Presented by:
Clyde Jonathan D’Silva

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Super critical Fluids and its Applications
INTRODUCTION
• Definition: Supercritical Fluid is any substance at a temperature and pressure above its Critical point.
• Example: Commonly used Supercritical fluids are CO2 & H2O.
Phase Diagram:
• Few SCF
PROPERTIES OF SCF
• Can penetrate solids like gas.
• Dissolves materials like liquid.
• There is no surface tension in SCF.
• It has a very good solvent property.
• In supercritical environment only one phase exists and hence no liquid-gas phase boundary.
• Close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties to be "fine-tuned”.
• All supercritical fluids are completely miscible with each other.
• So for a mixture, single phase can be guaranteed if the critical point of the mixture is exceeded.
• The critical point of a binary mixture can be estimated as the arithmetic mean of the critical temperatures and pressures of the two components,
• Tc(mix) = (mole fraction A) x TcA + (mole fraction B) x TcB.
• Most important properties is the solubility of material in the fluid. Solubility in a SCF tends to increase with density of the fluid (at const. temp.).
• Since density increases with pressure, solubility tends to increase with pressure. At constant density, solubility will increase with temperature.
• However, close to the critical point, the density can drop sharply with a slight increase in temperature.
• Therefore, close to the critical temperature, solubility often drops with increasing temperature, then rises again.
NATURAL OCCURRENCE
• Submarine -Volcanoes: Steam & gases which are releases from the volcanoes are in high pressure (about 300atm) & temperature (>275*C).
• Planetary –atmosphere: Many planets atmosphere is Supercritical environment for some fluid. Like –Venus, Jupiter etc.
APPLICATIONS
EXTRACTION
Basic procedure:
 Partition volatile substances by contacting Supercritical Fluid with feed material.
 Soluble material dissolve into the Supercritical Fluid.
 The extracted component then separated by changing pressure & temperature.
 Finally the SCF recompressed & recycled.
Advantages:
 It is relatively rapid for low viscosity & high diffusivity of SCF
 Easily recoverable by changing pressure and temp.
 Non-toxic solvents leave no harmful residue.
 Can be selective by controlling density.
 High boiling components are extracted at relatively low temp.
Uses:
 IT is largely used in Food & Flavouring industry.
 This method is used for Decaffenication of tea & coffee.
 Extraction of essential oils, aroma materials from spices etc.
NANO-PARTICLE SYNTHESIS
• Supercritical Fluid Precipitation technology produces particles with Nano-dimension.
• Supercritical fluids provide a number of ways of achieving this by rapidly exceeding the saturation point of a solute by dilution, depressurization or a combination of these.
• These processes occur faster in supercritical fluids than in liquids, promoting nucleation over crystal growth and yielding very small and regularly sized particles.
• Recent supercritical fluids have shown the capability to reduce particles up to a range of 5-2000 nm
• This technique is largely used in Pharmaceutical industry
MICRONIZATION
• Micronization is the process of reducing the average diameter of a solid material's particles. Usually, the term micronization is used when the particles that are produced are only a few micrometres in diameter.
• However, modern applications (usually in the pharmaceutical industry) require average particle diameters of the nanometer scale.
• Modern methods using supercritical fluids in the micronization process are
1. RESS process (Rapid Expansion of Supercritical Solutions)
2. SAS method (Supercritical Anti-Solvent)
3. PGSS method (Particles from Gas Saturated Solutions).
RESS METHOD
• The SCF is used to dissolve the solid material under high pressure and temperature, thus forming a homogeneous supercritical phase.
• The solution is expanded through a nozzle and small particles are formed.
• At the rapid expansion point right at the opening of the nozzle there is a sudden pressure drop that forces the dissolved material (the solid) to precipitate out of the solution.
• The crystals that are instantly formed enclose a small amount of the solvent that, due to the expansion, changes from supercritical fluid to its normal state (usually gas), thus breaking the crystal from inside-out. At the same time, further reduction of size is achieved while the forming and breaking crystals collide with each other at the vicinity of the nozzle. The particles that are formed this way have a diameter of a few hundreds of nanometers.
SAS METHOD
• In the SAS method, the solid material is dissolved in an organic solvent and a supercritical fluid is then also forced by means of pressure to dissolve in the system. In this way, the volume of the system is expanded, thus lowering the density, and therefore also the solubility of the material of interest is decreased. As a result, the material precipitates out of the solution as a solid with a very small particle diameter.
PGSS METHOD
• In the PGSS method the solid material is melted and the supercritical fluid is dissolved in it, like in the case of the SAS method. However, in this case the solution is forced to expand through a nozzle, and in this way nanoparticles are formed.
• In all three methods described, the effect that causes the small diameter of the solid particles is the supersaturation that occurs at the time of the particle formation
• The PGSS method has the advantage that because of the supercritical fluid, the melting point of the solid material is reduced. Therefore, the solid melts at a lower temperature than the normal melting temperature at ambient pressure
• These processes also do not demand long processing times, like the case in the traditional methods
Carbon capture and storage and Enhanced oil recovery
• Supercritical carbon dioxide is used to enhance oil recovery in mature oil fields.
• The CO2 is separated from other flue gases either pre- or post-combustion, compressed to the supercritical state, and injected into geological storage, possibly into existing oil fields to improve yields.
Chemical Reactions
• Changing the conditions of the reaction solvent can allow separation of phases for product removal, or single phase for reaction.
• Rapid diffusion accelerates diffusion controlled reactions.
• Temperature and pressure can tune the reaction down preferred pathways, e.g., to improve yield of a particular chiral isomer.There are also significant environmental benefits over conventional organic solvents.
Impregnation and dyeing
• Impregnation is the converse of extraction.
• A substance is dissolved in the supercritical fluid, the solution flowed past a solid substrate, and is deposited on or dissolves in the substrate.
• Dyeing, which is readily carried out on polymer fibres such as polyester using disperse (non-ionic) dyes, is a special case of this.
Biodiesel production
• Conversion of vegetable oil to biodiesel is via a transesterification reaction, where the triglyceride is converted to the methyl ester plus glycerol. This is usually done using methanol and caustic or acid catalysts, but can be achieved using supercritical methanol without a catalyst.
• This has the advantage of allowing a greater range and water content of feedstocks (in particular, used cooking oil), the product does not need to be washed to remove catalyst, and is easier to design as a continuous process.
Generation of pharmaceutical Co-crystals
• SCF act as a new media for the generation of novel crystalline forms of APIs (Active Pharmaceutical Ingredients) named as pharmaceutical cocrystals.
• Supercritical fluid technology offers a new platform that allows a single-step generation of particles that are difficult or even impossible to obtain by traditional techniques.
• The generation of pure and dried new cocrystals can be achieved due to unique properties of SCFs by using different supercritical fluid properties: supercritical CO2 solvent power, anti-solvent effect and its atomization enhancement.
Supercritical fluid chromatography
• Supercritical fluid chromatography (SFC) can be used on an analytical scale, where it combines many of the advantages of High performance liquid chromatography (HPLC) and Gas chromatography (GC).
• It can be used with non-volatile and thermally labile analytes (unlike GC) and can be used with the universal flame ionization detector (unlike HPLC), as well as producing narrower peaks due to rapid diffusion
• In practice, the advantages offered by SFC have not been sufficient to displace the widely used HPLC and GC, except in a few cases such as chiral separations and analysis of high-molecular-weight hydrocarbons.
• For manufacturing, efficient preparative simulated moving bed units are available.
• The purity of the final products is very high, but the cost makes it suitable only for very high-value materials such as pharmaceuticals.
Dry Cleaning
• Supercritical carbon dioxide (SCD) can be used instead of PERC (perchloroethylene) or other undesirable solvents for dry cleaning.
• Detergents that are soluble in carbon dioxide improve the solvating power of the solvent.
• Disadvantage: Supercritical carbon dioxide sometimes intercalates into buttons, and, when the SCD is depressurized, the buttons pop, or break apart.
Refrigeration
• Supercritical carbon dioxide is also an important emerging refrigerant, being used in new, low-carbon solutions for domestic heat pumps.
• These systems are undergoing continuous development with SCD heat pumps already being successfully marketed in Asia.
• Some systems developed by consortium of companies including Mitsubishi in Japan, develop high-temperature domestic water with small inputs of electric power by moving heat into the system from their surroundings. Their success makes a future use in other world regions possible.
Supercritical water power generation
• The efficiency of a heat engine is ultimately dependent on the temperature difference between heat source and sink (Carnot cycle).
• To improve efficiency of power stations the operating temperature must be raised. Using water as the working fluid, this takes it into supercritical conditions. Efficiencies can be raised from about 39% for subcritical operation to about 45% using current technology.
• Supercritical water reactors (SCWRs) are promising advanced nuclear systems that offer similar thermal efficiency gains.
• Carbon dioxide can also be used in supercritical cycle nuclear plants, with similar efficiency gains
Supercritical water oxidation
• Uses supercritical water to oxidize hazardous waste, eliminating production of toxic combustion products that burning can produce.
Antimicrobial Properties
• Beside other highly compressed fluids particularly CO2 at high pressures has antimicrobial properties.
• While its effectiveness has been shown for various applications, the mechanism of inactivation have not been fully understood.