UNIQUAC model for wax solution with pour point depressant

Abstract

It had been shown that after adding pour point depressant (PPD), the diffraction line intensities of paraffin mixtures progressively decreased without any significant variation of the Bragg angle values. This phenomena is due to the structure of paraffin mixture is partly transformed from orthorhombic into hexagonal form. Owing to the crystal lattice transformation, the amount of wax precipitated from oil treated with PPD in the experimental range is lower than that from untreated oil and the wax precipitated from treated oil is richer in the higher melting point paraffins than that from untreated oil. A thermodynamic model is established in this work to predict these experimental results. The liquid phase behavior is described by the LCVM mixing rule and an equation of state- G E model while the solid-phase non-ideality is represented by the UNIQUAC equation, respectively. New correlations for the melting points and solid–solid transition temperatures of treated paraffins are established based on the experimental results by differential scanning calorimeter (DSC). The experimental results indicated that the melting points and solid–solid transition temperatures of treated paraffins were both decreased. The calculation results for the amount and composition of wax precipitated from treated and untreated solutions at different temperatures have been compared with experimental observations. It has been shown that the predicted results agree well with the experimental ones.