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  • 151. Saeid, Soudabeh
    et al.
    Kråkström, Matilda
    Tolvanen, Pasi
    Kumar, Narendra
    Eränen, Kari
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Kronberg, Leif
    Eklund, Patrik
    Peurla, Markus
    Aho, Atte
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Salmi, Tapio
    Advanced Oxidation Process for Degradation of Carbamazepine from Aqueous Solution: Influence of Metal Modified Microporous, Mesoporous Catalysts on the Ozonation Process2020Annet (Annet vitenskapelig)
    Abstract [en]

    Carbamazepine (CBZ), a widely used pharmaceutical compound, is one of the most detected drugs in surface waters. The purpose of this work was to identify an active and durable catalyst, which, in combination with an ozonation process, could be used to remove CBZ and its degradation products. It was found that the CBZ was completely transformed after ozonation within the first minutes of the treatment. However, the resulting degradation products, 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM) and 1-(2-benzaldehyde)-(1H,3H)-quinazoline-2,4-dione (BQD), were more resistant during the ozonation process. The formation and degradation of these products were studied in more detail and a thorough catalytic screening was conducted to reveal the reaction kinetics of both the CBZ and its degradation products. The work was performed by non-catalytic ozonation and with six different heterogeneous catalysts (Pt-MCM-41-IS, Ru-MCM-41-IS, Pd-H-Y-12-EIM, Pt-H-Y-12-EIM, Pd-H-Beta-300-EIM and Cu-MCM-41-A-EIM) operating at two temperatures 20 °C and 50 °C. The influence of temperature on degradation kinetics of CBZ, BQM and BQD was studied. The results exhibited a notable difference in the catalytic behavior by varying temperature. The higher reactor temperature (50 °C) showed a higher activity of the catalysts but a lower concentration of dissolved ozone. Most of the catalysts exhibited higher removal rate for BQM and BQD compared to non-catalytic experiments in both temperatures. The Pd-H-Y-12-EIM catalyst illustrated a higher degradation rate of by-products at 50 °C compared to other catalysts.

  • 152. Salmi, Tapio
    et al.
    Eränen, Kari
    Tolvanen, Pasi
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Åbo Akademi University, Johan Gadolin Process Chemistry Centre (PCC), Laboratory of Industrial Chemistry and Reaction Engineering, Turku/Åbo, Finland.
    Russo, Vincenzo
    Determination of kinetics and equilibria of heterogeneously catalyzed gas-phase reactions in gradientless autoclave reactors by using the total pressure method: Methanol synthesis2019Inngår i: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Rapid methods are very valuable in the determination of the kinetic and mass transfer effects for heterogeneously catalyzed reactions. The total pressure method is a classical tool in the measurement of the kinetics of gas-phase reactions, but it can be successfully applied to the kinetic measurements of gas-phase processes enhanced by solid catalysts. A general theory for the analysis of heterogeneously catalyzed gas-phase kinetics in gradientless batch reactors was presented for the case of intrinsic kinetic control and combined kinetic-diffusion control in porous catalysts. The concept was applied to gas-phase synthesis of methanol from carbon monoxide and hydrogen on a commercial copper-based catalyst (CuO/ZnO/Al2O3 R3-12 BASF). The reaction temperature was 180–210 °C and the initial total pressure was varied between 11 and 21 bar in a laboratory-scale autoclave reactor equipped with a rotating basket for the catalyst particles. The initial molar ratios CO-to-H2 were approximately 1:2, 1:3 and 1:4. The experimental data from methanol synthesis were compared with numerical simulations and a good agreement between the experiments and model simulations was achieved. The predicted equilibrium agrees with previously reported values.

  • 153. Salmi, Tapio O
    et al.
    Wärnå, Johan P
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Chemical reaction engineering and reactor technology2010Bok (Annet vitenskapelig)
    Abstract [en]

    A Systematic Development of the Chemical Reaction Engineering Concept. The role of the chemical reactor is crucial for the industrial conversion of raw materials into products and numerous factors must be considered when selecting an appropriate and efficientchemical reactor. Chemical Reaction Engineering and Reactor Technology defines the qualitative aspects that affect the selection of an industrial chemical reactor and couples various reactor models to case-specific kinetic expressions for chemical processes. Offering a systematic development of the chemical reaction engineering concept, this volume explores:• essential stoichiometric, kinetic, and thermodynamic terms needed in the analysis of chemical reactors• homogeneous and heterogeneous reactors• residence time distributions and non-ideal flow conditions in industrial reactors• solutions of algebraic and ordinary differential equation systems• gas- and liquid-phase diffusion coefficients and gas-filmcoefficients• correlations for gas-liquid systems• solubilities of gases in liquids• guidelines for laboratory reactors and the estimation of kinetic parameters. The authors pay special attention to the exact formulations and derivations of mass energy balances and their numerical solutions. Richly illustrated and containing exercises and solutions covering a number of processes, from oil refining to the development of specialty and fine chemicals, the text provides a clear understanding of chemical reactor analysis and design.

  • 154. Salminen, Eero
    et al.
    Rujana, Luis
    Mäki-Arvela, Päivi
    Virtanen, Pasi
    Salmi, Tapio
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Åbo Akademi University, Department of Chemical Engineering, Process Chemistry Centre, Industrial Chemistry & Reaction Engineering, Åbo, Finland.
    Biomass to value added chemicals: Isomerisation of β-pinene oxide over supported ionic liquid catalysts (SILCAs) containing Lewis acids2015Inngår i: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 257, s. 318-321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The isomerisation of β-pinene oxide was studied over supported ionic liquid catalysts (SILCAs) consisting of Lewis acids in immobilized ionic liquid. SILCAs were demonstrated as efficient catalysts for the transformation of β-pinene oxide to myrtanal with the product distribution and activity being depend-ent on the nature of the ionic liquid and Lewis acid strength of catalytic species. With the catalystZnCl2/[N(3-OH-Pr)Py][NTf2]/ACC, the highest myrtanal molar yield obtained was 68%.

  • 155. Salminen, Eero
    et al.
    Virtanen, Pasi
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Åbo-Turku, Finland.
    Alkaline ionic liquids applied in supported ionic liquid catalyst for selective hydrogenation of citral to citronellal2014Inngår i: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 2, artikkel-id 3Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The challenge in preparation of ionic liquids containing a strong alkaline anion is to identify a suitable cation which can tolerate the harsh conditions induced by the anion. In this study, a commercial quaternary ammonium compound (quat) benzalkonium [ADBA] (alkyldimethylbenzylammonium) was used as a cation in the synthesis of different alkaline ionic liquids. In fact, the precursor, benzalkonium chloride, is a mixture of alkyldimethylbenzylammonium chlorides of various alkyl chain lengths and is commonly used in the formulation of various antiseptic products. The prepared ionic liquids were utilized as Supported Ionic Liquid Catalysts (SILCAs). Typically, a SILCA contains metal nanoparticles, enzymes, or metal complexes in an ionic liquid layer which is immobilized on a solid carrier material such as an active carbon cloth (ACC). The catalysts were applied in the selective hydrogenation of citral to citronellal which is an important perfumery chemical. Interestingly, 70% molar yield toward citronellal was achieved over a catalyst containing the alkaline ionic liquid benzalkonium methoxide.

  • 156.
    Sandström, Karin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Eriksson, Matias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Nordkalk AB.
    Estimating ash properties for new fuels in calcination kilns2019Konferansepaper (Annet vitenskapelig)
  • 157.
    Sandström, Robin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Innovations in nanomaterials for proton exchange membrane fuel cells2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Hydrogen technologies are rapidly receiving increased attention as it offers a renewable energy alternative to the current petroleum-based fuel infrastructure, considering that continued large-scale use of such fossil fuels will lead to disastrous impacts on our environment. The proton exchange membrane fuel cell should play a significant role in a hydrogen economy since it enables convenient and direct conversion of hydrogen into electricity, thus allowing the use of hydrogen in applications particularly suited for the transportation industry. To fully realize this, multiple engineering challenges as well as development of advanced nanomaterials must however be addressed.

    In this thesis, we present discoveries of new innovative nanomaterials for proton exchange membrane fuel cells by targeting the entire membrane electrode assembly. Conceptually, we first propose new fabrication techniques of gas diffusion electrodes based on helical carbon nanofibers, where an enhanced three-phase boundary was noted in particular for hierarchical structures. The cathode catalyst, responsible for facilitating the sluggish oxygen reduction reaction, was further improved by the synthesis of platinum-based nanoparticles with an incorporated secondary metal (iron, yttrium and cobalt). Here, both solvothermal and high-temperature microwave syntheses were employed. Catalytic activities were improved compared to pure platinum and could be attributed to favorably shifted oxygen adsorption energies as a result of successful incorporation of the non-precious metal. As best exemplified by platinum-iron nanoparticles, the oxygen reduction reaction was highly sensitive to both metal composition and the type of crystal structure. Finally, a proton exchange membrane based on fluorine and sulfonic acid functionalized graphene oxide was prepared and tested in hydrogen fuel cell conditions, showing improvements such as lowered hydrogen permeation and better structural stability. Consequently, we have demonstrated that there is room for improvement of multiple components, suggesting that more powerful fuel cells can likely be anticipated in the future.

  • 158.
    Sandström, Robin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Annamalai, Alagappan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Boulanger, Nicolas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ekspong, Joakim
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Mühlbacher, Inge
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Evaluation of Fluorine and Sulfonic Acid Co-functionalized Graphene Oxide Membranes in Hydrogen Proton Exchange Membrane Fuel Cell Conditions2019Inngår i: Sustainable Energy & Fuels, ISSN 2398-4902, Vol. 3, nr 7, s. 1790-1798Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of graphene oxide (GO) based membranes consisting of self-assembled flakes with a lamellar structure represents an intriguing strategy to spatially separate reactants while facilitating proton transport in proton exchange membranes (PEM). Here we chemically modify GO to evaluate the role of fluorine and sulfonic acid groups on the performance of H2/O2 based PEM fuel cells. Mild fluorination is achieved by the presence of hydrogen fluoride during oxidation and subsequent sulfonation resulted in fluorine and SO3- co-functionalized GO. Membrane electrode assembly performance in low temperature and moderate humidity conditions suggested that both functional groups contribute to reduced H2 crossover compared to appropriate reference membranes. Moreover, fluorine groups promoted an enhanced hydrolytic stability while contributing to prevent structural degradation after constant potential experiments whereas sulfonic acid demonstrated a stabilizing effect by preserving proton conductivity.

  • 159. Schoen, Claudia
    et al.
    Hartmann, Hans
    Schwabl, Manuel
    Feldmeier, Sabine
    Dahl, Jonas
    Rathbauer, Josef
    Vega, Daniel
    Boman, Christoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Oehman, Marcus
    New evaluation strategies regarding slag prediction in pellet boilers2014Inngår i: Papers of the 22nd european biomass conference: setting the course for a biobased economy, 2014, s. 368-372Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Pellet boilers are widely used for heat production. In most cases only wood pellets with low ash content are suitable for these appliances due to the increased risk of slagging. The ash fusion test (AFT) is the only standardized method currently available for the prediction of slagging but it frequently failed when solid biofuels were investigated. Therefore different laboratory methods for the prediction of slagging were applied in order to identify the most suitable method for reliable prediction of slagging tendencies. Three laboratory test methods were considered in this investigation: a rapid slag test (1), the so-called "CIEMAT method" (2) and the "slag analyser" (3). The suitability of the obtained results was validated by practical combustion tests in up to nine different pellet boilers. As the most promising method the slag analyser was identified. It will be further developed with the aim to be proposing as an additional standard method for determination of slag related problems in fixed bed combustion systems.

  • 160. Sefidari, H.
    et al.
    Ma, C.
    Fredriksson, C.
    Lindblom, B.
    Wiinikka, H.
    Nordin, L. O.
    Wu, G.
    Yazhenskikh, E.
    Müller, M.
    Öhman, M.
    The effect of co-firing coal and woody biomass upon the slagging/deposition tendency in iron-ore pelletizing grate-kiln plants2020Inngår i: Fuel Processing Technology, Vol. 199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Woody biomass is being considered a potential co-firing fuel to reduce coal consumption in iron-ore pelletizing rotary kilns. An important consideration is the slagging inside the kiln caused by ash deposition that can lead to process disturbances or shutdowns. In terms of ash chemistry, co-firing woody biomass implies the addition of mainly Ca and K to the Si- and Al-dominated coal-ash (characteristic of high-rank coals) and Fe from the iron-ore that are both inherent to the process. An alkali-laden gaseous atmosphere is also present due to the accumulation of alkali via the recirculation of flue gas in the system. The slagging propensity of blending woody biomass with coal in the grate-kiln process was studied based on the viscosity of the molten phases predicted by global thermochemical equilibrium modeling. This was carried out for variations in temperature, gaseous KOH atmosphere, and fuel blending levels. Results were evaluated and compared using a qualitative slagging indicator previously proposed by the authors where an inverse relationship between deposition tendency and the viscosity of the molten fraction of the ash was established. The results were also compared with a set of co-firing experiments performed in a pilot-scale (0.4 MW) experimental combustion furnace. In general, the co-firing of woody biomass would likely increase the slagging tendency via the increased formation of low-viscosity melts. The fluxing behavior of biomass-ash potentially reduces the viscosity of the Fe-rich aluminosilicate melt and intensifies deposition. However, the results also revealed that there are certain conditions where deposition tendency may decrease via the formation of high-melting-point alkali-containing solid phases (e.g., leucite).

  • 161. Sepman, Alexey
    et al.
    Ögren, Yngve
    Qu, Zhechao
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wiinikka, Henrik
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå University.
    Real-time in situ multi-parameter TDLAS sensing in the reactor core of an entrained-flow biomass gasifier2017Inngår i: Proceedings of the Combustion Institute, ISSN 1540-7489, E-ISSN 1873-2704, Vol. 36, nr 3, s. 4541-4548Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tunable diode laser absorption spectroscopy (TDLAS) was used to measure several important process parameters at two different locations inside the reactor of an atmospheric, air-blown 0.1 MWth biomass gasifier. Direct TDLAS at 2298 nm was employed for carbon monoxide (CO) and water vapor (H2O), calibration-free scanned wavelength modulation spectroscopy at 1398 nm for H2O and gas temperature, and direct TDLAS at 770 nm for gaseous elemental potassium, K(g), under optically thick conditions. These constitute the first in situ measurements of K(g) and temperature in a reactor core and in biomass gasification, respectively. In addition, soot volume fractions were determined at all TDLAS wavelengths, and employing fixed-wavelength laser extinction at 639 nm. Issues concerning the determination of the actual optical path length, as well as temperature and species non-uniformities along the line-of-sight are addressed. During a 2-day measurement campaign, peat and stem wood powder were first combusted at an air equivalence ratio (lambda) of 1.2 and then gasified at lambdas of 0.7, 0.6, 0.5, 0.4 and 0.35. Compared to uncorrected thermocouple measurements in the gas stream, actual average temperatures in the reactor core were significantly higher. The CO concentrations at the lower optical access port were comparable to those obtained by gas chromatography at the exhaust. In gasification mode, similar H2O values were obtained by the two different TDLAS instruments. The measured K(g) concentrations were compared to equilibrium calculations. Overall, the reaction time was found to be faster for peat than for stem wood. All sensors showed good performance even in the presence of high soot concentrations, and real-time detection was useful in resolving fast, transient behaviors, such as changes in stoichiometry. Practical implications of in-situ TDLAS monitoring on the understanding and control of gasification processes are discussed.

  • 162. Sepman, Alexey
    et al.
    Ögren, Yngve
    Qu, Zhechao
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wiinikka, Henrik
    Schmidt, Florian M.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Tunable Diode Laser Absorption Spectroscopy Diagnostics of Potassium, Carbon Monoxide, and Soot in Oxygen-Enriched Biomass Combustion Close to Stoichiometry2019Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, nr 11, s. 11795-11803Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combustion facilities run on pulverized biomass often exhibit fluctuations in fuel feeding and, thus, equivalence ratio and would benefit from fast process control based on optical λ sensors installed in the reactor core. The conversion of softwood powder is investigated in an atmospheric entrained-flow reactor (EFR) operated close to stoichiometry using two different burners (swirl and jet) and three oxygen concentrations (21, 30, and 40%). Tunable diode laser absorption spectroscopy (TDLAS) is used to conduct time-resolved (0.1–1 s) in situ measurements of the gas temperature, carbon monoxide (CO), water vapor (H2O), gaseous atomic potassium [K(g)], and soot volume fraction in the lower part of the reactor core and in the exhaust of the EFR. At both locations, the measurement parameters show significant, correlating fluctuations. The local equivalence ratio is derived from a comparison of measured CO and H2O concentrations (for fuel-rich and fuel-lean conditions, respectively) to thermodynamic equilibrium calculations (TEC) and found to vary in a wide range (0.8–1.3). Soot production decreases with an increasing local equivalence ratio and oxygen enrichment and is lower for the swirl compared to the jet burner. The measured K(g) concentrations follow the general behavior predicted by TEC around stoichiometry. In the relevant temperature range (1100–1700 K), K(g) is 2–4 orders of magnitude higher under fuel-rich than fuel-lean conditions, with a sharp transition at stoichiometry. While K(g) concentrations are lower than TEC in the reactor core and under fuel-rich conditions, excellent agreement is found at the exhaust after complete fuel conversion. Precise, wide dynamic range detection of K(g) using TDLAS enables discrimination between fuel-rich and fuel-lean conditions and has the potential for lambda sensing close to the hot reaction zone of combustion plants.

  • 163.
    Shanmugam, Kavitha
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Jansson, Stina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Gadhamshetty, Venkataramana
    Matsakas, Leonidas
    Rova, Ulrika
    Tysklind, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Christakopoulos, Paul
    Upadhyayula, Venkata K.K.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ecoefficiency of Thermal Insulation Sandwich Panels Based On Fly Ash Modified with Colloidal Mesoporous Silica2019Inngår i: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 7, nr 24, s. 20000-20012Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current practice of landfilling fly ash generated by waste incineration is nonsustainable, so alternative ways of using this material are needed. Silanization effectively immobilizes the heavy metal contaminants in the incineration fly ash and enables its circular utilization because silanized fly ash (SFA) has market value as a low-cost filler for polymer composites. This study examines the ecoefficiency of a thermal insulation panel that consists of a polyurethane (PU) foam core sandwiched between two epoxy composite skins prepared by reinforcing glass fibers (GF) and SFA in epoxy resin. The ecoefficiency of such panels was evaluated by comparing their life cycle environmental externality costs (LCEE) to their life cycle costs (LCC). The LCEE was calculated by monetizing the panels' environmental impacts, which were quantified by performing a life cycle assessment (LCA). The results revealed that the ecoefficiency of the composite panels is positive (47%) and superior to that of market incumbent alternatives with PU foam or rockwool cores and steel skins. The two market incumbents have negative ecoefficiencies, primarily due to their high LCEE. The environmental performance of the panel with SFA GF epoxy composite skins can be further improved by using lignin-based epoxy resin or thermoplastic polypropylene as the polymer matrix of composite skins. Overall, application as a filler in fabricating polymer composite skins of sandwich panels is an upcycling pathway of SFA that combines circular economy prospects with sustainability benefits.

  • 164.
    Sharifi, Tiva
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kwong, Wai Ling
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Berends, Hans-Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Larsen, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Messinger, Johannes
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Maghemite nanorods anchored on a 3D nitrogen-doped carbon nanotubes substrate as scalable direct electrode for water oxidation2016Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, nr 1, s. 69-78Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A hybrid catalyst 3D electrode for electrochemical water oxidation to molecular oxygen is presented. The electrode comprises needle shaped maghemite nanorods firmly anchored to nitrogen doped carbon nanotubes, which in turn are grown on a conducting carbon paper that acts as efficient current collector. In 0.1 M KOH this hybrid electrode reaches a current density of 1 mA/cm(2) (geometric surface) at an overpotential of 362 mV performing high chronoamperometric stability. The electrochemical attributes point toward efficient catalytic processes at the surface of the maghemite nanorods, and demonstrate a very high surface area of the 3D electrode, as well as a firm anchoring of each active component enabling an efficient charge transport from the surface of the maghemite rods to the carbon paper current collector. The latter property also explains the good stability of our hybrid electrode compared to transition metal oxides deposited on conducting support such as fluorine doped tin oxide. These results introduce maghemite as efficient, stable and earth abundant oxygen evolution reaction catalyst, and provide insight into key issues for obtaining practical electrodes for oxygen evolution reaction, which are compatible with large scale production processes. 

  • 165. Shen, Gulou
    et al.
    Held, Christoph
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Industrial Chemistry & Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Biskopsgatan 8, 20500 Åbo-Turku, Finland.
    Lu, Xiaohua
    Ji, Xiaoyan
    Modeling the Viscosity of Ionic Liquids with the Electrolyte Perturbed-Chain Statistical Association Fluid Theory2014Inngår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, nr 52, s. 20258-20268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, the friction theory (FT) and free volume theory (FVT) were combined with the electrolyte perturbed-chain statistical association fluid theory (ePC-SAFT) in order to model the viscosity of pure ionic liquids (ILs) and IL/CO2 mixtures in a wide temperature and pressure (up to 3000 bar) range and with viscosities up to 4000 mPa center dot s. The ePC-SAFT pure-component parameters for the considered imidazolium-based ILs were adopted from our previous work. These parameters were used to calculate the density and residual pressure of the pure ILs. The density and pressure were then used as inputs for pure-IL viscosity modeling using FVT or FT, respectively. The viscosity-model parameters of FT and FVT were obtained by fitting to experimental viscosity data of imidazolium-based ILs and linearized with the molecular weight of the IL-cation. As a result, the FT viscosity model can more accurately describe the experimental viscosity data of pure ILs than the FVT model, at the cost of an increased number of parameters used in the FT viscosity model. Finally, FT and FVT were applied to model the viscosities of IL/CO2 mixtures in good agreement to experimental data by adjusting one binary viscosity-model parameter between the IL-anion and CO2. The application of FT required fitting the viscosity model parameters of pure ILs to experimental viscosity data of pure ILs and of IL/CO2 mixtures. In contrast, the FVT viscosity model parameters were adjusted to the experimental viscosity data of pure ILs only.

  • 166. Shen, Hangjia
    et al.
    Gracia-Espino, Eduardo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wang, Le
    Qin, Danfeng
    Gao, Sanshuang
    Mamat, Xamxikamar
    Ren, Wei
    Wågberg, Thomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Hu, Guangzhi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Chinese Acad Sci, Xinjiang Tech Inst Phys & Chem, Urumqi 830011, Peoples R China.
    Microwave-assisted synthesis of multimetal oxygen-evolving catalysts2017Inngår i: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 81, s. 116-119Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Oxygen evolution reaction (OER) plays a pivotal role in water-splitting. Here, we report a facile method to synthesize multimetal supported on commercial carbon black via a time-saving microwave process. Crystalline FeNi3 nanoparticles homogeneously doped with Mo are formed via a microwave treatment and activated to metal oxyhydroxide in-situ during cyclic voltammetry test with overpotential of only 280 mV at 10 mA cm(-2) for OER in alkaline electrolyte, outperforming RuO2. Our synthesis methodology is a promising alternative for large-scale production, delivering a valuable contribution to catalyst preparation and electrocatalytic water oxidation research.

  • 167.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Structure analysis with relevance for complex materials – an outlook to X-ray absorption spectroscopy on phosphorus2019Konferansepaper (Annet vitenskapelig)
  • 168.
    Skoglund, Nils
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik, Energiteknik och termisk processkemi.
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik, Energiteknik och termisk processkemi.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Återvinning av fosfor och energi ur avloppsslam genom termiskbehandling i fluidiserad bädd: Utvärdering och optimering av prestandaför slutprodukten2012Rapport (Annet vitenskapelig)
    Abstract [sv]

    Förbränning av pelleterat rötslam i fluidbädd medger produktion av askpellets med högt innehåll av växttillgängligt fosfor. För att höja halten av K och Ca är sameldning med biobränsle lämpligt, exempelvis åkerbränslen. Bäddtemperaturen bör vara så hög som möjligt utan att påverka driftsäkerhet för att öka flyktigheten hos miljöpåverkande ämnen. Uppehållstiden för slampelletsen i bädden bör vara så låg som möjlig för att undvika att pelletsen nöts sönder.

  • 169.
    Skoglund, Nils
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Combustion of biosolids in a bubbling fluidized bed part 1: main ash forming elements and ash distribution with a focus on phosphorus2014Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, nr 2, s. 1183-1190Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This is the first in a series of three papers describing combustion of biosolids in a 5-kW bubbling fluidized bed, the ash chemistry, and possible application of the ash produced as a fertilizing agent. This part of the study aims to clarify whether the distribution of main ash forming elements from biosolids can be changed by modifying the fuel matrix, the crystalline compounds of which can be identified in the raw materials and what role the total composition may play for which compounds are formed during combustion. The biosolids were subjected to low-temperature ashing to investigate which crystalline compounds that were present in the raw materials. Combustion experiments of two different types of biosolids were conducted in a 5-kW benchscale bubbling fluidized bed at two different bed temperatures and with two different additives. The additives were chosen to investigate whether the addition of alkali (K2CO3) and alkaline-earth metal (CaCO3) would affect the speciation of phosphorus, so the molar ratios targeted in modified fuels were P:K = 1:1 and P:K:Ca = 1:1:1, respectively. After combustion the ash fractions were collected, the ash distribution was determined and the ash fractions were analyzed with regards to elemental composition (ICP-AES and SEM-EDS) and part of the bed ash was also analyzed qualitatively using XRD. There was no evidence of zeolites in the unmodified fuels, based on low-temperature ashing. During combustion, the biosolid pellets formed large bed ash particles, ash pellets, which contained most of the total ash content (54%–95% (w/w)). This ash fraction contained most of the phosphorus found in the ash and the only phosphate that was identified was a whitlockite, Ca9(K,Mg,Fe)(PO4)7, for all fuels and fuel mixtures. With the addition of potassium, cristobalite (SiO2) could no longer be identified via X-ray diffraction (XRD) in the bed ash particles and leucite (KAlSi2O6) was formed. Most of the alkaline-earth metals calcium and magnesium were also found in the bed ash. Both the formation of aluminum-containing alkali silicates and inclusion of calcium and magnesium in bed ash could assist in preventing bed agglomeration during co-combustion of biosolids with other renewable fuels in a full-scale bubbling fluidized bed.

  • 170.
    Skoglund, Nils
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik, Energiteknik och termisk processkemi.
    Grimm, Alejandro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhman, Marcus
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik, Energiteknik och termisk processkemi.
    Effects on ash chemistry when co-firing municipal sewage sludge and wheat straw in a fluidised bed: Influence on the ash chemistry by fuel mixing2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Municipal sewage sludge (MSS) is of interest for co-combustion with problematic fuels, such as agricultural residues, due to its high content of inorganic elements which may improve combustion properties of such problematic fuels. Ash transformation when co-combusting MSS with the agricultural residue wheat straw was examined using a bench-scale bubbling fluidised bed (5 kW). Wheat straw pellets were combusted with MSS both in a co-pelletized form and co-firing of separate fuel particles. This was done to examine whether there is any advantage to either approach of introducing MSS together with a problematic fuel.

    Co-combusting wheat straw with MSS changed the bed agglomeration characteristics from being caused by the formation of low-temperature melting potassium silicates in the fuel ash to being caused by a higher-temperature melting bed ash. This shift in ash chemistry had a significant positive effect on the initial defluidisation temperature. The cyclone ash and fine particulate matter changed from being dominated by alkali in general and alkali chlorides in specific to an increased phosphate and sulphate formation which reduces the risk of alkali-related fouling and corrosion. The influence of aluminosilicates may also play a role in the improvement of fuel ash behaviour.

  • 171.
    Song, Xiaowei
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Carbon dioxide binding at dry FeOOH mineral surfaces: evidence for structure-controlled speciation2013Inngår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 47, nr 16, s. 9241-9248Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Interactions between CO2(g) and mineral surfaces are important to atmospheric and terrestrial settings. This study provides detailed evidence on how differences in mineral surface structure impact carbonate speciation resulting from CO2(g) adsorption reactions. It was achieved by resolving the identity of adsorption sites and geometries of (bi)carbonate species at surfaces of nanosized goethite (alpha-FeOOH) and lepidocrocite (gamma-FeOOH) particles. Fourier transform infrared spectroscopy was used to obtain this information on particles contacted with atmospheres of CO2(g). Vibrational modes of surface hydroxo groups covering these particles were first monitored. These showed that only one type of the surface groups that are singly coordinated to Fe atoms (-OH) are involved in the formation of (bi)carbonate species. Those of higher coordination numbers (mu-OH, mu(3)-OH) do not participate. Adsorption geometries were then resolved by investigating the C-O stretching region, assisted by density functional theoretical calculations. These efforts provided indications leaning toward a predominance of mononuclear species, -O-CO2Hx=[0,1]. In contrast, monodentate binuclear species of (-O)(2)center dot COHx=[0,1], are expected to form at particle terminations and surface defects. Finally, calculations suggested that bicarbonate is the dominant species on goethite, while a mixture of bicarbonate and carbonate species is present on lepidocrocite, a result stemming from different hydrogen bonding patterns at these mineral surfaces.

  • 172.
    Sterchele, Stefano
    et al.
    Padova, Italy; Åbo-Turku, Finland.
    Biasi, Pierdomenico
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Åbo-Turku, Finland.
    Centomo, Paolo
    Padova, Italy.
    Campestrini, Sandro
    Padova, Italy.
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Rautio, Anne-Riikka
    Oulu, Finland.
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Åbo-Turku, Finland;.
    Salmi, Tapio
    Åbo-Turku, Finland.
    Zecca, Marco
    Padova, Italy.
    The effect of the metal precursor-reduction with hydrogen on a library of bimetallic Pd-Au and Pd-Pt catalysts for the direct synthesis of H2O22015Inngår i: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 248, s. 40-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two sets of bimetallic Pd-Pt (Pd: 1.0; Pt: 0.25-1.0%, w/w) and Pd-Au (Pd: 1.0; Au: 0.25-1.0%, w/w) catalysts have been used, with no added promoter, in the catalytic direct synthesis (CDS) of hydrogen peroxide from its elements at 2 °C with a CO2/O2/H2 mixture (72/25.5/2.5%, respectively). The catalysts were supported on the commercial macroreticular ion-exchange resin Lewatit K2621 and were obtained from the reduction with H2 of ion-exchanged cationic precursors at 5 bar and at 60 °C. The addition of Pt or Au to Pd produced an increase of the initial overall catalytic activity in comparison with monometallic Pd with both the second metals, but with Pt the increase was much higher than with Au. Moreover, the addition of 0.25% (w/w) Pt, or more, invariably made all the Pd-Pt catalysts less selective with respect to Pd alone. In the case of Au, by contrast, the addition of 0.25% w/w produced an increase, albeit small, of the selectivity. As the result, the most active and productive Pd-Pt catalyst was 1Pd025PtK2621 with 1891 mol(H2) mo l(Pd + Pt) - 1 h- 1 initially consumed, 1875 mol(H2 O2) mo l(Pd + Pt) - 1 h- 1 initially produced, a 45% selectivity towards H2O2 at 50% conversion of H2. In the case of the Pd-Au bimetallic catalysts, 1Pd025AuK2621 was the best one, with 1184 mol(H2) mo l(Pd + Pt) - 1 h- 1 initially consumed, 739 mol(H2 O2) mo l(Pd + Pt) - 1 h- 1 initially produced, a 55% selectivity towards H2O2 at 50% conversion of H2. Although the characterization of the Pd-Pt and Pd-Au catalysts with TEM showed that the morphology of the nanostructured metal phases in the Pd-Pt and Pd-Au catalysts was very different from each family to the other, no clear correlation between the size of the nanoparticles and their distribution and the catalytic performance was apparent. These catalysts were also generally different, especially the Pd-Au ones, from previously reported related materials obtained from the same support and the same precursor, but with a different reducing agent (formaldehyde). © 2014 Elsevier B.V. All rights reserved.

  • 173.
    Strandberg, Anna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Fuel conversion and ash formation interactions: a thermochemical study on lignocellulosic biomass2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Biomass is considered to be CO2 neutral, and to be able to reduce the dependency on fossil fuels the need for expanded and sustainable biomass feedstock is increasing. Ash-related problems are some of the most important aspects of this increasing use of new biomass assortments in thermal energy conversion systems. An improved basic understanding of fuel conversion, ash formation, ash transformation and ash interactions with the converting fuel is therefore important.

    In the present thesis, the main objective was to provide new knowledge on thermochemical fuel conversion, specifically on how ash formation interacts with fuel conversion for lignocellulosic biomasses. The main methods used were experimental characterization of decomposition behavior and analysis of morphology and elemental composition of samples, using different appliances, analytical methods and fuels. Multivariate data analysis was successfully used on thermogravimetric data for prediction of compositional data and fuel properties.

    New, detailed explanations of structural changes in char morphology and ash properties during conversion were provided including descriptions of the influences of ash formation on fuel conversion rates under different conditions. The influences were found different depending on both particle size and ash composition. One implication of these findings is that for fuels with low temperature melting ash, the diffusion barrier formed causes difficulties for typical thermogravimetric experiments aiming at determination of reactivity in the kinetically controlled regime. This is recommended to carefully consider for future studies. On a single pellet level, char encapsulation was not found to dominate and limit gas transport and conversion for any of the fuels tested. In practical applications, however, the situation may be different with thick ash layers accumulating on a fuel bed surface. Another important finding was the extensive formation of cracks and internal cavities during combustion of pellets, providing new insights in the fundamentals of fuel conversion.

    Clean woody fuels, rich in calcium, formed a porous ash layer with no sign of limiting char conversion rates. The phase chemical transformations involving carbonate and oxide formation from poplar pellets was studied in detail. For grassy fuels, on the other hand, low melting point silicates are expected to form. The physical properties of K-Ca-silicates from silicon rich straw fuels were also characterized, providing new insights on ash formation on micrometer scale resolution; at high temperature, the silicate melt formed bubbles on the surface that partially covered the char, while for lower temperature a more rigid net structure was formed.

  • 174.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Predicting fuel properties of biomass using thermogravimetry and multivariate data analysis2017Inngår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 156, s. 107-112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simple and reliable characterization methods for determining fuel properties of biomass are needed for several different applications. This paper describes and demonstrates such a method combining thermogravimetric analysis with multivariate data analysis, based on the thermal decomposition behavior of the fuel. Materials used for the tests were milled samples of wood chips thermally pretreated under different conditions in a torrefaction pilot plant. The predictions using the multivariate model were compared to those from a conventional curve deconvolution approach. The multivariate approach showed better and more flexible performance, with error of prediction of 2.7% for Mass Yield prediction, compared to the reference method that resulted in 29.4% error. This multivariate method could handle samples pretreated under more severe conditions compared to the curve deconvolution methods. Elemental composition, heating value and volatile content were also predicted with even higher accuracies. The results highlight the usefulness of the method and also the importance of using calibration data of good quality. (C) 2016 Elsevier B.V. All rights reserved.

  • 175.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wagner, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Molinder, Roger
    Wiinikka, Henrik
    Umeki, Kentaro
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Effects of pyrolysis conditions and ash formation on gasification rates of biomass char2017Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 31, nr 6, s. 6507-6514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pyrolysis conditions and the presence of ash-forming elements significantly influence char properties and its oxidation or gasification reactivity. In this study, intrinsic gasification rates of char from high heating rate pyrolysis were analyzed with isothermal thermogravimetry. The char particles were prepared from two biomasses at three size ranges and at two temperatures. Reactivity dependence on original particle size was found only for small wood particles that had higher intrinsic char gasification rates. Pyrolysis temperature had no significant effect on char reactivity within the range tested. Observations of ash formation highlighted that reactivity was influenced by the presence of ash-forming elements, not only at the active char sites but also through prohibition of contact between char and gasification agent by ash layer formation with properties highly depending on ash composition.

  • 176.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, SE 901 83, Sweden.
    Rudolfsson, M.
    Lestander, T. A.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Char conversion characterized by synchrotron based X-ray micro-tomography and SEM-EDS analysis2017Inngår i: European Biomass Conference and Exhibition Proceedings / [ed] Ek, L., Ehrnrooth, H., Scarlat, N., Grassi, A., Helm, P., ETA-Florence Renewable Energies , 2017, s. 485-491Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Fuel and ash properties were studied during fuel conversion by careful examination of char samples at different degrees of char oxidation. Two types of lignocellulosic pellets with different compositions of ash forming elements were used: poplar and straw from wheat. The charred pellets were investigated by synchrotron-based X-ray micro-tomography to create 3D images of the development of cracks, internal cavities, and ash layers during conversion. Furthermore, SEM-EDS was used to for detailed chemical and morphological information of the ash layers formed. The pore development during pellet conversion was found to deviate from what has previously been described for the structure of solid wood particles. Large cracks and internal cavities were formed extensively already during devolatilization. For poplar, no mobility of the ash forming elements were observed as the burnout proceeded. Ash layer properties varied between the two fuels: poplar formed a porous, permeable, low density and Ca rich ash, whereas wheat straw ash accumulated on the surface in the form of high density melt that develop into bubbles on the surface. As the conversion proceeded, the ash layer covered more of the active char surface area, but without totally blocking the gas transport.

  • 177.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Thyrel, Mikael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Skoglund, Nils
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Lestander, Torbjörn A.
    Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, Umeå, Sweden.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Backman, Rainer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Biomass pellet combustion: cavities and ash formation characterized by synchrotron X-ray micro-tomography2018Inngår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 176, s. 211-220Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ash formation during thermochemical conversion of biomass-based pellets influences both char conversion rates and ash-related operational problems. The objective of the present study was to provide detailed insights into changes in fuel and ash properties during fuel conversion. Pellets of poplar wood and wheat straw were used as model biofuels, representing vastly different compositions of ash-forming elements. Pellet samples at different char conversion phases were analyzed by synchrotron-based 3D X-ray micro-tomography, to map and visualize the development of cracks, internal cavities, and ash layers during conversion. The analysis of ash layers was complemented by scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. The results provide new insights into how large cracks and internal cavities are developed already during devolatilization, for example, the poplar wood pellets had a 64% void fraction after the devolatilization stage. As expected, there were large variations between the ash layer properties for the two fuels. A porous, low density, and calcium-rich ash was formed from the poplar fuel, whereas the wheat straw ash was a high-density silicate melt that developed into bubbles on the surface. As the conversion proceeded, the wheat straw ash covered parts of the active char surface area, but without blocking the gas transport.

  • 178.
    Strandberg, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wagner, David R.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Holmgren, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Molinder, Roger
    Energitekniskt Centrum, Piteå.
    Wiinikka, Henrik
    Energitekniskt Centrum, Piteå.
    Umeki, Kentaro
    Luleå Technical University.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Influence of Biomass Particle Properties and Pyrolysis Conditions on Char Reactivity2014Inngår i: Proceedings of Impacts of Fuel Quality on Power Production October 26 –31, 2014, Snowbird, Utah, USA, 2014Konferansepaper (Annet vitenskapelig)
  • 179.
    Strandberg, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    From torrefaction to gasification: Pilot scale studies for upgrading of biomass2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Increasing the share of biomass, preferably by replacing fossil fuels, is one way to mitigate the present climate change. Fossil coal can be directly replaced by co-combustion of coal and biomass and fossil engine fuels (gasoline and diesel) could potentially partly be replaced by synthetic renewable fuels produced via entrained flow gasification of biomass. The use of biomass in these processes is so far limited, partly because of the fibrous and hygroscopic nature of biomass which leads to problem in storing, transportation, handling and feeding.

    This thesis demonstrates how the challenging characteristics of raw biomass are mitigated by the pretreatment method torrefaction. Torrefaction is a process where biomass is heated in an oxygen deficient atmosphere to typically between 240 and 350°C for a time period of 2 minutes to 1 hour. Most of the torrefaction R&D in the literature have so far been performed with bench-scale batch reactors. For the purpose of carefully studying continuous torrefaction, a 20 kg/h torrefaction pilot plant was therefore designed, constructed and evaluated.

    The overall conclusion from this thesis is that the many benefits of torrefied biomass are valid also when produced with a continuous pilot plant and for typically Swedish forest biomasses. Some of the documented improved biomass properties are increased heating value, increased energy density, higher friability (lower milling energy) and less hydrophilic biomass (less moisture uptake). Most of the improvements can be attributed to the decomposition of hemicellulose and cellulose during torrefaction.

    The most common variables for describing the torrefaction degree are mass yield or anhydrous weight loss but both are challenging to determine for continuous processes. We therefore evaluated three different methods (one existing and two new suggestions) to determine degree of torrefaction that not require measurement of mass loss. The degree of torrefaction based on analyzed higher heating value of the raw and torrefied biomass (DTFHHV) predicted mass yield most accurate and had lowest combined uncertainty.

    Pelletizing biomass enhance transportation and handling but results from pelletization of torrefied biomass is still very limited in the literature and mainly reported from single pellet presses. A pelletization study of torrefied spruce with a ring die in pilot scale was therefore performed. The bulk energy density was found to be 14.6 GJ/m3 for pelletized torrefied spruce (mass yield 75%), a 40% increase compared to regular white pellets and therefore are torrefied pellets more favorable for long distance transports. More optimization of the torrefied biomass and the pelletization process is though needed for acquiring industrial quality pellets with lower amount of fines and higher pellet durability than attained in the present study.

    Powders from milled raw biomass are generally problematic for feeding and handling and torrefied biomass has been proposed to mitigate these issues. The influence of torrefaction and pelletization on powder and particle properties after milling was therefore studied. The results show that powder from torrefied biomass were enhanced with higher bulk densities, lower angle of repose as well as smaller less elongated particles with less surface roughness. Even higher powder qualities were achieved by pelletizing the torrefied biomass before milling, i.e. another reason for commercial torrefied biomass to be pelletized.

    Entrained flow gasification (EFG) is a promising option for conversion of biomass to other more convenient renewable energy carriers such as electricity, liquid biofuels and green petrochemicals. Also for EFGs are torrefied fuels very limited studied. Raw and torrefied logging residues were successfully gasified in a pilot scale pressurized entrained flow biomass gasifier at 2 bar(a) with a fuel feed corresponding to 270 kWth. Significantly lower methane content (50% decrease) in the syngas was also demonstrated for the torrefied fuel with mass yield 49%. The low milling energy consumption for the torrefied fuels compared to the raw fuel was beneficial for the gasification plant efficiency.

  • 180.
    Strandberg, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nordin, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Kollberg, Kristoffer
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Powder characteristics of torrefied and pelletized biomass2014Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Co-firing biomass with coal is an efficient way of mitigating severe climate change by reducing the total atmospheric greenhouse gas burden. Although biomass is considered close to CO2-neutral, present biomass based energy carriers all however suffer from several logistical challenges. The high moisture content, hydrophobic and fibrous nature, low energy density and bulky characteristics are all challenges impeding large-scale industrial use. The thermal pre-treatment method torrefaction enhances the above biomass fuel qualities and significantly facilitate large scale industrial use of biomass raw materials with respect to, handling, storage, feeding as well as for final conversion. In the present work we evaluate the influence of torrefaction on some fuel powder quality aspects. Five different types of torrefied pellets was compared to a reference (regular white wood pellets) with respect to milling energy and different powder characteristics such as aerated and tapped bulk density, particle size distribution, angle of repose and image analysis. Milling energy decreased by between 77 and 93 % for torrefied pellets compared to wood pellets, and the resulting black powders consisted of considerably smaller particle sizes. Particles from torrefied fuels were also less elongated and more circular/less rough, properties which positively influence flowability. Powder bulk density increased by 90 % at most. Angle of repose, previously documented to be negatively correlated to flowability, decreased from 66° for the reference powder to 57° for the torrefied sample with the lowest angle. Torrefaction temperature affected the results considerably more than moisture content prior to pelletization. The total evidences found therefore suggest a positive effect of torrefaction on both powder production and characteristics.

  • 181.
    Strandberg, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Ingemar
    Pommer, Linda
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nordin, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Evaluation of existing and new approaches to determine degree of torrefactionManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Torrefaction is a promising thermal pretreatment method for biomass in which many material properties are enhanced. The biomass components (hemicellulose, cellulose and lignin) degrade in this thermal process to different extents depending on type of process, treatment temperature, residence time and biomass type. Torrefaction severity is usually defined by biomass weight loss or mass yield, but other approaches to determine degree of torrefaction have also been suggested. For continuous and large scale facilities, mass yield can be challenging to determine and another approach to determine torrefaction severity is therefore desired. In this study, one existing and two new approaches for determining degree of torrefaction are presented, compared and evaluated including uncertainty analysis. The three approaches were based on analysis of; volatile matter, thermochemical properties (enthalpy of formation), and higher heating value. 

    All three methods were highly correlated to mass yield and independent of torrefaction process. The degree of torrefaction based on higher heating value predicted mass yield most accurate, had lowest measurement uncertainty and the results were independent of biomass type. In the evaluation of the method based on formation enthalpy it was revealed that the increase in heating values for torrefied biomasses could be explained by the combination of increase in enthalpy of formation and decrease in oxygen content.

  • 182.
    Strandberg, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Ingemar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Pommer, Linda
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wiklund-Lindström, Susanne
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Åberg, Katarina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Nordin, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Effects of temperature and residence time on continuous torrefaction of spruce wood2015Inngår i: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 134, s. 387-398Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    As a solid energy carrier, biomass generally has a few disadvantages, which limits its use for coal replacement and as a feedstock for entrained flow gasification. The hydrophilic and fibrous nature, the low calorific value and low bulk energy content imply high accumulated costs in the whole supply chain and severe challenges in more advanced conversion systems. By thermally pretreating the biomass by torrefaction, these properties may be significantly improved. A continuous torrefaction rotary drum reactor was designed, constructed and evaluated to enable an accurate process control and allow a homogeneous well-defined high quality product to be produced. The combined effects of torrefaction temperature (260–310 °C) and residence time (8–25 min) on a large number of product properties (> 25) were determined for Norway spruce. The resulting mass and energy yields were 46–97% and 62–99%, respectively. Exothermic reactions were evident both at low (260 °C) and high temperatures (310 °C) but with no thermal runaway observed. Increased torrefaction severity resulted in decreased milling energy consumption, angle of repose, mass and energy yield, content of volatile matter, hydrogen, cellulose and hemicellulose. Hydrophobicity, heating value, carbon and fixed carbon contents increased. For all responses, the effect of torrefaction temperature was larger than the effect of residence time. Substantial interaction effects were present for mass and energy yields, volatile matter and hydrogen content. Another correlation found was the relationship of hemicellulose degradation and the brittleness of the torrefied product. Data also suggest secondary char forming reactions during the torrefaction process, resulting in higher fixed carbon content in the torrefied material than expected. The results also suggest torrefaction temperature and residence time not to be totally interchangeable.

  • 183.
    Strandberg, Martin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Olofsson, Ingemar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Pommer, Linda
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wiklund-Lindström, Susanne
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Swedish Defence Research Agency, FOI.
    Åberg, Katarina
    Nordin, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Effects of temperature and residence time on torrefaction of spruce woodManuskript (preprint) (Annet vitenskapelig)
  • 184.
    Strunk, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Characterization of cellulose pulps and the influence of their properties on the process and production of viscose and cellulose ethers2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Today’s market offers an ever-increasing range of cellulose pulps (derivative pulps) made fromvarious wood types through different delignification processes. Each pulp segment has its uniquecharacteristics, which makes it difficult for the producer of cellulose derivatives to choose the mostsuitable pulp for optimum processability and product quality. The objective of this study was toimprove knowledge of cellulose pulps and to describe how different pulp properties affectprocessability and quality in the production of viscose dope and cellulose ethers.Ten pulp samples were investigated, originating from both sulfite and sulfate processes, with highand low viscosities and with softwood and hardwood as raw material. The pulps were analyzed fortheir properties and then processed to viscose dope and a cellulose ether in two separate pilotfacilities. The intermediates in the viscose process as well as the quality of the viscose dope andcellulose ether were analyzed and the results correlated to pulp properties.Multivariate regression methods were applied to investigate the dominating physical and chemicalproperties of each pulp and pulp segment, and to study the use of spectroscopic analyses inpredicting pulp origin, concentration and composition of hemicelluloses as well as the content ofreducing end groups in cellulose. For the production of viscose dope, the models presented showedthe most important pulp properties for good cellulose reactivity and viscose filterability. In addition,the properties affecting gel formation, flocculation, degree of substitution and clarity in theproduction of cellulose ether were highlighted. The study also emphasized the need to supplementthe use of conventional analyses on pulps and viscose intermediates with other analytical methods,such as molecular weight distribution and carbohydrate analysis, to better predict the quality ofboth viscose dope and viscose fiber.The results of the present study could be useful to predict the origin and properties of new pulps, toreplace or supplement otherwise expensive pulp analyses, and to assess the impact of pulpproperties on the production of cellulose derivatives without extensive pilot-scale trials.

  • 185.
    Strunk, Peter
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lindgren, Åsa
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Agnemo, Roland
    Eliasson, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Properties of cellulose pulps and their influence on the production of a cellulose ether2012Inngår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, nr 1, s. 24-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several grades of cellulose pulps were investigated for their influence on the product quality of a cellulose ether, ethyl hydroxyethyl cellulose (EHEC). The selection of the pulps was based on pulping process, original wood type and intrinsic viscosity. In total, five sulfite pulps and four sulfate pulps were chosen, of which all but one sulfate pulp were of dissolving grade. The physical and chemical properties of the pulps were analyzed as well as important qualitative parameters of the final product EHEC. The influence of pulp properties on EHEC quality was investigated by multivariate data analyses.Principal component analysis showed that due to the influence of all variables, the pulps aligned in groups in accordance to the selection criteria pulping process and wood type. Partial least square regression revealed that high gel formation in EHEC is explained by the pulp properties high intrinsic viscosity and high Mw in combination with high caustic absorption rate and high total caustic absorption. The amount of hemicelluloses, in particular xylose, also contributed to gel formation. High cloud point for an EHEC solution was explained by a high MSEO and low DSEt of the EHEC molecules, where in turn a high MSEO could be predicted by a high pore area, high PD and a low caustic absorption rate. A low DSEt could on the other hand be predicted by a low hemicellulose content and hence a high R18. In a separate model, the same pulp properties explaining MSEO and DSEt also predicted cloud point directly. Fock reactivity and viscose dope filterability, both test methods originating from the viscose manufacturing, were shown to predict cloud point but have low predictability on other EHEC quality parameters.The models achieved can thus be utilized to predict final EHEC product qualities for new pulps within the design set of the chosen pulps.

  • 186.
    Strunk, Peter
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lindgren, Åsa
    AkzoNobel Functional Chemicals AB, Stenungsund, Sweden.
    Eliasson, Bertil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Agnemo, Roland
    DomInnova, Domsjö Fabriker AB, Örnsköldsvik, Sweden.
    Chemical changes of cellulose pulps in the processing to viscose dope2012Inngår i: Cellulose Chemistry and Technology, ISSN 0576-9787, Vol. 46, nr 9-10, s. 559-569Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A selection of cellulose pulps was investigated for their chemical changes during the required process steps to viscose dope. The selection of the pulps was based on pulping process, original wood type and intrinsic viscosity. In total, five sulfite pulps and four sulfate pulps were chosen, of which all but one sulfate pulp were of dissolving grades. The physical and chemical properties of the pulps were analyzed as well as important qualitative parameters of the cellulose intermediates during mercerization, pre-aging and in the final viscose dope. Pre-aging curves were reported as a measure of each pulp's reactivity with respect to oxidative degradation, where high hemicellulose content and small pore area and pore diameter were found to hamper cellulose degradation. The correlations in pre-aged pulps of intrinsic viscosity to Mz, Mv and Mw were found to be ambiguous and show the need for a description of total molecular weight distribution of the alkali celluloses to better understand the degradation behavior of each pulp, instead of only intrinsic viscosity. It was also shown that R18 and R10 are insufficient analyses to determine pulp, and to predict viscose quality. Further, many pulps, independently of initial hemicellulose content, reached the same level of hemicellulose content after mercerization. The presence of crystalline hemicelluloses could be a possible cause for this level-off behavior, combined with hemicelluloses resistant to caustic lye treatment. The change of both low-molecular-weight celluloses and PD in the process to viscose dope was investigated due to the importance of these variables on dope spinnability and viscose fiber strength. Caustic resistance of cellulose and hemicelluloses and a more rigid fiber structure in some pulps are suggested to contribute to the different degradation behavior.

  • 187. Subhan, Sidra
    et al.
    Muhammad, Yaseen
    Sahibzada, Maria
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Subhan, Fazle
    Tong, Zhangfa
    Studies on the Selection of a Catalyst-Oxidant System for the Energy-Efficient Desulfurization and Denitrogenation of Fuel Oil at Mild Operating Conditions2019Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 33, nr 9, s. 8423-8439Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study reports the selection of an ideal catalyst–oxidant system for the energy-efficient catalytic oxidative desulfurization (CODS) of dibenzothiophene (DBT) and denitrogenation (CODN) of pyridine over Mn–Co–Mo/Al2O3 and acid-functionalized 1-butyl-3-methyl imidazolium chloride ([Bmim]Cl/ZnCl2) ionic liquid (IL) catalysts using H2O2 and NaClO as oxidants. The NaClO–catalyst system realized 100% CODS/CODN activity within 15 min at 25 °C at comparatively low activation energies of 4.9 and 5.4 kJ/mol for DBT and pyridine, respectively, under optimal conditions of oxidant-to-sulfur ratio of 4, oxidant-to-nitrogen ratio of 8, ionic liquid-to-oil ratio of 1.5/5, and 0.1 g of Mn–Co–Mo/Al2O3 catalyst for 15 mL of model fuel. Both catalytic activity and kinetics results revealed a NaClO–catalyst system with greater efficiency and lesser energy requirements than a H2O2–catalyst system, and hence the former realized enhanced CODS and CODN than the latter. Furthermore, the Mn–Co–Mo/Al2O3 catalyst favored CODS, while [Bmim]Cl/ZnCl2 possessed greater affinity for the CODN process, owing to the stronger nucleophilic interaction of the cationic species in IL toward hindered nitrogen compounds. Further justification for the CODS and CODN activities and textural characterization of the fresh and spent catalysts were provided by PXRD, XPS, SEM, EDX elemental mapping, and BET surface area characterizations. Based on the results, this study is potentially viable owing to its environmental greenness, enhancement in the calorific value of the final fuel, and genially benignant application in energy consumption via mild operating conditions and hence can be envisaged as a practicable alternative approach in industrial processing of fuel oils.

  • 188.
    Surowiec, Izabella
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Nowik, Witold
    Moritz, Thomas
    Mass spectrometric identification of new minor indigoids in shellfish purple dye from Hexaplex trunculus2012Inngår i: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 94, nr 2, s. 363-369Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Analysis of natural dyes in historical objects is important for both conservation purposes and to determine the origin and culture that produced it. Identification of a particular dye is usually made based on the presence of its main components, while consideration of minor components is important for differentiating between dyes originating from closely related species. Tyrian purple is one of the oldest dyes known to man and derives from different species of marine molluscs. In all of these species, indigotin, indirubin and their brominated analogues are the main colouring compounds. Here, we describe the identification of minor indigoids found in extracts of the pigment obtained from one of the Tyrian purple species, Hexaplex trunculus. Identification of these compounds was made based on isotopic patterns and accurate mass measurements of protonated molecular ions and their high collision energy fragments obtained in LC-MS/MS experiments. The unknown compounds appeared to be analogues of indirubin and its mono- and dibrominated derivatives with one CO group in the indirubin backbone substituted by a CNH group. Identification of these compounds facilitates the detection of dyestuffs from H. trunculus in historical objects and increases our knowledge about the dye biosynthesis and technology of Tyrian purple production. (C) 2012 Elsevier Ltd. All rights reserved.

  • 189. Tranvik, AC
    et al.
    Öhman, Marcus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik, Energiteknik och termisk processkemi.
    Sanati, M
    Bed material deposition in cyclones of wood fuel fired circulating fluidized beds (CFBs)2007Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, nr 1, s. 104-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bed material samples were collected at different times from a full-scale combustion boiler, and bed material deposits were taken from the cyclone and the riser at two different occasions from a wood-fired circulating fluidized bed boiler (104 MWth). The bed materials and the bed material deposits were analyzed with environmental scanning electron microscopy/energy-dispersive X-ray spectroscopy (ESEM/EDXS) to determine the characteristics of the formed bed particle layers and bed material deposits. On the basis of their elemental composition, the corresponding melting behavior was estimated, using data extracted from phase diagrams. The bed material was also fractionated by sieving, and the alkali metal concentration dependence on the particle size was determined. The bed material deposits found in the cyclone and the riser consisted of bed particles embedded in a low-temperature melting (sticky) alkali metal silicate (K and Na) that resemble the composition of the layer found around the cracks in older quartz bed particles. The alkali silicate formation, which is in progress in the vicinity of the formed cracks of older quartz bed particles, significantly transforms a large part of the bed particle and makes it less resistant against fragmentation. The results therefore suggest that elutriated alkali silicate-rich fragments from old quartz bed particles are responsible for bed material depositions in cyclones of wood-fired circulating fluidized beds (CFBs).

  • 190.
    Trubetskaya, Anna
    et al.
    Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads Bygning 229, Kgs. Lyngby 2800, Denmark.
    Arendt Jensen, Peter
    Degn Jensen, Anker
    Glarborg, Peter
    Hofmann Larsen, Flemming
    Larsen Andersen, Mogens
    Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures2016Inngår i: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 94, s. 117-129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The concentration and type of free radicals from the decay (termination stage) of pyrolysis at slow and fast heating rates and at high temperatures (above 1000 degrees C) in biomass char have been studied. A room temperature electron spin resonance spectroscopy study was conducted on original wood, herbaceous biomass, holocelluloses, lignin and their chars, prepared at high temperatures in a wire mesh reactor, an entrained flow reactor, and a tubular reactor. The radical concentrations in the chars from the decay stage range up between 7.10(16) and 1.5.10(18) spins g(-1). The results indicated that the biomass major constituents (cellulose, hemicellulose, lignin) had a minor effect on remaining radical concentrations compared to potassium and silica contents. The higher radical concentrations in the wheat straw chars from the decay stage of pyrolysis in the entrained flow reactor compared to the wood chars were related to the decreased mobility of potassium in the char matrix, leading to the less efficient catalytic effects of potassium on the bond-breaking and radical re-attachments. The high Si levels in the rice husk caused an increase in the char radical concentration compared to the wheat straw because the free radicals were trapped in a char consisting of a molten amorphous silica at heating rates of 10(3)-10(4) K s(-1). The experimental electron spin resonance spectroscopy spectra were analyzed by fitting to simulated data in order to identify radical types, based on g-values and line widths. The results show that at high temperatures, mostly aliphatic radicals (g = 2.0026-2.0028) and PAH radicals (g = 2.0027-2.0031) were formed.

  • 191.
    Trubetskaya, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Kling, J.
    Brown, A.
    Tompsett, G.
    Umeki, K.
    Effects of Lignocellulosic Compounds on the Yield, Nanostructure and Reactivity of Soot from Fast Pyrolysis at High Temperatures2017Konferansepaper (Annet vitenskapelig)
  • 192.
    Trubetskaya, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Kling, Jens
    Brown, Avery
    Tompsett, Geoffrey
    Umeki, Kentaro
    Effects of Lignocellulosic Compounds on the Yield, Nanostructure and Reactivity of Soot from Fast Pyrolysis at High Temperatures2017Konferansepaper (Annet vitenskapelig)
  • 193.
    Trubetskaya, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Broström, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Larsen Andersen, Mogens
    Talbro Barsberg, Søren
    Modeling of radical structures in biochar using DFT calculations2017Inngår i: ECI Digital Archives / [ed] Franco Berruti, Raffaella Ocone and Ondrej Masek, Digital Commons , 2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Carbon is a key ingredient for producing metals used for cellphones, laptop computers, photovoltaic panels, and related solid state silicon devices employed by mankind. Thus, introduction of an alternative reductant based on bioresources into steel manufacturing without significant investments in a new technology is of high importance and wide impact. The production of iron, steel, and many other metals can employ biocarbon as the needed reductant; but because of cost, coals are usually used instead. The anthropogenic CO2 emissions can be decreased by substitution of biochar in the production of silicon and metals due to the lower regeneration time of biomass < 10 years compared to 106-107 years for bituminous coal.

    This study aims to develop and to provide knowledge on the biochar structure at the molecular level including the presence of free radicals and oxygen heteroatoms that is essential for the understanding and prediction of biochar valuable properties in metallurgical applications. Both yields and biochar properties are important parameters for the optimization of pyrolysis conditions. Therefore, the pyrolysis conditions for the biochar application as a reducing agent in steel industry were optimized, and the molecular structure of the biochar by the combined use of experimental chemistry (Raman spectroscopy and Fourier transform infrared spectroscopy) and quantum chemistry computations (Density Functional Theory methods) was modified.

    The results indicated the formation of stable radicals from biomass pyrolysis at their termination stage which were quantified by the electron spin resonance spectroscopy. Based on the experimental and fitting results, PAH structures were selected as initial compounds for the DFT modeling. The comparison of hydroxylated with methylated PAH structures showed that hydroxylated PAH are excellent candidate to represent the radical structure based on the low bond dissociation energes. The bond dissociation energy of -10 Kcal mol-1 is in the range of the best known antioxidants. The results showed that the present DFT model predicts reasonably the biochar molecular structure, and can capture changes in the biochar molecular structure under different pyrolysis conditions.

  • 194.
    Trubetskaya, Anna
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Hofmann Larsen, Flemming
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ståhl, Kenny
    Umeki, Kentaro
    Potassium and soot interaction in fast biomass pyrolysis at high temperatures2018Inngår i: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 225, s. 89-94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study aims to investigate the interaction between potassium and carbonaceous matrix of soot produced from wood and herbaceous biomass pyrolysis at high heating rates at 1250°C in a drop tube reactor. The influence of soot carbon chemistry and potassium content in the original biomass on the CO2 reactivity was studied by thermogravimetric analysis. The XPS results showed that potassium incorporation with oxygen-containing surface groups in the soot matrix did not occur during high temperature pyrolysis. The potassium was mostly found as water-soluble salts such as KCl, KOH, KHCO3 and K2CO3 in herbaceous biomass soot. The low ash-containing pinewood soot was less reactive than the potassium rich herbaceous biomass soot, indicating a dominating role of potassium on the soot reactivity. However, the catalytic effect of potassium on the reactivity remained the same after a certain potassium amount was incorporated in the soot matrix during pyrolysis. Raman spectroscopy results showed that the carbon chemistry of biomass soot also affected the CO2 reactivity. The less reactive pinewood soot was more graphitic than herbaceous biomass soot samples with the disordered carbon structure.

  • 195.
    Ur Rehman, Bilal
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Modelling a Mineral Froth Flotation Process: Case Study: Minerals process at Boliden AB2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    We present an approach to model the dynamic of a copper flotation process. The conventional approach of system identification is applied to model the dynamics. In this research, experiments are performed to collect process data of determined input and output variables. It is followed by data pre-processing to handle outliers and to remove high frequency disturbances. Simulation and validation responses of linear estimated models, which captured the dynamic of the process, are presented. The long term goal is to use estimated models to design a models-based control system.

  • 196.
    Vaziri, Mojgan
    et al.
    Department of Wood Science and Technology, Luleå University of Technology.
    Orädd, Greger
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Lindgren, Owe
    Department of Wood Science and Technology, Luleå University of Technology,.
    Pizzi, Antonio
    Magnetic resonance imaging of water distribution in welded woods2011Inngår i: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 25, nr 16, s. 1997-2003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 197.
    Viggh, Erik
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Boström, Dan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Wilhelmsson, Bodil
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Raw meal and slag reactions during cement clinker formation2019Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Natural limestones as raw material for OPC clinker manufacturing contribute to emissions of CO2gases during the production of clinker. In addition, the mining of limestone can regionally be controlledby restrictions due to environmental concerns. Slags from the steel industry can replace limestone tominimize the use of the mineral deposits. Both materials have similar chemistry and are compatible asraw materials.Utilizing slags raises questions about how slag particles will react with other raw meal components asthe temperature in the kiln increases during clinker formation. This study establishes the chemical andmineralogical aspects of replacing a portion of the limestone with slags. Of interest is how the materialsreact during the formation of the liquid phase and the formation of phases containing MgO.Three different slags were examined, a basic oxygen furnace slag BOF, a crystalline blast-furnace slagand a granulated blast-furnace slag. In the study, the microstructural causes of reactivity, as well asmineral formation in the transition zone between raw meal components, developing liquid phase andslag particles were studied. Heated raw meals were studied using HT-QXRD, QXRD, SEM andthermodynamic modeling to describe the reactions of particles at higher temperatures. The resultsshow that the formation of clinker minerals is strongly influenced by the type and amount of slag. Thus,a careful selection must be done of both composition and quantity of metallurgical slags for naturallimestone replacement in order to maintain clinker quality.

  • 198. Virtanen, Pasi
    et al.
    Mikkola, Jyri-Pekka
    Åbo Akademi.
    Salmi, Tapio
    Miljövänliga katalysatorer av joniska vätskor2010Inngår i: Kemia, ISSN 0355-1628, nr 6, s. 32-34Artikkel i tidsskrift (Annet vitenskapelig)
  • 199. Virtanen, Pasi
    et al.
    Salmi, Tapio
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Laboratory of Industrial Chemistry and Reaction Engineering, Process Chemistry Centre, Åbo Akademi University, Piispankatu 8, FI-20500 Turku/Åbo, Finland.
    Kinetics of cinnamaldehyde hydrogenation by supported ionic liquid catalysts (SILCA)2009Inngår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 48, nr 23, s. 10335-10342Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 200. Virtanen, Pasi
    et al.
    Salminen, Eero
    Mikkola, Jyri-Pekka
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Industrial Chemistry & Reaction Engineering, Johan Gadolin Process Chemistry Centre, Åbo Akademi University.
    Modeling of Supported Ionic Liquid Catalysts Systems: From Idea to Applications2017Inngår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 56, nr 45, s. 12852-12862Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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