ln Keq = 3571.9/ T - 7.7618
ln Keq = 5791.2/ T - 11.762
-0.6
0.32
1.24
2.16
3.08
4
0.0019 0.0024 0.0029 0.0034
1/ T, K -1
ln K
eq
Butane on USY Zeolites
Butane on Beta Zeolites
ln Keq = 5002.8/ T - 13.312ln Keq = 6085.2/ T - 12.713
-2
-1
0
1
2
3
4
0.0019 0.0024 0.0029 0.0034
1/ T, K -1
ln K
eq
Isobutane on USY Zeolite
Isobutane on Beta Zeolite
0
0.06
0.12
0.18
0.24
0.3
0.035 0.04 0.045 0.05 0.055 0.061/ T0.5, K-0.5
Ta
u/ M
w0.
5, (
sec-
kmo
le/ k
g)
0.5
Butane on Beta Zeolites
Butane on USY Zeolites
0
0.048
0.096
0.144
0.192
0.24
0.035 0.04 0.045 0.05 0.055 0.06
1/ T0.5, K-0.5
Ta
u/ M
w0.
5, s
ec-
(km
ole
/ kg
)0.
5
Isobutane on Beta ZeolitesIsobutane on USY Zeolites
Conclusions TAP approach can be effectively used for transport studies Experimental procedure and method for quantifying TAP results are presented The understanding gained with TAP results should help in quantifying the frequency for periodic regeneration and the key features needed for the optimal catalysts design and regeneration techniques for solid acid alkylation processes
0
0.04
0.08
0.12
0.16
0 0.8 1.6 2.4 3.2 4
Time, sec
Flo
w R
esp
on
se
Isobutane on beta-zeolites
Argon on beta-zeolitesT = 359 K
0.0028
0.0058
0 11
Time, sec
Flo
w R
espo
nse
References:•Nayak S. V., Ramachandran P. A., Dudukovic M. P., 2007 “Transport in nanoporous Beta and ultrastable Y zeolite”, AIChE,fall meeting• Nayak S. V., Ramachandran P. A., Dudukovic M. P., 2008 “Adsorption-desorption and intraparticle diffusion model using LDF approximation”, in preparation
Acknowledgement: NSF Grant, EEC-0310689
Adsorption/Desorption Studies on Solid Acid Alkylation CatalystsS.V. Nayak, M.P. Dudukovic, and P. A. Ramachandran
Chemical Reaction Engineering Laboratory, Washington University in St.Louis
Methodology
TC
Pulse
valve
Microreactor
Mass spectrometer
Catalyst
Vacuum (10-8 torr)
Reactant
mixture
Temporal Analysis of Products (TAP) Pulse Response Experiment
TAP Reactor Model:Accumulation - Transport Term = Reaction Rate
Diffusion
SRx
CDV
t
CV rg
2
2
Problem: Safety, environmental and reliability issues associated with current liquid acid alkylation technologies
Challenge: Develop and demonstrate an environmentally friendly and competitive Solid Acid Catalyst (SAC) technology to replace HF and H2SO4 technologies
Different solid acid catalysts are tested for alkylation of isobutane and n-butene to form 2,2,4 trimethylpentane (gasoline)
• Zeolites• Supported Nafion • Hetropoly acids • Ion exchange resins Zeolites • High product selectivity (~ 85 – 95 %)• Rapid decrease in activity
Introduction
To understand and quantify the overall adsorption kinetics and transport processes of the reactant and products involved in
Solid Acid Alkylation Processes
Sub-Project Goal
0.01
0.013
0.016
0.019
0.022
0.025
0.035 0.04 0.045 0.05 0.055
1 / T0.5, K-1
Ta
u /
Mw
0.5, s
ec-
Km
ole
/kg
Isobutane on inert quartz
Argon on inert quartz
0
0.08
0.16
0.24
0.32
0.4
0.04 0.0428 0.0456 0.0484 0.0512 0.054
1 / T0.5, K-1
Ta
u /
Mw
0.5, s
ec-
Km
ole
/Kg
Isobutane on beta-zeolites
Argon on beta-zeolites
Modified residence time vs. inverse square root temperature for isobutane and argon over inert quartz particles
0
0.05
0.1
0.15
0.2
0 0.2 0.4 0.6 0.8 1
Time, sec
Flo
w r
esp
on
se
Isobutane on beta-zeolites
Argon on beta-zeolites
T = 591 K
T
M
D
L w
K
2
Knudsen Diffusion
TAP experimental responses of argon and isobutane over beta-zeolites
Modified residence time vs. inverse square root temperature for isobutane and argon over beta-zeolities
Results and Discussion
Residence time divided by the square root molecular weight vs. inverse square root of temperature(Nayak et al., 2007)
van’t Hoff plot for equilibrium constant(Nayak et al., 2007)
431.1e-06isobutaneUSY
296.8e-04n-butaneUSY
503.1e-06isobutaneBeta
487.5e-06n-butaneBeta
MoleculeZeolite
431.1e-06isobutaneUSY
296.8e-04n-butaneUSY
503.1e-06isobutaneBeta
487.5e-06n-butaneBeta
MoleculeZeoliteKmoleKj
H
/
,0eqK
Table1: Heat of Adsorption and pre-exponential factor (Nayak et al., 2007)
The catalytic cycle in alkylation reaction catalyzed by zeolites
Important questions How do organic molecules diffuse inside a nanoporous zeolite?
How does the intra-crystalline channel network of a zeolite influence diffusion, adsorption/ desorption and reaction pathway of organic molecules?
Occupied Pore
Empty Pore
Occupied Brønsted Acid Site
Occupied Pore
adsorption
diffusion diffusion
desorption
Single Pulse TAP ExperimentsInert zone Catalyst zone
t
Mean = Adsorption CapacitySpread = Diffusivity, Adsorption/
Desorption Constants
2
2
x
CD
t
C Iin
Iin
cat
Cg
tDcat
2Cg
x2 Rg (Cg , j ) 2
2
x
CD
t
C IIin
IIin
ArDin
Cg
xx0
2Ng(t)
Cg xLr2Lin Lcat
0
Inert Zone I Zeolite Zone Inert Zone II
Narrow Inlet BC Vacuum BC at outlet Observed Exit Flow
Theoretical Representation of TAP
Adsorption-Desorption and Intraparticle Diffusion model for Zeolite ZoneUsing LDF approximation (Nayak et al., 2008)
2
2
2
6
5
2
)(6
pd
e
iAverageieqpii
Rk
D
cKcc
2
6
5
2
)(6
pd
e
iAverageieqpiAverage
Rk
D
cK
b
i
d
aeq LA
N
k
kK
bi
ii ALN
Cc
/
porezeoliteintimediffusionticChracteris
reactorintimediffusionticChracteris
DR
DL
DR
DL
epp
Kb
Kpp
ebp i
i
/
/2
2
2
2
timedesorptionticChracteris
porezeoliteintimediffusionticChracteris
k
DR
D
Rk
d
ep
e
pd /1
3/
3
22
1
0
23 diAverage