Structure Change of Coals after Solvent Treatment

Abstract

It is known that polar solvents swell coal, break hydrogen-bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. In the efforts of maximizing a pretreatment concept on combustion efficiency and reduction of pollutant emissions, we characterize the extent of physical changes associated with the pretreatment including its surface area, pore volume and pore size distribution.

Beulah lignite and Illinois #6 bituminous coal are treated by a special solvent in a batch reactor at 70 to 130 ºC and 2000 to 8000 psi. Both N2-BET and CO2-DR methods are adopted in the characterization of raw and pretreated coals. N2 at 77 K in BET method cannot access the entire micropore structure, while CO2 at 298 K, however, has access to the entire micropore structure

After pretreatment and degassing prior to analysis, the surface area of as-received bituminous increased between 5 and 16% and that of as-received lignite increased by 16%; for dry bituminous, the surface area increased by 0.6% and for dry lignite it increased by 8%. Without degassing, the surface area of as-received bituminous increased between 8% and 27% and that of as-received lignite increased by 75%; for dry bituminous, the surface area increased by 3% while that of dry lignite decreased by 28%.

Keywords: coal pretreatment, surface area, pore volume