Magnetic Sorption Balance

Figure 14.13 Principle of a magnetic sorption balance (left conventional apparatus right magnetic suspension balance).

The Rubotherm system provides gravimetric sorption measurements carried out in a closed measuring cell completely thermostated up to 700 K or down to 77 K without temperature differences or corrosive parts inside the whole measuring cell with pressures up to 100 MPa and a mass sensitivity down to 1 gg using a magnetic suspension balance to measure mass transfer under controlled environments (14). 

In our work, sorption by PA-6 of CO2 saturated with succinic anhydride (SA, around 5 wt% in CO2) and of both supercritical and subcritical CO2/IO mol% 1,4-dioxane mixtures saturated with SA was investigated in order to achieve a better idea of the amount of supercritical fluid absorbed in the amorphous region of the polymer. A magnetic suspension balance was used to determine the amount of fluid absorbed by the polymer. The mass increase of the polymer samples due to sorption of the fluid and the density of the fluid were simultaneously recorded. 

Both ionic liquids synthesised with be tested for their ability for CO2 absorption up to 100 bar, as descibed in details by Karadas et al. 9. Measurements were performed using the high-pressure magnetic suspension balance (MSB) sorption device by Rubotherm... 

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. 

As the pressure measurements in oscillometric-manometric experiments only are needed to calculate the density of the sorptive gas = p (p, T)) in a sorption equilibrium state, it seems to be worthwhile to consider direct measurements of (p ), for example by using the buoyancy of a sinker at a magnetic suspension balance. Experiments of this type can be called oscillometric-densimetric measurements . They can be recommended to measure solubilities of gas mixtures in swelling (polymeric) sorbing materials. A scheme for such measurements is sketched in Figure 5.15. Equations to calculate the total mass of gas (m ) sorbed in the sorbent mass (m ) and the volume of the mass (m + m ) are the same as those given for oscillometric-manometric measurements in the next section (4.3). 

The magnetic suspension balance (MSB) [30] from Rubotherm GmbH, was used to measure the sorption of the HFC 134a/HFC 152a blends in PS. A schematic diagram of the MSB and its working procedmes is shown in Fig. 1. A detailed description on the sorption experiment can be found in our previous studies [31-33]... 

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