Coal Pitch Research Articles

Comparison of Coal Tar Pitch and Petroleum Pitches in the Reactions of Thermal Solvolysis of Thermosetting Polymers

Comparison of Coal Tar Pitch and Petroleum Pitches in the Reactions of Thermal Solvolysis of Thermosetting Polymers

Tensile strength of carbon composite materials: Influence of binding matrix

The calculated estimates of the strength and deformation characteristics of carbon composite materials based on carbon fibers with polymer, carbon and carbon-ceramic matrices obtained by various technologies are presented. The calculation method is based on the structural model of the strength of the composite material as a “bound” beam of reinforcing fibers. Good agreement of the calculated data with the experimental results indicates the applicability of the calculation model used for the design of new materials and products. It is also shown that the isostatic technology of obtaining carbon matrices based on coal pitch allows to obtain carbon composites with properties closest to carbon plastics, which are characterized by the best ability to realize the strength of reinforcing fillers.

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 mosaic coke from heavy‐phase coal pitch

AbstractMosaic coke is a considerable intermediate material to produce high‐quality special graphite (isotropic graphite and nuclear graphite). The properties of mosaic coke keep a key role on the quality of special graphite. For a detailed investigation on the feasibility of the production of high‐quality mosaic coke with heavy‐phase coal pitch as the raw material, five kinds of heavy‐phase coal pitches with varied basic physical properties were used as the raw materials to produce mosaic coke in this study. Briefly, Fourier‐transform infrared spectroscopy spectrum combined with curve fitting method have been used to determine the aromatic condensation index (Iar) of heavy‐phase coal pitch. The polarizing microscope incorporated with carbon theory, scanning electron microscopy, X‐ray diffraction, and Raman spectrum have been used to characterize the microstructure of mosaic cokes. The micro‐strength of mosaic cokes have been examined by the micro‐strength tester. The results have shown that the heavy‐phase coal pitches with Iar less than 0.91 are the potential raw materials to produce the high‐quality mosaic coke with higher micro‐strength (higher than 79%).

Self-Organization of Hexane-Insoluble Asphaltenes of Coal Pitch

Recently, there has been growing interest in asphaltenes, which are byproducts of petroleum processing and coal liquefaction. However, most data on the macromolecular structure and morphological characteristics of asphaltene aggregates relate to the petrochemical industry. We know that the concentration of asphaltene in solution affects the structure of their associates, which is also modified by the presence of various additives. The formation of planar associates of asphaltenes and condensed graphite-like structures are of particular interest. In order to optimize the graphitization of the anode mass, coal pitch (the β fraction) is investigated. In the heat treatment of the anode mass, the best binder is pitch with a high content of β fraction. The structuring of the asphaltene macromolecules in solution has not been studied for coal pitch. In the present work, in order to investigate the self-assembly of molecular aggregates of coal-pitch asphaltenes, the morphology and structure of powder particles for coal-pitch asphaltenes are investigated by various methods. The β fraction of pitch containing asphaltenes is separated by means of selectively soluble groups. Toluene and hexane are used as the selective solvents. On the basis of X-ray phase analysis, the coke residue of coal-pitch asphaltenes contains crystallites of naphthene–aromatic layers. The crystalline properties of the deposited asphaltene particles hardly depend on the deposition conditions. The powder mainly consists of turbostratic carbon structures.

Study on the properties of coal-based high-purity graphite

As one of the major value-added products of coal processing and utilization, coal pitch coke and coal tar pitch are used as raw materials to prepare high-purity graphite. The structure characteristics and properties were measured by experiments. The results show that the high-purity graphite has excellent physical properties: the skeletal density of 1.81–1.91 g/cm3, the Shore hardness of 45.5–66.6 Hs, the flexural strength of 33.0–46.1 MPa, the compressive strength of 65.6–75.8 MPa, the ash content of 67–181 ppm, the thermal expansion coefficient of 3.71–4.11 × 10–6/°C, and the electrical resistivity of 8.72–12.13 μΩ · m. Consequently, coal-based graphite materials have excellent properties and good application prospects in solar energy industry, which is an effective exploration for the transformation and upgrading of Chinese coal industry.

A multifactor coupling prediction model for the failure depth of floor rocks in fully mechanized caving mining: a numerical and in situ study.

To study the mining-induced failure depth of floor rocks in a fully mechanized mining caving field affected by different coal seam pitches, mining face lengths, burial depths and aquifer water pressures, multifactor-coupled orthogonal numerical tests on the failure depth of floor rocks were conducted. The numerical results show that the failure depth of floor rocks increases with increasing mining face length, coal seam pitch and burial depth. According to the relationship between failure depth and these impact factors, a multifactor-coupled prediction model for the failure depth of floor rocks was established. In addition, the in situ measurement of the failure depth of floor rocks in the Yitang Coal Mine in Huoxi coal field in Shanxi Province, China, was performed, and the in situ failure depths of floor rocks in the 100 502 (80 m) and 100 502 (180 m) mining faces were approximately 12.50–14.65 m and 17.50–19.20 m, in good agreement with the results of the multifactor prediction model. Furthermore, the sensitivity of each impact factor in the prediction model of the floor failure depth was further analysed by F-test and range analysis, and the impact order of studied factors on the floor failure depth is coal seam pitch > mining face length > burial depth > aquifer water pressure.

Optical and electrical characteristics of carbonized film prepared from coal tar pitch under a high magnetic field of 10 T

Carbon microcrystallites can become oriented in the carbonization process of coal tar pitch, which occurs with the characteristic where a mesophase is obtained, by using a magnetic field. An oriented film that has the ability to transmit visible light from 450 to 800 nm can be obtained by sandwiching an appropriate amount of coal pitch between two glass plates and heating in an inert atmosphere at 793 K under a magnetic field. This film can be used to obtain the same linearly polarized light as a commercially available polarizing element. The degree of orientation of the film prepared in a magnetic field of 3 T is not sufficient to use as a polarizer, but a magnetic field of 6 T is able to sufficiently suppress the passage of crossed polarized light. The electrical conductivity of the carbon film prepared at 793 K is improved by 10 times by the application of a magnetic field of 10 T. The electrical conductivity is sensitive to the magnetic field, and there is a possibility that it can be further improved by applying 10 T or more. Coal tar pitch is the residue after obtaining coke from coal, and the optical and electrical advantage of a material prepared in the magnetic field derived from such natural products is clarified.

Comparative analysis of petroleum and coal pitches using 1H and 13C NMR spectroscopy

Petroleum and coal pitches are known to be among the most important sources of raw materials for the production of carbon materials, including electro-carbon, heat- and chemical-resistant structural products, metal-carbon and carbon-carbon composite materials, graphite electrodes, self-baking anode paste, carbon fibres, blast furnace and cupola coke. The quality of the pitches is determined by the elemental and group composition, as well as their structural and physical-chemical properties. The study of the molecular structure and group composition of the organic components of the pitch and the identification of the effect of the composition on the performance of the products is of great interest for assessing the prediction of the behaviour of pitches during processing and the properties of the products obtained from them. The present work is devoted to the study of the group composition of two petroleum and two coal pitches using high-resolution NMR spectroscopy. The data of the ¹H and ¹³C NMR spectra allow the composition of the pitch product to be estimated without separation into fractions, which, in turn, combined with the accuracy of the method and the recording speed of the ¹H NMR spectra, increases the rapidity of this method of analysis. The combination of ¹N and ¹³C NMR data allows additional information on the correlation of physical parameters and pitch composition to be established. The calculation of the (H ar /H al ) parameter, corresponding to the ratio of the integral intensities of signals of aromatic and aliphatic hydrogen atoms, provides the possibility of using it as a structural characteristic for a particular sample. In order to ensure the correct contribution to the integral intensity of the signals, ¹³C NMR spectra were recorded in a pulse sequence with suppression of the spin-spin proton interaction only for the period of data reading for the purposes of minimising the nuclear Overhauser effect. The relaxation delay between pulses was set to 10 s. The study of petroleum and coal pitches using NMR spectroscopy showed the proton spectra of NMR data to be sufficiently informative and suitable for monitoring the technological process of pitch production.

Viscosity and Wetting Properties of Pitch

The viscosity, wetting properties, and fluidity threshold of coal and other pitches are considered. The fluidity threshold of coal pitch is determined, and the influence of heat treatment on this temperature is studied. The softening temperature and fluidity threshold of the pitch samples are compared. The relation between the viscosity of pitch and its composition, wetting properties, and mass loss on heating to 360°C is analyzed.

Preparation and Characterization of Coal Pitch-Based Needle Coke (Part I): The Effects of Aromatic Index (fa) in Refined Coal Pitch

Refined coal pitch is a recognized precursor to produce high-quality needle coke with its higher aromaticity, lower ash content, and a relatively narrow distribution of molecular weight. The aromatic index (fa) of refined coal pitch is one of the key roles in the production of high-quality needle coke. In order to a detailed study on the effects of fa on the microstructure and properties of needle coke, 9 kinds of refined coal pitches with varied fa were used as the raw materials to produce needle coke in this study. Briefly, 1H NMR was used to calculate the fa of each refined coal pitch. Polarizing microscope, scanning electron microscopy, microstrength tester, X-ray diffraction, Raman spectrum, and curve-fitted methods have been used to quantitatively examine the microstructure and microstrength of each needle coke. The results have shown that the refined coal pitch with the fa of 0.95–0.98 was the best precursor to produce high-quality needle coke.

Valuable Products from Coal Tar

Research on the production and properties of coal pitch is conducted in the laboratory at PAO Koks. One topic of interest is the distillation of coal tar to produce a broad tar and pitch fraction, whose quality is analyzed. It is possible to regulate the characteristics of pitch: its ash content and content of components insoluble in toluene (the α fraction) and components insoluble in quinoline (the α1 fraction).

Development of Coal Chemistry at PAO Koks

At PAO Koks, in view of the small quantity of available coal tar, it is preferable to construct a system for processing heavy tar by atmospheric–vacuum distillation, with collection of the following products: soft coal pitch, vacuum-treated binding pitch, raw materials for carbon black (anthracene fractions 1 and 2), adsorbing oil, and a broad fraction (phenol + naphthalene).

Modeling of Oxidation Process of Coal Tar Pitch in Rotating Kilns

In this paper, a three‐dimensional numerical model has been developed to study the process of oxidative weight increment of coal tar pitch in a rotating kiln. Based on the two‐fluid method, the gas phase is modeled by realizable k‐ε turbulent model and the solid phase is modeled by kinetic theory of granular flow. The dense gas‐solid flow, heat transfer, and oxidation reaction for the bed and freeboard regions are simultaneously solved. The model is applied to a rotating kiln with a cylinder of 0.75 m length and 0.4 m diameter in the front and circular truncated cone on exit side. The detailed verification of model is firstly performed by comparisons with the available experimental data. The particle velocity profiles, product gas compositions, and various forms of solid motion in rotary kilns are contrastively analyzed. Afterwards, simulations are carried out to obtain the primary hydrodynamic and reactive characteristics in the rotary kiln. At the steady state, the particle velocity peak is located at the active layer surface, while the velocity has the opposite direction in the passive layer. The bed region generally has a higher temperature than the freeboard due to the large thermal capacity. The concentrations of product gas compositions, such as CO2, CO, and CH4, and solid product of oxidation, increase sharply near the surface and then keep on the steady values inside the bed. The effects of rotational speed of the rotary kiln and flow rate of air are also studied. The increasing rotational speed significantly accelerates the particle movement of the active layer and raises the final oxidative yield of coal pitch spheres. By contrast, increasing the flow rate of air has little effect on the particle motion and oxidation yield of coal pitch.

Preparation and Performance of Anisotropic Mesophase of Coal Pitch in Chemical Industry Based on Computer Monitoring Technology

Asphalt and other organic compounds form an anisotropic structure in lithification. Its product is mesophase which has excellent property and low cost so that it has been widely used in carbon fiber, carbon foam, needle coke and lithium ion secondary battery and many other areas. It can be said that the studies of preparation and structure of anisotropic mesophase of coal asphalt have significance to process improvement and cost savings in these areas. This research carries out an in-depth study in this regard. The selected coal asphalt is used as the raw material to analyze the influence of constant temperature and thermal polymerization temperature to the softening point, yield, group composition and optical microform. The experimental results show that coal asphalt turns into mesophase pitch with softening point of 312? and yield of 79.1% if it is kept in a constant temperature of 420? for 5 hours. However, it turns into mesophase pitch with softening point of 305? and yield of 81.4% if it is kept in a constant temperature of 400? for 8 hours. It shows that high-quality mesophase can be obtained with scientific control of the duration of constant temperature and the thermal polymerization temperature.

Thermal-Decomposition Products of Hexane-Insoluble Asphaltenes from Coal Pitch

The thermal-destruction products of hexane-insoluble asphaltenes from coal pitch and petroleum asphaltenes are compared. The volatile thermal-decomposition products of the asphaltenes are studied by thermal analysis and gas–liquid chromatography and mass spectroscopy. The morphology and structure of the solid residue is investigated by scanning electron microscopy and X-ray phase analysis. By that means, the analysis of the thermal-decomposition products permits assignment of the asphaltenes to known structural types and prediction of the coke residue’s morphology. The volatile thermal-decomposition products from coal pitch are aromatic polycondensed compounds with 3–7 aromatic nuclei, including N- and S-bearing compounds. The thermal decomposition of petroleum asphaltenes is accompanied by the liberation of alkanes, alkenes, and O-bearing compounds, with chain length from C11 to C30. The content of arenes and polyaromatic hydrocarbons in the volatile thermal-decomposition products from petroleum asphaltenes is considerably less than the content of aliphatic hydrocarbons. Morphological data indicate that the solid thermolytic residues of the asphaltenes differ in structure. For petroleum asphaltenes, the structure is porous and, according to X-ray phase analysis, shows no signs of graphite-like structure. For the asphaltenes from coal pitch, the residue contains graphite-like structure and has a distinctive luster.

Pitch Production from Mixtures of Coal Tar and Rubber Crumbs

To expand the range of materials from which coal pitch may be produced, the interaction of coal tar with rubber crumbs from discarded tires is investigated. Ultrasound treatment of a tar–crumb mixture and subsequent oxidation in air at 240–360°C may be used to produce an analog of coal pitch (binder) and a light fraction. The binder characteristics may be regulated in terms of the softening temperature, which is determined by the duration of oxidation.

Modification of Electrode Pitch

The phenolic fraction of coal tar may be used to modify the group composition and rheology of pitch, according to the results of the present study. Modification of electrode pitch with a softening temperature of 55°C changes the group composition of the β fraction. That improves characteristics such as the sorptional capacity, limiting wetting angle, and wetting index. Theoretical and practical research shows that introducing 15–20% of the phenolic fraction in 1000 g of pitch improves its plasticity. The processes responsible for the characteristics of pitch in each technological step are studied. The thermochemical transformations of the pitch components with coal tar at low levels of pyrolysis are identified. By this means, the group composition of coal pitch may be modified.

Environmental and economic impacts assessment of prebaked anode production process: A case study in Shandong Province, China

Abstract With the development of China's electrolytic aluminum industry, the consumption of prebaked anode has increased rapidly. However, the prebaked anode production process shares common characteristics such as excessive energy consumption and air pollutants emission. Therefore, it is imperative to evaluate the environmental and economic impacts of prebaked anode production process comprehensively. Following the life cycle assessment approach, this study provides life cycle inventory for the production process of the localized prebaked anode in China. Similarly, the “cradle-to-gate” environmental impact and economic cost of prebaked anode were analyzed. From the perspective of source tracking, the key processes and materials are identified according to environmental impacts. The results show that top five environmental impact categories are: freshwater eutrophication, human toxicity, freshwater ecotoxicity, marine ecotoxicity and fossil depletion. The key processes with significant environmental impact are mixing molding process and coarse crushing process which accounted for 45.87% and 45.43% of the overall environmental impact load, respectively. The key materials with significant environmental impact are petroleum coke and coal pitch which accounted for 45.40% and 45.04% of the overall environmental impact load, respectively. The sensitivity of various allocation methods is analyzed. The allocation factor of market value allocation and mass allocation is 99.79% and 97.31%, respectively. According to the sensitivity analysis results, the top priority should be assigned to the optimization of the key process such as mixing molding process, followed by the coarse crushing process.

The effect of binder (coal tar and pitch) on coking pressure

In order to develop a technology for reducing coking pressure, the effect of the addition of binder (coal tar and pitch) on coking pressure was investigated from the viewpoint of plastic coal layer permeability, internal gas pressure generated in a pilot scale oven and coke quality. We also studied the selective addition of binder to high coking pressure coal as a method to decrease coking pressure effectively. In the plastic coal layer permeability experiment, the addition of binder greatly decreases ΔPmax of high coking pressure coal HP and fine solid binder reduces ΔPmax more than coarse solid binder. The addition of binder decreases internal gas pressure and the finer the particle size of solid binder is, the smaller the internal gas pressure becomes. Moreover, in the case of the same addition ratio of binder, the selective addition of binder to high coking pressure coal can reduce coking pressure more effectively than the uniform addition. The addition of binder to coal blend is promising in the point that it can improve coke quality as well as reduce coking pressure.