Extraction of Hemicelluloses from a Kraft Paper Pulp with an Ionic Liquid water Mixture

Annariikka Roselli

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

This study introduces the IONCELL-P(ulp) process, which refines hemicellulose-rich bleached paper grade pulp to high purity dissolving pulp and polymeric hemicelluloses without yield losses or polymer degradation. Both fractions, the cellulose and dissolved hemicellulose, can be recovered quantitatively, providing a basis for a new stream of hemicellulose products and dissolving pulp production. In order to provide valuable information for the process up-scaling, the features that affect the extraction (solvent and substrate properties, reaction conditions) and equipment requirements were studied profoundly. The studies progressed by examining the usability of the separated polymer fractions, by investigating the purity, reactivity and integrity of the polymers. The results revealed that the solvation selectivity towards hemicelluloses was governed by the molecule size of the carbohydrate polymers. Short hemicelluloses dissolve more readily in aqueous ionic liquids, while the cellulose fraction remains intact. Thus, the molar mass distribution (MMD)of the pulp is a decisive feature regarding the suitability of this pulp for the IONCELL-P process. A distinct difference in the size of hemicelluloses and cellulose allows for a more accurate tuning of the solvent-water mixture for the selective and efficient extraction of hemicelluloses. A selection of different cellulose dissolving ionic liquids were tested in the process and a joint behaviour of the solvent mixtures was found, when the β-value, describing the anion's ability to accept hydrogen bonds, was divided with the water molar fraction of the solvent system. The resulting β/χ(H2O)-value gives an approximation of the relative strength of the solvent, which is needed for maximal hemicellulose solvation, but it does not describe the limit, where a certain solvent mixture loses its selectivity towards hemicelluloses and begins to dissolve increasing amounts of cellulose. The selectivity of the solvent system was also investigated in the terms of pH.Low pH ionic liquids demanded less water to render them to hemicellulose solvents and they were less inclined to swell and dissolve cellulose. Combining these findings, the IONCELL-P process is most efficient when using a pulp with a distinct difference in the MMD between the cellulose and hemicellulose fractions and an ionic liquid with low pH and relatively high β-value. The IONCELLP purified pulp is highly reactive and suitable for various applications such as cellulose acetate production. The process preserves the cellulose I crystalline structure and neither of the fractions, cellulose or hemicellulose, undergoes degradation reactions.
Translated title of the contributionIonisiin nesteisiin perustuva hemiselluloosien eristys Kraft sellumassasta
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Sixta, Herbert, Supervising Professor
  • Hummel, Michael, Thesis Advisor
Publisher
Print ISBNs978-952-60-7569-3
Electronic ISBNs978-952-60-7568-6
Publication statusPublished - 2017
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • IONCELL-P
  • dissolving pulp
  • hemicellulose extraction
  • ionic liquids

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