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4. Volumetric – Gravimetric Measurements 229

In DGMs, approach to equilibrium can be accelerated by using Jäntti’s
method [2.4, 4.21], cp. Sect. 4.1. In both DGMs and DVMs, Knudsen pressure
differences at low sorptive gas pressure may cause thermal gas flow which can
interfere with balance’s measurements. As a result from Tab. 4.3 it can be said
that DGMs are recommended if coadsorption data of high precision and
reliability are needed and if there is enough time for measurements available.
However, if only data of moderate or low accuracy are needed, money for
investment being scarce and time is pressing, DVMs may very well be
appropriate as they quickly can provide data sufficient for basic decisions in –
for example – designing an industrial adsorption process.

No commercial instruments for DGMs or DVMs are available today.

5. LIST OF SYMBOLS AND ABBREVIATIONS

A list of most symbols and abbreviations used in this Chapter is given.

A surface area of a sample material

internal surface of an adsorption chamber

internal surface of a gas storage vessel prior
to a wall adsorption experiment

internal surface of a gas storage vessel after
a wall adsorption experiment

DGMs densimetric-gravimetric measurements (of
binary coadsorption equilibria)

DVMs densimetric-volumetric measurements (of
binary coadsorption equilibria)

g/mol molar mass of component (i = 1, 2) of a
sorptive gas mixture

kg mass of an adsorbate on a certain mass
of sorbent