Hydrogen content coals

Reforming for producing hydrogen from high hydrogen-content, coal-derived liquid fuels. 

Coals (the plural is deliberately used because coal has no defined, uniform nature or structure) are fossil sources with low hydrogen content. The structure of coals means only the structural models depicting major bonding types and components relating changes with coal rank. Coal is classified, or ranked, as lignite, subbituminous, bituminous, and anthracite. This is also the order of increased aromaticity and decreased volatile matter. The H C ratio of bituminous coal is about 0.8, whereas anthracite has H C ratios as low as 0.2. 

Properties. A high volatile western Kentucky bituminous coal, the tar yield of which by Fischer assay was ca 16%, gave a tar yield of ca 26% at a pyrolysis temperature of 537°C (146—148). Tar yield peaked at ca 35% at 577°C and dropped off to 22% at 617°C. The char heating value is essentially equal to that of the starting coal, and the tar has a lower hydrogen content than other pyrolysis tars. The product char is not suitable for direct combustion because of its 2.6% sulfur content. 

Nuclear magnetic resonance (nmr) is a nondestmctive means of measuring the amount of hydrogen in various materials for example, nmr has been used to determine the hydrogen content of coals (251). 

Flash Pyrolysis Coal is rapidly heated to elevated temperatures for a brief period of time to produce oil, gas, and char. The increase in hydrogen content in the gases and hquids is the result of removing carbon from the process as a char containing a significantly reduced amount of hydrogen. Several processes have been tested on a rela-... 

The process begins with a gasification process that converts coal into carbon monoxide and hydrogen. Part of this gas is sent to a water-gas shift reactor to increase its hydrogen content. The purified syngas is then cryogenically separated into a carbon monoxide feed for the acetic anhydride plant and a hydrogen-rich stream for the synthesis of methanol. 

Table 10.6 shows some of the major components of fuels that are used in power plants. The coal and heavy fuel are the conventional fuels for power plants, while the Orimulsion is a relative new product from Venezuela, which is attractive owing to a higher hydrogen content that leads to reduced emission of CO2. 

The effect of the mineral matter content and of the inorganic sulphur content on the hydrogenation of coal were also studied. 

Pyrolysis. In this context it is relevant to consider initially the effect of hydrogen contents on tar yields during pyrolysis (carbonization). This is particularly so, since, in all coal conversion processes little happens until the coal is at a temperature above that where active thermal decomposition normally sets in. In other words, all coal conversion processes may be regarded as pyrolysis under a variety of conditions which determine the nature of the primary decomposition and the reactions which follow. 

The steep dependence on hydrogen content of the tar yields obtained during the low temperature (500°C) fluidized bed carbonization of 14 Australian coals, ranging in rank from 72% to -89% (dry ash-free basis) carbon content, is clearly demonstrated in Fig. 5 (15,16). 

Figure 5. Dependence of tar yields from low-temperature (500°C), fluidized-bed carbonization of hydrogen content for some Australian coals (15, 16)...

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). 

Figure 14a. Response of coal conversion to aliphatic hydrogen content...

As expected, both the bottoms products and the residues, where formed, have substantially higher carbon and lower oxygen contents than the original fractions, but whereas in the bottoms products the hydrogen contents have increased, in the residues they are reduced. The bottoms products, including that from the whole coal, are remarkably similar in composition to each other. Lkkewise the residues are similar in composition to each other. 

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