The South African based petrochemical company, SASOL, operates three large plants for the recovery and purification of the chemical 1-hexene. The thermodynamic models available in commercial simulation packages fail to predict or correlate the plant data presently observed by SASOL. The focus of this project is the accruement of comprehensive and accurate modelling parameters that would assist SASOL in optimizing the operation of the three plants and meet their purity specifications. The experimental requirements of the project are the measurement of isothermal vapour-liquid equilibrium (VLE) data for selected binary systems, using a dynamic still. The binary systems investigated were 1-hexene + n-methylpyrrolidone (NMP) at 40, 62 and 90 °C, water + NMP at 70, 90 and 107 °C and 1-hexene + 3methylcyclopentene (3MCP) at 40, 50 and 60 °C. With respect to the modelling of the VLE data, the combined (gamma-phi) and direct (phi-phi) regression procedures were utilized. The results of the analysis show the combined method as the more flexible of the two, when used for low pressure systems. The excess Gibbs energy correlations investigated were the Margules, Van Laar, Wilson, NRTL and UNIQUAC. The NRTL and Van Laar models dominated the modelling results across the range of temperatures for each binary system and for both the direct and combined methods of data regression. The experimental data for the systems of water (1) + NMP (2) at 107 °C and at 70 °C were compared to literature data. The first system showed excellent correlation with the literature results while the second plot at 70 °C showed a positive bias of the experimental data between xj of 0.3 and 0.8. Thermodynamic consistency tests for the VLE data are also required to verify the accuracy of the data. For this project, the point and direct (Van Ness) consistency tests were used as the area test was considered as too mild. All systems passed the point and direct tests for the combined method and therefore verify the thermodynamic consistency of the experimental data. The systems failed in most cases for the direct method as the combined method is the more flexible of the two modelling methods. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

VLE data is essential for the design and optimisation of industrial separation processes. Carboxylic acids are of significant interest because of their importance in both industrial and biological processes. Carboxylic acids are used as raw materials for a wide range of products, which include soaps , detergents, nylon , biodegradable plastics, medical drugs and food additives, They are also used both as solvents and as additives and co solvents under a wide range of conditions. Carboxylic acids exhibit strong self and cross -association through hydrogen bonds in both liquid and vapour phases. A thorough understanding of how these molecules interact both with themselves and with other solvents becomes necessary if existing processes may be optimised and new processes developed. Vapour-liquid equilibrium (VLE) data were measured for carboxylic acid systems ranging from C3 to C6• New vapour-liquid equilibrium data were measured for the following binary carboxylic acid systems: • Propionic acid + Hexanoic acid at 20 kPa, 403.15 K, 408.15 K and 413.15 K. • Isobutyric acid + Hexanoic acids at 20 kPa, 413.15 K and 423.15 K. • Valerie acid + Hexanoic acid at 15 kPa, 423 .15 K and 433.15 K. • Hexanoic acid + Heptanoic acid at 10 kPa and 443.15 K. A highly refined dynamic VLE Still by Raal (Raal and Muhlbauer [1998]) was used to undertake the VLE measurements. The still was operated either isothermally or isobarically using a computer control scheme. The isobaric and isothermal control was measured to be ±0.03 kPa and ±0.02 K respectively. The experimental procedure was verified with the highly volatile cyclohexane (l) + ethanol (2) system. The cyclohexane (l) + ethanol (2) measured VLE data was found to be in good agreement with that of Joseph (2001) and passed both the direct test and point test for thermodynamic consistency. A high degree of confidence was then placed on the equipment set-up and experimental procedure, as well as the new carboxylic acids VLE data . The VLE data for all the systems measured were modelled. Two data reduction methods were used: I. The combined ( r- ¢ ) method u. The direct method (¢ - ¢ ) method. In the combined method, the vapour phase non-idea lity was corrected using the Pitzer-Curl (1957) correlation and the Hayden and O' Connell (1975) chemical theory approach. Three liquid phase activity coefficient models were used namely the Wilson, NRTL, and UNIQUAC equations. The Peng-Robinson equation of state (Peng and Robinson [1976]) in combination with the Twu and Coon mixin g rule was used in the direct method. Thermodynamic consistency tests were done on all the systems measured. The point test (Van Ness et a!. [1973]) and the direct test Van Ness ([ 1995]) were used for consistency tests . The direct test could not be carried out on the carboxylic acids data because of the model's inability to adequately characterise the experimental activity coefficients. Generally the models fitted the data well but failed to accurately predict the "S" shape of the carboxylic acids phase diagrams. Considerable work still exists for further investigation into carboxylic acids. Currently, many experimentalists are working in this area . Penget a!. (2004) present ed their progress on developing an equation of state incorporating chemical theory to specifically handle carboxylic acids at the ICCT conference in Beijing, 2004. Raal and Clifford (University of Kwa-Zulu Natal, Thermodynamics Research Unit) are currently developing activity coefficient models incorporating chemical theory for a binary mixture of carboxylic acids. This work is part of the continuing research to under stand the phase behaviour of carboxylic acids. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

The dynamic still originally designed by Raal (Raal and Muhlbauer [1998]) has been transformed into a valuable still that can now be used for measuring both low pressure vapour-liquid equilibria (VLE) for systems that are completely miscible and vapour-liquid-liquid equilibria (VLLE) for systems that are partially miscible. The resultant equilibrium data are important in the design and analysis of distillation and allied separation process equipment, with VLLE data, in particular, being useful in the design of heterogeneous azeotropic distillation columns. The original Raal still was based on the designs of Heertjies [1960] and Yerazunis [1964], who successfully used a packed equilibrium chamber where the liquid and vapour phases are forced downward co-currently to achieve rapid and dynamic equilibrium (Joseph et al [2001]). Direct analysis of the vapour composition prior to condensation through a new heated valving system with superheated sample conveyance to a gas chromatograph, a modification incorporated into the Raal still, ensured that accurate and reproducible equilibrium data were obtained. This new arrangement dispenses with the impossible task of getting the actual vapour composition that would result were the vapours allowed to condense and form two liquid phases. The initial testing of the still which established the operating procedures was conducted on two previously measured systems - the first which was homogeneous and the second heterogeneous. For the homogeneous system the new vapour sampling system was tested by comparing the measured composition to that of a condensed sample sent manually to the GC using a gas-tight syringe. In order to completely describe the VLLE for the systems studied, the liquid-liquid equilibrium (LLE) data for these systems were also measured. The LLE measurements were conducted in a newly-developed small jacketed glass cell with temperatures maintained constant by circulating water from a bath maintained at the desired temperatures. The main focus of this project was thus the development of an apparatus and procedures for measuring low pressure vapour-liquid-liquid equilibria. The project also went on to measuring and modeling VLE, VLLE and LLE data for selected binary and ternary systems. Both the Gamma-Phi and the Phi-Phi methods of VLE analysis were carried out on the measured data. The NRTL, Wilson, TK-Wi1son and UNIQUAC activity coefficient models were used in the Gamma- Phi method together with the Virial equation of state for vapour phase non-idealities. In the Phi-Phi method, The Peng and Robinson Equation of State (EOS), the Soave Redlich-Kwong EOS and the Stryjek and Vera modified Peng and Robinson EOS were all used, first with the classical mixing rules and then with the theoretically correct Wong and Sandler [1992] mixing rules. Ternary LLE binodal curves were correlated to the Hlavaty correlation, the beta function and the log gamma function while the corresponding tie-lines were fitted to the NRTL model. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

The thermodynamic knowledge of accurate phase equilibrium data plays an important role in the design and optimization of separation processes in chemical and engineering industries. Vapour-liquid equilibrium data are essential for the design of efficient separation processes such as distillation. The presented research study is mainly focused on the vapour-liquid equilibrium data measurement of fluorochemical and hydrocarbon binary systems at various temperatures and at high pressures. A new static analytical apparatus was constructed and commissioned for the measurement of accurate and precise vapour-liquid equilibrium data at temperatures and absolute pressures ranging from low temperatures to 323.15 K and 0 to 10 MPa respectively. The new apparatus incorporates the ROLSI TM sampler, a sampling technique developed by the CEP/TEP laboratory in Fontainebleau, France. Isothermal high pressure VLE data were measured for three binary systems comprising of hexafluoroethane (R116) + propane, HFPO + propane and ethane + octafluoropropane (R218). The R116 + propane system at 263.15 K was measured as a test system using the new static apparatus. These measurements helped to confirm the functioning of the experimental apparatus. The reliability and the reproducibility of the experimental procedure were also checked. The data obtained were in excellent agreement with data in the literature. Thereafter, measurements of previously unmeasured systems were undertaken. Isothermal vapour-liquid equilibrium data measurements for the ethane + octafluoropropane system were performed at five isotherms with temperatures and pressures ranging from 264.05 to 308.04 K and 0.298 to 4.600 MPa respectively. The five isotherms constitute new experimental data. The HFPO + propane system was also investigated and vapour-liquid equilibrium data were measured at three isotherms (283.05, 303.05 and 323.05 K) with pressures ranging from 0.437 to 2.000 MPa. The data measured also constitute a set of a new HPVLE data. The uncertainties in the measurement for both systems were within ± 0.09 K, ± 0.0016 MPa and less than 2% for temperatures, pressures and mole fractions, respectively. All experimental data were correlated via the direct method using the Peng-Robinson equation of state with the Mathias-Copeman alpha function and the Wong-Sandler mixing rules incorporating the NRTL activity coefficient model. The consistency of the measured VLE data was tested using the Van Ness point test which yielded few points of difference between the measured and calculated data, suggesting a low error rate. / 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.

Experimental vapour-liquid equilibria (VLE) data is required for the design of separation / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

This thesis discusses the preliminary development of a microfluidic system for low concentration vapour analysis incorporating a novel analyte preconcentration method to extend vapour detection limits. The topicality of this subject is evidenced by the urgent requirement to detect vapours released by explosives or their manufacturing byproducts, allied to recent reports of gas phase detection of pathogen-related chemical markers. Commercially available, non-microfluidic, sensitive, delayed response, broadly specific, gasphase analysis methods have been developed recently. However microfluidic analysis offers the prospect of both the improved specificity of liquid phase analytical methods and increased sensitivity with fast response times. The necessary conditions to achieve a viable microfluidic vapour analysis system are discussed from collection, sampling, assay and measurement perspectives. Efficient, rapid, vapour collection into a liquid phase is predicated by large surface area to volume ratio phase-interfaces, as occur within microfluidic devices. Accordingly, research has focussed on stable, segmented gas and liquid microflows. The literature has concentrated on fixed structures and precise flow rate control to produce such segmented flow. In contrast, we have investigated pressure driven flow and small active valves in combination with precision patterned passive valves to provide deterministic control over flow and thus define gas and liquid segment sizes. This has allowed introduction of larger, precise gas volumes and hence gas/liquid ratios while still maintaining more stable flow patterns than those previously reported in the literature. Ethanol was employed as a completely soluble, volatile, ‘model’ analyte to assess collection efficiency. Research into detection focussed on a number of optical methods utilising either ‘wet’ or enzymatic chemistries. The Phase-to-Phase Extraction via a Chemical Reaction to give Lower Limits of Chemical Detection hypothesis (for the purpose of brevity this is shortened to ‘Chemical Amplification’ within this dissertation) was proposed. Thorough testing of the hypothesis using an enzyme catalysed reaction scheme has demonstrated its validity, and potential value if applied to ‘real world’ systems, particularly those for detecting low solubility analytes such as the explosive 2,4,6-trinitrotoluene (TNT) or its byproduct 2,4- dinitrotoluene (2,4-DNT).

No description available.

The accurate estimation of atmospheric water vapour and the subsequent derivation of surface spectral reflectance from hyperspectral VNIR-SWIR remotely sensed data is important for many applications. A number of algorithms have been developed for estimating water vapour content from remotely sensed hyperspectral data that do not require in-situ measurements. Two algorithms, the Continuum Interpolated Band Ratio (CIBR) and the Atmospheric Precorrected Differential Absorption (APDA) have proven to be highly effective at estimating atmospheric water vapour. Although highly successful, the two methods still exhibit unwanted or spurious results when challenging conditions are encountered. Such conditions include the estimation of atmospheric water vapour over dark targets, when uncorrected atmospheric aerosols are present and over surfaces with complex spectral signatures.A differential absorption method called the Transmittance Slope Ratio (TSR) has been developed that negates these problems. The TSR method is comprised of a weighted mean radiance that is defined between two atmospheric water absorption features which is divided by a reference channel radiance to produce a measurable ratio value. This, is turn, may be related to a reference curve, such that, the TSR value may be expressed as an atmospheric water vapour content. To test the TSR method over real terrains, AVIRIS and HyMap measured hyperspectral radiometric data were used. Three test sites were used in total with each site allowing different aspects of the water vapour estimation to be critically examined. The sites are, Jasper Ridge and Moffett Field in California and Brukunga in South Australia.The TSR method is found to significantly improve estimated atmospheric water vapour over dark targets (with less than 3.5 % error for reflectances as low as 0.5 %), improvement over nonlinear surfaces, and finally, ++ / improvement in water vapour estimation when atmospheric aerosol conditions are not well known. In the final case the TSR method is found to estimate atmospheric water vapour with an error of less than 2 % when a 5 km visibility is assumed to be 25 km. The final result is at least an order of magnitude better than the CIBR and APDA methods.

The Global Positioning System (GPS) of navigation satellites was first developed for global navigation and position determination purposes. Signals from satellites are delayed by the Earths neutral atmosphere on propagating to ground-based receivers, termed the tropospheric delay. Although an unwanted term for precise positioning, the tropospheric delay may be converted to atmospheric water vapour, which is a vital parameter for weather forecasting.This research investigates the optimum GPS processing strategy to estimate atmospheric water vapour derived from ground-based GPS receivers particularly in the Australian region. For this purpose, GPS data observations from GPS permanent stations across Australia, mainly from the Australian Regional GPS Network, will be processed using scientific GPS software in post-processed mode and near real-time mode.This research shows that by applying high accuracy GPS data processing, the tropospheric delay could be estimated precisely. The quality of GPS data processing is indicated by the station coordinates repeatability since the coordinates can gauge at least a coarse assessment of the ability of the processing method to estimate the tropospheric delay.The precipitable water can be estimated from the wet component after separating the tropospheric delay into dry and wet components. High accuracy GPS data processing is dependent on the best choice of processing strategies, and the correct application of error-correction models and a priori constraints. This research finds that the GPS- PW estimation agrees with Radiosonde-PW estimation with an average of standard deviation at 2.5mm level for post-processed strategy and 2.8mm for near real-time strategy. The standard deviation of tropospheric parameter estimates is 1.1mm for post-processed strategy and 1.5mm for near real-time strategy.