Supercritical fractionation

Brunner et al [1, 2] investigated separations of fatty acids according to chain length, using methyl esters of different carbon chain length from C14 to Cl8, separation of tocopherols from a by-product of the edible oil production and separation of fish oil esters [3], Stahl et al [4] proposed the supercritical fractionation of orange peel oil and Reverchon et al [5,6] of an orange flower concrete. Different authors treated citrus peel oil [7,8] and citrus oil [9-12]. 

Shukla, A., Bhaskar, A.R., Rizvi, S.S.H., Mulvaney, S.J. 1994. Physicochemical and rheological properties of butter made from supercritically fractionated milk fat. J. Dairy Sci. 77,45-54. 

As was pointed out earlier, molecular distillation is normally used to fractionate mixtures of components of very low volatility. It is proposed that a supercritical fractionation process, as schematically shown in figure 6, can be used to produce fractions superior to that of molecular distillation. In order to test this, a molecular distillation model must be used. As a first approximation, the molecular distillation of high molecular weight alkanes is viewed as a simple flash. The vapour pressure data of Kudchadker et al[10] was used in the flash calculations. 

Figure 6. Countercurrent supercritical fractionation with reflux...

Calculations have also shown that the operating costs of a this supercritical fractionation unit may be marginally lower than that of a molecular distillation unit. 

Supercritical fractionation of high molecular weight alkane mixtures with propane or LPG may be used to produce products with lower polydispersity that that of molecular distillation. Operating temperatures just above the cloud point of the mixtures can be used compared to the high temperatures needed in molecular distillation. It was also shown that an optimum reflux ratio exists for every set of operating conditions. For this system it was also found that the operating costs of a supercritical fraction unit is marginally less than that of a molecular distillation unit. 

Supercritical fractionation of a liquid lipid feed material is usually carried out in a packed column. Standard columns are not available commercially and have to be custom built either in-house or by manufacturers of extraction units. Lab-scale and pilot-scale supercritical columns, 0.6-13.6 m high with internal diameters of 14.3-68 mm are available in research labs around the world and have been used for the processing of deodorizer distillates (56, 57, 86-90), vegetable and fish oils (91-105), cocoa butter, and milkfat (106-109). A schematic diagram of a typical SCCO2 fractionation column (2.8 m, 2.54 cm o.d.), which was designed and built... 

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... 

Supercritical fractionation was investigated for the special-purpose polymers of both the diol and triol of a glycidyl azide polymer and a hydroxy-terminated polybutadiene. Hydroxy polybutadiene is used on a large scale as an ingredient in plastic bonded explosive (PBX) propellant formulations the hydroxy functionality of the polybutadiene reacts with an isocyanate functionality of another prepolymer to form a urethane. In the polysiloxanes section we referred to functionally terminated polymers as macromonomers in the terminology of the urethane industry, however, isocyanate-terminated polyester polymers are normally referred to as prepolymers in their reaction to form the urethane, even though the prepolymers are typically between 1,000 and 10,000 molecular weight. 

Pratt, J. A., S.-H. Lee, and M. A. McHugh. 1993. Supercritical fractionation of copolymers based on chemical composition and molecular weight. J. Appl. Polym. Sci. 49 953-966. 

Perhaps of more importance, is that the SC-CO2 - based synthesis avoids the use of any inorganic catalyst that would have to be filtered out of the oil at the conclusion of a traditional glycerotysis reaction. The jettisoned CO2 is also available for reuse, or for diversion to other maim cturing processes, such as supercritical fractionation. This makes the above reaction conditions attractive for integrating into an all supercritical fluid-based mami cturing process that is enviromnentally-conq)atible. 

The candidate technologies for purification are many. Distillation, the work-horse of the chemical processes, leads the pack. Most of the synthesis effort to date has concentrated on the product purification step. This step is often the last step for liquid products especially in the chemical and petrochemical industries. The biochemical industry utilizes membrane and chromatographic processes more than the other industries due to the thermal stability and purity requirements. In the electronic industry, membrane processes are more prevalent due the ultra-purities necessary. Supercritical fractionation of alcohol water systems with the aid of a dense gas is an example of a purification step. 

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. 

Supercritical Fractionation. Fast Supercritical fractionation of tails in the molar mass distribution and/or the chemical composition distribution of a (co)polymer [47] during the polymerization process will indicate drifts in (co)polymer composition. Several important polymer properties strongly depend on such tails in the (co)polymer distribution. 

With the distribution and concentration considered, the lowest x-value at which this phenomenon appears is about 0.8. The value increases with average molecular weight and decreases with concentration (72, 13, 31). Therefore, if we want to calculate a complete "supercritical fractionation, it is useful to make these two effects balance by keeping the volume constant during the process. 

Supercritical fractionation has been touted for many years as an ideal process for fractionation of AMF [45-47], but no studies of its use for other oils and fats have been published. One of the main attractions for AMF was that it is possible to efficiently remove cholesterol from it [48]. Such studies came about at a time when cholesterol was first linked specifically to heart disease and arterial deterioration. The majority of people now recognize that this is only one factor in a very complex situation, and thus the need for cholesterol reduction is less important. Much of the published work has revolved around the use of carbon dioxide, this being the most common of the gases with a supercritical stage in their liquid state. The choice of carbon dioxide for this purpose is a mystery,... 

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