Science & Tech

Getting Rid of Greenhouse Gases With Membranes Inspired by Mother Nature

A new membrane inspired by what biology naturally does on its own might make it possible to separate out nearly 100% of all carbon dioxide from smoke emitted from coal-fired power plants.

Principle of how Sandia National Laboratories' CO2 separating 'memzyme' works. Photo: Sandia National Laboratories

It also appears it will be able to do that at much lower costs than any other technology currently available. 

That technology was developed by scientists at Sandia National Laboratories and the University of New Mexico. To learn more about the technology and its potential applications, Trillions spoke with one of the principals in this research, Dr. Susan Rempe, at her offices at Sandia National Laboratories.

Dr. Susan Rempe, Distinguished Member of the Technical Staff at Sandia National Laboratories. Photo: Sandia National Laboratories

Trillions: Please tell us about your role with Sandia Labs.

Dr. Susan Rempe: I am a Distinguished Member of the Technical Staff at Sandia National Laboratories, and I am located in New Mexico. I do fundamental basic research. My background is in physical chemistry and biophysics, and I’m a theoretician.

Trillions: What were some of the goals of this research project on “biologically inspired membranes” for greenhouse gas reduction?

Dr. Susan Rempe: The research was about trying to find a new way to separate CO2 from a mixture of gases. We know there are [already] ways to do that, but we wanted to find ways that are more efficient and more economic. So, we formed a team and brought our unique expertise to the problem, and we went from there.

Trillions: Tell us a little about what you actually created. You have something you’ve referred to as a “memzyme.” I’m sure that word alone will be something people will be interested in learning about, as well as how this built on earlier research by one of your colleagues and on what Mother Nature has done.

Dr. Susan Rempe: The “memzyme” is so-called because what we came up with was a membrane and the membrane contains an enzyme in its active layer. So we combined “membrane” with “enzyme” to come up with “memzyme.” The technology built on expertise within our team on fabricating membranes, on self-assembly of the supporting parts of the membrane and also expertise on enzyme design and re-engineering.

We have several people on our team – these include Jeff Brinker at Sandia National Labs at the University of New Mexico, Ying-Bing Jiang at the University of New Mexico and myself. I’m also affiliated with the University of New Mexico.

We weren’t the first to come up with the idea of incorporating an enzyme in a membrane, but we were the first to have the enzyme incorporated in nanoconfined areas of the membrane. Part of the enzyme is inspired by nature and what goes on in our bodies. Our bodies have to process CO2; from metabolism you regenerate CO2, and we have to get rid of it  through our lungs. There’s an enzyme in all of us called carbonic anhydrase. What it does is it converts CO2 into bicarbonate, and it does the reverse reaction as well. It catalyzes release and uptake of CO2 into aqueous solution. So that was our inspiration with the biological system.

Trillions: What was the challenge in getting down to the nano level that you talked about? As you said, you weren’t the first to do this, but you were the first to do it not at the microscopic but the “nano”-scopic level of things. What was the breakthrough that made that possible?

Dr. Susan Rempe: The breakthrough I think is really on the experimental side. It’s making a membrane that is both thin and narrow and has the right chemistry on the walls on the pores so that it stabilizes an aqueous solution loaded with enzymes. Our experimental colleagues were able to build these nanopores, these nano-scale pores, which are just a few nanometers in diameter and less than 20 nanometers in depth. This just fit a couple of enzymes in aqueous solution. The key there was to change the surface chemistry. They were able to do that by using a method that was invented here at Sandia, which was using an oxygen plasma with a technique called atomic-layer deposition to change the surface chemistry of nanopores.

They were able to change the surface chemistry so that at first, it was all hydrophobic and it repels water, and they were able to use the oxygen plasma to modify just a portion of the surface chemistry so that it was hydrophilic and water-loving. That was a very small region that becomes hydrophilic and water loving, and that’s the active layer of our membrane.

By making that really thin, the CO2 has a short transport pathway to cross the membrane, to make it aqueous. CO2 is more soluble in that solution, so it “selects” for CO2 out of that mixture of gases. Then incorporating that enzyme having that hydrophilic surface helps stabilize the enzyme. We know that from our modeling studies. It makes it so that the enzyme can be highly concentrated in the pores. So that’s another difference from anything out there developed before – that we have a highly-concentrated and stabilized solution of enzymes. So that means we can uptake and release more CO2 from the membrane.

The research team on the memzyme project. From left-to-right, Yaqin Fu (UNM), Ying-Bing Jiang (UNM), Susan B. Rempe (SNL), C. Jeffrey Brinker (SNL/UNM). Photo: Sandia National Laboratories

Trillions: This is the technique you refer to as the evaporation-induced self-assembly – the work that was based on some of the things that your colleague Jeff Brinker had done quite a long time ago.

Dr. Susan Rempe: Yes, that’s right. That’s one of the inventions – the evaporation-induced self-assembly [with] well-aligned arrays of nanopores. Then, on top of that, the oxygen plasma with atomic-layer deposition was also developed out of that lab, through Brinker with Ying-Bing Jiang. Then to modify the surface chemistry to make it a mixed chemistry. Then, on top of that, [to use] the modeling to help design the surface chemistry and understand what’s going on – which comes out of my lab.

Trillions: It sounds like a very impressive collaboration of bringing things together. How well did all this work from a technology standpoint? I know that you are doing this in a laboratory at this point, but how effective was it, both by itself as well as compared to others’ [approaches] to, for lack of a better term, carbon-dioxide scrubbing?

Dr. Susan Rempe: We had developed it in the laboratory at a very small scale, and it remains to be scaled up. We are still working on that step, making it large-scale and testing it in the real-world situation. Based on comparisons using the same gas mixtures and same conditions, when we look at other membranes, our membrane performs far, far better. Permeability is, mostly, 100 times better than about any other membrane we’ve seen, and we’re far more selective on CO2 over any other gas which crosses the membrane. Based on looking at that performance, we have an estimate of how much it would cost to separate CO2 emissions from [a] power plant. Our cost is far lower than what the current technology requires, which is liquid amine-based technology that you can use right now. The large-scale application remains to be developed and tested, but we’re excited and very optimistic that it’s going to work out.

Trillions: In terms of applications, it’s not just [for] emissions for a power plant. You in your paper have mentioned some other things which people might not think about. Could you give us some examples of some of the places where you think this might be applicable?

Dr. Susan Rempe: There are lots of possible applications. One of the third largest emitters of CO2 is from cement-processing plants. There are thousands and thousands of [them] in the country, and they’re all over the world. Our membrane could be used to separate CO2 from those emissions. Also, people don’t know that micro-breweries use CO2, purchase CO2 and also emit CO2. That’s more of a smaller-scale application. Enhanced oil recovery is another place CO2 is used. Gas companies purchase CO2 to recover oil from developed oil wells.

In submarines and space shuttles, you may also want to separate out CO2 and recycle it. So, there are many applications.

Trillions: What are some of the next steps for your group in developing this, both in terms of research and potentially the applications side of it?

Dr. Susan Rempe: Probably the number one next step is just working on making the membrane at a larger scale. A second step, for applications, is to test it under actual operating conditions. [This] means that [while] in the lab we’ve controlled what gas mixtures we’re looking at, [such as] CO2 and nitrogen mixtures. But in the real world there [are] contaminants. There’s SO2 (sulfur dioxide) and trace amounts of other contaminants in the gases. So, the next steps for us are to optimize our membranes so they’re stable and they’re functional and [provide] benefit at the maximum rate in the presence of different gas mixtures and with contaminants.

The paper Dr. Rempe and her colleagues recently published on this topic – “Ultra-thin Enzymatic Liquid Membrane for CO2 Separation and Capture” by Yaqin Fu, Ying-Bing Jiang, Darren Dunphy, Haifeng Xiong, Eric Coker, Stan Chou, Hongxia Zhang, Juan M. Vanegas, Jonas G. Croissant, Joseph L. Cecchi, Susan B. Rempe and C. Jeffrey Brinker – was published online on March 7, 2018, by Nature Communications.