In the extraction process, is the distribution coefficient constant?
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I would like to ask whether the distribution coefficient remains constant during the extraction process? How do I calculate it? By definition, the distribution coefficient is the ratio of the concentrations of the extracted component in the two phases at equilibrium. However, extraction involves at least three components; with constant temperature and pressure, there are countless possible equilibrium states for these three components, so the calculated distribution coefficients would also vary, right? How do I calculate it?
What is the relationship with three components? Extraction occurs in two phases, which are immiscible; therefore, it can be considered that the two phases are unrelated to each other. Some equilibria are merely those of the solute between the two phases. That is, it is the ratio of the concentrations of the solute in the two phases; given constant temperature and pressure, this ratio remains constant as well. The derivation process of the distribution coefficient is, in essence, the derivation of the equilibrium constant of the solute in each phase. This is my personal understanding; please correct me if I’m wrong.
Generally, the distribution coefficient is not a constant; it can be approximated as one, and when drawing equilibrium diagrams, it appears as a curve
Is the slope of the equilibrium line the distribution coefficient? In other words, if the equilibrium line is a straight line, then the distribution coefficient is constant; if the equilibrium line is curved, then it is not constant?
Suppose there are three components, A, B, and C, with A and B being either immiscible or partially miscible. We need to calculate the distribution coefficient of C between A and B. In the cases where there is more of A than B, or vice versa, the concentration of C in these two phases must be different, right? So is the distribution coefficient still a constant?
The approximation is a constant! ! ! ! !
Don’t make it so complicated, because in nature there are no real constants or linear relationships in the chemical properties; these are all artificial simplifications that represent unimportant disturbances. As long as C’s impact on AB is not too significant, it can be considered unaffected. Please take another close look at the chapter on extraction in Chemical Engineering Principles; it covers both simplified methods and complex algorithms. What needs to be mentioned here is that the extraction design process for large companies involves: laboratory extraction experiments + simulation calculations (based on experimental data) + scale-up. The best method for extraction is laboratory testing, as it is simple and accurate. Don’t just do calculations behind closed doors; experimentation is what matters! This is also key to modern science; domestic students, due to their strong grasp of theory, prefer to do calculations, which makes it easy to make mistakes.
This post was last edited by come_now on 2012-2-22 08:58. You have reversed the order of things; it is the distribution coefficient that determines the concentration ratio of the solute in the two phases, not the concentration first determining the distribution coefficient. The distribution coefficient is derived from the chemical reaction equilibrium constant.