Esta tese trata da utilização de líquidos iônicos como solventes para a absorção de CO2, e busca relacionar o efeito das diferentes interações intermoleculares existentes no próprio solvente, assim como as interações estabelecidas com o gás, na capacidade de absorção do dióxido de carbono. Uma vez que as propriedades macroscópicas de líquidos iônicos estão diretamente associadas a sua estrutura e às interações entre as espécies iônicas, procura-se relacionar propriedades macroscópicas termodinâmicas com evidências microscópicas por espectroscopia. Nesse sentido, será possível estabelecer relações entre a estrutura local dos íons e a capacidade de absorção do gás, ampliando, dessa maneira, o estudo sobre a utilização destes materiais como solventes absorvedores de CO2. Utilizando uma dupla abordagem experimental, uma termodinâmica e outra espectroscópica, esta tese foi dividida em três partes. Na primeira, o efeito do CO2 na estrutura de líquidos iônicos foi investigado por espectroscopia Raman. Com o intuito de sondar o domínio polar dos líquidos iônicos, foi estudado o efeito da pressão de CO2 na posição das bandas mais características dos ânions. Diferente dos resultados reportados na literatura, a maioria dos quais obtidos via simulação por dinâmica molecular, foi observada uma modificação das interações iônicas no domínio polar dos líquidos iônicos. Esta modificação estrutural provocada pelo CO2 mostrou-se dependente da intensidade das interações entre cátions e ânions do próprio líquido. A segunda etapa explora o efeito de grupos éter de um polímero, PEO, nas propriedades de [N4111][NTf2]. Valores negativos de entalpia de mistura, &#916;mixH < 0, sugerem interações favoráveis entre [N4111][NTf2] e PEO. Espectros Raman confirmam uma associação favorável entre o cátion N4111+ e PEO, onde cadeias de PEO provavelmente envolvem o cátion. Estas interações refletem diretamente na dinâmica do sistema, apresentando forte dependência com o tamanho da cadeia polimérica. O aumento da quantidade de CO2 absorvida com o aumento da quantidade de PEO na mistura foi explicado por interações mais favoráveis entre o gás e o polímero, como mostrado pelo aumento das negativas entalpias de solvatação do CO2 nas misturas. Por fim, a terceira parte investiga o efeito do ânion C(CN)3- na capacidade de absorção de CO2 por [C4C1Im][Ac]. Misturas de [C4C1Im][Ac] e [C4C1Im][C(CN)3] tiveram suas propriedades físico-químicas registradas, observando uma diminuição da viscosidade do fluido com a adição de C(CN)3-. Este resultado foi atribuído a uma reorganização da rede de ligações de hidrogênio. A presença do ânion C(CN)3- não afeta significativamente a reação química do CO2 com [C[N4111][NTf2]C1Im][Ac] (constante de equilíbrio é mantida), mas diminui a constante de Henry, apontando para maiores absorções físicas do gás. Apesar de não afetar a absorção química de CO2 por [C4C1Im][Ac], a presença do ânion C(CN)3- melhora consideravelmente a transferência de massa, aumentando a fluidez do líquido absorvente. / This thesis is aimed at discussing the use of ionic liquids as solvents for the absorption of CO2 and seeks to relate the effect of different intermolecular interactions in the solvent itself, as well as the interactions established with the gas, on the carbon dioxide absorption capacity. Since the macroscopic properties of ionic liquids are directly associated with their structure and the interactions between their ions, it is sought to relate macroscopic thermodynamic properties with microscopic spectroscopic evidences. Therefore, it will be possible to establish relations between the local structure of the ions and the absorption capacity of the gas, thus expanding the study on the use of these materials as CO2-absorbing solvents. Using a double experimental approach, one thermodynamic and the other spectroscopic, this thesis was divided into three parts. At first, the effect of CO2 on the structure of ionic liquids was investigated by Raman spectroscopy. In order to probe the polar domain of ionic liquids, the effect of CO2 pressure on the most characteristic bands of anions was investigated. Unlike the results reported in the literature, most of them obtained through molecular dynamics simulation, it was observed a modification on the ionic interactions in the ionic liquids polar domain. This structural change driven by CO2 revealed to be dependent on the intensity of cation-anion interactions of the liquid itself. The second step of this thesis explores the effect of ether groups of a polymer, PEO, on the properties of [N4111][NTf41112]. Negative values of mixing enthalpy, &#916;mixH < 0, suggest favorable interactions between [N4111][NTf2] and PEO. Raman spectra results also suggest a favorable interaction between N4111+ cation and PEO, where PEO chains probably wrap the cation. These interactions directly reflect on the dynamics of the system, which has a strong dependence on the polymer chain size. The increase of absorbed CO2 by increasing the amount of PEO in the mixture was explained by more favorable interactions between the gas and the polymer, as revealed by the increase in the negative values of CO2 solvation enthalpy in the mixtures. Lastly, the third part investigates the effect of adding C(CN)3- anion on the CO2 absorption capacity of [C4C1Im][Ac]. Studying the physicochemical properties of [C4C1Im][Ac] mixed with [C4C1Im][C(CN)3] it was observed a decrease in the fluid viscosity upon the addition of C(CN)3-. This behavior was attributed to a reorganization of the [C4C1Im][Ac] hydrogen bond network due to the presence of C(CN)3- anion. The presence of C(CN)3- anion does not affect significantly the chemical reaction between CO2 and [C4C1Im][Ac] (chemical equilibrium is kept constant), but Henrys law constants decrease, pointing to greater physical absorption of the gas. Although not affecting the CO2 chemical uptake by [C4C1Im][Ac], the presence of the C(CN)3- anion considerably improves mass transfer, increasing the fluidity of the absorbent liquid.

Esta tese trata da utilização de líquidos iônicos como solventes para a absorção de CO2, e busca relacionar o efeito das diferentes interações intermoleculares existentes no próprio solvente, assim como as interações estabelecidas com o gás, na capacidade de absorção do dióxido de carbono. Uma vez que as propriedades macroscópicas de líquidos iônicos estão diretamente associadas a sua estrutura e às interações entre as espécies iônicas, procura-se relacionar propriedades macroscópicas termodinâmicas com evidências microscópicas por espectroscopia. Nesse sentido, será possível estabelecer relações entre a estrutura local dos íons e a capacidade de absorção do gás, ampliando, dessa maneira, o estudo sobre a utilização destes materiais como solventes absorvedores de CO2. Utilizando uma dupla abordagem experimental, uma termodinâmica e outra espectroscópica, esta tese foi dividida em três partes. Na primeira, o efeito do CO2 na estrutura de líquidos iônicos foi investigado por espectroscopia Raman. Com o intuito de sondar o domínio polar dos líquidos iônicos, foi estudado o efeito da pressão de CO2 na posição das bandas mais características dos ânions. Diferente dos resultados reportados na literatura, a maioria dos quais obtidos via simulação por dinâmica molecular, foi observada uma modificação das interações iônicas no domínio polar dos líquidos iônicos. Esta modificação estrutural provocada pelo CO2 mostrou-se dependente da intensidade das interações entre cátions e ânions do próprio líquido. A segunda etapa explora o efeito de grupos éter de um polímero, PEO, nas propriedades de [N4111][NTf2]. Valores negativos de entalpia de mistura, &#916;mixH < 0, sugerem interações favoráveis entre [N4111][NTf2] e PEO. Espectros Raman confirmam uma associação favorável entre o cátion N4111+ e PEO, onde cadeias de PEO provavelmente envolvem o cátion. Estas interações refletem diretamente na dinâmica do sistema, apresentando forte dependência com o tamanho da cadeia polimérica. O aumento da quantidade de CO2 absorvida com o aumento da quantidade de PEO na mistura foi explicado por interações mais favoráveis entre o gás e o polímero, como mostrado pelo aumento das negativas entalpias de solvatação do CO2 nas misturas. Por fim, a terceira parte investiga o efeito do ânion C(CN)3- na capacidade de absorção de CO2 por [C4C1Im][Ac]. Misturas de [C4C1Im][Ac] e [C4C1Im][C(CN)3] tiveram suas propriedades físico-químicas registradas, observando uma diminuição da viscosidade do fluido com a adição de C(CN)3-. Este resultado foi atribuído a uma reorganização da rede de ligações de hidrogênio. A presença do ânion C(CN)3- não afeta significativamente a reação química do CO2 com [C[N4111][NTf2]C1Im][Ac] (constante de equilíbrio é mantida), mas diminui a constante de Henry, apontando para maiores absorções físicas do gás. Apesar de não afetar a absorção química de CO2 por [C4C1Im][Ac], a presença do ânion C(CN)3- melhora consideravelmente a transferência de massa, aumentando a fluidez do líquido absorvente. / This thesis is aimed at discussing the use of ionic liquids as solvents for the absorption of CO2 and seeks to relate the effect of different intermolecular interactions in the solvent itself, as well as the interactions established with the gas, on the carbon dioxide absorption capacity. Since the macroscopic properties of ionic liquids are directly associated with their structure and the interactions between their ions, it is sought to relate macroscopic thermodynamic properties with microscopic spectroscopic evidences. Therefore, it will be possible to establish relations between the local structure of the ions and the absorption capacity of the gas, thus expanding the study on the use of these materials as CO2-absorbing solvents. Using a double experimental approach, one thermodynamic and the other spectroscopic, this thesis was divided into three parts. At first, the effect of CO2 on the structure of ionic liquids was investigated by Raman spectroscopy. In order to probe the polar domain of ionic liquids, the effect of CO2 pressure on the most characteristic bands of anions was investigated. Unlike the results reported in the literature, most of them obtained through molecular dynamics simulation, it was observed a modification on the ionic interactions in the ionic liquids polar domain. This structural change driven by CO2 revealed to be dependent on the intensity of cation-anion interactions of the liquid itself. The second step of this thesis explores the effect of ether groups of a polymer, PEO, on the properties of [N4111][NTf41112]. Negative values of mixing enthalpy, &#916;mixH < 0, suggest favorable interactions between [N4111][NTf2] and PEO. Raman spectra results also suggest a favorable interaction between N4111+ cation and PEO, where PEO chains probably wrap the cation. These interactions directly reflect on the dynamics of the system, which has a strong dependence on the polymer chain size. The increase of absorbed CO2 by increasing the amount of PEO in the mixture was explained by more favorable interactions between the gas and the polymer, as revealed by the increase in the negative values of CO2 solvation enthalpy in the mixtures. Lastly, the third part investigates the effect of adding C(CN)3- anion on the CO2 absorption capacity of [C4C1Im][Ac]. Studying the physicochemical properties of [C4C1Im][Ac] mixed with [C4C1Im][C(CN)3] it was observed a decrease in the fluid viscosity upon the addition of C(CN)3-. This behavior was attributed to a reorganization of the [C4C1Im][Ac] hydrogen bond network due to the presence of C(CN)3- anion. The presence of C(CN)3- anion does not affect significantly the chemical reaction between CO2 and [C4C1Im][Ac] (chemical equilibrium is kept constant), but Henrys law constants decrease, pointing to greater physical absorption of the gas. Although not affecting the CO2 chemical uptake by [C4C1Im][Ac], the presence of the C(CN)3- anion considerably improves mass transfer, increasing the fluidity of the absorbent liquid.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

A new methodology is developed to calculate density of states of interstellar and atmospheric clusters that takes account of their loosely bound nature and incorporates kinetically important angular momentum constraints explicitly. The method is based on classical phase space integration for the intermonomer modes of the cluster with imposition of the constraints of selected total energy and total angular momentum. It achieves considerable efficiency via essentially analytic evaluation of the momentum space integrals coupled with efficient Monte Carlo sampling of configurations. The derivation for the equation for the density of states is outlined and all steps in the simplification of the accessible momentum space volume are detailed. The method is tested rigorously against an entirely analytic result obtained for the ideal case of a dimer with spherical top fragments and no interaction potential. Interstellar applications of the new approach are presented for (HCN)2 and (CO)2. The new intermononmer density of states has been integrated over metastable states to obtain the intermonomer partition function, which in turn is used to calculate the metastable equilibrium constants for interstellar clusters, which in turn is used tocalculate the second order rate constant of overall dimer formation in the interstellar environment. Atmospheric applications of the new approach are presented for (H2O)2. The new intermonomer density of states is convoluted with the intramonomer density of states to obtain the convoluted density of states. This convoluted density of states is then integrated over total energy and angular momentum to obtain the anharmonic partition function, which in turn is used to calculate the equilibrium constant for atmospheric clusters, which in turn is used to calculate the third order rate constant for overall dimer formation in the atmospheric environment. Kinetic quantities are also calculated with the intermonomer and convoluted density of states for interstellar and atmospheric clusters, respectively. These densities of states are combined with RRKM theory to compute unimolecular dissociation rate constants, which are then averaged with respect to the thermal capture flux distribution to compute average lifetimes as a function of temperature.

Reaction rate data at 50oC was generated in a batch reactor over a wide range of initial concentrations in the reaction mixture. In each case the reaction was allowed to reach equilibrium. Equilibrium conversion data clearly indicated that it is important to consider the non-ideality of the system. The NRTL activity model proved to be the most suitable model to calculate the activity based equilibrium constant, as the percentage standard deviation of the equilibrium constant calculated in this manner was only 7.6% for all the different experiments as opposed to 17.8% when the equilibrium constant was based on concentration. The NRTL parameters used were obtained from Gmehling&Onken (1977) who determined the parameters from vapour liquid equilibrium. The Langmuir-Hinshelwood kinetics proposed by Song et al. (1998) and Pöpken et al. (2000) provided an excellent representation of the reaction rate over a wide concentration range with an AARE of 6% and 5% respectively. It was shown that when the NRTL activities were used in the rate expression that a power law model provided a similarly accurate prediction of the reaction rate (AARE = 4.1%). When the Eley-Rideal reaction expression (in terms of the adsorption of methanol and water) was used, a slight improvement was achieved (AARE = 2.4%). As both the Langmuir-Hinshelwood and Eley-Rideal models require separate experiments for the measurement of adsorption constants, it seems that the activity based power law model should be the kinetic expression of choice. It can be concluded that a two parameter activity based rate expression predicts the reaction rate with similar accuracy as the multi-parameter adsorption models. This indicates that it is not necessary to know the concentration on the resin surface (adsorption models) or in the resin gel (absorption models) when describing the reaction rate as long as the bulk liquid phase activities can be adequately described. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted