Reaction of coals

Newer coal-based methods of acetylene manufacture under development include the AVCO process, based on the reaction of coal in a hydrogen plasma. Finely divided coal is passed through a hydrogen plasma arc generating temperature gradients of up to 15,000 K. About 67% of the coal is consumed, yielding char and acetylene in concentrations up to 16%. An energy requirement of 9.5 kW h/kg acetylene has been reported (33). 

Metal—Water Processes. The steam-iron process, one of the oldest methods to produce hydrogen, iavolves the reaction of steam and spongy iron at 870°C. Hydrogen and iron oxide are formed. These then react further with water gas to recover iron. Water gas is produced by reaction of coal with steam and air. 

The pyritic sulfur in coal can undergo reaction with sulfate solutions to release elemental sulfur (see Sulfurremoval and recovery). Processes to reduce the sulfur content of coal have been sought (75). The reaction of coal and sulfuric acid has been used to produce cation exchangers, but it was not very efficient and is no longer employed. Efforts have turned to the use of hot concentrated alkaH in a process called Gravimelt. 

If the initial reactions of coal are purely thermal, one might expect that the H-donor level will be of minor importance if times are kept short. In fact, all coals contain a certain portion of material that is extractable by pyridine. On heating coals to liquefaction temperatures, some additional material also becomes soluble in even non-donor solvents. Thus, there is a portion of all coals which can be solubilized with little dependence on the nature of the solvent. 

The important elementary reactions of coal liquefaction are the decomposition of coal structure with low bond dissociation energy, the stabilization of fragments by the solvent and the dissolution of coal units into the solution. 

Thermal Treatment of Various Aromatic Compounds. In order to study the reaction of coal structure, various aromatic compounds were chosen as the coal model and treated at 450°C. 

It may be considered that in the hydrogenation reaction of coal, the coal is subjected to consecutive changes in components and reactivity which results in a consecutive molecular lowering. 

Coal Products Isotopic Distribution by Structural Position. Other workers have also investigated deuterium uptake in coal pro-ducts by structural position. Schweighardt, et al. (26) examined a centrifuged liquid product from a Synthoil run which was heated to 450°C with deuterium gas, Kershaw and Barrass (27) examined the products from the reaction of coal with deuterium gas using SnCl2 as catalyst, and Franz (10) examined the products from the reaction of a subbituminous coal with Tetralin-1,l-d2 at 427°C and 500°C. 

Gas products from continuous supply reaction of coal/CaO mixture with steam. (Adapted from Shiying, L., Michiaki, H., Yoshizo, S., and Hiroyuki, H., Continuous Experiment Regarding Hydrogen Production by Coal/ CaO Reaction with Steam (HyPr-RING), 21st Pittsburgh Coal Conference, Osaka, Japan, Sep. 13-17,2004.)... 

Several important chemical reactions for the conversion of coal to methane are shown in Table 2. Steam conversion involves the reaction of coal with steam to produce hydrogen and carbon monoxide. Hydrogen conversion is a reaction in which coal and hydrogen react to form methane. Oxygen conversion produces hydrogen and carbon monoxide by partial oxidation of coal. Methan-ation involves a reaction in which methane and water are produced from carbon monoxide and hydrogen. The water gas shift reaction between carbon monoxide and steam produces carbon dioxide and hydrogen. 

Water gas, formed by the reaction of coal with oxygen and steam, is a mixture of CO, COj, and H. The ratio of to CO can be increased by adding water to this mixture, taking advantage of a reaction known as the water-gas shift reaction (Demirbas, 2007) ... 

Transalkylation involves the transfer of alkyl groups between aromatic nuclei, usually in the presence of strong Lewis acids. Heredy and Neuworth used this reaction to "depolymerize" coal. As a result of the reaction of coal with BF3 and phenol, the solubility of coal in phenol or pyridine increased substantially. Various modifications of this reaction have since been reported . Transall lation reactions in the presence of trifluoromethane sulfonic acid and aromatic hydrocarbons have recently been used by Benjamin et al. and Farcasiu et al. to identify structural features in coals and heavy petroleum ends, respectively. 

In ordar to determine the effect of coal rank (at established by reflectance measurement of vitrinite in coal) on the reactions of coal as related to carbonization, gasification, combustion, and other processes, a wide range of bituminous coals were studied. The results show that reflectance measurements can be used effectively (1) to determine accurately yields of coal carbonization products such as coke, tar, gas, light oil, and liquor from pilot and commercial coke oven (2) to obtain the heating value and specific gravity properties of gases from these processes (3) to determine the free swelling index and B.t.u. content of coals ... 

Reaction of Coals under Conditions of High Energy Input and High Temperature... 

In recent years there has been renewed interest in treating coal at high temperatures both by rapid processing in the more conventional type of carbonization apparatus (I) and by using such devices as flash tubes (5, 12, 13), lasers (13), arc image furnaces (9, 11), and plasma jets (3). All these methods produce conditions whereby the coal can be heated rapidly to a temperature well in excess of 1000°C. followed by quenching of the products. The work described here is an investigation into the reactions of coal in a plasma jet and has been reported briefly elsewhere (3). 

Materials. Analyses. The coal analyses are given in Table II both black durain and cannel coals are rich in sporinite material while the remainder are highly vitrainous. Two experiments were also carried out with material other than coal one with Neospectra carbon black and the other with a soot residue formed by the reaction of coal (CRC 802) in the plasma. The analysis (% daf basis) of the Neospectra carbon black was as follows C, 92.0 H, 0.8 N, 0.05 O by difference, 7.2 volatile matter, 9.2. All the materials were vacuum dried at 110°C. for several hours prior to use. 

The extent of the reactions of coal in the plasma jet depend upon the combination of a physical effect (the influence of the particle size on the rate of heating) and a chemical effect (the subsequent rapid release of volatile material leading, it is thought, to shattering of the particles). As a consequence of these two effects, high volatile coals of small particle size gave the maximum reaction as measured by the yield of acetylene. 

We have heard several papers on the reactions of coal or coal volatiles under conditions of very high energy input (in plasmas, laser irradiation, etc.). Potentially useful yields of valuable chemical raw materials result. The work therefore appears to be a new variety of cook-book preparative chemistry in which new and highly active species are involved as intermediates, and it is not easy for the ordinary chemist to visualize what goes on and what these intermediates are. Would any of the authors care to comment ... 

TABLE 5.2 Reactions of Coal Minerals at High Temperature... 

Combustible carbon carbon content remaining in the solid products derived from the combustion or reaction of coal, exclusive of carbonate in any form (ASTM D-5114 ASTM D-6316). 

The authors would like to thank Mr. Gerald Farber for the construction and operation of the equipment, the U.S. Bureau of Mines for the coal analysis and Robert Smol, Joe Forrest, and Robert Doering of Brook-haven National Laboratory for the gaseous and liquid product analysis. Acknowledgement is also made to the group at City University of New York, Arthur Squires, Robert Graaff, and Sam Dobner for their helpful discussions on rapid reactions of coal with hydrogen. 

Solvent Effects During the Reaction of Coal Model Compounds... 

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