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- Walter, Karin
(author)
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The use of Fenton chemistry for reducing the refining energy during TMP production : the effect of free ferrous and free or chelated ferric ions
- 2013
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Doctoral thesis (other academic/artistic)abstract
- The potential of using acid hydrogen peroxide under Fenton conditions to lowerthe electrical energy consumed during the production of Black spruce (Piceamariana) thermomechanical pulp (TMP) was investigated in pilot scale. Thechemical system, which consisted of ferrous sulphate, hydrogen peroxide andoptionally an enhancer (such as a chelating agent), was evaluated as an inter-stagetreatment. The produced TMPs were thoroughly characterised in order to explainthe effect of the chemical system on fibre development and to be able to propose amechanism for the impact on refining energy reduction. The possibility to improvethe optical properties by washing, chelating and sodium dithionite or hydrogenperoxide bleaching the treated pulps was evaluated. The system of lignocellulosicmaterial, a Norway spruce (Picea abies) TMP, and Fenton chemistry was alsoevaluated in a model study to understand more about how conditions such as e.g.initial pH, dissolved organic material and reaction time affect the reactions.Ferrous and ferric ions (free and chelated) and different anions were evaluated.Moreover, it was examined whether hydroxyl radicals could be detected andmonitored.The results obtained in pilot scale showed that it is possible to significantly reducethe specific energy consumption by approximately 20% and 35% at a freenessvalue of 100 ml CSF or a tensile index of 45 Nm/g by using 1% and 2% hydrogenperoxide respectively. The energy reduction was obtained without any substantialchange to the fractional composition of the pulp, although tear strength wasslightly reduced, as were brightness and pulp yield. No major differences betweenthe reference pulp and the chemically treated pulps were found with respect tofibre length, width or cross-sectional dimensions. However, the acid hydrogenperoxide-treated pulps tended to have more collapsed fibres, higher flexibility, alarger specific surface area and a lower coarseness value. The yield lossiiiaccompanying the treatment was mainly a consequence of degradedhemicelluloses. It was also found that the total charge of the chemically treatedpulps was higher compared to the reference pulps; something that may haveinfluenced the softening behaviour of the fibre wall.A washing or chelating procedure could significantly reduce the metal ion contentof the chemically treated TMPs. The amount of iron could be further reduced to alevel similar to that of untreated pulps by performing a reducing agent-assistedchelating stage with dithionite. The discoloration could not, however, becompletely eliminated. The brightness decrease of the treated pulps was thereforenot only caused by the greater iron content in the pulp, but was also dependent onthe type of iron compound and/or other coloured compounds connected with theacid hydrogen peroxide treatment. Oxidative bleaching using hydrogen peroxidewas more effective than reductive bleaching using sodium dithionite in regainingthe brightness that was lost during the energy reductive treatment.From the model study and by using a chemiluminescence method, it could beconcluded that hydroxyl radicals were present in the system of Fenton chemicalsand lignocellulosic material (TMP). Initial pH, retention time, pulp consistency,type of catalyst (free or chelated) and dissolved organic material had an impact onthe reactions between TMP and acid hydrogen peroxide. Different anions(sulphate, nitrate and chloride) of ferric ion salt gave a similar catalytic effect.There appeared to be more reactions with the TMP when there was less dissolvedorganic material in the liquid phase from the start. A catalyst of ferrous sulphatehad a greater impact on the pulp (increased total fibre charge and carbonyl groups,more dissolved organic material in filtrate) than ferric ions chelated withethylenediaminetetraacetic acid at an initial pH of about 3-7. If using ferric-EDG(ethanol diglycinic acid) as catalyst, the measured effect on the pulp was similar orless compared to using ferrous sulphate. Ferric-EDG, however, gave higherhydrogen peroxide consumption and more detectable hydroxyl radicals than usingferrous sulphate (initial pH 5-8). It is likely that the iron catalyst must bind to theTMP, or be in close proximity to it, for the hydroxyl radicals to be able to react withthe material.A mechanism was proposed: the hydroxyl radicals generated in the Fentonreaction will probably attack and oxidise the available outer fibre surfaces,weakening these layers, and simultaneously dissolve some of the organic material.This can facilitate fibre development, give a better bonding pulp and reduce theelectrical energy required during refining.
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| 2. |
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| 3. |
- Minahan, Joseph A., et al.
(författare)
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Magnon dispersion to four loops in the ABJM and ABJ models
- 2010
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Ingår i: Journal of physics. A, Mathematical and theoretical. - : IOP Publishing. - 1751-8113 .- 1751-8121. ; 43:27, s. 275402-
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Tidskriftsartikel (refereegranskat)abstract
- The ABJM model is a superconformal Chern-Simons theory with N = 6 supersymmetry which is believed to be integrable in the planar limit. However, there is a coupling-dependent function that appears in the magnon dispersion relation and the asymptotic Bethe ansatz that is only known to leading order at strong and weak coupling. We compute this function to four loops in perturbation theory by an explicit Feynman diagram calculation for both the ABJM model and the ABJ extension. The ABJM four-loop correction has mixed transcendentality, while the ABJ extension adds a term to the ABJM correction with highest transcendentality. We then compute the four-loop wrapping correction for a scalar operator in the 20 representation of SU (4) and find that it agrees with a recent prediction of the ABJM Y-system by Gromov, Kazakov and Vieira. We also propose a limit of the ABJ model that might be perturbatively integrable at all loop orders but has a short range Hamiltonian.
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| 6. |
- Cussens, James
(författare)
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Integrating Probabilistic and Causal Reasoning
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We examine the vexed question of connections between logical and probabilistic reasoning. The reason for making such a connection are examined. We give an account of recent work which uses loglinear models to make the connection. We conclude with an analysis of various existing approaches combining logic and probability.
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| 7. |
- Kolbinger, Vitus, et al.
(författare)
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Polymorphisms in potential mercury transporter ABCC2 and neurotoxic symptoms in populations exposed to mercury vapor from goldmining
- 2019
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Ingår i: Environmental Research. - : Elsevier BV. - 0013-9351. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- Background: Artisanal small-scale gold miners have high levels of mercury in human specimens often above recommended threshold values. There are differences reported in the manifestation of neurological symptoms of individuals with a comparable level of exposure to mercury, suggesting a genetic component influencing the susceptibility to mercury neurotoxicity. Objective: To investigate associations between polymorphisms (rs1885301, rs717620, rs2273697) in the potential Hg-transporter ABCC2 gene and neurological effects. Methods: 968 participants from the Philippines, Indonesia, Tanzania and Zimbabwe were included in this study (age 12–59 years). For the statistical analysis the countries were categorized into Africa (Philippines, Indonesia) and Asia (Tanzania, Zimbabwe). Study participants were from three exposure groups: without mercury exposure from goldmining (n = 129); living in mercury-contaminated areas (n = 281) and mercury working exposure (n = 558). To identify chronic inorganic mercury intoxication we applied a modified neurological score sum including eight binary coded parameters (from anamnestic, clinical and neurophysiological examinations). Associations between genotype and neurological score sum, as well as between genotype and separate neurological tests (ataxia of gait, dysdiadochokinesia, ataxia heel to shin, pencil tapping test and matchbox test) were evaluated. Results: We found that ABCC2 genotype were associated with performance on certain neurological tests: for rs1885301, A-allele carriers in the African populations showed significantly worse performance than GG carriers on the pencil tapping test; whereas for rs2273697, A-allele carriers in the African and Asian populations showed a significantly better performance than GG carriers on this test. When including an interaction term between genotype and exposure subgroup, interaction effects were also seen for the pencil tapping test and matchbox tests for rs2273697 in Asia. Conclusions: The results suggest that certain ABCC2 polymorphisms may influence the neurotoxic effects in mercury-burdened individuals. ABCC2 alleles associated with worse neurological performance in the present study. These alleles have previously been correlated with higher levels of urinary mercury concentrations in the same cohort. Taken together, these associations between ABCC2 genotype, mercury levels, and neurological effects support the hypothesis that some ABCC2 genotypes may have a higher neurotoxic potential, although further functional studies are needed to prove causation.
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| 8. |
- Degerstedt, Lars, 1965-, et al.
(författare)
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LinTest, A development tool for testing dialogue systems
- 2006
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Ingår i: INTERSPEECH 2006 and 9th International Conference on Spoken Language Processing. - Pittsburgh (PA), USA : ICSLP. - 9781604234497 ; , s. 489-492
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Konferensbidrag (refereegranskat)
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| 9. |
- Almered Olsson, Gunilla, 1951
(författare)
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Biobränsle i explosiv konflikt om resurser
- 2010
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Ingår i: Miljöforskning. - 1650-4925. ; :Nr 3 - juni 2010, s. 22-25
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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