Page 75 - Gas Adsorption Equilibria

1. Basic Concepts 61

sorbate and to determine the (sorptive gas dependent) void
volume of the sorbent by an optimization procedure:

Here should be chosen as bulk liquid density in a reference state (triple
state or liquid boiling state at ambient pressure) representing an approximate
value of the average sorbate density . The optimization function for this
model then reads in view of Eqs. (1.31), (1.43):

Here again T, are experimental data and
have to be determined from the minimization procedure.

To elucidate consequences of all four different model assumptions
for the volume of a porous sorbent/sorbate system, adsorption data
of nitrogen (5.0) on activated carbon (AC) Norit R1 Extra which have
been measured gravimetrically at 298 K, and the adsorbed masses calculated
from these data are shown in Figure 1.22, [1.50]. The lowest curve presents
the Note that these decrease at high gas densities as then seemingly
the increase in buoyancy of the sorbent/sorbate sample is larger than the
uptake of nitrogen gas, cp. Eq. (1.31). The other curves present data as
follows:

1) These are Gibbs excess masses calculated by using proposition
(P1), i. e.. using the helium volume approximation for (1.24) and
formula (1.27).

It should be noted that the numerical values of these data decrease at
high gas densities, i. e. for we have

* )
The model (1.43) easily can be generalized to multicomponent adsorption systems by

with i = 1, 2, 3,... being the mass adsorbed of component i and being the density
of pure component (i) in a reference liquid state [1.69].