Solvent Swelling of Coal

Solvent swelling of coal occurs when the phyacal dimensions of coal increase due to the presence of a solvent. Coal swelling occurs with changes to otha- coal properties, such as coal extraction yield or coal 

The overall implications of coal selling experiments suggest that the dissociation of the non-covalent bonds in coal is crucially important during coal swelling in solvents (Chen et al., 2011). The amount of coal swelling was measured by the swelling ratio, represented by the symbol, Q  

Q = (volume of swollen coal)/(volume of original coal) 

The rate at which coals swell is dictated by the rate at which the solvent diffuses into the coal. This is controlled by solvent properties, the size of the coal particles, and the average molecular weight between the cross-links of the coal matrix (Olivares and Peppas, 1992). Coal is a glassy solid at room temperature, but transitions to a flexible state as it absorbs solvent and the flexible nature of the swollen coal suggested lower effective cross-link density, and suggested that the elasticity of the solvent swollen coal may be predominantly rubber-like. The transition from the glassy to rubbery state is generally very sharp (Olivares and Peppas, 1992). 

Generally, with careful attention to coal history, solvent history, and solvent properties, the solvent extraction of coal may be a useful technique for application to coal science. Studies of the extraction process itself and the related solvent swelling can provide insights into coal matrix structure only with careful, well thought out, and reproducible analyses. The data may also provide detailed and valuable information about the chemical species present in both extract and raw coal. 

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