Supercritical fluids adsorption

KING Supercritical Fluid Adsorption at the Gas-Solid Interface... 

Further discussion on the theoretical aspects of supercritical fluid adsorption on solids can be found by consulting the papers of Findenegg (35-37). The importance of the high pressure... 

A normal phase lclulcl I reversed phase Supercritical fluid Adsorption Partition Bonded phase Ion exchange Exclusion Hydrophobic Zonal Frontal Linear... 

Separation Techniques. Current methods for separating fatty acids are by solvent crystaUi2ation or by the hydrophili2ation process. Other methods that have been used in the past, or perhaps could be used in the future, are panning and pressing, solvent extraction, supercritical fluid extraction, the use of metal salts in assisting in separation, separations using urea complexes, and adsorption/desorption. 

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. 

D. E. Martue, Unified theory of adsorption clrromatography gas, liquid and supercritical fluid mobile phases , 7. Chmmatogr. 451 17-30(1988). 

General trends are focused on reduced-solvent extractions or adsorption-based methods — enviromnentaUy friendly solvents for both solid and liquid samples. In recent decades, advanced techniques like supercritical fluid extraction (SFE), ° pressurized liquid extraction (PLE)," microwave-assisted extraction (MAE), ultrasound-assisted extraction, countercurrent continued extraction (www.niroinc.com), solid... 

Classical sample preparation methods such as distillation, soxhlet extraction are still used [839, 840], but specific techniques such as supercritical fluid extraction (SFE) [841], and increasingly in recent years, adsorption techniques such as solid phase micro-extraction (SPME) [841a] are also being used for isolation, separation, and identification of flavor and fragrance materials. 

Analytes can be separated from complex matrices by sample preparation techniques that include liquid extraction, supercritical fluid extraction, and solid-phase extraction. Dilute ionic analytes can be preconcentrated by adsorption onto an ion-exchange resin. Nonionic analytes can be concentrated by solid-phase extraction. Derivatization transforms the analyte into a more easily detected or separated form. 

It appears that temperatures in the range of 500.to 670 K for the adsorption of n-paraffins in the 560-740 K boiling range on type 5A molecular sieves should be considered for investigating the combination supercritical fluid volatility amplification-vapor phase molecular sieve process. The pressure of operation will be governed by the critical pressures of potential solvents with critical temperatures in this range. The supercritical solvent of choice should not be adsorbable on type 5A molecular sieves and should not be expensive. 

The combination supercritical fluid volatility amplification-molecular sieve process has the potential for producing two valuable products simultaneously from gas oil-lube oil petroleum stocks. In a flow-through molecular sieve bed, the leading adsorption front operates in the lean molecular sieve loading range, providing the conditions needed for the n-paraffin removal needed to produce low pour lube oil, while the trailing adsorption... 

U. Ullsten and K. E. Markides, Automated on-line solid phase adsorption/supercritical fluid extraction/supercritical fluid chromatography of analytes from polar solvents , J. Micmcolumn Sep. 6 385-393 (1994). 

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