerospace industry owing to excellent mechanical properties and resistance to ablation. However, traditional manufacturing relies on pitch precursor and hot isostatic pressure impregnation and carbonization (HIPIC) technology, which is time-consuming and expensive. In this study, we report an innovative method utilizing polyarylacetylene (PAA) resin and ultra-high pressure impregnation and carbonization (UHPIC) technology. The extremely high char yield of PAA resin (85 wt.%) and high isotropic pressure of UHPIC (over 200 MPa) promote the densification of the composite. As a result, we achieve a high-density (1.90 g/cm3) C/C composite with a high degree of graphitization (81%). This composite exhibits impressive properties, including flexural strength of 146 MPa, compressive strength of 187 MPa, and thermal conductivity of 147 W/(m K). When exposed to oxyacetylene flame at 3000 K for 100 s, it displays minimal linear ablation, with a rate of 1.27 × 10−2 mm/s. This study demonstrates the exceptional graphitizable characteristic of PAA resin, setting it apart from conventional resins. Our time-saving and cost-effective approach holds significant promise for aerospace applications, particularly in harsh aerodynamic heating environments.

Influence of Oxygen Uptake on Pitch Carbon Fiber.

Carbon fiber precursor materials, such as polyacrylonitrile, pitch, and cellulose/rayon, require thermal stabilization to maintain structural integrity during conversion into carbon fiber. Thermal stabilization mitigates undesirable decomposition and liquification of the fibers during the carbonization process. Generally, the thermal stabilization of mesophase pitch consists of the attachment of oxygen-containing functional groups onto the polymeric structure. In this study, the oxidation of mesophase pitch precursor fibers at various weight percentage increases (1, 3.5, 5, 7.5 wt%) and temperatures (260, 280, 290 °C) using in situ differential scanning calorimetry and thermogravimetric analysis isinvestigated. The results areanalyzed to determine the effect of temperature and weight percentage increase on the stabilization process of the fibers, and the fibers aresubsequently carbonized and tested for tensile mechanical performance. Thefindings provide insight into the relationship between stabilization conditions, fiber microstructure, and mechanical properties of the resulting carbon fibers.

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

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.

Evaluation of the utility of isotropic pitches as solvent components of spinnable mesophase pitch precursors for highly graphitizable functional carbon materials

Spinnable mesophase pitch (SMP) is an important graphitizable precursor for high-performance carbon materials. Generally, SMPs show fully developed anisotropic texture, and the pitches contain isotropic contents more than 30 wt%, which plays the role of solvent for the mesogenic components in the lyotropic liquid crystalline system of the pitch. Here, we prepared SMP by blending the mesogenic components of AR mesophase pitch with various isotropic pitches to evaluate the usability of isotropic pitches as solvents. The mesogenic components were prepared by tetrahydrofuran fractionation of AR mesophase pitch. Isotropic pitches with a softening point of 140–220 °C were prepared separately by simple heat treatment of slurry oil (SO) and coal tar pitch (CTP). SMPs were prepared by thermal blending of the above mentioned mesogenic components and isotropic pitches in various blending ratios. CTP-derived isotropic pitch showed better solvent performance than a SO-derived pitch in terms of anisotropic texture. SMP prepared by blending of the mesogenic components and CTP-derived isotropic pitch with a softening point of 180 °C at the ratio of 4/6 (w/w) showed almost 100% anisotropic texture; the carbon fiber derived from the pitch showed tensile strength of 2.7 GPa and Young’s modulus of 470 GPa after graphitization at 2,800 °C.

Mechanism for the catalytic thermal polycondensation of naphthalene at low temperature

Naphthalene is an important component of high temperature coal tar and its content can reach more than 10%. Catalytic polycondensation of naphthalene is an effective way to prepare mesophase pitch and functional carbon materials. In this work, anhydrous AlCl3 was used as a catalyst for the polymerization of naphthalene under atmospheric pressure below 170 °C and the reaction mechanism was then systematically investigated. The results indicate that at 110 °C, the polymer product is mainly composed of tricyclic compounds and the content of heavy products is only 29.5%. At 150 °C, four to five peri-condensed aromatic compounds turn to be the main components and the content of medium components remains about 50%. At 170 °C, there appear a large number of six-ring aromatic cores and the conversion of naphthalene reaches 90.7%. The polymer products exhibit good fluidity and solubility in THF, which can facilitate the high-temperature thermal polycondensation and subsequent graphitization process. With an AlCl3/naphthalene molar ratio of 1/100, the second to seventh order naphthalene oligomers are obtained by the simulation of the short chain oligomerization of naphthalene. In contrast, when the AlCl3/naphthalene molar ratio exceeds 10/100, acetylene and methylnaphthalene are produced by the catalytic pyrolysis of naphthalene. The mechanism of “Oligomerization-Pyrolysis-Aromatization” was then proposed to explain the molecular transformation from naphthalene to pitch, which should be useful for the production of mesophase pitch precursor.

In situ characterization of phase transformations in petroleum pitch by high temperature X-ray diffraction

The phase transformation from isotropic to mesophase of a petroleum-derived pitch was monitored by in situ X-ray diffraction at 410 °C. The kinetics of the transformation were characterized by monitoring the growth of a broad peak at 2θ∼24° and could be described by Avrami’s equation. The volatilization of low molecular weight components originally present in the pitch, or produced during the condensation reaction, was assessed by thermal gravimetry analysis, following the same thermal history. Ex situ characterizations of the pitch precursor before and after thermal treatment provided insight into the evolution of the molecular structure associated with mesophase generation (optical polarized microscopy, molecular weight distribution by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, X-ray photoelectron spectroscopy, Auger spectroscopy, and thermal stability). This investigation demonstrates the value of using complementary in situ and ex situ experimental techniques to characterize complex mechanisms during the processing of organic materials.

Controllable synthesis of a carbonaceous pitch from molecular dimension by a novel method of chlorination-dechlorination

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.

A solvothermal pre-oxidation strategy converting pitch from soft carbon to hard carbon for enhanced sodium storage

Due to its low cost and easy availability, the pitch is considered a promising precursor for soft carbon anodes. However, pitch-derived soft carbon shows a high graphitization degree and small interlayer spacing, resulting in its much lower sodium storage performance than hard carbon. We propose a novel pre-oxidation strategy to introduce additional oxygen atoms into the low-cost soft carbon precursor pitch to fabricate a defect-rich and large-interlayer spacing hard carbon anode (HPP-1100). Compared with the direct pyrolysis of pitch carbon, the sodium storage capacity of HPP-1100 is significantly improved from 120.3 mAh/g to 306.7 mAh/g, with an excellent rate and cycling capability (116.5 mAh/g at 10 C). Moreover, when assorted with an O3-Na(NiFeMn)1/3O2 cathode, the full cell delivers a high reversible capacity of 274.0 mAh/g at 0.1 C with superb cycle life. This work provides a new solution for realizing the application of low-cost pitch anodes in Na-ion batteries.

Understanding the correlation between microstructure and electrochemical performance of hybridized pitch cokes for lithium-ion battery through tailoring their evolutional structures from ordered soft carbon to disordered hard carbon

Pitch-derived cokes (PCs) with different optical textures and microstructures were produced by thermo-polymerization and subsequent heat treatment of a mixture of graphitizable and non-graphitizable precursors (i.e., naphthalene pitch and C9 resin). The effects of weight fractions of C9 resin and heat-treating temperatures on the evolutional microstructure and electrochemical performance of different hybridized PCs used as an anode material for lithium-ion batteries were investigated. The results show that the macro-texture, microstructure and structural evolution of PCs could be controlled by facilely tailoring the synthetic precursors through pitch-resin co-polymerizing reaction. The versatile and tunable structure of PCs closely dominates the inserting and extracting capability of lithium ions in the resultant PCs. With the introduction of C9 resin in the pitches from 0 to 100 wt%, the microstructure of resulting PCs changes from a highly oriented lamellar texture to a fine-grained mosaic texture (i.e., from anisotropic soft carbon to isotropic hard carbon). In addition, the electrochemical performance (e.g., in the range of 200–370 mA h g−1 for the specific capacity) of the PCs varies according to the textural orientation, microcrystallite sizes and graphitization degrees. The relationship between preliminary microstructure and electrochemical performance of PCs with controllable microstructure and crystalline orientation has been studied to understand the importance of structure control. Furthermore, this work provides a new strategy to adjust the electrochemical performance of hybridized PCs through tailoring the liquid crystal development of texture-tunable pitch precursor synthesis.

Properties of synthetic graphite from boric acid-added pitch: performance as anode in lithium-ion batteries

Synthetic graphite is produced by a heat treatment process using a carbon precursor (pitch, coke), but it is difficult to produce synthetic graphite of high quality due to the high-temperature process (minimum 3000 °C). Elements used as additive to lower temperature the graphitic process include boron, phosphorus, and nitrogen. Boron is known as a graphitization additive, because it accelerates the homogeneous continuous graphitization process of the entire carbon without any formation of specific carbon components such as graphite. In this study, various amounts of boron and PFO (pyrolysis fuel oil, carbon precursor) were used in an attempt to reveal the boron additive effect. Pitch was produced using a boric acid and pyrolysis fuel oil (PFO), and high-temperature carbonization was carried out at 2600 °C. As a result, synthetic graphite exhibiting high crystallinity at a relatively low temperature was produced. The electrochemical performance of several boron-doped and non-doped carbon materials with different structures as anodes in lithium-ion batteries was investigated by a structure analysis.

Effects of surface functional groups of coal-tar-pitch-derived nanoporous carbon anodes on microbial fuel cell performance

Coal tar pitch, the residue generated from distillation of coal tar, is cheap, abundant, and carbon enriched. This paper evaluates the effects of the surface modification of coal-tar pitch-derived nanoporous carbons (NPCs) as anode materials on the performance of Escherichia coli (E. coli)-based microbial fuel cells (MFCs) for the first time. The coal-tar pitch precursors are heated under N2 to 450 °C (450O) and 750 °C (750X) to obtain NPCs with different concentrations of oxygen-containing functional groups. 750X is, thereafter, doped with nitrogen atoms to generate a nitrogen-doped NPCs (750N). More biofilm is formed on the 750N anode than the 750X or 450O anode because of the higher electrical conductivity and biocompatibility of 750N. As a result, a higher power output of MFC is obtained when the 750N anode is used. The maximum power density of 750N is 3772 mW m−2, while that of 750X and 450O are 2876 mW m−2 and 3562 mW m−2, respectively, demonstrating that 750N is a potential sustainable anode material for high-performance MFC applications.

Carbon fiber synthesis from pitch: Insights from ReaxFF based molecular dynamics simulations

Despite the potential to lowering fabrication costs of pitch-based carbon fiber (CF) compared to polyacrylonitrile-based CF, large scale utilization is currently limited by the complexity in manufacturing. This is mainly due to the lack of consistency between the pitch structure/chemistry and CF properties under different processing conditions. Here, we employed full atomistic simulations based on reactive force fields to investigate the conversion of pitch precursors to CFs. It was found that at the carbonization stage, the consumption rates of precursors, gas formations, and solid yields (carbonized CFs) are all dependent on the composition and arrangement of molecular moieties in the precursor. Specifically, precursors with sp3 carbons in the cata-condensed core area have limited decomposition pathways (i.e., limited reaction sites), which leads to the formation of carbonized CFs with similar compositions. Furthermore, carbonized CFs possess distinct structural characteristics, and finally lead to the formation of CFs with different moduli. By analyzing CF crystallinity and elemental composition, general rationales are proposed for the selection of optimal precursors and processing conditions, and thus shed lights on parameter screening during industrial CF synthesis. For instance, inclusion of sp3 carbons in cata-condensed rings can be preferred over the presence of sp3 carbons on side chains.

Effects of Bromination-Dehydrobromination on the Microstructure of Isotropic Pitch Precursors for Carbon Fibers.

In this work, isotropic pitch precursors are synthesized by the bromination-debromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by bromination-debromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of bromination-dehydrobromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.