Page 277 - Gas Adsorption Equilibria

5. Oscillometry 263

These relations allow one to calculate from the experimental
quantities known parameters sorbent mass sorptive
gas density and sorbent and instrument related gas boundary layer mass
Actually, this later quantity can be determined from measurements
with non-sorbing pellets from equation (5.64) or measurements using
non-swelling sorbents from equation (5.65).

Calculations of uncertainties of are straightforward starting
from eqs. (5.64, 5.65). Numerical examples have shown that accurate
measurements at the pendulum, cp. eq. (5.39), are most important to get small
dispersions of and the relative values of these quantities
being normally between 1 % and 5 %, [5.16], [5.17].

3.4 Example

The solubility of carbon dioxide in a special polycarbonate (PC)
(Goodfellow, UK) has been investigated experimentally by oscillometric-
gravimetric measurements at T = 293 K for pressures up to 6 MPa, [5.7, 5.8].

In Table 5.3 some thermophysical properties of the PC are listed together
with the respective data of polymethylmethacrylate (PMMA) (Makrolon
2400) which will be discussed later in Sect. 4.4, [5.19, 5.28, 5.29]. The table
is followed by a sketch of the chemical structure of the basic elements of the
PC and PMMA.

In Figure 5.12 results of measurements are presented. The oscillometric data
show a monotonic increase with the gas pressure (p), while the
gravimetric data are strongly curved, clearly indicating the influence of
buoyancy. At pressures above 5 MPa the microbalance reading becomes even
negative, i. e. the effect of buoyancy becomes larger than the increase in mass
due to absorption of