Factors affecting the efficiency of the progresive freeze-concentration of true and colloidal solution

Abstract

In this research, the limiting partition coefficients (Ko) were determined. Factors affecting the progressive freeze concentration process were also investigated. Ko could be obtained from the effective partition coefficient (K), which was, in turn, obtained experimentally using the concentration polarization model. The factors studies in this research included the stirring speed at the ice-liquid interface, in the range of 200-1000 rpm; the advance rate of the ice front, in the range of 0.1-2.7 cm/h; and the type of solution, which included ionic solutions comprising LiCl, NaCl, KCl, and CsCl, non-ionic solutions comprising ribose, glucose, fructose, sucrose, and lactose; and colloidal solutions comprising dextran with the molecular weight ranging from 9,000-2,000,000 and the initial concentration ranging from 0.5-20% (w/w). It was found that, for the ionic solutions the Ko value depends directly on initial concentration (Co) and type of solution. It was also found that the Ko/Co ratio was linearly proportional to the hydration number of the cation of the solute, which could be ordered as follows: Li+, Na+, K+, Cs+. For the non-ionic solutions, the results were similar to those of the ionic solutions, except that the Ko value was not affected by the type of the solute. The Ko value of the colloidal solution (i.e. dextran) was found that to be not affected by the size of molecule and the initial concentration of the solution.