Lignin reactions in oxygen delignification catalysed by Mn(II)-substituted molybdovanadophosphate polyanion

Holzforschung ◽  
2004 ◽  
Vol 58 (6) ◽  
pp. 640-649 ◽  
Author(s):  
Armindo Gaspar ◽  
Dmitry V. Evtuguin ◽  
Carlos Pascoal Neto
Keyword(s):  
Eucalyptus Globulus ◽  
Oxidative Degradation ◽  
Reaction System ◽  
Reaction Products ◽  
Oxygen Delignification ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Qualitative And Quantitative ◽  
Lignin Model ◽  
Oxidative Delignification

Abstract The lignin oxidation in the oxygen delignification/bleaching process catalysed by Mn(II) substituted heptamolybdopentavanadophosphate polyanion (HPA-5-MnII) was studied using monomeric lignin model compounds and Eucalyptus globulus dioxane lignin adsorbed on the bleached sulphite pulp. The analysis of reaction products after lignin models oxidation in the presence HPA-5-MnII and the parent heptamolybdopentavanadophosphate polyanion (HPA-5) showed similar qualitative and quantitative patterns, indicating the identical lignin oxidative delignification mechanisms with both catalysts. The higher delignification selectivity of the pulp in the reaction system HPA-5-MnII/O2 than with HPA-5/O2 was explained by the protective effect of MnII in the heteropolyanion towards oxidative degradation of polysaccharides. The study of lignin adsorbed on bleached sulphite pulp, in the HPA-5-MnII/O2 delignification system, showed the cleavage of β-O-4 linkages as the major contribution to the lignin depolymerisation. The formation of Cα-O-polysaccharide linkages in β-O-4 structures of lignin during the delignification was observed.

Lignin Degradation in Oxygen Delignification Catalysed by [PMo7V5O40]8- Polyanion. Part II. Study on Lignin Monomeric Model Compounds

Holzforschung ◽  
2000 ◽  
Vol 54 (5) ◽  
pp. 511-518 ◽  
Author(s):  
D.V. Evtuguin ◽  
C. Pascoal Neto ◽  
H. Carapuça ◽  
J. Soares
Keyword(s):  
Reaction System ◽  
Veratryl Alcohol ◽  
Vanillyl Alcohol ◽  
Coupling Reactions ◽  
Reaction Products ◽  
Oxygen Delignification ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Oxidation ◽  
Lignin Model

Summary Vanillyl and veratryl alcohols were used as monomeric lignin model compounds in experiments aiming to enhance the understanding of the lignin oxidation mechanisms involved in the oxygen delignification in acidic media catalysed by [PMo7V5O40]8− (HPA-5) heteropolyanion. Based on the model compound experiments, the first step of lignin oxidation is suggested to be a one-electron oxidation by the catalyst. This step is followed by coupling reactions and/or by further oxidation by the catalyst. The ratio of coupling/oxidation reaction products depends on the oxidation conditions and decreases with temperature raise. The higher oxidation rate of vanillyl alcohol as compared to the veratryl alcohol in the reaction system O2/HPA-5 was explained by the redox properties of the catalyst. The insufficiently high redox potential of HPA-5 did not allow the efficient oxidation of veratryl alcohol. The former was oxidised by VO2 + ions dissociated from the HPA-5 under the acidic conditions. The reactivity of different lignin structural units in the reaction system O2/HPA-5 was estimated by electrochemical methods using various lignin model compounds.

scholarly journals A two-phase reaction system for selective oxidative degradation of lignin model compounds

BioResources ◽  
2020 ◽  
Vol 15 (3) ◽  
pp. 6526-6538
Author(s):  
Yueying Chen ◽  
Aiguo Xue ◽  
Haomin Jiang ◽  
Yujuan Cheng ◽  
Yuan Ren ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Oxidative Degradation ◽  
Reaction System ◽  
Value Added ◽  
Bottom Phase ◽  
Phase Reaction ◽  
Model Compounds ◽  
Two Phase ◽  
Lignin Model Compounds ◽  
Lignin Model

Lignin depolymerization through an oxidation method could provide value-added products, but it is challenging in terms of recovering catalysts or separating products in time to avoid over-oxidation. In this study, a process of selectively oxidative degradation of lignin model compounds was operated in a two-phase reaction system. Lignin model compounds of 4-benzyloxyphenol (PBP) or guaiacylglycerol-β-guaiacyl ether (GGE) in a bottom phase of 1-butyl-3-methylimidazole chloride ([BMIM]Cl) ionic liquid were selectively oxidized by H2O2 in the presence of a solid acid (SO42-/Fe2O3-ZrO2), and the degradation products immediately diffused into the upper organic solvent phase (butyl acetate). In this kind of reaction system, the yield of the products was improved due to the prolonged life of ∙OH in ionic liquid, and the product selectivity was maintained due to the timely product separation, and the ionic liquid and the catalyst were easily recycled.

Study of kinetics of reaction of lignin model compounds with propylene oxide

Holzforschung ◽  
2008 ◽  
Vol 62 (2) ◽  
pp. 169-175 ◽  
Author(s):  
Krishna K. Pandey ◽  
Tapani Vuorinen
Keyword(s):  
Chemical Reaction ◽  
Propylene Oxide ◽  
Aqueous Media ◽  
Reaction Products ◽  
Model Compounds ◽  
Rapid Reduction ◽  
Visible Absorption ◽  
Lignin Model Compounds ◽  
Lignin Model ◽  
Kinetics Of

Abstract The etherification of phenolic groups has been found to inhibit photodegradation in wood and lignin rich pulps. The precise understanding of kinetics of chemical reaction between lignins or their model compounds and the etherifying agent is the first step for developing a viable modification procedure. In this study, we have investigated the reaction of lignin model compounds (namely, phenol and guaiacol) with propylene oxide in aqueous media. The kinetics of etherification reaction was studied under varying pH conditions in the temperature range 30–60°C. The etherified reaction products were characterized by gas chromatogram-mass spectrum (GC-MS). The extent of etherification of phenols and the rate of chemical reaction was followed by UV-Visible absorption spectroscopy. The reaction between lignin model compounds and propylene oxide was indicated by a rapid reduction in the absorbance accompanied by the development of a new band corresponding to etherified products. The reaction kinetics was investigated at pH ∼12 under the condition of excess concentration of propylene oxide. The reaction followed first order kinetics and rate constants increased linearly with an increase in the temperature and concentration of propylene oxide. The MS fragment data of reaction product support the proposed reaction scheme. The activation energy of the reaction of propylene oxide with phenol and guaiacol, calculated with the Arrhenius equation, was 56.2 kJ mol-1 and 45.4 kJ mol-1, respectively.

The Reactions of Lignin Model Compounds with Hydrogen Peroxide at Low pH

Holzforschung ◽  
2003 ◽  
Vol 57 (1) ◽  
pp. 52-88 ◽  
Author(s):  
T. Kishimoto ◽  
J. F. Kadla ◽  
H.-m. Chang ◽  
H. Jameel
Keyword(s):  
Hydrogen Peroxide ◽  
Reaction System ◽  
Model Compounds ◽  
Reaction Conditions ◽  
Lignin Model Compounds ◽  
Lignin Model Compound ◽  
Lignin Model ◽  
Decreasing Ph ◽  
Hydroxyl Compounds ◽  
Acidic Hydrogen

Summary In peroxymonosulfuric acid bleaching, the presence of hydrogen peroxide is dependent on the reaction conditions and the conversion ratios used to generate the peroxy acid. Substantial amounts of hydrogen peroxide may be present in the reaction system under certain conditions. An understanding of the reactions of hydrogen peroxide under these conditions would be beneficial. Therefore, several simple lignin model compounds were reacted with acidic hydrogen peroxide, pH 1-3, at 70°C. In all cases the phenolic lignin model compounds reacted much faster than their non-phenolic counterparts. In fact, the extent of reaction was very much dependent on the structure of the lignin model compound. The α-hydroxyl compounds, 4-(1-Hydroxy-ethyl)-2-methoxy-phenol and 1-(3,4-Dimethoxy-phenyl)-ethanol, reacted faster than the corresponding α-carbonyl compounds with both reacting much faster than the aromatic compounds, with simple alkyl substituents. A new reaction mechanism for α-hydroxyl compounds is proposed, in which benzyl carbocation formation is followed by nucleophilic addition of hydrogen peroxide. Unlike the mechanisms proposed in the past, no evidence of aromatic hydroxylation via perhydronium ion was observed. The reactivities were very pH dependent, in that higher reactivity was associated with lower pH. Decreasing pH further increased the amount of condensation products identified, such that condensation was competitive with degradation. These condensation reactions were also present under the Caro's acid bleaching conditions at pH below 2. However, under all conditions the reactivity of acidic peroxide was found to be much less than that of peroxymonosulfuric acid.

Oxidative Degradation of Dimeric Lignin Model Compounds

2001 ◽  
pp. 197-210 ◽  
Author(s):  
Carmen Canevali ◽  
Franca Morazzoni ◽  
Marco Orlandi ◽  
Bruno Rindone ◽  
Roberto Scotti ◽  
...  
Keyword(s):  
Oxidative Degradation ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Lignin Model

Oxalate formation during ClO2 bleaching of bamboo kraft pulp

2020 ◽  
Vol 35 (1) ◽  
pp. 18-24
Author(s):  
Hailong Li ◽  
Chao Du ◽  
Shujuan Ge ◽  
Mengru Liu
Keyword(s):  
Chlorine Dioxide ◽  
Kraft Pulp ◽  
Reaction System ◽  
Kappa Number ◽  
Pulp Bleaching ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Bleaching Process ◽  
Prolonged Reaction Time ◽  
Lignin Model

AbstractThis study aimed to investigate the oxalate formation mechanism during chlorine dioxide ({\mathrm{ClO}_{2}}) bleaching of bamboo kraft pulp, and thus explore favourable {\mathrm{ClO}_{2}} bleaching conditions to better control oxalate formation. The amount of oxalate formed varied linearly with {\mathrm{ClO}_{2}} dosage within the whole research range, while it rose exponentially within the first 90 mins of pulp bleaching. Then the actual bleaching process was simulated by reacting {\mathrm{ClO}_{2}} with three representative lignin model compounds and comparatively studied. The rule of oxalate formation in the simulated reaction system was identical to that in pulp bleaching by {\mathrm{ClO}_{2}}, except for oxalate production by veratraldehyde with prolonged reaction time. Under identical conditions, vanillin formed the highest amount of oxalate, while veratraldehyde formed the least. Furthermore, the amount of oxalate formed increased by 19.59 mg/kg when the kappa number of the delignified pulp was reduced by one unit. Considering the satisfactory pulp brightness and decreased oxalate formation, the recommended conditions for {\mathrm{ClO}_{2}} bleaching of bamboo kraft pulp were a {\mathrm{ClO}_{2}} dosage of 4 %, 60 °C and 70 mins.

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