| 1. |
- Abebe, Mihret, et al.
(författare)
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Spherical and Porous Particles of Calcium Carbonate Synthesized with Food Friendly Polymer Additives
- 2015
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 15:8, s. 3609-3616
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Tidskriftsartikel (refereegranskat)abstract
- Porous calcium carbonate particles were synthesized by adding solutions of Ca2+ to solutions of CO32- containing polymeric additives. Under optimized conditions well-defined aggregates of the anhydrous polymorph vaterite formed. A typical sample of these micrometer-sized aggregates had: a pore volume of 0.1 cm(3)/g, a pore width of similar to 10 nm, and a specific surface area of similar to 25-30 m(2)/ g. Only one mixing Order (calcium to carbonate) allowed the formation of vaterite, which was ascribed to the buffering capacity and relatively high pH of the CO32- solution. Rapid addition of the calcium chloride solution and rapid stirring promoted the formation of vaterite, due to the high supersaturation levels achieved. With xanthan gum, porous and micrometer-sized vaterite aggregates could be synthesized over a wide range of synthetic conditions. For the Other food grade polymers, hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and sodium carboxyl methylcellulose, several intensive and extensive synthetic parameters had to be optimized to obtain pure vaterite and porous aggregates. HPMC and MC allowed well-defined spherical micrometer-sited particles to form. We expect that these spherical and porous particles of vaterite could be relevant to model studies as well as a controlled delivery of particularly large molecules.
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| 2. |
- Akhtar, Farid, et al.
(författare)
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Aluminophosphate monoliths with high CO2-over-N2 selectivity and CO2 capture capacity
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:99, s. 55877-55883
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Tidskriftsartikel (refereegranskat)abstract
- Monoliths of microporous aluminophosphates (AlPO4-17 and AlPO4-53) were structured by binder-free pulsed current processing. Such monoliths could be important for carbon capture from flue gas. The AlPO4-17 and AlPO4-53 monoliths exhibited a tensile strength of 1.0 MPa and a CO2 adsorption capacity of 2.5 mmol g-1 and 1.6 mmol g-1, respectively at 101 kPa and 0°C. Analyses of single component CO2 and N2 adsorption data indicated that the AlPO4-53 monoliths had an extraordinarily high CO2-over-N2 selectivity from a binary gas mixture of 15 mol% CO2 and 85 mol% N2. The estimated CO2 capture capacity of AlPO4-17 and AlPO4-53 monoliths in a typical pressure swing adsorption (PSA) process at 20°C was higher than that of the commonly used zeolite 13X granules. Under cyclic sorption conditions, AlPO4-17 and AlPO4-53 monoliths were regenerated by lowering the pressure of CO2. Regeneration was done without application of heat, which would regenerate them to their full capacity for CO2 adsorption.
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| 3. |
- Akhtar, Farid, et al.
(författare)
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Strong and binder free structured zeolite sorbents with very high CO2-over-N-2 selectivities and high capacities to adsorb CO2 rapidly
- 2012
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 5:6, s. 7664-7673
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Tidskriftsartikel (refereegranskat)abstract
- Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N-2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N-2 were determined and used to predict the co-adsorption of CO2 and N-2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N-2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 degrees C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N-2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g(-1)) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N-2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.
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| 4. |
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| 5. |
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| 6. |
- Akhtar, Farid, et al.
(författare)
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Structuring adsorbents and catalysts by processing of porous powders
- 2014
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 34:7, s. 1643-1666
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Tidskriftsartikel (refereegranskat)abstract
- Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.
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| 7. |
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| 8. |
- Antonsson, Kjell, et al.
(författare)
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Occurrence of the hermit beetle (Osmoderma eremita), in Sweden.
- 2003
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Ingår i: Entomologisk tidskrift. - 0013-886X. ; 124:4, s. 225-240
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Tidskriftsartikel (refereegranskat)abstract
- We have compiled data on the occurrence of a threatened beetle, Osmoderma eremita, in Sweden. The species inhabits tree hollows with wood mould. The data were compiled from field surveys conducted in 1993-2003, using pitfall traps at 401 localities and using wood mould sampling at 104 localities. We have also gone through published data and all larger Swedish museums and registered old records. O. eremita was recorded at about 30% of the field surveys. In Sweden, oak is by far the most important host tree species, but the beetle has also been found in other deciduous trees, such as beech, alder, ash and lime. Currently, 270 localities with Osmoderma eremita, defined as records of living adults, larvae, fragments of adult body parts, or excrements situated at least 1 km from each other, are known in Sweden. 129 of these localities are records of live beetles or larvae made after 1990. The species is found in the southern third of Sweden only, and there are more localities in the eastern part compared to the western. The great majority of the localities have been discovered during the last ten years. At some of the localities only excrements or fragments have been recorded, and the species might actually be extinct at some of these localities. Due to low search intensity historically, it is impossible to use these data to discover any changes in the distribution or occurrence over time. Because old, hollow oaks were much more frequent 200 years ago, we suggest that the species has decreased severely in Sweden since that time. Today, old oaks are rarely cut down but instead lack of grazing cattle is a threat because many sites regrow with dense tree stands which outcompete the old hollow trees. Many local extinctions could also be expected during the next few decades, because many of the localities have too few hollow trees and are too isolated. At many localities, lack of younger trees which can take over the role as host trees when the present trees die will also be a problem in the future.
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| 9. |
- Arauzo, P. J., et al.
(författare)
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Assessment of the effects of process water recirculation on the surface chemistry and morphology of hydrochar
- 2020
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 155, s. 1173-1180
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Tidskriftsartikel (refereegranskat)abstract
- The effect of two process water (PW) recirculation strategies after hydrothermal carbonization (HTC) of brewers spent grains (BSG) is evaluated with the focus on the hydrochar characteristics. The HTC process has been carried out under different operating conditions, which are residence time between 2 and 4 h and temperature in the range of 200-220 degrees C. The composition of the hydrochars reveals that operating conditions have a more significant effect than PW recirculation. The composition of the liquid produced by HTC with PW recirculation is essentially controlled by the operating temperature, for instance, the total organic carbon (TOC) in the PW changes in the narrow range of 200-220 degrees C. A detailed analysis of PW also has been done. The main components of the liquid phase are lactic, formic, acetic, levulinic, and propionic acid as well as 5-hydroxymethylfurfural, that affect the surface structure of the hydrochars.
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| 10. |
- Atluri, Rambabu, 1981-, et al.
(författare)
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Hydrothermal Phase Transformation of Bicontinuous Cubic Mesoporous Material AMS-6
- 2008
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 20:12, s. 3857–3866-
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Tidskriftsartikel (refereegranskat)abstract
- The controlled synthesis of ordered anionic surfactant templated mesoporous silica with cubic Ia3d̅ structure (AMS-6) is reported via prolonged periods of hydrothermal treatment (HT). The cubic Ia3d̅ mesophase transforms to hexagonal p6mm after 8 days of HT at 100 °C. Surprisingly, the hexagonal phase is stable only for a limited period after which a reversal to the cubic Ia3d̅ mesostructure is observed. Characterization methods such as powder X-ray diffraction (XRD), electron microscopy (SEM, TEM), N2-isotherms, magic-angle spinning (MAS) 29Si NMR spectroscopy, and thermogravimetric analysis (TGA) have been employed to follow structural and textural changes of the materials prepared. Data show that the resultant mesostructure and its textural properties are highly dependent on the period of HT with less unit-cell shrinkage on calcination after extensive HT. Furthermore, evidence of two different solid−solid phase mechanisms during HT is presented. The initial transition is consistent with a restructuring of the surfactant packing and a depletion of the organic moieties from the organo-silica wall as evident from 29Si NMR spectroscopy. The return to the bicontinuous cubic phase is driven by changes in charge matching at the organic−inorganic interface as a result of increases in the polymerization of the silica wall. The textural properties, and in particular the presence or absence of surface porosity, has been controlled through variations in hydrothermal treatment. These are associated with specific growth directions of cubic AMS-6 crystals. The synthetic method described allows us to easily prepare phase pure and intermediate mesostructured nanoparticles.
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| 11. |
- Atluri, Rambabu, et al.
(författare)
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Non-Surfactant Supramolecular Templating Synthesis of Ordered Mesoporous Silica
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:9, s. 3189-3191
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Tidskriftsartikel (refereegranskat)abstract
- Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.
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| 12. |
- Atluri, Rambabu, 1981-, et al.
(författare)
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Nonsurfactant Supramolecular Synthesis of Ordered Mesoporous Silica
- 2009
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:9, s. 3189-3191
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Tidskriftsartikel (refereegranskat)abstract
- Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.
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| 13. |
- Atluri, Rambabu, et al.
(författare)
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Self-Assembly Mechanism of Folate-Templated Mesoporous Silica
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:38, s. 12003-12012
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Tidskriftsartikel (refereegranskat)abstract
- A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30 degrees. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials.
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| 14. |
- Atluri, Rambabu, et al.
(författare)
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Structural variations in mesoporous materials with cubic Pm(3)over-barn symmetry
- 2010
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 133:1-3, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- The fine structural details of mesoporous materials possessing Pmn symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity–windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity–windows. Results support that whilst attainment of Pmn cubic packing is due to the overall surfactant geometry, the formation of cavity–windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.
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| 15. |
- Atluri, Rambabu, 1981-, et al.
(författare)
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Structural variations in mesoporous materials with cubic Pm3n symmetry
- 2010
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 133:1-3, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- The fine structural details of mesoporous materials possessing Pm3n symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity-windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity-windows. Results support that whilst attainment of Pm3n cubic packing is due to the overall surfactant geometry, the formation of cavity-windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.
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| 16. |
- Aziz, Baroz, 1980-, et al.
(författare)
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Carbon Dioxide Sorbents with Propylamine Groups-Silica Functionalized with a Fractional Factorial Design Approach
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:7, s. 3822-3834
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous silica particles (Davisil) were functionalized with aminopropyltriethoxysilane (APTES) in a fractional factorial design with 19 different synthesis and uptake experiments. The number of amino groups and the uptake of CO(2) were optimized in a 2(V)(5-1) design. Most important to functionalizationwas the amount of water present during synthesis, the reaction time, and pretreating the silica with a mineral acid; certain two-way interactions were shown to be statistically significant as well. Modifications performed at 110 or 80 degrees C showed no significant differences concerning amine content or uptake of CO(2). Properly choosing center points for the discrete variables is problematic and is somewhat related to the lack of fit with respect to CO(2) uptake; the regression was good. Solid-state (29)Si NMR showed that the APTES was mainly fully condensed. Specific surface areas did not correlate with the number of n-propylamine groups on the silica, which is indicative of differential levels of heterogeneity in the coverage of propylamines. The uptake of CO(2) and N(2) was measured from -20 to 70 degrees C and from 0 to 1 bar and parametrized by the Freundlich isotherm. Amine-modified silica adsorbed significant amounts of CO(2), especially at the low partial pressure, which is important for CO(2) capture from flue gas. At such pressures, samples with a high density of amine (4 amines/nm(2)) showed a much higher uptake of CO(2) than did those with densities of similar to 2-3 amines/nm(2), reflecting differential tendencies to form propylammonium-propylcarbamate ion pairs; these require close proximity among amine groups to form. Water affected the uptake of carbon dioxide in different ways. Certain samples took up more moist CO(2) gas than dry CO(2), and others took up less moist CO(2) than dry CO(2), which is indicative of differential tendencies toward water adsorption. We conclude that experimental design is a time-efficient approach to the functionalization of silica with propylamine groups.
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| 17. |
- Aziz, Baroz, 1980-, et al.
(författare)
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Kinetic control of particle-mediated calcium carbonate crystallization
- 2011
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 13:14, s. 4641-4645
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Tidskriftsartikel (refereegranskat)abstract
- By changing the temperature, pH, stirring rate, or time for calcium carbonate crystallization, complex shapes of aggregated calcium carbonates formed. Such shapes have earlier been ascribed to specific interactions with specialized additives. Without polymeric additives, aggregates of vaterite transformed more rapidly into calcite aggregates under slow than under fast stirring. With an anionic polyelectrolyte added, vaterite was stabilized. Larger polycrystalline aggregates of vaterite formed under rapid than under slow stirring, indicative of a particle mediated growth of aggregates controlled by convective currents. The size of the underlying nanoparticles was temperature dependent, with grain sizes of similar to 20 to 50 nm at 20 degrees C and similar to 350 nm at 90 degrees C. The small differences in free energy between the anhydrous polymorphs of calcium carbonate made both kinetic and equilibrium dependencies important.
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| 18. |
- Aziz, Baroz, 1980-, et al.
(författare)
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Quantification of chemisorption and physisorption of carbon dioxide on porous silica modified by propylamines : Effect of amine density
- 2012
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 159, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- Detailed molecular aspects of carbon dioxide sorption on porous silica with different amounts of tethered and cross-linked n-propylamine groups were investigated. Infrared spectroscopy was applied to directly quantify physisorbed and chemisorbed CO2 on the amine modified silicas. The fractions of physisorbed CO2 and various chemisorbed species were determined as functions of CO2 pressure and the amine density on the modified silica. Physisorbed CO2 was a minor portion of the total CO2 uptake at low pressures, but it’s contribution increased to ∼35% at 1 bar of CO2 when the propylamine surface density was low or medium (0.87-1.67 NH2/nm2). Chemisorption of CO2 dominated when the propylamine content was high (2.74 NH2/nm2). The quantities of propylammonium propylcarbamate ion pairs increased with increasing propylamine content. At low or medium amine surface densities (0.87-1.67 NH2/nm2) this increase was approximately proportional to the amine density, but the quantity of ion pairs increased very significantly when the propylamine content was high (2.74 NH2/nm2). This dependency on amine density is consistent with the idea that a sufficiently close proximity of propylamine groups allows a formation of ion pairs. The relative fractions of carbamic acid and silylpropylcarbamate were significant for materials on which ion pairs could not form. Furthermore, the quantities of carbamic acid increased with increasing amine densities suggesting that the ion pairs have a role to stabilize the labile carbamic acid through hydrogen bonds.
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| 19. |
- Aziz, Baroz, 1980-
(författare)
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Synthesis and modification of potential CO2 adsorbents : Amine modified silica and calcium carbonates
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prospect of rapid changes to the climate due to global warming is subject of public concern. The need to reduce the emissions of atmospheric green house gases and in particular carbon dioxide is greater than ever. Extensive research is performed to find new solutions and new materials, which tackles this problem in economically benign way. This thesis dealt with two potential adsorbents for post combustion carbon capture, namely, amine modified silica and calcium carbonates. We modified porous silica with large surface area by propyl-amine groups to enhance the carbon dioxide adsorption capacity and selectivity. Experimental parameters, such as reaction time, temperature, water content, acid and heat treatment of silica substrate were optimized using a fractional factorial design. Adsorption properties and the nature of formed species upon reaction of CO2 and amine-modified silica were studied by sorption and infrared spectroscopy. Physisorbed and chemisorbed amount of adsorbed CO2 were, for the first time, estimated directly in an accurate way. The effects of temperature and moisture on the CO2 adsorption properties were also studied. Crystallization of calcium carbonate as a precursor to calcium oxide, which can be used as carbon dioxide absorbent, was studied in the second part of this thesis. Structure of different amorphous phases of calcium carbonate was studied in detail. Crystallization of calcium carbonate with and without additives was studied. Parameters like stirring rate, temperature, pH and polymer concentration showed to be important in selection of phase and morphology. An aggregation mediated crystallization was postulated to explain the observed morphologies.
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| 20. |
- Azuara, Manuel, et al.
(författare)
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Influence of pressure and temperature on key physicochemical properties of corn stover-derived biochar
- 2016
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 186, s. 525-533
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on analyzing the effect of both the peak temperature and pressure on the properties of biochar produced through slow pyrolysis of corn stover, which is a common agricultural waste that currently has little or no value. The pyrolysis experiments were carried out in a fixed-bed reactor at different peak temperatures (400, 525 and 650 degrees C) and absolute pressures (0.1, 0.85 and 1.6 MPa). The inert mass flow rate (at NTP conditions) was adjusted in each test to keep the gas residence time constant within the reactor. The as-received corn stover was pyrolyzed into a biochar without any physical pre-treatment as a way to reduce the operating costs. The properties of biochars showed that high peak temperature led to high fixed-carbon contents, high aromaticity and low molar H:C and O:C ratios; whereas a high pressure only resulted in a further decrease in the O:C ratio and a further increase in the fixed-carbon content. Increasing the operating pressure also resulted in a higher production of pyrolysis gas at the expense of water formation.
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| 21. |
- Bacsik, Zoltán, et al.
(författare)
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Adsorption of Carbonyl Sulfide on Propylamine Tethered to Porous Silica
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:26, s. 7708-7713
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Tidskriftsartikel (refereegranskat)abstract
- Carbonyl sulfide (COS) reacts slowly with amines in the aqueous solutions used to absorb CO2 from natural gas and flue gas and can also deactivate certain aqueous amines. The effects of COS on amines tethered to porous silica, however, have not been investigated before. Hence, the adsorption of COS on aminopropyl groups tethered to porous silica was studied using in situ IR spectroscopy. COS chemisorbed mainly and reversibly as propylammonium propylthiocarbamate ion pairs [R-NH(C= O)S- +H3N-R] under dry conditions. In addition, a small amount of another chemisorbed species formed slowly and irreversibly. Nevertheless, the CO2 capacities of the adsorbents were fully retained after COS was desorbed.
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| 22. |
- Bacsik, Zoltan, et al.
(författare)
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Ammonium-Carbamate-Rich Organogels for the Preparation of Amorphous Calcium Carbonates
- 2017
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Ingår i: Minerals. - : MDPI AG. - 2075-163X. ; 7:7
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Tidskriftsartikel (refereegranskat)abstract
- Amine-CO2 chemistry is important for a range of different chemical processes, including carbon dioxide capture. Here, we studied how aspects of this chemistry could be used to prepare calcium carbonates. Chemically crosslinked organogels were first prepared by reacting hyperbranched polyethylene imine (PEI) dissolved in DMSO with carbon dioxide. The crosslinks of the organogel consisted of ammonium-carbamate ion pairs as was shown by IR spectroscopy. These carbamate-rich organogels were subsequently subjected to aqueous solutions of calcium acetate, and amorphous calcium carbonate (ACC) precipitated. The ACC did not crystalize during the mixing for up to 20 h, as was shown by a combination of IR spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal analysis. Some PEI had been included or adsorbed on the ACC particles. Traces of calcite were observed in one sample that had been subjected to water in a work-up procedure.
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| 23. |
- Bacsik, Zoltan, et al.
(författare)
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Effects of carbon dioxide captured from ambient air on the infrared spectra of supported amines
- 2016
-
Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031 .- 1873-3697. ; 87, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- Amino groups in highly dense coatings of amines on solid supports react with CO2 of ambient air and form ammonium-carbamate ion pairs. These ion pairs change the properties of the amine-modified supports. In numerous studies, the corresponding infrared (IR) spectra have been misinterpreted. The presumption has been that such ion pairs would not form in ambient air, and therefore IR bands have been assigned to moieties of the support and the amines. Here, we discuss common misunderstandings of the IR spectra of amine-modified supports and highlight that proper sample handling is necessary before employing different characterization techniques. We exemplify by performing an IR spectroscopic study of a propylamine-modified porous silica. Such amine-modified supports are relevant to applications in gas separation, catalysis, controlled drug delivery and adsorption of pollutants from water.
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| 24. |
- Bacsik, Zoltan, et al.
(författare)
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Mechanisms and Kinetics for Sorption of CO(2) on Bicontinuous Mesoporous Silica Modified with n-Propylamine
- 2011
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:17, s. 11118-11128
-
Tidskriftsartikel (refereegranskat)abstract
- We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.
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| 25. |
- Bacsik, Zoltan, et al.
(författare)
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Selective separation of CO2 and CH4 for biogas upgrading on zeolite NaKA and SAPO-56
- 2016
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 162, s. 613-621
-
Tidskriftsartikel (refereegranskat)abstract
- Several commercial and potential adsorbents were investigated for the separation of CO2 from CH4, which is relevant for the upgrading of raw biogas. The main focus of the paper was on the working capacities and selectivities of the adsorbents for a generic vacuum swing adsorption (VSA) process. Zeolites 4A and 13X had good estimated CO2-over-CH4 selectivities and reasonably high working capacities for the removal of CO2. A variant of zeolite A - vertical bar Na12-Kx vertical bar-LTA (with 1.8 <= x <= 3.2), had at least the same working capacity as zeolite 4A but with a significantly improved selectivity. Hence, the environmentally important CH4 slip can be minimized with this vertical bar Na12-Kx vertical bar-LTA sorbent. If a high working capacity for CO2 removal is the most important characteristic for a VSA process, then silicoaluminum phosphate, specifically SAPO-56, appeared to be the best candidate among the studied sorbents. In addition, SAPO-56 had a substantially high estimated CO2-over-CH4 selectivity with a value between similar to 20 and 30.
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| 26. |
- Bacsik, Zoltan, et al.
(författare)
-
Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines
- 2010
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:12, s. 10013-10024
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption-mediated CO2 separation can reduce the costs of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pm3n symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either co-synthesizing or post-synthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present the first direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogenous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the post-synthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in post-synthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate–ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine–propylamine distance must be small to allow the formation of carbamate–propylammonium ion pairs.
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| 27. |
- Bernin, Diana, 1979, et al.
(författare)
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Perspectives on NMR studies of CO2 adsorption
- 2018
-
Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294 .- 1879-0399. ; 33, s. 53-62
-
Tidskriftsartikel (refereegranskat)abstract
- There is a consensus about a long-term goal of a carbon-neutral energy cycle, but the CO2 emissions to the atmosphere are currently very large. Carbon Capture and Storage (CCS) technologies could allow a transformation of the global energy system into a carbon-neutral one and simultaneously keeping the temperature rises within agreed bounds. The CO2 separation step of CCS is, however, very expensive, and adsorption-driven technologies have been put forward as alternatives. Hence, a recent focus has been on studying solid adsorbents for CO2, which include activated carbons, zeolites, metal-organic frameworks, and amine-modified silica. In this context, we summarize the literature concerning CO2 sorption studied with Nuclear Magnetic Resonance (NMR), outline selected NMR methods, and present an outlook for further studies. (C) 2018 Elsevier Ltd. All rights reserved.
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| 28. |
- Björnerbäck, Fredrik, et al.
(författare)
-
Highly Porous Hypercrosslinked Polymers Derived from Biobased Molecules
- 2019
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 12:4, s. 839-847
-
Tidskriftsartikel (refereegranskat)abstract
- Highly porous and hyper-cross-linked polymers (HCPs) have a range of applications and are typically synthesized in an unsustainable manner. Herein, HCPs were synthesized from abundant biobased or biorelated compounds in sulfolane with iron(III) chloride as Lewis acid catalyst. As reactants, quercetin, tannic acid, phenol, 1,4-dimethoxybenzene, glucose, and a commercial bark extract were used. The HCPs had high CO2 uptake (up to 3.94 mmol g(-1) at 0 degrees C and 1 bar), total pore volumes (up to 1.86 cm(3) g(-1)), and specific surface areas (up to 1440 m(2) g(-1)). H-1 NMR, C-13 NMR, and IR spectroscopy, wide-angle X-ray scattering, elemental analysis, and SEM revealed, for example, that the HCPs consisted of amorphous and cross-linked aromatic and phenolic structures with significant contents of aliphatics, oxygen, and sulfur.
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| 29. |
- Björnerbäck, Fredrik, et al.
(författare)
-
Microporous Humins Prepared from Sugars and Bio-Based Polymers in Concentrated Sulfuric Acid
- 2019
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:1, s. 1018-1027
-
Tidskriftsartikel (refereegranskat)abstract
- Highly microporous humins were synthesized from readily available sugars and bio-based polymers (monosaccharides, disaccharides, and polysaccharides) in sulfuric acid followed by a diethyl ether wash and heat treatment at 400 degrees C. The relative sustainability, costs of production, and availability of the starting materials were improved significantly as compared with the 5-hydroxymethyl-furfural-based microporous humins recently studied by us. A multipronged approach was used to study the detailed characteristics of the adsorbents. Results from H-1 NMR, C-13 NMR, FTIR, WAXS, and elemental analysis were combined and showed that the adsorbents predominantly consisted of amorphous and aromatic carbon structures being rich in oxygen. They were highly porous, and the micropore volumes varied among the compositions as could be observed by analyzing CO2 and N-2 gas adsorption data. Comparably high CO2 uptakes of 4.25 and 1.94 mmol/g at 0 degrees C and 1 and 0.15 bar were observed. With the synthesis of microporous humins with varying porosities, the domain of potential applications of this class of materials could be expanded.
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| 30. |
- Björnerbäck, Fredrik, et al.
(författare)
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Microporous Humins Synthesized in Concentrated Sulfuric Acid Using 5-Hydroxymethyl Furfural
- 2018
-
Ingår i: ACS OMEGA. - : American Chemical Society (ACS). - 2470-1343. ; 3:8, s. 8537-8545
-
Tidskriftsartikel (refereegranskat)abstract
- A new class of highly porous organic sorbents called microporous humins is presented. These microporous humins are derived from sustainable and industrially abundant resources, have high heat of CO2 sorption, and could potentially be useful for the separation of carbon dioxide from gas mixtures. Their synthesis involves the polymerization of 5-hydroxymethyl furfural (HMF) in concentrated sulfuric acid and treatment with diethyl ether and heat. In particular, the porosities were tuned by the heat treatment. HMF is a potential platform chemical from biorefineries and a common intermediate in carbohydrate chemistry. A high uptake of CO2 (up to 5.27 mmol/g at 0 degrees C and 1 bar) and high CO2-over-N-2 and CO2-over-CH4 selectivities were observed. The microporous humins were aromatic and structurally amorphous, which was shown in a multipronged approach using C-13 nuclear magnetic resonance and Fourier transform infrared spectroscopies, elemental analysis, and wide-angle X-ray scattering.
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| 31. |
- Björnerbäck, Fredrik, 1984-
(författare)
-
Sustainable porous organic materials : Synthesis, sorption properties and characterization
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The resources available to us humans, including metals, minerals, biomass, air, water, and anything else on the planet, are being used at an increasing rate. This anthropogenic use of resources both depletes the resources and has negative impacts on other resources, e.g. the biosphere. Thus, developing (more) sustainable chemical and industrial processes are of the utmost importance for the well-being of the creatures of Earth and for the long-term sustainability of human society.This thesis focuses on organic porous materials, and more specifically their synthesis and characterization. Porous materials are, for example, used in detergents, water treatment, bio gas upgrading, carbon dioxide capture, as catalysts, in sensors, and in various biological applications. The application of porous materials can contribute to the drive towards a more sustainable society. However, porous materials are typically not sustainable themselves. Thus, there is a need to develop more sustainable porous materials. The synthesis and characterization of three different groups of porous organic materials are described in this thesis.In pulp- and paper manufacturing, lignin is separated from desirable products and is typically combusted for heat. In one section of this thesis, lignin was used to produce bio-oil for potential use in fuels and chemicals. However, the bio-oil process produced a solid by-product. The by-product was used to synthesize and study activated carbons with very high porosities and magnetic properties, a combination of properties that may prove to be useful in applications.Sugar is known to produce solid and unwanted compounds through reactions with acids. It is shown here that it is possible to produce highly microporous humins, i.e. organic porous materials with a large amount of small pores, using sulphuric acid and a range of saccharides and bio-based polymers. This work supports that solid by-products in a wide range of biomass conversion processes can be of high value, both economically and as replacements for less sustainable alternatives.The biosphere contains vast amounts of molecules with aromatic structures. The last section of this thesis shows how such aromatic molecules can be used to produce highly porous materials through Friedel-Crafts type chemistry using sulfolane as a solvent and iron chloride as a catalyst. This synthesis strategy produces high-performance materials, improves upon the sustainability of traditional Friedel-Crafts chemistry, and makes use of typically underutilized and abundant bio-based molecules.
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| 32. |
- Bogár, Krisztián, et al.
(författare)
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Heterogenized Wilkinson's Catalyst for Transfer Hydrogenation of Carbonyl Compounds
- 2011
-
Ingår i: European Journal of Organic Chemistry. - : Wiley-VCH Verlag GmbH 3690 & Co. KGaA, Weinheim. - 1434-193X .- 1099-0690. ; :23, s. 4409-4414
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Tidskriftsartikel (refereegranskat)abstract
- Wilkinson’s catalyst [RhCl(PPh3)3] was heterogenized on common silica by the use of a grafting/anchoring technique. The immobilized catalyst showed high activity and selectivity in transfer hydrogenation reactions of a range of carbonyl compounds in 2-propanol. Reactions carried out in 2-propanol at reflux afforded the corresponding alcohols in high yields in short reaction times. The heterogeneous feature ofthe catalyst allows for easy recovery and efficient reuse in the same reaction up to 5 times without any detectible loss of catalytic activity.
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| 33. |
- Buffoni, Lena, et al.
(författare)
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Open source languages and methods for cyber-physical system development : Overview and case studies
- 2021
-
Ingår i: Electronics (Switzerland). - Basel : MDPI AG. - 2079-9292. ; 10:8
-
Tidskriftsartikel (refereegranskat)abstract
- Industrial cyber-physical system products interleave hardware, software, and communication components. System complexity is increasing simultaneously with increased demands on quality and shortened time-to-market. To effectively support the development of such systems, we present languages and tools for comprehensive integrated model-based development that cover major phases such as requirement analysis, design, implementation, and maintenance. The model-based approach raises the level of abstraction and allows to perform virtual prototyping by simulating and optimizing system models before building physical products. Moreover, open standards and open source implementations enable model portability, tool reuse and a broader deployment. In this paper we present a general overview of the available solutions with focus on Modelica/OpenModelica, Bloqqi, and Acumen. The paper presents contributions to these languages and environments, including symbolic-numeric modeling, requirement verification, code generation, model debugging, design optimization, graphical modeling, and variant handling with traceability, as well a general discussion and conclusions.
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| 34. |
- Cadars, Sylvian, et al.
(författare)
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Dynamics and disorder in surfactant-templated silicate layers studied by solid-state NMR dephasing times and correlated line shapes
- 2008
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:25, s. 9145-9154
-
Tidskriftsartikel (refereegranskat)abstract
- Surfactant-templated layered silicates are shown to possess complex compositional, structural, and dynamic features that manifest rich and interrelated order and disorder at molecular length scales. Temperature-dependent 1D and 2D solid-state Si-29 NMR measurements reveal a chemical-exchange process involving the surfactant headgroups that is concomitant with reversible broadening of Si-29 NMR line shapes under magic-angle-spinning (MAS) conditions at temperatures in the range 205-330 K. Specifically, the temperature-dependent changes in the Si-29 transverse dephasing times T-2' can be quantitatively accounted for by 2-fold reorientational dynamics of the surfactant headgroups. Variable-temperature analyses demonstrate that the temperature-dependent Si-29 shifts, peak broadening, and 2D Si-29{Si-29} correlation NMR line shapes are directly related to the freezing of the surfactant headgroup dynamics, which results in local structural disorder within the silicate framework.
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| 35. |
- Cardenas, Edgar, 1990-
(författare)
-
Synthesis of zeolites from economic raw materials
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Synthesis methods using economic raw materials, such as kaolin and diatomite have been developed for the production of zeolites in the present work. Zeolite Y and ZSM-5 have been synthetized successfully from diatomite and kaolin, respectively. The synthesis of zeolite Y was extensively studied (Paper I) in order to obtain final products with high crystallinity and an appropriate SiO2/Al2O3 ratio to be suitable for application as catalyst. Then, the influence of the alkalinity (in terms of SiO2/Na2O ratio) on the outcome of the synthesis was studied. Thus, an optimum range of alkalinity that satisfies the requirements stated before was found. Additionally, the results also showed that diatomite produce similar products as colloidal silica, which may be expected since both silica sources are highly polymerized forms of silica.The synthesized zeolite Y crystals were also ion-exchanged with Lanthanum to obtain a Rare Earth zeolite Y (REY) catalyst (Paper V). The REY catalyst was shown to be thermally stable up to 800°C as expected for this catalyst. The REY catalyst was also evaluated in the reaction of Catalytic Cracking of cumene. The results of catalytic tests shown that the REY catalyst synthetized from diatomite holds activity towards the catalytic cracking of cumene.In addition, studies of synthesis of ZSM-5 zeolite from kaolin have been performed to understand the crystal growth and morphology, crystal size, and aluminum distribution. In particular, the influence of the gel on the morphology of the crystals (Paper II) has been studied. It was observed that when the crystal surface is in contact with the gel phase, dendritic features appear at the crystal surface, that become smoother as the reaction proceeds. On the contrary, when only liquid phase is in contact with crystal surface there is no presence of dendritic features and the growth rate is higher.Further studies demonstrated that the ZSM-5 crystals possess a non-homogeneous aluminum distribution, a phenomenon known as Al-zoning. A thorough characterization at distinct stages of the reaction has been performed (Paper III), on the different reaction mixture phases such as solid part, gel phase and liquid phase. The main finding was that the gel phase consists of a nanoparticle skeleton rich in alumina, filled by a silica rich matrix. In the beginning of crystallization, the silica rich matrix is preferentially consumed to form the crystals, leaving behind the alumina rich nanoparticle skeleton that is consumed later, resulting in the non-homogeneous distribution of aluminum in the crystals.Finally, studies of the microstructure of a TPA-ZSM-5 system using fumed silica as silicon source have been performed (paper IV). In this system, three stages of crystallization were observed. Stage I, formation of amorphous gel phase. Stage II formation of XRD amorphous spherical entities denoted as Condensed Agregates (CAs). Stage III, Crystallization of CAs into ZSM-5. This study was focused only in the stage III. Findings showed that ZSM-5 nanocrystals are formed in the core of the CA (beginning of stage III), surrounded by an amorphous shell composed of alumino-silica. As the crystallization proceeds, the amorphous shell crystallizes into ZSM-5 by competitive growth, but the nanocrystals of the core remain intact. Moreover, compositional analysis results showed that the silicon from the liquid phase provided most of the nutrients for growth of the ZSM-5 crystals resulting in polycrystalline ZSM-5 aggregates with an Al rich core - Si rich shell morphology.
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| 36. |
- Chen, Zheng, et al.
(författare)
-
Graphitic nitrogen in carbon catalysts is important for the reduction of nitrite as revealed by naturally abundant N-15 NMR spectroscopy
- 2021
-
Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :20
-
Tidskriftsartikel (refereegranskat)abstract
- Metal-free nitrogen-doped carbon is considered as a green functional material, but the structural determination of the atomic positions of nitrogen remains challenging. We recently demonstrated that directly-excited solid state N-15 NMR (ssNMR) spectroscopy is a powerful tool for the determination of such positions in N-doped carbon at natural N-15 isotope abundance. Here we report a green chemistry approach for the synthesis of N-doped carbon using cellulose as a precursor, and a study of the catalytic properties and atomic structures of the related catalyst. N-doped carbon (NH3) was obtained by the oxidation of cellulose with HNO3 followed by ammonolysis at 800 degrees C. It had a N content of 6.5 wt% and a surface area of 557 m(2) g(-1), and N-15 ssNMR spectroscopy provided evidence for graphitic nitrogen besides regular pyrrolic and pyridinic nitrogen. This structural determination allowed probing the role of graphitic nitrogen in electrocatalytic reactions, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nitrite reduction reaction. The N-doped carbon catalyst (NH3) showed higher electrocatalytic activities in the OER and HER under alkaline conditions and higher activity for nitrite reduction, as compared with a catalyst prepared by the carbonization of HNO3-treated cellulose in N-2. The electrocatalytic selectivity for nitrite reduction of the N-doped carbon catalyst (NH3) was directly related to the graphitic nitrogen functions. Complementary structural analyses by means of C-13 and H-1 ssNMR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and low-temperature N-2 adsorption were performed and provided support to the findings. The results show that directly-excited N-15 ssNMR spectroscopy at natural N-15 abundance is generally capable of providing information on N-doped carbon materials if relaxation properties are favorable. It is expected that this approach can be applied to a wide range of solids with an intermediate concentration of N atoms.
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| 37. |
- Cheung, Ocean, et al.
(författare)
-
Adsorption kinetics for CO2 on highly selective zeolites NaKA and nano-NaKA
- 2013
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 112, s. 1326-1336
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide removal from flue gas via swing adsorption processes requires adsorbents with a high CO2 selectivity and capacity. These properties are particularly valuable to reduce the cost of carbon capture and storage (CCS). Zeolite NaKA was studied for its ability to selectively adsorb CO2 from flue gas, as we previously observed that zeolite NaKA, with a K+/(K+ + Na+) ratio of 17 atomic%, was highly selective towards CO2 over N-2 adsorption by tuning the size of the pore window apertures [1]. The reduced pore apertures may, however, retard the adsorption rate of CO2. Here, we studied the kinetics of CO2 adsorption on regularly sized zeolite NaKA and on nano-sized zeolite NaKA. We used in situ infrared (IR) spectroscopy and observed that CO2 physisorbed relatively rapidly. Density functional theory (DFT) was used for quantum chemical calculations, and the results indicated that CO2 molecules bridged across two or three Na+ ions in the samples with no or very small amount of K. When more K+ ions are present the CO2 molecules no longer bridged across multiple metal ions and adopted an end-on configuration. The calculation showed a shift in the stretching vibration frequency of physisorbed CO2 as observed by IR spectroscopy. Nano-sized zeolite NaKA were synthesised and studied to improve the rate of CO2 adsorption, as the diffusion rate typically increases quadratically with decreasing particle size. Still, the CO2 adsorption rate on nano-sized zeolites NaA and NaKA did not increase significantly. For nano-sized zeolite NaA, we speculate that the absence of such an increased rate is an effect from a skin layer that had formed on the nano-sized zeolite NaA, a layer that was possibly related to intergrowths with extremely small crystals on the surface. The apparently slow adsorption kinetics of CO2 on nano-sized zeolite NaKA was more difficult to explain because it could relate to imperfections within the small crystals, remaining water, or other effects. Overall, the CO2 adsorption rates on zeolite NaKA crystals of different sizes were fast and relevant for the time scales required for adsorption based CCS processes, such as vacuum and temperature swing adsorption (VSA/TSA).
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| 38. |
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| 39. |
- Cheung, Ocean, et al.
(författare)
-
CO2 selective NaMg-CTS-1 and its structural formation from the titanium silicate based molecule sieve NaMg-ETS-4 upon dehydration
- 2014
-
Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 198, s. 63-73
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A range of titanium silicates (ETS-4 and CTS-1) with interesting gas separation properties were studied as CO2 adsorbents. Some of these adsorbents, in particular NaMg-CTS-1, showed the ability to selectively adsorb CO2-over-N2. Partially exchanged NaM-ETS-4 (M = Mg, Ca, Sr and Ba) were synthesised in the Na+ form and ion exchanged with group 2 cations. All but NaBa-ETS-4 transformed into their CTS-1 counterparts, when these partially exchanged Na-ETS-4 were dehydrated. The transformation from ETS-4 to CTS-1 was monitored and studied extensively using diffraction and spectroscopic techniques. Powder X-ray diffraction allowed us to follow the changes of the unit cell parameters occurred at different temperatures. We combined high energy X-ray total scattering (analysed by pair distribution functions – PDF analysis), electron diffraction, infrared, Raman and Nuclear Magnetic Resonance (NMR) spectroscopy to study the transformation of ETS-4 to CTS-1. We understood that under dehydration steps, there was significant disruption to the Ti–O–Ti chain along the b-axis, which occurred concurrently with the distortion of the double 3-rings alongside of these chains. These changes were partly responsible for the contraction of the ETS-4 framework (and successive transformation to CTS-1). The new information allowed us to understand the interesting structures and sorption properties of these adsorbents
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| 40. |
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| 41. |
- Cheung, Ocean, et al.
(författare)
-
Highly selective uptake of carbon dioxide on the zeolite vertical bar Na10.2KCs0.8 -LTA - a possible sorbent for biogas upgrading
- 2016
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:24, s. 16080-16083
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Tidskriftsartikel (refereegranskat)abstract
- The vertical bar Na10.2KCs0.8(8)[Al12Si12O48](8)(Fm3c)-LTA zeolite adsorbs CO2-over-CH4 with a high selectivity (over 1500). The uptake of carbon dioxide is also high (3.31 mmol g(-1), 293 K, 101 kPa). This form of zeolite A is a very promising adsorbent for applications such as biogas upgrading, where keeping the adsorption of methane to a minimum is crucial.
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| 42. |
- Cheung, Ocean, et al.
(författare)
-
K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO2
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:32, s. 9682-9690
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorbents with high capacity and selectivity for adsorption of CO2 are currently being investigated for applications in adsorption-driven separation of CO2 from flue gas. An adsorbent with a particularly high CO2-over-N-2 selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al similar to 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO2 capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na+ form. When approximately 26 at % of the extraframework cations were exchanged for K+ (NaK-ZK-4), the material still adsorbed a large amount of CO2 (4.35 mmol/g, 273 K, 101 kPa), but the N-2 uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO2 was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO2 was fast, even for the highly selective sample. The molecular details of the sorption of CO2 were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K+ exchanged zeolite K-ZK-4 upon adsorption of CO2 and N-2 for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 23:1 restricted the diffusion of CO2 and N-2 across the cages. These simulations could not probe the delicate details of the molecular sieving of CO2 over N-2. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO2 uptake (similar to 4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO2-over-N-2 selectivity.
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| 43. |
- Cheung, Ocean, 1986-
(författare)
-
Narrow-pore zeolites and zeolite-like adsorbents for CO2 separation
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A range of porous solid adsorbents were synthesised and their ability to separate and capture carbon dioxide (CO2) from gas mixtures was examined. CO2 separation from flue gas – a type of exhaust gas from fossil fuel combustion that consists of CO2 mixed with mainly nitrogen and biogas (consists of CO2 mixed with mainly methane) were explicitly considered. The selected adsorbents were chosen partly due to their narrow pore sizes. Narrow pores can differentiate gas molecules of different sizes via a kinetic separation mechanism: a large gas molecule should find it more difficult to enter a narrow pore. CO2 has the smallest kinetic diameter in zeolites when compared with the other two gases in this study. Narrow pore adsorbents can therefore, show enhanced kinetic selectivity to adsorb CO2 from a gas mixture.The adsorbents tested in this study included mixed cation zeolite A, zeolite ZK-4, a range of aluminophosphates and silicoaluminophosphates, as well as two types of titanium silicates (ETS-4, CTS-1). These adsorbents were compared with one another from different aspects such as CO2 capacity, CO2 selectivity, cyclic performance, working capacity, cost of synthesis, etc. Each of the tested adsorbents has its advantages and disadvantages. Serval phosphates were identified as potentially good CO2 adsorbents, but the high cost of their synthesis must be addressed in order to develop these adsorbents for applications.
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| 44. |
- Cheung, Ocean, et al.
(författare)
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Selective Adsorption of CO2 on Zeolites NaK-ZK‑4 with Si/Al of 1.8−2.8
- 2020
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:39, s. 25371-25380
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Tidskriftsartikel (refereegranskat)abstract
- Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO2 over N2. Here, we showed that the exchangeable cations (e.g., Na+ or K+) on zeolite ZK-4 play an important role in the CO2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8–2.8 had very high CO2 selectivity when an intermediate number of the exchangeable cations were K+ (the rest being Na+). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO2 uptake capacity and very high CO2-over-N2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO2 selectivity with an intermediate number of K+ cations. The high CO2 selectivity was related to the K+ cation in the 8-rings of the α-cage, together with Na+ cations in the 6-ring, obstructing the diffusion of N2 throughout the zeolite. The positions of the K+ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO2, as revealed by in situ X-ray diffraction. The CO2-over-N2 selectivity was somewhat reduced when the number of K+ cations approached 100%. This was possibly due to the shift in the K+ cation positions in the 8-ring when the number of Na+ was going toward 0%, allowing N2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.
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| 45. |
- Cheung, Ocean, et al.
(författare)
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Selective Adsorption of CO2on Zeolites NaK-ZK-4 with Si/Al of 1.8-2.8
- 2020
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 5:39, s. 25371-25380
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Tidskriftsartikel (refereegranskat)abstract
- Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO2 over N2. Here, we showed that the exchangeable cations (e.g., Na+ or K+) on zeolite ZK-4 play an important role in the CO2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8-2.8 had very high CO2 selectivity when an intermediate number of the exchangeable cations were K+ (the rest being Na+). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO2 uptake capacity and very high CO2-over-N2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO2 selectivity with an intermediate number of K+ cations. The high CO2 selectivity was related to the K+ cation in the 8-rings of the α-cage, together with Na+ cations in the 6-ring, obstructing the diffusion of N2 throughout the zeolite. The positions of the K+ cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO2, as revealed by in situ X-ray diffraction. The CO2-over-N2 selectivity was somewhat reduced when the number of K+ cations approached 100%. This was possibly due to the shift in the K+ cation positions in the 8-ring when the number of Na+ was going toward 0%, allowing N2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.
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| 46. |
- Cheung, Ocean, et al.
(författare)
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Silicoaluminophosphates as CO2 sorbents
- 2012
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 156, s. 90-96
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Tidskriftsartikel (refereegranskat)abstract
- Silicoaluminophosphates (SAPO-17, SAPO-35, SAPO-56 and SAPO-RHO) synthesised via hydrothermal means are tested for their abilities to adsorb carbon dioxide. These 8-ring microporous phosphates show high capacities to adsorb CO2. SAPO-RHO has a high uptake of CO2 and a very low uptake of N-2 due to its narrow pore window aperture at 273 K. Its significant uptake of N-2 at 77 K is rationalised by a temperature induced shrinkage effect. SAPO-56 has a slightly higher CO2 capacity (5.42 mmol/g, 273 K, 101 kPa) and is less water sensitive than zeolite 13X. Cyclic adsorption and in situ infrared spectroscopy (IR) reveal that SAPOs retain 95% of their original CO2 capacity after six cycles and that adsorption occurs via physisorption. The calculated heat of adsorption for CO2 (at 0.2-0.7 mmol/g loading) on SAPO-56 and SAPO-RHO lies in the physisorption range (similar to 35 kJ/mol). SAPOs, in particular SAPO-56 and SAPO-RHO, possess many desirable properties and are potentially good adsorbents for CO2 capture in swing adsorption processes.
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| 47. |
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| 48. |
- Cheung, Ocean, et al.
(författare)
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Zeolites and related sorbents with narrow pores for CO2 separation from flue gas
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:28, s. 14480-14494
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Forskningsöversikt (refereegranskat)abstract
- Adsorbents with small pores are especially relevant for capturing carbon dioxide at large emission sources. Such sorbents could be used potentially to reduce the energy demands for separating carbon dioxide from flue gas as compared with today's technologies. Here, we review the literature for crystalline, inorganic, and potentially inexpensive adsorbents. A number of different adsorbents with narrow pore openings are compared.
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| 49. |
- Church, Tamara L., et al.
(författare)
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Dispersed Uniform Nanoparticles from a Macroscopic Organosilica Powder
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:6, s. 2274-2281
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Tidskriftsartikel (refereegranskat)abstract
- A colloidal dispersion of uniform organosilica nanoparticles could be produced via the disassembly of the non-surfactant-templated organosilica powder nanostructured folate material (NFM-1). This unusual reaction pathway was available because the folate and silica-containing moieties in NFM-1 are held together by noncovalent interactions. No precipitation was observed from the colloidal dispersion after a week, though particle growth occurred at a solvent-dependent rate that could be described by the Lifshitz-Slyozov-Wagner equation. An organosilica film that was prepared from the colloidal dispersion adsorbed folate-binding protein from solution but adsorbed ions from a phosphate -buffered saline solution to a larger degree. To our knowledge, this is the first instance of a colloidal dispersion of organosilica nanoparticles being derived from a macroscopic material rather than from molecular precursors.
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| 50. |
- Church, Tamara L., et al.
(författare)
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Sustainability of microporous polymers and their applications
- 2017
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Ingår i: Science in China Series B. - : Springer Science and Business Media LLC. - 1674-7291 .- 1869-1870. ; 60:8, s. 1033-1055
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Forskningsöversikt (refereegranskat)abstract
- Microporous polymers (MPs) are studied for their intriguing chemistry and physics as well as their potential application in catalytic transformations, gas-separation processes, water purification and so on. Here, we critically review MPs with respect to the sustainability aspects of their synthesis as well as their applications that have sustainable character. Some MPs have been synthesized from monomers derived from biomass resources, but there is certainly a large potential for further developments. There are also opportunities to improve the sustainability of MP synthesis in terms of the use of solvents, catalysts, and related aspects. The applications of MPs in processes related to sustainability depend upon multiple properties. A rich and flexible chemistry is important to applications as catalysts for, among other useful reactions, the photoreduction of CO2 and selective oxidation. The (ultra) micropore volume of MPs are crucial in gas-separation applications such as CO2 capture, and the chemisorption of CO2 on MP-tethered alkylamines could offer a means to remove that gas from dilute mixtures. When it comes to the storage of H-2 and CH4 in MPs for onboard use in fuel cell or biogas cars, volumetric capacity is paramount, meaning that the density of the MPs must be considered. Finally, for use in separation and purifications from liquid mixtures (aqueous or hydrocarbon-based), crosslinked MPs are more limited than the solution-processable MPs that can be more easily processed into films and membranes.
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