Literature Survey of Two-Step Methane-syngas

Report
Literature Survey of Two-Step
Methane-syngas-methanol Processes
Group 4
David Bigelow, Sean Coluccio, Luke Rhodes, Peguy Touani
February 5, 2015
CHBE 446 0201
Background
CH4 + H2O → 3 H2 + CO
CO + 2 H2 → CH3OH
• The production of synthesis gas from methane
produces three moles of hydrogen gas for every
mole of carbon monoxide, while the methanol
synthesis consumes only two moles of hydrogen
gas per mole of carbon monoxide.
Background cont.
• To deal with the excess hydrogen, CO2 is injected
in the methanol reactor where it forms methanol
and water
CO2 + 3 H2 → CH3OH + H2O
Reactors and Catalysts
• There are two types of reactors used today: adiabatic
and isothermal
• Carbon monoxide and hydrogen react over a catalyst
to produce methanol
• Catalyst:
1. Zn/Cr2O3 at high pressure and temperature with
impure syngas
2. Cu/Zn/Al2O3 are widely use today and is used at lower
conditions
Step 1: Conversion of Methane to Syngas
• Preparation of Synthetic gas typically accounts for 5075% of the total capital cost of a Gas-to-Liquid (GTL)
plant
• Steam Reformation (SR) has been used for decades
and forms a hydrogen rich syngas
• Catalytic Partial Oxidation (CPOX) is a newer
technology that oxidizes methane to form syngas
Catalytic Partial
Oxidation
Steam Reformation
•
•
•
Methane is contacted with
steam over a heated catalyst at
high pressures and
temperatures to produce a high
hydrogen content syngas
Requires large heat
exchangers and a large initial
investment
Strict heat balance
requirements which makes it
hard to control and difficult to
scale down to a small size
•
Methane is reacted with oxygen
over a catalyst bed to yield
syngas at a 2:1 hydrogen ratio
•
Operated at moderate
pressures (0.5 - 4 MPa) which
is compatible with downstream
processes
•
Easier to control and
manipulate reactor sizing
•
Newer technology that lacks
research in comparison to
steam reformation
Step 2: Methanol Synthesis from Syngas
• CO + 2H2 ↔ CH3OH
• The original methanol synthesis process was
operated at high temperature and pressure
• Methanol is now generally synthesized using a
slightly different reaction, which has the
addition of CO2 as a reactant
• Modern plants will also use the heat produced
from the methanol synthesis for the steam
reformation reaction
Reactors
• Two main types of reactors are used today, adiabatic and
isothermal
• Adiabatic reactors generally use injection of cooled syngas,
whether it is fresh or recycled
• Isothermal reactors are continuously cooled, though
generally from another source, and operate similarly to heat
exchangers
• Both types of conventional reactors utilize fixed bed
catalysts
• The Liquid Phase Methanol Synthesis process is used less
often and utilizes slurry reactors instead of conventional
fixed bed reactors
Reactor Examples
Linde Isothermal Reactor
Lurgi Methanol Converter
(Isothermal)
http://www.zeogas.com/files/8393
9793.pdf
http://www.lindeindia.com/userfiles/image/File/Linde%20
Isothermal%20Reactor.pdf
Reactor Examples Cont.
Topsoe Collect, Mix, Distribute
Converter (Adiabatic)
http://www.topsoe.com/sites/default/files/topsoe_methanol_coal_ba
sed_plants.ashx_.pdf
Reactor Examples Cont.
Slurry Reactor
http://www.gasification.org/uploads/eventLibrary/gtc9807p.pdf
Catalysts
• The first catalyst used was
Zn/Cr2O3 at high pressure
and temperature with
impure syngas
• In 1966 a Cu/Zn/Al2O3
catalyst began seeing use,
and allowed operation at
much lower conditions
• This Cu/Zn/Al2O3 catalyst is
still used today, and remains
the popular choice for
methanol synthesis
Conclusion
• Two step process of:
1. Conversion Methane to Syngas
2. Methanol Synthesis from Syngas
• Varying forms of operation
• Most reactors use similar, using small range of catalysts
• Preferable for medium to large scale processes
References
• M. Lyubovsky, S. Roychoudhury, R. LaPierre. “Catalytic partial oxidation of
methane to syngas at elevated pressures. Catalysis Letters. Vol. 99, Nos. 3-4,
February 2005.
• http://bioweb.sungrant.org/Technical/Bioproducts/Bioproducts+from+Syngas/
Methanol/Default.htm
• http://www.syngaschem.com/syngaschem

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