CO2-Extraction Process

Energetic materials like TNT or other nitroaromatic compounds are readily soluble in liquid and supercritical carbon dioxide (SC-CO2). Extraction processes using SC-CO2 as an extracting solvent (supercritical fluid extraction SFE) permit the discharging of TNT and its breakdown products out of contaminated soils or other matrices [1],... 

The prior art section in the patent explains that conventional hexane exuaction of soy beans leaves constituents in the extracted meal that give raw, grassy, and bitter flavors that are detrimental to the meal s organoleplic quality. Emphasis has been directed to replace the hexane used in the tfaditional process with work focused on the development of a supercritical CO2 extraction process. Most of the research effort has been directed to achieving a high quality of oil. When soy bean flakes are extracted with CO2, the color, quality, metals content etc., of the oil are excellent, but the residual flake still retains some of the grassy and bitter off flavors. 

Table 14.8 Overview of the calculated mass transfer resistances in the CO2 extraction process of MMA from PMMA latex particles.

Table 14.9 Overview of purchased and installed costs per unit for the high-pressure CO2 extraction process of residual monomer [44].

The extraction of oil from crushed and cooked seeds can be carried out by different techniques. These are mechanical pressing, solvent extraction, enzymes and high-pressure CO2 extraction processes. 

Effect of solvent flow rate. The effect of solvent flow rate has been studied by Rebolleda et al., (Rebolleda et al., 2012) and their results are presented in Figure 7 at a constant pressure and temperature. Extraction curves, expressed in dependence on the solvent-to-feed ratio, are not significantly affected by SC-CO2 flow rate. This behavior supports the fact that solubility, not external mass transfer, is controlling the SC-CO2 extraction process of com germ oil. 

The plant owners claim that CO2 extraction process has added advantage that the treatment of brown rice removes the surface fat, which extends the shelf life, because this fat becomes easily oxidized and usually contains most of the pesticides. Furthermore, the cooking time of the brown rice is reduced, the rice is softened, and retains all vitamins and trace elements, that is, maintain a higher nutrition value, which is not the case for white, polished rice. 

Solvent extraction removes chlorophyll and other pigments to give a light-colored product but increases processing costs. Furthermore, solvent extraction removes p-carotene and reduces vitamin A activity (89) (see Terpenoids Vitamins). Supercritical CO2 extraction at 30 and 70 MPa (4,350 and 10,150 psi) and 40°C removed 90 and 70% carotene and lutein, respectively, from alfalfa LPC (96). This process avoids organic solvent residues and recovers valuable by-products. 

Low cholesterol egg products are formed by extraction of cholesterol from the egg. Attempts have been made to extract cholesterol by using hexane or by supercritical CO2 extraction methods (24,25). A whole egg product in which 80% of the cholesterol is removed by a process using beta-cyclodextrin, a starch derivative, added to egg yolks has been introduced. The cyclodextrin binds up to 80% of the cholesterol, the mixture is centrifuged, and the Hquid separated. The cholesterol-reduced yolk is then blended with egg white, pasteurized, and packed in asceptic containers to give a Hquid whole egg product having a shelf Hfe of 60 days under refrigeration (see Eood packaging). 

With SC-CO2 high solubilities can be attained by increasing the pressure, and reactions can be carried out over a wide range of temperatures, pressures and densities. SC-CO2 is readily available, nontoxic, nonflammable, chemically inert under many conditions, inexpensive, environmentally acceptable and easy to remove and recycle. It has received considerable attention as a reaction medium for organic synthesis [77d, 80] as well as in some large-scale extraction processes in food chemistry [81], The Diels-Alder reaction in SC-CO2 has been investigated quite thoroughly. 

Adrian et al. (2000) have reported a novel high-pressure liquid-liquid extraction process with reference to processing in biotechnology the example of cardiac glycosides (digitoxin and digoxin) is cited. A completely miscible, binary system of water and a hydrophobic organic solvent like ethanol can split into two liquid phases when a near-critical gas (e.g. CO2) is added. The near-critical C02/water/l-propanol system is reported, for which possibilities for industrial exploitation exist. 

This chapter reviews recent findings about the health benefits of phytochemicals present in fruits, vegetables, nuts, seeds, and herbs, including phenolics, carotenoids, sterols, and alkaloids. These phytochemicals are extracted using emerging technologies such as supercritical carbon dioxide (SC-CO2) extraction, PEF, MWE, HPP, UE, and OH. The impact of important parameters related to sample preparation (particle size and moisture content) and extraction process (temperature, pressure, solvent flow rate, extraction time, and the use of a cosolvent) on the efficiency of extraction and on the characteristics of the extracted products is evaluated based on an extensive review of recent literature. The future of extraction of phytochemicals is certainly bright with the... 

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. 

The critical temperature of pure CO2 is 31°C [7]. For the subcritical range of 31-50°C, the fluid entering the extraction cell will consist of two phases - a liquid methanol phase and a supercritical phase. It has been reported that the diffusivity of liquid is about 10-100 times smaller than that of the supercritical fluid [6] and this implies that the difficulty of mass transfer associated with the former is also magnified by the same factor. In an extraction process, mass transfer occurs during 1) the fluid s penetration of the matrix s pores and 2) the subsequent transport of the analyte (solute) from the matrix into the bulk fluid [6]. The presence of entrained liquid methanol droplets will thus greatly increases the amount of mass transfer resistance present in the system. Such resistance is reduced upon an increase in temperature and this accounts for the rise in extraction efficiency observed in the temperature range of 45-50°C. 

Of the various extraction processes the decaffeination with supercritical CO2 exhibits the most commercial advantages for bulk production. The process is a discontinuous one. Fig. 1.4-3 shows a number of serially arranged extractors (5) charged with the supercritical CO2 feed by the centrifugal circulation pump (1). 

No other solvent extraction process other than the CO2 technology allows such a strong influence on loading, phase equilibrium, and selectivity. Unfortunately, the solubility of extracted substances in CO2 is relatively low, compared with the usual solvents which give absolute miscibility with the extracted valuable materials in most cases. The determination of solubility and solvent ratios is therefore important for the economy of the process. 

The extraction of spice oleoresins is relatively new, and industrial plants have been in operation for about the last ten years. Because the CO2 extracts are different to the conventional processed oleoresins, the acceptance in the food industry is growing slowly. The spice plants are much smaller than the decaffeination and hop plants, and use extractors of between 200 and 8001. The same is true for medical herbs and high value fats and oils, which are more or less at the beginning of development. 

Schoeller-Bleckmann started about 1979 with CO2 extraction and focused his research work in 1983 on decaffeination processes [9,104], From the beginning of this development work great attention was paid to the idea that caffeine can be recovered according to the first process proposed by Mr. Zosel. 

Because of these advantages the CO2 extraction is a very successful technology for hops, with the result that nearly all hop-extraction plants have changed to the CO2 process in the last twenty years [21]. 

Extraction with supercritical CO2 is a technical process of increasing importance. It provides a mild and rapid technique for the extraction of low- or medium-polarity substances. Supercritical CO2 is used for supercritical fluid extraction (SFE) in important technical processes such as the decaffeination of coffee and the extraction of hops, as well as the extraction of naturally occurring compounds from biomaterials. As many applications are performed in the pharmaceutical, polymer, environmental and nutritional fields, direct on-line SFE-NMR would be an ideal tool to monitor the various extraction processes. 

Figure 7.2.20 Continuous-flow 1 H NMR spectrum (400 MHz) of the triglycerides separated during the extraction process of coffee with supercritical CO2...

The fractions obtained by supercritical CO2 extraction are different from those by dry fractionation. There are differences in the fatty acid and triacylglycerol compositions and melting profiles (Table 8.1). As the characteristics of the fractions depend on the conditions of the processes and the number of fractions obtained, any comparison between fractions should take into account not only the type of processes employed but also the specific process conditions. 

Supercritical CO2 extraction has potential for the removal of cholesterol. Careful manipulation of process conditions is necessary to obtain efficient removal of cholesterol. When supercritical CO2 extraction is used to fractionate milk fat, the liquid fraction is enriched in cholesterol while that of the solid fraction is reduced (Arul et al., 1988b). 

The use of adsorbents in conjunction with appropriate conditions for supercritical CO2 extraction enhances the efficiency of cholesterol extraction. Selective removal of 97% of cholesterol has been achieved with the use of silica gel as an in-line adsorbent (Huber et ah, 1996). Removal of 96% of cholesterol in milk fat fractions can be achieved by a combined supercritical C02 extraction and an alumina adsorption process (Mohamed et al., 1998). 

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