In liquid extraction

In the context of the discovery of amines and oxygen-containing organic compounds, the question arises as to whether the presence of atomic carbon in olivine or MgO crystals could have led to the formation of amino acids. Knobel et al. (1984) reported the detection of amino acids in liquid extracts of the reaction mixtures at the 1983 ISSOL conference yields were, however, extremely low, the total yield being 1.5-3.0 x 10-7 g per gram of MgO. These results were the subject of considerable attention in the media. 

Dinudear iron-sulfur dusters, 47 219, 426 EPR spectra, 47 426-435, 449 interconversions, 47 482-483 site-directed mutagenesis, 47 451-456 spin-lattice relaxation, 47 435-436 Dinudear macrocydic systems, 45 89-95 Di-n-octyl phosphinic acid, in liquid extraction, 9 40... 

As the potentialities of liquid extraction as a separation method were developed, the need for efficient, continuously operated, multistage equipment became apparent. It was natural therefore to turn to devices which had been so successful in other similar fluid-contacting operations, such as the bubble-tray tower and the packed tower of distillation. These devices have proved to be disappointing in liquid-extraction service, however for example, bubble-tray towers provide tray efficiencies in liquid-extraction operations of less than 5% (S7), and conventional packed towers show heights of transfer units of 10 to 20 ft. or more (T3). 

The reason for the disparity in performance of such devices in the two services has been clearly outlined by Hachmuth (HI). Bubble-tray towers for distillation, for example, use as the source of energy for dispersion of the gas and for developing the desirable turbulent flow conditions both the expansion of the vapor as it experiences a pressure drop in flowing through the tray, and the liquid head available between trays. In liquid extraction only the liquid head is available. When it is considered that the difference in densities of the contacted phases in distillation may be of the order of 50 to 60 lb./cu. ft., whereas in extraction it is more likely to be of the order of 5 or less, it is easy to understand that in the latter case there is simply insufficient energy available from this source to provide for adequate dispersion and interphase movement. Interfacial area between phases remains small, turbulences developed are of a low order, and mass transfer rates are disappointingly small. 

A large number of impeller types have been studied over the years, but interest has centered on three designs marine-type propellers, flat-or curve-bladed turbines, and flat paddles, with the first two of greater interest than the third. Propellers produce axial flow of the liquids and are turned in such fashion as to direct flow against the bottom of the tank. Turbines provide radial flow, but in any case the presence of baffles strongly influences the flow pattern in the tank. The effectiveness of these in liquid extraction has not been well established, but it appears that there... 

Otos could be computed. All the Hixson and Smith data plot well in this fashion, and the straightness of the lines indicate the utility of the time-of-a-transfer-unit concept. Hixson, Drew, and Knox (H3) showed that a characteristic agitation number may be defined as the product of 0tOE and a velocity term for the agitated system. If then the mass transfer coefficient varies as the first power of the chosen velocity term, the agitation number would be constant for a given ratio of interfacial surface to total number of moles of extract phase. In liquid extraction, speed of agitation influences both terms of the quantity Ke[Pg.307]

G.S. Laddha and T.E. Degaleesan, Transport Phenomena in Liquid Extraction, Tata McGraw-Hill, New York, 1978. 

The separation of the liquid components in the presence of a supercritical solvent occurs much as it does in liquid extraction with the entrainer, ammonia, concentrating in the liquid to increase the relative volatility of the butene to butadiene. The butadiene migrates to the ammonia-rich phase while the solvent gas phase or "vapor" will contain the butene. 

The SISAK (Short-lived Isotopes Studied by the AKUFVE-technique, where AKUFVE is s Swedish acronym for an arrangement of continuous investigations of distribution ratios in liquid extraction) system performs continuous liquid-liquid extractions using small-volume separator centrifuges [66]. Activities are delivered to the apparatus with an aerosol... 

Laddha, G. S., and Degaleesan, T. E., Transport Phenomena in Liquid Extraction," Tata McGraw-Hill Publ. Co. Ltd., New Delhi, 1978. 

These systems are common in liquid extraction and also in a multiphase reactor with an organic and an aqueous phase. Common sources of pollution are incomplete separation and contamination due to trace organics in the aqueous phase. An example is in alkylation reactions (e.g., n-butane reaction with olefins to form isooctanes). Strong acids, such as sulfuric and hydrofluoric acids, are used as catalysts, and the recovery and the recycle of acid need to be optimized in order to reduce the waste generation. 

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. 

Pipe Lines The principal interest here will be for flow in which one liquid is dispersed in another as they flow cocurrently through a pipe (stratified flow produces too little interfacial area for use in liquid extraction or chemical reaction between liquids). Drop size of dispersed phase, if initially very fine at high concentrations, increases as the distance downstream increases, owing to coalescence [see Holland, loc. cit. Ward and Knudsen, Am. Inst. Chem. Eng. J., 13, 356 (1967)] or if initially large, decreases by breakup in regions of high shear [Sleicher, ibid., 8, 471 (1962) Chem. Eng. Set, 20, 57 (1965)]. The maximum drop size is given by (Sleicher, loc. cit.)... 

In some cases, especially with multiple solutes and complex phase equilibria, it may be useful to perform laboratory batch experiments to simulate a continuous, countercurrent, multistage process. These experiments can be used to test/verify calculation results and determine the correct distribution of components. For additional information, see Treybal, Chap. 9 in Liquid Extraction, 2d ed. (McGraw-Hill, 1963), pp. 359-393, and Baird and Lo, Chap. 17.1 in Handbook of Solvent E raction (Wiley, 1983 Krieger, 1991). 

Handbook of Solvent Extraction, Lo, Baird, and Hanson, eds, (Wiley, 1983 Krieger, 1991)] recommends the following equation from Lad-dha and iSegaleesan [Transport Phenomena in Liquid Extraction (McGraw-Hill, 1978), p. 233] to estimate the overall volumetric mass-transfer coefficient ... 

Minimum Packing Size and Drop Size For a given application there will be a minimum packing size or dimension below which random packing is too small for good extraction performance [Lewis, Jones, and Pratt, Trans. Inst. Chem. Eng., 29, pp. 126-148 (1951) Gayler and Pratt, Trans. Inst. Chem. Eng., 31, pp. 69-77 (1953) and Laddha and Degaleesan, Transport Phenomena in Liquid Extraction... 

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