ROLE OF MICROPOROUS SURFACE-AREA IN UNCATALYZED CARBON GASIFICATION

The gasification in oxygen and carbon dioxide of two high-surface-area synthetic carbons was studied in order to investigate the role of microporous surface area in uncatalyzed carbon gasification. The identification of the appropriate total surface area for carbon gasification is critical to the calculation of meaningful intrinsic reactivities and is the logical starting point in the quest for an improved fundamental understanding of the factors that determine carbon gasification reactivity. Two microporous chars having markedly different macropore volumes were selected for study. Low-temperature gasification reactivities vapor adsorption isotherms, and adsorption equilibration times were measured for the chars at various stages of conversion, and individual surface features of char particles were examined as a function of conversion by a captive-particle SEM technique. Gasification of the highly macroporous Spherocarb carbon is believed to be strictly intrinsic between 400 and 600-degrees-C, with complete reactant penetration into microporous regions lying between larger pores. There is evidence that the rate of gasification of the nonmacroporous sucrose char, on the other hand, was limited by slow microporous diffusion causing incomplete penetration of carbon dioxide into the micropores. The severity of microporous diffusion limitations during the gasification of most carbons should lie between that observed for the highly macroporous Spherocarb carbon, with its highly accessible microporous area, and the essentially nonmacroporous sucrose char with its less accessible microporous area.