The Diffusion of the Industrial Revolution: U.S. and Europe.
From Diffusion Research To Industrial Process
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Transcript of From Diffusion Research To Industrial Process
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From Diffusion Research to
Industrial ProcessesDechema, Frankfurt,Oct26th2006
Douglas M.Ruthven, University of Maine,
Orono, ME04469, U.S.A.
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From Diffusion Research to
Industrial ProcessesKinetic vs Equilibrium Separations:
Most adsorption Separations Selectivitydepends on equilibrium differences.
A few important separations depend on
differences in kinetics.
Examples: Linear/Branched paraffins
Air Separation for N2Olefin/Paraffin separation
N2/CH4Separation (Natural Gas)
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Olefin/Paraffin SeparationsHigh demand for light olefins (for
polyethylene/polypropylene production).Recovery of olefins from cat-cracker off-gas is
preferred route.Requires C2H4/C2H6 and C3H6/C3H8 separation.
C3H6separation is especially important.
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Processes for Olefin/Paraffin
SeparationCryogenic Distillation: Relative volatility is
small so process is energy intensive.Extractive Distillation.
Adsorption offers promising alternative.
Cationic zeolites show equilibrium selectivity forolefins (~12 on 5A).
Olex process (UOP) uses simulated counter-current flow to achieve a pure product withlimited selectivity.
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Traditional 8-Ring Zeolites for
Olefin/Paraffin Separation (5A)Equilibrium and Kinetic Data at 323K
K Kratio D(cm2s-1) DratioC2H4 5100 ~10
-6
} 15 } 1.0
C2H6 340 ~10-6
C3H6 8.3x104
1.4x10-8
} 12 } 2
C3H8 6800 7x10-9
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Traditional 8-Ring Zeolites for
Olefin/Paraffin Separation (4A)Equilibrium and Kinetic Data at 323K
K Kratio D DratioC2H4 4600 1.5x10
-11
} 15 } 3
C2H6 300 5.5x10-12
C3H6/C3H8 Kinetics too slow on 4A
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Olefin/Paraffin Separation by Adsorption
Olefins are preferentially adsorbed (stronger
equilibrium and faster kinetics).Recovery of preferentially adsorbed component
at high purity is difficult requires very high
equilibrium selectivity or diffusivity ratio.Traditional adsorbents (4A, 5A or 13X) do not
give required product purity.Look for adsorbents with high enough kineticselectivity to give molecular sieve separation.
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Structure of DDR38-ring silica framework: 2-dimensional channels
(4.4x3.6A)
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Chabazite Structure (CHA)
Cages (free volume ~3803) interconnected through tetrahedrallyoriented 8-ring windows free aperture 3.7 4.1
SiCHA, SAPO-34: cation free versions
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CHA VariantsBond Lengths (Angstroms)
AlO =1.75;
(1/2)(AlO + P-O) =1.64Si-O= 1.61
Reduction in unit cell volume and windowdimensions with Si/Al Ratio:
CHA > SAPO34 > AlPO34 > SiCHA
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Modified CHA Adsorbents8-Ring Zeolites (Angstroms)
4A 3.8x4.25A 4.2x4.2
CHA 3.9x4.1
SAPO34 3.8x4.3
AlPO34 3.7x4.5
SiCHA 3.65x4.3
DDR3 3.6x4.4 (not CHA)
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Olefin/Paraffin SeparationDiffusion in Type A and CHA Zeolites
Diffusion in CHA Zeolites
1.00E-15
1.00E-14
1.00E-13
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
2.3 2.5 2.7 2.9 3.1 3.31000/T
Do(cm
2/sec)
C3H6 - SAPO 34
C3H6 - ALPO 34
C3H6 - SiCHA
C3H8 - ALPO 34
C3H8 - Si CHA
D and E are sensitive to subtle differences in T Odistance
Diffusion in Zeolite A
1.00E-12
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4
1000/T
Do
(cm
2/sec)
C2H6 -5A
C3H8 - 5A
C2H4 - 4A
C2H6 - 4A
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C o rre la t io n o f D if fus iv ity with Windo w D im e ns io n
1 . 0 0 E - 1 2
1 . 0 0 E - 1 1
1 . 0 0 E - 1 0
1 . 0 0 E - 0 9
1 . 0 0 E - 0 8
1 . 0 0 E - 0 7
3 . 5 3 . 6 3 . 7 3 . 8 3 . 9 4 4 . 1 4 . 2 4 . 3
Mi ni m um D ia m e t e r ( A ng s t r o m )
C 3 H6 a t 3 2 3 K
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Olefin/Paraffin SeparationVariation of D and Kinetic Selectivity with Unit Cell Size
From Reyes et al. U.S. Patent 6,730,142 B2 May 4, 2004
Diffusion of Propane and Propylene in CHA Zeolites
1.00E-11
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06
770 780 790 800 810 820 830
Unit Cell Volume (A3)
Diffusivity(cm
2/sec)an
d
DiffusivityRatio
DC3H6/DC3H8
DC3H6
T = 323K
10,000
1,000
100
1.00E-11
1.00E-10
1.00E-09
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Comparison of Activation Energies
0
2
4
6
8
10
12
14
16
18
CaA SAPO34 ALPO34 SiCHA
Zeolite Type
.
E
(kc
al/mole)
Propane
Propene
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Preferred Adsorbents for C3H6 (323K)
K Kratio D(cm2s-1) DratioSiCHA:
C3H6 700 8x10-11
} 0.8 } 11,500
C3H8 900 7x10-15
DD3RC3H6 1000 5X10
-12
} 1 ?? } 10,000
C3H8 No data 6x10-16
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Olefin/Paraffin SeparationComparative Uptake Rates for C3H6 and C3H8
in SiCHA at 80oC
From Olson et al. Microporous and Mesoporous Mats. 67, 27-33(2004)
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N2/CH4 SeparationPipeline specifications for natural gas limit N2
content to < 3%.Many gas reservoirs contain higher N2 %.
On non-polar adsorbents CH4
is adsorbedmore strongly.
On polar adsorbents N2 and CH4 are adsorbed
at similar rates and with similar equilibria.For an efficient separation adsorbent should
adsorb N2 preferentially
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Titanosilicates ETS-4A Tuneable Adsorbent
Dimensions of unit cell
(and 8-ring windows)depend on dehydration
temperature
From Kuznicki et al.Nature, 412, 720 (2001)
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ETS-4 (270o
C dehydration)
Sr-ETS-4; High kinetic selectivity N2/CH4 (Farooq)
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N2 CH4 SeparationLittle difference in either kinetics or equilibrium
on most adsorbents.SrETS4 offers good kinetic selectivity with
N2 (minor component) as the preferredspecies.
PSA Process with periodic thermalregeneration to remove higher hydrocarbons.
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ConclusionsOlefin/Paraffin Separation
Small differences in T O distances lead to
changes in free aperture of 8-rings. This has a large impact on the diffusional activation
energy (and hence on D) for critically sized
molecules. SiCHA andDDR3 have high kinetic selectivity for
C3H6/C3H8 (Dratio> 104).
Under properly selected operating conditions (PSAor TSA) propylene can be recovered at high purityand high yield.
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Conclusions (contd.)Purification of N2containing Natural Gas
CH4 and N2 are adsorbed at similar rates andsimilar strength on most polar adsorbents.
SrETS-4 dehydrated at 270DegC shows high kinetic
selectivity for N2/CH4, so N2 is preferentiallyadsorbed, yielding a pure CH4 product.
Traces of higher hydrocarbons are slowly adsorbed
necessitating periodic regeneration at elevatedtemperature.
Further Details
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Further Details
D.M.Ruthven and S.C.Reyes
Adsorptive Separation of Light Olefins from
Paraffins Microporous and Mesoporous Materialsin press.
D.H.Olson
U.S.Patent 6,488,741 (Dec3, 2002)D.H.Olson et al.
Micro and Mesoporous Mats. 67,27 (2004)
S.C.Reyes et al. Ibid. in press (2006)S.C.Reyes et al.
U.S.Patent 6,730,142 (May 4, 2004)