THE PORE STRUCTURE OF ACTIVATED CHARS OF BROWN-COAL HUMIC ACIDS OBTAINED AT INCREASED RATE OF CARBONIZATION

Brown coal humic acids, after pyrolysis at a heating rate of 600-degrees-C/min, have been activated in steam to different burn-offs. Carbonaceous adsorbents were obtained with well developed micro-, meso-, and macroporous structures, and nitrogen BET surface areas of about 1000-1500 m2/g. An increase in the heating rate during pyrolysis to 600-degrees-C/min (from the standard rate of 5-degrees-C/min) strongly enhances macropore development during subsequent activation, although micro- and mesopore volumes remain similar. The pore structure parameters of the activated chars based on the adsorption of nitrogen have been compared with those obtained from benzene and cyclohexane adsorption. The differences observed are less pronounced for benzene than for cyclohexane. The kind of nonporous carbonaceous standard employed, whether ungraphitized (Elftex 120) or graphitized (Spheron 6-2700), has little effect upon the results of calculations of the mesopore size distribution, but a marked effect on parameters derived from the as plot. For those chars that, in addition to their microporous system, were characterised by a significant contribution of mesoporosity, the values of V(m) (from the BET plot) are visibly lower than the respective values of V(B) (from the position of point B). An attempt was made to use the existence of these differences in calculations of the surface area of the mesopores.