Re: Methanol production from atmospheric CO2

On May 11, 10:38 pm, "rgigli" <rgigli @ (no-spam) libero.it> wrote:
<eunome...@xxxxxxxxxxxx> ha scritto nel messaggionews:66b05d29-abaf-4bc4-9cd0-20f93d407f1d@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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

If you read the ZSW literature they talk of efficiencies of 60% being
possible with "certain high temperature processes". Their 38%
efficiency calc is based on very ordinary electrolyzers. Even PEM
electrolyzers (if wind or solar power was used) would be more
efficient. The biggest energy input is electrolysis of water to
produce hydrogen. High temperature electrolysis over metal oxide
membranes means that heat has already started the process of
disassociation. As you can imagine a nuclear reactor only converts
40% of its heat to electricity. It would be best if we can split the
water with just pure heat.

There is something called thermochemical water splitting. Last I
looked into it a US process based on a copper iodine cycle could get
very high efficiencies at only 340C-500C or so all without involving
electricity or temperatures of 850C or so that would require a molten
metal reactor.
.

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