Get­ting Rid of Green­house Gases with Mem­branes In­spired by Mother Na­ture

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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. 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.

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 wa­terlov­ing, 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.

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.

© San­dia Na­tional Labs

© San­dia Na­tional Labs

© San­dia Na­tional Labs

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