Effect of temperature and solvent on coal extraction under mild conditions

Abstract

A western Kentucky coal was extracted with a series of eighteen organic solvents of varying base strength under mild temperature and pressure conditions. Solvents ranged from strongly basic, such as ethylenediamine to nonpolar nonbasic solvents, such as benzene. The relationships between the coal dissolution and the solvent properties show that extractability seems related more to solvent basicity (represented by its electron donor number) than to its acidity (acceptor number). Ethylenediamine was found to be a superior solvent for extracting coals under mild conditions. The coal extraction processes performed at different temperatures, for coal samples of different rank in ethylenediamine and N-methyl-2-pyrrolidinone have produced some interesting results: (1) up to ca. 80 wt.% of a western Kentucky coal could be extracted with ethylenediamine at 225°C within 1 h; (2) significant incorporation of (ca. 10%) strongly basic solvent molecules into the structural network of coal derived materials was observed for extraction over a temperature range of ca. 150°C to 300°C; and (3) the difference between coal extractability and extract yield varies depending upon the extracting temperature and the basicity of the solvent used.