On the Course of Delignification During Kraft Pulping

Abstract

Keywords Kraft pulping Delignification Course of process Aryl ether cleavage Methylation Schlüsselwörter (Sachgebiete) Sulfatkochung Delignifizierung Prozeßverlauf Arylätherspaltung Methylierung On the Course of Delignification During Kraft PulpingSummary The correlation between aryl ether cleavage reactions and the initial and main (= bulk) phases of delignification during kraft pulping is supported by the behaviour of pre-methylated samples of softwood shavings. Methylation with diazomethane virtually eliminates the initial phase of delignification which is consistent with the view that cleavage of a-and /?-aryl ether bonds in phenolic arylpropane units is responsible for the lignin degradation during this phase. Methylation with methanolic hydrochloric acid considerably retards the delignification during the bulk phase in accordance with the assumption that cleavage of /3-aryl ether bonds in non-phenolic arylpropane units is the rate-determining reaction in the overall delignification during this latter phase. Finally, äs expected, methylation with dimethyl sulfat-alkali blocks delignification almost completely during the initial phase and further reduces the rate of delignification during the bulk phase. Über den Verlauf der Delignifizierung während der Kraftkochung ZusammenfassungDie Zuordnung von Arylätherspaltungsreaktionen zur Anfangs-und Hauptphase der Delignifizierung während der Kraftkochung wird durch das Verhalten von vormethylierten Proben von Nadelholzspänen gestützt: Methylierung mit Diazomethan eliminiert im wesentlichen die Anfangsphase der Delignifizierung. Dies stimmt mit dem Vorschlag überein, wonach die Spaltung von a-und 0-Arylätherbindungen in phenolischen Arylpropaneinheiten für den Ligninabbau während der Anfangsphase verantwortlich ist. Methylierung mit methanolischer Salzsäure verzögert stark die Delignifizierung während der Hauptphase, in Übereinstimmung mit der Annahme, daß die Spaltung von /?-Arylätherbindungen in nicht-phenolischen Arylpropaneinheiten die geschwindigkeitsbestimmende Teilreaktion der Delignifizierung während der Hauptphase darstellt. Schließlich blockiert Methylierung mit Dimethylsulfat-Alkali erwartungsgemäß die Delignifizierung während der Anfangsphase fast vollständig und setzt die Delignifizierungsgeschwindigkeit während der Hauptphase weiterhin herab.

Pyrolysis-gas chromatography/Mass spectrometry analysis of phenolic and etherified units in natural and industrial lignins

“…Veratrylglycerol--guaiacyl ether (a non-phenolic b-O-4 lignin model dimer) was synthesized by the method described by Adler et al 20 Exhaustive methylation of lignins was performed by a modification of procedures previously described. 21,22 A sample of 8 mg of lignin was dissolved in 1 mL of dioxane, and methylated with 1 mL of ethereal diazomethane (0.25 M) and 2 mL of methanol. Methylation was continued over 5 days, keeping the samples under magnetic stirring and adding 0.5 mL of fresh diazomethane per sample every 24 h. Then diazomethane was destroyed (by daylight) and solvent removed under vacuum (Speed-vac).…”

Demonstration ofIn Situ Oxidative Degradation of Lignin Side Chains by Two White-rot Fungi Using Analytical Pyrolysis of Methylated Wheat Straw

“…10 Exhaustive methylation was performed by a modification of procedures previously described. 11,12 100 mg of light petroleum-extracted straw were shaken for 7 days at room temperature in 10 mL of dioxan, and then methylated with 2.5 mL of ethereal diazomethane and 5 mL of methanol. Methylation was continued during 5 days, keeping the samples under magnetic stirring and adding 2 mL of fresh diazomethane per sample every 24 h.…”

Impact of effective alkali and sulfide profiling on Eucalyptus globulus kraft pulping. Selectivity of the impregnation phase and its effect on final pulping results

“…50% of total Na 2 S charge 100% of total Na 2 S charge Several authors have demonstrated that, in the initial phase of kraft delignification, the main lignin reactive structures are α-and β-ethers containing free phenolic hydroxyl groups. 26 The α-aryl ether bonds in both open and cyclic phenylcoumaran structures are readily cleaved by hydroxyl ions and the rate is independent of the hydroxide ion concentration, provided the phenolic hydroxyl group in the substrate is completely ionized. The cleavage of β-aryl ether structures (β-O-4) bonds are cleaved by hydrosulfide ions, after the conversion of that structure into the quinone methide structure by OH − .…”