A exploração de processos viáveis para a conversão da biomassa lignocelulósica em combustíveis limpos e produtos químicos de alto valor agregado, para complementar ou substituir produtos derivados de fontes não renováveis, é crucial para um desenvolvimento sustentável. A valorização e modificação dos componentes lignocelulósicos, torna-se imprescindível para viabilizar o sistema de biorrefinaria. A lignina, macromolécula aromática dominante na natureza, é um destes componentes que, devido a sua estrutura e composição, oferece rotas únicas para a produção de vários químicos de valor agregado. Este trabalho tem como objetivo avaliar o efeito de reações de oxidação em ligninas de bagaço e de palha de cana-de-açúcar, e de casca de café, na obtenção de compostos aromáticos de baixa massa molar, em especial a vanilina, e adicionalmente, verificar a aplicabilidade da lignina oxidada residual na obtenção de matrizes para liberação controlada de herbicida, buscando alternativas para agregar valor à lignina proveniente de resíduos agroindustriais e contribuir com a viabilização de biorrefinarias. Para isso, os materiais lignocelulósicos foram pré-tratados com ácido diluído e submetidos a deslignificação alcalina para obtenção da lignina. As frações obtidas durante cada etapa foram avaliadas quanto a composição química e Espectrometria no Infravermelho (FTIR), e as ligninas obtidas, foram ainda avaliadas por Espectrometria no Ultravioleta (UV) e por Ressonância Magnética Nuclear (1H RMN, 13C RMN e 2D RMN). As ligninas obtidas foram oxidadas em diferentes condições: oxidação enzimática utilizando lacase, em meio ácido e em meio alcalino com H2O2 e oxidação úmida em meio aquoso e alcalino utilizando H2O2. A fração líquida obtida foi analisada por Cromatografia Líquida de Alta Eficiência (CLAE) para identificar e quantificar os aldeídos aromáticos e outros compostos de degradação, enquanto a fração sólida, constituída pela lignina residual oxidada, foi avaliada por FTIR e UV. As ligninas oxidadas provenientes das condições que resultaram em um maior rendimento de vanilina, foram aplicadas na formulação de matrizes para liberação controlada de ametrina. Os resultados mostraram que a lignina de bagaço e de palha de cana não oxidadas são compostas principalmente por unidades siringil e guaiacil, respectivamente, e predominância de ligações ?-O-4, enquanto a lignina de casca de café foi composta principalmente por unidades hidroxil e predominância de ligações C-C, indicando uma estrutura mais condensada. Das oxidações avaliadas, a oxidação em meio alcalino (NaOH 10%) utilizando H2O2 9,1% gerou um maior rendimento de vanilina quando utilizada lignina de bagaço (8,13 mg/g lignina) e de casca de café (1,15 mg/g lignina), e H2O2 6,1% quando utilizada lignina de palha (6,48 mg/g lignina). A aplicação das ligninas oxidadas permitiu a obtenção de matrizes capazes de liberar o herbicida ametrina com diferentes cinéticas, dependendo das propriedades e das proporções das ligninas empregadas. / The exploration of feasible paths for the conversion of the lignocellulosic biomass into clean fuels and high value chemicals, to complement or replace products derived from non-renewable sources, is crucial for a sustainable development. The efficient utilization of the lignocellulosic components is of fundamental importance for the economic viability of biorefineries. Lignin, nature\'s dominant aromatic polymer, is a major component of the biomass that, due to its structuture and chemical composition, is a unique feedstock for producing high-value chemicals. The aim of this study is to seek for alternatives for adding value to lignin from agro-industrial waste in order to contribute to the vialbility of biorefineries. To achieve this, we evaluated the effect of oxidation reactions in sugarcane bagasse and straw lignin, and coffee husk, for obtaining aromatic compounds of low molecular weight, especially vanillin. In addition, the applicability of the residual oxidized lignin for obtaining matrices for the controlled release of herbicides was also examined in this work. For this purpose, the lignocellulosic materials were pretreated with dilute acid and subjected to alkaline delignification to achieve separation of the lignin. The fractions obtained at each stage were analyzed for chemical composition and with Infrared Spectroscopy (FTIR). The lignins were also analyzed using UV-vis Spectroscopy (UV) and Nuclear Magnetic Resonance (1H NMR, 13C NMR and HSQC). The lignins obtained were subjected to oxidation using different physiochemical conditions - enzymatic oxidation with laccase, oxidation in acidic and alkaline medium with H2O2 and wet oxidation in aqueous and alkaline medium using H2O2.The obtained liquid fraction was analyzed by High Performance Liquid Chromatography (HPLC) to identify and quantify the aromatic aldehydes and other compounds of lignin degradation, while the solid fraction, comprising the oxidized residual lignin, was analyzed by FTIR and UV. The oxidized lignins derived from the conditions that have resulted in a maximun yield of vanillin, were applied in the formulation of controlled release matrices of ametryne. Results for non oxidized lignin showed bagasse and straw lignin being composed mainly of syringyl and guaiacil units, respectively, linked predominantly by ?-O-4 bonds, while coffee husk lignin was mainly composed of hydroxyl units linked by C-C bonds predominantly, indicating a more condensed structure. Of all the oxidation reactions, the oxidation in alkaline medium (NaOH 10%) using H2O2 9.1% showed the highest yield of vanillin with bagasse lignin (8.13 mg/g lignin) and coffee husk lignin (1.15 mg/g lignin), and H2O2 6.1% with straw lignin (6.48 mg/g lignin). The application of oxidized lignins as matrices resulted in the release of the herbicide ametryne with different kinetics, depending on the proportions and properties of the lignins applied.

There has been an increase in the production of bio-fuels. Organosolv delignification, high temperature ethanol/water environments, can be used to separate lignin, cellulose, and hemicelluloses in the bio-mass for bio-fuel production. These environments have been shown to induce stress corrosion cracking (SCC) in 316L stainless steel. Previous research has been done in mixed solvent environments at room temperature to understand SCC for stainless steels, but little is known about the behavior in high temperature environments. Simulated organosolv delignification environments were studied, varying water content, temperature, pHe, and Cl- content to understand how these constituents impact SCC. In order for SCC to occur in 316L, there needs to be between 10 and 90 volume % water and the environment needs to be at a temperature around 200°C. Once these two conditions are met, the environment needs to either have pHe < 4 or have more than 10 ppm Cl-. These threshold conditions are based on the organosolv delignification simulated environments tested. SCC severity was seen to increase as water content, temperature, and Cl- content increased and as pHe decreased. To prevent failure of industrial vessels encountering organosolv delignification environments, care needs to be taken to monitor and adjust the constituents to prevent SCC.

With the dwindling availability of petroleum, focus has shifted to renewable energy sources such as lignocellulosic biomass. Lignocellulosic biomass is composed of three main constituents, lignin, cellulose and hemicellulose. Due to the low value of cellulosic ethanol, utilization of the lignin component is necessary for the realization of an economically sustainable biorefinery model. Once depolymerized, lignin has the potential to replace petroleum-derived molecules used as bulk and specialty aromatic chemicals. Numerous lignin depolymerization strategies focus on cleavage of β-aryl ether linkages, usually at high temperatures and under reductive conditions. Alternatively, selective benzylic oxidation strategies have recently been explored for lignin and lignin models. In this work, heterogeneous catalytic methods using supported base metals and layered-double hydroxides were evaluated for the oxidation of lignin models both before and after benzylic oxidation. Additionally, by studying putative reaction intermediates, insights were gained into the mechanisms of oxidative fragmentation of the model compounds. Generally, it was found that after benzylic oxidation models were more susceptible to oxidative fragmentation. Indeed, several heterogeneous oxidation systems were found to convert lignin models to oxygenated aryl monomers (mainly benzoic acids and phenols) using inexpensive primary oxidants (i.e., hydrogen peroxide and molecular oxygen). Reactions were conducted at relatively mild temperatures and at low oxygen concentrations for the purpose of an easy transition to large-scale experiments. Finally, the catalytic systems that resulted in significant cleavage of lignin models were applied to a Kraft lignin. Oxidation of Kraft lignin resulted a mixture of products for which analytical data and increased solubility are consistent with interunit cleavage within the lignin macromolecule.

La première partie de ce projet à consisté à isoler la lignine à partir de liqueurs industrielles et à la purifier pour s’affranchir des sucres, des minéraux et autres constituants. Pour cela, un protocole efficace en trois étapes a été proposé pour obtenir des échantillons de lignine avec une pureté satisfaisante (95%) et pour récupérer 68% de la lignine initialement présente dans la liqueur alcaline de départ. La lignine alcaline purifiée a ensuite été caractérisée d’un point de vue moléculaire et par analyses thermiques. L’élucidation de la structure de la lignine alcaline a permis d’appréhender sa fonctionnalisation par oxydation. Les analyses par chromatographie d’exclusion stérique de la lignine après oxydation ont montré une diminution de la masse molaire confirmant ainsi le clivage. Trois fractions différentes ont été isolées après l’oxydation de la lignine selon le solvant d’extraction ; d’une part des oligomères (plus ou moins fonctionnalisés) et d’autre part des molécules aromatiques (dont15% de vanilline). Ce travail de thèse aura abouti à la synthèse de composés aromatiques à haute valeur ajoutée (vanilline) et d’oligomères de lignine fonctionnalisés par des fonctions acide carboxylique. Les applications envisageables de ces « polyacides » issus de lignine sont nombreuses pour la formation de nouveaux polymères bio-sourcés tels que des polyesters, polyamides ou encore polyuréthanes. / A valorization of alkaline lignin from an industrial pulping liquor has been proposed for this project. Before considering any chemical modification or potential applications, the lignin structure has been elucidated. An efficient three-steps protocol for extraction and purification of lignin from industrial liquor has been established. This protocol leads to high purity sample of lignin (95%) and allows the recovery (68%) of the lignin initially present in the alkaline liquor. Alkaline lignin has been characterized utilizing analytical methods and thermogravimetric analysis. This precise structure elucidation was critical for proceeding to chemical modification of alkaline lignin. Chemical modification of alkaline lignin has been done by oxidation in alkaline media. Three major oxidized products have been isolated depending on the extraction solvent: oligomers bearing carboxylic groups and aromatic molecules. This thesis work led to the synthesis of value-added bio-sourced chemicals and functionalized oligomers. The polyacids from lignin obtained should be studied to form new biobased polymers such as polyesters, polyamids or polyurethanes.