Distribution coefficients thermodynamic definition

With the definition of the thermodynamic distribution coefficient, Equation (10.252) can be written as... 

Kinetics of mass transfer prevents a growing crystal from achieving the thermodynamically possible value of the distribution coefficient. Figure 8.2-12 shows that the impurities enrich close to a growing crystal surface (phase boundary Ph). Due to the single-sided mass transfer, impurity i enriches near the growing phase boundary to y,. The definition of the thermodynamic distribution coefficient... 

The membrane process can be kinetically or thermodynamically controlled. Thermodynamic control exists if there is a limit set by the distribution coefficient or a reaction equilibrium constant which is approached asymptotically at a slow rate. The process will be kinetically controlled if it is far away from the thermodynamic limit or if this limit is removed. The removal of amaonia from an aqueous effluent by the liquid membrane process will be used as an example to illustrate the difference between the two definitions. On account of solubility of ammonia in the membrane phase the same distribution coefficient will apply at the two surfaces of the membrane phase. The internal phase thus cannot take up more ammonia than given by the distribution coefficient at the internal surface. In turn, the maximum amount of ammonia... 

The numerical values of chromatographic partition coefficient, regarded as a constant of physical equilibrium, depend on the standard states chosen for the solute in the two phases that participate in the distribution process. Consequently the standard thermodynamic properties take values which depend on this choice. A standard thermodynamic property should always be accompanied by an explicit definition of standard states. 

The basic assumption in any chromatographic theory is that retention is determined by the thermodynamic factors. In such a way, mobile and stationary phases are interpreted as true thermodynamic phases with volumes Vm and Vs, respectively, so that retention volume depends on the partition (distribution) equilibrium coefficient A" of the solute in these two phases Vr = Vm +KVs-By definition, all enthalpic and entropic interactions between the macromolecules and the chromatographic surface occur in the stationary phase. If the size of macromolecules in solution is comparable with the internal diameter of pores, the entire pore volume represents the stationary phase. Vs = Vp, yet the mobile phase is formed by the interstitial volume only, Vm = Vq. This is not always the case for... 

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