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- Areskogh, Dimitri, 1982-
(författare)
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Structural Modifications of Lignosulphonates
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignosulphonates are by‐products from the sulphite pulping process for the manufacture ofspecialty dissolving pulps and paper. During the liberation of the cellulose, the lignin isfractionated and solubilised through covalent addition of sulphonic acid groups at variouspositions in the structure. The formed sulphonated lignin, lignosulphonate is then furtherisolated and refined. The amphiphilic nature of lignosulphonates has enabled them to be used as additives to varioussuspensions to improve their dispersion and stability. The by far largest utilisation oflignosulphonates is as dispersants in concrete. Here, lignosulphonates act by dispersing cementparticles to prevent flocculation, un‐even particle distribution and reduced strengthdevelopment. The dispersion is achieved through steric and electrostatic repulsion of the cementparticles by the lignosulphonate polymer. This behaviour is intimately linked with the overallsize and amount of charged groups in the dispersing polymer. Traditional modifications oflignosulphonates have been limited to removal of sugars, filtration and fractionation. Thesemodifications are not sufficient for utilisation of lignosulphonates in high‐strength concrete. Heresynthetic dispersants and superplasticisers are used which are considerably more efficient evenat low dosages. To compete with these, additional modifications of lignosulphonates are likely tobe necessary. The molecular weight and functional group composition have been identified anddescribed as the most interesting parameters that can be modified. Currently, no suitable method exists to increase the molecular weight of lignosulphonates.Oxidation by the natural radical initiating enzyme laccase is an interesting tool to achieve suchmodifications. In this thesis several aspects of the mechanism through which this enzyme reactswith lignin and lignosulphonate structures have been elucidated through model compoundstudies. Further studies showed that laccase alone was a highly efficient tool for increasing themolecular weight of commercial lignosulphonates at low dosages and in short incubation times.Immobilisation of the laccase to a solid support to enable re‐utilisation was also investigated. Modification of functional group composition of lignosulphonates was achieved throughozonolysis and the Fenton’s reagent, a mixture of hydrogen peroxide and iron(II)acetate.Introduction of charged carboxylic groups was achieved through opening of the benzyl rings oflignosulphonates. It was found that a two‐stage process consisting of laccase oxidation followedby ozonolysis was an efficient technique to create a polymer enriched with carboxylic acidgroups with a sufficient molecular size. Oxidation by the Fenton’s reagent was shown to yield similar modifications as the combinedlaccase/ozonolysis treatment albeit with less pronounced results but with a large level of controlthrough variation of a number of reaction parameters. The Fenton’s reagent can therefore be aninteresting alternative to the aforementioned two‐stage treatment. These modifications are interesting for large‐scale applications not only because of theirsimplicity in terms of reaction parameters but also because of the ubiquity of the used enzymeand the chemicals in the pulp and paper industry.
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| 2. |
- Helander, Mikaela, 1982-
(författare)
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The Use of Membrane Filtration to Improve the Properties of Extracted Wood Components
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The forest is alarge and important natural resourcein Sweden, and approximately 70% of the country’s land area is woodland. Wood is an excellent raw material for the replacement of oil-based products because it is renewable, biodegradable and carbon neutral. Furthermore, the forest industry is searching for new processes and methods to utilise by-product streams in a so-called integrated biorefinery. A key to the success of producing new products from wood could be pure and homogenous raw materials. Because wood contains a large variety of components with different characteristics and sizes, cross-flow filtration (CFF) will be a key separation technique to obtain homogenous and pure raw materials in the biorefinery concept.Different wood material components have been studied in this thesis. The first part of this work focuses on kraft lignin. Kraft lignin is interesting because approximately 3.5-4 million metric tonnes are produced in Sweden annually (~7million tonnes of kraft pulp/year in 2012), and today it is mainly used as fuel. The second part of this thesis deals with materials in hot water extract (i.e., galactoglucomannan, but also other components). These extracted materials are interesting because similar materials are extracted in thermomechanical pulping process by-product streams. Finally, nanocellulose has been studied since it is an interesting raw material for future applications.Through CFF, kraft lignin from black liquor has been fractionated into raw material samples with more homogeneous characteristics such as molecular weight, aromatic hydroxyl groups and thermal properties. From dynamic mechanical analysis, low molecular weight fractions were found to have the highest degree softening. To precipitate low molecular weight fractions (<1000 Dacut-off) into a convenient solid, lower temperatures than forhigh molecular weight fractions were needed. To produce low molecular weight lignin (<5000 Da cut-off) from re-dissolved LignoBoost lignin, lower lignin concentrations and higher pH and ionic strength were found to increase the permeate fluxat the tested conditions.Nanocellulose has been producedby a novel process called nanopulping and has subsequently been size fractionated by CFF to obtain more homogenous nanocellulose.CFF and adsorption chromatography can be used to isolate dissolved wood components, yielding several upgraded products: lignin, lignin-carbohydrate complexes, and galactoglucomannan.
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| 3. |
- Sjöde, Anders, 1977-
(författare)
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Chemical characterization in the biorefinery of lignocellulose : Formation and management of oxalic acid and analysis of feedstocks for bioethanol production
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The pulp and paper industry is entering a new era. Pulp mills will be transformed to biorefineries that produce not only pulp, but also biofuels and novel products from lignocellulose. This thesis addresses problems connected with the industrial transition to environmental-friendly technologies and the implementation of the biorefinery concept. Peroxide bleaching and enhanced recirculation of process water may lead to increased problems with oxalate scaling. Enzymatic elimination of the oxalate problem could be the ultimate industrial solution. The activities of oxalate oxidase, oxalate decarboxylase and a novel oxalate-degrading enzyme provided by Novozymes have been tested in industrial bleaching filtrates. Chemical characterization of the filtrates was used in combination with multivariate data analysis to identify potential enzyme inhibitors. A method based on oxalate oxidase was developed to determine the levels of oxalic acid in process water. The precursors of oxalic acid formed during bleaching of pulp have been reassessed. New experimental data indicate that alkaline oxidative degradation of dissolved carbohydrates is the main source of oxalic acid. These findings are contradictory to previous hypotheses, which have been focused on lignin. Xylan was more important than lignin as precursor of oxalic acid under peroxide-bleaching conditions. Hot-water extraction of hemicelluloses from softwood mechanical pulp prior to the peroxide-bleaching stage reduced the formation of oxalic acid by one third. Lignocellulosic materials were characterized chemically with regard to their suitability as feedstocks in biorefineries producing bioethanol. Four agricultural and agro-industrial residues were investigated; cassava stalks, peanut shells, rice hulls, and sugarcane bagasse. Pretreated sugarcane bagasse was the material that was most susceptible to hydrolysis by cellulolytic enzymes. Waste fiber sludges from three pulp mills were characterized. The waste fiber sludge with the lowest content of lignin was hydrolyzed most efficiently by the enzymes. Oligomeric xylan fragments were isolated as by-products from a waste fiber sludge. Hydrolysis of the waste fiber sludges resulted in solid residues with improved fuel properties. The waste fibers were found to be suitable as a feedstock for the production of biofuels in a pulp mill-based biorefinery.
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