Modelagem da atividade de agua usando metodos de contribuição de grupos

Orientador: Antonio Jose de A. MeirellesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosResumo: A atividade de água (aw) é uma propriedade físico-química definida como a razão entre a pressão parcial da água numa amostra e a pressão de vapor da água na mesma temperatura. É importante na área de alimentos, já que muitas das reações químicas, enzimáticas e microbiológicas que influenciam a estabilidade do alimento são dependentes da quantidade de água disponível no meio. Modelos termo dinâmicos de contribuição de grupos têm sido usados para correlacionar e predizer a atividade de água em soluções contendo compostos bioquímicos de interesse. Entretanto, poucos dados estão disponíveis na literatura para esses sistemas. Neste trabalho, as atividades de água de algumas soluções binárias e ternárias relacionadas com alimentos foram medidas com um higrômetro elétrico e modeladas usando os métodos de contribuição de grupos ASOG e UNIFAC. Os solutos utilizados foram: polietilenoglicóis, polióis, aminoácidos e maltodextrinas. Usando dados experimentais medidos neste trabalho e dados da literatura, os parâmetros de interação entre os grupos característicos de cada soluto foram estimados. Para os sistemas contendo maltodextrinas e nas soluções contendo aminoácidos, o fenômeno de dissociação parcial foi considerado e o modelo UNIFAC, combinado com equações de solvatação, foi empregado nas predições de aw e pH. A validade do método foi testada para os aminoácidos em água e dois sistemas tampão. Desvios médios de 0,62% para a atividade de água e 2,49% para o pH foram obtidos. Para os sistemas contendo polietilenoglicóis, um novo grupo específico [CH2CH2O] dessas moléculas foi incluído no conjunto de parâmetros dos modelos ASOG e UNIFAC. As correlações com os modelos UNIFAC e ASOG forneceram, respectivamente, um desvio médio de 0,545% e 1,499% entre as atividades de água calculadas e as experimentais. Por outro lado, as predições de aw para as soluções poliméricas de maltodextrinas usando parâmetros da literatura ajustados para soluções de açúcares em água, não foram satisfatórias. As correlações obtidas para os polióis apresentaram boa concordância com os dados experimentais quando a divisão de grupos CHnOH (n=l ou 2) proposta na literatura foi empregada no modelo UNIFAC. O modelo ASOG, por outro lado, apresentou desvios mais altos nesses sistemas se comparados com os do modelo UNIFAC quando os parâmetros dos grupos POH foram reajustados. Os resultados obtidos foram satisfatórios e indicam que ajustes de alguns parâmetros de interação dos modelos termodinâmicos estudados melhoram as correlações assim como as predições da atividade de água em sistemas contendo solutos da área de alimentosAbstract: Water activity (aw) is a physicochemical property defined as the ratio between partial pressure of water in a sample and the vapor pressure of pure water at the same temperature. It is important in food engineering since many chemical, enzymatic and microbiological reactions which influence food stability are dependent on the availability of water. Thermodynamical models of group-contribution have been used to correlate and predict the water activity in solutions containing biochemical solutes of interest in food engineering. However, few data are available in the literature for these kinds of systems. In this work, the water activities of some binary and ternary food-related solutions were measured with an electric hygrometer and modeled using the group-contribution methods ASOG and UNIF AC. The solutes used were poly (ethylene glycol)s, polyols, amino acids and maltodextrins. Using own experimental data and some data obtained from literature sources, the interaction parameters between characteristic groups of these solutes were estimated. For the maltodextrins and amino acids systems, only predictions were attempted with parameters from literature. In the solutions containing amino acids, the partial dissociation phenomenon was considered and the UNIF AC model, combined with solvation equations, was used for the water activity and pH predictions. The validity of the method was tested for the aminoacids in water and two buifer solutions. Mean deviations of 0.62% for the water activity and 2.49% for pH were obtained. For the poly (ethylene glycol)s systems, a new specific group [CH2CH2O] was included in the set of parameters for the ASOG and UNIF AC models. The correlations with the UNIFAC and ASOG models provided, respectively, a 0.545% and 1.499% mean deviation between experimental and calculated aw values. Otherwise, the aw predictions for the maltodextrin systems using literature parameters fitted for sugar solutions, were not good to represent the aw lowering behavior of these polymers. The correlations obtained for polyols were in good agreement with experimental data when the groups Ca,OR (n=l ou 2) proposed in the literature were used for the correlations in the UNIFAC model. The ASOG method provided higher deviations in these systems than the UNIFAC model when the groups POR (OR bounded to consecutive carbon atoms) were fitted. The results obtained were satisfactory and they indicate that the adjustments of some interaction parameters for the thermodynamical models, improve the correlations as well as prediction capability of water activity in the food-related systems studiedMestradoMestre em Engenharia de Alimento

Job of method of contribution of groups in the calculation and prediction of fisi-quimicas properties

Orientador: Antonio Jose de Almeida MeirellesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosResumo: Métodos de contribuição de grupos têm sido ferramenta útil no cálculo de coeficientes de atividade nos mais variados sistemas. Em sistemas aquosos, e mais especificamente naqueles que possuem compostos biológicos como açúcares, arninoácidos, sais orgânicos, polímeros, etc., o uso de métodos de contribuição de grupos para a correlação e predição do equilíbrio de fases tem crescido nos últimos anos. Em alimentos e em biotecnologia, os sistemas são geralmente multicomponentes e por essa razão, a aplicação de métodos de contribuição de grupos torna-se atraente partindo-se do princípio que, de posse dos parâmetros de interação entre grupos, é possível calcular propriedades de sistemas mais complexos a partir de parâmetros obtidos da correlação a dados experimentais de sistemas mais simples. Neste trabalho, os métodos de contribuição de grupos ASOG, UNIF AC, VERS e UNIMOD foram empregados em diferentes sistemas para a correlação e predição de propriedades fisico-químicas. Os compostos estudados foram: polióis, aminoácidos, maltodextrinas e polietileno glicóis (pEG)s, sendo os três primeiros compostos geralmente encontrados em sistemas alimentícios, e o PEG é bastante utilizado em sistemas aquosos bifásicos para o estudo do equilíbrio e separação de biomoléculas. Propriedades fisico-químicas como atividade de água, solubilidade, depressão do ponto de congelamento, pH, espalhamento de luz, entalpia de diluição e viscosidade, são algumas das propriedades determinadas e/ou retiradas da literatura usadas para a correlação e predição empregando os modelos acima citados. A intenção deste trabalho foi então, testar os métodos de contribuição de grupos para o cálculo de propriedades fisico-químicas tratando também das particularidades de cada sistema estudado, como a dissociação parcial dos aminoácidos, o efeito de proximidade dos grupamentos hidroxilas nos polióis e a polidispersão das maltodextrinas. Também são apresentados resultados da correlação e predição de viscosidades de sistemas aquosos contendo PEGs por um modelo semi-empírico que não trata da contribuição de grupos mas considera a hidratação das moléculas desses polímeros em meio aquosoAbstract: Group contribution methods have been used as a useful tool for calculating activity coefficients in different types of systems. In aqueous systems, specifically those containing biological compounds such as sugars, amino acids, organic salts, polymers, etc., the use of group contribution models for correlating and predicting phase equilibrium has increased in the last years. In the food and in the biotechnology areas, the systems are generally multicomponent, and for this reason, the use of group-contribution methods becomes an attractive tool considering the possibility of calculation of properties in complex systems with parameters adjusted for simple ones. In this work, the group-contribution models ASOG, UNIF AC, VERS and UNIMOD were utilized in different types of systems for the correlation and prediction of physical chemical properties. The studied compounds were: polyols, amino acids, maltodextrins and polyethylene (glycols) (pEG)s, which the first three compounds are found in food systems, and PEGs are wide used in aqueous-two-phase systems to study equilibrium and separation of biomolecules. Physical-chemical properties such as water activity, solubility, fteezing point depression, pH, light scattering, enthalpy of dilution and viscosity are some of the properties experimentally determined and/or found in literature used in this work for the correlation and prediction using the above cited models. Thus, the objective of this work was to test the group-contribution models for calculating physical-chemical properties considering the particularities of each system such as partial dissociation phenomena in aqueous amino acid systems, proximity effect of hydroxyl groups in polyols, and polydispersity of maltodextrins. It is also presented in this work, the results of viscosity correlation and prediction in aqueous PEG solutions by a semi-empirical equation that does not consider group contributions but take into account the hydration of the polymer molecules in aqueous mediaDoutoradoDoutor em Engenharia de Alimento

Physicochemical Properties of the System N,N-Dimethyl-dipropylene-diamino-triacetonediamine (EvA34), Water, and Carbon Dioxide for Reactive Absorption

Aqueous solutions of N,N-dimethyl-dipropylene-diamino-triacetonediamine (EvA34)are promising solvents for CO2 capture. Therefore, in the present work, a compre-hensive experimental study was carried out to determine data on physico-chemicalproperties of EvA34 and its mixtures with H2O and CO2. The liquid density and thedynamic viscosity was studied for pure EvA34, as well as for unloaded and CO2-loaded aqueous solutions of EvA34. The liquid heat capacity was studied for pure EvA34and unloaded aqueous solutions of EvA34. Furthermore, data on the vapor pressure ofpure EvA34 was recorded. The pH-value was measured for unloaded and CO2-loadedaqueous solutions of EvA34 and the dissociation constants of EvA34 were determinedfrom titration curves. Moreover, data on the solubility of CO2 in aqueous solutions ofEvA34 and data on the CO2-containing species in the liquid phase of these solutionswere recorded. Most of the new data was taken at temperatures between 293 and 393K. The mass fraction of EvA34 in the unloaded aqueous solutions was either ~ w0EvA34= 0.1 g/g or ~ w0EvA34 = 0.4 g/g. The CO2-loading was up to ~?CO2 = 6.2 mol/mol. Thenew data were compared to corresponding data of two standard amines that are usedfor CO2 capture: monoethanolamine (MEA) and a blend of methyl-diethanolamineand piperazine (MDEA/PZ). The comparison revealed that EvA34 combines favorableproperties of MEA and MDEA/PZ in one molecule

Triacetoneamine-derivates (EvAs) for CO2-absorption from Process Gases

New amines for reactive absorption of CO2 from process gases were investigated in a comprehensive experimental screening. All studied amines are derivates of triacetoneamine and differ only in the substituent of the triacetoneamine ring structure. The amines are abbreviated by the acronym EvA with a consecutive number, designating the derivate. About 50 EvAs were considered in this work from which 26 were actually synthesized and investigated in aqueous solution.The following properties were studied: solubility of CO2, rate of absorption of CO2, liquid–liquid and solid–liquid equilibrium, foaming behavior, dynamic viscosity, and acid constants. The nine most promising EvAs were evaluated with the NoVa short-cut method (Vasiliu et al., 2020). The method yields estimates for the specific energy demand and recirculation rate for a given purification task. Two typical purification tasks were considered: the CO2-removal from natural gas and from synthesis gas, respectively. Some of the EvAs showed significantly improved performance compared to monoethanolamine (MEA) and a solvent-blend of methyl-diethanolamine and piperazine (MDEA/PZ)

Speciation in CO2-loaded Aqueous Solutions of Sixteen Triacetoneamine-derivates (EvAs) and Elucidation of Structure-property Relationships

The speciation in CO2-loaded aqueous solutions of 16 different derivates of triacetoneamine (EvAs) was investigated in a comprehensive NMR-spectroscopic study. About 350 experiments were carried out for CO2-loadings up to 3 moles CO2 per mole amine, temperatures between 20 °C and 100 °C, and a mass fraction of EvA in the unloaded solvent of 0.1 g/g. The observed CO2-containing species were primary and secondary carbamates, alkylcarbonate, (bi)carbonate, and molecular CO2. Some EvAs can form zwitterions with a ring structure, which have an important influence on the speciation. From the comprehensive set of data, relationships between the chemical structure of the EvAs and the observed speciation in aqueous solution were established. These results were related to application properties of the EvAs that were taken from previous work. Based on the findings, some general guidelines for the design of new amines were derived and applied for proposing new amines for CO2-absorption

Speciation in CO2-loaded aqueous solutions of sixteen triacetoneamine-derivates (EvAs) and elucidation of structure-property relationships

The speciation in CO2-loaded aqueous solutions of 16 different derivates of triacetoneamine (EvAs) was investigated in a comprehensive NMR-spectroscopic study. About 350 experiments were carried out for CO2-loadings up to 3 moles CO2 per mole amine, temperatures between 20 °C and 100 °C, and a mass fraction of EvA in the unloaded solvent of 0.1 g/g. The observed CO2-containing species were primary and secondary carbamates, alkylcarbonate, (bi)carbonate, and molecular CO2. Some EvAs can form zwitterions with a ring structure, which have an important influence on the speciation. From the comprehensive set of data, relationships between the chemical structure of the EvAs and the observed speciation in aqueous solution were established. These results were related to application properties of the EvAs that were taken from previous work. Based on the findings, some general guidelines for the design of new amines were derived and applied for proposing new amines for CO2-absorption