Page 280 - Gas Adsorption Equilibria

266 Chapter 5

In what follows we first will briefly describe the experimental device,
Sect. 4.2, then the basic equations are given from which the mass of gas
sorbed in a sorbent of mass and the volume of the sorbent/sorbate
system can be calculated, Sect. 4.3. In Sect. 4.4 we present as an example data
(p, T, for sorbed in polymethylmethacrylate (PMMA) (Makrolon
2400) at 308 K for pressures up to 6 MPa, [5.27].

4.2 Experimental

Figure 5.13 shows a schematic diagram of an installation designed for
oscillometric-manometric measurements of gas solubilities in swelling
materials [5.27]. The instrument consists of a rotational pendulum
complemented by a gas storage vessel and – for measurement of cosorption
equilibria with gas mixtures – a gas chromatograph. In addition a system for
gas supply and evacuation of the apparatus as well as thermometers,
manometers, a gas circulation pump and thermostats are needed. These
elements are connected by proper tubing and valves as indicated in the figure.
Stainless steel of high quality including electropolishing of all inner surfaces
to reduce and stabilize wall adsorption is highly recommended. More details
of the instrument and especially of the pendulum are given in [5.2, 5.7, 5.27].

Figure 5.14 shows a photo of a training instrument designed, built, and
operated at IFT, University of Siegen, during 1999-2001. The pendulum (left)
is covered by a plexiglass vessel allowing observation of the rotational
oscillations of the pendulum. It is coupled not only to a gas storage vessel but
also to a microbalance (center) and an impedance analyzer (right), cp. Chap.
6, to perform various kinds of combined measurements. This simple
instrument allowed also to measure gas adsorption in nearly rigid non-
swelling porous materials like zeolite or activated carbon. Results of test
measurements were identical within experimental uncertainties with those
gained by traditional manometric or gravimetric measurements.