Partial Oxidative Cracking of Polycyclic Aromatic Compounds under Supercritical Water Conditions ...

186 Pages·2012·2.86 MB·English

Partial Oxidative Cracking of Polycyclic
Aromatic Compounds under Supercritical
Water Conditions for Heavy Hydrocarbons
Upgrading

Ahmad Rafizan Mohamad Daud

Department of Chemical Engineering
Imperial College London of Science, Technology and Medicine

Thesis submitted for the degree of Doctor of Philosophy (PhD) to Imperial
College London of Science, Technology and Medicine

October 2011
DECLARATION OF ORIGINALITY

This is to certify that this thesis was carried out by the author. The contents stated in
this work are the original effort of the author and all else is appropriately referenced.

Ahmad Rafizan Mohamad Daud
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ABSTRACT

Heavy hydrocarbon upgrading is attracting more interest amidst growing supply of
heavier crudes. These materials, often distinguished by high aromatic and asphaltene
contents generate larger volumes of residue upon processing. The present study
investigates the potential of partial oxidative cracking in water as an alternative to the
conventional thermal cracking or hydrocracking upgrading routes. Sub and
supercritical water partial oxidative cracking experiments have been carried out in a
batch micro-bomb reactor using model compounds of three to five-membered ring
polycyclic aromatic hydrocarbons (PAHs).

The goal is twofold; to establish the optimum operating window for the PAH oxidative
cracking and to evaluate the reactivity patterns between different PAH compounds. It
was found that partial oxidative cracking of PAH depends strongly on reaction
temperature and oxidant concentration. Using a 0.38 O/O atomic ratio (38% of the
stoic
oxygen needed for complete combustion), phenanthrene and anthracene were
converted at short reaction time of 0 min into mostly oxygenated intermediates (DCM
solubles) at subcritical water conditions. Under the more reactive supercritical water
conditions, ring cleavage products, which include phenols, aromatic acids, ketones
and unsubstituted aromatics (DCM solubles) were favoured. Most of these
intermediates were formed via middle ring oxygenation which could potentially
contribute to higher cracking efficiency upon subsequent thermal treatment. In addition
to the target compounds, polymerized materials (DCM insolubles) were also produced
under both conditions. A good compromise between the two major product streams
was obtained at 400 oC whereby the DCM fraction contains a balanced mixture of
oxygenated and cracking compounds.

PAHs exhibit higher degree of stability with increasing ring size. A higher reaction
temperature of 450 oC was needed in order to convert pyrene and benzo[a]pyrene.
The reactivity order with respect to PAH conversion into the desirable DCM soluble
fraction was established as follows: anthracene > phenanthrene > pyrene >
benzo[a]pyrene.

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ACKNOWLEDGEMENT

A special thank is due to my supervisors, Dr. Marcos Millan G-Agorio, Dr. Klaus
Hellgardt and Prof. Rafael Kandiyoti. Their guidance and knowledge have enabled me
to see through the difficulties and challenges in completing this research work.
Likewise, they have always been a source of great encouragement and their
assistances either help solved the enormous research related issues, or simply a
source of inspiration that keeps my motivation going.

I am also very grateful to both of my sponsors, Universiti Teknologi MARA and The
Ministry of Higher Education of Malaysia for giving me this marvellous opportunity and
the much needed monetary support. This study also benefited from invaluable
contributions provided by members of the department and colleagues for the past four
enduring years. To name a few: Mrs. S. Payne, Mrs. S. Underwood, Dr. Trevor
Morgan, Dr. Cesar Berrueco, Dr. Fessehaye Zemichael, Dr. Silvia Venditti, Dr. Yatika
Somrang, Dr. Nicolas Spiegl and John Blamey. A massive thank you to all wonderful
friends in the group: Pedro Arcelus, Khairul Rostani, Holda Puron and others who
make this research group a great place for studying and having fun.

Finally, I would also like to present my heartiest appreciation to my beloved wife,
Nadiah Saari (good luck with your thesis too) and our little “moonlight”, Aiyla Nuha for
their love, care and understanding. We did it!
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TABLE OF CONTENTS

DECLARATION OF ORIGINALITY .............................................................................. 2
ABSTRACT .................................................................................................................. 3
ACKNOWLEDGEMENT ............................................................................................... 4
TABLE OF CONTENTS ............................................................................................... 5
LIST OF TABLES ......................................................................................................... 9
LIST OF FIGURES .................................................................................................... 11
LIST OF FIGURES .................................................................................................... 11
1 INTRODUCTION ................................................................................................ 17
1.1 Petroleum Residue ..................................................................................... 17
1.2 Residue Upgrading Approach ..................................................................... 18
1.3 The Concept of Partial Oxidative Cracking ................................................. 20
1.4 Objectives of the Present Study .................................................................. 22
1.5 Outline of the Thesis ................................................................................... 23
2 BACKGROUND .................................................................................................. 25
2.1 Properties of Heavy Hydrocarbons ............................................................. 25
2.1.1 Physicochemical properties of vacuum residues ..................................... 25
2.1.2 Vacuum residue compositions ................................................................ 26
2.1.3 Structural properties of asphaltenes ....................................................... 28
2.2 Residue Upgrading Technologies ............................................................... 30
2.2.1 Recent development in residue upgrading technologies ......................... 32
2.2.2 Challenges in processing high aromatic concentration feeds .................. 36
2.3 Partial Oxidative Cracking under Sub and Supercritical Water Conditions .. 40
2.3.1 Properties and role of supercritical water ................................................ 40
2.3.2 Hydrocarbon conversion in sub and supercritical water without the addition
of oxidant ............................................................................................................ 45
2.3.3.1 Saturate, aromatic and heteroatomic compounds ........................... 45
2.3.3.2 Heavy hydrocarbons ....................................................................... 48
2.3.3 Elements of partial oxidative cracking investigations ............................... 50
2.3.3.1 Reactor setup ................................................................................. 50
2.3.3.2 Choice of oxidant ............................................................................ 52
2.3.3.3 Choice of catalyst ............................................................................ 54
2.3.4 Effect of Operating Parameters ............................................................... 56
3 EXPERIMENTAL ................................................................................................ 62
3.1 Materials ..................................................................................................... 62
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3.2 Batch Reactor Setup .................................................................................. 62
3.3 Experimental Procedure ............................................................................. 65
3.4 Analytical Techniques ................................................................................. 68
3.4.1 Ultraviolet Fluorescence Spectroscopy (UV-F) ....................................... 68
3.4.2 Gas Chromatography (GC) ..................................................................... 69
3.4.3 Gas Chromatography/Mass Spectroscopy (GC/MS) ............................... 71
3.4.4 Size Exclusion Chromatography (SEC) .................................................. 71
3.4.5 Fourier Transform-Infrared Spectroscopy (FT-IR) ................................... 72
3.4.6 Surface area measurements ................................................................... 73
4 DETERMINATION OF OXIDANT CONCENTRATION AND CHANGES TO
EXPERIMENTAL PROCEDURE ................................................................................ 74
4.1 Reactor Evaluation ..................................................................................... 74
4.2 Temperature Profile .................................................................................... 76
4.3 Repeatability and Errors Estimation ............................................................ 79
4.4 Non-oxidative Cracking in Supercritical Water ............................................ 81
4.5 Oxidative Cracking in Supercritical Water ................................................... 84
4.5.1 Conversion and products yield ................................................................ 85
4.5.2 Characterization of the DCM soluble fraction .......................................... 86
4.5.3 Characterization of the DCM insoluble fraction ....................................... 92
4.6 Modifications to the Experimental Procedure .............................................. 93
5 EFFECT OF KEY OPERATING PARAMETERS ON THE CRACKING OF
PHENANTHRENE ..................................................................................................... 97
5.1 Introduction ................................................................................................. 97
5.2 Experimental .............................................................................................. 98
5.3 Results and Discussion .............................................................................. 99
5.3.1 Effect of temperature .............................................................................. 99
5.3.1.1 Conversion and product distributions .............................................. 99
5.3.1.2 Characterization of DCM soluble fraction ...................................... 105
5.3.1.3 Characterization of DCM insoluble fraction ................................... 111
5.3.1.4 Characterization of water soluble fractions .................................... 115
5.3.1.5 Summary ...................................................................................... 116
5.3.2 Effect of reaction time ........................................................................... 117
5.3.2.1 Conversion and product distributions ............................................ 117
5.3.2.2 Characterization of DCM soluble fraction ...................................... 121
5.3.2.3 Characterization of DCM insoluble fraction ................................... 125
5.3.2.4 Summary ...................................................................................... 129
5.4 Kinetic Analysis ........................................................................................ 130
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5.5 Conclusions .............................................................................................. 134
6 INFLUENCE OF WATER DENSITY AND AIR AS OXIDANT ON THE
CONVERSION OF PHENANTHRENE ..................................................................... 135
6.1 Introduction ............................................................................................... 135
6.2 Experimental ............................................................................................ 136
6.3 Results and Discussion ............................................................................ 137
6.3.1 Influence of water density ..................................................................... 137
6.3.1.1 Conversion and product distributions ............................................ 137
6.3.1.2 Characterization of DCM soluble products .................................... 139
6.3.1.3 Characterization of DCM insoluble products. ................................ 143
6.3.1.4 Summary ...................................................................................... 144
6.3.2 Molecular oxygen from air as oxidant.................................................... 144
6.3.2.1 Conversion and product distributions ............................................ 144
6.3.2.2 Characterization of the DCM soluble fraction ................................ 147
6.3.2.3 Characterization of the DCM insoluble fraction.............................. 148
6.3.2.4 Summary ...................................................................................... 149
6.3.3 Reaction pathways in supercritical water partial oxidation system ........ 149
6.4 Transport Limitations on Rates of Solid Catalyzed Reactions ................... 151
6.5 Conclusions .............................................................................................. 154
7 REACTIVITY OF THREE TO FIVE-MEMBERED RING PAH TOWARD PARTIAL
OXIDATIVE CRACKING .......................................................................................... 155
7.1 Introduction ............................................................................................... 155
7.2 Experimental ............................................................................................ 156
7.3 Results and Discussion ............................................................................ 157
7.3.1 Effect of reaction temperature ............................................................... 157
7.3.1.1 PAH conversion and yield of DCM soluble and insoluble fractions 157
7.3.1.2 Characterization of DCM soluble fraction ...................................... 160
7.3.1.3 Kinetics of partial oxidation of polycyclic aromatic hydrocarbon .... 166
7.3.2 Effect of reaction time ........................................................................... 167
7.3.3 Anthracene oils ..................................................................................... 170
7.4 Conclusions .............................................................................................. 171
8 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK .............. 172
8.1 Conclusions .............................................................................................. 172
8.2 Recommendations for Future Work .......................................................... 175
REFERENCES ........................................................................................................ 176
APPENDIX............................................................................................................... 184
A. ............................................................................................................................. 184
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A.1 Calibration Curves .................................................................................... 184
A.2 Experimental Data .................................................................................... 185

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LIST OF TABLES

Table 2-1 Yield of AR and VR as volume % of crude oil. Data adapted from Furimsky
[11]............................................................................................................................. 26
Table 2-2 SARA components of several Venezuelan vacuum residues as published in
[47]............................................................................................................................. 26
Table 2-3 Residue conversion technologies commercially available to refiners. ......... 33
Table 2-4 Comparison of water properties at ambient and supercritical condition.
Reproduced from [84]. ............................................................................................... 41
Table 2-5 Comparison of phenanthrene degradation per millilitre of water obtained
from studies under sub and supercritical condition. .................................................... 48
Table 3-1 Regions of the infrared spectrum adapted from [131]. ................................ 73
Table 4-1 Conversion and products yield for phenanthrene partial oxidative cracking
obtained at 450 oC, 60 min reaction time, 0.38 O/O atomic ratio and 0.18 g/mL
stoic
water density. ............................................................................................................. 81
Table 4-2 Phenanthrene (PHT) degradation under non-oxidative supercritical water at
450 oC, 10 min reaction time and 0.18 g/mL water density. ........................................ 82
Table 4-3 Comparison of the phenanthrene degradation obtained from present study
to those from literature. .............................................................................................. 83
Table 4-4 Likely products obtained from the DCM soluble fraction as identified by a
GC/MS. ...................................................................................................................... 84
Table 4-5 Oxidative cracking of Phenanthrene (PHT) at 450 oC, 34 MPa and 60 minute
reaction time at different oxidant concentrations. ....................................................... 85
Table 5-1 Conversion and product yield for phenanthrene partial oxidative cracking as
a function of temperature. Experiments were carried out at 0 min reaction time using
0.38 O/O atomic ratio and 0.16 g/mL water density. ............................................ 100
stoic
Table 5-2 Molecular mass of the DCM soluble fractions obtained at different
temperatures. ........................................................................................................... 111
Table 5-3 Conversion and product yields of phenanthrene partial oxidative cracking as
a function of reaction time. Experiments were carried out at between 280-450 oC using
0.38 O/O atomic ratio and 0.16 g/mL water density. ............................................ 118
stoic
Table 5-4 Product distribution of phenanthrene partial oxidative cracking produced at
400 oC for different reaction times. xx represents major species identified and x
represents the minor species found in the fraction. .................................................. 122
Table 5-5 Experimental measurements of reaction rate constants for partial oxidative
cracking of phenanthrene at reaction temperatures between 280-350 oC. ............... 132
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Table 6-1 Product distribution of phenanthrene partial oxidative cracking produced at
300 and 400 oC for 0 min and 0.35 g/mL water density. xx represents major species
and x represents minor species identified in the DCM soluble fraction. .................... 140
Table 6-2 Characteristics of the fresh and spent catalysts ....................................... 146
Table 7-1 Experimental measurements of reaction rate constants for partial oxidative
cracking of polycyclic aromatic hydrocarbon at reaction temperatures between 280-
450 oC. ..................................................................................................................... 166
Table 7-2 DCM soluble and DCM insoluble yields of polycyclic aromatic hydrocarbon
partial oxidative cracking as a function of reaction time. Experiments were carried out
at 450 oC using 0.38 O/O atomic ratio and 0.16 g/mL water density. ................... 168
stoic
Table 7-3 Yields of DCM solubles and DCM insolubles obtained from anthracene oil
partial oxidative cracking at 400 oC for 0-60 min reaction time ................................. 170
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