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Catalytic Hydrogenation and Hydrodesulfurization of Model ... · PDF file ix List of Tables Table 1.1 Summary of Recent Advances in Hydroprocessing with Sulfides 5 Table 1.2 Summary

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  • Catalytic Hydrogenation and Hydrodesulfurization of Model Compounds

    Haiyan Zhao

    Dissertation submitted to the faculty of Virginia Polytechnic Institute and State University in partial fulfillment of the requirement of the degree of

    Doctor of Philosophy In

    Chemical Engineering

    S. Ted Oyama, Chairman

    Luke Achenie

    David F. Cox

    James Tanko

    March 19th, 2009

    Blacksburg, Virginia

    Key words: HDS, ROP, HYD, 2MT, H2 storage, Bimetallic, Phosphides, EXAFS, FTIR

    Copy right 2009, Haiyan Zhao

  • Catalytic hydrogenation and hydrodesulfurization of model compounds

    Haiyan Zhao

    Abstract

    This dissertation describes two related studies on hydrogenation and

    hydrodesulfurization of heterocyclic S-containing compounds.

    Alkyl substituted thiophenes are promising candidates for hydrogen carriers as the

    dehydrogenation reactions are known to occur under mild conditions. Four types of

    catalysts including supported noble metals, bimetallic noble metals, transition metal

    phosphides and transition metal sulfides have been investigated for 2-methylthiophene

    (2MT) hydrogenation and ring opening. The major products were tetrahydro-2-

    methylthiophene (TH2MT), pentenes and pentane, with very little C5-thiols observed.

    The selectivity towards the desired product TH2MT follows the order: noble metals >

    bimetallics > phosphides > sulfides. The best hydrogenation catalyst was 2% Pt/Al2O3

    which exhibited relatively high reactivity and selectivity towards TH2MT at moderate

    temperatures. Temperature-programmed desorption (TPD) of hydrogen indicated that

    the H2 desorption amount was inversely related to the rate of TH2MT formation.

    Temperature programmed reaction (TPR) experiments revealed that pentanethiol became

    the major product, especially with HDS catalysts like CoMoS/Al2O3 and WP/SiO2, which

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    indicates that poisoned or modified conventional HDS catalysts would be good

    candidates for further 2MT hydrogenation studies.

    The role of tetrahedral Ni(1) sites and square pyramidal Ni(2) sites in Ni2P

    hydrotreating catalysts was studied by substitution of Ni with Fe. The Fe component was

    deemed as a good probe because Ni2P and Fe2P adopt the same hexagonal crystal

    structure, yet Fe2P is completely inactive for hydrodesulfurization (HDS). For this

    purpose a series of NiFeP/SiO2 catalysts were prepared with different Ni:Fe molar ratios

    (1:0, 3:1, 1:1, 1:3, and 0:1) and investigated in the HDS of 4,6-dimethyldibenzothiophene

    at 300 and 340 oC. The uniformity of the NiFe series was demonstrated by x-ray

    diffraction analysis and by Fourier transform infrared (FTIR) spectroscopy of adsorbed

    CO. The position of substitution of Fe was determined by extended X-ray absorption

    fine structure (EXAFS) analysis. It was found that at 300 oC the HDS activity of the

    catalysts decreased with increasing Fe content and that this could be explained by the

    substitution of Fe at the more active Ni(2) sites. As temperature was raised to 340 oC,

    the activity of the Fe-containing samples increased, although not to the level of Ni2P, and

    this could be understood from a reconstruction of the NiFe phase to expose more Ni(2)

    sites. This was likely driven by the formation of surface Ni-S bonds, which could be

    observed by EXAFS in spent samples.

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    To my parents

    for their constant support and love

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

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    Acknowledgement  

    I am extremely grateful to my advisor and mentor Dr. S. Ted Oyama for his guidance and

    continued words of encouragement. Thank you for preparing me to think independently, to be a

    serious research scientist and to seek the perfection and art of science and engineering. Your

    advice will be my fortune in my life. I also greatly appreciate the advice and support from my

    committee members Dr. David Cox, Dr. James Tanko and Dr. Luke Achenie.

    I greatly appreciate the friendships and supports of present and past group members.

    Thank you for providing me this unique research environment to help me grow: Dr. Pelin

    Hacarlioglu, Dr. Travis Gott, Jason Gaudet, Dr. Hankwon Lim, Dr. Yungeng Gu, Dr. Yuying

    Shu and Dr. Yong-Kul Lee. I am also very thankful to Yujung Dong and John Brooks as an

    extended support from Dr Cox’s lab. I would also like to thank the Chemical Engineering

    Department staff, Riley Chan, Chris Moore, Diane Cannaday, Mike Vaught and Tina Kirk for

    their constant support and help during the past five years.

    I can never express enough my sincere love and gratitude to my parents for their

    unconditional love, encouragement, and sacrifices in my life and studies. Thank you all for

    always being there and being my pillar stone.

    Finally, special thanks to my English teachers and mentors, Johnny and Nancy McCord,

    for their friendship and big hearts. Special thanks also to Jay and Michele Lester in ICF and

    friends in BBC bible study group to help me with my life here and also grow spiritually.

     

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    Table of content

    Chapter 1

    Introduction

    1.1 Oragnosulfur model compounds 1

    1.2 Sulfur containing model compounds reaction mechanism 2

    1.3 State of art for catalytic materials and alternative hydrodesulfurization processes 4

    1.4 Goals 10

    1.5 Dissertation overview 12

    Reference 14

    Chapter 2

    Transition metal phosphides

    2.1 General properties 28

    2.2 Synthesis of transition metal phosphides 31

    2.3 Catalytic properties in hydrotreating 33

    2.4 Kinetic pathways in HDS and in HDN 41

    2.5 Bimetallic phosphide systems 49

    2.6 Conclusions 53

    Reference 54

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    Chapter 3

    Hydrogen Storage Using Heterocyclic compounds: The Hydrogenation of 2-

    Methylthiophene

    3.1 Introduction 63

    3.2 Experimental 68

    3.2.1 Materials 68

    3.2.2 Metal phosphides synthesis 69

    3.2.3 Characterization 70

    3.2.4 Reactivity Studies 71

    3.2.5 Temperature Programmed Desorption (TPD) and Temperature Programmed

    Reaction (TPR) 72

    3.3 Results and discussion 73

    3.3.1 CO Chemisorption and O2 Chemisorption 73

    3.3.2 Reactivity 75

    3.3.3 TPD and TPR 84

    3.3.3.1 TPD of H2 84

    3.3.3.2 TPR of 2MT and H2 87

    3.4 Conclusions

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