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  • 1.
    Agthe, Michael
    et al.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Wetterskog, Erik
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Salazar-Alvarez, German
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Bergström, Lennart Magnus
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes2014In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 8, p. 1443-1450Article in journal (Refereed)
    Abstract [en]

    The growth modes of self-assembled mesocrystals and ordered arrays from dispersions of iron oxide nanocubes with a mean edge length of 9.6 nm during controlled solvent removal have been investigated with a combination of visible light video microscopy, atomic force microscopy and scanning electron microscopy. Mesocrystals with translational and orientational order of sizes up to 10 μm are formed spontaneously during the final, diffusion-controlled, drop-casting stage when the liquid film is very thin and the particle concentration is high. Convection-driven deposition of ordered nanocube arrays at the edge of the drying droplet is a manifestation of the so called coffee-ring effect. Dendritic growth or fingering of rapidly growing arrays of ordered nanocubes could also be observed in a transition regime as the growth front moves from the initial three-phase contact line towards the centre of the original droplet.

  • 2.
    Aguilar, Wilson
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Study of the Synthesis of ZSM-5 from Inexpensive Raw Materials2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    ZSM-5 is an aluminosilicate with high silica ratio with suitable properties for catalysis, ion exchange, adsorption and membrane applications. ZSM-5 is usually produced industrially from concentrated systems in which there is formation of an amorphous gel phase. Typical syntheses of ZSM-5 require sources of silicon and aluminium, a mineralizer and an organic molecule as so-called templating agent. The silicon and aluminum sources widely used for the synthesis are pure reagent chemicals and in particular quaternary ammonium compounds like tetrapropyl ammonium hydroxides (TPA-OH), are employed as templating agents. Unfortunately, these compounds are rather expensive. Demand for inexpensive sources of aluminosilicates for the synthesis of ZSM-5 has increased during the last two decades. Natural raw materials such as kaolin clay and diatomaceous earth (diatomite) are two potential inexpensive sources of silica and alumina. Moreover, the molecule n-butylamine (NBA) has been reported as a low-cost templating agent to replace the quaternary ammonium compounds. The aim of this work was to show for the first time that leached metakaolinite or diatomite in combination with sodium hydroxide and n-butylamine could be used as inexpensive raw materials for the synthesis of ZSM-5 without using an additional source of silica. After synthesis optimization, both sources of aluminosilicate were found to behave differently during the course of synthesis and led to slightly different products. The chemical composition of the raw materials and the products were determined using inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). Crystallinity was examined by X-ray diffractometry (XRD), the morphology was studied by extreme-high-resolution scanning electron microscopy (XHR-SEM) and the specific surface area was estimated from nitrogen adsorption data by the BET method. The chemical composition of individual crystals was determined by energy dispersive spectrometry (EDS). Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and reduced the amount of impurities. The final ZSM-5 products had a SiO2/Al2O3 ratio in the range 20 – 40. The use of leached diatomite allowed reaching higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of mordenite were formed, which was related to the high calcium content of diatomite. Another considerable advantage of diatomite over kaolin is that diatomite does not require heat treatment at high temperature to convert the kaolin to reactive metakaolin. Further characterization of the system by XHR-SEM and EDS at low voltage was carried out in order to understand the nucleation and early growth of the ZSM-5 zeolite crystals. The observations with unprecedented detail strongly suggest that nucleation and the succeeding growth occurs on the gel surface. The growth rates in the various crystallographic directions already at an early stage are such that the shape of the growing crystals resembles that of the final crystals. However, as the early growth is interface mediated, the growth rate along the gel particles is high and the gel particles will become partially embedded inside the growing crystals at an early stage. The Si and Al nutrients are probably transported along the solid/liquid interface and possibly through the liquid in the form of nanoparticles detaching from the gel. The organic template was initially contained in the liquid. However, it remains unclear at which stage the template becomes incorporated in the solid material. EDS at low voltage was also used to gain compositional information about the sodium/calcium ion exchanged products and extraneous phases when kaolin and Bolivian montmorillonite clay were used for the synthesis of zeolite A by alkali fusion. In order to evaluate the cation exchange capacity (CEC) of the synthesized zeolite, ICP-SFMS and EDS were compared. The EDS method used in this work resulted in (Na,Ca)/Al ratios in equivalent moles very close to 1.0 as expected and was therefore found more reliable than ICP-SFMS to measure cation exchange capacity for zeolite A. To summarize, the present work shows that it was possible to synthesize well-crystallized ZSM-5 zeolite from inexpensive raw materials such as leached metakaolin or leached diatomite, sodium hydroxide and n-butyl amine. Furthermore, the crystallization mechanism evidenced in this system might be more general and also apply for other concentrated systems, e.g. those using TPA as structure-directing. Finally, this work displays that EDS at low voltage can provide valuable local compositional information in the field of zeolite synthesis.

  • 3.
    Aguilar, Wilson
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Garcia, Gustavo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Comparison between leached metakaolin and leached diatomaceous earth as raw materials for the synthesis of ZSM-52014In: SpringerPlus, E-ISSN 2193-1801, Vol. 3, no 1Article in journal (Refereed)
    Abstract [en]

    Inexpensive raw materials have been used to prepare ZSM-5 zeolites with SiO2/Al2O3 molar ratios in the range 20 - 40. Kaolin or Bolivian diatomaceous earth was used as aluminosilicate raw materials and sodium hydroxide and n-butylamine were used as mineralizing agents and template. Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and to reduce the amount of iron and other impurities. After mixing the components and aging, hydrothermal treatment was carried out and the products were recovered The results clearly show for the first time that well-crystallized ZSM-5 can be directly prepared from leached metakaolin or leached diatomaceous earth using sodium hydroxide and n-butylamine as mineralizing agents and template under appropriate synthesis conditions. A longer induction time prior to crystallization was observed for reaction mixtures prepared from leached diatomaceous earth, probably due to slower digestion of the fossilized diatom skeletons as compared with that for microporous leached metakaolin. The use of leached diatomaceous earth allowed higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of Mordenite formed, which was related to the high calcium content of diatomaceous earth. Another considerable advantage of diatomaceous earth over kaolin is that diatomaceous earth does not require heat treatment at high temperature for metakaolinization.

  • 4.
    Aguilar-Mamani, Wilson
    et al.
    Department of Chemistry, Faculty of Science and Technology, San Simon University, UMSS, Cochabamba.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Solution-mediated growth of NBA-ZSM-5 crystals retarded by gel entrapment2018In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 487, p. 57-64Article in journal (Refereed)
    Abstract [en]

    The synthesis of flat tablet-shaped ZSM-5 crystals from a gel using metakaolin as aluminosilicate source and n-butyl amine as structure directing agent was investigated. The evolution inside the solid phase was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry and mass spectrometry. A kinetic study indicated that the nucleation of the majority crystals occurred concurrently with the formation of the gel upon heating the starting liquid suspension. Microstructural evidences undeniably showed that the gel precipitated on ZSM-5 crystals and mineral impurities originating from kaolin. As a result, crystal growth was retarded by gel entrapment, as indicated by the configuration and morphology of the embedded crystals. The results presented herein are harmonized with a solution-mediated nucleation and growth mechanism. Our observations differ from the autocatalytic model that suggests that the nuclei rest inside the gel until released when the gel is consumed. Our results show instead that it is crystals that formed in an early stage before entrapment inside the gel that rest inside the gel until exposed at the gel surface. These results illustrate the limitation of the classical method used in the field to determine nucleation profiles when the crystals become trapped inside the gel.

  • 5.
    Aguilar-Mamani, Wilson
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Department of Chemistry, Faculty of Science and Technology, San Simon University, Cochabamba, Bolivia.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Internal structure of a gel leading to NBA-ZSM-5 single crystals2018In: Journal of porous materials, ISSN 1380-2224, E-ISSN 1573-4854, Vol. 25, no 6, p. 1551-1559Article in journal (Refereed)
    Abstract [en]

    Porous gel structures are formed during the synthesis of the zeolite ZSM-5 due to the reaction between a source of aluminosilicate, sodium hydroxide, water and a structure directing agent, such as e.g. tetrapropylammonium (TPA) or n-butylamine (NBA). In the present work, the formation of the gel in a heterogeneous system leading to the crystallization of NBA-ZSM-5 zeolite from leached metakaolin was studied extensively. The solid and liquid phases obtained after separation were analyzed by inductively coupled plasma sector field mass spectrometry, dynamic light scattering, extreme high resolution-scanning electron microscopy, energy dispersive spectroscopy, high resolution-transmission electron microscopy, X-ray diffraction and nitrogen gas adsorption. The main gel phase formed after hydrothermal treatment exhibited a sponge-like structure resembling those forming in (Na, TPA)-ZSM-5-based systems. For the first time, the walls of the main gel were shown to be inhomogenous and to possess a biphasic internal structure consisting of a mesoporous skeleton of aluminosilicate nanoparticles embedded in a silicate-rich soluble matrix of soft matter. The data presented in this paper is of primary importance to understand the mechanism by which the gel is consumed and contributes to the growth process of the zeolite crystals.

  • 6.
    Aiello, R.
    et al.
    University of Calabria.
    Artioli, G.
    University of Milan.
    Carotenuto, L.
    MARS Center, Naples.
    Colella, C.
    University of Naples.
    Norby, P.
    University of Oslo.
    Sterte, Johan
    Zeolite synthesis in microgravity2005In: Topical teams in life & physical sciences: towards new research applications, Noordwijk, Netherlands: ESTEC , 2005, p. 78-85Chapter in book (Other academic)
    Abstract [en]

    The results of activities performed by the members of the Topical Team on 'Zeolites synthesis in microgravity' are discussed. A method was developed using a two-temperature synthesis procedure to distinguish between the nucleation and growth phase of the crystallization. The experiments have investigated the possibility of suppressing secondary nucleation by imposing a temperature gradient. Optical thickness of the solution has been monitored by interferometry. The Team, on the basis of findings, has elaborated a research program on zeolite film deposition that includes microgravity experimentation.

  • 7.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bergström, Lennart M.
    Department of Materials and Environmental Chemistry, Stockholm University.
    All-Zeolite Membranes2010Conference paper (Refereed)
  • 8.
    Akhtar, Farid
    et al.
    Stockholm University, Department of Materials and Environmental Chemistry.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Wirawan, Kompiang
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    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.
    Hierarchically porous binder-free silicalite-1 discs: a novel support for all-zeolite membranes2011In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 21, no 24, p. 8822-8828Article in journal (Refereed)
    Abstract [en]

    Thermal expansion mismatch between the zeolite film and the support is an important cause for the formation of defects and cracks during the fabrication and use of zeolite membranes. We have studied how silicalite-1 discs with a permeability comparable to commercially available alumina supports can be produced by pulsed current processing (PCP) as a novel substrate for all-zeolite membranes. Hierarchically porous and mechanically strong membrane supports where the surface area and crystallography of the silicalite-1 particles were maintained could be obtained by carefully controlling the thermal treatment during PCP consolidation. In situ X-ray diffraction and dilatometry showed that the coefficient of thermal expansion (CTE) of the silicalite-1 substrate was negative in the temperature range 200-800 degrees C while the commonly used alumina substrate displayed a positive CTE. The critical temperature variation, Delta T, and thicknesses for crack-free supported zeolite films with a negative CTE were estimated using a fracture energy model. Zeolite films with a thickness of 1 mu m can only sustain a relatively modest Delta T of 100 degrees when supported onto alumina substrates while the all-zeolite membranes can support temperature variations above 500 degrees

  • 9.
    Akhtar, Farid
    et al.
    Department of Materials and Environmental Chemistry, Stockholm University.
    Ojuva, Arto
    Stockholm University, Department of Materials and Environmental Chemistry.
    Wirawan, Kompiang
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    PCP procesing of Zeolite supports for all-zeolite membranes2011Conference paper (Refereed)
  • 10.
    Akhtar, Farid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sjöberg, Erik
    Korelskiy, Danil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Rayson, Mark
    Department of Chemistry, The University of Surrey, Guildford.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Bergström, Lennart
    Department of Materials and Environmental Chemistry, Stockholm University.
    Preparation of graded silicalite-1 substrates for all-zeolite membranes with excellent CO2/H2 separation performance2015In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 493, p. 206-211Article in journal (Refereed)
    Abstract [en]

    raded silicalite-1 substrates with a high gas permeability and low surface roughness have been produced by pulsed current processing of a thin coating of a submicron silicalite-1 powder onto a powder body of coarser silicalite-1 crystals. Thin zeolite films have been hydrothermally grown onto the graded silicalite-1 support and the all-zeolite membranes display an excellent CO2/H2 separation factor of 12 at 0 °C and a CO2 permeance of 21.3×10-7 mol m-2 s-1 Pa-1 for an equimolar CO2/H2 feed at 505 kPa and 101 kPa helium sweep gas. Thermal cracking estimates based on calculated surface energies and measured thermal expansion coefficients suggest that all-zeolite membranes with a minimal thermal expansion mismatch between the graded substrate and the zeolite film should remain crack-free during thermal cycling and the critical calcination step.

  • 11.
    Andersson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    CFD optimization of photochemical UV reactors for VOC degradation2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In 2016 the World Health Organization released a report on Ambient Air Pollution, in this it was stated that one out of every nine deaths all around the world in 2012 were due to air-pollution-related conditions. Urban air pollution involves a broad range of compounds from many diverse sources. Volatile Organic Compounds (VOCs) are some of the important compounds. Almost all VOCs are known to have effect on human health, many of them are carcinogenic. VOCs also contribute to the ground level photochemical smog and the reduction of the stratospheric ozone layer. Therefore, it is important to control the emissions of VOCs from industries and restaurants.

    Today most big scale VOC removal is done by thermal or catalytic incineration. While smaller scale air purification is done by using adsorbing materials such as activated carbon. Both these methods have their drawbacks. A promising technology, which is also environmentally friendly, is UV reactors.

    This thesis is a collaboration with the company Centriair, a company developing and selling UV reactors mainly for odor removal. The UV reactors which are in use today show acceptable performance, with a conversion of 50-60%. However, they have yet to be optimized to get the most out of the reactors. The aim was to try to reach an as high conversion of VOCs as possible in a prototype scale compared to a reference reactor, also in prototype scale. The reactors were simulated using the Computational Fluid Dynamic (CFD) software COMSOL Multiphysics® 5.2a. The simulation was based on earlier lab scale experiments with UV reactors.

    The conclusion from doing this thesis is that the most important challenge with a UV reactor up-scaling and optimization is the dark zones and the bypassing effect given by these. It is very important that the irradiation reaches the whole reactor and that all gas is affected by it. It is also important that the gas is given time to stay by the light sources as long as possible. Two reactors in this thesis had very high conversion results and thus showed potential of being very effective UV reactors. These two reactors showed conversion results of 45% respective 61% higher than the reference reactor used by Centriair today.

  • 12.
    Andersson, Charlotte
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Factors affecting MFI membrane quality2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Zeolites are crystalline aluminosilicates with molecular sieving properties and are widely used in industrial applications such as catalysis, sorption and ion-exchange. Zeolite membranes are highly interesting due to their capability to continuously separate molecules under severe conditions. The MFI zeolite structure has suitable pore diameter for many applications, and its thermal and chemical stability is high. In order to obtain high performance MFI membranes, a thin and defect free film is needed for high flux and high selectivity. In this thesis, parameters affecting quality of zeolite membranes have been investigated. Different MFI-zeolite membranes were prepared using seed crystals and hydrothermal synthesis. Thereafter, membranes were characterized using scanning electron microscopy, single gas permeation measurements, porosimetry and separation experiments. The effect of grain boundaries was investigated by preparing membranes with small crystal size. It was found that a high amount of grain boundaries reduced the quality of the membranes. In another study, the effect of exposure to aqueous solutions was found to increase the amount of non-zeolitic pores in the membrane, and thus it decreased the quality of the membrane. However, no such effect was found for ethanol that was identified as a safe rinsing media. Membranes with different Si/Al ratio were also prepared and evaluated. It was observed that the Si/Al ratio of a MFI membrane influences the performance of the membrane. It was found that an increase of aluminium makes the membrane more polar which leads to an improved adsorption of, and selectivity for polar molecules. The effect of support invasion was also evaluated and the regularity and extension of the support invasion was observed to affect membrane quality. The effect of heating rate during calcination was investigated and no correlation between heating rate and membrane quality was observed. Calcination of membranes was studied in-situ by high temperature synchrotron radiation and a model for crack formation was postulated. In summary, this work has shown that in order to obtain high quality membranes, the amount of grain boundaries, the film thickness and support invasion should be controlled. To obtain the best performance of the membranes the Si/Al ratio should be chosen with respect to the application. Finally, water exposure affects the lifetime of the MFI membranes in certain applications.

  • 13.
    Andersson, Charlotte
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Properties of molecular sieve membranes2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Zeolites are crystalline aluminosilicates with molecular sieving properties and are widely used in industry for catalysis, sorption and ion-exchange applications. Zeolite membranes are commercially interesting since this technology may be employed for continuous separation of molecules under severe conditions. MFI zeolite has suitable pore diameter for many applications and relatively high thermal and chemical stability. Zeolite films in membranes must be thin, to obtain a high flux and free from defects for high selectivity. Many parameters are affecting the properties of zeolite films and in this thesis some of them are investigated. MFI zeolite membranes were prepared using seed crystals and hydrothermal synthesis and characterized with scanning electron microscopy, single gas permeation measurements, porosimetry and separation experiments. Membranes grown in one or several steps with seeding in-between the synthesis steps were compared. It was observed that membranes comprised of small crystals and consequently high concentration of grain boundaries had low separation performance. Grain boundaries could also be opened by extensive rinsing, which reduced membrane quality. The influence of the calcination rate on the performance of zeolite membranes of a particular type was also studied. It was demonstrated that the calcination rate does not affect the membrane quality.

  • 14. Andersson, Charlotte
    et al.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Effects of exposure to water and ethanol on silicalite-1 membranes2008In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 313, no 1-2, p. 120-126Article in journal (Refereed)
    Abstract [en]

    The effects of long exposures to ethanol, water and 0.1 M aqueous solutions of ammonia, sodium hydroxide, tetrapropylammonium hydroxide (TPAOH) and hydrochloric acid on thin TPA-silicalite-1 membranes were studied. Single gas permeation experiments, porosimetry and scanning electron microscopy were used to characterize the membranes. It was found that a short exposure (24 h) will only dissolve synthesis residues and will not affect membrane quality negatively. The only medium that had an effect after 24 h was sodium hydroxide, which almost dissolved the film completely. After exposing TPA-silicalite-1 membranes for 30 days in the various liquids, the membrane quality decreased in the order ethanol < 0.1 M hydrochloric acid < 0.1 M TPAOH < water < 0.1 M ammonia < 0.1 M sodium hydroxide due to dissolution of the silicalite-1 crystals. This study has shown that prolonged exposure to aqueous solutions will lead to dissolution of silicalite-1 crystals causing an increase in micro- and mesopores in the film. The amount and size of the pores will depend on the pH of the aqueous medium. Higher pH gives a higher dissolution and hence more non-zeolitic pores in the silicalite-1 film. Ethanol has no effect on the dissolution of the zeolite film even after 30 days. This finding has an effect in membrane preparation and in several membrane applications such as pervaporation and separation of hydrocarbons isomer mixtures.

  • 15. Andersson, Charlotte
    et al.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Jareman, Fredrik
    Luleå tekniska universitet.
    Sterte, Johan
    Silicalite-1 membranes with small crystal size2004In: Recent advances in the science and technology of zeolites and related materials. Part A: proceedings of the 14th International Zeolite Conference, Amsterdam: Elsevier, 2004, p. 626-631Conference paper (Refereed)
    Abstract [en]

    Silicalite-1 membranes with small crystal size were prepared using a multiseeding method, where the support was repeatedly seeded and exposed to a short hydrothermal treatment up to five times. The film were characterized using SEM, single gas permeation, porosimetry and mixture separation experiment Films with three or four layers were of high quality i.e with minor defects according to the porosimetry experiments but showed poor separation of binary mixtures. This result may be attributed to the small crystal size and/or large amount of grain boundaries in the films.

  • 16.
    Andersson, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Semi-deterministic chemo-mechanical model of boundary lubrication2012In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 156, p. 343-360Article in journal (Refereed)
    Abstract [en]

    A model for tribofilm growth is developed. The model is used in combination with numerical contact mechanics tools to enable evaluation of the combined effects of chemistry and contact mechanics. The model is tuned with experimental data and is thereafter applied to rough surfaces. The growth of the tribofilm is evaluated for 3 different contact cases and short-term tribofilm growth behaviour is analyzed. The results show how tribofilms grow in patches. The model is expected to be used as a tool for analysis of the interaction between rough surfaces.

  • 17. Anthonis, Marc Henry
    et al.
    Bons, Anton-Jan
    Deckman, H. W.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Lai, Wenyih F.
    Peters, J.A.J.
    Crystalline molecular sieve layers and processes for their manufacturePatent (Other (popular science, discussion, etc.))
    Abstract [en]

    A process is described for the manufacture of crystalline molecular sieve layers with good para-xylene over meta-xylene selectivity's good para-xylene permeances and selectivities. The process requires impregnation of the support prior to hydrothermal synthesis using the seeded method and may be undertaken with pre-impregnation masking. The crystalline molecular sieve layer has a selectivity (.alpha..sub.x) for para-xylene over meta-xylene of 2 or greater and a permeance (Q.sub.x) for para-xylene of 3.27.times.10.sup.-8 mole(px)/m.sup.2.s.Pa(px) or greater measured at a temperature of .gtoreq.250.degree. C. and an aromatic hydrocarbon partial pressure of .gtoreq.10.times.10.sup.3 Pa.

  • 18.
    Antzutkin, Oleg
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kota, Hanumantha Rao
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Ikumapayi, Fatai
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Gunneriusson, Lars
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Johansson, Björn
    New Boliden AB.
    Berggren, Andreas
    New Boliden AB.
    Larsson, Anna-Carin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsmo, Seija
    LKAB.
    Interactions in multi-component mineral systems2011Conference paper (Other academic)
  • 19.
    Antzutkin, Oleg
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kota, Hanumantha Rao
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Ikumapayi, Fatai
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Johansson, Björn
    New Boliden AB.
    Berggren, Andreas
    New Boliden AB.
    Larsson, Anna-Carin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsmo, Seija
    LKAB.
    Interactions in multi-component mineral systems2010Conference paper (Other academic)
  • 20.
    Arkhipov, Victor P.
    et al.
    Kazan National Research Technological University.
    Idiyatullin, Zhamil Sh
    Kazan National Research Technological University.
    Potapova, Elisaveta
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Filippov, Andrei
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Micelles and aggregates of oxyethylated isononylphenols and their extraction properties near cloud point2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 20, p. 5480-5487Article in journal (Refereed)
    Abstract [en]

    We used nuclear magnetic resonance (NMR) spectroscopy and dynamic light scattering (DLS) techniques to study the structural and dynamic properties of micellar solutions of nonionic surfactants of a homologous series of oxyethylated isononylphenols - C9H19C6H 4O(C2H4O)nH, where n = 6, 8, 9, 10, or 12 - in a wide range of temperatures, including cloud points. The radii of the micelles and aggregates, as well as their compositions at different concentrations of surfactant, were determined. Using aqueous phenol solutions as a model, we studied the process of cloud point extraction with oxyethylated isononylphenols

  • 21.
    Arkhipov, Victor
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Potapova, Elisaveta
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Filippov, Andrei
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Micelle structure and molecular self-diffusion in isononylphenol ethoxylate–water systems2013In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 51, no 7, p. 424-430Article in journal (Refereed)
    Abstract [en]

    The structure and dynamic properties of micellar solutions of nonionic surfactants of a series of isononylphenol ethoxylates, C9H19C6H4O(C2H4O)nH (where n = 6,8,9,10, and 12), were studied by NMR diffusometry, dynamic light scattering, and viscosimetry. The sizes of the micelles were determined for different surfactants and at different surfactant concentrations. The numbers of water molecules bound by a micelle and by one oxyethylene group of the surfactant were estimated

  • 22.
    Arman, S.Y.
    et al.
    Department of Mining and Metallurgical Engineering, Amirkabir University of Technology.
    Omidvar, H.
    Department of Mining and Metallurgical Engineering, Amirkabir University of Technology.
    Tabaian, S.H.
    Department of Mining and Metallurgical Engineering, Amirkabir University of Technology.
    Sajjadnejad, M.
    Department of Mining and Metallurgical Engineering, Amirkabir University of Technology.
    Fouladvand, Shahpar
    Department of Mining and Metallurgical Engineering, Amirkabir University of Technology.
    Afshar, Sh.
    Department of Chemistry, Iran University of Science and Technology.
    Evaluation of nanostructured S-doped TiO2 thin films and their photoelectrochemical application as photoanode for corrosion protection of 304 stainless steel2014In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347Article in journal (Refereed)
    Abstract [en]

    Undoped and S-doped TiO2 thin films were prepared on titanium substrate through a sol–gel method. The photoelectrochemical behavior of S-doped TiO2 thin film (as photoanode) was studied. The effect of Sulfur doping on structural, optical and morphological properties of TiO2 was studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR, UV–ViS and FE-SEM. Superiority of the S-doped TiO2 film was shown through taking advantage of linear sweep voltametry measurement, open-circuit potential of 304 stainless steel as well as potetiodynamic polarization technique. Results showed that S-doped TiO2 thin film is an efficient photoanode with long term stability (several hours).

  • 23.
    Bayat, Mohammad
    et al.
    Faculty of Chemical Engineering, Research and Technology Centre for Membrane Processes, Iran University of Science and Technology (IUST), Tehran, Iran.
    Nabavi, Mohammad Sadegh
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mohammadi, Toraj
    Faculty of Chemical Engineering, Research and Technology Centre for Membrane Processes, Iran University of Science and Technology (IUST), Tehran, Iran.
    An experimental study for finding the best condition for PHI zeolite synthesis using Taguchi method for gas separation2018In: Chemical papers, ISSN 2585-7290, Vol. 72, no 5, p. 1139-1149Article in journal (Refereed)
    Abstract [en]

    Phillipsite zeolite particles and membranes were successfully synthesized at different operational and environmental conditions. Using an L9 orthogonal array of the Taguchi method, effects of experimental condition—synthesis temperature (130–150 °C), synthesis time (2–3 days), number of synthesized layers (1–3), and seeding suspension percentage—for membrane preparation with respect to CO2/CH4 ideal selectivity were investigated. The results showed that the ideal selectivity was improved up to 4.20 from 1.15 by increasing the number of synthesized layers, synthesis temperature, and seed solution concentration and by decreasing synthesis time. Moreover, the best synthesis conditions were defined based on the Taguchi method results and the membrane was synthesized with the highest ideal selectivity which was around 4.40. In addition, it was shown that T zeolite is formed beside PHI zeolite at low temperature even with long synthesis time.

  • 24.
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Characterization of iron ore green pellets by scanning electron microscopy and X-ray microtomography2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cryogenic scanning electron microscopy (cryo-SEM), image analysis (IA) of SEM micrographs and X-ray microtomography (XMT) were used to obtain new information about the morphology of iron ore green pellets in this work. Cryo-SEM and freeze fracturing was used to observe entrapped air bubbles and arrangement of particles around the bubbles and in the matrix of wet green pellets. The observations of samples prepared by plunge and unidirectional freezing indicate that unidirectional freezing facilitates the observation of entrapped bubbles with minimum formation of artifacts, whereas plunge freezing enables observation of the degree of water filling at the outer surface of wet pellets with minimum amount of artifacts. It was also observed in the wet pellets that the size of the water domains in the matrix is quite small and the finer grains are mixed with coarser grains resulting in a denser matrix, whereas no fine grains were observed in the vicinity of the air bubbles. Two types of pellets prepared with and without addition of extra flotation reagent prior to balling were studied using IA and XMT. IA of scanning electron micrographs of epoxy impregnated pellets was used to separate bubble porosity from packing porosity and to quantify the former. The individual SEM micrographs acquired by a backscattered electron detector were reconstructed to provide the entire two-dimensional (2D) sections of the pellets. The 2D data obtained by IA were unfolded to three-dimensional (3D) by stereology and relatively good agreement with XMT data was observed. The size and amount of air bubbles could be quantified with both techniques. The addition of extra flotation reagent was found to increase the number of entrapped air bubbles and slightly decrease the median bubble diameter. The additional entrapped air bubbles due to the addition of extra flotation reagent was shown to be responsible for the difference in total porosity observed by mercury porosimetry between the two types of pellets. Mercury intrusion porosimetry (MIP) is shown in this work to produce inappropriate results with regard to the porosity due to bubble entrapment, it only provides values for total porosity and the throat size distribution of the porosity. In summary, this work has shown that cryo-SEM, IA of SEM micrographs and XMT are powerful and very useful methods for characterization of the morphology of iron ore green pellets.

  • 25.
    Bhuiyan, Iftekhar Uddin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Microstructural characterization of iron ore green pellets2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this thesis work was to develop new methodologies to characterize iron ore green pellets, in wet and dry state. The new characterization methods applied and developed in this work were mainly based on scanning electron microscopy (SEM) to gather both qualitative and quantitative data on different components of the pellets, i.e. mineral particles, water, bentonite and entrapped bubbles.In a first attempt to preserve the structure of wet iron ore green pellets by freezing before investigation by cryogenic SEM, wet pellets were frozen in liquid nitrogen by direct plunging or a new method developed in the present work denoted unidirectional freezing. The former method was found useful to study the degree of water filling at the outer surface of the pellet but led to artifacts in the interior of the pellet. The latter method was developed to confirm that the spherical cavities observed in dry pellets were related to entrapped bubbles in wet pellets. Capillaries were observed at the outer surface of the pellets and fine particles were lacking within a layer of approximately 100 µm from the outer surface and also in the direct vicinity of the air bubbles in the interior of the pellets.More advanced freezing methods were subsequently employed to reveal the artifact free microstructure of bentonite in wet pellets. In order to verify the observations made on a slice of a wet pellet frozen by plunging in liquid ethane, SEM investigations were also carried out on a bentonite suspension and a bentonite-iron ore slurry, which could be cryo-fixed by the most reliable freezing method, i.e. high pressure freezing. All microstructures were comparable and consisted in a voluminous network of well-dispersed clay platelets. This network was found to collapse upon drying. Bentonite was drawn to the contact points between the particles and formed what appeared as bridges, which may impart strength to the dry pellets. A combination of energy dispersive spectroscopy (EDS) and imaging by low-loss backscattered electrons at low voltage evidenced the presence of very finely divided silicate species on the magnetite particles. In order to visualize the three dimensional structure of dispersed bentonite clay with unprecedented resolution, a method based on SEM imaging with a monochromatic and decelerated beam was used for the first time. The recorded images showed very well-dispersed clay platelets forming a fine network of Y shaped contacts, which is quite different from earlier reports of much coarser structures formed as a result of poor sample preparation. Finally, in order to gain quantitative data about the porosity due to bubble entrapment in dry pellets, the entire cross-section of dry epoxy embedded and polished pellets were recorded by SEM. The three-dimensional bubble size distribution was unfolded from 2D SEM data using image processing, image analysis and stereological principles. The same type of pellets was also investigated by X-ray micro-tomography (XMT). The resulting three-dimensional dataset allowed the validation of the unfolding procedure based on stereology. However, the lack of resolution obtained by XMT was shown to lead to slight discrepancies with the SEM data for small bubble sizes. Entrapped air bubbles due to the addition of extra flotation reagent in pellets were shown to be responsible for additional porosity observed by mercury intrusion porosimetry (MIP). In summary, useful characterization methods for iron ore pellets based on SEM have been developed in this work, which opens up new possibilities to for instance study agglomeration processes in more detail.

  • 26.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsberg, Fredrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsmo, S.P.E.
    LKAB, Research & Development, 983 81 Malmberget.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Consideration of X-ray microtomography to quantitatively determine the size distribution of bubble cavities in iron ore pellets2013In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 233, p. 312-318Article in journal (Refereed)
    Abstract [en]

    X-ray microtomography data of iron ore green pellets of approx. 12 mm in diameter were recorded using a commercial instrument. The reconstructed volume after thresholding represented a unique dataset consisting of a three-dimensional distribution of equiaxed objects corresponding to bubble cavities. This dataset was used to successfully validate a stereological method to determine the size distribution of spherical objects dispersed in a volume. This was achieved by investigating only a few cross-sectional images of this volume and measuring the profiles left by these objects in the cross-sectional images. Excellent agreement was observed between the size distribution of the bubble cavities obtained by directly classifying their size in the reconstructed volume and that estimated by applying the aforementioned stereological method to eight cross-sectional images of the reconstructed volume. Subsequently, we discuss the possibility of calibrating X-ray tomography data quantitatively using the size distribution of the bubble cavities as a figure of merit and the results obtained by applying the stereological method to SEM images as reference data. This was justified by considering the validity of the stereological method demonstrated by tomography, the accurate thresholding made possible by back-scattered electron imaging and the solid reproducibility of the results obtained by SEM. Using different threshold values for binarization of the X-ray microtomography data and comparing the results to those obtained by SEM, we found that X-ray microtomography can be used after proper calibration against SEM data to measure the total porosity of the bubble cavities but can only provide a rough estimate of the median diameter because of the limited resolution achieved in this study.

  • 27.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsmo, S.P.E.
    LKAB.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Quantitative image analysis of bubble cavities in iron ore green pellets2011In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 214, no 3, p. 306-312Article in journal (Refereed)
    Abstract [en]

    Scanning electron microscopy and image analysis was used for quantitative analysis of bubble cavities in iron ore green pellets. Two types of pellets prepared with and without addition of flotation reagent prior to balling were studied. The bubble cavity porosity amounted to 2.8% in the pellets prepared without addition of flotation reagent prior to balling. When flotation reagent was added prior to balling, the bubble cavity porosity increased by a factor of 2.4 and the median bubble diameter was decreased slightly. It was also shown that mercury intrusion porosimetry is not suitable for determination of the distribution of bubble cavities. Finally, our data suggested that the difference in total porosity determined by mercury intrusion porosimetry and pycnometry between the two types of pellets was due to the bubble cavities.

  • 28.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Forsmo, S.P.E.
    LKAB Research and Development.
    Forsberg, Fredrik
    Air bubbles in iron ore green pellets due to flotation reagent: characterization by scanning electron microscopy and X-ray microtomography2011Conference paper (Other academic)
  • 29.
    Bhuiyan, Iftekhar Uddin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Schröppel, Birgit
    Natural and Medical Sciences Institute (NMI), University of Tübingen.
    Kaech, Andres
    Center for Microscopy and Image Analysis, University of Zurich.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Forsmo, Seija P.E.
    LKAB, Research & Development, 983 81 Malmberget.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Microstructure of Bentonite in Iron Ore Green Pellets2014In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 20, no 1, p. 33-41Article in journal (Refereed)
    Abstract [en]

    Sodium-activated calcium bentonite is used as a binder in iron ore pellets and is known to increase strength of both wet and dry iron ore green pellets. In this article, the microstructure of bentonite in magnetite pellets is revealed for the first time using scanning electron microscopy. The microstructure of bentonite in wet and dry iron ore pellets, as well as in distilled water, was imaged by various imaging techniques (e.g., imaging at low voltage with monochromatic and decelerated beam or low loss backscattered electrons) and cryogenic methods (i.e., high pressure freezing and plunge freezing in liquid ethane). In wet iron ore green pellets, clay tactoids (stacks of parallel primary clay platelets) were very well dispersed and formed a voluminous network occupying the space available between mineral particles. When the pellet was dried, bentonite was drawn to the contact points between the particles and formed solid bridges, which impart strength to the solid compact.

  • 30.
    Bjorklund, Robert B.
    et al.
    Linköping University.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sterte, Johan
    Arwin, Hans
    Linköping University.
    Vapor adsorption in thin silicalite-1 films studied by spectroscopic ellipsometry1998In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 102, no 12, p. 2245-2250Article in journal (Refereed)
    Abstract [en]

    Thin films of silicalite-1 grown on silicon substrates were studied by spectroscopic ellipsometry. Analysis of spectra using an optical model consisting of a single porous layer on silicon yielded average film thicknesses of 84 and 223 nm for films synthesized for 10 and 30 h. Void fraction for the films was 0.32-0.33. Vapor adsorption from a nitrogen carrier gas at room temperature was monitored by ellipsometry. Isotherms for different adsorbates were obtained by analysis of spectra taken at different vapor concentrations using an optical model where the void volume was filled with both nitrogen and condensed vapors. Quantification of the condensed vapor amount was based on the changes in refractive index when adsorbates replaced nitrogen in the pores. Adsorbate volumes for water, toluene, 1-propanol, and hexane were 0.12, 0.12, 0.15, and 0.17 cm3 liquid g-1 film, respectively.

  • 31.
    Björklund, Robert B.
    et al.
    Linköping University.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Carlsson, Bill
    Vadstena Varmförzinkning AB.
    Ellipsometric study of oxide removal from steel surfaces in hydrochloric acid solutions1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, no 2, p. 494-499Article in journal (Refereed)
    Abstract [en]

    Iron oxide films formed on three different steel surfaces by thermal oxidation were removed in hydrochloric acid solutions at 20 C. The oxide removal process in flowing solutions was followed in situ by ellipsometry. Two different removal mechanisms were observed in 0.5-2 M HCl, one where undermining of the film resulted in large intact pieces of the oxide leaving the substrate surface at the end of the removal period, and one where the film scaled off the surface in small pieces during the entire removal process. Oxide films which exhibited the undermining mechanism were found to contain about 10% hematite (Fe2O3) and 90% magnetite (Fe3O4). The scaling off mechanism was observed for films which were nearly pure magnetite. Optical models were constructed using data from scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements for the thicknesses and compositions of films after different immersion times in HCl solutions. Spectra calculated from the models agreed well with the experimental spectra.

  • 32.
    Björkvall, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Studie om dynamiken i en pilotrullkrets med rulltrumma2018Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Luossavaara-Kiirunavaara AB (LKAB) produce pellets from magnetite iron ore. Pellets are formed by balling moist iron ore concentrate to green pellets, which are then burned to pellets. The green pellets are formed in balling circuits consisting of balling drums and roller decks for screening. In 2017 a pilot scale balling circuit with a drum was completed in LKAB's agglomeration laboratory in Malmberget. The purpose of the pilot balling circuit is to predict the dynamics in a full scale balling circuit under different conditions.

    This master degree project is an initial attempt to study the response in LKAB's pilot circuit in terms of green pellet quality and dynamics in the circuit. The goal was to determine an effective way to run experiments and to investigate whether the pilot circuit can predict the dynamics of balling in large-scale circuits. Pelletizing production is within LKAB's core competence, and therefore the origin and character of the reagents, as well as the design of the pilot balling drum circuit, are confidential. Code names are used for both iron ore concentrates and reagents.

    The work began by creating a test procedure with the aim of running as many different mixtures as possible in the pilot balling circuit during a normal working day. Five different mixtures could be run. Four different additives were tested: bentonite, a flotation reagent (FLOT), an organic binder (OB) and a new development product (UTV). The first experiment in the pilot balling circuit was run with varying doses of bentonite because its impact in balling is well known at LKAB. Experiment two and three, with FLOT and OB, could be compared to previous experience from large scale test runs. The fourth and last experiment was a test of how the pilot circuit predicted the behavior of a new development product UTV. Each type of experiment was performed twice.

    The pilot balling circle predicted well both dynamics and green pellet quality in all three experiments where experience from large-scale runs was available. The new, unknown, UTV product showed improved green pellet quality, without affecting adversely on the dynamics of the circuit. UTV can therefore be an interesting option for a future large scale run at LKAB.

    The developed working schedule worked very well. A "basic analysis package" has been created to facilitate planning of future experiments in the pilot balling circuit. The number of persons needed to run the circuit depends on the number of mixtures and analyzes. For smaller experiments, at least five people is required, in addition to the leader of the experiments. More advanced experiments will demand seven people.

  • 33.
    Bleken, Bjørn Tore L.
    et al.
    Department of Chemistry, InGAP Center for Research-based Innovation, University of Oslo Blindern.
    Wragg, David Stephen
    Department of Chemistry, InGAP Center for Research-based Innovation, University of Oslo Blindern.
    Arstad, Bjørnar
    SINTEF Materials and Chemistry, Blindern.
    Gunnæs, Anette Eleonora
    Department of Physics, University of Oslo FERMiO.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Helveg, Stig
    Haldor Topsøe A/S.
    Lundegaard, Lars Fahl
    Haldor Topsøe A/S.
    Beato, Pablo
    Haldor Topsøe A/S.
    Bordiga, Silvia
    Department of Chemistry, InGAP Center for Research-based Innovation, University of Oslo Blindern.
    Olsbye, Unni
    Department of Chemistry, InGAP Center for Research-based Innovation, University of Oslo Blindern.
    Svelle, Stian
    Department of Chemistry, InGAP Center for Research-based Innovation, University of Oslo Blindern.
    Lillerud, Karl Petter
    Department of Chemistry, InGAP Center for Research-based Innovation, University of Oslo Blindern.
    Unit cell thick nanosheets of zeolite H-ZSM-5: Structure and activity2013In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 56, no 9-10, p. 558-566Article in journal (Refereed)
    Abstract [en]

    nosheets of zeolite H-ZSM-5 were synthesized and characterized by X-ray diffraction, transmission electron microscopy (TEM), N2- physisorption, FT-IR spectroscopy, 27Al and 29Si MAS NMR spectroscopy in addition to catalytic testing in conversion of methanol to hydrocarbons (MTH). It was found that Rietveld analysis, involving anisotropic broadening parameters, gave average crystallite dimensions in good agreement with TEM images. The selectivities in MTH is intact in the mesoporous nanosheet H-ZSM-5 with the largest difference being a higher C3/C2 ratio compared to regular H-ZSM-5.

  • 34.
    Carabante, Ivan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Arsenic (V) adsorption on iron oxide: implications for soil remedeation and water purification2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Addition of iron oxide based adsorbents to arsenic contaminated soils has been proposed as a mean to reduce the mobility of arsenic in the soil. However, the conditions in the soil such as pH value, the presence of phosphate after addition of fertilizer to the soil or the presence of Zn (II) as a co-contaminant may affect the adsorption of arsenate on the iron oxide and may therefore have implications for the mobility of arsenic in the remediated soil.In the present work, a new flow method was developed to study the adsorption of arsenate on synthetic iron oxide with high surface area (ferrihydrite) in situ by means of Attenuated Total Reflection – Fourier Transform Infrared (ATR – FTIR) spectroscopy and the method was used for studying how the adsorption of arsenate was affected by the pH/pD value, the presence of phosphate and Zn (II) in the system. The highest adsorption of arsenate was found at pD 4 and decreased as the pD value increased. The arsenate complexes formed on ferrihydrite appeared to be very stable at pD 4, while the stability decreased as the pD value increased. Arsenate showed a higher adsorption affinity than phosphate on ferrihydrite under the conditions studied. However, phosphate was able to replace about 10 % of pre-adsorbed arsenate on ferrihydrite at pD 4 and about 20 % of the pre-adsorbed arsenate at pD 8.5 in equimolar concentrations of phosphate and arsenate. Phosphate replaced 30 % of pre-adsorbed arsenate at pD 4 and up to 50 % of pre-adsorbed arsenate at pD 8.5 when the concentration of phosphate in the system was 5 times higher than that of arsenate. Batch adsorption experiments indicated an enhancement in the arsenate removal from a ferrihydrite suspension in the presence of Zn (II) at pH 8 in accordance with previous reports. However, no adsorption of arsenate on ferrihydrite in the presence of high concentrations of Zn (II) in the system was observed by infrared spectroscopy. Instead, precipitation of zinc hydroxide carbonate followed by arsenate adsorption on the zinc precipitate was found to be the most likely explanation of these results.Although iron oxides are selective towards arsenate, high specific surface areas are required to achieve sufficiently high adsorption capacity. A method of increasing the specific surface area of coarse hematite particles to obtain a good adsorbent was also developed in the present work. The method comprises an acid treatment to produce iron ions followed by hydrolysis to precipitate an iron oxy-hydroxide coating on the hematite particles. While the arsenate adsorption capacity of the original coarse hematite particles was found to be negligible, the sintered coarse hematite particles showed good potential as an adsorbent for arsenate with an adsorption capacity of about 0.65 mg[As]/g.The method developed for studying adsorption on iron oxides by in situ ATR - FTIR spectroscopy was further developed for studying the adsorption of flotation collectors on iron oxides. Iron ore is often separated from gangue minerals by means of reverse flotation in which a surfactant should selectively adsorb on the gangue mineral rendering it hydrophobic. However, unwanted adsorption of the surfactants on the iron oxide has been reported to affect the production of iron ore pellets. A method was developed to study the adsorption of the surfactant Atrac 1563 on synthetic hematite in situ by means of ATR - FTIR spectroscopy. The adsorption of Atrac 1563 on hematite at pH 8.5 was found to mostly occur via interactions between the polar ester and ethoxy groups of the surfactant and the hematite surface.

  • 35.
    Carabante, Ivan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Study of arsenate adsorption on iron oxide by in situ ATR-FTIR spectroscopy2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stabilization of arsenic contaminated soils by iron oxides has been proposed as a remediation technique to prevent leaching of arsenate into the environment. However, fundamental studies are needed to establish under which conditions the complexes formed are stable. A new method based on ATR-FTIR spectroscopy was adapted to study the adsorption of arsenate species on iron oxides. The measurements required the use of D2O as solvent. The amount of arsenate complexes adsorbed on the iron oxide increased with decreasing pD in the range studied, viz. pD 4-12. Arsenate complexes adsorbed at pD 4 desorbed from the film to some extent as the pD was increased to 8.5 or 12. The stability of arsenate complexes adsorbed on the iron oxide evidently changed with the change in pD, most likely due to the electrostatic repulsion between the negatively charged oxoanion and the more negatively charged iron oxide as the pD increased. From competitive adsorption experiments it was found that arsenate species were more strongly bonded to the iron oxide than phosphate species. Furthermore, it was found that two different phosphate complexes formed on the iron surface at pD 4, one deuterated and the other one de-deuterated. The complexes showed very different stability. The deuterated phosphate complex was desorbed easily from the iron oxide film as arsenate was added to the system whereas the de-deuterated phosphate complex only desorbed slightly from the film upon adding arsenate.This work has increased the fundamental knowledge of the iron oxide/arsenate/phosphate system, which will be of importance for the development of more effective soil remediation techniques.

  • 36. Carabante, Ivan
    et al.
    Grahn, Mattias
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    In situ ATR-FTIR studies on the competitive adsorption of arsenate and phosphate on ferrihydrite2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 351, no 2, p. 523-531Article in journal (Refereed)
    Abstract [en]

    In the present study, in-situ ATR-FTIR spectroscopy was used for the first time to study the competitive adsorption of phosphate and arsenate on ferrihydrite. Deuterium oxide was used as solvent to facilitate the interpretations of recorded infrared spectra.It was found that arsenate and phosphate adsorbed more strongly at lower pD values, showing similarities in the adsorption behavior as a function of pD. However, arsenate complexes were found to be more strongly adsorbed than phosphate complexes in the pD range studied. About five times higher concentration of phosphate in solution was needed to reduce the absorbance due to pre-adsorbed arsenate to the same relative level as for pre-adsorbed phosphate, which was desorbed using a solution containing equal (molar) concentrations in arsenate and phosphate. At pD 4, two phosphate complexes were adsorbed on the iron oxide, one deuterated and one de-deuterated. When phosphate was pre-adsorbed and arsenate subsequently added to the system, the deuterated phosphate complex desorbed rapidly while the de-deuterated phosphate complex was quite stable. At pD 8.5, only the de-deuterated phosphate complex was adsorbed on the iron oxide. Moreover, the arsenate adsorbed was also predominantly de-deuterated as opposite to the arsenate adsorbed at pD 4. During the substitution experiments the configuration of these complexes on the iron oxide surface did not change. To the best of our knowledge, this is the first time this difference in stability of the different phosphate complexes is reported and shows the power of employing in-situ spectroscopy for this kind of studies.

  • 37. Carabante, Ivan
    et al.
    Grahn, Mattias
    Holmgren, Allan
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    The influence of Zn2+ ions on the adsorption of arsenate onto ferrihydrite studied by in situ ATR-FTIR spectroscopy2010Conference paper (Other academic)
  • 38.
    Carabante, Ivan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kumpiene, Jurate
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Adsorption of As (V) on iron oxide nanoparticle films studied by in situ ATR-FTIR spectroscopy2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 346, no 1-3, p. 106-113Article in journal (Refereed)
    Abstract [en]

    Stabilization of arsenic contaminated soils by iron oxides has been proposed as a remediation technique to prevent leaching of arsenate into the environment. Fundamental studies are needed to establish under which conditions the complexes formed are stable. In the present work, a powerful technique, viz. ATR-FTIR spectroscopy, is adapted to studies of adsorption of arsenate species on iron oxides. This technique facilitates acquisition of both quantitative and qualitative in situ adsorption data.In the present work, about 800 nm thick films of 6-lineferrihydrite were deposited on ZnSe ATR crystals. Arsenate adsorption on the ferrihydrite film was studied at pD values ranging from 4 to 12 and at an arsenate concentration of 0.03 mM in D2O solution. The amount of adsorbed arsenate decreased with increasing pD as a result of the more negatively charged iron oxide surface at higher pD values. The adsorption and desorption kinetics were also studied. Arsenate showed a higher adsorption rate within the first 70 minutes and a much lower adsorption rate from 70 up to 300 minutes. The low adsorption rate at longer reaction times was partly due to a low desorption rate of already adsorbed carbonate species adsorbed at the surface. The desorption of carbonate species was evidenced by the appearance of negative absorption bands. The desorption of adsorbed arsenate complexes was examined by flushing with D2O at pD 4 and 8.5 and it was found that the complexes were very stable at pD 4 suggesting formation of mostly inner-sphere complexes whereas a fraction of the complexes at pD 8.5 were less stable than at pD 4, possibly due to the formation of outer-sphere complexes.In summary, the ATR technique was shown to provide in situ information about the adsorption rate, desorption rate and the speciation of the complexes formed within a single experiment, which is very difficult to obtain using other techniques.

  • 39.
    Carabante, Ivan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kumpiene, Jurate
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Influence of Zn(II) on the adsorption of arsenate onto ferrihydrite2012In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 46, no 24, p. 13152-13159Article in journal (Refereed)
    Abstract [en]

    Addition of iron oxide to arsenic-contaminated soil has been proposed as a means of reducing the mobility of arsenic in the soil. Arsenic and zinc are common coexisting contaminants in soils. The presence of zinc therefore may affect the adsorption properties of arsenic on iron oxide, and may thus affect its mobility in the soil. The influence of Zn(II) on the adsorption of arsenate ions on iron oxide was studied. Batch adsorption experiments indicated that Zn(II) increased the arsenate removal from a solution by ferrihydrite at pH 8. However, ATR-FTIR spectroscopy showed that no adsorption of arsenate on a ferrihydrite film occurred at pD 8 in the presence of Zn(II). Precipitation of zinc hydroxide carbonate followed by arsenate adorption onto the precipitate was found to be a plausible mechanism explaining the arsenate removal from a solution in the presence of Zn(II) at pH/pD 8. The previously suggested mechanisms attributing the enhanced removal of arsenate from solution in the presence of Zn(II) to additional adsorption on iron oxides could not be verified under the experimental conditions studied. It was also shown that at pH/pD 4, the presence of Zn(II) in the system did not significantly affect the adsorption of arsenate on ferrihydrite.

  • 40.
    Carabante, Ivan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Kumpiene, Jurate
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A powerful method for studying the adsorption of As(V) on iron oxides in situ2008In: Arsenic in the environment - Arsenic from nature to humans: Book of Abstracts, 2008Conference paper (Other academic)
  • 41.
    Carabante, Ivan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Kumpiene, Jurate
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Fredriksson, Andreas
    Mining Technology R and D, LKAB Kiruna Mine.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Reutilization of porous sintered hematite bodies as effective adsorbents for arsenic(V) removal from water2014In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, no 32, p. 12689-12696Article in journal (Refereed)
    Abstract [en]

    A method was developed to enhance the arsenic adsorption capacity of porous bodies of sintered hematite. The method comprised the formation of a coating of 1 wt % iron oxide nanoparticles on the raw material. The nanoparticles showed two distinct habits: spherical habit, likely ferrihydrite, and acicular habit, likely goethite and/or akaganéite. The specific surface area of the hematite raw material increased from 0.5 to 3.75 m2/g, and the adsorption capacity increased from negligible to 0.65 mg of [As]/g as calculated from equilibrium and breakthrough adsorption data. Equilibrium adsorption data of arsenate on the adsorbent from a solution at pH 5 followed the Langmuir model, while breakthrough adsorption data for a 500 μg/L arsenate solution at pH 5 followed the Thomas model. The adsorbed arsenic could be desorbed using distilled water at pH 12. These results show the potential for the reutilization of waste products comprising coarse hematite bodies as adsorbents.

  • 42.
    Carvalho, Lara
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Furusjö, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. IVL – Swedish Environmental Institute, Stockholm, Sweden.
    Ma, Chunyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lundgren, Joakim
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Öhrman, Olov G. W.
    IVL – Swedish Environmental Institute, Stockholm, Sweden;RISE Energy Technology Center AB, Piteå, Sweden.
    Wetterlund, Elisabeth
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria.
    Alkali enhanced biomass gasification with in situ S capture and a novel syngas cleaning: Part 2: Techno-economic analysis2018In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 165, no Part B, p. 471-482Article in journal (Refereed)
    Abstract [en]

    Previous research has shown that alkali addition has operational advantages in entrained flow biomass gasification and allows for capture of up to 90% of the biomass sulfur in the slag phase. The resultant low-sulfur content syngas can create new possibilities for syngas cleaning processes. The aim was to assess the techno-economic performance of biofuel production via gasification of alkali impregnated biomass using a novel gas cleaning systemcomprised of (i) entrained flow catalytic gasification with in situ sulfur removal, (ii) further sulfur removal using a zinc bed, (iii) tar removal using a carbon filter, and (iv) CO2 reductionwith zeolite membranes, in comparison to the expensive acid gas removal system (Rectisol technology). The results show that alkali impregnation increases methanol productionallowing for selling prices similar to biofuel production from non-impregnated biomass. It was concluded that the methanol production using the novel cleaning system is comparable to the Rectisol technology in terms of energy efficiency, while showing an economic advantagederived from a methanol selling price reduction of 2–6 €/MWh. The results showed a high level of robustness to changes related to prices and operation. Methanol selling prices could be further reduced by choosing low sulfur content feedstocks.

  • 43.
    Creaser, D.
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    Chalmers University of Technology.
    Hudgins, R.R.
    University of Waterloo.
    Silveston, P.L.
    University of Waterloo.
    Oxygen partial pressure effects on the oxidative dehydrogenation of propane1999In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 54, no 20, p. 4365-4370Article in journal (Refereed)
    Abstract [en]

    The effect of the gas-phase oxygen partial pressure for the oxidative dehydrogenation of propane over a V-Mg-O catalyst was investigated to explore reasons for improved propene yields when dehydrogenation was carried out under periodic operation. Steady-state experiments were performed in which the oxygen partial pressure was varied over a large range at constant propane partial pressures. In addition, the catalyst mass was varied to control the propane conversion so that selectivity and yield could be compared at a constant propane conversion. At the same propane conversion, propene selectivity increased as the partial pressure of oxygen decreased. Thus, propene yields can be improved at steady state by employing low oxygen partial pressures. It is likely that this is the reason for the higher propene yields observed under unsteady-state or periodic operation. It appears that the reaction mechanism must consist of more than one pathway for production of carbon oxides

  • 44.
    Creaser, Derek
    Luleå tekniska universitet.
    Crystal population balance model for nucleation and growth of colloidal TPA-silicalite-11999In: Porous materials in environmentally friendly processes: Proceedings of the 1st International FEZA Conference, Eger, Hungary, 1-4 September, 1999, Amsterdam: Elsevier, 1999, p. 117-124Conference paper (Refereed)
    Abstract [en]

    A model describing the crystallization of colloidal TPA-silicalite-1 is developed and tested. The nucleation rate is approximated from experimental data. Crystal growth is surface-reaction limited and the Gibbs-Thomson effect suppresses growth of small crystals, resulting in an induction period. Slow crystal growth during the nucleation period results in the narrow crystal size distribution typically observed for colloidal TPA-silicalite-1 syntheses.

  • 45.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    University of Waterloo.
    Hudgins, R.R.
    Chalmers University of Technology.
    Silveston, P.L.
    Chalmers University of Technology.
    Cyclic operation of the oxidative dehydrogenation of propane1999In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 54, no 20, p. 4437-4448Article in journal (Refereed)
    Abstract [en]

    The cyclic operation of the oxidative dehydrogenation of propane over a V-Mg-O catalyst by the alternate feeding of propane and oxygen gas mixtures was investigated. Generally, the response of the reaction products following a step-change in composition determined the cyclic conditions that resulted in an improved yield of propene. By alternating propane and oxygen with a 1 : 1 cycle split, time-average propene yields higher than steady state could be obtained. The optimal cycle period was about 60 s. This same period provided high propane conversion, as well as high propene selectivity. The cycle split could be varied by shortening the oxygen-feed half of the cycle with little effect on the time-average results. The oxygen half-cycle needed only to be long enough to reoxidize the catalyst. The propane feed scheme was varied by feeding increasing amounts of propane in the oxygen half-cycle. The change in feed scheme caused an increase in the time-average propane conversion that resulted in some further improvement in the propene yield despite some loss in propene selectivity.

  • 46.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Hudgins, R.R.
    Department of Chemical Engineering, University of Waterloo.
    Silveston, P.L.
    Department of Chemical Engineering, University of Waterloo.
    Transient kinetic analysis of the oxidative dehydrogenation of propane1999In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 182, no 1, p. 264-269Article in journal (Refereed)
    Abstract [en]

    Oxidative dehydrogenation of propane was studied using various transient techniques. Results support a redox mechanism in which propane reduces the catalyst, which is reoxidized by gas-phase oxygen. Only lattice oxygen participates in propene formation. Desorbable oxygen is a major source of poor selectivity, although lattice oxygen also causes total oxidation. Consequently, propene selectivity in the absence of gas-phase O2is superior to co-feed, steady-state selectivity at the same propane conversion. Propene selectivity is further improved by increasing the degree of catalyst reduction.

  • 47.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Hudgins, R.R.
    Department of Chemical Engineering, University of Waterloo.
    Silveston, P.L.
    Department of Chemical Engineering, University of Waterloo.
    Transient study of oxidative dehydrogenation of propane1999In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 187, no 1, p. 147-160Article in journal (Refereed)
    Abstract [en]

    Kinetics and the mechanism of the oxidative dehydrogenation of propane were investigated using various transient techniques. Results support a redox reaction mechanism in which propane and intermediate products react with lattice oxygen, reducing the catalyst surface, which is reoxidized by gas-phase O2. Partial reduction of the catalyst occurs during the start-up to a steady state. Successive pulsing with C3H8 reduced V5+ in the magnesium ortho-vanadate phase to V2+. Carbon-containing species were observed upon interruption of the reaction, although only minute amounts were formed. Cycling increases the amount of the carbon deposited, but this carbon is reactive and most of it is oxidized in the succeeding O2 pulse. Temperature-programmed oxidation (TPO) experiments on the catalyst used in steady-state operation revealed mainly strongly bound carbonaceous matter on the catalyst, but this carbon deposition did not affect catalyst activity. Thus, adsorbed oxygen is an important source of total combustion. Our experiments show, however, that lattice oxygen also produces total oxidation. Propene selectivity of the reaction in the absence of gas-phase O2 was superior to steady-state selectivity, at the same propane conversion. Propene selectivity could be further improved by increasing the degree of reduction of the catalyst

  • 48.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, Bengt
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Hudgins, Robert
    Department of Chemical Engineering, University of Waterloo.
    Silveston, Peter
    Department of Chemical Engineering, University of Waterloo.
    Kinetic modelling of oxygen dependence in oxidative dehydrogenation of propane2000In: Canadian Journal of Chemical Engineering, ISSN 0008-4034, E-ISSN 1939-019X, Vol. 78, no 1, p. 182-193Article in journal (Refereed)
    Abstract [en]

    Several Mars-Van Krevelen-type redox kinetic models were developed for the catalytic oxidative dehydrogenation of propane and examined for their ability to predict high propene yields at low oxygen/propane feed ratios. The intent in this study was to use modelling as a means of extracting further mechanistic insight from experimental data rather than to identify the best model. Thus, a conventional redox model with a consecutive reaction mechanism and a single pathway for the production of carbon oxides predicts higher propene selectivity but only at the expense of low propane conversion. Experimental data indicated, however, that even at the same propane conversion, propene selectivity increased as the oxygen partial pressure was lowered. Models that successfully describe the data had an additional carbon oxide production path involving the reaction of propane with deeply oxidizing surface oxygen species. Kinetic models and experimental data examined do not fully resolve how these deeply oxidizing surface oxygen species are formed. However, they do reflect the accepted view that lattice oxygen selectively produces propene whereas more weakly bound surface adsorbed oxygen reacts to completely oxidize propane.

  • 49.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Potapova, Elisaveta
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Application of AFM to probe micro- and nano-sized magnetite particle interaction in Ca2+ solution2014In: Proceedings of the International Summer School on Application of Scanning Probe Microscopy in Life Sciences, Soft Matter and Nanofabrication", Aalborg: River Publishers, 2014Conference paper (Other academic)
    Abstract [en]

    Natural magnetite is used for producing iron ore pellets, one of the raw materials in steel production. The quality of produced pellets depends on many factors, including the properties of the magnetite concentrate fed to pelletization. To be able to minimize the effect of the variations in feed properties on pellets quality, investigation of magnetite particle interaction with a focus on the surface properties is required. Atomic force microscopy (AFM), using the colloidal probe technique, is a suitable tool for measuring such particle-particle interaction in-situ. Natural particles are usually of micro-sizes (m-s) and have different sizes and shapes, which complicates an accurate investigation of particle interaction with AFM. To overcome such difficulties, synthetic nanoparticles are used instead. Process water chemistry is one of the factors affecting magnetite surface properties. Partial dissolution of calcite and apatite minerals, present in iron ore, results in high Ca2+ concentrations in the process water, which has been shown to have a major effect on the charge of the magnetite particles [1, 2]. The aim of this study was therefore to investigate forces and aggregation between magnetite particles, of micro- and nano-size (n-s), in Ca2+ solutions at various pH values. The spherical monodispersed magnetite nano-sized particles, with a diameter of approx. 10 nm, were synthesized by the precipitation technique [3]. Measurements were performed for m-s probe/m-s layer and m-s probe/n-s layer systems. Natural magnetite particles of 10-30 µm size were glued to NP-S cantilevers (Digital Instruments/Bruker, Santa Barbara, CA) with a measured spring constant of 0.12 N/m. Nano-sized particles were deposited on the glass slides by dip-coating. Roughness (Ra) of the n-s layers was measured with AFM and was about 10 nm for areas 1×1µm2, a representative high-resolution image is shown in Figure 1. Particle interaction was similar for m-s and n-s magnetite particles at pH 4 and 6. At pH 10, the interaction behavior was different due to probable surface modification of natural magnetite particles by ions from process water. The adhesion force for both interacting systems was measured, see ref. [4] for a detailed description of the results. To verify that ϛ-potential measurements could be used to predict the interaction between charged particles (in this case silica and magnetite) in solutions containing inorganic ions, force measurements between n-s magnetite layer and a SiO2 spherical probe (3.5 µm in diameter) were performed and correlated with the ϛ-potential results for these particles in the same solutions. Also, a DLVO simulation was performed to theoretically confirm the experimental interaction based on surface charge trends. An example of the simulated force curves is shown in Figure 2. The interaction between the probe and the magnetite surface was attractive at pH 4 and 6 but became repulsive at pH 8 and 10, which is in agreement with what could be expected from the ϛ-potential results for these particles.

  • 50.
    Dobryden, Illia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Potapova, Elisaveta
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy2015In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 42, no 4, p. 319-326Article in journal (Refereed)
    Abstract [en]

    Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle–particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite–magnetite, bentonite–magnetite, silica–bentonite, and silica–magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite–magnetite and bentonite–silica systems and slightly increased for the magnetite–bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite–silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

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