Kinetics and Effects of H2 Partial Pressure on Hydrotreating of Heavy Gas Oil
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Saskatchewan's Research Archive Kinetics and Effects of H2 Partial Pressure on Hydrotreating of Heavy Gas Oil A Thesis Submitted to the College of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Chemical Engineering University of Saskatchewan Saskatoon By Majak Mapiour Oct2009 © Copyright Majak Mapiour, Oct 2009. All rights reserved COPYRIGHT It is my consent that the libraries of the University of Saskatchewan may make this thesis freely available for inspection. Besides, I agree that permission for copying of this thesis in any manner, either in whole or in part, for scholarly purposes be granted primarily by the professor(s) who supervised this thesis work or in their absence by the Head of the Department of Chemical Engineering or the Dean of the College of Graduate Studies. Duplication or 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 the author of this thesis and to the University of Saskatchewan in any use of the material therein. Request for permission to copy or to make any other use of the material in this thesis in whole or in part should be addressed to: The Head Department of Chemical Engineering University of Saskatchewan 105 Maintenance Road Saskatoon, Saskatchewan S7N 5C5 Canada i ABSTRACT The impact of H2 partial pressure (H2 pp) during the hydrotreating of heavy gas oil, derived from Athabasca bitumen, over commercial NiMo/γ-Al2O3 catalyst was studied in a micro-trickle bed reactor. The experimental conditions were varied as follows: temperature: 360 to 400ºC, pressure: 7 to 11 MPa, gas/oil ratio: 400 to 1270 mL/mL, H2 purity range of 0 to 100 vol. % (with the rest either CH4 or He), and LHSV range of 0.65 to 2 h-1. The two main objectives of the project were to study the nature of the dependence of H2 pp on temperature, pressure, gas/oil ratio, LHSV (Liquid Hourly Space Velocity), and H2 purity. The project was divided into three phases: in phase one the effect of H2 purity on hydrotreating of heavy gas oil (HGO) was studied, in phase two the nature of H2 pp dependency and the effect of H2 pp on hydrotreating of HGO was investigated, and in phase three kinetic studies were carried out using different kinetic models. The objective of phase one was to study the effect of hydrogen purity on hydrotreating of HGO was studied in a trickle bed reactor over a commercial Ni−Mo/γ- alumina catalyst. Methane was used as a diluent for the hydrogen stream, and its effect on the catalyst performance was compared to that of helium, which is inert toward the catalyst. Furthermore, a deactivation study was conducted over a period of 66 days, during which the catalyst was subjected to H2 purities ranging from 75 to 95% (with the rest methane); no significant deterioration in the hydroprocessing activities of the catalyst was observed. Therefore, it was concluded that methane was inert toward a ii commercial Ni−Mo/γ-alumina catalyst. However, its presence resulted in hydrogen partial pressure reduction, which in turn led to a decrease in hydrodesulphurization (HDS), hydrodenitrogenation (HDN), hydrodearomatization (HDA) conversions. This reduction can be offset by increasing the total pressure of the system. HDS, HDN, HDA, and mild hydrocracking (MHC) conversions were studied. Also determined were cetane index, density, aniline point, diesel index, and fractional distribution of the products. The main objective of phase two was to study the effects of H2 pp on hydrotreating conversions, feed vaporization, H2 dissolution, and H2 consumption were studied. The results show that HDN and HDA are significantly more affected by H2 partial pressure than HDS; with the HDN being the most affected. For instance as the inlet H2 partial pressure was increased from 4.6 to 8.9 MPa HDS, HDN, and HDA conversions increased for 94.9%, 55.1%, and 46.0% to 96.7%, 83.9%, and 58.0% , respectively. Moreover, it was observed that H2 dissolution and H2 consumption increased with increasing H2 pp. No clear trend was observed for the effect of H2 pp on feed vaporization. In phase three the kinetics of HDS, HDN, and HDA were studied. The power law, multi-parameter, and Langmuir - Hinshelwood type models were used to fit the data. The prediction capacities of the resulting models were tested. It was determined that, while multi-parameter model yielded better prediction, L-H had an advantage in that it took a lesser number of experimental data to determine its parameters. Kinetic fitting of the data to a pseudo-first-order power law model suggested that conclusions on the effect of H2 pp on hydrotreating activities could be equally drawn from either inlet or iii outlet hydrogen partial pressure. However, from the catalyst deactivation standpoint, it is recommended that such conclusions are drawn from the outlet H2 partial pressure, since it is the reactor point with the lowest hydrogen partial pressure. iv ACKNOWLEDGEMENT I would like to acknowledge the input and contribution of a number of persons who helped in this endeavor: My supervisors Drs A. K. Dalai and J. Adjaye for every second that they invested in supporting and guiding me in every step of the project. Dr. V. Sundaramurthy for being a source of encouragement and inspiration when the “going got tough”. Drs. Dr. Richard W. Evitts and Hui Wang for their time, contribution, and guidance. Mr. Ted Wallenting for being funny and extremely patient and for turning experimental difficulties into laughter. Mr. Richard Blondin for always “going the extra mile”. Mr. Dragan Celkic for always being helpful and punctual. My friends Philip, Chiryu, and Cristina for their constant support. They spent countless hours proof-reading my works. I would like to thank all members of Catalysis and Chemical Reaction Engineering Laboratories (Department of Chemical Engineering, U of S) for being so cooperative and understanding. Financial assistance from NSERC IPS is gratefully acknowledged. Above all, I wholeheartedly thank God for placing such wonderful individuals on my path, and may He continue to bless every single one of them abundantly. v DEDICATION This thesis is dedicated to: My parents, Loi and Grace, for all the sacrifices they made so that I could get an education My brothers and sisters for being my role models My friends and lab-mates for making this a fun journey vi TABLES OF CONTENTS COPYRIGHT i ABSTRACT ii ACKNOWLEDGEMENT v DEDICATION vi TABLE OF CONTENTS vii LIST OF TABLES xiv LIST OF FIGURES xviii NOMENCLATURE and ABBREVIATIONS xxiv DEFINITION AND TERMINOLOGIES xxvii 1.0 INTRODUCTION 1 1.1 Research background 1 1.2 Knowledge gaps 3 1.3 Hypothesis 4 1.4 Research objectives 4 2.0 LITERATURE REVIEW 6 2.1 Hydrotreating 9 2.1.1 Hydrotreating reactions 9 2.1.2 Hydrotreating operating variables 9 2.1.2.1 Temperature 14 vii 2.1.2.2 Liquid Hourly Space velocity (LHSV) 14 2.1.2.3 Gas/oil ratio 15 2.1.2.4 H2 purity 15 2.1.3 Hydrotreating catalysts 15 2.1.3.1 Hydrotreating catalyst structure 16 2.1.3.2 Hydrotreating catalyst deactivation 18 2.1.4 Corrosion concerns 19 2.1.5 Environmental concerns 20 2.2 Hydrodesulphurization reactivity and mechanism 21 2.3 Hydrodenitrogenation reactivity and mechanism 22 2.4 Hydrodearomatization reactivity and mechanism 25 2.5 Hydrotreating reactor 25 2.6 H2 cycle in hydrotreating 26 2.7 H2 purity in hydrotreating 27 2.7.1 Importance of H2 purity 27 2.7.2 Major impurity in the recycle H2 stream 27 2.7.3 H2 recovery process 28 2.8 H2 partial pressure 29 2.8.1 Importance of H2 partial pressure 29 2.8.2 Dependent nature of H2 partial pressure 30 2.9 Inlet versus outlet H2 partial pressure 31 2.9.1 H2 consumption 31 2.9.1.1 Chemical H2 consumption 32 2.9.1.2 Dissolved H2 losses 34 viii 2.9.2 Determination of inlet and outlet H2 partial pressure 35 2.10 Laws and Principles explaining gas-gas and gas-liquid interactions 36 2.10.1 Le Chatelier's Principle 36 2.10.2 Dalton’s Law 37 2.10.3 Henry’s Law 37 2.10.4 Raoult’s Law 37 2.10.4.1 Positive Deviation 37 2.10.4.2 Negative Deviation 38 2.11 Effects of H2 partial pressure on hydrotreating activities 38 2.11.1 Effect of H2 partial pressure on HDA 38 2.11.2 Effect of H2 partial pressure on HDN and HDS 39 2.12 Kinetics Models for HDS, HDN, and HDA 41 2.12.1 Power Law Model 42 2.12.2 Langmuir-Hinshelwood Model 44 2.12.3 Multi-parameter Model 51 2.12.4 Mass transfer evaluation 52 2.12.5 Heat transfer evaluation 54 3.0 EXPERIMENTAL 55 3.1 System description 55 3.2 Catalyst loading 55 3.3 Experimental procedure 57 3.4 Experimental plan 58 3.4.1 Phase I – Effect of H2 purity on hydrotreating activities 59 ix 3.4.2 Phase II –Effect of H2 partial pressure on hydrotreating Activities 60 3.4.3 Phase III –Kinetic modeling 61 3.5 Analysis of feed and liquid products 62 3.5.1 N-S analysis 62 3.5.2 13C NMR analysis 63 3.5.3 Simulated distillation 65 3.5.4 Cetane number, aniline point, and diesel index 67 3.5.5 Mild hydrocracking (MHC) 67 4.0 RESULTS AND DISCUSSION 70 4.1 Phase I: Effect of H2 purity on hydrotreating activities 69 4.1.1 Effect of the Hydrogen Purity 69 4.1.2 Effect of Methane on catalyst performance 78 4.1.3 Long term effect of Methane on catalyst performance 82 4.1.4 Variables affecting H2 partial pressure 83 4.2 Phase II: Effect of H2 partial pressure on Hydrotreating activities