Dissolving and extraction

A standard practice for preparing polymer solution contains information on solvents, their concentration, temperature, pressure, mixing time, and heating. The annex contains information on the best solvents for 75 typical polymers with different degrees of substitution or modification. Frequently, temperature and concentration of solution is also 

Solvent extraction is used on textile materials to determine naturally occurring oily and waxy materials that have not been completely removed from the fibers. The percentage of extracted material is given in relationship to the dry mass of fiber. Solvents used for extraction including l,l,2-trichloro-l,2,3-trifluoroethane and dichloromethane but these may be replaced by other solvents by mutual agreement. The Soxhlet extraction and gravimetric determination are used. 

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It is common to find that a chemical added to soil becomes increasingly difficult to remove with time. The mechanism described earlier is one that would account for this observation. A compound added to soil may initially crystallize rapidly into a structure that is easily dissolved and extracted from soil. With time, its crystalline structure rearranges to a less soluble, lower energy, and thus less easily extractable form [7],... 

Sodium valproate i.v. 200 mg b.d. - To reconstitute, inject the solvent provided (4 mL) into the vial, allow to dissolve and extract the appropriate dose. Due to displacement of solvent by sodium valproate the concentration of reconstituted sodium valproate is 95 mg/mL. Give as a slow intravenous injection over 3-5 minutes. 

Any attempt to design an effective procedure for the isolation of humic substances from soil should take account of the properties of the solvents or extractants to be used, of the solutes or material to be extracted, and of the types of associations that can exist between these solutes and other soil colloidal constituents. This chapter outlines some aspects of the composition, properties, and associations of soil humic substances which are relevant to their extraction, and it considers some of the properties of solvents that are used or might be considered for use as extractants of humic substances, or of molecules associated with these substances. It then compares the effectiveness and outlines some of the limitations of a selected number of solvents and procedures for dissolving and extracting humic substances. 

A fourth alternative for carrying out the naphthalene extraction utilizes the dissolving capacity of near-critical liquid CO2. This operating mode is illustrated in figure 6.1 by the LV tie line. Liquid CO2 is employed to dissolve and extract the naphthalene from the mixture, and the liquid solution leaving the extractor is heated to vaporize the CO2 and recover the naphthalene. The CO2 is then condensed and recycled to the extractor. 

Chapter 8 briefly introduced the concept of supercritical fluids in the context of undersea thermal vents. The supercritical point for water occurs at a temperature of 705°F (374°C) and a pressure of 222.3 bar (atmosphere). Above this temperature, no pressure can condense water to its liquid state. For carbon dioxide (CO2), the critical temperature (88.0°F or 31.1°C) and critical pressure (73.8 bar) are much lower. Above the supercritical point, CO2 behaves as a liquidlike gas liquidlike densities, gaslike viscosities. The solubility properties of supercritical CO2 are mnable by varying temperature and/or pressure. Density and dielectric constant increase with increasing pressure and decreasing temperature. Water and ionic substances are insoluble in supercritical CO2. The ability of supercritical CO2 to dissolve and extract relatively non-polar substances has been known for decades. The range may be extended by adding polar solvents such as methanol or acetone. The addition of surfactants helps to disperse microscopic particles to form colloidal suspensions. Carbon dioxide is nonflammable, nontoxic, and inexpensive. 

After screening tests have been completed, instrumental techniques such as ultraviolet (UV)-visible spectrophotometry, liquid chromatography (LC), and gas chromatography (GC) are used to confirm the presence of heroin. To analyze an unknown opiate by instrumental analysis, the sample is dissolved and extracted with a suitable solvent. The UV spectrum of pure heroin prepared in dilute acid is shown in Figure 3A. In dilute aqueous acid, the absorbance maximum is 279 nm. 

Solvents, such as acetone or chloroform, reduce the water-holding capacity of the SC by dissolving and extracting intercellular lipids (Thune 1996b Abeck et al. 1997)- Lipids can be completely removed, and then the corneocytes adhere tightly to one another by the single ceramide 1 outer layer of the involucrum, which prevents corneosome destruction (Chapman et al. 1991) and disturbs desquamation (Rawlings et al. 1995). 

As far as reprocessing in the U/Pu fuel cycle is concerned, several chemical separation techniques have been proposed and developed in the past few decades. The most efficient process to date remains the PUREX process (Plutonium and Uranium Recovery by Extraction). This process uses nitric acid HNO3 and organic solvents to dissolve and extract selectively U and Pu, resulting in two separate product streams (U on one side and Pu on the other side of the process chain). As far as reprocessing in the Th/ U fuel cycle is concerned, THOREX (Thorium Oxide Recovery by Extraction) technology must be used, also based on dissolution in nitric acid and solvent extraction (however, with special care for the extraction of Pa, for the separa-tion of U and U, and for the dissolution of thorium dioxide in pure nitric acid). 

Hot compressed water can be generally described as water at temperature above 150°C and various pressures. Depending upon the temperature and pressure, hot compressed water can exhibit stimulating physical and chemical properties. Water plays a very active role as its dielectric constant sharply decreases and helps the reaction to proceed. Low relative dielectric constant in this state enhances the ionic reaction suitable for a variety of syntheses or some degradation reactions. Depending on the temperature and pressure, hot compressed water supports either free radical or ionic reactions. At high pressures and below the critical temperature, ionic reactions dominate and thus ionic and polar species of biomass are extracted. At high temperatures and low pressures, free-radical reactions are superior and non-polar substances are readily dissolved and extracted (Mohanty et al., 2014). 

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