Supercritical fractionation applications

Another important aspect of supercritical fluids application is in polymer fractionation, in order to obtain mono-dispersed molecular weights. The simulation of the fractionation of polyethylene from ethylene and hexane solutions into fractions of different molecular weights was proposed by Chen et al. [7]. 

Supercritical carbon dioxide, ethane, and propane have been examined for the fractionation of paraffin wax. The original feed contained wax molecules with 10-35 carbon atoms. A narrower carbon distribution is needed in the printing ink, cosmetics, and pharmaceutical applications. Based on the cost analyses, vacuum distillation was proposed to be a cheaper option for light paraffin wax, whereas supercritical fractionation... 

The unique characteristics of gases at supercritical conditions, which are between those for liquids (density) and gases (viscosity and diffusivity) enable that different processes could be realized as for example the selective extraction of specihc components from the complex mixtures, the particle micronization, the supercritical fractionation, the production of materials with unusual and specihc structure, etc. Many similar processes, based on supercritical huids use are today the part of intensive investigations, while others have already been patented and applied in the pilot-plant scale. Obviously, in the recent past there is not always the advantage for all investigated supercritical processes because of high hnancial investment necessary for their implementation in industry compared to other conventional methods. However, it is important to notice the substantial increase of scientihc research published in many journals, which include the new potential use and application of supercritical huids. 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

Purification of poloxamers has been extensively investigated due to their use in medical applications, the intention often being to remove potentially toxic components. Supercritical fluid fractionation and liquid fractionation have been used successfully to remove low-molecular weight impurities and antioxidants from poloxamers. Gel filtration, high-performance liquid chromatography (HPLC), and ultrafiltration through membranes are among the other techniques examined [5]. 

Food Applications, Carbon dioxide, a nontoxic material, can be used to extract thermally labile food components at near-ambient temperatures. The food product is thus not contaminated with residual solvent, as is potentially the case when using conventional liquid solvents such as methylene chloride or hexane. In the food industry, C02 is not recorded as a foreign substance or additive. Supercritical solvents not only can remove oils, caffeine, or cholesterol from food substrates, but can also be used to fractionate mixtures such as glycerides and vegetable oils into numerous components. 

The objective of this panel was to develop protocols that could be used today with a minimum of methods development. The panel members recognized that promising research is currently underway to develop new techniques for sample preparation. However, procedures such as supercritical fluid extractions or preparative ion chromatographic separation of polar fractions are still considered to be in a research phase and not yet ready for general laboratory application. The procedures presented will be periodically reviewed and updated as the state of available technology improves. 

There are a number of published applications in which spices are extracted with liquid carbon dioxide to isolate a flavour- or aroma concentrate [22,48,54], Liquid CO2 dissolves the essential oils and lighter fractions of the oleoresins. Supercritical CO2 is generally a better extracting-solvent than liquid CO2, because higher densities, equivalent to higher solubility, can be achieved by raising the pressure. 

The supercritical fluid extraction of oil seeds has been investigated extensively by several authors [34,98]. Possible applications of supercritical fluids in the edible-oil industry include deacidification, deodorization, and fractionation of crude oils and chemical conversion (like hydrogenation, and enzymatic reactions). 

Szekely, E., Simandi, B., Illes, R., Molnar, P., Gebefugi, I., Kmecz I., and Fogassy, E. Application of supercritical fluid extraction for fractionation of enantiomers, J. Supercritical Fluids 2003, accepted for publication. 

The phase behavior of solids in supercritical fluids has practical significance as well as academic interest. Since the mid-1970 s, it has been recognized that supercritical fluids can be useful as solvents for commercial-scale extractions. While a variety of applications are documented in the literature (2,6), supercritical-fluid (SCF) extraction has been particularly useful in upgrading petroleum fractions (7), extracting volatile components from coal (8), and deashing oil shale (9) and coal liquids (10). The... 

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