Supercritical fluid RESS

Keywords Microencapsulation Fluidized-bed Supercritical Fluids RESS process... 

Homogeneous precipitation of particles from supercritical solvents (rapid expansion of supercritical fluids (RESS)). Applications are microparticles for pharmaceutics [45]. 

Keith P. Johnston/ Ph.D./ P.E./ Profe.s.sor of Chemical Engineering, University of Texas (Austin) Member, American In stitute of Chemical Engineers, American Chemical Society, Univ. of Texas Separations Re.search Program. (Supercritical Fluid Separation Proce.s.se.s)... 

Entries on new materials, including re-cyclate plastics, fullerenes, hard-surfaced polymers, dendrimers, transflective materials, rapid prototyping materials, silicone nitride, supercritical fluids, bulk molding compounds, conversion coatings, folic acid, replacements for chloro-fluorocarbons ... 

Manoi, K. and Rizvi, S. S. H. (2008). Rheological characterizations of texturized whey protein concentrate-based powders produced by reactive supercritical fluid extrusion. Food Res. Int. 41, 786-796. 

Supercritical fluid extraction (SFE) is a technique in which a supercritical fluid [formed when the critical temperature Tf) and critical pressure Pf) for the fluid are exceeded simultaneously] is used as an extraction solvent instead of an organic solvent. By far the most common choice of a supercritical fluid is carbon dioxide (CO2) because CO2 has a low critical temperature (re = 31.1 °C), is inexpensive, and is safe." SFE has the advantage of lower viscosity and improved diffusion coefficients relative to traditional organic solvents. Also, if supercritical CO2 is used as the extraction solvent, the solvent (CO2) can easily be removed by bringing the extract to atmospheric pressure. Supercritical CO2 itself is a very nonpolar solvent that may not have broad applicability as an extraction solvent. To overcome this problem, modifiers such as methanol can be used to increase the polarity of the SFE extraction solvent. Another problem associated with SFE using CO2 is the co-extraction of lipids and other nonpolar interferents. To overcome this problem, a combination of SFE with SPE can be used. Stolker et al." provided a review of several SFE/SPE methods described in the literature. 

If simple sample pretreatment procedures are insufficient to simplify the complex matrix often observed in process mixtures, multidimensional chromatography may be required. Manual fraction collection from one separation mode and re-injection into a second mode are impractical, so automatic collection and reinjection techniques are preferred. For example, a programmed temperature vaporizer has been used to transfer fractions of sterols such as cholesterol and stigmasterol from a reversed phase HPLC system to a gas chromatographic system.11 Interfacing gel permeation HPLC and supercritical fluid chromatography is useful for nonvolatile or thermally unstable analytes and was demonstrated to be extremely useful for separation of compounds such as pentaerythritol tetrastearate and a C36 hydrocarbon standard.12... 

Kado, N. Y., J. M. Wing, P. A. Kuzmicky, J. E. Woodrow, H. Ning, J. N. Seiber, and D. P. H. Hsieh, Quantitative Integration of the Salmonella Microsuspension Assay with Supercritical Fluid Extraction of Model Airborne Vapor-Phase Mutagens, Mutat. Res., 271, 253-260 (1992). 

Lemert, R.M., Johnston, K.P., "Chemical Complexing Agents for Enhanced Solubilities in Supercritical Fluid Carbon Dioxide," submitted to I EC Res., 1990. 

Once the extraction is complete, the static/dynamic selection valve is repositioned to the dynamic mode to allow flow. Subsequently, pressure and density are rapidly reduced to prevent significant losses of the supercritical fluid from the syringe pump tank and the extraction effluent, which is being transferred for collection. With a non-re-stricted transfer, the flow of supercritical fluid effluent is rapid. This desire for rapid depressurization led to the development of a delivery nozzle which would ensure collection of the extracted solutes without losses. Details of this delivery system can be found in the next section. 

Delivery of Extract Delivery Nozzle. Delivery of the extraction effluent is conducted via the six port static/dynamic valve while in the dynamic mode. Generally, extractions are conducted at a high density in the static mode. Once the extraction is complete, the valve is re-positioned into a dynamic evacuation, pressure or density is reduced rapidly to prevent significant losses of the supercritical fluid and the extraction effluent is transferred for collection. The extract leaves through the heated static/dynamic valve to the heated lines then to the delivery nozzle(s). Figure 8 shows a diagram of the delivery nozzle and its components. 

Lin, Y., Liu, C., Wu, H., Yak, H.K., Wai, C.M. 2003. Supercritical fluid extraction of toxic heavy metals and uranium from acidic solutions with sulfur-containing organo-phosphorus reagents. Ind. Eng. Chem. Res. 42 (7) 1400-1405. 

Ganapathy, S. Carlier, C. Randolph, T. W. O Brien, J. A. Influence of Local Structural Correlations on Free-Radical Reactions in Supercritical Fluids A Hierarchical Approach, Ind. Eng. Chem. Res. 1996, 35, 19-27. 

Matson, D. W. Fulton, J. L. Petersen, R. C. Smith, R. D. Rapid Expansion of Supercritical Fluid Solution Solute Formation of Powders, Thin Films and Fibers. Ind. Eng. Chem. Res. 1987, 26, 2298-2306. 

D.W. Matson, J.L. Fulton, R.C. Petersen, R.D. Smith, Rapid expansion of supercritical fluid solutions solute formation of powders, thin films and fibers, Ind. Eng. Chem. Res. 26 (1987) 2298-2306. 

S. Rokushika, K. Naikwadi, et al., Liquid crystal stationary phases for gas chromatography and supercritical fluid chromatography, HRC CC J. High Res. Chromatogr. Chromatog. Commun., 5 480-484(1985). 

Palakodaty S, York P. 1999. Phase behavior effects on particle formation processes using supercritical fluids. Pharm. Res. 16(7) 976-985. 

Chester, T. L., and Innis, D. P. (1986). Separation of oligo- and polysaccharides by capillary supercritical fluid chromatography. J. High Res. Chromatogr. Chromatogr. Commun. 9 209-212. 

Lee, C. H. Holder, G. D., Use of Supercritical Fluid Chromatography for Obtaining Mass Transfer Coefficients in Fluid-Solid Systems at Supercritical Conditions, Ind. Eng. Chem. Res., 1995, 34, 906-914... 

The effect of cyclopentadienyl-ring substituents on the reactivity of the group VII half-sandwich complexes (t7 -C5R5)M(CO)2L[M = Mn and Re R = H, Me, and Et (Mn only) L = Kr and Xe] toward CO in supercritical fluid solution at room temperature has been investigated (70). The reactivity of the corresponding alkane complexes ( 7 -C5R5)Mn(CO)2(n-heptane) (R = H, Me, and Et) toward small molecules such as CO, N2, and H2 in n-heptane solution steadily increased in the order H < Me < Et (71). These results indicated that steric rather... 

Lin M, Katsumura Y, Muroya Y, He H. (2006) A high temperature/pressure optical cell for absorption studies of supercritical fluids by laser photolysis. Indian J Radiat Res 3-. 69-77. 

---