Isotropic Pitch Research Articles

Insight into the reactivity of aromatic-rich fractions co‑carbonized with polyethylene glycol for preparation of isotropic pitch with superior spinnability

Co‑carbonization of aromatic-rich distillate oil (HCTO-RF) with polyethylene glycol (PEG) is a reliable process to prepare isotropic pitch with superior spinnability for producing carbon fibers. In the study, HCTO-RF was fractioned into light fraction, middle fraction, and heavy fraction. The chemical structural features of each fraction and their co‑carbonization routes with PEG under the same reaction conditions were characterized and investigated. The results reveal that the light fraction was mainly composed of molecules containing one and two aromatic hexagonal rings with numerous longer alkyl side chains. The middle fraction was rich in less polycondensed two and three aromatic hexagonal ring compounds, which contained a certain number of naphthenic structures. The heavy fraction was mainly composed of four aromatic hexagonal ring compounds with higher condensation degrees and less short alkyl side chains. The co‑carbonization reaction of PEG and the three fractions proceed by the routes: the radicals produced from the homolysis of the CO and CC bonds of PEG molecules; the activation of the aromatic units triggered by abstracting hydrogen; the polycondensation of activated aromatic units. The heavy fraction exhibited the most availability for co‑carbonization reaction, followed by the middle fraction and the light fraction the worst.

Molecular structure effects of mesophase pitch and isotropic pitch on morphology and properties of carbon nanofibers by electrospinning

Carbon nanofibers (CNFs) with high specific surface area and flexible lap structure are highly desirable for numerous applications such as adsorption films, supercapacitors, heat dissipation elements, and composites. In this work, CNFs were prepared using two major categories of pitches, isotropic pitch (IP) and mesophase pitch (MP), as raw materials to compare their molecular structure effects on the morphology and properties of CNFs. The analysis of scanning electron microscopy results found that some fusions among nanofibers easily formed in IP-derived electrospun nanofibers (IP-SNFs) while an independent and smooth nanofiber morphology were observed in MP-derived electrospun nanofibers (MP-SNFs). Besides, composed of high aromatic molecules content and appropriate aliphatic components, MP-SNFs showed a mitigating exothermic reaction and MP-CNFs exhibited higher specific surface area, conductivity and thermal diffusion coefficient. While with too abundant aliphatic components in IP, there was a violent exothermic reaction of IP-SNFs during the stabilization process, endowing the corresponding IP-CNFs with poor performances. Therefore, thermal behavior of SNFs varied with the molecular structure differences of IP and MP, which had a significant influence on the microstructure and properties of their CNFs.

Modification of isotropic pitch by tailoring chemical structure and fraction contents for enhancing carbon fiber mechanical properties

The composition of isotropic pitch (IP) is the key factor to determine the performance of carbon fibers (CFs). It is necessary to investigate the effect of chemical structure of pitch and compositions change on the performance of CFs. An isotropic pitch was fractionated into seven fractions by solvent fractionation to characterize the molecular structural features by FT-IR, 1H NMR etc. The oxidative reactivity of pitch fibers, mechanical properties, microstructure and morphology of CFs derived from four IPs with different components were characterized and evaluated. The results revealed that with the removal of light fractions, the synergistic effect between pitches components in melting significantly decreased, leading to the decrease of spinnability of pitch and deteriorating the uniformity of carbon fiber microstructure. The oxidative reactivity of the pitch fibers gradually decreased with the removal of light fractions. The reason was that these light fractions contained more alkyl side chains, which were preferentially attacked by oxygen at the low oxidation temperature, than that of these heavy fractions. The mechanical properties of CFs showed an increase first and then decrease with the removal of these light fractions. Especially, the carbon fiber derived from the isotropic pitch (H80-T20I) exhibited an excellent high tensile strength of 1190 MPa.

Physical Properties Enhancement of Carbon Fiber Obtained from Isotropic Pitch Doped by Ultra-Long Carbon Nanotubes

Physical Properties Enhancement of Carbon Fiber Obtained from Isotropic Pitch Doped by Ultra-Long Carbon Nanotubes

Modeling of Anisotropy Dynamics of the Proton Pitch Angle Distribution in the Earth’s Magnetosphere

Last years the attention to research of anisotropy of the charged particle pitch angle distribution has considerably increased. Therefore for research of anisotropy dynamics of the proton pitch angle distribution is used the two-dimensional Phenomenological Model of the Ring Current (PheMRC 2-D), which includes the radial and pitch angle diffusions with consideration of losses due to wave-particle interactions. Experimental data are collected on the Polar/MICS satellite during the magnetic storm on October 21–22, 1999. Solving the non-stationary two-dimensional equation of pitch angle and radial diffusions, numerically was determined the proton pitch angle distribution anisotropy index (or parameter of the proton pitch angle distribution) for the pitch angle of 90 degrees during the magnetic storm, when the geomagnetic activity Kp-index changed from 2 in the beginning of a storm up to 7+ in the end of a storm. Dependence of the perpendicular proton pitch angle distribution anisotropy index with energy E = 90 keV during the different moments of time from the McIlwain parameter L (2.26 < L < 6.6) is received. It is certain at a quantitative level for the magnetic storm on October 21–22, 1999, when and where on the nightside of the Earth’s magnetosphere (MLT = 2300) to increase in the geomagnetic activity Kp-index there is a transition from normal (pancake) proton pitch angle distributions to butterfly proton pitch angle distributions. That has allowed to determine unequivocally and precisely the anisotropy dynamics of the proton pitch angle distribution in the given concrete case. It is shown, that with increase of the geomagnetic activity Kp-index the boundary of isotropic proton pitch angle distribution comes nearer to the Earth, reaching L ≈ 3.6 at Kp = 7+

Preparation of isotropic spinnable pitch with high-spinnability by co-carbonization of coal tar pitch and bio-asphalt

Co-carbonization of coal tar pitch (CTP) with bio-asphalt (BA) was performed to prepare spinnable pitch with suitable softening point and excellent spinnability for general purpose carbon fiber. The co-carbonization mechanism and the correlation between spinnability and molecular structure of prepared pitch were clarified. BA produced from the pyrolysis of biomass is abundant of aliphatic units and oxygen-containing groups, leading to high reactivity during carbonization. The co-carbonization reactions mainly depend on the mutual cross-linking among CTP and BA molecules, which are principally triggered by active oxygen-containing groups of BA. The formed cross-linked macromolecules could further promote the polymerization degree of pitch molecules; thus, the spinnable pitch with suitable softening point could be obtained by simply thermal treatment of blended pitches at a relatively moderate condition (<350 °C). The properties of the pitch could be optimized by changing the blending ratio of CTP to BA. Moreover, the prepared carbon fibers demonstrated distinct features, especially surface profiles. It is expected to provide a new strategy for the preparation of isotropic spinnable pitch in a relatively simple approach.

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.

Anisotropic phase transition via high temperature thin-layer evaporation of a petroleum-based isotropic pitch

Preparation of anisotropic pitch with the moderate softening point suitable for carbon material processing from heavy oil is challenging. This is because it is very difficult to suppress excessive thermal reactions that occur during the phase transition from isotropic to anisotropic phase. Due to the thermal reaction, the softening point rises excessively and infusible particles are formed, which in turn leads to severe processibility and performance degradation of the final carbon materials. Although many efforts has been devoted to prepare 100% anisotropic pitches suitable for carbon material processing so far, not a proper method for mass production was developed. In this study, we applied high temperature thin-layer evaporation (TLE) process for the phase transition of a petroleum-derived isotropic pitch. Temperature dependence of phase transition was closely examined for the temperature between 300°C and 420°C. As a result, a noticeable number of anisotropic spheres was observed at 370°C; the spheres were grown and merged together to for a bulk phase with the 84% anisotropy at 390°C. Finally, a 100% mesophase pitch was obtained in a short time of 10min at 410°C with a high production yield of 36.0%.

Effects of the degree of oxidation of pitch fibers on their stabilization and carbonization behaviors

The stabilization of isotropic pitch (IP)-derived pitch fibers (PFs) and mesophase pitch (MP)-derived PFsin air was performed at different heating rates and with different final stabilization temperatures. The stabilized fibers (SFs) and carbon fibers (CFs) were characterized by elemental analysis, FT-IR, TG-MS and SEM to investigate the influence of the degree of oxidation of the SFs on the microstructures and mechanical properties of the CFs. Results showed that a slow heating rate during stabilization was beneficial to the oxidative cross-linking of PFs, and the corresponding CFs had a higher carbonization yield and tensile strength at the lower heating rate. When both IPF and MPF were stabilized at 270 oC, the two resulting CFs all reached their optimal performance. In addition, the FTIR peak intensity ratio of the C=O band at about 1700 cm–1 to the C=C band at 1600 cm–1 of the SFs had a good relationship to the carbonization yield and tensile strength of the CFs, and thiscan beusedto optimize the degree of oxidation of the SFs. Moreover, insufficiently stabilized fibers released a great deal of H2 and CH4, causing some porosity in the resulting CFs with a low tensile strength, especially forthe insufficiently stabilized IPCF. While over-stabilized fibers released a large amount of CO and CO2, causing cracked textures in the corresponding CFs, especially inthe over-stabilizedMPCF. Therefore, this research into the stabilization and carbonization behaviors of pitch fibers has great significance for improving the mechanical properties of pitch-based CFs.

A Generalized Method for Calculating Atmospheric Ionization by Energetic Electron Precipitation

AbstractAccurate specification of ionization production by energetic electron precipitation is critical for atmospheric chemistry models to assess the resultant atmospheric effects. Recent model‐observation comparison studies have increasingly highlighted the importance of considering precipitation fluxes in the full range of electron energy and pitch angle. However, previous parameterization methods were mostly proposed for isotropically precipitation electrons with energies up to 1 MeV, and the pitch angle dependence has not yet been parameterized. In this paper, we first characterize and tabulate the atmospheric ionization response to monoenergetic electrons with different pitch angles and energies between ∼3 keV and ∼33 MeV. A generalized method that fully accounts for the dependence of ionization production on background atmospheric conditions, electron energy, and pitch angle has been developed based on the parameterization method of Fang et al. (2010, https://doi.org/10.1029/2010GL045406). Moreover, we validate this method using 100 random atmospheric profiles and precipitation fluxes with monoenergetic and exponential energy distributions, and isotropic and sine pitch angle distributions. In a suite of 6,100 validation tests, the error in peak ionization altitude is found to be within 1 km in 91% of all the tests with a mean error of 2.7% in peak ionization rate and 1.9% in total ionization. This method therefore provides a reliable means to convert space‐measured precipitation energy and pitch angle distributions into ionization inputs for atmospheric chemistry models.

Polymerization kinetics and control of the components of a mesophase pitch

It is important to increase the content of pyridine soluble in mesophase pitch to improve its spinnability. A naphthalene isotropic pitch was used as the raw material to prepare mesophase pitch by polymerization. The components of the polymerized products were analyzed by solvent extraction with benzene and pyridine, and classified as benzene soluble (BS), pyridine insoluble (PI) and benzene insoluble but pyridine soluble (BI-PS). The effects of polymerization temperature, time and the components of the raw material on the distribution of the components and optical texture of the mesophase pitch were investigated. The reaction kinetic constants were calculated assuming a consecutive reaction from BS to BI-PS, then to PI. Results show that a mesophase pitch with a relatively uniform distribution of components is obtained after reaction at 430 °C for 20 h from an isotropic pitch pre-polymerized at 400 °C for 10 h. The mesophase pitch synthesis reaction has a significant auto-acceleration effect in that the reaction rate constant of a heavy component is larger than a light one. The reaction rate becomes faster and faster as the molecular weight of the pitch increases in the latter stage of the synthesis reaction. Therefore, the initial component of raw pitch, reaction temperature and time have a decisive influence on the distribution of components in the mesophase pitch.

Controllable synthesis of isotropic pitch precursor for general purpose carbon fiber using waste ethylene tar via bromination–dehydrobromination

Nowadays, the substantial amount of waste ethylene tar (ET) lacks a clean and efficient route for utilization. In this work, a feasible approach was developed to fabricate general purpose carbon fiber (GPCF) using ET as a raw material. The method of bromination–dehydrobromination was used to synthesize controllably isotropic pitch precursor for GPCF. The results show that bromination–dehydrobromination reaction promotes the cyclization and aromatization of small molecules and relatively low molecular weight components and also prevents excess condensation during thermal treatment. The molecular structure of pitch precursor generated from bromination–dehydrobromination reaction has more linear and cross-linked structures as more naphthenic groups and the side chain of aromatic rings. The spinnability of pitch precursors and the mechanical performance of GPCFs are optimized when 10 wt% of bromine is introduced in synthetic reaction. The tensile strength, Young’s modulus, and elongation property of the final GPCF are 1072 ± 66 MPa, 47 ± 7 GPa, and 2.3%, respectively, with the diameter of 10.3 ± 0.5 μm.

Effect of hybrid reinforcement of carbon fiber and stable particles on pitch based carbon carbon composites

Carbon matrix carbon (c/c) composites were investigated to study the effect of incorporating stable particulate reinforcement along with chopped carbon fibers to check the effect of hybrid reinforcement. Robust c/c composites were fabricated by isotropic petroleum pitch matrix in single-step carbonization without re-impregnation process. Dense and rigid composites with density ranging from 1.65–1.75 g cm−3 were developed. Distinctive properties comprising coefficient of friction, coefficient of thermal expansion, high temperature dimensional and weight stability, shrinkage, hardness, weight loss, breaking energy and compressive strength were assessed and compared with the reference c/c composite. Secondary stable additives such as silicon carbide, molybdenum di-silicide, graphite, CNT, fly ash and alumina were added 5% by weight in the composites. Specimens containing advanced ceramic particles showed appreciable improvement in hardness, thermal, and mechanical response while composites with fly ash and graphite addition showed the converse effects. From the research, we were able to alter the properties and tailor them according to the application such as compression and friction coefficient was improved to have application in brake discs for automobiles. Also, the thermal shielding has been improved by incorporating thermally dormant material such as fly ash and Incorporation of hard and stable reinforcement has brought about noticeable changes consequently hybrid reinforcement improved the overall performance of the material even after ablation in oxy-acetylene flames.

Thermodynamic study of phase transition behavior between the isotropic phase and mesophase using benzene-soluble and benzene-insoluble as phase indicators

Preparing carbonaceous mesophase pitch precursor by thermal treatment of isotropic pitch is a feasible and effective method for fabricating various high-performance carbon materials including high-modulus carbon fiber, needle coke, graphite, etc. However, the industrial production of qualified mesophase with desirable properties needs to be further improved in many regions. Especially, during pitch preparation, the transformation from isotropic phase to mesophase is difficult to be controlled since it significantly depends on reaction conditions, raw material and preparation parameters. While the optimization of the production conditions of mesophase with special properties requires time-consuming and costly exploratory experiments due to the lack of the fundamental understanding in the transformation behavior from isotropic phase to mesophase. This paper elaborates a fundamental work seeking a more suitable and accurate thermodynamic model and a parameter estimation method to describe phase transition behavior using benzene-soluble (BS) and benzene-insoluble (BI) fractions of coal tar-based pitch as indicators of isotropic phase and mesophase, respectively. The combined equation of simplified statistical associating fluid theory with anisotropic pseudopotential (SSAFT-APP) is used to describe phase transition, and the related parameters of each equation are estimated based on average molecular weight and carbon aromaticity of BS and BI fractions, respectively. The mesophase content of various samples prepared by annealing the mixtures of BS and BI fractions under different mixing ratios are used to calibrate the computed data. The results show that BS fraction has a restraining effect on the formation of mesophase when BI fraction is lower than 60 wt%, while this effect becomes weak with a higher content of BI fraction. A phase diagram is proposed by substituting the estimated parameters in SSAFT-APP equation with experimental data. Mesophase is able to be generated when the adding amount of BI fraction is increased to 12 wt%, and 100% mesophase could be obtained when the ratio of BI fraction is higher than 94 wt%. This work is expected to shed light on the phase transition behavior between isotropic phase and mesophase during pitch preparation from coal tar. In addition, based on the thermodynamic study optimizing preparation conditions and a novel method for obtaining the products with an optimal proportion between isotropic phase and mesophase is proposed.

Preparation and characterization of high-spinnability isotropic pitch from 1-methylnaphthalene-extracted low-rank coal by co-carbonization with petroleum residue

Coal extract produced by solvent extraction of low-rank coal is not suitable for spinning due to its high oxygen content. In order to effectively overcome this limitation, soft pitch was produced by co-carbonization of coal extract and petroleum residues. The decrease in oxygen content was confirmed by physical property analyses of the soft pitches blended at different mixing ratios. A bridge/hydroaromatic structure of the soft pitch was observed during the co-carbonization. The produced spinnable pitch had a high spinnability and a softening point of 230 °C. This spinnable pitch, prepared by solvent extraction of low-rank coal, showed excellent spinnability and was heat-treated at 800 °C for 5 min to produce isotropic carbon fibers having diameters of 7 μm and a tensile strength of 1189 MPa. Thus, the co-carbonization of coal extract and petroleum residue is an effective method for the production of inexpensive spinnable pitch for isotropic carbon-fiber manufacture.

The Preparation and Properties of Isotropic Pitch-Based Carbon Felt Prepared by Solvent-Supported Dual Concentric Electrospinning

An isotropic pitch was electrospun in the form of a felt, by adopting a specially-designed dual concentric nozzle system. In the dual nozzle system, the solvent of tetrahydrofuran (THF) flowed independently through the outer nozzle, and relieved the problem of the too rapid coagulation of pitch fibers in the inner nozzle. Unlike the non-woven pitch fabric prepared by conventional electrospinning, the pitch felt had a characteristic morphology of fiber bundles, highly isolated from each other with few fusion points between fibers. The felt morphology was retained, during carbonization of the pitch felt. In consequence, the carbon felt took a sponge-like form, and showed extremely low bulk density of ca. 4.2×10−2 g/cm3, almost one tenth of that of the polyacrylonitrile-based carbon fibers in the form of non-woven fabric. The cross-section of the felt fibers exhibited the shape of a dog bone, due to asymmetric shrinkage of fibers during electrospinning. Physical properties of the felt were affected by pitch concentration, flow rate, and carbonization temperature.

Facile Preparation and Characterization of Carbon Fibers with Core-Shell Structure from Graphene-Dispersed Isotropic Pitch Compounds.

In this study, isotropic pitch-based carbon fibers were prepared from a mixture of petroleum residue and graphene nanoplatelets with different contents. The softening point and synthetic yield of synthesized isotropic pitches were analyzed and compared to characterize the nature of the pitches. The surface and thermal characteristics of the fibers were observed using scanning electron microscopy and thermogravimetric analysis (TGA), respectively. From the results, it was observed that the prepared carbon fibers had an interesting core-shell structure. In the TGA analysis with air, the carbon fiber having 0.1 wt.% of graphene showed a higher residue yield than that of the sample having 1.0 wt.% of graphene. This result can be explained due to the graphene being placed on the surface region of the carbon fibers and directly helping to increase the surface area of the carbon fibers, resulting in rapid oxidation due to the enhanced contact area with oxygen.

Effect of the pre-treated pyrolysis fuel oil: coal tar pitch ratio on the spinnability and oxidation properties of isotropic pitch precursors and the mechanical properties of derived carbon fibers

Pitch precursors affording excellent spinnability, high-level oxidation-resistance, and good carbonization yields were prepared by bromination–dehydrobromination of various ratios of pyrolyzed fuel oil and coal tar pitch. The pitches exhibited spinnabilities that were much better than those of pitches prepared via simple distillation. A pitch prepared using a 1:2 ratio of fuel oil and coal tar pitch exhibited the best tensile strength. Pitch fibers of diameter 8.9 ± 0.1 μm were stabilized at 270 °C without soaking time after heating at a rate of 0.5 °C/min and carbonized at 1100 °C for 1 h after heating at 5 °C/min. The resulting carbon fibers exhibited a tensile strength, elongation, Young’s modulus, and average diameter of 1700 ± 170 MPa, 1.6 ± 0.1%, 106 ± 37 GPa, and 7.1 ± 0.2 μm, respectively.

Thermolysis of Petroleum Pitch from Different Sources

The thermolysis of isotropic pitch prepared from heavy pyrolytic tar and heavy catalytic-cracking gas-oil is investigated. The basic properties of the isotropic pitch are investigated in the course of thermolysis at different temperatures. Optimal temperatures for thermolysis so as to obtain fibrous pitch are established: 350°C for isotropic pitch from heavy pyrolytic tar; and 400°C for isotropic pitch from heavy catalytic-cracking gas-oil. In both cases, the duration of thermolysis is 4 h. Then the formation of mesophase begins. Its content in the pitch after 6 h is 10%.

Enhancing the oxidative stabilization of isotropic pitch precursors prepared through the co-carbonization of ethylene bottom oil and polyvinyl chloride

An isotropic pitch precursor for fabricating carbon fibres was prepared by co-carbonization of ethylene bottom oil (EBO) and polyvinyl chloride (PVC). Various pre-treatments of EBO and PVC, and a high heating rate of 3°C/min with no holding time, were evaluated for their effects on the oxidative stabilization process and the mechanical stability of the resulting fibres. Our stabilization process enhanced the volatilization, oxidative reaction and decomposition properties of the precursor pitch, while the addition of PVC both decreased the onset time and accelerated the oxidative reaction. Aliphatic carbon groups played a critical role in stabilization. Microstructural characterization indicated that these were first oxidised to carbon–oxygen single bonds and then converted to carbon–oxygen double bonds. Due to the higher heating rate and lack of a holding step during processing, the resulting thermoplastic fibers did not completely convert to thermoset materials, allowing partially melted, adjacent fibres to fuse. Fiber surfaces were smooth and homogeneous. Of the various methods evaluated herein, carbon fibers derived from pressure-treated EBO and PVC exhibited the highest tensile strength. This work shows that enhancing the naphthenic component of a pitch precursor through the co-carbonization of pre-treated EBO with PVC improves the oxidative properties of the resulting carbon fibers.