The adsorption of gases at low and moderate concentrations. Part I.—Deduction of the theoretical adsorption isostere and isotherm. Part II.—Experimental verification of the form of the theoretical isosteres and isotherms

Abstract

In a previous paper by the author it was pointed out that for small adsorptions the adsorption isotherm could be represented by the simple relation α = α 0 c where α is the amount absorbed and c is the equilibrium concentration out­side the adsorbent. The present paper embodies an attempt to evaluate α 0 in the case of gases, and to connect it theoretically with other physical properties. In addition an adsorption formula is developed which applies to gases up to moderate adsorptions, that is up to 30 per cent, of the saturation value. We will first examine the case of a gas at low concentrations. We will assume that upon the surface of the adsorbent there is a certain volume, determined, presumably, by the range of molecular action, which is occupied by the adsorbate. Then, for the change of energy involved in the adsorption at constant temperature of 1 grm. molecule of the gas by an infinite amount of adsorbent we can write down three expressions. The first of these is that obtained from thermodynamical reasoning by the author, and we write the change of energy as E = V { T (∂ p /∂ T ) α - p } = RT 2 ∂ p /p∂ T - RT = RT 2 (∂ log c /∂ T ) α , where p V = RT and p = c RT.