Extraction constant defined

This equilibrium may be used to define an extraction constant (Kex) in the usual way. It should be noted that under some conditions, especially when larger ions are involved, a second equilibrium involving complexation of a further molecule of (non-deprotonated) ligand may also be present. 

For a two phase system (water and a water nonmiscible organic solvent) containing a hydrophobic salt QX dissolved in water (Q + X QXs), the conditional extraction constant e is defined Cqxs = QX[Q ]w [X 1w where Cqxs is the total concentration of Q (quat) and X (corresponding anion) present in the organic phase in the molar ratio 1 to 1 and [Q ]w [X ]w te the respective... 

Since [HAJa, and [BJotj are easily measurable qnantities, it is common to define the extraction constant K.. for this model ... 

It is of interest to see how the information on the magnetic properties of the individual radicals relates to the spin-chemicaUy observed spin relaxation in the Ru-chromo-phore linked radical pairs. As detailed in Ref. 23, the relaxation rate constant defined in Scheme 10.1 can be extracted from the magnetic field dependence of the radical pair recombination kinetics. The pertinent data points for DCA-POZ and DCA-PSZ are shown in Fig. 10.5 together with the theoretical field dependence of and its various contributions. For DCA-PTZ, no significant deviation from the DCA-POZ case is observed. 

An adaptation of the distribution constant defined in Equation (23-3) could be made for solutes in chromatojp-aphy. As in liquid-liquid extraction, however, solutes may be present in several chemical forms, and therefore a quantity analogous to the distribution ratio (Section 23-1), called the partition ratio, is preferred. The partition ratio must be a somewhat more broadly defined term than the distribution ratio in liquid-liquid extraction for two reasons. First, in chromatography, concentrations of solute in the two phases are usually unknown and may be unmeasurable, as when adsorption is important. Second, instead of the two phases being merely an aqueous phase and an immiscible organic solvent, in chromatography they can be any one of innumerable combinations of solid or liquid stationary phases and liquid or gas... 

Solvent extraction of ionic compounds from the aqueous to organic phase is well known to analytical and industrial chemists. For the extraction equilibrium of Q" X salt, Qaq + Xaq (Q X )oj.g, the stoichiometric extraction constant Eqx is defined by Schill and Modin [31,32] as... 

To include the effects of competing side reactions such as association or dissociation equilibria of ion pairs in the organic phase, and pH-dependent equilibria in the aqueous phase, they also define a conditional extraction constant ... 

The corresponding equilibrium constant given below is defined as the extraction constant ... 

The equilibrium constant Kg (HAx> lor this process (the extraction constant) is defined by... 

The short time exposure SPME measurement described has an advantage associated with the fact that the rate of extraction is defined by diffusivity of analytes through the boundary layer of the sample matrix, and their corresponding diffusion coefficients, rather than distribution constants. 

Dual solvent fractional extraction (Fig. 7b) makes use of the selectivity of two solvents (A and B) with respect to consolute components C and D, as defined in equation 7. The two solvents enter the extractor at opposite ends of the cascade and the two consolute components enter at some point within the cascade. Solvent recovery is usually an important feature of dual solvent fractional extraction and provision may also be made for reflux of part of the product streams containing C or D. Simplified graphical and analytical procedures for calculation of stages for dual solvent extraction are available (5) for the cases where is constant and the two solvents A and B are not significantly miscible. In general, the accurate calculation of stages is time-consuming (28) but a computer technique has been developed (56). 

The equilibrium constant is defined by K, K = y/x, and the portion coefficient is also defined by K as a ratio of CAu/CA1 which is constant. Based on the value of K, single or multi-stage extractions are performed to do a perfect job in bioseparation. 

In the preceding solvent extraction models, it was assumed that the phase flow rates L and G remained constant, which is consistent with a low degree of solute transfer relative to the total phase flow rate. For the case of gas absorption, normally the liquid flow is fairly constant and Lq is approximately equal to Li but often the gas flow can change quite substantially, such that Gq no longer equals Gj. For highly concentrated gas phase systems, it is therefore often preferable to define flow rates, L and G, on a solute-free mass basis and to express concentrations X and Y as mass ratio concentrations. This system of concentration units is used in the simulation example AMMONAB. 

Solvent Composition and Recovery. The solvent was defined as the product fraction which is soluble in the hot filtrate and the THF extraction of the filter cake and which boiled between 232 C and 482 C at atmospheric pressure. One of the requirements of a commercial coal liquefaction process is that a least as much solvent be created as is used in the process. In addition, the composition of the solvent must be kept constant if it is to be... 

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