Compounds from aqueous solutions

In the isolation of organic compounds from aqueous solutions, use is frequently made of the fact that the solubility of many organic substances in water is considerably decreased by the presence of dissolved inorganic salts (sodium chloride, calcium chloride, ammonium sulphate, etc.). This is the so-called salting-out effect. A further advantage is that the solubility of partially miscible organic solvents, such as ether, is considerably less in the salt solution, thus reducing the loss of solvent in extractions. 

Another method of removing mercury compounds from aqueous solution is to treat them with water-soluble reducing agents, thus hberating metallic mercury (26). The use of formaldehyde (qv) at a pH of 10—12 also is recommended. 

The results available on the synthesis of niobium and tantalum fluoride compounds from aqueous solutions are in good correlation with the concept of... 

Shimoda, M., Wu, Y., and Osajima, Y. (1996). Aroma compounds from aqueous solution of haze (Rhus succedanea) honey determined by adsorptive column chromatography. /. Agric. Food Chem. 44, 3913-3918. 

Applications The scientific literature on this relatively new approach is still quite limited. SPME-HPLC-MS is suitable for quantitation of polar and semipolar organic compounds from aqueous solutions. 

Adsorption from liquids is less well understood than adsorption from gases. In principle the equations derived for gases ought to be applicable to liquid systems, except when capillary condensation is occurring. In practice, some offer an empirical fit of the equilibrium data. One of the most popular adsorption isotherm equations used for liquids was proposed by Freundlich 21-1 in 1926. Arising from a study of the adsorption of organic compounds from aqueous solutions on to charcoal, it was shown that the data could be correlated by an equation of the form ... 

Dousova et al. [142] found that calcined Mg/Al LDHs were effective in removal of As (V) compounds from aqueous solutions at 293 K and neutral pH utilizing the memory effect . More than 70 % of As (V) compoimds were removed from aqueous solution at low sorbent-solution ratios. Parida et al. also studied the affinity of Mg/Fe LDHs toward the removal of inorganic selenite (SeOs ) from aqueous media [143]. The results indicated that the efficacy of SeOs removal increases with a decrease in either pH or temperature. 

Ethers are good for extracting organic compounds from aqueous solutions because the density of ethers is less than water, causing the ether layer to float on top of the water layer. 

Extraction of organic compounds from aqueous solutions... 

Figure 9.4 Correlation between distribution ratios of various neutral organic compounds from aqueous solution to 1-octanol (Korenman, Ya.L, Distribution Ratios of Organic Compounds, Voronezh University Press, Voronezh, Russia, 1992. p. 336) and to [C4CjIm][Pp5] (literature and our own data, [Huddleston, J.G., Visser, A.E., Reichert, V.M., Willauer, H.D., Broker, G.A., Rogers, R.D., Green Chem., 3, 156-164, 2001 Carda-Broch, S., Berthod, A., Armstrong, D.W., Anal. Bioanal. Chem., 375, 191-199, 2003 Pletnev, l.V, Smirnova, S.V., Khachatryan, K.S., Zernov, W, Rus. Chem. /.-/. Russ. Chem. Soc., 48, 51-58, 2004]).

Adsorption of Ionized Organic Compounds from Aqueous Solutions to Charged Mineral Surfaces... 

Figure 11.6 Sorption isotherms for two kinds of nonionic organic compounds from aqueous solutions to suspended kaolinite (a) slightly monopolar compound, pyrene, showing a linear isotherm up to its solubility (Backhus, 1990), and (b) monopolar compound, 1,3,5-trinitrobenzene, showing a hyperbolic isotherm (Had-erlein et al., 1996).

In contrast, organophilic PV membranes are used for removal of (volatile) organic compounds from aqueous solutions. They are typically made of rubbery polymers (elastomers). Cross-linked silicone rubber (PDMS) is the state-of-the-art for the selective barrier [1, 43, 44]. Nevertheless, glassy polymers (e.g., substituted polyacetylene or poly(l-(trimethylsilyl)-l-propyne, PTMSP) were also observed to be preferentially permeable for organics from water. Polyether-polyamide block-copolymers, combining permeable hydrophilic and stabilizing hydrophobic domains within one material, are also successfully used as a selective barrier. 

One important potential application of supercritical extraction is the recovery of polar organic compounds from aqueous solutions. Such mixtures arise frequently as products of biochemical syntheses. In many cases, the costs of the energy-intensive separations are high and there is substantial incentive for the development of more efficient processes. 

Nicell JA, Bewtra JK, Biswas N, St. Pierre CC, Taylor KE. Enzyme catalyzed polymerization and precipitation of aromatic compounds from aqueous solution. Can J Civ Eng 1993 20 725-735. 

It has been demonstrated that mixed oxides obtained from calcined LDHs have the ability to act as sorbents for a variety of anionic compounds from aqueous solution. This ability is because of the propensity for the mixed oxide to hydrate and re-form an LDH in such conditions and is of particular interest for the decontamination of waste-water. Hermosin et al. have found, for example, that MgAl-LDHs calcined at 500 °C are potential sorbents for the pollutants trinitrophenol and trichlorophenol from water [208, 209]. The adsorption mechanism was shown, using PXRD, to involve reconstruction of the LDH, with the uptake of the phenolate anions into the interlayers. Similarly, the ability of calcined MgAl-LDHs to remove nitriloacetate anions from solution has been demonstrated [210]. Calcined LDHs have been utilized also for the sorption of radioactive anions, such as 111, from aqueous solution [211]. A particularly attractive feature of the use of calcined LDHs for the remediation of waste-water is that the sorption capacity of the material may be regenerated via calcination of the rehydrated LDH. 

Alvarez-Gallegos, A. and Pletcher, D. (1999) The removal of low level organics via hydrogen peroxide formed in a reticulated vitreous carbon cathode cell, Part 2. The removal of phenols and related compounds from aqueous solutions. Electrochim. Acta 44, 2483-2492. 

Supercritical fluids such as carbon dioxide can be used as solvents to extract organic compounds from aqueous solutions. In order to achieve recoveries of these products often in low concentration, cosolvents as methanol or other alcohols have been added to improve the solubility and the selectivity of the primary fluid. To optimize the extract recovery, the knowledge of phase equilibria of the ternary system carbon dioxide-methanol-water is required at different temperatures and pressures. 

Separation of volatile organic compounds from aqueous solutions Styrene butadiene block copolymer P for VOC as high as 5000. H2O flux increased rapidly with temperature thereby decreasing /3 for VOCs [106]... 

Dutta BK and Sikdar SK. Separation of volatile organic compounds from aqueous solutions by pervaporation using S-B-S block copolymer membranes. Env. Sci. Tech. 1999 33(10) 1709-1716. 

Samparanpiboon P, Jiraratananon R, Uttapap D, Peng X, and Huang RYM. Separation of aroma compounds from aqueous solution by pervaporation using poly-octylmethylsiloxane (POMS) and poly-dimethylsiloxane (PDMS) membranes. J. Memb. Sci. 2000 71 55. 

Sirkar KK, Yang D, Majumdar S, Kovenklioglu S, and Sengupta A. Hollow fiber-containing liquid membrane pervaporation for removal of volatile organic compounds from aqueous solution. Patent No. US 5637224 Kind A Date 19970610. 

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