Carbon dioxide based supercritical

Wong, J. M. Johnston, K. P. Solubihzation of biomolecules in carbon dioxide based supercritical fluids. Biotechnol. Prog. 1986, 2, 29-39. 

In preparative liquid-carbon-dioxide-based supercritical flow chromatography (SFC), smaller particles in the 5-10 /tm range are used due to the decreased viscosity of the mobile phase. The pore size of the particles should be large enough to allow the molecules to readily diffuse into and out of the pores. In reversed-phase HPLC, longer alkyl chains provide better load- ability because of the higher volume of interaction be-... 

Carbon Dioxide Based Supercritical Fluid Chromatography... 

RANDALL Carbon Dioxide Based Supercritical Fkdd Chromatography 143... 

Hoefling TA, Newman DA, Enick RM, Beckman EJ. Eflfect of structure on the cloud-point curves of silicone-based amphiphiles in supercritical carbon dioxide. J Supercrit Fluids 1993 6 165-171. 

Carbon dioxide based chromatography, with a mobile phase of carbon dioxide and mixtures of carbon dioxide plus modifiers ranging from suboritlcal to supercritical states, is a young but exciting area for study. Investigators can choose from a wide range of possible experiments from fundamental physicochemical studies to semi-empirical frameworks to analytical methods-development for complex mixture separation. It is hoped that the preliminary results described in this paper will be useful to others in this area and will stimulate future work that will result in routine optimization schemes for SFC separations like those presently under development for LC separations. 

Furthermore, one of the advantages of carbon dioxide-based SFE is that normally extractions are carried out at low temperatures. The resolution of this dilemma can be as simple as adding a short sub-step in the beginning to remove the ethyl alcohol in the extraction thimble. Recall that the capsaicin extraction is carried out at 40 C and a density of 0.70 g/mL. The ethyl alcohol can be readily removed at a density of 0.25 g/mL at 40 C in a short three-minute dynamic extraction step. This is well below the "threshold-density" at which the capsaicin would extract or be soluble in supercritical carbon dioxide. The mechanism of using the carbon dioxide to remove ethyl alcohol from the extraction thimble under supercritical conditions is quite different than the evaporation mechanism that would be taking place in the solid trap after expansion of the carbon dioxide plus ethyl alcohol to a mixture of gas plus condensing liquid. Note that the fact that ethanol can be pre-extracted ahead of the analyte of interest demonstrates that the role of the modifier in this application is mainly matrix modification had a more polar solvent (like that afforded by a mixture of ethanol in carbon dioxide) been necessary to solvate the capsaicin, the pre-extraction step to remove the ethanol would have been detrimental to the extraction of the capsaicin. 

Beckman s comprehensive review paper [5] describes chemical reactions in carbon dioxide-based solvents, and evaluates their green character. The title of the paper - Supercritical and near-critical CO2 in green chemical synthesis and processing - is revealing of the new trends in the use of carbon dioxide. 

In 1999 Blanchard et al. reported a good solubility of carbon dioxide in l-butyl-3-methylimidazolium hexafluorophosphate at high pressures, while the ionic liquid did not dissolve in carbon dioxide. Therefore, supercritical carbon dioxide is suited to extract organic solutes from ionic liquids, and also continuous flow homogeneous catalysis in ionic liquids carbon dioxide systems is possible. First spectroscopic studies show that the anion dominates the interactions with carbon dioxide by Lewis acid-base interactions. However, the strength of carbon dioxide anion interactions did not correlate with carbon dioxide solubility. Thus, strong anion-carbon dioxide interactions were excluded as major cause for the carbon dioxide solubility in ionic liquids. Instead, a correlation of carbon dioxide solubility and the ionic liquid molar volume was observed. Additionally, a significant volume decrease of dissolved carbon dioxide was... 

Chenglong, D., Cailiang, Z., Wenyi, H., Kung-Chin, C., Ly, J. L. (2013). Thermoplastic polyurethane microcellular fibers via supercritical carbon dioxide based extrusion foaming, Polym. Eng. ScL, 53(11), 2360-2369. 

Based on a research on the application of supercritical technology for the extraction and evaluation of the nutritional and functional composition of this oilseed and experiments with particle samples of average size around 1.0 mm diameter and average moisture content aroimd 3.0%, it was possible to establish the optimum extraction parameters, i.e., a pattern of extraction using carbon dioxide in supercritical state (CO2) based on the optimum parameters of temperature and pressure to Brazil nut oil. The results of the global yield isotherms are shown in Figure 2. Data represent the average extraction values at temperatures of 40, 50, and 60 ° C and pressures of 200, 250, and 300 bar. 

The combination of ionic liquids with supercritical carbon dioxide is an attractive approach, as these solvents present complementary properties (volatility, polarity scale.). Compressed CO2 dissolves quite well in ionic liquid, but ionic liquids do not dissolve in CO2. It decreases the viscosity of ionic liquids, thus facilitating mass transfer during catalysis. The separation of the products in solvent-free form can be effective and the CO2 can be recycled by recompressing it back into the reactor. Continuous flow catalytic systems based on the combination of these two solvents have been reported [19]. This concept is developed in more detail in Section 5.4. 

Polymerization of methyl methacrylate in supercritical carbon dioxide with PDMS based stabilizers A study on the effect of stabilizer anchor groups... 

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