NONISOTHERMAL CRYSTALLIZATION KINETICS OF BINARY-MIXTURES OF N-ALKANES - IDEAL EUTECTIC AND ISOMORPHOUS SYSTEMS

The liquid-solid phase behaviour and thermal characteristics of n-C25H 52 + n-C28H58 and n-C44H90 + n-C50H102 binary systems have been studie d using differential scanning calorimetry (d.s.c.). Both the melting a nd crystallization thermograms for 12-C25H52 + n.C28H58 mixtures exhib ited two major peaks (alpha and beta) corresponding to the liquid-soli d and solid-solid transitions. Hence, isomorphous solid solutions were formed in these mixtures. The n-C44H90 + n-C50H102 mixtures displayed eutectic or isomorphous behaviour depending on the thermal treatment of prepared samples. A recently proposed model for the non-isothermal crystallization kinetics of pure n-paraffins has been extended to bina ry mixtures by deriving appropriate mixing rules for the three paramet ers in the model. Accurate predictions of the onset-of-crystallization temperature for the n-C25H52 + n-C28H58 and the n-C44H90 + n-C50H102 binary systems were obtained at different cooling rates. Predictions o f the relative crystallinity in the isomorphous mixtures have been pre sented and compared with the data.