ADSORPTION ON NONPOROUS SOLIDS

It is a well-known fact that the two-parameter BET equation gives too high adsorption values at x (or p/p0) > 0.35. The reason for this is the assumption that at x = 1 an infinite number of layers are adsorbed. Experimental data for nonporous adsorbents show that the number of adsorbed layers close to x = 1 is far from infinite; in fact, it is in the vicinity of 5 or 6. A modified BET equation is derived, employing a third parameter k, which is a measure of the attractive force field of the adsorbent. The equation is identical with one derived by Anderson in 1946, but the model on which it is based, the derivation, and the method of application are different. Examples of the application of the modified BET equation are presented, and certain conclusions are drawn about the BET parameters vm and c. © 1969.