Composition liquid extraction

In a liquid-liquid extraction, the analyte (or interferent) is extracted from one liquid phase into a second, immiscible liquid phase. When the analyte is involved in secondary equilibrium reactions, it is often possible to improve selectivity by carefully adjusting the composition of one or both phases. 

Details of the tantalum and niobium extraction process depend on the type of raw material used, decomposition method, initial solution composition, extractant type, equipment specifications, type of final products and desired purity. Therefore, process parameters are usually defined individually for each specific case. This may be the reason for the existence of the wide variety of publications devoted to the liquid-liquid extraction of tantalum and niobium. Nevertheless, some common features of the process should be emphasized. 

The unique advantage of the plasma chemical method is the ability to collect the condensate, which can be used for raw material decomposition or even liquid-liquid extraction processes. The condensate consists of a hydrofluoric acid solution, the concentration of which can be adjusted by controlling the heat exchanger temperature according to a binary diagram of the HF - H20 system [534]. For instance, at a temperature of 80-100°C, the condensate composition corresponds to a 30-33% wt. HF solution. 

In this process, the two streams flow countercurrently through the column and undergo a continuous change in composition. At any location are in dynamic rather than thermodynamic equilibium. Such processes are frequently carried out in packed columns, in which the liquid (or one of the two liquids in the case of a liquid-liquid extraction process) wets die surface of the packing, thus increasing the interfacial area available for mass transfer and, in addition, promoting high film mass transfer coefficients within each phase. 

Perry et al. (1997) give a useful summary of solubility data. Liquid-liquid equilibrium compositions can be predicted from vapour-liquid equilibrium data, but the predictions are seldom accurate enough for use in the design of liquid-liquid extraction processes. 

SUGDEN, S. (1924)/. Chem. Soc. 125,1177. A relation between surface tension, density, and chemical composition. Touloukian, Y. S. (ed.) (1970-77) Thermophysical Properties of Matter, TPRCData Services (Plenum Press). Treybal, R. E. (1963) Liquid Extraction, 2nd edn (McGraw-Hill). 

Example The equation yx+1 — (a + I )yr + wyx l = 0, yQ = cQ and ym+i = x 1+ i/k represents the steady-state composition of transferable material in the raffinate stream of a staged countercurrent liquid-liquid extraction system. 

The complex composition of aqueous environmental sample matrices, especially sewage and marine water samples, and the low concentrations in which the surfactants are generally found, have made it necessary to perform an initial stage of concentration and purification of the analytes prior to its analysis. Traditionally, such steps were carried out off-line with procedures based on liquid—liquid extraction (LLE), sublation or steam distillation, followed by chromatographic clean-up steps. 

Mixture experimental designs can be used to optimise the composition of extraction liquids in liquid-liquid extraction in biomedical analysis, which was demonstrated by Wieling et al. [4,5]. 

Several studies attempted to relate the partition coefficient P of a solute in a liquid chromatographic or a gas chromatographic system with the composition of the two phases, one of which has a varying composition [19-23]. Tijssen et al. [24] and Schoenmakers [25] derived a relation between the partition coefficient and a binary mobile phase in reversed-phase HPLC from the solubility parameter theory of Hildebrand et al. [26]. Similarly, a relation can be derived for liquid-liquid extraction with extraction liquids composed of three components ... 

In the previous section, the optimisation of liquid-liquid extraction with the help of mixture designs justified by the solubility theory was examined. A relation was derived between the partition coefficient and the mixture composition for liquid-liquid extraction with extraction liquids composed of three components, and a special cubic mixture model was obtained (equation (3)). 

The most economical procedure for a liquid-liquid extraction would be a single step extraction, since extraction procedures including several steps with the same or with different solvents are laborious and economically disadvantageous. Optimisation of extraction of more than one solute, which give different selective interactions (different response surfaces in the same mixture space), may require several extraction steps with different optimal extraction solvents or separate analysis of each analyte. However, procedures can be used, which select a composition of the extraction liquid that provides satisfactory partition coefficients or extraction yields for all solutes to be extracted. 

J. Wieling, P.M.J. Coenegracht, C.K. Mensink, J.H.G. Jonkman and D.A. Doombos, Selection of Robust Combinations of Extraction Liquid Composition and Internal Standard Monte Carlo Simulation of Improvement of Methods with Liquid-Liquid Extraction prior to HPLC, Journal of Chromatography, 594 (1992) 45-64. 

Compared to refined vegetable oils, the compositions of crude vegetable oils and oil and fat products are more complicated. These samples contain proteins, carbohydrates, and minerals that interfere with HPLC separation and reduce the lifetime of the HPLC column. These compounds need to be largely eliminated from the extract before HPLC analysis. Saponification and heating are used to weaken sample matrices to allow the solvent to fully access all tocopherols and tocotrienols of the sample. Liquid/liquid extraction is used to remove these polar compounds from the organic solvent layer that contains tocopherols and tocotrienols. The normal-phase HPLC method is usually used for crude vegetable oils and vegetable oil products reversed-phase HPLC can be used for animal fat products. 

Liquid-liquid extractions (13) permit the elimination of slightly polar molecules (phospholipids, fatty acids, etc) that may interfere in the HPLC determination of carbohydrates. Hence, for solid foodstuffs, some form of extraction will be required prior to the chromatographic procedure, and even in liquid food samples it may be necessary to modify the solvent composition of the liquid phase to make it compatible with the HPLC eluent. The major role of the extracting solvent is to obtain all of the carbohydrate present in the food sample dissolved in a liquid phase, be it for direct injection into the chromatograph or for subsequent cleanup stages prior to HPLC. 

Most coal liquids are composed of similar major chemical species, which may differ in exact composition. Liquid sulfur dioxide can be used to extract all the aromatic species of the coal liquid, free of saturated hydrocarbons and ash percursors. After removing the SO2 by degassing, distillation under reduced pressure can yield all the phenols and aromatic from the S02-solu-bles of the coal liquid. The residue, which is similar to GPC -fraction 2 of the S02 solubles, can be called coal asphaltenes. 

The equilibrium tie-line intersect on curve segment D,R,P represents a feed-raffinate three-component liquid composition (wt%) in equilibrium with the same tie-line intersect point on curve segment P,E,M. This P,E,M curve point is the three-component composition solvent-extract liquid phase. 

He, T., Versteeg, L.A.M., Mulder, M.H.V. and Wessling, M. (2004) Composite hollow-fiber membranes for organic solvent-based liquid-liquid extraction. Journal of Membrane Science, 234, 1. 

Other extraction methods used in the lipid extraction include supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE). With SEE, good extraction yields have been obtained for nonpolar lipids including ester-ified fatty acids, acylglycerols, and unsaponifiable matter. However, complex polar lipids are only sparingly soluble in supercritical carbon dioxide alone and polar modifiers, such as methanol, ethanol, or even water is required to improve the extraction of polar lipids (10). SFE has been used for the extraction of lipids especially from various food matrices, such as different nuts, edible oils, and seeds (11). The recoveries of lipids in SFE were on the same levels than with conventional solvent extraction methods (12,13), no significant differences between the fatty acids extracted were observed. PLE has also been used in lipid extraction, although only in very few applications (14). The elevated temperatures used in PLE can cause alteration of the lipid composition. 

A separation is diluted when the distillate or the bottom product is less than 5 wt% with respect to the feed. The distillation (simple, extractive or azeotropic) might not be the most economical, but other methods, such as liquid-liquid extraction, stripping, crystallization, adsorption, or membrane permeation, should be tried. The decision depends on the mixture composition and the nature of the components. 

Toluene, Benzene, and BTX Recovery. The composition of aromatics centers on the C - and Cg-fraction, depending somewhat on the boiling range of the feedstock used. Most catalytic reformate is used direcdy in gasoline. That part which is converted to benzene, toluene, and xylenes for commercial sale is separated from the unreacted paraffins and cycloparaffins or naphthenes by liquid—liquid extraction or by extractive distillation. It is impossible to separate commercial purity aromatic products from reformates by distillation only because of the presence of azeotropes, although complicated further by the closeness in boiling points of the aromatics, /o-paraffin, and unreacted C6, C -, and Cg-paraffins. 

The treatment scheme for the first irradiated targets (8) was based on the TLAHNO-/DTPA system implemented by liquid-liquid extraction. After dissolution of the Pu/Al targets by nitric acid, the solution was adjusted to low acidity by addition of Al(NO-)-. (OH) and then countercurrently contacted with an organic isoiution of the composition 0.64 M TLA.HNO- in dodecane containing 3 vol % 2-octanol. The co-extracted elements are then separated by selective stripping as follows ... 

If the equilibrium ratios are functions of phase compositions as occurs in liquid extraction or extractive distillation, it is necessary to include more variables in the iterative process. It was later shown (3) that for liquid extraction problems with known stage temperatures, the minimum number of iteration variables for quadratic convergence is nm, the n vapor flow rates, and n(m — 1) of the phase compositions. The total number of variables is n(2m + 2) because the temperatures are known. The iteration sequence is completely different for this case as compared with the previous case with composition independent equilibrium ratios. 

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