Oil shale kerogen-derived adsorbents and their application to trichloroethylene adsorption from aqueous solutions

This paper examines microporous oil shale kerogen-derived semicokes as potential sorbents for environmental cleanup applications. This carbonaceous residue ("semicoke") left behind during the processing of oil shale kerogen is the main source of adsorptive potential in the processed oil shale. The surface area and porosity of model microporous semicokes were determined using N2 and CO2 adsorption techniques. The model semicoke material had a BET surface area of 494 m2/g of char (net of the minerals), which could be increased by mild thermal activation in the air at 698 K (425 degrees C) to 857 m2/g-char. The semicokes were tested as potential sorbents by measuring their efficacy at removing trichloroethylene (TCE) from aqueous solutions at 295 K in the con-centration range from about 0.1 to 7 mg/L. TCE adsorption isotherms were determined for seven different sorbents - the model semicoke, the air-activated model semicoke, raw unprocessed oil shale, three commercially prepared semicokes, and, for reference, a commercial granulated activated carbon. The present results show that the kerogen-derived carbons have TCE adsorptive capacity values which are comparable to those of a commercial activated carbon (e.g., 70 mg/g-C). The results pointed to the importance of a particular micropore size range for adsorption. While air activation increased the pore volume and surface area of the materials as measured by nitrogen and carbon dioxide, this did not result in an increase in adsorptive capacity for TCE. The critical pore size appears to be in the range of 0.5-0.8 nm.