Supercritical water extractions content

Fignre 6.20 shows the plots for yields of hydrogen from snpercritical water extraction of shell samples versns cellulose content at different temperatures. The yields of hydrogen from supercritical water extraction increase with increasing cel-Ixflose contents of the shell samples (Demirbas, 2004). 

Fig. 6.20 Plots for yields of hydrogen from supercritical water extraction of shell samples versus cellulose content at different temperatures...

Carotenoids A large number of solvents have been used for extraction of carotenoids from vegetables matrices, such as acetone, tetrahydrofuran, n-hexane, pentane, ethanol, methanol, chloroform [427-431], or solvent mixtures such as dichloromethane/methanol, tetrahydrofuran/methanol, -hexane/acetone, or toluene or ethyl acetate [424,432-435], SPE has been used as an additional purification step by some authors [422,426], Supercritical fluid extraction (SEE) has been widely used, as an alternative method, also adding CO2 modifiers (such as methanol, ethanol, -hexane, water, methylene chloride) to increase extraction efficiency [436-438], In addition, saponification can be carried out, but a loss of the total carotenoid content has been observed and, furthermore, direct solvent extraction has been proved to be a valid alternative [439],... 

Decontamination of soils using supercritical fluids is an attractive process compared to extraction with liquid solvents because no toxic residue is left in the remediated soil and, in contrast to thermal desorption, the soils are not burned. In particular, typical industrial wastes such as PAHs, PCBs, and fuels can be removed easily [7 to 21]. The main applications are in preparation for analytical purposes, where supercritical fluid extraction acts as a concentration step which is much faster and cheaper than solvent-extraction. The main parameters for successful extraction are the water content of the soil, the type of soil, and the contaminating substances, the available particle-size distribution, and the content of plant material, which can act as adsorbent material and therefore prolong the extraction time. For industrial regeneration, further the amount of soil to be treated has to taken into account, because there exists, so far, no possibility of continuous input and output of solid material for high pressure extraction plants, so that the process has to be run discontinuously. 

The potential use of supercritical water appears especially attractive for the extraction of brown coals with their high water content, 5Q-70% for Victorian brown coals, thus removing the need for a coal-drying stage. The drying and extraction of these low rank coals would occur in a single process. The purpose of the present study was to investigate the feasibility of the extraction of Australian black and brown coals with supercritical water. The... 

COMMERCIAL PROCESS. A practical example of a supercritical fluid extraction process is the decaffeination of coffee. Coffee beans are first soaked in water to make the extraction more selective and then are loaded into an extraction vessel through which supercritical CO2 is circulated to dissolve the caffeine. In a separate scrubbing vessel the caffeine is transferred from the CO2 to water, also at high pressure. Extraction is continued until the caffeine content of the beans, originally... 

Three distinct processes were experimentally studied a coupled process for deacidi%ing and enriching the plqrtosterol content of rice bran oil (RBO) by continuous countercurrent colnitmar fiactionation, a scale up of a coupled supercritical fluid extraction (SFE)/ supercritical fluid chromatogr hy (SFC) process for the enrichment of phytosterol in com bran oil, and a unit process involving the snbcritical water extraction of berry substrates. The e q)erimental aspects of the first two processes are described in the literature (36, 37), and will not be repeated here. Research is currently underw to couple the described process below with other unit processes involving both subcritical water and siq)ercritical carbon dioxide. 

This review focuses on the extraction of lipids from plant and muscle tissues using supercritical CO2 with an emphasis on the effect of structural and compositional differences as well as C02/lipid/protein/water interactions. The effect of moisture content ranging from 3-20% in oilseeds to 3-64% in muscle tissues on hpid and water extractability and residual proteins is demonstrated. 

Seabra et al., [17] performed fractionated high pressme extractions from dry and in natura elderberry pomace in order to obtain anthocyanin rich extracts. Experiments were carried out using CO2 supercritical fluid extraction followed by enhanced solvent extraetion (ESE) with C02/ethanol-water mixtures (1-100%, v/v), to obtain anthocyanin rich fractions in the second step, at 313 K and 20 MPa. Higher extract yields, anthocyanin contents and antioxidant activities occurred by the presence of water, both in the raw material and in the solvent mixture. The CO2 dissolved in the ESE solvent mixture favored either anthoeyanin contents or antioxidant activities, which were not directly related. 

Markova, M.E., Uryash, V.F., Gruzdeva, A.E., Grishatova, N.V., Kokurina, N.Yu., and Uryash, A.V., Determination of water content in biological active additives for food prepared by supercritical fluid extraction. In. Biotechnology, Biodegradation, Water and Foodstuffs, Zaikov, G.E. and Krylova, L.P., Eds, NY Nova Sci. Publ. Inc., 2009,... 

In summary it can be said that supercritical CO2 is a moderate solvent for the investigated group of carbamates, although the chemical structure would support more polar solvents for complete removal. The pressure and temperature influences are not really important, so gentle extraction conditions can be applied. Water used as a matrix- or CC>2-modifier is appropriate, with an optimum water content of around 10-15%. An amount of 7 - 15 kg CO2 per kg rice provides an acceptable effect for pesticide reduction. 

The effects of this variable depend on both the matrix and the analytes. Thus, hydrophobic matrices facilitate penetration of supercritical CO, also, because the fluid is water-immiscible, the presence of moisture can make the analytes inaccessible to it. Figure 7.9A illustrates the influence of this variable on the kinetics of extraction of pyrene from natural sludge, both as collected (45 /o moisture) and after air-drying (2% moisture) [40]. However, water added to the sample can facilitate extraction (e.g. that of caffeine from coffee beans. Fig. 7.9B). Natural samples with a high moisture content can plug restrictors as a result of the water they contain freezing at restrictor tips. This problem can be overcome by raising the restrictor temperature, at the expense of losses in the more volatile analytes. 

The crushed seeds of Crotalaria spectabilis were first contacted with supercritical carbon dioxide and, as expected, the oils comprising the bulk of the seed material were preferentially extracted. The addition of ethanol and water as co-solvents in the fluid phase led to the appearance of monocrotaline in the extract. Monocrotaline contents as high as 24% of the total extract could be obtained with carbon dioxide-ethanol mixtures. 

A detailed description of the experimental apparatus and procedure used for the aqueous study are given elsewhere (Roop and Akgerman, Ind. Eng. Chem. R., in review) Static equilibrium extractions were carried out in a high pressure equilibrium cell (300 mL Autoclave). After the vessel is initially charged with 150 mL of water containing 6.8 wt.% phenol and supercritical carbon dioxide (and a small amount of entrainer, if desired), the contents were mixed for one hour followed by a two hour period for phase separation. Samples from both the aqueous phase and the supercritical phase were taken for analysis and the distribution coefficient for phenol calculated. 

In summary, phenol (a model toxic pollutant) was successfully extracted from both water and soil (dry and wetted) using supercritical carbon dioxide. It was found that entrainers greatly enhance the distribution coefficient of phenol for each system. However, the choice of a good entrainer is not independent of the contaminated matrix or, in the case of soil, its moisture content. Benzene was successfully extracted from both dry and wetted soil using pure carbon dioxide. Entrainers such as methanol could serve to decrease the distribution of such hydrophobic systems, indicating that further investigation in this area is warranted. 

In addition to extraction from solids, supercritical fluids can be used to extract aromatic molecules from liquids. Senorans et al. have utilized carbon dioxide to extract high-quality brandy aroma using a countercurrent supercritical fluid extractor. The aroma quality is influenced by the extraction conditions. Medina and Martinez studied alcohol removal from beverages using supercritical carbon dioxide, to produce beverages with low-alcohol content but sufficient flavor, because of three key benefits 1) water and salts are not appreciably removed by the carbon dioxide 2) proteins and carbohydrates are not extracted or denatured and 3) there is a good control in the aroma recovery. The alcohol removal efficiency increases with the extraction pressure raffinate alcohol concentration can be reduced up to 3 wt.% at 250 bar and 40°C, from 6.2 wt.% in the feed. " ... 

The water content of the raw coffee beans is adjusted to 20-35% and is contacted with supercritical CO2 at 250 atm and 80 °C. At these conditions, supercritical CO2 will also extract caffeine. How, then, is the process operated so as to maintain the caffeine content of the coffee constant ... 

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