Supercritical Fluid Extraction

Megha Rajasekhar(1RV14CH022)Shri Lakshmi S B(1RV14CH041)Supercritical Fluid ExtractionMASS TRANSFER II SELF STUDY

Supercritical Fluid Supercritical fluid is a substance which exists at a temperature and pressure beyond the critical pointIt has the properties of both a gas and a liquidIt dissolves substances like a liquid and diffuses through solids like a gas Hence making it suitable for extraction

Supercritical Fluid ExtractionSupercritical CO2 is most widely used solvent In food industry for decaffeination of coffee, extraction of essential oils, etc.Extraction of antioxidants from fruits and vegetables in cosmetic industry

CO2 as solventCarbon dioxide has relatively low critical pressure (74 bar) and temperature (32C) .CO2 is relatively non-toxic, non-flammable, available in high purity at relatively low cost.CO2 can be easily removed from the extract.Protects samples against any oxidative degradation.The main drawback of CO2 is its lack of polarity for the extraction of polar analytes . This can be countered by the addition of modifiers.

CO2 as solventFor a wide range of solutes, CO2 gives better yields compared to organic solvents like ethane, propane, ethylene, dimethyl ether in sub and supercritical conditionsBetter substitute for polluting organic solventsFor the extraction of oils, supercritical CO2, second to N2O, fares better than supercritical trifluoromethane and SF6

Alternate solventsNO2 was considered better suited for polar compounds because of its permanent dipole moment. This fluid has been shown to cause violent explosions when used for samples having high organic content and is therefore used only when absolutely necessary.SF6 is a non-polar molecule and as a supercritical fluid, it has been shown to selectively extract aliphatic hydrocarbons from a mixture containing both aliphatic and aromatic hydrocarbons. Freons, especially CHClF2 (Freon-22), has on several occasions been shown to increase the extraction efficiency compared to conducting extractions with CO2

AdvantagesLow temperature processing reduces degradation of temperature and oxygen-sensitive components.Extract and raffinate are free of solvent and can be used in food.Volatile components are not lost as in other methodsReplace harmful organic solvents

DisadvantagesRelatively high pressures are required. High initial capital cost of high-pressure equipmentHazards of high pressure and the use of inflammable solvents are unfavorable

ProcessThe system consists of a pump, a pressure cell to contain the sample and a collecting vessel.The supercritical fluid diffuses into the matrixThe analyte gets dissolved into the supercritical fluidThe dissolved material is swept from the extraction cell into a separator at lower pressure and the extracted material settles out. The CO2 can be cooled and recycled or discharged to atmosphere.The pressure requirement is at least 74 bars. Most extractions are conducted at less than 350 bar and sometimes at 800 bar for extraction of vegetable oils.

Effect of matrix on SFEDifferent factors such as the particle size, shape, surface area, porosity, moisture, level of extractable solutes and the nature of the matrix will affect the supercritical fluid extraction results. Decreasing the particle size of solid matrices leads to a higher surface area, making extraction more efficient. Yet, excessive grinding may hinder the extraction due to readsorption of the analytes onto matrix surfaces. This could be avoided by increasing the flow rate

Effect of Pressure and TemperatureFour parameters decide the solute behavior in supercritical mediaThe miscibility or threshold pressure, which corresponds to the pressure at which the solute partitions into the supercritical fluid The pressure at which the solute reaches its maximum solubility The fractionation pressure range, which is the pressure region between the miscibility and solubility maximum pressuresPhysical properties of the solute, particularly its melting point

Effect of Pressure and TemperatureAn elevation of pressure at a given temperature results in an increase in the fluid density, which means an enhanced solubility of the solutes. But, the higher the extraction pressure, the smaller is the volume of fluid necessary for a given extraction.Increase in temperature, decreases the density of the solvent but increases the volatility of solute.For a non-volatile solute increase in temperature increases extraction

Effect of flow rateThe speed of the supercritical fluid flowing through the cell has a strong influence on the extraction efficiencies. The slower the fluid velocity, the deeper it penetrates the matrix and becomes saturated with the solute in the vesselBut larger fluid velocities are required to prevent re-absorption of solute into matrixFor a given extraction cell, the flow rate can be easily changed by using a new restrictor with a different inside diameter.

Effect of modifiersModifiers are added to the primary fluid to enhance extraction efficiency. The nature of the modifier depends on the nature of the solute to be extractedModifier must be a good solvent in its liquid state for the target analyte. Polar modifiers increase the extraction efficiency of polar analytes e.g. water and methanol are used with CO2

Effect of timeMaximize the contact of the supercritical fluid solvent with the sample material in order to enhance the efficiency1020 min static extraction prior to dynamic extraction improved the extract recoveriesIncreased dynamic extraction time enhance the extraction

Effect of waterWater opens pores, swells the matrix, thereby allowing the fluid better access to analytes, and aid in flow through the matrix.Increase the polarity of the fluidHighly water soluble analyte will prefer to partition into the aqueous phase in case of excess water

Collection methodsSolvent collection CO2analyte mixture is depressurized directly in contact with the solvent OR CO2analyte mixture is first depressurized to gas phase in a glass transfer tube before contacting the solventSolid trapping - CO2 and the analytes are depressursied and the analytes are collected directly onto silica gel, or bonded phase packing or onto glass or stainless steel beads

Collection methods

Decaffeination of CoffeeCaffeine is chemically bound in an acid structure present in the coffee beanThus large amounts of CO2 are required for extractionWater somehow acts as a chemical agent, freeing caffeine from its bound form in the coffee matrixThe amount of CO2 required can be theoretically calculated. The solubility of caffeine is about 0.2 wt% at 60C and 300 bar. If the caffeine content of coffee is about 1 wt%, 5 times the amount of CO2 is required for complete extraction.

SummaryBetter extraction solubility, higher purity products, environmentally friendlyQuicker process due to faster diffusionRequires maintenance of high pressures and temperatureWidely used for lab analysis than in industries

ReferencesSupercritical Fluid Extraction of Fungal Oil Using CO 2, N20, CHF 3 and SF 6 - Keiji Sakaki, Toshihiro Yokochi, Osamu Suzuki and Toshikatsu HakutaSupercritical Fluid Extraction - S. S. H. Rizvi, Institute of Food Science, Cornell UniversitySupercritical fluid extraction in plant essential and volatile oil analysis - Seied Mahdi Pourmortazavi, Seiedeh Somayyeh HajimirsadeghiSupercritical Fluid Extraction (SFE) for the Removal of Lipid and Interfering Compounds Prior to Radiocarbon Dating of Archaeological Artifacts - Jerry W. King, Jenny Phomakay, Oscar Guevara, & Keerthi Srinivas, University of Arkansas