Page 115 - Gas Adsorption Equilibria

2. Volumetry / Manometry 101

Figure 2.10. Sensor gas calorimeter (SGC) for simultaneous measurements of adsorption
isotherms and enthalpies. © IFT, University of Siegen, 2003.
E-mail: zimmermann@ift.maschinenbau.uni-siegen.de

The instrument is complemented by a gas reservoir and several solenoid
valves for the dozing of the gases coming from the gas reservoirs in order to
adjust the sorptive gas pressure (p) inside the adsorption vessel. The capillary
(3) connecting the adsorption vessel with valves and the sorptive gas reservoir
outside the thermostat has to be chosen carefully: diameter and length should
be such that the sorptive gas coming from the reservoir assumes the
temperature of the thermostat (T*), but also evacuation of the adsorption
vessel, which for example is necessary for activation processes of the sorbent
material, does not take too long or even becomes practically impossible.

Auxiliary equipment like vacuum system, thermostat, a data acquisition
system including a PC and safety installations also have to be provided.
Depending on the specific surface and the density of the material used for
examination an amount between 0.5 g and 2g has to be filled into the
adsorption vessel. At the beginning of an experiment the sample material is
activated by simultaneous evacuation and heating up of the adsorption vessel
outside the thermostat. For activated carbon sorbent materials temperatures
about (100°C - 150°C) are recommended. For zeolite sorbent materials often
activation temperatures about (400°C) and even higher may be needed.