- Rapid Expansion of Supercritical Solution (RESS),
- in which a drug is dissolved in an SCF such as CO
- and then sprayed into a collection chamber. The solvent is then rapidly removed, resulting in well-defined, uniform drug particles. RESS is a simple and effective technique, but is restricted by the limited solubility of drugs in SCFs.
- Gas Anti-Solvent (GAS)
- is another popular technique, shown in
- (
- ). In this case, a gas such as CO
- is added to an organic solution of a desired drug, resulting in the expansion of the organic solvent and the precipitation of uniform drug particles. The precipitation is easily tuned by adjusting temperature and CO
- pressure, allowing close control of particle size and morphology. GAS takes advantage of the organic solvent’s strength coupled with the tunable solvent expandability. However, it requires semi-batch operation.
- Supercritical Anti-Solvent (SAS) and Solution Enhanced Dispersion by Supercritical fluids (SEDS)
- allow for continuous operation and control. In both of these processes, the drug solution is sprayed into the SCF or mixed with the SCF and sprayed into a collection vessel. Nozzle design and inlet stream flow rates can be adjusted to control the process while utilizing the solvent’s tunability.
- Gas eXpanded Liquids (GXLs),
- organic solvents mixed with carbon dioxide gas, which expands their volume by a factor of 10 or more. Nutraceuticals production has moved in the direction of GXLs, by using ethanol cosolvent as a polar modifier with scCO
- . This results in a solvent medium that can combine synthesis and product recovery in a simplified and efficient “one pot” system.
- Near-critical Water (NCW),
- which offers organic solubilities and the potential for reversible acid/base catalysis.
- Organic/Aqueous Tunable Solvents (OATS),
- or water-soluble catalysts (including both aqueous organometallic complexes and enzymatic biocatalysts) that can perform difficult transformations on highly hydrophobic substrates.
- Miscible water/organic systems,
- where a catalyst is modified for aqueous solubility;
- Miscible poly(ethylene glycol)/organic systems,
- where a catalyst is modified for PEG solubility;
- Immiscible fluorous/organic liquid/liquid or solid/liquid systems,
- where the catalyst is modified for fluorous solubility;
- Immiscible water/organic systems
- involving phase transfer catalysts.
http://www.che.gatech.edu/ssc/eckert/.Dr. Christopher L. Kitchens is a Post Doctoral Researcher in the Eckert-Liotta Joint Research Group at Georgia Institute of Technology. He received a B.S. in Chemistry from Appalachian State University and a Ph.D. in Chemical Engineering from Auburn University, where he worked on nanoparticle synthesis and processing in tunable fluids.
Dr. Jason P. Hallett is a Research Engineer in the Eckert-Liotta Joint Research Group at Georgia Institute of Technology. He received a B.S. in Chemical Engineering from the University of Maine and a Ph.D. in Chemical Engineering from Georgia Institute of Technology, where he worked on novel methods for homogeneous catalyst recycle.References
Dr. Jason P. Hallett is a Research Engineer in the Eckert-Liotta Joint Research Group at Georgia Institute of Technology. He received a B.S. in Chemical Engineering from the University of Maine and a Ph.D. in Chemical Engineering from Georgia Institute of Technology, where he worked on novel methods for homogeneous catalyst recycle.References
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