Carbon-capture breakthrough: Porous material polymerizes carbon dioxide at natural gas wellheads

Jun 03, 2014
This illustration shows the carbon polymerization process created at Rice University. A high-resolution PDF is available upon request. Credit: Tanyia Johnson/Rice University

Rice University scientists have created an Earth-friendly way to separate carbon dioxide from natural gas at wellheads.

A porous material invented by the Rice lab of chemist James Tour sequesters , a greenhouse gas, at ambient temperature with pressure provided by the wellhead and lets it go once the pressure is released. The material shows promise to replace more costly and energy-intensive processes.

Results from the research appear today in the journal Nature Communications.

Natural gas is the cleanest fossil fuel. Development of cost-effective means to separate carbon dioxide during the production process will improve this advantage over other fossil fuels and enable the economic production of gas resources with higher carbon dioxide content that would be too costly to recover using current carbon capture technologies, Tour said. Traditionally, carbon dioxide has been removed from natural gas to meet pipelines' specifications.

The Tour lab, with assistance from the National Institute of Standards and Technology (NIST), produced the patented material that pulls only carbon dioxide molecules from flowing natural gas and polymerizes them while under pressure naturally provided by the well.

When the pressure is released, the carbon dioxide spontaneously depolymerizes and frees the sorbent material to collect more.

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All of this works in ambient temperatures, unlike current high-temperature capture technologies that use up a significant portion of the energy being produced.

"If the oil and gas industry does not respond to concerns about carbon dioxide and other emissions, it could well face new regulations," Tour said, noting the White House issued its latest National Climate Assessment last month and, this week, set new rules to cut carbon pollution from the nation's power plants.

"Our technique allows one to specifically remove carbon dioxide at the source. It doesn't have to be transported to a collection station to do the separation," he said. "This will be especially effective offshore, where the footprint of traditional methods that involve scrubbing towers or membranes are too cumbersome.

"This will enable companies to pump carbon dioxide directly back downhole, where it's been for millions of years, or use it for enhanced oil recovery to further the release of oil and natural gas. Or they can package and sell it for other industrial applications," he said.

Particles of nitrogen-containing porous carbon are able to capture carbon dioxide from natural gas under pressure at a wellhead by polymerizing it, according to researchers at Rice University. When the pressure is released, the carbon dioxide returns to gaseous form. Credit: Tour Group/Rice University

The Rice material, a nanoporous solid of carbon with nitrogen or sulfur, is inexpensive and simple to produce compared with the liquid amine-based scrubbers used now, Tour said. "Amines are corrosive and hard on equipment," he said. "They do capture carbon dioxide, but they need to be heated to about 140 degrees Celsius to release it for permanent storage. That's a terrible waste of energy."

Rice graduate student Chih-Chau Hwang, lead author of the paper, first tried to combine amines with porous carbon. "But I still needed to heat it to break the covalent bonds between the amine and carbon dioxide molecules," he said. Hwang also considered metal oxide frameworks that trap carbon dioxide molecules, but they had the unfortunate side effect of capturing the desired methane as well and they are far too expensive to make for this application.

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The porous carbon powder he settled on has massive surface area and turns the neat trick of converting gaseous carbon dioxide into solid polymer chains that nestle in the pores.

"Nobody's ever seen a mechanism like this," Tour said. "You've got to have that nucleophile (the sulfur or nitrogen atoms) to start the polymerization reaction. This would never work on simple activated carbon; the key is that the polymer forms and provides continuous selectivity for carbon dioxide."

Methane, ethane and propane molecules that make up may try to stick to the carbon, but the growing polymer chains simply push them off, he said.

The researchers treated their carbon source with potassium hydroxide at 600 degrees Celsius to produce the powders with either sulfur or nitrogen atoms evenly distributed through the resulting . The sulfur-infused powder performed best, absorbing 82 percent of its weight in carbon dioxide. The nitrogen-infused powder was nearly as good and improved with further processing.

Tour said the material did not degrade over many cycles, "and my guess is we won't see any. After heating it to 600 degrees C for the one-step synthesis from inexpensive industrial polymers, the final carbon material has a surface area of 2,500 square meters per gram, and it is enormously robust and extremely stable."

Explore further: Capturing carbon to produce more oil: Climate solution or folly?

More information: Paper: dx.doi.org/10.1038/ncomms4961

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User comments : 17

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jscroft
3.9 / 5 (7) Jun 03, 2014
"... the final carbon material has a surface area of 2,500 square meters per gram..."

No matter how well I understand the arithmetic, things like this never cease to amaze me.
Caliban
4.2 / 5 (5) Jun 03, 2014
Hmmm...

In theory, it ought to be possible to push pressurized atmosphere or water through this same material -or one with analogous characteristics, and remove CO2, as well.

A real breakthrough advance, though, regardless of other possible applications.

EyeNStein
1 / 5 (1) Jun 03, 2014
I can see that Heating then cooling the absorber cyclically with a heat pump or using the compression of the gas to reach 140C would be such a burden ;-)
My Pizza gets hotter than that!
Nonetheless this is a useful advance and some excellent materials science.
tomkparker
not rated yet Jun 03, 2014
non-scientist here..., could anyone guess whether this could work in a smoke stack too? If so, I wonder if it could save the coal industry....?
RealScience
5 / 5 (3) Jun 03, 2014
@tomparker - it should work, but the exhaust gas would have to be pressurized to capture the carbon dioxide. Some of the energy used to pressurize the gas could be reclaimed on depressurizing, so the first question would be how much it would decrease the power plant's net output.

Another potential problem is that coal exhaust can have lots of things other than air, water and CO2 in it, and some of these could conceivable poison the absorber, but it looks pretty robust so my guess is that it would survive.

Straw_Cat
5 / 5 (3) Jun 04, 2014
In some locations, ones with fair to high solar levels, the CO2 could also be a feedstock for growing algae, which can then be processed to provide fats for some industrial uses, as a chemical feedstock, and/ or to create biofuels and lubricants.

The processed algae remains can be used for various applications like animal feed, or composted to be a soil supplement/ fertilizer.
antialias_physorg
5 / 5 (3) Jun 04, 2014
could anyone guess whether this could work in a smoke stack too? If so, I wonder if it could save the coal industry....?

You have to deduct the amount of energy needed to create this material if you want to use it as an energy sink.

The way they envision this to be used is just to get some CO2 out while pumping stuff from underground reservoirs so that pipleines will not be damaged ... and then release the CO2 elsewhere - so there is no net CO2 reduction the way it'll be used (just a minor shift in location).

If you were to use it in smokestacks to save the coal powerplants you'd have to keep dumping cartloads of this tuff in, keep it pressurized, and then store it (pressurized) somewhere...forever. That takes vastly more energy than it would save (and would cost quite a pretty penny to boot, as the storage costs would eventually snowball into infinity)
Tessellatedtessellations
5 / 5 (1) Jun 04, 2014

The way they envision this to be used is just to get some CO2 out while pumping stuff from underground reservoirs so that pipleines will not be damaged ... and then release the CO2 elsewhere - so there is no net CO2 reduction the way it'll be used (just a minor shift in location).
(pressurized) somewhere...forever. That takes vastly more energy than it would save (and would cost quite a pretty penny to boot, as the storage costs would eventually snowball into infinity)


Why not recycle? Move the loaded material to the nearest gas well and offload the CO2 down the well and then take the the stuff back to the smoke stack? Coal plants are usually supplied by trains which would be an efficient way to transport the stuff to the well, assuming the wells are also near a railroad.

My main concern would be that the well fracked the reservoir to hell such that the CO2 would leak.
RealScience
not rated yet Jun 04, 2014
@AA - According to the article, the proposal is to use the material to separate CO2, not to store it permanently in the material. And one of the purposes the article lists would be to then sequester the CO2 underground.

From the article:
When the pressure is released, the carbon dioxide spontaneously depolymerizes and frees the sorbent material to collect more.
....
"This will enable companies to pump carbon dioxide directly back downhole, where it's been for millions of years ...


If used in a coal power plant, transport would be an added cost. Either to transport the CO2 (either in the absorbing material back and forth, or the CO2 after release) to be pumped into a suitable underground repository (such as an old gas well), or to transport coal to a power plant built over an old natural gas field (coal and electricity being relatively easy to move).
jscroft
2 / 5 (4) Jun 05, 2014
We're so concerned about carbon neutrality... what about OXYGEN neutrality?

Sqeuestering CO2 from industrial processes that burn hydrocarbons in air breaks the cycle that returns all that bound O2 back to a breathable form via photosynthesis. So you get to be carbon-neutral... but only at the cost of slowly leaching oxygen from the atmosphere.

Of course the argument is that the net effect on O2--even from all the industry we can throw at it--is still pretty trivial. Right? Interesting that this knife doesn't seem to cut both ways.
Caliban
3.7 / 5 (3) Jun 05, 2014
Interesting that this knife doesn't seem to cut both ways.


Prolly because it's not sharp enough to --kinda like yer mind.

This is FOSSIL CO2 we are talking about. If it is returned to our present day atmosphere, it would INCREASE its oxidative effects.

Are you saying that we need more rust, more cancer, and enhanced combustion in open air?

jscroft
1 / 5 (1) Jun 06, 2014
Nooooo, Your Sharpness. I was responding to the comments about collecting CO2 output from fossil-fuel POWER PLANTS, which burn hydrocarbons in air and generate NEW CO2.

You know... the comments right above MY comment? See, that's what WE were talking about, toolbox.

Anyway. Tell me more about the "oxidative effects" of fossil CO2!
Captain Stumpy
5 / 5 (3) Jun 06, 2014
You know... the comments right above MY comment? See, that's what WE were talking about, toolbox.
@jscroft
sorry to interrupt.
when posting a reply to a comment, normally people quote the comment they are replying to in order to establish context as well as show continuation, like I did above. this can be done via the quote button below the comment, or by using quote marks in the post.
this saves people from getting confused

you should have caught on to this by now...
Caliban
1 / 5 (1) Jun 06, 2014
Nooooo, Your Sharpness. I was responding to the comments about collecting CO2 output from fossil-fuel POWER PLANTS, which burn hydrocarbons in air and generate NEW CO2.

You know... the comments right above MY comment? See, that's what WE were talking about, toolbox.

Anyway. Tell me more about the "oxidative effects" of fossil CO2!


Uh, huh, and I was responding to your claim that increased CO2 emissions would cycle increased O2 back into the atmosphere, and the predictable effects of such an increase.

Stay sharp, though.
Urgelt
4.5 / 5 (2) Jun 09, 2014
Diminishing atmospheric O2 isn't a concern at present.

The atmosphere contains 21% oxygen. CO2 is present at about 400 ppm. Human activity appears to have raised CO2 from 280 to 400 ppm in under 200 years. It's true that burning fossilized carbon consumes atmospheric oxygen, but not enough to make a real dent.

The danger to atmospheric O2 isn't direct, but indirect. Photosynthesis, which keeps the O2 level steady, could falter in the tropics if the temperature rises too high. Sunlight reaching the antarctic and arctic isn't going to rise, so even if temperatures there become more conducive to photosynthesis, it probably won't offset losses in the tropics.

If the tropics become a vast dead belt around the middle of the planet, it *will* cause O2 levels to slide downward.

How much of a slide depends on lots of assumptions. We've never destabilized Earth's ecosystems to that extent .before, and might not be doing so now. (Though if methane clathrates destabilize, watch out.)
jscroft
1 / 5 (1) Jun 09, 2014
when posting a reply to a comment... you should have caught on to this by now...


Yes yes, thank you, message received: accidental troll food is still troll food nevertheless. :)

Diminishing atmospheric O2 isn't a concern at present.


Of COURSE it isn't! After all, it may be just as DEMONSTRABLY a problem as the change in CO2 levels (and just as firml tied to human activity haha), but nobody's figured out how to use it as a argument in favor for Leftist political policy!
jscroft
1 / 5 (1) Jun 09, 2014
Uh, huh, and I was responding to your claim that increased CO2 emissions would cycle increased O2 back into the atmosphere, and the predictable effects of such an increase.


No, dummy. I said if you take carbon out of the ground, burn it in air, and then sequester the resulting CO2, you've just sequestered atmospheric O2 as well. Why are you even arguing? This is junior high school chemistry stuff.

Oh, right. 'Cause you're a TROLL.

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