
Crystalline nets harvest water from desert air, turn CO2 into liquid fuel - sohkamyung
https://www.sciencemag.org/news/2019/09/crystalline-nets-harvest-water-desert-air-turn-carbon-dioxide-liquid-fuel
======
Mirioron
It's a cool idea and all, but how do the calculations look for actually moving
enough air through the "net"?

One cubic meter of air at 100% humidity and 25C only holds 22g of water. For
the 8 liters per day value it doesn't seem like an unreachable amount: 363
cubic meters of air need to pass through the filter. You probably need to more
than double that number due to relative humidity not being at 100% and we
probably won't get all the water in the air, but it seems reachable.

On the other hand, 22500 liters per day seems quite crazy. I'm interested to
see how they're going to tackle this.

~~~
kwhitefoot
At 100% humidity and 20 C air holds 18 g H2O per cubic metre so to deliver 22
500 kg of water per day they must entirely dessicate 1.25e6 m3 of air. Air is
about 4 kg per m3 so this means moving 5 000 tonne of air through the system.

If the energy cost of moving the air is equivalent to lifting it is, say, two
metre then the energy required to do this is 5e6 * 9.8 * 2 joule, about 2e9 J
or 555 kWh so it would need something like 250 m2 of solar panels at 20 5
efficiency for 10 hours.

At higher temperatures 100 % is more water but that only changes the yield by
at most a factor of about three.

Of course the humidity in the areas where this would be used is much lower so
the amount of air to be processed is correspondingly higher.

I'm not saying it can't work, or guaranteeing that I haven't slipped a decimal
place somewhere but these figures suggest to me that it would be very
expensive and might be outcompeted by piping in water from desalination
plants.

~~~
Someone
_”Air is about 4 kg per m³”_

[https://en.wikipedia.org/wiki/Density_of_air](https://en.wikipedia.org/wiki/Density_of_air)
gives around 1.3 kg/m³ for dry air. If you add the 18 grams of water you give,
you only get around 1.32 kg/m³.

⇒ I think 4 kg/m³ is too high.

~~~
mnw21cam
Humid air is actually _less_ dense than dry air, as any aircraft pilot should
be able to tell you. That's because the water molecule H2O has a molecular
weight of 18, while O2 has a molecular weight of 32 and N2 has a molecular
weight of 28.

------
corodra
There's plenty of people here who have done some fantastic math that throws
red flags at this "I'm going to save the world" project. And each of you are
beautiful people.

What gets to me, these overly complicated dehumidifiers keep popping up every
6 months and make a big buzz. And each time, "Look at this brand new thing
that no one has ever thought to do!" That's the part driving me crazy. It's
the same investment sham, over and over. Slightly different method, but the
same idea "We tested a dehumidifier in a place with high humidity. We
collected water. Throw money at us." I give it props for at least being done
in Arizona. But Arizona has higher humidity than a lot of the other water
problem areas in the world.

But I'm the asshole because I don't say "I'm curious how they're going to
overcome the humidity problem."

No, they're not going to solve it. They're going to disappear. Why? Because
they took the money and ran. Like the hundreds of other assholes who keep
coming up with these middle school "I know how to save the world" ideas.

~~~
magduf
>I give it props for at least being done in Arizona. But Arizona has higher
humidity than a lot of the other water problem areas in the world.

It does? Have you ever lived there? I'm not sure about actual humidity number
comparisons between there and other deserts, but during the summer it's so dry
that whenever I spilled water on the floor, I didn't even bother cleaning it
up, because it would evaporate in seconds while I was watching it. Seriously,
if you're trying to test a device like this within the US, I don't know any
lower-humidity place to go than the Sonoran Desert of Arizona.

~~~
corodra
First, it doesn't state Sonoran Desert. Just "In the desert of Arizona". That
entire region of America is a desert if you grew up in places like Florida or
the western part of the Pacific Northwest. Because this article already treats
the idea of "pulling water out of air" as some brand new concept that's never
been done before, I already assume they're not using the scientific definition
of desert.

However, check out NOAA. Here's a chart of average relative humidity of cities
throughout the US ([https://www1.ncdc.noaa.gov/pub/data/ccd-
data/relhum18.dat](https://www1.ncdc.noaa.gov/pub/data/ccd-
data/relhum18.dat)). From 1950 to 2018.But you'll notice in the Arizona
cities, plenty times of the year, the average humidity is between 40%-60%.

Still, this is better than the Water Abundance X-Prize winner from Oct 2018.
The article was on HN: [https://www.fastcompany.com/90253718/a-device-that-
can-pull-...](https://www.fastcompany.com/90253718/a-device-that-can-pull-
drinking-water-from-the-air-just-won-the-latest-x-prize) These bastards
"tested" it in Hawaii of all places.

So yes, I'll say I give them props for doing this in Arizona. But I'm not
going to do backflips. There's still plenty of humidity in Arizona. Especially
if you time your testing in the right time of year. But I mean, when huge
investment money is on the line, no one would ever dare cheat or try to tip
things in their favor unethically. Oh no. Never. That's just silly talk. No
one has ever lied in experiments to make wheel barrows of money...cough
Theranos cough.

Plus water evaporating from the ground isn't just based on lack of air
humidity. It's also on heat of the ground. Just straight up steaming away.
Same happens here in Florida, but you can't really confuse Florida with dry
air.

~~~
leereeves
> Here's a chart of average relative humidity of cities throughout the US
> ([https://www1.ncdc.noaa.gov/pub/data/ccd-
> data/relhum18.dat](https://www1.ncdc.noaa.gov/pub/data/ccd-
> data/relhum18.dat)). From 1950 to 2018.But you'll notice in the Arizona
> cities, plenty times of the year, the average humidity is between 40%-60%.

I think you're reading that wrong. Doesn't M stand for "Max" and A for
"Average"?

If so, the average in southern Arizona cities is 15%-30% and in northern
Arizona cities 30%-50% (which matches my experience).

------
elevenoh
> Last year, he formed a company called Water Harvesting that this fall plans
> to release a microwave-size device able to provide up to 8 liters per day.
> The company promises a scaled-up version next year that will produce 22,500
> liters per day, enough to supply a small village. “We’re making water
> mobile,” Yaghi says. “It’s like taking a wired phone and making a wireless
> phone.”

Any ballpark estimates on the cost for a residential use unit? i.e.
200L-1000L/day

Also, is it feasible for this to markedly effect downstream areas?

i.e. If there's eastwardly wind flowing through Nevada where machines are
extracting humidity at an extreme scale, how might the 30%+ humidity-requiring
plants (i.e. that Jamaican Yerba) in Utah hold up?

water wars 2.0, version: air.

humidity credits & humidity sink surveillance with humidobfuscation
'consultants'.

~~~
ac29
>Also, is it feasible for this to markedly effect downstream areas?

> i.e. If there's eastwardly wind flowing through Nevada where machines are
> extracting humidity at an extreme scale, how might the 30%+ humidity-
> requiring plants (i.e. that Jamaican Yerba) in Utah hold up?

There is a LOT of water in the air, 12,900 km3 [0]. As a comparison, the US
uses 1.2 km3 of water per day (all uses combined.)

[0] [https://www.usgs.gov/special-topic/water-science-
school/scie...](https://www.usgs.gov/special-topic/water-science-
school/science/how-much-water-there-earth)

[1] [https://www.usgs.gov/special-topic/water-science-
school/scie...](https://www.usgs.gov/special-topic/water-science-
school/science/total-water-use-united-states)

Interestingly in that second link - the largest category of water usage is for
thermoelectric power generation, actually using more than irrigation. I
wouldn't have guessed that, and as we start to rely less on burning things for
power, that number should come significantly down.

~~~
masonic

      the largest category of water usage is for thermoelectric power generation, actually using more than irrigation
    

Isn't there a lot of overlap there? Hydroelectric doesn't _consume_ the water,
it just takes energy from its gravity.

~~~
minitoar
Thermoelectric sort of does consume it, I guess. They inject the water down
into geysers to produce steam. My home town, Santa Rosa, California, gets most
(all?) of its power from thermoelectric.
[https://en.wikipedia.org/wiki/The_Geysers](https://en.wikipedia.org/wiki/The_Geysers)

~~~
sbierwagen
To be clear, when the article says "thermoelectric", they're talking about any
power plant that heats up water to generate steam, which is to say, every
coal, nuclear, and combined-cycle natural gas power plant in the country.

~~~
minitoar
Ah...makes sense.

------
mdorazio
"Supported by a solar panel to power a fan and heater, which speed the cycles,
the device produces up to 1.3 liters of water per kilogram of MOF per day from
desert air."

This is _pretty good_ , but not yet amazing. It's more energy efficient than a
compressor-based dehumidifier, but probably still less efficient than trucking
water in from somewhere a few hundred miles away where it's plentiful.

Either way, the big question to me is how well it will hold up over hundreds
of cycles - there's no report here that I see on whether or not the MOF will
also trap dust particles and other things that are likely to decrease
efficiency over time.

~~~
semi-extrinsic
> whether or not the MOF will also trap dust particles and other things

This is the crux of the matter, yes. Of course you will need filtration to
avoid clogging your MOF with sand and dust. Then you increase the power draw,
having to push the air through a filter, and you have added a potentially
expensive consumable.

As TFA states, people have been making MOFs since the mid 90s. And people have
been scrambling for applications since. The unanswered questions are, as
always: Can they be made cheaply enough? Do they last long enough?

~~~
TheGallopedHigh
As per the article, they can make and Aluminium based MOF for $3 per kilo, so
yes.

~~~
cycrutchfield
It says bulk aluminum costs $3 per kilo, not MOF-303.

------
dimes
I want to hear more about the bit mentioned at the end:

> At the meeting, Thomas Rayder, a graduate student at Boston College,
> reported building on the idea. He encapsulated a pair of enzymelike
> catalysts in a zirconium-based MOF to drive a series of reactions that
> convert gaseous CO2 to methanol, a liquid fuel.

> When they were unprotected by the MOFs, Rayder found, the two catalysts
> didn’t produce any methanol because they were quickly deactivated, likely by
> reacting with each other. But safely ensconced in the MOFs, they could make
> methanol at temperatures and pressures far below those used in existing
> methanol plants, offering a potentially cheaper and greener way to make the
> fuel.

~~~
semi-extrinsic
The paper probably isn't out yet. But there is quite some previous research on
using MOFs to make fuel from CO2:

[https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=MOF+...](https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=MOF+co2+methanol&btnG=)

The challenge in that regard is always: turning CO2 to fuel takes at least as
much chemical energy as was released from burning the fuel to CO2 in the first
place. If you have that (presumably emissions-free) energy available, it's
infinitely better to _not burn the fuel in the first place_ and use the
emissions-free energy for something else.

~~~
reissbaker
Could you put a nuclear power plant far away from human civilization, and then
use nuclear power to convert excess atmospheric CO2 to liquid fuel, and ship
the liquid back to civilization? Reduces the NIMBYism (and risk) of nuclear,
while also reducing atmospheric CO2.

~~~
icebraining
I'm not sure there's a place far away enough, while still relatively free from
regular natural disasters (and human disasters, like war). It's not like high-
voltage transmissions lines are very lossy, so if putting plants far away was
enough to assuage the nuclear fears, we'd probably have them already.

~~~
mnw21cam
The main problem with putting nuclear reactors far enough away from everyone
is that they need to be cooled, which means a water supply. There aren't that
many places that have plenty of water for cooling, but no people. And most of
the places that do fit that description already have a nuclear power station.

------
liability
It seems everybody wants to be a moisture farmer, but these _" novel
dehumidifier in the desert"_ schemes have thusfar always failed.

~~~
cbanek
I never wanted to be a moisture farmer, I just wanted to go to Tosche Station
to pick up some power converters!

Although, realistically, it could still be useful in non-desert places? How
about drinking water on ocean vessels?

~~~
coderintherye
Most ocean vessels will have a reverse osmosis "watermaker" to convert salt
water to fresh water

[https://en.wikipedia.org/wiki/Watermaker](https://en.wikipedia.org/wiki/Watermaker)

~~~
newnewpdro
Which require regular maintenance and the primary membrane, a wear item, isn't
exactly cheap to replace.

Having more options is definitely welcome.

------
pvaldes
I would love to be wrong and stupid, but can't fall to think in another
Theranos when I read this. Maybe is the style of the writing, dunno. Of course
sucking all the water from the desert air would have a profound impact on its
vegetation and fauna.

Unless we are talking about coastal waters, importing trucks of water from
areas with more vegetation and water excedent seems a more economic and
sensible solution.

------
underscoremark
The thermodynamics of this rarely matches peoples' optimism about it.

[https://www.youtube.com/results?search_query=thunderf00t+wat...](https://www.youtube.com/results?search_query=thunderf00t+water+busted)

------
cbanek
This is really interesting! As someone who lives in the desert, I would want
one of these.

But nothing comes for free - it seems like the output would be dependent on
the humidity level of the air. If everyone was running these, would it be as
effective? My gut says yes, just due to how much airmass there is, and even
the heat from the ground should provide some mixing. But I am not sure of the
napkin calculation, which I'm sure they've done.

Also at higher temperatures, the air can hold _more_ water vapor. This is why
humidity is relative to the maximum amount of water the air can hold.

The CO2 capture potential is also really impressive.

[edit: got it backward as to temp vs holding capacity, doh.]

~~~
laurencerowe
It's the other way around, at lower temperatures the air can hold less water
vapor. That's why you see condensation forming on cold things.

~~~
cbanek
Doh, you're totally right. Although still, in the desert, there isn't much
water in the air even if it's really hot.

[https://www.engineeringtoolbox.com/moisture-holding-
capacity...](https://www.engineeringtoolbox.com/moisture-holding-capacity-air-
d_281.html)

~~~
quickthrower2
Easy to get confused because humidity % tends to be higher at a lower
temperature (morning dew for example).

~~~
elevenoh
Why is this?

~~~
grzm
Say you have a given amount of water vapor in the air. Relative humidity as a
percentage reflects the amount of water vapor in the air compared with the
maximum amount of water vapor the air could hold at that temperature (and
pressure). The amount of water vapor the air can hold depends on the
temperature, with higher temperatures able to carry more water vapor.

As the temperature goes down, the amount of water vapor stays the same while
the amount the air can carry decreases, so the relative humidity goes up.

[https://en.wikipedia.org/wiki/Relative_humidity](https://en.wikipedia.org/wiki/Relative_humidity)

------
bayindirh
So, is this the first step of making windtraps[0] a reality?

[0]:
[https://dune.fandom.com/wiki/Windtrap](https://dune.fandom.com/wiki/Windtrap)

~~~
Swannie
Yeah, my first thoughts too!

------
pojzon
Looks like the next "crowd funding scam" we see alot lately.

Ill wait some time for someone to do a napkin math to debunk that as a valid
product.

~~~
TheGallopedHigh
It’s published in a reputable journal, I’d say it’s more than a crowdfunding
scam.

------
beautifulfreak
I wonder if the MOFs self assemble. I just started searching, but if any
experts here know how they're made, please explain. I found an article that
says the organic linkers are "ditopic or polytopic organic carboxylates (and
other similar negatively charged molecules)," but MOFs are crystalline, so do
they have to be baked? I get the impression that they're pretty easy to
create, and can be designed to have affinity for any molecule. I really wonder
if hydrogen storage will ever be solved.
[https://science.sciencemag.org/content/341/6149/1230444](https://science.sciencemag.org/content/341/6149/1230444)

------
pard68
What about he environmental impact of sucking the small amount of water
present in the air out of it? I am sure some animal or plant depends on it.
Don't get me wrong, I would let an animal die to save a human any day, but is
this needed? Seems people having been making due in these climates for
thousands of years. If this is as good as they claim this will only attract
people to these locations instead of places which already have an abundance of
water, since people generally find arid climates more comfortable than humid
ones.

~~~
thinkcontext
The amount of air that can pass through a microwave size device is miniscule
compared to the amount of air over a desert.

------
tangue
Seems logical to see that after all these Dune related posts on HN.

------
mc32
How much more effective are they versus low tech alternatives like:
[https://www.nydailynews.com/news/world/world-driest-
desert-c...](https://www.nydailynews.com/news/world/world-driest-desert-chile-
harvests-water-fog-article-1.1304082)

------
mendelmaleh
I wonder what impact will this have on the desert itself

~~~
briga
Seems like a good way to eliminate a lot of life in the desert. Presumably
that air moisture gets cycled through the plants and animals in that
environment. No water = no life.

Mind you, humans have already drastically altered the deserts by rerouting
rivers and building dams, so it wouldn't be the first time an environment has
been changed by technology

------
ollie87
Heh it's the Lars Moisture Farm

------
imvetri
Now set a restriction on pollution or kill it so there is no trace.

Else this man's water will be polluted. Thats how you pay respect, not by
using more of your intellect.

------
bryanrasmussen
probably I'm paranoid but I worry this could be one of those kinds of
inventions humans are good at that in small amounts are really beneficial but
when scaled up start to have unintended harmful side effects only by then it's
too late or too big to stop.

~~~
SturgeonsLaw
I'm not sure it'll be scaled up to the point where it would affect things in a
big way. We've had technology that can extract water from air with electricity
for well over a hundred years (vapour compression refrigeration) and so far it
hasn't caused any issues.

The ocean is a huge source of water with a massive surface area which would
constantly provide a source of humidity, and the lower vapour pressure caused
by removing water from air in substantial amounts would encourage further
evaporation.

That said, local effects would be more pronounced than global effects.

------
Ghostboccia94
Wow

