1. No category

CBE301. Chemical and Biomolecular Engineering Laboratory
(2015 spring)
Experiment 1
n-Butane / iso-Butane Adsorptions with
Molecular Sieve 5A (CaA Zeolite)
Zeolites : Microporous Crystalline Aluminosilicates
Natural Zeolites
Synthetic Zeolites
 Zeolite (= “boiling stone”) : produces steams
under heating.
 Natural zeolite is generated by hot spring &
volcano activities.
 Over 150 zeolite structural types have been
identified (about 40 natural zeolite)
Compositions and Structures
Mn+2/nO
Extra-framework
cation
•
[Al2O3
•
xSiO2]
Framework
•
yH2O
Adsorbed phase
Overall charge of TO4 (T: Si or Al)
SiO4 : neutral [(+4) + 4×(-1)]
AlO4 : -1 [(+3) + 4×(-1)]
 Crystalline microporous aluminosilicate minerals → high surface area (100 – 800 m2/g)
 Three-dimensional network of AlO4 and SiO4 tetrahedra linked by sharing all of the
oxygens
 For charge-balancing, extra-framework cation Mn+ is required nearby the aluminum
sites within the zeolite micropores
 Si-O-Si, Si-O-Al bonds are thermodynamically allowed, but not Al-O-Al bond
 1 ≤ Si/Al ≤ ∞ : depending on the structural type
Framework Structures: 3-Letter Codes
http://izasc.ethz.ch/fmi/xsl/IZA-SC/ft.xsl
SOD structure
Sodalite (Si/Al=1)
LTA structure
NaA (Si/Al=1)
FAU structure
NaX (Si/Al=1.2)
NaY (Si/Al=2.5)
MFI structure
ZSM-5 (Si/Al>10)
Silicalite (Si/Al=∞)
Typical Synthesis of Zeolite : Hydrothermal Crystallization
1. Amorphous inorganic precursors containing silica and alumina are mixed together with a
cation source (generally Na+), usually in a highly basic (high pH) medium.
2. The initial synthesis gel is heated in the temperature range of 80 – 200 °C within a sealed
autoclave for hydrothermal crystallization.
3. For some time after raising to synthesis temperature, the reactants remain amorphous.
4. After the above “induction period”, crystalline zeolite product can be detected.
Example of Zeolite Synthesis : NaA Zeolite (LTA Structure)
▶ Batch composition: 3.165Na2O : Al2O3 : 1.926SiO2 : 128H2O
Zeolite synthesis compositions are often
indicated in an ‘oxide formula’
▶ Procedure (for 10 g dry product)
(1) [80 mL water + 0.723 g sodium hydroxide], mix gently until NaOH is completely
dissolved. Divide into two equal volumes in polypropylene bottles.
(2) [One-half of (1) + 8.258 g sodium aluminate], mix gently in capped bottle until clear.
(3) [Second half of (1) + 15.48 g sodium metasilicate], mix gently in capped bottle until clear.
(4) [(2) + (3)], pour silicate solution into aluminate solution quickly; a thick gel should form.
Cap tightly and mix until homogenized.
▶ Crystallization
Vessel: 100-150 mL polypropylene bottle (sealed)
Temperature: 100 ℃
Time: 3-4 hours
Agitation: stirred or unstirred
Important Properties of Zeolites
: Cation-Exchange
Mn+2/nO
Extra-framework
cation
•
[Al2O3
•
xSiO2]
Framework
•
yH2O
Adsorbed phase
Water Softner
(Detergent Builder)
Na+
Na+
Na+
Ca2+
Na+
Ca2+
Na+
Na+
Important Properties of Zeolites
: Thermal Stability
 Generally speaking, zeolites are thermally stable
even at very high temperatures.
 The degradation temperature of low-silica zeolite
(Si/Al<3) is around 700 ℃, while highly siliceous
zeolites are stable even up to 1000 ℃.
 The presence of steam dramatically facilitates the
structural collapse of zeolites at the same
temperature.
 Thermal stabilities of highly aluminous zeolites
are greatly affected by the types of extraframework cations.
Important Properties of Zeolites
: Chemical Stability
 All zeolites are very stable in organic solvents and in neutral water
 High-silica zeolites are unstable at strongly basic condition
(silicon is leached out)
 Low-silica zeolites are unstable in acidic condition
(aluminum is leached out)
In general, high-silica zeolites are thermochemically more stable than
low-silica zeolite.
Sieve (체)
Important Properties of Zeolites
: Molecular Sieving Effect
Pore aperture size
KA : ~3 A
NaA : ~4 A
CaA : ~4.5 A
Figure. Correlation between effective pore size of various zeolites in
equilibrium adsorption over temperature 77 to 420 K, with the kinetic
diameters of various molecules as determined from the Lennard-Jones
potential relation. (from Breck, 1974)
Example of Molecular Sieving
 5A zeolite (CaA zeolite, pore aperture size: 4.5 A) is commercially used in large-scale
to separate n-butane/iso-butane
 Due to the molecular sieving effect, only a smaller n-butane can diffuse to the pore of
CaA, but a larger iso-butane cannot.
4A
n-butane
(kinetic diameter : 4.3 A)
5A
iso-butane
(kinetic diameter : 5.0 A)
 Using such size-selective adsorption properties of zeolites, pressure swing adsorption
(PSA) process can be designed for the separation of mixed gases.
Pressure Swing Adsorption (PSA)
 PSA : Continuous cyclic separation process for gas mixture under the pressure change
(swing) with difference of affinity between certain molecules and adsorbents (e.g., zeolites,
activated carbon, molecular sieves, etc.).
 Application : Air separation, H2 purification from steam reforming, hydrocarbon
separation, natural gas upgrading, and flue/exhaust gas purification
Adsorption Isotherm Measurement
Vm: manifold volume (calibrated)
Vcell: cell volume except the volume of sample
Vtot: Vm+Vcell
<Helium determination of Vtot and Vcell>
Since He does not adsorb at all, it can be used for determining the cell
volume except the volume of sample.
PVm = P`Vtot
r = Vtot/Vm = P/P`
<Adsorbed amount>
ni: ‘increment’ of adsorption capacity during i th dosing
n1 = P1Vm/RT1 - P1`Vtot/RT1` = Vm/R * (P1/T1 - rP1`/T1`)
n2 = (P2Vm/RT2 + P1`Vcell/RT1`) - P2`Vtot/RT2`
Dosing amount through
manifold during 2nd dosing
Remained gas amount in the
cell during previous dosing
= (P2Vm/RT2 + P1`(r-1)Vm/RT1`) - rP2`Vm/RT2`
= Vm/R * (P2/T2 + P1`(r-1)/T1` - rP2`/T2`)
ni = Vm/R * (Pi/Ti + Pi-1`(r-1)/Ti-1` - rPi`/Ti`)
Ni (total adsorbed amount until i th dosing) = n1 + n2 + ··· + ni
Example of Gas Adsorption-Desorption Isotherm
Experiment
Temperature
controller
Adsorption measurement instrument
Pressure indicator
Pressure sensor
Helium
Vacuum
n-Butane
iso-Butane
Cell
Heating mantle
Experiment
1. Degassing 5A (CaA) Zeolite Beads
1) Weight an empty cell.
2) Put approximately 1 g of 5A zeolite
beads into the cell.
3) Weigh (sample+cell).
4) Connect the cell to the adsorption
measurement instrument.
5) Cover the cell with a heating mantle
and increased the temperature to 673
K under vacuum. Maintain the
temperature at 673 K for 4 h.
6) After 4 h, remove the heating mantle
and cool down. Backfill the cell with
helium gas up to about 1 atm.
7) Weigh (degassed sample+cell).
8) Calculate the weight of degassed
sample.
9) Connect the cell again to the
adsorption measurement instrument
and evacuate again.
Experiment
1. Degassing 5A (CaA) Zeolite Beads
3. Set 673 K
2. Open
3. Open
1
1) Weight an empty cell.
2) Put approximately 1 g of 5A zeolite
beads into the cell.
3) Weigh (sample+cell).
4) Connect the cell to the adsorption
measurement instrument.
5) Cover the cell with a heating mantle
and increased the temperature to 673
K under vacuum. Maintain the
temperature at 673 K for 4 h.
6) After 4 h, remove the heating mantle
and cool down. Backfill the cell with
helium gas up to about 1 atm.
7) Weigh (degassed sample+cell).
8) Calculate the weight of degassed
sample.
9) Connect the cell again to the
adsorption measurement instrument
and evacuate again.
Experiment
1. Degassing 5A (CaA) Zeolite Beads
1. Set 298 K
Cool down
3. Backfill with He
2. Close
4. Close
5. Weight
1) Weight an empty cell.
2) Put approximately 1 g of 5A zeolite
beads into the cell.
3) Weigh (sample+cell).
4) Connect the cell to the adsorption
measurement instrument.
5) Cover the cell with a heating mantle
and increased the temperature to 673
K under vacuum. Maintain the
temperature at 673 K for 4 h.
6) After 4 h, remove the heating mantle
and cool down. Backfill the cell with
helium gas up to about 1 atm.
7) Weigh (degassed sample+cell).
8) Calculate the weight of degassed
sample.
9) Connect the cell again to the
adsorption measurement instrument
and evacuate again.
Experiment
1. Degassing 5A (CaA) Zeolite Beads
1. Open
2. Open
1) Weight an empty cell.
2) Put approximately 1 g of 5A zeolite
beads into the cell.
3) Weigh (sample+cell).
4) Connect the cell to the adsorption
measurement instrument.
5) Cover the cell with a heating mantle
and increased the temperature to 673
K under vacuum. Maintain the
temperature at 673 K for 4 h.
6) After 4 h, remove the heating mantle
and cool down. Backfill the cell with
helium gas up to about 1 atm.
7) Weigh (degassed sample+cell).
8) Calculate the weight of degassed
sample.
9) Connect the cell again to the
adsorption measurement instrument
and evacuate again.
Experiment
2. Determining Vtot and Vcell
3. Open
1. Close
2. Close
1) Fill the helium in the manifold up to ~1 atm
(P).
2) Open the valve connecting the manifold and
sample cell.
3) After equilibration, check the equilibrium
pressure, P`.
4) Calculate the Vtot and Vcell by using equations,
PVm = P`Vtot and Vtot = Vm + Vcell
(Vm is a known value.)
5) Evacuate the cell and manifold again.
Experiment
2. Determining Vtot and Vcell
1) Fill the helium in the manifold up to ~1 atm
(P).
2) Open the valve connecting the manifold and
sample cell.
3) After equilibration, check the equilibrium
pressure, P`.
4) Calculate the Vtot and Vcell by using equations,
PVm = P`Vtot and Vtot = Vm + Vcell
(Vm is a known value.)
5) Evacuate the cell and manifold again.
1. Open
Experiment
2. Determining Vtot and Vcell
1) Fill the helium in the manifold up to ~1 atm
(P).
2) Open the valve connecting the manifold and
sample cell.
3) After equilibration, check the equilibrium
pressure, P`.
4) Calculate the Vtot and Vcell by using equations,
PVm = P`Vtot and Vtot = Vm + Vcell
(Vm is a known value.)
5) Evacuate the cell and manifold again.
1. Open
2. Open
Experiment
3. Measuring Adsorption-Desorption Isotherms
<Adsorption>
1) Fill n-butane or iso-butane gas in the manifold
up to your desired pressure.
if the equilibrium pressure < 0.3 atm, 0.6 atm
if the equilibrium pressure > 0.3 atm, (equilibrium
pressure in the earlier cycle + 0.3 atm)
1. Close
2. Close
3. Open
2) Open the valve that connects the manifold and
the cell.
3) After 5 min equilibration, record the final
equilibrium pressure.
4) Close the valve that connects the manifold and
the cell
5) Repeat (1-4) until the final equilibrium
pressure becomes ~1 atm.
Experiment
3. Measuring Adsorption-Desorption Isotherms
<Adsorption>
1) Fill n-butane or iso-butane gas in the manifold
up to your desired pressure.
if the equilibrium pressure < 0.3 atm, 0.6 atm
if the equilibrium pressure > 0.3 atm, (equilibrium
pressure in the earlier cycle + 0.3 atm)
1. Open
2) Open the valve that connects the manifold and
the cell.
3) After 5 min equilibration, record the final
equilibrium pressure.
4) Close the valve that connects the manifold and
the cell
5) Repeat (1-4) until the final equilibrium
pressure becomes ~1 atm.
Experiment
3. Measuring Adsorption-Desorption Isotherms
<Adsorption>
1) Fill n-butane or iso-butane gas in the manifold
up to your desired pressure.
if the equilibrium pressure < 0.3 atm, 0.6 atm
if the equilibrium pressure > 0.3 atm, (equilibrium
pressure in the earlier cycle + 0.3 atm)
1. Close
2) Open the valve that connects the manifold and
the cell.
3) After 5 min equilibration, record the final
equilibrium pressure.
4) Close the valve that connects the manifold and
the cell
5) Repeat (1-4) until the final equilibrium
pressure becomes ~1 atm.
Experiment
3. Measuring Adsorption-Desorption Isotherms
<Desorption>
1) Remove n-butane or iso-butane gas in the
manifold down to your desired pressure by
using a vacuum pump.
if the equilibrium pressure > 0.3 atm, 0.2 atm
if the equilibrium pressure < 0.3 atm, 0 atm
1. Open
2) Open the valve that connects the manifold and
the cell.
3) After 5 min equilibration, record the final
equilibrium pressure.
4) Close the valve that connects the manifold and
the cell
5) Repeat (1-4) until the final equilibrium
pressure becomes ~ atm.
Experiment
3. Measuring Adsorption-Desorption Isotherms
<Desorption>
1) Remove n-butane or iso-butane gas in the
manifold down to your desired pressure by
using a vacuum pump.
if the equilibrium pressure > 0.3 atm, 0.2 atm
if the equilibrium pressure < 0.3 atm, 0 atm
1. Open
2) Open the valve that connects the manifold and
the cell.
3) After 5 min equilibration, record the final
equilibrium pressure.
4) Close the valve that connects the manifold and
the cell
5) Repeat (1-4) until the final equilibrium
pressure becomes ~0.2 atm.
Experiment
3. Measuring Adsorption-Desorption Isotherms
<Desorption>
1) Remove n-butane or iso-butane gas in the
manifold down to your desired pressure by
using a vacuum pump.
if the equilibrium pressure > 0.3 atm, 0.2 atm
if the equilibrium pressure < 0.3 atm, 0 atm
1. Close
2) Open the valve that connects the manifold and
the cell.
3) After 5 min equilibration, record the final
equilibrium pressure.
4) Close the valve that connects the manifold and
the cell
5) Repeat (1-4) until the final equilibrium
pressure becomes ~0.2 atm.
Questions