Characterization of porosity via secondary reactions. Quarterly technical progress report, 15 June 1992--30 September 1992

Abstract

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. For example, electron microscopy tends to be qualitative; small angle X-ray or small angle neutron scattering (SAXS/SANS) can suffer from sensitivity to interpretive models, and the inability to distinguish porosity that communicates with the surface from that which does not; and gas adsorption techniques also have several well known drawbacks. The latter, however, are perhaps the most reliable in general, but yield pore size distributions indirectly via surface area and pore volume measurements, and can also be laborious and time-consuming. Therefore, there is still a critical need for practical and fade techniques to characterize the porosity of coal chars.