Page 149 - Gas Adsorption Equilibria

3. Gravimetry 135

has to be checked at very high balance loads and / or high sorptive gas
densities which may change the magnetic field providing coupling between
the inner and the external part of the suspension balance.
What has already been said at the end of Sect. 2.1.3 is also valid here: To
obtain accurate values of the Gibbs excess mass, it is essential to know
system’s parameters and the sorptive gas density fairly
accurately which means inequalities and
to hold. Also relative uncertainties of forces should be
less than With these accuracies one normally can expect
relative uncertainties of Gibbs excess masses cp.
examples given in the next section.

2.3 Examples

Gravimetric measurements of pure gas adsorption equilibria on porous
solids are normally performed for either of two purposes:

a) at low pressures and temperatures to get information on the
porous structure of the material, i. e. to “characterize” it, or
b) at higher pressures and temperatures to
determine the sorption capacity (and kinetic properties) of the material for
industrial adsorption processes like air separation, natural gas purification
etc.

In this section we will present several examples of gravimetrically
measured gas adsorption data serving mainly purpose (b) without excluding
(a):

1. Adsorption of CO, on activated carbon NORIT R1 EXTRA
at 298 K for pressures (p < 6 MPa);

2. Adsorption of on zeolite Köstrolith SX6 at 293 K, 313 K, 333 K for
pressures (p < 0.15 MPa);

3. Adsorption of and on zeolite Köstrolith SX6 with small amounts of
water permanently presorbed at 313 K for pressures (p < 0.12 MPa);
Adsorption of on zeolite Nal3X with presorbed water;