Supercritical extraction process

Supercritical Extraction. The use of a supercritical fluid such as carbon dioxide as extractant is growing in industrial importance, particularly in the food-related industries. The advantages of supercritical fluids (qv) as extractants include favorable solubiHty and transport properties, and the abiHty to complete an extraction rapidly at moderate temperature. Whereas most of the supercritical extraction processes are soHd—Hquid extractions, some Hquid—Hquid extractions are of commercial interest also. For example, the removal of ethanol from dilute aqueous solutions using Hquid carbon dioxide... 

Supercritical extraction has been used increasingly in recent years for specialized processes. These processes include separation of drugs from plants, oils from vegetable seeds, impurities from labile materials, and chemical feedstocks from coal and petroleum residual. The utility of supercritical extraction processes stems principally from the enhanced solubility characteristics of CO2 near its critical point and the ease with which the solvent can be recovered for recycle. 

In a supercritical extraction process a solvent is contacted with a solute at conditions near a critical point of the solvent plus solute mixture. The mixture may exhibit multiphase behavior invoving vapor, liquid, and solid phases, depending on the mixture composition and temperature and pressure conditions. 

In Figure 2.2-10 a number of P c-sections of a p,q-system at temperatures around the critical temperature of component A are shown. At T=TV the critical point l=g and the / point and g point of the S2hg equilibrium in Figure 2.2-10b coincide in a horizontal point of inflexion. As a result, at higher temperatures (Figure 2.2-10c) the solubility curve of the solid in the supercritical gas still shows a point of inflexion. This results in a sharp increase of the solubility of the solid in the supercritical gas. This effect plays an important role in supercritical extraction processes. 

As one can see from Table 6.6-2 the decaffeination of coffee and tea is the largest application for supercritical fluid extraction, in terms of annual capacities and investment costs. Since the beginning of the 1970s, to the early 1990s, nearly 50% of the whole production capacity for decaffeination of coffee and tea changed to the supercritical extraction process. As the market for decaffeinated coffee is stable, no further plants have been installed within the past eight years. 

The second largest application is in the extraction of hops. In the last twenty years nearly all producers of hop extracts have changed to the supercritical extraction process. Even in the Eastern European countries the methylene chloride process was stopped several years ago. 

These flat screens have allowed miniaturisation of the whole computer screen assembly, and substantially less plastic, glass and electrical components are required. In addition, transport and packaging are reduced, and the enormous volume of these products means that even small improvements may have major environmental benefits. Ongoing work at York University has discovered that these liquid crystal molecules may be effectively recovered from TFT screens via a supercritical extraction process, giving the potential for reuse of these useful high value fluorinated compounds [79],... 

Promising applications of SFC include group separations (paraffins, olefins and aromatics) in petrochemical samples, monitoring of supercritical extraction processes (caffeine from coffee, nicotine from tabacco) and oligomer separations. However, it is in the field of applications that SFC has yet to prove its value. Unique separations that can be accomplished with SFC, but not with either GC or LC, have yet to be demonstrated. 

Although C02 is the most common solvent for supercritical extraction processes because of it s abundance, non-toxicity and non-flammability, other compounds may prove to be better solvents in certain instances. In choosing a solvent, a balance between solubility and selectivity has to be struck. In the case of solutes with a melting point well below the decomposition temperature, it is usually desirable to perform a liquid-supercritical fluid extraction to circumvent the problems associated with handling solids at high pressures. In... 

In the case of a flash this is simply the K-value. In this example, a K-value of 1.98 was obtained. The selectivities of the proposed supercritical extraction process will be compared with this value. 

The design and development of supercritical extraction processes depend on the ability to model and predict the solubilities of solid solutes in supercritical solvents. The prediction is usually difficult due to the large differences in sizes and molecular interactions between the solvent and solute molecules. 

To make supercritical extraction processes more economic, separation of solute and solvent can be performed thanks to a membrane system. Sartorelli and Brunner [19] demonstrated that a membrane separation process can be proposed instead of the typical supercritical fluid cycle in the case of supercritical extraction to drastically reduce the energy losses. In fact, a stream of low volatile compounds (LVC) extracted by SC CO2 can be discharged of 80%-90% of LVC using a nanofiltration membrane with a drop of pressure equal to 2 MPa instead of about 20 MPa in the typical supercritical fluid cycle. 

A recent development in liquid-liquid extraction has been the use of supercritical fluids as the extraction-solvent. Carbon dioxide at high pressure is the most commonly used fluid. It is used in processes for the decaffeination of coffee and tea. The solvent can be recovered from the extract solution as a gas, by reducing the pressure. Supercritical extraction processes are discussed by Humphrey and Keller (1997). 

Effect of Unlike-Pair Interactions on Phase Behavior. No adjustment of the unlike-pair interaction parameter was necessary for this system to obtain agreement between experimental data and simulation results (this is, however, also true of the cubic equation-of-state that reproduces the properties of this system with an interaction parameter interesting question that is ideally suited for study by simulation is the relationship between observed macroscopic phase equilibrium behavior and the intermolecular interactions in a model system. Acetone and carbon dioxide are mutually miscible above a pressure of approximately 80 bar at this temperature. Many systems of interest for supercritical extraction processes are immiscible up to much higher pressures. In order to investigate the transition to an immiscible system as a function of the strength of the intermolecular forces, we performed a series of calculations with lower strengths of the unlike-pair interactions. Values of - 0.90, 0.80, 0.70 were investigated. 

Since the first large-scale supercritical extraction process was commercialized for the decaffeination of green coffee with carbon dioxide a decade ago, scientists and engineers in the food industry have been paying considerable attention to this technique for similar separations, i.e., removal of cholesterol from butter, removal of cocoa butter from cocoa beans, and extraction of hops, spices, and... 

The equilibrium solubility of Lovastatin in carbon dioxide at 55 C and 75 C and for pressures up to 400 bar was obtained using the HPLC apparatus and reported in Table II and Figure 9. The data exhibit both the abrupt change in solubility above the solvent s critical point, as well as the retrograde behavior, both of which characterize supercritical extraction processes. The solubilities were reproducible to within 5%. 

Our results indicate that single-stage supercritical extraction processes are limited in their ability to separate trace components from complex mixtures even with the use of co-solvents. However, two-stage processes such as the ones developed here can significantly improve the degree of separation. Utilization of the multicomponent temperature-solubility cross-over region is a promising isolation technique. However, when the substrate contains a wide variety of components, multiple separations may be necessary to complete the isolation and the yields may be low. 

The supercritical extraction process of a model adsorbed species as described earlier from the MgO(OOl) surface was investigated on the basis of above MD calculations. Fig. 14 shows the dynamic behaviour of the fluid and adsorbed species on MgO(OOl) surface at 300K and 88.9atm which is not supercritical condition (Tr = 0.89, Pr = 0.67). Although the adsorbed species thermally vibrated on MgO(OOl) surface and slightly migrated on the surface, it was not extracted from the surface. 

Supercritical CO2 has been considered as a potential alternative to conventional solvents due to its relative non-toxicity and non-flammability, as well as its low critical temperature and pressure. Supercritical fluid extraction (SFE) has been used for example in the extraction of fatty acids from diverse matrices such as grape seeds , ginseng seeds, wood pulp , and infant formula . The absence of oxygen and light during the supercritical extraction process helps prevent degradation of the extract. For example, Tipsrisukond, et al." found... 

We consider application of Eqs. (I.6-16)-(1.6-I8) to (he calculation of the solubility of naphthalene (component 2) in carbon dioxide (component I) at 3S°C and at high pressures. Data for these conditions (Tsekhanskaya et al.T) are shown as open circles in Fig. 1.6-2. Particularly noteworthy is the dramatic enhancement In solubility—several orders of magnitude—that occurs with increasing pressure near foe critical pressure of foe solvent gas. The solubility enhancement, which obtains for temperatures slightly higher than the critical temperature of a solvent gas (the critical temperature of COi is 3l°C), is the basis for certain "supercritical extraction processes ase Paulaitis et a1.Ba for discussions of fols topic. 

After adjusting the pressure again for possible loss CO2 if necessary, the reactor is charged again with a new aqueous substrate phase for repeated use of the catalyst phase. Obviously, the system is readily applicable to continuous-flow processing using countercurrent flow techniques as established in liquid/supercritical extraction processes [40]. 

Supercritical fluids are effective at much lower temperatures than distillation, and their application in separation avoids degradation and decomposition of heat-labile compounds. Attractiveness of supercritical extraction processes are due to the sensitivity of responses to process variables, promise of complete and versatile regeneration of solvents, energy savings, enhanced solute volatilities, solvent selectivities, favorable transport properties for solvents, and state governed effectiveness of solvents which enables the use of low cost, non-toxic, environmentally acceptable solvents. The impact of inherent characteristics of supercritical fluids on separations is summarized in Table 21.1.5. 

The further growth of the solid particles in the solution inside the precipitation chamber is another mechanism that can strongly modify the morphology of particles. Although slow, this mechanism is responsible for the formation of more complex morphologies. A pronounced effect of co-solvent can lead to specific morphologies as well. This effect is well known in supercritical extraction processing and has been used to improve the solubility of poorly soluble... 

Several current applications have been widely publicized. Kerr-McGee developed its ROSE (Residuum Oil Supercritical Extraction) process in the 1950s IGupta and Johnston. 2008 Hunphrey and Keller. 1997 Johnston and Lemert. 1997 McHugh and Krukonis. 19941. When oil prices went up, the process attracted considerable attention, since it has lower operating costs than conpeting processes. The ROSE process uses an SCF such as propane to extract useful hydrocarbons from the residue left after distillation. This process utilizes the high tenperatures and pressures expected for residuum treatment to lead naturally to SCF extraction. 

Poco JF, Coronado PR, Pekala RW, Hrubesh LW (1996) A rapid supercritical extraction process for the production of silica aerogels. Mater Res Soc Symp Proc 431 297-302... 

Gross J, Corrmado PR, Hmbesh LW (1998) Elastic properties of silica aerogels from a new rapid supercritical extraction process. J Non-Cryst Solids 225 282-286... 

Scherer GW, Gross J, Hmbesh LW, Coronado PR (2002) Optimization of the rapid supercritical extraction process fm a ogels. J Non-Cryst SoUds 311 259-272... 

IF Poco, PR Coronado, RW Pekala, LW Hrubesh, A Rapid Supercritical Extraction Process for the Production of Silica Aerogels MRS Apr 8-12 1996 Spring Meeting... 

Supercritical extraction processes show similar requirements with regard to high pressure fluid machinery as do high pressure processes for reactions. However, since the principal solvent is usually CO2 the corrosion and erosion aspects are less demanding than is the case in reaction processing. Also the temperature will not usually be high since a limit to the allowable temperature is often set by the properties of the components and the required quality of the products. 

Figure 10.5 Generalised schematic of supercritical extraction process.

Gross J., Coronado P.R., Hrubesh L.W. Elastic properties of silica aerogels from a new rapid supercritical extraction process. J. Non-Cryst. Solids. 1998 225 282-286 Hench L.L. Use of drying control chemical addition (DCC As) in controlling sol-gel processing. In Science of Ceramic Chemical Processing, L.L. Hench, D.R. Ulrich, eds. New York John Wiley, 1986, pp. 52-64... 

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