The effect of primary quinoline-insoluble material on the formation of secondary quinoline-insolubles in electrode binder pitches

The influence of primary quinoline-insoluble material (QI) on the subsequent formation of secondary QI has been investigated using two pitches derived from the same tar feedstock. One was prepared by heat treating the pitch without prior modification of the tar, and the other after nearly all the primary QI had been removed from the tar by filtration. No significant differences were observed between the two pitches in terms of the rate of secondary QI formation or softening point increase.     

Rheological characteristics of coal tar and petroleum pitches with and without additives

An extensive study of rheological characteristics of coal tar and petroleum pitches with and without additives, namely, petroleum coke, natural graphite and carbon black has been made. It is found that all pitches, pure or mixed with a carbon additive are not Newtonian as reported in the literature, but behave Theologically as Bingham plastics with certain yield stress and plastic viscosity at all temperatures of measurement between 85–180°C. The yield stress and plastic viscosity both decrease with increase in temperature of the pitch. A pure petroleum pitch having the same softening point as that of a coal tar pitch is found to have a lower viscosity compared to that of the latter at all temperatures of measurement. This suggests that the criterion of softening point as a measure of suitability of a coal tar pitch binder in the manufacture of artificial carbon is not sufficient for petroleum pitches. Addition of ten parts of carbon black by weight of pitch results in a considerable decrease in viscosity change with temperature of the coal tar pitch compared to almost insignificant change in the case of the petroleum pitch of the same softening point. However, the addition of petroleum coke or natural graphite makes the pitch more viscous but does not change the temperature dependence of viscosity of either of the two types of pitches. The implications are discussed.     

压力对溶剂法脱除焦油沥青中固体颗粒物的影响

精制沥青是制备各种功能炭材料的前体,焦油沥青需要预处理脱除其中的固体颗粒物（称为喹啉不溶物,QI）以得到精制沥青,压力是脱除QI的重要条件。本文以煤焦油沥青和添加生物质沥青的混合沥青为原料,研究压力对溶剂法脱除固体颗粒物的影响,测试不同压力下精制沥青的QI含量及产率,利用纳米粒度分析仪、扫描电子显微镜和高温黏度测定仪对QI颗粒形貌、粒度及脱除体系黏度进行表征和测定,分析压力对固体颗粒物絮凝沉降的影响规律。研究结果表明,增加压力对沥青收率升高有明显影响,使精制煤焦油沥青的收率由常压的64.6%（质量分数）提升至1MPa时的84.3%（质量分数）,精制沥青的QI含量维持在0.06%~0.1%（质量分数）之间。添加15%生物质沥青的混合沥青,产率则由常压时的55.7%（质量分数）提升至1MPa时的72.5%（质量分数）。压力对精制沥青的QI含量影响较小,压力增大,溶剂对沥青组分尤其是重质组分的溶解能力增强,使精制沥青产率升高。较高压力也使体系的黏度略微增大,造成部分QI颗粒沉降困难,不过影响较小。中间相沥青制备的结果表明,精制沥青可以制备出具有流域型结构的中间相沥青,添加生物质沥青更好地改进了流域型的显微结构。     

Production of petro/coal tar pitch by joint distillation of coal tar and heavy pyrolytic oil

The properties of petro/coal tar pitch and distillate fractions obtained in the joint distillation of coal tar and heavy pyrolytic oil from ethylene production are described. The petro/coal tar pitch is particularly reactive in heat treatment and air-blowing. The petro/coal tar pitch may be used as less carcinogenic binder and impregnating electrode pitch.     

Influence of wet and preheated coal charging on the nature of quinoline insolubles of coal tars and their derived pitches

Differences between primary quinoline insoluble (QI) material of coal tars and their derived pitches caused by preheating carbonization have been studied using microscopic techniques, Coulter Laser particle size analysis and solid-state ¹³C NMR. The selected tars were produced from the same coal using wet and preheated charging at the INCAR experimental coking test plant, which operates on a semi-industrial scale. Specific operational conditions were successfully applied not only to reduce the ash content and the QI and toluene insoluble (TI) contents in the tars produced by the preheating process, but also to modify the nature of the QI particles. In addition, structural changes in the insoluble materials formed during the pitch production from the tar have been monitored.     

The microstructure of nuclear graphite binders

The microstructures of the binder in two grades of nuclear graphite, Gilsocarbon graphite and Pile Grade A graphite, were characterized by light microscopy, transmission electron microscopy and high resolution transmission electron microscopy. A variety of structures of carbon were observed, including a well-graphitized structure, nanosized graphite particles, quinoline insoluble (QI) particles, chaotic structures and non-graphitizing carbon. QI particles were observed on the surface of mesophase spheres as well as inside mesophase spheres. The aggregation of QI particles on the surface of mesophase spheres, or very near the surface in mesophase spheres, appears to have a significant influence on the development of the mesophase structure, resulting in refinement of the mesophase spheres before their coalescence. The chaotic structure, which is turbostratic and isotropic, is suggested to have developed from the isotropic pitch remaining between mesophase spheres. The non-graphitizing carbon consisted of flat and curved single layer graphene fragments with a size typically less than 1 nm. The formation of the various structures in the two graphites is attributed to the introduction of different pitches at stages of the graphite manufacture.     

Observed changes in pitch properties aged at elevated temperatures

Several coal tar and petroleum-based binder and impregnating pitches have been aged in an inert atmosphere at 185°C for periods up to four weeks. The effect of the measured changes in the pitch properties with respect to the processing and properties of graphite artifacts is discussed.     

提高沥青中喹啉不溶物含量的研究

针对煤焦油和沥青中QI含量较低的情况,将来自针状焦项目的 QI残渣与原料焦油按一定比例混合,配制成调制油,采用这种调制油生产中温沥青和改质沥青,提高了产品的QI,显著提高了产品的一级品率。     

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.     

沥青粘结剂产炭率对制品性能的影响

研究了粘结剂沥青产炭率与块状炭制品材料性能的关系,拟通过提高粘结剂沥青产炭率的方法改善炭制品的性质。实验采用比目前工业沥青粘结剂产炭率更高的沥青作为粘结剂,经过混捏、成型和焙烧制成炭制品。研究发现,采用产炭率高的粘结剂可以得到性能较好的产品,但对于强度来说,过高产炭率的粘结剂并不总是正面影响的,应考虑到粘结剂中β组分的含量。     

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).     

Estimating the concentration of secondary quinoline insolubles

The concentration of secondary quinoline insolubles (SQI) in coal tar pitches corresponds to the increase of quinoline insolubles (QI) due to the heat treatment. A series of experimental pitches was used for the analytical estimate of SQI by several methods sensitive to heat treatment.The determination of the size of QI by small angle, forward-scattering light from a laser beam projected through a stream of isolated QI dispersed in toluene yielded results most suitable for the quantitative estimate of SQI concentration in heat treated coal tar pitches.     

SEM study of binder coke in electrode carbon

As part of a study on the use of coal-tar pitches as binders in electrode carbons for the aluminium industry, the object of the present work was to attempt to identify textural components in electrode binder cokes. Accordingly, four experimental carbons, made using the same petroleum coke as filler and four coal-tar pitches of differing characteristics as binders, were examined in a scanning electron microscope (SEM) after embedding in resin, polishing and etching in atomic oxygen. Binder cokes could be distinguished from the filler particles and could be characterized in terms of the content of three components, termed lamellar, intermediate and granular. The textural composition of the binder cokes was dependent upon the character of the pitch and the type of quinoline-insoluble components present. Pitch cokes, made by carbonizing the pitches alone, differed markedly from the corresponding binder cokes. The findings are considered in terms of current ideas on pitch carbonization.     

Quantitative description and modification of cocarbonization compatibility of pitch fractions

The cocarbonization properties of the benzene-soluble fractions (BS) of several pitches with benzene-insoluble fractions (BI) of SRC pitches were studied, changing their mixing ratio in order to evaluate their compatibility for needle-coke formation; the smallest BS content required may reflect its cocarbonization ability to provide the carbonizing mixture with fusibility or suitable reactivity for this purpose. More than 90% of BS content was required for the BS—BI mixture of smallest compatibility, whereas only 10% was enough for the mixture of best compatibility. Ethylene tar BS of poor compatibility with solvent-refined-coal BI could be modified and improved for this purpose by catalytic reaction with aluminium chloride at 260 ° C, whereas ferric or cupric chloride failed. Based on the analytical study of BS and these results, the compatibility of pitch fractions is discussed from the viewpoint of pitch structure.     

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.     

Low shear rheological behaviour of two-phase mesophase pitch

The low shear rate rheology of two phase mesophase pitches derived from coal tar pitch has been investigated. Particulate quinoline insolubles (QI) stabilised the mesophase spheres against coalescence. Viscosity measurements over the range 10–10⁶ Pa s were made at appropriate temperature ranges. Increasing shear thinning behaviour was evident with increasing mesophase content. At low mesophase contents the dominant effect on the near Newtonian viscosity was temperature but at higher contents it was the shear rate; temperature dependence declined to near zero. The data indicated that agglomeration could be occurring at intermediate mesophase volume fractions, 0.2–0.3. The Krieger–Dougherty function and its emulsion analogue indicated that in this region the mesophase pitch emulsions actually behaved like ‘hard’ sphere systems and the effective volume fraction was estimated as a function of shear rate illustrating the change in extent of agglomeration. At the higher volume fractions approaching the maximum packing fraction, which could only be measured at higher temperatures, the shear thinning behaviour changed in character and it is considered that this is possibly due to shear induced deformation and breakup of dispersed drops in the shear field.     

Modification of the carbonization properties of coal-tar pitch by supercritical fluid extraction

The carbonization properties of coal-tar pitch were modified by supercritical fluid (SCF) extraction. Pitches extracted with supercritical toluene (SCFE pitch) contained none of the quinoline insoluble (QI) matter responsible for anisotropic structures with small unit sizes. The size of anisotropic structures from SCFE pitches was closely related to the β-resin (toluene insoluble and quinoline soluble fraction) content. Anisotropic structures from blended pitches prepared to have the same β-resin content as SCFE pitches (by blending toluene soluble (TS) and β-resin fractions obtained through a conventional liquid solvent extraction) were smaller. Extraction of the β-resin fraction with supercritical toluene could be interpreted by the co-solvent effects of the TS fraction dissolved in the extract phase. The high concentration of TS fraction in the extract phase enhanced the solubility of the β-resin fraction into this phase. In the raffinate phase, the heavier β-resin components, which are unsuitable for the development of mesophase structures, coagulated and formed unextractable QI matter through reduction in the concentration of the TS fraction. Since the TS concentration in both the phases depends on pressure and the ratio of the amounts of supercritical toluene and pitch, the control of the β-resin content in the SCFE pitches is possible through the adjustment of these two parameters.     

The manufacture of high-value carbon from coal-tar pitch

World-wide, 17 million ta^?1 of coal-tar are obtained as a by product in the chamber coking process for the production of metallurgical coke. Refining of this aromatic raw material yields coal-tar pitch which is the traditional coal-derived starting material for the manufacture of carbon precursors and carbon artefacts. Considerable progress has been made in the elucidation of the physical and chemical nature of this material by means of chromatography, n.m.r. spectroscopy, thermal analysis and chemical reactions schemes. The dominant fields of application of pitch are the manufacture of pitch coke and electrode binders. Delayed coking and horizontal chamber coking are the technologies currently used for the production of cokes with low sulphur and metal content, for anodes for the aluminium-refining industry and the electric steel process. Coal-tar pitch, low in quinoline-insolubles (QI), is an excellent raw material for the manufacture of needle-cokes with a low coefficient of thermal expension (CTE). The separation of inherent QI can be performed via gravity settling in aliphatic hydrocarbon mixtures, by centrifugation in a disc separator or by filtration. The possible co-carbonization with aromatic petroleum-derived residues yields premium coke suitable for the manufacture of UHP-electrodes. New developments in the production of coke from coal-tar pitch aim to improve coke yields and increase anisotropy (i.e. low CTE and high electrical conductivity values). Further technological progress has been made in the manufacture of hard pitch which can be used as a starting material for the production of pitch coke in the chamber coking process and for the production of electrode binders by means of a continuous flash process with optimized thermal and pressure treatment of pitch, thus facilitating the ‘tailored’ manufacture of binder pitches of different qualities.     

煤焦油喹啉不溶物压滤脱除和超净沥青制备

以高温煤焦油为原料,在自制小型压滤装置上脱除喹啉不溶物(QI),并对滤后煤焦油进行超临界流体萃取分馏制备超净沥青。结果表明,当滤布孔径1 250目、温度125℃、压力0.5MPa时,煤焦油中的QI质量分数可降低到0.037%。对压滤后的焦油进行超临界萃取,所制沥青的QI和甲苯不溶物质量分数分别达到0.10%和20.31%,可满足制备高性能炭素材料前驱体的要求。     

Research on high-quality pitch-based materials

A method of continuous solvent fractionation of coke oven tar to make an insoluble pitch and an oil fraction has been demonstrated. The distillation residue of the oil fraction (oil pitch) can be further processed to give high-quality electrode coke, carbon fibre precursor, composite-impregnating pitch or components for tar/resin paints. The insoluble pitch gives pitch coke suitable for anode manufacture. Thermal treatment of mixtures of the insoluble pitch and the oil pitch facilitates the production of a wide range of electrode binders and impregnating pitches.