Solid residues from supercritical

Grandmaison, J.L. Ahmed, A. Kalaiguine, S. "Solid residues from supercritical extraction of wood characterization of their constituents." In This Volume. 

Solid Residues from Supercritical Extraction of Wood... 

SFE. SFE has been established as the extraction method of choice for solid samples. The usefulness of SFE for soil samples has been demonstrated for carbamate,organophosphorus and organochlorine pesticides. However, SFE is more effective in extracting nonpolar than polar residues. In order to obtain a greater extraction efficiency for the polar residues of imidacloprid, the addition of 20% methanol as modifier is required. Extraction at 276 bar and 80 °C with a solvent consisting of supercritical carbon dioxide modified with methanol (5%) for 40 min gives a recovery of 97% (RSD = 3.6%, n = 10). It is possible to use process-scale SFE to decontaminate pesticide residues from dust waste. ... 

The popularity of this extraction method ebbs and flows as the years go by. SFE is typically used to extract nonpolar to moderately polar analytes from solid samples, especially in the environmental, food safety, and polymer sciences. The sample is placed in a special vessel and a supercritical gas such as CO2 is passed through the sample. The extracted analyte is then collected in solvent or on a sorbent. The advantages of this technique include better diffusivity and low viscosity of supercritical fluids, which allow more selective extractions. One recent application of SFE is the extraction of pesticide residues from honey [27]. In this research, liquid-liquid extraction with hexane/acetone was termed the conventional method. Honey was lyophilized and then mixed with acetone and acetonitrile in the SFE cell. Parameters such as temperature, pressure, and extraction time were optimized. The researchers found that SFE resulted in better precision (less than 6% RSD), less solvent consumption, less sample handling, and a faster extraction than the liquid-liquid method [27]. 

Corrosion can be a problem, especially if a chlorine-containing compound is decomposed. This may require that the reactor be made of titanium. The corrosion can be reduced by the use of sodium carbonate.207 Use of this system at 380°C reduced the content of polychlorinated biphenyls in a sample from 20 mg/L to less than 0.5 /tg/L. Trichloroethylene, 1,1,1-trichloroethane, and trichloroacetic acid were destroyed with 99.96% efficiency at 450°C for 60 ss using 1.5% hydrogen peroxide plus sodium bicarbonate.208 Sodium nitrate or sodium nitrite could be used in place of the hydrogen peroxide. Nitrates, ammonium hydroxide, and amines, all are converted to nitrogen at 350-360 C. Emulsions of petroleum, water, and solids can be broken by heating to 350oC. Supercritical water has been used to recover 2,4-diamino-toluene from distillation residues from the manufacture of 2,4-toluenediisocyanate.209... 

In this paper we report our efforts to characterize the solid residues produced in a series of experiments with the semicontinuous extraction of Populus tremuloides (aspen wood) in supercritical me-thanol iSi, at temperatures ranging from 250 to 350°C (Supercritical Extraction residues or SCE residues), by using wet chemistry and chromatographic, thermogravimetric and spectral methods such as DRIFTS 2 > and ESCA. ... 

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. 

Stahl interfaced supercritical fluid extraction (SFE) with TLC more than 15 years ago (84), and the great interest today in SFE, e.g., for extraction of pesticide residues from foods and environmental samples, should lead to development of many applications of this sample preparation method prior to TLC. As an example, hydroperoxides in combustion aerosols were separated from solid matrixes using SFE with on-line sample transfer to TLC plates (84a). 

The adaptation of supercritical fluid extraction (SFE) in routine residue and metabolism analysis as well as other extraction/separation laboratories and applications has been slow. This is despite the demonstrated feasibility of using SFE for the removal of sulfonylureas, phenylmethylureas and their metabolites from soil and plant materials (1-2), as well as widespread demonstrated use of supercritical fluid extraction for other applications (3-6). The reason for this is simple. Although automated, SFE extraction apparatus typically only analyzes a single sample at a time. The technique could not compete effectively with the productivity of an experienced technician performing many sample extractions simultaneously. In essence, with a one vessel automated supercritical fluid extractor, operator attendance is high and throughput is about the same or even less than current conventional liquid-liquid and solid-liquid extraction techniques. 

When the analytes are to be retained in a sorbent, the sample (which can be solid, semi-solid, liquid or gaseous) is inserted in the solid state into the extraction cell. Samples in the latter three forms are supported on an appropriate material in order to ensure effective attack by the supercritical fluid. Solid supports are not used for liquid, gaseous and semi-solid samples only, however. Some research work conducted so far on solid samples has involved not natural samples but synthetic ones prepared from a selected sorbent (a natural matrix where the presence of the analytes of interest was previously excluded or a synthetic support such as polyurethane foam or glass wool) with which a solution containing the analytes was homogenized. Quantitative evaporation of the analyte solvent is mandatory as any residual solvent may alter the polarity of the supercritical fluid and hence its action to an extent dependent on the particular fluid and solvent properties, and also on the amount of solvent retained. 

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. 

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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