Characterization of porosity via secondary reactions: Quarterly technical progress report, 1 October 1994--31 December 1994

Specific surface area, as well as its accessibility to gaseous reactants, are of paramount importance for all heterogeneous interactions occurring at coal char surfaces. Accessibility of this surface area is governed by the pore structure morphology of the char; i.e., pore size distribution, tortuosity, intersections, shape, etc. The porosity morphology of coal chars varies over a considerable range and is determined by a large number of factors including the nature of the porosity of the precursor material prior to carbonization, the carbonization process, and extent and method of any subsequent activation or gasification. A persistent problem in this area has been the reliable, quantitative measurement and characterization of the resultant porosity, especially the micropores. The following was accomplished during the reporting period: use of the random pore model as a method of rationalizing the data obtained from CO and CO{sub 2} TPD spectra has been initiated; and {alpha}-plot data obtained for Wyodak coal char samples prepared at various degrees of burn-off, ranging from 0--75% burn-off, in 0.1 MPa oxygen at 470 C, were used to compare with random pore model predictions. Conclusions derived from this analysis include: the random pore model predictions are consistent with the evolution of sample surface area and porosity with burn-off as determined for the Wyodak coal char samples; and the parameters obtained from the random pore model provide a reasonably good comparison with the {alpha}-plot data