Supercritical water extractions residues

Extraction from Aqueous Solutions Critical Fluid Technologies, Inc. has developed a continuous countercurrent extraction process based on a 0.5-oy 10-m column to extract residual organic solvents such as trichloroethylene, methylene chloride, benzene, and chloroform from industrial wastewater streams. Typical solvents include supercritical CO9 and near-critical propane. The economics of these processes are largely driven by the hydrophihcity of the product, which has a large influence on the distribution coefficient. For example, at 16°C, the partition coefficient between liquid CO9 and water is 0.4 for methanol, 1.8 for /i-butanol, and 31 for /i-heptanol. 

Extraction of residues from soil samples is much more difficult than their extraction from plant or water samples. The pesticide residues in the soil exist often in several forms as bound residue , which may affect the extraction efficiency of pesticides from the soil. Then, various extraction methods such as organic solvent extraction, Soxhlet extraction, sonication extraction, microwave dissolution and supercritical fluid extraction (SEE) are used. Some extraction methods are described in the following. 

Before the extraction procedure may commence, the sample must be prepared in such a way that it is in a condition for extraction of the analyte(s). For analyzing sulfonamide residues in liquid samples such as milk, a pretreatment dilution step with water prior to direct fluorometric detection may be required (207). Dilution of milk with aqueous buffer (208) or sodium chloride solution (209) prior to sample cleanup has also been reported. For the analysis of honey a simple dissolution of the sample in water (210, 211) or aqueous buffer (212) is generally required. Semisolid samples such as muscle, kidney, and liver, require, however, more intensive sample pretreatment. The analyte(s) must be exposed to extracting solvents to ensure maximum extraction. The most popular approach for tissue break-up is through use of a mincing and/or homogenizing apparatus. Lyophilization (freeze-drying) of swine kidney has been carried out prior to supercritical-fluid extraction of trimethoprim residues (213). 

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. 

For the toluene extractions, the work-up procedure was as described previously (j> ). In the supercritical water experiments, most of the extract was insoluble in water, after cooling and lowering of the pressure, and precipitated out in the condenser and receiver from which it was collected by washing with acetone and then THF. The remainder of the extract was found in the aqueous suspension which was evaporated to dryness on a rotary evaporator and the residue extracted with acetone and THF. The solvents were removed under reduced pressure from the combined acetone and THF solutions to give the total extract. This was then extracted with hot toluene and the cooled solution filtered to give the preasphaltene fraction. After the toluene was removed under reduced pressure from the filtrate, the residue was re-dissolved in a small volume of toluene and a 20 fold excess of pentane added to precipitate the asphaltene which was filtered off. The pentane and toluene were then removed from the filtrate under reduced pressure to give the oil. For the NaOH extractions, the NaOH solutions were neutralised with HC1. The insoluble extract was washed with water and then extracted with THF. Removal of the THF gave the total extract. 

The new process involves the production of de-oiled lecithin by subjecting crude lecithin to supercritical CO2 extraction. The soy bean oil dissolves in CO2 and lecithin does not. One of the examples relates that 1,000 g of cmde lecithin is extracted with CO2 at 60 °C and 400 aun for 4 hours. The CO2 extracts 380 g of a yellow, clear oil, 30 g of water, and the residual material, 580 g of a solid, light yellow substance, which is the deoiled lecithin, is removed from the extraction vessel at the end of the cycle. 

Similarly, the decomposition of rubber with supercritical water has been investigated by Funazukuri et alP5 Treatment of rubber with water at temperatures of about 380 °C led to a conversion of 43 48% of the raw tyre into oil. Elementary analysis showed that about half of the sulfur contained in the original sample is extracted into the oil, whereas the other half remains in the solid residue. 

Analysis of plants normally involves a sample preparation stage such as extraction or distillation followed by analysis with gas chromatography or liquid chromatography. The common methods used currently for the isolation of essential oils from natural products are steam distillation and solvent extraction (Ozel Kaymaz, 2004). Losses of some volatile compounds, low extraction efficiency, degradation of xmsaturated compounds through thermal or hydrolytic effects, and toxic solvent residue in the extract may be encountered with these extraction methods. Recently, more efficient extraction methods, such as supercritical fluid extraction (SFE) (Simandi et al., 1998) and accelerated solvent extraction (ASE) (Schafer, 1998) have been used for the isolation of organic compounds from various plants. Subcritical or superheated water extraction (SWE) is non-toxic, readily available, cheap, safe, non-flammable and is a recyclable option. 

The fipronil standard, more than 99% pure, was obtained from Chem Service (West Chester, Pennsylvania, U.S.A.). The fipronil standard solution was prepared in ethyl acetate. Mallinckrodt (Phillipsburg, New Jersey, U.S. A.) supplied all the nanograde solvents for pesticide-residue analyses. Several adsorbents—such as octadecyl silane (35-75 mesh, Supelco), chromossorb (100-120 mesh, Johns Manville), florisil (100-200 mesh, Riedel), silica gel 60 (70-230 mesh, Merck), and XAD-7 (20-60 mesh, Rohm and Haas)—were tested as sorbents in the SPE cartridges. Different modifiers (hexane, acetone, methanol), various temperature (50, 60°C), and pressure conditions (120, 250, and 300 atm) were tested for supercritical fluid extraction. The water was purified with a Millipore Milli Q Plus System (Bedford, Massachusetts, U.S.A.). 

Solid-phase extraction (SPE) using small, disposable cartridges, columns, or disks is employed for isolation and cleanup of pesticides from water and other samples prior to TLC analysis, especially using reversed-phase (RP) octa-decyl (C-18) bonded silica gel phases. Microwave-assisted extraction (MAE) is a time- and solvent-saving method for removing residues from samples such as soils. Supercritical fluid extraction (SEE) has been used for sample preparation in the screening of pesticide-contaminated soil by conventional TLC and automated multiple development (AMD). Ultrasonic solvent extraction (USE) and videodensitometry have been combined for quantification of pesticides in sod. Matrix solid-phase dispersion (MSPD) with TLC and GC has been used to determine diazinon and ethion in nuts. 

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. 

Supercritical water and carbon dioxide are attractive for extractions as they are cheap (not always with regard to the operational costs), contaminant free, and cheaper to dispose of than organic solvents. In addition, supercritical extraction does not leave a chemical residue, which is an important aspect in the food industry. For CO2, the critical parameters are rather low (31 °C and 74bar) compared to water and many other gases (Table 3.3.12). This helps to prevent thermal degradation of components that are being extracted. For these reasons supercritical CO2 is the solvent of choice, for example, to extract caffeine from green coffee beans. 

SFE of fruits and vegetables and meat products has been reported, but the sample preparation techniques necessary to obtain reproducible results are extremely time consuming. Solid absorbents such as Hydromatrix, Extrelut " anhydrous magnesium sulfate or absorbent polymers are required to control the level of water in the sample for the extraction of the nonpolar pesticides. Without the addition of Hydromatrix, nonpolar pesticides cannot penetrate the water barrier between the sample particles and the supercritical CO2. The sample is normally frozen and the addition of dry-ice may be required to reduce losses due to degradation and/or evaporation. Thorough reviews of the advantages and limitations of SFE in pesticide residues... 

Bacterial mutagenesis tests have been conducted with distilled water solutions of the freeze-dried residues [concentrated up to 3000-fold (7)] and partially freeze-dried samples [concentrated 10-fold (49)]. High salt concentrations in such concentrates may cause toxicity problems in the bacterial tests. The use of dimethyl sulfoxide, methanol, or supercritical carbon dioxide to extract the organics from the freeze-dried residues for mutagenicity test purposes should be investigated. 

If the bonded water is extracted by dry CO2 the enzyme is denaturated and loses its activity. Therefore a certain amount of water is necessary in the supercritical fluid because acting with water-saturated CO2 again causes an inhibition of the enzyme and consequent loss of activity. The optimal water concentration has to be determined for each enzyme separately. Table 9.2-1 shows the residual activity of lipase from Candida cylindracea, esterase from Mucor mihei, and esterase from Porcine liver after a incubation time of 22 hours in supercritical CO2 at 40°C. It is obvious that higher water concentrations cause a strong reduction in the residual activity compared to the activity of the untreated enzyme, which was set as 100 %. Further, the system-pressure has an influence because at higher pressures the activity-loss is lower with a larger amount of water in the system [7,8],... 

After the reaction, urea is separated by extraction with water whereas the polyol remains as a residue in the reactor. Therefore, under supercritical conditions the polyether polyols are separated from the mixture at the same time that the ammonolysis reaction progresses. The diamines and the diol can be separated by distillation or precipitation. The phosgenation of the amine leads to the corresponding diisocyanate, which together with the polyol and the diol may be used in the recovery of the raw polyurethane. 

Some triazines, including atrazine and simazine, were extracted from water by SEE after preconcentration on sohd-phase extraction disks.The freeze-dried residue or SPE disk was then introduced into the extraction cell and eluted with either pure CO2 or methanol or acetone-modified CO2. SEE has been applied in combination with online sohd-phase extraction for pesticides, including triazines. However, this technique is still used mainly on solid matrixes. The main limitation with aqueous matrixes remains the miscibility of water with supercritical carbon dioxide. Recoveries of nonpolar pesticides, extracted by SEE technique using octacedyl-bonded silica, are generally effective with CO2 elution alone. This is not the case for semipolar and polar compounds, such as triazines and their degradation products. For example, the addition of... 

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