Supercritical swelling

Fahing et al. [24] studied the modifier effects in the supercritical fluid extraction of organics from soils and clays. Swelling experiments showed that unmodified carbon dioxide did not cause swelling of the soil whereas carbon dioxide modified with water did cause rapid swelling of soil, thereby facilitating extraction of the organics. 

As an alternative to distillation, extraetion with a eo-solvent that is poorly mis-eible with the ionie liquid has often been used. There are many solvents that can be used to extract product from the ionic liquid phase, whether from a monophase reaction or from a partially miscible system. Typical solvents are alkanes and ethers (15). Supercritical CO2 (SCCO2) was recently shown to be a potential alternative solvent for extraction of organics from ionic liquids (22). CO2 has a remarkably high solubility in ionic liquids. The SCCO2 dissolves quite well in ionic liquids to facilitate extraction, but there is no appreciable ionic liquid solubilization in the CO2 phase in the supercritical state. As a result, pure products can be recovered. For example, about 0.5 mol fraction of CO2 was dissolved at 40°C and 50 bar pressure in [BMIMJPFe, but the total volume was only swelled by 10%. Therefore, supercritical CO2 may be applied to extract a wide variety of solutes from ionic liquids, without product contamination by the ionic liquid (29). 

Surface engineering of polymers by infusion. Supercritical-fluid contact can reversibly swell some polymer surfaces and films thus helping to enhance impregnation by monomers with subsequent polymerization to form nanocomposite anchored layers. - ... 

Gas concentrations (partial pressures) at temperatures above critical can act as supercritical solvents. Elastomers in this environment are subject to high swells and subsequent extraction of plasticizers, low molecular weight polymers etc. 

In order to overcome the main limitations of the impregnation processes, connected to the limited solubility of the compounds in the supercritical fluids, Perman [68] proposed an alternative method. A supercritical impregnation process was coupled with a liquid solvent (preferentially water) to enhance the drug solubilization. The system composed of a liquid drug solution and the polymeric support was pressurized with the supercritical fluid. Consequently, the swelled polymer allows rapid diffusional transport of the solute into the polymeric substrate. In different examples, bovine serum albumin microspheres were impregnated with insulin, trypsin and gentamicin (see Table 9.9-5). 

Mobile fluid interaction with the stationary phase in SFC was investigated with mass spectrometric tracer pulse chromatography (96). Using capillary supercritical fluid chromatography, the effect of methanol as an additive was studied on the partition behavior of n-pentane into 5 % phenylmethylsilicone stationary phase. The results showed that the mobile fluid uptake by the stationary phase decreased with increasing temperature and pressure. Thus suggests that stationary phase swelling, may occur in SFC. 

For some experiments, pre-treatment of the coal with potassium hydroxide was employed in amounts of 5% of the weight of the coal charged to the reactor. Other pre-treatment methods investigated Include contact with 10% HC1 under varying conditions and soaking in N,N - dimethylacetamide (DMA) to promote swelling of the coal prior to supercritical desulfurization in alcohol. 

Some problems have been experienced due to swelling of the stationary phase by the supercritical fluid. This is especially serious for columns that have high stationary loads, and it affects the column performance.7 More experience is needed, and new columns may be required. 

Fig. 3. SEM images of various dry powders for inhalation, (a) Spray-dried particles (see Subheading 3.1.)- Reproduced from ref. 5. (b) Particles prepared by emulsification techniques (see Subheading 3.2.1.), Reproduced from ref. 10. (c) Particles prepared by supercritical C02 swelling (see Subheading 3.2.2.), The particles in panel b were the starting material for these particles. Reproduced from ref. 10. (d) TI particles (see Subheading 3.4.2.),...

The excellent compatibility of supercritical carbon dioxide and fluoropolymers has been exploited in preparing compositions by swelling fluoropolymers by supercritical carbon dioxide at high temperatures and pressures. The resulting compositions can be processed by molding, extrusion, and other methods. In addition, such compositions can be sintered at considerably lower temperatures [19]. 

Potential interactions of a supercritical fluid with a polymeric material may include the following (i) sorption of carbon dioxide by polymers (ii) swelling of polymers by carbon dioxide (Hi) dissolution of polymers in carbon dioxide (iv) dissolution of carbon dioxide in polymers (v) plasticization and decrease of the glass transition... 

Which extraction mode is the better remains a controversial issue. While the static mode provides longer contact between the sample and solvent, swells the matrix and facilitates penetration of the extractant in its interstices — thereby increasing its efficiency — the dynamic mode allows the analyte to be continuously exposed to the pure (clean) solvent, thus favouring displacement of the analyte s partitioning equilibrium to the mobile phase. Most SFE methods use both modes a static step is employed to ensure close contact between the sample and supercritical fluid without consuming much extractant that is followed by a dynamic step where the extracted analytes are driven to the restrictor and equilibrium is allowed to complete. 

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