Multisolvent Successive Extractive Refining of Coal

Abstract

Abstract A selected group of commercial solvents, namely, anthracene oil (AO), ethylenediamine (EDA), and liquid paraffin (LP), were used for successive extraction of Assam coal. Hot AO provided a wide range of mixed solvents that dissociate chemically and interact favorably with dissociated and undissociated coal macro-molecules (“like dissolves like”). This resulted to the enhancement of the EDA extractability of the AO-pretreated residual coal. EDA is a good swelling solvent and results in physical dissociation of coal molecules. The residual coal obtained after EDA extraction was subjected to extraction with LP, an H-donor, high-boiling (330°-360°C) solvent. LP thermally dissociates coal macromolecules and interacts with the coal at its plastic stage at the free radical pockets. The mechanism and molecular dynamics of the multisolvent successive extraction of Assam coal using AO-EDA-LP solvents are discussed. In early attempts, successive extractions did not modify the extraction yield in the single solvent showing the maximum extraction. However, the AO-EDA-LP extraction resulted in the extraction of 70% coal, more than for any of the individual solvents used. Therefore, AO-EDA-LP extraction of coal affords a process yielding a superclean, high-heating value fuel from coal under milder conditions. Several uses of superclean coal have been recommended. Present studies have revealed a new concept concerning the structure of coal having 30% polyaromatic condensed entangled rings and 70% triaromatic-heterocyclic-naphthenic-aliphatic structure. The insolubility of coal is due to the polyfunctional-hetero-cyclic-condensed structure having a polyaromatic core with intermacromolecular entanglements.