Flexible MOFs for Gas Separation A Case Study Based on Static and Dynamic Sorption Experiments Dr. Robert Eschrich 1 Christian Reichenbach 1, Andreas Möller 1, Jens Möllmer 2, Marcus Lange 2, Hannes Preißler 2, Roger Gläser 2, Matthias Thommes 3 1 3P INSTRUMENTS GmbH & Co. KG 2 INC Leipzig e.v. 3 Quantachrome Instruments 1 2018-05-08 CPM8 www.dynamicsorption.com
H 2 (Metrz-ia) 3 Accessible in a multigramm scale X-ray cristallography 47 % porosity V Pore,theor. = 0.42 cm 3 g -1 N 2 / 77 K CO 2 / 273 K Loading n / mmol g -1 V P, theor. = 0.42 cm 3 g -1 V P, exp = 0.03 cm 3 g -1 Loading n / mmol g -1 Desorption Adsorption V P, theor. = 0.42 cm 3 g -1 V P, exp = 0.38 cm 3 g -1 Relative pressure p / p 0 Relative pressure p / p 0 J. Lincke, PhD-Thesis, Universität Leipzig, 2012. J. Lincke, D. Lässig, H. Krautscheid, Tetrahedron Letters 2010, 51, 653. 2 www.dynamicsorption.com
S. Kitagawa, K. Uemura, Chem. Soc. Rev. 2005, 34, 109, S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. 2004, 116, 2388-2430; Angew. Chem. Int. Ed. 2004, 43, 2334-2375. 3 www.dynamicsorption.com S. Horike, S. Shimomura, S. Kitagawa, Nat. Chem. 2009, 1, 695-704. loading 1. Generation Type III Reversible network collapse Type I 2. Generation Guest-induced renewal Guest-induced transformation Type II 3. Generation gate opening pressure
1. Pure Component Sorption 2. In situ PXRD Interpretation of stepped Isotherms with C 4 -Hydrocarbons 3. Mixture Sorption Conclusions on Separation Effects and the Influence of the Structural Flexibility TCI Deutschland GmbH, http://www.tcichemicals.com/eshop/de/de/category_index/03900/. A. Schneemann, V. Bon, I. Schwedler, I. Senkovska, S. Kaskel, R. A. Fischer, Chem.Soc.Rev. 2014, 43, 6062. 4 www.dynamicsorption.com
Isotherms Linear Logarithmic loading n / mmol g -1 loading n / mmol g -1 pressure p / kpa pressure p / kpa stepped isotherm with strong hysteresis in low pressure region (< 5 kpa) hysteresis dependent on pressure and temperature Structural change? 5 www.dynamicsorption.com
Comparison of and at 298 K Linear Logarithmic loading n / mmol g -1 loading n / mmol g -1 pressure p / kpa pressure p / kpa V P, exp = 0.31 cm 3 g -1 () and 0.34 cm 3 g -1 () adsorption is much slower than adsorption! 6 www.dynamicsorption.com
loading n / mmol g -1 relative uptake Uptake Curves an indication for the rate of adsorption, T = 298 K Phase 1, T = 298 K, P < 0.1 kpa Phase 1 time t / min pressure p / kpa 7 www.dynamicsorption.com
loading n / mmol g -1 relative uptake Uptake Curves an indication for the rate of adsorption Phase 2, T = 298 K, P 30 kpa, T = 298 K Phase 2 time t / min pressure p / kpa 8 www.dynamicsorption.com
loading n / mmol g -1 relative uptake Uptake Curves an indication for the rate of adsorption gate opening, T = 298 K, 0.1 kpa < p < 1.1 kpa, T = 298 K gate opening time t / min pressure p / kpa gate opening has influence on rate of adsorption Can this be utilized for a kinetic separation? 9 www.dynamicsorption.com
loading n / mmol g -1 relative uptake Uptake Curves an indication for the rate of adsorption, T = 298 K t 0.5 = 14 min t 0.5 = 667 min gate opening time t / min pressure p / kpa gate opening has influence on rate of adsorption Can this be utilized for a kinetic separation? 10 www.dynamicsorption.com
Experimental Setup Coupling of sorption experiments with powder x-ray diffractometry structural changes oberservable? Gas Supply Detector X-ray source Cu-K a 11 www.dynamicsorption.com
Adsorption of intensity loading n / mmol g-1 vacuum pressure p / kpa Structural Change observable during adsorption 12 www.dynamicsorption.com
Desorption of intensity loading n / mmol g-1 vacuum pressure p / kpa Closed structure is retained after desorption. Open structure is retained after resolvatization Monoclinic crystal structure before and after gate-opening With Guest-induced transformation 3. Generation Type II 13 www.dynamicsorption.com
Static Volumetric-Gravimetric Measurements with / Gas Mixtures loading n / mmol g -1 p total = 40 kpa total molar fraction of in adsorbate x n p total = 40 kpa molar fraction of in gas phase y n molar fraction of in gas phase y n High experimental effort continous mixing of the gas phase GC analysis before and after each experiment partial loadings Calculation of the mixture isotherm with the IAST thermodynamically ideal behaviour 14 www.dynamicsorption.com
molar fraction of x n and x iso in adsorbate selectivity for Static Volumetric-Gravimetric Measurements with / Gas Mixtures T = 313 K, p total = 40 kpa time t / min faster adsorption of opens pore structure change in selectivity over time can be observed time t / min 15 www.dynamicsorption.com
relative uptake Static Volumetric-Gravimetric Measurement: Uptake Curves n:iso=75:25 50:50 25:75 t 0.5 = 14 min 55 min 391 min Equilibrium times for different gas mixtures Partial pressure of determines the time until equilibrium more = faster equilibrium time time t / min 16 www.dynamicsorption.com
rel. breakthrough / % Breakthrough Curve Experiment 100 Sorption takes place in open system Pressure is constant Gas Mixtures only Outlet composition is recorded over time Fixed Bed Adsorber: Gas must not pass without interaction 80 60 40 20 0 0.0 0.2 0.4 0.6 0.8 1.0 time-on-stream / s n adsorbed = n in(t)dt n out(t)dt n adsorbed = V in (t) y in(t) V m dt Vout(t) y out(t) V m dt 17 www.dynamicsorption.com
Breakthrough Curves n : iso = 80:20 n : iso = 50:50 n : iso = 25:75 specific time t / min g-1 total specific time t / min g-1 BTC from and Combination of equilibrium and kinetic effects Adsorption of is favored in the dynamic measurement 18 Relative concentration Relative concentration relative concentration total total specific time t / min g-1 C4 mixtures in N2: 313 K, Flow: 3 cm3 min-1 ptotal = 100 kpa, pc4 = 40 kpa www.dynamicsorption.com
Comparison of Selectivities: Dynamic vs. Static molar fraction of in adsorbate x n eff. selectivity b n/iso (dynamic) 4.7 3.9 ~0.5 1.8 ideal selectivity a n/iso (equilibrium) T = 313 K, p total = 40 kpa Calculating the partial loadings by integrating over the Breakthrough curves Determining effective selectivity β Values are very different from thermodynamic selectivity α Gate opening influences selectivity in dynamic processes molar fraction of in gas phase y n 19 www.dynamicsorption.com
Enrichment of on the surface in equilibrium Sorption-induced structural changes determined with XRD gate opening dependent on partial pressure Stepwise breakthrough curves for ; spontaneous Breakthrough for Enrichment of on the surface in dynamic measurements Kinetics of gate-opening determine selectivities interesting for gas separation applications 20 www.dynamicsorption.com
21 www.dynamicsorption.com