| Naslov: | Modelling-assisted optimisation of hemicellulose-derived monosaccharide valorization : dissertation |
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| Avtorji: | ID Jakob, Ana (Avtor)
ID Grilc, Miha (Mentor) Več o mentorju...  |
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| Datoteke: |  Ana_Jakob.pdf (11,80 MB)
MD5: E696DDE9FA7A4BF95013A962BCF75334
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| Jezik: | Angleški jezik |
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| Vrsta gradiva: | Doktorsko delo/naloga |
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| Tipologija: | 2.08 - Doktorska disertacija |
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| Organizacija: | FPŠ - Fakulteta za podiplomski študij
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| Opis: | Hemicellulose, one of the key components of lignocellulosic biomass, and its sugar monomers offer significant potential as a substrate for producing value-added platform chemicals. With both pentoses (xylose and arabinose) and hexoses (glucose, galactose, and mannose), the conversion of hemicellulose can yield various products including furfural, hydroxymethylfurfural (HMF), and levulinic acid. This doctoral thesis investigates the dehydration of various hemicellulose-derived monosaccharides, utilizing catalyst-free systems, as well as homogeneous and heterogeneous catalysts, in both aqueous and organic solvents. Monosaccharide conversion was evaluated in a catalyst-free aqueous solution at temperatures ranging between 130 – 190 °C. Conducting dehydration reactions under simple, hydrothermal conditions highlighted the differences in the reactivity of individual monosaccharides. Experimental data from extensive activity testing enabled the development of accurate kinetic models. Aiming at the optimization of reaction parameters relevant to the post-Organosolv production of furanics and levulinic acid, sulfuric and formic acid were introduced into the reaction system as homogeneous acid catalysts. Reaction kinetics of acid catalysed conversion using sulfuric and formic acid indicated a significant reduction in the activation energy of ketose dehydration. In addition, the addition of both acids enhanced the dehydration rates and promoted the conversion of HMF towards levulinic acid due to its low activation energies 86 – 91 kJ mol−1 and high reaction rate constants. The established kinetic model for individual saccharides was proven to be robust and able to accurately predict optimal reaction conditions for two distinct industrially relevant hemicellulose streams. In pursuit of a more sustainable and recyclable catalyst, various zeolites, specifically H-BEA, were tested. Although H-BEA exhibited excellent catalytic activity, its selectivity towards furanics remained limited in aqueous media. The low activation energy for HMF rehydration facilitated the formation of levulinic acid even at a moderate reaction temperature of 165 °C. Notably, the addition of THF as an organic solvent in combination with H-BEA, drastically improved the product selectivity towards furanics, particularly furfural. In addition to H-BEA zeolite, various types of zeolites with different Si/Al ratios were studied. Catalyst characterization revealed a strong correlation between catalytic activity and acidity. The addition of THF resulted in 90 mol % of furfural after only 30 min, demonstrating an exponential increase in dehydration rates and a decrease in activation energies. This zeolite-THF system was therefore applied for tandem reactions involving both xylose dehydration and furfural hydrogenation. The addition of metallic active sites via a Ni/H-BEA catalyst, and a hydrogen atmosphere, resulted in the catalytic hydrogenation of xylose to tetrahydrofurfuryl alcohol. Adjusting reaction temperatures allowed the production of secondary hydrogenated (2-methylfuran and 2-methyltetrahydrofuran) and dehydration products (tetrahydropyran), while the addition of water as a co-solvent with THF resulted in the complete inhibition of dehydration reactions and the selective formation of xylitol. Through a systematic study of reaction conditions and the development of comprehensive kinetic models, this work provides an in-depth investigation of monosaccharide dehydration. This doctoral thesis represents a comprehensive study to systematically investigate both catalytic and non-catalytic dehydration of five relevant monosaccharides, providing a methodical kinetic modelling approach that addresses the challenges associated with the complexity related to hemicellulose conversion. |
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| Ključne besede: | hemicellulose, monosaccharides, kinetic modelling, furanics, catalysis, dissertations |
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| Status publikacije: | Objavljeno |
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| Verzija publikacije: | Objavljena publikacija |
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| Kraj izida: | Nova Gorica |
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| Kraj izvedbe: | Nova Gorica |
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| Založnik: | A. Jakob |
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| Leto izida: | 2025 |
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| Leto izvedbe: | 2025 |
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| Št. strani: | XXIV, 25-204 str. |
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| PID: | 20.500.12556/RUNG-9826 |
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| COBISS.SI-ID: | 226676995 |
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| UDK: | 54 |
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| NUK URN: | URN:SI:UNG:REP:IAKGIQNR |
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| Datum objave v RUNG: | 19.02.2025 |
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| Število ogledov: | 182 |
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| Število prenosov: | 1 |
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| Metapodatki: |    |
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