Effective distribution coefficient

The assumption of equiUbrium between soHd and bulk melt is frequently violated because of lack of complete mixing ia the melt. A steady-state fictitious stagnant-film treatment may be employed to arrive at an effective distribution coefficient,... 

Fig. 6. Effective distribution coefficient vs interfacial distribution coefficient k and dimensionless zone-travel velocity to be used in place of in...

There have been many modifications of this idealized model to account for variables such as the freezing rate and the degree of mix-ingin the liquid phase. For example, Burton et al. [J. Chem. Phy.s., 21, 1987 (1953)] reasoned that the solid rejects solute faster than it can diffuse into the bulk liquid. They proposed that the effect of the freezing rate and stirring could be explained hy the diffusion of solute through a stagnant film next to the solid interface. Their theoiy resulted in an expression for an effective distribution coefficient k f which could be used in Eq. (22-2) instead of k. 

Aim of the directed crystallization is in most cases to reach a crystal coat of highest possible purity. The most used measure to qualify the purification effect of the crystallization is the effective distribution coefficient k ff. For the case of crystallization processes in which the concentration of the feed remains constant the effective distribution coefficient is defined as the ratio of the impurity concentration in the crystal product C to the impurity concentration in the feed cq ... 

Several investigations (8.9 show, that the effective distribution coefficient can be described as a function of the growth rate. Own experiments show that a model to calculate the purity in dependence of the real growth rate is rather realistic. To considerate irregularities by the calculation of k ff, the effective distribution coefficient is presented as a function of the ideal growth rate of the crystal layer V, 3 and the growth rate deviation dy. ... 

In this equation a, b and e are constants depending on the physical properties of the material to be separated. In Figure 2 the effective distribution coefficient is plotted over the growth rate on the example of a binary mixture of dodecanole with 3,3% impurity of decanole. One curve represents the measured purities (l ff real) is compared to the curve of k ff for the ideal growth rate and... 

Figure 2. Effective distribution coefficient k ff as a function of the growth rate...

IV. EFFECTIVE DISTRIBUTION COEFFICIENT AND AVERAGE SEPARATION FACTOR... 

A number of years ago Seno and Yamabe [25] derived equations that examined the amounts of adsorbed amino acid on an ion exchanger in the presence of competing ions. More recently HelfEerich [26] derived equations describing the effective distribution coefficients of amino acids on a strong-acid (cation) and strong-base (anion) exchanger as a function of pH, amino acid concentration and added electrolyte. 

The Helfferich equations describing the effective distribution coefficients of amino acids on a strong-acid cation and a strong-base anion exchanger were derived using the following simplifying assumptions [26] ... 

The effective distribution coefficient on cation and anion exchanger... 

With subsequent zone passes, back-mixing becomes increasingly significant. When the number of zone passes becomes very large, the concentration profile reaches the ultimate distribution and subsequent passes have no influence. The number of zone passes required to approach the ultimate distribution is about twice the number of zone masses in the rod for small effective distribution coefficients. Thus, longer zones permit the attainment of the ultimate distribution sooner. On the other hand, the attainable separation increases as the zone size becomes smaller (permitting less back-mixing) (1,4). 

The first step is the calculation of the effective distribution coefficient, for the... 

Effective distribution coefficient of a solute between an organic solvent and water,... 

A term which is very conveniently applicable in chromatography is effective distribution coefficient (B). This may be defined as the total amount of substance present in the mobile phase divided by the total amount present in the stationary phase. 

Figure 8.3 The effect of B (effective distribution coefficient) and number of plates on band position and band shape.

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