Network structure of coals and association behavior of coal-derived materials

The characteristics of two kinds of network structure models, i.e., covalen t and non-covalent network models, were given. The applicability of these n etwork models was examined mainly from the amount of solvent-soluble compon ents that originally existed in coal. More than 50% of extraction yields ob tained with carbon disulfide-N-methyl-2-pyrrolidinone (CS2-NMP) mixed solve nt with an additive for several bituminous coals suggest that the non-coval ent network model is better than the covalent one for those coals. But netw ork structures for other coals, which gave a low extraction yield such as l ignites, are not clear. Association behaviors of coal-derived materials are also reviewed from their solubility, molecular weight, viscosity, and vapo r pressure. Small-angle neutron scattering (SANS) measurements of coal extr acts in the solution show the formation of large associates. Interactions r esponsible for the association of coal-derived materials such as coal extra cts and liquefaction products are considered to be hydrogen bonds, pi-pi in teractions between aromatic rings, and electrostatic interactions. No clear evidence for the contribution of charge transfer interactions has been obt ained. (C) 2000 Elsevier Science B.V. All rights reserved.