Carbonization temperature pitches

The conditions of pyrolysis either as low or high temperature carbonization, and the type of coal, determine the composition of Hquids produced, known as tars. Humic coals give greater yields of phenol (qv) [108-95-2] (up to 50%), whereas hydrogen-rich coals give more hydrocarbons (qv). The whole tar and distillation fractions are used as fuels and as sources of phenols, or as an additive ia carbonized briquettes. Pitch can be used as a biader for briquettes, for electrode carbon after coking, or for blending with road asphalt (qv). 

The market for tar-based road binders has declined considerably for a variety of reasons. Less cmde tar is available and the profits from the sales of electrode pitch and wood-preservation creosote or creosote as carbon-black feedstock are higher than those from road tar. In most industrial countries, road constmction in more recent years has been concentrated on high speed motorways. Concrete, petroleum bitumen, or lake asphalt are used in the constmction of these motorways. In the United Kingdom, for example, the use of tar products in road making and maintenance had fallen from 330,000 t in 1960 to 100,000 t in 1975 and is less than 100 t in 1994, mainly based on low temperature pitch which is not suitable for electrode or briquetting binders, but which is perfectly satisfactory as the basis for road binders. 

A carbon rod is used as a current collector for the positive electrode in dry cells. It is made by heating an extruded mixture of carbon (petroleum coke, graphite) and pitch which serves as a binder. A heat treatment at temperatures of about 1100 °C is used to carbonize the pitch and to produce a solid structure with low resistance. For example, Takahashi [23] reported that heat treatment reduced the specific resistance from 1 Q cm to 3.6xlO"1Qcm and the density increased from 1.7 to 2.02 gem- 1. Fischer and Wissler [24] derived an experimental relationship [Eq. (1)] between the electrical conductivity, compaction pressure, and properties of graphite powder ... 

These methods, described above, are to produce material (still loosely called mesophase) which essentially is a feedstock for other process developments. This "mesophase" prepared at temperatures below normal carbonization temperatures can be called low temperature mesophase pitch (LTMP). The term mesophase pitch has crept into the vocabulary of this subject and is thought to refer mainly to mesophase as a feedstock. Its anisotropy can be detectable by polarized light optical microscopy. 

Figure 35. Mechanical properties of carbon/carbon epoxy-resin hybrid composites, compared with the properties of the composite skeletons before resin impregnation (61,62). The composite skeletons were prepared from Sigrafil HM 3 PAN-based fiber, rigidized with a phenolic resin, and densified by four cycles with coal-tar pitch plus sulfur the carbonization temperature was 1000°C. (a) Young s modulus.

VARIATION IN CARBON FIBER MODULUS AS A FUNCTION OF CARBONIZING TEMPERATURE. PRECURSOR WAS A CAT CRACKER BOTTOM PITCH EXTRACTED WITH A SOLVENT HAVING A SOLUBILITY PARAMETER OF 8. -... 

Figure 14 ELECTRICAL RESISTIVITY OF SOLVENT EXTRACTED PITCH BASE CARBON FIBER AS A FUNCTION OF CARBONIZATION TEMPERATURE...

The diameter of the electrospun pitch fibers was in the micrometer range and difficult to become thinner due to the low boiling point (65-67 °C) of the solvent tetrahydrofiiran (THF). Electrical conductivity was increased on increasing the carbonization temperature from 0 (700 °C) to 83 S cm (1200 °C). 

Fig. 4.23 Adsorption isotherms of butane vapour at difTerent temperatures on a sample of carbon (prepared by heating a mixture of coke and pitch at 600°C), burnt off by 0.27%.

When the recycle soot in the feedstock is too viscous to be pumped at temperatures below 93°C, the water—carbon slurry is first contacted with naphtha carbon—naphtha agglomerates are removed from the water slurry and mixed with additional naphtha. The resultant carbon—naphtha mixture is combined with the hot gasification feedstock which may be as viscous as deasphalter pitch. The feedstock carbon—naphtha mixture is heated and flashed, and then fed to a naphtha stripper where naphtha is recovered for recycle to the carbon—water separation step. The carbon remains dispersed in the hot feedstock leaving the bottom of the naphtha stripper column and is recycled to the gasification reactor. 

Carbon—Carbon Composites. Above 300°C, even such polymers as phenoHcs and polyimides are not stable as binders for carbon-fiber composites. Carbon—carbon composites are used at elevated temperatures and are prepared by impregnating the fibers with pitch or synthetic resin, foUowed by carbonization, further impregnation, and pyrolysis (91). 

Ultramarine blues are prepared by a high temperature reaction of intimate mixtures of china clay, sodium carbonate, sulfur, siHca, sodium sulfate, and a carbonaceous reducing agent, eg, charcoal, pitch, or rosin. 

States or Australia. In some cases, pot stills, arranged in cascade, are still used. The more sophisticated plants employ one or more carbon steel or cast-iron vessels heated electrically and equipped with temperature controls for both the bulk Hquid and the vessel walls. Contact time is usually 6—10 h. However, modem pitches are vacuum-distilled, producing no secondary quinoline insolubles, to improve the rheological properties. 

The increasing use of carbon-bonded and carbon-impregnated refractories is providing another growing market for refined tars. These vary from a soft pitch to a refined tar of as low as 30°C equiviscous temperature (EVT) (see Refractories). Liquid fuels were formerly important outlets for coal-tar, pitch—oil blends, and topped tar which could not be disposed of more profitably (79). However, as a result of reduced tar suppHes this usage has been phased out. 

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