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| 2. |
- Bylin, Susanne, 1982
(författare)
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Mechanisms of Biopolymer Solvation: Development of a two-component ionic liquid solvent system
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ionic liquids are of potential interest in the processing of lignocellulosic biomass, and/or its components, for the purpose of producing renewable and value-added biomaterials. An understanding of how solvation can be achieved and the way in which the feedstock biopolymers are affected, however, needs to be gained prior to a viable implementation. In this thesis, the solvation of the wood biopolymers cellulose, xylan and lignin in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate (EMIMAc) in a novel combination with the second system component 1-methylimidazole (MIM) have been investigated:The solvation of dissolving pulp, beech xylan and LignoBoost lignin model materials, was studied using FBRM (focused beam reflectance measurements) particle characterization in combination with microscopic analysis (cellulose and xylan), determination of molecular weights (xylan and lignin) and 13C- and 31P-NMR (nuclear magnetic resonance spectroscopy) of lignin.It was concluded that the most efficient solvation of cellulose and xylan occurred using 3-4% and 9% IL (n/n anhydroglucose units and n/n anhydroxylose Units), respectively, while polymer integrity was maintained. Cellulose solvation was found to be greatly dependent on the IL to AGU ratio whereas xylan solvation varied greatly with temperature. Moreover, a theoretical model was developed for the solvation of cellulose in the present system. The solvation of lignin was achieved at ~20% lignin loading (w/w), in any combination of MIM/EMIMAc. Regeneration of lignin resulted in two sets of fractions; one exhibiting a general and higher apparent molecular weight (Mw) along with an enrichment of condensed/aliphatic ether linkages and aliphatic hydroxyls, and the other exhibiting a lower apparent Mw and an enrichment of carboxylic and phenolic groups. The knowledge of biopolymer solvation gained in the present solvent system provides future opportunities of tuning extraction and/or fractionation processes to suite the specifications of a particular biomass-derived product.
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| 3. |
- Becker, Elin, 1981
(författare)
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Interactions of methane and carbon monoxide with platinum - Supported catalysts and chemical sensors
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims at increasing the understanding of the interactions of methane and carbon monoxide with platinum in connection to catalysis and sensor technology for emission control. Specifically, the low-temperature oxidation of methane and carbon monoxide over supported platinum catalysts and the sensor response mechanism towards CO of platinum-based chemical field effect sensors were studied. Flow-reactor experiments and in situ spectroscopic methods (mainly FTIR and energy dispersive XAS) in combination with mass spectrometry were employed at both steady-state and transient reaction conditions. The results show that the support material for platinum has a considerable impact on the low-temperature activity for oxidation of both CO and methane in oxygen excess. Under such conditions methane oxidation over platinum is generally low due to oxygen-poisoning, hindering the dissociative adsorption of methane. However, by employing transient operation of the feed-gas composition, the activity for methane oxidation can be substantially increased. A new method was developed and applied for analysis of in situ XAS spectra. It was found that transient operation of the feed-gas affects the surface composition of reactants and the state of the catalyst surface. At low temperatures, the CO oxidation reaction often suffers from self-poisoning by carbon monoxide. By supplying oxygen to the reaction through alternative routes, e.g. via additional compounds or via the support material, the low-temperature activity for CO oxidation can be significantly increased. Further, the CO coverage and the reduction of oxygen from the surface of platinum-based field effect sensors were found to be important factors in the sensing mechanism towards carbon monoxide of such devices.
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| 4. |
- Hosseini Bab Anari, Elham, 1982
(författare)
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Toward Safer Energy Storage Solution by Development of Fluorine-Free Battery Electrolyte
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Portable electronic devices such as mobile phones, laptops, cameras and electronic vehicles (EVs) which contain lithium-ion batteries (LIBs), are indispensable part of our modern society. The safety of conventional electrolytes of LIBs, composed of fluorinated lithium salts and organic solvents is the source of some concerns. While the former is meta-stable at room temperature, quite expensive to synthesis and unsafe in the presence of moisture, the latter have high vapor pressure and are also flammable. Therefore, development of more stable salts and electrolytes are highly desirable, especially in the light of increased use of battery technology in e.g. electric vehicles (EVs).In order to mitigate the challenges with current fluorine containing electrolytes, we set out to develop a new class of safer, fluorine-free anions based on the concept of pseudo-delocalized Mickey MouseTM anions. Their Lithium and sodium salts have been synthesized for the first time, and fully characterized by different analytical methods such as NMR, mass spectroscopy and elemental analysis. Thermogravimetry analysis and X-ray crystallography were conducted to reveal both basic properties in terms of thermal stability and solubility of the salts. To further assess their properties as electrolytes, ion conductivity and electrochemical stability windows (ESWs) were performed.
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| 5. |
- Karkela, T., et al.
(författare)
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RECENT FINDINGS ON RUTHENIUM CHEMISTRY IN A SEVERE ACCIDENT
- 2015
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Ingår i: Proceedings of the International OECD-NEA/NUGENIA-SARNET Workshop on the Progress in Iodine Behaviour for NPP Accident Analysis and Management.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The chemistry of radiotoxic ruthenium in a severe nuclear power accident has actively been investigated especially during the last decades. The Ru studies have covered the release from a fuel, the transport in the primary circuit and the behaviour in the containment building. The gathered experimental data have been utilized to understand the key parameters governing the Ru chemistry in a severe accident (SA) and to check the ability of the existing models of SA analysis codes to explain the experimental results. To further increase the knowledge on Ru behaviour, the collaboration on international level has been intensive. Lately, the widest and most active networks have been EU SARNET and EU SARNET2. The valuable effort of these networks on sharing information of e.g. national programs and on interpreting the experimental results is continued in EU NUGENIA program. More detailed studies on separate phenomena have been conducted e.g. as part of OECD/NEA STEM/START and ISTP/VERDON programs. Furthermore, Phébus FP tests have produced valuable data on integral phenomena.The large-scale integral and semi-integral experiments have confirmed that Ru release depends strongly on carrier gas. Ru is significantly released from an irradiated fuel sample under oxidizing conditions, in particular when air is involved. In addition, the oxidation of UO2 fuel seems to lead to a higher Ru release than in case of MOX fuel. Ruthenium can be transported to the containment atmosphere both in gaseous and particulate forms. The small-scale separate-effect experiments gave a detailed view on Ru transport. A high fraction of ruthenium was detected as particles at the outlet of the model primary circuit in an air atmosphere. However, the observed gaseous Ru fraction is higher than what could be expected based on thermodynamic equilibrium calculations. Further studies on the effect of flow residence time in a temperature gradient for the equilibrium of Ru oxides have been conducted.The effect of other fission products in the gas phase, as well as FP deposits on the surface of primary circuit, on the Ru transport has been investigated. For example, caesium containing deposits seemed to trap gaseous ruthenium effectively. Similarly in case of control rod residues, silver particles in the gas phase of the circuit acted as a sink for gaseous Ru. In an air ingress accident, the effect of air radiolysis products on the Ru chemistry becomes important. As the main air radiolysis products can be considered as oxidizing agents, their ability to oxidize the lower oxides of Ru to higher oxidation state has been examined.Most of Ru in the containment building ends up as deposits on the containment surfaces and in the sump. Experiments on the radiolytical revaporisation of ruthenium deposits on the epoxy paint surface indicated the release of gaseous ruthenium and it was enhanced under humid atmosphere and elevated temperature. It appeared that the products of air radiolysis caused by γ-radiation promoted the formation of gaseous ruthenium from Ru oxide deposits on paint in a higher amount than could be expected by pure ozone action. Concerning the irradiation tests of perruthenate aqueous solutions, they indicated the formation of gaseous Ru by γ-radiolysis products in solution.
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| 6. |
- Nyström, Anna, 1974
(författare)
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Modeling and Simulation of a Semi-batch Reactor
- 2007
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Ingår i: The 48th Scandinavian Conference on Simulation and Modeling (SIMS 2007), 30-31 October, 2007, Göteborg (Särö), Sweden. - 1650-3740. ; 2007, s. 173-182
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The operation of an industrial semi-batch reactor, in which the bulk chemical EHEC, ethyl hydroxyethyl cellulose, is produced, is studied and simulated. In the reactor a strongly exothermic polymerization reaction takes place followed by a slightly exothermic reaction, and we want to minimize the duration of the operation of the process. Various operational as well as quality and safety related constraints have to be met during the batch. The complete process model, derived from measurements, first principles, and reasoning about effects on molecular level, is stated. The model includes heat and mass balances of the reactor, a pressure model, models of PID controllers, the jacket and the condenser. Technical limitations, for instance maximal and minimal jacket temperature changes due to limitations in the heat exchanger, have been modeled as constraints. The equations have been implemented in SIMULINK, MATLAB and the model predicts the process variables rather well over time. During the first reaction, the model is not able to reproduce the jacket temperature to the desired accuracy, but the other variables have acceptable predictions. An optimization problem is formulated, wherein the total batch time is minimized under the constraints of the differential algebraic equation system and other constraints originating from the process, for instance limited pump capabilities. As a first step in optimizing the operation of the process, a series of simulations has been performed in order to decrease the total batch time. It is concluded that a 10 % shorter batch time than today is possible if the quality is discarded, and a 5 % shorter batch time can be reached while using the existing requirements for the quality.
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| 7. |
- Alnegren, Patrik, 1988
(författare)
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Corrosion of Ferritic Stainless Steel Interconnects for Solid Oxide Cells – Challenging Operating Conditions
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solid oxide cells (SOC) have the potential to revolutionize electricity production by being able to both produce electricity with very high efficiency from a variety of fuels or to produce fuels from electricity and abundant raw materials such as water or carbon dioxide. Some material challenges remain to be solved before large-scale commercialization can be achieved. Interconnects made from ferritic stainless steels are key components in solid oxide cells, but the conditions within the cells cause them to degrade from high temperature corrosion. This thesis seeks out the potentially demanding operating conditions for solid oxide cells and focuses on investigating the effect of changing the environment on the degradation of ferritic stainless steels. Tests in which steel coupons were exposed to different atmospheres were performed to simulate the degradation of an interconnect inside an operating solid oxide cell. The effect of operating solid oxide fuel cells in electrolysis mode was specifically investigated, which means that interconnects were exposed to pure oxygen instead of ambient air and higher steam content on the fuel side. It was found that at 850 °C, ferritic stainless steels with 18-26% chromium content did not oxidize faster when the oxygen pressure was increased. However, the microstructure of the formed oxide scales on the steels was found to depend on oxygen concentration which caused oxide spallation for some steels at lower oxygen pressures. Experiments in hydrogen with high steam content, representing the other side of the interconnect, revealed an increase in the oxidation rate of the steel if the chromium content in the steel was too low, due to a change of the oxidation mechanism. Dilution of the same atmosphere with argon changed the oxidation mechanism to more protective behavior, which led to new insights in designing relevant simulated solid oxide cell fuel side conditions. It was also found that the oxidation rate of ferritic stainless steels in fuel side atmosphere can be significantly reduced by the physical vapor deposition (PVD) of cerium onto the surface. Even with applied cerium, however, steels with lower chromium content might still be at risk of rapid oxidation due to iron-rich oxide formation. A close-to-reality atmosphere was also simulated by exposing a ferritic steel simultaneously to air on one side and hydrogen on the other, which resulted in severely accelerated corrosion at 600 °C. Areas of up to 30 µm thick iron oxide were formed on the air side after 1000 h and grew to cover most of the surface after 3000 h. This dual atmosphere effect was concluded to have an inverse relation to temperature since accelerated corrosion was not observed at 700 and 800 °C. In addition, it was found that the corrosion resistance could be improved if the steel was pre-oxidized in air before exposure to dual atmosphere.
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| 8. |
- Goebel, Claudia, 1988
(författare)
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Corrosion of Ferritic Stainless Steels Used in Solid Oxide Fuel Cells
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solid oxide fuel cells (SOFC) are energy conversion systems with clean emissions (depending on the fuel used) and high electrical efficiencies, which could potentially replace conventional conversion systems such as combustion engines. However, other issues, such as high costs and limited lifetime, must be resolved before widespread commercialization of SOFCs can be achieved. One of the major cost factors and the component that reduces the lifetime of SOFCs immensely, is the interconnect, which electrically connects multiple fuel cells to form a stack. Interconnects are typically made of ferritic stainless steels, and, due to high temperatures (600 °C – 900 °C) and the aggressive environments prevalent in fuel cells, the interconnects corrode over time. The protective Cr2O3 that forms on ferritic stainless steels at high temperatures mitigates the corrosion process to a certain extent. However, this oxide layer leads to two other issues: (i) vaporization of hexavalent Cr species, which leads to cathode poisoning and (ii) an increase in the electrical resistance of the interconnect caused by a continuously growing oxide layer. Both these problems can be reduced to a certain extent with coatings. Especially spinel coatings have been proven highly effective at decreasing Cr-evaporation. The first part of this work examines the influence of the Co3O4 spinel coating on area specific resistance (ASR). It was found that the Co3O4 thickness of Crofer 22 APU, which was exposed in air for 500 h at 600 °C, did not significantly impact the ASR, and, instead, the main contributor to overall resistance was the thermally grown Cr2O3. The second part of this work focuses on the long-term stability of Ce/Co-coated (10 nm Ce/640 nm Co) AISI 441. Coated AISI 441 was exposed by AB Sandvik Materials Technology for up to 37 000 hours at 800 °C in laboratory air. Subsequent analysis showed very low Cr-evaporation rates compared to uncoated AISI 441, and ASR values below 40 mΩcm2, suggesting that, under these conditions, the coating is effective in reducing Cr-evaporation rates and Cr2O3-growth rates even after long exposure times. The last part of the work analyzes the influence of pre-oxidation on the dual atmosphere effect at 600 °C with regard to two parameters: the pre-oxidation time and the pre-oxidation location. It was demonstrated that longer pre-oxidation times for AISI 441 result in extended resistance against dual atmosphere corrosion on the air-facing side. It was also found that the pre-oxidation layer on the hydrogen-facing side is more important for corrosion resistance in dual atmosphere than the pre-oxidation layer on the air-facing side.
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| 9. |
- Ahlbom, Anders, 1993
(författare)
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Hydrothermal Liquefaction of Kraft Lignin - The influence of capping agents and residence time
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the context of exploring alternatives to replace fossil resources, lignin has been acknowledged as a renewable source of various aromatic compounds that have the potential of being precursors to chemicals as well as fuel additives. Originating from lignocellulosic biomass such as wood, lignin is an amorphous polymer with a high content of aromatic units and, in order to harness these units, it must be depolymerised. A major problem with current depolymerisation techniques, however, is that lignin repolymerises after being depolymerised, and forms an undesirable char fraction. The addition of capping agents and fine-tuning the reaction conditions can be used to mitigate such formation of char. This work has investigated the depolymerisation of kraft lignin in hydrothermal conditions under varying temperatures (290-335 °C), residence times (1-12 min) and charges of isopropanol (IPA/dry lignin, 0-4.9) which, aside from being a co-solvent, was hypothesised as acting as a capping agent. The influence of these reaction parameters on the molecular weights, yields and elemental compositions of the products was studied, along with changes in the molecular structure compared to the starting lignin. The product is a suspension of solid material, i.e. char, in an aqueous phase and thus any desired organic liquid phase requires extraction from the aqueous product. While the yield of char increased with temperature and residence time, it decreased with increasing isopropanol loading, suggesting that the isopropanol does in fact act as a capping agent. Most of the lignin forms a water-soluble fraction that precipitates when the aqueous product phase is acidified, thereby forming the precipitated solids fraction (PS). The components remaining dissolved after acidification of the product phase are known as acid soluble organics (ASO). A portion of the ASO fraction was aromatic monomers, with guaiacol dominating: this result was expected since the lignin was sourced from softwood. The amount of such monomers increased with residence time in the reactor. Molecular weight analyses showed a rapid depolymerisation of the lignin within 1 min of hydrothermal liquefaction (HTL) treatment via a significant decrease in the molecular weight of all product fractions: char, PS and ASO. Moreover, the carbon-oxygen inter-unit linkages were found to break in this timeframe as well. The repolymerisation reactions started to exceed depolymerisation between residence times of 4 and 12 min, causing the weight average molecular weight (Mw) to increase again. Although minimising the residence time allows the char yield and Mw to be kept low, more monomers were formed at longer residence times. This calls for careful tuning of the residence time in the HTL of kraft lignin.
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| 10. |
- Arora, Prakhar, 1987
(författare)
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Catalytic Upgrading of Waste Oils to Advanced Biofuels – Deactivation and Kinetic Modelling Study
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demand for liquid hydrocarbons as transportation fuels is enormous and ever growing. Advanced biofuels is one of the promising solutions to keep pace with the global transition to cleaner energy by reducing greenhouse gas emissions from the transport sector. It is possible to selectively remove oxygen from waste oils like tall oil, used cooking oil etc. via a catalytic hydrodeoxygenation (HDO) process to produce advanced biofuels. These biofuels have similar molecules as in the traditional fossil-based fuels and exhibit improved performance. This thesis focuses on aspects of catalyst deactivation and kinetic modelling of HDO reactions. In the first study, the influence of iron (Fe) as a poison during HDO of a model compound for renewable feeds (Oleic acid) over molybdenum based sulfided catalysts was investigated. Fe is a potential contaminant in renewable feeds due to corrosion during transportation and storage in iron vessels. A series of experiments with varying Fe-oleate concentration in the feed over MoS2/Al2O3 and NiMoS/Al2O3 catalysts. There was a salient drop in the activity of the catalysts. At higher Fe concentration, for the NiMoS catalyst, the selectivity for the direct hydrodeoxygenation product (C18 hydrocarbons) increased. However, it was opposite for the MoS2 catalyst. There was a decrease in the yield of direct hydrodeoxygenation products and an increase in yield of decarbonated products. It was proposed that Fe interacted with these two catalyst systems differently. Fe influenced the critical step of creation of sulfur vacancies in a negative way which resulted in lower activity. Microscopic analysis indicated that Fe was preferentially deposited close or around the nickel promoted phase, which explained why the role of Ni as a promoter for the decarbonation route was subdued for the NiMoS catalyst. In the second study, the kinetics during HDO of stearic acid (SA) over a sulfided NiMo/Al2O3 catalyst were explored to investigate the reaction scheme. Model compounds like octadecanal (C18=O) and octadecanol (C18-OH) were employed to understand the reaction steps and quantify the selectivity. A Langmuir–Hinshelwood-type kinetic model was used to investigate the kinetics. The results from the proposed kinetic model were found to be in good agreement with experimental results. In addition, the model could effectively reproduce the observed experimental profiles of different intermediates like C18=O and C18-OH and illustrate phenomena like inhibiting effects of the fatty acid.
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