Page 95 - Gas Adsorption Equilibria

2. Volumetry / Manometry 81

As we here are mainly interested in adsorption measurement techniques
for industrial purposes, i. e. at elevated pressures (and temperatures), we
restrict this chapter to volumetric instruments which on principle can do this
for pure sorptive gases (N = 1), Sect. 2. Thermovolumetric measurements, i.
e. volumetric/manometric measurements at high temperatures (300 K - 700 K)
are considered in Sect. 3. In Section 4 volumetric-chromatographic
measurements for multi-component gases (N>1), are considered as mixture
gas adsorption is becoming more and more important for a growing number
of industrial gas separation processes. In Section 5 we discuss combined
volumetric-calorimetric measurements performed in a gas sensor calorimeter
(GSC). Finally pros and cons of volumetry/manometry will be discussed in
Sect. 6, and a list of symbols, Sect. 7, and references will be given at the end
of the chapter.

2. VOLUMETRIC MEASUREMENT OF PURE GAS
ADSORPTION EQUILIBRIA (N = 1)

2.1 Experimental

An instrument for volumetric measurements of pure gas adsorption
basically consists of a gas storage vessel (volume and an adsorption
chamber being connected by a tube bearing a valve. Both vessels
should completely be placed within a thermostat (water, oil, air etc.) and
provided with tubes for gas supply and evacuation as well as with
thermometers and manometers to measure the temperature (T) and pressure
(p) inside the vessels, cp. Figure 2.1.

For pressures above ambient all vessels and tubes should be manufactured
of stainless steel, inside surfaces should be electropolished or, preferably
gilded. For pressures below ambient, i. e. vacuum systems glass should be
preferred. Sealing materials should be chosen according to the sorptive gases
to be used and the ranges of temperature and pressure of operation. For
corrosive gases and high pressures the use of metallic sealings (silver, steel)
always is recommended. The adsorption chamber includes a sample of
sorbent material of mass which prior to measurement should have been
“activated” at higher temperature and in vacuum for several hours to reduce
the amount of pre-adsorbed molecules. Standard procedures for activation
have been described in [2.2, 2.5 – 2.7].