| 1. |
- Creaser, Derek, et al.
(författare)
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Kinetic modelling of oxygen dependence in oxidative dehydrogenation of propane
- 2000
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Ingår i: Canadian Journal of Chemical Engineering. - : Wiley. - 0008-4034 .- 1939-019X. ; 78:1, s. 182-193
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Tidskriftsartikel (refereegranskat)abstract
- Several Mars-Van Krevelen-type redox kinetic models were developed for the catalytic oxidative dehydrogenation of propane and examined for their ability to predict high propene yields at low oxygen/propane feed ratios. The intent in this study was to use modelling as a means of extracting further mechanistic insight from experimental data rather than to identify the best model. Thus, a conventional redox model with a consecutive reaction mechanism and a single pathway for the production of carbon oxides predicts higher propene selectivity but only at the expense of low propane conversion. Experimental data indicated, however, that even at the same propane conversion, propene selectivity increased as the oxygen partial pressure was lowered. Models that successfully describe the data had an additional carbon oxide production path involving the reaction of propane with deeply oxidizing surface oxygen species. Kinetic models and experimental data examined do not fully resolve how these deeply oxidizing surface oxygen species are formed. However, they do reflect the accepted view that lattice oxygen selectively produces propene whereas more weakly bound surface adsorbed oxygen reacts to completely oxidize propane.
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| 2. |
- Jareman, Fredrik, et al.
(författare)
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Modelling of single gas permeation in real MFI membranes
- 2004
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 236:1-2, s. 81-89
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Tidskriftsartikel (refereegranskat)abstract
- A novel permeation model for flow through defects and zeolite pores in real MFI membranes, also accounting for substrate effects has been developed. Defect distributions for two types of MFI membranes were determined from porosimetry data using the model, which incorporated the Horvath Kawazoe (micropores) or the Kelvin equation (mesopores). The narrowest (1.08 nm) and also most common defects were found to be separated with a distance of 10–40 μm according to the model. Diffusion coefficients for hydrogen, helium, nitrogen and SF6 in the zeolite were further determined from single gas permeation data using the model using the independently determined defect distribution. The coefficients are consistent with values previously reported in the literature.
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| 3. |
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| 4. |
- Lassinantti, Magdalena, et al.
(författare)
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Preparation and evaluation of thin ZSM-5 membranes synthesized in the absence of organic template molecules
- 2001
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Ingår i: Catalysis Today. - 0920-5861 .- 1873-4308. ; 67:1-3, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- Porous α-alumina supports with a pore size of 100 nm were seeded with colloidal TPA-silicalite-1 crystals with a size of 120 nm. The seeded supports were calcined and treated in a synthesis solution free from organic template molecules to form ZSM-5 films on the supports. According to SEM images, the films were about 2 μm thick and no defects could be found on the as-synthesized membranes. Single gas permeation data was collected and good quality membranes (defined as having a non-detectable permeance of SF6 after drying at 100°C) were further evaluated using binary/ternary gas mixtures. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Water was selectively separated from a helium-diluted vaporized water/ethanol azeotrope with a maximum selectivity of 12.4.
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| 5. |
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| 6. |
- Li, Qinghua, et al.
(författare)
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Synthesis and characterization of zoned MFI films by seeded growth
- 2002
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 56:3, s. 291-302
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Tidskriftsartikel (refereegranskat)abstract
- Supported zoned and sandwiched MFI films were prepared by a two-step crystallization procedure, using seeds. In this work, a zoned MFI film is defined as one assembled by crystals propagating from the support to the film top surface with varying Al content along the length of the crystal. A sandwiched MFI film is referred to as one assembled by at least two layers of crystals. Six types of films were prepared, both zoned and sandwiched, with a high or a low Al-content in the ZSM-5 part and with varying order of the layers, i.e. ZSM-5 coated with silicalite-1 or vice versa. The films were characterized by SEM and TEM. The Al-distribution was measured by cross-sectional EDS, and the preferred orientation of the crystals could be determined by XRD. Truly zoned films are obtained when the compositional difference between the layers is relatively small, and the synthesis conditions are similar or when the first layer is silicalite-1. If the first layer is ZSM-5 and the synthesis conditions and/or the composition vary too much, a discontinuity occurs at the interface between the layers, and sandwiched film results, where nucleation of the second layer is initiated by secondary nucleation or by applying seeds.
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| 7. |
- Li, Qinghua, et al.
(författare)
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The nucleation period for crystallization of colloidal TPA-silicalite-1 with varying silica source
- 2000
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811 .- 1873-3093. ; 40:1-3, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- The effect of varying silica source on the nucleation and crystallization of TPA-silicalite-1 was investigated. A direct experimental method, involving a two-stage varying-temperature synthesis, was used to determine the nucleation period for colloidal crystals of TPA-silicalite-1 with different silica sources, including tetraethoxysilane (TEOS) and amorphous silica (Ludox TM and Ludox LS). For syntheses performed at 60°C with TEOS as silica source, the duration of the nucleation was about 72 h, and a very rapid increase in the crystal population occurred during the initial crystallization time. However, with the amorphous silica sources (Ludox TM or Ludox LS), the duration of the nucleation period was extended to about 120 h, and the nucleation profile consisted of a self-accelerating nucleation rate at the beginning of the nucleation period. The two-stage synthesis method could be used to determine the nucleation profile for the various silica sources. However, this technique overestimated the crystal concentration at the earliest stage of nucleation with amorphous silica. The use of amorphous silica gave rise to a broader crystal size distribution compared to that of TEOS. However, it was found that for both TEOS and amorphous silica the vast majority of the nucleation occurred during an induction period when little or no crystal growth was observed. In addition, Raman spectroscopy revealed structural differences between Ludox TM and Ludox LS which may account for differences in the nucleation processes observed for these two amorphous silicas.
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| 8. |
- Li, Qinghua, et al.
(författare)
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Zoned MFI films by seeding
- 2001
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Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; 2001:6, s. 527-528
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of zoned MFI films consisting of intergrown TPA-silicalite-1 and ZSM-5 crystals are described.
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| 9. |
- Papadakis, Klaus, et al.
(författare)
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Evaluation of a NOx reduction system on an engine rig under stationary operation
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028. ; 30-31:1-4, s. 215-222
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Tidskriftsartikel (refereegranskat)abstract
- The NOx storage and reduction approach was applied on a full-scale engine rig under stationary operation. NOx reduction experiments were performed and a catalyst model developed and tested. The exhaust system was equipped with a bypass system. A NOx reduction of 25-53% was achieved. At low temperature, higher values were reached when the exhaust gas bypass was longer than the injection period.
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| 10. |
- Papadakis, Klaus, et al.
(författare)
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Stationary NOx storage and reduction experiments on a heavy-duty diesel engine rig using a bypass system
- 2003
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Ingår i: Society of Automotive Engineers - Technical Paper Series. - 0099-5908. ; , s. 117-122
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Tidskriftsartikel (refereegranskat)abstract
- This work concerns exhaust gas cleaning for heavy-duty diesel engines by means of NOx storage and redn. technol. A full-scale engine rig has been constructed, and stationary NOx redn. tests performed. In the NOx storage and redn. approach, NOx is stored on a BaO surface as Ba(NO3)2 under long lean conditions and desorbed and reduced under short rich conditions. The rich conditions are created by injection of diesel fuel into the exhaust stream. The stationary NOx redn. tests have been performed at nine load points on an engine rig. They have shown that a stationary NOx redn. of between 25-53% is achievable at most load points depending on the temp. The high oxygen content in the exhaust gas leads to the oxidn. of the injected hydrocarbons and thus to a high fuel penalty. To lower the fuel consumption, the mass flow through the catalyst has been reduced under the regeneration periods. This was done using a bypass system with a pneumatic valve control. The extent of the reduced catalyst flow has been examd.
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