SUPER CRITICAL FLUID EXTRACTION

[Audio] I love you. SUPER CRITICAL FLUID EXTRACTION.

[Audio] I love to you very much. Introduction. Extraction is a typical unit operation that finds extensive applications in chemical engineering and food engineering. Previously its known as leaching. The processing tool (technology) for extraction of active principles (solute) from the solids using an organic solvent or water as the extracting liquid source. Extraction can be defined as the removal of soluble material from an insoluble residue, either liquid or solid, by treatment with a liquid solvent. It is, therefore, a solution process and depends on the mass transfer phenomena Generally in food engineering, it could be extraction of vegetable oils from the oilseeds, or extraction of natural food colors viz., curcumin from turmeric or annatto dye from annatto seeds (Bixa Orellana), or extraction of coffee seeds using hot water. If the extraction is done at the boiling point of the solvent, we call it a decoction. Extraction operations can be subdivided into solid-liquid extraction and liquid-liquid extraction..

SUPER CRITICAL FLUID EXTRACTION (SCFE). Solvent extraction process we have studied is an excellent process except for the presence of residual solvents which are mostly organic solvents, and hence, may be carcinogenic In this respect, a safe solvent like carbon dioxide under supercritical conditions could be a better alternative for extraction, particularly from natural products like coffee, tea, tobacco, cocoa, hops, spices, and oilseeds to extract the active principles in them. This technique is popularly known as Super Critical Fluid Extraction (SCFE) method and is a novel technique in the extraction process that has its origin in the early 1960s. Supercritical fluids have been investigated since the last century, with the strongest commercial interest initially focusing on the use of supercritical toluene in petroleum and shale oil refining during the 1970s. Supercritical water is also being investigated as a means of destroying toxic wastes, and as an unusual synthesis medium. The biggest interest for the last decade has been the applications of supercritical carbon dioxide,.

Fluids beyond their critical conditions are known as supercritical fluids, and they exhibit behavior and Physicochemical properties of both liquids and gases. For example, carbon dioxide (CO2) which is mostly used as a supercritical fluid in food processing extractions is a gas at supercritical conditions (Tc = 31 °C and pc = 73 atm.), and has the flowability of gas, but has its density comparable to that of liquids, and hence, has the solubilizing power of a liquid. After extraction, the solvent (CO2) can be removed simply by releasing the pressure when the CO2 leaves the solute and escapes as a gas. Thus, in general, fluids near their critical points have the dissolving power comparable to that of liquids and have the transport properties of the gas. This unusual combination of Physico -chemical properties can be judiciously exploited to carry out separation operations by extraction which may be otherwise difficult by traditional extraction processes using organic solvents or water. Supercritical fluids can produce a product with no solvent residues. Examples of pilot and production scale products include decaffeinated coffee, cholesterol-free butter, low-fat meat, evening primrose oil, squalene from shark liver oil, etc.

What does "supercritical" mean? Any substance is characterized by a critical point that is obtained at specific conditions of pressure and temperature. When a compound is subjected to a pressure and a temperature higher than its critical point, the fluid is said to be " supercritical ". In the supercritical region, the fluid exhibits particular properties and has an intermediate behavior between that of a liquid and a gas. In particular, supercritical fluids (SCFs) possess liquid-like densities, gas-like viscosities, and diffusivities intermediate to that of a liquid and a gas. The fluid is said "supercritical" when it is heated above its critical temperature and compressed above its critical pressure ..

Advantages of SCFE Method Quick extraction process Improved separation process, Lower operating costs It has no problem of residual solvents, and – results in products that are relatively pure. Various gases used for the SCFE process are CO2, ethane, ethylene, and N 2 O. CO2 has the unique advantage of having properties that are much different from those of water or non-polar organic solvents. In addition to it, CO 2 has the following advantages : CO 2 is most unobjectionable as a solvent from the health point of view and scores over most of the organic solvents. It is ubiquitous in nature. It is inexpensive and readily available in pure form. It is inert and does not react with the solute during extraction. It is neither inflammable nor toxic. It does not corrode the container in its native form or in combination with moisture. Hence, CO2 is a better candidate as SCFE fluid for the extraction of natural products for edible purposes..

Properties of supercritical fluid. Supercritical fluid have highly compressed gases, which combine properties of gases and liquids in an intriguing manner. Supercritical fluids can lead to reactions, which are difficult or even impossible to achieve in conventional solvents. Supercritical fluids have solvent power similar to light hydrocarbons for most of the solutes. However, fluorinated compounds are often more soluble in supercritical CO2 than in hydrocarbons; this increased solubility is important for polymerization. Solubility increases with increasing density (that is with increasing pressure). Rapid expansion of supercritical solutions leads to precipitation of a finely divided solid. This is a key feature of flow reactors. The fluids are commonly miscible with permanent gases (e.g. N2 or H2) and this leads to much higher concentrations of dissolved gases than can be achieved in conventional solvents..

Schematic Representation of SCFE. The SCFE process system consists of two units: extraction unit and expansion unit separated by an expansion valve..

SCFE Process. Supercritical fluid extraction is commonly carried out considering two basic steps: 1. Extraction of soluble substances from the matrix by the supercritical fluid 2. Separation or fractionation of the extracted compounds SCFE Process Like any other batch extraction process, the material is fed into a cylindrical vessel A (known as extraction section). The vessel is filled with CO2 or the SCFE solvent and is pressurized using a compressor until the desired pressure is reached which is read on the pressure gauge. Usually the pressures are of the order of 75–300 atm (7.5 to 30 MN/m2 ), and ideally, for CO2 the pressure is up to 150 atm, beyond which the increase in density of supercritical CO2 is marginal. The preferred temperature range is 35–80 °C. The system is allowed to equilibrate for sufficient time with the food solids and the supercritical fluid (CO2). Indeed the diffusion of SCF into the solid matrix is rapid, but the solubility of solute into the solvent is slow which may require prolonged contact time for better extraction..

The extracted CO 2 is taken into another chamber B (known as separation section) by opening valve V1 and keeping valve V2 closed. When the expansion valve V1 is opened, care should be taken to see that the temperature does not fall because of Joule–Thomson effect. Sometimes the expansion valve is heated slowly to avoid cooling. Later on, valve V1 is closed. All extracted material with solvent at higher pressure is trapped in the expansion tank. Then the valve V2 is slowly opened to release the CO 2 pressure. Once the pressure is released, CO 2 loses its supercritical nature; and hence, the solubility of the solute drastically reduces. Thus, the solute is separated in chamber B. The CO 2 is either lost off or recycled into the compressor for the next extraction. The spent solids are discharged from the extraction chamber subsequently to feed a fresh batch. In some cases, an entrainer is used along with SCF to help better extractability. Various types of entrainers are in use. Applications of SCFE in Food Processing Decaffeination of coffee Extraction of hops used in the beer manufacture Extraction of oleoresins from spices.

In addition to the above which have reached commercial success, there are many more applications: Extraction of flavors and aromas Extraction of food colorants from natural sources like extraction of annatto dye from Bixa Orellana seeds Extraction and concentration of Eicosa Pentaenoic Acid (EPA) from fish Extraction of cholesterol from eggs Extraction of cholesterol from butter, lard, and tallow Extraction of nicotine from tobacco Extraction of stimulants from tea, cocoa, etc. Extraction of edible oils from the oil seeds Extraction of soyabean oil Extraction of oil from corn, wheat germ, sunflower, safflower seeds, and peanuts Extraction of natural products viz., steroids, alkaloids, and anticancer agents.

Some specific applications found in the literature based on an International Symposium on Supercritical Fluids, Societe Francaise De Chimia , Paris, 1985 (McHugh 1990) are as follows: Extraction of limonene and cineole Removal of cholesterol from butter, beef tallow Extraction of prime rose seeds Extraction of ginger and rosemary Extraction of pepper Extraction of some flavor components Extraction of fatty acids of oils from natural triglycerides Processing of fermentation broths by SCF extraction.

Constraints in SCFE Processing The constraints faced in SCFE processing are two-fold: Thermodynamic Operational The high-pressure fluid phase equilibrium data for the solvent and the solute is generally lacking. Experimental measurements are very difficult in view of the very high pressures involved. Hence, we resort mostly to predictive equations based on equations of state. Another important parameter in SCFE is the polarity of the solute being extracted. The operational constraints are based on the equipment. Generally, the SCFE equipment is operated in a batch manner. Since the process conditions are extreme especially in terms of pressure (imagine the vessels operating at 100 atm. pressure!), loading and unloading of the batch and making the equipment every time leak proof is a stupendous task. Design and mechanical fabrication of the vessels to withstand to such high pressures, welding joints for the flanges, etc. are all to be meticulously done. Setting up special requirements for the sealing elements is very essential..

In addition to the above, the following are some operational constraints : Maintaining temperatures of the order of 100 °C which is of significance with regard to seals, etc. Meeting the food quality requirements in terms of corrosion-resistant equipment and piping. Pipelines for flowing supercritical fluids at high pressures, the bends and joints for the piping, etc. Valves to particularly arrest flow rate of fluids at supercritical conditions; frequent operations of valves should not give way for leaks. After every filling of the feed, quick closing of the lid, bolts and nuts joints, etc. are to be ensured. The carry over the problem of the feed solids, if the bulk densities are low (0.2–0.3 kg/lit) along with the SCF (whose density is approximately 0.9 kg/lit) into the separating chamber is a recurring nuisance. Channeling of the fluid in the extraction tank without adequately coming in contact with all the solids. Thus, the operational difficulties restrict the commercialization of SCFE processes.

Application SCFE IN Fruits & Vegetable Processing.

Application SCFE In Herbs. olive fatty acids lutein— zeaxanth.in oil h in-a. • r v different activity vity activity activity activity activity activity anti uct.ivity vity 35 40 214 rnin -+- 35 static —E 0 32 2 SO 90 28 62 78 2 -+ 0.4 60 80 30 -V 30 -+- 0—01 -F 25_8 SO 30 ruin tie 30 40 2.4 12 35 40 80 60 40 —e— 0.02 -+- 30 45 -9— I OO.G 30 70 20 _ •S 40 120 + 30 100 30 SO -+- 30 SO -C_ 30 4 cycles 30 40 300 rnin eso -+- 40 —C_ 120 tie 25 40 30 40 35 35 SO 30 —f— 240 30 18-0 S —+- 30. SO 90 rnir-. (static) e, 4.8 40 240 -.

Case Study. In this case study, the main parameters affecting the supercritical fluid extraction of bioactive compounds from cyanobacteria Spirulina ( Arthospyra platensis) will be described. Among the compounds with antioxidant activity from Spirulina, vitamin E (a-tocopherol) has been selected for its importance as a lipid-soluble antioxidant compound and because SFE has shown several advantages compared to the extraction with organic solvents (use of non-toxic solvents, high enrichment factors, selectivity, etc.). Optimization has been carried out using a response surface methodology (RSM) considering several factors such as extraction pressure and temperature and modifier content. The response selected in this work was the concentration of vitamin E achieved in the process at the pilot scale. In the first step, the extraction time was determined by studying the kinetics of the extraction. After that, the experimental design was run considering the two solvents, pure CO2 and CO2 plus 10% ethanol as co-solvent, and the response was optimized in order to select those conditions in which there is a high enrichment of vitamin E..