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Deactivation of cobalt and nickel catalysts in Fischer-Tropsch synthesis and methanation
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

            A potential route for converting different carbon sources (coal, natural gas and biomass) into synthetic fuels is the transformation of these raw materials into synthesis gas (CO and H2), followed by a catalytic step which converts this gas into the desired fuels. The present thesis has focused on two catalytic steps: Fischer-Tropsch synthesis (FTS) and methanation. The Fischer-Tropsch synthesis serves to convert synthesis gas into liquid hydrocarbon-based fuels. Methanation serves instead to produce synthetic natural gas (SNG). Cobalt catalysts have been used in FTS while nickel catalysts have been used in methanation.

            The catalyst lifetime is a parameter of critical importance both in FTS and methanation. The aim of this thesis was to investigate the deactivation causes of the cobalt and nickel catalysts in their respective reactions.

            The resistance to carbonyl-induced sintering of nickel catalysts supported on different carriers (γ-Al2O3, SiO2, TiO2 and α-Al2O3) was studied. TiO2-supported nickel catalysts exhibited lower sintering rates than the other catalysts. The effect of the catalyst pellet size was also evaluated on γ-Al2O3-supported nickel catalysts. The use of large catalyst pellets gave considerably lower sintering rates. The resistance to carbon formation on the above-mentioned supported nickel catalysts was also evaluated. Once again, TiO2-supported nickel catalysts exhibited the lowest carbon formation rates. Finally, the effect of operating conditions on carbon formation and deactivation was studied using Ni/TiO2 catalysts. The use of higher H2/CO ratios and higher pressures reduced the carbon formation rate. Increasing the temperature from 280 °C to 340 °C favored carbon deposition. The addition of steam also reduced the carbon formation rate but accelerated catalyst deactivation.

            The decline in activity of cobalt catalysts with increasing sulfur concentration was also assessed by ex situ poisoning of a cobalt catalyst. A deactivation model was proposed to predict the decline in activity as function of the sulfur coverage and the sulfur-to-cobalt active site ratio. The results also indicate that sulfur decreases the selectivity to long-chain hydrocarbons and olefins.

Place, publisher, year, edition, pages
Stockholm: US-AB , 2016. , xii, 124 p.
Series
TRITA-CHE-Report, ISSN 1654-1081
Keyword [en]
cobalt, nickel, Fischer-Tropsch synthesis, methanation, deactivation, carbonyl, sintering, carbon fomation. sulfur, poisoning
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-190593ISBN: 978-91-7729-060-5OAI: oai:DiVA.org:kth-190593DiVA: diva2:952256
Public defence
2016-09-23, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 308733
Note

QC 20160817

Available from: 2016-08-17 Created: 2016-08-12 Last updated: 2016-08-18Bibliographically approved
List of papers
1. Deactivation of supported nickel catalysts during CO methanation
Open this publication in new window or tab >>Deactivation of supported nickel catalysts during CO methanation
2014 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 486, 143-149 p.Article in journal (Refereed) Published
Abstract [en]

Deactivation of Ni-based catalysts was investigated during CO methanation over different supported catalysts. X-ray diffraction and temperature-programmed hydrogenation analyses were used to investigate nickel particle sintering and carbon formation during the first 24 h on stream. Titania-supported catalysts presented high resistance towards carbon deposition and nickel particle growth in comparison with the other tested catalysts. Particle size effects on these two deactivation causes were also evaluated. It was shown that carbon formation rates are higher on bigger crystal particles. However, it was found that titania-supported nickel catalysts reduced at high temperatures show the opposite effect. This difference is most probably due to a stronger interaction between nickel and TiOx (x < 2) species on smaller crystals which changes the CO dissociation properties and, in consequence, carbon formation rates.

Keyword
Methanation, Deactivation, Support, Titania, Carbon formation
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-157220 (URN)10.1016/j.apcata.2014.08.021 (DOI)000344439400016 ()2-s2.0-84908648449 (ScopusID)
Funder
EU, FP7, Seventh Framework Programme, 308733Swedish Energy Agency
Note

QC 20141209

Available from: 2014-12-09 Created: 2014-12-08 Last updated: 2016-08-17Bibliographically approved
2. CO methanation over TiO2-supported nickel catalysts: A carbon formation study
Open this publication in new window or tab >>CO methanation over TiO2-supported nickel catalysts: A carbon formation study
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2015 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 502, 276-286 p.Article in journal (Refereed) Published
Abstract [en]

A systematic study on titania-supported nickel catalysts was performed in order to evaluate the effect of different process conditions on catalyst stability. Reaction tests and temperature-programmed-hydrogenation analyses were used in order to evaluate the effect of temperature, feed composition, water and reduction conditions on catalyst deactivation and carbon deposition. It was shown that high H-2/CO ratios and syngas partial pressures decrease the rate of carbon formation. Moreover, increasing temperature enhanced the formation of more stable carbon species and thus catalyst deactivation. The temperature-programmed hydrogenation analyses also revealed that water reduces the rate of carbon deposition. However, water enhanced catalyst deactivation when the catalysts were reduced at high temperatures. This negative effect of water is probably due to a progressive destruction of the strong-metal-support interaction characteristic of titania-supported nickel catalysts reduced at high temperatures. (C) 2015 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Methanation, Deactivation, Nickel, Titania, Carbon formation
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-174939 (URN)10.1016/j.apcata.2015.06.029 (DOI)000361162200033 ()2-s2.0-84934759326 (ScopusID)
Funder
Swedish Energy Agency
Note

QZ 20151019

Available from: 2015-10-19 Created: 2015-10-09 Last updated: 2016-08-17Bibliographically approved
3. Further insights into the effect of sulfur on the activity and selectivity of cobalt-based Fischer–Tropsch catalysts
Open this publication in new window or tab >>Further insights into the effect of sulfur on the activity and selectivity of cobalt-based Fischer–Tropsch catalysts
2016 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 275, 119-126 p.Article in journal (Refereed) Published
Abstract [en]

 A sulfur poisoning study was performed by ex situ poisoning of a platinum-promoted cobalt/alumina catalyst with different sulfur amounts. The poisoned catalyst samples were tested at relevant Fischer–Tropsch reaction conditions and at the same CO conversion in order to evaluate the effect of sulfur on catalyst activity and product selectivity. It was found that the activity and the selectivity to long-chain hydrocarbons decrease with increasing sulfur content. Moreover, it was found that sulfur has no significant effect on the CO2 selectivity. It was also shown that sulfur significantly enhances olefin hydrogenation. Finally, a deactivation model relating the catalyst activity and the sulfur to cobalt active site ratio was proposed and used to describe the experimental results.

Keyword
Fischer–Tropsch, Sulfur, Cobalt, Deactivation, Selectivity
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-182347 (URN)10.1016/j.cattod.2015.10.039 (DOI)000382420300017 ()
Note

QC 20160926

Available from: 2016-02-18 Created: 2016-02-18 Last updated: 2016-09-26Bibliographically approved
4. The effect of catalyst pellet size on nickel carbonyl-induced particle sintering under low temperature CO methanation
Open this publication in new window or tab >>The effect of catalyst pellet size on nickel carbonyl-induced particle sintering under low temperature CO methanation
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2016 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 514, 91-102 p.Article in journal (Refereed) Published
Abstract [en]

Abstract The present work aims to evaluate the effect of catalyst pellet size on deactivation due to nickel carbonyl-induced particle sintering. For that purpose, a γ-Al2O3-supported nickel catalyst was prepared and tested under low temperature and high CO partial pressure. A total of four different pellet sizes were employed in the present study. It was found that the deactivation rate decreases with increasing pellet size. A very severe deactivation was observed when using small pellets. Large pellets exhibited instead a more stable performance. This difference in catalyst stability was explained by X-ray diffraction analyses which revealed that the growth of the nickel particles was very severe when using small pellets. An evaluation of heat and mass transfer phenomena in these four pellets was also conducted. It was found that, under the present low temperature reaction conditions, the temperature at the catalyst external surface can greatly differ from that in the bulk gas when using sufficiently large pellets. It was also shown that, for large pellets, the major part of the interior of the catalyst is exposed to negligible CO partial pressures and high temperatures, fact that can reduce the potential for nickel carbonyl formation.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Methanation, Deactivation, Nickel carbonyl, Sintering, Heat and mass transfer, Alumina
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-182353 (URN)10.1016/j.apcata.2015.12.034 (DOI)000371551200010 ()2-s2.0-84955264386 (ScopusID)
Funder
EU, FP7, Seventh Framework Programme, 308733
Note

QC 20160330. QC 20160407

Available from: 2016-02-18 Created: 2016-02-18 Last updated: 2016-08-17Bibliographically approved

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