Page 274 - Gas Adsorption Equilibria

260 Chapter 5

of sealing material (teflon, gylon, silver) turned out to be most important and
for a while has been a source of frustration.

Also it should be mentioned that by adding a gas chromatograph or a mass
spectrometer to the instrument, Fig. 5.9, cosorption equilibria of gas mixtures
in swelling sorbents can be measured. The theory of measurements of this
type is based on the theory of oscillometric-gravimetric sorption
measurements of pure gases, Sect. 3.3. In addition concentrations of the
sorptive gas originally supplied to the system and those in sorption
equilibrium i=l…N) have to be taken into account.

Finally we would like to point out that by combined oscillometric-
gravimetric measurements of adsorption equilibria in rigid, i. e. non-swelling
materials the volume of the sorbent-sorbate system in the limit of
saturation can be determined. An example for this is given in Fig. 5.8
referring to the adsorption of on AC Norit R1 Extra at 293 K. Here
can be calculated by differentiating to the gas density, i. e. by the
slope of the straight line interpolating these data [5.7].

3.3 Theory

In this section we will provide the reader with the basic equations allowing
one to calculate from combined oscillometric and gravimetric measurements
both the mass of gas adsorbed or absorbed in a swelling sorbent material
of mass and its volume in the sorbate state at given pressure (p) and
temperature (T) of the sorptive gas and sorbent material. We start by
mentioning the result of oscillometric measurements, cp. Sect. 2.2, namely the
relation (5.25)

Here the (dimensionless) quantity is calculated from 3 oscillometric
experiments via equation (5.39). On the r.h.s. of (5.52) indicates the mass
of gas sorbed within the mass of sorbent is the mass of gas included
in the interstitial volume of gas between the sorbent pellets which also is
moved along with the pendulum, cp. Fig. 5.4, i. e. we have

with