Changes in the surface area of a Wyoming sub-bituminous coal with progressive extraction have been investigated. Surface areas were determined from CO, adsorption isotherms at 196 K using the BET equation with 9.234 nm2 for the molecular cross-sectional area of the CO, molecule at 196 K. Surface areas of the extracted coal varied with extraction time, yield and with the nature of the solvent. A maximum surface area of 265 m2/g was obtained from a four-hour treatment using tetralin at 350ยฐC as the solvent. The raw coal had a surface area of 99 m*/g.
Processes to utilize coal as a practical fuel are generally based upon gasification, extraction, or hydrogenation. These processes have in common that they are rate processes and the magnitudes of the rates are related directly to the surface area of the solid provided transport processes acting within the porous structure can bring reactant in and products out with small concentration gradients. Coal, as mined, is a relatively porous material having a large internal surface area and consequently small pores.
The relatively high internal surface area of original coal should be preserved during processing to permit high rates of reactions or extractions. Accordingly, internal structure and area should be measured during processing to determine if the high surface area is being utilized and preserved. If not, the processing variables should be modified to do this whenever possible.
The extent of solvent interaction with the porous structure of a Wyodak, Roland seam, sub-bituminous coal has been studied in this paper. The changes in the internal structure of this coal are followed by measuring the surface areas of the raw coal and coal subsequent to extraction, using the well known Brunauer-Emmett-Teller method'. * Detailed design and experimental results are presented in reference 3