Towards an understanding of the coal structure: a review

Abstract

This review is limited to studies that directly refer to the following concepts: (i) macromolecular structure of coal; (ii) the contribution of relatively low molecular substances in the structure; (iii) factors effecting capabilities of solvents in coal extraction and the extraction mechanism; as well as (iv) intermolecular forces occurring in coal organic matter. Although concept (i) was introduced in the 1970s, no great progress has been achieved. Available data for a few coals indicate that mass distribution of the macromolecular part are in the 1300–3500 amu range. There are no experimental data available that could describe the structure of the macromolecular part of coal. Referring to item (ii), the presence of significant amount of various substances in the ∼100–500 amu range in coals was evidenced by mass spectrometry methods (field ionization mass spectrometry (FIMS) and matrix-assisted laser desorption/ionization–time-of-flight (MALDI–TOF)). As for item (iii), major contributors that influence solvent extraction capability is the electron-donicity of the solvent as well as the shape and size of its molecules. One major step of the mechanism of coal extraction is the substitution phenomenon. Presumably (in reference to item (iv)), all known intermolecular forces hold together coal organic matter. However, only hydrogen bonds can be directly detected, as yet.