The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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SO2-Ethanol-Water (SEW) Fractionation of Lignocellulosics

Mikhail Iakovlev

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the School of Chemical Technology for public examination and debate in Auditorium Puu 2 at the Aalto University School of Chemical Technology (Espoo, Finland) on the 21st of October 2011 at 12 noon.

Overview in PDF format (ISBN 978-952-60-4314-2)   [1269 KB]
Dissertation is also available in print (ISBN 978-952-60-4313-5)

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.

This thesis consists of an overview and of the following 6 publications:

  1. Mikhail Iakovlev, Timo Pääkkönen, and Adriaan van Heiningen. 2009. Kinetics of SO2-ethanol-water pulping of spruce. Holzforschung, volume 63, number 6, pages 779-784. © 2009 Walter de Gruyter. By permission.
  2. Mikhail Iakovlev and Adriaan van Heiningen. 2011. SO2-ethanol-water (SEW) pulping: I. Lignin determination in pulps and liquors. Journal of Wood Chemistry and Technology, volume 31, number 3, pages 233-249.
  3. Mikhail Iakovlev, Herbert Sixta, and Adriaan van Heiningen. 2011. SO2-ethanol-water (SEW) pulping: II. Kinetics for spruce, beech, and wheat straw. Journal of Wood Chemistry and Technology, volume 31, number 3, pages 250-266.
  4. Mikhail Iakovlev and Adriaan van Heiningen. Efficient fractionation of spruce by SO2-ethanol-water (SEW) treatment: Material balances show complete recovery of carbohydrates and sulfur. Submitted.
  5. Mikhail Iakovlev and Adriaan van Heiningen. 2012. Kinetics of fractionation by SO2–ethanol–water (SEW) treatment: understanding the deconstruction of spruce wood chips. RSC Advances, volume 2, number 7, pages 3057-3068. © 2012 Royal Society of Chemistry (RSC). By permission.
  6. Mikhail Iakovlev, Eero Hiltunen, and Adriaan van Heiningen. 2010. Paper technical potential of spruce SO2-ethanol-water (SEW) pulp compared to kraft pulp. Nordic Pulp and Paper Research Journal, volume 25, number 4, pages 428-433. © 2010 by authors.

Keywords: biomass, biorefinery, fractionation of softwoods, sulfur dioxide -ethanol-water fractionation

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Last update 2012-07-20