Heterogeneous Oxidation of Alcohols

235 Pages·2009·1.83 MB·English

by  Hamza Mounzer

Heterogeneous Oxidation of
Alcohols

By

Hamza Mounzer

A thesis submitted to
The University of Birmingham
for the degree of
DOCTOR OF PHILOSOPHY

Department of Chemical Engineering
School of Engineering
The University of Birmingham
March 2009
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To My Mother,
In the Heavens…

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Acknowledgements

I would like to express my deepest and sincerest gratitude to the following people
and organisation for their support and assistance:

Dr Joe Wood for his patience, guidance and efforts in helping me throughout my
research. Particular thanks must be extended to Prof. Mike Winterbottom and Prof E.
Hugh Stitt for their support and advice.

My colleagues and friends in the Department of Chemical Engineering especially Dr
Fabio Chiti, Mr Andrea Gabriele, Dr Andreas Tsoligkas, Dr James Bennett, Dr. Aman
Dhir, Mr Gareth Thompson and Mr Nima Niknaf.

I also wish to express a debt of gratitude to Johnson Matthey for providing catalyst and
all the helpful discussions I had with their personnel.

Finally I wish to personally thank my family for their indispensable support through the
good times and the difficult ones, the support staff at the Department of Chemical
Engineering and TOOL for the inspiration.

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ABSTRACT

The selective oxidation of alcohols is one of the most challenging reactions in
green chemistry. While the current chemical industry uses organic and inorganic
oxidants to produce carbonyl compounds, it is highly desirable to use a heterogeneous
catalyst for the efficient oxidation of alcohols. The present research is focused on
increasing the activity and selectivity towards the corresponding carbonyl of the
heterogeneous oxidation for alcohols.
The low activity of 5 wt.%Pt-1 wt. %Bi/Carbon for the oxidation of 2-octanol was
investigated in a 500ml stirred tank reactor. The fast reaction rate drops dramatically
from 0.23 M/hr to 0.006 M/hr after 15 minutes reaction time when heptane was used as
solvent. Different possible causes such as overoxidation, leaching and poisoning were
examined. It was found that the loss of high conversion rate was due to product
adsorption and hence, different solvents were investigated. A mixture of 16-18% v/v
dioxane in heptane was able to effectively regenerate active sites and allow a constant
reaction rate of 0.07M/hr. The effects of temperature and pressure were also studied.
Gas-liquid, liquid-solid and internal mass transfer effects were determined experimentally
and semi-empirically. Six different Langmuir-Hinshelwood rate models were examined
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where a modified model based on Schuurman et al. (1992) was found to adequately
describe the experimental data.
The novel 2.5%Au-2.5%Pd/titania catalyst was investigated for the oxidation of
benzyl alcohol. Different parameters such as catalyst oxidation state, pressure and stirrer
design were studied to increase the activity and selectivity of the catalyst. The selectivity
was shown to be highly dependent on the oxygen concentration. Therefore, the pressure,
temperature, catalyst treatment were optimised and the reactor configuration was re-
designed to enhance oxygen transport to the catalyst. While the conversion rate was
unaffected by the oxygen concentration, the catalyst pre-treatment significantly increased
the reaction rate. Eventually, the use of a Rushton Turbine at 20 rps with a shower disc
sparger and a treated catalyst allowed the selectivity to reach 93%. The reaction could be
described with a Power Law model satisfactorily. Transition Metal Oxide catalysts such
as AgO/SiO ,Fe O /SiO , CuO/SiO andCuO/Al O were investigated as an
2 2 3 2 2 2 3
alternative to the expensive noble metal based catalyst. However, it was shown that such
catalysts are ineffective for the oxidation of different alcohols by studying the effects of
different engineering parameters. The maximum conversion reached was 15% with
calcined copper oxide catalyst for 1-octanol oxidation.

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Contents Page

1. Introduction 1
1.1 The Emergence of Catalysis in the Chemical Industry 1
1.2 Green Chemistry and Alcohol Oxidation 3
1.3 Aims of this Thesis 4
1.4 Scope of the Thesis 7

2. Literature Review 8
2.1 Oxidation Mechanism on Noble Metals 8
2.2 Oxidation Catalysts 11
2.2.1 Noble Metals 12
2.2.1.1) Au and Au-Pd catalyst 12
2.2.1.2) Palladium and platinum 17
2.2.2 The role of promoters 18
2.2.3 Oxygen adsorption 21
2.2.4 Catalyst Preparation 23
2.2.5 Metal Particle Size, Loading and Distribution 25
2.2.6 Catalyst supports 26
2.2.7 Catalyst Deactivation 31
2.2.7.1) Overoxidation 31
2.2.7.2) Poisoning
32
2.2.7.3) Metal leaching/ Particle agglomeration 34
2.2.7.4) Fouling/coking 34
2.2.8 Reaction Kinetics with Deactivated Catalyst 36
2.3 Solvent Effects 37
2.4 Temperature Effects on the Oxidation 41
2.5 Stirred Tank Reactors 42
2.5.1 Reactor Design 42
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2.5.1.1) Reactor Geometry 43
2.5.1.2) Impeller types 46
2.5.1.3) Baffles 50
2.5.1.4) Gas Spargers 50
2.5.2 Advantages and Disadvantages of the STR 51
2.6 External Mass Transfer 52
2.6.1 Gas-Liquid Mass Transfer 56
2.6.2 Liquid-Solid Mass Transfer 57
2.7 Internal Mass Transfer 60
2.8 Reaction Modelling and Kinetics 63

Experimental and Analytical methods
3. 67
3.1 Chemicals, Gases and Catalysts 67
3.2 Experimental Setup 68
3.2.1 Baskerville Reactor 68
3.2.2 Experimental Procedure 71
3.2.3 Laboratory Scale Setup
73
3.2.4 Laboratory Scale Procedure 73
3.3 Quantitative and Qualitative Analytical Methods 73
3.4 Catalyst Characterisation 75
3.4.1 Chemisorption 75
3.4.2 X-Ray Diffraction (XRD) 80
3.4.3 Scanning Electron Microscopy with Energy Dispersive X-
80
ray (SEM-EDX)

4. Heterogeneous Oxidation of 2-Octanol on 5%Pt-1%Bi/Carbon 81
4.1 Oxidation of 2-Octanol on 5%Pt-1%Bi/carbon in heptane 82
4.2 Deactivation causes 85
4.2.1 Noble metal overoxidation 85
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4.2.2 Noble metal leaching/agglomeration 86
4.2.3 Catalyst poisoning 87
4.3 Measurement of quantity of adsorbed ketone 89
4.3.1 Laboratory scale experimental setup 89
4.3.2 Octanone adsorption quantification
90
4.4 Solvents effects 94
4.4.1 DMSO 94
4.4.2 P-xylene 95
4.4.3 Dioxane 95
4.4.4 Dioxane/heptane 96
4.5 Internal Mass Transfer 100
4.6 Temperature effects and Arrhenius plot 101
4.7 Effect of pressure 103
4.8 Measurement of Mass Transfer Coefficients 106
4.8.1 Solid-Liquid Mass Transfer 108
4.8.2 Determination of Mass Transfer Coefficient 109
4.9 Langmuir-Hinshelwood Kinetic Model 113
4.10 Catalyst pre-treatment and recycling 121
4.11 Catalyst characterisation using CO Pulse Chemisorption 123

Selective Oxidation of Benzyl Alcohol on 2.5%Au-
5. 125
2.5%Pd/Titania
5.1 Initial oxidation of BnOH with Au-Pd/Titania 126
5.2 Selectivity and Mechanism Investigation 128
5.2.1 Pressure Effects 130
5.2.2 Stirring Effects 132
5.2.3 Reactor Optimisation 134
5.2.4 Mechanism Investigation 136
5.2.5 Catalyst pre-treatment
141
5.3 Temperature effects 143
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5.4 Measurement of Mass Transfer Coefficients 146
5.5 Kinetic Evaluation 148
5.6 Catalyst Characterisation 151

6. Selective Oxidation of Alcohols on Metal Oxides 167
6.1 Introduction and Mechanism 168
6.2 Alcohol Oxidation and TPR Characterisation 171
6.2.1 AgO/SiO 172
2
6.2.2 Fe O /SiO 177
2 3 2
6.2.3 CuO/SiO AND CuO/Al O 179
2 2 3

7. Conclusion and Recommendations 186
7.1 Conclusion 186
7.1.1 2-Octanol Oxidation with 5%Pt-1%Bi/carbon 186
7.1.2 Benzyl Alcohol Oxidation with 2.5%Au-2.5%Pd 188
7.1.3 Alcohol Oxidation with Transition Metal Oxides 190
7.2 Recommendations for Future Works 191

Appendix A: External Mass Transfer Sample Calculation for
193
Chapter IV)
Appendix B:
199
Internal Mass Transfer Sample Calculation for Chapter IV)
Appendix C:
201
Matlab Program Sample for Chapter IV)
Appendix D:
206
Supplementary Information used for calculations
Appendix E:
212
Transition Metal Oxide
References 214

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