The effect of the substrate on pitch wetting behaviour

The wetting behaviour of a petroleum pitch (modified with a surfactant) and a binder coal-tar pitch was studied using different substrates. The results show that both the pitch and the substrate have a significant influence on wetting behaviour, and consequently, on their mutual interactions during the mixing stage. Low values of surface tension and viscosity in the pitches lead to lower wetting temperatures. It was found that with petroleum coke and magnesia as substrates, the wetting occurs at lower temperatures than with graphite and carbon black for all pitches. Moreover, experiments carried out with amorphous and crystalline alumina revealed that the crystalline order affects the wetting behaviour considerably. Thus, whereas the pitch wets the corundum (crystallized alumina), it does not wet the amorphous alumina (basic, acid and neutral alumina).     

Influence of granular carbons on pitch properties

This paper deals with the study of the variation of properties of four pitches (a commercial impregnating coal tar pitch, an air-blown and two thermally treated pitches) when mixed with four granular carbons (anthracite, graphite, green petroleum coke and foundry coke). As a first step, optical microscopy was used to determine the distribution of the pitch among the granular carbons. The anthracite seems to attract the primary quinoline insolubles present in the commercial and thermally treated pitches. This allows the mesophase spheres to coalesce at unusually low temperatures during the mixing process. In general, the toluene insoluble content of the pitch showed a significant increase after mixing with the granular carbons. This is an indication of the interactions between the different granular carbons and some compounds present in the pitches. Analytical techniques like size exclusion chromatography and differential scanning calorimetric analysis were used in order to obtain information about the characteristics of the components of the pitches that interact with the different granular carbons and their effect on pitch properties. Graphite seems to interact preferentially with the larger molecules whereas the green petroleum coke acts on a wider molecular range.     

The influence of the type of quinoline insolubles on the quality of coal tar binder pitch

Seven pitches containing three types of quinoline insolubles, QI, were produced from a single coke oven coal tar. The tar was centrifuged into QI-rich and QI-lean fractions. A blend of the two fractions yielded a typical graphite electrode binder pitch. The QI content of the pitch derived from the QI-lean tar was increased through the addition of natural QI concentrate, or QI as a furnace carbon black, or QI as mesophase by means of heat treatment. The pitches were evaluated as binders by measuring the flexural strength of 19 mm diameter graphite electrodes. The results show that the typical electrode pitch is superior, and that increasing the QI content of the QI-lean material did not upgrade it. The results also show that the flexural strength of the derived graphite is not simply related to the coking value of a binder.     

Improvement and control of the quality of binder pitch for graphite electrodes

Factors influencing the coke yield and the softening point (SP) of pitches were studied to ascertain procedures for the improvement and control of their quality. The coke yield of pitches from different tar sources is expressed as a linear function of the BI content. Pitches were prepared by distillation under constant operating conditions. The coke yields of pitches, determined by thermogravimetric analysis (TGA), increased with their benzene insoluble (BI) content, which is controlled by reflux heat treatment. Softening point increased with the nitrogen content as well as BI content. Therefore, increasing the BI content and decreasing the nitrogen content increases coke yield without any change in the softening point of binder pitches for graphite electrodes.     

Preparation,modification, and characterization of pitches from apricot stones

Apricot stones steam pyrolysis tar and mixtures with petroleum pitch were modified by sulfuric acid and heat treatment at various temperatures for the purpose of obtaining a raw material for the production of carbon-related materials. The products obtained were characterized by elemental analysis, total carbon contents, FTIR spectroscopic analysis, ¹H and ¹³C NMR spectroscopic analyses, softening point measurement, and oxygen functional group content. During the acid and heat treatment, the reactions of polycondensation and polymerization occur. The heat-treatment modification of the pitches decreases the oxygen-containing groups and sulfur content and increases the content of aromatic structures. Chemical transformations and the removal of light components increase the softening point of the pitches. The results show that apricot stones tar with some additional modifications can be used as a raw material for the production of advanced carbon materials.     

Determination of viscoelastic properties of pitches by torsional creep

Creep behavior of a petroleum pitch and of two kinds of coal tar pitch, as they are and as mixed in various portions, were studied by measuring the torsional creep at temperatures of 30–90°C. The pitches used were viscoelastic, and viscous and elastic terms were separately evaluated from the steady state viscosity η and the steady state creep compliance J_e^o. The viscosity shows a negative temperature dependence, from which the activation energy for steady state flow is found as 63 kcal/mol for all pitches used. The compliance J_e^o, increases with increase in temperature. This indicates the importance of inter- and intra-molecular potential energy in the elasticity of pitch. A time-temperature superposition rule was found to be satisfactorily applicable to the creep data observed. A rheological meaning of the softening point of pitch is discussed, and the importance of differences in steady state creep compliance is emphasized. Viscoelastic analysis was found to be useful in giving important parameters for the characterization of pitch-like materials.     

改性煤沥青在炭素生产中的应用

概述了沥青的分类和性质以及沥青改性、改性方法,讲述了在改性煤沥青生产应用中的要求,改性沥青的应用过程、效果和缺点。根据实验数据阐述了在改性煤沥青生产应用中的温度选择。结果表明,改性煤沥青特有的高软化点和粘度决定了在熔化、输送和混捏过程对温度的要求较高。数据分析表明软化点不能够准确指导下料温度,而粘度与下料温度呈正比例关系。因此,粘度可以作为下料温度的一个可靠的参考指标。     

Pressure effects on the yield and on the microstructure formation in the pyrolysis of coal tar and petroleum pitches

The pyrolysis of coal tar and petroleum pitches was studied under nitrogen pressures from 2 to 150 bar at temperatures between 300 and 600°C. The resulting residues were investigated by TGA, polarized-light microscopy and X-ray diffraction. It is shown that increasing pressure does not only increase the coke yield but also lowers the temperature at which pyrolysis is completed. This “chemical” effect of pressure is stronger with petroleum pitch. Increasing the pressure also improves preorder and graphitizability of the residues. Simultaneously, the microstructure becomes coarser and more Isotropie, i.e. that the enlarged areas of optical anisotropy exhibit no preferred orientation.     

Production of isotropic coke by thermocracking of the anthracene fraction of coal tar

The properties of coke obtained by heat treatment of the anthracene fraction of coal tar under pressure (by thermocracking) are investigated. Pressures up to 5 MPa are used; the temperature is 500 or 550°C. For comparison, pitch coke is obtained from oxidized pitch with softening temperatures of 166.2 and 190.2°C. The coke yield from thermocracking is 70–75%. The following properties of the coke are determined: the actual density, the ash content, the yield of volatiles, the optical microstructure, the elementary composition, the change in volume on heating to 2400°C, the impurity composition, and the X-ray structural characteristics. High temperatures (at least 550°C) and heating rate of the anthracene fraction facilitate the formation of a large quantity of active radicals, which instantaneously form the three-dimensional coke structure, preventing the growth and coalescence of mesophase particles; isotropic coke is formed, with a microstructure score of 2.2. At 500°C, anisotropic coke is formed, with a microstructure score of 4.3. Despite the high softening temperature and the content of the α1 fraction, the high-temperature pitch does not form isotropic coke on carbonization. The macrostructure of the coke obtained by thermocracking is monolithic, with fine pores. The thermocracking conditions (temperature, pressure, presence of H₂) facilitate partial destruction and hydrogenation of the heterocyclic compounds. As a result, the coke has a reduced N, S, and O content. For pitch coke, the nitrogen content is 20–40% higher. The lack of ash in the anthracene fraction of coal tar results in ash- and metal-free coke. The coke obtained by thermocracking also has satisfactory X-ray structural characteristics and undergoes practically no expansion on graphitization, in contrast to pitch coke. In view of the technological convenience (absence of liquid products, high coke yield) and the quality of the coke, the production of isotropic coke by thermocracking may be regarded as a promising means of supplying the raw material used to produce artificial graphite.     

煤沥青基中间相沥青的制备研究

以纯化的煤焦油沥青为原料,考察了热聚合温度和恒温时间对中间相沥青的收率、光学显微形态、软化点和族组成的影响.结果表明:反应温度在420℃,恒温5 h时得到了软化点为312℃的流线体型中间相沥青,其收率为79.1%;热聚合反应在相对较低的温度400℃,反应时间为10 h时形成了软化点为305℃、收率为81.4%的优质广域型可纺性中间相沥青.对该原料煤沥青而言,通过控制热聚合反应温度和恒温时间可以达到制备优质中间相的目的.     

Influence of pitch composition and surface properties of petroleum coke on their interaction during the preparation of carbon/carbon composites

The influence of pitch composition and surface properties of petroleum coke on the interaction of pitch and coke in the composite is studied. The adsorption results and EPR data indicate that recombination of paramagnetic centers and interaction of oxygen functional groups occur during the preparation of the composite. As a result of interaction between petroleum coke and pitch, polar compounds are concentrated in the adsorption layer. The baking criterion is used for the characterization of the baking ability of the pitches obtained as a result of different oxidation treatments of commercial coal tar pitch. It is determined that physico-chemical properties of the obtained pitches influence the value of the “baking criterion”. The kind of thermo-oxidation treatment of the parent pitch should be chosen hence achieving the maximum value of the baking criterion. For this purpose, the maximal part of the pitch has to take part in the adsorption layer.     

Effect of different oxidation treatments on the chemical structure and properties of commercial coal tar pitch

Different oxidation treatment was used for the increase of the softening point of a commercial coal tar pitch. H₂SO₄, HNO₃, H₂O₂ and air are selected as treatment reagents. These preliminary investigations show that the oxidation treatment of commercial coal tar pitch with different reagents at 160 °C and heat treatment to 250 °C causes considerable changes in the chemical composition of obtained pitches. This leads to increase of TI and QI fraction, and results in considerable increase in the softening point of the pitches. The yield of modified pitches is considerable in the case of treatment with H₂SO₄, H₂O₂, and HNO₃ and lesser in the case of air blowing. The data obtained also indicate some differences in the composition and softening point of pitches obtained after modification with different reagents. These differences could influence the applicability of the obtained pitches in the various areas of carbon material production.     

Comparative studies of the modification of coal-tar pitch

Properties of coal-tar pitches modified by sulfur addition, air blowing, and nitrogen blowing were compared to find an appropriate method of preparing a matrix precursor for carbon/carbon (C/C) composites. Raw and modified pitches were characterized by softening point, thermal analysis (TGA), elemental analysis, solubility in toluene and quinoline, and gel permeation chromatography. Both sulfur addition and air blowing very effectively increased softening point and coke yield by dehydrogenative polymerization of pitch molecules. Air-blown pitch, however, had less thermal stability than the pitch with added sulfur and showed more weight loss at high temperatures. Property changes in nitrogen-blown pitch were mainly induced by eliminating volatile matter of low molecular weight. Sulfur addition is suggested to be the most promising method for preparing matrix precursor because it had the highest yield among those with similar softening points.     

Rheological behavior and thermal properties of pitch/poly(vinyl chloride) blends

The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior and thermal properties of a coal tar pitch was investigated with a view to developing an appropriate viscoelastic binder for the injection molding of graphite components. Dynamic mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to the pitch increased melt viscosity substantially and resulted in strong shear thinning behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen atmosphere revealed interactions between the PVC and pitch degradation pathways: the blends underwent significant thermal decomposition at lower temperatures but showed enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000 °C was further improved by a heat treatment (temperature scanned to 400 °C) in air or oxygen. However, carbon yield decreased with addition of PVC. In addition, the degree of ordering attained following a 1 h heat treatment at 2400 °C also decreased with increasing PVC content.     

Synthesis of pitch materials from hydrogenation of anthracite

A Pennsylvania anthracite was ground, carefully dried and hydrotreated into materials with properties resembling those of pitches. The hydrotreatment was carried out using two hydrogen donors, 9,10-dihydroanthracene (DHA) and 1,2,3,4-tetrahydronaphthalene (THN), and two catalysts, molybdenum hexacarbonyl (Mo(CO)₆) and ammonium tetrathiomolybdate (ATTM). Due to the high reactivity at low temperatures, the degree of hydrogenation was probed in the temperature range 300, 350 and 400 °C. The optimum hydrogen donor, catalyst and hydrogenation temperature were 1,2,3,4-tetrahydronaphthalene, ammonium tetrathiomolybdate and 300 °C, respectively. This was reflected in an increase in the hydrogen-to-carbon atomic ratio (H/C) from 0.33 for the original anthracite to 0.42 for the pitch-like material from anthracite. Further, differential scanning calorimetry (DSC) showed that the anthracite-derived pitch material had a glass transition temperature (T_g) around 81.6 °C and softening point of 205.7 °C. This indicates that the softening behavior of the anthracite-derived pitch is similar to that of high-softening-point coal tar pitches. The anthracite-derived pitch material was evaluated by producing a small carbon body directly from the anthracite-derived pitch, and partial binding was observed.     

Rheological properties of carbon mixes at low shear rates using a capillary rheometer

A capillary rheometer is used to measure the rheological properties of green carbon mixes consisting of petroleum coke and carbon black as filler and pitch tar as binder. It has been shown that in the low shear rate range (0·3 to 2·0 sec^?1), the carbon mixes behave as Bingham body with yield stress of 6 × 10⁵ dyn/cm² and plastic viscosity of 2 × 10⁶ poise.     

Growth and coalescence of mesophase in pitches with carbon black additives and in coal

The techniques of polatized light optical microscopy and of washing the surfaces of solid pyrolysis products with chloroform prior to SEM examination are used to monitor the growth and coalescence of growth units of mesophase in a petroleum pitch, a coal extract and a caking coal. Additions of 1 wt% of carbon black retard growth and coalescence and promote clustering of these units because of adhesion of carbon black particles. This has the effect ultimately of reducing the size of the optical texture in coke from the coal extract, but not with coke from the petroleum pitch which has lower viscosity. With the coal, mesophase growth units tend to form clusters and do not coalesce. Mesophase can form an anisotropic skin on the inside of developing pores (bubbles) in the fluid phase and this may limit their growth.     

Étude des phénomènes de mouillabilité du carbone par le brai liquide

One of the processes used in the manufacture of carbon/carbon composites makes use of impregnation with pitch of a multidirectional structure of carbon rods made of carbon fibres at high temperature followed by carbonization under high pressure. A densification of the composite is obtained by repeated impregnations.Since the mechanical properties of the composites must likely depend on the quality of the interface formed between the carbon rod and the liquid pitch matrix, the wetting properties of pitches of various origins and properties (Table 1) were studied for several carbon rods (Table 2). A tensiometric method based on the weight of pitch lifted during immersion of the carbon rod at 350°C was used (Fig. 1).Measurements of the surface energy of the pitches in the liquid state at 350°C (Table 3) and in the solid state at room temperature (Table 4) show that the surface energy is practically independent of the origin of the pitch and that the surface polarity of the pitch is negligible. On the contrary, the values of the contact angle at 350°C is higher for the petroleum pitch No. 1 than for the coal tar pitches (Table 5).The wettability criteria, i.e. the spreading coefficient S and the wetting tension τ, derived from the measured surface energy and contact angle, confirm the lower wetting ability of the petroleum pitch (Fig. 2). These criteria may explain why the densification process (number of impregnations and carbonization cycles necessary to reach an apparent density of the composite of 1.90) is much more difficult with petroleum pitch. On the contrary, the adhesion criterion factor, expressed as the reversible energy of adhesion between the liquid and the solid at 350°C, has the same value whatever the origin of the pitch. Since the degree of adhesion might influence the quality of the carbon/carbon interface in the composite, the same value of the adhesion criterion factor may explain why all composites, at equivalent density, show about the same compression and torsion strengths.The difference between the wettability and adhesion for the pitches of different origins is due to the difference in the spreading pressure π; this quantity measures the decrease of the surface energy of the carbon rod resulting from the adsorption of the pitch vapor. The calculations reveal that, whatever the surface energy of the carbon rod, the petroleum pitch leads to a larger reduction of the surface energy of the solid than the coal tar pitches (Fig. 3).The wettability and adhesion criteria adopted in this study seem to (at least to a first approximation) explain the dependence of the mechanical properties of the carbon/carbon composites on the type of pitch and on the processing conditions.     

Carbon foams prepared from coal tar pitch for building thermal insulation material with low cost

A new approach is provided to resolve the large-scale applications of coal tar pitch. Carbon foams with uniform pore size are prepared at the foaming pressure of normal pressure using coal tar pitch as raw materials. The physical and chemical performance of high softening point pitch(HSPP) can be regulated by vacuumizing owing to the cooperation of vacuumizing and polycondensation. Results indicate that the optimum softening point and weight ratio of quinoline insoluble are about 292℃ and 65.7%, respectively. And the optimum viscosity of HSPP during the foaming process is distributed in the range of 1000-10000 Pa·s. The resultant carbon foam exhibits excellent performance, such as uniform pore structure, high compressive strength(4.7 MPa), low thermal conductivity(0.07 W·m~(-1) ·K~(-1)), specially, it cannot be fired under the high temperature of 1200 ℃.Thus, this kind of carbon foam is a potential candidate for thermal insulation material applied in energy saving building.     

沥青球的空气氧化稳定化反应特性研究

用 TGA、 DTG和 DTA法研究了石油沥青球和煤沥青球在空气中的热反应特性,研究了沥青球氧化稳定化的反应特点及其与沥青球组成与结构的关系。结果表明：石油沥青球由于与氧气的反应活性较强,更难于不熔化;增加萘含量和提高原沥青的软化点有利于沥青球的不熔化。