Isotropic Pitch Precursors Research Articles

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.

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.

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 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.

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.

Preparation of isotropic pitch precursor for pitch-based carbon fiber through the co-carbonization of ethylene bottom oil and polyvinyl chloride

For the first time, polyvinyl chloride (PVC) was used as an easily-handled chlorine source for preparation of isotropic pitch-based carbon fiber (IPCF) incorporating ethylene bottom oil (EO) as a raw material. Pitch precursors were prepared by the chlorination–dehydrochlorination triggered by chlorine radicals originated from PVC; aromatization and poly-condensation reactions occurred by polyene-type radicals from PVC. Radical production and co-carbonization were facilitated by pretreatments of EO through vacuum distillation, bromination, and additional heat treatment. Pitches were prepared by the co-carbonization of pretreated EO and EO containing 20wt% PVC, and had higher yields and better spinnability than those by simple distillation.

Preparation of isotropic spinnable pitch and carbon fiber by the bromination–dehydrobromination of biotar and ethylene bottom oil mixture

An isotropic pitch which has a relatively high softening point and an excellent spinnability for general performance carbon fiber was successfully prepared through the low-temperature co-carbonization with ethylene bottom oil (EO). The special bromination and dehydrobromination reaction of the mixed biotar and EO was adapted at a relatively low temperature for minimizing the phase separation of the two raw materials. The optimized reaction conditions for bromination and dehydrobromination were the heat treatments at 110 °C for 1 h with 20 wt% of Br2 addition and at 320 °C for 3 h under N2 atmosphere, respectively. After removal of volatile matters by thin layer evaporation at 350 °C, the target spinnable isotropic pitch, which has a relatively softening point of 205 °C and excellent spinnability, was successfully obtained with high synthetic yield of 45 wt%. The carbon fiber fabricated using the obtained isotropic pitch precursor showed an enormous tensile strength of 1200 MPa by heat treatment alone at 800 °C for 5 min.

Electroless copper deposition on a pitch-based activated carbon fiber and an application for NO removal

Pitch fibers were prepared from petroleum-derived isotropic pitch precursors using melt-blown spinning. Activated carbon fibers (ACF) were formed from pitch fibers and after stabilization, carbonization and steam thermal activation were then further activated with Pd–Sn catalytic nuclei in a single-step process. The activated ACF were then used as supporters in the specific, electroless deposition of fine copper particles. Field emission scanning electron microscopy-energy dispersive X-ray spectroscopy results showed that the ACF were uniformly coated with nearly pure fine copper particles, and the copper content on the ACF increased with deposition time. The amounts of copper on the ACF and their crystalline characteristics were analyzed using an inductively coupled plasma and a X-ray diffractometry, respectively. With the copper particles-deposited on the ACF, the removal of nitrogen monoxide (NO) for four different deposition times (5, 10, 15 and 20 min) was tested. Experiments on the removal of NO were carried out in a packed bed tubular reactor with various reaction temperatures ranging between 423 and 673 K. For all deposition times, the NO removal efficiency increased with increasing reaction temperature up to 673 K. The NO removal efficiency was the highest when the amount was Cu/ACF = 110 mg/g (deposition time of 5 min), however, decreased at Cu/ACF beyond 110 mg/g (deposition times of 10, 15, 20 min) due to the decreased adsorption as a result of the increased amount of copper.

The effect of processing conditions on microstructure of Pd-containing activated carbon fibers

Palladium-doped activated carbon fibers are being evaluated as candidate materials for enhanced hydrogen storage at near ambient conditions. Pd-doped fibers were spun using a Pd salt mixed with an isotropic pitch precursor. Experimental techniques such as in situ X-ray analysis, thermogravimetric studies, scanning transmission electron microscopy and gas adsorption were employed to understand how processing conditions for the production of Pd-doped activated carbon fibers affect the microstructure, pore development, and dispersion of metal particles throughout the fibers. The results showed that PdO phase is present in the stabilized fibers and that this oxide phase is stable up to about 250 °C. The oxide phase transforms into Pd metal with increasing heat treatment temperature, going through the formation of an intermediate carbide phase. Sintering of Pd particles was observed with heat treatment at temperatures over 750 °C. It was also found that pore development during physical activation with CO 2 was not significantly affected by the presence of Pd particles within the fibers.

Activation behaviors of isotropic pitch-based carbon fibers from electrospinning and meltspinning

Pitch fibers were prepared from identical petroleum-derived isotropic pitch precursors (IPPs) by both meltspinning and electrospinning. The fibers obtained were stabilized, carbonized, and then finally activated by steam at various conditions. The specific surface area of the noble electrospun (E-spun) fibers was calculated to be 6.4 times larger than that of meltspun (M-spun) fibers due to their finer diameter. The activation was considered as first-order reaction with frequency factor 6.55 × 10 −4 s −1 and the activation energy of 162.3 kJ/mol for E-spun fibers, and for the M-spun fibers with respective values of 4.45 × 10 −4 s −1 and 183.5 kJ/mol. The activation rates of the E-spun fibers were calculated to be 13–20 times faster than those of M-spun fibers in the activation temperatures. The higher activation rates for the E-spun fibers were rationalized on the basis of the higher frequency factors and the lower activation energy due to their finer diameters and less ordered structure than those of M-spun fibers.

Preparation of carbonized fiber web from electrospinning of isotropic pitch

The petroleum-based isotropic pitch precursor (IPP) with a broad molecular weight distribution was electrospun. After the dimethylformamide (DMF) soluble fraction was cut off from the IPP, the DMF insoluble pitch (DIP) solution in tetrahydrofuran (THF) was electrospun into web, and then it was stabilized, carbonized. Cutting out the DMF soluble fraction from the IPP improved the spinnability in comparison with the IPP solution itself at the same spinning conditions. The prepared fibers showed dumb-bell like cross-sectional shape indicating incompletion of the splitting in the spinning process with the fiber size of 4–6 μm in long axis and 2–3 μm in short axis. The fibers were randomly layered to be a web. The electrical conductivity of the web increased from 63 to 83 S/cm with an increase in carbonization temperature from 1000 to 1200 °C, and are high enough conductivity for applications to various kinds of electrodes.

Effect of precursor composition on the activation of pitchbased carbon fibers

Pure and silver-containing carbon fibers were prepared from isotropic pitch precursors supplied by Conoco, Inc., and a Korean research team and activated in carbon dioxide to varying degrees of burn-off. The specific activation rates for the carbon fibers were measured as well as the nitrogen adsorption characteristics of the activated carbon fibers. Scanning electron microscopy was used to investigate the surface morphology and the behavior of silver particles during the activation process. Molecular composition of the two pitch precursors was determined using a gas chromatograph mass spectrometer and a MALDI TOF mass spectrometer. Results showed that specific surface area increased with the burn-off, and the trends were similar for the pure and silver-containing fibers formed from both isotropic pitch precursors. However, the catalytic behavior of silver during activation, the activation rate, and even the pore characteristics of the activated fiber were found to be dependent on the molecular composition of the precursor pitch.

The Desirable Condition of the Air-blowing Reaction on Isotropic Pitch Precursor for General Purpose Carbon Fiber

Coal tar pitch was air-blown under the various pressures and temperatures to investigate their roles on the properties of isotropic pitch fiber precursor derived from the pitch. The quality of the precursor pitches was evaluated in terms of their spinning continuity, stabilization reactivity and strength of the resultant carbon fibers. The pitches were also characterized by means of solvent fractionation and NMR spectroscopy. Lower pressure and temperature were confirmed to produce better precursor pitches for the general purpose carbon fiber of higher quality. Although the yield of the pitch was low. Efficient removal of lighter fraction without excess condensation of heavier fraction favored the quality of the pitch. The distillation before the air-blowing to remove lower boiling substances was found also effective to give better precursor pitch for the general purpose cabon fiber of higher quality. In contrast, the prehydrogenation allowed development of mesophase and decreased the 13-resin content in the air-blown pitch, being not recommended in the pretreatment.

Influence of Properties of Coal Tars on Preparation of Isotropic Pitch Precursor, General Purpose Carbon Fiber and Activated Carbon Fiber

The isotropic precursor pitches for general purpose carbon fibers and activated carbon fibers were prepared from coal tars of various origins through air-blowing reaction. The coal tars and isotropic pitches were characterized by means of solvent fractionation and NMR spectroscopy. The quality of the isotropic pitches was evaluated in terms of their spinning continuity, stabilization reactivity, strength of the resultant carbon fibers and yield of activated carbon fibers. The coal tar carrying higher aliphatic carbon content was found to produce the general purpose carbon fibers of high quality at a lower yield. In contrast all tars provided the activated carbon fiber of the same surface area at the same yield of 9% on coal tar base regardless of their variable properties.

96/03159 - Continuous removal of sulfur oxides at ambient temperature, using activated carbon fibers and particulates

Granular activated carbons have been used commercially as adsorbent for removal of sulfur oxides. More recently, new developments have shown that activated carbon fibers can function as active catalysts for SO{sub 2} removal. For the past few years, we have been involved in the synthesis of activated carbon fibers (ACF) from a range of isotropic pitch precursors, and have shown that they can exhibit significantly different properties. In collaboration with Japanese researchers, we have also found that certain of these ACFs are highly active for continuous removal of SO{sub 2} at room temperature, with the production of sulfuric acids. In this paper, we describe the performance of commercial and internally-synthesized activated carbon fibers and particulates for this application, using a model flue gas mixture. The catalytic activity is monitored continuously in a unit that has recently been setup. Both particulates and fibers showed activities for SO{sub 2} removal. However, activated carbon fibers exhibited much higher activity and lower pressure drop. The effects of heat treatment of activated carbons and the composition of the reactant gases were also examined.

Carbon Fiber Composite Molecular Sieves for Gas Separation

IntroductionCarbon fibers are produced commercially from rayon, phenolics, polyacrylonitrile (PAN), or pitch. The last are further divided into fibers produced from isotropic pitch precursors, and those derived from pitch that has been pretreated to introduce a high concentration of carbonaceous mesophase. Over the past few decades, interest in research and manufacturing carbon fibers has overwhelmingly centered on producing fibers with high tensile strength and high modulus for lightweight, high performance composites, where polymers, metals, and carbon can form the continuous matrix. The fibers most commonly used in advanced materials are produced from PAN or mesophase pitch. Graphitized mesophase pitch fibers tend to have higher modulus and lower tensile strength than the PAN-based equivalents. They have advantages in applications requiring high stiffness, high electrical and thermal conductivity, low thermal expansion, and high temperature oxidation resistance, while PAN fibers are employed where high strength is required.

Preparation of isotropic pitch precursors for general purpose carbon fibers (GPCF) by air blowing—I. Preparation of spinnable isotropic pitch precursor from coal tar by air blowing

A QI-free coal tar pitch with a softening point around 80°C was air blown in an autoclave at 330°, 360° and 380°C, respectively, for various periods in order to prepare a pitch precursor for GPCF. Air blowing markedly increased the softening point and contents of solvent insoluble fractions such as BI, QI, as well as atomic C H ratio. The pitches blown at 360°C for 2 to 4 h showed excellent spinnability into thin fibers of 12 to 14 μm in diameter at a wide range of 255° to 330°C. Structural characterization by NMR, FT-IR and elemental analysis on the blown pitches showed that distillation of lighter fractions, aromatization and polymerization of the remaining fractions due to oxidative dehydrogenation raised their softening points. Although all blown pitches stayed completely isotropic, further heat treatment at 380°C under N 2 flow for 14 to 21 h allowed generation of mesophase spheres in the isotropic matrix. After the carbonization at 600°C, all pitches showed anisotropic texture, suggesting that blown pitches maintain fusibility and reactivity to follow the growth and development of mesophase spheres in the successive carbonization.

Preparation of isotropic pitch precursors for general purpose carbon fibers (GPCF) by air blowing—II. Air blowing of coal tar, hydrogenated coal tar, and petroleum pitches

Three representative isotropic pitches, coal tar pitch NP80, its hydrogenated NHP and petroleum pitch A60, were air blown at 330°C in order to study comparatively their oxidation reactivities in the preparation of isotropic pitch precursors with a high softening point. They showed different oxidation behaviors during air blowing. Coal tar pitch with a low softening point of 80°C showed the most rapid rise of softening point but suffered the smallest pitch yield. Air-blown coal tar pitches, NP80-1 and NHP-1, exhibited a higher degree of aromatic condensation and larger QI content than the petroleum one even when their softening points were around 280°C. The structure characterization of the parent and air-blown pitches by FT-IR, FD-mass and solution 1H-, 13C-NMR suggests the mechanism of air blowing to raise the softening point. Unexpectedly slow rises in softening points of hydrogenated coal tar and petroleum pitches appear to be ascribed to their alkyl and naphthenic groups, which may terminate the chain reaction of oxidation.

Preparation of isotropic pitch precursors for general purpose carbon fibers (GPCF) by air blowing—III. Air blowing of isotropic naphthalene and hydrogenated coal tar pitches with addition of 1,8-dinitronaphthalene

Isotropic naphthalene and hydrogenated coal tar pitches with a lower softening point were air blown at 330°C with or without addition of 1,8-dinitronaphthalene (DNN) in order to prepare a fully isotropic pitch with a higher softening point. The softening point of the naphthalene and hydrogenated coal tar pitches could be raised to approximately 240°C and 275°C, respectively, by air or nitrogen blowing with 5 to 15 wt% DNN, while the softening point of naphthalene pitch was only raised to 200~210°C by air blowing without DNN. To retain the isotropic texture of naphthalene pitch, the reaction conditions, including amounts of additive, blowing temperatures, soak times at the blowing temperature, as well as blowing atmospheres need to be controlled. Air blowing at the high temperature of 330°C promoted the dehydrogenation and aromatization through a significant reduction of aliphatic or naphthenic hydrogens. Thermal decomposition of DNN during blowing treatment created NO 2 or NO which may initiate oxidation or radical reactions, accelerating the condensation of naphthalene and hydrogenated coal tar pitches.