SCF extraction

Supercritical Fluid Extraction. Supercritical fluid (SCF) extraction is a process in which elevated pressure and temperature conditions are used to make a substance exceed a critical point. Once above this critical point, the gas (CO2 is commonly used) exhibits unique solvating properties. The advantages of SCF extraction in foods are that there is no solvent residue in the extracted products, the process can be performed at low temperature, oxygen is excluded, and there is minimal protein degradation (49). One area in which SCF extraction of Hpids from meats maybe appHed is in the production of low fat dried meat ingredients for further processed items. Its apphcation in fresh meat is less successful because the fresh meat contains relatively high levels of moisture (50). 

Adsorption and Desorption Adsorbents may be used to recover solutes from supercritical fluid extracts for example, activated carbon and polymeric sorbents may be used to recover caffeine from CO9. This approach may be used to improve the selectivity of a supercritical fluid extraction process. SCF extraction may be used to regenerate adsorbents such as activated carbon and to remove contaminants from soil. In many cases the chemisorption is sufficiently strong that regeneration with CO9 is limited, even if the pure solute is quite soluble in CO9. In some cases a cosolvent can be added to the SCF to displace the sorbate from the sorbent. Another approach is to use water at elevated or even supercritical temperatures to facilitate desorption. Many of the principles for desorption are also relevant to extraction of substances from other substrates such as natural products and polymers. 

Residuum oil supercritical extraction (ROSE) (petroleum deasphalting) Polymer and edible oils fractionation CO2 enhanced oil recovery Analytical SCF extraction and chromatography Infusion of materials into polymers (dyes, pharmaceuticals)... 

Experimental gas-solid mass-transfer data have been obtained for naphthalene in CO2 to develop correlations for mass-transfer coefficients [Lim, Holder, and Shah, Am. Chem. Soc. Symp. Ser, 406, 379 (1989)]. The mass-transfer coefficient increases dramatically near the critical point, goes through a maximum, and then decreases gradually. The strong natural convection at SCF conditions leads to higher mass-transfer rates than in liquid solvents. A comprehensive mass-transfer model has been developed for SCF extraction from an aqueous phase to CO2 in countercurrent columns [Seibert and Moosberg, Sep. Sci. Techrwl, 23, 2049 (1988) Brunner, op. cit.]. 

Principles and Characteristics Supercritical fluid extraction uses the principles of traditional LSE. Recently SFE has become a much studied means of analytical sample preparation, particularly for the removal of analytes of interest from solid matrices prior to chromatography. SFE has also been evaluated for its potential for extraction of in-polymer additives. In SFE three interrelated factors, solubility, diffusion and matrix, influence recovery. For successful extraction, the solute must be sufficiently soluble in the SCF. The timescale for diffusion/transport depends on the shape and dimensions of the matrix particles. Mass transfer from the polymer surface to the SCF extractant is very fast because of the high diffusivity in SCFs and the layer of stagnant SCF around the solid particles is very thin. Therefore, the rate-limiting step in SFE is either... 

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

C02 as anti-solvent The introduction of C02 to a reaction mixture selectively precipitates the organometallic hydrogenation catalysts, followed by SCF extraction of the products and recovery of the catalyst in active form. 

C02 as adjustable-solvent In this case, the reaction is carried out in scCOz under truly monophasic conditions and the catalyst is selectively precipitated through a change in temperature and/or pressure. Again, product isolation is achieved by SCF extraction. 

Applications for SCF Extraction Supercritical fluid extraction has been mainly used for the extraction of natural extracts for aromatic substances and essences, and for various active substances for pharmaceuticals. Alternative possibilities include... 

For the liquid-liquid extraction, the effects of total system pressure can be ignored for all classical practical purposes except for the SCF extraction. 

In related work,20 these same authors evaluated a fluorinated crown ether carboxylic acid,. rym-difluorobenzo-16-cniwn-5 oxyacetic acid, for use in the SCF extraction of uranyl ion and lanthanides, again from a cellulose matrix. Although this compound... 

Kalinoski et al. [32] has applied this method to the determination of tri-chothecene mycotoxins in wheat. The methods were based on chemical ionisation MS and collision-induced dissociation tandem MS and enabled the rapid identification of ppm levels of several trichothecene mycotoxins. Supercritical carbon dioxide is shown to allow identification of mycotoxins with minimum sample handling in complex natural matrices such as wheat. Tandem MS techniques are employed for unambiguous identification of compounds of varying polarity, and false positives from isobaric compounds are avoided. Capillary column SCFC-MS of a SCF extract of the same sample was also performed, and detection limits in the ppb range appear feasible. 

Metabolites of chlorobenzene in biological materials cannot be determined in routine practice because of the lack of standard methods for measuring these metabolites. Further research on supercritical fluid (SCF) extraction holds great promise for meeting the goals of quantitative, rapid, easily performed, low cost, and safe procedures for the determination of nonpolar organic analytes such as chlorobenzene in biological samples. 

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... 

In this paper, we present the results of an experimental study on the phase behavior of well-characterized binary mixtures which represent the more complex mixtures that arise in SCF extractions of petroleum residua and coal liquids. These binary mixtures consist of pentane and toluene with meso-tetraphenylporphyrin (TPP). Porphyrins occur naturally in crude oils (11,12) and represent an important class of high molecular-weight constituents of these oils, including those which contain heavy metals, such as nickel and vanadium. 

The potential for supercritical fluid extraction and purification of substances of high aggregated economic value is enormous in Brazil due the overwhelming biodiversity of its forests, comprising from 55,000 to 350,000 of known species of plants in the world [5], Studies of the economic viability of SCF extraction of several... 

Residuum oil supercritical extraction-petroleum deasphalting Polymer fractionation Edible oils fractionation Analytical SCF extraction and chromatography Reactive separations... 

Coupling SCF Extraction with Nanofiltration for Process Intensification. 185... 

COUPLING SCF EXTRACTION WITH NANOFILTRATION FOR PROCESS INTENSIFICATION... 

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