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The increased demand of fossil fuel along with the depletion of economical crude oil resources, environmental challenges such as the accumulation of CO2 and other greenhouse gases in the atmosphere and the reduction of the dependence on imported oil are some of the motivations for the huge interest in biofuels. Biobutanol produced from ABE fermentation has been considered to be a good partial replacement for fossil fuels. However, challenges such as the need for inexpensive feed-stocks, improved fermentation performance to achieve higher final butanol concentration and higher yield, an efficient method for solvent recovery, and water recycle are the main obstacles to make the production of this alcohol economically viable. Pervaporation, a membrane-based process, is considered to be an attractive separation method to remove butanol from ABE fermentation broth. Among the membranes used for butanol separation, PDMS membranes showed reasonable performance such as good permeability, and appropriate selectivity for butanol separation by pervaporation. However, PDMS membranes need to be improved in terms of performance to be applicable in large scale butanol production plants. In this study, activated carbon nanoparticles have been embedded into the matrix of the PDMS membrane to improve its separation performance and, in particular, the permeation flux and butanol selectivity. Result showed that the presence of nanoparticles improves the PDMS membrane performance up to a certain particle loading. Moreover, it was shown that the operating conditions have a major impact on the pervaporation membrane separation process. The best membrane for pervaporation separation of butanol from binary aqueous solutions was obtained for a 6 wt% particle concentration where the total permeation flux and butanol selectivity increased by 42.6% and 51.9%, respectively, compared to neat PDMS membranes. Moreover, the best performance for the separation of butanol from ABE model solutions was achieved for an 8 wt% nanoparticle loading. Both the selectivity for butanol and the total permeation flux more than doubled in comparison to neat PDMS membranes prepared in this study. Moreover, in order to compare the PDMS/AC mixed matrix membrane performance for pervaporation separation of butanol from binary and ABE model solutions with PDMS membranes available on the market, experiments were also performed with a commercial PDMS membrane. Result of butanol separation from ABE model solutions showed that mixed matrix membranes with 8 wt% nanoparticles loading had a higher permeation flux than that of the commercial membranes. It was clearly shown that the presence of activated carbon nanoparticles in the matrix of the PDMS would be beneficial for the pervaporation separation of butanol from ABE fermentation broths. To better comprehend how the presence of activated carbon nanoparticles in the polymeric membranes enhance the performance of the membranes, a series of numerical simulations were performed. A finite difference model was developed to simulate the mass transfer of permeating components through mixed matrix membranes by pervaporation for a wide range of relative permeability, nanoparticle loading, particle shape, particle size and different filler adsorption isotherms. Finally, an investigation has been performed to optimize the butanol pervaporation separation process from ABE fermentation broth at an industrial scale.

[pt] As nanopartículas fluorescentes são uma classe de compostos bastante recente e fascinante. Entre estas nanopartículas, têm-se os semicondutores quantum dots - QD (nanopartículas de confinamento quântico) e, as novas nanopartículas carbono dots, CD (nanopartículas de confinamento quântico baseadas em carbono). As nanopartículas fluorescentes podem ter várias utilidades, particularmente em análises químicas, como sensores e em biotecnologia. Ao contrário dos semicondutores QD, que possuem metais tóxicos no seu núcleo, nanopartículas de carbono não contêm componentes tóxicos, sendo vantajosas biologicamente e biodegradáveis. Os CDs têm área superficial muito alta (até 3600 m2/g) com vários grupos funcionais, que podem ser usados para imobilização na superfície de um suporte. Estes vários grupos funcionais influenciam as propriedades óticas dos CDs. Como estas propriedades podem ser mudadas em função do ambiente químico, conferem aos CDs uma característica notável na aplicação em sensores. CDs formam suspensões muito estáveis em meio aquoso, podendo ser sintetizados a partir de vários compostos moleculares, tais como sacarose, glicose, ureia, ácido cítrico, entre outros. Como as propriedades físico-químicas e óticas dos CDs dependem de seus precursores, tem-se em vista neste trabalho: a exploração do uso de aminofenol como precursor na síntese de CDs via solvólise hidrotérmico até os nanomateriais obtidos atingirem fluorescência vermelha dos nanomateriais obtidos; efetuar a purificação dos nanomateriais sintetizados, no seu limite; realizar a caracterização morfológica e estrutural dos CDs obtidos, através de diferentes técnicas físico-químicas, avaliando as suas propriedades fotoluminescentes; desenvolver a metodologia de imobilização covalente dos CDs na superfície de sílica gel mesoporosa; e estudar se o material híbrido pode ser aplicado como adsorvente. Imagens de Microscopia de Força Atômica indicam partículas entre 1,0 e 7,0 nm, e dependem do solvente, já que as partículas menores aparentam dispersão melhor em solvente menos polares. Os espectros de UV-Vis e de Fluorescência confirmam a presença de CDs com transições pi - pi asterisco em acetato de etila, a 290 nm, e em heptano, a 278 nm. O deslocamento batocrômico com o pico de emissão variando de 501 nm a 535 nm com a mudança de solvente, indica que este pode ser utilizado para avaliar a polaridade local, por exemplo, em biopolímeros. Variados suportes de sílica–gel (octadecil, mercaptopropil, aminopropil e SiO2) foram utilizados no estudo de adsorção. Os resultados apontam para um processo de cinética de segunda ordem, sob o modelo de Langmuir, indicando maior afinidade dos CDs com a aminopropil-sílicagel. No estudo foi apresentado que o tratamento térmico da aminopropil-sílicagel (SiO2-NH2) com CDs adsorvidos leva à imobilização de CDs à superfície de suporte através de ligações covalentes. Como este material híbrido (SiO2-NH2/CDs) exibe propriedades de adsorção para metais e compostos poliaromáticos, foi estudada a adsorção de uma mistura contendo 23 cátions metálicos em SiO2-NH2/CDs e o efeito da acidez do meio na sorção de íons. Os resultados obtidos em solução aquosa demonstraram que íons com afinidade por ligantes oxigenados, tais como Bi, Tl, Cr, Al, Fe, são melhor adsorvidos no material sintetizado. / [en] Fluorescent nanoparticles are a very new and fascinating class of compounds. Among these are the semiconductors quantum dots (quantum confinement nanoparticles - QD) and also the new types of nanoparticles that are generally called carbon dots, CD (carbon based quantum confinement nanoparticles). Fluorescent nanoparticles can have several uses, particularly in chemical analysis: as sensors and in biotechnology for drug delivery and theranostics. Unlike QD semiconductors that have toxic metals in their core, carbono nanoparticles do not contain toxic components, being biologically beneficial and biodegradable. CDs have a very high surface area (up to 3600 m2/g) with various functional groups and can be used for immobilization on the surface of a support. Due to their functional groups, optical properties of CDs can be changed depending on the chemical environment, a notable feature of CDs in sensor applications. CDs form very stable suspensions in aqueous media and can be synthesized from molecular compounds such as sucrose, glucose, urea, citric acid and so on. It is worth noting that physicochemical and optical properties of CDs depend on their precursors. The aim of this work is to explore the use of aminophenol as a precursor in the synthesis of CDs via hydrothermal solvolysis to achieve red photoluminescence of the obtained nanomaterials; carrying out the purification of synthesized nanomaterials, at its limit; perform the morphological and structural characterization of the obtained carbon dots, through different physicochemical techniques, evaluating their photoluminescent properties; to develop the methodology of covalent immobilization of CDs on the surface of mesoporous silica gel, and to study the hybrid material as adsorbent. Atomic Force Microscopy images indicate particles between 1.0 to 7.0 nm depending on the solvent, as smaller particles appear better dispersibility in less polar solvents. The UVVis and Fluorescence spectra confirm the presence of CDs with pi-pi asterisk transitions at 290 nm in ethyl acetate and at 278 nm in heptane, they also indicate a bathochromic shift with the emission peak going from 501 nm to 535 nm with a solvent change, which can be used to assess local polarity, eg in biopolymers. Adsorption was verified using various silica-gel supports (Octadecyl, Mercaptopropyl, Aminopropyl and SiO2) indicating greater affinity with aminopropylsilica-gel, indicating a second-order kinetic process under the Langmuir model. It has been shown that the thermal treatment of aminopropyl-silica (SiO2-NH2) with adsorbed CDs leads to covalent immobilization of CDs to the support surface. This hybrid material (SiO2-NH2/CDs) could exhibit adsorption properties for metals and polyaromatic compounds. Therefore, the adsorption of a mixture containing 23 metals ions on SiO2-NH2/CDs was studied. The effect of the acidity of the medium on ion sorption was studied. It has been shown that ions with affinity for oxygenated ligands (such as Bi, Tl, Cr, Al, Fe) are better collected.