Laser alignment, Raman path alignment and Calibration

171 Pages·2016·7.09 MB·English

POLITECNICO DI MILANO
Scuola di Ingegneria Industriale e dell’Informazione
Corso di Laurea Magistrale in Chemical Engineering

DESIGN AND DEVELOPMENT OF AN OPERANDO
RAMAN ANNULAR REACTOR FOR COMBINED
SPECTROSCOPIC AND KINETIC STUDIES

Relatore: Prof. Matteo Maestri

Correlatori: Prof. Alessandro Donazzi
Dr. Ali Maghsoumi

Tesi di Laurea Magistrale di:
Federico Consonni (Matricola: 836240)
Fabio Nanni (Matricola: 836759)

Anno Accademico 2015 – 2016
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Table of Contents
List of Figures ......................................................................................................................................................... 7
List of Tables ......................................................................................................................................................... 11
Abstract .................................................................................................................................................................. 12
Riassunto ................................................................................................................................................................ 13
1. State of the art ............................................................................................................................................... 14
1.1 Introduction ............................................................................................................................................. 14
1.2 Structure-performance relationship ...................................................................................................... 15
1.3 Raman spectroscopy in catalysis ........................................................................................................... 17
1.4 Raman cells for Raman spectroscopy of solids in controlled environment ................................... 20
1.4.1 Ex situ, in situ and operando cells............................................................................................. 20
1.4.2 Evolution of in situ and operando Raman cells ......................................................................... 21
1.5 Objective of this work ............................................................................................................................ 24
1.6 Thesis summary ....................................................................................................................................... 27
2. Raman spectroscopy .................................................................................................................................... 29
2.1 Basic theory .............................................................................................................................................. 29
2.1.1 Selection rules for vibrational spectroscopies.......................................................................... 30
2.1.2 Advantages of Raman spectroscopy ......................................................................................... 32
2.1.3 Limitations of Raman spectroscopy ......................................................................................... 32
2.1.4 Raman spectra .............................................................................................................................. 33
2.2 Raman instrumentation .......................................................................................................................... 36
2.2.1 Pre-sample components ............................................................................................................. 36
2.2.2 Post-sample components............................................................................................................ 37
2.2.3 Jasco Raman ................................................................................................................................. 40
2.3 Case study: CO adsorption on Rh ........................................................................................................ 44
2.3.1 Software description .................................................................................................................... 44
2.3.2 Setup of the instrument: Laser alignment, Raman path alignment and Calibration .......... 45
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2.3.2.1 Laser alignment .................................................................................................................... 45
2.3.2.2 Raman path alignment ........................................................................................................ 46
2.3.2.3 Calibration ............................................................................................................................ 48
2.3.3 Spectrum recording ..................................................................................................................... 50
2.3.4 Experimental Results................................................................................................................... 53
2.4 Conclusions .............................................................................................................................................. 56
3. Design of an operando Raman reactor ..................................................................................................... 57
3.1 Constraints in operando Raman ............................................................................................................... 57
3.1.1 Kinetic Constraints ...................................................................................................................... 58
3.1.2 Optical Constraints ...................................................................................................................... 59
3.1.3 Material constraints ..................................................................................................................... 61
3.1.4 General features of the solution ................................................................................................ 63
3.2 Design procedure .................................................................................................................................... 64
3.3 Basic design .............................................................................................................................................. 66
3.3.1 System geometry .......................................................................................................................... 67
3.4 Integrated Raman-oven design ............................................................................................................. 69
3.4.1 System geometry .......................................................................................................................... 69
3.4.2 Modelling in OpenFOAM .......................................................................................................... 70
3.4.2.1 Results ................................................................................................................................... 70
3.5 External Raman probe design ............................................................................................................... 74
3.5.1 System geometry and constraints .............................................................................................. 74
3.5.2 Thermal insulation modelling and selection ............................................................................ 75
3.5.3 Modelling of Internal Temperature Profiles ............................................................................ 80
3.5.3.1 Results ................................................................................................................................... 83
3.5.4 Modelling of external temperature profiles .............................................................................. 84
3.5.4.1 Results ................................................................................................................................... 87
3.6 Experimental Setup ................................................................................................................................. 89
3.6.1 Plant construction ........................................................................................................................ 89
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3.6.1.1 Raman probe supporting structure ................................................................................... 96
3.6.2 Experimental temperature Profiles ........................................................................................... 98
3.6.3 Comparison with model results ................................................................................................. 99
3.6.4 Experimental temperature profile with drilled oven ............................................................ 100
3.7 Conclusions ............................................................................................................................................ 102
4. Experimental tests ...................................................................................................................................... 104
4.1 Plant description .................................................................................................................................... 104
4.1.1 Feed section ................................................................................................................................ 105
4.1.2 Reactor section ........................................................................................................................... 107
4.1.3 Analysis section .......................................................................................................................... 107
4.2 Instrument calibration .......................................................................................................................... 110
4.2.1 Flow controller calibration ....................................................................................................... 110
4.2.2 GC calibration ............................................................................................................................ 111
4.3 Testing of operando Raman rector ........................................................................................................ 115
4.3.1 Focusing procedure ................................................................................................................... 115
4.3.2 Comparison with ex situ data .................................................................................................... 120
4.4 Results of operando tests ........................................................................................................................ 122
4.4.1 Temperature stability of Raman spectra ................................................................................. 122
4.4.2 In situ measurements of model reactions ................................................................................ 123
4.4.3 First operando test: catalyst conditioning .................................................................................. 127
4.4.3.1 Standard conditioning procedure .................................................................................... 127
4.4.3.2 Phenomenology of catalyst conditioning ....................................................................... 128
4.4.3.3 First conditioning run – results ....................................................................................... 129
4.4.3.4 Second conditioning run – results .................................................................................. 133
4.4.3.5 Discussion of results ......................................................................................................... 137
4.5 Conclusions ............................................................................................................................................ 139
5. Conclusions ................................................................................................................................................. 140
Appendix A - Principles of Raman Spectroscopy ......................................................................................... 143
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A.1 History ................................................................................................................................................. 143
A.2 Primary principle ................................................................................................................................ 144
A.3 Molecular vibrations .......................................................................................................................... 145
A.4 Vibrations of polyatomic molecules ................................................................................................ 147
A.4 Factors determining vibrational frequencies .................................................................................. 147
A.5 Origin of Raman spectra ................................................................................................................... 148
A.6 Resonance Raman and fluorescence ............................................................................................... 150
Appendix B - CFD ............................................................................................................................................. 152
B.1 OpenFOAM ....................................................................................................................................... 152
B.1.1 Mesh generation ......................................................................................................................... 153
B.1.2 Numerical methods ................................................................................................................... 154
B.1.2.1 Solvers ................................................................................................................................. 154
B.1.2.2 Radiation models ............................................................................................................... 155
Appendix C - Catalyst preparation ................................................................................................................... 156
C.1 Support preparation ........................................................................................................................... 156
C.2 Preparation of catalytic powders ...................................................................................................... 157
C.3 Preparation of the catalytic slurry .................................................................................................... 159
C.4 Preparation of supported catalyst .................................................................................................... 160
Acknowledgments .............................................................................................................................................. 164
References ............................................................................................................................................................ 165

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List of Figures
Figure 1.1 - Development of ammonia production and world population [3]. ........................................... 14
Figure 1.2 - Chronology of occurrences of Raman spectroscopy containing publications in
heterogeneous catalysis literature [12]. .............................................................................................................. 17
Figure 1.3 - Designs of reaction in-situ Raman cells. (A) Schrader [31] , (B) Lunsford [32], (C) Volta [33],
(D) Stair [34]. (Source: M.A. Bañares [11]). ...................................................................................................... 22
Figure 1.4 - Designs of Raman cells that deliver catalyst performance corresponding to those of ideal
reactors. (A) Mestl et al. [35]; (B) Bañares et al. [36]. ...................................................................................... 23
Figure 1.5 - Schematic representation of a reactor set-up with combined UV-Vis/Raman spectroscopy
for analysis through a quartz tube reactor [37]. ................................................................................................ 24
Figure 1.6 - Sketch of the annular reactor used in experimental tests. ......................................................... 26
Figure 2.1 - Energy level diagram showing the states involved in Raman signals [50]............................... 29
Figure 2.2 - Polarizability change in a CO molecule by symmetric stretching. .......................................... 30
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Figure 2.3 - Raman spectrum of CCl with a 488 nm laser excitation. ......................................................... 34
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Figure 2.4 - Schematic of a typical continuous wave gas laser. ...................................................................... 36
Figure 2.5 - Beam Splitter and Dichroic Mirror. .............................................................................................. 37
Figure 2.6 - Effect of edge and notch filters on incoming wavelength. ....................................................... 38
Figure 2.7 - Example of a white light grating. .................................................................................................. 39
Figure 2.8 - Schematic of a photon counting detector. ................................................................................... 40
Figure 2.9 - Jasco NRS-4100 Raman spectrometer, with laser source and external probe on the bottom
right. ........................................................................................................................................................................ 41
Figure 2.10 - Block diagram of Jasco Raman‟s components. ......................................................................... 41
Figure 2.11 - Automatic stage and objective lens revolver. ............................................................................ 42
Figure 2.12 -Micro Spectra Measurement screen. ................................................................................................... 44
Figure 2.13 - Optical Alignment window. ............................................................................................................. 45
Figure 2.14 - Wrong and good laser alignments. ............................................................................................. 46
Figure 2.15 - Slit focusing system. ...................................................................................................................... 47
Figure 2.16 - Raman path alignment window. .................................................................................................. 47
Figure 2.17 - Example of Raman path alignment in X-Y directions. ........................................................... 48
Figure 2.18 - Silicon spectrum before calibration. ........................................................................................... 49
Figure 2.19 - Silicon spectrum after calibration. .............................................................................................. 49
Figure 2.20 - Microscope View window. ................................................................................................................ 50
Figure 2.21 - Measurement Parameter window. ..................................................................................................... 51
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Figure 2.22 - Three recording options: single point, line and mapping. .............................................................. 53
Figure 2.23 - Micro Imaging Analysis main screen. .............................................................................................. 53
Figure 2.24 - CO over Rh Raman spectrum. .................................................................................................... 54
Figure 2.25 - CO-Rh Raman peaks. ................................................................................................................... 55
Figure 3.1 - Sketch of the annular reactor used for operando experiments. ................................................... 59
Figure 3.2 - Effect of probe tilting on Raman signal collection. ................................................................... 60
Figure 3.3 - Relation between laser beam width and working distance. ....................................................... 61
Figure 3.4 - Schematic explanation of refraction through a glass medium. ................................................. 61
Figure 3.5 - Transmission spectrum of uncoated sapphire glass windows [62]. ......................................... 62
Figure 3.6 - Preliminary scheme of operando Raman annular reactor. ........................................................ 63
Figure 3.7 - Flow diagram illustrating the design procedure. ......................................................................... 64
Figure 3.8 - Temperature profile inside the oven. ........................................................................................... 66
Figure 3.9 - System geometry of solution with Raman probe positioned in the oven: probe (orange),
oven (green), quartz disc (blue), quartz reactor (black) and hot air (purple). .............................................. 67
Figure 3.10 - Detail of the hole for the Raman probe, respectively with and without the quartz glass... 68
Figure 3.11 - system geometry of second solution: Raman probe is completely outside the oven. ......... 69
Figure 3.12 - Alumina tube mesh. ...................................................................................................................... 70
Figure 3.13 - Simulation result for the case at 600 °C. .................................................................................... 71
Figure 3.14 - Different mesh discretization. ..................................................................................................... 71
Figure 3.15 - Temperature profiles of different meshes. ................................................................................ 72
Figure 3.16 - Temperature profiles for cases studied with mesh B. .............................................................. 72
Figure 3.17 - Sketch of the system with all components from a lateral and frontal cut. ............................ 75
Figure 3.18 - Radial dimensions of alumina tube, quartz reactor and insulator. ......................................... 77
Figure 3.19 - Temperature profiles at different insulator thermal conductivities. ...................................... 78
Figure 3.20 - Thermal conductivities of different materials and target value. ............................................. 79
Figure 3.21 - Different temperature profiles depending on q values. ......................................................... 80
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Figure 3.22 - Front and lateral section of the modelled system. .................................................................... 81
Figure 3.23 - Top vision of stainless steel tube with different boundary conditions.................................. 81
Figure 3.24 - Comparison of model results for the four different cases. ..................................................... 83
Figure 3.25 - System geometry of external system: probe (orange), insulator (green), air (blue). ............. 85
Figure 3.26 - Temperature profile in the whole system. ................................................................................. 87
Figure 3.27 - Temperature profile in the probe. .............................................................................................. 87
Figure 3.28 - Temperature plot over the central line of air and probe regions. .......................................... 88
Figure 3.29 - Steel supports of the tube. ........................................................................................................... 89
Figure 3.30 - Thermocouple inserted in the welded tube. .............................................................................. 90
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Figure 3.31 - Heating tape mounted on steel tube (A) and sheet of steel to level out the heat (B). ........ 90
Figure 3.32 - Window in the steel tube for the Raman probe. ...................................................................... 91
Figure 3.33 - Calcium Silicate cap....................................................................................................................... 91
Figure 3.34 – MICROTHERM® MPS microporous insulator. .................................................................... 92
Figure 3.35 - Hole in the insulator for the Raman probe. .............................................................................. 92
Figure 3.36 - Internal part of the insulator: glass fiber is used to maintain the reactor with the same axis
of the insulator. ..................................................................................................................................................... 93
Figure 3.37 - Insulator, hosting the steel tube, aligned with the oven. ......................................................... 93
Figure 3.38 - Insulation of the space between oven and microporous insulator. ....................................... 94
Figure 3.39 - Inlet (A) and outlet (B) oven insulations, using calcium silicate and quartz fibre. .............. 94
Figure 3.40 – Final layout of the whole reactor. .............................................................................................. 95
Figure 3.41 - Nitrogen cooling system. ............................................................................................................. 95
Figure 3.42 - Raman probe support structure. ................................................................................................. 96
Figure 3.43 - Comparison between different temperature profiles. .............................................................. 98
Figure 3.44 - Comparison between model and experimental data for the four cases: (A) Tsp oven =
700°C, (B) Tsp oven = 750°C, (C) Tsp oven = 800°C and (D) Tsp oven = 850°C .................................. 99
Figure 3.45 - Temperature profile with drilled oven. .................................................................................... 100
Figure 4.1 - Laboratory rig where all experimental tests were carried out. ................................................ 104
Figure 4.2 - P&ID of the plant. ........................................................................................................................ 105
Figure 4.3 – Generic feed line. .......................................................................................................................... 106
Figure 4.4 - Six-way valve positions: (A) carrier to the column, (B) sample to the column. ................... 108
Figure 4.5 – Thermal conductivity detector. ................................................................................................... 109
Figure 4.6 - CO flow controller calibration. ................................................................................................... 111
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Figure 4.7 - – Example of a GC analysis. ........................................................................................................ 111
Figure 4.8 - GC calibration of Carbon Monoxide. ........................................................................................ 113
Figure 4.9 - (A, B) Proper and improper vertical alignment of lens and steel tube. (C, D) Proper and
improper angular alignment of lens and steel tube. ....................................................................................... 115
Figure 4.10 - Flow diagram illustrating the adopted focusing procedure. .................................................. 116
Figure 4.11 - Raman spectrum of sapphire disk............................................................................................. 117
Figure 4.12 - Raman spectrum of reactor quartz. .......................................................................................... 118
Figure 4.13 - Focusing point (A) and Raman spectrum (B) of the Rh/α-Al2O3 catalyst in room
temperature conditions, under N flow. .......................................................................................................... 119
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Figure 4.14- Comparison of alumina tube Raman spectra record in ex situ Raman spectrometer (green)
and in operando reactor (blue). ............................................................................................................................ 121
Figure 4.15 - Raman spectra of the catalyst sample (under N flow) at various temperatures................ 123
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Figure 4.16 - Time resolved Raman spectra during methane pyrolysis at 500°C. ..................................... 124
Figure 4.17 - Time resolved Raman spectra during oxidation in air at 500°C. .......................................... 125
Figure 4.18 - Time resolved Raman spectra during methane pyrolysis at 500°C. 2nd experiment. ......... 126
Figure 4.19 - Conditioning process scheme. ................................................................................................... 128
Figure 4.20 - Raman spectrum of non-conditioned catalyst at 25°C. Spectrum recorded under CPO
conditions, after the catalyst was conserved in ambient air conditions. ..................................................... 129
Figure 4.21 - Raman spectra of catalyst during first conditioning run at 300°C. 15‟ passed from one
measurement to the other.................................................................................................................................. 130
Figure 4.22 - Raman spectra of catalyst during the first conditioning run. Spectra at 25, 400, 450 and
500°C are reported from bottom to top. ........................................................................................................ 131
Figure 4.23 - - Raman spectra of catalyst during CPO conditioning at 500, 550, 600 and 700°C. ....... 132
Figure 4.24 - Comparison between Raman spectra at 700°C (first run) and 25°C (second run). .......... 133
Figure 4.25 - Comparison between Raman spectra recorded at room temperature. ................................ 134
Figure 4.26 - Comparison between Raman spectra recorded at 300°C. ..................................................... 135
Figure 4.27 - Raman spectra of catalyst during CPO conditioning at 400, 450, 500, 550, 600 and 700°C.
............................................................................................................................................................................... 136
Figure 4.28 - CH conversion in consecutives CPO conditioning runs. .................................................... 137
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Figure A.1 - Energy level diagram showing the states involved in Raman signals [50]. ........................... 145
Figure A.2 - Potential energy diagram for a harmonic oscillator. ................................................................ 146
Figure A.3 - Harmonic and Morse potential energy curves. ........................................................................ 146
Figure A.4 - Normal vibration modes in H O molecule. ............................................................................. 147
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Figure A.5 - Relationships among wavenumber, reduced mass and force constant. ............................... 149
Figure A.6 - Mechanisms of various light scattering processes. (a) Rayleigh scattering, (b) Raman
scattering, (c) Pre-resonance Raman, (d) Resonance Raman, (e) Fluorescence. ....................................... 150
Figure B.1 - Example of geometry used to generate an OpenFOAM mesh. The geometry was generated
with OpenSCAD. ............................................................................................................................................... 153
Figure B.2 - Example of mesh created with snappyHexMesh with all steps from blockMesh to the final
mesh. ..................................................................................................................................................................... 154
Figure B.3 - Example of calculation of view factor between surface A1 and A2. .................................... 155
Figure C.1 - Temperature ramp for the alumina calcination. ....................................................................... 157
Figure C.2 - Sketch of the ball mill. ................................................................................................................. 159
Figure C.3 – Ball mill. ......................................................................................................................................... 160
Figure C.4 - Alumina tube covered with Teflon. ........................................................................................... 160
Figure C.5 - Dip coating equipment. ............................................................................................................... 161
Figure C.6 – Dip coating equipment. .............................................................................................................. 161
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