Page 203 - Gas Adsorption Equilibria

4. Volumetric – Gravimetric Measurements 189

Similarly one may proceed in order to get the absolute masses adsorbed
in this case using for instead of the helium approximation
(2.7) the model equation (2.9).

One may argue that combined volumetric – gravimetric measurements of
pure gas adsorption equilibria could provide a means to measure the mass
adsorbed and the void volume of the sorbent and the sorbate phase
simultaneously. Unfortunately this does not hold true. Instead, specializing
equations (4.1–4.6) to the case of pure gases and combining
them one gets

As all quantities in this relation either can directly be measured or are the
results of measurements, it provides a consistency condition for the volumetric
– gravimetric experiment performed, but does not allow one to determine
either or without introducing an additional hypothesis, cp. Eq. (2.7).

If the two sorptive gas components (1,2) are mixed with a carrier gas (0)
which is not adsorbed on the sorbent material considered, equations (4.15)
have to be modified. This situation may occur for example in purification
processes of air or natural gas including polar components which are strongly
adsorbed on zeolitic sorbent materials compared to non-polar components like
Then the basic equations (4.2 – 4.5) should be substituted
by

The mass of inert gas originally provided to the storage vessel of
the instrument, Fig. 4.1 can be calculated from the EOS of the gas mixture
with components (1, 2, 0) cp. Eq. (4.7),