Carbon subcritical

Achiral-chiral chromatography has also been accomplished using subcritical fluid chromatography (Phinney et al., 1998). In this work, the structurally related [3-blockers, 1,4-benzodiazepines, and two cold medicines were separated using methanol or ethanol modified carbon dioxide mobile phases. The (3-blockers were separated using cyanopropyl and Chiracel OD columns connected in series. Likewise, an amino bonded phase and Chiracel OD column were used for the separation of the 1,4-benzodiazepines. Guaifenesin and phenylpropanolamine from cough syrup were separated on cyanopropyl and Chiralpak AD columns in series. 

Pirkle-type CSPs do not involve ionic interactions and therefore are almost exclusively operated in the normal-phase mode. The use of subcritical carbon dioxide based mobile phase, i.e., subcritical fluid... 

Ary Ihydantoins Whelk-Ol 2-Propanol-hexane or methanol— (subcritical) carbon dioxide 165... 

Alcohols and ketones, arylnaphthalenes Whelk-O 1 and poly Whelk-O (= its polysil-oxane borne analog) Subcritical carbon dioxide-based mobile phase at cryogenic temperatures 166... 

The mixture to be separated is fed, together with the entrainer, to the middle of the first column. Flere, the solvent, carbon dioxide and acetone, is supercritical to provide high solubility of the monoglycerides. The supercritical phase leaves the top of column I and goes to the lower part of column II. In column II, the binary solvent entrainer is subcritical and in the bottom of this column, the monoglyceride leaves, together with the entrainer. Part of it is returned as reflux to column I, whereas the rest goes to distillation for the separation of acetone. With a bottom temperature of... 

In addition, the polymerization itself can be performed in subcrit-ical carbon dioxide as solvent. Not that the critical point of carbon dioxide is at 37°C and 73 bar. 

The current trend of consumer preference towards natural products requires new processing methods for spice-oils and extracts, without the addition of external material. In recent years there has been an increased interest in supercritical and subcritical extraction [26,27], which use carbon dioxide as a solvent [34,35,36]. Carbon dioxide (CO2) is an ideal solvent for the extraction of natural products because it is non-toxic, non-explosive, readily... 

Extraction of stevia sweeteners from dried leaves can be accomplished with acetonitrile in the presence of calcium carbonate solution (116) or with boiling water adjusted to pH 9.0 (107). Ahmed and Dobberstein (117) extracted stevioside and rebaudioside A and C from dried leaves of S. rebaudiana in a micro-Soxhlet apparatus. They observed that chloroform/methanol provided the best results, compared to chloroform or to chloroform/methanol/water. Extraction of stevioside, rebaudioside A and C, and dulcoside A can also be performed by subcritical fluid extraction using C02 and methanol as a modifier. Such an extraction technique has been gaining popularity as an analytical tool because it is rapid, simple, and less expensive in terms of solvent cost (110). Beverages, tabletop sweeteners, beverages containing pulp, and candies are prepared as indicated in Sec. I.C (110,115,118). 

Other researchers have found that as temperature increases, the activity passes through an optimum (Miller et al., 1991 Rantakayla and Aaltonen, 1994 Steytler et al., 1991 Yoon et al., 1996 Zheng and Tsao, 1996). It is believed that this bell-shaped behavior is the result of increasing activity as temperature increases to the optimum, followed by a decrease in activity above the optimum because of thermal denaturation. In one instance, another contributing factor to the lower activity below the optimum temperature was that the carbon dioxide was subcritical (Miller et al., 1991). Yoon et al. (1996) observed optimal temperatures for activity only at certain concentrations of products. No explanation was provided. 

Organophosphorus insecticides including diazinon, ronnel, parathion ethyl, methiadathion and trichlorovinphos have been extracted from soil by subcrit-ical carbon dioxide containing 3% methyl alcohol. At a pressure of 35.5 MPa and 50 °C, recoveries of 85% were obtained [280,315]. 

Di Corcia [368] used subcritical water (phosphate-buffered) extraction with a graphitised carbon black cartridge to recover terbuthylazine herbicide and its metabolites from soil. 

Field and Monohan [430] sequentially extracted Dacthal and its mono-and diacid metabolites from soils by first performing a supercritical carbon dioxide extraction to recover Dacthal, followed by a subcritical (hot) water extraction step to recover metabolites. Dacthal was recovered from soil in 15 minutes by supercritical carbon dioxide at 150 °C and 400 bar. The mono-and diacid metabolites were extracted from soil in 10 minutes under the sub-... 

Peytavin et al. [17] have reported on the chiral resolution of mefloquine, halofantrine, enpiroline, quinine, quinidine, chloroquine, and primaquine by subcritical fluid chromatography on a (S) naphthylurea column (250 X 4.6 mm ID). The mobile phase consisted of carbon dioxide, methanol, and triethylamine at a 3-ml/min flow rate. Except for primaquine and... 

In brief, the salts that are classified as Type 1 have increasing solubility with increasing temperature, whereas Type 2 salts show an opposite trend. For example, sodium carbonate, a Type 2 salt, has a 30 wt.% solubility under ambient conditions and its solubility near the critical point approaches zero [36] whereas sodium chloride, a Type 1 salt, has a 37 wt.% solubility under subcritical conditions at 300 °C and about 120 ppm at 550 °C [46]. 

If such a zone exists on Jupiter, it is narrow. Where the temperature is 300 K (clearly suitable for organic molecules), the pressure (about 8 atm) is still subcritical. At about 200 km down, where the jovian pressure is supercritical, the temperature rises above 500 K, approaching the upper limit where carbon-carbon bonds are stable.24... 

A solvothermal process is one in which a material is either recrystallized or chemically synthesized from solution in a sealed container above ambient temperature and pressure. The recrystallization process was discussed in Section 1.5.1. In the present chapter we consider synthesis. The first solvothermal syntheses were carried out by Robert Wilhelm Bunsen (1811-1899) in 1839 at the University of Marburg. Bunsen grew barium carbonate and strontium carbonate at temperatures above 200°C and pressures above 100 bar (Laudise, 1987). In 1845, C. E. Shafhautl observed tiny quartz crystals upon transformation of freshly precipitated silicic acid in a Papin s digester or pressure cooker (Rabenau, 1985). Often, the name solvothermal is replaced with a term to more closely refer to the solvent used. For example, solvothermal becomes hydrothermal if an aqueous solution is used as the solvent, or ammothermal if ammonia is used. In extreme cases, solvothermal synthesis takes place at or over the supercritical point of the solvent. But in most cases, the pressures and temperatures are in the subcritical realm, where the physical properties of the solvent (e.g., density, viscosity, dielectric constant) can be controlled as a function of temperature and pressure. By far, most syntheses have taken place in the subcritical realm of water. Therefore, we focus our discussion of the materials synthesis on the hydrothermal process. 

The most influential parameter on the reaction products is the reaction temperature. Under subcritical conditions only a hydrolytic separation of 80 % (y-HCH) respectively 60 % (HCB) of the chlorine atoms was detected. In supercritical water the decomposition of the organic attached chlorine in y-HCH and HCB into inorganic chloride amounts more than 99 % Cl at 500 °C. In parallel there is a considerable decomposition of the hydrocarbon framework mainly to water soluble hydrocarbons and to gaseous products like carbon dioxide. SCWO conditions leads to a completely decomposition of theese compounds into environmental friendly reaction products without the formation of Cl2, HCl and dioxines. 

An industrially spent hydrotreating catalyst from naphtha service was extracted with tetrahydrofuran, carbon dioxide, pyridine and sulfur dioxide under subcritical and supercritical conditions. After extraction, the catalyst activity, coke content, and pore characteristics were measured. Tetrahydrofuran was not effective in the removal of coke from catalyst, but the other three solvents could remove from 18% to 54% of the coke from catalyst. 

In this project, the feasibility of catalyst regeneration by supercritical fluid extraction was studied. A spent catalyst from an industrial naphtha hydrotreater was extracted with tetrahydrofuran, pyridine, carbon dioxide, and sulfur dioxide under subcritical and supercritical conditions. The coke reduction and changes in the catalyst pore characteristics were measured and to a limited extent the catalyst activity was evaluated. It is shown that by supercritical extraction, the coke content of spent hydrotreating catalysts can be reduced and the catalyst pore volume and surface area can be increased. 

The effectiveness of tetrahydrofuran, pyridine, carbon dioxide, and sulfur dioxide as solvents to remove the coke from catalyst under supercritical and subcritical conditions was studied. The critical properties of these solvents are listed in Table I and the extraction conditions are shown in Table II. 

Supercritical fluids, most commonly carbon(IV) oxide, occasionally modified by a small addition of a polar solvent (methanol, acetonitrile, or water). Supercritical fluid extraction (SEE) uses water as the most popular additive, because increasing the temperature from 50 to 400 °C at a pressure exceeding the critical level makes it possible to achieve transition of extractant from the subcritical to the supercritical state and leaching of the compoimds in the order of polar to moderately polar [86]. 

With an increased interest and awareness of the impact of society and industry on the environment, there has been a significant attempt in recent years to reduce or replace the usage of organic solvents. Much early work in this area concentrated on the application of supercritical and subcritical carbon dioxide, but in recent years superheated (or subcritical/pressurized hot) water (SHW) has become of interest for both chromatography and extraction [43,54], The earliest work was reported by GuUlemin et al. [55], who used the term thermal aqueous liquid chromatography. As well as using SHW for the separation of... 

Supercritical fluid chromatography using carbon dioxide as the eluent is often carried out subcritically at 20°C or 25°C, because the more dense eluent... 

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