
Scientists say we’re on the cusp of a carbon dioxide–recycling revolution - masonic
http://www.sciencemag.org/news/2018/03/scientists-say-we-re-cusp-carbon-dioxide-recycling-revolution
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drewbuschhorn
As a former chemist involved in the field, no, we're really not.

Reading the Joule letter referenced, it's basically just cheerleading, which
does need to happen every few years to keep people going.

Last I was involved, all the major non-nanosurface based catalysts either had
horrible separability or cycles in the 1k range.

Commercial catalysts frequently have cycles in the billions. When someone
cracks this nut, they'll make money hand over fist, but we're not there yet.

JACS has a review article every few years on this for anyone with high school
chem and an actual interest.

~~~
neltnerb
Not to mention that basically all the collected data and goals are centered on
flue gas with high CO2 concentrations.

It's contradictory, if you have isolated fossil power and for some reason have
excess renewable power co-located to convert the waste back to chemicals, then
just turn off the fossil power... unless this is a load balancing play, which
it is not ever going to be good for.

And the original oil and coal is better for converting to chemicals anyway!

~~~
masonic

       flue gas with high CO2 concentrations
    

Wouldn't such a technology be useful in "scrubbing" exhaust from electrical
plants, at least?

~~~
wffurr
The power requirements are such that you could just deliver that power to the
grid in place of the fossil fuel generated power you are cleaning.

~~~
neltnerb
Exactly. The maximum efficiency of conversion to electricity in a thermal
plant is maybe 30-40% even ignoring losses in converting back to hydrocarbons.
But even 99% would be a loss relative to simply using the original
hydrocarbons.

This is a rube goldberg machine, taking high value hydrocarbons that could be
converted to commodity and fine chemicals and instead burning them and taking
the released carbon and... putting it back together? It's not even a very
efficient perpetual motion machine.

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eloff
How can you burn fossil fuels to produce electricity, to use to turn the
combustion byproducts back into fuel at any reasonable level of efficiency?
Some people here are saying the electricity doesn't matter, because it is from
renewable sources - but then you could just shut down that dirty coal plant
and use the renewable energy directly. Something doesn't add up here.

~~~
kragen
Basically this is a reasonable idea for transport fuels. Sunlight gives you
1000 W/m², or 160 W/m² at 16% photovoltaic efficiency. A Boeing 777 has a
surface area on top of something under 1000 m², and so if you cover it with
solar panels, you get 160 kW when the sun is shining directly on it. But its
engines produce somewhere between 700 and 1100 kN at a cruising speed of 900
kph, or 250 m/s, which if you work it out means it would need 175–275 MW if
the engines are 100% efficient, a bit over 1000 times what it can gather from
the sun. (A bit less since it's not running the engines at full power when
it's cruising, but a lot more when you take into account that the engines are
quite inefficient.)

There are ways you can design the plane to use less power, and Solar Impulse 2
demonstrated that it is in fact possible to fly on solar power alone, but
Solar Impulse 2 also took 23 days to go around the world, has a maximum speed
of 140 km/h, and has a maximum passenger capacity of 1, rather than a few
hundred. Design compromises like these are necessary to lower the power
intensity of flight to a solar-feasible level. So, it's likely that liquid-
fueled aircraft (the 777 burns kerosene) will continue to have substantial
advantages over solar aircraft for the foreseeable future.

The obvious solution is to use some 10⁸ m² of area on the ground — something
like a 10 km by 10 km square for each 777 in flight — to generate electricity
to produce the liquid fuels for the liquid-fueled aircraft. That sounds like a
ridiculous thing to do, building a city-sized solar plant for a single
airplane, and today it would be — the photovoltaic modules would cost US$5
billion and installing them would cost another US$5 billion, for a total of
US$10 billion. The entire Boeing 777 development cost was only US$5 billion,
and each plane sells for US$300M or so. So the cost of the power plant would
be something like 30× as high as the cost of the airplanes themselves.

From an exponential point of view, though, that's only 5 doublings. If the
price-performance of photovoltaic modules improves by a factor of 2 five
times, the power plant falls to the cost of the plane. If PV modules continue
dropping in price by 30% per year, as they have been for the last four years
or so, that crossover happens in 2028; if they continue dropping in price by
20% per year, as they have been over a somewhat longer period, it happens in
2033. It's only in a scenario where PV modules effectively stop dropping in
price where this remains a ridiculous idea.

The same logic applies, but in a weaker form and a nearer crossover, for other
challenging transport fuel uses such as ships and trucking.

~~~
entee
This is an excellent point, however even so you'd still have another problem.
Let's say this all works great, and we get to the prices that make it
feasible. You're still just adding one go around to the carbon cycle. The fuel
you burn at the power plant once gets back converted to fuel once, then turns
into CO2 that you can't recover when coming out the back of a 777.

The only way this technology gets to the point where it's net carbon neutral
or negative is if it can process the highly dilute CO2 coming out of the free
air efficiently rather than the highly concentrated CO2 coming out of a power
plant. I have a sense that the dilute case is quite a bit more challenging to
make work at scale and efficiently.

~~~
kragen
Atmospheric carbon dioxide removal via direct air capture is feasible already.
The cost is small compared to the price of the fuel; estimates range from
US$30–1000 per tonne. More details are at
[https://pubs.acs.org/doi/10.1021/acs.chemrev.6b00173](https://pubs.acs.org/doi/10.1021/acs.chemrev.6b00173)

~~~
cma
That is a big range. One ton of Diesel is $788, but produces about 3 tons of
CO2.

~~~
mistermann
Wait, burning diesel produces energy and mass?

~~~
changoplatanero
Diesel isn't the only ingredient in the reaction. Most of the weight in co2
comes from the oxygen that is taken from the atmosphere.

~~~
Someone
Indeed. Atomic weights are: carbon 12; oxygen 16. So the oxygen in CO2 is
32/12 = 8/3 as heavy as the carbon inside it.

So, if 100% of diesel were carbon that gets burned, you would get 3.67 tons of
CO2. That leaves room for incomplete combustion and for other things than
carbon (hydrogen, nitrogen, sulphur, etc).

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rossdavidh
I would need to see something about how much electricity they're talking about
here. I am not seeing a way to do this with less than the electricity you got
from burning the fossil fuels in the first place (and inevitably, somewhat
more). The only way I could see this being useful is if at some point in the
future we are no longer burning fossil fuels for electricity, and we want to
get the CO2 back out of the atmosphere. But, you know, turning them into
living trees is not a bad way to do that, and it already exists...

~~~
davidp
You're mostly right, except that trees are now understood to not be a great
way to sequester carbon: They eventually grow old and die, and the carbon in
them is released as they rot. Over (non-geological) time trees are net carbon
neutral.

~~~
eloff
I hear that mentioned a lot. But there are some important considerations.
Taking previously unforrested land and converting it to forests will sequester
carbon for as long as that condition holds. Planting trees and either letting
them grow into old growth forests or using them for lumber can sequester
carbon for centuries. Don't underestimate the value of buying time to
transition to clean energy and develop more advanced technology.

~~~
ianai
That’s my thinking as well. This problem arose on the human timeline. It must
also be solved on the human timeline. The real requirement is th carbon being
out of th it within the human timeline and that the sequester process be
continued. Seems like a net boon to the economy that way.

I know I’d love to see homes built out of wood more often, as well.

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titojankowski
YC’s new "Carbon Removal Technologies" RFS:
[https://www.ycombinator.com/rfs/#carbon](https://www.ycombinator.com/rfs/#carbon)

Index of 82 startups and projects mining carbon from the air:
[http://airminers.org](http://airminers.org)

(disclosure: airminers.org co-creator)

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throwaway5752
For those that saying this will take energy, this is a means of storing and
concentrating enormous by diffuse renewable energy resources. _Of course_ it's
highly endergonic, but that's not the point.

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sandworm101
No. Co2 is a very low-energy chemical. Converting it into nearly anything else
will take far more energy than other sources. This is possible, but not
economical without massive insentives. Maybe once all the oil is truly gone
will this become a thing.

~~~
mkempe
Are you aware of photosynthesis? free use of plentiful energy? do you have
something against the kingdom of plants?

~~~
eloff
Which requires massive amounts of energy. It's not particularly efficient.

~~~
ianai
Efficiency is great unless it’s not scalable. We need a way that reliably
pulls carbon out of the atmosphere and scales. It’s even better if it’s dead
easy to “deploy”. Plants are less efficient at absorbing sunlight than solar
panels, but they are viable in places solar panels are not and definitely
scale plenty well.

~~~
sandworm101
Plants are not efficient. They dont scale. Nor do they even trap carbon.
Plants turn carbon into plant matter ... which eventually rots or otherwise
breaks down and releases that carbon. Only in special places like bogs or
permafrost does the carbon remain for an extended time. Plants dont turn
carbon into something inert and storable like coal.

Solar panels can reduce carbon emmissions, but to actually take the carbon out
of the air and keep it out means converting it into something akin to coal.
This takes massive power, which must in turn come from a green source.

~~~
mkempe
CO2 levels have steadily declined from 3,000 ppm over the last 150 million
years. How do you explain such enormous, steady decline if plants do "[not]
even trap carbon"?

Further, how do you explain the Carboniferous CO2-fixation that started with
CO2 at 4,500 ppm and ended down below 210 ppm?

Contrary to your claims that only bogs or permafrost could keep plant-fixed
carbon in the long run, phytoplankton absorb carbon in vast quantities, and
when they sink their accumulation in sea floors for millions of years is the
primary origin story of oil and coal.

Scientists say that plant life has exerted and continues to exert "massive
power" over geological eras. Are they in error?

~~~
eloff
Plant life typically decomposes and so it's carbon neural. I can't speak to
the plankton, but I definitely want to look that up now, because 70% of the
surface is water. That could be a big effect. I do want to point out that the
carboniferous was unique though - microorganisms had not yet evolved to be
able to digest the cellulose of trees. So there was millions and millions of
years of trees growing, dying, and sequestering carbon. That doesn't happen
anymore.

~~~
mkempe
On the one hand I commend you for wanting to learn about the role of
phytoplankton in carbon fixation -- if you don't know about it, what else
might you not know? On the other hand I am disheartened that you confuse
lignin with cellulose. It is lignin that evolved at the outset of the
Carboniferous, and which fungi and co did not yet have the ability to break
down.

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88e282102ae2e5b
> it’s really a matter of maybe 5 to 10 years.

So...not holding my breath.

~~~
pmontra
If they make estimates like us, software developers, this is likely 50 to 100
years :-)

The real revolution is that we won't have to drill oil and everybody will be
able to make fuel from the air anywhere in the world. The economic and
political consequences will be huge.

However this process doesn't seem able to reduce greenhouse gases in the air.
They say the fuel they get is carbon monoxide, methane, ethylene.

Methane burns like this: CH4 + 4 O2 = 2 H2O + CO2. The process to create that
methane from CO2 probably starts with one molecule of CO2 because there is
only one C in CH4, so we had one CO2 and we end up with one CO2.

Carbon monoxide burns like 2 CO + O2 = 2 CO2.

Ethylene burns like C2H4 + 3 O2 = 2 CO2 + 2 H2O.

They also seem to preserve the number of total CO2 molecules around.

To really reduce the CO2 in the air we should find a way to turn it into
stone, something like this plant in Iceland [https://qz.com/1100221/the-
worlds-first-negative-emissions-p...](https://qz.com/1100221/the-worlds-first-
negative-emissions-plant-has-opened-in-iceland-turning-carbon-dioxide-into-
stone/)

~~~
tehwalrus
> They also seem to preserve the number of total CO2 molecules around.

Of course, they are chemical reactions. Did you think they would _destroy_
atoms?

The idea here is to make renewable hydrocarbons: when you burn them, they are
only putting CO2 that came from the atmosphere back, not releasing new CO2
from fossil fuels.

It assumes that you power this fuel-generator with renewable energy, of
course.

~~~
pmontra
> destroy atoms?

Obviously not, that would be far too much energetic :-)

If the goal is removing CO2 the reaction should combine some C into something
that doesn't burn, but that's not going to happen if the goal is creating
fuel.

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SomewhatLikely
How would this compare to the approaches attempting to use algae?

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chopin
So, I am burning some carbo hydrates to water and carbon dioxide and then...
generate carbo hydrates out of it? Mmmh, something doesn't sound right.

~~~
notabee
That's right, it doesn't sound right because you're making the assumption that
the energy to do this would come from non-renewable energy sources. The value
of this technology is to sequester carbon or convert energy output that's
variable over time from renewables to a more consistent form of energy without
digging more carbon out of the ground.

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coldtea
> _In terms of how close we are to industrial impact—it’s really a matter of
> maybe 5 to 10 years._

No matter how old you are when you read that, be prepared to continue to
listen that the same technology is "5 to 10 years" away for the rest of your
life.

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noddy1
If this could be applied to making palm oil substitute, that might be the only
thing that can stop deforestation of indonesia/borneo/PNG

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meganibla
Enter climate change caused by too little carbon dioxide in the atmosphere

~~~
TheAdamAndChe
Sinusoidal homeostasis around a set point is far superior to exponential
growth in one direction.

~~~
meganibla
Surprisingly, I find nothing to disagree with in your strawman argument ;p

