This thesis reports studies of methane dehydro-aromatization (MDA) over Zn-based/HZSM-5 catalysts and the catalytic conversion of acetylene gas (C2H2) on grain surface reactions using time-of-flight mass spectrometry (TOF-MS). Both catalytic reactions generate polycyclic aromatic hydrocarbons (PAHs) as their final products. For the MDA reaction, the performance of Zn-based/HZSM-5 catalysts prepared by wet impregnation method was investigated under the conditions of atmospheric pressure and supersonic jet expansion (SJE). The experimental results revealed that, under the SJE condition, the Zn/HZSM-5 catalysts exhibited high catalytic activity. It was also found that because of the rapid migration of H+ ions on the catalyst, the activation of CH4 at active sites of nano-ZnO is facile. A new reaction mechanism involving an active “ZnO-CH3+...-H-ZnO” intermediate formed as a result of synergetic action between ZnO and HZSM-5 has been proposed for the dissociation of methane and dehydrogenation. However, under atmospheric pressure, the catalytic activity of the Zn/HZSM-5 catalysts was low. The physical properties of the catalyst were characterized by Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), temperature-programmed reduction of H2 (H2-TPR), temperature -programmed desorption of NH3 (NH3-TPD), X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermogravimetric (TG/ DTG), and high-resolution transmission electron microscopy (HRTEM) techniques. For the catalytic conversion reaction of acetylene gas to form PAHs, the grains used were olivine and pyroxene-type silicates as well as alumina. Gas-phase PAHs were produced by the catalytic reaction of acetylene over crystalline silicates and alumina in a pulsed jet expansion condition and the gaseous products detected using time-of-flight mass-spectrometry (TOF-MS). In a separate experiment, further confirmation of the catalytic conversion of PAHs was obtained with the acetylene gas at atmospheric pressure flowing continuously through a fixed-bed reactor. The gas effluent and carbonaceous compounds deposited on the catalysts were dissolved separately in dichloromethane and analyzed using gas-chromatography-mass spectrometry (GC-MS). Amongst the samples studied, alumina showed higher activity than the olivine and pyroxene-type silicates grains. A mechanism for PAH formation is proposed in which the Mg2+ in silicates and Al3+ ions in Al2O3 act as Lewis acid sites for the acetylene reactions. Experimental investigation indicated that these silicates and Al2O3 particles are capable of providing catalytic centers for adsorption and activation of acetylene molecules that are present in the circumstellar environments of mass-losing carbon stars. The structure and physical properties of the particles were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and high-resolution transmission electron microscopy (HRTEM) techniques. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

ABSTRACT Recent studies have shown that R. rhodochrous DAP 96253 has the ability to delay the ripening of many climacteric fruit, by potentially degrading volatile compounds released by plant cells during the ripening process. Rhodococcus rhodochrous DAP 96253 cells were cultured on YEMEA medium supplemented with inducers, (16mM cobalt and 125mM urea), that over-expressed nitrile hydratase (NHase) and amidase (AMDase) enzymes. Cells were cultured on propylene/ ethylene as sole carbon source to induce alkene monooxygenase (AMO) like activity. Induced R. rhodochrous DAP 96253 cells displayed an 83% increase in final total dry weight compared to cells previously cultured on non-induced medium. Induced R. rhodochrous DAP 96253 cells displayed a 53-85% increase in NHase activity after exposure to propylene/ethylene, and cells displayed a 24-53% increase in NHase activity after exposure to fruit. Non-induced R. rhodochrous DAP 96253 cells displayed a 1-5% increase in NHase activity after propylene/ethylene, and cells displayed an 18-38% increase in NHase activity after exposure to fruit. Propylene/ethylene induced nitrilase activity in non-induced R. rhodochrous DAP 96253cells. Experimental results suggest that R. rhodochrous DAP 96253 may use NHase, amidase, nitrilase, and AMO like activity to delay ripening of climacteric fruit. Rhodococcus rhodochrous 96253 cells cultured on propylene/ethylene and cofactors (16mM cobalt and 125mM urea) displayed improved ability to delay ripening of fruit.

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Thermodynamics plays an important role for separation processes in chemical industries. Phase equilibrium is of special interest in chemical engineering as separation processes such as distillation and extraction involve phase contacting. The main focus of this research was the measurement of new phase equilibrium data for acetonitrile and water with heavy hydrocarbons that included: heptanoic acid, 1-nonanol, dodecane and 1-dodecene. Hence, binary vapour-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE) and vapour-liquid-liquid equilibrium (VLLE) data were investigated. The VLE and VLLE data were measured with the modified apparatus of Raal (Raal and Miihlbauer, 1998). The modification, undertaken by Ndlovu (2005), enabled measurement for VLLE systems. Isothermal binary VLE data for the (nonanol + 1-dodecene) system at 403.15 K was measured and VLLE data for the systems (acetonitrile + 1-dodecene) at 343.15 K, and (nonanol + water) at 353.15 K were investigated. The LLE data were measured with the modified apparatus of Raal and Brouckaert (1992). The modification, introduced by Ndlovu (2005), improved thermal insulation and the sampling procedures. Binary LLE data for the systems (acetonitrile + 1-dodecene) at 1 atm and (water + 1-nonanol) at 1 atm were measured. Furthermore, ternary data at 323.15 K and 1 atm were also measured for the systems containing water + acetonitrile with the each of the following components: heptanoic acid, 1-nonanol, dodecane and 1-dodecene. The experimental VLE data were regressed using two different methods: the combined method and the direct method. For the combined method, the second virial coefficients were calculated from the methods of Pitzer and Curl (1957) and Tsonopoulos (1974). The activity coefficients were calculated using three local-composition based activity coefficients models: the model of Wilson (1964), the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Anderson and Prausnitz (1978). For the direct method, the equation of state of Stryjek and Vera (1986) and the alpha function of Twu et al. (1991) in the equation of state of Peng and Robinson (1976) were employed. In addition, the mixing rules of Wong and Sandler (1992) and Twu and Coon (1996) were utilised. Furthermore, the point test of Van Ness et al. (1973) and the direct test of Van Ness (1995) were employed to test the thermodynamic consistency of the experimental VLE data measured in this work. The experimental binary LLE data were regressed using the three-suffix Margules model, Van Laar (1910) model and the NRTL model of Renon and Prausnitz (1968) to obtain the temperature dependence of the model parameters. The experimental ternary LLE data were subjected to a two part correlation: the tie-line correlation and the binodal curve correlation. The tie-lines were correlated with the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Anderson and Prausnitz (1978). The binodal curves were correlated with the Hlavaty (1972) equation, B-density function equation of Letcher et al. (1989) and the log y equation of Letcher et al. (1986). / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.

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A new vapor-liquid equilibrium apparatus was constructed to measure temperature, pressure, and phase compositions up to 8 MPa. Systems of CO(,2) with 2-methyl-1-pentene, 1-hexene, 1-heptene and m-xylene were studied at 303.15 K, 323.15 K, and 343.15 K. / A general method was proposed for equation of state construction. Two equations of State were constructed. Using critical temperature, critical pressure, critical compressibility factor and acentric factor, these equations can predict saturation properties of normal fluids. / The equations were extended to mixtures using van der Waals' one fluid theory, Lee-Kesler corresponding state approach and a virial-like approach. They had limited predictive abilities compared to cubic equations. / A correlation for third virial coefficients of nonpolar gases was developed. The correlation requires the knowledge of critical temperature, critical pressure and acentric factor and is applicable to mixtures of nonpolar gases including quantum gases. Predictions are in good agreement with reported experimental data.

Concern about the possible contamination by metals, hydrocarbons and PCBs of Tees Bay and the Tees estuary, and potential sources of such materials has led to this study of surficial sediments. Surface sediment samples were collected from the Tees estuary and Tees Bay and were analysed for grain size, organic carbon content, metals, hydrocarbons (aliphatic and polyaromatic) and polychiorinated biphenyls (PCB5). The Tees estuary sediments are largely organic-rich clayey-silts, while the Bay sediments are organic-poor sands. All of the metals measured (Cd, Co, Cr, Cu, Ni, Pb and Zn) have significantly higher concentrations in the sediments of the Tees estuary than in those of Tees Bay (F<0.01), and the mean averages decrease in the order Zn > Pb> Cr> Cu > Ni > Co> Cd. These significantly higher concentrations remain apparent when the data are normalized to remove the effect of grain size variation, suggesting that the sediments of the Tees estuary are enriched in metals in comparison with the sediments of Tees Bay and that these differences are not the result of the different grain size distributions. Metal partitioning was determined by sequential extraction, using the scheme of Tessier et al. (1979) as recently modified by Ajayi and Van Loon (1989), in order to assess the likely behaviour of metals in the sediments studied. The results of the sequential extraction showed that the partitioning patterns of Cd, Cr, Cu and Zn differed between the marine and estuarine sediments. In the Tees Bay sediments the residual fraction hosted >50% of all of the metals, except Cd and Pb. In the Tees estuary, however, this fraction only accounted for >50% of the Cd, Co and Ni. Significant portions of Cd are contained in fractions 1 and 2 in both the Tees estuary sediments and those from Tees Bay. Because of the toxicity and availability of Cd this may pose a serious problem to the ecosystem. The total Pb in the sediments is also quite high, particularly in the Tees estuary, and even the small proportion in fraction 2 could cause deleterious effects. High concentrations of Cd and Pd, in Tees Bay and the Tees estuary sediments, and Cr and Zn, in Tees estuary sediments, were associated with fraction 3. Concern is directed to heavy metals associated with fraction 3 because changing environmental conditions can transfer these elements from the sediments into the aqueous phase. Cu was the only metal significantly associated with fraction 4. This fraction is likely to have an important role as a sink for trace metals, particularly for Cu and to a lesser extent Cr and Zn. Petroleum hydrocarbons, both aliphatic and polyaromatic (PAHs), were detected and quantified in all samples. The distributions of the n-alkanes, acyclic isoprenoids (especially pristane from coal), triterpanes and steranes, in most sediments from both areas, were indicative of pollution by fossil fuels. On the other hand, a few sediments from the estuary contain hydrocarbons from both biogenic and anthropogenic sources. Polyaromatic hydrocarbon assemblages observed in the samples were relatively rich in hydrocarbons having petrogenic origins. However, the presence of pyrolytic derived components was also indicated by several characteristic component composition ratios. Single PCB congeners were determined in the sediments studied. The PCB profile is fairly constant in sediments from both areas and similar to that of Aroclor 1260 and 1254. The similarity to the commercial mixtures, with only a slight enrichment of the lighter congeners, indicates that sources responsible for PCB pollution are located in the Tees area. The sediments of the Tees estuary tend to be more highly polluted, by metals, hydrocarbons and PCBs, than those of the Bay, particularly in the middle section of the estuary. However, there is a general decrease in the concentrations of these compounds from the middle to the mouth of the estuary, while within the Bay area offshore sites showed higher concentrations. Distributions of inorganic and organic constituents in the Tees Bay were significantly influenced by the organic carbon content and particle size of sediments.