Biologically inspired membrane purges coal-fired smoke of greenhouse gases

April 11, 2018 by Neal Singer, Sandia National Laboratories
Sandia National Laboratories fellow and University of New Mexico regents’ professor Jeff Brinker led work to develop the inexpensive memzyme capable of ridding coal smoke of carbon dioxide, the most prevalent greenhouse gas. Credit: Randy Montoya

A biologically inspired membrane intended to cleanse carbon dioxide almost completely from the smoke of coal-fired power plants has been developed by scientists at Sandia National Laboratories and the University of New Mexico.

The patented work, reported recently in Nature Communications, has interested power and energy companies that would like to significantly and inexpensively reduce emissions of , one of the most widespread greenhouse gases, and explore other possible uses of the invention.

The memzyme meets the Department of Energy's standards by capturing 90 percent of power plant carbon dioxide production at a relatively low cost of $40 per ton.

Researchers term the membrane a "memzyme" because it acts like a filter but is near-saturated with an enzyme, carbonic anhydrase, developed by living cells over millions of years to help rid themselves of carbon dioxide efficiently and rapidly.

"To date, stripping carbon dioxide from smoke has been prohibitively expensive using the thick, solid, polymer membranes currently available," says Jeff Brinker, a Sandia fellow, University of New Mexico regents' professor and the paper's lead author.

"Our inexpensive method follows nature's lead in our use of a water-based membrane only 18 nanometers thick that incorporates natural enzymes to capture 90 percent of carbon dioxide released. (A nanometer is about 1/700 of the diameter of a human hair.) This is almost 70 percent better than current commercial methods, and it's done at a fraction of the cost."

Coal power plants are one of the United States' largest energy producers, but they have been criticized by some for sending more carbon dioxide into the atmosphere than any other form of electrical power generation. Still, coal burning in China, India and other countries means that U.S. abstinence alone is not likely to solve the world's climate problems.

But, says Brinker, "maybe technology will."

The device's formation begins with a drying process called evaporation-induced self-assembly, first developed at Sandia by Brinker 20 years ago and a field of study in its own right.

Enzymatic liquid membrane design and mechanism of carbon dioxide capture and separation. The Sandia/University of New Mexico membrane is fabricated by formation of 8-nanometer diameter mesopores. Using atomic layer deposition and oxygen plasma processing, the silica mesopores are engineered to be hydrophobic except for an 18-nm-deep region at the pore surface which is hydrophilic. Through capillary condensation, carbonic anhydrase enzymes and water spontaneously fill the hydrophilic mesopores to form an array of stabilized enzymes with an effective concentration greater than 10 times of that achievable in solution. These catalyze the capture and dissolution of carbon dioxide at the upstream surface and the regeneration of carbon dioxide at the downstream surface. The high enzyme concentration and short diffusion path maximizes capture efficiency and flux. Credit: Sandia National Laboratories

The procedure creates a close-packed array of silica nanopores designed to accommodate the carbonic anhydrase enzyme and keep it stable. This is done in several steps. First, the array, which may be 100 nanometers long, is treated with a technique called atomic layer deposition to make the nanopore surface water-averse or hydrophobic. This is followed by an oxygen plasma treatment that overlays the water-averse surface to make the nanopores water-loving or hydrophilic, but only to a depth of 18 nanometers. A solution of the enzyme and water spontaneously fill up and are stabilized within the water-loving portion of the nanopores. This creates membranes of water 18 nanometers thick, with a carbonic anhydrase concentration 10 times greater than aqueous solutions made to date.

The solution, at home in its water-loving sleeve, is stable. But because of the enzyme's ability to rapidly and selectively dissolve carbon dioxide, the catalytic membrane has the capability to capture the overwhelming majority of carbon dioxide molecules that brush up against it from a rising cloud of coal smoke. The hooked molecules then pass rapidly through the membranes, driven solely by a naturally occurring pressure gradient caused by the large number of carbon dioxide molecules on one side of the membrane and their comparative absence on the other. The chemical process turns the gas briefly into carbonic acid and then bicarbonate before exiting immediately downstream as . The gas can be harvested with 99 percent purity—so pure that it could be used by oil companies for resource extraction. Other molecules pass by the membrane's surface undisturbed. The enzyme is reusable, and because the water serves as a medium rather than an actor, does not need replacement.

The nanopores dry out over long periods of time due to evaporation. This will be checked by water vapor rising from lower water baths already installed in to reduce sulfur emissions. And, enzymes damaged from use over time can easily be replaced.

Says Brinker, "The very high concentration of carbonic anhydrase, along with the thinness of the water channel, result in very high carbon dioxide flux through the membrane. The greater the carbonic anhydrase concentration, the greater the flux. The thinner the membrane, the greater the flux."

The membrane's arrangement in a generating station's flue would be like that of a catalytic converter in a car, suggests Brinker. The membranes would sit on the inner surface of a tube arranged like a honeycomb. The flue gas would flow through the membrane-embedded tube, with a carbon dioxide-free gas stream on the outside of the tubes. Varying the tube length and diameter would optimize the carbon dioxide extraction process.

"Energy companies and oil and gas utilities have expressed interest in optimizing the gas filters for specific conditions," says Susan Rempe, Sandia researcher and co-author, who suggested and developed the idea of inserting into the water solution to improve the speed by which carbon dioxide could be taken up and released from the membrane. "The enzyme can catalyze the dissolution of a million carbon dioxide molecules per second, vastly improving the speed of the process. With optimization by industry, the memzyme could make electricity production cheap and green," she says.

The separation process could increase the amount of fuel obtained by enhanced oil recovery using carbon dioxide injected into existing reservoirs.

A slightly different enzyme, used in the same process, can convert methane—an even more potent greenhouse gas—to the more soluble methanol for removal, she says.

Prior cleansing by industrial scrubbers means that the rising smoke will be clean enough not to significantly impair efficiency, says University of New Mexico professor and paper co-author Ying-Bing Jiang, who originated and developed the idea of using watery membranes based on the human body's processes to separate out carbon dioxide. The membranes have operated efficiently in laboratory settings for months.

The procedure also could sequester dioxide on a spacecraft, the authors mention, because the membranes operate at ambient temperatures and are driven solely by chemical gradients.

Explore further: Blowing bubbles to catch carbon dioxide

More information: Yaqin Fu et al. Ultra-thin enzymatic liquid membrane for CO2 separation and capture, Nature Communications (2018). DOI: 10.1038/s41467-018-03285-x

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5 / 5 (3) Apr 11, 2018
Coal is dying (yay!). Seems like this could mitigate carbon emissions from natural gas powered generating facilities as well. Why no mention of that? I wonder how well this scales down? Could it help reduce carbon emissions from smaller power sources as well? In any case, this looks like a good technology to reduce the damage while we transition to carbon-free renewables.
5 / 5 (4) Apr 11, 2018
Coal plants produce about 1.4 tons of C02 per Mwh - At $40 per ton - this would add about 5.6 cents per Kwh to the generation cost. Gas plants only produce .475 tons per Mwh (same reference) so it would only add 1.9 cents Kwh. Just another nail in the coffin of fossil fuels.
5 / 5 (3) Apr 11, 2018
It seems like the process would also work with biomass power plants, to produce negative net-carbon emissions.
5 / 5 (6) Apr 11, 2018
Well, I found here a few numbers for some powerplants

Let's see. The worst polluter in the world is the Scherer plant in Juliet, GA with 25.3 million tons CO2 annually (incidentally it was awarded the prize for "Plant of the Year by the Powder River Basin Coal Users' Group." in 2017. I find this somewhat funny. )

At 40$ per ton this would mean an additional cost (not including installation of the system) of roughly a billion dollars per year.
At about 17GWh output per year this will mean a surcharge to the end user of around 6ct per kWh (assuming they pass it on directly without adding a percentage - in which case the added cost will be higher)

I'm not sure this will fly.
5 / 5 (4) Apr 11, 2018
This is not a nail in the coffin. This is a lifeline. They will be able to burn every last hydrocarbon in Earth and claim they're doing no harm. The harm would be greatly reduced, like 90%, so maybe that's okay.

The plain fact is that we should pay more for energy. The reason we have trouble is that we've never had to pay for disposal of the waste products (tragedy of the commons). They talked about a carbon tax in the 90's, and then came impeachment. You don't really think it was about sex, do you?
5 / 5 (3) Apr 11, 2018
If it works with just a chemical gradient at ambient pressure, couldn't it remove CO2 from the air? Just have a slight vacuum or any kind of low CO2 atmosphere on the back side. Then you could make up for the last 200 years of fossil fuel use.
4 / 5 (4) Apr 11, 2018
Or set it up on the sound walls along highways. Higher CO2 on the inside, trap it at the source. Doesn't have to be perfect, just has to be constant.

Still worried about "costs" (while oddly ignoring all the costs of dumping in the atmosphere that you don't want to pay for)? And you think people won't pay more for energy? And solar and wind have carbon in their manufacture?

Fine, don't tax energy for carbon per BTU. Tax everything for embodied carbon. Every product, every building involves the generation of CO2. Spread the tax to everything, and no one sector can complain they are being disadvantaged.

You don't want to pay that tax? Then find a way to manufacture your product in a carbon-neutral way. You will have the competitive advantage in the regulated free market (which would be a level field with regard to carbon), and you will make profits at the expense of your rivals. Good for you.
5 / 5 (1) Apr 11, 2018
Tax everything for released fossil carbon. Credit for carbon-negative operations.
5 / 5 (3) Apr 11, 2018
It appears that the estimated cost per ton of CO2 captured, $40/ton, is not the final cost. After the CO2 has been removed, it must be disposed of by sequestration or sale. The $40/ton apparently does not include the disposal cost or sales revenue. If the CO2 can be sold, then the cost should be less than $40/ton. If the CO2 must be sequestered, perhaps by deep well injection, then the cost would be more than $40.
4.2 / 5 (5) Apr 11, 2018
Just what we need. Another excuse to keep this stone-age technology in service.
1 / 5 (4) Apr 11, 2018
CO2 is beneficial, sry but the Sun drives the climate.

Increased levels of carbon dioxide (CO2) have helped boost green foliage across the world's arid regions over the past 30 years through a process called CO2 fertilisation, according to CSIRO research.
Thorium Boy
1.7 / 5 (6) Apr 11, 2018
God I hate greenies. The problem with coal smoke isn't C02, it's fly ash, NOX, Sulfur dioxode, CO. Idiots wasting their money on this.
1 / 5 (5) Apr 11, 2018
@Thorium Boy, Thanks don't forget mercury, that's the real issue with coal pollution, not CO2..
The greens really are idiots.
5 / 5 (6) Apr 12, 2018
God I hate greenies. The problem with coal smoke isn't C02, it's fly ash, NOX, Sulfur dioxode, CO. Idiots wasting their money on this.

God, I hate people that think a process can only ever have one problem. Shortsightedness taken to its extreme.
5 / 5 (4) Apr 12, 2018
So "greenies" are idiots because they object to coal, not because coal is good, but because coal is even worse? We know coal is even worse; the topic of this article was CO2.

Look in the mirror when you're calling names, and you might get it right.

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