Supercritical fluid carbon dioxide fractions

Nguyen, LJ., Anstee, M. and Evans, D.A. (1 998) Extraction and fractionation of spices using supercritical fluid carbon dioxide. Presented at The 5th International Symposium on Supercritical Fluids, Nice, France. 

Supercritical fluid carbon dioxide (SC-CO2) fractionation of fish oil ethyl esters (EE) was employed to prepare EE of two omega-3 fatty acids, all cis-5,8,11,14, 17-eicosapentaenoic acid (EPA) and all cis-4,7,10,13, 16,19-docosahexaenoic acid (DHA) in 90% purity and to separate the synthetic triacylglycerols (TG), trieicosapentaenoylglycerol (tri-EPA), and tridocosahexaenoyl-glycerol (tri-DHA) in > 92% purity from other reaction mixture components. In the synthesis, glycerine reacted with EE and sodium glyceroxide catalyst to form TG. 

Metal-complexation/SFE using carbon dioxide has been successfully demonstrated for removal of lanthanides, actinides and various other fission products from solids and liquids (8-18), Direct dissolution of recalcitrant uranium oxides using nitric acid and metal-complexing agents in supercritical fluid carbon dioxide has also been reported (79-25). In this paper we explored supercritical fluid extraction of sorbed plutonium and americium from soil using common organophosphorus and beta-diketone complexants. We also qualitatively characterize actinide sorption to various soil fractions via use of sequential chemical extraction techniques. 

G. Perretti, A. Motori, E. Bravi, F.Favati, L. Montanari, P. Fantozzi, Supercritical carbon dioxide fractionation of fish oil fatty acid ethyl esters. The Journal of Supercritical Fluids 40 (2007), p. 349-353. 

A cylindrical extractor, 1-m long, is filled with crushed-vegetable-oil seeds. The oil is to be extracted with pumping supercritical carbon dioxide at a density of 500 kg/m3 through the packed bed. The estimated solubility of the oil in the dense gas at this density is 3.425 kg/m3. The superficial velocity of the carbon dioxide in the bed will be 1 mra/s. This fluid velocity is sufficiently small for the fluid to become saturated with oil. We are required to estimate the minimum time of operation for complete extraction of the oil from the bed. The initial oil fraction is 12% (wt/wt) based on wet seeds, the void fraction of the bed is 40%, and the density of the particles is 900 kg/m3. 

We have demonstrated in this paper that two and four samples can be extracted in parallel with supercritical carbon dioxide without significant impact on data quality. Modifications made to an off-line extractor involved addition of a multiport manifold for the distribution of supercritical fluid to four extraction vessels and of a 12-port, two-way switching valve that allowed collection of two fractions per sample in unattended operation. The only limitation that we have experienced with the four-vessel extraction system was in the duration of the extraction. When working with 2-mL extraction vessels and 50-/zm restrictors, and using the pressure/temperature conditions mentioned above, the 250-mL syringe pump allows us a maximum extraction time of 60 min. During this time, two 30-min fractions can be collected with the present arrangement. 

It is not surprising that fatty acids inhibit COX and LOX enzymes due to their structural similarities with arachidonic acid. A supercritical fluid extract from the fruits of Sabal serrulata (also called Serenoa repens Small. Arecaceae) has been utilized for the treatment of benign prostatic hyperplasia (BPH) and non-bacterial prostatitis. The extract was demonstrated as a dual inhibitor of COX and 5-LOX pathways with IC50 at 28.1 pg/ml and 18.0 (ig/ml, respectively. A further evaluation of the supercritical carbon dioxide extract showed the acidic lipophilic fraction, most likely fatty acids, had the same dual inhibitory activities as the parent extract [121]. 

Based on its ability to enhance solvating power by increasing fluid density, supercritical fluid extraction offers an attractive alternative for fractionation of fats and oils. It works by the phenomena of selective distillation and simultaneous extraction, as has been shown by many researchers [3-5]. While the use of supercritical fluids in the extraction of numerous biomaterials has been reported, its commercialization has been limited to the decaffeination of coffee and tea and to the extraction of flavors from hops and spices. The chemical complexity of most food ingredients and their tendency to react and degrade at elevated temperatures, emphasize the difficulties of supercritical solvent selection. Carbon dioxide is the preferred supercritical solvent (its properties have previously been cited [6]). 

SCF technology has spread quickly from molecules such as naphthalene to more complex substances such as polymers, biomolecules, and surfactants. Supercritical fluids can be used to reduce the lower critical solution temperature of polymer solutions in order to remove polymers from liquid solvents(6.26 The technology has been extended to induce crystallization of other substances besides polymers from liquids, and has been named gas recrystallization(4). In other important applications, SCF carbon dioxide has been used to accomplish challenging fractionations of poly(ethylene glycols) selectively based on molecular weight as discussed in this symposium, and of other polymers(. ... 

More than one hundred years ago, certain fundamental principles in supercritical extraction had already been known, but viable processes for using this technique developed slowly. In the past two decades, process engineers in several industries have been interested in using supercritical fluids to extract soluble nonvolatile components from mixtures. One of many examples is enhanced oil recovery using carbon dioxide. Another is the fractionation of cod-liver oil using supercritical ethane (1). 

FIGURE 3 Mole fraction solubility (y) of phenanthrene in supercritical carbon dioxide versus pressure. (From Anitescu, G. and Tavlarides, L. L., J. Supercrit. Fluids, 10(3), 175-189, 1997.). Three isothermal lines cross at the crossover pressure of 165 bar. 

The use of critical fluids for the extraction and refining of components in natural products has now been facilitated for over 30 years. Early success in the decaffeination of coffee beans and isolation of specific fractions from hops for flavoring beer, using either supercritical carbon or liquid carbon dioxide, are but two examples of the commercial application of this versatile technology. Critical fluid technology, a term that will be used here to embrace an array of fluids under pressure, has seen new and varied applications which include the areas of engineering-scale processing, analytical, and materials modification. 

As we related in the introduction to Appendix A, this patent should be read by everyone involved in research and process development using supercritical fluids. In his examples, Zosel describes results on neat solubility, separations of liquids and solids, fractionations, etc. A wealth of information is given on the performance of various gases, e.g., ethylene, ammonia, ethane, carbon dioxide, in dissolving a variety of compounds. Several interesting experiments carried out in a plexiglass autoclave are descrited, and certain phase separations are noted. Some of the information can be found in other references, of course, but not in such succinct form. It is of pedagogical value to reproduce one of the examples here. 

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