Impregnations with Supercritical Carbon Dioxide

Other reagents and solvents were obtained from commercial sources. The samples were prepared by mixing various chiral bases with racemic acids in 0.5 1 molar ratio. A porous supporting material (Perfilt), impregnated with these mixtures, was put into the extractor vessel and extracted with supercritical carbon dioxide. 

In contrast to the decaffeination of coffee, which is primarily executed with green coffee, black tea has to be extracted from the fermented aromatic material. Vitzthum and Hubert have described a procedure for the production of caffeine-free tea in the German patent application, 2127642 [11]. The decaffeination runs in multi-stages. First, the tea will be clarified of aroma by dried supercritical carbon dioxide at 250 bar and 50°C. After decaffeination with wet CO2 the moist leaf-material will be dried in vacuum at 50°C and finally re-aromatized with the aroma extract, removed in the first step. Therefore, the aroma-loaded supercritical CO2 of 300 bar and 40°C will be expanded into the extractor filled with decaffeinated tea. The procedure also suits the production of caffeine-free instant tea, in which the freeze-dried watery extract of decaffeinated tea will be impregnated with the aromas extracted before. 

Ma, X. Tomasko, D. L. Coating and Impregnation of a Nonwoven Fibrous Polyethylene Material with a Nonionic Surfactant Using Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 1997, 736, 1586-1597. 

Ma X, Tomasko DL. Coating and impregnation of a nonwoven fibrous polyethylene material with a nonionic surfactant using supercritical carbon dioxide. Ind Eng Chem Res 1997 36 1586-1597. 

Polymerization and Grafting onto Nanotubes Supercritical fluids are widely used in the manipulation of porous materials. Supercritical carbon dioxide can be used for the impregnation of carbon nanotubes with NVK and AIBN with subsequent polymerization. ... 

The electrically conductive composites prepared by these methods are not sufficiently conductive for shielding of electromagnetic interference. Still more effective in producing conductive aramids is electroless plating. A high electrically conductive fiber is obtained. The fiber is impregnated with metal complexes using supercritical carbon dioxide. 

When decaffeinating tea, it is not as easy to avoid aroma and flavour losses as in the case of coffee. In some processes involving supercritical carbon dioxide, the flavour and aroma components are extracted before decaffeination, and the tea is subsequently re-impregnated with these components after decaffeination (section 5.4.5). When using organic solvents as extractants, careful attention to the conditions is required to minimise these losses. Although decaffeination of... 

A. M. A. Dias, M. E. M. Braga, I. J. Seabra, P. Ferreira, M. H. Gil, H. C. de Sousa, Development of natural-based wound dressings impregnated with bioactive compounds and using supercritical carbon dioxide. International Journal of Pharmaceutics 408 (2011), p. 9-19. 

Swelling can be advantageous in that it enables pemieation and diffusion of the supercritical fluid into the polymer network. Fragrances, dyes, or medicinal substances loaded in the supercritical fluid can readily impregnate into the polymer and load the polymer with the aforementioned additives. Upon release of the pressure, only the supercritical fluid (i.e., carbon dioxide) flashes off. This avenue has led to a plethora of controlled (timed) release products. 

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