The Use of Membrane Filtration to Improve the Properties of Extracted Wood Components

Detta är en avhandling från Stockholm : KTH Royal Institute of Technology

Sammanfattning: 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.