In the Name of God

1. In the Name of God Tracing the dynamics, self-diffusion, and structure of simple guest molecules inside the nanoporous Li-LSX zeolite by MD simulation M. H. Kowsari 1,2 1 Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, 45137-66731, Iran. 2 Center for Research in Climate Change and Global Warming (CRCC), IASBS, Zanjan 45137-66731, Iran 8th Theoretical and Computational Chemistry Workshop, Isfahan University of Technology, Isfahan, Feb 27–28, 2019.

2. Outline • Introduction to Air Separation by Zeolites • Li-LSXZeolite as the Proper N2Sorbent from Air Our Simulation Results: • Part I. Study ofSingle-component (Pure)Gas (N2 or O2) in Li-LSX Zeolite (M. H. Kowsari, Micropor. Mesopor. Mater.,2018, 264, 181) • Part II.Study of the Binary Mixtures of N2 and O2 in Li-LSX Zeolite (M. H. Kowsari, J. Phys. Chem. C, 2017, 121, 1770) We Study the DynamicalBehavior, Self-diffusion,and StructuralProperties of Guest Gases Inside the Pores of Li-LSX Zeolite.

3. Air Separation Technologies • Various technologies are used for the air separation process: • Cryogenic Distillation Technique is still used today to produce high purity gases. This method operated at extremely low temperature and high pressure to separate components according to their different boiling temperatures. • Pressure Swing Adsorption (PSA) and Vacuum PSA Technologies which are typically used to separate a single component gas from a mixture of gases under pressure at near-ambient temperatures according to the specie's molecular characteristics and affinity for an adsorbent material (e.g., zeolites) • Zeolites used as absorbents { important points: surface interactions between the zeolite and the specific component and/or size species/pores (molecular sieving)} The differences in diffusion coefficients of the guest species inside the pores of zeolites basically control of separation procedure. • If a gas mixture such as air, for example, is passed under pressure through a vessel containing an adsorbent bed of zeolite that attracts nitrogen more strongly than it does oxygen, part or all of the nitrogen will stay in the bed, and the gas coming out of the vessel will be enriched in oxygen. When the bed reaches the end of its capacity to adsorb nitrogen, it can be regenerated by reducing the pressure, thereby releasing the adsorbed nitrogen. It is then ready for another cycle of producing oxygen enriched air.

4. Li-LSX Zeolite as Sorbent for Air Separation Zeolite Li-LSX, from FAU zeolite family with |Li96| [Si96 Al96 O384] formula unit (Si/Al=1), is suitable for selectively adsorbs N2 over O2. Different Cationic Sites in FAU Zeolite Only the Li-III cations interact with the gas. J. Phys. Chem.B 2000, 104, 5272 & 2005, 109, 4738.

5. Li-LSX FAU-Type Zeolite Contains Three Different Li+ Sites

6. Zoom on Li-LSX Supercages of the Simulation Box Only the Li-III cations interact selectively with the N2 gas.

7. Adsorption Isotherms Using Grand Canonical Monte Carlo Adsorption GCMC simulations were performed using MUSIC code. maximumN2 loading (molecule/uc): 16 maximumO2 loading (molecule/uc): 4 N2 O2 Adsorption isotherms for N2 and O2 in Li-LSX as single component at 298 K It is seen that the amount of N2 adsorption on this zeolite is more than that of O2. experiment data from: AIChE Journal 46, 2305 (2000)

8. Simulation box: 2×2×2 replica of the cubic unit cell of Li-LSX; All atoms of zeolite are fixed at the X-ray positions [1]except ofLi-III cationic sites, which are considered in both of fixed and mobileform. The gases were modeled as rigid sites and inserted randomly in the pores using of Mercury program or a monte carlo simulation; different N2 loading (molecule/uc): 2, 4, 8, 12, 16, 20 different O2 loading (molecule/uc): 2, 3, 4, 8 The intermolecular interactions: LJ (12–6)and coulombic potentials by the reported parameters in Ref. [2] NVT Hoover and NVE MD simulations using the Verlet leapfrog by DL_POLY Different Temperatures: 260, 298, 400, 500, 600, and 700 K Periodic boundary conditions and Ewald Sum. were employed time step =1 fs; Rcutoff = 20 Å MD Simulation Details in This Work [1] Chem. Mater.;10, 2197–2204, 1998 [2] Mol. Simul.; 15, 197–221, 1995

9. Part I. Study ofSingle-component (Pure)Gas (N2 or O2) in Zeolite Li-LSX

10. The MSD of Pure N2 in Li-LSX at Different Loadings and Temperatures

11. N2 Self-diffusion Coefficients from Pure Gas Simulations in Li-LSX Table 1.Simulated diffusion coefficients (in 10−8 m2s-1), of N2 molecule in Li-LSX framework using of fixed Li-III model (with that Diffusion values using of mobile Li-III model in parentheses) from MSD plots. Dfixed < (Dmobile) N2 N2

12. The MSD of Pure O2 in Li-LSX at Different Loadings and Temperatures

13. O2 Self-diffusion Coefficients from Pure Gas Simulations in Li-LSX Table 2.Simulated diffusion coefficients (in 10−8 m2s-1), of O2 molecule in Li-LSX framework using of fixed Li III model (with that Diffusion values using of mobile Li III model in parentheses) from MSD plots. Dfixed ≈ (Dmobile) O2 O2

14. Effects of Loading and Temperature on the Computed Self-Diffusion [18] M. H. Kowsari, J. Phys. Chem. C, 2017, 121, 1770

15. More Characteristic Dynamics

16. Effects of Temperature and the Li-III situation on (guest-Li-III) RDFs

17. Zoom on the Selected Supercages of the Simulation Boxes

18. The (Guest-Framework X site) RDFs: X: Li-I, Li-II, Li-III, O, Al, Si

19. Part II. Study of the Binary Mixtures of N2 and O2 in Zeolite Li-LSX Simulations of the Air Binary Mixture of(16N2-4O2 /uc.) or (8N2-2O2 /uc.) in Li-LSX

20. Binary Gas Mixtures in Li-LSX with Fixed Li-III Model Interaction of (N2—Li-III) is stronger than the (O2—Li-III) fixed Li-III MSD > MSD O2 N2 O2 diffuses faster than N2 loading: 16N2&4O2 /uc.

21. Binary Gas Mixtures in Li-LSX with Mobile Li-III Model The high temperature conditions can not be used for separation of N2 from air by Li-LSX. The lower temperature is proper for separation process. At low T : MSD > MSD O2 N2 At high T : MSD ≈ MSD N2 O2 loading: 16N2&4O2 /uc. mobile Li-III

22. N2 and O2 Self-diffusion Coefficients from Mixture Simulations Table 3.Simulated diffusion coefficients (in 10−8 m2s-1), of N2 and O2 molecules in Li-LSX framework using of fixed Li III model (with that Diffusion values using of mobile Li III model in parentheses) from MSD plots of (16 N2 + 4 O2) per unitcell binary mixture. Dfixed < Dmobile Dfixed ≈ Dmobile N2 O2 N2 O2

23. Effects of Temperature and Loading on the Computed Self-Diffusion and Diffusion Selectivity

24. Calculated Activation Energy for the Diffusion Process

25. Effect of Li-III Situation on the VACFs of Guests within Li-LSX The VACF of N2 is very sensitive to the mobile/fixed Li-III model. The VACF of O2 is not sensitive to the mobile/fixed Li-III model.

26. Effect of Li-III Situation on the VACFs of Guest within Li-LSX The VACF of N2 is rather similar to the VACF of O2 in mobile Li-III model. The VACF of N2 is very different with the VACF of O2 in fixed Li-III model.

27. Comparison of (Li-III - Guest) RDF in Binary Mixture Simulations The N2 sorption is localized at the low-energy site, (due to coulombic interaction) which is close to the Li-III cations. loading: 16N2&4O2 /uc.

28. Comparison of (Li-III - Guest) RDF in Binary Mixture Simulations The contribution of coulombic interactions between O2 molecules and Li-III cations is relatively weaker than that of N2 molecules; Sorption of N2 with Li-III cations is much stronger than that of O2 loading: 16N2&4O2 /uc.

29. The (Guest-Li site) RDFs: Three Different Li+ Sites

30. mobile Li-III-mix16-4-298K

31. Fixed Li-III-mix16-4-298K

32. co-workers in initial stages: Prof. M. Ashrafizaadeh Prof. H. Sabzyan Dr. M. Bamdad Acknowledgments • Thanks from the Department of Chemistry of Isfahan University of Technology and TCCW Committeefor Organization • Financial support of the IASBS is acknowledged. Thanks for your attention