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Sökning: swepub > Umeå universitet > Mikkola Jyri Pekka

  • Resultat 1-10 av 334
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1.
  • Pezoa-Conte, R., et al. (författare)
  • Deconstruction of the green alga Ulva rigida in ionic liquids : closing the mass balance
  • 2015
  • Ingår i: Algal Research. - : Elsevier. - 2211-9264. ; 12, s. 262-273
  • Tidskriftsartikel (refereegranskat)abstract
    • Algae are known to grow at high rates compared to terrestrial plants that contain comparable amounts of carbohydrates by weight. Therefore, this renders them attractive in terms of any biorefinery concept. In this work the green alga Ulva rigida, containing 40 wt.% of carbohydrates was pretreated with a switchable ionic liquid (SIL), distillable ionic liquid (DIL) and low-viscosity ionic liquid (LVIL). The SIL DBU–MEA–SO2 was prepared from a mixture of mono-ethanolamine (MEA) and 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU) that was coupled with sulfur dioxide (SO2), whereas the DIL [TMGH+][EtCO2−] (1,1,3,3-tetramethylguanidine propionate) was synthesized by a simple acid–base neutralization reaction. Consequently, the LVIL [HDBU+][5OF−] protonated 1,8-diazabicyclo-[5,4,0]-undec-7-ene- 2,2,3,3,4,4,5,5-octafluoro-1-pentoxide was used as received. The treatments were carried out in the temperature range of 100–160 °C for 6 h. The products obtained after the treatments were analyzed using different techniques like ICP, OES, SEM, TEM, TGA, FTIR and carbohydrate determination by GC. Upon treatment with DIL up to 67 wt.% of carbohydrates could be dissolved. For the first time, processing of U. rigida was carried out in ionic liquids so that the mass balance of the process was obtained. It can be concluded that 1,1,3,3-tetramethylguanidine propionate shows significant potential when aiming at releasing carbohydrates from algal biomass that, consequently, can be applied in the production of platform chemicals and/or biofuels such as bioethanol.
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2.
  • Ma, Chunyan, et al. (författare)
  • Towards negative carbon emissions : Carbon capture in bio-syngas from gasification by aqueous pentaethylenehexamine
  • 2020
  • Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 279
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, an aqueous pentaethylenehexamine (PEHA) solution was studied for CO2 removal from bio-syngas for the first time. Firstly, pure CO2 absorption in aqueous PEHA solution under different conditions was conducted, and 20 wt% PEHA solution was identified as the best option. Secondly, the capture of CO2 was tested with synthetic syngas from a gas cylinder, and the species other than CO2 showed a negligible impact on CO2 removal. Finally, to evaluate the practical feasibility of using aqueous PEHA solution on the downstream CO2 capture, the pilot experiments of gasification with boreal forest-based biomasses were designed to provide real syngas with a realistic distribution in composition for further testing. The results showed that the operating conditions and the type of feedstocks affected the distribution in the bio-syngas composition. Among these feedstocks, at the optimal oxygen supply, using spruce needles generated the highest yields of CO and H2 and, meanwhile, gave rise to similar yields of other gases such as CO2, CH4, etc. The influence of the species other than CO2 for CO2 removal was negligible. Additionally, aqueous PEHA solution was tested as a biomass pretreatment agent, showing that no significant changes could be identified by the ultimate analysis (except for increased nitrogen content), but the yields of CO were affected negatively. On the other hand, when using the pretreated biomass by the aqueous PEHA solution, the NH3 concentration in bio-syngas reached to the highest (4000 parts per million), which slightly affected the CO2 absorption capacity and initial absorption rate of 20 wt% PEHA solution in a positive way.
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3.
  • Khasevani, Sepideh G., et al. (författare)
  • The beauty of being complex: Prussian blue analogues as selective catalysts and photocatalysts in the degradation of ciprofloxacin
  • 2022
  • Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 410, s. 307-319
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the performance of four Prussian blue analogues (PBAs) as catalysts for the selective degradation of ciprofloxacin in water, under both dark and illumination conditions. We show that no light is actually needed to induce a selective degradation of the molecular target, while light irradiation spurs the process, without, however, resulting in the commonly reported photolysis-supported breaking down. We present a systematic characterization of the PBAs aiming at interpreting the catalytic outcomes in the light of a classic coordination chemistry analysis, empowered by the most recent findings in literature. We show that varying the transition metal binding the N atom of the cyanide bridge is key to promote photoinduced charge generation and transfer, which effectively disrupts the molecular target. The analysis of the materials before and after the irradiation with solar simulated light results in a change of the lattice parameters, indicating the possibility of a light-induced spin cross-over.
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4.
  • Asres, Georgies Alene, et al. (författare)
  • Ultrasensitive H2S gas sensors based on p-type WS2 hybrid materials
  • 2018
  • Ingår i: Nano Reseach. - : Springer. - 1998-0124 .- 1998-0000. ; 11:8, s. 4215-4224
  • Tidskriftsartikel (refereegranskat)abstract
    • Owing to their higher intrinsic electrical conductivity and chemical stability with respect to their oxide counterparts, nanostructured metal sulfides are expected to revive materials for resistive chemical sensor applications. Herein, we explore the gas sensing behavior of WS2 nanowire-nanoflake hybrid materials and demonstrate their excellent sensitivity (0.043 ppm-1) as well as high selectivity towards H2S relative to CO, NH3, H2, and NO (with corresponding sensitivities of 0.002, 0.0074, 0.0002, and 0.0046 ppm-1, respectively). Gas response measurements, complemented with the results of X-ray photoelectron spectroscopy analysis and first-principles calculations based on density functional theory, suggest that the intrinsic electronic properties of pristine WS2 alone are not sufficient to explain the observed high sensitivity towards H2S. A major role in this behavior is also played by O doping in the S sites of the WS2 lattice. The results of the present study open up new avenues for the use of transition metal disulfide nanomaterials as effective alternatives to metal oxides in future applications for industrial process control, security, and health and environmental safety.
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5.
  • Berglund, Linn, et al. (författare)
  • Switchable ionic liquids enable efficient nanofibrillation of wood pulp
  • 2017
  • Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 24:8, s. 3265-3279
  • Tidskriftsartikel (refereegranskat)abstract
    • Use of switchable ionic liquid (SIL) pulp offers an efficient and greener technology to produce nanofibers via ultrafine grinding. In this study, we demonstrate that SIL pulp opens up a mechanically efficient route to the nanofibrillation of wood pulp, thus providing both a low cost and chemically benign route to the production of cellulose nanofibers. The degree of fibrillation during the process was evaluated by viscosity and optical microscopy of SIL treated, bleached SIL treated and a reference pulp. Furthermore, films were prepared from the fibrillated material for characterization and tensile testing. It was observed that substantially improved mechanical properties were attained as a result of the grinding process, thus signifying nanofibrillation. Both SIL treated and bleached SIL treated pulps were fibrillated into nanofibers with fiber diameters below 15 nm thus forming networks of hydrophilic nature with an intact crystalline structure. Notably, it was found that the SIL pulp could be fibrillated more efficiently than traditional pulp since nanofibers could be produced with more than 30% less energy when compared to the reference pulp. Additionally, bleaching reduced the energy demand by further 16%. The study demonstrated that this switchable ionic liquid treatment has considerable potential in the commercial production of nanofibers due to the increased efficiency in fibrillation.
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6.
  • Bernardini, A., et al. (författare)
  • Direct synthesis of H2O2 over Pd supported on rare earths promoted zirconia
  • 2015
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 256, s. 294-301
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work Pd (0.3 or 0.6 wt.%) was supported on both ZrxM1-xO2 (M = La, Y, Ce) and on mechanical mixtures of CeO2 and ZrO2. The synthesized catalysts were characterized by XRD, TPR, AAS and CO chemisorption and tested for the direct synthesis of hydrogen peroxide in a high pressure semibatch apparatus. The reactants conversion was limited in order to avoid mass-transfer limitations. No selectivity enhancers of any kind were used and the all the materials were halide free. Small metal particles were obtained (1-2.6 nm). Supports with smaller pore diameters leaded to larger Pd particles, which in turn were found to preferentially support the formation of the peroxide. Moreover, supports with higher reducibility favored the production of H2O2, probably due to an easier reduction of the active metal, essential to achieve high selectivity. Notwithstanding the absence of enhancers, the specific activity and selectivity recorded were very high.
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7.
  • Bui, Thai Q., et al. (författare)
  • Mesoporous Melamine-Formaldehyde Resins as Efficient Heterogeneous Catalyst for Continuous Synthesis of Cyclic Carbonates from Epoxides and gaseous CO2
  • 2020
  • Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 8:34, s. 12852-12869
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein we report the application of inexpensive mesoporous melamine-formaldehyde resins (MMFR and MMFR250) obtained by a novel template-free and organosolvent-free hydrothermal method as efficient heterogeneous catalysts for direct synthesis of cyclic carbonates from CO2 and epoxides (epichlorohydrin, butylene oxide and styrene oxide). The catalytic activity of the melamine resins was attributed to the abundant Lewis basic N-sites capable of activating CO2 molecules. Based on CO2-Temperature programmed desorption, the concentration of surface basic sites for MMFR and MMFR250 were estimated to be 172 and 56 µmol/g, while the activation energy of CO2 desorption (strength of basic sites) were calculated to be 92.1 and 64.5 kJ/mol. We also observed considerable differences in the catalytic activity and stability of polymeric catalysts in batch and in continuous-flow mode; due to the existence of a synergism between adsorption of CO2 and cyclic carbonates (poison). Our experiments also revealed important role of catalyst surface chemistry and CO2 partial pressure upon catalyst poisoning. Nevertheless, owing to their unique properties (large specific surface area, large mesoporous and CO2 basicity) melamine resins presented excellent activity (turnover frequency 207-2147 h-1), selectivity (>99%) for carbonation of epoxides with CO2 (20 bar initial CO2 or CO2:epoxide mole ratio ~1.5) under solvent-free and co-catalyst-free conditions at 100-120 oC. Most importantly, these low-cost polymeric catalysts were reusable and demonstrated exceptional stability in a flow reactor (tested upto 13 days time on stream, weight hourly space velocity 0.26-1.91 h-1) for continuous cyclic carbonate production from gaseous CO2 with different epoxides (conversion 76-100% and selectivity >99%) under industrially relevant conditions (120 oC, 13 bar, solvent-free/co-catalyst-free) confirming their superiority over the previously reported catalytic materials.
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8.
  • Bukhanko, Natalia, et al. (författare)
  • Gas phase synthesis of isopropyl chloride from isopropanol and HCl over alumina and flexible 3-D carbon foam supported catalysts
  • 2017
  • Ingår i: Applied Catalysis A. - : Elsevier. - 0926-860X .- 1873-3875. ; 542:25, s. 212-225
  • Tidskriftsartikel (refereegranskat)abstract
    • Isopropyl chloride synthesis from isopropanol and HCl in gas phase over ZnCl2 catalysts supported on Al2O3 as well as flexible carbon foam was studied in a continuous reactor. A series of catalytic materials were synthesised and characterised by BET, XPS, SEM, TEM, XRD and NH3-TPD methods. Catalytic activity tests (product selectivity and conversion of reactants) were performed for all materials and optimal reaction conditions (temperature and feedstock flow rates) were found. The results indicate that the highest yield of isopropyl chloride was obtained over 5 wt.% ZnCl2 on commercial Al2O3 (No. II) (95.3%). Determination of product mixture compositions and by-product identification were done using a GC-MS method. Carbon foam variant catalyst, 5 wt.% ZnCl2/C, was found to perform best out of the carbon-supported materials, achieving ∼75% yield of isopropyl chloride. The kinetic model describing the process in a continuous packed bed reactor was proposed and kinetic parameters were calculated. The activation energy for the formation of isopropyl chloride reaction directly from isopropanol and HCl was found to be ∼58 kJ/mol.
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9.
  • Duan, Ran, et al. (författare)
  • Fibre Stress-Strain Response of High-Temperature Chemi-Thermomechanical Pulp Treated with Switchable Ionic Liquids
  • 2016
  • Ingår i: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 11:4, s. 8570-8588
  • Tidskriftsartikel (refereegranskat)abstract
    • The removal of lignin from a high-temperature chemi-thermomechanical pulp (HT-CTMP) using a switchable ionic liquid prepared from an organic superbase (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)), monoethanol amine (MEA), and SO2 was investigated. The objective was to measure the fibre properties before and after removal of the lignin to analyse the contributions from lignin in the HT-CTMP fibre to the tensile properties. It was found that the fibre displacement at break - measured in zero span, which is related to fibre strain at break - was not influenced by the lignin removal in this ionic liquid system when tested dry. There was a small increase in displacement at break and a reduction in tensile strength at zero span when tested after rewetting. At short span, the displacement at break decreased slightly when lignin was removed, while tensile strength was almost unaffected when tested dry. Under rewetted conditions, the displacement at break increased and tensile strength decreased after lignin removal. Nevertheless, no dramatic differences in the pulp properties could be observed. Under the experimental conditions, treatment with the ionic liquid reduced the lignin content from 37.4 to 15.5 wt%.
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10.
  • Golets, Mikhail, 1987-, et al. (författare)
  • A kinetic study of the liquid phase acetoxylation of α-pinene
  • 2012
  • Ingår i: Topics in catalysis. - : Springer. - 1022-5528 .- 1572-9028. ; 55:7-10, s. 649-656
  • Tidskriftsartikel (refereegranskat)abstract
    • The present study introduces kinetic modeling of liquid phase α-pinene acetoxylation with acetic acid over an ion-exchange resin catalyst. The reaction was carried out in a laboratory scale high-pressure autoclave. α-terpinyl (35 wt%) and bornyl (40 wt%) acetates were the primary products. The predominant reaction pathways were identified and evaluated.
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