A Case Study Based on Static and Dynamic Sorption Experiments · 1 Flexible MOFs for Gas Separation ‒ A Case Study Based on Static and Dynamic Sorption Experiments Dr. Robert Eschrich1

1 www.dynamicsorption.com

Flexible MOFs for Gas Separation ‒ A Case Study Based on Static and Dynamic Sorption Experiments

Dr. Robert Eschrich1 Christian Reichenbach1, Andreas Möller1, Jens Möllmer2, Marcus Lange2, Hannes Preißler2, Roger Gläser2, Matthias Thommes3

1 3P INSTRUMENTS GmbH & Co. KG 2 INC Leipzig e.V. 3 Quantachrome Instruments

2018-05-08 CPM8


N2 / 77 K

VP, theor. = 0.42 cm3 g-1 VP, exp = 0.03 cm3 g-1

3

CO2 / 273 K

VP, theor. = 0.42 cm3 g-1 VP, exp = 0.38 cm3 g-1

Desorption

Adsorption

J. Lincke, PhD-Thesis, Universität Leipzig, 2012. J. Lincke, D. Lässig, H. Krautscheid, Tetrahedron Letters 2010, 51, 653.

H2(Metrz-ia)

Accessible in a multigramm scale X-ray cristallography 47 % porosity VPore,theor. = 0.42 cm3 g-1

Relative pressure p / p0

Load

ing

n /

mm

ol g

-1

Relative pressure p / p0

Load

ing

n /

mm

ol g

-1

3 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. S. Horike, S. Shimomura, S. Kitagawa, Nat. Chem. 2009, 1, 695-704.

1. Generation

2. Generation

Type I

Type II

Type III

Reversible network collapse

Guest-induced renewal

Guest-induced transformation

gate opening

pressure

load

ing

3. Generation


1. Pure Component

Sorption

2. In situ PXRD

Conclusions on Separation Effects and the

Influence of the Structural Flexibility

3. Mixture Sorption

Interpretation of stepped Isotherms with C4-Hydrocarbons

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.


pressure p / kPa pressure p / kPa

load

ing

n /

mm

ol g

-1

load

ing

n /

mm

ol g

-1

n-Butane Isotherms

• stepped isotherm with strong hysteresis in low pressure region (< 5 kPa) • hysteresis dependent on pressure and temperature Structural change?

Linear Logarithmic


Gleichgewichtsdaten von n- bzw. Isobutan

• VP, exp = 0.31 cm3 g-1 (n-Butane) and 0.34 cm3 g-1 (Isobutane)

• Isobutane adsorption is much slower than n-Butane adsorption!

pressure p / kPa pressure p / kPa

load

ing

n /

mm

ol g

-1

load

ing

n /

mm

ol g

-1

n-Butane n-Butane

Isobutane Isobutane

Comparison of n-Butane and Isobutane at 298 K

Linear Logarithmic


Phase 1

pressure p / kPa

load

ing

n /

mm

ol g

-1

Uptake Curves – an indication for the rate of adsorption

time t / min

rela

tive

up

take

n-Butane

Isobutane

n-Butane, T = 298 K

Phase 1, T = 298 K,

P < 0.1 kPa


Phase 2

pressure p / kPa

load

ing

n /

mm

ol g

-1


time t / min

rela

tive

up

take

n-Butane

Isobutane

n-Butane, T = 298 K

Phase 2, T = 298 K, P ≥ 30 kPa


gate opening

• gate opening has influence on rate of adsorption • Can this be utilized for a kinetic separation?

pressure p / kPa

load

ing

n /

mm

ol g

-1


time t / min

rela

tive

up

take

n-Butane

Isobutane

n-Butane, T = 298 K

gate opening, T = 298 K,

0.1 kPa < p < 1.1 kPa


gate opening

• gate opening has influence on rate of adsorption • Can this be utilized for a kinetic separation?

pressure p / kPa

load

ing

n /

mm

ol g

-1


time t / min

rela

tive

up

take

Isobutane n-Butane

t0.5 = 14 min

n-Butane, T = 298 K

t0.5 = 667 min


Coupling of sorption experiments with powder x-ray diffractometry structural changes oberservable?

Gas Supply

Detector X-ray source

Cu-Ka

Experimental Setup


inte

nsi

ty

pressure p / kPa

load

ing

n /

mm

ol g

-1

n-Butane

Adsorption of n-Butane

• Structural Change observable during n-Butane adsorption

vacuum


pressure p / kPa

load

ing

n /

mm

ol g

-1

n-Butane

Desorption of n-Butane

• Closed structure is retained after desorption. Open structure is retained after resolvatization • Monoclinic crystal structure before and after gate-opening • With n-Butane Guest-induced transformation 3. Generation – Type II

inte

nsi

ty

vacuum


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

molar fraction of n-Butane in gas phase yn

mo

lar

frac

tio

n o

f n

-Bu

tan

e in

ad

sorb

ate

x n

load

ing

n /

mm

ol g

-1


Static Volumetric-Gravimetric Measurements with n-Butane/Isobutane Gas Mixtures

ptotal= 40 kPa

ptotal= 40 kPa

total

n-Butane

Isobutane


• faster adsorption of n-Butane opens pore structure • change in selectivity over time can be observed

time t / min time t / min

mo

lar

frac

tio

n o

f n

-Bu

tan

e x n

an

d Is

ob

uta

ne

xis

o in

ad

sorb

ate

sele

ctiv

ity

for

n-B

uta

ne

Static Volumetric-Gravimetric Measurements with n-Butane/Isobutane Gas Mixtures

n-Butane

Isobutane

T = 313 K, ptotal= 40 kPa


• Equilibrium times for different gas mixtures

• Partial pressure of n-Butane determines the time until equilibrium

more n-Butane = faster equilibrium time

n:iso=75:25 50:50 25:75

t0.5 = 14 min 55 min 391 min

time t / min

rela

tive

up

take

Static Volumetric-Gravimetric Measurement: Uptake Curves


• 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

𝑛adsorbed = 𝑛 in(𝑡)d𝑡 − 𝑛 out(𝑡)d𝑡

𝑛adsorbed = 𝑉 in(𝑡)𝑦in(𝑡)

𝑉md𝑡 − 𝑉 out(𝑡)

𝑦out(𝑡)

𝑉md𝑡

0.0 0.2 0.4 0.6 0.8 1.00

20

40

60

80

100

rel. b

reakth

rou

gh

/ %

time-on-stream / s

Breakthrough Curve Experiment


• BTC from n-Butane and Isobutane

Combination of equilibrium and kinetic effects

• Adsorption of n-Butane is favored in the dynamic measurement

n : iso = 25:75 n : iso = 50:50 n : iso = 80:20

C4 mixtures in N2: 313 K, Flow: 3 cm3 min-1

ptotal = 100 kPa, pC4 = 40 kPa

specific time t / min g-1

rela

tive

co

nce

ntra

tio

n

Breakthrough Curves

Rel

ativ

e co

nce

ntra

tio

n

Rel

ativ

e co

nce

ntra

tio

n

specific time t / min g-1 specific time t / min g-1

total

total

total

n-Butane

n-Butane n-Butane

Isobutane

Isobutane

Isobutane


eff. selectivity bn/iso

(dynamic)

3.9

4.7

1.8 • 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

~0.5

ideal selectivity an/iso

(equilibrium)

mo

lar

frac

tio

n o

f

n-B

uta

ne

in a

dso

rbat

e x n


Comparison of Selectivities: Dynamic vs. Static

T = 313 K, ptotal= 40 kPa


• Enrichment of Isobutane on the surface in equilibrium

• Sorption-induced structural changes determined with XRD

• gate opening dependent on n-Butane partial pressure

• Stepwise breakthrough curves for n-Butane; spontaneous Breakthrough for Isobutane

• Enrichment of n-Butane on the surface in dynamic measurements

• Kinetics of gate-opening determine selectivities interesting for gas separation applications


Documents

A Case Study Based on Static and Dynamic Sorption Experiments · 1 Flexible MOFs for Gas Separation ‒ A Case Study Based on Static and Dynamic Sorption Experiments Dr. Robert Eschrich1