Microporous activated carbons are energetically heterogeneous in nature. Heterogeneity may be either due to variation in pore size or due to the presence of heteroatoms on the surface of the carbon. The study of microporosity of carbon is of vital importance because it could limit the commercial application of this adsorbent. Activated carbons play an important role in gas separation and removal of toxic chemicals present in air and water. The common way of characterisation of active carbon is by using adsorption method. The surface energy of carbon often determines its acid/base properties and its interaction with adsorptives in general and polar moieties in particular. This paper describes the use of inverse gas chromatographic technique for characterisation of carbon in respect of surface energy parameters. The activated carbon of varying microporosity were prepared in the lab by controlling operating parameters like residence time, flow rate of activating agents, etc., in CO_2 atmosphere for this purpose. The stainless steel column of 1/8" I.D., 6" length were prepared using carbon granules as stationary phase. Series of alkanes have been used as probe material. The retention times of these probes were measured at infinite dilution. The column temperature was varied from 30 deg C to 350 deg C. In this study, the isosteric heat of adsorption of various microporous carbon samples was evaluated from retention data. Significant enhancement in the isosteric heat of adsorption has been observed with increase of microporosity. Molecular sieving properties have also been studied by measuring retention time of branched alkanes.
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