VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD

Catalyst deactivation bycarbon formation

Johanna KihlmanEnergy Lab 2.0 meets Neo-Carbon Energy15.2.2017

BACKGROUND

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Two target processes: biofuels and SOFCBI

OFU

ELPR

ODU

CTIO

NBI

OFU

ELPR

ODU

CTIO

NFU

ELCE

LLS

FUEL

CELL

S

STEAM REFORMERFeed gas: biomass gasification gasT = 800 – 1000 °CMain challenge: tars and sulfur

STEAM REFORMERFeed gas: Natural gas + Anodeoff-gasT = 500 – 700 °CMain challenge: low O/C ratio

PROJECTSNextUCG (Varkaus demo)VETAANI2G2020

PROJECTStage-SOFC

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Two catalysts: Nickel and precious metal

Ref: WO 2011/107661 A1, WO 07116121 A1, WO 03000829 A1

Doped-ZrO2+ Lower operation temperature, < 700 °C+ Tolerates catalyst poisons+ Selective removal of heavy PAH

Nickel+ Robust, commercial in steam-reforming- Deactivates easily by coke

Precious metals+ Less prone to coking as Ni- Expensive

Carbon formation

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Reactions

Steam reforming reactions:-ΔH0

298 (kJ/mol)CH4 + H2O ↔ CO + 3H2 -206CnHm + nH2O ↔ nCO + (n + 0.5m)H2 <0

Carbon formation:CH4 ↔ C + 2H2 -75CnHm → nC + 0.5mH2CnHm → olefins → coke

Reactions source: J. Rostrup-Nielsen and L. Christiansen, Concepts in Syngas Manufacture, Catalytic Science Seriesvol 10, Imperial College Press, 2011 London.

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Biomass gasification gas composition

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Types of carbon

Encapsulating / Pyrolytic carbonespecially above ~700 oC

Whisker carbonusually below ~700 oC

Encapsulating / Gum carbonusually below ~500 oC

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Types of carbon

Source: J. Rostrup-Nielsen, Catalytic Steam Reforming, Catalysis - Science and Technology, Vol 5, Springer-Verlag, 1984 Berlin.

530 °C

600 °C

730 °C

430 °C

WHISKERPYROLYTIC

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Carbon formation

§Whisker carbon forms oncatalyst

§ Pyrolytic carbon formsthermally

Whisker carbon

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Characteristics of whisker carbon

Whisker carbon• Appears usually below ~700 oC• Catalytic reaction on nickel• Forms carbon nanotubes i.e. whiskers• Destroys the catalyst irreversibly• Inhibited by H2S

Figure a: Helveg, S. et al., Catal Today178 (2011) 42-6.

Source: Kihlman, J. et al., Int JHydro Ene 40 (2015) 1548-58.

Pyrolytic carbon

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Types of carbon

Pyrolytic coke• Especially above ~700 oC• Encapsulates the catalyst• Increases the pressure drop• Inhibits the access of reactive

components to the catalyst surface

Source: Kihlman, J. et al., Int JHydro Ene 40 (2015) 1548-58.

What affects carbonformation?

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What affects carbon formation??Hydrocarbons

Source: J. Rostrup-Nielsen, Catalytic Steam Reforming, Catalysis - Science and Technology, Vol 5, Springer-Verlag, 1984 Berlin.

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What affects carbon formation??Steam

Steam reforming reactions:-ΔH0

298 (kJ/mol)CH4 + H2O ↔ CO + 3H2 -206CnHm + nH2O ↔ nCO + (n + 0.5m)H2 <0

We can add H2O to avoid carbon formation to some extent...BUT the more water we add, the more we need to heat it up > feasibility ofthe process!

Carbon formation:CH4 ↔ C + 2H2 -75CnHm → nC + 0.5mH2CnHm → olefins → coke

Reactions source: J. Rostrup-Nielsen and L. Christiansen, Concepts in Syngas Manufacture, Catalytic Science Seriesvol 10, Imperial College Press, 2011 London.

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What affects carbonformation??Steam

Source: J. Rostrup-Nielsen, Catalytic Steam Reforming,Catalysis - Science and Technology, Vol 5, Springer-Verlag,1984 Berlin.

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What affects carbon formation??Pressure

Generally, the higherpressure, the more carbon.

A small increase inpressure can already leadto carbon formation.

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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 reactionsthat inhibit carbon accumulation.

Source: Kihlman, J. et al., submitted.

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Estimating whisker carbon formation frommethane

Principle of equilibrated gas1 can be used to predict carbon formation in thenatural gas (methane) steam reforming.

Suitable for only methane, the more higher hydrocarbons, the less precise isthe result.

Source: J. Rostrup-Nielsen and L. Christiansen, Concepts in Syngas Manufacture, Catalytic Science Series vol 10, ImperialCollege Press, 2011 London.

Conclusions

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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 complicatedthe gas is, the less precise the predictions are.

ØCarbon formation can be avoidedØPractical research work is often needed

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Second test: Monolith front faceafter 2300 h on-streamNo clogging problems, pressure droplow & steady throughout the test

Catalyst long-term test at the Lahti plant

Monolith front face after24 h on-streamFront face clogged by carbon formedfrom tar at high temperature

What affects carbon formation??Reactor and operation

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Acknowledgements

The research under this project is receiving funding from the Fuel Cell and HydrogenJoint Undertaking (FCH JU) under grant agreement 621213 STAGE-SOFC and TheFinnish Funding Agency for Technology and Innovation (Tekes), Outotec Oyj, HelsinginEnergia, Metso Power Oy, Huoltovarmuuskeskus, Gasum Oy, Neste Oil Oyj, SvensktGastekniskt Center AB and VTT Technical Research Centre of Finland through VETAANIproject (Grant Agreement No. 238/31/11).

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.

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