Page 23 - Gas Adsorption Equilibria

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In Chap. 4 a combination of both the volumetric/manometric and the
gravimetric method is discussed. For pure gas adsorption systems it does not
lead to new information but only is resulting in a consistency relation of the
volumetric and the gravimetric data. However, for binary mixtures with non-
isomeric components it does allow one to determine coadsorption equilibria
without analyzing the sorptive gas phase, i. e. without using either a gas
chromatograph or a mass spectrometer. Similar measurement methods result
in combining direct gas density measurements using buoyancy effects of
sample masses, with either volumetric or gravimetric (or calorimetric)
measurements. These methods, namely the densimetric-volumetric or the
densimetric-gravimetric method, are discussed in brief in Chap. 4, Sect. 3.5.

In Chap. 5 measurements of gas adsorption by slow rotational oscillations
of the sorbent material are discussed. This method uses the inertia of mass to
detect changes caused by gas adsorption. Combined with gravimetric or
volumetric measurements it allows the measurement of gas solubilities in
non-rigid, i. e. swelling sorbent materials as for example polymers.

The dielectric properties of a sorbent material are changed upon gas
adsorption. This effect can be used to indirectly determine masses adsorbed
by monitoring the (frequency dependent) dielectric permittivity of the sorbent
material. After combining these data with either volumetrically or
gravimetrically determined calibration data, the mass of the adsorbed gas can
be measured at other pressures and temperatures of the gas by dielectric
measurements only. Measurements of this type are very useful in industrial
applications. For example an increasing content of carbon monoxide in an
activated carbon adsorption reactor indicating local heating effects, can be
detected immediately and thus help to avoid overheating and even burning.

Adsorption isotherms, i. e. the thermal equations of state of the masses
adsorbed are discussed in Chap. 7 for pure and mixture gas adsorption
systems as well. This information should allow the reader to choose the
isotherm for his data correlation problem properly and also to extend the
range of adsorption data known of the system by cautious extrapolation.

As mentioned above multicomponent gas adsorption equilibria can be
measured by

a) a method allowing one to measure the total mass adsorbed like volumetry
or gravimetry, and to analyze the gas phase to determine the masses of
components adsorbed via the mass balance related to this component, or