Carbonization Of Coal Tar Pitch Research Articles

Rheological properties and carbonization of coal-tar pitch

During the carbonization of coal-tar pitch the viscosity of the pitch decreased at 200–360°C, reached a minimum at 360–400°C, and then increased at 400–450°C. The decrease of the viscosity of the pitch after its melting may be attributed to the solubilization of benzene insolubles (BI) (β-resin and quinine insolubles) by the solvation of benzene solubles (BS) to BI, in addition to the increase of thermal movements of pitch with increasing temperature. The viscosity increase above 400°C can be explained by the growth of a high molecular weight mesophase. The addition of extra β-resin to the pitch resulted in the formation of smaller anisotropic domains, compared with the carbonization of the pitch alone. β-Resin seems to become nuclei for thermal condensation, leading to the rapid solidification of the mesophase. This hinders the growth of the mesophase to a large anisotropic domain.

95/05918 Carbonization of coal-tar pitch under controlled atmosphere - Part I: Effect of temperature and pressure on the structural evolution of the formed greeen coke

95/05918 Carbonization of coal-tar pitch under controlled atmosphere - Part I: Effect of temperature and pressure on the structural evolution of the formed greeen coke

95/05919 Carbonization of coal-tar pitch under controlled atmosphere - Part II: Effect of temperature and pressure on the electrical property evolution of the formed green coke

95/05919 Carbonization of coal-tar pitch under controlled atmosphere - Part II: Effect of temperature and pressure on the electrical property evolution of the formed green coke

Carbonization of coal-tar pitch under controlled atmosphere—Part II: Effect of temperature and pressure on the electrical property evolution of the formed green coke

The carbonization of an industrial coal-tar pitch was studied by using a tube bomb, as a function of carbonization temperature (550 °C–580 °C) and inert gas pressure (1–20 bar), and resultant green cokes were evaluated according to electrical resistivity determined using the Van der Pauw method. At 550 °C, the carbonization pressure increase leads to an uniaxial arrangement of the produced green coke sample and to a progressive increase of the resistivity component perpendicular to the tube bomb axis. At 580 °C, these changes appear only above 15 bar. These results are in good agreement with those obtained in the first part of this work, confirming the intimate correlation between carbonization temperature and pressure and the necessity of a compromise between them, to produce green cokes with oriented uniaxial texture.

Carbonization of coal-tar pitch under controlled atmosphere—Part I: Effect of temperature and pressure on the structural evolution of the formed green coke

The carbonization of an industrial coal-tar pitch was studied, by using a tube bomb, as a function of carbonization temperature (520 °C–580 °C) and inert gas pressure (1–20 bar) and resultant green cokes were evaluated according to yield and observation under polarized light microscopy. At 520 °C, green cokes present large isotropic domains as well as Brooks and Taylor's spheres whatever the pressure applied, indicating that the pyrolysis duration seems to be too short to obtain an entirely anisotropic texture. When carbonization temperature increases, samples present an entirely anisotropic texture. An increase of carbonization pressure from 5 to 10 bar leads to a sharp increase of the coke yield and of the uniaxial arrangement, this latter being progressive with increasing pressure at 550 °C and appearing only at pressures greater than 15 bar at 580 °C. Carbonization temperature and pressure are intimately correlated. The temperature increase involves a higher solidification rate, whereas the pressure increase delays the volatile departure and consequently the solidification rate. It is necessary to obtain a compromise between them so as to produce green cokes with oriented uniaxial texture.

Effect of Iodine Treatment on Carbonization of Coal Tar Pitch

The effect of iodine treatment on carbonization of coal tar pitch was investigated. Coal tar pitch with softening point of 101°C was used as a starting material. The pitch specimen, molded into 6 mm in diameter and 20mm in length, and iodine powder of about twice of the specimen weight were put into a test tube. After sealing the tube, they were heated at 90°C for iodine treatment. The specimens were preoxidized at 170°C for 3 hours in air flow to stabilize the pitch. Then preoxidized specimens were heated for carbonization at a rate of 2.5°C/min up to 800°C in Ar flow. The duration at the highest temperature was 1 hour. From the result of solvent fractionation using benzene and pyridine, iodine treatment and preoxidation treatment was known to increase molecular weight of components in the pitch. Carbon yield of the specimen was increased from 56% to 76% by iodine treatment for 20 hours. Microstructure of the carbonized specimens changed from flow type texture to mosaic one with increasing period of the iodine treatment.

Carbonization behavior of pitches containing fine molybdenum particles

In the carbonization of coal tar pitch and naphthalene pitch containing fine molybdenum particles, it was found by using a tritium tracer method that the fine molybdenum particles added into pitch in advance can selectively catalyze the dehydrogenation and polycondensation of saturated hydrocarbons below 700 C, and thereby the carbonization yield of coal tar pitch containing partially saturated structures or aliphatic side chains in its component molecules increased. Further, it could be inferred that the fine molybdenum particles mainly accelerate the release of the hydrogen which is difficult to isotopically exchange with water in the preparation of tritiated pitch in the presence of Pt/Al[sub 2]O[sub 3].

Carbonization of coal tar pitch denitrogenated by metal sulfates

After adsorbtion removal of nitrogen compounds with dried metal sulfates, carbonization of extracted fractions from a coal tar pitch (CTP, N = 1.1 wt %) was studied for production of needle coke of low nitrogen content without puffing since nitrogen in the coke is believed to provoke puffing at rapid graphitization. A nitrogen-free coke (N, 0.01 wt%) with excellent flow texture was produced from the early two eluents of MI-TS (methanol-insoluble but toluene-soluble) by removing the basic nitrogen compounds through the sulfate column. Adsorbing denitrogenation through batch treatment with the supported sulfate also significantly reduced the nitrogen content of cokes produced from TS (toluene-soluble) without deterioration of their anisotropic texture. A low-nitrogen coke (N, 0.26 wt %) from the denitrogenated TS exhibited much smaller volume increase of micropores (< 0.1 μm) after rapid graphitization than coke from the original CTP, suggesting very little puffing. The efficiency of combining extractive fractionation for NH species with adsorbing separation of basic nitrogens is briefly discussed for practical application in order to minimize the amount of adsorbent.

Characterization of Structural Change during Carbonization of Coal-tar Pitch

Coal-tar pitch was heat-treated at various temperatures up to 1000°C and the weight loss (Δw/w) measurement, CHN analysis, polarized-light microscopic observation, IR and ESR spectra, and X-ray diffraction study were done. These data gave us the feature of structural change of coal-tar pitch through carbonization reaction, especially the change which occurred in the temperature range of pitch solidifying was remarkable. The behavior of structural change varied with the heat-treatment temperature (HTT) 500-600°C as a border. At HTT 600°C the bulk mesophase was formed completely and absorption bands except aromatic rings disappeared in IR spectrum, and the value of interlayer spacing showed for a typical disoriented carbon, that was 3.44A. The radical concentration (N) was the maximum at this HTT 600°C.By plotting log N against Δw/w, a linear relationship was observed. This relationship suggests that the amount of released components is in proportion to the amount of breaking hydrocarbon chains, and it brings the radical formation.

Assessment of thermal reactivity of nitrogen heterocompounds during carbonization of coal-tar pitch

Non-isothermal thermogravimetry was used to compare the thermal reactivities of nitrogen heterocompounds and aromatic hydrocarbons during the carbonization of coal-tar pitch. The samples for analysis were obtained by solvent extraction of a commercial binder pitch followed by size exclusion chromatography of the extract on Sephadex LH-20. The results demonstrate that although the nitrogen heterocompounds have enhanced thermal reactivity compared with the aromatic hydrocarbons, the enhancement is not as large as considered previously, which may require a re-assessment of the influence of heteroatoms on the mechanism of carbonization.

Carbonization of coal-tar pitch into lump needle coke in a tube bomb

The carbonization of coal-tar pitches and their QI (quinoline insoluble)-free fractions was studied by evaluating their lump cokes produced in a tube bomb at various temperatures (470 to 550° C) and pressures (0 to 75 kg cm−2 gauge). The lump coke from QI-free fractions had a comparable anisotropic development and coefficient of thermal expansion (CTE). The carbonization temperature and pressure were found to influence strongly the properties of the cokes. At the highest temperature of 550° C, the most appropriate pressure for the best needle coke was 15 kg cm−2 G (gauge). Either higher or lower pressure increased the CTE value of coke. In contrast, at a moderate temperature of 500° C, the higher pressure produced the better coke. At the lowest temperature of 470° C, it took 10 h to complete the carbonization, and the lowest pressure allowed the best extent of uniaxial arrangement. Among the cokes prepared under the present conditions, the Carbonization at 500° C under 40 kg cm−2 G produced the best needle coke with a CTE value as low as 0.1 × 10−6° C−1. The carbonization scheme leading into the needle coke is discussed for a better understanding of how the carbonization temperature and pressure cooperatively influence the quality of the resultant coke, in relation to the carbonization reactivity of coal-tar pitch.

Effect of Existence of Carbon Fiber on Carbonization of Coal-Tar Pitch under Pressure

Carbon fiber/coal-tar pitch composite (51wt%carbon fiber) and a coal-tar pitch were carbonized up to 650°C in argon atmosphere at300kg/cm2.The carbonization under pressure was carried out in sealed gold tube, which was set in a stellite bomb.The composite and the pitch thus carbonized were re-heated under normal pressure to investigate the effect of carbon fiber on the mesophase formation at the initial stage of carbonization, coke yield and graphitization of the pitch.The mesophase formation in the pitch matrix of the composite was delayed under pressure.At the appearance of the mesophase spheres it was found to coalesce with each other, which seemed to accelerate by the presence of carbon fiber.Under pressure and with the presence of carbon fiber the coke yield from pitch increased.The stacking of lammelar molecules was oriented concentrically around the carbon fibers, when the bulk mesophase formed at 650°C.The composite obtained at 650°C under pressure was re-heated from 1000°C to2500°C under normal pressure, formation of crack was observed in the coke matrix and also at the boundary of coke matrix and carbon fiber.The graphitizability of the coke matrix in the composite measured from the crystallite size and the interlayer spacing showed similar behaviour as the coke obtained from the pitch alone.

Isotropic and High Density Carbon made from Carbonaceous Powder prepared by Distillation under Reduced Pressure

It is attempted to produce high density, high strength and isotropic carbon made from carbonaceouspowder.The carbonaceous powder was prepared by carbonization of coal-tar pitch at a temperature of 440-500°C and subsequent distillation under reduced pressure.The distillation was performed at a temperature of 300-500°C below the carbonization temperature.In some cases additional quinoline extraction was carried out on the powder.Green carbon body was formed without binder pitch under isostatic pressure at room temperature.The body was heat-treated at a temperature of 1100-2800°C.Bulk density, weight loss, shrinkage, strength, lattice parameter, crystallite size and BAF of the obtained carbon body were measured.It is confirmed that high density, high strength and isotropic carbon made from the carbonaceous powder and the following results were obtained.1) BS (benzene soluble) fraction, β-resin (benzene insoluble and quinoline soluble) fraction and QI (quinoline insoluble) fraction were able to fractionate by distillation under reduced pressure.Concentration gradient of each fraction seems to exist in the carbonaceous powder.2) Using the powder prepared by a lower temperature of the carbonization and/or the distillation, the carbon body had higher balk density and higher strength.3) The β-resin fraction had the effects of increasing the green density and enhancing the shrinkage of carbon body during the heat treatment.

Behavior of Spherulite (Meso-Carbon Microbeads) During Carbonization of Coal-tar Pitch

At the early stage of carbonization of coal-tar pitch, a lot of small anisotropic sphere has been occured. According to rise of heating temperature, they have grown to 20-30μ in diameteer, combined then with each others, begun to flow, and finally solidified forming manifold coks-structures. It is therefore, considered that behavior of sphere must decisively influence on coks structure obtained.To advance the present knowledges about behavior of sphere, morever, following examinations are carried out;Optical character of this sphere reinvestigated under the transmitted-reflected microscope, using polished thin section of sphere isolated by quinoline.For getting new information about physical structure of sphere, spherules etched by heated quinoline are investigated under micro-interference microscope.Coks-structures are also examined under the scanning microscoppe.

151. Microstructures formed in the carbonization of coal-tar pitch

151. Microstructures formed in the carbonization of coal-tar pitch

Mesophase microstructures in carbonized coal-tar pitch

Polarized-light micrography has been employed to investigate the microstructure of the coalesced mesophase formed in the carbonization of coal-tar pitch. Prominent features in the polarizedlight extinction contours are the nodal points which do not move when the plane of polarization is rotated. These nodal points are found to correspond to two types of linear defects in the stacking of the aromatic layer planes. When the mesophase is further carbonized, the nucleation, growth and percolation of gas bubbles cause extensive plastic deformation of the mesophase. This deformation leads to an increasingly fine texture of extinction contours and nodal points.