Extraction by Supercritical Fluids

In the extraction by supercritical fluids process, pulverized coal is treated with compressed gases at temperatures on the order of 175°C-200°C (345°F-390°F) whereupon a portion of the coal passes into solution in the compressed gas (Nowacki, 1979 Ceylan and Olcay, 1981). The solution is then transferred to a second vessel and in so doing leaves the inorganic matter and undissolved coal behind. Release of the pressure on the second vessel causes separation of the extract the gas is recompressed and recycled to the process. 

The quoted advantages for this process over the liquid solvent extraction processes are as follows (1) filtering to remove insoluble residue may not be necessary (2) recovery of the gaseous solvent appears to be virtually complete and (3) more mobile liquids of higher hydrogen content are obtained. The disadvantages are as follows (1) the yield of extract is considerably less than that obtained by conventional (liquid) extraction and (2) operation at the higher pressures may cause a severe escalation of the process economics. 

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The development of methods of analysis of tria2ines and thek hydroxy metabohtes in humic soil samples with combined chromatographic and ms techniques has been described (78). A two-way approach was used for separating interfering humic substances and for performing stmctural elucidation of the herbicide traces. Humic samples were extracted by supercritical fluid extraction and analy2ed by both hplc/particle beam ms and a new ms/ms method. The new ms /ms unit was of the tandem sector field-time-of-flight/ms type. 

Bonazzi et al. [18] reported the determination of miconazole and other imidazole antimycotics in creams by supercritical fluid extraction and derivative ultraviolet spectroscopic method. Cream based pharmaceuticals were mixed with celite and anhydrous sodium sulfate and extracted by supercritical fluid extractor (SFE) with... 

Non-ionic surfactants of a commercial washing powder were separated by supercritical fluid chromatography (SFC) and determined by APCI-MS. The constituents were first extracted by supercritical fluid extraction (SFE) using C02 with or without methanol as a modifier. Variations of the conditions resulted in a selective extraction of the analytes, which could be determined without further purification. Six groups of surfactants were observed, four of which are alkyl-polyethoxylates. The presence of APEO could be excluded by identification recording SFC-FTIR (Fourier transform infrared) spectra [31]. 

Extraction by supercritical fluids, in particular carbon dioxide and propane, is currently being investigated as a means of controlling the size and shape of particles for inhalation. Supercritical fluids are liquids above their critical pressure and temperature [28]. Under these conditions the molecules exhibit the flow, polarity, and solvency properties common of liquids but have the diffusivities and reactivities characteristic of gases. 

Supercritical drying (SCD) The wet cake of sol pillared bentonite (sol-PILB) was dispersed into absolute ethanol and filtrated, washed with ethanol for several times to replace the water by ethanol. The cake was transferred to a cartridge and the ethanol was extracted by supercritical fluid (CO2) for 3 h under 3000 psi, at 323 K. The flow rate was controlled around 2.5 ml/min. The sample was then calcined at 773 K for 12 h and labeled as sample SCD. 

Heaton et al. have reported the supercritical fluid chromatography of taxicin I and taxicin II extracted by supercritical fluid extraction of Taxu baccata, the English yew tree [41]. They compared capillary- and packed- column SFC and concluded that packed-column SFC was better than capil4 lary-column SFC for quantitative analysis of these compounds. Capillary SFC was done on either a biphenyl or carbowax column with unmodified carbon dioxide as the mobile phase. The packed-column SFC was performed on a nitrile column with a mobile phase consisting of a methanol gradient with carbon dioxide. 

The coke extraction by supercritical fluids is strongly dependent on the type of catalyst. The three-dimensional USYZ is easier accessible for the solvent than the two-dimensional ZSM-5 and the one-dimensional H-modernite. For USYZ there is an optimal temperature, at which the supercritical fluid has the highest ability for coke extraction. For ZSM-5 the coke content and the rest of the acid centres of catalyst are strongly dependent on the temperature. At 623 K the acid centres decreased only about 5%, but at 673 K they were almost totally decimated. Due to the faint coking tendency of ZSM-5 the supercritical fluid plays only a small role for the regeneration of the catalyst. But the supercritical fluid can ameliorate the product distribution of the EBD on ZSM-5. For H-mordenite the conversion of EB is strongly dependent on the temperature in the range of 623 - 673 K because of its one-dimensional channel system. 

One promising way to seperate halogenated flame retardents out of polymer composites seems to be the extraction by supercritical fluids like C02.. Main objective of this paper is to find the suitable conditions for high extraction efficiencies. For model mixtures involving the flame retardents TBBA, TBPA and HBCD the extraction efficiency from the inert matrix MgS04 was examined in relation to extraction pressure, temperature and time. The data form the basis for realistic tests on ABS composites with different flame retardents. 

Polynuclear Aromatic Hydrocarbons in Environmental Materials Extraction by Supercritical Fluid Extraction... 

Ca. 3.5 g sediment were extracted by supercritical fluid extraction (CO2 and 20% methanol) after HCl addition. The extraction recovery for TBT (verified with a TBT-spiked sediment) was (82 + 6)%. Grignard derivatization was performed, using 2 mol L EtMgCl in tetrahydrofuran. Separation was by CGC (column of 30 m length, internal diameter of 0.25 mm, DB-5 as stationary phase, 0.1 pm film thickness He as carrier gas at 2 mL min injector temperature at 40 °C column temperature ranged from 40 to 290 °C). Detection was FPD (temperature of 225 °C). Calibration was carried out with butyltin chloride calibrants calibration graph and standard additions of tripropyltin as internal standard. 

Ca. 1 g sample was extracted by supercritical fluid extraction with CO2 and a mixture of acetic acid and 0.2% tropolone with hexane as solvent (pressure of 50 atm, temperature of 50 Q. Ethylation was carried out with 2 mol L ethylmagnesium chloride. TPeT was added as internal standard. Separation was by capillary GC (column of 30 m length, 0.25 mm internal diameter, DB-17 as stationary phase, 0.25 pm film thickness H2 as carrier gas at 5 mLmin N2 as make-up gas at 30 mLmin injector temperature of 250 °C column temperature ranging from 60 to 280 °C). Detection was by FPD (detector temperature of 300 °C). Recoveries were assessed by standard additions results were (82 4)% for DBT, (75 + 2)% for TBT and (65 + 3)% for TPhT. Calibration was by calibration graph and standard additions, using the calibrants provided by SM T. 

Akgeniian, A. and Madras, G. (1994) Fundamentals of solids extraction by supercritical fluids in Supercritical Fluids Fundamentals and Application Kiran, E. and Levelt Sengers, J.M.H., Eds., N ATO-ASI Series, Series E Applied Sciences, 273,669-695. 

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