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Process investigations on second generation lignin as a source of high-value molecules
No full textThere is an increasing demand of renewable biomass-derived fuels, generally known as biofuels, in order to overcome the need of fossil ones, and ultimately, deal with the environmental regulations imposed by the recent international agreements, which will hopefully lead to a limitation of global warming below 2 °C. The human being has used biomasses to solve its energetic and non-energetic needs for millennia before the Industrial Era, but in the 21st century there is the need to go a little bit further, for this reason, it is born the concept of biorefinery, or biofactory, in contrast with the oil-based refinery. In a fully integrated biorefinery, biomasses with variable origin are transformed through chemical and biochemical processes in a plethora of chemicals, fuels like ethanol and FAMEs, but also polymer monomers, drug precursors and food additives. The biorefinery will provide the scale dimensions and production flexibility to compete with the oil industry and, ultimately, will cause a global change in the geography of the energy and chemical industry. However, the development of efficient models of biorefinery based on non-edible second generation biomasses is still economically tricky, and there the need to couple fuels production with high-value chemical building blocks. Particular attention should be addressed to lignin fraction which is the most underutilized component of lignocellulosic biomass. Despite lignin is an incredible source of aromatic compounds, it is commonly intended to landfill or, in the best case, used as solid combustible. In this sense, this work has dealt with the development of processes for the transformation of industrial lignin streams into chemicals of interest for the industry, as alternative to pyrolysis or mere combustion. On one hand, we investigated the reductive route which involves the use of H2 firstly, to carry out the hydrogenolysis of lignin to give a phenols-rich bio-oil, and secondly, to transform this phenols mixture to other products through a hydrodeoxygenation reaction. On the other hand, we explored the oxidative route which involves the use of an oxidant to break down lignin matrix to functionalized phenols and carboxylic acids. Both pathways offer the opportunity to produce significant quantities of renewable building blocks, which will ultimately support the economic sustainability of the integrated biorefinery. The following paragraphs resume the content of the main chapters of this dissertation. The hydrodeoxygenation (HDO) of guaiacol has been chosen as a model process for the upgrading of lignin-derived bio-oils. Tests were carried out in a batch reactor at 350 °C, 40 bar of H2, in the presence of several Mo-based catalysts prepared by impregnation of ammonium molybdate on SiO2, Al2O3, NaY zeolite, MgO, activated carbon and graphite. These materials have been characterized by means of: N2 physisorption, XRD, FESEM/EDS, XPS, TPR-H2, TPD-NH3, with the aim of correlating the physical and chemical properties of the prepared samples with the resulting features in the HDO reaction. Mo on activated carbon showed the best performances towards guaiacol demethoxylation, exhibiting complete conversion, 72 % of selectivity to phenol and 19 % to p- and o-cresol. The high surface area and low acidity of activated carbon allow good dispersion of MoOx which exhibits characteristic fragments with lamellar shape, capable to provide large active surface with localized acidity. A phenolic bio-oil, derived from an industrial hydrogenolysis facility treating 2nd generation lignin, was used as starting material for the recovery of phenolic monomers by means of an ad hoc vacuum distillation apparatus. The initial 20 %wt content of monomers was efficiently separated with the 90 % of yield, showing guaiacol, phenol and ethylphenol as main components. Afterwards, the distillate was upgraded through an HDO reaction in order to narrow the compounds distribution and to improve the stability of the mix. The process was carried out under similar conditions as the ones adopted in Chapter 3, allowing achieving the complete demethoxylation of the mix with high selectivity. Notably, the presence of the Mo-base catalyst over activated carbon significantly enhanced the performances of the reaction. Wet air oxidation (WAO) of lignocellulosic biomasses is a promising route for the production of renewable and valuable compounds, involving air as primary oxidant and mild reaction temperatures. In this work, an industrial residue of bioethanol production, steam exploded lignin derived from wheat straw, undergoes a WAO process with the aim to achieve more insights on the process performances in terms of potential yields of aromatic compounds and carboxylic acids (CAs). The experiments were carried out in a pressurized 50 ml batch reactor loaded with water or other aqueous solutions as solvent, the standard conditions were 150 °C of temperature, 20 bar of initial air pressure and 2 h. Afterwards, several solvothermal pretreatments were applied in order to depolymerize and solubilize lignin under inert atmosphere; the residues-free solutions obtained in this way were used as substrate for the WAO reaction. The choice of the pretreatment temperature, solvent alkalinity and presence of perovskite catalysts were evaluated with regard to the mass yields of resulting aromatic compounds and CAs, their carbon content and the products distribution. Best performance exhibits a lignin dissolution ratio of 53 % with 1.3 % of yield towards aromatic compounds where vanillin is the principal product (59.1 %) but also the 32 % of yield in CAs with glycolic acid as major product (40.9 %). Acetovanillone (AV) was selected as lignin model molecule in order to investigate its behavior under the WAO reaction conditions. The experiments were carried out in a pressurized 50 ml batch reactor loaded with NaOH 2 M as solvent, the reaction takes 1 h with temperatures ranging from 130 to 190 °C and air pressures between 5 and 30 bar. A heterogeneous catalyst, the perovskite-type mixed oxide LaFeO3 was synthetized and used as catalyst in order to improve the activation of molecular oxygen. Vanillin yield resulted to benefit from high reaction temperature showing a maximum carbon yield of 22 %, instead the formation of carboxylic acids from the oxidative degradation of AV largely benefits from high pressure of air, exhibiting an overall carbon yield of 35 %. The produced compounds include oxalic, glycolic, lactic, malonic and levulinic acid
Wet Air Oxidation of Acetovanillone over LaFeO3 as Catalyst: A Model Reaction for Lignin Valorization
Full text linkWet air oxidation (WAO) of lignocellulosic biomasses is a promising route for the production of renewable and valuable compounds. In this work, acetovanillone (AV) was selected as lignin model molecule in order to investigate its behavior under the WAO reaction conditions. The experiments were carried out in a pressurized 50 ml batch reactor loaded with NaOH 2M as solvent, the reaction takes 1 h with temperatures ranging from 130 to 190 °C and air pressures between 5 and 30 bar. The perovskite-type mixed oxide LaFeO3 was synthetized and used as heterogeneous catalyst in order to improve the activation of molecular oxygen. Vanillin yield resulted to benefit from high reaction temperature showing a maximum carbon yield of 22%, instead the formation of carboxylic acids from the oxidative degradation of AV largely benefits from high pressure of air, exhibiting an overall carbon yield of 35%. The produced compounds include oxalic, glycolic, lactic, malonic, and levulinic aci
Hydrodeoxygenation of guaiacol over Mo-based catalysts: A model reaction for the upgrading of lignin-derived bio-oils
No full text
Hydrodeoxygenation of guaiacol over molybdenum-based catalysts: The effect of support and the nature of the active site
No full textThe hydrodeoxygenation (HDO) of guaiacol has been chosen as a model process for the upgrading of lignin-derived bio-oils. Tests were carried out in a batch reactor at 350 °C, 4000 kPa of H2, in the presence of several Mo-based catalysts prepared by impregnation of ammonium molybdate on SiO2, Al2O3, NaY zeolite, MgO, activated carbon, and graphite. These materials have been characterized by means of: N2 physisorption, XRD, FESEM/EDS, XPS, TPR-H2, and TPD-NH3, with the aim of correlating the physical and chemical properties of the prepared samples with the resulting features in the HDO reaction. Mo on activated carbon showed the best performances towards guaiacol demethoxylation, exhibiting complete conversion, 72 % of selectivity to phenol, and 19 % to p- and o-cresol. The high surface area and low acidity of activated carbon allow good dispersion of MoOx which exhibits characteristic fragments with a lamellar shape, able to provide a large active surface with localized acidity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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