ESTiG - Dissertações de Mestrado Alunos
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- Adsorção de dióxido de carbono em zeolita NaY "binder-free"Publication . Pires, Marcella Golini; Golini Pires, Marcella; Silva, José A.S.Diante do cenário de grande desenvolvimento da industrialização mundial nas últimas décadas e as consequências geradas por tal fato, sendo observadas atualmente pelo aumento significativo da concentração de dióxido de carbono (CO2) e outros gases de efeito estufa na atmosfera, que são bastante prejudiciais ao meio ambiente, tem ocorrido a mobilização de empresas, as quais vem investindo fortemente em pesquisas e alternativas capazes de capturar e armazenar o CO2 e também a sua separação de correntes contendo N2 e H2. Uma das possibilidades encontradas mais viáveis, do ponto de vista do baixo custo de energia empregado e do baixo custo econômico envolvido, tem sido utilizar processos de adsorção em zeólitas binder-free comerciais. A permuta iônica em zeólitas é bastante importante pois permite aumentar a eficiência dos processos de adsorção com zeólitas, através de alterações no equilíbrio e cinética de adsorção de vários compostos, como o CO2, e a sua seletividade de separação de uma forma energeticamente eficiente. Nesse aspecto, o presente trabalho foi dedicado a estudar a zeólita NaY binder-free comercial para a captura do CO2, utilizando o processo de adsorção, em que foram realizados estudos do equilíbrio de adsorção por cromatografia gasosa através de curvas de ruptura, em leito fixo, para componente único puro CO2, a fim de obter suas isotérmicas de adsorção nas temperaturas de 313, 333 e 353 K, com pressões parciais na faixa entre 0,1 e 3,5 bar. Os resultados experimentais mostraram que as maiores capacidades de adsorção de CO2 pela zeólita NaY binder-free comercial foram obtidas a 3,5 bar, sendo a carga de CO2 a 313 K igual a 6,52 mol/Kg. Enquanto que, à mesma pressão, a carga de CO2 a 333 K é igual a 5,85 mol/Kg e a 353 K é igual a 5,15 mol/Kg. Os dados de equilíbrio de adsorção foram melhor ajustados e representados pelo modelo Dual-Site Langmuir, uma vez que apresentou um valor de coeficiente de determinação R2=0,9996, capacidade de adsorção total igual a 7,12 mol/Kg e entalpia de adsorção Δ𝐻𝑎𝑑𝑠 variando entre -29,21 KJ/mol e -51,71 KJ/mol.
- Catalytic application of carbon nanotubes obtained from plastic solid waste in the removal of quinoline from isooctane by selective oxidation with hydrogen peroxidePublication . Piccinin, Larissa; Gomes, Helder; Vieira, Admilson Lopes; Díaz de Tuesta, Jose LuisDifferent carbon nanotubes were tested in two-phase oxidative processes using hydrogen peroxide as oxidant in order to remove and degrade a model contaminant, quinoline, from isooctane, which simulated contaminated fossil fuels. The CNTs were produced by chemical vapor deposition (CVD) from different polymers. The use of low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP) and a mixture of these three in the proportion of 35:25:40, respectively, resulted in the CNTs defined as CNT LDPE 600, CNT LDPE 800, CNT HDPE 800, CNT PP 800 and CNT MIX 800, where 600 or 800 represent the temperature of pyrolysis considered in the synthesis. The use of such polymers simulated the production of CNTs from residual plastic. Prior to the biphasic oxidation runs, the organic phase underwent oxidation tests, being concluded that isooctane was not oxidized under the conditions used. Possible adsorption on the materials was also tested in the organic phase and in the biphasic medium. In both cases no significant adsorption was obtained. The produced CNTs were tested as catalysts in the oxidative processes of hydrogen peroxide in aqueous solution (CWPO) and in the biphasic medium. The performance of each material was analyzed in 24-hour reaction tests, at 80 °C, through monitorization of H2O2 degradation, quinoline concentration in oily and aqueous media, total organic carbon concentration, aromatics concentration in oily and aqueous media, and pH measurement. In addition to the tests carried out with the CNTs produced, a commercial CNT was also tested for comparison. Finally, all catalysts used fulfilled the proposed objective, 100% of quinoline being removed from the oily phase in the biphasic oxidation runs, up to 8 h of reaction, and degrading 100% of the contaminant by CWPO in 4 h. Other analyses revealed a complete degradation of H2O2 with all CNTs in the CWPO tests and in the biphasic oxidation runs, except for the commercial CNT in the biphasic oxidation run. The analysis of TOC and aromatics concentration show significant decreases with all tested carbon nanomaterials, while pH had a slight decrease in the CWPO runs and an increase in the biphasic oxidation runs. In summary, all carbon materials produced were efficient in the proposed process and are comparable to the performance obtained by the commercial CNT.
- Composição química e atividade biológica de bagas do Zimbro (Juniperus communis L.)Publication . Bacém, Isabel; Amaral, Joana S.As bagas do zimbro (Juniperus communis L.) são tradicionalmente utilizadas em Trás-os-Montes como condimento em pratos de carne de caça, com o objetivo de lhes conferir um aroma e sabor particulares. São ainda utilizadas na aromatização de bebidas, tais como o gin e bebidas tradicionais. As bagas estão também descritas como tendo propriedades medicinais, com especial ênfase para as suas atividades diurética e antisséptica. Neste trabalho estudou-se a composição química de três amostras de bagas do zimbro, uma colhida na natureza e duas adquiridas comercialmente (vendidas como condimentos alimentares em supermercados), no que respeita à sua composição nutricional (proteínas, gordura, hidratos de carbono, humidade e cinzas), ácidos gordos e compostos bioativos. A composição em ácidos gordos foi determinada por cromatografia gasosa com detetor de ionização em chama (GC-FID). A determinação do teor de fenóis totais, flavonóides totais, poder redutor e atividade antioxidante pelo método do DPPH, para os extratos metanólicos das três amostras de bagas e de uma amostra de folhas colhidas na natureza, foi realizada utilizando métodos espetrofotométricos. Por último, para uma amostra de óleo essencial de bagas do zimbro, realizaram-se ensaios de atividade antimicrobiana face a diversas bactérias gram-positivas e gram-negativas e uma levedura. Verificou-se a ocorrência de teores superiores de fenóis totais e flavonoides nas folhas comparativamente às bagas, bem como uma superior capacidade antioxidante dos extratos de folhas, expressa em capacidade captadora do radical DPPH e poder redutor. O óleo essencial revelou capacidade de inibir o crescimento de Candida albicans, Bacillus cereus, B. subtillis, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae e Enterococcus faecalis, não apresentando, contudo, atividade face a Pseudomonas aeruginosa e Proteus mirabilis nas concentrações testadas. Os resultados obtidos contribuem para o conhecimento mais aprofundado das bagas do zimbro e sugerem que o seu uso como condimento pode ser benéfico no que respeita a qualidade e segurança alimentar.
- Determination of kinetic parameters using Rancimat analysisPublication . Ouarouer, Yosra; Peres, António M.; Pereira, J.A.; Zaghdoudi, KhalilThe physicochemical quality parameters, the total phenols contents and the oxidative stabilities at 120 to 160 ºC of commercial extra-virgin olive oils were assessed, allowing to confirm the quality grade as well as to group them according to the total phenols contents as low (88±7 mg CAE/kg), medium (112±6 mg CAE/kg) and high (144±4 mg CAE/kg) phenols levels. The results pointed out that oils with higher total phenols contents were more thermally stable. Kinetic and thermodynamic parameters were determined using the activated complex/transition-state theory, showing that their values did not significantly differ for the two highest total phenols contents, suggesting a hypothetically threshold saturation of the beneficial effect. High total phenols content would imply a significant more negative temperature coefficient, higher temperature acceleration factor, greater activation energy and frequency factor, higher positive enthalpy of activation, lower negative entropy of activation and greater positive Gibbs free energy of activation. The results confirmed that the lipid oxidation was a non-spontaneous, endothermic and endergonic process with activated formed complexes structurally more ordered than the reactants. A negative deviation from the Arrhenius behavior was observed for all oils being the super-Arrhenius behavior more marked for oils with lower total phenols contents.
- Development of functional finishes based on natural products for leather applicationsPublication . Colucci, Giovana; Barreiro, M.F.; Fernandes, Isabel P.; Sipoli, Caroline CasagrandeNanoemulsions are biphasic systems characterized by having droplets with nanometer size range, which confers them several advantages, such as high hydration capacity and increased bio-efficacy of the functionalities incorporated therein. In this context, the objective of this work was to develop a water-in-oil (W/O) nanoemulsion system based on natural compounds, like sweet almond oil and Cinnamomum zeylanicum aqueous extract, in order to produce a moisturizing and antimicrobial spray for leather application. Firstly, a systematic study was performed by testing different base formulations to establish the procedure for nanoemulsion preparation using a high-pressure homogenizer (HPH). A total of 16 base formulations were prepared by varying the W/O ratio and emulsifier composition. These samples were then analyzed by microscopic and visual analysis in order to evaluate the droplets size and morphology together with stability along the time. Based on these results, the best formulation revealed to be the system S4, corresponding to a W/O ratio of 40/60 (v/v), and Span 80/Tween 80 mixture (54/46 ratio, v/v) as emulsifier. Using this formulation, nanoemulsions functionalized with cinnamon at contents of 1.25%; 2.5%; 3.75%; 5% (w/v; water base) were prepared. Afterwards, these products, together with the base system, were characterized by Confocal Laser Scanning Microscopic (CLSM), color parameters, evaluated concerning the antimicrobial and antioxidant bioactivities, and stability. As results, CLSM confirmed the nature of the water-in-oil system, revealing also a change in the nanoemulsions microstructure due to the increase of cinnamon extract concentration. The color measurement evidenced a luminosity diminishing and a color variation to yellow and red as the extract content was increased. In addition, the formulations containing the cinnamon extract evidenced antimicrobial and antioxidant activity. The absence of bioactivity for the base nanoemulsion corroborated the effect of the cinnamon extract in the detected antimicrobial and antioxidant. Furthermore, for the antimicrobial activity, the formulations containing the extract presented a prolonged effect against E. coli and S. aureus bacteria, being detected similar inhibition zones for all the tested extract concentrations. Regarding the antioxidant activity, the rise in the extract concentration resulted in a relevant increase of this property. Finally, and according to the performed accelerated stability tests, a high stability against centrifugation for the base nanoemulsion was detected, evidencing that the presence of the extract contributes to the formulation instability. Beyond this, all the formulations showed high stability against thermal stress. From a general perspective, the results obtained are of great importance for the product design and development having in view the application as leather preservative and moisturizer, since the formulations presented antioxidant and antimicrobial activity, parameters that contribute to the protection and preservation of the shoes. In addition, their stability points for a good shelf life of these systems, being suitable for storage under commercialization conditions.
- Evaluation of new carbon-coating methods for the development of magnetic nanoparticles targeted for biomedical applicationsPublication . Magallanes, Nerea Seoane; Gomes, Helder; Triviño, Jose Luis Díaz de TuestaNanoscience has recently experienced a strong development, Magnetic Nanoparticles (MNPs) are one of the most attractive nanomaterials. Focusing on the biomedical applications, this thesis has as main objective the development of new carbon coating methods in order to reach the maximum biocompatibility of MNPs upon synthesis. During the research carried out, two different approaches were evaluated to coat a magnetic core composed of magnetite, using phloroglucinol and glyoxal, following the idea of making the process more sustainable and biocompatible. The difference between those approaches resides on the use of PF-127 as porogen agent during the coating step. However, some significant differences were found for the material synthesized without PF-127 as porogen agent, with the most important one being the lack of stabilization in water, a crucial characteristic of MNPs for biomedical applications. This mishap leaded to the continuation of the methodology development with just one material. The material selected was evaluated as nanocarrier to load and deliver drugs using doxorubicin (DOX) and omeprazole (OME). The delivery was tested at different pH values in order to evaluate its influence, as human body has different pH in a normal tissue (pH 7.4) than in the intracellular tumor environment (pH 4.5) or in its surroundings (pH 6.0).
- Microencapsulation using alginate systems: spray-coagulation versus superhydrophobic surfaces approachPublication . Cuma, Diana Francisco; Barreiro, M.F.; Fernandes, Isabel P.The use of biopolymers such as alginate has been growing in the last decades due to properties such as biocompatibility, non-toxicity and biodegradability. In this work the microencapsulation of a hydrophobic (curcumin) and a hydrophilic (safranin), used as model compounds with alginate matrices, was studied by comparing two encapsulation methods (spray coagulation and superhydrophobic surfaces) and by testing three calcium sources (calcium chloride, calcium gluconate and calcium lactate) to promote the alginate ionic crosslinking. The microspheres obtained through the spray/coagulation technique were characterized in terms of load, encapsulation efficiency and rehydration capacity. The release profiles of both active principles were evaluated. The results revealed that when calcium chloride is used a higher encapsulation efficiency was obtained (99.25% and 98.50%, respectively for curcumin and safranin), followed by calcium gluconate (98.45% and 97.55 for curcumin and safranin) and finally calcium lactate (97.91% for curcumin and 97.42 for safranin). Regarding the release profile, a lower release was achieved, for both compounds, when calcium chloride was used (5.70% of curcumin in ethanol medium, and 4.15% of safranin in distilled water), followed by the calcium gluconate crosslinked microspheres (8.3% for curcumin and 4.42% for safranin). Calcium lactate crosslinked microspheres give rise to the systems with higher release (12.1% for curcumin and 4.76% for safranin). The microspheres had a spherical conformation and the larger particle size (volume distribution) was obtained with the calcium gluconate-based systems (131.46, 78.85 and 91.46 μm for curcumin, safranin and empty microspheres, respectively). The calcium chloride-base systems give rise to the smallest ones (91.65, 60.10 and 80.31 μm, respectively for curcumin, safranin and empty microspheres). Through Fourier Transform Infrared Spectroscopy the contribution of the calcium source and the active principle on the microspheres spectra was identified, and thermogravimetric analysis evidenced an increasing of the thermal stability due to the alginate crosslinking effect, particularly when calcium chloride was used. Regarding the comparison of the two microencapsulated systems, the superhydrophobic surfaces showed a good performance having in view the encapsulation with alginate systems, since no loss of the active principle to the surface during the process was observed (qualitative analysis). This constitute an advantage particularly for the case of the hydrophilic active principles.
- Modelação e simulação matemática da adsorção em leito fixo. Aplicação à adsorção de CO2 em Zeólito 4APublication . Páscoa, Ângela Patrícia Coelho; Silva, José A.C.; Almeida, João P.A aplicação da adsorção como um meio de separar misturas é hoje considerada uma técnica competitiva entre outras clássicas como a destilação, extracção, etc. O método recorre geralmente à coluna de adsorção contendo um sólido microporoso com propriedades específicas para separar as misturas em causa. Nesse aspecto, a presente dissertação foi dedicada à formulação de um modelo matemático para simular o comportamento de adsorção de misturas gasosas que fluem através de um leito fixo contendo adsorventes microporosos. Determinou-se a solução numérica das equações diferenciais parciais acopladas dos balanços de massa e energia resultantes do modelo, através da aplicação do método numérico das linhas (MOL) em linguagem de programação MATLAB. Os parâmetros físicos do modelo foram determinados com base em resultados de equilíbrio e cinética de adsorção e também de correlações disponíveis na literatura. O efeito dos vários parâmetros do modelo também foi estudado através de exemplos numéricos de simulação como: Dispersão axial no leito, resistência à transferência de massa através do modelo "Linear Driving Force - LDF", e tipo de isotérmica de adsorção. Finalmente o modelo foi validado com a solução numérica de várias experiências de adsorção do CO2 em zeólito 4A em leito fixo.
- Selective denitrification by peroxidation of 4-nitrophenol using Janus-structured amphiphilic carbon nanotubesPublication . Sanches, Flávia Kim; Gomes, Helder; Triviño, Jose Luis Díaz de Tuesta; Pricila, PricilaIndustrial pollution has grown a lot in recent times, mostly formed by oily compounds, affecting not only the environmental but also human health. As the concern increases, so does the search for effective treatment, a few years the use of different nanostructure porous carbon materials are being used in catalysis. Therefore, in this work carbon nanotubes (CNTs) were tested as catalysts in the selective denitrification of oily wastewater containing 4-nitrophenol (4-NP) by catalytic wet peroxide oxidation (CWPO). The CNTs were prepared by chemical vapor deposition, feeding sequentially ethylene (E) and/or acetonitrile (A) during different times until 20 min, resulting in samples E20, E15A5, E10A10, E5A15, E1A19 and A20, the number denoting the time feeding of each precursor and the order of appearance of the letter indicating the order of each precursor. The synthesized CNTs were tested in the CWPO of 4-NP in aqueous solutions and in simulated oily wastewater (2,2,4-trimethylpentane and water) at 80 ºC, initial pH = 3.5, C4-NP = 1 g/L, CH2O2 = 3.56 g/L, and Ccatalyst = 2.5 g/L. The catalysts A20, E1A19 and E5A15 promoted a faster decomposition of H2O2 and a lower degradation of 4-NP in the aqueous system, whereas the catalysts E20, E15A5 and E10A10 (more hydrophobic character than previous ones) displayed the opposite trend, since E20 was able to remove 99% of the pollutant and A20 only 69% after 8 h of reaction. E15A5 and E10A10 catalysts were able to remove 100% of 4-NP after 24 h of reaction. In biphasic L-L media all catalysts presented a great conversion of 4-NP after 24 h of reaction. E15A5, E10A10 and E1A19 catalyst allow to completely remove 4-NP and E5A15, A20 and E20 led to obtain a removal of 99%, 99% and 98%, respectively. Besides that, the aromaticity was also measured for comparation of materials. The lower concentration of aromatic intermediates was obtained E15A5 and E10A10 (126.34,249.10 mg/L, respectively), and lower pH (2.42, 2.38, respectively), which supports the formation of carboxylic acids. The highest removals conversions obtained with E15A5 and E10A10 is ascribed to the capacity to stabilize Pickering emulsions by E15A5 and E10A10. The amphiphilic characteristic of this material ensures a closer contact between the liquid phases, allowing higher mass transfer.
- Sustainable polymer solutions through biomass liquefaction processesPublication . Bourogaa, Intissar; Barreiro, M.F.; Fernandes, Isabel P.; El Aissi, RadhiaIn a context of better management of land resources and development of renewable biomass-based chemicals, lignin offers excellent alternative to replace certain fossil-based derivatives. Through the integration of green chemistry into biorefineries, and the use of low environmental impact technologies, we can establish future supply chains for genuinely green and sustainable chemical products. Indeed, lignin can be converted into polyols via several processes, mainly liquefaction. Liquefaction is considered an efficient method to generate polyols with high content of reactive hydroxyl groups. These final products can be used as raw materials for polymer synthesis, like in the production of polyurethanes and polyesters. In our study this alternative has been adopted; namely by using conventional heating system and microwave heating. The difference between the two is essentially based on energetic terms, given that liquefaction processes are usually carried out at high temperatures, using different types of liquefaction solvents and in the presence of acid catalysts. The use of microwave heating system has various advantages in terms of speed and consumed energy. The objective of this study was to compare the liquefaction of sodium lignosulphonate lignin by conventional heating system and microwave system. The liquefaction was carried out using polyethylene glycol (Mw 400) and glycerol as solvents, and sulphuric acid as catalyst, and the conversion yield determined, aiming at achieve the best liquefaction conditions. In fact, several process conditions were tested namely the catalyst content (1, 2 and 3%, (w/w, solvent-basis) and liquefaction temperature (140, 160 and 180°C). The obtained polyols were characterized in terms of their most relevant technical properties: hydroxyl number (IOH), viscosity, and unreacted biomass. The chemical structure, which was evaluated by Fourier Transform Infrared analysis (FTIR) was also checked. Finally, the properties of the generated polyols were compared in order to evaluate the efficiency of both systems.