Browsing by Author "Casimiro, Filipa M."
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- Determinação experimental do equilíbrio líquido-vapor em misturas com relevância na indústria das biorrefinariasPublication . Casimiro, Filipa M.; Ferreira, Olga; Pinho, Simão; Pereira, CarlaAs biorrefinarias de segunda geração incluem o tratamento de diversos compostos orgânicos oxigenados tais como álcoois, ésteres, açúcares e ácidos carboxílicos, cujas misturas apresentam um equilíbrio de fases altamente não-ideal. Neste contexto, são fundamentais novos dados experimentais para o desenvolvimento de modelos termodinâmicos mais robustos que explicitamente levam em consideração os efeitos associativos. Com a finalidade de obter informação para aperfeiçoar estes métodos, neste trabalho utilizou-se uma célula de recirculação dinâmica para a medição experimental do equilíbrio líquido-vapor (ELV) de misturas binárias de acetato de isopropilo e um álcool (1-propanol, 2-propanol, 1-butanol ou 2-butanol), à pressão constante de 101,32 kPa. Na literatura, existem apenas alguns conjuntos de dados disponíveis relativos ao sistema acetato de isopropilo + 2-propanol. As misturas de acetato de isopropilo + 2-propanol e acetato de isopropilo + 1-propanol apresentam comportamento azeotrópico, enquanto as restantes são misturas zeotrópicas. A aplicação de vários testes de consistência termodinâmica (teste de Herington, teste de Van Ness, teste da diluição infinita e teste dos componentes puros) mostrou a elevada qualidade dos dados. Para todas as misturas binárias, obteve-se o fator global de qualidade máximo (igual a um), com exceção do sistema binário acetato de isopropilo + 1-butanol, com um fator global de qualidade de 0,92. Tanto os modelos NRTL e UNIQUAC são capazes de representar adequadamente os dados experimentais, com desvios médios absolutos na composição da fase vapor e na temperatura de δy = 0,019 e δT = 0,15 K, respetivamente. O modelo UNIFAC modificado (Dortmund) é capaz de prever o ELV, com δy = 0,009 e δT = 0,34 K. Neste modelo, os maiores desvios são observados no sistema acetato de isopropilo + 2-propanol, apresentando um desvio médio em relação à composição de vapor e à temperatura de δy = 0,014 e δT = 0,59 K, respetivamente. Os dados de ELV isobáricos obtidos neste estudo, e os parâmetros de interação binária estimados, são informação fundamental para o projeto e otimização de processos de separação, como a destilação, no intuito de obter de forma eficiente os compostos puros.
- Enhancing trans-resveratrol topical delivery and photostability through entrapment in chitosan/gum Arabic Pickering emulsionsPublication . Sharkawy, Asma; Casimiro, Filipa M.; Barreiro, M.F.; Rodrigues, AlírioThe surfactant-free nature and higher stability of Pickering emulsions make them preferable solutions over conventional emulsions for skin applications. In this work, Pickering emulsions stabilized by chitosan/gum Arabic (CH/GA) nanoparticles were tested as vehicles for trans-resveratrol topical delivery. Skin absorption was examined ex vivo using Franz diffusion cells and porcine skin. Pickering emulsions allowed higher cutaneous retention and lower permeation of resveratrol, in comparison with a control solution based on a 20% v/v ethanol. The total amount of resveratrol retained in the skin, 24 h after the application, was 11.60% and 10.82% of the applied dose for the tested Pickering emulsion-based formulations prepared with 0.5% and 1.5%w/v CH/GA nanoparticles, respectively. In contrast, resveratrol skin retention from the control solution was only 2.86%. Confocal laser scanning microscopy revealed enhanced skin deposition of Nile Red to deeper layers from the Pickering emulsionbased formulations. Moreover, Pickering emulsions led to trans-resveratrol photostability increase, as measured after exposure to UV for 4 h. These results show that the CH/GA Pickering emulsions are promising solutions for the topical delivery of trans-resveratrol and have the potential to be used as green cosmetic products.
- Hardwood and softwood lignins from sulfite liquors: structural characterization and valorization through depolymerizationPublication . Casimiro, Filipa M.; Costa, Carina A.E.; Vega-Aguilar, Carlos; Rodrigues, AlírioThis work aims to evaluate the structural characteristics and study the oxidative depolymerization of lignins obtained from hardwood and softwood sulfite liquors. Lignins were obtained after ultrafiltration and freeze- drying of the sulfite liquors and characterized based on inorganic content, nitrobenzene oxidation, 13C NMR, and molecular weight determination. The structural characteristics achieved allow evaluating the potential of each lignin through oxidative depolymerization to produce added-value phenolic monomers. Hardwood and softwood lignins were submitted to alkaline oxidation with oxygen and the reaction conditions optimized to obtain a final oxidation mixture with the maximum yield of phenolic monomers. Through oxidation with O2, hardwood lignin generates mostly syringaldehyde while lignin from softwood biomass mainly produces vanillin; moreover, a lower reaction time and the interruption of O2 admission avoid the degradation of the oxidation products in the final mixture for both lignins, more evidenced to hardwood lignin due to its higher reactivity. From the results, it is possible to conclude that a phenolic aldehyde-rich oxidation mixture could be obtained, confirming the viability of lignin as raw material to produce added-value products as vanillin and syringaldehyde.
- Kinetics of oxidative degradation of lignin-based phenolic compounds in batch reactorPublication . Casimiro, Filipa M.; Costa, Carina A.E.; Botelho, Cidália; Barreiro, M.F.; Rodrigues, AlírioVanillin, vanillic acid, acetovanillone, syringaldehyde, syringic acid, and acetosyringone are products obtained from lignin oxidation in an alkaline medium. The evaluation of their individual degradation under oxidation conditions mimicking lignin oxidation is an important tool to better understand this reaction and maximize the yield of target value-added products. In this context, the main objective of the present work was to study the kinetics of degradation of the selected ligninbased phenolic compounds. The effect of temperature, initial concentration, and oxygen partial pressure was evaluated, and a simple mathematical model was developed to describe the data from the degradation of the phenolics during oxidation reactions. The results indicate that, for all the evaluated compounds, the reaction order is first order with respect to both the initial phenolic compound concentration and oxygen concentration. A high degradation rate was found for the reactions performed at 413 K, and an activation energy in the range of 53−86 kJ/mol was found for all the studied phenolic compounds. Moreover, syringic acid is the phenolic compound more prone to degradation, while vanillin is the less one.
- Lignin valorization for added-value chemicals: kraft lignin versus lignin fractionsPublication . Costa, Carina A.E.; Casimiro, Filipa M.; Rodrigues, Alírio; Vega-Aguilar, CarlosLignin is a raw material that can potentially be converted into valuable compounds through depolymerization reactions in addition to its use as a polymer or material. However, the chemical recalcitrance and the heterogeneous composition and structure of lignin make it challenging to establish processes that add value to this complex aromatic biopolymer. In this work, solvent fractionation was applied to obtain lignin fractions with a narrowed molecular weight and specific structural characteristics, improving its homogeneity and purity. A kraft lignin was submitted to fractionation using different ratios of acetone, ranging from 60 to 15% v/v, in aqueous mixtures. The composition, structure, and molecular weight of each fraction were studied and their potential applications were evaluated. The most water-soluble fraction has more phenolic OH, less aliphatic OH groups, and shows the lowest content of aryl-ether linkages, which is in accordance with its highest degree of condensation. On the other hand, the insoluble fraction from the mixture with 60% of acetone has the lowest molecular weight and the highest content of inorganic material. Radar plots were applied for lignin fractions evaluation and the fraction with the highest potential (IF 30:70) was submitted to alkaline oxidation with O-2. The results were compared with the products yielded from kraft lignin. An increase of about 13 and 19% was found for vanillin and syringaldehyde, respectively, when the fraction IF 30:70 was submitted to oxidation. In conclusion, the proposed fractionation process showed to be an effective method to obtain lignin fractions with specific composition and structural characteristics that could improve its potential as a source of high added-value monomeric phenolic compounds.
- Vapor–liquid equilibrium of binary mixtures containing isopropyl acetate and alkanols at 101.32 kPaPublication . Casimiro, Filipa M.; Constantino, Dânia S.M.; Pereira, Carla S.M.; Ferreira, Olga; Rodrigues, Alírio; Pinho, SimãoIsobaric vapor-liquid equilibria of binary mixtures of isopropyl acetate plus an alkanol (1-propanol, 2-propanol, 1-butanol, or 2-butanol) were measured at 101.32 kPa, using a dynamic recirculating still. An azeotropic behavior was observed only in the mixtures of isopropyl acetate + 2-propanol and isopropyl acetate + 1-propanol. The application of four thermodynamic consistency tests (the Herington test, the Van Ness test, the infinite dilution test, and the pure component test) showed the high quality of the experimental data. Finally, both NRTL and UNIQUAC activity coefficient models were successfully applied in the correlation of the measured data, with the average absolute deviations in vapor phase composition and temperature of 0.01 and 0.16 K, respectively.