2004: the Effects of Activated Carbon Physical and Chemical Characteristics on the Adsorption Energy and Affinity Coefficient of Dubinin-raushkevich Equation

Where V is the adsorbed gas volume at relative pressure of P/P0; V0 maximum volume of adsorbed gas in micropores; R the universal gas constant (0.0083144 kJ/K mol); T the analysis temperature (K); and E is the adsorption energy (kJ/mol). From the linearized plot of DR equation, V0 and E are calculated. By using a conversion factor the equivalent liquid volume or micropore volume can be calculated from V0. Often E is expressed as βE0. β is a constant known as similarity or affinity coefficient, and E0 is the adsorption energy of a reference vapor (usually benzene). β is an important parameter that is used in pore size distribution or average pore width calculations [e.g., 1-4]. Several correlations have been proposed to predict the value of β based on the physical properties of adsorbate and reference vapor [5]. This includes ratios of molecular polarizabilities or liquid molar volumes for adsorbate with respect to the reference vapor. All of the proposed correlations are independent of the adsorbent surface chemistry. This is based on the original assumption of Dubinin equation that: (1) adsorption forces are due to dispersion interactions (non-specific or non-polar interactions); and (2) the adsorbent surface behaves similarly for both adsorbate and reference vapors. Therefore, the effect of adsorbent surface on β (i.e., E/E0) is canceled out.