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- Gavrilovic, Ljubisa, et al.
(författare)
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Deactivation of Co-based Fischer-Tropsch catalyst by aerosol deposition of potassium salts
- 2018
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Ingår i: Industrial & Engineering Chemistry Research. - Washington, USA : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 57:6, s. 1935-1942
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Tidskriftsartikel (refereegranskat)abstract
- A 20%Co/0.5%Re/γAl2O3 Fischer-Tropsch catalyst was poisoned by four potassium salts (KNO3, K2SO4, KCl, K2CO3) using the aerosol deposition technique, depositing up to 3500 ppm K as solid particles. Standard characterization techniques (H2 Chemisorption, BET, TPR) showed no difference between treated samples and their unpoisoned counterpart. The Fischer-Tropsch activity was investigated at industrially relevant conditions (210 °C, H2:CO = 2:1, 20 bar). The catalytic activity was significantly reduced for samples exposed to potassium, and the loss of activity was more severe with higher potassium loadings, regardless of the potassium salt used. A possible dual deactivation effect by potassium and the counter-ion (chloride, sulfate) is observed with the samples poisoned by KCl and K2SO4. The selectivity towards heavier hydrocarbons (C5+) was slightly increased with increasing potassium loading, while the CH4 selectivity was reduced for all the treated samples. The results support the idea that potassium is mobile under FT conditions. The loss of activity was described by simple deactivation models which imply a strong non-selective poisoning by the potassium species.
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| 4. |
- Gavrilovic, Ljubisa, et al.
(författare)
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Fischer-Tropsch synthesis : Investigation of the deactivation of a Co catalyst by exposure to aerosol particles of potassium salt
- 2018
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Ingår i: Applied Catalysis B. - : Elsevier. - 0926-3373 .- 1873-3883. ; 230, s. 203-209
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Tidskriftsartikel (refereegranskat)abstract
- The influence of potassium species on a Co based Fischer-Tropsch catalyst was investigated using an aerosol deposition technique. This way of poisoning the catalyst was chosen to simulate the actual potassium behaviour during the biomass to liquid (BTL) process utilizing gasification followed by fuel synthesis. A reference catalyst was poisoned with three levels of potassium and the samples were characterized and tested for the Fischer-Tropsch reaction under industrially relevant conditions. None of the conventional characterization techniques applied (H2 Chemisorption, BET, TPR) divulged any difference between poisoned and unpoisoned samples, whereas the activity measurements showed a dramatic drop in activity following potassium deposition. The results are compared to previous results where incipient wetness impregnation was used as the method of potassium deposition. The effect of potassium is quite similar in the two cases, indicating that irrespective of how potassium is introduced it will end up in the same form and on the same location on the active surface. This indicates that potassium is mobile under FTS conditions, and that potassium species are able to migrate to sites of particular relevance for the FT reaction.
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| 5. |
- Gavrilovic, Lubisa, et al.
(författare)
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The effect of aerosol-deposited ash components on a cobalt-based Fischer–Tropsch catalyst
- 2019
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Ingår i: Reaction Kinetics, Mechanisms and Catalysis. - : Springer. - 1878-5190 .- 1878-5204. ; 127:1, s. 231-240
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Tidskriftsartikel (refereegranskat)abstract
- The effect of ash salts on Co-based Fisher–Tropsch catalysts was studied using an aerosol deposition technique. The major elements in the ash were found to be K, S and Cl. The ash was deposited on a calcined catalyst as dry particles with an average diameter of approx. 350 nm. The loading of ash particles was varied by varying the time of exposure to the particles in a gas stream. Catalyst characterization did not reveal significant differences in cobalt dispersion, reducibility, surface area, pore size, or pore volume between the reference and the catalysts with ash particles deposited. Activity measurements showed that following a short exposure to the mixed ash salts (30 min), there were no significant loss of activity, but a minor change in selectivity of the catalyst . Extended exposure (60 min) led to some activity loss and changes in selectivity. However, extending the exposure time and thus the amount deposited as evidenced by elemental analysis did not lead to a further drop in activity. This behavior is different from that observed with pure potassium salts, and is suggested to be related to the larger size of the aerosol particles deposited. The large aerosol particles used here were probably not penetrating the catalyst bed, and to some extent formed an external layer on the catalyst bed. The ash salts are therefore not able to penetrate to the pore structure and reach the Co active centers, but are mixed with the catalyst and detected in the elemental analysis.
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| 6. |
- Lögdberg, Sara, et al.
(författare)
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Effect of water on the space-time yield of different supported cobalt catalysts during Fischer-Tropsch synthesis
- 2011
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 393:1-2, s. 109-121
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Tidskriftsartikel (refereegranskat)abstract
- The effect of partial pressure of water on the Fischer-Tropsch (FT) rate of six cobalt-based catalysts supported on three different carrier materials (gamma-Al2O3, alpha-Al2O3, TiO2) with varying Co particle sizes was investigated in a fixed-bed reactor by changing space velocity and by external water vapour addition. A typical catalyst pellet size (<100 mu m) for industrial slurry-bed FT reactors was used. Water was found to have a positive kinetic effect, at least up to moderate amounts, on the FT rate of all catalysts in the present study, including the gamma-Al2O3-supported catalyst with pores smaller than similar to 10 nm. The reason for the apparent negative effect on the space-time yield at a direct exposure of Co supported on narrowpore gamma-Al2O3 to high partial pressures of water is due to a rapid and extensive deactivation. This could be ascribed to formation of hard-to-reduce oxidized cobalt species. The choice of support material was found to have a major effect on the response to changes in partial pressure of water, both with respect to deactivation behaviour and kinetics. However, there is a minor Co-particle size effect on the magnitude of the kinetic effect of water, larger Co particles showing a more positive response. Different extents of mass transfer limitations and/or differences in fugacities of H-2, CO and water among the six catalysts could be ruled out as causes for the observed differences.
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| 7. |
- Lögdberg, Sara, et al.
(författare)
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On the selectivity of cobalt-based Fischer-Tropsch catalysts : Evidence for a common precursor for methane and long-chain hydrocarbons
- 2010
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 274:1, s. 84-98
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Tidskriftsartikel (refereegranskat)abstract
- A total of 36 cobalt-based supported catalysts were investigated in the Fischer-Tropsch reaction at industrially relevant process conditions: 483 K, 20 bar, molar H-2/CO ratio = 2.1, pellet size: 53-90 mu m. The effect of adding water vapour to the feed was investigated for 20 of the catalysts, and a H-2/CO ratio of 1.0 was used for a few catalysts. The catalysts differed in support material, Co loading, promoters, Cl content, Co particle size (larger than similar to 6 nm), morphology, degree of reduction and preparation technique and showed a large variation in selectivity. For each set of process conditions, a linear relationship seems to exist between the selectivity to methane (and other light products) and C5+ indicating a common precursor, i.e. a common monomer pool, for all hydrocarbon products. A high selectivity to C5+ is mainly an effect of a high intrinsic chain-growth probability and unlikely to be a result of an enhanced cc-olefin readsorption. The universal effect of external water addition on the hydrocarbon selectivities is limited to a decrease in the methane selectivity. A small proportion of the catalysts developed "pure methanation" sites upon exposure to high partial pressures of water.
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