Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed February 25, 2010). PDF text: 201 p. : col. ill. ; 4 Mb. UMI publication number: AAT 3386550. Includes bibliographical references. Also available in microfilm and microfiche formats.

No description available.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1960. / Includes bibliographical references (p. 100-102).

The measurement of vapour-liquid equilibrium data is extremely important as such data are crucial for the accurate design, simulation and optimization of the majority of separation processes, including distillation, extraction and absorption. This study involved the measurement of vapour-liquid equilibrium data, using a modified version of the static total pressure apparatus designed within the Thermodynamics Research Unit by J.D. Raal and commissioned by Motchelaho, (Motchelaho, 2006 and Raal et al., 2011). This apparatus provides a very simple and accurate means of obtaining P-x data using only isothermal total pressure and overall composition (z) measurements. Phase sampling is not required. Phase equilibrium measurement procedures using this type of apparatus are often tedious, protracted and repetitive. It is therefore useful and realizable in the rapidly advancing digital age, to incorporate computer-aided operation, to decrease the man hours required to perform such measurements. The central objective of this work was to develop and implement a control scheme, to fully automate the original static total pressure apparatus of Raal et al. (2011). The scheme incorporates several pressure feedback closed loops, to execute process step re-initialization, valve positioning and motion control in a stepwise fashion. High resolution stepper motors were used to engage the dispensers, as they provided a very accurate method of regulating the introduction of precise desired volumes of components into the cell. Once executed, the control scheme requires approximately two days to produce a single forty data points (P-x) isotherm, and minimizes human intervention to two to three hours. In addition to automation, the apparatus was modified to perform moderate pressure measurements up to 1.5 MPa. Vapour-liquid equilibrium test measurements were performed using both the manual and automated operating modes to validate the operability and reproducibility of the apparatus. The test systems measured include the water (1) + propan-1-ol (2) system at 313.15 K and the n-hexane (1) + butan- 2-ol system at 329.15 K. Phase equilibrium data of binary systems, containing the solvent morpholine-4-carbaldehyde (NFM) was then measured. The availability of vapour-liquid equilibrium data for binary systems containing NFM is limited in the literature. The new systems measured include: n-hexane (1) + NFM (2) at 343.15, 363.15 and 393.15 K, as well as n-heptane (1) + NFM (2) at 343.15, 363.15 and 393.15 K. The modified apparatus is quite efficient as combinations of the slightly volatile NFM with highly volatile alkane constituents were easily and accurately measured. The apparatus also allows for accurate vapour-liquid equilibrium measurements in the dilute composition regions. A standard uncertainty in the equilibrium pressure reading, within the 0 to 100 kPa range was calculated to be 0.106 kPa, and 1.06 kPa for the 100 to 1000 kPa pressure range. A standard uncertainty in the equilibrium temperature of 0.05 K was calculated. The isothermal data obtained were modelled using the combined (-) method described by Barker (1953). This involved the calculation of binary interaction parameters, by fitting the data to various thermodynamic models. The virial equation of state with the Hayden-O’Connell (1975) and modified Tsonopoulos (Long et al., 2004) second virial coefficient correlations were used in this work to account for vapour phase non-ideality. The Wilson (1964), NRTL (Renon and Prausnitz, 1968), Tsuboka-Katayama-Wilson (1975) and modified Universal Quasi-Chemical (Anderson and Prausnitz, 1978) activity coefficient models were used to account for the liquid phase non-ideality. A stability analysis was carried out on all the new systems measured to ensure that two-liquid phase formation did not occur in the measured temperature range. A model-free method based on the numerical integration of the coexistence equation was also used to determine the vapour phase compositions and activity coefficients from the measured P-z data. These results compare well with the results obtained by the model-dependent method. The infinite dilution activity coefficients for the systems under consideration were determined by the method of Maher and Smith (1979b), and by suitable extrapolation methods. Excess enthalpy and excess entropy data were calculated for the systems measured, using the Gibbs-Helmholtz equation in conjunction with the fundamental excess property relation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Salts in solution should be removed by desalination techniques to prevent equipment fouling and corrosion. Common desalination technologies are energy intensive such as Multi Stage Flash (MSF) distillation which requires 14.5 J/m3 (Ribeiro. J, 1996) of energy. Desalination technologies produce purified water and a concentrated salt solution, where the salt concentration is dependent on the desalination technology used. This work investigates gas hydrate technology as a possible desalination technology. Hydrates are composed of guest molecules and host molecules. Guest molecules may be in the form of a liquid or gas. During hydrate formation, host molecules, water, form a cage enclosing the guest molecule. Common hydrate formers or guest molecules such as; methane, ethane, propane and carbon dioxide are currently being investigated in literature, for use in gas hydrate desalination technology. Common hydrate formers form hydrates at low temperatures; below 288 K and high pressures; above 2 MPa. To increase the temperature and reduce the pressure at which gas hydrates form, commercially available hydrofluorocarbon hydrate formers such as R14, R32, R116, R134a, R152a, R218, R404a, R407c, R410a and R507 are preliminarily investigated in this work. The criteria for choosing the most suitable fluorine-based formers require the former to be: environmentally acceptable where it is approved by the Montreal Protocol; non-toxic where it has a low acute toxicity; non-flammable; chemically stable; a structure II hydrate to simplify the washing process; available in commercial quantities; low cost in comparison to other hydrate formers; compatible with standard materials and contain a high critical point for a large heat of vaporisation (McCormack and Andersen, 1995). Taking all these criteria into account, R134a was chosen for further investigation as a possible hydrate former. In this work, hydrate-liquid-vapour phase equilibrium measurements are conducted using the isochoric method with a static high pressure stainless steel equilibrium cell. The Combined Standard Uncertainty for the 0-1 MPa pressure transducer, 0-10 MPa pressure transducer and the Pt100 temperature probes are ±0.64 MPa, ±5.00 MPa and ±0.09 K respectively. Vapour pressure measurements for Hydrofluoropropyleneoxide, CO2, R22 and R134a were measured to verify the pressure and temperature calibrations. Hydrate test systems for R22 (1) + water (2) and R134a (1) + water (2) were measured to verify calibrations, equipment and procedures. New systems measured included R134a (1) + water (2) + {5wt%, 10wt% or 15wt%} NaCl (3). For the system R134 (1) + water (2) at 281 K the dissociation pressure is 0.269 MPa. However, addition of NaCl to the system resulted in a shift of the HVL equilibrium phase boundary to lower temperatures or higher pressures. The average shift in temperature between the system R134a (1) + water (2) containing no salt and the systems containing {5, 10 and 15} wt% NaCl are -1.9K, -4.8K and -8.1K respectively. In this work, the measured systems were modelled using two methods of approach. The first method is where hydrofluorocarbon hydrate former solubility is included, (Parrish et al., 1972) and the second is where hydrofluorocarbon hydrate former solubility is ignored, (Eslamimanesh et al., 2011). From these models, it is found that hydrofluorocarbon solubility could not be neglected. In this work, the hydrate phase was modelled using modifications of the van der Waals and Platteeuw model, (Parrish et al., 1972). The liquid and vapour phases are modelled using the Peng- Robinson equation of state with classical mixing rules (Peng, 1976). The electrolyte component is modelled using the Aasberg-Peterson model (Aasberg-Petersen et al., 1991) modified by Tohidi (Tohidi et al., 1995). The percent absolute average deviation (%AAD) for the systems, which includes solubility, is 0.41 for R22 (1) + water (2) and 0.33 for R134a (1) + water (2). For the system R134a (1) + water (2) + {5 wt%, 10 wt% or 15 wt%} NaCl (3) the % AAD is 5.14. Using the hydrate former, R134a, is insufficient to ensure gas hydrate technology is competitive with other desalination technologies. Hydrate dissociation temperature should be increased and pressure decreased further to ambient conditions. As evident in literature, promoters, such as cyclopentane, are recommended to be added to the system to shift the HLV equilibrium phase boundary as close to ambient conditions as possible. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

The principal theory concerning the origin of the elements heavier than the Fe-peak, such as Ba, strongly suggest that for old, metal-poor environments, the rapid (r-) process is the most likely path taken in their synthesis, while the slow (s-) process becomes more substantial in younger, more metal-rich stellar populations. In this work I test this theory by evaluating the isotope ratios of Ba. It is understood that Ba consists of seven stable isotopes, five of which are synthesised by the two neutron-capture processes. The two odd isotopes, 135,137Ba, as well as 138Ba are synthesised via both the r- and s-processes while two of the even isotopes, 134,136Ba are synthesised via the s-process only. The relative contribution of the r- and s-process to these isotopes can be understood via nucleosynthesis calculations and is described using the parameter fodd, where fodd = [N (135Ba) + N (137Ba)] /N (Ba). Low values of fodd (~0.11) indicate an s-process regime, while high values of fodd (~0.46) indicate an r-process regime. In the Ba II 4554 A line the even isotopes lie close to the line centre, while the odd isotopes, which are hyperfine split because of their non-zero nuclear spin, lie in the wings of the line. From an analysis of the line profile shape, one can determine whether Ba has been synthesised primarily through the r-process or s-process; a broad, asymmetric line would indicate a high r-process contribution, while a line with a deeper core and shallower wings would indicate a high s-process contribution. Using the radiative transfer code ATLAS, which assumes local thermodynamic equilibrium (LTE) and employs 1-dimensional (1D) KURUCZ06 model atmospheres, I synthesised line profiles for six metal-poor stars: HD140283, HD122563, HD88609, HD84937, BD-04 3208 and BD+26 3578 - for a range of isotope ratios. All six are of sufficiently low metallicity that Ba was expected to have an r-process origin. These were fit to high resolution (R\equiv \lamda/\Delta\lamda = 90 000 - 95 000), high signal-to-noise to the Ba II 4554 A line which has multiple components. In the first test, synthetic spectra were computed using the non local thermodynamic equilibrium (NLTE) radiative transfer code MULTI. The synthetic line profiles were fit to a number of lines in HD140283. Although this technique might have improved the fit in the line core, it was found that such a treatment did not improve upon fitting errors associated with the best fit 1D LTE synthetic profiles. The second test used a 3-dimensional (3D) radiative transfer code (LINFOR3D) that employed 3D, time-dependent atmospheres produced with CO5BOLD. The 3D synthetic pro les were fit to a selection of Fe lines and improvements over the poor fits produced by the 1D LTE synthesis were seen. It was found that the 3D synthesis could almost completely reproduce the line asymmetries seen in the observed stellar spectrum. This result suggests that further work to refine the 3D calculations and synthesis code would be valuable.

Submitted in fulfillment of the requirements of the degree of Master of Engineering, Durban University of Technology, Durban, South Africa, 2016. / Separation processes in the chemical process industries is dependent on the science of chemical thermodynamics. In the field of chemical separation process engineering, phase equilibrium is a primary area of interest. This is due to separation processes such as distillation and extraction which involves the contacting of different phases for effective separation. The focal point of this research project is the measurement and modeling of binary vapour-liquid equilibrium (VLE) phase data of systems containing ether-alcohol organic compounds. The VLE data were measured with the use of the modified apparatus of Raal and Mühlbauer, (1998). The systems of interest for this research arose from an industrial demand for VLE data for systems containing ether-alcohol organic compounds. This gave rise to the experimental VLE data isotherms being measured for the following binary systems: a) Methyl tert-butyl ether (1) + 1-pentanol (2) at 317.15 and 327.15 K b) Methyl tert-butyl ether (1) + 2, 2, 4-trimethylpentane (2) at 307.15, 317.15 and 327.15K c) 2, 2, 4-Trimethylpentane (1) + 1-pentanol (2) at 350.15, 360.15 and 370.15K d) Diisopropyl ether (1) + 2,2,4-trimethylpentane (2) at 320.15, 330.15 and 340.15K e) Diisopropyl ether (1) + 1-propanol (2) at 320.15, 330.15 and 340.15K f) Diisopropyl ether (1) + 2-butanol (2) at 320.15, 330.15 and 340.15K The data for all the measured binary systems investigated at these temperatures are currently not available in the open source literature found on the internet and in library text resources. The systems were not measured at the same temperatures because certain system isotherm temperatures correlate to a pressures above 1 bar. This pressure of 1 bar is the maximum operating pressure specification of the VLE apparatus used in this project. The experimental VLE data were correlated for model parameters for both the  and methods. For the method, the fugacity coefficients (vapour-phase non-idealities) were tabulated using the virial equation of state and the Hayden-O’Connell correlation (1975); chemical theory and the Nothnagel et al. (1973) correlation method. The activity coefficients (liquid phase non-idealities) were calculated using three local-composition based activity coefficients models: the Wilson (1964) model, the NRTL model (Renon and Prausnitz, 1968); and the UNIQUAC model (Abrams and Prausnitz, 1975). Regarding the direct method, the Soave-Redlich-Kwong (Redlich and Kwong, 1949) and Peng-Robinson (1976) equations of state ii were used with the temperature dependent alpha-function (α) of Mathias and Copeman (1983) with the Wong-Sandler (1992) mixing rule. Thermodynamic consistency testing, which presents an indication of the quality and reliability of the data, was also performed for all the experimental VLE data. All the systems measured showed good thermodynamic consistency for the point test of Van Ness et al. (1973) - the consistency test of choice for this research. This however, was based on the model chosen for the data regression of a particular system. Therefore, the combined method of VLE reduction produced the most favourable results for the NRTL and Wilson models. / M

A free energy formalism is developed in order to describe phase equilibria in binary alloys. The proposed phenomenological approach uses a limited number of experimental data to provide a global thermodynamic description of a system including its equilibrium and metastable phase diagrams. Emphasis is placed on the description of short range order by means of the cluster variation method. A microscopic theory is also developed in order to predict the enthalpies of formation of transition metal alloys as well as the short range order dependence of these enthalpies. The theory uses a tight-binding Hamiltonian together with the generalized perturbation method. 0ff~diagonal disorder is taken into account, and charge transfer is treated self consistently in the random alloy. All input parameters to the theory are obtained from ab-initio calculations for the pure elements. In this regard, the model can be considered parameter free. The phenomenological approach has been used to analyzed the Al-Ni, Ni~Cr, and Al~Li systems. It is found that the vibrational entropy of‘ formation plays an important role in the thermodynamics of the Al-Li and Ni-Cr alloys. The approach allows an accurate description of stable and metastable order-disorder or order-order equilibria existing in the Ni-Al or AL~Li systems. The model is used to predict a metastable clustering tendency in Al-Li alloys which appears to have been recently confirmed by experiment. The microscopic theory has been applied to the VB-VIE and IVB-VIIIB (Ni, Pt, Pd) alloys. The calculations are in good agreement with the available experimental data and phase diagram information. It is shown that off-diagonal disorder and electronic self-consistency play a crucial role in the accuracy of the results.

Le lithium est une matière première en demande croissante suite au fort développement des appareils nomades et des véhicules électriques. Ce manuscrit s’intéresse à la production de lithium à partir d’une ressource naturelle : les saumures lithinifères. Une étude bibliographique sur l’extraction du lithium présent dans les saumures a mis en avant que cette dernière requiert des quantités importantes d’énergie, d’eau et de réactifs. Cela met ainsi en évidence l’enjeu environnemental et la nécessité d’améliorer les procédés existants. A cette fin, la présente étude allie la modélisation à un travail expérimental. Le modèle sélectionné pour calculer les coefficients d’activité des éléments dissous dans les saumures est le modèle de Pitzer (1991). Un travail de paramétrisation a été effectué pour mettre au point une base de données thermodynamiques disposant des éléments nécessaires (propriétés des sels, paramètres d’interaction) à la description des systèmes électrolytiques d’intérêt. Après un travail de validation appuyé sur des données expérimentales issues de la bibliographie, cette base de données, associée au logiciel PhreeqC pour les calculs géochimiques, permet de simuler différentes transformations des saumures (dilution, évaporation, ajout de réactifs). L’outil mis en place a permis d’analyser des scenarios exploratoires de production de zabuyelite (Li2CO3) et d’effectuer une étude de sensibilité des paramètres opératoires. Des travaux expérimentaux sur des saumures modèles ont été effectués sur deux pilotes distincts : une enceinte climatique et une unité d’évaporation. Les techniques d’analyses utilisées pour suivre l’évolution de la composition de la saumure et la qualité des cristaux sont la chromatographie ionique, la DRX et l’EDX. Le modèle mis au point permet de décrire les systèmes salés complexes à l’équilibre à 25°C. Il parvient à décrire les essais dans le pilote d’évaporation du LaTEP à condition que l’on émette l’hypothèse que la zabuyelite ne précipite pas au cours du temps (sursaturation nécessaire). Il pourrait certainement être optimisé au niveau thermodynamique (spéciations, constantes de solubilité), mais également en y ajoutant une dimension cinétique et transferts liquide-vapeur. / Lithium is a critical element regarding to the development of portable devices and electric vehicles. This manuscript is dedicated to lithium production from natural lithium bearing brines. A bibliographic review shows that lithium production consumes lots of water, energy and reactive. It underlines environmental issues and the necessity to improve existing processes. In order to achieve this, modeling and experimental work are associated for this study. The Pitzer model (Pitzer, 1991) is used to calculate the activity coefficients of dissolved aqueous species in brines. After parametrization (salt properties, interaction parameters) and validation with experimental data from literature, a database was optimized to allow the description of key electrolytic systems. Associated with phreeQC software, it is possible to simulate transformations of the brine (such as dilution, evaporation, reactions). It can be used as a predictive tool to explore zabuyelite (Li2CO3) production and study the sensibility of the operative parameters (temperature, pH, pCO2). Experimental work on model-brines was done on two separate pilots: a climatic chamber and a crystallization unit. The evolution of the brine composition and quality of crystals produced was monitored by ionic chromatography, XRD and EDX. The model designed in this study can describe the equilibrium of complex brines at 25°C. It can also describe the experiment in the crystallization unit if a hypothesis of supersaturation (Li2CO3) is used. It could be improved thermodynamically with more speciation and solubility constants, and also with kinetics and liquid-vapor transfers.

This dissertation study describes the development of novel heteroepitaxial growth of 3C-SiC layers by chemical vapor deposition (CVD). It was hypothesized that chloride addition to the "traditional" propane-silane-hydrogen precursors system will enhance the deposition growth rate and improve the material quality via reduced defect density. Thermodynamic equilibrium calculations were performed to obtain a criterion for which chloride specie to select for experimentation. This included the chlorocarbons, chlorosilanes, and hydrogen chloride (HCl) chloride containing groups. This study revealed no difference in the most dominant species present in the equilibrium composition mixture between the groups considered. Therefore, HCl was the chloride specie selected to test the hypothesis. CVD computerized fluid dynamic simulations were developed to predict the velocity, temperature and concentration profiles along the reactor. These simulations were performed using COMSOL Multiphysics and results are presented. The development of a high-temperature (1300 °C -1390°C) 3C-SiC growth process resulted in deposition rates up to ~38 µm/h. This is the highest value reported in the literature to date for 3C-SiC heteroepitaxy. XRD FWHM values obtained varied from 220 to 1160 arcsec depending of the process growth rate or film thickness. These values are superior or comparable to those reported in the literature. It was concluded from this study that at high deposition temperatures HCl addition to the precursor chemistry had the most significant impact on the epitaxial layer growth rate. Low-temperature (1000-1250°C) 3C-SiC growth experiments evidenced that the highest deposition rate that could be attained was ~2.5 µm/h. The best quality layer achieved in this study had a FWHM of 278 arcsec; which is comparable to values reported in the literature and to films grown at higher deposition temperatures in this study. It was concluded from this work that at lower deposition temperatures the HCl addition was more beneficial for the film quality by enhancing the surface. Surface roughness values for films grown with HCl additive were 10 times lower than for films grown without HCl. Characterization of the epitaxial layers was carried out via Nomarski optical microscopy, FTIR, SEM, AFM, XRD and XPS.