Page 106 - Gas Adsorption Equilibria

92 Chapter 2

4.2 Theory

Let us assume a certain amount of gas mixture with known mass
concentrations and molar concentrations is in the storage
vessel of the instrument, Fig. 2.6. The adsorption chamber
including the sorbent mass has been evacuated. Upon opening the valve
connecting both vessels, adsorption occurs. Recirculating the gas in the
system will enhance equilibrium between the gas and the sorbate phase. If this
is attained, a gas sample may be taken to determine its molar concentrations
, i = 1...N). From this information the masses of components i =
1...N of the adsorbate can be determined as follows: First we note the mass
balances of all components

Here is the mass of component i of the sorptive gas filled to the storage
vessel It can be calculated from the relation

with the total number of mols of the gas originally supplied being given
by the thermal equation of state (EOS)

Here

is the compressibility or real gas factor of the gas mixture. Its numerical value
can be calculated from an analytical EOS, [2.9-2.25] measured values from
pressure and Temperature (T) and known molar concentrations
of the gas.

Similarly to (2.21-2.23) we have for the mass of component i in the
sorptive gas