SO2-ethanol-water (SEW) fractionation of lignocellulose

Mikhail Iakovlev

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    This study deals with SO2-ethanol-water (SEW) fractionation as a potential method for a Lignocellulosic Biorefinery to achieve high yield separation of the three important components of biomass; cellulose, hemicelluloses and lignin. Representatives of all principal biomass species were successfully treated by SEW fractionation at similar rates. The kinetics of delignification, polysaccharides removal and cellulose hydrolysis at different temperatures and SO2 concentrations are described and interpreted from the viewpoint of acid-catalysed degradation of the biomass polymers. The fractionation pattern is compared to that of commercial acid sulfite cooking. The kinetics of delignification, hemicelluloses removal and cellulose hydrolysis during SEW fractionation each follow a two phase behaviour. The delignification is first order in lignin and SO2. The observed lignin sulfonation and delignification patterns can be explained using Hägglund's consecutive fast sulfonation-slow hydrolysis scheme. During the initial phase of fractionation, the hemicelluloses removal and cellulose hydrolysis rates are related to the delignification rate, while in the following bulk phase the former two processes proceed independently from the latter. It is proposed that during the initial phase the hemicelluloses are removed together with lignin in the form of lignocarbohydrate complexes, while cellulose is protected by lignin from hydrolytic attack leading to a lower hydrolysis rate. Most hemicellulose side units as well as acetyl groups are cleaved during the first phase, while the glucomannan and xylan backbone polymers are removed at a considerably lower rate in the second (bulk) phase following first order kinetics in the residual polysaccharides. The observed polysaccharides dissolution behaviour can be interpreted in terms of low glucomannan stabilisation by crystallisation on cellulose at the applied conditions. Minimal cellulose dissolution occurs during fractionation, but the cellulose degree of polymerisation decreases by hydrolysis following zero-order kinetics. The products include cellulosic fibres and a spent liquor containing lignin and hydrolysed hemicellulose sugars, the latter present up to 50% in monomeric form. The investigated overall and carbohydrate material balances show no carbohydrate losses as further supported by very low amounts of formed oxidation and dehydration products. The properties of the fibre products are evaluated and their potential applications are discussed. The amount of sulfur bound to lignin is 2-3 times lower than that in acid sulfite cooking, and accounts for less than 1.1% on wood. The rest of SO2 (95-97%) can be fully recovered by distillation.
    Translated title of the contributionSO2 -ethanol-water (SEW) fractionation of lignocellulose
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • van Heiningen, Adriaan, Supervising Professor
    • van Heiningen, Adriaan, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-4313-5
    Electronic ISBNs978-952-60-4314-2
    Publication statusPublished - 2011
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • biomass
    • biorefinery
    • fractionation of softwoods
    • SO2 -ethanol-water fractionation

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