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- Mischphasenthermodynamik (2)
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Eingeladener Vortrag
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Experimental results are reported for the solubility of carbon dioxide in liquid mixtures of water and the ionic liquid 1-n-butyl-3-methylimidazolium methylsulfate ([bmim][CH3SO4]). Three (gas-free) solvent compositions were considered with mass fractions of [bmim][CH3SO4] of w' ≈ 0.15, 0.50, and 0.87 (mole fractions x' ≈ 0.013, 0.066, and 0.33). In the isothermal experimental series, the temperature was about (293, 333, and 373) K. The total pressure ranged up to about 10 MPa. The molality of carbon dioxide in the solvent mixture of (water + [bmim][CH3SO4]) (the mole fraction of carbon dioxide in the liquid) ranged up to approximately 1.64 mol·kg1 (about 0.0332). The experimental results are used to determine Henry's constant of carbon dioxide in the liquid mixtures of (water + [bmim][CH3SO4]) as well as the partial molar volume of that gas at infinite dilution in those solvent mixtures. The phase equilibrium is described by applying an extension (to solvent mixtures) of Pitzer's molality scale-based equation for the Gibbs excess energy.
Adding some salt to a homogeneous aqueous liquid solution of an organic solvent often results in a liquid–liquid phase split. However, such a phase split can also be achieved by charging such a liquid with a gas, in particular when the temperature is close to the critical temperature of that specific gas. This phenomenon is called 'salting out by a near-critical gas'. It might be applied in a high-pressure extraction process, for example, to separate and recover valuable biomolecules from aqueous phases. Using a neutral gas like, for example, ethene for pressurizing additionally allows to adjust the pH of the coexisting liquid phases and to influence the partitioning of biomolecules when they change their electric net charge with the pH of the solution. The design of such separation processes requires not only reliable information on the phase forming system, that is, the ternary system (near-critical gas + water + organic solvent), but also on the partitioning of typical solutes to the coexisting phases. The present publication reports data (from an experimental study with a static-analytical device) for the partitioning of four biomolecules, that is, L-histidine, Aspirin, cimetidine, and 4-dimethylaminoantipyrine (at nearly infinite dilution) to coexisting liquid phases of the high-pressure three-phase liquid–liquid–vapor (L1L2V) equilibrium of the ternary system (ethene + water + 2-propanol) at (293 and 333) K and pressures from about (5.5 to 17) MPa. The coexisting liquid phases are characterized by distinctly different compositions, the aqueous phase being more hydrophilic than the alkanol-rich phase. Moreover, electrolytes were additionally added to adjust the pH conditions in the liquid phases. The pH-dependent dissociation equilibrium and the related net charge of the biomolecules primarily determine the partitioning behavior: The pH effect is stronger than the impact of varying pressure or temperature. For example, a switch from basic to acidic conditions can invert the partitioning, if that switch at the same time effects a change in the net charge of the solute, for example, from an ionic to a neutral molecule (or vice versa). The ionic solute is more hydrophilic (and thus prefers the aqueous phase), whereas the neutral or zwitterionic solute is less hydrophilic (i.e., more lipophilic) and consequently prefers the propanol-rich liquid phase.
The solubility of a single gas as well as the simultaneous solubility of several gases in an ionic liquid is of great interest in many areas of chemical engineering, particularly in heterogeneous catalysis. One of the most interesting features involved in the study of the simultaneous solubility of several gases in a pure ionic liquid is the difference between experimental data and predictions for the simultaneous solubility (based on experimental data for the solubility of the single gases). The well soluble gas might act as a cosolvent or as an antisolvent for a sparsely soluble second gas. New experimental results and a correlation are presented for the simultaneous solubility of hydrogen (i.e., a sparsely soluble gas) and carbon dioxide (a well soluble gas) in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf2N]) at temperatures between 293 K and 373 K and pressures up to about 9.2 MPa. The experimental results reveal that carbon dioxide acts as a cosolvent for hydrogen in that particular ionic liquid. A correlation shows that the cosolvency effect can be modeled by considering interaction parameters between hydrogen and carbon dioxide in liquid [hmim][Tf2N]. The correlation can also be used to quantify that cosolvency effect: one mole of carbon dioxide in 1000 g of [hmim][Tf2N] increases the solubility of (small amounts of) hydrogen by about 20%.
Poly(p-phenylenediamine) (PpPD)/carboxylic acid-functionalized multiwalled carbon nanotubes (c-MWCNTs) nanocomposites were prepared by chemical oxidative polymerization using potassium persulfate (K2S2O8) as an oxidant. Field-emission scanning electron microscopy (FE–SEM) and field-emission Transmission electron microscopy (FE–TEM) showed that a tubular layer of PpPD was coated on the surface of carbon nanotubes with a thickness of 10–20 nm. FT–IR analysis provided an evidence for the formation of nanocomposites. The thermal stability of nanocomposites was improved by addition of c-MWCNTs as confirmed by thermogravimetric analysis (TGA). XRD spectra showed that the crystalline nature of PpPD was not affected much by the addition of c-MWCNTs. As the content of c-MWCNTs was increased, the electrical conductivity of the nanocomposites increased due to the interaction between polymer and nanotubes that enhances electron delocalization.
In a mutual framework agreement, the two German national institutes BAM (Federal Institute of Materials Research and Testing) and PTB (Physikalisch-Technische Bundesanstalt) agreed upon the development, provision, and dissemination of national measurement standards for chemical analysis via primary reference measuring systems.
Traceability to national standards and international comparability is of key importance for the acceptance of measurement results in metrology.