Supercritical Fluid (SCF) ?

A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. 

It can effuse through porous solids like a gas, overcoming the mass transfer limitations that slow liquid transport through such materials.

SCF are much superior to gases in their ability to dissolve materials like liquids or solids. In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be “fine-tuned”.

There is no surface tension in a supercritical fluid, as there is no liquid/gas phase boundary. By changing the pressure and temperature of the fluid, the properties can be “tuned” to be more liquid-like or more gas-like.

One of the most important properties is the solubility of the material in the fluid. Solubility in a supercritical fluid tends to increase with the density of the fluid (at constant temperature). Since density increases with pressure, solubility tends to increase with pressure.

The relationship with temperature is a little more complicated. 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.

Many pressurized gases are supercritical fluids. For example, nitrogen has a critical point of 126.2 K (−147 °C) and 3.4 MPa (34 bar). Therefore, nitrogen (or compressed air) in a gas cylinder above this pressure is a supercritical fluid.

These are more often known as permanent gases. At room temperature, they are well above their critical temperature, and therefore behave as a nearly ideal gas, like CO2 at 400 K above. However, they cannot be liquified by mechanical pressure unless cooled below their critical temperature, requiring gravitational pressure to produce a liquid or solid at high temperatures.

 Above the critical temperature, elevated pressures can increase the density enough that the SCF exhibits liquid-like density and behaviour.  At very high pressures, an SCF can be compressed into a solid because the melting curve extends to the right of the critical point in the P/T phase diagram below

 While the pressure required to compress supercritical CO2 into a solid can be, depending on the temperature, as low as 570 MPa, that required to solidify supercritical water is 14,000 MPa.

Supercritical C02 Fluid

Due to their high density, supercritical fluids have high solvation power and thus can be used as solvents.  The most widely employed supercritical fluid is carbon dioxide (SC-CO₂)

Phase Diagrams

Fig.1  Pressure/ Temperature Diagram

Fig 2. Density /Pressure Diagram

The appearance of a single-phase can also be observed in the density-pressure phase diagram for carbon dioxide (Fig. 2). At well below the critical temperature, e.g., 280 K, as the pressure increases, the gas compresses and eventually (at just over 40 bar) condenses into a much denser liquid, resulting in the discontinuity in the line (vertical dotted line). The system consists of 2 phases in equilibrium, a dense liquid and a low-density gas. As the critical temperature is approached (300 K), the density of the gas at equilibrium becomes higher, and that of the liquid lower. At the critical point, (304.1 K and 7.38 MPa (73.8 bar)), there is no difference in density, and the 2 phases become one fluid phase. Thus, above the critical temperature, gas cannot be liquefied by pressure.

At slightly above the critical temperature (310 K), in the vicinity of the critical pressure, the line is almost vertical. A small increase in pressure causes a large increase in the density of the supercritical phase. Many other physical properties also show large gradients with pressure near the critical point, e.g. viscosity, relative permittivity and solvent strength, which are all closely related to the density.

At higher temperatures, the fluid starts to behave more like an ideal gas, with a more linear density/pressure relationship, as can be seen in Figure 2. For carbon dioxide at 400 K, the density increases almost linearly with pressure.

Our Primary Application is SFE, SFF, SFC and PSFC

1. Supercritical fluid extraction SFE

Why is carbon dioxide used most often in SFE?

Supercritical fluid extraction has emerged as an attractive separation technique for the food and pharmaceutical industries due to a growing demand for “natural” processes that do not introduce any residual organic chemicals.

Supercritical carbon dioxide is by far the most used supercritical fluid. It is non-flammable and non-toxic. The unique solvent properties of supercritical carbon dioxide have made it a desirable compound for separating antioxidants, pigments, flavours, fragrances, fatty acids, and essential oils from plant and animal materials.

In the supercritical state, carbon dioxide behaves as a lipophilic solvent and therefore, can extract most nonpolar solutes. The separation of the carbon dioxide from the extract is simple and nearly instantaneous. No solvent residue is left in the extract as would be typical with organic solvent extraction.

Unlike liquid solvents, the solvating power of supercritical carbon dioxide can be easily adjusted by slight changes in the temperature and pressure, making it possible to extract compounds of interest.

With the addition of small amounts of polar co-solvents, even polar materials can be extracted. Additional advantages of carbon dioxide are that it is inexpensive, it is available in high purity, it is FDA approved, and it is generally regarded as a safe compound (GRAS, Generally Recognized As Safe)

Supercritical carbon dioxide is also desirable for the extraction of compounds that are sensitive to extreme conditions because it has a relatively low critical temperature (31°C). It is used on a large scale for the decaffeination of green coffee beans, the extraction of hops for beer production, and the production of essential oils and pharmaceutical products from plants. 

CO2 extraction of cannabis and hemp at high pressures (>5000 psi, >345 bar) offers the dual advantage of high yields and short run times.

The advantages of supercritical fluid extraction (compared with liquid extraction) are that it is relatively rapid because of the low viscosities and high diffusivities associated with supercritical fluids.

The extraction can be selective to some extent by controlling the density of the medium, and the extracted material is easily recovered by simply depressurizing, allowing the supercritical fluid to return to the gas phase and evaporate leaving little or no solvent residues.  Some systems will also recycle CO2.

CO2 is a low-cost resource and climatic neutral.

There are a few laboratory test methods that include the use of supercritical fluid extraction as an extraction method instead of using traditional solvents.

Many large scale units are operated worldwide for the extraction of solid natural materials, mainly for food ingredients and phytopharmaceuticals. Residual organic solvents and other impurities can also be removed from final active compounds or high-grade polymers

2. Supercritical Fluid Fractionation (SFF)

Supercritical Fluid has a very high selectivity at attractive costs, especially under continuous operation. This is used in an industrial environment to increase value and quality.  Popular are Polymer fractionation (speciality lubricants, Pharmaceuticals, aroma production from fermented and distilled beverages, polyunsaturated fatty acids, active compounds from the fermentation broth, pollution abatement on aqueous stream etc.

3. Supercritical Fluid Chromatography (SFC)

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 traditional HPLC detectors including RI, UV-VIS, ELSD, MS.

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.

4. Preparative-scale Supercritical Fluid Chromatography (PSFC)

Industrial development is focused on the purification of polyunsaturated fatty acids and enantiomers

Mixtures with other solvents

Supercritical fluids are completely miscible with another solvent so that a binary mixture forms a single gaseous phase if the critical point of the mixture is exceeded. However, exceptions are known in systems where one component is much more volatile than the other, which in some cases form two immiscible gas phases at high pressure and temperatures above the component critical points. This behaviour has been found for example in the systems N₂-NH₃, NH₃-CH₄, SO₂-N₂ and n-butane-H₂O.

Mixture with other Solvents

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) × Tc(A) + (mole fraction B) × Tc(B).

For greater accuracy, the critical point can be calculated using equations of state, such as the Peng-Robinson, or group-contribution methods. Other properties, such as density, can also be calculated using equations of state.

Research and Development Applications

More recently, supercritical fluids have found application in a variety of fields, ranging from the extraction of floral fragrance from flowers to applications in food science such as creating decaffeinated coffee, functional food ingredients, pharmaceuticals, cosmetics, polymers, powders, bio- and functional materials, nano-systems, natural products, biotechnology, fossil and biofuels, microelectronics, energy, and environment.

Much of the excitement and interest of the past decade is due to the enormous progress made in increasing the power of relevant experimental tools. The development of new experimental methods and improvement of existing ones continues to play an important role in this field, with recent research focusing on the dynamic properties of fluids.

Impregnation

The great diffusivity of supercritical fluid permits to reach homogeneous distribution of active compounds in various porous matrixes: drug in patches or medical devices, preservatives in wood,  deacidification and reinforcement agents in books, aromas in food products, concrete carbonation for mechanical properties improvement etc.

Particle design

Many pharmaceutical companies use Supercritical Fluids for the manufacture of new drug delivery systems (micro/nanoparticles, complex microspheres/capsules, coated tablets and beads. Some also perform polymer powder engineering to manufacture speciality products, Paint companies experiment with creating a new form of paint.

Decomposition of Biomass

Supercritical water can be used to decompose biomass via supercritical water gasification of biomass. This type of biomass gasification can be used to produce hydrocarbon fuels for use in an efficient combustion device or to produce hydrogen for use in a fuel cell. In the latter case, hydrogen yield can be much higher than the hydrogen content of the biomass due to steam reforming where water is a hydrogen-providing participant in the overall reaction.

Dry-cleaning

Supercritical carbon dioxide (SCD) can be used instead of PERC (perchloroethylene) or other undesirable solvents for dry-cleaning. Supercritical carbon dioxide sometimes intercalates into buttons, and, when the SCD is depressurized, the buttons pop, or break apart. Detergents that are soluble in carbon dioxide improve the solvating power of the solvent. CO2-based dry-cleaning equipment uses liquid CO2, not supercritical CO2, to avoid damage to the buttons.

Chemical reactions

Changing the conditions of the reaction solvent can allow the 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 the yield of a particular chiral isomer. There are also significant environmental benefits over conventional organic solvents. Industrial syntheses that are performed at supercritical conditions include those of polyethene from supercritical ethene, isopropyl alcohol from supercritical propane, 2-butanol from supercritical butene, and ammonia from a supercritical mix of nitrogen and hydrogen. Other reactions were, in the past, performed industrially in supercritical conditions, including the synthesis of methanol and thermal (non-catalytic) oil cracking. Because of the development of effective catalysts, the required temperatures of those two processes have been reduced and are no longer supercritical.

Impregnation and dyeing

Impregnation is, in essence, 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. Carbon dioxide also dissolves in many polymers, considerably swelling and plasticising them and further accelerating the diffusion process.

Nano and microparticle formation (Micronization)

The formation of small particles of a substance with a narrow size distribution is an important process in pharmaceutical and other industries. Supercritical fluids provide several 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 or spinodal decomposition 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.

Generation of pharmaceutical co-crystals

Supercritical fluids act as a new media for the generation of novel crystalline forms of APIs (Active Pharmaceutical Ingredients) named 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 (crystalline molecular complexes comprising the API and one or more conformers in the crystal lattice) can be achieved due to the unique properties of SCFs by using different supercritical fluids properties: supercritical CO2 solvent power, anti-solvent effect and its atomization enhancement.

Aerogel Drying

The manufacture of highly efficient insulation material  or special porous materials (Catalyst, porous supports) on a large scale from both inorganic (e.g. Silica ) and organic sol-gel polymers

Supercritical drying (Critical point drying)

Supercritical drying is a method of removing solvent without surface tension effects. As a liquid dries, the surface tension drags on small structures within a solid, causing distortion and shrinkage. Under supercritical conditions, there is no surface tension, and the supercritical fluid can be removed without distortion. Supercritical drying is used in the manufacturing process of aerogels and drying of delicate materials such as archaeological samples and biological samples for electron microscopy.

Supercritical water oxidation

Supercritical water oxidation uses supercritical water as a medium in which to oxidize hazardous waste, eliminating the production of toxic combustion products that burning can produce.

The waste product to be oxidised is dissolved in the supercritical water along with molecular oxygen (or an oxidising agent that gives up oxygen upon decomposition, e.g., hydrogen peroxide) at which point the oxidation reaction occurs. [citation needed]

Supercritical water hydrolysis

Supercritical hydrolysis is a method of converting all biomass polysaccharides as well the associated lignin into low molecular compounds by contacting with water alone under supercritical conditions. Supercritical water acts as a solvent, a supplier of bond-breaking thermal energy, a heat transfer agent and as a source of hydrogen atoms. All polysaccharides are converted into simple sugars in near-quantitative yield in a second or less. The aliphatic inter-ring linkages of lignin are also readily cleaved into free radicals that are stabilized by hydrogen originating from the water. The aromatic rings of the lignin are unaffected under short reaction times so that the lignin-derived products are low molecular weight mixed phenols. To take advantage of the very short reaction times needed for cleavage a continuous reaction system must be devised. The amount of water heated to a supercritical state is thereby minimized.

Supercritical water gasification

Supercritical water gasification is a process of exploiting the beneficial effect of supercritical water to convert aqueous biomass streams into clean water and gases like H2, CH4, CO2, CO etc. [26]

Supercritical fluid in power generation

The efficiency of a heat engine is ultimately dependent on the temperature difference between heat source and sink (Carnot cycle). To improve the efficiency of power stations the operating temperature must be raised. Using water as the working fluid takes it into supercritical conditions. Efficiencies can be raised from about 39% for the 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 power plants, with similar efficiency gains.[29] Many coal-fired supercritical steam generators are operational all over the world and have enhanced the efficiency of traditional steam-power plants.

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. The method of using supercritical methanol for biodiesel production was first studied by Saka and his co-workers. 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 the catalyst, and is easier to design as a continuous process.

Enhanced oil recovery and carbon capture and storage

Supercritical carbon dioxide is used to enhance oil recovery in mature oil fields. At the same time, there is the possibility of using “clean coal technology” to combine enhanced recovery methods with carbon sequestration. The CO2 is separated from other flue gases, compressed to the supercritical state, and injected into geological storage, possibly into existing oil fields to improve yields.

At present, only schemes isolating fossil CO2 from natural gas use carbon storage, (e.g., Sleipner gas field), but there are many plans for future CCS schemes involving pre- or post-combustion CO2. There is also the possibility to reduce the amount of CO2 in the atmosphere by using biomass to generate power and sequestering the CO2 produced.

Enhanced geothermal system

The use of supercritical carbon dioxide, instead of water, has been examined as a geothermal working fluid.

Refrigeration

Supercritical carbon dioxide is also emerging as a useful high-temperature refrigerant, being used in new, CFC/HFC-free domestic heat pumps making use of the transcritical cycle. These systems are undergoing continuous development with supercritical carbon dioxide heat pumps already being successfully marketed in Asia. The EcoCute systems from Japan are some of the first commercially successful high-temperature domestic water heat pumps.

Supercritical fluid deposition

Supercritical fluids can be used to deposit functional nanostructured films and nanometre-size particles of metals onto surfaces. The high diffusivities and concentrations of precursor in the fluid as compared to the vacuum systems used in chemical vapour deposition allow the deposition to occur in a surface reaction rate limited regime, providing stable and uniform interfacial growth. This is crucial in developing more powerful electronic components, and metal particles deposited in this way are also powerful catalysts for chemical synthesis and electrochemical reactions. Additionally, due to the high rates of precursor transport in solution, it is possible to coat high surface area particles which under chemical vapour deposition would exhibit depletion near the outlet of the system and be likely to result in unstable interfacial growth features such as dendrites. The result is very thin and uniform films deposited at rates much faster than atomic layer deposition, the best other tools for particle coating at this size scale.

Antimicrobial properties  

CO2 at high pressures has antimicrobial properties. While its effectiveness has been shown for various applications, the mechanisms of inactivation have not been fully understood although they have been investigated for more than 60 years.

Future Trends for Industrial Development

Regulation Issues

In most countries, most organic solvents are banned for food production or authorized with extremely low residual concentrations. Similarly, pesticide removal from natural materials is of growing interest as it is already operated on ginseng. Moreover, in the long term, the regulation will prefer SFE/SFC development about several issues e.g. work ambience control, ozone depletion, VOC release control and residual concentration in the final product for consumer and environmental protection

Quality Consideration

SFE/SFC are being used for the preparation of high-value products such as food supplements and nutraceuticals for which the “natural” character of the preparation mode has a high marketing value. The same applies to phytopharmaceuticals to move them from chemical to naturals. Furthermore, Supercritical treatment leads to the elimination of pests often present in tropical natural raw materials. CO2 is decontaminating the products

Innovative Products

The pressure on climatic change is activating the creation of new food ingredients and new food products.  Also in the Pharmaceutical industry, there is a strong development focus on new drug delivery systems that open new therapeutic routes for many major drugs related to widespread diseases (asthma, diabetes, cancer etc).

 We like to assist you in creating value for your employer!

In a globalized world, competition is growing and revenues are declining. Those that apply innovation and increase quality, productivity and product safety will always be ahead of the mee-too creators.  Please contact us to evolve new :

• innovative Processes
• flavours and fragrances
• food ingredients
• nutraceuticals
• pharmaceutical active principles
• cosmetic “active ” principles
• Chemical processes
• Materials
• Pollution abatement

Creating Value Monopolies with SCF Technologies.

Many universities and companies believe that supercritical fluid technology is too expensive because of high investment costs in comparison with classical low-pressure equipment. However, in a global economy, everyone is merely competing.  Western Business School has evolved the idea that it is easy to make much more money with money in combination with disruptive technologies. Hedge Fund started to bundle very many investors and to consolidate the available funds into large streams. This led to over-capacities in many industries, especially in food and housing. The downwards spiral of profit margins started to get in motion. Then the money started to move into low-cost economies to control and acquire low-cost raw materials. Now, large sums are invested in artificial intelligence with the aim to reduce the highest cost component in products, labour costs. This is a nil sum game that creates poverty. Ultimately the taxpayer has to pay the bill.

In a sustainable world, we must return to create values for buyers of manufactured products. Supercritical CO2 Fluid Technologies can create very many different and positive Values for a broad range of people. Ultimately this determines the economics of any unique process.

1. SCF offer important advantages over organic solvent technologies, such as ecological friendliness, carbon neutrality and ease of product fractionation.
2. There are fewer industrial units for the separation of components from liquid mixtures using subcritical Fluid in the market (less value competition)
3. CO2 is a readily available and low-cost solvent. Water is the cheapest solvent and many compounds dissolve in water
4. The process is a «many in one process», this encourages innovation and you don’t have to procure HPLC, GC and other equipment.
5. You obtain solvent-free products, dry products, no-co-products, and you operate with low temperature In many countries, organic solvent residues in food and pharmaceuticals are prohibited
6. The process can easily be linked with micronization and crystallization from SC CO2 by fluid expansion.
7. No additional cost for EX-Prove production sites, for additional solvent movement facilities.
8. Besides the commonly use gas, Carbon dioxide for a sub or supercritical extraction, other sub or supercritical solvents can be used. Sub or supercritical CO2 or H2O is non-carcinogenic, non-toxic, non-mutagenic, non-inflammable and thermodynamically stable. Recognised as GRAS Technology (Generally Recognized as Safe), Investors trust this technology
9. CO2 does not normally oxidize substrates and products, allowing the process to be operated at a lower temperature. Many compounds are highly soluble in water.
10. Regulation tends to be regularly adapted.  Suddenly some components become unwanted. just adapt your process.
11. High efficiency, effectiveness and productivity technology
12. Using high-quality equipment, you may depreciate your investment over three to four years

Please contact us to discuss your project now!