Catalyst deactivation by carbon formation Johanna Kihlman Energy Lab 2.0 meets Neo-Carbon Energy

Transcription

1 VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD Catalyst deactivation by carbon formation Johanna Kihlman Energy Lab 2.0 meets Neo-Carbon Energy

2 BACKGROUND

3 Two target processes: biofuels and SOFC BIOFUEL PRODUCTION PROJECTS NextUCG (Varkaus demo) VETAANI 2G2020 STEAM REFORMER Feed gas: biomass gasification gas T = C Main challenge: tars and sulfur FUEL CELLS PROJECT Stage-SOFC STEAM REFORMER Feed gas: Natural gas + Anode off-gas T = C Main challenge: low O/C ratio 17/02/2017 3

4 Two catalysts: Nickel and precious metal Nickel + Robust, commercial in steam-reforming - Deactivates easily by coke Doped-ZrO 2 + Lower operation temperature, < 700 C + Tolerates catalyst poisons + Selective removal of heavy PAH Precious metals + Less prone to coking as Ni - Expensive Ref: WO 2011/ A1, WO A1, WO A1 17/02/2017 4

5 Carbon formation

6 Reactions Steam reforming reactions: -ΔH (kj/mol) CH 4 + H 2 O CO + 3H C n H m + nh 2 O nco + (n + 0.5m)H 2 <0 Carbon formation: CH 4 C + 2H 2-75 C n H m nc + 0.5mH 2 C n H m olefins coke Reactions source: J. Rostrup-Nielsen and L. Christiansen, Concepts in Syngas Manufacture, Catalytic Science Series vol 10, Imperial College Press, 2011 London. 17/02/2017 6

7 Biomass gasification gas composition 17/02/2017 7

8 Types of carbon Encapsulating / Gum carbon usually below ~500 o C Whisker carbon usually below ~700 o C Encapsulating / Pyrolytic carbon especially above ~700 o C 17/02/2017 8

9 Types of carbon 730 C 530 C PYROLYTIC WHISKER 430 C 600 C Source: J. Rostrup-Nielsen, Catalytic Steam Reforming, Catalysis - Science and Technology, Vol 5, Springer-Verlag, 1984 Berlin. 17/02/2017 9

10 Carbon formation Whisker carbon forms on catalyst Pyrolytic carbon forms thermally 17/02/

11 Whisker carbon

12 Characteristics of whisker carbon Figure a: Helveg, S. et al., Catal Today 178 (2011) Whisker carbon Appears usually below ~700 o C Catalytic reaction on nickel Forms carbon nanotubes i.e. whiskers Destroys the catalyst irreversibly Inhibited by H 2 S Source: Kihlman, J. et al., IntJ 17/02/2017 Hydro Ene 40 (2015)

13 Pyrolytic carbon

14 Types of carbon Pyrolytic coke Especially above ~700 o C Encapsulates the catalyst Increases the pressure drop Inhibits the access of reactive components to the catalyst surface 17/02/2017 Source: Kihlman, J. et al., Int 14J Hydro Ene 40 (2015)

15 What affects carbon formation?

16 What affects carbon formation?? Hydrocarbons Source: J. Rostrup-Nielsen, Catalytic Steam Reforming, Catalysis - Science and Technology, Vol 5, Springer-Verlag, 1984 Berlin. 17/02/

17 What affects carbon formation?? Steam Steam reforming reactions: -ΔH (kj/mol) CH 4 + H 2 O CO + 3H C n H m + nh 2 O nco + (n + 0.5m)H 2 <0 We can add H 2 O to avoid carbon formation to some extent... BUT the more water we add, the more we need to heat it up > feasibility of the process! Carbon formation: CH 4 C + 2H 2-75 C n H m nc + 0.5mH 2 C n H m olefins coke Reactions source: J. Rostrup-Nielsen and L. Christiansen, Concepts in Syngas Manufacture, Catalytic Science Series vol 10, Imperial College Press, 2011 London. 17/02/

18 What affects carbon formation?? Steam Source: J. Rostrup-Nielsen, Catalytic Steam Reforming, Catalysis - Science and Technology, Vol 5, Springer-Verlag, 1984 Berlin. 17/02/

19 What affects carbon formation?? Pressure Generally, the higher pressure, the more carbon. A small increase in pressure can already lead to carbon formation. 17/02/

20 What affects carbon formation?? Sulfur For whisker carbon, sulfur inhibits the carbon growth. - More than 50 ppmv of sulfur can inhibit whisker carbon completely. For pyrolytic carbon, sulfur deactivates gasification and steam reforming reactions that inhibit carbon accumulation. Source: 17/02/2017 Kihlman, J. et al., submitted. 20

21 Estimating whisker carbon formation from methane Principle of equilibrated gas 1 can be used to predict carbon formation in the natural gas (methane) steam reforming. Suitable for only methane, the more higher hydrocarbons, the less precise is the result. Source: J. Rostrup-Nielsen and L. Christiansen, Concepts in Syngas Manufacture, Catalytic Science Series vol 10, Imperial College Press, 2011 London. 17/02/

22 Conclusions

23 Conclusions There are different types of carbon Carbon formation is affected by: Catalyst Temperature Pressure Feed gas composition Hydrocarbons Steam Oxygen Sulfur Reactor design Operation parameters Estimations can be done by thermodynamic calculations, but the more complicated the gas is, the less precise the predictions are. Carbon formation can be avoided Practical research work is often needed 17/02/

24 What affects carbon formation?? Reactor and operation Catalyst long-term test at the Lahti plant Monolith front face after 24 h on-stream Front face clogged by carbon formed from tar at high temperature Second test: Monolith front face after 2300 h on-stream No clogging problems, pressure drop low & steady throughout the test 17/02/

25 Acknowledgements This research work has been done together with: Noora Kaisalo, Juli Sucipto, Mari-Leena Koskinen-Soivi, Päivi Jokimies, Katja Heiskanen, Pekka Simell, Matti Reinikainen, Juha Lehtonen and Marita Niemelä. The research under this project is receiving funding from the Fuel Cell and Hydrogen Joint Undertaking (FCH JU) under grant agreement STAGE-SOFC and The Finnish Funding Agency for Technology and Innovation (Tekes), Outotec Oyj, Helsingin Energia, Metso Power Oy, Huoltovarmuuskeskus, Gasum Oy, Neste Oil Oyj, Svenskt Gastekniskt Center AB and VTT Technical Research Centre of Finland through VETAANI project (Grant Agreement No. 238/31/11). 17/02/

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