Michael Matthäi

THERMODYNAMIC FUNCTIONS OF THE SOLID-LIQUID TRANSITION OF HYDROCARBON MIXTURES

ABSTRACT The dependences of the melting temperature and the enthalpy of fusion on the composition are the essential factors for modelling precipitation and solubility of solid hydrocarbons in crude oils and crude oil products. Long-chain iso-alkanes and cyclic alkanes must be considered besides of n-alkanes. Therefore a degree of isomerization and cyclization was defined using the refractive index and the carbon number. The melting temperatures and the enthalpies of fusion of different n-alkanes and fractions of crude oil were determined by differential scanning calorimetry. Both parameters can be correlated with the degree of isomerization and cyclization by a quadratic fuction.

Influences on the Needle Penetration of Petroleum Wax

Abstract This paper deals with the dependence of needle penetration of petroleum waxes on structure and content of the crystalline fraction as well as the viscosity of the amorphous fraction. The crystallinity is defined as the relation of the total crystallization enthalpy of the respective wax to the ideal crystallization enthalpy of the n-alkane that is equivalent to the average C atom number of the wax. The viscosity of the amorphous phase is defined by the viscosity of the molten wax at 100°C. It is shown that both parameters have a decisive influence on the needle penetration–temperature behavior of waxes. The complete cross-linking of the crystal lattice is of great significance for the properties. Influences of wax composition on crystallinity and viscosity are discussed.

Modelling of the solvent-deoiling process of waxes by continuous thermodynamics

ABSTRACT 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.