MODELLING OF THE SOLVENT-DEOILING PROCESS OF WAXES BY CONTINUOUS THERMODYNAMICS

Industrial waxes as petroleum slack waxes are multicomponent mixtures of mainly paraffinic species. Usually, for application the oily components of the waxes are undesired. Therefore, separation processes are needed which, in some cases, base on a solvent-deoiling process. Modelling such a process is the aim of this paper. For this purpose the solid-liquid equilibrium of a wax-solvent system is considered. To take into account the polydispersity of the wax continuous thermodynamics is applied. We assume the wax to consist of n-alkanes and of non-n-alkanes including all the other types of paraffinic species. Corresponding to that, the composition of both types of alkanes is described by separate Gaussian distributions with respect to the number of carbon atoms. The model requires information about how the molar enthalpy and entropy of fusion for both kinds of alkanes depend on the number of carbon atoms. Restricting to the interesting range 20-50 of the number of carbon atoms we assume linear relations The lower values of the enthalpy and entropy of fusion for the non-n-alkanes compared to those of the n-alkanes are described by the so-called degree of isomerization and cyclization. This quantity correlates to the refraction index that is easy available. The model needs only one interaction parameter to fit. We show experimental and calculated results for three systems consisting of a slack wax and a solvent mixture of 1,2-dichloroethane and toluene. The model is able to describe reasonably the enrichment of n-alkanes for the deoiled wax and the opposite for the the oily phase.