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  • 4301.
    Vargas, Marcia
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    López, J.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Drying of Rice and Sorghum in a Rotary Dryer1997In: IADC, Vol. A: Proceedings of the Inter-American Drying Conference / [ed] Silva, M.A., Rocha, S.C.S., São Paulo, Brazil: State University of Campinas , 1997, p. 218-225Conference paper (Refereed)
  • 4302.
    Vargas, Marcia
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Influencia de un Sólido sobre el Secado de Mezclas Líquidas Parcialmente Miscibles2006In: Nexo, ISSN 1818-6742, Vol. 19, no 1, p. 64-72Article in journal (Refereed)
  • 4303.
    Vargas, Marcia
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Peugnet, A.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Zeledón, A.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Evaluation of a Rotary Drier of a Sugar Cane Refinery1998In: IACChE'98: Proceedings of the 18th Inter-American Congress of Chemical Engineering, Mayagüez, Puerto Rico: University of Puerto Rico at Mayagüez (UPRM) , 1998Conference paper (Refereed)
  • 4304.
    Vasiliev, Petr
    et al.
    Stockholm University, Department of Materials and Environmental Chemistry, Arrhenius Lab.
    Akhtar, Farid
    Stockholm University, Department of Materials and Environmental Chemistry, Arrhenius Lab.
    Grins, Jekabs
    Stockholm University, Department of Materials and Environmental Chemistry, Arrhenius Lab.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Andersson, Charlotte
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Bergström, Lennart
    Stockholm University, Department of Materials and Environmental Chemistry, Arrhenius Lab.
    Strong hierarchically porous monoliths by pulsed current processing of zeolite powder assemblies2010In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 2, no 3, p. 732-737Article in journal (Refereed)
    Abstract [en]

    Binderless hierarchically porous monoliths have been produced from silicalite-1 and ZSM-5 zeolite powders by a rapid and facile powder processing method where the zeolite powders are assembled in a graphite die and subjected simultaneously to a compressive pressure and a pulsed current. Pulsed current processing (PCP) or, as it is commonly called, spark plasma sintering, enables rapid thermal processing of zeolite powder assemblies with heating and cooling rates at 100 degrees C/minute or more, which results in the formation of strong powder bodies without any addition of secondary binders. Nitrogen adsorption measurements show that it is possible to form strong zeolite monoliths by PCP that maintain between 85 and 95% of the surface area of the as-received silicalite-1 and ZSM-5 powders. Line-broadening analysis of X-ray powder diffraction data by the Rietveld method and high-resolution electron microscopy showed that the formation of strong interparticle bonds is associated with a local amorphization reaction at the interfacial contact points between the zeolite particles. The PCP-treated binderless ZSM-5 monoliths display a high selectivity in xylene isomer separation.

  • 4305.
    Vastesson, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Guo, Maoxiang
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Haraldsson, Tommy
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    van der Wijngaart, Wouter
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems. KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Polymer Nanoliter Well Arrays for Liquid Storage and Rapid On-demand Electrochemical Release2018In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 267, p. 111-118Article in journal (Refereed)
    Abstract [en]

    Polymer microfluidic systems are of increasing importance in several applications in biomedicine and biosensing. The integrated encapsulation, storage, and controlled release of small amounts of liquid in such systems remains an unresolved technical challenge. Here, we report two methods for the room-temperature and adhesive-free sealing of 1–330 nanoliter volumes of liquid in off-stoichiometry thiol-ene polymer well arrays by spontaneous bonding to 200 nm thin gold films. Sealed well arrays were stored for more than one month in a liquid environment with <10% liquid loss, and for more than one week in air with minimal loss. We demonstrated that controlling the electrical potential and polarity over encapsulated wells allowed for selecting one of two well opening mechanisms: slow anodic electrochemical etching, or rapid electrolytic gas pressure-induced bursting of the gold film. The results may find potential applications in diagnostic testing, in vivo drug delivery, or in spatio-temporal release of chemical compounds in biological assays.

  • 4306.
    Vastesson, Alexander
    et al.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Zhou, Xiamo
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Sandström, Niklas
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Saharil, Farizah
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Supekar, Omkar
    Indian Institute of Technology, Bombay, India.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    van der Wijngaart, Wouter
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Haraldsson, Tommy
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    ROBUST MICRODEVICE MANUFACTURING BY DIRECT LITHOGRAPHY AND ADHESIVE-FREE BONDING OF OFF-STOICHIOMETRY THIOL-ENE-EPOXY (OSTE+) POLYMER2013In: 17th IEEE International Conference on Solid-State Sensors, Actuators and Microsystems & EUROSENSORS XXVII (IEEE TRANSDUCERS 2013), IEEE conference proceedings, 2013, p. 408-411Conference paper (Refereed)
    Abstract [en]

    We here demonstrate, for the first time, the use of direct lithography in off-stoichiometry thiol-ene-epoxy (OSTE+) to fabricate a microdevice. First, the photolithographic property of OSTE+ is shown by using a photomask to create micropillars with an aspect-ratio of 1:10 in a 2 mm thick layer. Secondly, a three-layer OSTE+ microdevice containing in-/outlet holes, channels, and pillars is fabricated by using a combination of direct lithography and adhesive-free dry bonding. The resulting microdevice shows desirable properties, such as leak-free filling and hydrophilic surfaces. This fabrication method enhances the microstructurability of OSTE+ beyond that of conventional soft lithography replica molding of other polymers, such as PDMS.

  • 4307.
    Vaziri, Mojgan
    et al.
    Department of Wood Science and Technology, Luleå University of Technology.
    Orädd, Greger
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology.
    Lindgren, Owe
    Department of Wood Science and Technology, Luleå University of Technology,.
    Pizzi, Antonio
    Magnetic resonance imaging of water distribution in welded woods2011In: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 25, no 16, p. 1997-2003Article in journal (Refereed)
    Abstract [en]

    This study was performed for a better understanding of water effect on welded wood and improving its water resistance. In this article, we have also attempted to demonstrate the feasibility of using Magnetic Resonance Imaging technology to study water movement in welded woods. Water distribution in welded woods of Scots pine (Pinus sylvestris) and beech (Fagus sylvatica) was investigated by Magnetic Resonance Imaging. Axial specimens were cut from beech and sapwood of Scots pine in longitudinal direction of wood grain. Two pieces of each wood species were welded together by a linear vibration machine. Sub-samples measuring 30 mm x 20 mm x 100 mm were cut from the welded specimens for Magnetic Resonance Imaging. The results showed that weldline of Scots pine was more resistant to water than weldline of beech. Pine joint was still holding after 40 h immersion in water, while a rapid wetting of the beech joint resulted in breakage of the joint in even less than an hour. This preliminary study also showed that MRI is a powerful tool to measure water distribution in welded woods and highlighted the potential of this technique to enhance understanding of wood welding. (C) Koninklijke Brill NV, Leiden, 2011

  • 4308.
    Velasco, Jorge A.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Catalytic partial oxidation of methane over nickel and ruthenium based catalysts for GTL applications2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Gas to Liquids (GTL) process is an important alternative for monetizing natural gas through the production of long-chain liquid hydrocarbons, e.g. diesel fuel. The GTL process involves three main steps: synthesis gas production to obtain H2 and CO, Fischer-Tropsch synthesis to obtain a synthetic crude oil, and upgrading/refining to obtain final products. Since the synthesis gas production is the most expensive step, there is great interest in optimizing and exploring new routes for syngas production.

    This thesis focuses on the conversion of methane, the main component of natural gas, into synthesis gas by catalytic partial oxidation (CPO). Several aspects of the CPO reaction in the context of the GTL technology are discussed. The work contributes to an increased knowledge concerning utilizing a CPO reactor as pre-reformer in the synthesis gas production process as well as the influence of catalyst properties and composition on the catalytic behavior when using nickel and ruthenium-based catalysts in the CPO reaction.

    The thesis is a summary of five publications. The first two publications (Papers I and II) review the current status of both the GTL technology and the catalytic partial oxidation of methane. Paper III analyzes a process configuration comprising of a CPO pre-reformer followed by an autothermal reforming (ATR) reactor using a thermodynamic equilibrium approach. It was found that a proper manipulation of the process conditions is needed to obtain a suitable synthesis gas for GTL applications simultaneously of minimizing the risk of carbon formation in the CPO reactor; the operation of the CPO reactor demanded low O2/CH4 and H2O/CH4 feed molar ratios. Accordingly, in paper IV, the partial oxidation of methane at low O2/CH4 and H2O/CH4 ratios is investigated over nickel and ruthenium catalysts supported on MgO/MgAl2O4 and compared with a commercial nickel-based catalyst. The extent or impact of the combustion and reforming reactions along the catalytic bed are substantially influenced by catalyst properties and composition. Deactivation by carbon formation is also discussed; ruthenium-containing catalysts might positively overcome carbon formation. To gain greater insight concerning the influence of the catalyst composition and properties on carbon formation, a set of nickel and bimetallic nickel-ruthenium catalysts, supported on α-Al2O3, γ-Al2O3 and MgO/MgAl2O4, is tested in the CH4 decomposition reaction in Paper V. For these catalysts, the resistance towards carbon formation is mainly correlated with the nickel particle size. 

  • 4309.
    Velasco, Jorge A.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA - Universidad Mayor de San Andrés, Bolivia.
    Lopez Nina, Luis Gagarin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA - Universidad Mayor de San Andrés, Bolivia.
    Cabrera, Saul
    UMSA - Universidad Mayor de San Andrés, Bolivia.
    Boutonnet, Magali
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Järås, Sven
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Synthesis gas production for GTL applications: Thermodynamic equilibrium approach and potential for carbon formation in a catalytic partial oxidation pre-reformer2014In: Journal of Natural Gas Science and Engineering, ISSN 1875-5100, E-ISSN 2212-3865, Vol. 20, p. 175-183Article in journal (Refereed)
    Abstract [en]

    The present work is focused on synthesis gas production for Gas to Liquids (GTL.) applications. A thermodynamic equilibrium approach has been chosen in order to address the methane reforming processes in presence of steam and oxygen (i.e. autothermal reforming "ATR" and catalytic partial oxidation "CPO"). The effect of operational variables on the performance of the reforming units has been analyzed at conditions typical for GTL processes. Also, the performance of a synthesis gas generation unit (SGU) comprising a CPO pre-reformer followed by an ATR reactor has been investigated. The potential for carbon formation in the CPO pre-reformer has been evaluated by applying the "equilibrated gas principle". Our results show that synthesis gas production can be strongly influenced by changes in operating variables such as the steam-to-carbon (S/C) and the oxygen-to-carbon (O-2/C) ratios, recycled gas (tail gas) compositions, and operating pressures and temperatures; however, effective operation of the SGU (CPO + ATR) requires an correct combination of these variables in order to accomplish the synthesis gas requirements of the Fischer-Tropsch synthesis. Likewise, it is shown that the risk of carbon formation in the CPO reactor can be reduced or even eliminated by a proper manipulation and combination of such variables.

  • 4310.
    Velasco, Jorge A.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Lopez Nina, Luis Gagarin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology. UMSA Universidad Mayor de San Andres, Bolivia.
    Velasquez, Miguel
    Boutonnet, Magali
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Cabrera, Saul
    Järås, Sven
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Gas to liquids: A technology for natural gas industrialization in Bolivia2010In: Journal of Natural Gas Science and Engineering, ISSN 1875-5100, E-ISSN 2212-3865, Vol. 2, no 5, p. 222-228Article in journal (Refereed)
    Abstract [en]

    Gas-to-Liquids (GTL) technology converts natural gas, through Fischer-Tropsch synthesis, into liquid and ultra-clean hydrocarbons such as light oils, kerosene, naphtha, diesel, and wax. Bolivia has natural gas reserves that reach 48.7 trillion cubic feet and produces nearly 40.0 million cubic meters per day, from which, around 88% are exported to Brazil and Argentina. In spite of these considerable amounts of natural gas reserves and production, the country experiences a shortage of diesel which cannot be solved using conventional refining processes due the light nature of its crude oil. Thus, the GTL process seems to be a promising solution for Bolivia's diesel problems, at the same time that its natural gas reserves could be monetized. Although GTL can be considered as a well proven and developed technology, there are several aspects along the main processing steps (synthesis gas generation, Fischer-Tropsch synthesis, and product upgrading) to be considered at the time of implementing a GTL plant. The aim of this paper is to give an overall view of some relevant issues related to Gas-to-Liquids technology as an option for natural gas industrialization in Bolivia, and also to provide a landscape of Bolivian natural gas industry.

  • 4311.
    Velasco, Jorge A.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Montes, Vicente
    Organic Chemistry Department, University of Córdoba, Córdoba, Spain.
    Kusar, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Cabrera, Saul
    Instituto del Gas Natural, San Andrés Higher University, La Paz, Bolivia.
    Boutonnet, Magali
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Järås, Sven
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Methane partial oxidation and methane decomposition over Ni andNi-Ru supported catalysts for synthesis gas productionManuscript (preprint) (Other academic)
    Abstract [en]

    Nickel and nickel-ruthenium based catalysts were compared in the catalytic partial oxidation (CPO) of methane and in the equilibrium of the methane decomposition reaction. A hydrotalcite-derived material as well as α- Al2O3 and γ-Al2O3 were used as catalyst supports. The catalysts were characterized by H2 chemisorption, N2 physisorption, temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO) and transmission electron microscopy (TEM). Catalyst properties and composition influenced the catalytic performance during partial oxidation (i.e. activity and temperature profiles). During methane decomposition equilibrium tests, all catalysts presented smaller equilibrium constants than those calculated on the basis of graphite; the deviation from graphite data was mainly associated with maximum nickel particle size (for both Ni and bimetallic Ni-Ru supported catalysts). Among all catalysts, the bimetallic Ni-Ru catalyst supported on hydrotalcite-derived material showed an interesting enhanced behavior; however, resistance towards catalyst deactivation, by mechanisms different than carbon formation, still needs to be improved. 

  • 4312.
    Vera, C. M.
    et al.
    Phenomenex Australia Pty Ltd, Lane Cove, NSW 2067, Australia..
    Shock, D.
    Phenomenex Australia Pty Ltd, Lane Cove, NSW 2067, Australia..
    Dennis, G. R.
    Univ Western Sydney, Sch Sci & Hlth, Australian Ctr Res Separat Sci, Penrith, NSW 2751, Australia..
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Enmark, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Shalliker, R. A.
    Univ Western Sydney, Sch Sci & Hlth, Australian Ctr Res Separat Sci, Penrith, NSW 2751, Australia.
    Contrasting selectivity between HPLC and SFC using phenyl-type stationary phases: A study on linear polynuclear aromatic hydrocarbons2015In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 119, p. 40-43Article in journal (Refereed)
    Abstract [en]

    A selectivity study was undertaken using two types of phenyl-type (Synergi polar RP and Cosmosil 5PBB) stationary phases in supercritical fluid chromatography. The mobile phases used in the SFC environment employed CO2 with methanol as the modifier. These columns were tested using linear polynuclear aromatic hydrocarbons as the test solutes. The retention behaviour of these PAHs in SFC was compared to their behaviour in HPLC and there were very distinct differences. On the Synergi-polar stationary phase the PAH selectivity was highly dependent on the methanol modifier concentration, but in comparison on the Cosmosil column, the selectivity between the members of this PAH test group showed almost no change as a function of the methanol concentration, even though the retentivity on the Cosmosil stationary phase was far greater than the Synergi stationary. In fact, the mobile phase played a very passive role in the separations observed on the Cosmosil stationary phase. (C) 2014 Elsevier B.V. All rights reserved.

  • 4313.
    Vera, C. M.
    et al.
    Phenomenex Australia, Pty Ltd, Lane Cove, NSW 2067, Australia.
    Shock, D.
    Phenomenex Australia, Pty Ltd, Lane Cove, NSW 2067, Australia.
    Dennis, G. R.
    Australian Centre for Research on Separation Science, School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
    Samuelsson, Jörgen
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Enmark, Martin
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Fornstedt, Torgny
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Shalliker, R. Andrew
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. Australian Centre for Research on Separation Science, School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
    A preliminary study on the selectivity of linear polynuclear aromatic hydrocarbons in SFC using phenyl-type stationary phases2015In: Microchemical journal (Print), ISSN 0026-265X, E-ISSN 1095-9149, Vol. 121, p. 136-140Article in journal (Refereed)
    Abstract [en]

    The retention behaviour of a homologous series of polyaromatic hydrocarbons was evaluated on two phenyl-type stationary phases in reversed phase supercritical fluid chromatography (SFC). These phases were the Synergi polar-RP phase and the Cosmosil 5PBB phase, both of which are polar end-capped and incorporate an ether in a propyl chain that tethers the phenyl ring to the silica surface. The Cosmosil 5PBB phase also has five bromine atoms on the phenyl ring. The retention capacity of the Cosmosil column was substantially greater than the Synergi column. However, selectivity on the Cosmosil column was effectively independent of the acetonitrile modifier composition in the CO2 mobile phase, whereas, selectivity on the Synergi column was greatly affected by the acetonitrile modifier in the CO2 mobile phase. The results from this study showed that selectivity and retention studies in HPLC cannot be used to predict selectivity and retention behaviour in SFC. (C) 2015 Elsevier B.V. All rights reserved.

  • 4314.
    Vera, Nemanova
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Biomass gasification in ABFB: Tar mitigation2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biomass gasification may be an attractive alternative for meeting future energy demand. Although gasification is a mature technology, it has yet to be fully commercialised due to tar formation. This study focuses on the tar mitigation in gas produced in an atmospheric bubbling fluidised bed (ABFB) gasification system.

    Previous studies indicated significant tar variability along the system. In this work the experimental procedure has been improved for reliable results and better understanding of tar variability in the producer gas. After having introduced a new sample point for tar analysis to the system, experimental results indicated tar reduction in the gasifier, probably due to continuous accumulation of char and ash in the bed, as well as in the ceramic filter owing to thermal and catalytic effects.

    Iron-based materials, provided by Höganäs AB, were applied in a secondary catalytic bed reactor for tar decomposition in the producer gas. It was found that tar concentration depends on catalytic and gasification temperatures and catalyst material. When changing the gasification temperature from 850 °C to 800 °C the conditions in the producer gas also changed from reductive to oxidative, transforming the initial metallic state of catalyst into its oxidised form. It may be concluded that the catalysts in their metallic states in general exhibit a better tar cracking capacity than their corresponding oxides.

    Due to the low reactivity of petroleum coke, an alternative may be to convert it in combination with other fuels such as biomass. Co-gasification of petroleum coke and biomass was studied in this work. Biomass ash in the blends was found to have a catalytic effect on the reactivity of petroleum coke during co-gasification. Furthermore, this synergetic effect between biomass and petcoke was observed in the kinetics data. 

  • 4315.
    Vernersson, Thomas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Mass transport in proton conducting membranes for the direct methanol fuel cell2005Licentiate thesis, comprehensive summary (Other scientific)
  • 4316.
    Vernersson, Thomas
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Johansson, Kristina
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Alvfors, Per
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    On-Board Hydrogen Storage for Fuel Cell Vehicle2001In: Proceedings of the 36th Intersociety Energy Conversion Engineering Conference: Savannah, GA: 29 July 2001 through 2 August 2001, 2001, p. 581-588Conference paper (Refereed)
    Abstract [en]

    Methods for onboard storage of hydrogen were evaluated for use in a fuel cell vehicle. Compressed hydrogen gas and cryogenic liquid hydrogen seem to be the two most viable options. Both these storage options were modelled, for storage of 5 kg hydrogen, to be implemented in an automotive fuel cell system simulation model. Hydrogen discharge was simulated for different values of cell stack operating pressure and temperature, using a constant rate of hydrogen release, and the power requirement for heating of the hydrogen to fuel cell stack operating temperature was calculated. The calculations show that compressed gaseous hydrogen storage requires a heating capacity of 0.72 - 1 kW for stack operating temperatures of 343-368 K. In the case of liquid hydrogen storage, heating demand for vaporisation and heating of the fuel was calculated to between 10 and 13 kW for stack operating temperatures of 343-368 K. The fuel cell stack produces surplus heat that can be used for fuel heating. Calculations show that the heat content of the cooling medium is sufficient to heat the fuel stream to approximately 20 K below stack temperature, with temperature differences in heat exchangers being the limiting factor. The radiator/compartment heating and humidifier will also extract heat from the cooling medium. However, to reach system temperature an auxiliary heat source will be required. This could be in the form of an electrical heater or a hydrogen burner. Also, for liquid hydrogen storage, a power demand arises for maintaining operating pressure inside the storage vessel during hydrogen release. This was calculated to between 13 and 28 W for the fuel cell stack operating conditions simulated, and this power demand can be supplied by directing a stream of released and heated hydrogen through a coil running inside the storage vessel.

  • 4317.
    Vernersson, Thomas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lafitte, B.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Jannasch, P.
    A sulfophenylated polysulfone as the DMFC electrolyte membrane - an evaluation of methanol permeability and cell performance2006In: Fuel Cells, ISSN 1615-6846, E-ISSN 1615-6854, Vol. 6, no 5, p. 340-346Article in journal (Refereed)
    Abstract [en]

    A sulfophenylated polysulfone (PSU-sph), carrying 0.8 sulfonic acid units per repeating unit of the polymer, is evaluated as a membrane electrolyte for DMFC applications. The liquid uptake, methanol transport characteristics, electrolyte conductivity, and fuel cell performance are investigated. The methanol transport and DMFC performance results are compared to those of Nafion(R) 117. The PSU-sph membrane investigated shows superior qualities with regard to methanol crossover, with a methanol permeability of approximately 25% compared to that of Nafion(R). The conductivity measured to be 15% compared to that of Nafion(R). However, this could not fully account for the internal resistance of the cell, implying that the contact resistance between the electrodes and electrolyte is higher when PSU-sph is used, probably because the electrodes are developed for use with Nafion(R) membranes. The stability of the PSU-sph membrane seems promising, with very low degradation observed over a period of 72 hours. It was concluded that although the mass transport properties of the PSU-sph membrane sample investigated were superior, it could not match the performance of Nafion(R) 117 in a DMFC application. However, a higher degree of sulfonation may have a significant positive effect on cell performance. The results also showed that a fully intergrated MEA is needed to fully assess new membrane materials.

  • 4318.
    Vernersson, Thomas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    A model for mass transport in the electrolyte membrane of a DMFC2007In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 37, no 4, p. 429-438Article in journal (Refereed)
    Abstract [en]

    A steady state model for multicomponent mass transport was derived for the direct methanol fuel cell membrane. Data for development and validation of the model was taken both from experiments and literature. The experimental data was collected in a polarisation cell, where mass transport of methanol across the electrolyte membrane was measured through a potentiostatic method. The results from modelling and experiments showed good agreement. The model was capable of describing the non-linear response in mass transport to increased methanol feed concentration. The model also accurately described the change in membrane conductivity with methanol concentration. From the model transport equations, it was also possible to derive some characteristic transport parameters, namely the electro osmotic drag of both water and methanol, diffusive drag of water and methanol, and effective, concentration dependent, diffusion coefficients for methanol and water.

  • 4319.
    Vesterlind, Eva-Lotta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    High temperature CTMP from birch2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is intended to contribute to understanding of the chemithermomechanical pulping of birch intended for high freeness grades. It focuses on the effects that conditions during pre‐treatment, i.e. the chemical addition of sodium sulphite and sodium hydroxide and the temperature in pre‐heater, have on the energy consumption and process runnability in terms of disc clearance. Pulp properties are evaluated in regard to brightness and the relation between bulk and internal bond strength. Pilot trials showed that pre‐heating birch chips to high temperature prior to refining (HT CTMP > 140°C), facilitated defibration and considerably lowered energy consumption. This made it possible to produce pulp with very high freeness. Despite the low energy input at high pre‐heating temperature, shive content remained low or was even reduced in the high freeness range. Mill trials confirmed the positive effect of a high pre‐heating temperature on energy consumption and on pulp properties. Furthermore it was shown that the internal bond strength in sheets from birch CTMP, in terms of Scott‐Bond at a given bulk, compared well with that of Spruce CTMP. Moreover, the shive content of birch CTMP produced using the high temperature technique was lower than that of spruce CTMP at a given bulk. A new laboratory technique ʹthe shavings methodology was used in combination with multivariate data analysis to investigate the effect of various pre‐treatments on native wood brightness. This method looks directly on the changes in brightness of the green wood as such. It revealed that the brightness of green birch wood is sensitive to increases in relative humidity and temperature. It also indicated that using a relatively high pre‐heating temperature (~140–155°C) when manufacturing birch CTMP is not necessarily detrimental to pulp brightness, provided the chemical charge is properly adjusted. However, at very high temperature (>160°C), the time in the pre‐heater should be kept short. Measurement of frictional behaviour, at simulated CTMP conditions, showed that the coefficient of friction of birch was greatly affected by chemical modification. Thus extraction raised the coefficient of friction. This rise can probably be attributed to reduced lubrication by the extractive substances and to the higher moisture content in the extracted samples. Sulphonation of the birch samples with 3 % Na2SO3 and 2 % NaOH (pH 13.5) gave a local maximum around 140–155°C. The local peak may be correlated with the reduction in energy consumption when the pre‐heating temperature is increased in the production of birch CTMP. Birch wood and spruce wood are also shown to have distinct differences in frictional performance. The coefficient of friction between birch and steel is higher than that between spruce and steel. The high stiffness and density of the birch wood and differences in the amount and composition of birch and spruce extractive substances probably account for the observed variations.

  • 4320.
    Veuro, Niina
    KTH, School of Chemical Science and Engineering (CHE).
    Kallkällor i Täby och Vallentuna kommuner – Inventering och vattenkvalitet2015Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Water has always been important for people and other living organisms. Earlier, when the the springs where important sources of water, the extracted water often had a good quality due to the natural cleansing processes. Furthermore, the springs are important habitats for animals and plants.  Mostly, springwater is excellent drinking water, and may also have a historic value. Therefore, several springs were localised and their water qualities were examined  A survey of  the springs in Täby and Vallentuna municipalities has been made. Relevant water quality parameters were investigated, both in the field and in the laboratory.  The parameters examined were: flow, temperature, pH, conductivity, alkalinity, chlorinity, taste, smell, color, dissolved gases, CODMn, phosphorus, sulfur, and the most common metals with ICP-OES.  Furthermore a survey of the geology and the human impact has been performed.

    In total 16 springs were visited, of which all but one were investigated. All springs had a normal temperature of spring water. The flow was estimated or calculated to be under 0,5  l/s in all springs. The pH-values were between six and eight in all springs and the alkalinity was high in most springs. Springs with high alkalinities also had high contents of the dominating positive ions sodium, potassium, calcium and magnesium. In some springs with low alkalinities iron, manganese and copper occurred in high concentrations. Taste, odor and color varied froma  good crystal clear water to a brown and smelly water.  Most of the springs contain high quantities of  oxygen gas and carbon dioxide.  Some springs contained high concentrations of chloride, phosphorus and copper, which indicate a human impact.

    Five of the springs have good  water qualities and these springs are excellent goals for excursions.  The water qualities of these springs meet the requirements for drinking water in Sweden. By proper signs at each spring, the public can be informed about the water quality and also about the historical traditions of the spring.  

    In five of the springs, the water quality is poor and the water does not satisfy the requirements for the drinking water quality. Some of these springs could be restored and cared for by ceaning away debris, leaves and branches.  Old crumbling structures should also be removed. 

  • 4321.
    Vidaurre, Marcia
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), PO Box 5595, Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Continuous drying of a solid wetted with ternary mixtures1997In: AIChE Journal, ISSN 0001-1541, E-ISSN 1547-5905, Vol. 43, no 3, p. 681-692Article in journal (Refereed)
    Abstract [en]

    The influence on drying selectivity of the continuous-contact mode between a solid wetted with ternary mixtures and a gas stream was theoretically studied. The liquid mixtures, ethanol–isopropanol–water and water–ethanol–acetone, were used. A mathematical model describing a gas-phase-controlled process was developed, and the influence of the process variables was studied by simulations. In addition to the inlet composition of the moisture and temperature of the solid, gas composition has the most important effect on selectivity. Small changes of gas composition, either imposed or spontaneous, may modify completely the process trajectory. The extent of these effects depends on the ratio between the flow rates of inlet gas and liquid contained in the solid. Because of their effects on the evolution of temperature and composition, the operating pressure and energy sources other than convection are also useful in controlling the selectivity. Since all these variables determine the composition of the remaining liquid and thereby product quality, their influence should be predictable. The model may be a valuable tool for exploring the process, provided that drying is gas-phase-controlled.

  • 4322.
    Vidaurre, Marcia
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), PO Box 5595, Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Modelling Gas-Phase-Controlled Continuous Drying of a Solid wetted with a Ternary Mixture1994In: Drying 94, Vol. A: Proceedings of the 9th International Drying Symposium (IDS’94) / [ed] V. Rudolph, R.B. Keey, Australia: The University of Queensland , 1994, p. 247-254Conference paper (Refereed)
  • 4323.
    Vidaurre, Marcia
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), PO Box 5595, Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Selectivity during Convective Evaporation of a Multicomponent Liquid Film1993In: IACChE'93: Proceedings of the 15th Inter-American Congress of Chemical Engineering, 1993Conference paper (Refereed)
  • 4324.
    Viklund, Peter
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Pettersson, Rachel
    Outokumpu Stainless.
    HCl-induced high temperature corrosion of austenitic stainless steels under thermal cycling conditions and the effect of preoxidation2011In: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 76, no 1/2, p. 111-126Article in journal (Refereed)
    Abstract [en]

    Gaseous HCl released during combustion is one reason for the severe materials degradation often encountered in power generation from waste and biomass. In this study, three stainless steels (the low alloyed EN 1.4982, the standard EN 1.4301 and the higher alloyed EN 1.4845) were tested by repeated thermal cycling in an environment comprising N2–10%O2–5%H2O–0.05%HCl at both 400 and 700 °C. The materials were exposed with ground surfaces and preoxidised at 400 or 700 °C. A positive effect of preoxidation is evident when alloys are exposed at 400 °C. Oxide layers formed during preoxidation effectively suppress chlorine ingress for all three materials, while chlorine accumulation at the metal/oxide interface is detected for surface ground specimens. The positive effect of preoxidation is lost at 700 °C and corrosion resistance is dependent on alloying level. At 700 °C metal chloride evaporation contributes significantly to the material degradation. Based on the results, high temperature corrosion in chlorinating environments is discussed in general terms.

  • 4325.
    Vilaplana, Francisco
    et al.
    Division of Glycoscience, School of Biotechnology, AlbaNova University Centre, KTH Royal Institute of Technology, Stockholm, Sweden / Department of Fibre and Polymer Technology, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Nilsson, Johanna
    Department of CollectionsThe Royal Armoury, Skokloster Castle, Hallwyl Museum, Stockholm, Sweden.
    Sommer, Dorte V. P.
    School of Conservation, Royal Danish Academy of Fine Arts Schools of Architecture, Design and Conservation, Copenhagen, Denmark.
    Karlsson, Sigbritt
    University of Skövde. Department of Fibre and Polymer Technology, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Analytical markers for silk degradation: comparing historic silk and silk artificially aged in different environments2015In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 407, no 5, p. 1433-1449Article in journal (Refereed)
    Abstract [en]

    Suitable analytical markers to assess the degree of degradation of historic silk textiles at molecular and macroscopic levels have been identified and compared with silk textiles aged artificially in different environments, namely (i) ultraviolet (UV) exposure, (ii) thermo-oxidation, (iii) controlled humidity and (iv) pH. The changes at the molecular level in the amino acid composition, the formation of oxidative moieties, crystallinity and molecular weight correlate well with the changes in the macroscopic properties such as brightness, pH and mechanical properties. These analytical markers are useful to understand the degradation mechanisms that silk textiles undergo under different degradation environments, involving oxidation processes, hydrolysis, chain scission and physical arrangements. Thermo-oxidation at high temperatures proves to be the accelerated ageing procedure producing silk samples that most resembled the degree of degradation of early seventeenth-century silk. These analytical markers will be valuable to support the textile conservation tasks currently being performed in museums to preserve our heritage.

  • 4326.
    Vilaplana, Francisco
    et al.
    Universidad Politecnica de Valencia.
    Osorio-Galindo, M.
    Iborra-Clar, A.
    Alcaina-Miranda, M. I.
    Ribes-Greus, A.
    Swelling behavior of PDMS-PMHS pervaporation membranes in ethyl acetate-water mixtures2004In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 93, no 3, p. 1384-1393Article in journal (Refereed)
    Abstract [en]

    Pervaporation composite membranes were prepared with a three-layer structure: a PP support, a PEI microporous structure, and a PDMS-PMHS selective layer. Swelling tests were performed in water, ethyl acetate, and four different ethyl acetate-water mixtures, to calculate the diffusional and swelling parameters. Moreover, the dynamic-mechanical properties of the membranes were obtained before and after the swelling experiments, and their relaxation spectra were characterized with the Fuoss-Kirkwood equation and analyzed in terms of the free volume parameter. It was found that the ethyl acetate possesses high affinity with the composite membranes and that the absorption of these small molecules substantially modifies the viscoelastic behavior and structure of the active layer. The combination of swelling experiments and the study of the mechanical relaxations proved to be an appropriate technique to investigate the behavior of pervaporation membranes immersed in different mixtures.

  • 4327.
    Vilaplana, Francisco
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Ribes-Greus, Amparo
    Universidad Politecnica de Valencia.
    Karlsson, Sigbnitt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    PMSE 354-Analytical assessment of the quality properties of recycled styrenic polymers using spectroscopy and chromatography2008In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 235Article in journal (Other academic)
  • 4328.
    Vilaplana, Francisco
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Ribes-Greus, Amparo
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Quality assessment of recycled plastics2008Conference paper (Other academic)
    Abstract [en]

    The project develops polymer characterization models, which are to be used in determination of polymeric properties ofrecycled plastics. In Europe, new standards are developed within the CEN bodies and a new standard on plastic recycling willbe released. The project develops knowledge about the properties that are important for quality assessments and presentlythree items are under investigation: a) degree of degradation, b) degree of blending and c) presence of low molecular weightcompounds. The analytical methods investigated are DSC, TGA, FTIR and chromatography. In a later step, validation of themethods will be made.

  • 4329. Villanueva, M.
    et al.
    Martínez, Jesús
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Gamero, R.
    Instant beans obtained from simultaneous processes of drying and size reduction2006In: XXII Interamerican Congress of Chemical Engineering, CIIQ 2006 and V Argentinian Congress of Chemical Engineering, CAIQ 2006 - Innovation and Management for Sustainable Development, Asociacion Argentina de Ingenieros Quimicos , 2006Conference paper (Refereed)
    Abstract [en]

    The kinetics of the drying of beans in simultaneous processes of contact drying and particle size reduction has been experimentally studied, and the particle size distribution of the final dried solid has been analyzed. The work is focused on some operating parameters, such as drying temperature, stirring speed and bean load mass, that influence on the dehydration of beans during those simultaneous processes. Drying rate curves were developed from the experimental data of moisture content changing with time, and particle size distribution of the final dried solid was analyzed. The results reveals that drying temperature, stirring speed and mass load are crucial for both the drying processing and the quality of the final product. The particle size reduction itself improves the drying rate as well since the heat and mass transfer area increases with the grain destruction. The final product contains values between 40-50% of suitable size for commercial proposes. The simultaneous process of two operations shows advantages as energy saving and fast processing that would be greatly significant once brought to industrial scale since the milling process needed afterwards would be reduced.

  • 4330.
    Villanueva, Melina
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Gamero, Rafael
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Instant Beans Obtained from Simultaneous Processes of Drying and Size Reduction2006In: IACChE 2006 / [ed] Oscar Pagola, Buenos Aires, Argentina: Argentine Association of Chemical Engineers (AAIQ) , 2006, p. 01d-425Conference paper (Refereed)
  • 4331. Villaverde, Juan Jos
    et al.
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Ligero, Pablo
    Vega, Alberto de
    Structural characterization of Acetosolve lignin from Miscanthus sinensis2008In: 10th EWLP: European Workshop on Lignocellulosics and Pulp, 2008, p. 262-265Conference paper (Refereed)
  • 4332. Virtanen, Pasi
    et al.
    Mikkola, Jyri-Pekka
    Åbo Akademi.
    Salmi, Tapio
    Miljövänliga katalysatorer av joniska vätskor2010In: Kemia, ISSN 0355-1628, no 6, p. 32-34Article in journal (Other academic)
  • 4333. Virtanen, Pasi
    et al.
    Salmi, Tapio
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Piispankatu 8, FI-20500 Turku/Åbo, Finland.
    Kinetics of cinnamaldehyde hydrogenation by supported ionic liquid catalysts (SILCA)2009In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 48, no 23, p. 10335-10342Article in journal (Refereed)
    Abstract [en]

    The research of ionic liquids and their applications in catalysis are attracting increasing attention in chemistry and chemical engineering. A supported ionic liquid catalyst (SILCA) consists of immobilized catalytic species (e.g., transition-metal particles, metal complexes, or enzymes) residing in an ionic liquid layer immobilized on a porous solid support. The kinetics of cinnamaldehyde hydrogenation over SILCAs that contained palladium nanoparticles in ionic liquid, which, in turn, was immobilized oil active carbon cloth (ACC), was studied and modeled in detail. A mechanistic kinetic model, which describes the differences of the activity and selectivity of the catalysts consisting of different ionic liquids, was developed. The model explained the experimental results well.

  • 4334. Virtanen, Pasi
    et al.
    Salminen, Eero
    Mikkola, Jyri-Pekka
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Industrial Chemistry & Reaction Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University.
    Modeling of Supported Ionic Liquid Catalysts Systems: From Idea to Applications2017In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 56, no 45, p. 12852-12862Article in journal (Refereed)
    Abstract [en]

    The modeling of chemical reactions studied in small scale, often carried out in Academia, is very important since it gives more information about the system and better possibilities to scale-up the processes in the future. Supported ionic liquid catalysts (SILCAs) have been studied in a number of different processes. However, the modeling of these processes have been studied only in a few cases. In this paper the sample cases are reviewed. These processes include hydrogenation of unsaturated aldehydes as well as isomerization of terpenes, α- and β-pinene oxides.

  • 4335.
    Vogt, Carmen M.
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Shi, J.
    Torres, N. F.
    Fadeel, B.
    Laurent, S.
    Bridot, J. -L
    Müller, R. N.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Functional Materials, FNM (Closed 20120101).
    Optimised synthetic route for tuneable shell Si02@Fe304 core-shell nanoparticles2009In: Advances in material design for regenerative medicine, drug delivery, and targeting/imaging, Materials Research Society, 2009, p. 209-214Conference paper (Refereed)
    Abstract [en]

    Multifunctional nanoparticles (that have in their structure different components that can perform various functions) are subject of intensive research activities as they find a large variety of applications in numerous biomedical fields from enhancement of image contrast in MRI to different magnetically controllable drug delivery systems. In this study we report on the synthesis of well-separated, monodisperse single core-shell Si02@Fe304 nanoparticles with an overall diameter of ̃30 nm. The influence of stirring rate and reaction time on synthesis of tuneable shell thickness core-shell nanoparticles is reported. Particles' cell toxicity and performance as MRI contrast agents were also studied due to their promising biological applications (as contrast agents, cell labelling and separation, drug delivery systems, etc.) and results are promising in terms of MRI performance as well as having no significant cytotoxicity.

  • 4336. Voiges, Kristin
    et al.
    Adden, Roland
    Rinken, Marian
    Mischnick, Petra
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Critical re-investigation of the alditol acetate method for analysis of substituent distribution in methyl cellulose2012In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 19, no 3, p. 993-1004Article in journal (Refereed)
    Abstract [en]

    The alditol acetate method is a common procedure for sugar analysis, also applied to determine the substituent distribution in monomer units of polysaccharide ethers like methyl cellulose by gas liquid chromatography. Consisting of several preparation and work-up steps this procedure is both time consuming and prone to side reactions that promote discrimination of single constituents, especially when no peralkylation step is performed prior to hydrolysis. As a consequence results scatter in dependence on individual treatment and conditions. In the context of this work these critical points were overcome by strict but simplified work-up procedures and using acid instead of alkaline catalyzed acetylation. Under the acidic conditions the tedious removal of borate is no longer necessary and a reduced time requirement was achieved as well as good reproducibility. Comparison with independent reference methods excluded a systematic error of the method and confirmed the results obtained. Without peralkylation, i.e. in the presence of free hydroxyl groups, another fast modification of the method using DMSO as solvent, no removal of borate, and 1-methylimidazole as catalyst for acetylation was found to produce a systematic error.

  • 4337.
    Voisin, Hugo P.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Siqueira, Gilberto
    Hausmann, Michael K.
    Studart, Andre R.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    3D Printing of Strong Lightweight Cellular Structures Using Polysaccharide-Based Composite Foams2018In: ACS sustainable chemistry & engineering, ISSN 2168-0485, Vol. 6, no 12, p. 17160-17167Article in journal (Refereed)
    Abstract [en]

    Polysaccharides are attractive sustainable resources for the fabrication of advanced materials, but the assembly of these building blocks into complex-shaped structures combining the high strength and low weight required in many applications remains challenging. We have investigated and optimized the rheological and mechanical properties of polysaccharide-based composite foams based on mixtures of methylcellulose (MC), cellulose nanofibrils (CNF), montmorillonite (MMT), and glyoxal and tannic acid. Such foams were found to be stabilized by the coadsorption of MC, CNF, and MMT at the air-water interface, while the complexation of the polysaccharides with tannic acid improved the foam stability. Tannic acid could also be used to tune and optimize the microstructure and the viscoelastic properties of the wet foam for direct ink writing of robust cellular architectures. Glyoxal had no noticeable effect on the properties of the wet foams but significantly enhanced the water resilience and stiffness of the lightweight material obtained after drying at ambient pressure and elevated temperatures with minimum shrinkage. The foams possessed a high porosity and displayed a specific Youngs modulus and yield strength that outperformed other biobased foams and commercially available expanded polystyrene. The strong and water-resilient 3D printed foams can be surface modified using, for example, aminosilanes, which opens up applications for air purification and thermal insulation.

  • 4338.
    von Kraemer, Sophie
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Membrane Electrode Assemblies Based on Hydrocarbon Ionomers and New Catalyst Supports for PEM Fuel Cells2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The proton exchange membrane fuel cell (PEMFC) is a potential electrochemicalpower device for vehicles, auxiliary power units and small-scale power plants. In themembrane electrode assembly (MEA), which is the core of the PEMFC single cell,oxygen in air and hydrogen electrochemically react on separate sides of a membraneand electrical energy is generated. The main challenges of the technology are associatedwith cost and lifetime. To meet these demands, firstly, the component expensesought to be reduced. Secondly, enabling system operation at elevated temperatures,i.e. up to 120 °C, would decrease the complexity of the system and subsequentlyresult in decreased system cost. These aspects and the demand for sufficientlifetime are the strong motives for development of new materials in the field.In this thesis, MEAs based on alternative materials are investigatedwith focus on hydrocarbon proton-conducting polymers, i.e. ionomers, and newcatalyst supports. The materials are evaluated by electrochemical methods, such ascyclic voltammetry, polarisation and impedance measurements; morphological studiesare also undertaken. The choice of ionomers, used in the porous electrodes andmembrane, is crucial in the development of high-performing stable MEAs for dynamicoperating conditions. The MEAs are optimised in terms of electrode compositionand preparation, as these parameters influence the electrode structure andthus the MEA performance. The successfully developed MEAs, based on the hydrocarbonionomer sulfonated polysulfone (sPSU), show promising fuel cell performancein a wide temperature range. Yet, these membranes induce mass-transportlimitations in the electrodes, resulting in deteriorated MEA performance. Further,the structure of the hydrated membranes is examined by nuclear magnetic resonancecryoporometry, revealing a relation between water domain size distributionand mechanical stability of the sPSU membranes. The sPSU electrodes possessproperties similar to those of the Nafion electrode, resulting in high fuel cell performancewhen combined with a high-performing membrane. Also, new catalystsupports are investigated; composite electrodes, in which deposition of platinum(Pt) onto titanium dioxide reduces the direct contact between Pt and carbon, showpromising performance and ex-situ stability. Use of graphitised carbon as catalystsupport improves the electrode stability as revealed by a fuel cell degradation study.The thesis reveals the importance of a precise MEA developmentstrategy, involving a broad methodology for investigating new materials both as integratedMEAs and as separate components. As the MEA components and processesinteract, a holistic approach is required to enable successful design of newMEAs and ultimately development of high-performing low-cost PEMFC systems.

  • 4339.
    von Kraemer, Sophie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lafitte, Benoit
    Polymer and Materials Chemistry, Department of Chemistry, Lund University.
    Puchner, Mario
    Polymer and Materials Chemistry, Department of Chemistry, Lund University.
    Jannasch, Patric
    Polymer and Materials Chemistry, Department of Chemistry, Lund University.
    Substitution of Nafion with Sulfonated Polysulfone in Membrane-Electrode Assembly Components for 60-120 °C PEMFC Operation2008In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 155, no 10, p. B1001-B1007Article in journal (Refereed)
    Abstract [en]

    To investigate the influence of sulfonated polysulfone (sPSU) in membrane–electrode assemblies (MEAs), sPSU-based gas diffusion electrodes (GDEs) and sPSU membranes were studied both as complete MEAs and as separate components in assembled MEAs at 60–120°C. The complete sPSU MEAs showed mass-transport limitations, irrespective of ion exchange capacity, compared to Nafion MEAs. Cyclic voltammetry and low-current impedance analysis revealed comparable electrochemically active catalyst areas and kinetic properties in the sPSU and Nafion GDEs, while gas-crossover measurements showed a lower gas permeability in sPSU compared to Nafion. The sPSU and Nafion GDEs, deposited on Nafion membranes, possessed comparable fuel cell characteristics at 120°C and 100% relative humidity, demonstrating no considerable limitations when utilizing sPSU as an alternative to Nafion in the GDE, thus implying a sufficient gas permeability in the sPSU GDE at high humidity. Furthermore, the results clearly showed that the sPSU membrane induced mass-transport limitations in both sPSU and Nafion GDEs, revealing that the limiting factor of the sPSU MEAs was primarily the membrane-induced cathode flooding due to unoptimized water transport in the sPSU membrane. The work demonstrates the importance of electrochemical evaluation of ionomers as complete MEAs and as separate components when studying MEAs.

  • 4340.
    von Kraemer, Sophie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Puchner, Mario
    Division of Polymer and Materials Chemistry, Lund University.
    Jannasch, Patric
    Division of Polymer and Materials Chemistry, Lund University.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Erratum: Gas Diffusion Electrodes and Membrane Electrode Assemblies Based on a Sulfonated Polysulfone for High-Temperature PEMFC [J. Electrochem. Soc., 153, A2077 (2006)]2006In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 12, p. L35-L35Article in journal (Refereed)
  • 4341.
    von Kraemer, Sophie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Puchner, Mario
    Division of Polymer and Materials Chemistry, Lund University.
    Jannasch, Patric
    Division of Polymer and Materials Chemistry, Lund University.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Gas Diffusion Electrodes and Membrane Electrode Assemblies Based on a Sulfonated Polysulfone for High-Temperature PEMFC2006In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 11, p. A2077-A2084Article in journal (Refereed)
    Abstract [en]

    Membrane electrode assemblies MEAs with a sulfonated polysulfone sPSU as the proton-conducting phase were fuel cellevaluated at varying temperatures in over-humidified conditions. The sPSU was prepared by a direct polycondensation involvinga commercially available sulfonated naphthalene diol monomer. The gas diffusion electrodes GDEs and MEAs were successfullyfabricated and a thorough morphological study was subsequently carried out on GDEs with varying sPSU contents and inksolvents. The scanning electron microscopy and porosimetry studies revealed highly porous GDE morphologies at sPSU contentsbelow 20 wt %. Double-layer capacitance measurements showed an almost fully sPSU-wetted electronic phase when the sPSUcontent was 10 wt %. The MEAs were prepared by applying the GDEs directly onto sPSU membranes. MEAs with a total Ptloading of 0.2 mg/cm2 were successfully fuel cell operated at 120°C. The MEAs showed mass-transport limitations in the rangeof 600–800 mA/cm2, most probably caused by abundant water due to the overhumidified measuring conditions. The low resistanceof the MEAs indicated a well-integrated structure between the GDEs and the membrane.

  • 4342.
    von Kraemer, Sophie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Sagidullin, Alexandr I.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Persson, E.
    Polymer and Materials Chemistry, Department of Chemistry, Lund University.
    Jannasch, P.
    Polymer and Materials Chemistry, Department of Chemistry, Lund University.
    Pore Size Distribution and Water Uptake in Hydrocarbon and Perfluorinated Proton-Exchange Membranes as Studied by NMR Cryoporometry2008In: Fuel Cells, ISSN 1615-6846, E-ISSN 1615-6854, Vol. 8, no 3-4, p. 262-269Article in journal (Refereed)
    Abstract [en]

    Sulfonated polysulfone (sPSU) membranes were analysed by nuclear magnetic resonance (NMR) cryoporometry, conventional gravimetric water uptake measurements as well as by differential scanning calorimetry (DSC). NMR cryoporometry is based on the relation between the pore size and the melting point depression of the pore-filling liquid, i.e. water in fuel cell membranes; thus providing a relation between the amount of molten water and the temperature shift, i.e. the pore size, in hydrated membranes. An sPSU membrane with high ion-exchange capacity (IEC 1.45 mequiv. g –1) possessed a significant amount of large pores after hydrothermal pretreatment at 80

  • 4343.
    von Kraemer, Sophie
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Wikander, Kjell
    Applied Surface Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lundblad, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Palmqvist, Anders E. C.
    Applied Surface Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology.
    Evaluation of TiO2 as catalyst support in Pt-TiO2/C composite cathodes for the proton exchange membrane fuel cell2008In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 180, no 1, p. 185-190Article in journal (Refereed)
    Abstract [en]

    Anatase TiO2 is evaluated as catalyst support material in authentic Pt-TiO2/C composite gas diffusion electrodes (GDEs), as a different approach in the context of improving the proton exchange membrane fuel cell (PEMFC) cathode stability. A thermal stability study shows high carbon stability as Pt nanoparticles are supported on TiO2 instead of carbon in the Pt-TiO2/C composite material, presumably due to a reduced direct contact between Pt and C. The performance of Pt-TiO2/C cathodes is investigated electrochemically in assembled membrane-electrode assemblies (MEAs) considering the added carbon fraction and Pt concentration deposited on TiO2. The O-2 reduction current for the Pt-TiO2 alone is expectedly low due to the low electronic conductivity in bulk TiO2. However, the Pt-TiO2/C composite cathodes show enhanced fuel cell cathode performance with growing carbon fraction and increasing Pt concentration deposited on TiO2. The proposed reasons for these observations are improved macroscopic and local electronic conductivity, respectively. Electron micrographs of fuel cell tested Pt-TiO2/C composite cathodes illustrate only a minor Pt migration in the Pt-TiO2/C structure, in which anatase TiO2 is used as Pt support. On the whole, the study demonstrates a stable Pt-TiO2/C Composite material possessing a performance comparable to conventional Pt-C materials when incorporated in a PEMFC cathode.

  • 4344.
    Vujic, Bojan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Computationally based analysis of the energy efficiency of a CO2 capture process2017In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 174, p. 174-188Article in journal (Refereed)
    Abstract [en]

    We propose a model for thermodynamic evaluation of the energy efficiency of a CO2 capture in a temperature-pressure swing adsorption. Major parts of this model are computational prediction of the adsorbed gas loading as a function of temperature and partial CO2 pressure, evaluation of the energy expenses under specified conditions for the working capacity, regenerability of the sorbent and purity of the captured CO2, as well as determination of the most optimal desorption conditions in terms of desorption pressure and temperature. The proposed model can be applied for fast evaluation of the energy costs of the CO2 capture process with the use of both experimental or simulation adsorption data with respect to pressure and temperature. We tested this model analyzing data obtained from Grand Canonical Monte Carlo simulations for more than thousand different zeolite structures. Within our approach it is possible to evaluate a theoretical limit of the energy expenses for each specific material and to use the proposed method in screening different structures for the most efficient sorbent material from the energy efficiency point of view under specified requirements for the working capacity of the process, regenerability and purity of captured CO2. We show that setting realistic from the industrial point of view parameters of the CO2 capture cycle leads to substantial reduction of the number of suitable zeolite structures, and to increase of the energy penalty of the CO2 capture compared to evaluations based on minimization of the parasitic energy only.

  • 4345.
    Vílchez, José F.
    et al.
    Faculty of Chemical Engineering, National University of Engineering (UNI), Managua, Nicaragua.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Retención de Aroma durante el Secado de Extracto de Café en un Sistema Cerrado2006In: Nexo, ISSN 1818-6742, Vol. 19, no 1, p. 73-77Article in journal (Refereed)
  • 4346.
    Wagner, David R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    The effect of particle size, temperature, and residence time on biomass devolatilization behavior in a wire-mesh reactor2014In: Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014Conference paper (Other academic)
  • 4347.
    Wagner, David R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Time-dependent variations of activation energy during rapid devolatilization of biomass2016In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 118, p. 98-104Article in journal (Refereed)
    Abstract [en]

    Industrial gasifiers and combustors are assumed to reach particle heating rates of 10(5)-10(6) degrees C/s and understanding how particles behave in these extreme conditions can improve the utilization of solid fuels in these reactors and in downstream applications. By studying intermediate devolatilization processes during solid fuel pyrolysis, detailed models for solid fuel conversion can be formulated. Key objectives of this study included (1) investigate possible mechanisms that promote the formation of synthesis gas components and char, (2) compare the devolatilization behavior of pyrolysis by varying particle size, hold time, and temperature and (3) correlate char deactivation with hold time. The objectives of the study were accomplished using a wire-mesh reactor with a uniform heating rate of 500 degrees C/s in nitrogen under atmospheric pressure. A design of experiments approach was used to quantify the effects that hold time, temperature, and particle size had on char yield, evolved gas composition, and apparent activation energy of pine stem wood and wheat straw. Key results indicate that with increased temperature and hold time more volatiles evolve from the fuels and favor carbon monoxide and methane production at higher temperatures. Apparent activation energy of the volatile matter decreases with hold time. An abbreviated model for apparent activation energy correlates well with experimental data and assumes that along a devolatilization pathway, that not all volatiles are driven from the fuel.

  • 4348.
    Wagner, David R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Holmgren, Per
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Strandberg, Anna
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Wiinikka, Henrik
    Energitekniskt Centrum, Piteå.
    Molinder, Roger
    Energitekniskt Centrum, Piteå.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fate of Inorganic Species during Biomass Devolatilization in a Drop Tube Furnace2014In: Impacts of Fuel Quality on Power Production October 26–31, 2014, Snowbird, Utah, USA, 2014Conference paper (Other academic)
  • 4349.
    Wagner, David R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Zhechao, Qu
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Broström, Markus
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Florian, Schmidt
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Validation of reacting flow models via tunable diode laser absorption spectroscopy2014In: Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014Conference paper (Other academic)
  • 4350.
    Wahlström, Jens
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olander, Lars
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Services Engineering.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Size, Shape, and Elemental Composition of Airborne Wear Particles from Disc Brake Materials2010In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 38, no 1, p. 15-24Article in journal (Refereed)
    Abstract [en]

    During braking, both the rotor and pads experience wear, generating particles that may become airborne. In field tests, it is difficult to distinguish these particles from others in the surrounding environment, so it is preferable to use laboratory test stands to study the amount of airborne wear particles generated. The purpose of this work is to investigate the possibility of separate, capture, and analyze airborne wear particles generated by a disc brake in a disc brake assembly test stand. This test stand used allows the cleanliness of the air surrounding the test specimens to be controlled and thus the airborne portion of the wear particles to be studied separately. One pair each of low-metallic (LM) and non-asbestos organic (NAO) brake pads was tested against grey cast iron rotors. Before testing, the elemental contents of the brake materials were analyzed using glow discharge optical emission spectroscopy (GDOES). The concentration and size of airborne wear particles were measured online during testing. In addition, airborne wear particles were collected on filters during the tests and afterward analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The analyzed wear particles contained elements such as iron, titanium, zinc, barium, manganese, and copper. Both the low-metallic and non-asbestos organic type of brake pads tested display a bimodal size distribution with peaks at 280 and 350 nm. Most of the airborne particles generated have a diameter smaller than 2.5 mu m.

84858687888990 4301 - 4350 of 4815
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