Crystallization kinetics of palm oil

Abstract

The quality and yield of oils obtained by fractionation processes depend mainly on the separation efficiency of fat crystals from the mother liquor; this process is, to a large extent, determined by crystal-size distributions. The size of the crystals is influenced by the crystallization conditions applied, and the quantitative data on crystallization kinetics are a useful tool to optimize and control such a process. The crystallization work described concerns the fractionation of edible oils and fats. Palm oil was chosen as a model system.

We quantified the growth and primary nucleation rates of saturated crystals in palm oil. The growth rate was proportional to the degree of supersaturation of the oil component studied, suggesting that the screw dislocation mechanism as described by Burton, Cabrera and Frank is determinative of the growth rate. Also the primary nucleation rate depends on the degree of supersaturation and can be described by the Becker and Döring equation. Special attention was paid to the experimental setup, which enabled us to measure the rate constants of both mechanisms separately. The kinetic data obtained were used to predict solid phase curves. The agreement between measured and predicted solid phase curves is satisfactory and in conformity with our model description. The results of our experiments also show that the crystallization kinetics of oils and fats can be described by the equations often used for inorganic systems.