Courses > Theses (Phd)

Theses (Phd) 2017

Theses (Phd) 2016

Melhoria de propriedades físicas de filmes e revestimentos comestíveis de zeína

Thesis (Phd)          05/12/2016

Talita Macedo dos Santos

The production of biodegradable materials has been increasingly studied and encouraged, due to the increased awareness of environmental risks caused by the extensive disposal of petroleum plastics, especially those used in food packaging. Zein, a protein obtained from corn gluten, is characterized by a lower hydrophilicity than other proteins, which implies a higher resistance to humidity. The general objective of this work is to study different modifications and a combination of different technologies from the zein polymeric matrix in order to obtain films with potential of use for food packaging or coating, contributing to increase of its shelf life. For the preliminary tests, the solvents ethanol (from 70 to 95%) with and without acetic acid 5% and the plasticizers glycerol and oleic acid (1:0, 2:1, 1:1, 1:2 and 0:1, total of 20%) were tested, and physical (solubility, WVP, contact angle, mechanical properties) and morphological properties (OM, SEM) were evaluated. Ethanol 80% without acetic acid was chosen as the solvent, and a ratio of 2:1 (13.3% and 6.7% of zein mass, respectively) of glycerol and oleic acid was defined for the plasticizers. In the crosslinking study with non-oxidized or oxidized tannic acid, crosslinker concentration (from 0 to 8%) and dispersion pH (from 4 to 9) were varied and physical, optical (color, opacity), chemical (FTIR) and thermal (TGA, DSC) properties were analyzed. The results showed that higher amounts of tannic acid and pH values resulted in films with better general properties, notably lower water solubility and better mechanical properties. Oxidized tannic acid provided a more expressive improvement in the properties of tensile strength, water vapor permeability and water solubility. The use of 4% tannic acid and pH 9 was chosen as the best treatment for crosslinking. In the study of the treatment with UV-ozone (UVO) for functionalization with nisin, films were evaluated after treatment with UVO at different times and then with immersion in nisin (FTIR, XPS, MEV, AFM and zone of inhibition test). It was shown that the treatment with UVO is effective for the formation of negative charges on the film surface, with increased hydrophilicity, maintaining mechanical and structural properties. It was verified by the XPS technique that nisin was adsorbed on the surface of the films, especially after previous treatment of UVO for 120 s, indicating that the combination between UVO and immersion in nisin is viable for functionalization of zein films with nisin; However, further studies are needed to verify the antimicrobial activity of these films after surface adsorption of nisin. In the guava coating study, fruits coated with zein (Z) and zein crosslinked with tannic acid (CZ) were submitted to survival analysis, physical analyzes (mass loss, color, firmness), respiration rate (CO2) and ethylene production, pH, total titratable acidity, total soluble solids, vitamin C, chlorophyll, carotenoids, hydrogen peroxide content, lipid peroxidation and superoxide dismutase (SOD) and catalase (CAT) enzymes. The coatings showed to be effective in delaying the ripening of guavas, with delay of fruit color change, decrease of respiratory rate and ethylene production, maintenance of firmness, soluble solids, chlorophyll and H2O2 content, with more expressive effect of the crosslinked coating. The results indicated that zein coatings evaluated allowed increase the shelf life of fruits, especially the ZR coating.

Materiais nanoporosos para aplicação ambiental com ênfase na adsorção de contaminantes – Estudos experimental e teórico

Nanoporous materials for environmental application with emphasis on contaminant adsorption - Experimental and theoretical studies

Thesis (Phd)          12/11/2016

José Euranio de Aguiar

Improper disposal of effluents containing contaminants can cause serious environmental problems. The dye can be highly toxic to aquatic systems; still in its composition may carries a high nutrient content can thus promote the process of eutrophication contributing to cyanobacterial bloom that can release toxins harmful to health of living beings. This study evaluated nanoporous materials as adsorbents, one Lamellar Double Hydroxide (LDH) two heterostructure Porous Lamellar (HPL), one pilarred clay the natural clay and five commercial activated carbon for adsorption and removal of dyes and neurotoxins. The materials were characterized by XRD, N2 adsorption-desorption, FTIR, XPS, SEM, elemental analysis, TPD to obtain information on their chemical, structural and textural characteristics. Experiments using a batch system of stirred tanks were performed to determine the effect of pH, contact time and the initial concentration in the adsorption of contaminants. The materials HPL type was evaluated for their ability adsorption of binary mixtures of dyes. Three of the activated carbons were evaluated in the adsorption of a neurotoxin (STX). For the tests in stirred tanks was used a rotary agitation system with acrylic tubes containing a predefined volume of dye and toxin solution in contact with a predetermined mass of adsorbent. The concentrations of the molecules were determined by spectrofotometric and HPLC methods for the dyes and toxins respectively with the aid of a mass balance of the initial phase and the fluid phase. In order to describe the behavior of adsorption isotherms, equilibrium data were correlated with the Langmuir (L), Langmuir-Freundlich (LF), Redlich-Peterson (RP) and Henry model for the dyes and toxins, respectively. For the multicomponent system were used Extended Langmuir (EL), Langmuir Interaction Factor (LIF), Extended Langmuir-Freundlich (ELF), Redlich-Peterson Interaction Factor (RPIF) models and the Ideal Adsorbed Solution Theory (IAST) model. The dye adsorption mechanism in the LDH and carbons were evaluated using Monte Carlo approach. The influence of pH, contact time and initial concentration were of extreme importance for the understanding of adsorption processes in the respective materials for each contaminant and each analyzed system. The implemented isotherm models were suitable for adsorption of contaminants represent the data in the single system. For the binary system involving dyes models were unsatisfactory. The quantities of absorbed contaminants were very representative for all materials evaluated in single and multicomponent systems, which suggests that promising in water and wastewater treatment processes. The results suggest that the molecular simulation can be used as a useful tool for material characterization and elucidation of the quantitative adsorption of contaminants.

Avaliação e desenvolvimento de catalisadores nanoporosos ácidos para a obtenção de ésteres sintéticos lubrificantes a partir do ácido ricinoléico.

Thesis (Phd)          04/04/2016

Rosana Maria Alves Saboya

Currently, the domestic market of basestock oils and finished lubricants has accompanied the world increasing demand for lubricants obtained from renewable sources and higher quality products, bio-lubricants. Synthetic esters form a large group of products, which can be either from petrochemical or oleochemical origin. Due to the wide interest in environmentally friendly products, synthetic esters derived from vegetable oils have received special attention. However, this raw material can compete with the chain of the food industry. This fact has generated great efforts in the development of products from sources that do not interfere in the food industry. In this sense, from the castor bean is obtained one of the most important non-edible oils. The great interest in this oil is also attributed to the high ricinoleic acid content (≈ 90 %). The ricinoleic acid has been reported in the literature as the feedstock to esterification reaction for biodiesel production using short chain alcohols in the presence of mineral acids such as H2SO4. However, the use of alcohols with C8 to C14 is more interesting for the production of esters when the aim is its use as lubricant. In this study the esterification reaction of ricinoleic acid with 2-ethylhexanol with various solid acid catalysts was evaluated. This study focused on synthesis of acid catalysts using two types of support: mesoporous silica SBA-15 and porous clay heterostructures (PCH). Comparative studies were also carried out for commercial catalysts such as ion-exchange resins. It has been synthesized a set of WO3 based catalysts supported on porous clay heterostructured with different zirconium contents in their pillars. The catalysts with a tungsten content of 20 wt.% and a molar ratio Si/Zr = 15 in the pillars exhibited the highest conversion, reaching a conversion value close to 60 and 91 % after 8 and 24 h, respectively. SBA-15 silica synthesized by different procedures was used as catalytic support in the preparation Nb2O5 catalyst. The catalyst prepared by hydrothermal method with niobium oxide content of 12 wt.% exhibited the highest conversion, reaching a conversion value 80 % after 8 h. Among the evaluated resins, Amberlite-15 showed the best catalytic performance in terms of conversion of ricinoleic acid. The resins were quite active in the reaction of esterification of ricinoleic acid with 2-ethyl-1-hexanol. Such activity may be related to a homogeneous small contribution due to leaching of sulfonic acid groups in the reaction medium.

Avaliação da estabilidade e adsorção de co2 em estruturas metalorgânicas

Thesis (Phd)          31/03/2016

Juliana Amorim Coelho

For the development of any adsorption process, it is important that the adsorbent presents a good adsorption capacity and high selectivity for the target adsorbate. Metal-organic frameworks (MOFs) are formed by metals or metal oxides and organic linkers that bond together to generate crystalline networks. The wide variety of metals, organic linkers and synthesis methodologies allows for the design of materials with different structures and properties. For CO2 separation processes, thermal stability and moisture stability are critical properties that must be taken into account. MOFs CuBTC and MOF-74(Mg), for example, have the highest reported CO2 uptakes, but both suffer from surface area reduction and/or loss of crystallinity when exposed to water. In this work, a study of the stability on three commercial MOFs (Basolite® F300, C300 and A520) was performed. The thermal stability of the materials was assessed by thermogravimetric analysis (TGA), temperature programmed X-ray diffraction (TXRD) and adsorption equilibrium isotherms of CO2 and CH4 after degassing at different temperatures. The water stability was evaluated by adsorption equilibrium isotherms of water measured in this work and from literature. Basolite® A520, a recently synthetized aluminium fumarate MOF, showed a high stability to water and it was the adsorbent chosen for further experimental and theoretical study in processes involving CO2 adsorption, purification of natural gas and biogas (separation CO2/CH4) and flue gas (separation CO2/N2), on presence and absence of water. The experimental studies were developed using gravimetric and dynamic methods. The adsorption capacity of CO2, CH4 and N2 at 303 K and 1.0 bar was 2.1, 0.77 and 0.21 mmol/g, respectively, and the CO2 adsorption capacity remained constant after exposure to humidity and regeneration. The isosteric heats of adsorption were 21, 15, 14 and 44 kJ/mol for CO2, CH4, N2 and H2O, respectively. Fixed bed experiments were performed at 303 K to determine breakthrough curves of CO2, water vapor and CO2/water vapor mixture. Binary breakthrough (CO2/H2O) indicated a reduction of only 17% in CO2 adsorption capacity for a stream with 14% RH. Binary experiments with mixtures CO2/CH4 and CO2/N2 indicated CO2 selectivity for both separation processes. Molecular simulation studies were performed in this MOF to evaluate CO2 and N2 adsorption capacity individually and in the presence of water. A molecular model was developed to obtain fundamental adsorption data. The model was validated by experimental data reproducing previous breakthrough experiments of CO2/H2O adsorption mixture. We found that H2O has fixed adsorption sites whereas CO2 and N2 are distributed more evenly through the pores of the MOF. As the amount of water increases, clustering occurs next to the Al-O-Al-O centers of the MOF framework. Consideration of sitting and segregation of the molecules inside the pores helps explain changes in CO2 selectivity in the presence of water. The results indicate that the presence of water increases the selectivity of CO2 over N2, however, does not interfere in selectivity of CO2 over methane.

Produção de Ácido Lático a partir da Conversão Hidrotérmica do Glicerol via Catálise Homogênea e Heterogênea

Thesis (Phd)          29/01/2016

Anne Kerolaine de Oliveira Rodrigues

The use of alternative energy sources is a of the major current priorities, that appears to circumvent the serious problems caused by technological development. Accordingly, biodiesel arises as an alternative fuel to petroleum. However, high biodiesel production generates a large quantity of glycerin (10 wt%) which is considered an unwanted byproduct. To increase the market values of the biodiesel byproduct, it is necessary to convert glycerin into other chemicals, such as in lactic acid, which is becoming increasingly important due to their promising polymers applications - eg.: poly(lactic acid) (PLA) - as an alternative to replace petrochemical plastics. In the present study the hydrothermal process was used for lactic acid production, replacing the fermentation process that is currently used to obtain this product. For hydrothermal conversion of glycerol into lactic acid by homogeneous catalysis, NaOH and KOH catalysts were used. And for hydrothermal glycerol lactic acid by heterogeneous catalysis, Cu/SiO2 catalyst was used. Initial glycerol concentration (0.51-17.1 M), temperature (160-280 °C), pressure (2- 43 bar), water/glycerol volumetric ratio (0.8 to 31), catalyst/glycerol molar ratio (0.01 to 1.02) and total reaction time (3-4 hours) were the variables studied with temperature and water/glycerol volumetric ratio having the major influence. In addition, a first-order kinetic model for glycerol concentration versus time was developed and verified experimentally under conditions with different temperatures. Comparing the results obtained from hydrothermal conversion by homogeneous and heterogeneous catalysis, it was observed that KOH was catalyst with the best performance. The highest yield obtained was 87.5% at 220 °C and 28.8 bar, after 3 h, from a solution water/glycerol volumetric ratio equal to 0.8 and KOH/glycerol molar ratio equal to 0.03. From this result, hydrothermal process can be seen as a promising method to add value to glycerol.