Click here to load reader

Coke Deposition Hydro Processing

  • View
    219

  • Download
    0

Embed Size (px)

Text of Coke Deposition Hydro Processing

  • 8/3/2019 Coke Deposition Hydro Processing

    1/182

    University of Alberta

    The Impact of Multiphase Behaviour on Coke Deposition in Heavy OilHydroprocessing Catalysts

    by

    Xiaohui Zhang

    A thesis submitted to the Faculty of Graduate Studies and Research in partialfulfillment of the requirements for the degree of Doctor of Philosophy

    in

    Chemical Engineering

    Department of Chemical and Materials Engineering

    Edmonton, Alberta

    Fall 2006

  • 8/3/2019 Coke Deposition Hydro Processing

    2/182

    Abstract

    Coke deposition in heavy oil catalytic hydroprocessing remains a serious problem. The

    influence of multiphase behaviour on coke deposition is an important but unresolved

    question. A model heavy oil system (Athabasca vacuum bottoms (ABVB) + decane) and

    a commercial heavy oil hydrotreating catalyst (NiMo/-Al2O3) were employed to study

    the impact of multiphase behaviour on coke deposition.

    The model heavy oil mixture exhibits low-density liquid + vapour (L1V), high-density

    liquid + vapour (L2V), as well as low-density liquid + high-density liquid + vapour

    (L1L2V) phase behaviour at a typical hydroprocessing temperature (380C). The L2

    phase only arises for the ABVB composition range from 10 to 50 wt %. The phase

    behaviour undergoes transitions from V to L2V, to L1L2V, to L1V with increasing

    ABVB compositions at the pressure examined. The addition of hydrogen into the model

    heavy oil mixtures at a fixed mass ratio (0.0057:1) does not change the phase behaviour

    significantly, but shifts the phase regions and boundaries vertically from low pressure to

    high pressure.

    In the absence of hydrogen, the carbon content, surface area and pore volume losses for

    catalyst exposed to the L1 phase are greater than for the corresponding L2 phase despite a

    higher coke precursor concentration in L2 than in L1. By contrast, in the presence of

    hydrogen, the carbon content, surface area and pore volume losses for the catalyst

    exposed to the L2 phase are greater than for the corresponding L1 phase. The higher

    hydrogen concentration in L1 appears to reverse the observed results. In the presence of

    hydrogen, L2 was most closely associated with coke deposition, L1 less associated with

  • 8/3/2019 Coke Deposition Hydro Processing

    3/182

    coke deposition, and V least associated with coke deposition. Coke deposition is

    maximized in the phase regions where the L2 phase arises. This key result is inconsistent

    with expectation and coke deposition models where the extent of coke deposition, at

    otherwise fixed reaction conditions, is asserted to be proportional to the nominal

    concentration of coke precursor present in the feed.

    These new findings are very significant both with respect to providing guidance

    concerning possible operation improvement for existing processes and for the

    development of new upgrading processes.

  • 8/3/2019 Coke Deposition Hydro Processing

    4/182

    Acknowledgements

    This project would not have been a success without the unselfish contribution and help of

    many people. Professor John M. Shaw gave me insightful supervision and endlessencouragement and support throughout the entire project. Not only is he a fantastic

    supervisor, but also a good friend in my whole life. Professors Murray R. Gray and Alan

    E. Nelson gave me most constructive criticism and valuable suggestions, which made this

    project successful and shining. Thank you is far from what I want to say to them.

    I would like to thank Drs. Yadollah Maham and Richard McFarlane for their willingness

    to spend time on polishing and revising my presentations and thesis. Thanks also go to

    Bei Zhao, Jessie Smith, Martin Chodakowski and Xiangyang Zou for their contribution tothis project.

    I would like to thank all colleagues in the Petroleum Thermodynamics and Bitumen

    Upgrading group and all support staff in the Department of Chemical and Materials

    Engineering. Without your help and cooperation, this undertaking would not have been

    possible.

    I gratefully acknowledge the Scholarship programs at the University of Alberta and

    research funds from the sponsors of the NSERC Industrial Research Chair in PetroleumThermodynamics (Alberta Energy Research Institute, Albian Sands Energy Inc.,

    Computer Modelling Group Ltd., ConocoPhillips Inc., Imperial Oil Resources, NEXEN

    Inc., Natural Resources Canada, Petroleum Society of the CIMM, Oilphase-DBR,

    Oilphase a Schlumberger Company, Schlumberger, Syncrude Canada Ltd., NSERC).

    No words could describe my debt to my parents and my siblings for their sacrifices and

    for giving me the opportunity to pursue higher education. My success is attributed to their

    incessant encouragement and support.

    Special thanks to my lifes partner, Chongguo, for her love, her sacrifice, her

    encouragement, , to make one of the most important steps in my life successful.

  • 8/3/2019 Coke Deposition Hydro Processing

    5/182

    Table of Contents

    1. INTRODUCTION...........................................................................................1

    1.1 Background..............................................................................................................................................1

    1.2 Coke Deposition Phenomena..................................................................................................................2

    1.2.1 Coke Deposition Models on Catalyst ................................................................................................2

    1.2.2 Coke Deposition along Catalyst Beds in Trickle-Bed Reactors ........................................................3

    1.2.3 Coke Suppression by Addition of Solvents .......................................................................................4

    1.3 What Can Be Learned from Carbon Rejection Processes?.................................................................4

    1.4 Preceding Work.......................................................................................................................................5

    1.5 Hypothesis................................................................................................................................................6

    1.6 Objectives.................................................................................................................................................8

    1.7 Thesis Outline ..........................................................................................................................................9

    2. LITERATURE REVIEW...............................................................................10

    2.1 Heavy Oils ..............................................................................................................................................10

    2.1.1 Heavy Oils/Bitumen-Our Future Energy Resource .........................................................................10

    2.1.2 Characteristics of Heavy Oils/bitumen............................................................................................11

    2.1.3 Asphaltenes......................................................................................................................................12

    2.2 Heavy Oil Catalytic Hydroprocessing .................................................................................................15

    2.2.1 Introduction .....................................................................................................................................15

    2.2.2 Fixed-Bed Processes........................................................................................................................17

    2.2.3 Moving-Bed Processes ....................................................................................................................19

    2.2.4 Ebullated-Bed Processes..................................................................................................................21

    2.2.5 Slurry Phase Process........................................................................................................................24

    2.2.6 Catalyst Characteristics ...................................................................................................................25

    2.3 Catalyst Coking .....................................................................................................................................27

    2.3.1 Catalyst Fouling Mechanisms..........................................................................................................27

  • 8/3/2019 Coke Deposition Hydro Processing

    6/182

    2.3.2 Fouling by Coke..............................................................................................................................27

    2.3.3 Coke Formation Chemistry..............................................................................................................29

    2.3.4 Coke Deposition Modes ..................................................................................................................31

    2.3.5 Coke Formation Kinetics.................................................................................................................322.3.6 Minimisation of Catalyst Fouling....................................................................................................35

    2.4 The Role of Phase Behaviour in Coke Formation .......................................................................