| 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
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:17, s. 11118-11128
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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)
-
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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