Dissertations / Theses on the topic 'Phase equilibria'

Thesis (MScEng)--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: Supercritical extraction is being investigated as a possible alternative to the processes currently used in the fractionation of paraffinic waxes. By removing the lighter carbon fractions from the wax, the wax hardness will be improved and its melting temperature range reduced, hence improving the performance of the wax product in certain applications. In order to evaluate and operate such an extraction process optimally, it is necessary to have a thermodynamic model that accurately represents the process system. There are, however, currently no predictive models available for these systems. In order to fit present models to the systems, accurate phase equilibrium data of the supercritical solvent - n-alkane systems are needed. Unfortunately, the amount of reliable published data on these systems in the required operating range is very limited. A view cell was designed and developed with which these high pressure equilibria could be studied. The binary phase equilibria of supercritical CO2 with n-CI2, n-CI6, n-C20, n-C24, n-C28 and n-C36 and of supercritical ethane with n-CI6, n-C24 and n-C28 were measured in the temperature range 313 - 367 K. It was found that the systems with these two solvents have very different types of phase behaviour. The n-alkane solubility is much higher in ethane, but supercritical CO2 will provide a much better degree of control over the selectivity achieved in an extraction process. 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 and that the Soave-Redlich- Kwong equation fitted the ethane - n-alkane systems the best. The interaction parameters of both these equations of state display a functional relationship with temperature and nalkane acentric factor, making it possible to determine parameter values for application at other operating temperatures and with other n-alkane systems. It was found that the current equations of state were not able to represent the phase equilibria accurately over the entire range of operating conditions. The poor performance of the equations of state can be attributed to inherent flaws in the existing equations of state.
AFRIKAANSE OPSOMMING: Superkritiese ekstraksie word tans ondersoek as 'n moontlike altematief vir die prosesse wat huidiglik gebruik word om paraffiese wasse te fraksioneer. Die Iigter koolstofwasse word verwyder om die washardheid te verhoog en die temperatuurgebied waaroor die was smelt te verklein. Dit verbeter dan die was se kwaliteit en werkverrigting. Modelle wat die superkritiese ekstraksie proses akkuraat kan voorstel word egter benodig om die ekstraksie proses te kan evalueer en optimaal te bedryf. Daar is tans geen modelle beskikbaar wat die proses direk kan voorstel nie. Akkurate fase-ewewigsdata word benodig om bestaande modelle aan te pas vir gebruik in hierdie sisteme. Daar is egter baie min betroubare faseewewigsdata vir die superkritiese oplosmiddel - n-alkaan sisteme beskikbaar in die literatuur. 'n Sig-sel, waarrnee hierdie hoe druk data gemeet kan word, is ontwerp en ontwikkel. Die volgende binere fase ewewigte is in die temperatuur gebied 313 - 367 K gemeet: superkritiese CO2 met n-CI2, n-CI6, n-C20, n-C24, n-C28 en n-C36, en superkritiese Etaan met n-CI6, n-C24 en n-C28. Daar is gevind dat hierdie twee superkritiese oplosmiddelsisteme verskillende tipes fase-ewewigsgedragte openbaar. Die n-alkane het 'n baie boer oplosbaarheid in Etaan, maar deur superkritiese C02 in 'n ekstraksie kolom te gebruik, sal tot beheer oor die selektiwiteit van die ekstraksieproses lei. Uit die verskillende toestandsvergelykings wat ondersoek is, is daar gevind dat die Patel- Teja vergelyking die CO2 sisteme die beste kon beskryf en dat die Soave-Redlich-Kwong vergelyking die beste vergelyking was om die Etaan sisteme mee te modelleer. Beide die toestandsvergelykings se interaksie parameters het 'n funksionele verband met temperatuur en die n-alkaan asentrise faktor getoon. Dit is dus moontlik om waardes vir die parameters vir sisteme by ander temperature en met ander n-alkaan tipes te bepaal. Daar was gevind dat die bestaande toestandsvergelykings nie die die fase-ewewigte oor die hele eksperimenele gebied akkuraat kon voorstel nie. Dit kan toegeskryf word aan foute wat inherent is aan die vergelykings.

Phase equilibria are at the heart of many properties of substances, such as their solubility, manufacturability, and stability. They are of significant industrial and commercial interest, perhaps most importantly to the pharmaceutical industry where drug stability and solubility are two of the largest challenges of drug development. The focus of this thesis then was to develop a molecular level understanding of phase equilibria, and produce tools and models to predict phase stability. An emphasis was given to exploring solid-solid and solid-liquid equilibria and stability. Specifically, the work presented here aimed to elucidate what drives the formation of multicomponent crystals, improve available models for exploring phase equilibria phenomena and explore solubility prediction from first principles as a potentially more powerful alternative to correlation based methods. These three fundamental areas were explored by employing molecular simulation in combination with the machinery of statistical mechanics, utilising advanced sampling methods and free energy calculations. This approach has led to the development of a foundation for understanding multicomponent crystal formation in terms of molecular affinities and packing, the characterisation of a set of soft coarse-grained potentials for use in phase equilibria studies, which overcome the main limitations of the most widely used potential, and finally, the development of a novel method for solubility prediction from first principles. Here, this novel method was successfully applied to an ionic (aqueous sodium chloride) and small molecular (urea in methanol and aqueous urea) system. In the future, these results are expected to lead to a set of guidelines for predicting (and perhaps prohibiting) multicomponent crystal formation, the development of a higher class of coarse-grained transferable force field with utility in studying phase equilibria, and powerful approach for predicting solubility of even large, flexible molecules (such as pharmaceuticals).

The main objectives of this work are the study of solid-liquid equilibrium of salts in pure and mixed solvents, and of biomolecules, such as amino acids and peptides, in water. The correlation and prediction of properties for mixtures containing charged electric species, the electrolytes, is of great relevance for the chemical industry. A brief discussion about the whole interest of this work and the need of concentrating efforts to develop accurate models for electrolyte systems is initially focused. The fundamental concepts of electrolyte thermodynamics and industrial examples where electrolytes play an important role are given. The available different models to correlate and/or predict properties and phase equilibria for this kind of mixtures are reviewed and compared. An isothermal analytical method, which has been implemented to measure salt solubilities, is described in detail. The experimental solubilities obtained for NaCl, KCl, NaBr and KBr, in the pure solvents water, methanol, ethanol and in the mixed solvents water/methanol, water/ethanol and methanol/ethanol in the temperature range between 25 oC and 80 oC are given. The new experimental data is used together with additional information published by other authors, concerning solid-liquid equilibrium of salts in pure and mixed solvents and osmotic coefficients in pure solvents, in order to establish an extensive and reliable database. This is adopted for the development of consistent thermodynamic models. Two UNIQUAC based models are suggested: the UNIQUAC + Pitzer-Debye-Hückel model, and the UNIQUAC model with linear temperature dependent solvent/salt parameters. A new developed approach for correlating salt solubilities, based on the symmetric convention of normalization of the activity coefficients and on the mole fraction concentration scale on ionized basis is presented. In this way, it is possible the direct access to the salt solubility product in terms of its calorimetric properties such as the melting temperature, enthalpy of fusion and heat capacity change. The capabilities of these models for the correlation and prediction of solid-liquid equilibrium and other thermodynamic properties are discussed. The results indicate that this procedure and these models are satisfactory for solid-liquid equilibrium calculations. The work on weak electrolytes consists of the development of a new group-contribution method. This includes two terms: the UNIFAC model to account for the short-range interaction forces, and a Debye-Hückel expression for the long-range forces. New UNIFAC groups have been assigned to describe the amino acids and peptides studied, and the chemical equilibrium is taken into account simultaneously with the physical equilibrium. Using this approach, the temperature and pH effects on the solubilities of amino acids in aqueous solutions are taken into consideration. This model predicts very successfully the pH influence on the solubilities of amino acids and therefore may be used for engineering purposes.

Bibliography: pages 167-169.
The computation of chemical and phase equilibria is an essential aspect of chemical engineering design and development. Important applications range from flash calculations to distillation and pyrometallurgy. Despite the firm theoretical foundations on which the theory of chemical equilibrium is based there are two major difficulties that prevent the equilibrium state from being accurately determined. The first of these hindrances is the inaccuracy or total absence of pertinent thermodynamic data. The second is the complexity of the required calculation. It is the latter consideration which is the sole concern of this dissertation.

Doutoramento em Engenharia Química
Em consequência de uma série de problemas ambientais, económicos e políticos relacionados com o uso de combustíveis convencionais, vários países estão agora a focar as suas atenções em combustíveis alternativos. O biodiesel está na linha da frente das alternativas ao petróleo no sector dos transportes, sendo considerado uma opção a curto prazo visto que o seu preço é competitivo e não são necessárias mudanças nos motores para implementar o seu uso. De entres os possíveis processos de produzir biodiesel, a reacção de transesterificação com catálise básica é o método preferido. Depois da reacção são sempre necessários processos de purificação de modo ao biodiesel produzido cumprir os standards definidos para os combustíveis alternativos, reduzindo problemas de motor e consequentemente aumentando a sua aceitação por parte dos consumidores. De entre as especificações encontram-se o conteúdo em água, em álcool e em glicerol. Ser-se capaz de descrever correctamente o equilíbrio de fases de sistemas que são de interesse para os processos de purificação de biodieseis numa gama alargada de condições termodinâmicas é uma condição necessária para uma correcta simulação do processo industrial, de modo a se atingir uma elevada produtividade a baixos custos de operação. O uso de moléculas oxigenadas como combustíveis representa uma alteração significativa em termos da termodinâmica de soluções. Para combustíveis baseados em petróleo as equações de estado cúbicas e os modelos clássicos de coeficientes de actividade mostraram ser apropriados, no entanto para combustíveis novos como o biodiesel, sendo mais complexos do ponto de vista das interacções intermoleculares com formação de dipolos e pontes de hidrogénio, são necessários modelos termodinâmicos mais complexos para descrever essas interacções. Neste trabalho a CPA EoS (Cubic-Plus-Association Equation of State) será desenvolvida de modo a permitir uma descrição adequada dos equilíbrios líquido-vapor e líquido-líquido para uma serie de sistemas binários e multicomponentes contendo água, ácidos gordos, ésteres de ácidos gordos, glicerol e álcoois.
As a consequence of a range of environmental, economical and political problems related to the use of conventional petroleum based fuels, several countries are now focusing their attention on alternative fuels. Biodiesel is at the forefront of the alternatives to petroleum based fuels in the transportation sector, being considered an important short-time option since its price can be competitive with conventional diesel and no motor changes are required. Among the various approaches to produce biodiesel, basic catalyzed transesterification is the preferable method. After the transesterification reaction purification steps are always necessary in order to provide the fuel with the quality levels required by the standards for alternative fuels, reducing engine problems and consequently increasing consumers’ acceptance. Among the specifying minimums are the water, the alcohol and the glycerol contents. Being able to correctly describe the phase equilibria of systems of interest for the biodiesel purification processes in a broad range of thermodynamic conditions is a necessary condition for a correct simulation of the industrial process, in order to achieve high productivity and low operating costs. The use of oxygenated molecules as fuels represents a significant change in terms of solution thermodynamics. While for petroleum-based fuels, cubic equations of state and classic activity coefficient models have proved to be appropriate, new fuels, such as biodiesel, are more complex from the point of view of intermolecular interactions with dipoles and hydrogen bonding being important on these systems. To be able to represent such interactions more complex engineering thermodynamics models are required. In this work the CPA EoS (Cubic – Plus – Association Equation of State) will be developed to provide an adequate description of the vapor-liquid and liquidliquid phase equilibria of several binary and multicomponent systems containing water, fatty acids, fatty acid esters, glycerol and alcohols.

Vapor-liquid equilibria (VLE) in alkanes and alcohols was measured and a contribution Patel-Teja (GPT) equation proposed in this work. systems of nmodified Group of state was Isothermal vapor-liquid equilibria at temperatures between 298.7K and 333. 7K have been measured for the binary systems n-pentane + n-hexane. n-pentane + noctane. n-pentane + n-decane. and n-pentane + l-propanol. The data were found to be consistent according to a point-to-point consistency test and were correlated using the Wilson. NRTL. and UNIQUAC activity coefficient models. The parameters of the models were estimated using the maximum likelihood principle. A new version of the Group contribution Patel-Teja equation of state was proposed in which a new temperature dependent group interaction expression was introduced. Group interaction parameters for four constituent groups of the alcohols and n-alkanes (viz. CH 2• CH 3 • CH and OH) were determined. These parameters were then used for the prediction of VLE in mixtures of n-alkane + n-alkane. n-alkane + n-alcohol. and n-alcohol + n-alcohol. VLE predictions with the new GPT equation of state were found to be superior to predictions with the original group contributions with molecular equations. The modified equation can be used in systems of nalkanes and alcohols where data for molecular parameters are lacking. The proposed temperature dependence of the group interaction parameters improved predictions over a wide range of temperature and pressure.

This thesis describes the investigation of phase behaviour of binary and ternary mixtures at high pressure. The particular applications chosen to be explored in this phase behaviour investigation were supercritical fluid electrodeposition (SCFED) and carbon capture and storage (CCS). Chapter 1 introduces the phase behaviour of mixtures. Chapter 2 describes the equipment and analytical techniques used throughout this thesis including the high-pressure variable-volume view cell, electrical conductivity cell, high pressure FTIR cell, and high-pressure optical fiber phase analyser. Chapter 3 details the solubility and conductivity investigation of several supporting electrolytes in difluoromethane (CH2F2), which provided an electrochemical bath with sufficient conductivity for electrodeposition in supercritical fluids. The most effective supporting electrolyte amongst the eight ionic compounds tested was [N(nC4H9)4][Al(OC(CF3)3)4] which was found to give a moderate solubility and the highest conductivity (222 Scm2mol-1) in CH2F2. [N(nC4H9)4][Al(OC(CF3)3)4] was followed by [N(nC4H9)4][FAP] and [N(nCH3)4][FAP], , making all of them to be satisfactory potential supporting electrolytes for SCFED. Chapter 4 describes the investigation of water solubility in CO2/N2 mixtures relevant to the CCS process. The scope of the investigation covers a wide pressure range and two levels of N2 (xN2= 0.05 and xN2= 0.10). This experimental study was conducted by using the FTIR technique as described in further detail in Chapter 2. It was found that the presence of N2 in CO2 lowered the solubility of H2O in supercritical CO2 with N2 compared to pure CO2. The solubility of water also decreases significantly when the concentration of N2 is increased from 5% to 10%. Chapter 5 further explores the role of phase behaviour in the application of CCS with the investigation of the phase envelope of the ternary mixtures of CO2 and permanent gases (Ar, N2, and H2). Three ternary mixtures were measured (90% CO2 + 5% N2 + 5% Ar, 98% CO2 + 1% N2 + 1% Ar, and 95% CO2 + 3% H2 + 2% Ar) by using the fiber optic reflectometer, as described in further detail in Chapter 2. The experimental data presented in this part also have been used to validate the equation of state for the CCS applications. It was found that the phase envelope of CO2 shifted to a higher pressure and the two-phase region become broader with the presence of permanent gases. Overall, both GERG-2004 and gSAFT provide a good agreement between the predicted and experimental data for all the ternary mixtures investigated, with the exception of the bubble-point line for the 3%H2 + 2%Ar + 95% CO2 mixture. Finally, Chapter 6 summarises the research that was conducted in this thesis. It also evaluates the progress made towards achieving the aims initially set-up in Chapter 1.

Titaniferous magnetite (titanomagnetite) offers a unique opportunity for the production of three valuable products from one resource. It generally contains economically appreciable reserves of vanadium and iron as well as significant contents of titanium. Titanomagnetite is typically smelted in blast or electric furnaces in the presence of reductant and fluxes (dolomite and quartz) to produce a valuable vanadium bearing pig iron and a virtually valueless titaniferous slag. The titaniferous slag by-products are generally defined by the Ca-Mg-Al-Si-Ti-O system. These fluxed slags can contain as high as 20-40wt% TiO2 (titania). The lack of interest in processing titaniferous slags to produce saleable titania materials is attributed to the presence of chemically inert phases, like the spinel solid solution [Mg(Al,Ti,V)2O4] that cannot be handled by the available titania slag upgrading technologies. The understanding of phase relations in titaniferous slags is thus important in order to be able to implement a suitable fluxing strategy for the production of a treatable titaniferous slag with no inert spinel phase. The available phase equilibria data established in air for titaniferous slags is inconclusive about the possible crystallisation of the detrimental spinel. However, literature on phase compositions of plant titaniferous slags are conclusive about the crystallisation of Mg(Al,Ti,V)2O4 in high MgO and Al2O3 bearing slags. It is thus clear that the understanding of phase relations in titaniferous slags requires further development. The objective of the current project was to investigate the phase equilibria and beneficiation of titaniferous slags to produce a saleable titania product. As a development to previous work, the composition of the slag for review was based on the available work, namely; TiO2 = 37.19wt%, SiO2 = 19.69wt%, and Al2O3 = 13.12wt%, at varying proportions of CaO (30- 0wt%) and MgO (0-30wt%). The phase equilibria studies followed a systematic approach involving the review and validation of the available equilibrium phase diagram produced in air, followed by the determination of updated phase equilibria at low oxygen partial pressures (pO2) of 10-16 atm applicable to titanomagnetite smelting. The generic approach of studying phase equilibria in multicomponent systems was followed, namely; (1) literature survey of the available thermodynamic and phase equilibria data applicable to the reviewed system, (2) calculation and re-drawing of the equilibrium phase diagrams using FactSage thermochemical software, and (3) equilibration-quench-(electron probe micro analysis) (EPMA) experiments to the validate calculated equilibrium phase relations. A titaniferous slag with little crystallisation of the inert spinel phase, based from the best fluxing strategy with an MgO-free limestone, was produced by smelting in conventional (using alumina crucible) and cold copper crucible induction furnaces for subsequent beneficiation using the established Upgraded Slag (UGS) process. A conceptual flowsheet for the production of vanadium, steel and titanium products was therefore designed and subsequently subjected to economic evaluation using the discounted cash flow (DCF) modelling approach. Thermodynamic and phase equilibria literature for the Ca-Mg-Al-Si-Ti-O system demonstrated that this system and some subsystems are well researched in air, and not as much in low pO2 atmospheres applicable to smelting operations. The FactSage software used in the current study for the calculation of phase equilibria in the Ca-Mg-Al-Si-Ti-O system applicable to titaniferous slags does not have tialite (Al2TiO5) modelled as a component in the customary pseudobrookite solution database - Al2TiO5 is a component of the pseudobrookite solution reported in literature for the current system. Hence, a private pseudobrookite solution database applicable to the reviewed system, i.e. MgTi2O5-Al2TiO5-Ti3O5, was developed and incorporated into FactSage before any calculation could be conducted. Thermodynamic modelling of the MgTi2O5-Al2TiO5-Ti3O5 system was conducted through the CALculation of PHase Diagram (CALPHAD) method. The sublattice model coupled with compound energy formalism (CEF) and Redlich-Kister polynomial were adopted. The model information was incorporated into FactSage to create a private database for subsequent calculations of phase equilibria of titaniferous slags. The equilibrium phase diagram for the Ca-Mg-Al-Si-Ti-O system in the same compositional range as in the available literature was then calculated in air. The liquidus surfaces and phase relations in the equilibrium phase diagrams of available literature and FactSage calculation are fairly comparable. However, at high MgO concentrations: FactSage calculation predicts that Mg(Al,Ti)2O4 is the primary phase, followed by successive crystallisation of pseudobrookite solid solution (MgTi2O5-Al2TiO5) and forsterite (Mg2SiO4); and the available literature reports MgTi2O5-Al2TiO5 as the primary phase, followed by Mg2SiO4. The crystallisation of spinel phase in the available phase diagram produced in air is not predicted. The crystallisation of the spinel solid solution phase in titaniferous slags is extensively reported in the open literature. Equilibration-quench-EPMA experimental results produced in air generally compared well to the FactSage calculations. The inability of the available phase diagram to predict spinel phase crystallisation was attributed to the lack of sensitive analytical techniques in the late 1960s, when the available phase diagram was developed. The phase equilibria of titaniferous slags were further calculated at low pO2 atmospheres of 10-16 atm. In the reviewed compositional range of titaniferous slags, the liquidus surface and Ti3+/Ti4+ mass fraction ratio increased with decreasing the pO2. There was no significant difference in terms of the crystallisation of phases between the calculated results in air and at pO2 of 10-16 atm, except that the size of the primary phase field at higher MgO concentrations than the composition for the minimum liquidus temperature increased and the pseudobrookite solution included Ti3+ bearing phase, i.e. MgTi2O5-Al2TiO5-Ti3O5. Equilibration-quench-EPMA experimental results produced at pO2 of 10-16 atm generally compared well to the FactSage calculations. The new phase equilibria at low pO2 of 10-16 atm shows that the crystallisation of the chemically inert Mg(Al,Ti)2O4 in titaniferous slags would occur if the slag contains high Al2O3 concentration and MgO concentration of 2wt% and above. However, the crystallisation of Mg(Al,Ti)2O4 in titaniferous slag is not significantly sensitive to variation in the TiO2 concentration in, and basicity of the slag. To produce a titaniferous slag with minimum possible inert spinel content for subsequent beneficiation, the South African Main Magnetite Layer (MML) titanomagnetite concentrate was smelted in the presence of an MgO-free lime and low ash Sasol carbon (SASCARB) reductant. This smelting approach would produce a titaniferous slag with about 4wt% MgO, which would come from the titanomagnetite - based on the phase equilibria, this slag should crystallise a small amount of the inert spinel. When the smelting was conducted in an alumina crucible placed inside a conventional induction furnace, the slag was inevitably contaminated by Al2O3 from the refractory container. This slag crystallised a significant Mg(Al,Ti)2O4 with the content approximated by the MgO concentration - the significant Mg(Al,Ti)2O4 crystallisation was attributed to the Al2O3 saturation in the titaniferous slag. A titaniferous slag containing a treatable ulvospinel phase was produced in a cold copper crucible induction furnace - the crystallisation of the ulvospinel, instead of the chemically inert spinel solid solution was attributed to the saturation of the slag by iron from the incomplete reduction process due to the inevitable stoppage of the heat supply to the induction furnace as soon as the susceptor iron metal and produced pig iron settled at the bottom of the copper crucible. For the purpose of demonstrating the feasibility of producing titania products from titaniferous slags, this slag was also subjected to beneficiation using UGS process. The current study successfully demonstrated that the titaniferous slags can be beneficiated to saleable titania products using the UGS process: the TiO2 in the Mg(Al,Ti)2O4 bearing waste titaniferous slag produced by the defunct Evraz Highveld Steel and Vanadium Corporation (EHSV) was upgraded from about 33wt% to 75wt%, while the TiO2 in the titaniferous slags produced in conventional and cold crucible induction furnaces were upgrade from about 30wt% to 67wt% and 22.00wt% to 90.45wt%, respectively. The remaining impurities in the 75wt% and 67wt% TiO2 UGS products were mainly MgO and Al2O3 contained in the refractory spinel solid solution. In the case of the 67wt% TiO2 product, there was excess Al2O3 in the spinel structure - the excess Al2O3 remained in the glass phase. Though the 90.45wt% TiO2 product is attractive for use as feedstock for the production of the preferred chloride pigment, this product however contained finer PSD and higher concentrations of impurities such as SiO2, Al2O3, and CaO, than the specification for the chloride process feedstock. This product was thus not a suitable feedstock for the chloride pigment production. Further optimisation of the UGS conditions has a potential to reduce the concentrations of impurities to levels suitable for feedstock for the preferred chloride pigment production process. Further investigations are also required to study the feasibility of the chlorination of micro-pellets of the UGS product. Since the UGS product is mainly composed of rutile structure, it would not be a suitable feed for the sulfate pigment production as the sulfuric acid lixiviant is unable to dissolve the rutile structure. Only if soluble in sulfuric acid, this high TiO2 bearing UGS product produced from titaniferous slags could be used as advantageous feedstock for the sulfate pigment production in terms of the minimization of the reagent consumption and the amount of the toxic sulfate waste. Based on the work of the current study, literature data and Pyrosim simulations, a conceptual process flowsheet for the production of vanadium slag, steelmaking pig iron and titania product was proposed. The economic modelling of the conceptual flowsheet for a 20 year operational projection showed that the process is economically viable. The process economic viability is sensitive to variation in the Opex and Revenue. In addition, additives, such as the amount and type of reductant, fluxes, and reagents account for about 75% of the Opex. It is possible that the additives are overestimated in the process as the recycle streams were not included in the proposed process and economic model. At the same time, the economic model does not consider the environmental and waste management costs. Hence, the economic analysis is considered to be preliminary in nature, or indicative at best. The current study has demonstrated that (1) a titaniferous slag containing little or no inert spinel phase that is suitable for upgrading can be produced when the MgO content in the slag is below 2wt% - the best approach to producing a slag with minimum possible MgO content would be to smelt the titanomagnetite in the presence of an MgO-free limestone flux and low ash reductant, and (2) it is technically and economically feasible to produce three products, i.e. V slag, steelmaking pig iron, and titania product, from titanomagnetite.

Mestrado em Engenharia Química
O aumento do preço do petróleo e o seu consumo excessivo, o esgotamento das reservas de petróleo e as alterações climáticas resultantes da emissão de gases com efeito de estufa, tornaram necessário o desenvolvimento de combustíveis alternativos com base em fontes renováveis. Os biocombustíveis são uma alternativa aos combustíveis fósseis, sendo o biodiesel e o bioetanol os mais produzidos actualmente. O bioetanol é produzido a partir de várias fontes renováveis, como a cana-deaçúcar, beterraba, milho, trigo ou madeira, que contêm elevadas percentagens de açúcares. Esses açúcares podem ser facilmente convertidos em etanol a partir da fermentação. Para separar o etanol da água, obtido na fermentação, várias técnicas podem ser utilizadas, como a destilação, adsorção, extracção líquido-líquido, entre outras. Neste trabalho foi estudado o equilibro de fases presente na extracção líquido-líquido. Foram medidas tie-lines para dois sistemas líquido-líquido, óleo de rícino + água + etanol e laurato de metilo + água + etanol. O biodiesel é produzido a partir de óleos vegetais e gorduras animais, a partir da reacção de transesterificação com álcoois de cadeia curta. Nesta reacção os óleos e gorduras reagem com o álcool na presença de um catalisador, para se obterem os correspondentes ésteres alquílicos. O conhecimento do equilíbrio de fases dos sistemas que contêm álcoois e ésteres de ácidos gordos, é necessário para conceber e desenvolver os processos de purificação e produção do biodiesel. Foi medido o equilíbrio líquido-vapor (VLE) de sistemas de ésteres metílicos de ácidos gordos + álcoois, uma vez que os dados existentes na literatura relativamente a estes compostos são escassos. A equação de estado CPA (Cubic-Plus-Association) foi aplicada com sucesso aos dados experimentais de equilíbrio líquido-vapor. ABSTRACT: With the increase of the oil price and its excessive consumption, the depletion of oil resources and climate change derived from the emission of greenhouse gases, the development of alternative fuels based on renewable sources became necessary. Biofuels are an alternative for fossil fuels, being the most important today the biodiesel and bioethanol. Bioethanol is produced from many renewable sources, such as sugar cane, sugar beet, corn, wheat and wood, which contain high percentages of sugars. These sugars can be easily converted to ethanol by fermentation. To recover the ethanol from fermentation broths, several techniques can be used, such as distillation, adsorption, liquid-liquid extraction, among others. In this work, the phase equilibria in liquid-liquid extraction was studied. Liquid-liquid equilibria (LLE) tie-lines were measured for two systems, castor oil -water-ethanol and methyl laurate-water-ethanol. Biodiesel is produced from vegetable oils and animals fats, through transesterification with lower alcohols. In this reaction vegetable oils and/or animal fats react with an alcohol in the presence of a catalyst, to give the corresponding alkyl esters. The knowledge about the phase equilibria of systems containing an alcohol and a fatty acid ester is thus necessary to correctly design and develop biodiesel production and purification processes. The vapor–liquid equilibria (VLE) for fatty acid methyl esters + alcohols systems was measured with an ebuliometer, as information about this kind of data was surprisingly scarce in the literature. The CPA (Cubic-Plus-Association) Equation of State was successfully applied to model the new experimental VLE data.

The fuel industry in many parts of the world is blending alcohols with motor fuel either to extend the fuel or to improve its octane rating or both. Unfortunately alcohols are hygroscopic and as a result, water becomes a component of the fuel. This can lead to phase separation and the formation of a water-rich layer which could have serious corrosion consequences. In an attempt to understand the phase-splitting in alcohol-petrol-water blends, phase equilibria in ternary systems (alcohol-hydrocarbon-water) have been determined by experiment. The phase equilibria in these ternary systems are also discussed in terms of modern theories of liquid mixtures and the UNIQUAC theory is applied to the "ethanol + benzene + water" ternary system. The alcohols are all the C₁, C₂, C₃ and C₄ alcohols, and the hydrocarbons include those typically found in petrol, e.g. cyclohexane, benzene and substituted benzenes.

The objectives of this work are to measure phase equilibria in the carbon dioxide + pyrrole system and to correlate and predict the phase behavior of this system with a thermodynamic model. This binary system is of interest due to the growing applications of supercritical carbon dioxide as a solvent or reaction medium for pyrrole. Polypyrrole is an electrically conducting polymer of interest in a number of applications such as anti-static coatings. Pyrrole has also been used as a reactant in enzymatic reaction. Knowledge of the phase behavior of carbon dioxide + pyrrole system is therefore necessary for evaluating optimal conditions and feasibility of such applications. Phase equilibria in the carbon dioxide + pyrrole system were measured at 313 K, 323 K, and 333 K using a synthetic method. Liquid-vapor (LV) phase behavior and liquid-liquid (LL) phase behavior were observed. The pressure in the experiments ranged from 84 to 151.1 bar. The Patel-Teja equation of state and the Mathias-Klotz-Prausnitz mixing rule with two temperature independent parameters was able to correlate the phase equilibrium data satisfactorily and was used to predict the phase behavior at other temperatures. A pressure-temperature diagram was then constructed from these calculations and suggests that the carbon dioxide + pyrrole system exhibit type IV phase behavior in the classification of Scott and van Konynenburg.

The Ph.D. project compiled in this thesis has focused on the role of the solvent in solid-liquid phase equilibria and in nucleation kinetics. Six organic substances have been selected as model compounds, viz. ortho-, meta- and para-hydroxybenzoic acid, salicylamide, meta- and para-aminobenzoic acid. The different types of crystal phases of these compounds have been explored, and their respective solid-state properties have been determined experimentally. The solubility of these crystal phases has been determined in various solvents between 10 and 50 oC. The kinetics of nucleation has been investigated for salicylamide by measuring the metastable zone width, in five different solvents under different experimental conditions. A total of 15 different crystal phases were identified among the six model compounds. Only one crystal form was found for the ortho-substituted compounds, whereas the meta-isomeric compounds crystallized as two unsolvated polymorphs. The para-substituted isomers crystallized as two unsolvated polymorphs and as several solvates in different solvents. It was discovered that the molar solubility of the different crystal phases was linked to the temperature dependence of solubility. In general, a greater molar solubility corresponds to a smaller temperature dependence of solubility. The generality of this relation for organic compounds was investigated using a test set of 41 organic solutes comprising a total of 115 solubility curves. A semi-empirical solubility model was developed based on how thermodynamic properties relate to concentration and temperature. The model was fitted to the 115 solubility curves and used to predict the temperature dependence of solubility. The model allows for entire solubility curves to be constructed in new solvents based on the melting properties of the solute and the solubility in that solvent at a single temperature. Based on the test set comprising the 115 solubility curves it was also found that the melting temperature of the solute can readily be predicted from solubility data in organic solvents. The activity of the solid phase (or ideal solubility) of four of the investigated crystal phases was determined within a rigorous thermodynamic framework, by combining experimental data at the melting temperature and solubility in different solvents and temperatures. The results show that the assumptions normally used in the literature to determine the activity of the solid phase may give rise to errors up to a factor of 12. An extensive variation in the metastable zone width of salicylamide was obtained during repeated experiments performed under identical experimental conditions. Only small or negligible effects on the onset of nucleation were observed by changing the saturation temperature or increasing the solution volume. The onset of nucleation was instead considerably influenced by different cooling rates and different solvents. A correlation was found between the supersaturation ratio at the average onset of nucleation and the viscosity of the solvent divided by the solubility of the solute. The trends suggest that an increased molecular mobility and a higher concentration of the solute reduce the metastable zone width of salicylamide.
QC 20100831

Experimental investigation of phase equilibria at supercritical fluid conditions was carried out for four binary mixtures and two ternary mixtures consisting of supercritical carbon dioxide and aromatic compounds (naphthalene, biphenyl, m-terphenyl and phenanthrene). A new technique, the first freezing point method, was developed in this study to determine the pressure-temperature (P-T) projection of the solid-liquid-gas (S-L-G) three-phase coexistence curves for binary and ternary mixtures at supercritical fluid conditions. In addition, the equilibrium liquid compositions along the three-phase coexistence curves were also determined. A temperature minimum in the P-T projection of the three-phase coexistence curve was observed for each of the binary mixtures. The liquid-gas (L = G) critical loci of two binary mixtures consisting of super-critical carbon dioxide and a solid (naphthalene or biphenyl) were determined. The bubble-point pressures along three isotherms as well as the solubilities of carbon dioxide in liquid naphthalene and biphenyl were also measured. By means of the intersection method, the upper critical end points (UCEP) were established to be 333.4 K, 25.9 MPa and 0.16 mole fraction of naphthalene for naphthalene-carbon dioxide mixture and 328.5 K, 48.5 MPa and 0.18 mole fraction of biphenyl for biphenyl-carbon dioxide mixture. A "crossover region" was found in the study of isothermal solubilities of super-critical CO$\sb2$ in liquid biphenyl at a pressure of about 36 MPa. Below the crossover region pressure, an increase in temperature caused a decrease in solubility of carbon dioxide in the liquid phase, while above the crossover region pressure the opposite effect occurs. A rational explanation was given. The P-T projection of the solid 1-solid 2-liquid gas (S$\sb1$-S$\sb2$-L-G) four-phase coexistence curve of two ternary mixtures--naphthalene-biphenyl-carbon dioxide and naphthalene-phenanthrene-carbon dioxide--were determined. The results indicate that the assumption of an unchanged eutectic composition of the solids with pressure may lead to a not negligible error in the measurements. The freezing point depression of the solid under the pressure of a supercritical solvent and the solubility behaviour in the vicinity of the lower critical end point (LCEP) and the UCEP were explored and discussed. The slopes of the depression curves at the triple points of the solids were predicted. Two different approaches, based respectively on the compressed gas model (equation of state) and the expanded liquid model (activity coefficient model), were developed to describe the S-L-G three-phase equilibria and the solubilities of supercritical carbon dioxide in the melted solids. Using the Peng-Robinson equation of state with the modified correction factors, $\alpha$, together with the composition-dependent mixing rules, the correlations of the experimental results were accomplished with satisfactory accuracy. The merits of these two approaches in the representation of the S-L-G three-phase equilibria were compared.

The objective of this thesis is to study the phase equilibria ofbinary mixtures using molecular simulation. Vapor-liquid,vapor-solid, liquid-liquid, and liquid-solid coexistence lines arecalculated for binary mixtures of Lennard-Jones spheres using MonteCarlo simulation and the Gibbs-Duhem integration technique. Completephase diagrams, i.e., showing all types equilibrium betweenvapor, liquid, and solid phases are constructed. The calculations presented in this thesismark the first time that molecular simulation hasbeen used to obtain phase diagrams describing all types of equilibriabetween vapor, liquid, and solid phases.We present complete phase diagrams for binary Lennard-Jones mixtureswith diameter ratios ranging from 0.85 to 0.95 and attractivewell-depth ratios ranging from 0.45 to 1.6, at reduced pressuresranging from 0.002 to 0.1. The Lorentz-Berthelot combining rules areused to calculate the cross-species interaction parameters. Wesystematically explore how the complete phase diagrams change as afunction of the diameter ratio, well-depth ratio, binaryinteraction parameter, and system pressure.

We first calculate complete phase diagrams for several binary mixtures at a single pressure and find that for well-depth ratios of unity (equal attractions among species) there is no interference between the vapor-liquid and solid-liquid coexistence regions. As the well-depth ratio increases or decreases from unity, the vapor-liquid and solid-liquid phase envelopes widen and interfere with each other, leading to the appearance of a solid-vapor coexistence region. For diameter ratios of 0.95, the solid-liquid lines have a shape characteristic of a solid solution (with or without a minimum melting temperature); as the diameter ratio decreases the solid-liquid lines fall to lower temperatures until they eventually drop below the solid-solid coexistence region, resulting in either a eutectic or peritectic three-phase line.

We then vary the binary interaction parameter in the Berthelotcombining rule to study the effect of unlike pair attractions onbinary mixture phase behavior. When the binaryinteraction parameter is unity we find a vapor-liquid coexistence region with a eutectic solid-liquidcoexistence region. These two regions are separated by a completelymiscible liquid phase. When the binary interactionparameter is less than unity we find that the vapor-liquid andsolid-liquid coexistence regions interfere. This interference resultsin the appearance of a vapor-solid coexistence region bounded above and below bysolid-liquid-vapor coexistence lines. We also find that when the binary interaction parameter is less than unity, there is a region ofliquid-liquid immiscibility that is metastable with respect to thesolid-fluid phase equilibria.

Next we calcuate temperature versus composition phase diagrams for one mixture at five reduced pressures in order to examine the effects of pressure on complete phase behavior. We observe interference between the vapor-liquid and solid-liquid coexistence regions at the lowest pressure. As the pressure increases, the vapor-liquid coexistence region shifts to higher temperatures, while the solid-liquid coexistence region remains essentially unaffected. Eventually, the vapor-liquid coexistence region lifts off the solid-liquid coexistence region, ending the interference. We then present pressure versus temperature projections for several mixtures to explore how the three-phase loci change with variations in diameter ratio and well-depth ratio. We find that as the diameter ratio decreases, the maximum pressure in the solid-liquid-vapor locus decreases and the characteristic shape of the solid-liquid coexistence region changes from peritectic to eutectic. As the well-depth ratio decreases, the maximum pressure in the solid-liquid-vapor locus increases.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Bibliography: v.2, leaves 200-208.
by Athanassios Z. Panagiotopoulos.
Ph.D.

Alloys of the elements Mo, Pd and Rh have been studied since complexes of these with Ru and Tc are found as metallic inclusions in irradiated oxide fuels, and it is considered that knowledge of the constitution of these multicomponent alloys may assist in understanding the history and character of such fuel. Samples were prepared either by arc melting or rapid solidification from Mo-Pd and Mo-Rh and ternary Mo-Pd-Rh systems. Rapid solidification was employed in an attempt to overcome the problem of slow diffusion in these systems particularly at lower temperatures. The usefulness of rapidly solidified materials in the constitutional investigation of these particular systems has been proved. Constitutional studies were made of binaries Mo-Pd and Mo-Rh using optical microscopy SEM analyses and X-ray diffraction methods. The phase boundaries in both binaries at temperatures ranging from 881 to 1100 °C were established satisfactorily. No intermediate phase was found at the temperatures of interest. Differences from published diagrams are suggested. An isothermal section of Mo-Pd-Rh ternary system was established at 1100 °C by constitutional studies employing the same techniques as utilised in the binary investigations. The section involves only the bcc fcc and hcp phases.T he bcc solid solution is restricted to the Mo comer while the fcc and hcp phases are stable over wide ranges of compositions. A three phase region (bcc + hcp + fcc ) is located near the Mo-Pd edge binary. The phase boundary composition limits found in the relevant binaries agree very well with those of the two-phase fields in the ternary . Thermodynamic coefficients for the phases in the relevant binaries Mo-Pd , Mo-Rh and Pd-Rh were derived by the assessment of available phase diagram and thermodynamic data using the Lukas program ; the resulting coefficients were input to reestablish the binaries. Very good agreement was found with the experimental phase diagrams and the comparison of integral molar free energies and the partial free energies of Mo with experimental values was very satisfactory. The coefficients established in the binary computations were combined with the lattice stability values of components and the ideal term to compute ternary isothermal sections-No ternary interaction terms were involved. The isothermals between 1373 - 2673 K were constructed. The isothermal calculated at 1373 K matches very well with the constitutionally established one except for the prediction of a more restricted hcp phase. The location of the three phase region is the same on both the experimental and calculated isothermal-Solidus , liquidus and secondary surfaces counters were constructed satisfactorily. Some attempts have been made to improve the 1373K isothermal section calculated employing the relevant binary coefficients only , by introducing ternary interaction terms. But these attempts were ineffective because of the lack of ternary thermodynamic values and insufficient ternary phase diagram data.