Page 21 - Gas Adsorption Equilibria

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As new materials with tailored micro- and nanostructures are developed and
synthesized in an increasing number of laboratories around the world, it is to
be expected that adsorption as a separation technology for gaseous (and
liquid) mixtures will be of growing importance and impact to chemical,
biochemical and environmental technology as well as to other fields of
sciences (medicine, pharmacy) and engineering.

3. EXPERIMENTAL METHODS

Gas adsorption equilibria can be measured by several basically different
methods. In this section we are going to outline the classical ones, namely
volumetry/manometry and gravimetry as well as some newer ones,
oscillometry and impedance spectroscopy. Emphasis is given to the
underlying physical principles. Complementary remarks deal with
possibilities to measure binary coadsorption equilibria with and without gas
phase analysis. Technical details of all the measurement methods are given in
the subsequent chapters, Chaps. (2-6). Prior to considering the measurement
methods some general remarks on experimental work with gas adsorption
systems are in order.

Most important in all kinds of experiments is monitoring of the procedure
and of all data. A notebook, either paper based or electronic can be very
helpful in this respect. The record of the experiment should include

a) Name and place of the laboratory, the experimenter, date and
environmental data like temperature, pressure and humidity of
ambient air.
b) Detailed description of the solid material (sorbent) used for
adsorption including manufacturer, chemical analysis, purity, form,
information on particle size, bulk density, helium atmosphere
density etc.
c) Activation or preparation procedure of the sorbent material prior to
adsorption of gases on it, i. e. degasification procedure, vacuum
treatment, heating and cooling procedure, sampling and storage
conditions, All sorbent materials may change their adsorption
properties over the years due to internal physico-chemical
processes, but also due to uptake of gases and vapors (humidity)
from the ambient air. This especially for carbon based sorbent
materials should be taken into account.