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ETHYLBENZENE DEHYDROGENATION INTO STYRENE: KINETIC MODELING · PDF fileETHYLBENZENE...

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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

  • viii

    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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