Izak Nieuwoudt

Measurement of phase equilibria of supercritical carbon dioxide and paraffins

High pressure phase equilibria of supercritical carbon dioxide with n-alkanes, n-C12, n-C16, n-C20, n-C24, n-C28 and n-C36, have been measured over the temperature range of 313–367 K, and are reported in this work. Of the various equations of state investigated, it was found that the Patel Teja equation of state provided the best fit of the CO2–n-alkane systems.

Phase equilibrium of propane and alkanes: Part I. Experimental procedures, dotriacontane equilibrium and EOS modelling

Abstract In order to study the equilibria of long-chain alkanes and supercritical fluids, a high-pressure phase equilibrium cell has been designed, constructed, commissioned and tested against reliable literature data. Phase equilibrium data for propane-dotriacontane (nC32H66) have been measured between 378.2 and 408.2 K. Emphasis was placed on measuring equilibrium data in the mixture critical region. Ten cubic and five non-cubic equations of state have been applied to the phase equilibrium data at 408.2 K. The modified Patel–Teja (MPT), as a cubic EOS, and statistical associating fluid theory (SAFT), as a non-cubic EOS, give the best-fit of the data at 408.2 K. The phase equilibrium predictions of the SAFT EOS significantly deteriorated as the critical point of the solvent was approached.

Measurement of phase equilibria of supercritical ethane and paraffins

Abstract This work entails the design and development of a static variable-volume cell with the aim to measure high-pressure phase equilibria of mixtures of supercritical solvents and paraffinic hydrocarbons. The cell was used to measure the ethane–n-alkane phase equilibria and densities near the critical point of the mixture. Experimentally determined phase equilibria are reported for the binary mixtures of supercritical ethane with n-C16, n-C24 and n-C28 in the temperature range of 313–352 K. Several equations of state (EOS) were fitted to this data, and it was found that the Soave–Redlich-Kwong equation gives a reasonable representation of the measured phase equilibria but fails in the representation of the mixture densities—a known problem of cubic EOS. The use of the Patel–Teja EOS resulted in the smallest error in the liquid phase density representation.

Phase equilibrium of propane and alkanes part II: hexatriacontane through hexacontane

Abstract In this work phase equilibrium measurements for binary systems of supercritical propane with the n-alkanes C 36 H 74 , C 38 H 78 , C 40 H 82 , C 44 H 90 , C 46 H 94 , C 54 H 110 and C 60 H 122 , in the temperature range 378.2–408.2 K, are reported. In this temperature range the isopleths can be approximated as straight lines. A plot of the phase transition pressure as a function of carbon number at constant temperature and mass fraction yields a linear relationship. These linear relationships can be used for interpolation and limited extrapolations. The equilibrium data indicate that propane can be used for the fractionation of alkane mixtures. The SAFT EOS, using two binary interaction parameters, can be used to describe the equilibrium data provided that the temperature is not too close to the critical temperature of the solvent. The binary interaction parameters tend towards constant values for high carbon number alkanes.

Paraffin wax fractionation: state of the art vs. supercritical fluid fractionation

Supercritical fluid fractionation of paraffin wax is compared with current state of the art processes i.e. short path distillation (SPD) and static crystallisation. Detailed cost analyses of the different processes are made and compared. From these cost analyses it appears that SPD is the cheaper fractionation process for light paraffin wax. However, supercritical fluid fractionation appears to be the more attractive option for the fractionation of medium to heavy paraffin waxes.

The fractionation of high molecular weight alkane mixtures with supercritical fluids

Summary In this study it was shown that propane or mixtures of propane and butane may be used as supercritical solvents to fractionate mixtures of high molecular weight alkanes. By using an optimum reflux ratio, selectivities better than that of molecular distillation can be obtained. It was also found that for the system in this study, the operating costs of a supercritical extraction unit may be marginally lower than that of a molecular distillation unit.

Oligomer fractionation with supercritical fluids

Abstract A technical comparison of supercritical fluid fractionation and short path distillation for the processing of oligomers is presented. Through experiments and models it is shown that a supercritical fluid fractionation column can produce much sharper cuts than a single short path distillation unit. At comparable conditions the supercritical fluids ethane and CO 2 gives virtually the same separation factors for alkane mixtures. The advantage of using ethane is the much lower pressures that would be required. Unlike short path distillation, supercritical fluid processing caused no discoloration of the bottoms products.