Hquid-liquid extraction

The main objective for calculating the number of theoretical stages (or mass-transfer units) in the design of a hquid-liquid extraction process is to evaluate the compromise between the size of the equipment, or number of contactors required, and the ratio of extraction solvent to feed flow rates required to achieve the desired transfer of mass from one phase to the other. In any mass-transfer process there can be an infinite number of combinations of flow rates, number of stages, and degrees of solute transfer. The optimum is governed by economic considerations. 

The other common objective for calculating the number of countercurrent theoretical stages (or mass-transfer units) is to evaluate the performance of hquid-liquid extraction test equipment in a pilot plant or to evaluate production equipment in an industrial plant. Most liq-uid-hquid extraction equipment in common use can oe designed to achieve the equivalent of 1 to 8 theoretical countercurrent stages, with some designed to achieve 10 to 12 stages. 

Investigated explosives included 2,4,6-trinitrotoluene (TNT), 2,4,6,N-tetranitro-N-methylaniline (tetryl), l,3,5-trinitro-l,3,5-triazacyclohexane (RDX), 1,3,5,7-tetranitro-l,3,5,7-tetrazacyclooctane (HMX) and pentaerythritol tetranitrate (PETN). The temperature of the injector, cooled with liquid CO2, was —5°C for 0.3 min, programmed from —5 to 250° C, at a rate of 200°C/min, with a final hold time of 8.4 min. The column temperature was 80° C for 2 min, programmed to 250° C at 25°C/min, with a final hold of 2 min. Electron ionization (El) in the positive-ion mode was used. Figure 4 shows the mass chromatograms of a mixture of explosives (lOppb each), extracted from water by Hquid—liquid extraction and X 100 concentration. Identification was based on typical fragment ions for each one of the explosives. 

Fig. 9.1 Spray column for Hquid-liquid extraction. The water phase flows from top to bottom, the toluene as the lighter phase from bottom to top. If the column is always filled with water at the marked height, the toluene breaks into drops at the feeding point. When the drops have reached the water interface, they coalesce and form a continuous toluene phase. The phenol transfers from the water phase to the toluene phase.

Aqueous systems have been used in separations, coatings, and synthesis. Aqueous biphasic systems have been developed for hquid-liquid extractions using water-soluble polymers such as polyethylene glycol, and inorganic salts such as ammonium chloride or potassium phosphate (Rogers et al., 1998), (Sherman et al., 1998). These systems have been investigated for use in the separation and recovery of heavy metals from mixed wastes and in the recovery of colored impurities from textile waste streams (Sherman et al., 1998). 

T. Misek, General Hydrodynamic Design Basis for Columns, in Hquid-Liquid Extraction Equipment,... 

In most cases, the use of chromatography in trace analysis needs preliminary preparation of analytical samples. For such purpose, beside classical hquid-liquid extraction, special systems were developed for extraction from or into the gas phase, or for extraction with the participation of solid phases. These systems enabled very low and very selective determination in the final step, even for microsamples. 

The flow diagram in Figure 10.4 is intended as a guide and is the way the author would normally approach a new HPLC analysis. Reversed-phase chromatography is assumed and this will mean evaporation of solvent and dissolution in mobile phase if using the hquid-liquid extraction path. No mention has been made of direct aqueous injection as the times that this technique can be employed in environmental analysis are few indeed. It can be seen that the author s choice of detector is fluorescence then electrochemical then UV. 

A combination of hquid-liquid extraction and SPE was applied in the sample pretreatment of bovine milk and liver samples in the PBI LC-MS analysis of ivermectins [88]. ECNI with methane was performed to the intact molecular anion and some structure-informative fragments of two ivermectin components at m/z 874 and 860. The molecular anion and four fragment ions were used for regulatory confirmation. Signals were observed from on-colunm injections of 4 ng in extracts equivalent to 2 ml milk or 0.2 g liver. 

Of course, liquid-hquid extraction also may be a useful option when the components of interest simply cannot be separated by using distillation methods. An example is the use of hquid-liquid extraction employing a steam-strippable solvent to remove nonstrippable, low-volatility contaminants from wastewater [Robbins, Chem. Eng. Prog., 76(10), pp. 58-61 (1980)]. The same process scheme often provides a cost-effective alternative to direct distillation or stripping of volatile impurities when the relative volatility of the impurity with respect to water is less than about 10 [Robbins, U.S. Patent 4,236,973 (1980) Hwang, Keller, and Olson, Ind. Eng. Chem. Res., 31, pp. 1753—1759 (1992) and Frank et al., Ind. Eng. Chem. Res., 46(11), pp. 3774-3786 (2007)]. 

Another category of useful hquid-liquid extraction applications involves the recovery of antibiotics and other complex organics from fermentation broth by using a variety of ojq genated organic solvents such as acetates and ketones. Although some of these products are unstable at the required extraction conditions (particularly if pH must... 

Reaction-extraction This technique involves chemical modification of solutes in solution in order to more easily extract them in a subsequent extraction operation. Applications generally involve modification of impurity compounds to facilitate purification of a desired product. An example is the oxygenation of sulfur-containing aromatic impurities present in fuel oil by using H2O2 and acetic acid, followed by hquid-liquid extraction into an aqueous acetonitrile solution [Shiraishi and Hirai, Energy and Fuels, 18(1), pp. 37-40 (2004) and Shiraishi et al., Ind. Eng. Chem. Res., 41, pp. 4362-4375 (2002)]. Another example involves esterification of aromatic alcohol impurities to facihtate their separation from apolar hydrocarbons by using an aqueous extractant solution [Kuzmanovid et al., Ind. Eng. Chem. Res., 43(23), pp. 7572-7580 (2004)]. 

Phase separations are a crucial step in every work-up procedure. While it is relatively straightforward to automate a filtration step to separate a solid and a liquid phase, automated Hquid-liquid extraction is more difficult to achieve. This is essential for automating multistep solution synthesis, but can also be advantageous in solid-phase chemistry, as it is then possible to use non-volatile cleavage agents and to conveniently remove them (e. g., to cleave products from the support by saponification and to remove the salts formed during the reaction). 

Probably the simplest approach to automate Hquid-liquid extraction is to perform the phase separation by volume. Known volumes of wash or extraction solvent and organic phase are mixed, the phases are allowed to separate, and then only, e.g., 90% of the organic phase is retracted to make sure that no aqueous phase is withdrawn. Obviously, this step can be repeated to optimize recovery. This procedure can be carried out on most synthesizers with essentially no modification of the hardware. 

With low detection limit techniques, the identity, migration levels and accumulation of antioxidants and their degradation products in food, in hquids and in pharmaceutical solutions can be controlled. HPLC or GC-MS offers functional methods together with, e.g., hquid-liquid extraction (LLE). Recently, solid phase extraction (SPE) has been used successfully with lower detection hmits and smaller errors than LLE. SPE is a technique that uses a small amount of solvent and that efficiently concentrates solutions of analytes depending on, e.g., polarity. 

Norberg, J., Thordarson, E., Mathiasson, L., and Jonsson, J. A., Microporous membrane hquid-liquid extraction coupled onhne with normal-phase liquid chromatography for the determination of cationic surfactants in river and waste water, J. Chromatogr. A, 869, 523-529, 2000. 

Increasing the temperature of water extractions also increases the amount of matrix materials that are coextracted, especially for samples high in organic matter. Coextractants can reduce trapping efficiency and reproducibility on solid-phase traps. Using microporous membrane hquid-liquid extraction (MMLLE) in place of a sohd trap can more selectively trap PAHs from hot water extracts and minimize or eliminate sample cleanup. " The extraction solvent, cyclohexane, is immobilized in the pores of a polypropylene membrane where hquid-liquid mass transfer occurs. Limits of quantitation of about 1 for very small samples (5 to 10 mg) with an average... 

Y. Takagai and S. Igarashi, Homogeneous hquid-liquid extraction and micellar eleetrokinetie ehromatography using sweeping effect concentration system for determination of trace amounts of several polycyclic aromatic hydrocarbons. Ana/. Bioanal. Chem., 373, 87—92, 2002. 

The stability constants of the 1 1 alkali metal picrate complexes of diketone 18. heptacyclic terpyridyl 27 and flexible terpyridine 28 were estimated by hquid-liquid extraction, and the resulting log fj values for Na" " and are also given in Fig. 4. The affinities of 18 and 27 for these alkali metals are remarkably high for hosts containing only five or three ligand atoms, respectively. In water-saturated chloroform, pentadentate host 18 binds Na" and K more strongly than do most crown ethers. Compared to naphtho-18-crown-6 (26), 18 binds Na " 4000 times better, and K 40 times better. Even tridentate host 27 extracts alkali metal picrates into chloroform, whereas flexible model system 28 is ineffective under the same experimental conditions. The potent complexation... 

Liu J-F, Chao J-B, Jiang G-B. Continuous flow liquid membrane extraction A novel automatic trace-enrichment technique based on continuous flow hquid-liquid extraction combined with supported liquid membrane. Anal Chim Acta 2002 455 93-101. 

Sandahl M, Mathiasson L, Jdnsson jA. On-hne automated sample preparation for HPLC using parallel supported liquid membrane extraction and microporous membrane hquid-liquid extraction. J Chromatogr A 2002 975 211-217. 

The recovery of pure aromatics from hydrocarbon mixtures is not possible using distillation process because the boiling points of many non-aromatics are very close to benzene, toluene, etc. Also, azeotropes are formed between aromatics and aliphatics. Three principle methods are used for separation azeotropic distillation, hquid-liquid extraction, and extractive distillation. Three major commercial processes have been developed for separation Udex, Sulpholane, and Arosolvan. Over 90% plants now use one of these processes. Each use an addition of solvent such as a mixture of glycols, tetramethylene sulfone, or N-methyl-2-pyrrohdone to aid in the extraction of aromatics. This occurs with high precision and efficiency. Pure benzene, toluene, and xylene are produced by these processes. 

An alternative nonchromatographic separation such as continuous Hquid-liquid extraction can also provide a simple and effective speciation approach. 

Methylmercury and phenylmercury are determined down to lOpgml by Hquid-liquid extraction from 3mol aqueous HCl into benzene, and addition of K I to the separated organic phase. Inactive chloride is completely displaced by... 

Aerosols are collected with filters made of glass fibres, with pores up to 5 p.m, and next dissolved in a proper solvent or solvent mixture. Chemical warfare agents or their degradation products, which are dissolved in water or other solvents, are extracted by hquid-liquid extraction (LLE), sohd-phase extraction (SPE), sohd-phase microextraction (SPME), and stirr bar sorptive extraction (SBSE) methods. Head space (HS) analysis is also employed. In the case of the SPE method, XAD-4 and XAD-2 resins are frequently used. 

Hankemeier et al., studied large-volume injection combined with GC/DD-FTIR. A loop-type injection interface was chosen because of its rather simple optimization. Large-volume injection by means of a loop-type interface can be carried out successfully in conjunction with GC/DD-FTIR. The hyphenation permits enhanced detectability of analytes by about two orders of magnitude when compared with conventional split/splitless ones. As demonstrated, the determination and identification of PAHs in river water is possible down to a level of 0.5 p-g/L, even when using simple micro hquid-liquid extraction as a sample preparation technique. The present system may, therefore, be considered a viable approach to trace-level environmental analysis. 

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