| Author |
Message |
Nathan Erickson (Nerickso)
Intermediate Member
Username: Nerickso
Post Number: 11
Registered: 2-2007
| | Posted on Wednesday, March 05, 2008 - 3:41 pm: | |
David,
Wow, great poster, great visualizations.
My first question is do you have any idea about the strength of the affinity between the CO2/N2 and the Zeolite walls.
My second is do you have a guess as to how much CO2 one of these zeolites could potentially trap?
P.S. I really liked the color scheme. |
Billy Miller III (Brm813)
Advanced Member
Username: Brm813
Post Number: 24
Registered: 2-2007
| | Posted on Wednesday, March 05, 2008 - 3:58 pm: | |
David,
Very nice presentation. Easy to follow and understand. I was curious, though, how many atoms are in your systems? Also, how do you model the gaseous molecules (nitrogen and carbon dioxide) interacting with the zeolites that are not in the gas phase (assume)? Once again, nice job. Zeolites have pretty interesting structures from what I can tell.
-Billy |
Josh Blechle (Jmb182)
Member
Username: Jmb182
Post Number: 7
Registered: 2-2007
| | Posted on Wednesday, March 05, 2008 - 5:25 pm: | |
David,
Cool poster! I have at least one question, though. This may have been said somewhere, but since I don't see it... could you tell me what program you are using to do these calculations? |
Erin Futrell (Stylish9)
Member
Username: Stylish9
Post Number: 6
Registered: 3-2008
| | Posted on Wednesday, March 05, 2008 - 7:49 pm: | |
David,
Awesome poster. I have a question that might be rather trivial...but what exactly is the importance of zeolites? I had not heard of them until I read your poster. |
Jonathan Smith (Jmsmith)
Advanced Member
Username: Jmsmith
Post Number: 27
Registered: 2-2004
| | Posted on Wednesday, March 05, 2008 - 8:08 pm: | |
David,
Great presentation and an exciting new angle on this research! I wondered if one could interpret the decreased diffusion with larger numbers of molecules in a similar manner to viscosity? If so does the numbers you get begin to approach some measure of viscosity of CO2 at the given temperature (even though gases are not very viscous)?
Jonathan |
Nick Hopkins (Nick_hopkins)
Member
Username: Nick_hopkins
Post Number: 10
Registered: 3-2008
| | Posted on Wednesday, March 05, 2008 - 8:29 pm: | |
David,
Loved the poster, really nice. Easy to follow while maintaining direction. However, I'm with Erin: what exactly are uses for zeolites? Along that line, what can we expect to see as a result of this research for further study? |
Felix Kwabena Amankona-Diawuo (Amankonf)
Member
Username: Amankonf
Post Number: 10
Registered: 2-2007
| | Posted on Wednesday, March 05, 2008 - 9:34 pm: | |
Nice poster Dave!
I don't really have any questions for you but I wanted to help answer the questions of Erin and Nick (since I work with the same system).
So,zeolites are pretty cool and also capable of preferentially adsorbing CO2 over other gases. One obvious application is sequestration of CO2 from the atmosphere. There was an article in WIRED recently about Professor Omar Yaghi from UCLA who has developed a way to make zeolitic crystals that can adsorb up to 80 times its volume of CO2 (http://www.wired.com/science/discoveries/multimedia/2008/02/gallery_nanotech).
Apparently, his work was published in SCIENCE magazine but I haven't been able to see that article yet.
Hope that was helpful.
-felix
|
David Selassie (Selassid)
Member
Username: Selassid
Post Number: 7
Registered: 2-2007
| | Posted on Wednesday, March 05, 2008 - 11:36 pm: | |
Let me try to answer everything in one go.
And thanks, Felix, for stealing one of my answers.
Our simulations are run on a code base that Dani's group has been developing and is not part of a commercial package. So there is this big crazy Fortran program that Felix (last year) and I have had to examine and modify in order to implement the modeling functionality we want (although much has been done by previous groups and I thank them).
The number of atoms in our simulation is around 10,000. One unit cell of ITQ-3 has 128 Oxygens and 64 Silicon atoms and our MD runs have from 1-8 molecules of each gas per UC. The total simulation area is also 4x4x3 UC (in ITQ-3).
Our zeolites are modeled as rigid frameworks (no zeolite atoms move during the simulation) in which the gaseous adsorbate molecules explore, so the zeolites would be like a solid. We model all interactions (both adsorbate-adsorbate (N-O for example) interactions and adsorbate-adsorbent (Si-N for example)) in the same way using the shown L-J and coulombic potentials. So there is no difference other than that the potentials can force the adsorbate gasses to move around while the zeolite atoms must stay fixed.
Zeolites can hold up to 40 times as much carbon dioxide at a given pressure than empty space. So there is a really strong interaction between the adsorbed carbon dioxide and the zeolite (and less strong interaction between nitrogen and the zeolite). As the poster says, the deepest PE wells for carbon dioxide are at around -3000K and nitrogen only has half as deep PE wells. Our free energy calculations show that the adsorption process is quite favorable.
The trend of decreasing diffusion coefficients as the number of molecules increases can be simply explained by the pores that the molecules are in are more crowded. Imagine trying to make your way across a room to the popcorn during a crowded party. If the party is not that crowded, it will take less time to make it to the popcorn than if the room is packed; in the same way, molecules explore less area in the zeolite if the pores are packed.
Also notice that the diffusion of nitrogen decreases with increasing carbon dioxide concentration, this is showing that carbon dioxide is blocking nitrogen from exploring and is the source of the adsorption selectivity of ITQ-3.
I am not exactly sure if this is what you were getting at, Jonathan, when you asked about the viscosity of the gas. Explicitly viscosity is not something we have looked at, but I would guess that as you increase the pressure of a gas it becomes more viscous? Our simulations are run at constant temperature (298K) and I would guess that, since there is much more concentrated carbon dioxide in the zeolite than in equivalent empty space, it would be more viscous.
Sorry if that didn't really answer the question, but I hope you have a better understanding of the diffusion trends now.
Further study on this project has included adding aluminum into the zeolite framework to give it a charge and seeing how that affects adsorption. Also Felix's poster describes a quantum mechanical method for modeling interactions that we might use.
If you guys have any more questions, I'd be happy to answer them.
- David |
Elizabeth Koballa (E_koballa)
Intermediate Member
Username: E_koballa
Post Number: 14
Registered: 3-2008
| | Posted on Thursday, March 06, 2008 - 11:35 pm: | |
Wow this is really interesting, I hope to see it applied to an extremely groundbreaking invention. Any ideas guys?
On the message board for the Wired article, there seems to be a lot of hubbub about the crystals not having a lot of application. Someone just needs to be creative. |
Brent Krueger (Krueger)
Advanced Member
Username: Krueger
Post Number: 53
Registered: 2-2004
| | Posted on Friday, March 07, 2008 - 12:27 am: | |
Great poster -- it has been great to see everything coming together on this project over the last few years. Have you published this stuff yet?
My question is a bit historical -- I recall a time when the Kohen group was comparing the importance of electrostatic interactions relative to LJ. Now that you have these great looking simulation results, have you gone back to look at this particular topic? |