High Temperature Carbonization

Basieally, the high temperature furnace elevates the temperature in a uniform manner to inerease the fiber modulus and a smaller d tex fiber will give a higher modulus for a given 

220 HCN evolved and O2 chemically bonded Ladder polymer formation and oxidation of polymer 

260 Little change. No modulus Increase No chain scission 

300 Large CO2 and H2O evolution, also CO, HCN and some nitriles. No modulus increase CO2 from -COOH groups in oxidized polymer. No cross-linking 

400 CO2, H2O, CO, HCN and NH3 evolved. Small evolution of C3 hydrocarbons and nitriles. Modulus increase Cross-linking by intramolecular H2O elimination 

Four main products are obtained by low-temperature carbonization processes (1) the final coke or char, (2) an organically complex tar, (3) gases, and (4) aqueous liquor. The proportions are determined, in part, by the rate and the time of heating. 

Both fluidized-bed and fixed-bed systems have been used the former system requires direct contact with another heating medium, whereas fixed-bed sysfems may be heated directly or indirectly. Carriers can vary and among the carriers for direct heating are steam, air, recycle gases, sand, and metal balls containing a salt to take advantage of the latent heat of fusion. Superheated steam at 540°C-650°C (1000°F-1200°F) has been effective but may actually be economically unfavorable. The commercial aspects of the process usually involve ovens or kilns that are heated externally by a fuel gas, usually by-product gas from the coke ovens themselves. 

The process by-product (tar) was also considered to be valuable insofar as it was nsed as a feedstock for an emerging chemical industry and was also converted to gasoline, heating oils, and lubricants. The coals that were preferred for low-temperature carbonization were nsnally lignites or subbituminous (as well as high-volatile bituminous) coals that yield porous solid products over the temperature range 600°C-700°C (1110°F-1290°F). 

The reactivity of the semicoke prodnct was usually equivalent to that of the parent coals. Certain of the higher-rank (caking) coals were less suitable for the process (unless steps were taken to destroy the caking properties) becanse of the tendency of these higher-rank coals to adhere to the walls of the carbonization chamber. 

On a commercial scale, the low-tanperature carbonization of coal was employed extensively in the industrialized nations of Europe but suffered a major decline after 1945 as oil and natural gas became more widely available, but the subsequent rapid escalation in oil prices as well as newer and more restrictive environmental regulations have stimulated (and reactivated) interest in the recovery of hydrocarbon liquids from coal by low-temperature thermal processing. 

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Coke oven light oil is a by-product of the manufacture of coke for the steel industry. When coal is subjected to high temperature carbonization, it yields 16—25 Hters /tonne of light oil that contains 3—6 vol % of mixed xylenes. 

High Temperature Carbonization. When heated at temperatures in excess of 700°C (1290°F), low temperature chars lose their reactivity through devolatilization and also suffer a decrease in porosity. High temperature carbonization, at temperatures >900° C, is, therefore, employed for the production of coke (27). As for the low temperature processes, the tars produced in high temperature ovens are also sources of chemicals and chemical intemiediates (32). 

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). 

Because of its high reactivity, production of barium by such processes as electrolysis of barium compound solution or high temperature carbon reduction is impossible. Electrolysis of an aqueous barium solution yields Ba(OH)2, whereas carbon reduction of an ore such as BaO produces barium carbide [50813-65-5] BaC2, which is analogous to calcium carbide (see Carbides). Attempts to produce barium by electrolysis of molten barium salts, usually BaCl25 met with only limited success (14), perhaps because of the solubiUty of Ba in BaCl2 (1 )-... 

Recently, Tanuma and Palnichenko [24] have reported a new form of carbon which they call Carbolite formed by quenching high temperature carbon vapour onto a metal substrate. Hexagonal Carbolite I was formed from an Ar-rich gas a rhombohedral form, Carbolite II, was formed from an Ar-Hj gas mixture. 

Most of the coke produced in the United States today comes from the high-temperature carbonization of coal. The coke is used pnmarily by the metallurgical industries as a fuel and in the rendering of iron from iron ore m the blast furnace... 

S. Sato, H. Awaji and H Aku2awa, Fracture Toughness of Reactor Graphite at High Temperature, Carbon, 1978, Vol. 16, No. 2, pp 95 102... 

Hoch-wald, m. (high) forest, timber forest, -warmeverkohlung, /, high-temperature carbonization. 

Table 1.28 Some salient features of low-temperature carbonization (LTQand high-temperature carbonization (HTC).

Li, W., S.K. Gangwal, R.P Gupta, and B.S. Turk, Development of Fluidizable Lithium Silicate-Based Sorbents for High Temperature Carbon Dioxide Removal, 2006 Pittsburgh Coal Conference, Pittsburgh, PA, September 2006. 

Chung, S.J. et al., Dual-phase inorganic metal-carbonate membrane for high temperature carbon dioxide separation, Ind. Eng. Chem. Res., 44, 7999, 2005. 

Dynamics of High-Temperature Carbon Monoxide Chemisorption on Platinum-Alumina by Fast-Response IR Spectroscopy... 

Coke. Metallurgical coke is obtained by high-temperature carbonization of coal. It is a poorly graphitized form of carbon it is mainly used in blast furnace for steel manufacture (see Iron, 5.10). 

In order to overcome these problems, hybridization of both materials (C and Si) in one electrode material by HTC seemed to be a promising option [75]. For this purpose, pre-formed silicon nanoparticles were dispersed into a dilute solution of glucose followed by hydrothermal treatment at 180 °C. The carbon-coated particles were then further treated at 750 °C in order to improve the conductivity and structural order of the carbon layer. It was shown that the hydrothermal treatment, following by high temperature carbonization, resulted in formation of a few nanometer thin layer of SiOx layer on the Si nanoparticles, effectively leading to a Si/SiOx/C nanocomposite. Some TEM micrographs of these materials are shown in Fig. 7.8. 

Fig. 2.26 The three-dimensional Johnson model of PAN-based high-temperature carbon fibers.

High temperature carbon reduction (Lucke et al. 2005). The technique is based on indnctive high temperatnre heating (>1,500°C ) leading to carbon monoxide. It enables complete dehydration and decomposition in a single continuous process. 

In its commercial plants Sasol has to date used only iron based catalysts. (The preparation and properties of these catalysts have been reviewed elsewhere (2).) Not only is iron by far the cheapest of the metals (see Table I) but iron catalysts also produce large amounts of low molecular weight olefins which are important in the Sasol process. (These olefins are oligomerized to either gasoline or diesel fuel and this allows the production of these two liquid fuels to match the market requirement.) A major drawback of iron is that at high temperatures carbon deposition occurs which results in catalyst disintegration. 

Similar results were achieved over a Rh/alumina monolith catalyst " using catalytic POX for the reforming of a simulated JP-8 military feed containing 500 ppm of sulfur (as benzothiophene or dibenzothiophene). Stable performance for over 500 h with complete conversion of the hydrocarbons to syngas at 1,050°C, 0.5 s contact time, and LHSV of about 0.5 h was reported. At this high temperature, carbon formation was not reported and the sulfur exited as hydrogen sulfide. 

Dr. Friedel. No. Products of the pyrolysis of coal under high temperature carbonization conditions surely must arise from degradation. The quantitative prediction of C7 alkane isomers from coal may possibly indicate a relationship in compositions of coal and petroleum. The hydrocarbons from each perhaps should be similar since both are supposedly derived from organic plants ... 

Gates from the flash and laser irradiation of Pittsburgh seam (hvab) coal were investigated to determine the action of high temperatures on coal. Temperatures in excess of 1000°C. were reached with both types of irradiation. Craters about 300 microns in diameter were produced in the coal with millisecond pulses from the laser unit rated at 1.7 joules output. Gaseous products from the laser and flash irradiations showed 21% and 8% acetylene, respectively. Diacetylene, vinylacetylene, and other products to molecular weight 130 were indicated in the mass spectrum of the gas from the laser study. The results indicated that the distributions of products obtained from the flash and laser irradiations of coal were different from that produced in high temperature carbonization. 

Table I. Gaseous Products from laser and Flash Irradiations and High Temperature Carbonization of Pittsburgh Seam (hvab) Coal...

At temperatures of about 4000°K., the free energy of formation of acetylene from its elements approaches zero, and the equilibrium yield of acetylene is appreciable. The system is complicated, however, by other reactions and phase changes which occur at these high temperatures. Carbon sublimes at about 4000°K., various species of carbon Ci, C2, and Ca are formed, and dissociation of molecular hydrogen occurs. 

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