Characterization of dissolved lignins from acetic acid Lignofibre (LGF) organosolv pulping and discussion of its delignification mechanisms

Heli Kangas (Corresponding Author), Tiina Liitiä, Stella Rovio, Taina Ohra-aho, Harri Heikkinen, Tarja Tamminen, Kristiina Poppius-Levlin

    Research output: Contribution to journalArticleScientificpeer-review

    15 Citations (Scopus)

    Abstract

    Birch chips were cooked by means of the Lignofibre (LGF) organosolv process in acetic acid (AA) and phosphinic acid (H3PO2) at 150°C. The delignification rate and structure of the dissolved lignin was followed as a function of time. The degree of delignification increased steadily up to 88% during the 120 min treatment time. The dissolved lignins were precipitated from the spent liquor (SL) by water addition, washed, and purified for the analyses. Elemental analysis, 31P nuclear magnetic resonance (NMR), heteronuclear single-quantum coherence (HSQC) NMR, pyrolysis-gas chromatography/mass spectrometry (GC/MS), and gel permeation chromatography (GPC) were applied for the structural elucidation. It was found that the cleavage of the ß-aryl ether linkages is the main reaction leading to delignification, accompanied by the formation of free phenolic hydroxyl groups and reduction in the content of aliphatic hydroxyl groups. The structure of the dissolved lignin remained the same after the drastic changes at the early stages of cooking (up to 30 min cooking time), indicating that secondary reactions (e.g., condensation) do not take place to a significant extent. H3PO2 probably enhances the acidolysis reaction via an ester derivative that both boosts the cleavage reaction and prevents the formation of the carbocation intermediate that induces condensation. Homolytic cleavage reactions may take place parallel to the acidolytic reactions.
    Original languageEnglish
    JournalHolzforschung
    Volume69
    Issue number3
    DOIs
    Publication statusPublished - 2015
    MoE publication typeA1 Journal article-refereed

    Keywords

    • acetic acid
    • degradation mechanism
    • delignification
    • lignin
    • Lignofibre (LGF) process
    • organosolv pulping
    • phosphinic acid

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