16. How are supercritical fluids formed? Particles are compressed by high pressure Not gas Particles have a large amount of kinetic energy (due to high temperature) Not liquid Have properties intermediate between those of gases and liquids
17. How are supercritical fluids formed? Separate phases of CO2 Meniscus is easily observed
19. How are supercritical fluids formed? Gas and liquid densities to become more similar
20. How are supercritical fluids formed? Meniscus no longer seen; One homogenous phase phase occurs
21. What are the properties of supercritical fluids?
22. Solvating Power Solvating power: ability of a solvent to dissolve a solute Good solvent - Near liquid density
23. Diffusivity High diffusivity Due to its gas-like properties Lower density than liquid: more space for particles to move High temperatures: particles move faster
28. Polarity Most supercritical fluids behave like non-polar solvents Possible to tune their polarity by adding a polar co-solvent e.g. ethanol Increases the solubility for specific compounds
29.
30.
31. Why Carbon Dioxide? Low critical temperature (31°C) Safe to use Non-toxic Non-flammable Chemically inert
32. Why Carbon Dioxide? Inorganic No residual VOCs Reusable Supercritical CO2 as a solvent can be recovered and recycled Odourless No unpleasant odours
37. Fluoropolymer Production Problems with present dispersion mediums: Using water: Low product quality Using organic compounds: Severe environmental hazards
39. Cleaning Process is similar to extraction – Substances “extracted” are impurities, etc Applications: Precision cleaning Dry cleaning Preserving artworks
40. Formation of nanoparticles Rapid Expansion of Supercritical Solutions (RESS) Sudden pressure drop Dissolved material precipitated out Crystals formed enclose a small amount of the supercritcal solvent Supercritical fluid changes to its normal state (usually gas) Crystal broken from inside-out Forms nanoparticles
41. Formation of nanoparticles Advantages of using supercritical fluid Easy isolation Particles formed are shown to be extremely homogeneous in size Short processing times
42. Drying Normal Drying (follow green arrow) Problems: Surface tension in the liquid body pulls against solid structures Breaks delicate structures
46. Manufacturing Incorporation of aforementioned processes Better alternative to traditional solvents Sustainable way to meet rising needs of growing population
47. Medicine Preparation and coating of drugs Formation of powders of macromolecules Microporous Foams for tissue engineering Sterilisation
48. Geothermal Energy Generation Current system: Water is pumped deep underground to collect heat Supercritical CO2 to replace water Flows more freely through rock Eliminates need to pump fluid CO2 sequestration
49. Recycling Radioactive Wastes Used to recover uranium from ashes of radioactive garbage Nearly 10% of radioactive ash weight Worth about $900 per pound
55. Conclusion High initial start-up costs associated with developing task-specific equipment Solutions: Further research to develop technology Prohibition of certain traditional solvents that although are cheaper (in the short-term), are detrimental to our environment/human health Cost/benefit analysis of the technology