understanding the adsorption of polycyclic aromatic hydrocarbons from aqueous phase onto ...

146 Pages·2011·1.81 MB·English

UNDERSTANDING THE ADSORPTION OF
POLYCYCLIC AROMATIC HYDROCARBONS FROM
AQUEOUS PHASE ONTO ACTIVATED CARBON

by

Ayodeji Awoyemi

A thesis submitted in conformity with the requirements
for the degree of Master of Applied Science
Graduate Department of Chemical Engineering and Applied Chemistry
University of Toronto

© Copyright by Ayodeji Awoyemi (2011)
Understanding the Adsorption of Polycyclic Aromatic Hydrocarbons from
Aqueous Phase onto Activated Carbon
Ayodeji Awoyemi
Master of Applied Science
Department of Chemical Engineering and Applied Chemistry
University of Toronto
2011

ABSTRACT
Non-competitive adsorption of polycyclic aromatic hydrocarbons (PAHs)
from water onto activated carbon was studied alongside the performance of CO -
2
activated petroleum coke as a low-cost adsorbent.
PAH adsorption was a two-stage process: a short, fast initial period followed
by a long, slow period corresponding to the intra-particle diffusion of PAH molecules
in macropores and micropores. The adsorption capacity was determined by total
surface area accessible to PAH and the availability of active surface chemical groups.
The positive dependence of adsorption capacity on surface oxygen groups and
temperature was observed, suggesting a chemical nature of PAH adsorption. The
interaction between PAH-activated carbon was however, weak and energetically
similar to that of hydrogen bonds. Overall, PAH adsorption was an exothermic
process that combined physisorption and chemisorption.
CO -activated petroleum coke had a greater SSA-normalized capacity than
2
coal-derived commercial activated carbon (0.26 vs. 0.19 mg/m2). The capacity was
significantly increased by post-oxidation to 0.62 mg/m2.

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ACKNOWLEDGEMENTS
I owe special debts to all those who have contributed to molding me at home,
in school and in the society at large. Due to the limitations of space, I cannot,
unfortunately, print out a comprehensive list here to thank all. If, as one of those who
helped, you have not been identified nominally, I awfully regret.

If it had not been the Lord who was on my side, I would have fallen by the
wayside in the course of this program. To God, the father who does not change like
shifting shadows, I owe a lot.

Prof. Charles Q. Jia, you believed in me even when I did not believe in myself.
Thanks for challenging me to be a better researcher at every turn. The lessons learnt
from you are mine to run with in life! I cannot but acknowledge the support of the
members of the green technology laboratory with whom I shared lab space for these
past years. I have won a friend in each of you- Li, Jenny, Eric, Ming, Joy, Azadeh, Ti,
and Yesul. The succor found in those encouraging words from you during those
lonely and sometimes fruitless hours in the laboratory cannot be over emphasized.
Prof. Shitang Tong stood out as a resource person anytime I ran out of ideas.

To my family members, you have been a great help and encouragement.
Thanks for the shoulders to lean on at any time. I am eternally indebted to God for
having you. Words cannot fully express the depth of the gratitude I owe my dear
mum, for the challenging circumstances she encountered in bringing me up.

Eyitope, a thousand miles might have separated us, but the story of this thesis
would not have been enjoyable for me without knowing you were waiting at the other
end of the line for my everyday progress report. I could not have asked for more.

The e8 organization is gratefully acknowledged for the e8 education for
sustainable energy development masters scholarship (2009/2010 cycle).

May everyone concerned, mentioned or at heart, be rewarded by Him
bounteously.
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Table of Contents

ABSTRACT........................................................................................................... II
ACKNOWLEDGEMENTS.................................................................................. IV
TABLE OF CONTENT......................................................................................... V
LIST OF TABLES................................................................................................. VIII
LIST OF FIGURES............................................................................................... X
LIST OF APPENDICES……………………..…………………………………. XII

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

1.1. PAHs as Persistent Pollutants.................................................................. 1

1.2. Activated Carbons as PAHs Adsorbent………….................................. 2

1.3. Objectives................................................................................................... 3

2. ACTIVATED CARBONS AND PAHS........................................ 5

2.1. Activated Carbon (AC)………………..................................................... 5
2.1.1. Industrial Applications……………………………………………... 5
2.1.2. Raw Materials……………………………………………………… 6
2.1.3. Production Processes……………………………………..………... 7
2.1.3.1. Physical activation……………………………………….. 8
2.1.3.2. Chemical activation……………………………………… 9
2.1.4. Control of Porosity of Activated Carbons……….………………… 12

2.2. Polycyclic Aromatic Hydrocarbons (PAHs)………………................... 14
2.2.1. Sources of PAHs………………………………………………….... 19
2.2.2. Health Impact of PAHs…………………………………………….. 20
2.2.3. Environmental Fate and Regulations of PAHs…………………….. 22
2.2.4. Trace Level Detection Techniques of PAHs………………..……... 23
2.2.5. PAHs Removal Techniques………………………………………... 24

3. THEORIES OF AQUEOUS PHASE PAH ADSORPTION….. 26

3.1. Physical vs. Chemical Adsorption………..………………………….... 26

3.2. Adsorption Kinetics……………………………………………………. 28
3.2.1. Empirical Models (Global Rate Models)………………………….. 28
3.2.1.1. Pseudo-first-order...…………………………………….... 28
3.2.1.2. Pseudo-second-order……………………..……………… 29
3.2.1.3. The Elovich model…………………………………….… 30
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3.2.2. Mechanistic Models……………………………………………….. 30
3.2.2.1. Film diffusion model…………………………………….. 31
3.2.2.2. Intra-particle diffusion models…………………………... 32
3.3. Adsorption Isotherm………………………………………………….... 34
3.3.1. Classifications of Adsorption Isotherms…………………………... 34
3.3.2. Isotherm Models……………………….…………………………... 36
3.3.2.1. Langmuir isotherm model……………………………….. 36
3.3.2.2. Freundlich isotherm model…………………………….... 37
3.3.2.3. Some other common models…………………………….. 38
3.3.3. Proposed Mechanisms of PAH Adsorption from Aqueous Phase.... 40

4. EXPERIMENTAL……………………………………................. 42

4.1. Synthesis of Activated Carbons………………...................................... 42
4.1.1. Reagents and Materials……………………………...……………... 42
4.1.2. Instruments and Procedure……………………………………….… 43
4.1.2.1. Physical activation of delayed coke……………………… 44
4.1.2.2. Surface oxidation………………………………………… 45
4.1.2.3. Templating and chemical activation of coal tar pitch.…… 46

4.2. Characterization of Activated Carbons……………………………….. 47
4.2.1. Reagents and Materials……………………………...……………... 47
4.2.2. Instruments and Technique………………………………………… 48
4.2.2.1. Porous structure analysis…………………………………. 48
4.2.2.2. Surface morphology analysis…………………………….. 49
4.2.2.3. Surface chemistry analysis……………………………….. 49

4.3. PAH Adsorption Experiment………………...………………………… 51
4.3.1. Materials and Reagents…………………………………………….. 51
4.3.2. Instruments and Procedure………………………....………………. 52
4.3.2.1. Adsorption kinetics study…………………………....….... 53
4.3.2.2. Solid phase extraction/GC-MS analysis………………….. 54
4.3.2.3. Adsorption isotherm study……………………………….. 56

4.4. Adsorption Data Quality and Repeatability…………………………... 56

5. RESULTS AND DISCUSSION..………………………………. 58

5.1. Characterization of Activated Carbon………………………………… 58
5.1.1. Porous Structure Analysis…………………………...……………... 58
5.1.2. Morphology………………………………………………………… 61
5.1.3. Surface Functionality………………………………………………. 62

5.2. Adsorption Study……………………………………………………….. 65
5.2.1. Adsorption Kinetics Study…………………………………………. 66
5.2.1.1. Effect of mixing strength…………………………………. 66
5.2.1.2. Effect of porous structure………………………………… 68
5.2.1.3. Effect of surface functionality…………………….…….... 77
5.2.1.4. Effect of initial concentration…………………………...... 80
5.2.1.5. Effect of adsorbate………………….…………………….. 83
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5.2.2. Adsorption Isotherm Study……………………………………….… 87
5.2.2.1. Effect of porous structure…………………………………. 87
5.2.2.2. Effect of surface functionality…………………………….. 90
5.2.2.3. Effect of adsorbate………………………………………… 93
5.2.2.4. Temperature effect……………………………………….... 94
5.2.2.5. Thermodynamic analysis of PAH adsorption……………... 96

6. CONCLUSIONS AND RECOMMENDATIONS…………….… 99

6.1. Conclusions………………………………………………………………. 99

6.2. Recommendations……………………………………………………….. 101

REFERENCES…………………………………………………………………. 103

APPENDICES…………………………………………………………………... 119

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List of Tables
Table 1-1 Organic Compounds Amenable to Adsorption by GAC………..……… 3
Table 2-1 Data Pertaining to the 17 Designated Priority PAHs……….………….. 16
Table 2-2 PAH Concentration Range in Different Matrices at
Various Locations…………………………………………………………. 20
Table 2-3 Carcinogenicity of Selected PAHs………………………………...…… 21
Table 3-1 Differences between Physisorption and Chemisorption….……….......... 27
Table 4-1 Adsorbents and Naming Nomenclature………………………………… 42
Table 4-2 Reagents used in Synthesis of Activated Carbons……………………… 43
Table 4-3 Instruments Employed in Carbon Activation……….……………...…… 43
Table 4-4 Treatment Conditions for Physical Activation…….………………...….. 45
Table 4-5 Templated Carbons Preparation Mixing Ratios……………………...…. 47
Table 4-6 Materials used in Carbon Characterization……………………………... 47
Table 4-7 Carbon Characterization Instruments……………………………...……. 48
Table 4-8 Materials and Reagents Employed in Adsorption Experiment….…….... 52
Table 4-9 Instruments Employed in Adsorption Experiment….……….………..… 52
Table 4-10 Adsorption Data Quality……………………………………..………... 57
Table 5-1 Porous Structural Characteristics of Utilized Carbons…………………. 59
Table 5-2 Amount of Surface Oxygen Groups on Surface Oxidized Carbons……. 64
Table 5-3 Global Rate Parameters for Long Term Fluorene Adsorption….…...…. 68
Table 5-4 Global Rate Parameters for Short Term Naphthalene Adsorption…...… 73
Table 5-5 Diffusion Parameters for Different Activated Carbons….…………...… 76
Table 5-6 Rate Parameters for Naphthalene Adsorption on Surface Oxidized
Activated Carbons……………………………………….……………..….. 78

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Table 5-7 Rate Parameters for Initial Naphthalene Concentration
Effect on the Adsorption Process…....……………..……………………… 81
Table 5-8 Diffusion Parameters for the Effect of Initial Concentration on PAH
Adsorption………………………………………………………………… 83
Table 5-9 Rate Parameters for the Adsorption of Naphthalene and Fluorene…….. 84
Table 5-10 Diffusion Parameters for the Adsorption of Naphthalene and
Fluorene…………………………………………………………………… 85
Table 5-11 Naphthalene Adsorption Isotherm Parameters for Different
Adsorbents……………………………………………………………..….. 89
Table 5-12 Naphthalene Adsorption Isotherm Parameters on Surface
Oxidized Activated Carbons…………….………….…………………..… 92
Table 5-13 Naphthalene and Fluorene Adsorption Isotherm Parameters………… 93
Table 5-14 Naphthalene Adsorption Isotherm Parameters at Different
Temperature………………………………………………………………. 96
Table 5-15 Thermodynamics Properties of the Adsorption of Naphthalene on
MPC-CO ………………………………………………………………… 97
2

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List of Figures
Figure 2-1 Alberta Oil Sands Upgrading Coke Inventory………….………….….. 7
Figure 3-1 Schematic Diagram of Heterogeneous Adsorption Process…………… 31
Figure 3-2 IUPAC Types of Adsorption Isotherm…………………………...….… 35
Figure 4-1 Schematic Representation of the Physical Activation Set-up……......… 45
Figure 4-2 Adsorption Kinetic Experimental Protocol….…………..………...…… 54
Figure 5-1 N Adsorption Isotherms at 77K of Employed Carbons…………....….. 58
2
Figure 5-2 SEM Images of Employed Carbons……………………………..…....... 62
Figure 5-3 FTIR Spectra for Employed Carbons………………………………....... 63
Figure 5-4a Effect of Mixing Strength on Adsorption of Mixture of PAHs for
15 Minutes……...…………………………………………………….….… 66
Figure 5-4b Effect of Mixing Strength on Adsorption of Naphthalene……………. 67
Figure 5-5 Long Term Fluorene Adsorption on Four Types of Adsorbent……...… 68
Figure 5-6 Validation of Kinetic Model Choice…………………………………… 70
Figure 5-7 Short Term Naphthalene Adsorption on Four Types of Adsorbent…..... 72
Figure 5-8a HPDM Regression of Naphthalene Adsorption onto Various
Carbons……………………………………………………………….….… 74
Figure 5-8b Weber-Morris Plot of Naphthalene Adsorption onto Various
Carbons………………………………………………………….……….... 75
Figure 5-9 Naphthalene Adsorption on Surface Oxidized Activated Carbons….… 78
Figure 5-10 Effect of Initial Naphthalene Concentration on Adsorption onto
PC-CO ………….……………………………………………………....… 80
2
Figure 5-11 Plot of PAH Sorbed Capacity against Time Showing Initial
Concentration Effect……………………………………...…….…………. 81
Figure 5-12a Adsorption of Fluorene and Naphthalene over a Short Period…....… 83
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Figure 5-12b Adsorption of Fluorene and Naphthalene over a Long Period……… 84
Figure 5-13 Naphthalene Adsorption Isotherm on Different Adsorbents at 25°C… 88
Figure 5-14 Naphthalene Adsorption Isotherm on Surface Oxidized Activated
Carbons at 25°C...……….…………………………………………………. 91
Figure 5-15 Naphthalene and Fluorene Adsorption Isotherm on PC-CO at 25°C... 93
2
Figure 5-16 Naphthalene Adsorption Isotherm on MPC-CO at Different
2
Temperature……………………………………………………………....... 95

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