Le furfural est un intermédiaire chimique biosourcé produit à l'échelle industrielle par déshydratation des pentoses issus de la biomasse lignocellulosique. Le procédé industriel utilise une catalyse homogène à base d’acide sulfurique. L'objectif de ces travaux de thèse vise à rechercher une voie catalytique durable, faisant appel à une catalyse hétérogène solide acide en phase aqueuse. L’utilisation de réacteurs fermé et à flux continu a été comparée, tout en évitant le recours aux solvants organiques d’extraction. Pour ce faire, une large gamme de catalyseurs acides hétérogènes a été caractérisée et évaluée en réacteur fermé afin de rechercher des corrélations entre performances catalytiques et propriétés physico-chimiques. Ces études ont permis de montrer que l'utilisation de solutions aqueuses d'acide acétique, en synergie avec certains catalyseurs hétérogènes, conduit aux meilleurs résultats, à savoir un rendement en furfural de 60%. Elles ont également permis de sélectionner les familles de catalyseurs acides, potentiellement stables et sélectifs, pour des études plus approfondies en réacteur continu. Deux familles de catalyseurs ont ainsi été étudiées afin d'augmenter leur sélectivité en furfural et leur stabilité. Des catalyseurs à base de charbons fonctionnalisés avec de l'acide citrique ont montré des résultats très satisfaisants, et une excellente stabilité. La modification de catalyseurs à base de niobium par des phosphates a permis d'améliorer la sélectivité en furfural et de mettre en évidence l'importance de la nature des sites acides à la surface du solide / Furfural is a chemical intermediate produced in industry by dehydration of pentoses issued from the lignocellulosic biomass. Sulfuric acid is currently used in the industrial process. The aim of this thesis is the search for a sustainable catalytic way based on solid acid catalysts in aqueous phase. Both batch and fixed-bed reactors have been compared, taking care to avoid the use of extractive organic solvents. Thus, a large range of heterogeneous acid catalysts was characterized and evaluated in batch reactor in order to obtain correlations between catalytic performances and physico-chemical properties. These studies have shown that the use of aqueous acetic acid solutions, in synergy with selected heterogeneous catalysts, leads to the best results, furfural yield of 60%. It was also possible to select families of acid catalysts, potentially stable and selective for deeper studies in continuous reactor. Two catalyst types have been optimized in order to increase their furfural selectivity and their stability. Carbon-based catalysts, functionalized with citric acid, have shown good furfural yield as well as an excellent stability. Niobium-based catalysts modified with phosphates led to increased furfural selectivity and also highlighted the importance of the nature of acid sites on the solid surface

Made available in DSpace on 2015-05-14T13:21:34Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2349929 bytes, checksum: 3d3e0699d877063cdd3b4736536785b4 (MD5) Previous issue date: 2014-03-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / A simple and rapid method for determination of furfural in yeast-distilled beverages from sugar cane by liquid-liquid extraction (LLE) is proposed. The techniques of extraction and / or preconcentration allows analytes can be determined by separation of sample components due, mainly, the solubility differences that allows the separation of one or more matrix components by contact and mechanical stirring of a solvent immiscible or slightly miscible in the matrix. The component to be separated (analyte) must be soluble in this solvent. In the proposed method equal amounts of standard sample and chloroform are mixed, the mixture is stirred mechanically for about 2 minutes, forming an emulsion. After this, it´s expected one minute to complete phase separation. Once the analyte is in the extractor solvent (chloroform) it was separated from the mixture and subjected to spectrophotometric analysis in the UV region (279 nm). The stability of the standard solution of furfural and waste disposal were evaluated. The viability of the LLE method was evaluated in the determination of furfural in samples of sugar cane spirits. The proposed method was compared with the reference method based on gas chromatography with flame ionization detector (FID) (GC-FID), no statistical difference between the results was observed. The LLE method was sensitive, accurate and precise with recoveries in the range 102-109%, linear range of 0,2 to 8 mg 100 ml-1, limits of detection and quantification of 0,0118 mg 100 mL-1 and 0,0203 mg 100 ml-1, respectively, repeatability factor of 0,026. The LLE methodology was validated and successfully applied to the analysis of eight cachaças samples demonstrating the feasibility and reliability of the method. The levels of furfural, in the analyzed cachaças was between 0,4 to 1,1 mg 100 mL-1 and is therefore, beverages analyzed, within the limit of 5 mg 100 mL-1, established by legislation. / Um método simples e rápido para determinação de furfural em cachaças por extração líquidolíquido (LLE) é proposto. As técnicas de extração e/ou pré-concentração permitem que analitos sejam determinados por meio da separação de componentes da amostra devido, principalmente, às diferenças de solubilidade que possibilitam a separação de um ou mais componentes da matriz por meio do contato e agitação mecânica de um solvente imiscível ou pouco miscível na matriz. O componente a ser separado (analito) deve solúvel neste solvente. No método proposto, são misturadas quantidades iguais de amostra/padrão e de clorofórmio, esta mistura é agitada mecanicamente por cerca de 2 minutos, formando uma emulsão. Após isto, espera-se mais um minuto para haver a completa separação de fases. Uma vez que o analito encontra-se no solvente extrator (clorofórmio), este foi separado da mistura e submetido à análise espectrofotométrica na região do UV (em 279 nm). A estabilidade da solução padrão de furfural e o descarte dos resíduos foram avaliados. A viabilidade do método LLE foi avaliada na determinação de furfural em amostras de cachaça. O método proposto foi comparado com o método baseado na cromatografia gasosa com detector de ionização de chama (GC-FID), nenhuma diferença estatística entre os resultados foi observada. O método LLE mostrou-se sensível, exato e preciso com recuperações na faixa de 102 a 109%, faixa linear de 0,2 a 8 mg 100 mL-1, limites de detecção e quantificação de 0,0118 mg 100mL-1 e 0,0203 mg 100mL-1, respectivamente, fator de repetitividade de 0,026. A metodologia de LLE foi validada e aplicada com sucesso na análise de oito amostras de cachaças demonstrando assim, a viabilidade e confiabilidade do método. Os teores de furfural, nas cachaças analisadas, variaram de 0,4 a 1,1 mg 100 mL-1, estando pois, as bebidas analisadas, dentro do limite, de 5 mg 100 mL-1, estabelecido pela legislação.

Face à une demande sans cesse croissante en ressources fossiles et une prise de conscience sociétale des enjeux environnementaux, un intérêt de plus en plus important est porté à la valorisation de la biomasse lignocellulosique comme source pour l'énergie et la chimie fine.Parmi les molécules d'intérêt pouvant provenir de la lignocellulose, le xylose un sucre en C5 est obtenu par hydrolyse de la fraction hémicellulosique. Ce dernier peut être hydrogéné en xylitol, un édulcorant. Les catalyseurs utilisés pour réaliser cette réaction ne sont pas stables ou sont à base de métaux nobles. Un des objectifs de ce travail est le développement d'un catalyseur actif, sélectif, stable et à base de métaux non nobles pour cette réaction. Des catalyseurs à base de cobalt se sont avérés actifs et sélectifs pour cette réaction d'hydrogénation du xylose en xylitol. La déshydratation du xylose conduit au furfural qui peut être hydrogéné en alcool furfurylique ou hydrogénolysé en 2-méthylfurane. Un catalyseur à base de cobalt supporté sur un support SBA-15 s'est avéré très actif et sélectif pour d'hydrogénation du furfural en alcool furfurylique. Une étude systématique des conditions expérimentales a été réalisée et le catalyseur a été recyclé. L'identification des sites actifs a été réalisée grâce à une corrélation entre les caractérisations physico-chimiques du catalyseur et sa réactivité lors de l'hydrogénation du furfural en alcool furfurylique. L'hydrogénolyse du furfural en 2-méthylfurane a elle été réalisée en présence d'un catalyseur à base de cuivre supporté et a permis l'obtention de 45 % du produit désiré. / With the increase in the fossil resources demand and a societal awareness of environmental issues, a high interest has been devoted to the use of lignocellulosic biomass as a source for energy and fine chemicals.Among the molecules of interest which come from lignocellulose, xylose, a C5 sugar is obtained by hydrolysis of the hemicellulosic fraction. Xylose can be hydrogenated to xylitol, a sweetener. Today the catalysts used for this reaction are not stable or are based on noble metals. One objective of this work is the development of an active, selective, stable catalyst and based on non-noble metals for this hydrogenation reaction. Cobalt based catalysts have proved to be active and selective for the hydrogenation reaction of xylose to xylitol.The dehydration of xylose affords furfural than can be further converted to furfuryl alcohol by hydrogenation or to 2-methylfuran by hydrogenolysis reaction. A cobalt based catalyst supported on SBA-15 was active and selective in the hydrogenation of furfural to furfuryl alcohol. The study of the experimental conditions was performed and the catalyst was recyclable. The nature of the active site in the hydrogenation of furfural to furfuryl alcohol was determined by a correlation between the physic-chemical properties of the catalyst and its reactivity. The hydrogenolysis of furfural to 2-methylfuran was carried out in the presence of a copper based catalyst and 45 % yield was obtained in liquid phase.

Doctor of Philosophy / Department of Chemical Engineering / Bin Liu / In the course of mitigating our dependence on fossil energy, it has become an urgent issue to develop unconventional and innovative technologies based on renewable energy utilization for fuels and chemicals production. Due to the lack of fundamental understanding of catalytic behaviors of the novel chemical compounds involved, the task to design and engineer effective catalytic systems is extremely challenging and time-consuming. One central challenge is that an intricate balance among catalytic reactivity, selectivity, durability, and affordability must be achieved pertinent to any successful design. In this dissertation, density functional theory (DFT), coupled with modeling techniques derived from DFT, is employed to gain insights into molecular interactions between elusive intermediates and targeted functional catalytic materials for novel electrochemical and heterogeneous catalytic processes. Two case studies, i.e., electroreduction of furfural and step-catalysis for cyclic ammonia production, will be discussed to demonstrate the capability and utility of DFT-based theoretical modeling toolkits and strategies. Transition metal cathodes such as silver, lead, and nickel were evaluated for furfuryl alcohol and 2-methylfuran production through detailed DFT modeling. Investigation of the molecular mechanisms revealed that two intermediates, mh6 and mh7 from mono-hydrogenation of furfural, are the key intermediates that will determine the product formation activities and selectivities. Nickel breaks the trends from other metals as DFT calculations suggested the 2-methylfuran formation pathway is most likely different from other cathodes. In this work, the Brønsted–Evans–Polanyi relationship, derived from DFT energy barrier calculations, has been found to be particularly reliable and computationally efficient for C-O bond activation trend predictions. To obtain the solvation effect on the adsorptions of biomass-derived compounds (e.g., furfural and glycerol), influence of explicit solvent was probed using periodic DFT calculations. The adsorptions of glycerol and its dehydrogenation intermediates at the water-platinum surface were understood via various water–adsorbate, water–water, and water–metal interactions. Interestingly, the bond-order-based scaling relationship established in solvent-free environment is found to remain valid based on our explicit solvent models. In the second case study, step-catalysis that relies on manganese’s ability to dissociate molecular nitrogen and as a nitrogen carrier emerges as an alternative route for ammonia production to the conventional Haber-Bosch process. In this collaborative project, DFT was used as the primary tool to produce the mechanistic understanding of NH3 formation via hydrogen reduction on various manganese nitride systems (e.g., Mn4N and Mn2N). Both nickel and iron dopants have the potential to facilitate NH3 formation. A broader consideration of a wide range of nitride configurations revealed a rather complex pattern. Materials screening strategies, supported by linear scaling relationships, suggested the linear correlations between NHx (x=0, 1, 2) species must be broken in the development of optimal step catalysis materials. These fundamental findings are expected to significantly guide and accelerate the experimental material design. Overall, molecular modeling based on DFT has clearly demonstrated its remarkable value beyond just a validation tool. More importantly, its unique predictive power should be prized as an avenue for scientific advance through the fundamental knowledge in novel catalysts design.

Dissertação (Mestrado em Engenharia Química) - Centro Universitário FEI, São Bernardo do Campo, 2017.

This research mainly includes two parts. First, monodispersed silica spheres with diameter about 58 and 73 nm were successfully synthesized. The tablet-like silica template could be made using a stainless steel mold by pressing the mold with a pressure ~ 10 MPa. The advantage of this molding process is it takes only a short time to accomplish the total fabrication. Second, infiltration of the carbon precursor was done using the monomers resorcinol (R) and furfural (F) in the interval of tablet-like silica template, and then polymerization and drying. It was subsequently carbonized in N2 atmosphere at 800 ¢J and then the silica template was removed by 20 wt % HF solution. The activated porous carbon material has larger specific surface area than the traditional powder carbon material. The chemical activation process by KOH plays a vital role in raising the specific surface area, since the KOH would etch the carbon pore surface to produce a large number of micropores (diameter < 2 nm), forming a macro-micro or meso-micro porous carbon materials. The F/R molar ratios for polymerization between 2.0 to 3.0 were applied and the carbon yields of these resins were higher than 51% in this range. An F/R ratio below 2.0 or 3.0 gave a lower carbon yield when carbonization at 800 ¢J. X-ray diffraction analyses on the macroporous carbon materials indicate a semi-crystalline structure which belong to the hexagonal crystal system with (002) d-spacing of = 0.373 nm, which is larger than the 0.339 nm of graphite. In Raman spectra analysis, the integral area of D-peak (ID) and G-peak (IG) is an index to define the degree of graphitization. The ratios ID/IG of lie between 1.7 - 1.8, which are larger than that of graphite (ID/IG = 0.1 - 0.3), so the FR series macroporous carbon is mostly amorphous and is far from highly crystallized structure. The un-activated macroporous carbon materials has open pore structure, the pore diameter is 56 nm which is classified to the macroporous scale. The nitrogen adsorption/desorption isotherm of the porous carbon materials belongs to the type IV, with H1 type hysteresis. The BET results show that the specific surface area increases with increasing KOH concentration; whereas the open pore structure remain the same. SEM observations reveal the pore structure doesn¡¦t collapse but the pore wall does become thinner. From this work, macroporous carbon materials with total pore volume as high as 2.23 cm3/g and the specific surface area as high as 658 m2/g have successfully been synthesized. Activation by KOH creates more micropores on its carbon walls, resulting in a macro-microporous carbon material having two scales of pores in the same time and with a high surface area of 1404 m2/g.

Commercial activated carbon and newly polymer-derived carbon were utilized to selectively remove the model fermentation inhibitor, furfural, from water solution during bio-ethanol production. Morphology, pore structure and surface chemistry of the sorbents were characterized. The oxygen groups on the carbon surface were believed to have contributed to the decrease on the selectivity of activated carbon between furfural and sugars (Sugars are the valuable source of bio-ethanol production and should not be separated from solution). Oxidization of activated carbon by nitric acid generated more information which supports the above assumption. Different adsorption isotherm models and kinetic models were studied to fit commercial activated carbon and polymer-derived carbon individually. Bacterial cell growth, sugar consumption, and ethanol yield during the fermentation were investigated after inhibitors were selectively removed from the broth. The fermentation time was reduced from one week to one day after inhibitor removal. Different methods of sorbent regeneration were investigated, including thermal regeneration, pH adjustment and organic solvent stripping. Low ethanol-containing water solution appears to be the most cost-effective way to regenerate the spent sorbent in the industrial application. A sorption/desorption cycle was designed and the sorbents were regenerated in a fixed-bed column system using ethanol-containing liquid from fermentation. The results were stable after running 20 times of sorption/desorption cycle.

Given the volatile, generally high price of crude oil, as well as environmental concerns associated with its use as a fuel, development of alternative energy sources is currently of considerable interest. Lignocellulose-derived energy has the potential to supplant traditional fossil fuels in the future because of its economic and environmental advantages. Lignocellulosic biomass is abundant and renewable. Lignocellulose is primarily composed of cellulose, hemicellulose and lignin, which can be converted by acid hydrolysis to simple sugars used in fermentation to produce biofuels. In this study, hemicellulose was hydrolyzed with different concentrations of hydrochloric acid at different temperatures. The resulting components were analyzed by high performance liquid chromatography (HPLC). The hydrolysis of cellulose was similarly characterized, with two additional parameters, the degree of polymerization (DP) and the crystallinity index (CrI), which were analyzed by Ubbelohde viscometer and X-ray diffraction respectively. The experimental results indicate that the hydrolysis rate of hemicellulose and the generation rate of furfural and 5-hydroxymethylfurfural (HMF) increased with increasing hydrochloric acid concentrations and reaction temperatures. In the selected five monosaccharides, xylose, glucose, mannose, arabinose and galactose, xylose has the highest hydrolysis rate and the accumulation of furfural during xylose hydrolysis is also the highest. Moreover, the hydrolysis rate of cellulose and the generation rate of glucose also increased with increasing hydrochloric acid concentrations and reaction temperatures. DP and CrI, both decreased when the cellulose was treated in concentrated hydrochloric acid. The rate of change of DP increased with the concentrations of acid and the reaction temperatures. The change rate of CrI increases by increasing concentration of acid and the temperature when it is above 0℃, while the CrI index decrease sharply when the reaction temperature was kept below 0℃. Experimental results also show that the hydrolysis rate of cellulose is much lower than that of hemicellulose.

The Knoevenagel reaction was applied to form a carbon-carbon double bond between the aldehydes (HMF, furfual) and an alpha di-carbonyl compound. The alpha di-carbonyl compound used was malonic acid, which can be bio-derived from glucose along fermentation routes. The effects of solvents (THF, water, ethanol, isopropanol, ethyl ether, toluene) and catalysts (e.g. homogeneous and heterogeneous amines, solid basic oxides) on the yields of alpha-beta unsaturated acids were investigated. It was found that the homogeneous amines worked well in THF solvent (90-100% conversion, 99% selectivity for furfural and HMF), while the poly(styrene) supported ethylenediamine gave a higher conversion and selectivity for HMF (65± 5%, 99% selectivity) over furfural (58 ± 7%, 99% selectivity). This trend was also present in competition reactions where both HMF and furfural were reacted in the same vessel. á-â Unsaturated mono-acids for both HMF and furfural were identified as minor side products. However, levulinic acid did not work as well under the conditions studied. Lastly, among the solvents studied, several caused precipitation of the Knoevenagel products.

O presente trabalho apresenta um estudo sistemático para a obtenção de um filme polimérico a partir da eletrooxidação do furfural (2-furanoaldeído). O filme foi crescido sobre a superfície do eletrodo de platina (Pt) e sobre carbono vítreo reticulado (CVR). Três técnicas eletroquímicas foram usadas: cronopotenciometria com correntes de 10 mA, voltametria cíclica por ciclagens sucessivas no intervalo de potencial de 2,0 V à 2,70 V (Ag/AgCl) e a cronoamperometria, no potencial de 2,65 V (Ag/AgCl). Diferentes eletrólitos foram testados em solução aquosa sobre Pt. O sal biftalato de potássio foi o eletrólito suporte mais adequado para formação do filme sobre ambos eletrodos, Pt e CVR. Os resultados obtidos confirmam a formação de um filme branco sobre a superfície dos eletrodos, entretanto, com alguma solubilização no próprio meio. Esta solubilidade do filme em meio aquoso permitiu atribuir-lhe características de polieletrólito. Evidências desta característica se confirmam pelas propriedades físico-químicas das soluções do filme testadas resultando no aumento da acidez e no aumento da condutividade do meio, quando se comparam as soluções de biftalato ácido de potássio com as do filme polimérico Os resultados revelam a formação de um filme poroso e espesso sobre a superfície dos eletrodos, com características que dependem do método eletroquímico empregado, bem como do tempo de polarização. A visualização do filme foi registrada por fotografias digitais e caracterizada por microscopia eletrônica de varredura. O crescimento do filme pelo método cronopotenciométrico forneceu os melhores resultados em termos de aderência e volume. Uma observação importante refere-se ao caráter condutor do filme formado, uma vez que medidas eletroquímicas dos eletrodos modificados não acusaram um decaimento significativo das correntes. Além das medidas eletroquímicas, a condutividade do polímero, determinada pelo método das quatro pontas, resultou num valor de 100 µS cm-1 para o obtido potenciostaticamente e de 150 µS cm-1 para o obtido galvanostaticamente. A caracterização do filme envolveu as medidas térmicas de calorimetria diferencial de varredura (DSC) e a análise termogravimétrica (TGA). As medidas espectroscópicas como o ultravioleta, infravermelho, Raman, ressonância magnética nuclear de H1 e de C13 diretamente com o filme formado ou através de suas soluções em solventes adequados, confirmaram a participação de ambos os anéis ftálico e furânico na estrutura do filme.