Page 31 - Gas Adsorption Equilibria

Chapter 1

BASIC CONCEPTS

Abstract The basic concepts of adsorption phenomena of gases on the surface of solid materials
are presented and discussed in brief. Different types of adsorption processes are
characterized by their molecular mechanism and energy of adsorption or desorption
respectively. Technically important classes of sorbent materials are mentioned and
characterized. The concepts of mass and volume of an adsorbed phase are illustrated
with regard to the experimental techniques available today for investigation.
List of Symbols. References.

1. INTRODUCTION

In this chapter we will discuss some of the basic concepts which are used
to describe adsorption phenomena of pure and mixed gases on the surface of
solids. We here prefer a physical point of view, restricted to physisorption
phenomena where adsorbed molecules (admolecules) always are preserved
and are not subject to chemical reactions or catalysis. Also, we always have
industrial applications of physisorption processes in mind, i. e. we prefer
simple and phenomenological concepts based on macroscopic experiments
often being embedded within the framework of thermodynamics. That is, we
prefer to take only those aspects of the molecular situation of an adsorption
system into account which have been or at least can be proved experimentally
and are not subject to mere speculation.

Adsorption phenomena can be due to several different molecular
mechanisms. These are described and characterized in brief by their
respective enthalpies in Sect. 2. Several classes of sorbent materials used for
different industrial purposes such as separation of gas mixtures, recovery of
volatile solvents or energetic purposes like adsorption-based air conditioning
systems, are presented in Sect. 3. This section is complemented by an
overview of most often used methods to characterize porous sorbent materials
given in Sect. 4. The basic concepts of mass and – to a lesser extent – volume
of a sorbed phase are discussed in Sect. 5. In Sect. 6 a short overview of the