Liquefaction, Carbonization, and Modification of Low Rank Coals

Abstract

Susceptibility of low rank coals to the extractive liquefaction, the extent of which was defined by the conversion of the coal into quinoline-soluble matter, was studied using a series of non-hydrogenative solvents at 370°C under atmospheric nitrogen in order to find the effective solvent and pretreatment to enhance their susceptibility to the economical process. The carbonization properties of the coals were also studied because the liquefaction and carbonization have common bases. Ashland A 240 petroleum pitch was found to be much superior to pyrene for the liquefaction of slightly fusible West-Kentucky(WK) No.14 which contained considerable sulfur and ashes, although both solvents were non-solvolytic.
Pretreatment of leaching in distilled water for 400 days, reffuxing with boiling water for 30 h, and washing with dilute mineral acid for 30 h were found to diminish significantly the sulfur and ash contents, markedly increasing the fluidity of the coal measured by Gieseler plastometry. Its fluidity was further enhanced by the presence of proper additive. Such pretreatment brought about a high liquefaction yield of the coal with pyrene over 90%, and improved remarkably its carbonization properties, which were defined by the free swelling index and the extent of anisotropic development, in the cocarbonization with the additive (10-20% addition). Fourier-transform infrared spectra revealed some notable changes in the absorption bands which may be ascribed to the phenoxyl or hydrogen-bonded carbonyl groups. Such changes may indicate the certain extent of depolymerization of coal molecules or removal of metal ions from the oxygen-containing groups. The mechanism and economy of slightly fusible coals in the liquefaction and carbonization are discussed from the views of adequate selection of the pretreatment and the solvent.