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ETHYLBENZENE DEHYDROGENATION INTO STYRENE:
KINETIC MODELING AND REACTOR SIMULATION
A Dissertation
by
WON JAE LEE
Submitted to the Office of Graduate Studies of
Texas A&M University in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY
December 2005
Major Subject: Chemical Engineering
ETHYLBENZENE DEHYDROGENATION INTO STYRENE:
KINETIC MODELING AND REACTOR SIMULATION
A Dissertation
by
WON JAE LEE
Submitted to the Office of Graduate Studies of Texas A&M University
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY
Approved by:
Co-Chairs of Committee, Rayford G. Anthony Gilbert F. Froment Committee Members, Daniel F. Shantz Michael P. Rosynek Head of Department, Kenneth R. Hall
December 2005
Major Subject: Chemical Engineering
iii
ABSTRACT
Ethylbenzene Dehydrogenation into Styrene:
Kinetic Modeling and Reactor Simulation. (December 2005)
Won Jae Lee, B.S., SungKyunKwan University;
M.S., Pohang University of Science and Technology
Co-Chairs of Advisory Committee: Dr. Rayford G. Anthony Dr. Gilbert F. Froment
A fundamental kinetic model based upon the Hougen-Watson formalism was
derived as a basis not only for a better understanding of the reaction behavior but also
for the design and simulation of industrial reactors.
Kinetic experiments were carried out using a commercial potassium-promoted
iron catalyst in a tubular reactor under atmospheric pressure. Typical reaction conditions
were temperature = 620oC, steam to ethylbenzene mole ratio = 11, and partial pressure
of N2 diluent = 0.432 bar. Experimental data were obtained for different operating
conditions, i.e., temperature, feed molar ratio of steam to ethylbenzene, styrene to
ethylbenzene, and hydrogen to ethylbenzene and space time. The effluent of the reactor
was analyzed on-line using two GCs.
Kinetic experiments for the formation of minor by-products, i.e. phenylacetylene,
-methylstyrene, -methylstyrene, etc, were conducted as well. The reaction conditions
were: temperature = 600oC ~ 640oC, a molar ratio of steam to ethylbenzene = 6.5, and
iv
partial pressure of N2 diluent = 0.43 bar and 0.64 bar. The products were analyzed by
off-line GC.
The mathematical model developed for the ethylbenzene dehydrogenation
consists of nonlinear simultaneous differential equations in multiple dependent variables.
The parameters were estimated from the minimization of the multiresponse objective
function which was performed by means of the Marquardt algorithm. All the estimated
parameters satisfied the statistical tests and physicochemical criteria. The kinetic model
yielded an excellent fit of the experimental data.
The intrinsic kinetic parameters were used with the heterogeneous fixed bed
reactor model which is explicitly accounting for the diffusional limitations inside the
porous catalyst. Multi-bed industrial adiabatic reactors with axial flow and radial flow
were simulated and the effect of the operating conditions on the reactor performance was
investigated.
The dynamic equilibrium coke content was calculated using detailed kinetic
model for coke formation and gasification, which was coupled to the kinetic model for
the main reactions. The calculation of the dynamic equilibrium coke content provided a
crucial guideline for the selection of the steam to ethylbenzene ratio leading to optimum
operating conditions.
v
To my late grandfather
To my parents
To my wife
vi
ACKNOWLEDGEMENTS
I would never have made it without the help of a lot of people around me. I
gratefully acknowledge Dr. Rayford G. Anthony and Dr. Gilbert F. Froment, co-chairs
of committee, for their guidance, patience, and encouragement during my research. I
wish to thank Dr. Daniel F. Shantz and Dr. Michael P. Rosynek for serving as the
advisory committee members.
I would like to thank my friends in the Kinetics, Catalysis, and Reaction
Engineering Laboratory for the friendship, help and discussions: Dr. Xianchun Wu, Dr.
Sunghyun Kim, Rogelio Sotelo, Bradley Atkinson, Hans Kumar, Luis Castaneda, Celia
Marin, and Nicolas Rouckout. I am grateful for sharing the priceless friendship with my
fellow Korean students in the Department of Chemical Engineering. I also thank all the
members in Vision Mission Church for their countless prayers in my Lord Jesus Christ.
I thank my parents and parents-in-law for their prayers and support throughout
the years. Most importantly, I would like to thank my wife, Sohyun Park, for the
encouragement and love she has given me ever since I pursued the degree.
vii
TABLE OF CONTENTS
Page
ABSTRACT ................................................................................................................. iii
DEDICATION ............................................................................................................. v
ACKNOWLEDGEMENTS ......................................................................................... vi
TABLE OF CONTENTS ............................................................................................. vii
LIST OF FIGURES...................................................................................................... xii
LIST OF TABLES ....................................................................................................... xix
CHAPTER
I INTRODUCTION....................................................................................... 1
II LITERATURE REVIEW............................................................................ 4
2.1 Chemistry of Ethylbenzene Dehydrogenation ................................... 4 2.2 Role of Promoter in Ethylbenzene Dehydrogenation ........................ 4 2.3 Role of Steam in Ethylbenzene Dehydrogenation ............................. 9 2.4 Kinetics of Ethylbenzene Dehydrogenation ...................................... 10 2.5 Kinetics of Coke Formation............................................................... 14 2.5.1 Introduction............................................................................ 14 2.5.2 Deactivation by Site Coverage............................................... 17 2.5.3 Deactivation by Site Coverage and Pore Blockage ............... 18 2.6 Deactivation Phenomena in Ethylbenzene Dehydrogenation............ 19 2.7 Industrial Processes............................................................................ 20 2.7.1 Adiabatic Reactor................................................................... 20 2.7.2 Isothermal Reactor ................................................................. 22 2.8 Alternative Processes ......................................................................... 22 2.9 Minor by-products in Ethylbenzene Dehydrogenation...................... 23 2.9.1 Impurities in Styrene Monomer ............................................. 23 2.9.2 Specification of Styrene Monomer ........................................ 24
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CHAPTER Page
III EXPERIMENTAL METHODS .................................................................. 27
3.1 Introduction........................................................................................ 27 3.2 Feed and Reactor Section................................................................... 27 3.3 GC Analysis Section.......................................................................... 33 3.3.1 On-line GC Analysis for Major Reactions............................. 33 3.3.2 Off-line GC Analysis for Minor Side Reactions.................... 37 3.4 Catalyst Characterization: Nitrogen Adsorption................................ 42
IV EXPERIMENTAL RESULTS.................................................................... 43
4.1 Experimental Results for the Major Reactions .................................. 43 4.1.1 Experimental Procedure......................................................... 43 4.1.2 Nitrogen Adsorption .............................................................. 45 4.1.3 Long Run Test........................................................................ 47 4.1.4 Effect of Temperature ............................................................ 54 4.1.5 Effect of Feed Composition ................................................... 59 4.1.5.1 Effect of Steam to Ethylbenzene Feed Ratio........... 59 4.1.5.2 Effect of Styrene to Ethylbenzene Feed Ratio ........ 59 4.1.5.3 Effect of Hydrogen to Ethylbenzene Feed Ratio..... 63 4.2 Experimental Results for the Minor Side Products............................ 68 4.2.1 Experimental Procedure......................................................... 68 4.2.2 Effect of Temperature and Partial Pressure of Ethylbenzene and Steam........................................................ 69
V KINETIC MODELING OF ETHYLBENZENE DEHYDROGENATION............................................................................. 77
5.1 Introduction........................................................................................ 77 5.2 Formulation of Rate Equations .......................................................... 79 5.2.1 Thermal Reaction
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