| 1. |
- Anselm, Jonas, et al.
(författare)
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Bannlys alla politiska beslut som ger mer klimatutsläpp
- 2014
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Ingår i: Dagens Nyheter.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Torftig valdebatt. Dagspolitiken klarar inte att hantera ödesfrågan om klimatet, vilket oroar oss. Vi föreslår därför ett ”utsläppsmoratorium”: inga beslut får tas som ökar utsläppen av växthusgaser. Principen måste kopplas till mål om exempelvis förnybar energi och grön infrastruktur, skriver 23 forskare och debattörer.
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| 2. |
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| 3. |
- Carvalho, Danila, 1984-
(författare)
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Study on the structure and properties of xylan extracted from eucalyptus, sugarcane bagasse and sugarcane straw
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulosic biomasses are an important source of chemical components such as cellulose, lignin and hemicelluloses, and can be used for a variety of purposes in both the pulp and paper and chemical conversion industries. Xylan, the main hemicellulose found in hardwood and grass plants, plays an important role during the pulping/pretreatment process reactions, including those used in 2nd generation bioethanol production. It may also play an important role in the production of certain novel materials.This thesis evaluates the composition of eucalyptus (Eucalyptus urophylla x Eucalyptus grandis), sugarcane bagasse and sugarcane straw, with a specific focus on the structure and properties of xylan. The chemical characterization of biomasses showed that sugarcane bagasse and straw contain larger amounts of extractives, ash and silica than eucalyptus. The large amount of silica leads to an overestimation of the Klason lignin content, if not corrected. By using a complete mass balance approach, sugarcane bagasse and straw were shown to contain smaller amounts of lignin (18.0% and 13.9%, respectively) than previously reported for these raw materials, and certainly a much smaller amount of lignin than was found in eucalyptus (27.4%). The hemicellulose content in sugarcane bagasse (28.7%) and straw (29.8%) was much higher than that in eucalyptus (20.3%).In order to investigate the structure of the xylan in greater detail, it was extracted with dimethyl sulfoxide from holocellulose, obtained by either peracetic acid or sodium chlorite delignification. The structure of the isolated xylans was confirmed by FTIR and 1H NMR analysis. In eucalyptus, the O-acetyl-(4-O-methylglucurono)xylan (MGX) was identified. This had a molar ratio of xylose units to branches of 4-O-methylglucuronic acid of 10:1.1 and a degree of acetylation of 0.39. All 4-O- methylglucuronic acid groups were attached to position O-2 of the xylose units, which had an acetyl group in position O-3. The acetyl groups were distributed in positions O-3 (64%), O-2 (26%) and O-2,3 (10%). The MGX had a molecular weight (Mw) of about 42 kDa.In bagasse and straw, arabinoxylan (AX) was identified. This had a molar ratio of xylose units to arabinosyl substitutions of 10:0.5 for bagasse and 10:0.6 for straw. A degree of acetylation was 0.29 and 0.08 for bagasse and straw, respectively. The arabinose units were attached preferentially to position O-3 in AX. In the xylan from bagasse, the acetyl groups were found in positions O-3 (60%), O-2 (13%) and O-2,3 (27%), while in the xylan from straw, the acetyl groups were distributed between positions O-3 (67%) and O-2 (33%). The AX had a molecular weight (Mw) of about 38 kDa and 30 kDa for bagasse and straw, respectively.The differences in the structure of xylan present in the various biomasses played an important role during hydrothermal pretreatment, which is often used as the first step in 2nd generation ethanol production. The varying amounts of uronic acid and acetyl groups resulted in different starting pH levels of liquor and, thus, affected the chemical transformation in the biomasses in different ways. The hydrothermal pretreatment resulted mostly in the removal and/or transformation of hemicelluloses, but also in the formation of a significant number of pseudo-lignin structures. In addition, in eucalyptus, pseudo-extractives structures were generated. The sugarcane straw showed the highest mass loss during the investigated pretreatment.
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| 4. |
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| 5. |
- Danielsson, Sverker, et al.
(författare)
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A novel approach for applied membrane filtration on processing flows
- 2012
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Konferensbidrag (refereegranskat)abstract
- Membrane filtration technique shows exclusively properties for optimized filtration for a given size, from micrometer to nanometer scales compared to other industrial filtration. However, there is a trade off in flux that has delayed the implementation of the membrane techniques for a wider range of applications. For a specific flow in a process stream, the limited flux through the membrane means large membrane area is demanded, that results in a return of investments not accepted by industry. On the other hand, as the energy prices increases and environmental issues become more and more important as design parameters, the membrane techniques will due to its excellent separation performance be of interest, and from a life cycle analysis (LCA) a feasible approach.In this project the process flows in pulp and paper sector, and in particular the waste water treatment, are studied based on membrane technology. The purpose is to obtain a procedure to evaluate the membrane technique so that the results are guiding for extended studies. Two different representative integrated mills have been in focus, one thermo-mechanical pulp mill and one kraft pulp mill. The waste water streams that result in challenges for treatment process and that due to membrane filtration give reject / accept of greater values are studied. The possible benefit is two-fold the waste can be used as a resource of added valued products and the energy demanding waste water treatment decreases.A membrane filtration equipment from Alfa Laval LabStak M20 was used in this study on different streams for a pulp and paper mill. In this unit several membranes can be tested at the same time in order to briefly evaluate a type of membrane which suitable for the prevailing conditions, ranging from RO, NF, UF and MF depending on molecular weight cut-off (MWCO) and pore size. The volume concentrations factor (VFC) ranged from 1-4 in this study and the reduced TOC indicates satisfactory results. As pointed out, a trade off in decrease flux during filtration was in the order of 20%, to be considered in process design. The result gives indication of feasible way to use membrane filtration techniques as a tool for creating new business opportunities and elucidate the potential in reducing the water and energy consumption. The technique is demonstrated to gained parameters of importance for the pulp and paper sector. However, also applicable for other industry sectors when dealing with large scale processing flows
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| 6. |
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| 7. |
- Danielsson, Sverker, et al.
(författare)
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Influence of birch xylan adsorption during kraft cooking on softwood pulp strength
- 2005
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 20:4, s. 436-441
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Tidskriftsartikel (refereegranskat)abstract
- The dissolution, degradation and redeposition of xylan in the kraft cooking of birch pulp were investigated. The molecular weight of the dissolved xylan was determined through gel permeation chromatography, and the loss in molecular weight could be correlated with the amount of degraded xylan in the initial stages of the kraft cook. This indicates that peeling is the only significant xylan degradation reaction taking place early in the cook. Two different birch black liquors containing xylan with molecular weights of 12.20 g/mol and 5.95 g/mol, respectively, were added to softwood kraft cooks in order to determine the effect of birch xylan on pulp strength properties. The results show an increase in both tensile strength and tensile stiffness. The magnitude of the strength increase was greatly affected by the molecular weight of the xylan added. Adding high-molecular-weight xylan increased the tensile strength by more than 10%, as measured at a beating degree of 1000 PFI revolutions. Tensile stiffness was also increased by xylan addition, though more so when the xylan was of high rather than low molecular weight.
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| 8. |
- Danielsson, Sverker, et al.
(författare)
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Kinetic study of Hexenuronic and Methylglucuronic acid reactions in pulp and in dissolved xylan during kraft pulping of hardwood
- 2006
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 45:7, s. 2174-2178
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Tidskriftsartikel (refereegranskat)abstract
- During kraft pulping, the side group in the xylan backbone, 4-O-methyl-D-glucuronic acid, is partly converted to hexenuronic acid. Simultaneously, degradation reactions of these side groups take place. The rates of these reactions were studied during the kraft pulping of hardwood and were shown to be strongly affected by the location of the x Ian; dissolved xylan had markedly higher methylglucuronic acid and hexenuronic acid contents than pulp xylan did. The degree of substitution of methyl-lucuronic acid in dissolved xylan was found to be higher at reduced cooking temperatures; no such change was seen for pulp xylan. A kinetic model was developed that included the energies of activation for formation (129 U/mol) and degradation (143 U/mol) of hexenuronic acid and dearadation (141 kJ/mol) of methylglucuronic acid and bulk delignification (118 kJ/mol, in accordance with earlier studies). Decreased cooking temperatures thus increase the number of acidic charged groups in the pulp and in dissolved xylan.
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| 9. |
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| 10. |
- Danielsson, Sverker
(författare)
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Sorption and desorption of black liquor xylan onto cellulose fibers
- 2014
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 48:9-10, s. 819-823
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Tidskriftsartikel (refereegranskat)abstract
- The potential of xylan as a polymer in different new materials is large and not yet utilized. The availability in kraft pulp mills is large as the polymeric xylan dissolved in process liquors corresponds to up to 160 kg/adt and is today burnt to recover energy. A pre-requisite for using black liquor xylan in high-value products is to purify it from inorganic material and lignin in a technically effective and economical feasible way. This study combines two known properties of xylan: its affinity to cellulose and its solubility in alkali. The aim is to design an efficient separation process to produce black liquor xylan of high purity. A very pure xylan was reached with as low lignin contents as 1%. The hydroxide ion concentration was varied in the sorption step and it was found that an increase in hydroxide ion concentration resulted in a decreased amount of isolated xylan, decreased degree of substitution of uronic acids, but no effect on the lignin content and ash content was seen.
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