Extraction of coal

As early as 2500 bce m India indigo was used to dye cloth a deep blue The early Phoenicians discovered that a purple dye of great value Tyrian purple could be extracted from a Mediterranean sea snail The beauty of the color and its scarcity made purple the color of royalty The availability of dyestuffs underwent an abrupt change m 1856 when William Henry Perkin an 18 year old student accidentally discovered a simple way to prepare a deep purple dye which he called mauveme from extracts of coal tar This led to a search for other synthetic dyes and forged a permanent link between industry and chemical research... 

The Pott-Broche process (101) was best known as an early industrial use of solvent extraction of coal but was ended owing to war damage. The coal was extracted at about 400°C for 1—1.5 h under a hydrogen pressure of 10—15 MPa (100—150 atm) using a coal-derived solvent. Plant capacity was only 5 t/h with an 80% yield of extract. The product contained less than 0.05% mineral matter and had limited use, mainly in electrodes. 

The analysis of geochemical liquids such as crude oils, hydrothermal bitumens, extracts of coals, and host rocks containing dispersed organic matter or pyrolysates... 

In addition to energy and environmental outputs in each step, energy and environmental inputs from raw materials use are also included. Generally, life cycle flows include all raw materials used for extraction. Likewise, life cycle flows from intermediate energy sources such as electricity, back to the extraction of coal, oil, natural gas, limestone, and other primary resources should be included. 

Yu X, Wang X, Bartha R, et al. 1990. Supercritical fluid extraction of coal tar contaminated soil. Environ Sci Technol 24 1732-1738. 

Table 6 Extraction of coal extract solution with toluene...

Hubert Tschamler They were derived either from mean values observed for model compounds of known structure or from the properties of solvent extracts of coals. In the latter case an accurate value for %H i can be derived by measuring proton spin resonance in solution and this, combined with the optical densities observed in the infrared spectra, gives the specific extinction coefficients. (See J. F. M. Oth, E. de Ruiter and H. Tschamler, Brennstoff-Chem. 42, 378 (1961) also Ref. 7). 

For each run, coal samples of approximately 50 grams were dried, at 100°C. for 4 hours and weighed after cooling in a desiccator for % hour. In the early experiments, coal and solvent were mixed in the autoclave, and runs were performed. It was found that the time necessary for the autoclave and mixture to be heated from room temperature to reaction temperature was 1 hours. When extraction fraction vs. time was plotted, it showed that at higher temperatures more than 80% of the total possible extraction of coal dissolved before the system reached the reaction temperature. Consequently, the data obtained in the first 2 hours were incorrect. 

Solvent extraction of coal can be explained by a series of independent first-order reactions, the residue of one reaction being the reactant for another reaction. It can be formalized as follows ... 

Figure 12. Variation of fraction extraction with time for the second stage of two-stage solvent extraction of coal first stage at 250°C. for 8 hours not shown...

Figure 15. Arrhenius plot for the second stage of a two-stage extraction of coal for two values of x first stage at 250° not shown...

Nondestructive solvent extraction of coal is the extraction of soluble constituents from coal under conditions where thermal decomposition does not occur. On the other hand, solvolysis (destructive solvent extraction) refers to the action of solvents on coal at temperatures at which the coal substance decomposes and in practice relates in particular to extraction at temperatures between 300 and 400°C (572 and 752°F). In the present context (i.e., the solvents extraction of coal), the solvent power of the extracting liquid appears to be determined solely by the ability of the solvent to alter the coal physically (by swelling). In this respect, the most effective solvents are aromatics, phenol derivatives, naphthol derivatives, anthracene, and phenanthrene. 

For the purposes of this chapter, the solvent extraction of coal is limited to those investigations and test methods that are separate form the high-temperature treatment of coal with solvents in which the production of liquid products (liquefaction) is the goal. 

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