Coal solvent fractionation scheme

The general solvent fractionation scheme and the composition and analysis of the coal liquid fractions were described previously (1,2). 

The solvent fractionation scheme for separating coal liquid products into flve fractions propane-soluble (oil) propane-insoluble and pentane-soluble (resin) pentane-insoluble and benzene-soluble (asphaltene) benzene-insoluble and carbon disulfide-soluble (carbene) and carbon disulfide-insoluble (carboid) was described previously (1,2). 

An important point that cannot be overly emphasized is that coal-derived asphaltenes and petroleum asphaltenes are considerably different materials. Other than the fact that they are derived using essentially the same solvent fractionation scheme, the two have little in comfnon. For example, asphaltenes from the liquefaction of coal are known to be much more highly aromatic (46) than asphaltenes from petroleum (47, 48). During the present investigation, it was determined that the ESR behavior of the two types of materials is also quite different. 

These yields are also given on the basis of 100 g of original dry coal before fractionation. The bottom line of the table shows the mass of each fraction obtained from 100 g of dry coal. For every 100 g of original dry coal an additional 100 g of extraneous material was present. Elemental balances and other evidence (]J showed this to be made up almost entirely of phenol chemically combined with the coal material, with traces present of residual solvent associated with the fractions as a result of the coal preparation and fractionation scheme. Note that with fractions A and B no solid residue was obtained. 

Solvent Fractionation. To facilitate later structural analysis, we separated the coal into structural types by solvent fractionation. Some other workers using the phenol depolymerization method to solubilize coal have used gas chroma-tography/mass spectroscopy (GC/MS) techniques to identify individual compounds (11, 13). However, with material containing large amounts of phenol and other polar groups, elaborate preparation and separation schemes have to be used to avoid contamination of the chromatography columns. As the emphasis of the present work was on structural characterization of the whole coal rather than on detailed examination of small parts of it in order to elucidate the chemistry of the phenolation reaction, we used the relatively simple scheme shown in Figure 1. 

In order to overcome these problems, the flow schemes as shown in Figures 1 and 2 were developed. These incorporate the use of Kerr-McGee Corporation s Critical Solvent Deashing and Fractionation Process (CSD) for recovery of the SRC. The Kerr-McGee Process adds extra flexibility since this process can recover heavy solvent for recycle, which is not recoverable by vacuum distillation. EPRI contracted with Conoco Coal Development Company (CCDC) and Kerr-McGee Corporation in 1977-1978 to test these process concepts on continuous bench-scale units. A complementary effort would be made at the Wilsonville Pilot Plant under joint sponsorship by EPRI, DOE, and Kerr-McGee Corporation. This paper presents some of the initial findings. 

An example of the difference of the solvent extracts from the bulk material comes from a series of studies on the exhaustive extraction of coal by boiling pyridine and fractionation of the regenerated soluble solids by sequential selective extraction schemes (Berkowitz, 1979). Subsequent analyses showed that the petroleum ether-soluble material was mostly composed of hydrocarbons (e.g., paraffins, naphthenes, and terpenes), while the ether-soluble, acetone-soluble, and acetone-insoluble fractions were resinlike substances with 80 to 89% carbon and 8 to 10% hydrogen. Indeed, this and later work (Vahrman, 1970) led to the concept that coal is a two-component or two-phase system (Derbyshire et al., 1991 Yun et al., 1991). 

In summary, the results from this and other studies (30, 31, 32) unambiguously demonstrate that simple solvent extraction of coal liquids does not yield chemically well-defined fractions. Consequently, detailed molecular analysis is a prerequisite for an in-depth analysis/prediction of the production and/or upgrading of coal liquids and for the correct evaluation of process effectiveness. In addition, implementation of routine process control/monitoring schemes employing fractions obtained from separation of products/reactants necessarily requires calibration by detailed molecular analysis. Finally, the separation method(s) should produce fractions possessing chemical significance. 

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