A phenomenological adsorption equilibrium law extracted from experimental and theoretical considerations applied to the activated carbon + methanol pair

Different adsorption equilibrium laws have been developed, among them Dubinin's equations, which apply well to microporous solid adsorbents, but are limited for the low values of m and when saturation is approached. Another simple and phenomenological law is offered here, based only on the hypothesis that the adsorbed phase has the same specific heat as the bulk liquid phase, which yields: A = R · T · Ln(PsP) = A(m) + B(m) · T, whereA(m) + B(m) have physical meanings. The functions. A(m) and B(m) are extracted from the analysis of isosteres measured on the Activated Carbon + Methanol pair. The presented experimental set up permits isostere measurements through a wide range (0.1 <P < 70 kPa; − 10 <T < 130dgC; 7 <m < 322 g/kg) with good precision and faster than the measurement of isotherms. The experimental plots show that the Polanyi postulate is not fulfilled for the low values of m. But the expression A = A(m) + B(m) · T represents well every measured isostere in the whole range and the isosteric heat of adsorption with only seven coefficients. This expression could be applied to other pairs of solid microporous adsorbent + adsorbate, it is only necessary to measure eight equilibrium points (four values of m, two points for each). Moreover, this expression is very convenient to use in numerical calculations.