Physical changes in the pore structure of coal with chemical processing

Abstract

The physical structure of Roland Seam coal was characterized by studying the surface areas, pore volumes, and pore distributions of raw coal, extracted coals, and reacted coals. BET surface areas were measured by carbon dioxide adsorption at 195/sup 0/K and nitrogen adsorption at 77/sup 0/K. Pore volumes were calculated by the difference in the reciprocals of measured apparent and actual densities. Distribution curves were generated by measuring mercury penetration as a function of pressure. The data gathered suggests a micropore structure having a 34 A average diameter and random constrictions of the order of 4 A. Extraction generates new micropores and degrades the micropore structure. Changes in the pore distribution and the generation of new pores indicate that resistance to extraction due to the pore structure is minimal, while pore-volume data confirm the preferential liquefaction of lower-molecular-weight material. Increases in surface roughness due to pretreatment of the coal indicate a higher selectivity of solvents after hydrogenation of the coal. A study of the BET constant implies that the surface becomes more favorable to carbon dioxide adsorption with increasing extraction.