Coal-derived pitch coke

Calcined coke is a petroleum coke or coal-derived pitch coke obtained by heat treatment of green coke to about 1600 K. It will normally have a hydrogen content of <0.1 wt%. See Coal-derived pitch coke, green coke, petroleum coke... 

Coal-derived pitch coke is the primary industrial solid carbonization product obtained from coal tar pitch, and is mainly produced in chamber or delayed coking processes. 

Coal-derived pitch coke, although it exhibits a pre-graphitic microstructure, has often a lower graphitizability than petroleum coke. Fractions of coal tar pitches (obtained by extraction or filtration) may form cokes with needle-like structures and have an improved graphitizability. The usually lower grcg>hitizability compared to petroleum coke is due to an inhibition ofmesophase growth because of chemical and physical differences of the cokes. See coal tar pitches, coke, petroleum coke... 

In recent years researchers at West Virginia University have developed coal-derived pitches on a laboratory scale in quantities sufficient to make 1 kg samples of calcined coke for fashioning graphite test specimens. The pitches were derived by uhlizmg solvent extraction with N-methyl pyrrohdone (NMP). This solvent is able to isolate coal-based pitches m high yield and with low mineral matter content [13]. It is this work that will form the basis of the discussion for the later part of this chapter. 

Table 19. Effect of blending hydrogenated coal-derived pitch and coal extract on green coke yields, WVGS 13423 ...

Adschiri et al. removed 70 wt.% of the nitrogen from coal-derived pitches by catalytically hydrotreating the pitch in a supercritical toluene-tetralin mixture at 450 °C [67]. These pitches could be used for the production of high-quality electrode carbon. The more conventional process for this reaction involves catalytic hydrotreating of the pitch in the liquid phase. The higher dif-fusivities in the SCF resulted in higher reaction rates. Moreover, catalyst coking could be reduced effectively due to the increased pressure and hence the solvent power of the SCF. 

It has been demonstrated that a solvent-extraction procedure with N-methyl pyrrolidone is capable of producing coal-derived extract pitches with low-ash contents. Moreover, the properties of the pitches can be varied by partial hydrogenation of the coal prior to extraction. The yield of the pitches along with the physical and chemical properties of the cokes and graphites vai in an understandable fashion. 

Coal tar enamel This is derived from the coking of coal and is further distilled to produce coal tar pitches. It is used for hot application on-site. It will crack and craze if exposed to sunlight but has been employed successfully for over 50 years for the protection of underground or immersed structures. The main use is now for the exteriors of buried or immersed pipelines. Different types of enamel are available to give various degrees of heat resistance. It is now generally used for pipelines below 155 mm diameter. 

Fig. 29. Effect of heat treatment on the reactivity of carbons derived from coal tar pitch and delayed petroleum coke. Reaction with carbon dioxide at 1150°. [After P. L. Walker, Jr., and D. O. Baumbach, unpublished results 1969.]...

Under the optical microscope the texture of products derived from the three coals studied show an anisotropy of the type which already has been described for similar materials (I, 4, 9). The texture of the l.t. pitch coke is entirely isotropic, whereas the h.t. pitch coke is characterized by a pronounced anisotropy in bands. The anisotropy of the carbonization products of mixtures of l.t. and h.t. pitches varies linearly as a function of the composition of the mixture (8). 

Test Samples. Main properties of the residual oils used in the present test are represented in Table II. It should be noted in this table that No. 1 is propane deasphalted asphalt Nos. 2 to 7 are petroleum pitches derived from residual oil heat treated under various conditions No. 8 is KRP pitch made by Kureha Chemical Industry from crude oil heat treated with hot steam at temperatures over 1,000°C and Nos. 9 and 10 are both residual oils from coal, No. 9 being solvent refined coal made by NKK and No, 10 being heat treated coal tar pitch. These Nos. 1 to 10 are typical examples of binding material for coke-making in Japan. 

T he carbon electrodes used in the production of aluminum by the Hall-Heroult process normally are produced from a combination of calcined coke and a pitch binder. While coal tar pitch traditionally has been used as the binder in electrode fabrication, variations in methods of production and the diversity of sources of supply result in variations in pitch quality. In addition, some locations in North America import pitch from areas such as Europe and Japan. With the desire for a more consistent quality product and more accessible sources of supply, alternative methods of producing binder pitch have been sought. This has led to a number of studies in the production of binder pitch from petroleum-derived materials (1-5). In these developments, the preferred feedstock... 

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