Xylose

Summary

Xylose ( ξύλον, , "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is derived from hemicellulose, one of the main constituents of biomass. Like most sugars, it can adopt several structures depending on conditions. With its free aldehyde group, it is a reducing sugar. Structure The acyclic form of xylose has chemical formula HOCH2(CH(OH))3CHO. The cyclic hemiacetal isomers are more prevalent in solution and are of two types: the pyranoses, which feature six-membered C5O rings, and the furanoses, which feature five-membered C4O rings (with a pendant CH2OH group). Each of these rings is subject to further isomerism, depending on the relative orientation of the anomeric hydroxy group. The dextrorotary form, -xylose, is the one that usually occurs endogenously in living things. A levo

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https://en.wikipedia.org/wiki/Xylose

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Lignocellulosic biomass is a sustainable source of renewable carbon, and it is the most abundant form of terrestrial biomass. The three main constituents of lignocellulosic biomass are cellulose, hemicellulose, and lignin. The monomers from these biopolymers can be valuable feedstocks for a future sustainable chemical industry, and they include glucose from cellulose, predominantly xylose from hemicellulose, and aromatic molecules from lignin. Even though both glucose and xylose are already established feedstocks for further upgrading in biorefineries, the upgrading of lignin to higher value-added chemicals has not achieved the same success, despite the tremendous need for renewable aromatic molecules. Developing methods for the high-yield depolymerization of lignin can dramatically increase the efficiency and profitability of biorefineries. The main limiting factor in producing high-quality lignin is the inter-unit carbon-carbon linkages in the chemical structure of lignin, and also the formation of these bonds during the extraction process, known as repolymerization or condensation. In the first part of my thesis, I study the possibility of avoiding the condensation of lignin by preventing the formation of C-C linkages. This is achieved by adding formaldehyde, as a protection group, to the pretreatment of lignocellulosic biomass. The results show a near theoretical yield of monomers from the stabilized lignin after depolymerization by hydrogenolysis. This method was then further expanded by screening other protecting groups in order to develop a comprehensive picture of the chemistry involved in this process, and to optimize the process notably to be able to yield a narrower product distribution. Even though this method provides high-quality lignin, there is a need for developing a fractionation process for large-scale production of isolated lignin. This can facilitate the implementation of the process in biorefineries and also further studies on developing new upgrading pathways. The second part of this thesis presents a protocol that fractionates lignocellulosic biomass into pure parts of three main constituents in large laboratory-scale with high extraction yields. The results show extraction yields higher than 95% for each biopolymer. The highly digestible cellulose fraction and high-quality lignin can be depolymerized into their constituent monomers with conventional methods. However, the hemicellulose fraction is obtained as functionalized sugars due to its reaction with aldehyde during pretreatment. The third part of my work presents a non-destructive method for the prediction of the potential yield of monomers from the depolymerization of isolated lignin. A novel 2D heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) spectroscopy technique can be used for simultaneous identification and quantification of chemical groups in the structure of lignin. Standard 2D-HSQC NMR spectroscopy does not provide accurate quantification for polymers and oligomers such as lignin due to errors that are principally caused by differences in relaxation times for different parts of the oligomer chain. However, these errors can be avoided by extrapolation to time-zero 13C HSQC (HSQC0) for series of spectrums, acquired with different repetition times. The prediction results show agreement within a few percentage points with experimental results determined by gas chromatography (GC) after hydrogenolysis.

EPFL2019

Sustainable polyesters via direct functionalization of lignocellulosic sugars

Adrien Julien Demongeot, Graham Reid Dick, Maxime Alexandre Clément Hedou, Harm-Anton Klok, Yves Leterrier, Jeremy Luterbacher, François Maréchal, Véronique Michaud, Thibault Rambert, Christèle Rayroud

The development of sustainable plastics from abundant renewable feedstocks has been limited by the complexity and efficiency of their production, as well as their lack of competitive material properties. Here we demonstrate the direct transformation of the hemicellulosic fraction of non-edible biomass into a tricyclic diester plastic precursor at 83% yield (95% from commercial xylose) during integrated plant fractionation with glyoxylic acid. Melt polycondensation of the resulting diester with a range of aliphatic diols led to amorphous polyesters (Mn = 30–60 kDa) with high glass transition temperatures (72–100 °C), tough mechanical properties (ultimate tensile strengths of 63–77 MPa, tensile moduli of 2,000–2,500 MPa and elongations at break of 50–80%) and strong gas barriers (oxygen transmission rates (100 µm) of 11–24 cc m−2 day−1 bar−1 and water vapour transmission rates (100 µm) of 25–36 g m−2 day−1) that could be processed by injection moulding, thermoforming, twin-screw extrusion and three-dimensional printing. Although standardized biodegradation studies still need to be performed, the inherently degradable nature of these materials facilitated their chemical recycling via methanolysis at 64 °C, and eventual depolymerization in room-temperature water.

2022

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Polysaccharide depolymerization is an essential step for valorizing lignocellulosic biomass. In inexpensive systems such as pure water or dilute acid mixtures, carbohydrate monomer degradation rates exceed hemicellulose—and especially cellulose—depolymerization rates at most easily accessible temperatures, limiting sugar yields. Here, we use a reversible stabilization of xylose and glucose by acetal formation with formaldehyde to alter this kinetic paradigm, preventing sugar dehydration to furans and their subsequent degradation. During a harsh organosolv pretreatment in the presence of formaldehyde, over 90% of xylan in beech wood was recovered as diformylxylose (compared to 16% xylose recovery without formaldehyde). The subsequent depolymerization of cellulose led to carbohydrate yields over 70% and a final concentration of ~5 wt%, whereas the same conditions without formaldehyde gave a yield of 28%. This stabilization strategy pushes back the longstanding kinetic limits of polysaccharide depolymerization and enables the recovery of biomass-derived carbohydrates in high yields and concentrations.

2018

EPFL2019