Volumetric-gravimetric measurements

In practice combined volumetric-gravimetric measurements have been fairly successful [0.31]. Also densimetric-volumetric and densimetric gravimetric measurements using magnetic suspension balances (2 positions and 3 positions types respectively) can be recommended. If swelling sorbent materials are considered (slow) oscillometric measurements are recommended. Chap. 5. In case of multicomponent sorption systems (N > 2) a gas analyzing system has to be used in any case. 

Figure 4.1. Experimental setup of a multipurpose instrument for coadsorption measurements of multicomponent gas mixtures on porous solids. The instrument allows volumetrie-chromatographic, gravimetric-chromatographic and also combined volumetric-gravimetric measurements for binary coadsorption equUihria.

One may argue that combined volumetric - gravimetric measurements of pure gas adsorption equilibria could provide a means to measure the mass adsorbed (m ) and the void volume of the sorbent and the sorbate phase (V ) simultaneously. Unfortunately this does not hold true. Instead, specializing equations (4.1. 6) to the case of pure gases (mi—>m, m2 = 0) and combining them one gets... 

In this section we want to present data for binary coadsorption equilibria of gas mixtures on activated carbon (NORIT R 1) which have been taken by combined volumetric-gravimetric measurements. We start with a set of data which have been measured with the instrument depicted in Figs. 4.1,4.2. Then we describe in brief a new type of volumetric-gravimetric instrument including a magnetic suspension balance allowing also measurements with corrosive sorptive gases. Equilibria as well as kinetic data taken at this instrument will be presented. Finally we hint at a commerciahzed version of this instrument offered by BEE - Japan company. 

Figure 4.4. Schematic diagram of an installation for volumetric-gravimetric measurements of binary coadsorption equilibria without using a gas chromatograph. The installation includes a magnetic suspension balance (RUBOTHERM, Bochum, Germany) allowing also measurements with corrosive gases in a large range of temperature (T < 1500 K) and pressure (p < 100 MPa).

Figure 4.6 b. Coadsorption equilibria of a binary gas mixture CH4 / N2 with ycH4 = 9 % on AC Norit R 1 at 298 K. Data were taken by volumetric - gravimetric measurements [4.4],... 

This is due to the fact that the basic data of volumetric-gravimetric measurements, i. e. the suspension balance recording ( 1) and the sorptive gas pressure (p) at least can be taken every second to give via equations (4.1 - 4.4) and an efficient data acquisition and handling system the number of moles of both components being adsorbed as a sequence of time. 

Instrument for automated combined volumetric-gravimetric measurements of binary coadsorption equilibria of gas mixtures with non-isometric components. The RUBOTHERM magnetic suspension balance is on the left side. The large white closet includes the volumetric / manometiic part of the instrument and is manufactured by BEL-Japan, Osaka. (Reprint by permission of BEL-Japan.)... 

VGMs volumetric-gravimetric measurements (of adsorphon equilibria)... 

It should be emphasized that in principle impedance measurements also can be added to other experimental methods aiming at an analysis of gas sorption systems. Examples for these are volumetric-gravimetric measurements. Chap. 4, oscillometric measurements. Chap. 5, or ZLC-... 

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