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Mohanty Thesis

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Effect of citric acid on hydrotreating activity of NiMo catalysts A thesis submitted to the college of graduate studies and research in partial fulfillment of the requirements for the degree of Masters of Science in the Department of Chemical and Biological Engineering University of Saskatchewan Saskatoon, Saskatchewan by Sidhartha Mohanty December 2011 Copyright Sidhartha Mohanty, December 2011. All rights reserved.i COPYRIGHT The author has consented that the libraries of the University of Saskatchewan may make this thesis freely available for inspection. Furthermore, the author agrees that permission for the copying of this thesis in any manner, either in whole or part, for scholarly purposes be granted primarily by the professor(s) who supervised this thesis or in their absence by the Department Head of Chemical Engineering or the Dean of the College of Graduate Studies. Duplication, publication, or any use of this thesis, in part or in whole, for financial gain without prior written approval by the University of Saskatchewan is prohibited. It is also understood that due recognition shall be given to the author of this thesis and to the University of Saskatchewan for any use of the material in this thesis. Request for permission to copy or make use of the material in this thesis in whole or in part should be addressed to: The Department Head of Chemical and Biological Engineering College of Engineering University of Saskatchewan 57 Campus Drive Saskatoon SK Canada S7N 5A9 ii ABSTRACT With depleting reserves of sweet crude oil, there is an increasing demand world over to process heavy crudes. Canadas Athabasca oil sands basin is a rich source of this heavy feedstock derived from bitumen. However, the heavy gas oil feedstock derived from this bitumen has very high quantities of S (4 wt %) and N (0.4 wt %). In order to meet todays strict environmental regulations, design of hydrotreating catalysts with increased active site density and improved intrinsic catalytic activity per site is critical. This work, in the first phase deals with the modification of the Al2O3 support to increase its acidity and in subsequent phases, citric acid has been used as an additive to enhance the formation of Type II NiMoS sites. Mesostructured alumino-silicate (MAS) materials were synthesized from ZSM-5 nanoclusters and used as catalysts supports for the hydrotreatment of a model compound and real feed stock. The alumino-silicate materials exhibited different acid strengths and textural properties depending on the duration of hydrothermal treatment of the zeolite seeds. The acidity of the MAS materials were found significantly higher than Al-SBA-15 and Al2O3 materials. The activity of NiMo catalysts supported on MAS materials were evaluated using the hydrodesulfurization of dibenzothiophene (DBT). The NiMo catalyst supported on mesoporous alumino silicate obtained after 16 hrs of hydrothermal treatment of the ZSM-5 precursors was found to be the most active in the HDS of DBT. Similarly, hydrotreating tests revealed that the composite made of 5 wt % MAS-16 and 95 wt % -Al2O3 was best suited for hydrotreating reactions with real feedstock. This support showed optimum acidity and excellent dispersion of the active species and was selected as the support of choice for all further hydrotreating reactions with real feed stock. iii In the second stage of this work citric acid (CA) in varying ratios was used to prepare NiMo catalysts supported on a composite of -Al2O3 and mesoporous alumino-silicates. Citric acid was found to form a complex with both Ni and Mo simultaneously. However, the promoting effect of citric acid in the hydrotreating was observed mostly due to the formation of a stable nickel-citrate complex. The hydrotreating activity of the synthesized catalysts is evaluated using heavy gas oil (HGO) derived from Athabasca bitumen, in a trickle bed continuous reactor. The Mo loading, Ni loading and the citric acid to nickel molar ratios were optimized on the basis of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activity of HGO. The best performing catalyst for the hydrotreating of heavy gas oil was obtained for a Mo loading of 13 wt %, Ni loading of 7 wt % and CA/Ni molar ratio of 1. The sulfur and nitrogen conversions for the best catalyst were found to be 93 wt % and 74 wt % respectively. iv ACKNOWLEDGEMENT I would first like to thank my supervisors, Dr. Ajay Dalai and Dr. John Adjaye, for their valuable guidance and supervision throughout my research work. I greatly appreciate the effort made by them to review and provide recommendations to my written materials. I would also like to thank the other two members of my MSc. supervisory committee, Dr. Yongfeng Hu and Dr. Hui Wang, for their contributions to my graduate studies. Secondly, I would also like to thank Mr. Richard Blondin, Mr. Dragan Cekic, and Heli Eunike for their assistance in the laboratory work that contributed to my project. My thanks also go to the Natural Sciences and Engineering Research Council of Canada and Syncrude Canada Limited for their much-appreciated financial assistance. I also greatly appreciate the work done by the Saskatchewan Structural Science Center and Geology Department of University of Saskatchewan, University of New Brunswick, and the University of Western Ontario for their assistance in the catalyst characterizations. Lastly, I would like to express my gratitude to all the professors, post-doctorate fellows, and graduate students that have contributed to my graduate study at the University of Saskatchewan. Finally, I thank God Almighty for his blessings. v DEDICATION In loving memory of my jeje (Grandfather), Shri Jadumani Mohanty (1923- 2010) vi TABLE OF CONTENTS COPYRIGHT ................................................................................................................................................. i ABSTRACT .................................................................................................................................................. ii ACKNOWLEDGEMENT ........................................................................................................................... iv DEDICATION .............................................................................................................................................. v TABLE OF CONTENTS ............................................................................................................................. vi LIST OF TABLES ........................................................................................................................................ x LIST OF FIGURES .................................................................................................................................... xii NOMENCLATURE .................................................................................................................................... xx CHAPTER 1 INTRODUCTION .................................................................................................................. 1 1.1 Research Background ....................................................................................................................... 1 1.2 Knowledge Gaps ............................................................................................................................... 5 1.3 Hypothesis......................................................................................................................................... 6 1.4 Research Objectives .......................................................................................................................... 7 CHAPTER 2 LITERATURE REVIEW ..................................................................................................... 10 2.1 Global Demand for Oil ................................................................................................................... 10 2.2 Bitumen and Heavy Gas Oil ........................................................................................................... 13 2.3 Hydroprocessing ............................................................................................................................. 15 2.3.1 Hydrodemetallization .................................................................................................................. 15 2.3.2 Hydrodcracking ........................................................................................................................... 17 2.3.3 Hydrotreating .............................................................................................................................. 17 2.4 Need for Hydroprocessing .............................................................................................................. 18 2.4.1 Strict Environmental Regulations ............................................................................................... 18 2.4.2 Increasing middle distillate fraction ............................................................................................ 19 2.4.3 Improving Product Quality ......................................................................................................... 20 2.5 Hydrotreatment ............................................................................................................................... 20 2.5.1 Hydrotreating Process Description ...............

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