Heterogeneously Catalyzed Oxidation Reactions Using ... - CHEC

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egeneration by reduction surface cleaning high toluene selectivity limited by oxygen availabilty CHAPTER 5 Figure 5‐12: Schematic catalytic processes at the catalyst interface depending on the pressure; (a) different availability of oxygen (red) and benzyl alcohol (green); left: situation on the catalyst surface upon exposure to the benzyl alcohol‐rich phase, right: exposure to the CO2‐rich phase; (b) distribution of benzyl alcohol‐rich phase on catalyst particles depending on the solvent power of CO2. Note that the extensive pore system of the catalyst has been omitted for clarity reasons. Due to the high viscosity and polarity and the small amounts as compared to the CO2‐rich phase, the phase rich in organic substrate was apparently accumulating in the reactor (and the overall system) resulting in a higher benzyl alcohol/benzaldehyde concentration as compared to the feed and consequently a longer residence time. Applying conditions where the feed composition is in a single phase causes the subsequent dissolution of excess benzyl alcohol (or benzaldehyde etc.) in the reactor. The complex transport of the phase rich in organic substrate is one reason why no direct comparison of batch and continuous experiments is possible and needs further investigation. Still, both under batch and continuous flow, biphasic conditions gave the highest reaction rate. The accumulation is noticeable by an intermediate change in the exit flow of the substrate during the phase transition. The measurement is tedious though it does not require further equipment. This method could potentially be exploited to (automatically) determine phase transitions for this and similar systems. (a) (b) SURFACE EXPOSED TO... BzOH-rich phase CO2-rich phase CATALYST PARTICLES IN THE BIPHASIC REGION BzOH-rich phase Pd-containing catalyst shell low BzOH solubility high BzOH solubility Pressure 148 deactivation by oxidation surface blocking low toluene selectivity high O 2 availability → possibly higher reaction rate
5.5 Conclusions 5.5 Conclusions The phase behavior of ternary systems consisting of benzyl alcohol – O2 – CO2 and benzaldehyde – H2O – CO2 was modeled using the Cubic plus Association Equation of State. The predicted dew points were validated against experimental data measured at conditions relevant to the selective catalytic oxidation of benzyl alcohol in pressurized CO2 as a solvent. A good agreement between model and experimental dew point measurements was found. The pressure of dew points for substrate mixtures are in general higher than for the corresponding product mixtures implying that the optimal pressure is defined by the former mixtures. Since the dew point plays a crucial role in catalytic studies with pressurized CO2, the model was applied in the catalytic oxidation of benzyl alcohol. The reaction rate was found to depend on the number of phases present in the reactor, the model thus supplying valuable information towards the optimal reaction conditions. The model further indicated that catalytic data especially at higher pressures than in previous studies are required. Biphasic conditions at pressures close to the dew point resulted in the highest reaction rate with toluene formed as a side product in noticeable amounts. When operated in a single phase, products from overoxidation became the dominating side products and long equilibration times where observed presumably due to surface blocking by benzoic acid. Under biphasic conditions, the organic substrate accumulated in the reactor (and also in the system in general) causing an enhanced substrate concentration and a longer residence time which needs to be investigated more thoroughly in the future. 149
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TECHNICAL UNIVERSITY OF DENMARK (DT
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Preface The present dissertation su
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the carboxylic acid, ceria inhibite
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Resume Denne afhandling giver indle
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hvorimod mængden af katalysator ku
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2.3.8 Oxidation of sulfides .......
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5.3.5 Macroscopic mass transport in
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Chapter 1 Introduction With its gre
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1. Introduction Scheme 1‐1: High
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1. Introduction Figure 1‐2: Phase
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1. Introduction [28] S. Bawaked, N.
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2.1 Introduction 2.1 Introduction E
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2.2.1 Synthesis of gold catalysts 2
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2.2 Catalyst synthesis for oxidatio
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2.2 Catalyst synthesis for oxidatio
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2.3 Selective liquid‐phase oxidat
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Table 2-1: Overview over alcohol ox
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Ph O O Ph (4) (5) 2.3 Selective liq
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Table 2-4: Side-chain oxidation of
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2.3.4 Oxidation of cyclohexane 2.3
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Table 2-5: Oxidatin of cyclohexane.
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Table 2-6: Ring hydroxylation of ar
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Table 2-7: Aerobic oxidation of ami
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Table 2-8: Oxidation of hydroquinon
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Table 2-9: Oxidation of silanes wit
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Table 2-10: Oxidation reactions cat
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2.4 Strengths and opportunities of
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2.6 References 2.6 References [1] M
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2.6 References [56] H. Tumma, N. Na
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2.6 References [113] C. Keresszegi,
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2.6 References [169] Q. Zhu, Y. Lia
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2.6 References [223] M. Fetizon, M.
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Chapter 3 Selective Liquid-Phase Ox
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3.2 Experimental 3.2.1 Catalyst pre
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3.3 Results Scattering amplitudes a
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Absorption (a.u.) 1.2 1.0 0.8 0.6 0
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Conversion (%) 100 90 80 70 60 50 4
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3.3 Results Figure 3‐5: In situ X
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3.3 Results Table 3‐2: Conversion
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3.3 Results In order to gain insigh
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3.3 Results the cost of selectivity
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3.4 Discussion synergetic interacti
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Page 113 and 114: 3.6 References [29] T. Mitsudome, Y
Page 115 and 116: Chapter 4 Selective Side-Chain Oxid
Page 117 and 118: 4.2 Experimental single‐step flam
Page 119 and 120: 4.2 Experimental alcohol (Aldrich,
Page 121 and 122: 4.3 Results Scheme 4‐1: Oxidation
Page 123 and 124: 4.3 Results Figure 4‐2: Formation
Page 125 and 126: 4.3 Results oxidation by either 2,6
Page 127 and 128: Absorption (a.u.) Absorption (a.u.)
Page 129 and 130: 4.3 Results atomic mixing of Ag and
Page 131 and 132: 4.3 Results Figure 4‐7: Influence
Page 133 and 134: 4.4 Discussion and mechanistic cons
Page 135 and 136: 4.5 Conclusions heterogeneous radic
Page 137 and 138: 4.6 References [29] S.I. Zabinsky,
Page 139 and 140: Chapter 5 Experimental Determinatio
Page 141 and 142: 5.2 Experimental The most important
Page 143 and 144: 5.2 Experimental Eurotherm 2216e te
Page 145 and 146: Figure 5-1: Schematic view of the e
Page 147 and 148: (Eq. 5‐5) AB i j ε AB i j β 5.2
Page 149 and 150: (a) (b) (c) (d) (e) (f) (g) (h) (i)
Page 151 and 152: 5.3 Results two association sites o
Page 153 and 154: Pressure (bar) 150 145 140 135 5.3
Page 155 and 156: 5.3 Results Figure 5‐7: Oxidation
Page 157 and 158: Weight (g) 5.3 Results Figure 5‐8
Page 159 and 160: 5.4 Discussion catalytic reactions
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Page 165 and 166: 5.6 References [29] I. Tsivintzelis
Page 167 and 168: 6.1 Introduction 6.1 Introduction A
Page 169 and 170: 6.2 Experimental [38]. In a typical
Page 171 and 172: 6.3 Results out in 1 mm quartz tube
Page 173 and 174: 6.3 Results Figure 6‐2: Structure
Page 175 and 176: 6.3 Results Figure 6‐4: Epoxidati
Page 177 and 178: 6.3 Results Figure 6‐6: Compariso
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Page 181 and 182: 6.3 Results investigated the epoxid
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Page 185 and 186: 6.3 Results Figure 6‐11: EXAFS an
Page 187 and 188: 6.4 Discussion would need to be for
Page 189 and 190: 6.5 Conclusions Formation of the ep
Page 191 and 192: 6.6 References [28] J. Perles, N. S
Page 193 and 194: Chapter 7 Concluding Remarks 7.1 Co
Page 195 and 196: 7.2 Final remarks and outlook speci
Page 197 and 198: Acknowledgements Acknowledgements T
Page 199: Curriculum Vitae Matthias Josef Bei
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