Page 125 - Gas Adsorption Equilibria

2. Volumetry / Manometry 111

5. In situ activation procedures
Prior to adsorption experiments the sorbent sample should be activated
by heating the adsorption chamber to (say) 420 K for activated carbons,
670 K for zeolites, degassing etc. During this procedure the mass of
sorbent is changed by typically 1 % or more. This change normally can
not be included in volumetric experiments but must be taken into account
afterwards, at least approximately.

Volumetric / manometric adsorption experiments do not give information on
the kinetics of the process; they are not useful at extreme low or high
pressures as pressure measurements in these regions become difficult and
accurate EOS of the sorptive gases not always are available. Also there may
be problems with the thermostatization of the vessels as during expansion the
gas (normally) is cooled down due to the Joule-Thomson-effect and it will
take some time till heat transfer (and radiation) bring both sorbent and
sorptive gas to the same temperature again. This is especially important for
desorption experiments which will take even longer till thermal equilibrium is
reached [2.7, 2.20].

7. LIST OF SYMBOLS

A collection of most of symbols used in this Chapter including their SI-
units is given.

kg Gibbs excess mass of an adsorbed phase

kg mass of component i = 1 . . .N of a sorptive
gas mixture supplied to the storage vessel
prior to adsorption

kg mass of component i = 1...N being
adsorbed on a certain mass of sorbent

kg mass of component i = 1 . . .N of a sorptive
gas in an adsorption equilibrium state

kg Gibbs excess mass of component i of an
adsorbed phase