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1.
  • Dahlin, Sandra, et al. (författare)
  • Effect of biofuel- and lube oil-originated sulfur and phosphorus on the performance of Cu-SSZ-13 and V2O5-WO3/TiO2 SCR catalysts
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier B.V.. - 0920-5861 .- 1873-4308. ; 360, s. 326-339
  • Tidskriftsartikel (refereegranskat)abstract
    • Two different SCR catalysts, V2O5-WO3/TiO2 and Cu-SSZ-13, were exposed to biodiesel exhausts generated by a diesel burner. The effect of phosphorus and sulfur on the SCR performance of these catalysts was investigated by doping the fuel with P-, S-, or P + S-containing compounds. Elemental analyses showed that both catalysts captured phosphorus while only Cu-SSZ-13 captured sulfur. High molar P/V ratios, up to almost 3, were observed for V2O5-WO3/TiO2, while the highest P/Cu ratios observed were slightly above 1 for the Cu-SSZ-13 catalyst. Although the V2O5-WO3/TiO2 catalyst captured more P than did the Cu-SSZ-13 catalyst, a higher degree of deactivation was observed for the latter, especially at low temperatures. For both catalysts, phosphorus exposure resulted in suppression of the SCR performance over the entire temperature range. Sulfur exposure, on the other hand, resulted in deactivation of the Cu-SSZ-13 catalyst mainly at temperatures below 300-350 °C. The use of an oxidation catalyst upstream of the SCR catalyst during the exhaust-exposure protects the SCR catalyst from phosphorus poisoning by capturing phosphorus. The results in this work will improve the understanding of chemical deactivation of SCR catalysts and aid in developing durable aftertreatment systems. 
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2.
  • Eriksson, Gunnar, et al. (författare)
  • Combustion and fuel characterisation of wheat distillers dried grain with solubles (DDGS) and possible combustion applications
  • 2012
  • Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 102, s. 208-220
  • Tidskriftsartikel (refereegranskat)abstract
    • The present transition to a sustainable global energy system requires that biomass is increasingly combusted for heat and power production. Agricultural fuels considered include alkali-rich fuels with high phosphorus content. One such fuel is wheat distiller’s dried grain with solubles (wheat DDGS) from wheat-based ethanol production. Further increases in ethanol production may saturate the current market for wheat DDGS as livestock feed, and fuel uses are therefore considered. Fuel properties of wheat DDGS have been determined. The ash content (5.4 ± 1.6 %wt d.s.) is similar to many agricultural fuels. In comparison to most other biomass fuels the sulphur content is high (0.538 ± 0.232 %wt d.s.), and so are the contents of nitrogen (5.1 ± 0.6 %wt d.s.), phosphorus (0.960. ± 0.073 %wt d.s.) and potassium (1.30 ± 0.35 %wt d.s.). To determine fuel-specific combustion properties, wheat DDGS and mixes between wheat DDGS and logging residues (LR 60 %wt d.s. and DDGS 40 %wt d.s.), and wheat straw (wheat straw 50 %wt d.s., DDGS 50 %wt d.s.) were pelletized and combusted in a bubbling fluidised bed combustor (5 kW) and in a pellets burner combustor (20 kW). Pure wheat DDGS powder was also combusted in a powder burner (150 kW). Wheat DDGS had a high bed agglomeration and slagging tendency compared to other biomass fuels, although these tendencies were significantly lower for the mixture with the Ca-rich LR, probably reflecting the higher first melting temperatures of K–Ca/Mg-phosphates compared to K-phosphates. Combustion and co-combustion of wheat DDGS resulted in relatively large emissions of fine particles (<1 μm) for all combustion appliances. For powder combustion PMtot was sixteen times higher than from softwood stem wood. While the Cl concentrations of the fine particles from the the mixture of LR and wheat DDGS in fluidised bed combustion were lower than from combustion of pure LR, the Cl- and P-concentrations were considerably higher from the wheat DDGS mixtures combusted in the other appliances at higher fuel particle temperature. The particles from powder combustion of wheat DDGS contained mainly K, P, Cl, Na and S, and as KPO3 (i.e. the main phase identified with XRD) is known to have a low melting temperature, this suggests that powder combustion of wheat DDGS should be used with caution. The high slagging and bed agglomeration tendency of wheat DDGS, and the high emissions of fine particles rich in K, P and Cl from combustion at high temperature, mean that it is best used mixed with other fuels, preferably with high Ca and Mg contents, and in equipment where fuel particle temperatures during combustion are moderate, i.e. fluidised beds and possibly grate combustors rather than powder combustors.
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3.
  • Ge, Yaxin, et al. (författare)
  • Effects of used bed materials on char gasification : Investigating the role of element migration using online alkali measurements
  • 2022
  • Ingår i: Fuel processing technology. - : Elsevier. - 0378-3820 .- 1873-7188. ; 238
  • Tidskriftsartikel (refereegranskat)abstract
    • Online alkali measurements using surface ionization are employed to study alkali release during heating of used industrial fluidized bed materials and gasification of biomass-based char and bed material mixtures. The alkali release from the bed materials starts at 820 °C and increases with temperature, the time a bed material has experienced in an industrial process, and in the presence of CO2. Online alkali measurement during heating of char mixed with used bed material shows significant alkali uptake by the char. Complementary SEM-EDS studies confirm the alkali results and indicate that other important inorganic elements including Si, Mg, and Ca also migrate from the bed material to the char. The migration of elements initially enhances alkali release and char reactivity, but significantly reduces both during the final stage of the gasification. The observed effects on char gasification become more pronounced with increasing amount of bed material and increasing time the material experienced in an industrial process. The ash-layer on the used bed material is concluded to play an important role as a carrier of alkali and other active components. The char and bed material systems are closely connected under operational conditions, and their material exchange has important implications for the thermal conversion.
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6.
  • Yu, Xiaowen, et al. (författare)
  • Hydrogen Evolution Linked to Selective Oxidation of Glycerol over CoMoO4—A Theoretically Predicted Catalyst
  • 2022
  • Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 12:14
  • Tidskriftsartikel (refereegranskat)abstract
    • Electrochemical valorization of biomass waste (e.g., glycerol) for production of value-added products (such as formic acid) in parallel with hydrogen production holds great potential for developing renewable and clean energy sources. Here, a synergistic effort between theoretical calculations at the atomic level and experiments to predict and validate a promising oxide catalyst for the glycerol oxidation reaction (GOR) are reported, providing a good example of designing novel, cost-effective, and highly efficient electrocatalysts for producing value-added products at the anode and high-purity hydrogen at the cathode. The predicted CoMoO4 catalyst is experimentally validated as a suitable catalyst for GOR and found to perform best among the investigated metal (Mn, Co, Ni) molybdate counterparts. The potential required to reach 10 mA cm−2 is 1.105 V at 60 °C in an electrolyte of 1.0 ᴍ KOH with 0.1 ᴍ glycerol, which is 314 mV lower than for oxygen evolution. The GOR reaction pathway and mechanism based on this CoMoO4 catalyst are revealed by high-performance liquid chromatography and in situ Raman analysis. The coupled quantitative analysis indicates that the CoMoO4 catalyst is highly active toward C—C cleavage, thus presenting a high selectivity (92%) and Faradaic efficiency (90%) for formate production. 
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7.
  • Zacharias, Savannah C., et al. (författare)
  • Exploring Supramolecular Gels in Flow-Type Chemistry-Design and Preparation of Stationary Phases
  • 2021
  • Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 60:28, s. 10056-10063
  • Tidskriftsartikel (refereegranskat)abstract
    • Two major challenges facing chemical synthesis are product isolation and catalyst recovery. One method to overcome these challenges is to perform the synthesis in a flow system with a catalytic stationary phase. However, the polymeric catalytic materials used in flow systems are often laborious to produce. In this study, we investigate a novel supramolecular gel as a catalytic stationary phase material. The gel is based on a modular, easy to synthesize, oxotriphenylhexanoate (OTHO) gelator comprised of a catalytic unit designed to catalyze the Knoevenagel reaction. The catalytic organogel enhances the rate of product formation and can be reused five times. Use of the OTHO to construct catalytic gels is a flexible technique that can be utilized to improve product isolation and reduce wastage of the catalyst.
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8.
  • Bauhn, Lovisa, 1981, et al. (författare)
  • The fate of hydroxyl radicals produced during H2O2 decomposition on a SIMFUEL surface in the presence of dissolved hydrogen
  • 2018
  • Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 507, s. 38-43
  • Tidskriftsartikel (refereegranskat)abstract
    • Over geologic timescales hydrogen peroxide will be one of the most important radiolytic oxidants challenging the spent fuel integrity in a deep repository. Consequently, the reaction between hydrogen peroxide and different kinds of UO 2 based materials has been the subject of several studies over recent decades. Parts of these studies have investigated the effect of dissolved hydrogen on this reaction, as large amounts of hydrogen are expected to be produced by anoxic corrosion of iron in the deep repositories. In some of the studies hydrogen has been shown to offset the radiolysis-driven oxidative dissolution of the fuel despite the expected inertia of hydrogen at repository temperatures. However, the underlying mechanism is primarily based on the effect of the metallic particles contained in the spent fuel. One clue to the mechanistic understanding is whether or not a reaction takes place between dissolved hydrogen and hydroxyl radicals adsorbed to a fuel surface resulting from the decomposition of H 2 O 2 . In the study presented here this reaction could be confirmed in an autoclave system with SIMFUEL, a hydrogen peroxide spiked solution, and deuterium gas. The results show that the studied reaction does not only occur, but accounts for a substantial part of the hydrogen peroxide consumption in the system. Only a very minor part, 0.02%, of the total consumed hydrogen peroxide caused oxidative dissolution of the SIMFUEL. The conclusion is supported by quantitative measurements of HDO, dissolved U in solution and O 2 in the gas phase.
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9.
  • Corcoran, Angelica, 1988, et al. (författare)
  • Comparing the structural development of sand and rock ilmenite during long-term exposure in a biomass fired 12 MWth CFB-boiler
  • 2018
  • Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 171, s. 39-44
  • Tidskriftsartikel (refereegranskat)abstract
    • Oxygen Carrier Aided Combustion (OCAC) is a novel combustion concept with the purpose to increase the overall efficiency in conventional circulating fluidized bed (CFB) boilers. By replacing the commonly used bed material with an oxygen carrier (OC), the conceptual idea is to utilize the fluid dynamics in a CFB and the inherent oxygen transport supported by the OC to increase the oxygen distribution within the furnace in time and space. The OCAC concept has been successfully validated and further reached long-term demonstration in full scale operation (75-MW th ). This work presents a first evaluation of how ilmenite particles are affected in regard to mechanical resistance during long-term exposure to OCAC conditions in Chalmers 12-MW th CFB-boiler. A sand and a rock ilmenite are evaluated with regard to their mechanical stability. For evaluation, samples of the fresh materials and samples collected during operation in the Chalmers boiler are investigated. The study shows that the two materials differ in how the mechanical degradation occurs with exposure time. The sand ilmenite form cavities which are held together by an ash layer before they are shattered into numerous pieces, whereas the rock ilmenite develops distinct cracks that cause splitting of the particles.
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10.
  • Jogi, Ramakrishna, et al. (författare)
  • Understanding the formation of phenolic monomers during fractionation of birch wood under supercritical ethanol over iron based catalysts
  • 2020
  • Ingår i: Journal of the Energy Institute. - : Elsevier. - 1743-9671 .- 1746-0220. ; 93:5, s. 2055-2062
  • Tidskriftsartikel (refereegranskat)abstract
    • The liquefaction of biomass in ethanol, at the critical point, has high potential due to low temperature and pressure (243 °C, 63 bar) when compared with water (374 °C, 220 bar). The current study deals with the fractionation of birch wood powder which was liquefied under supercritical ethanol over acidic or non-acidic catalysts, 5 wt % Fe-Beta-H-150 and 5 wt % Fe–SiO2, respectively. Based on the results, the reaction mechanism for the formation of lignin degradation products was proposed. The main phenolic product was isoeugenol over 5 wt % Fe-Beta-H-150 while intermediate products, i.e. such as coniferyl, and sinapyl alcohol, 4-propenyl syringol, syringaresinol, as well as syringyldehyde reacted rapidly further. The thermodynamic analysis was performed by Joback approach and using Gibbs-Helmholtz equation supporting the obtained results.
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11.
  • Maric, Jelena, 1983, et al. (författare)
  • Valorization of Automobile Shredder Residue Using Indirect Gasification
  • 2018
  • Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:12, s. 12795-12804
  • Tidskriftsartikel (refereegranskat)abstract
    • Dual fluidized bed (DFB) gasification offers the possibility to convert solid fuels into a valuable gas, comprised of syngas, and hydrocarbons that can be readily handled in petrochemical units. DFB gasifiers are especially suitable for nonhomogeneous fuels, such as waste fractions. In this work, the possibility to use DFB gasification as a recycling/valorization method of automobile shredder residue is investigated. The gasification tests were carried out in the Chalmers 2–4 MWth gasifier over 4 days. The effects of ash on the gas and tar compositions, as well as on the activity of the bed inventory, were evaluated. The results show that 60% of the total carbon in the fuel can be recovered in the form of a permanent gas, whereby the produced gas contains 12%mol of C2–3 hydrocarbons. The tar levels measured in the produced gas were high, although it was clear that decomposition into monomer-like compounds occurred in the reactor, which resulted in the production of valuable petrochemical compounds, corresponding to 8–9% of the carbon in the feed. Using a higher operating temperature was found to be beneficial in terms of obtaining a higher gas yield, regardless of the level of ash enrichment in the system. The high ash levels in the fuel feed did not negatively affect the technical operation of the fluidized bed. Possible routes of carbon recovery are discussed.
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12.
  • Mukesh, Chandrakant, et al. (författare)
  • Production of C-14 Levulinate Ester from Glucose Fermentation Liquors Catalyzed by Acidic Ionic Liquids in a Solvent-Free Self-Biphasic System
  • 2020
  • Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:10, s. 4828-4835
  • Tidskriftsartikel (refereegranskat)abstract
    • Herein, we present the C-14 levulinate ester of 2,3-butanediol as the product of sugar fermentation liquors. The designed Brønsted acidic ionic liquid (BAIL) catalysts enable self-induced phase separation with ester products, and the role of anions has been investigated. Esterification reactions were carried out by 2,3-butanediol (2,3-BDO) and levulinic acid in solvent-free media and low temperatures (60–105 °C). For comparison, sulfuric acid, amberlite IR-120, and sulfonic acid-functionalized pyridinium ionic liquids with different anions were utilized as a catalyst upon esterification reaction. The diester product, namely, butane-2,3-diyl bis(4-oxopentanoate), was formed with a good yield (85%) and selectivity (85%) after complete conversion of 2,3-BDO in 24 h at 80 °C. The low yield (8%) of the monoester was observed. The monoester and diester were separated by a liquid–liquid extraction method. The ester products were characterized by various instrumental techniques such as 1H and 13C NMR, GC–FID, LC–MS, and FT-IR spectroscopy. The Hammett acidity functions of BAILs were determined from UV–vis spectroscopy. The catalyst was successfully recycled and reused in the processes. The spent BAILs were reused in six consecutive cycles with only a ∼7% diminished diester yield and selectivity. The produced levulinate ester will be useful as biofuel additives, solvents, plasticizers, and other applications.
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13.
  • Wang, Kai, et al. (författare)
  • A one-carbon chemicals conversion strategy to produce precursor of biofuels with Saccharomyces cerevisiae
  • 2023
  • Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 208, s. 331-340
  • Tidskriftsartikel (refereegranskat)abstract
    • Utilization of one-carbon chemicals such as CO2, formate, and methanol by microorganisms can enable the sustainable production of fuels and chemicals. However, the low conversion efficiency of these chemicals by microorganisms is a major challenge. To address this, we designed a one-carbon strategy that can utilize CO2 and its derivative formate. Here, a platform yeast strain with improved formate utilization and NAD(P)H production was constructed and evaluated for its ability to produce free fatty acids (FFAs). Based on 13C-marked analysis, the one-carbon assimilation efficiency of the platform strain reached 11.24%. Through continuous optimization, under conditions of glucose feeding the formate utilization rate of the final strain reached 0.48 g/L/h, with the final titer of FFAs reached 10.1 g/L, which represented improvements of 21.8 times and 33.7 times, respectively. As such, the produced FFAs can be easily transformed into biodiesel by combining them with downstream technologies in future research.
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14.
  • Yahia, Mohamed, et al. (författare)
  • Effect of incorporating different ZIF-8 crystal sizes in the polymer of intrinsic microporosity, PIM-1, for CO2/CH4 separation
  • 2021
  • Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 312
  • Tidskriftsartikel (refereegranskat)abstract
    • Effective and economical carbon dioxide-methane separation (CO2/CH4) is highly desirable in several industries such as sweetening natural gases and renewable natural gas (RNG) from biogas and landfills. Among the different separation technologies, membrane separation has been shown to have lower cost of production and lower CH4 losses. In this study, Zeolitic Imidazole Frameworks (ZIF-8) crystals with sizes varying from 45 nm to 450 nm were synthesized and incorporated in the polymer of intrinsic microporosity, PIM-1, to form mixed matrix membranes (MMMs). The structure, morphology, and physicochemical properties of the MMMs were characterized by 1H NMR, FTIR, XRD, TGA, and SEM. ZIF-8 crystal size was controlled using the concentration of sodium formate. The influence of the ZIF-8 crystal size on MMMs was studied by sorption, gas permeability, and aging of the membranes. The MMMs with ZIF-8 crystals of 120 nm particle diameter yielded the greatest improvement in gas transport properties; the CO2/CH4 selectivity-CO2 permeability was 11.4 and 9700 Barrer compared to PIM-1 with 6.4 and 9300 Barrer respectively. The former is near the Robeson 2008 upper bound, while PIM-1 is on the 1991 upper bound. After 40 days of aging, selectivity increased and permeability decreased; the changes were parallel to the Robeson upper bounds indicating increased polymer packing and diffusivity selectivity.
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15.
  • Balachandran, Srija, et al. (författare)
  • Comparative study for selective lithium recovery via chemical transformations during incineration and dynamic pyrolysis of EV li-ion batteries
  • 2021
  • Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 11:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective leaching of Li from spent LIBs thermally pretreated by pyrolysis and incineration between 400 and 700 °C for 30, 60, and 90 min followed by water leaching at high temperature and high L/S ratio was examined. During the thermal pretreatment Li2CO3 and LiF were leached. Along with Li salts, AlF3 was also found to be leached with an efficiency not higher than 3.5%. The time of thermal pretreatment did not have a significant effect on Li leaching efficiency. The leaching efficiency of Li was higher with a higher L/S ratio. At a higher leaching temperature (80 °C), the leaching of Li was higher due to an increase in the solubility of present Li salts. The highest Li leaching efficiency of nearly 60% was observed from the sample pyrolyzed at 700 °C for 60 min under the leaching condition L/S ratio of 20:1 mL g−1 at 80 °C for 3 h. Furthermore, the use of an excess of 10% of carbon in a form of graphite during the thermal treatment did not improve the leaching efficiency of Li.
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16.
  • Bylin, Susanne, 1982 (författare)
  • Mechanisms of Biopolymer Solvation: Development of a two-component ionic liquid solvent system
  • 2014
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Ionic liquids are of potential interest in the processing of lignocellulosic biomass, and/or its components, for the purpose of producing renewable and value-added biomaterials. An understanding of how solvation can be achieved and the way in which the feedstock biopolymers are affected, however, needs to be gained prior to a viable implementation. In this thesis, the solvation of the wood biopolymers cellulose, xylan and lignin in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate (EMIMAc) in a novel combination with the second system component 1-methylimidazole (MIM) have been investigated:The solvation of dissolving pulp, beech xylan and LignoBoost lignin model materials, was studied using FBRM (focused beam reflectance measurements) particle characterization in combination with microscopic analysis (cellulose and xylan), determination of molecular weights (xylan and lignin) and 13C- and 31P-NMR (nuclear magnetic resonance spectroscopy) of lignin.It was concluded that the most efficient solvation of cellulose and xylan occurred using 3-4% and 9% IL (n/n anhydroglucose units and n/n anhydroxylose Units), respectively, while polymer integrity was maintained. Cellulose solvation was found to be greatly dependent on the IL to AGU ratio whereas xylan solvation varied greatly with temperature. Moreover, a theoretical model was developed for the solvation of cellulose in the present system. The solvation of lignin was achieved at ~20% lignin loading (w/w), in any combination of MIM/EMIMAc. Regeneration of lignin resulted in two sets of fractions; one exhibiting a general and higher apparent molecular weight (Mw) along with an enrichment of condensed/aliphatic ether linkages and aliphatic hydroxyls, and the other exhibiting a lower apparent Mw and an enrichment of carboxylic and phenolic groups. The knowledge of biopolymer solvation gained in the present solvent system provides future opportunities of tuning extraction and/or fractionation processes to suite the specifications of a particular biomass-derived product.
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17.
  • Palme, Anna, 1986, et al. (författare)
  • Development of an efficient route for combined recycling of PET and cotton from mixed fabrics
  • 2017
  • Ingår i: Textiles and Clothing Sustainability. - : Springer Science and Business Media LLC. - 2197-9936. ; 3:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Most textile waste is either incinerated or landfilled today, yet, the material could instead be recycled through chemical recycling to new high-quality textiles. A first important step is separation since chemical recycling of textiles requires pure streams. The focus of this paper is on the separation of cotton and PET (poly(ethylene terephthalate), polyester) from mixed textiles, so called polycotton. Polycotton is one of the most common materials in service textiles used in sheets and towels at hospitals and hotels. A straightforward process using 5–15 wt% NaOH in water and temperature in the range between 70 and 90 °C for the hydrolysis of PET was evaluated on the lab-scale. In the process, the PET was degraded to terephthalic acid (TPA) and ethylene glycol (EG). Three product streams were generated from the process. First is the cotton; second, the TPA; and, third, the filtrate containing EG and the process chemicals. The end products and the extent of PET degradation were characterized using light microscopy, UV-spectroscopy, and ATR FT-IR spectroscopy, as well as solution and solid-state NMR spectroscopy. Furthermore, the cotton cellulose degradation was evaluated by analyzing the intrinsic viscosity of the cotton cellulose. The findings show that with the addition of a phase transfer catalyst (benzyltributylammonium chloride (BTBAC)), PET hydrolysis in 10% NaOH solution at 90 °C can be completed within 40 min. Analysis of the degraded PET with NMR spectroscopy showed that no contaminants remained in the recovered TPA, and that the filtrate mainly contained EG and BTBAC (when added). The yield of the cotton cellulose was high, up to 97%, depending on how long the samples were treated. The findings also showed that the separation can be performed without the phase transfer catalyst; however, this requires longer treatment times, which results in more cellulose degradation.
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19.
  • Achour, Abdenour, 1980, et al. (författare)
  • Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM
  • 2023
  • Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective transformation of BHMF (2,5-bis(hydroxymethyl)furan) to THFDM (tetrahydrofuran-2,5-dimethanol) over a variety of structured Ni/Sx-Z1−x catalysts was investigated. The effects of support, Ni loading, solvent, temperature, pressure, and particle size on the conversion and selectivity were studied. Among them, the 10 wt% Ni catalyst supported on the SiO2:ZrO2 weight ratio of 90:10 (10NiS90Z10) exhibits the best performance in terms of BHMF conversion and THFDM selectivity. Its good performance was attributed to its well-balanced properties, that depend upon the ZrO2 content of the support in combination with SiO2, the active Ni sites-support interaction, and acidity/basicity ratio of each catalyst resulting in different Ni dispersions. Importantly, the 10NiS90Z10 catalyst showed a stable selectivity to THFDM (>94%), with 99.4% conversion of BHMF during 2 h reaction time. Poor catalytic activity resulted from excessive ZrO2 content (>10 wt%). The structural, textural, and acidity properties of NiSi100−y-Zry catalysts, tuned by selectively varying the Ni amount from 5 to 15 wt%, were critically investigated using numerous material characterization techniques. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any measurable loss of catalytic activity.
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20.
  • Adanez-Rubio, Inaki, et al. (författare)
  • Cu-Mn oxygen carrier with improved mechanical resistance: Analyzing performance under CLC and CLOU environments
  • 2021
  • Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 217
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical Looping Combustion process allows combustion of gaseous, liquid or solid fuels with CO capture. The oxygen necessary for combustion can be supplied using lattice oxygen (CLC) or oxygen uncoupling (CLOU) mechanisms. The present work studies the effects of kaolin addition on Cu–Mn oxygen carrier behavior for CLC and CLOU processes. Cu–Mn oxygen carrier was prepared by granulation with a composition: 27.2 wt% CuO, 52.8 wt% Mn O and 20 wt% kaolin. Oxygen release rates and fluidization behavior were analyzed by TGA and batch fluidized bed reactor. The oxygen carrier was studied for CH and synthetic biogas combustion in a 500 W CLC continuous unit for 50 h of combustion at temperatures up to 930 °C. No agglomeration problems were observed. Results found during biogas combustion were similar to methane combustion. The addition of 20 wt% kaolin changed the mixed oxide chemical composition generating Cu Mn O and improved significantly the oxygen carrier mechanical resistance, increasing the extrapolated lifetime to 19,000 h, 3.6 times over the value found for any Cu based oxygen carrier in CLC. However, the oxygen carrier reactivity had an important decrease with respect to a similar oxygen carrier without kaolin addition, whose fraction in oxygen carrier must be optimized. 2 3 4 4 th 1.2 1.8 4
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21.
  • Adanez-Rubio, Inaki, et al. (författare)
  • Development of new Mn-based oxygen carriers using MgO and SiO 2 as supports for Chemical Looping with Oxygen Uncoupling (CLOU)
  • 2023
  • Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 337
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical Looping with Oxygen Uncoupling (CLOU) is a technological adaptation of CLC, most applicable for the combustion of solid fuels. In the CLOU process, an oxygen carrier in the fuel reactor, avoiding the direct contact of the fuel with the air, releases the oxygen needed for the fuel combustion. The oxygen carrier is regenerated with air in the interconnected air reactor. The present work explores the behavior of the system Mn/Mg/Si as oxygen carriers for chemical-looping with oxygen uncoupling (CLOU). Six different mixed oxides of the system Mn/Mg/Si were investigated for the CLC/CLOU process. Materials were prepared by spray drying with different metal ratios used in the investigation. The properties of interest for the viability of these materials are the lattice oxygen supply for CLC and the gaseous oxygen release for CLOU, properties that were explored in a TGA. Further, the fluidization behavior and the mechanical resistance were investigated in a batch fluidized bed reactor. In the TGA it was observed that the most reactive oxygen carriers for the CLOU process were materials without Si in the structure, more specifically M24Mg76 and M48Mg51 which had a molar ratio of Mn/Mg of 0.17 and 0.51 respectively. It was also observed that for the oxygen carriers with Si in the composition, the regeneration was very poor. Oxygen carriers M24Mg76 and M48Mg51 were selected for batch fluidized bed reactor testing showing good behavior with respect to the CLOU reactivity, and mechanical stability. One of the materials, the M24Mg76 showed activation during the experiments in the batch fluidized bed reactor experiments, increasing the oxygen transport capacity by 20 % during the experiment. However, 10 vol% of O2 was needed to regenerate both oxygen carriers at 850 °C. No agglomeration tendencies were seen, and the attrition rate was low, obtaining high-extrapolated lifetime values. The fact that highly reactive oxygen carriers can be made with cheap and highly available metals oxides, i.e. Mn and Mg, makes this system very promising and a possible alternative to benchmark Cu-based CLOU materials.
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22.
  • Ahlbom, Anders, 1993 (författare)
  • Hydrothermal Liquefaction of Kraft Lignin - The influence of capping agents and residence time
  • 2021
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In the context of exploring alternatives to replace fossil resources, lignin has been acknowledged as a renewable source of various aromatic compounds that have the potential of being precursors to chemicals as well as fuel additives. Originating from lignocellulosic biomass such as wood, lignin is an amorphous polymer with a high content of aromatic units and, in order to harness these units, it must be depolymerised. A major problem with current depolymerisation techniques, however, is that lignin repolymerises after being depolymerised, and forms an undesirable char fraction. The addition of capping agents and fine-tuning the reaction conditions can be used to mitigate such formation of char. This work has investigated the depolymerisation of kraft lignin in hydrothermal conditions under varying temperatures (290-335 °C), residence times (1-12 min) and charges of isopropanol (IPA/dry lignin, 0-4.9) which, aside from being a co-solvent, was hypothesised as acting as a capping agent. The influence of these reaction parameters on the molecular weights, yields and elemental compositions of the products was studied, along with changes in the molecular structure compared to the starting lignin. The product is a suspension of solid material, i.e. char, in an aqueous phase and thus any desired organic liquid phase requires extraction from the aqueous product. While the yield of char increased with temperature and residence time, it decreased with increasing isopropanol loading, suggesting that the isopropanol does in fact act as a capping agent. Most of the lignin forms a water-soluble fraction that precipitates when the aqueous product phase is acidified, thereby forming the precipitated solids fraction (PS). The components remaining dissolved after acidification of the product phase are known as acid soluble organics (ASO). A portion of the ASO fraction was aromatic monomers, with guaiacol dominating: this result was expected since the lignin was sourced from softwood. The amount of such monomers increased with residence time in the reactor. Molecular weight analyses showed a rapid depolymerisation of the lignin within 1 min of hydrothermal liquefaction (HTL) treatment via a significant decrease in the molecular weight of all product fractions: char, PS and ASO. Moreover, the carbon-oxygen inter-unit linkages were found to break in this timeframe as well. The repolymerisation reactions started to exceed depolymerisation between residence times of 4 and 12 min, causing the weight average molecular weight (Mw) to increase again. Although minimising the residence time allows the char yield and Mw to be kept low, more monomers were formed at longer residence times. This calls for careful tuning of the residence time in the HTL of kraft lignin.
  •  
23.
  • Andersson, Viktor, 1983, et al. (författare)
  • Alkali interactions with a calcium manganite oxygen carrier used in chemical looping combustion
  • 2022
  • Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 227
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical-Looping Combustion (CLC) of biofuels is a promising technology for cost-efficient CO2 separation and can lead to negative CO2 emissions when combined with carbon capture and storage. A potential challenge in developing CLC technology is the effects of alkali metal-containing compounds released during fuel conversion. This study investigates the interactions between alkali and an oxygen carrier (OC), CaMn0.775Ti0.125Mg0.1O3-δ, to better understand the fate of alkali in CLC. A laboratory-scale fluidized bed reactor is operated at 800–900 °C in oxidizing, reducing and inert atmospheres to mimic CLC conditions. Alkali is fed to the reactor as aerosol KCl particles, and alkali in the exhaust is measured online with a surface ionization detector. The alkali concentration changes with gas environment, temperature, and alkali loading, and the concentration profile has excellent reproducibility over repeated redox cycles. Alkali-OC interactions are dominated by alkali uptake under most conditions, except for a release during OC reduction. Uptake is significant during stable reducing conditions, and is limited under oxidizing conditions. The total uptake during a redox cycle is favored by a high alkali loading, while the influence of temperature is weak. The implications for the understanding of alkali behavior in CLC and further development are discussed.
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24.
  • Andersson, Viktor, 1983, et al. (författare)
  • Gaseous alkali interactions with ilmenite, manganese oxide and calcium manganite under chemical looping combustion conditions
  • 2024
  • Ingår i: Fuel Processing Technology. - 0378-3820 .- 1873-7188. ; 254
  • Tidskriftsartikel (refereegranskat)abstract
    • Alkali species present in biomass pose significant challenges in chemical looping combustion (CLC) processes and other thermal conversion applications. The interactions between different alkali species and three common oxygen carrier (OC) materials that are considered to be state of the art in CLC applications have been investigated. A dedicated fluidized bed laboratory reactor was used to study interactions of KCl, NaCl, KOH, NaOH, K2SO4 and Na2SO4 with manganese oxide, calcium manganite and ilmenite. Alkali vapor was generated by injecting alkali salts under reducing, oxidizing and inert conditions at 900 °C. Gaseous species were measured online downstream of the reactor, and the efficiency of alkali uptake was determined under different conditions. The result show significant alkali uptake by all OCs under the studied conditions. Ilmenite shows near complete alkali uptake in reducing conditions, while manganese oxide and calcium manganite exhibited less effective alkali uptake, but have advantages in terms of fuel conversion and oxidizing efficiency. Alkali chlorides, sulfates and hydroxides show distinctly different behavior, with alkali hydroxides being efficiently captured all three investigate OC materials. The findings contribute to a deeper understanding of alkali behavior and offer valuable guidance for the design and optimization of CLC with biomass.
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25.
  • Arora, Prakhar, 1987 (författare)
  • Catalytic Upgrading of Waste Oils to Advanced Biofuels – Deactivation and Kinetic Modelling Study
  • 2018
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The demand for liquid hydrocarbons as transportation fuels is enormous and ever growing. Advanced biofuels is one of the promising solutions to keep pace with the global transition to cleaner energy by reducing greenhouse gas emissions from the transport sector. It is possible to selectively remove oxygen from waste oils like tall oil, used cooking oil etc. via a catalytic hydrodeoxygenation (HDO) process to produce advanced biofuels. These biofuels have similar molecules as in the traditional fossil-based fuels and exhibit improved performance. This thesis focuses on aspects of catalyst deactivation and kinetic modelling of HDO reactions.   In the first study, the influence of iron (Fe) as a poison during HDO of a model compound for renewable feeds (Oleic acid) over molybdenum based sulfided catalysts was investigated. Fe is a potential contaminant in renewable feeds due to corrosion during transportation and storage in iron vessels. A series of experiments with varying Fe-oleate concentration in the feed over MoS2/Al2O3 and NiMoS/Al2O3 catalysts. There was a salient drop in the activity of the catalysts. At higher Fe concentration, for the NiMoS catalyst, the selectivity for the direct hydrodeoxygenation product (C18 hydrocarbons) increased. However, it was opposite for the MoS2 catalyst. There was a decrease in the yield of direct hydrodeoxygenation products and an increase in yield of decarbonated products. It was proposed that Fe interacted with these two catalyst systems differently. Fe influenced the critical step of creation of sulfur vacancies in a negative way which resulted in lower activity. Microscopic analysis indicated that Fe was preferentially deposited close or around the nickel promoted phase, which explained why the role of Ni as a promoter for the decarbonation route was subdued for the NiMoS catalyst.   In the second study, the kinetics during HDO of stearic acid (SA) over a sulfided NiMo/Al2O3 catalyst were explored to investigate the reaction scheme. Model compounds like octadecanal (C18=O) and octadecanol (C18-OH) were employed to understand the reaction steps and quantify the selectivity. A Langmuir–Hinshelwood-type kinetic model was used to investigate the kinetics. The results from the proposed kinetic model were found to be in good agreement with experimental results. In addition, the model could effectively reproduce the observed experimental profiles of different intermediates like C18=O and C18-OH and illustrate phenomena like inhibiting effects of the fatty acid.
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26.
  • Arora, Prakhar, 1987 (författare)
  • Deactivation of Catalysts and Reaction Kinetics for Upgrading of Renewable Oils
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The transport sector is one of the main contributors of greenhouse gas emissions in the world. Advanced biofuels from renewable oils can play a decisive role in reducing carbon emissions from the transport sector. Advanced biofuels from waste streams like tall oil, used cooking oil etc. can lower the CO2 emissions in a range of up to 90% making our future and society more sustainable. Catalytic hydrodeoxygenation (HDO) is a process in which oxygen is selectively removed from renewable oils to produce advanced biofuels. These biofuels are drop-in hydrocarbons which can substitute fossil-based fuels without infrastructure or vehicle changes. This thesis focuses on aspects of catalyst deactivation and reaction kinetics during the production of such biofuels via HDO reactions. Renewable oils can be sourced from varied streams like tall oil (paper industry residue), animal fats, used cooking oil etc. due to which their composition and innate contaminants can vary significantly. Phosphorus, alkali metals like potassium or sodium, iron, silicon, chlorides etc. are some of the common poisons present in renewable feedstocks which can cause catalyst deactivation during the upgrading process. In the first section of this thesis, the influence of iron (Fe), phosphorus (from phospholipid) and potassium (K) as poisons during HDO of fatty acids over molybdenum based sulfided catalysts was investigated. A range of concentration of poisons was evaluated to show that these poisons severely impacted the activity of catalysts. A change in selectivity was also seen, which is an important parameter to consider during the industrial production of biofuels. Different characterization techniques were employed to study the poison distribution on catalyst samples from lab experiments as well as from a refinery. It was suggested that Fe deposits preferentially near Ni-rich sites which deteriorated the ability of these catalysts to create active sites i.e. via sulfur vacancies. However, phosphorus resulted in irreversible phase transformation of the support to aluminum phosphate (AlPO4) which resulted in catalyst deactivation via pore blockage. In the comparative experiments, with spherical catalyst particles (1.8 mm), the Fe caused the strongest deactivation among P and K, based on the quantity added to feed oil. Although, considering the decrease in surface area per unit of deposited element after the experiment, then P caused the most deactivation. It was concluded that Fe deposited mostly near to the outer surface irrespective of concentration while P and K penetrated deeper in catalyst particles such that the distribution profile was dependent on the concentration. Reaction kinetics of HDO of fatty acids provides critical knowledge which could be applied at the refining scale in process design and optimization. The activity and selectivity of NiMo catalyst during HDO of stearic acid was studied by varying reaction conditions like temperature, pressure, feed concentration and batch-reactor stirring rate and using intermediates like octadecanal and octadecanol. A deeper understanding of the reaction scheme and selectivities was developed based on the experimental results. A Langmuir–Hinshelwood-type mechanism was used to develop a kinetic model which well-predicted the changes in selectivities at varying reaction conditions.
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27.
  • Arora, Prakhar, 1987, et al. (författare)
  • The role of catalyst poisons during hydrodeoxygenation of renewable oils
  • 2021
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 367, s. 28-42
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.
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28.
  • Auvray, Xavier, 1986, et al. (författare)
  • Aging of Cu/SSZ-13 for NH3 SCR in mixed lean condition
  • 2018
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Two catalytic methods have been developed to remove the NOx emissions from diesel vehicles and comply with the emission regulations: the NOx storage and reduction process (NSR) and the reduction of NOx with NH3 (SCR). Advanced systems combining these two methods for an optimum efficiency are now studied. SCR catalysts are subjected alternating lean and rich conditions as well as to high temperatures in rich conditions during deSOx of the LNT material. The purpose of the present work is therefore to determine the response of a Cu/SSZ-13 to several aging treatments at 800°C involving rich and/or lean exposure. Deactivation was observed after all types of aging. However strong differences in deactivation degree exists between aging procedures. Lean aging, for 8h at 800°C, was the most moderate aging tested although it brought about significant activity loss below 250°C. Alternating between long lean periods and short rich periods caused slightly stronger deactivation, which was most significant at 200°C. However, the switching frequency between lean and rich had negligible influence on subsequent activity. As shown in Figure 1, SCR activity after 8h exposure in H2 was outstandingly low. It increased monotonically with temperature to reach a maximum of 58% NO conversion. Further investigation pertaining to the rich treatment was performed. The aging time was reduced to 2h and, for direct comparison, a 32h cycling aging was performed, implying a total rich time of 2h. Both samples were severely impacted over the whole temperature range. It revealed that 2h in rich conditions led to stronger deactivation than 8h in lean and lean/rich conditions, emphasizing the deterioration power of H2. Aging caused by rich conditions was so dominant that additional 30h in lean has negligible influence on SCR below 300°C. However, the long additional exposure to lean conditions lowered significantly the SCR activity between 400 and 500°C.
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29.
  • Bac, Selin, et al. (författare)
  • Exceptionally active and stable catalysts for CO2 reforming of glycerol to syngas
  • 2019
  • Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 256
  • Tidskriftsartikel (refereegranskat)abstract
    • CO2 reforming of glycerol to syngas was studied on Al2O3-ZrO2-TiO2 (AZT) supported Rh, Ni and Co catalysts within 600–750 °C and a molar inlet CO2/glycerol ratio (CO2/G) of 1–4. Glycerol and CO2 conversions decreased in the following order: Rh/AZT > Ni/AZT > Co/AZT. Reactant conversions on Rh/AZT exceeded 90% of their thermodynamic counterparts at 750 °C and CO2/G = 2–4 at which the activity of Ni/AZT was boosted to ˜95% of the thermodynamic CO2 conversion upon increasing the residence time. The loss in CO2 conversions was below 13% during the 72 h longevity tests confirming the exceptional stability of Rh/AZT and Ni/AZT. However, Co/AZT suffered from sintering, carbon deposition and oxidation of Co sites, demonstrated via TEM-EDX, XPS, XANES and in-situ FTIR experiments. Characterization of Rh/AZT revealed no significant signs of deactivation. Ni/AZT preserved most of its original metallic pattern and gasified carbonaceous deposits during earlier stages of the reaction.
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30.
  • Baena-Moreno, Francisco, 1992, et al. (författare)
  • Potential of organic carbonates production for efficient carbon dioxide capture, transport and storage: Reaction performance with sodium hydroxide–ethanol mixtures
  • 2023
  • Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 9:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon dioxide storage is one of the main long-term strategies for reducing carbon dioxide emissions in the atmosphere. A clear example is Norway's Longship project. If these projects should succeed, the transport of huge volumes of carbon dioxide from the emissions source to the injection points may become a complex challenge. In this work, we propose the production of sodium-based organic carbonates that could be transported to storage sites and be reconverted to CO2. Solid carbonates can be transported in considerably lower volumes than gases or pressurized liquids. Sodium-based carbonates are insoluble in most of the organic solvents and will therefore precipitate in contrast to in aqueous solutions. Particularly, here we focus on sodium hydroxide-ethanol mixtures as solvents for precipitating sodium ethyl carbonate and sodium bicarbonate. Previous works on this approach used limited sodium hydroxide concentrations, which are insufficient to prove the effectiveness of the proposed process. In this paper, we studied higher sodium hydroxide concentrations in sodium hydroxide-ethanol mixtures than previously reported in the literature. To this end, we use the following strategy: (1) In-line monitoring of the formation of carbonates using an in-line FTIR; (2) In-line measurements of the weight increase, which correspond directly to the captured carbon dioxide and reveal the absorption capacity; (3) Characterization of the solids with X-ray diffraction and scanning electron microscope. Our FTIR results confirmed that both sodium ethyl carbonate and sodium bicarbonate were formed, which agrees with X-ray diffraction and scanning electron microscope. With this reactor design, the absorption capacities reached approximately 80–93% of the theoretical values (4.8–13.3 g/L respectively). We hypothesize that full conversion is hampered because the gas might take preferential paths due to gel formation during the experiments.
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31.
  • Belkheiri, Tallal, 1985, et al. (författare)
  • Hydrothermal Liquefaction of Kraft Lignin in Subcritical Water: Influence of Phenol as Capping Agent
  • 2018
  • Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:5, s. 5923-5932
  • Tidskriftsartikel (refereegranskat)abstract
    • The depolymerization of LignoBoost Kraft lignin in subcritical water, i.e. hydrothermal liquefaction (HTL), was investigated using ZrO 2 , K 2 CO 3 , and KOH as catalysts in a fixed-bed reactor with recirculation. Focus was placed on the effect exerted by the concentration of the phenol in suppressing repolymerization, which is responsible for forming char. Feeds with various concentrations of phenol (2-10%) were investigated, and the results showed that phenol partially prevents repolymerization even at low concentrations. The bio-oil yield of (61.0 ± 2.7) % was fairly stable when the concentration of phenol was varied. In the case of the formation of char on the catalyst, the char yield revealed a weakly decreasing trend (14.6-12.3%) when the amount of phenol in the feed was increased. The results also showed that the phenolic monomers that are alkylated, such as o-/p-cresols, increased significantly with increasing concentrations of phenol, while aromatic compounds, based on a guaiacol ring structure, showed decreasing trends.
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32.
  • Belkheiri, Tallal, 1985 (författare)
  • LIGNIN HYDROTHERMAL LIQUEFACTION IN SUBCRITICAL WATER TO PRODUCE BIOFUEL AND CHEMICALS
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Lignin is one of the most abundant amorphous macromolecules found in nature. Along with cellulose and hemicellulose, it forms a main component of biomass, and is mainly responsible for providing strength, rigidity and resistance to degradation. From a chemistry perspective, lignin is an important source of aromatics. In the kraft process, lignin is recovered in the form of “black liquor”, which is considered a low-value by-product. Nowadays, energy efficiency measures in the pulp and paper industry have improved to a level of having an energy surplus in the mill, making it is possible to add value to the black liquor, which represents the surplus energy, in various ways. One scenario is to extract lignin from the black liquor, which has become technically feasible by developing LignoBoost technology, and then converting the lignin into high-value products, such as specialty chemicals or bio-fuel. In this work, hydrothermal liquefaction (HTL) of LignoBoost kraft lignin has been carried out in a small pilot plant, using sub-critical water as the medium, ZrO2, K2CO3/Na2CO3 and/or KOH/NaOH as the catalytic system, methanol as the co-solvent and phenol as the capping agent to suppress repolymerisation (e.g. formation of char). With the aim of developing the HTL process, different investigations were carried out to study the influence of methanol, the pH (8.9-10.4) through the use of different concentrations of potassium hydroxide and the use of phenol as the capping agent (2-10%); different fractions of sodium in alkali (Na/(Na+K) from 0.0-1.0) were also investigated. The reactions were performed in a fixed-bed reactor (500 cm3) at 350°C with the exception of the methanol investigation, where it was varied between 280 and 350°C, and a pressure of 25 MPa. The reactor outlet was comprised mainly of two liquid phases: one aqueous and one oil. The pH and methanol investigations showed different results in terms of operability and yields. The yields of bio-oil, WSO and char were affected by different levels of pH and concentrations of methanol. In addition, the use of methanol led to operational difficulties due to the extensive formation of solids. For the phenol and sodium/potassium investigations, the overall yield was not affected considerably either by different phenol concentrations (2-10%) or sodium fractions in the alkali. It was possible to lower the phenol concentration in the feed to 2% and maintain fairly constant overall yields. In the case of the sodium series, it was shown that it was also possible to replace the potassium ion in the feed with the sodium ion without it having a strong effect on the product yield. This HTL process gave the same major individual compounds such as guaiacol, anisole, catechol and alkylphenols, in all of the investigations undertaken, with different trends and influences being observed depending on the parameters studied.
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33.
  • Berdugo Vilches, Teresa, 1985, et al. (författare)
  • Mapping the effects of potassium on fuel conversion in industrial-scale fluidized bed gasifiers and combustors
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Potassium (K) is a notorious villain among the ash components found in the biomass, being the cause of bed agglomeration and contributing to fouling and corrosion. At the same time, K is known to have catalytic properties towards fuel conversion in combustion and gasification environments. Olivine (MgFe silicate) used as gasifier bed material has a higher propensity to form catalytically active K species than traditional silica sand beds, which tend to react with K to form stable and inactive silicates. In a dual fluidized bed (DFB) gasifier, many of those catalytic effects are expected to be relevant, given that the bed material becomes naturally enriched with ash elements from the fuel. However, a comprehensive overview of how enrichment of the bed with alkali affects fuel conversion in both parts of the DFB system is lacking. In this work, the effects of ash-enriched olivine on fuel conversion in the gasification and combustion parts of the process are mapped. The work is based on a dedicated experimental campaign in a Chalmers DFB gasifier, wherein enrichment of the bed material with K is promoted by the addition of a reaction partner, i.e., sulfur, which ensures K retention in the bed in forms other than inactive silicates. The choice of sulfur is based on its affinity for K under combustion conditions. The addition of sulfur proved to be an efficient strategy for capturing catalytic K in olivine particles. In the gasification part, K-loaded olivine enhanced the char gasification rate, decreased the tar concentration, and promoted the WGS equilibrium. In the combustion part, K prevented full oxidation of CO, which could be mitigated by the addition of sulfur to the cyclone outlet.
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34.
  • Berdugo Vilches, Teresa, 1985 (författare)
  • Strategies for controlling solid biomass conversion in dual fluidized bed gasifiers
  • 2016
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In the chemical industry, Synthesis Gas (syngas) has been traditionally produced by steam reforming of natural gas and naphtha. Steam gasification of biomass offers an alternative route for the production of syngas from renewable sources. However, the product of biomass gasification cannot be used directly in most applications, as it contains impurities, such as tar species. Tar, which is the Achilles heel of the biomass gasification technology, is a complex mixture of hydrocarbons, which can condensate at temperatures as high as 300oC, causing clogging of pipes and coolers, deactivating downstream catalysts, and forcing unscheduled shut-downs of the whole process.Gas cleaning and upgrading techniques, as well as methods for controlling the formation of tar are required to limit the tar concentration to acceptable levels. Numerous investigations of this topic have led to the merging of the fields of steam reforming and gasification, whereby catalytic materials are placed inside the gasifier with the goal of steam reforming the undesirable tar species and converting them into valuable syngas. The feasibility of integrating gasification and catalytic steam reforming has been confirmed in several pilot and demonstration plants, with promising results. The preferred technology is indirect gasification in a dual fluidized bed (DFB) reactor, as it enables hosting of the catalyst in the steam gasifier.The levels of tar in biomass gasification remain high, and there is a lack of understanding as to how to control efficiently fuel conversion in general, and tar formation in particular. Efforts to reduce the load of tar have ranged from modifying the gasifier design to testing different catalytic materials, passing through optimization of operating conditions (e.g., temperature, steam-to-fuel ratio). However, previous investigations have mainly focused on assessing the marginal improvement in product gas quality that occurs after a modification in the operation. This work aims instead at identifying the most effective measures to control fuel conversion in DFB gasifiers, with the ambition of contributing to the rational operation and design of the gasifier.In this work, fluid-dynamics and chemical aspects of fuel conversion are explored experimentally under conditions relevant to industrial steam gasifiers. It is concluded that the activity of the catalyst is the primary tool to control both tar and char conversion, whereas the fluid dynamics of the bed plays a secondary role. Once the bed is well-fluidized, further optimization of the gasifier design results in relatively low improvement in terms of tar conversion, as compared to the benefits of using active bed materials. Accordingly, to improve the reliability of the biomass-to-syngas process, research efforts should be directed to understand catalyst activation, the functioning of the catalyst, and the mechanism underlying catalytic decomposition of tar.
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35.
  • Bergman, Jenny, et al. (författare)
  • Co-detection of dopamine and glucose with high temporal resolution
  • 2018
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Neuronal activity and brain glucose metabolism are tightly coupled, where triggered neurotransmission leads to a higher demand for glucose. To better understand the regulation of neuronal activity and its relation to high-speed metabolism, development of analytical tools that can temporally resolve the transients of vesicular neurotransmitter release and fluctuations of metabolites such as glucose in the local vicinity of the activated neurons is needed. Here we present an amperometric biosensor design for rapid co-detection of glucose and the neurotransmitter dopamine. The sensor is based on the immobilization of an ultra-thin layer of glucose oxidase on to a gold-nanoparticle-covered carbon fiber microelectrode. Our electrode, by altering the potential applied at the sensor surface, allows for the high-speed recording of both glucose and dopamine. We demonstrate that, even though glucose is electrochemically detected indirectly through the enzymatic product and the electroactive dopamine is sensed directly, when exposing the sensor surface to a mixture of the two analytes, fluctuations in glucose and dopamine concentrations can be visualized with similar speed and at a millisecond time scale. Hence, by minimizing the enzyme coating thickness at the sensor surface, dual detection of glucose and dopamine can be realized at the same sensor surface and at time scales necessary for monitoring fast metabolic alterations during neurotransmission. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
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36.
  • Bergvall, Niklas, et al. (författare)
  • Slurry Hydroconversion of Solid Kraft Lignin to Liquid Products Using Molybdenum- and Iron-Based Catalysts
  • 2022
  • Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 36:17, s. 10226-10242
  • Tidskriftsartikel (refereegranskat)abstract
    • Kraft lignin is an abundantly available and largely underutilized renewable material with potential for production of biobased fuels and chemicals. This study reports the results of a series of slurry hydroprocessing experiments with the aim of converting solid Kraft lignin to liquid products suitable for downstream refining in more conventional reactors. Experiments reported in this study were conducted by feeding a lignin slurry to an already hot, liquid-filled reactor to provide momentaneous heating of the lignin to the reaction temperature. This modified batch procedure provided superior results compared to the regular batch experiments, likely since unwanted repolymerization and condensation reactions of the lignin during the heating phase was avoided, and was therefore used for most of the experiments reported. Experiments were performed using both an unsupported Mo-sulfide catalyst and Fe-based catalysts (bauxite and hematite) at varied reaction temperatures, pressures, and catalyst loadings. The use of Mo-sulfide (0.1% Mo of the entire feed mass) at 425 °C and 50 bar resulted in complete conversion of the Kraft lignin to nonsolid products. Very high conversions (>95%) could also be achieved with both sulfided bauxite or hematite at the same temperature and pressure, but this required much higher catalyst loadings (6.25% bauxite or 4.3% hematite of the total feed mass), and around 99% conversion could be achieved at higher temperatures but at the expense of much higher gas yields. Although requiring much higher loadings, the results in this study suggest that comparatively nonexpensive Fe-based catalysts may be an attractive alternative for a slurry-based process aimed at the hydroconversion of solid lignin to liquid products. Possible implementation strategies for a slurry-based hydroconversion process are proposed and discussed.
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37.
  • 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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38.
  • Cañete Vela, Isabel, 1992, et al. (författare)
  • Feedstock recycling of cable plastic residue via steam cracking on an industrial-scale fluidized bed
  • 2024
  • Ingår i: Fuel. - 0016-2361. ; 355
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of plastic materials in a circular way requires a technology that can treat any plastic waste and produce the same quality of product as the original. Cable plastic residue from metal recycling of electric wires is composed of cross-linked polyethene (XLPE) and PVC, which is a mixture that cannot be mechanically recycled today. Through thermochemical processes, polymer chains are broken into syngas and monomers, which can be further used in the chemical industry. However, feedstock recycling of such a mixture (XLPE, PVC) has been scarcely studied on an industrial scale. Here, the steam cracking of cable plastic was studied in an industrial fluidised bed, aiming to convert cable plastics into valuable products. Two process temperatures were tested: 730 °C and 800 °C. The results show that the products consist of 27–31 wt% ethylene and propylene, 5–16% wt.% other linear hydrocarbons, and more than 10 wt% benzene. Therefore, 40%–60% of the products are high-value chemicals that could be recovered via steam cracking of cable plastic.
  •  
39.
  • Chandolias, Konstantinos, 1985-, et al. (författare)
  • Effects of Heavy Metals and pH on the Conversion of Biomass to Hydrogen via Syngas Fermentation
  • 2018
  • Ingår i: BioResources. - : BioResources. - 1930-2126. ; 13:2, s. 4455-4469
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of three heavy metals on hydrogen production via syngas fermentation were investigated within a metal concentration range of 0 to 1.5 mg Cu/L, 0 to 9 mg Zn/L, 0 to 42 mg Mn/L, in media with initial pH of 5, 6, and 7, at 55 degrees C. The results showed that at lower metal concentration, pH 6 was optimum while at higher metal concentrations, pH 5 stimulated the process. More specifically, the highest hydrogen production activity recorded was 155% +/- 12% at a metal concentration of 0.04 mg Cu/L, 0.25 mg Zn/L, and 1.06 mg Mn/L and an initial medium pH of 6. At higher metal concentration (0.625 mg Cu/L, 3.75 mg Zn/L, and 17.5 mg Mn/L), only pH 5 was stimulating for the cells. The results showed that the addition of heavy metals, contained in gasification-derived ash, can improve the production rate and yield of fermentative hydrogen. This could lead to lower costs in gasification process and fermentative hydrogen production and less demand for syngas cleaning before syngas fermentation.
  •  
40.
  • Cheah, You Wayne, 1993 (författare)
  • Hydrotreatment of lignin and its bio-oils over transition metal sulfide-based supported and unsupported catalysts
  • 2021
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The scarcity of fossil feedstocks and the deterioration of the current global climate condition have prompted the search for reliable alternatives for fossil fuel replacement. Biomass feedstocks such as lignin can be used to produce renewable bio-oils that can fill the gap left by fossil-derived oils. Such bio-oils require an upgrading process, such as catalytic hydrodeoxygenation (HDO), to improve their quality for use as advanced biofuels and chemicals. Transition metal sulfides (TMS) are typically used in the traditional petroleum refining industry for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) applications. This thesis focuses on the hydrotreatment of a model bio-oil compound, propylguaiacol (PG), and an actual bio-feedstock, Kraft lignin (KL), over TMS-based supported and unsupported catalysts.  In the first study, catalysts based on MoS2 supported on γ-Al2O3 and promoted by transition metals, such as Nickel (Ni), Copper (Cu), Zinc (Zn), and Iron (Fe) were evaluated for the HDO of PG in a batch reactor setup. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a 94% yield of deoxygenated cycloalkanes, however, 42% of the phenolics remained in the reaction medium after 5 h for the sulfided Cu-promoted catalyst. It was also found that the sulfided Zn- and Fe-promoted catalysts gave a final yield of 19% and 16% at full PG conversion, respectively, for deoxygenated aromatics. A pseudo-first kinetic model that took into consideration the main side reactions was developed to elucidate the deoxygenation routes for the HDO of PG using sulfided catalysts. The developed kinetic model was able to describe the experimental results well with a coefficient of determination of 97% for the Ni-promoted catalyst system. This work also demonstrated that the activity of the transition metal promoters for the HDO of PG correlated to the yield of deoxygenated products from the hydrotreatment of Kraft lignin. The main focus of the second study was on the effect of the annealing treatment of a hydrothermally synthesized unsupported MoS2 catalyst. The prepared unsupported catalysts were studied and evaluated for the HDO of PG. The annealing treatment of the as-synthesized catalyst under N2 flow at 400 °C for 2 h was found to enhance the HDO activity of PG. The effect on catalysts activity of hydrothermal synthesis time and acid addition combined with the annealing treatment was also studied for the same model reaction. The annealed MoS2 with a synthesis time of 12 h in an acidic environment was found to have improved crystallinity and to exhibit the highest degree of deoxygenation of all the studied catalysts, moreover, giving a full PG conversion after 4 h and a final 4-propylbenzene selectivity of 23.4 %. An acidic environment during the synthesis was found to be crucial in facilitating the growth of MoS2 micelles, resulting in smaller particles that affected HDO activity. The annealed unsupported MoS2 that gave the best performance for HDO of PG was further evaluated for the hydrotreatment of KL. The annealed unsupported MoS2 demonstrated a high capacity for deoxygenation with a selectivity of 78.6% and 20.1% for cycloalkanes and aromatics from KL, respectively. The results also indicate that a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield.
  •  
41.
  • Cheah, You Wayne, 1993, et al. (författare)
  • Role of transition metals on MoS 2 -based supported catalysts for hydrodeoxygenation (HDO) of propylguaiacol
  • 2021
  • Ingår i: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 5:7, s. 2097-2113
  • Tidskriftsartikel (refereegranskat)abstract
    • Transition metal sulfides (TMSs) are typically used in the traditional petroleum refining industry for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) applications. Bio-oils require an upgrading process like catalytic hydrodeoxygenation (HDO) to produce advanced biofuels and chemicals. Herein, MoS /γ-Al O promoted by transition metals like nickel (Ni), copper (Cu), zinc (Zn), and iron (Fe) was evaluated for the HDO of a bio-oil model compound, 4-propylguaiacol (PG) in a batch reactor at 340 °C under 50 bar H pressure. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a high 94% yield of deoxygenated cycloalkanes, however for the sulfided Cu-promoted catalyst, 42% of phenolics remain in the reaction medium after 5 h. The results also revealed that the sulfided Zn and Fe-promoted catalysts gave a final yield of 16% and 19% at full PG conversion, respectively, for deoxygenated aromatics. A kinetic model considering the main side reactions was developed to elucidate the reaction pathway of demethoxylation and dehydroxylation of PG. The developed kinetic model was able to describe the experimental results well with a coefficient of determination of 97% for the Ni-promoted catalyst system. The absence of intermediates like 4-propylcyclohexanone and 4-propylcyclohexanol during the reaction implies that direct deoxygenation (DDO) is the dominant pathway in the deoxygenation of PG employing sulfided catalysts. The current work also demonstrated that the activity of the transition metal promoters sulfides for HDO of PG could be correlated to the yield of deoxygenated products from the hydrotreatment of Kraft lignin. 2 2 3 2
  •  
42.
  • Cheah, You Wayne, 1993, et al. (författare)
  • Thermal annealing effects on hydrothermally synthesized unsupported MoS2 for enhanced deoxygenation of propylguaiacol and kraft lignin
  • 2021
  • Ingår i: Sustainable Energy and Fuels. - 2398-4902. ; 5:20, s. 5270-5286
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalytic hydrodeoxygenation (HDO) is an important hydrotreating process that is used to improve the quality of bio-oils to produce biomass-derived fuel components and chemicals. Molybdenum disulfide (MoS2) has been widely used as a catalyst in hydrodesulfurization (HDS) applications for several decades, which can be further improved for effective unsupported catalyst synthesis. Herein, we studied a universally applicable post-annealing treatment to a hydrothermally synthesized MoS2 catalyst towards developing efficient unsupported catalysts for deoxygenation. The effect of the annealing treatment on the catalyst was studied and evaluated for HDO of 4-propylguaiacol (PG) at 300 °C with 50 bar H2 pressure. The annealing of the as-synthesized catalyst under nitrogen flow at 400 °C for 2 h was found to enhance the HDO activity. This enhancement is largely induced by the changes in the microstructure of MoS2 after the annealing in terms of slab length, stacking degree, defect-rich sites and the MoS2 edge-to-corner site ratio. Besides, the effect of hydrothermal synthesis time and acid addition combined with the annealing treatment on the MoS2 catalytic activity was also studied for the same model reaction. The annealed MoS2 with a synthesis time of 12 h under an acidic environment was found to have improved crystallinity and exhibit the highest deoxygenation degree among all the studied catalysts. An acidic environment during the synthesis was found to be crucial in facilitating the growth of MoS2 micelles, resulting in smaller particles that affected the HDO activity. The annealed unsupported MoS2 with the best performance for PG hydrodeoxygenation was further evaluated for the hydrotreatment of kraft lignin and demonstrated a high deoxygenation ability. The results also indicate a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield. This research uncovers the importance of a facile pretreatment on unsupported MoS2 for achieving highly active HDO catalysts.
  •  
43.
  • Costa, Diogo Ribeiro, et al. (författare)
  • Oxidation of UN/U 2 N 3 -UO 2 composites: an evaluation of UO 2 as an oxidation barrier for the nitride phases
  • 2021
  • Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 544
  • Tidskriftsartikel (refereegranskat)abstract
    • Composite fuels such as UN-UO2 are being considered to address the lower oxidation resistance of the UN fuel from a safety perspective for use in light water reactors, whilst improving the in-reactor behaviour of the more ubiquitous UO2 fuel. An innovative UN-UO2 accident tolerant fuel has recently been fabricated and studied: UN microspheres embedded in UO2 matrix. In the present study, detailed oxidative thermogravimetric investigations (TGA/DSC) of high-density UN/U2N3-UO2 composite fuels (91-97 %TD), as well as post oxidised microstructures obtained by SEM, are reported and analysed. Triplicate TGA measurements of each specimen were carried out at 5 K/min up to 973 K in a synthetic air atmosphere to assess their oxidation kinetics. The mass variation due to the oxidation reactions (%), the oxidation onset temperatures (OOTs), and the maximum reaction temperatures (MRTs) are also presented and discussed. The results show that all composites have similar post oxidised microstructures with mostly intergranular cracking and spalling. The oxidation resistance of the pellet with initially 10 wt% of UN microspheres is surprisingly better than the UO2 reference. Moreover, there is no significant difference in the OOT (~557 K) and MRT (~615 K) when 30 wt% or 50 wt% of embedded UN microspheres are used. Therefore, the findings in this article demonstrate that the UO2 matrix acts as a barrier to improve the oxidation resistance of the nitride phases at the beginning of life conditions.
  •  
44.
  • De Abreu Goes, Jesus, 1989 (författare)
  • Aging effects on commercial lean NOx trap catalysts
  • 2018
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • As a countermeasure to global warming, vehicles with low carbon emissions are being investigated by promoting lean-burn engines and high combustion efficiencies. However, one limitation to the increasing use of these engines is the need to develop corresponding catalytic systems for controlling the nitrogen oxide (NOx) emissions in their lean exhaust. Lean NOx trap (LNT) represents a simple and cost-efficient technology for the abatement of NOx emissions from lean-burn gasoline and diesel engines. It consists of trapping NOx emissions from lean exhaust and then, before NOx slip becomes significant, the NOx stored is released and reduced to N2 under rich exhaust conditions. Although LNTs have been commercialized for some applications, the durability of LNT catalysts still remains problematic; sulfur poisoning and thermal aging are the major causes of deactivation. In this work, commercial LNT catalysts were aged and characterized in order to elucidate the effect of aging on their performance and to establish a correlation with an accelerated aging method. A vehicle-aged catalyst was driven in the vehicle chassis dynamometer for 100 000 km, while a rapid-aged catalyst was treated at 800 °C for a period of time equivalent to a driving distance of 160 000 km. Engine dynamometer studies were performed with the purpose of testing the NOx storage and reduction performance of the LNT samples. This testing campaign was followed by running some vehicle emission cycles in the vehicle chassis dynamometer with a 2.0 l Volvo diesel vehicle with the aim of studying the catalysts’ performance under real driving conditions and monitoring the gradual deterioration of the vehicle-aged catalyst during aging. Afterwards, detailed characterization studies were carried out on a flow reactor with small cylindrical cores extracted from commercial LNT catalysts. Physicochemical characterization techniques were also employed in this investigation. The catalyst evaluation revealed that aging resulted in a significant deterioration of NOx storage and reduction functions as a consequence of precious metal sintering, loss of surface area of the NOx storage and support compounds, phase transitions of the adsorber material, and a large accumulation of poison species, especially at the catalyst inlet. Among the aged samples examined, the middle (lengthwise) vehicle-aged sample showed the highest catalytic activity since it was exposed to both chemical poisoning and thermal degradation to a lesser extent. It was found that the oven-aged method proposed in this study is definitely a good approach to mimic the long-term catalytic activity in which the thermal stress applied is able to replicate the NO oxidation and NOx storage activity of a 100 000 km vehicle-aged catalyst.
  •  
45.
  • De Abreu Goes, Jesus, 1989, et al. (författare)
  • Chapter 5: Mechanism and Kinetics of NOx Storage
  • 2018
  • Ingår i: RSC Catalysis Series. - Cambridge : Royal Society of Chemistry. - 1757-6733 .- 1757-6725. ; 2018-January, s. 127-156
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • In this chapter, experimental studies and kinetic models are presented to elucidate the fundamental mechanisms for NOxstorage on the NOxstorage and reduction (NSR) catalysts. A well-accepted reaction pathway for NOxstorage includes, as an initial step, the oxidation of NO to NO2under lean conditions, and subsequently storage on the NOxstorage sites in the form of nitrites or nitrates. NO can also be stored directly in the presence of NO and oxygen, in the so-called nitrite route. However, the NOxstorage process is largely influenced by the primary gas components in the exhaust stream, such as CO2, H2O and SO2. In particular, significant attention has been focused on sulphur poisoning and the interaction of SO2with different NSR components due to its large potential of harming NSR catalyst activity. Finally, a kinetic model describing in detail the sulphur poisoning over a commercial LNT catalyst is discussed. The model can well describe the gradual deactivation of the catalyst during sulphur exposure.
  •  
46.
  • De Abreu Goes, Jesus, 1989, et al. (författare)
  • Correlation between Vehicle- and Rapid- Aged Commercial Lean NOx Trap Catalysts
  • 2017
  • Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 10:4, s. 1613-1626
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NOx storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, and one reason for this could be limited NO oxidation. In addition, the oven-aged sample was found to be well correlated to the vehicle-aged catalyst. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance under real driving conditions and monitor the gradual deterioration of the vehicle-aged catalyst during the vehicle aging testing.
  •  
47.
  • De Abreu Goes, Jesus, 1989, et al. (författare)
  • Detailed Characterization Studies of Vehicle and Rapid Aged Commercial Lean NOx Trap Catalysts
  • 2018
  • Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 57:29, s. 9362-9373
  • Tidskriftsartikel (refereegranskat)abstract
    • Commercial lean NOxtrap (LNT) catalysts were aged and characterized to elucidate the effect of aging on their performances and examine the deactivation of a rapid-aged catalyst toward an improved correlation with respect to a vehicle-aged catalyst. Detailed characterization studies were carried out on the flow reactor with small cylindrical cores extracted from the commercial LNT catalysts. Physicochemical characterization techniques were also implemented. The catalyst evaluation revealed that aging resulted in a significant deterioration of NOxstorage and reduction functions as a consequence of precious metal sintering, loss of surface area of the NOxstorage and support materials, phase transitions of the adsorber compounds, and large accumulation of poison species. Among the aged samples examined, the middle (lengthwise) vehicle-aged sample showed the highest NOxconversion, while the oven-aged catalyst was the most active of the aged samples for water gas shift reaction and oxygen storage.
  •  
48.
  • Deshpande, Raghu, 1979- (författare)
  • The initial phase of the sodium bisulfite pulping of softwood dissolving pulp
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The sulfite pulping process is today practised in only a small number of pulp mills around the globe and the number of sulfite mills that use sodium as the base (cation) is less than five. However, due to the increasing interest in the wood based biorefinery concept, the benefits of sulfite pulping and especially the sodium based variety, has recently gained a lot of interest. It was therefore considered to be of high importance to further study the sodium based sulfite process to investigate if its benefits could be better utilized in the future in the production of dissolving pulps. Of specific interest was to investigate how the pulping conditions in the initial part of the cook (≥ 60 % pulp yield) should be performed in the best way.Thus, this thesis is focused on the initial phase of single stage sodium bisulfite cooking of either 100 % spruce or 100 % pine wood chips. The cooking experiments were carried out with either a lab prepared or a mill prepared cooking acid and the temperature and cooking time were varied. Activation energies for different wood components were investigated as well as side reactions concerning the formation of thiosulfate and sulfate.
  •  
49.
  • Di, Mengqiao, 1994 (författare)
  • CO Oxidation over Oxide Supported Platinum Catalysts
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Catalytic oxidation of carbon monoxide (CO) is one of the most studied reactions that still needs to be improved because of its practical use in the chemical industry including feedstock purification and applications such as emission control, in-door air cleaning, improvement of fuel cell efficiency, etc. Concerning CO emissions, the transportation sector is a large contributor. The development of modern powertrains and driving patterns lead to cold exhausts. Thus, catalysts must be active for CO oxidation at low temperatures, which is a challenge. Further, CO oxidation is influenced by other compounds in the exhausts that may either promote or inhibit essential catalytic functions. For combustion exhausts, water is definitely inevitable and nitrogen oxides are common components. This work scrutinizes the kinetics of CO oxidation over Pt/alumina and Pt/ceria catalysts through analysis of reaction orders obtained experimentally from flow-reactor measurements and theoretically by kinetic Monte Carlo simulations and connects this to kinetic model formulation. Further, the catalytic structure-function relationship is explored by operando infrared and X-ray absorption spectroscopy. The influence of water and nitrogen oxide on the CO oxidation kinetics is investigated with in situ infrared spectroscopy. Finally, iron oxide is explored as an active support for platinum with a focus on the structural dynamics of Pt/FeOx under reaction conditions. The results show that reaction orders depend on reaction conditions and operating mechanism, and the adsorbate-adsorbate interactions play a crucial role. Pt/ceria is active at lower temperatures than Pt/alumina thanks to lattice oxygen in the ceria support that participates according to a Mars-van Krevelen mechanism. This mechanism is promoted by water but inhibited by nitrogen oxide through nitrate formation. On Pt/alumina, the reaction proceeds via the Langmuir-Hinshelwod mechanism, which is also promoted by water and inhibited by nitrates. Finally, using iron oxide as support for Pt opens for a catalyst design with a support even more interacting with Pt than ceria in terms of redox properties at low temperatures.
  •  
50.
  • Di, Wei, 1986 (författare)
  • A tandem Catalyst for hydrogenation of CO2 to light olefins — The role of the zeolite component
  • 2023
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The catalytic conversion of waste CO2 into light olefins offers a sustainable pathway for green chemicals production in the future. Over a tandem catalyst with the bifunctional active sites for methanol synthesis (CTM) and methanol to olefins (MTO), CO2 can be efficiently converted via intermediate methanol into a mixture of light olefins (ethylene, propene, butene). In the study of CO2 hydrogenation, the moderately acidic SAPO-34 molecular sieve is often used as the MTO catalyst component. SAPO-34 performs well for the formation of C-C bonds without fast coking, and minimal further hydrogenation of olefins. These qualities give the catalyst a long lifetime and high selectivity for light olefins. Unfortunately, under high-pressure hydrothermal conditions, it easily suffers structural damage. In this context, the SSZ-13 zeolite, an alternative MTO catalyst with higher hydrothermal stability, but also stronger acidity, was systematically investigated and modulated with the aim to achieve high selectivity for light olefins and high stability during CO2 hydrogenation. Firstly, in order to identify the effect of zeolite acidity on product distribution and coke deposition, two types of SSZ-13 zeolites with similar bulk composition, but different protonic acid site distributions, were synthesized. They were combined with a stable CTM catalyst (bulk indium oxide, In2O3) as a tandem catalyst and were evaluated in CO2 hydrogenation. The SSZ-13 with isolated acid sites had a lower Brønsted acid site (BAS) density and exhibited a higher selectivity for light olefins compared with the one with paired protonic acid sites. By exchanging Na+ cations to tailor the BAS density of SSZ-13 zeolite, the comparative experiments further indicated that the BAS density, rather than BAS distribution, had a high correlation with the selectivity for light olefins, which proved that the BAS density had the primary impact on the product distribution. The high BAS density promoted hydrogenation which reduced the selectivity for light olefins, while low BAS density tended to accumulate excessive coke leading to catalyst deactivation, but with improved selectivity for olefins. Thereafter, over the tandem catalysts with the optimized BAS density, a transient experiment with varying reaction conditions was carried out to investigate the coke evolution during CO2 hydrogenation. The results indicated that the coking behavior of SSZ-13 zeolite was significantly affected by reaction conditions. By manipulating the reaction temperature and pressure, the active coke species, or so-called hydrocarbon pool species (HCPS), can be deposited inside the zeolite in a targeted manner, thereby modifying the catalyst to achieve a higher MTO activity and lower olefin hydrogenation activity. Continuous transient experiments further revealed a dynamic equilibrium between the formation and degradation of coke inside SSZ-13 zeolite. This balance is established under the appropriate BAS density and optimized reaction temperature and pressure. Using the conditions of 20 bar and 375 ℃, with a H2 to CO2 mole ratio of 3, the results obtained for the pre-coked tandem catalysts of In2O3 and SSZ-13 (BAS density = 0.23 mmol*g-1) exhibited very stable activity, with selectivity for light olefins around 70% ± 2% (among hydrocarbon products), and low average coke deposition rate of 0.016 wt.%*h-1 over 100 h time-on-stream. This result also experimentally confirmed the success of pre-coking modification and verified the balance mechanism of coke accumulation.
  •  
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