Volumetric-densimetric measurement

Abstract Combined volumetric and gravimetric measurements allow one to determine the coadsorption equilibria of binary gas mixtures without sorptive gas analysis, i. e. without using a gas chromatograph or mass spectrometer. The experimental setup, a basic theory and several examples of this method are presented. Two modifications of it, namely densimetric - gravimetric and densimetric - volumetric measurements are outlined. These especially are suited to do quick but still accurate measurements of binary coadsorption equilibria for industrial process control and / or design. These methods also can be used to measure adsorption of gases and vapors on walls of vessels, tubes or surfaces of any other solid materials. List of symbols. References. 

Densimetric-volumetric measurements have been performed recently at our Institute determining again coadsorption equilibria of (CO2, CH4) on AC D47/3 at T = 293 K for pressures up to 1.4 MPa, cp. Sect. 3.4. Results are identical within experimental uncertainties with those received by densimetric-gravimetric measurements. Sect. 3.4. Hence discussion of this method can be postponed to Sect. 4 where all experimental methods outlined in this chapter will be evaluated from both the experimental and the theoretical point of view. 

Table 4.3. Comparison of experimental pros and cons of densimetric-gravimetric measurements (DGMs) and densimetric-volumetric measurements (DVMs) of binary gas adsorption equilibria without analyzing the sorptive phase.

DVMs densimetric-volumetric measurements (of binary coadsorption equilibria)... 

For binary coadsorption equilibria with non-isomeric gas components (Ml 7 M2) gravimetric-chromatographic measurements are not needed. Instead densimetric-volumetric measurements are recommended [6]. The measurement procedure can be grasped from the experimental scheme sketched in Figure 5 below. Basically, a gas expansion experiment is combined with a density measurement of the equilibrium sorptive gas mixture by the buoyancy of a sinker coupled to a magnetic suspension balance. 

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. 

In this chapter we will present experimental information (Sect. 2.1), the theory of measurement (Sect 2.2), and uncertainties (Sect 2.3), and several examples (Sect. 2.4) of this method. Two modified versions of the measurement procedure which may be called densimetric-gravimetric and densimetric-volumetric / manometric methods (which especially seems to be suited for online industrial coadsorption measurements) are also outlined (Sect. 3). These methods also may be used to measure adsorption of gases and / or vapors on surfaces of arbitrary sohd materials as for example the inner walls of vessels, tubes, valves etc. of the experimental device(s) used (Sect.3.6). Advantages and disadvantages of the methods proposed are discussed in Sect. 4. A list of symbols used is given in Sect. 5, followed by references to journal articles and books cited. 

Comparison of Densimetric-Gravimetric and Densimetric-Volumetric Binary Coadsorption Measurements... 

In this article a short overview is given of the measurement methods for adsorption equilibria of pure and mixed gases most often used today. After presenting the traditional volumetric and gravimenic method, modem combinations of it, namely the densimetric-volumetric and the densimetric-gravimetric method to measure binary coadsorption equilibria are presented in brief (Section 2). 

Figure 4.18. Instrument for volumetric-densimetric measurements of binary coadsorption equilibria of gas mixtures on porous solids without using a gas chromatograph. The sorptive gas prepared in the system is assumed to be a binary mixture with known initial molar concentrations ( y, y2 ) IFT University of Siegen, 2002.

Figure 4.20. Schematic diagram ofan instrument to measure wall adsorption by using the volumetric - densimetric method.

Finally we would like to mention that binary coadsorption equilibria of non-isomeric gas components also can be measured without gas phase analysis by volumetric-gravimetric or gravimetric-densimetric, i. e. combined weighing and density measurements. Both procedures can be realized in an installation similar to that shown in Figure 4. Details are given in [1, Chapts 3,4]. 

Keller J. U., lossifova N. and Zirnmermann W., Volumetric - Densimetric Measurements of the Adsorption Equilibria of Binary Gas Mixtures, Adsorption Science Technology, 23 (No. 9) (2005)... 

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