scholarly journals Valorization of Lignin via Oxidative Depolymerization with Hydrogen Peroxide: Towards Carboxyl-Rich Oligomeric Lignin Fragments

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2717
Author(s):  
Ulrike Junghans ◽  
Justin J. Bernhardt ◽  
Ronja Wollnik ◽  
Dominik Triebert ◽  
Gerd Unkelbach ◽  
...  

The extraction and characterization of defined and carboxyl-rich oligomeric lignin fragments with narrow molecular weight distribution is presented herein. With regard to the well-known pulp bleaching process, oxidative lignin depolymerization was investigated using hydrogen peroxide in an aqueous alkaline solution (i.e., at T = 318 K, t = 1 h) and subsequent selective fractionation with a 10/90 (v/v) acetone/water mixture. While the weight average molecular weight (MW) of lignin in comparison to the starting material was reduced by 82% after oxidation (T = 318 K, t = 1 h, clignin = 40 g L−1, cH2O2 = 80 g L−1, cNaOH = 2 mol L−1) and subsequent solvent fractionation (T = 298 K, t = 18 h, ccleavage product = 20 g L−1), the carboxyl group (–COOH) content increased from 1.29 mmol g−1 up to 2.66 mmol g−1. Finally, the successful scale-up of this whole process to 3 L scale led to gram amounts (14% yield) of oligomeric lignin fragments with a MW of 1607 g mol−1, a number average molecular weight (MN) of 646 g mol−1, a narrow polydispersity index of 3.0, and a high –COOH content of 2.96 mmol g−1. Application of these oligomeric lignin fragments in epoxy resins or as adsorbents is conceivable without further functionalization.

BioResources ◽  
2015 ◽  
Vol 10 (3) ◽  
pp. 4137-4151 ◽  
Author(s):  
Aikfei Ang ◽  
Zaidon Ashaari ◽  
Edi Suhaimi Bakar ◽  
Nor Azowa Ibrahim

An alkali lignin (OL) with a weight-average molecular weight (Mw) of 11646 g/mol was used to prepare low-molecular weight lignin for resin synthesis. The low-molecular weight lignin feedstock was obtained via base-catalysed depolymerisation (BCD) treatments at different combined severity factors. Sequential fractionation of the OL and BCD-treated lignins using organic solvents with different Hildebrand solubility parameters were used to alter the homogeneity of the OL. The yield and properties of OL itself and OL and BCD-treated OL dissolved in propan-1-ol (F1), ethanol (F2), and methanol (F3) were determined. Regardless of the treatment applied, a small amount of OL was dissolved in F1 and F2. The BCD treatment did not increase the yield of F1 but did increase the yields of F2 and F3. Gel permeation chromatography (GPC) showed that the repolymerization reaction occurred in F3 for all BCD-treated OL, so these lignins were not suitable for use as feedstocks for resin production. The GPC, 13Carbon-nuclear magnetic resonance, and Fourier transform infrared spectroscopy analyses confirmed that the F3 in OL exhibited the optimum yield, molecular weight distribution, and chemical structure suitable for use as feedstocks for resin synthesis.


Vestnik MGTU ◽  
2021 ◽  
Vol 24 (3) ◽  
pp. 267-276
Author(s):  
Y. A. Kuchina ◽  
I. N. Konovalova ◽  
V. Y. Novikov ◽  
N. V. Dolgopyatova ◽  
V. Ya. Kuznetsov

Due to its biocompatibility with human and animal tissues, low toxicity, and biodegradability, chondroitin sulfate (CS) is of great interest for medicine. Since CS is used as a pharmaceutical preparation, its molecular weight and solubility determine the possibilities of its use. This work presents the results of studying the chemical and enzymatic destruction of CS macromolecules and its effect on the molecular weight, solubility and crystallinity degree of the polysaccharide. CS was obtained from the cartilaginous tissue of the Arctic skate ( Amblyraja hyperborea ). At the stage of cartilage tissue fermentolysis, the enzymes pancreatin, hepatopancreatin and protosubtil were used. The obtained CS samples were identified by IR spectroscopy. Enzymatic destruction of glycosidic bonds in cholesterol macromolecules was carried out with a 1 % solution of the enzyme hepatopancreatin, chemical destruction with hydrogen peroxide and hydrochloric acid. The CS content in the samples was determined by the Dische method. The chemical composition of CS samples was evaluated by standard methods. The average molecular weight (MW) was determined using high performance liquid chromatography and the nephelometric method. The crystallinity degree (CD) was determined by graphical processing of diffraction patterns obtained by X-ray phase analysis of CS samples. It was found that under the action of hepatopancreatin and hydrogen peroxide, deep destruction of chondroitin sulfate occurs, to the formation of low molecular weight and oligomeric fragments. Under conditions of acid destruction in 0.5 N HCl for 20 min the MW of chondroitin sulfate is reduced by 10 % compared to the initial one. Acid destruction causes a significant decrease in the CD of the CS samples. For CS samples not degraded in acid, the solubility in distilled water increases with decreasing MW and CD. The solubility of CS after acid destruction in the range of pH = 5-9 units is 99.0 ± 0.5 %. This high solubility is most likely explained by the significant content of the amorphous phase in the samples.


RSC Advances ◽  
2017 ◽  
Vol 7 (84) ◽  
pp. 53117-53125 ◽  
Author(s):  
Jae-Young Kim ◽  
Shin Young Park ◽  
Jae Hoon Lee ◽  
In-Gyu Choi ◽  
Joon Weon Choi

The purpose of this study was to investigate the impact of lignin structure, especially its average molecular weight (Mw) on the distribution of catalytically depolymerized products.


2010 ◽  
Vol 62 (2) ◽  
pp. 340-346 ◽  
Author(s):  
S. H. Jee ◽  
Y. J. Kim ◽  
S. O. Ko

Dissolved organic matter (DOM) has significant influence on the transport and fate of contaminants in multiple phases and it has potential hazard by acting as a precursor of disinfection by-products in water supply. The changes in DOM characteristics, especially by oxidative polymerization might result in different behaviour in the interaction with many contaminants. The aim of this work was to verify the catalytic effects of peroxidase on oxidative polymerization of humic and fulvic substances by examination of the structural characteristics. Transformation of humic acid (HA) and fulvic acid (FA) by oxidative polymerization catalyzed by horseradish peroxidase and hydrogen peroxide were investigated. Size exclusion chromatography, excitation–emission matrices spectra (EEMs), synchronous fluorescence spectra, and infrared spectroscopy was used to evaluate the structural transformation of HA and FA. Molecular weight of HA and FA was continuously changed and their weight-average molecular weight (MWw) reached maximum after 8 h. The MWw of HA and FA were proportionally increased with a dosage of horseradish peroxidase and hydrogen peroxide, indicating that HA and FA was transformed into larger and complex molecules. Spectroscopic results indicated that HA and FA structure contains strong polycyclic aromatic structures with more aromatic rings and a higher degree of conjugation.


Biomass ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 11-28
Author(s):  
Danielle Munick de Albuquerque Fragoso ◽  
Henrique Fonseca Goulart ◽  
Antonio Euzebio Goulart Santana ◽  
Samuel David Jackson

In this work, a waste-derived lignin with abundant uncondensed linkages, using accessible solvents (acetone/water mixture) and low-cost catalysts showed successful depolymerization for the production of target molecules 4-ethylphenol, 4-propyl-2,6-dimethoxyphenol and 4-propyl-2-methoxyphenol. Lignin samples were obtained from sugar-cane bagasse residue by an organosolv process. Four alumina-based catalysts (Pt/Al2O3, Rh/Al2O3, Ni/Al2O3 and Fe/Al2O3) were used to depolymerize the sugar cane lignin (SCL) in an acetone/water mixture 50/50 v/v at 573 K and 20 barg hydrogen. This strategic depolymerisation-hydrogenolysis process resulted in the molecular weight of the SCL being reduced by half while the polydispersity also decreased. Catalysts significantly improved product yield compared to thermolysis. Specific metals directed product distribution and yield, Rh/Al2O3 gave the highest overall yield (13%), but Ni/Al2O3 showed the highest selectivity to a given product (~32% to 4-ethylphenol). Mechanistic routes were proposed either from lignin fragments or from the main polymer. Catalysts showed evidence of carbon laydown that was specific to the lignin rather than the catalyst. These results showed that control over selectivity could be achievable by appropriate combination of catalyst, lignin and solvent mixture.


Author(s):  
C. E. Cluthe ◽  
G. G. Cocks

Aqueous solutions of a 1 weight-per cent poly (ethylene oxide) (PEO) were degassed under vacuum, transferred to a parallel plate viscometer under a nitrogen gas blanket, and exposed to Co60 gamma radiation. The Co60 source was rated at 4000 curies, and the dose ratewas 3.8x105 rads/hr. The poly (ethylene oxide) employed in the irradiations had an initial viscosity average molecular weight of 2.1 x 106.The solutions were gelled by a free radical reaction with dosages ranging from 5x104 rads to 4.8x106 rads.


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