Re: Methanol production from atmospheric CO2


"Rob Dekker" <rob@xxxxxxxxxxx> ha scritto nel messaggio
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"rgigli" <rgigli @ (no-spam) libero.it> wrote in message
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<eunometic@xxxxxxxxxxxx> ha scritto nel messaggio
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On May 7, 3:00 am, "Romeo Gigli" <rgigli @ (no-spam) libero.it> wrote:
Is there a chance to produce liquid fuels (for example, methanol or
dymethil
ether) useful for private transportation from natural (and potentially
very
dangerous...) CO2, using low temperature waste heat (and if necessary
electricity/hydrogen) from "clean" energy sources (geothermal, solar,
wind
or even nuclear) ? I'm very curious, which are in particular the
temperatures and energies needed?
...
Certainly, the economics of the process are all to be seen

There are several methods: In Germany about 15 years ago the 'ZSW'
'zentrum fur sonnen-energie und wasserstoff'
extractracted C02 from the atmosphere, reacted it with copper-zinc
catalysts at 200 atm with electrolytically obtained hydrogen gas to
produce methanol.
...

Thanks very much, very interesting. My own curiosity is if there is a
process which needs, rather than electricity, only (or almost only that)
low-medium temperature heat from a
"clean" source, I thought for example geothermal or high temperature
thorium breeders - and how much heat in that case it would need. For a
38% electricity to chemical energy efficiency if we choice to use a only
thermal process it needs about 13 kWh thermal per liter of MeOH, not so
difficult to achieve if only low temp heat is needed


Low temperature heat produces work at low efficiency. Check the Carnot
limit.


Yes, of course, but I guess if we use low temperature heat ususally "vented"
to the environment from thermal plants (geothermal, thermal solar, high
temperature nuclear reactors), this heat even used with a low efficicency is
pratically free - though I suspect that the biggest part of the energy input
is electricity to extract CO2 from ambient and produce H2 by electrolisys
and not the
heat to produce the chemical reaction : CO2 + 3 H2 = CH3OH + H2O

But I wonder if it makes any sense at all to create Methanol (or any other
liquid fuel for that matter) using any form of energy.
The efficiency of the ZSW process is 38% as given in this thread. When
burned in an ICE at 20%-25% efficiency that means that overall the
efficiency is below 10%. And the ZSW process uses electricity as input !
To get electricity from heat, an efficiency of 20-60% is common (20% for
low heat, 60% for high heat). So now we are talking efficiencies of 2 - 6
% from heat to power at the wheels. That is pathetic, considering that
alternatives such as CNG get 25% efficiency and plug-in hybrids can go as
high as 40% heat to power at the wheels


I perfectly agree with you here, but what I meant is that in a post carbon
and post peak-oil economy, we will always need a lot of (possibly cleaner
than gasoline/diesel fuels, like MeOH and DME) liquids fuels at least for
that transportation not possible to electrificate (ships, airplanes,
plug-ins themself for ranges longer than the battery autonomy, etc...). If
the process is not highly energy intensive (for example, it needs only 10
kWh thermal per liter vs the 5 kWh/l of heating value of methanol) and in
particular needs almost only low temperature heat (for example, produced by
high temperature thorium breeders or geothermal/solar plants), then it' s a
strategy we should seriously think about, even for only a few % of our
liquid fuels need (the remaining part easily electrificable)




.

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