.. Detailed experimental and thermodynamic studies of. the isothermal phase equilibria for the / Thesis (Ph.D.)-University of Natal, 1990.

The vapour recirculation apparatus of Moodley [2002] was modified, reconstructed, and commissioned in order to be used in the acquisition of high-pressure vapour-liquid equilibrium (HPVLE) data at low temperatures. The original equipment of Moodley [2002] was modified with the aim of achieving the desired operating temperature range which the original equipment was unable to achieve. Major modifications were carried out on the cooling circuit allowing the equipment to reach temperatures as low as -30°C, a significant improvement to the original equipments minimum attainable temperature of -5°C. Modifications were also successfully carried out on the vapour recirculation pump of Moodley [2002], which failed when operated over extended periods at high pressures thus enabling the equipment to operate at pressures up to 10.0 bar, an improvement on the previous pressure operating limit of 6.9 bar. The operating limits of the equipment were tested through measurement of pure-component vapour-pressures of isopentane at temperatures between -14 and +27.9°C and pressures up to 10.1 bar and on propane at temperatures between -30.1 and +26.0°C and pressures up to 9.7 bar. The isopentane vapour-pressure measurements had an average deviation of ±0.49% when compared to literature data while the propane vapour-measurements had a maximum average deviation of ±0.35% when compared to literature data indicating that the equipment was capable of measuring accurate vapour-pressure data at temperatures down to -30°C and pressures up to 10.0 bar. The equipment was thereafter used in the acquisition of binary HPVLE data. Considerable time was spent developing and practicing the techniques used in the binary HPVLE measurements. Binary measurements were performed on the test system propane + 1- propanol at 19.9°C. To gain more confidence in the binary HPVLE measurements another test system, propane + isopentane was selected and binary HPVLE measurements were performed at 25°C and 0°C. The equipment was able to reproduce relatively accurate binary HPVLE results for the test systems at the selected isotherms. The equipment was thereafter used in the acquisition of a new set of binary HPVLE data for the propane + isopentane system at -10°C however owing to time constraints and chemical availability the acquisition of a complete set of data was not possible. The binary HPVLE data was thereafter regressed via the direct method. The Peng-Robinson (PR) equation of state (EOS) and the Soave-Redlich-Kwong (SRK) EOS were each coupled with the Mathias Copeman alpha function together with the Wong-Sandler mixing rule and the NRTL local composition model and applied to the binary systems at each of the isotherms investigated. Regressed data showed a relatively good agreement with measured experimental data for both binary systems investigated at all of the isotherms except the new -10°C isotherm of the propane + isopentane system. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Acetylpropionyl (2,3-pentanedione) and diacetyl (2,3-butanedione) are by-products of sugar manufacture. Both diketones have many uses, mainly food related. Vapour-liquid equilibrium data and infinite dilution activity coefficients are required to design purification processes for these chemicals. A review of available experimental methods revealed that the vapour and liquid recirculating still is most appropriate when both isobaric and isothermal VLE are required. The low-pressure dynamic still of Raal and Muhlbauer (1998) used in this study incorporates many features to ensure that measurements are of excellent quality (as demonstrated by Joseph et al., 2001). VLE measurements were made for the following systems: • Acetone with diacetyl at 30 C, 40 C, 50 C and 40 kPa • Methanol with diacetyl at 40 C, 50 C, 60 C and 40 kPa • Diacetyl with 2,3-pentanedione at 60 C, 70 C, 80 C and 40 kPa • Acetone with 2,3-pentanedione at 50 C, 30 kPa and 40 kPa. All the systems, except for methanol with diacetyl, displayed close to ideal behaviour. This was expected as they are mixtures of ketones. Solution thermodynamics allows one to perform data reduction of the measured VLE data to ensure accurate extrapolation and interpolation of the measurements. Furthermore, the quality of the data can be judged using thermodynamic consistency tests. The data were represented by the Gamma-Phi approach to VLE (the preferred method for low-pressure VLE computations). The two-term virial equation of state was used to account for vapour phase non-ideality. Second virial coefficients were calculated by the method of Hayden and 0'Connell (1975). The liquid phase non-ideality was accounted for by the Wilson, NRTL or UNIQUAC models. The best fit models are proposed for each system, as are parameters as functions of temperature for the isobaric data. The data were judged to be of high thermodynamic consistency by the stringent point test (Van Ness and Abbott, 1982) and the direct test (Van Ness, 1995) for thermodynamic consistency. The data sets were rated, at worst, "3" on the consistency index proposed by Van Ness (1995). A rating of "I" is given for a perfectly consistent data set and "10" for an unacceptable data set. For the system acetone with 2,3-pentanedione, isobars at 30 kPa and 40 kPa were measured. The results from the reduction of the 30 kPa set were used to accurately predict the 40 kPa data set. Infinite dilution activity coefficients were measured by the inert gas stripping method (based on the principle of exponential dilution). In order to specify the appropriate dilutor flask height (to ensure equilibrium is achieved), mass transfer considerations were made. These computations ensured that the gas phase was in equilibrium with the liquid phase at the gas exit point. The following infinite dilution activity coefficients were measured: • Acetone in diacetyl at 30 C • Methanol in diacetyl at 40 C • Diacetyl in 2,3-pentanedione at 60°C • Acetone in 2,3-pentanedione at 50 C. The ketone mixtures, once again, displayed close to ideal behaviour. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

No abstract available. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2004.

In this work VLE data was measured on three different pieces of equipment. Measurements were undertaken in the laboratory of Professor Gmehling in Oldenburg, Germany using two different static cells and in the Thermodynamics Research Unit (TRU), University of Natal, South Africa using a specially designed dynamic still. The three pieces of equipment used are as follows: i.) Static apparatus of Rarey and Gmehling (1993), ii.) Static apparatus of Kolbe and Gmehling (1985) as modified by Fischer and Wilken (2001), and, iii.) Dynamic apparatus ofHarris et al. (2003b). In total 370 data points were measured; fourteen sets of VLE data and eight vapour pressure data sets were measured. The work undertaken in Germany measured the systems hexane (1) + N-methylformarnide (2), benzene (1) + N-methylformamide (2), cWorobenzene (1) + N-methylformarnide (2) and acetonitrile (1) + N-methylformamide (2), at 363.15 K using the equipment of Rarey and Gmehling (1993). The systems CO2 (1) + Napthalene (2) at T = 372.45 K, 403.85 K and 430.65 K and CO2 (1) + Benzoic acid (2) at T= 403.28 K, 432.62 K and 458.37 K were measured on the equipment of Kolbe and GmeWing (1985) (as modified by Fischer and Wilken (2001)). Apart from the CO2 (1) + Napthalene (2) system at T = 372.45 K, all the above-mentioned data are new data. The equipment designed in the TRU was designed to operate between 300 and 700 K and between 1 kPa and 30 MPa. The equipment is of the dynamic recirculating VLE still type (DRVS) and is based on the principles of low-pressure stills. The still is constructed from uniquely machined Stainless-steel components and standard commercial Stainless-steel tubing and valves and is computer controlled to operate either isobarically or isothermally. Vapour pressures were measured on the new equipment for n-heptane, n-decane, n-dodecane, n-hexadecane, l-octadecene, 1-hexadecanol and d,l-menthol at low pressures and for acetone at high pressures. These vapour pressure measurements were used as test systems and ranged from 1.00 kPa to 1 000 kPa and from 308.33 K to 583.90 K. Cyclohexane (1) + ethanol (2) at 40 kPa and n-dodecane (1) + l-octadecene (2) at 26.66 kPa were measured as two isobaric VLE test systems. The VLE data measured for d,l-menthol (1) + l-isomenthol (2) at T= 448.15 K and n-dodecane (1) + l-octadecene (2) at P = 3.0 kPa represent new data measured on the equipment. All the VLE systems were modeled. Two data reduction methods were investigated: i.) the combined (r-rf) method, and, ii.) the direct method (H) method. Several different Gibbs excess models (Wilson, NRTL and UNIQUAC), equations of state (PengRobinson and virial) and mixing rules (Huron-Vidal, Wong-Sandler and Twu-Coon) were used in different combinations to find the best fit for the data. The Maher and Smith (1979) method was used to determine infinite dilution activity coefficients from the very smooth data of the N-methylformamide systems. Excess properties were determined for the CO2 (1) + Napthalene (2) and the CO2 (1) + Benzoic acid (2) systems. Although the equipment of Hams et al. (2003b) was able to measure data at high temperatures and elevated pressures, the precission of the data was not as good as was expected. Measuring the system temperature at elevated temperatures was especially problematic. The problem is attributed to the large mass of Stainless-steel used in the construction of the apparatus. To rectify this problem it is suggested that the equipment be modified to be lighter in weight and only capable of measuring VLE at moderate pressures (less than 3 MPa). / Thesis (Ph.D.)-University of Natal, Durban, 2004.