Conversion of coal

The conversion of coal to gas on an industrial scale dates to the early nineteenth century (14). The gas, often referred to as manufactured gas, was produced in coke ovens or similar types of retorts by simply heating coal to vaporize the volatile constituents. Estimates based on modem data indicate that the gas mixture probably contained hydrogen (qv) (ca 50%), methane (ca 30%), carbon monoxide (qv) and carbon dioxide (qv) (ca 15%), and some inert material, such as nitrogen (qv), from which a heating value of approximately 20.5 MJ/m (550 Btu/fT) can be estimated (6). 

In Germany, large-scale production of synthetic fuels from coal began in 1910 and necessitated the conversion of coal to carbon monoxide and hydrogen. 

A. Sass, "The Garrett Research and Development Company Process for the Conversion of Coal iato Liquid Fuels," paper presented at 65th Annual AIChE Meeting New York, Nov. 29, 1972. 

Further details and specialized information on the mechanisms, product qualities, and proce.sses applied to the heating of coal in solvents can be found in the abundant literature [20]. What follows are some of the results of research conducted at West Virginia University, where investigations of the conversion of coal into pitches suitable for graphite production have been carried out... 

The conversion of coal into hquid materials can be accomphshed by pyrolysis or by direct liquefaction— heating coal in the presence of a hydrogen source. Neither of these routes is yet economically feasible. 

Barik S, Corder RE, Clausen EC, et al. 1987. Biological conversion of coal synthesis gas to methane. 

The overall conversion of coal to liquid and gaseous products was obtained from the formula ... 

Conversion of coal to benzene or hexane soluble form has been shown to consist of a series of very fast reactions followed by slower reactions (2 3). The fast initial reactions have been proposed to involve only the thermal disruption of the coal structure to produce free radical fragments. Solvents which are present interact with these fragments to stabilize them through hydrogen donation. In fact, Wiser showed that there exists a strong similarity between coal pyrolysis and liquefaction (5). Recent studies by Petrakis have shown that suspensions of coals in various solvents when heated to 450°C produce large quantities of free radicals (. 1 molar solutions ) even when subsequently measured at room temperature. The radical concentration was significantly lower in H-donor solvents (Tetralin) then in non-donor solvents (naphthalene) (6). 

To improve selectivity and conservation of hydrogen over present liquefaction technology in the conversion of coal to high quality liquids, we believe that thermal reactions should be kept as short as possible. Catalytic processes must be used for upgrading but should be used in a temperature regime which is optimal for such catalysts. 

Working co-operatively with others, we have found some indication that certain alilphatic linkages between aromatic nucleii are involved in the rapid dissolution of coal. The absolute aliphatic hydrogen content as determined by P. Solomon using FTIR (22) shows a very good linear relationship with conversion of coal in 3 minutes to pyridine soluble materials (Figure 14a). 

In step one, conversion of coal to a THF soluble product is rapid. The THF solubles are unstable in the presence of a coal derived solvent, but in the absence of hydrogen. In step two, the addition of molecular hydrogen to the system or of Tetralin to the solvent to increase hydrogen transfer to the coal increases the THF soluble conversion but does not lower the sulfur... 

Figure 11, Sequential conversion of coal to distillable products, char, and gas under alternate reaction conditions...

We have discovered that ZnC, in combination with methanol, constitutes an active liquid-phase catalytic medium for conversion of coal to pyridine-soluble material. There are several possible explanations for this effect improved contact between coal and melt higher activity of the ZnCl2 in the methanol medium methylation of cleaved bonds resulting in reduced char formation and extraction of the reaction products leaving the coal more accessible. 

For the study of catalyst concentration tin as stannous chloride was used as the catalyst and the concentration range studied was 0 - 15% by weight of the coal. Stannous chloride is one of the best, if not the best, catalyst for conversion of coal to liquid products. For the study of the effect of the reactor temperature, the temperature range studied was from 400 - 700°C. 

The conversion of coal to liquid fuels is usually carried out in the presence of an H-donor solvent (H-don) such as Tetralin. 

The table also shows the results of experiments with the donors and coal in phenanthrene as solvent. Consistent with the transfer of hydrogen in a radical process, those donors less reactive toward C130 than Tetralin are also less effective than Tetralin in conversion of coal to a phenanthrene-soluble product. However, in contrast to the chemistry of Step 2 we see that those donors that are more reactive toward C130 than Tetralin are also less effective in their action with coal. Thus this simple conversion scheme is suspect. 

Since the suggested conversion process does not include a thermally promoted bond-scission step, the question arises of how the addition of hydrogen results in the bond breaking necessary for significant reduction in molecular weight. We have already noted that the nucleophilic action of the basic methanol system was sufficient to cleave diphenyl ether, and a similar route is available in the basic i-PrOH and C0/H20 systems. On the other hand, we showed in control experiments that strongly basic conditions alone were not sufficient for significant conversion of coal. 

Develop technologies and catalysts for the cleaner use of coal as a fuel and for the conversion of coal to other fuels. 

Some chemical processes use energy directly to drive the transformation. For example, the conversion of iron ore, iron oxide, to iron metal requires chemical energy to remove the oxygen atoms. In early times the iron ore was heated with charcoal in more recent times it is heated with refined coal (coke), but in both cases the result is conversion of coal or wood into carbon monoxide, which is toxic but can be burned to carbon dioxide to generate needed heat. There is now interest in devising processes that do not use carbon in this way, but use electrical energy to avoid the production of carbon oxides. 

For the conversion of coal to pure hydrogen, data provided by a study from Foster Wheeler (1996) have been used. As the specific C02 emissions already surpass those from the operation of conventional gasoline cars, C02 capture and storage needs to be applied to dispose of harmful GHG emissions down to about 6 gC02/MJ of pure hydrogen. In turn, the specific coal demand increases to about 2.302 MJ/MJ of pure hydrogen. 

Conversion of coal to more desirable forms of energy such as ... 

Pyrolysis. Conversion of coal by pyrolysis involves heating coal to a temperature of 500 to 700°C. Gases and liquids are evolved from the coal at these temperatures, leaving char which has a lower H/C ratio than the original coal ... 

Heat recovery efficiency is a consideration of major importance in the conversion of coal to secondary fuels. This parameter is defined as the percent of the heating value of the coal used which is recovered as heating value in the desired secondary fuel. Heat recovery efficiency which can be attained in a coal conversion process depends firstly on the theoretical chemical and thermodynamic requirements of the process, and secondly on the practical realization of the process. The first factor determines the theoretical maximum heat recovery efficiency that can be obtained under ideal circumstances. The second factor determines the extent to which the practical process approaches the theoretical ideal. 

Several aspects of the concept of theoretical heat recovery efficiency can be understood by considering an idealized conversion of coal to a secondary fuel having a high H/C ratio, such as methane. In the following discussion, it is assumed that the conversion reactions proceed to completion at a temperature of 15 C and a pressure of 1 atmosphere although, of course, this cannot be realized in practice. Coal is assumed to have the idealized chemical formula of C1Q Hg. 

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. 

Varghese, P. Whitehurst, D.D. Fundamental Studies in the Conversion of Coals to Fuels of Increased Hydrogen Content, Electric Power Research Institute Report AP-2117. 1981. 

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