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| 2. |
- Abdelaziz, Omar Y., et al.
(författare)
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On the Oxidative Valorization of Lignin to High-Value Chemicals : A Critical Review of Opportunities and Challenges
- 2022
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 15:20
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Forskningsöversikt (refereegranskat)abstract
- The efficient valorization of lignin is crucial if we are to replace current petroleum-based feedstock and establish more sustainable and competitive lignocellulosic biorefineries. Pulp and paper mills and second-generation biorefineries produce large quantities of low-value technical lignin as a by-product, which is often combusted on-site for energy recovery. This Review focuses on the conversion of technical lignins by oxidative depolymerization employing heterogeneous catalysts. It scrutinizes the current literature describing the use of various heterogeneous catalysts in the oxidative depolymerization of lignin and includes a comparison of the methods, catalyst loadings, reaction media, and types of catalyst applied, as well as the reaction products and yields. Furthermore, current techniques for the determination of product yields and product recovery are discussed. Finally, challenges and suggestions for future approaches are outlined.
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| 3. |
- Abdelaziz, Omar Y., et al.
(författare)
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Oxidative Depolymerisation of Lignosulphonate Lignin into Low-Molecular-Weight Products with Cu–Mn/δ-Al2O3
- 2019
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 62, s. 639-648
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Tidskriftsartikel (refereegranskat)abstract
- Lignin depolymerisation receives great attention due to the pressing need to find sustainable alternatives to fossil sources for production of fuels and chemicals. In this study, alumina-supported Cu–Mn and Ni–Mo catalysts were tested for oxidative depolymerisation of a technical lignin stream—sodium lignosulphonates—to produce valuable low-molecular-weight aromatics that may be considered for applications in the fuels and chemicals sector. The reactions were performed at elevated temperature and oxygen pressure, and the product mixtures were analysed by size exclusion chromatography, two-dimensional nuclear magnetic resonance spectroscopy and supercritical fluid chromatography mass spectrometry. The best performance was obtained with Cu–Mn/δ-Al 2 O 3 , which was thoroughly characterised before and after use by nitrogen physisorption, scanning electron microscopy, energy dispersive spectroscopy, powder X-ray diffraction, thermal gravimetric analysis, inductively coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. Major products identified were vanillin, p-hydroxybenzaldehyde, vanillic acid and p-hydroxybenzoic acid as well as smaller aliphatic aldehydes, acids and lactones.
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| 4. |
- Abdelaziz, Omar Y., et al.
(författare)
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Oxidative Depolymerization of Kraft Lignin for Microbial Conversion
- 2019
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:13, s. 11640-11652
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Tidskriftsartikel (refereegranskat)abstract
- The valorization of lignin is being increasingly recognized as crucial to improve the economic viability of integrated biorefineries. Because of its inherent heterogeneity and recalcitrance, lignin has been treated as a waste product in the pulp and paper industry, but new technologies are now being explored to transform lignin into a sustainable resource and enhance its value chain. In the present study, alkaline oxidative depolymerization was investigated as a potential form of pretreatment to enable further biological conversion of LignoBoost kraft lignin (LB). LB lignin oxidation reactions were studied at various temperatures (120-200 °C) and O2 partial pressures (3-15 bar) to identify the optimal conditions for obtaining a biocompatible, oxidatively depolymerized lignin (ODLB) stream. The low molecular weight compounds resulting from this treatment consisted mainly of aromatic monomers and carboxylic acids. The highest yield of aromatic monomers, 3 wt %, was obtained at 160 °C and 3 bar O2. The yield of carboxylic acids increased with both increasing temperature and O2 pressure, exceeding 13% under the harshest conditions investigated. The growth of four aromatic-catabolizing bacterial strains was examined on reaction product mixtures, all of which showed growth on agar plates utilizing ODLB as the sole source of carbon and energy. Rhodococcus opacus and Sphingobium sp. SYK-6 were found to consume most of the aromatic monomers present in the ODLB (e.g., vanillin, vanillate, acetovanillone, and guaiacol). The findings of this study indicate that pretreatment by oxidative depolymerization has potential in the biological valorization of technical lignin streams, for the production of valuable chemicals and materials.
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| 5. |
- Abdelaziz, Omar Y., et al.
(författare)
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Oxidative Depolymerization of Kraft Lignin to Aromatics Over Bimetallic V–Cu/ZrO2 Catalysts
- 2023
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Ingår i: Topics in Catalysis. - 1022-5528. ; 66:17-18, s. 1369-1380
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Tidskriftsartikel (refereegranskat)abstract
- Zirconia-supported vanadium–copper catalysts (VCux:yZr) were used for the oxidative depolymerization of softwood LignoBoost Kraft lignin (LB). Various VCux:yZr catalysts were prepared (x:y = 0:1, 1:4, 1:2, 3:4, 1:1, and 1:0) by incipient wetness impregnation, and reactions were performed in alkaline water at 150 °C under an O2 pressure of 5 bar for 10 min. 1H–13C HSQC NMR spectroscopy was used for product identification and quantification. The most promising catalyst was VCu1:2Zr, giving a total monomer yield of 9 wt% and the highest selectivity for vanillin (59%). This catalyst was characterized before and after use by N2 physisorption, XRD, TGA, SEM-EDS, and XPS. Cleavage of the main interunit linkages in LB, including the β-O-4 bonds and recalcitrant C–C bonds, was also observed. The findings of this study demonstrate the potential of the V–Cu/ZrO2 catalyst system in the production of value-added aromatics from technical lignin under relatively mild conditions. This would contribute to the more sustainable use of an underutilized side-stream in forest-based industries, provided catalyst reuse can be successfully demonstrated.
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| 6. |
- Walch, Florian, et al.
(författare)
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Oxidative depolymerization of Kraft lignin to high-value aromatics using a homogeneous vanadium–copper catalyst
- 2021
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Ingår i: Catalysis Science and Technology. - 2044-4753. ; 11, s. 1843-1853
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Tidskriftsartikel (refereegranskat)abstract
- Lignin, the world's most abundant biopolymer with high aromaticity, has huge potential as a renewable feedstock replacing petroleum for the production of chemicals, fuels and functional materials. The enhanced utilization of lignin would improve the economic viability of existing pulp and paper mills, as well as lignocellulosic biorefineries, where lignin is highly available, but mostly incinerated for energy recovery. Catalysis could be of crucial importance to improve current depolymerization strategies, and hence contribute to a more sustainable and responsible use of terrestrial resources. In the present study, the impact of different homogeneous transition-metal catalysts on the oxidative depolymerization of a technical softwood Kraft lignin was investigated. The reactions were carried out using molecular oxygen under rather mild operating conditions and the produced aromatic monomers included, among others, vanillin, vanillic acid and acetovanillone. The best performing system incorporated a VO(acac)2–Cu(OAc)2 (V–Cu) catalyst, resulting in a bio-oil yield of approximately 50% and a total increase in aromatic monomers of 27%, on a weight basis. Moreover, a favorable combined effect between VO(acac)2 and Cu(OAc)2 was suggested by NMR spectroscopy. UHPLC-HRMS and corresponding statistical analysis revealed a more than 30-fold increase in two aromatic molecules with an oxoacetic functionality and oxalic acid as well as a focusing effect on selected molecules, when employing the V–Cu catalyst. The findings of this study indicate that the V–Cu catalyst system is promising for the efficient conversion of technical lignin into value-added aromatic chemicals. However, catalyst recycling and reuse must be demonstrated, for successful implementation under industrial conditions.
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| 7. |
- Zhu, Ping, et al.
(författare)
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New synthetic approaches to biofuels from lignocellulosic biomass
- 2020
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Ingår i: Current Opinion in Green and Sustainable Chemistry. - : Elsevier BV. - 2452-2236. ; 21, s. 16-21
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Forskningsöversikt (refereegranskat)abstract
- Lignocellulose from terrestrial plant biomass is abundant and contains polymeric carbohydrates and lignin; both recognized as attractive renewable feedstocks for energy, chemicals and materials as alternatives to fossils to meet the targets for future sustainable development. Liquid biofuels are particularly important renewable commodities because of the vast infrastructure already in place to use them, especially for transportation, and efficient synthetic approaches and viable commercial manufacture processes are under development for both drop-in fuels and new fuel compounds. This work surveys the recent trends in lignocellulosic biomass conversion into fuels, and highlights innovative synthetic approaches based on novel chemo- and bio-catalyst systems and process strategies using biomass-derived carbohydrates and technical lignin.
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