文档介绍：THERMODYNAMICS
Thermodynamics of Adsorption
in Porous Materials
A. L. Myers
Dept. of Chemical Engineering, University of Pennsylvania, Philadelphia, PA 19104
Thermodynamic equations are de®eloped for adsorption of ponent gas mix-
tures in microporous adsorbents based on the principles of solution thermodynamics.
The con®entional spreading pressure and surface area ®ariables, which describe 2-D
films, must be abandoned for adsorption in micropores, in which spreading pressure
cannot be measured experimentally or calculated from intermolecular forces. Adsorp-
tion is di®ided into two steps:() 1 pression of the gas, () 2 isothermal
immersion of clean adsorbent in pressed gas. Thermodynamic functions( Gibbs
free energy, enthalpy, and entropy) from solution thermodynamics pro®ide plete
thermodynamic description of the system. Applications are described for characteriza-
tion of adsorbents, gas storage at high pressure, mixture adsorption, enthalpy balances,
molecular simulation, adsorption calorimetry, and shape selecti®ity in catalysis.
Introduction
Brief history of adsorption thermodynamics
The concept of surface excess in adsorption was intro- ing, because the evolution of a heat of adsorption requires a
duced by J. Willard Gibbs, but the interpretation and appli- change in loading. The existence of other heats of adsorption
y
cation of the Gibbsian version of thermodynamics of surfaces such as the ‘‘differential heat of adsorption’’ equal to Žqst
was impeded by the abstruse nature of his writingŽ Gibbs, RT ., the ‘‘equilibrium heat of adsorption’’ obtained by per-
1928. . The thermodynamics textbook by Lewis and Randall forming the differentiation in Eq. 1 at constant spreading
exerted an enormous influence upon the development pressure, and othersŽ. Valenzuela and Myers, 1989 adds to
of thermodynamics in the first half of the 20th century. How- the confusion. Agreement within the munity
ever, their short section on t