O modelo F–SAC (Functional–Segment Activity Coefficient), recentemente introduzido, combina a ideia de contribuição de grupos com a teoria de superfícies de contato COSMO–RS. Este modelo tem uma dependência reduzida dos parâmetros de interação binária quando comparado com as variantes do modelo UNIFAC e precisão melhorada quando comparada com modelos baseados em COSMO. No presente trabalho uma modificação na formulação do modelo F–SAC é proposta para a inclusão de interações dispersivas. Para testar esta modificação, foram considerados os dados experimentais de alcanos, ciclo–alcanos, alcenos, aromáticos e perfluorocarbonetos. O modelo proposto foi capaz de correlacionar entalpias de vaporização de substâncias puras, não consideradas em versões anteriores do modelo. Uma vez que a capacidade calorífica de líquidos está intimamente relacionada com a entalpia de vaporização, o modelo também pode prever a capacidade calorífica de substâncias puras. Em relação ao coeficiente de atividade em diluição infinita e dados de equilíbrio líquido–vapor, o modelo modificado manteve o bom desempenho do modelo original, também semelhante a outros modelos similares, como variantes do modelo UNIFAC. Além disso, o modelo modificado pode agora calcular valores consistentes para a entalpia e entropia de excesso para sistemas onde as interações são principalmente dispersivas. Para estes sistemas, a maioria dos modelos de coeficiente de atividade prevê entalpia de excesso zero, contrabalançando valores de energia de Gibbs de excesso confiáveis com entropias de excesso distorcidas. / The recently introduced F–SAC (Functional–Segment Activity Coefficient) model combines the group contribution idea with a COSMO–RS surface contacting theory. This model has a reduced dependency on binary interaction parameters when compared to classical UNIFAC type models and improved accuracy when compared with COSMO based models. In the present work a modified F–SAC formulation is proposed for including dispersive interactions. For testing the modification, experimental data of alkanes, cycloalkanes, alkenes aromatics and perfluorocarbons were considered. The proposed model was able to correlate pure compound enthalpies of vaporization, not considered in previous versions of the model. Since the heat capacity of liquids is closely related to the enthalpies of vaporization, the model also can predict pure compound heat capacity of liquids. Regarding mixture infinite dilution activity coefficient and vapor–liquid equilibrium data, the modified model maintained the good performance of the original model, also similar to other competing models such as UNIFAC variants. Additionally, the modified model now can compute consistent values for the excess enthalpy and entropy for systems where the interactions are mainly dispersive. For these systems, most activity coefficient models predict zero excess enthalpies, counterbalancing that with distorted excess entropies.

Neste trabalho, o modelo F-SAC (Functional-Segment Activity Coefficient) foi revisado e estendido de modo a representar, simultaneamente, coeficiente de atividade à diluição infinita (IDAC), equilíbrio líquido-líquido (LLE) e equilíbrio líquido-vapor (VLE), em amplos intervalos de temperatura. Originalmente, o modelo F-SAC foi calibrado essencialmente com dados experimentais de IDAC para diversas misturas. Investigouse, portanto, a possibilidade de o modelo levar também em consideração sistemas que apresentem LLE. Para a presente investigação, dois conjuntos de misturas industrialmente interessantes foram selecionados: hidrocarbonetos (alcanos, cicloalcanos, alcenos, cicloalcenos e compostos aromáticos) + n-formilmorfolina (NFM) e hidrocarbonetos + água. Foram propostas duas modificações na equação que calcula a energia de interação entre os grupos: (i) inspirado pelo comportamento típico observado na expansão isobárica de líquidos, um novo parâmetro foi proposto de modo a diminuir o (pequeno) erro sistemático do modelo com a temperatura no termo sem associação; (ii) em misturas associativas, utilizou-se uma equação similar para representar a dependência da energia de ligação de hidrogênio entre dois segmentos com a temperatura. Na estimação de parâmetros do modelo foram utilizados 1130 pontos experimentais de LLE, para 105 sistemas binários e 16 ternários, juntamente com um 815 dados experimentais de IDAC, resultando numa nova tabela de parâmetros. Ao total, foram estimados 42 parâmetros dos grupos e subgrupos. Os resultados do F-SAC foram comparados, quando possível, com diferentes versões do UNIFAC encontradas na literatura. O modelo proposto foi capaz de correlacionar a maior parte dos dados de IDAC e LLE utilizados. Para os dados de IDAC, foram observados desvios médios absolutos de 0,139 e 0,608 unidades de ln para o F-SAC e o UNIFAC(PSRK), respectivamente. Para os dados de LLE, foram observados desvios semelhantes. Finalmente, o F-SAC foi utilizado para representar dados de VLE para os sistemas de compostos aromáticos + NFM. Observou-se desvios médios relativos de 0,038 e 0,082 no cálculo da pressão de bolha utilizando-se o F-SAC e o UNIFAC(PSRK), respectivamente. Estes resultados comprovam a boa capacidade preditiva do modelo, uma vez que nenhum dado de VLE foi utilizado nas estimações. Conclui-se, desta forma, que o modelo FSAC pode ser usado para representar, simultaneamente, IDAC, LLE e VLE de misturas com e sem ligação de hidrogênio, utilizando um único conjunto de parâmetros. / In this work, the F-SAC model (Functional -Segment Activity Coefficient) has been revised and extended in order to simultaneously represent activity coefficient at infinite dilution (IDAC), liquid-liquid equilibrium (LLE) and vapor-liquid equilibrium (VLE), in a wide range of temperature. Originally, the F- SAC model was calibrated essentially with IDAC experimental data for several mixtures. In the present work, the possibility of also taking into account LLE was investigated. For this study, two sets of industrially interesting mixtures were selected : hydrocarbons (alkanes, cycloalkanes, alkenes, cycloalkenes and aromatics) + n-formylmorpholine (NFM) and hydrocarbons + water. Modifications were suggested in the equation that computes the interaction energy for each contact between two segments: (i) inspired by the typical behavior observed in the isobaric expansion of liquids, a new parameter has been proposed in order to reduce the (small) systematic error with the temperature for non-associating systems; (ii) for associating mixtures, a similar equation was proposed to represent the temperature dependence of the hydrogen bond energy between two segments. In the parameterization of the model, 1130 LLE experimental points were used, for 105 binary and 16 ternary systems, along with 815 IDAC experimental points, resulting in a new parameter table. A total of 42 parameters for groups and subgroups were calibrated. The F-SAC results were compared, whenever possible, with different versions of the UNIFAC model, freely available in the literature. The proposed model was able to correlate most of the IDAC and LLE data. For IDAC data, absolute average deviations were 0.139 and 0.608 ln units using F-SAC and UNIFAC(PSRK), respectively. Similar deviations were observed for LLE data. Finally, F-SAC was used to represent VLE data for aromatics + NFM systems. The absolute relative deviations were 0.038 and 0.082 in the bubble pressure calculations for F-SAC and UNIFAC(PSRK), respectively. The VLE results indicate a strong predictive ability of the suggested model, since no VLE data was used in the parameter estimation procedure. The results also indicate that the F-SAC model can be used to represent, simultaneously, IDAC, LLE and VLE for associating and non-associating mixtures, with a single set of parameters.

Atualmente, pelo menos para fins de engenharia, os modelos preditivos de maior sucesso para coeficientes de atividade são os baseados em grupos funcionais, tais como UNIFAC e suas variantes. Enquanto esses modelos requerem grandes quantidades de dados experimentais, os baseados em COSMO-RS (COnductor-like Screening MOdel - for Real Solvents) requerem a calibração de um pequeno conjunto de parâmetros universais. No entanto, a precisão requerida por tarefas de engenharia, tais como a otimização de sistemas de separação, é maior do que a obtida por esta última categoria de modelos. Assim, um novo modelo é proposto neste trabalho, aqui chamado de F-SAC (Functional-Segment Activity Coefficient). Este novo modelo também é baseado no conceito de grupos funcionais, mas a energia de interação entre os grupos vem da teoria COSMO-RS. No presente trabalho, foram consideradas apenas misturas em que não há formação de ligação de hidrogênio ou quando esta pôde ser assumida negligenciável. Assim, foram necessários apenas três parâmetros para descrever cada grupo funcional. A princípio, uma vez ajustados os parâmetros de cada grupo, estes funcionariam para descrever a interação para qualquer par de grupos. Esta é a principal vantagem do modelo proposto. O número de parâmetros do modelo cresce proporcionalmente ao número de grupos funcionais, enquanto que no UNIFAC o número de parâmetros de interação cresce proporcionalmente ao quadrado do número de grupos. Para o banco de dados experimentais de coeficientes de atividade em diluição infinita considerado, a correlação do F-SAC apresentou um erro médio absoluto de 0,07 unidades de ln, enquanto que os modelos UNIFAC (Do) e COSMO-SAC apresentaram, respectivamente, erros de 0,12 e 0,21. O F-SAC foi também avaliado para mais de 1000 misturas binárias de um soluto dissolvido em líquido iônico com dados disponíveis na literatura. O modelo apresentou uma boa correlação aos dados experimentais, com erro médio absoluto de 0,17 unidades de ln, similar ao apresentado pelas misturas orgânicas. O poder de predição do novo modelo foi avaliado utilizando dados de equilíbrio líquido-vapor não considerados no procedimento de ajuste do modelo. Uma ótima concordância com os dados experimentais foi possível em toda a faixa de composição, bem como na predição de azeótropos. Esses resultados demonstram o potencial do modelo proposto. / At present, at least for engineering purposes, the most successful predictive models for activity coefficients are those based on functional groups, such as UNIFAC and its variants. While these models require large amounts of experimental data, the ones based on COSMO-RS require the calibration of a small set of universal parameters. However, the resolution required by engineering tasks, such as the optimization of separation systems, is higher than that obtained by COSMO-RS models. Thus, in this work a novel Functional-Segment Activity Coefficient (F-SAC) model is proposed. This new model is also based on the concept of functional groups, but the interaction energy between groups comes from the COSMO-RS theory. In this study, we considered only mixtures where there is no formation of hydrogen bonds or when they could be assumed negligible. Then, only three parameters were required to describe each functional group. In principle, once the parameters for each functional group are properly calibrated, they should work to describe the interactions with any other group. This is the main advantage of the proposed model, the number of model parameters grows linearly with the number of functional groups, whereas in UNIFAC the number of interaction parameters exhibit quadratic growth with respect to the number of groups. For the experimental database of infinite dilution activity coefficients considered, the correlation of F-SAC have shown a mean absolute error of 0.07 ln-unit. The UNIFAC (Do) and COSMO-SAC models presented errors of 0.12 and 0.21, respectively. F-SAC was also evaluated for more than 1000 binary mixtures of solute in ionic liquid with data available in the literature. Again, the model have shown good correlation to the experimental data, with mean absolute error of 0.17 ln-unit, similar to the performance with the organic mixtures. The predictive strength of the model was assessed by using vaporliquid equilibrium data not considered in the model fitting process. Very good agreement with experimental data was possible over the entire composition range, as well as in the prediction of azeotropes. These results demonstrate the potential of the proposed method.

Submitted by Celso Magalhaes (celsomagalhaes@ufrrj.br) on 2017-06-14T14:33:49Z No. of bitstreams: 1 2016 - Camila de Souza Silva.pdf: 1802766 bytes, checksum: 154ae702e6dbdd0afdc13fb202a08682 (MD5) / Made available in DSpace on 2017-06-14T14:33:49Z (GMT). No. of bitstreams: 1 2016 - Camila de Souza Silva.pdf: 1802766 bytes, checksum: 154ae702e6dbdd0afdc13fb202a08682 (MD5) Previous issue date: 2016-08-02 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Equilibrium data at low and high pressures are important to correct establish conditions of temperature and pressure for separation processes, and to supply the capacity of the solvent, the compositions of the phases and the selectivity of the solvent. The separation of ethanol-water system is of great importance for the industry due to numerous applications of anhydrous ethanol. In all of these applications, ethanol must be free of water and it is necessary to add a third component in the distillation to break the azeotrope. It can be add different solvents, as benzene, hexane, ethyleneglycol, salts, and, in the last years, many studies have been done with ionic liquids. So, the purpose of this work is to use an ionic liquid (1-ethyl-3-methylimidazolium chloride) as the third component, looking for the ethanol dehydration. Because of that, it was done a study to evaluate the effect of this ionic liquid in the liquid-vapor equilibrium behavior between water and ethanol. Experimental data were measured, in triplicate, under normal pressure, in an Othmer-type ebulliometer (300 mL of volume), with two condensers, and made of borosilicate glass. The sample analysis was done in a digital densimeter. The ionic liquid used was recovered from one solution to another, just by adding the required amount to complete each mass fraction. Experimental data was measured with ethanol-water solutions varying the molar concentrations from 0.2 to 0.99, and ionic liquid weight fraction masses from 5 to 60%, to evaluate the behavior of the equilibrium data of the ethanol+water+[emim][Cl] system. The experiments showed that [emim][Cl] with a minimum mass fraction of 20% is a promising solvent because it could ?break? the azeotrope between water and ethanol, and higher mass fraction of ionic liquid were better to enrich the vapor phase in ethanol. NRTL model was used to correlate experimental vapor-liquid equilibrium of the ternary system, estimating the binary parameters, applying the bubble point methodology. The deviations of temperature and vapor phase composition were 0.147 ?C and 0.049, respectively. The relative volatility was greater than 1 for the mass fractions from 20%. The activity coefficients decrease with the increase in the molar concentration of ethanol. Values of the excess Gibbs free energy show a positive deviation for all mass fractions worked, and the experimental data were consistent thermodynamically / Os dados de equil?brio a press?es baixas e elevadas s?o importantes para estabelecer as condi??es corretas de press?o e temperatura para os processos de separa??o e para fornecer a capacidade do solvente, as composi??es das fases e a seletividade do solvente. A separa??o do sistema etanol-?gua ? de grande import?ncia para a ind?stria devido a numerosas aplica??es do etanol anidro. Em todas essas aplica??es, o etanol deve ser livre de ?gua e, para isso, ? necess?rio adicionar um terceiro componente na destila??o para quebrar o aze?tropo. Podem ser adicionados diferentes solventes como o benzeno, hexano, etilenoglicol, sais e, nos ?ltimos anos, tem-se visto muitos estudos com l?quidos i?nicos. Com isso, o objetivo deste trabalho ? a utiliza??o de um l?quido i?nico (1-etil-3-metil imidaz?lio cloreto) como terceiro componente, visando a desidrata??o do etanol, al?m da avalia??o do efeito deste l?quido i?nico no comportamento do equil?brio l?quido-vapor entre a ?gua e o etanol. Os dados experimentais foram medidos, em triplicata, sob press?o normal, em um ebuli?metro tipo Othmer (300 mL de volume), com dois condensadores, feitos de vidro de borosilicato. As determina??es das amostras foram feitas em um dens?metro digital. Os dados foram medidos com solu??es de etanol-?gua em diferentes concentra??es molares (0,2 a 0,95), variando a fra??o m?ssica de l?quido i?nico de 0,05 a 0,60, para avaliar o comportamento dos dados de equil?brio do sistema etanol-?gua-[emim][Cl].Os resultados mostraram que o [emim][Cl] ? um solvente promissor, pois "quebra" o aze?tropo entre a ?gua e etanol a partir de 20% de l?quido i?nico, e a concentra??o de etanol na fase vapor foi maior com o aumento da fra??o m?ssica de LI.O modelo NRTL foi utilizado para correlacionar os dados experimentais de equil?brio, estimando-se os par?metros bin?rios, aplicando-se a metodologia do ponto de bolha. Os desvios em rela??o ? temperatura e a composi??o molar da fase vapor foram 0,147 ?C e 0,049, respectivamente. O l?quido i?nico, recuperado de uma solu??o para outra, passou por uma an?lise de RMN para avaliar se n?o houve altera??o na sua estrutura e, constatou-se que, ap?s ser recuperado, e novamente reutilizado, o solvente n?o perdeu as caracter?sticas originais. As volatilidades relativas foram superiores a 1 para as fra??es m?ssicas a partir de 20%, confirmando a quebra do aze?tropo. A energia livre de Gibbs em excesso apresentou valores que mostram um desvio positivo para todas as fra??es m?ssicas trabalhadas e os dados experimentais foram consistentes termodinamicamente

Atualmente, pelo menos para fins de engenharia, os modelos preditivos de maior sucesso para coeficientes de atividade são os baseados em grupos funcionais, tais como UNIFAC e suas variantes. Enquanto esses modelos requerem grandes quantidades de dados experimentais, os baseados em COSMO-RS (COnductor-like Screening MOdel - for Real Solvents) requerem a calibração de um pequeno conjunto de parâmetros universais. No entanto, a precisão requerida por tarefas de engenharia, tais como a otimização de sistemas de separação, é maior do que a obtida por esta última categoria de modelos. Assim, um novo modelo é proposto neste trabalho, aqui chamado de F-SAC (Functional-Segment Activity Coefficient). Este novo modelo também é baseado no conceito de grupos funcionais, mas a energia de interação entre os grupos vem da teoria COSMO-RS. No presente trabalho, foram consideradas apenas misturas em que não há formação de ligação de hidrogênio ou quando esta pôde ser assumida negligenciável. Assim, foram necessários apenas três parâmetros para descrever cada grupo funcional. A princípio, uma vez ajustados os parâmetros de cada grupo, estes funcionariam para descrever a interação para qualquer par de grupos. Esta é a principal vantagem do modelo proposto. O número de parâmetros do modelo cresce proporcionalmente ao número de grupos funcionais, enquanto que no UNIFAC o número de parâmetros de interação cresce proporcionalmente ao quadrado do número de grupos. Para o banco de dados experimentais de coeficientes de atividade em diluição infinita considerado, a correlação do F-SAC apresentou um erro médio absoluto de 0,07 unidades de ln, enquanto que os modelos UNIFAC (Do) e COSMO-SAC apresentaram, respectivamente, erros de 0,12 e 0,21. O F-SAC foi também avaliado para mais de 1000 misturas binárias de um soluto dissolvido em líquido iônico com dados disponíveis na literatura. O modelo apresentou uma boa correlação aos dados experimentais, com erro médio absoluto de 0,17 unidades de ln, similar ao apresentado pelas misturas orgânicas. O poder de predição do novo modelo foi avaliado utilizando dados de equilíbrio líquido-vapor não considerados no procedimento de ajuste do modelo. Uma ótima concordância com os dados experimentais foi possível em toda a faixa de composição, bem como na predição de azeótropos. Esses resultados demonstram o potencial do modelo proposto. / At present, at least for engineering purposes, the most successful predictive models for activity coefficients are those based on functional groups, such as UNIFAC and its variants. While these models require large amounts of experimental data, the ones based on COSMO-RS require the calibration of a small set of universal parameters. However, the resolution required by engineering tasks, such as the optimization of separation systems, is higher than that obtained by COSMO-RS models. Thus, in this work a novel Functional-Segment Activity Coefficient (F-SAC) model is proposed. This new model is also based on the concept of functional groups, but the interaction energy between groups comes from the COSMO-RS theory. In this study, we considered only mixtures where there is no formation of hydrogen bonds or when they could be assumed negligible. Then, only three parameters were required to describe each functional group. In principle, once the parameters for each functional group are properly calibrated, they should work to describe the interactions with any other group. This is the main advantage of the proposed model, the number of model parameters grows linearly with the number of functional groups, whereas in UNIFAC the number of interaction parameters exhibit quadratic growth with respect to the number of groups. For the experimental database of infinite dilution activity coefficients considered, the correlation of F-SAC have shown a mean absolute error of 0.07 ln-unit. The UNIFAC (Do) and COSMO-SAC models presented errors of 0.12 and 0.21, respectively. F-SAC was also evaluated for more than 1000 binary mixtures of solute in ionic liquid with data available in the literature. Again, the model have shown good correlation to the experimental data, with mean absolute error of 0.17 ln-unit, similar to the performance with the organic mixtures. The predictive strength of the model was assessed by using vaporliquid equilibrium data not considered in the model fitting process. Very good agreement with experimental data was possible over the entire composition range, as well as in the prediction of azeotropes. These results demonstrate the potential of the proposed method.

A database containing Henry's law constants, infinite dilution activity coefficients and solubility data of industrially important chemicals in aqueous systems has been compiled. These properties are important in predicting the fate and transport of chemicals in the environment. The structure of this database is compatible with the existing DIPPR® 801 database and DIADEM interface, and the compounds included are a subset of the compounds found in the DIPPR® 801 database. Thermodynamic relationships, chemical family trends, and predicted values were carefully considered when designating recommended values. Henry's law constants and infinite dilution activity coefficients were measured for toluene, 1-butanol, anisole, 1,2-difluorobenzene, 4-bromotoluene, 1,2,3-trichlorobenzene, and 2,4-dichlorotoluene in water using the inert gas stripping method at ambient pressure (approximately 12.5 psia) and at temperatures between 8°C and 50°C. Fugacity ratios, required to determine infinite dilution activity coefficients for the solid solutes, were calculated from literature values for the heat of fusion and the liquid and solid heat capacities. Chemicals were chosen based on missing or conflicting data from the literature. A first-order temperature-dependent group contribution method was developed to predict Henry's law constants of hydrocarbons, alcohols, ketones, and formats where none of the functional groups are attached directly to a benzene ring. Efforts to expand this method to include ester and ether groups were unsuccessful. Second-order groups were developed at a reference condition of 298.15 K and 100 kPa. A second-order temperature-dependent group contribution method was then developed for hydrocarbons, ketones, esters, ethers, and alcohols. These methods were compared to existing literature prediction methods.

Geologic sequestration of carbon dioxide (CO 2) in a deep, saline aquifer is being proposed for a power-generating facility in Florida as a method to mitigate contribution to global climate change from greenhouse gas (GHG) emissions. The proposed repository is a brine-saturated, dolomitic-limestone aquifer with anhydrite inclusions contained within the Cedar Keys/Lawson formations of Central Florida. Thermodynamic modeling is used to investigate the geochemical equilibrium reactions for the minerals calcite, dolomite, and gypsum with 28 aqueous species for the purpose of determining the sensitivity of mineral precipitation and dissolution to the temperature and pressure of the aquifer and the salinity and initial pH of the brine. The use of different theories for estimating CO2 fugacity, solubility in brine, and chemical activity is demonstrated to have insignificant effects on the predicted results. Nine different combinations of thermodynamic models predict that the geochemical response to CO2 injection is calcite and dolomite dissolution and gypsum precipitation, with good agreement among the quantities estimated. In all cases, CO2 storage through solubility trapping is demonstrated to be a likely process, while storage through mineral trapping is predicted to not occur. Over the range of values examined, it is found that net mineral dissolution and precipitation is relatively sensitive to temperature and salinity, insensitive to CO2 injection pressure and initial pH, and significant changes to porosity will not occur.

Values of the rate constant for the alkaline hydrolysis of methyl acetate in various aqueous-organic solvent mixtures (dimethyl sulfoxide 0<x40.2, dioxane 0 <, x., < 0.2, methyl ethyl ketone 0<x<0.06 and diglyme, i. e. ether-bis (2-methyloxethyl) 0x<0.10) have been determined for the temperatures 15 0 C, 25 0C and 35 0C conductometrically. To interpret these results the approach adapted is to experimentally determine the activity coefficient of the ester (YE ) and the activity of the water (aH20', mechanistically, at least one molecule of water is involved in the rate-determining step) and then to use the Bronsted-Bjerrum equation to determine the residual activity coefficient ratio of the participating ions, y (Yf - for Oil the transition state). Values of YE and aH 20 have been determined by a transpiration method, using gas-chromatographic analysis of the vapours of solutions of methyl acetate in aqueous-organic solvent mixtures of dir. ethyl sulfoxide, dioxane, methyl ethyl ketone and diglyme in the same composition ranges as above, tetrahydrofuran 04x org z<, 0.15, methanol, ethanol and tert-butanol in t1h6e range 04x0.20'at 25oC. These results indicate that on changing org the solvent composition YE varies by a larger factor than is predicted for the ratio YOH-/yýO_ by the Debye-Iluckel approach, and hence is the dominant factor in determining the effects of solvent composition on the rates of the hydrolysis. This is in contradiction to the assumptions of the electrostatic theories of Laidler and Eyring, and of Amis and Jaffe. The gas-chromatographic results also indicate that whilst the concentration of the water varies in each mixture studied, the activity coefficient varies in the opposite way to produce almost constant values of aý, 0* Using the transpiratioii/gas-chromatogralýlic method, the thermodynamic properties of the ternary systems, methyl acetate-water-organic Solvcat, using the organic solvents mentioned above (excepting, diglyme) have been investigated, and the results indicate that the variation of *ýE with solvent composition, for the dilute solutions of ester used, can be estimated from the thermodynamic properties of the binary water-organic solvent mixtures, using the Gibbs-Dahem equation. Single ion activity coefficients in the literature for small negative ions, to represent the OH_ ion, and for large ions, to rep-resent the transition state ion, have been used to explain the experimentally fomd variation of the residual activity coefficient -ratio with solvent composition. Hence, it is concluded that the importance of the parameters involved in the hydrolysis of esters - an ion-molecule reaction - in aqueousorganic solvent mixtures are in the order of Ymolecule > aH 20> YOH_/YM+ -> (dielectric constant), and that the nonelectrostatic effects -- thermodynamic effects - are more important in these studies than the electrostatic effects. From a preliminary investigation of the data in the literature the thermodynamic approach also yields a valid interpretation of the effect of solvent composition on the rates of the acid hydrolysis of esters.

Magister Scientiae - MSc (Environ & Water Science) / There are growing concerns around the environmental issues related to processed water as the demand for potable water is on the increase in South Africa. Effluents discharged from various sectors such as water treatment facilities pose a constant threat to the environment and natural water resources, including rivers and groundwater due to their poor chemical and physical composition. As a result, the demand for predicting the elevated concentrations of salts in a spatial and temporal dimension is constantly growing. The effluent at the eMalahleni water reclamation plant in Mpumalanga, South Africa, is being processed through a triple reverse osmosis that improves the water quality of the mine water to potable standards. Two water quality streams emerge from this process, i.e. a potable standard and the other a brine concentrate which is stored in ponds. Brine ponds are used for inland brine disposal in the eMalahleni water reclamation plant. The large volumes and limited capacity to store brines has placed great emphasis on enhanced evaporation rates to increase the efficiency of the ponds. In order to improve the rate of brine evaporation in the pond, an understanding of the effect of brine salt content and other parameters affecting the rate of evaporation is required. This study aimed at establishing the physical and chemical behaviour of the brine from the eMalahleni plant in a controlled environment. The investigation incorporated actual brine from the eMalahleni plant as well as synthetic salts typical of the major components of the eMalahleni brine.

Values of the rate constant for the alkaline hydrolysis of methyl acetate in various aqueous-organic solvent mixtures (dimethyl sulfoxide 0<x40.2, dioxane 0 <, x., < 0.2, methyl ethyl ketone 0<x<0.06 and diglyme, i. e. ether-bis (2-methyloxethyl) 0x<0.10) have been determined for the temperatures 15 0 C, 25 0C and 35 0C conductometrically. To interpret these results the approach adapted is to experimentally determine the activity coefficient of the ester (YE ) and the activity of the water (aH20', mechanistically, at least one molecule of water is involved in the rate-determining step) and then to use the Bronsted-Bjerrum equation to determine the residual activity coefficient ratio of the participating ions, y (Yf - for Oil the transition state). Values of YE and aH 20 have been determined by a transpiration method, using gas-chromatographic analysis of the vapours of solutions of methyl acetate in aqueous-organic solvent mixtures of dir. ethyl sulfoxide, dioxane, methyl ethyl ketone and diglyme in the same composition ranges as above, tetrahydrofuran 04x org z<, 0.15, methanol, ethanol and tert-butanol in t1h6e range 04x0.20'at 25oC. These results indicate that on changing org the solvent composition YE varies by a larger factor than is predicted for the ratio YOH-/yýO_ by the Debye-Iluckel approach, and hence is the dominant factor in determining the effects of solvent composition on the rates of the hydrolysis. This is in contradiction to the assumptions of the electrostatic theories of Laidler and Eyring, and of Amis and Jaffe. The gas-chromatographic results also indicate that whilst the concentration of the water varies in each mixture studied, the activity coefficient varies in the opposite way to produce almost constant values of aý, 0* Using the transpiratioii/gas-chromatogralýlic method, the thermodynamic properties of the ternary systems, methyl acetate-water-organic Solvcat, using the organic solvents mentioned above (excepting, diglyme) have been investigated, and the results indicate that the variation of *ýE with solvent composition, for the dilute solutions of ester used, can be estimated from the thermodynamic properties of the binary water-organic solvent mixtures, using the Gibbs-Dahem equation. Single ion activity coefficients in the literature for small negative ions, to represent the OH_ ion, and for large ions, to rep-resent the transition state ion, have been used to explain the experimentally fomd variation of the residual activity coefficient -ratio with solvent composition. Hence, it is concluded that the importance of the parameters involved in the hydrolysis of esters - an ion-molecule reaction - in aqueousorganic solvent mixtures are in the order of Ymolecule > aH 20> YOH_/YM+ -> (dielectric constant), and that the nonelectrostatic effects -- thermodynamic effects - are more important in these studies than the electrostatic effects. From a preliminary investigation of the data in the literature the thermodynamic approach also yields a valid interpretation of the effect of solvent composition on the rates of the acid hydrolysis of esters. / Ministry of Science and Higher Education of Iran