Isotropic carbon and graphite fibers from chemically modified coal-tar pitch

A precursor for a general purpose carbon fiber was prepared from coal tar pitch (CP) modified with 10 % p-benzoquinone (BQ) at 380 ?C for 3 hours. Such a modification raised the softening of the pitch from 85 ?C to 271 ?C at a yield of 43 %. The modified pitch was spun smoothly at a rate of 480 m/min into a fiber of 20 Μm diameter. The fiber was stepwise stabilized at 236 ?C (5 ?C/min) and 312 ?C (1 ?C/min) for 3 hours at each temperature. Successively,carbonization and graphitization were performed at 1,000 ?C and 2,400 ?C, respectively, for one hour. Both the carbonized and graphitized fibers exhibited tensile strength of 570 MPa. The structural parameters of carbon and graphite fibers were their orientation values of 56.2 and 58.1 %, relatively low Lc(002) of 11.24 and 25 å, and large interlayer spacing (d₀₀₂) of 3.86 and 3.49 å, respectively.     

Chemical changes during the mild air oxidation of pitch

The chemical changes occurring during mild oxidation of petroleum and coal tar pitch were studied by elementary analysis, solubility measurements, IR and nuclear magnetic resonance spectroscopy and chromatography. The oxidized pitches were compared with pitches which were distilled to give similar softening points. A mild oxidation was shown to induce dehydrogenative polymerization of the pitch components without introducing appreciable amounts of oxygen into the products. The greater reactivity of the petroleum pitch constituents to oxygen is attributed to the presence of alkyl substituents. Study of the mesophase formation and X-ray analysis of the derived graphites showed that mild air oxidation did not affect the subsequent graphitic development.     

Activated carbon fibers from electrospinning of polyacrylonitrile/pitch blends

The electrospinnability of pitch was improved by blending in a solution of polyacrylonitrile (PAN) resulting in the reduction of the average fiber diameter from 2000 to 750 nm. The compositions showing good spinnability are proposed within the soluble concentrations in the ternary phase diagram of the PAN-pitch-solvent, which contains lower concentration of the pitch. Activated carbon fibers were derived by stabilization, carbonization and steam activation at 700, 800, 900 and 1000 °C of the PAN/pitch electrospun fibers. The Brunauer, Emmett, Teller (BET) specific surface area ranged from 732 to 1877 m²/g.     

Production of coal pitch by the oxidation of coal extracts in anthracene oil

If anthracene oil is used to produce extracts from 2B, D, 2G, GZh coal, coal pitch may be produced by oxidation of the extracts using atmospheric oxygen. The resulting pitch is characterized by higher yield and by a greater coke residue than is observed in pitch produced from anthracene oil without added coal in analogous conditions. Ultrasound treatment for 3 h on an IL10-0.63 unit ensures complete solution of the coal (4–9%) in the anthracene oil. The mineral component of the coal also enters the solution and is then concentrated in the pitch formed. To reduce the ash content of the pitch, ash must preliminarily be removed from the initial coal. For the example of 2B and D coal, it is found that reducing the ash content of the coal to ~1% and subsequent solution in the anthracene oil to a coal concentration of 5–8% yields a coal extract such that pitch with no more than 0.4% ash and up to 41% coke residue is formed on oxidation by atmospheric oxygen.     

Thermooxidation of coal tar pitch with the return of pitch distillates

The thermooxidation of moderate-temperature coal tar pitch with the return of pitch distillates is investigated, in conditions such that high-temperature grade-C pitch is obtained. Gas-liquid chromatography shows that the content of polycyclic aromatic hydrocarbons included in the list published by the United States Environmental Protection Agency (EPA) is not significantly different in the pitch samples before and after oxidation.     

沥青基碳纤维的研发及产业化

沥青基碳纤维是碳纤维的一个重要品种,但我国在沥青基碳纤维的研发和生产较国外还有很大差距。介绍了我国沥青基碳纤维研发和产业化现状,就其中的关键工艺(纺丝沥青调制和熔融纺丝)进行了综合分析。通用级沥青基碳纤维在国内已有一定的科研和生产基础,近期可望完成自主技术工业化装备的建立和生产;高性能沥青基碳纤维的研发虽然较为充分,但用于纺丝的中间相沥青的制备和连续长丝工艺的开发还要经过努力才能实现产业化,以摆脱美日的技术和产品的封锁。     

Microstructure peculiarities of carbon materials based on coal-tar pitch hardened on the surface of thermally expanded graphite flakes

The structure of self-caking artificial graphite based on coal-tar pitch hardened at 225, 275, and 450°C by oxidation with atmospheric oxygen on the surface of thermally expanded graphite (TEG) flakes was studied by scanning electron microscopy. In the course of the preparation of the material after hardening, the flakes covered with pitch were tightly compressed on grinding to molding powder in a ball mill and during the extrusion of laboratory workpieces in a rigid matrix to result in a laminar structure of the test materials. It was found that the caking capacity of TEG flakes and pitch layers decreased as the temperature of oxidation was increased. The thicknesses of pitch layers and TEG flakes were estimated based on the distance between the layers of the material.     

煤沥青球的氧化不熔化过程特性

氧化不熔化过程是煤沥青基球状活性炭制备中的核心工艺,对其过程特性和动力学机理的认识是实现氧化过程工艺优化的关键。本文以煤沥青萃取球为原料,通过实验研究,重点探讨了粒径范围、升温速率和氧化温度对其氧化不熔化过程的影响,并确定氧化动力学参数及其反应机理函数。结果表明：氧化不熔化过程可分为轻组分热解、初步氧化、氧化增重和恒温氧化失重4个阶段。煤沥青球经过氧化不熔化后,C、H含量减少,O含量增加,表面光滑平整。减小粒径并选取合适的升温速率（0.25～0.5℃·min^-1）以及氧化温度（275～325℃）,更有利于氧化不熔化快速稳定地进行。粒径范围为0.3～0.6 mm的煤沥青球在升温速率为0.5℃·min^-1、氧化温度为300℃的条件下活化能最小,各个阶段的值分别为83.34、293.19、302.25和357.05 kJ·mol^-1。     

Benefits of ultrasound in pitch production from coal tar and its mixtures with styrene distillation residue

Ultrasound treatment of coal tar increases the yield of pitch by a factor of 1.5 in subsequent oxidation by atmospheric oxygen. The yield of pitch may be regulated in terms of its softening temperature by changing the oxidation time. To obtain standard pitch, the following conditions are employed: ultrasound treatment for 3 h; initial oxidation temperature 260–270°C; final oxidation temperature 360–370°C; rate of air supply 63 L/h; oxidation time ~30–70 min, depending on the requirements on the final product. The concentration of aromatic derivatives of benzo[a]pyrene type in the pitch produced and in the liquid fraction (which may be used as a fuel) is considerably less than in the current industrial method. After ultrasound treatment, a 1: 1 mixture of coal tar and rectification residues from styrene yields pitch with satisfactory characteristics on oxidation by atmospheric air. That expands the range of raw materials for pitch production.     

Studies on oxidation of precursor carbon fibres of petroleum pitch by gas chromatography

Volatile products of precursor carbon fibres of petroleum pitch oxidized in oxygen were investigated. Concentration changes in CO, CO₂, and H₂O as a function of temperature and oxidation time were determined quantitively by gas chromatrography. The oxidation of precursor pitch fibres is the most efficient in the temperature range between 453–498 K during 2–4 hours.     

Study of oxidation of pitch fibres

The studies conducted led to the following conclusions: effective oxidation of pitch fibres begins at a temperature slightly above the flow temperature of the starting pitch; oxidation is limited by diffusion of gaseous products so that it is expedient to use initial fibres with a diameter of 10 µm and to conduct the process in conditions of effective blowing with air.Translated from Khimicheskie Volokna, No. 1, pp. 20–21, January–February, 1995.     

Low-temperature oxidation of pitch,petroleum, and shale semicokes

The oxidation of pitch, petroleum, and shale tar semicokes with air oxygen at 150–340°C was studied gravimetrically and by Fourier-transform IR diffuse reflectance spectroscopy. The oxidation led to a decrease in the intensities of the vibrational bands of aliphatic C-H bonds, and a noticeable reduction in the intensities of the vibrational bands of aromatic C-H bonds was observed for petroleum and shale tar semi-cokes. Below 200°C, oxygen enters to form largely ketone or/and aldehyde C=O groups; however, the carboxyl, anhydride, lactone, and C-O-C vibration bands appear as the oxidation temperature is increased.     

芳香族硝基化合物改性煤沥青研究

以煤沥青为原料,通过添加不同含量的芳香族硝基化合物对煤沥青进行改性处理,采用TG、CO2反应性、XRD和SEM对改性沥青焦进行表征。结果表明,芳香族硝基化合物有效地促进了煤沥青在炭化过程中的焦化缩聚,使产物沥青焦结构更加致密,并在一定程度上改变了沥青焦的氧化行为,从而显著提高了沥青黏结焦的抗氧化性能。     

中间相沥青制备方法及应用

由于中间相沥青原料丰富、价格低廉、性能优异以及具有较高端炭产率等优点,因此中间相沥青被广泛应用于制造多种重要的高级炭材料,如超高模量碳纤维、超高比表面积活性炭、超高功率电极用针状焦、中间相沥青基泡沫炭等,而这些高级炭材料已被广泛应用于日常生活、工业和国防等众多领域且都已发挥着巨大作用。因此开展对中间相沥青的制备方法和应用研究具有重要的理论和实际意义。     

Oxidative stabilization of pitch-polyacrylonitrile composite nanofibers electrospun by incorporating high-percentage inexpensive pitch

Polyacrylonitrile (PAN)-based composite nanofibers incorporated with high-percentage inexpensive pitch were successfully prepared by a simple electrospinning technique. Low-softening-point naphthalene pitch (NP) has the merit of high solubility but inevitably brings about preoxidation problem. Thus the influence of different preoxidation strategies on the morphology, composition, and structure of composite nanofibers was systematically investigated. The results show that there exists a ternary phase diagram consisting of PAN-pitch-solvent and a suitable apparent viscosity of homogeneous solution, which favors the smooth electrospinning and good adjustment for the diameter of carbon nanofibers (100–500 nm). The crystallinity, crystalline order, and electrical conduction of composite nanofibers are enhanced by incorporating graphitizable NP, for example, the electrical resistance of 50% NP-PAN composite nanofiber films after 800°C carbonization decreases about 30%. Both increasing the oxidation temperature and extending the oxidation time are beneficial to the oxidative stabilization of composite nanofibers with a suitable NP percentage below 50%. Gradient heating (240–340°C) and pressurized (0.08 MPa) preoxidations could accelerate the oxidative stabilization of composite nanofibers with a high NP percentage up to 110% and significantly shorten the oxidation time by half. Therefore, this study paves the road for facile preparation of cost-competitive carbon nanofibers with controllable morphology, structure, and properties.     

Observations on a low-angle X-ray diffraction peak for AR-HP mesophase pitch

Using wide angle x-ray diffraction on AR-HP mesophase pitch, a diffraction peak was detected at approximately 7° (2Θ). The low-angle peak was reproducible using different diffractometers and different sample-to-detector distances, and was observed for all pitch samples irrespective of the flow history, but not for carbon fibers derived from the same precursor fibers. The interplanar 002 peak at ∼25° was observed at the equatorial position, whereas, the peak at 7° was in the meridional position, i.e., the peaks are nominally 90° apart in an azimuthal scan. This signifies that the low angle peak was due to diffraction from planes that are orthogonal to (002) planes. The 7° peak is equivalent to a d-spacing of 1.25 nm, which corresponds to the nominal lateral dimension of the mesogen molecules that constitute the mesophase pitch. A typical MALDI analysis showed predominance of molecular weights of ∼500 au. Edges of such a constituent of mesophase pitch molecules, which lead to a lateral ordered spacing of approximately 1.1 nm, can lead to a diffraction peak at approximately 7°.     

Unusual structures in mesophase from a petroleum pitch

Cokes from the carbonization of a petroleum pitch possess an optical texture containing anisotropic spherules with an unusual structure. These spherules (10 to 20 μm diameter) were found to be present in the original pitch and could be removed as a quinoline-insoluble fraction. This suggests that the spherules are formed during the modification of the pitch after initial fractionation of the petroleum feed-stock. The optical texture of these spherules, examined by polarized light optical microscopy, reveals a complicated ‘rosette’ structure quite unlike the structure of the spheres of mesophase now known as ‘Brooks and Taylor’ spheres. An EDAX analysis of polished segments of the spherules indicated no unusually high concentration of inorganic matter, e.g. vanadium, suggesting that the spherules did not originate from asphaltenes. The influence of such spherules or inclusions in the parent pitch upon properties of resultant cokes is briefly commented upon.     

Unfired refractories bonded with coal tar pitch

Conclusions Medium-temperature coal tar pitches are effective bonds for making unfired dolomite and dolomite —magnesite refractories by pressing bodies heated to 100–120°C. The features of the refractories with a pitch bond are the higher contents of carbon resistant to oxidation (about 4%), and the higher compressive strength (400–500 kg/cm²), and finally the higher hydration resistance (10 days).Refractories bonded with pitch are much better than products containing tar, and accordingly offer a greater resistance when used in oxygen converter linings.Translated from Ogneupory, No. 3, pp. 6–15, March, 1971.     

中间相沥青熔纺异形纤维的工艺研究 Ⅰ.中间相沥青的性质与异形喷丝板的设计

讨论了用于纺制异形纤维的两种中间相沥青的性质，并根据中间相沥青熔体的模口膨化比等性质，设计制造了用以纺制中空、条形、Ｙ形等异形纤维的喷丝板。异形喷丝孔的当量直径、截面积、孔长等特征尺寸决定了熔体在喷丝孔中的流变行为，建议采用当量异形度作为纤维的异形度指标。     

Influence of primary QI and particulate matter on pitch carbonizations

The carbonization behaviour of coal-tar and petroleum pitches is influenced by the presence of particulate matter in the pitch. Several types of particulate matter consisting of carbon blacks of different oxygen contents and degrees of agglomeration and silica with hydrophobic and hydrophilic surfaces were added to pitches. Particle sizes were less than 100 nm in diameter. The influence on optical texture of coke structure was most pronounced for the agglomerated carbon blacks which trapped pitch in inter-particle voids creating an isotropic carbon at low wt % additions. The non-agglomerated hydrophobic silica progressively reduced the size of anisotropy with additions. The hydrophilic silica caused intermediate effects. Surface activity of additives influences carbonization chemistry. Reactivities of cokes to carbon dioxide (k/s⁻¹) were not affected by structural changes but coke microstrengths were very dependent upon size of agglomeration of carbon black additives.