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