Table of Contents
Cover
Related Titles
Title Page
Copyright
List of Contributors
Preface
Chapter 1: General Introduction to Microwave Chemistry
1.1 Electromagnetic Waves and Dielectric Materials
1.2 Microwave Heating
1.3 The Various Types of Microwave Heating Phenomena
1.4 Fields of Applications with Microwave Heating
1.5 Microwaves in Solid Material Processing
1.6 Microwaves in Organic Syntheses
1.7 Microwave Chemical Equipment
1.8 Chemical Reactions Using the Characteristics of Microwave Heating
1.9 Microwave Frequency Effect in Chemical Syntheses
1.10 Summary
References
Part I: Fundamentals
Chapter 2: Loss Mechanisms and Microwave-Specific Effects in Heterogeneous Catalysis
2.1 Introduction
2.2 Heterogeneous Catalyst Systems
2.3 Physics of Microwave Absorption
2.4 Microwave Loss Processes in Solids
2.5 Loss Processes and Microwave-Specific Catalysis: Lessons from Gas–Carbon Reactions
2.6 Final Comments on Microwave-Specific Effects in Heterogeneous Catalysis
Acknowledgments
References
Chapter 3: Transport Phenomena and Thermal Property under Microwave Irradiation
3.1 Introduction
3.2 Bubble Formation
3.3 Convection
3.4 Surface Tension
3.5 Discussion of Nonthermal Effect for Nanobubble Formation
References
Chapter 4: Managing Microwave-Induced Hot Spots in Heterogeneous Catalytic Systems
4.1 What Are Hot Spots?
4.2 Microwaves in Heterogeneous Catalysis
4.3 Microwave-Induced Formation of Hot Spots in Heterogeneous Catalysis
References
Part II: Applications – Preparation of Heterogeneous Catalysts
Chapter 5: Preparation of Heterogeneous Catalysts by a Microwave Selective Heating Method
5.1 Introduction
5.2 Synthesis of Metal Catalysts on Carbonaceous Material Supports
5.3 Photocatalysts
5.4 Microwave-Assisted Syntheses of Catalytic Materials for Fuel Cell Applications
5.5 Other Catalysts Prepared by Microwave-Related Procedures
5.6 Concluding Remarks
References
Part III: Applications – Microwave Flow Systems and Microwave Methods Coupled to Other Techniques
Chapter 6: Microwaves in Cu-Catalyzed Organic Synthesis in Batch and Flow Mode
6.1 Introduction
6.2 Microwave-Assisted Copper Catalysis for Organic Syntheses in Batch Processes
6.3 Microwave-Assisted Copper Catalysis for Organic Syntheses in Flow Processes
6.4 Concluding Remarks
References
Chapter 7: Pilot Plant for Continuous Flow Microwave-Assisted Chemical Reactions
7.1 Introduction
7.2 Continuous Flow Microwave-Assisted Chemical Reactor
7.3 Pilot Plant
7.4 Conclusions
Acknowledgment
References
Chapter 8: Efficient Catalysis by Combining Microwaves with Other Enabling Technologies
8.1 Introduction
8.2 Catalysis with Hyphenated and Tandem Techniques
8.3 Microwave and Mechanochemical Activation
8.4 Microwave and UV Irradiation
8.5 Microwave and Ultrasound
8.6 Conclusions
References
Part IV: Applications – Organic Reactions
Chapter 9: Applications of Microwave Chemistry in Various Catalyzed Organic Reactions
9.1 Introduction
9.2 Microwave-Assisted Reactions in Organic Solvents
9.3 Microwave-Assisted Reactions in Water-Coupling Reactions
9.4 Conclusions and Prospects
Acknowledgments
References
Chapter 10: Microwave-Assisted Solid Acid Catalysis
10.1 Introduction
10.2 Microwave-Assisted Clay Catalysis
10.3 Zeolites in Microwave Catalysis
10.4 Microwave Application of Other Solid Acid Catalysts
10.5 Conclusions and Outlook
References
Chapter 11: Microwave-Assisted Enzymatic Reactions
11.1 Introduction
11.2 Synthewave (ProLabo)
11.3 Discover Series (CEM)
11.4 Mechanism of the Microwave-Assisted Enzymatic Reaction
References
Part V: Applications – Hydrogenation and Fuel Formation
Chapter 12: Effects of Microwave Activation in Hydrogenation–Dehydrogenation Reactions
12.1 Introduction
12.2 Specific Features of Catalytic Reactions Involving Hydrogen
12.3 Hydrogenation Processes under MW Conditions
12.4 Dehydrogenation
12.5 Hydrogen Storage
12.6 Hydrogenation of Coal
Acknowledgment
References
Chapter 13: Hydrogen Evolution from Organic Hydrides through Microwave Selective Heating in Heterogeneous Catalytic Systems
13.1 Situation of Hydrogen Energy and Feature of Stage Methods
13.2 Selection of Organic Hydrides as the Hydrogen Carriers
13.3 Dehydrogenation of Hydrocarbons with Microwaves in Heterogeneous Catalytic Media
13.4 Dehydrogenation of Methane with Microwaves in a Heterogeneous Catalytic System
13.5 Problems and Improvements of Microwave-Assisted Heterogeneous Catalysis
Acknowledgments
References
Part VI: Applications – Oil Refining
Chapter 14: Microwave-Stimulated Oil and Gas Processing
14.1 Introduction
14.2 Early Publications
14.3 Use of Microwave Activation in Catalytic Processes of Gas and Oil Conversions
14.4 Prospects for the Use of Microwave Radiation in Oil and Gas Processing
Acknowledgment
References
Part VII: Applications – Biomass and Wastes
Chapter 15: Algal Biomass Conversion under Microwave Irradiation
15.1 Introduction
15.2 Microwave Effect on Hydrothermal Conversion – Analysis Using Biomass Model Compounds
15.3 Hydrolysis of Biomass Using Ionic Conduction of Catalysts
15.4 Dielectric Property of Algal Hydrocolloids in Water
15.5 Summary and Conclusions
Acknowledgments
References
Chapter 16: Microwave-Assisted Lignocellulosic Biomass Conversion
16.1 Introduction
16.2 Lignocellulosic Biomass Conversion
16.3 Multi-mode Continuous Flow Microwave Reactor
16.4 Direct-Irradiation Continuous Flow Microwave Reactor
16.5 Pilot-Plant-Scale Continuous Flow Microwave Reactor
16.6 Summary and Conclusions
References
Chapter 17: Biomass and Waste Valorization under Microwave Activation
17.1 Introduction
17.2 Vegetable Oil and Glycerol Conversion
17.3 Conversion of Carbohydrates
17.4 Cellulose Conversion
17.5 Lignin Processing
17.6 Waste and Renewable Raw Material Processing
17.7 Carbon Gasification
17.8 Prospects for the Use of Microwave Irradiation in the Conversion of Biomass and Renewables
Acknowledgment
References
Part VIII: Applications – Environmental Catalysis
Chapter 18: Oxidative and Reductive Catalysts for Environmental Purification Using Microwaves
18.1 Introduction
18.2 Microwave Heating of Catalyst Oxides Used for Environmental Purification
18.3 Microwave-Assisted Catalytic Oxidation of VOCs, Odorants, and Soot
18.4 Microwave-Assisted Reduction of NO
x
and SO
2
18.5 Conclusions
References
Chapter 19: Microwave-/Photo-Driven Photocatalytic Treatment of Wastewaters
19.1 Situation of Wastewater Treatment by Photocatalytic Classical Methods
19.2 Experimental Setup of an Integrated Microwave/Photoreactor System
19.3 Microwave-/Photo-Driven Photocatalytic Wastewater Treatment
19.4 Microwave Discharge Electrodeless Lamps (MDELs)
19.5 Summary Remarks
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: General Introduction to Microwave Chemistry
Figure 1.1 Resonance of dielectric to electromagnetic waves and positioning of the analytical equipment.
Figure 1.2 Image of dipole rotation for polar molecule in an electric field (
E
field).
Figure 1.3 Fields of applications with microwave heating.
Figure 1.4 (a) Details of the experimental setup and positioning of the samples in the single-mode microwave resonator; (i) maximal position of the electric field (
E
field) density and (ii) maximal position of the magnetic field (
H
field) density. (b) Photograph of the single-mode microwave resonator and the 2.45 GHz semiconductor microwave generator.
Figure 1.5 Actual photograph displaying the different sizes (and sectional areas) of the waveguides used for 915 MHz microwaves (left), 2.45 GHz microwaves (center), and 5.8 GHz microwaves (right).
Figure 1.6 Frequency spectral distribution of the 2.45 GHz microwave radiation emitted from the (a) magnetron generator and (b) the semiconductor generator.
Figure 1.7 Photograph of a GaN semiconductor generator (right) and a magnetron generator (left).
Figure 1.8 Photograph of the inner chamber of a microwave apparatus with microwaves emitted from the two semiconductor generators (GaN; maximum power at 250 W).
Figure 1.9 Transmission electron microscopy (TEM) image of SnO
2
/TiO
2
nanoscale mesoscopic structures.
Figure 1.10 Pictures of naked Ti metal and TiN after microwave irradiation with a commercial microwave oven.
Figure 1.11 (a) Microwave nanometallic ink continuous processor system and (b) microwave processing of (i) nano-Ag ink, (ii) nano-Cu ink, and (iii) nano-CuO ink on a PET plastic base.
Figure 1.12 Photograph of the solutions before (a) and after (b–d) the synthesis of cyclohexanol from cyclohexanone in the presence of 2-propanol and Wilkinson's catalyst on removing dissolved oxygen by the pipette degassing method after a 10-min heating period: (b) 915 MHz, (c) 2.45 GHz, and (d) oil bath.
Figure 1.13 Hofmann elimination reaction taking place by selective heating.
Figure 1.14 Factors of the samples, heat, and electromagnetic waves (microwaves) in the fields of chemical reactions and materials processing; relationships between each factor are also shown.
Figure 1.15 (a) Details of the experimental setup and positioning of the samples in the single-mode 5.8 GHz microwave resonator; (i) maximal position of the electric field (
E
field) density and (ii) maximal position of the magnetic field (
H
field) density. (b) Photograph of the single-mode microwave resonator and the 5.8 GHz semiconductor microwave generator; the photograph also shows the actual position of the sample at the
H
field maximum.
Chapter 2: Loss Mechanisms and Microwave-Specific Effects in Heterogeneous Catalysis
Figure 2.1 Energy transfer processes in the heating of a heterogeneous catalyst by microwave radiation.
Figure 2.2 Space–charge (Maxwell–Wagner) recombination dielectric loss process in a solid.
Figure 2.3 Surface sites that can couple to the incident microwave radiation and result in localized heating.
Figure 2.4 Dipolar loss processes that can result in microwave-specific chemical reactivity at the surface through (a) accelerated atom transfer to a substrate (enhanced Mars van Krevelen mechanism) and (b) selective coupling to an adsorbed substrate.
Figure 2.5 Proposed mechanisms for microwave enhancement of gas–carbon reactions: (a) microwave-induced space charges (electron–hole pairs) react with a substrate and (b) the dipoles of the surface oxides couple to the microwave and are rapidly ejected from the surface.
Chapter 3: Transport Phenomena and Thermal Property under Microwave Irradiation
Figure 3.1 Microwave reactor with DLS.
Figure 3.2 Time-averaged autocorrelation function (a) with PSL before irradiation, (b) with PSL during irradiation, and (c) without PSL during irradiation.
Figure 3.3 Size and temperature profiles for water and ethylene glycol during and after microwave irradiation.
Figure 3.4 Maximum size and irradiation time versus irradiation power during and after microwave irradiation (90 °C).
Figure 3.5 Microwave reactor with PIV system.
Figure 3.6 Convection observation of droplet by PIV system.
Figure 3.7 Angular velocity of circular flow for water droplet.
Figure 3.8 Angular velocity of circular flow for ethylene glycol droplet.
Figure 3.9 Microwave reactor for surface tension measurement.
Figure 3.10 Drop profile: (a) raw image and (b) edge for surface tension measurement.
Figure 3.11 Surface tension of water droplet as a function of time and temperature (solid symbols: with MW; unfilled symbols: without MW) for 300 W, 120 s. (a) Time and (b) temperature.
Figure 3.12 Surface tension of ethylene glycol droplet as a function of time and temperature (solid symbols: with MW; unfilled symbols: without MW) for 300 W, 120 s. (a) time and (b) temperature.
Chapter 4: Managing Microwave-Induced Hot Spots in Heterogeneous Catalytic Systems
Figure 4.1 Simulated temperature distribution in water and cyclohexane solvents in the presence of Pt/activated carbon (AC) catalyst particles subjected to microwave radiation. The simulation was carried out using an RF module and the COMSOL Multiphysics software Version 4.3a.
Figure 4.2 High-speed camera photograph of the electrical arc discharge occurring on the activated carbon in toluene solvent under the microwaves'
E
-field irradiation: (a) after 3 s of microwave irradiation, (b) after 16 s of irradiation, (c) under continuous irradiation, and (d) emitted light reaching maximal intensity.
Figure 4.3 Product yields of 4-methylbiphenyl in toluene solvent under irradiation with the microwaves'
H
-field and
E
-field components and oil-bath heating.
Figure 4.4 SEM images of Pd/AC catalyst surface: (a) 0 min irradiation, (b) after 30 min of microwave irradiation after formation of hot spots, and (c) under conditions of no formation of hot spots.
Figure 4.5 Distribution of the microwaves'
E
fields (2.45 GHz) around two activated carbon particles in toluene solvent simulated with the COMSOL Multiphysics software Version 4.3a. Colored images (a-i), (b-i), and (c-i) display the
E
-field intensity in two activated carbon particles in toluene together with the magnitude of the gap between the particles, whereas (a-ii), (b-ii), and (c-ii) graphics show the magnitude of the
E
field (V m
−1
) within this gap.
Figure 4.6 Observation of hot spots generated in activated carbon particles fixed at various intervals on a glass plate: (a) photograph of the initial sample; (b) formation of hot spots between the AC particles under microwave irradiation; and (c) observed distance between the particles in the fourth column with an optical microscope.
Figure 4.7 Photograph of the reactor introduced into (a-i) the vertically positioned waveguide and (b-i) horizontally positioned waveguide. Appearance of the Pd/AC catalyst in solution under
E
field (a-ii),
H
field (a-iii), and
H
field (a-iv; conical reactor) in the vertically positioned waveguide, and under the
E
field (b-ii) and
H
field (b-iii) in the horizontally positioned waveguide. Note that the photographs of a-ii and a-iv were taken in a slant position.
Figure 4.8 Illustration of the
E
and
H
fields in the reactor and the AC particles in a different location of the waveguides, and image of the polarization on the activated carbon surface. (a) Vertical waveguide and
E
-field condition; (b) vertical waveguide and
H
-field condition; (c) horizontal waveguide and
E
-field condition; and (d) horizontal waveguide and
H
-field condition. Note that the circular red-dotted line denotes the electric field produced by the magnetic field.
Figure 4.9 (a) Low-resolution SEM image of Pt/CMCs and (b) transmission electron microscope (TEM) image of Pt-deposits on CMCs at greater resolution.
Figure 4.10 High-speed camera photograph of the electrical arc discharge occurring on the Pd/AC catalyst surface during the reaction in the 25-mm wide tube reactor under 550-W microwave irradiation and at a stirring rate of (a) 0 rpm, (b) 0 rpm, and (c) 1500 rpm.
Chapter 5: Preparation of Heterogeneous Catalysts by a Microwave Selective Heating Method
Figure 5.1 Scanning electron microscopic images of TiO
2
/activated carbon particulates under various synthesis conditions: reaction temperatures were (a) 70 °C, (b) 80 °C, (c) 90 °C, and (d) 120 °C under microwave heating conditions; using the oil-bath heating method the reaction temperatures were (e) 80 °C and (f) 90 °C; (g) naked activated carbon as the control.
Figure 5.2 SEM–EDX pattern of TiO
2
coating on the activated carbon particulates upon heating to a temperature of 70 °C by the microwave method.
Figure 5.3 Plot illustrating the decrease in TiO
2
particle size on the AC surface at various reaction temperatures.
Figure 5.4 Relative dielectric losses (
ϵ
r
″) at the microwave frequency of 2.45 GHz and at various temperatures (a) for the aqueous dispersion of activated carbon and titanium oxysulfate and (b) for pure water.
Figure 5.5 Cartoon illustrating the growth mechanism of TiO
2
/AC particles produced by the microwave heating method at (a) a temperature of 70 °C and (b) at temperatures greater than 80 °C.
Figure 5.6 (a) Photodecomposition kinetics of isopropanol with the microwave-synthesized and oil-bath-synthesized TiO
2
/AC particles. (b) Photodegradation dynamics of isopropanol and formation and degradation of the intermediate product acetone in the presence of TiO
2
alone (no AC support).
Figure 5.7 (a) Model of a direct methanol fuel cell; the actual fuel cell stack is the layered cube shape in the center of the image. (b) Scheme of a proton-conducting fuel cell.
Figure 5.8 TEM images of (a) the microwave-assisted synthesis of Pt nanoparticles supported on Vulcan carbon XC-72 and of the (b) commercially available E-TEK Pt/C catalyst (nominal Pt loading 20 wt%).
Figure 5.9 TEM micrographs of Pt/C nanocomposites obtained by the (a) impregnation method and by the (b) microwave synthesis method.
Figure 5.10 TEM micrographs of Pt/Co
3
O
4
/C obtained by the (a) impregnation method and by the (b) microwave synthesis method.
Figure 5.11 TEM images of microwave-synthesized Pt/CNTs from ethylene glycol solutions of H
2
PtCl
6
at different pH's in the presence of CNTs: (a) pH 3.6; (b) pH 5.8; (c) pH 7.4, and (d) pH 9.2.
Figure 5.12 SEM (left) and TEM (right) images of the basic ZnO structures synthesized by microwave irradiation: (a, b) nanorods, (c, d) nanoneedles, (e, f) nanocandles, (g, h) nanodisks, (i, j) nanonuts, (k, l) microstars, (m, n) microUFOs, and (o, p) microballs.
Figure 5.13 Schematic diagram of the proposed formation processes of some basic ZnO structures: (a) nanorods or nanocandles, (b) nanoneedles, (c) nanodisks or nanonuts, (d) microstars, (e) microUFOs, and (f) microballs.
Figure 5.14 Scanning electronic microscopic spectra of (a) (NH
4
)
3
PW
12
O
40
, (b) Cs
3
PW
12
O
40
, (c) Ag
3
PW
12
O
40
, and (d) Cu
3
(PW
12
O
40
)
2
.
Figure 5.15 Diffuse reflectance UV–vis spectra of (a) H
3
PW
12
O
40
, (b) (NH
4
)
3
PW
12
O
40
, (c) Cs
3
PW
12
O
40
, (d) Ag
3
PW
12
O
40
, and (e) Cu
3
(PW
12
O
40
)
2
.
Figure 5.16 Scanning electron microscopic images of the Ni/C nanocomposites prepared by solution dispersion at (a) 5000× magnification; (b) 10 000× magnification; (c) 25 000× magnification; and (d) 75 000× magnification.
Figure 5.17 Scheme illustrating the possible pathway in the hydrogenation of acetophenone, which upon further hydrogenation yields styrene and ethylbenzene.
Figure 5.18 Conversion of methanol to formaldehyde after 80 min at 60 °C under 1 atm O
2
for the three spinel catalysts under varying MeOH:H
2
O ratios.
Chapter 6: Microwaves in Cu-Catalyzed Organic Synthesis in Batch and Flow Mode
Figure 6.1 Experimental setup for local temperature measurements at local Cu-catalyst-deposited section.
Figure 6.2 Microwave temperature profiles obtained at various axial positions from the multisegmented Cu/TiO
2
/SiO
2
micro fixed-bed reactor using
p
-xylene as nonabsorbing solvent.
Figure Scheme 6.1 The Ullmann-type C−O coupling from 4-chlorpyridine·HCl and phenol using microwaves and Cu nanoparticles.
Figure Scheme 6.2 Microwave-assisted synthesis of 5,6-dihydroindolo[1,2-
a
]quinoxaline using a CuI–ligand based catalyst.
Figure Scheme 6.3 The Ullmann-type C−O coupling from 4-chlorpyridine·HCl and phenol using microwaves and Cu nanoparticles.
Figure Scheme 6.4 Microwave-assisted solvent-free and ligand-free copper-catalyzed cross-coupling between halopyridines and nitrogen nucleophiles.
Figure Scheme 6.5 Microwave-assisted copper-catalyzed hydroxylation of aryl halides to a variety of alkylated phenols.
Figure Scheme 6.6 Arylation of various substituted phenols with various aryl halides.
Figure Scheme 6.7 Production of
N
-aryl-α-amino acids via a microwave-assisted copper-catalyzed
N
-arylation of various α-amino acids and aryl halides.
Figure Scheme 6.8 Microwave-assisted copper-catalyzed
N
-arylation of N−H heteroarenes with various heteroarenes.
Figure Scheme 6.9 Microwave-assisted multicomponent reaction of alkyne, halide, and sodium azide catalyzed by copper apatite as heterogeneous base and catalyst in water.
Figure Scheme 6.10 Microwave-assisted Cu(0)-catalyzed Ullmann coupling toward the production of anilinoanthraquinones.
Figure Scheme 6.11 Catalyzed transesterification of glyceryl tributyrate with methanol using MW-treated Cu/ZnO catalysts.
Figure Scheme 6.12 The Ullmann-type C−O coupling from 4-chlorpyridine·HCl and phenol using microwaves and Cu nanoparticles.
Figure Scheme 6.13 The Heck reaction used in the stop-flow microwave reaction.
Figure Scheme 6.14 Microwave-assisted flow synthesis of benzaldehyde under isothermal conditions.
Figure Scheme 6.15 Cycloaddition reactions under continuous-flow and microwave conditions.
Figure 6.3 Microwave heating pattern in a multimode-type microwave cavity. Effect of sample position (a) on heating rates (b) and heating efficiency (c).
Figure 6.4 Microwave heating pattern in a monomode-type microwave cavity. Effect of sample position on heating rates and heating efficiency.
Figure 6.5 (a) Loss tangent and (b) heating efficiency as a function of temperature and
d
/½
λ
(ratio of load diameter over half wavelength) for ethylene glycol at stop-flow conditions. The loss tangent monotonously decreases with temperature from 0.94 to 0.05.
Figure 6.6 (a) Temperature increase as a function of time and (b) heating efficiency dependence on
d
/½
λ
(ratio of load diameter over half wavelength) in case of ethylene glycol under continuous-flow conditions. Flow rate: 15 ml min
−1
. Microwave irradiation at 2.45 GHz at a constant applied power of 100 W.
Figure 6.7 Influence of the direction of the probe insertion on the temperature profiles obtained by modeling, (a) probe inserted from the outlet and (b) probe inserted from the inlet. See Figure 6.1 for dimensions of the reactor assembly.
Figure 6.8 Influence of the direction of the probe insertion on the temperature profiles obtained by modeling (lines) and experiments (data points). Solid line and squares: probe inserted from inlet, dotted line and triangles: probe inserted from outlet.
Figure Scheme 6.16 Liquid-phase heterogeneously Cu-catalyzed Ullmann C−O cross-coupling reaction.
Figure Scheme 6.17 Liquid-phase homogeneously acid-catalyzed synthesis of aspirin.
Figure Scheme 6.18 The Diels–Alder cycloaddition reaction used in Pd-coated MW capillary.
Figure Scheme 6.19 Catalyst coating procedure for the wall-coated Cu/ZnO catalytic reactor used in the Ullmann-type C−O coupling reaction toward 4-phenoxypyridine.
Figure Scheme 6.20 Cu-catalyzed Ullmann etherification of a 4-chloropyridine and potassium phenolate flow in DMA to 4-phenoxypyridine.
Figure Scheme 6.21 Micro-fixed-bed reactor setup using in-line microwave and temperature controlling applied in the Cu/TiO
2
catalzyed C−O coupling reaction.
Figure Scheme 6.22 Ester formation from acetic acid and ethanol.
Figure 6.9 Schematic view of a dedicated microwave setup (with labeling of all the parts) designed for continuous-flow fine-chemicals synthesis and multiphase flow handling. Red lines designate field pattern. Arrows signify flow of energy (purple), signals (green), liquids (blue), and movement of stub tuner, short circuit (gray). Design: TU/e; manufacturer: Fricke und Mallah GmbH, Germany.
Figure 6.10 Experimental validation of the predicted conversion of acetic acid and the production rate of the ethyl acetate for the esterification reaction in the packed-bed reactor as a function of the number of cavities in series. Symbols: experimental results, lines: theoretical predictions.
Figure 6.11 Schematic of a multi-tubular milli-reactor/heat exchanger (MTMR) setup. (a) Complete assembly. (b) Tube distribution. (c) Schematic of the MTMR assembly with coated milli-reactor tubes in the microwave cavity.
Figure Scheme 6.23 Multicomponent reaction of benzaldehyde, piperidine, and phenylacetylene to produce 1,3-diphenyl-2-propynyl piperidine.
Figure 6.12 Weight-loss profile of Cu thin film over time (normalized with residence time,
τ
) measured by Inductively Coupled Plasma (ICP) analysis.
Chapter 7: Pilot Plant for Continuous Flow Microwave-Assisted Chemical Reactions
Figure 7.1 Basic structure of the continuous flow microwave-assisted chemical reactor.
Figure 7.2 Electric field intensity distribution in the apparatus (a) with adjusting by stub tuner and (b) without stub tuner.
Figure 7.3 Result of water heating test when microwaves at 23 and 100 W were irradiated.
Figure 7.4 Configuration of the two-branch waveguide used in this study.
Figure 7.5 Calculation results of reflection coefficient when the length of
C
was changed.
Figure 7.6 Schematic of the four-branch waveguide.
Figure 7.7 Electric field intensity distribution in the four-branch waveguide.
Figure 7.8 Configuration of the microwave apparatus.
Figure 7.9 Overview of the pilot plant for continuous flow microwave-assisted chemical reactions combined with microreactors.
Figure 7.10 Block diagram of the pilot plant.
Figure 7.11 Result of water heating tests.
Figure 7.12 Energy absorption efficiency by water in the four reaction fields.
Figure 7.13 Experimental apparatus and condition for the Sonogashira coupling reaction by microwave heating method using the pilot plant.
Figure 7.14 Experimental apparatus and condition for the Sonogashira coupling reaction by oil-bath heating method.
Figure 7.15 Relation between yield and residence time in the Sonogashira coupling reaction.
Figure 7.16 Yields obtained by microwave heating method in the four reaction fields.
Chapter 8: Efficient Catalysis by Combining Microwaves with Other Enabling Technologies
Figure 8.1 Phenomena related to acoustic cavitation.
Figure 8.2 Hybrid metallic microreactor tightly fixed with an ultrasonic plate.
Figure 8.3 Loop MW/US reactor for simultaneous and sequential irradiation. 1, US nonmetallic horn; 2, MW oven; 3, optical fiber thermometer; 4
,
pump; 5, flow meter; 6, thermometer; 7, inlet and sampler; 8, heat exchanger; and 9, external flask.
Figure 8.4 MW/UV combined technology with EDL lamps.
Figure 8.5 SEM images of Ta
2
O
5
powder, ball milled for (a) 0 h, (b) 6 h, (c) 8 h, and (d) 12 h.
Figure 8.6 TEM micrographs of iron oxide nanoparticles on mesoporous aluminosilicates synthesized via a dry-milling protocol.
Figure Scheme 8.1 MW-assisted preparation of 1,1-diarylsubstituted alkenes.
Figure 8.7 Schematic illustration of CuO nanosheets and dendrites prepared using MW hydrothermal synthesis.
Figure Scheme 8.2 Heck reactions under MW or MW/US irradiation.
Chapter 9: Applications of Microwave Chemistry in Various Catalyzed Organic Reactions
Figure 9.1 The introduction of microwaves to a sample causes increased vibrations among the molecules, which in turn leads to improved heat transfer.
Figure 9.2 Reaction scheme used to compare microwave heating from conventional heating (Biginelli reaction).
Figure 9.3 The gold-catalyzed cyclization of various aromatic compounds comparing direct heating and microwave irradiation.
Figure 9.4 The use of microwave in the synthesis of bromorhodamines was made regiospecific by employing microwave irradiation.
Figure 9.5 Synthesis of thiazol[5,4-
f
]quinazoline (numbers in parentheses indicate the time and yield for microwave-assisted reactions).
Figure 9.6 Synthesis of flavones and chromones.
Figure 9.7 Synthesis of 7-aryl-2-alkylthio-4,7-dihydro-1,2,4-triazolo[1,5-
a
]pyrimidine-6-carboxamide using microwave irradiation.
Figure 9.8 Heck reaction scheme and catalytic cycle.
Figure 9.9 Reaction scheme for early reports of coupling reactions performed in water.
Figure 9.10 Microwave-mediated synthesis of resveratrol using Heck coupling reaction.
Figure 9.11 Illustration for the immobilization of benzothiazolate-oxime Pd catalyst for the microwave-mediated Heck coupling.
Figure 9.12 Heck coupling reaction with ultralow Pd as reported by Leadbeater
et al.
[28].
Figure 9.13 Heck coupling of arylboronic acid and an electron-poor olefin.
Figure 9.14 Suzuki coupling reactions comparing those put only in room temperature from those subjected under microwave.
Figure 9.15 IL and microwave assisted of functionalized aryl compounds in the presence of Pd and base Et
3
N.
Figure 9.16 IL and microwave-assisted coupling reactions between a halobenzene and an alkene.
Figure 9.17 Proposed catalytic cycle for the Suzuki coupling between a bromobenzene and an alkeneboronic acid.
Figure 9.18 Direct coupling between a boronic acid and a PEG-functionalized benzene triflate in the presence of Pd catalyst.
Figure 9.19 Solvent-free microwave-assisted synthesis of 2,5′ : 2′,5″-terthiophene 3.
Figure 9.20 Using microwave for the synthesis of polythiophenes could lead to a myriad of possible products with different electronic properties.
Figure 9.21 Synthetic scheme for the coupling between a bromobenzene and an aromatic alkyne using microwave and water without any metal.
Figure 9.22 Simultaneously cooling the products of a coupling reaction directly from the microwave reactor could lead to improved product ratios.
Figure 9.23 Fluorous synthesis of biaryls using microwave.
Chapter 10: Microwave-Assisted Solid Acid Catalysis
Figure Scheme 10.1
Figure Scheme 10.2
Figure Scheme 10.3
Figure Scheme 10.4
Figure Scheme 10.5
Figure Scheme 10.6
Figure Scheme 10.7
Figure Scheme 10.8
Figure Scheme 10.9
Figure Scheme 10.10
Figure Scheme 10.11
Figure Scheme 10.12
Figure Scheme 10.13
Figure Scheme 10.14
Figure Scheme 10.15
Figure Scheme 10.16
Figure Scheme 10.17
Figure Scheme 10.18
Figure Scheme 10.19
Figure Scheme 10.20
Figure Scheme 10.21
Figure Scheme 10.22
Figure Scheme 10.23
Figure Scheme 10.24
Figure Scheme 10.25
Figure Scheme 10.26
Figure Scheme 10.27
Figure Scheme 10.28
Figure Scheme 10.29
Figure Scheme 10.30
Figure Scheme 10.31
Figure Scheme 10.32
Figure Scheme 10.33
Figure Scheme 10.34
Figure Scheme 10.35
Figure Scheme 10.36
Figure Scheme 10.37
Chapter 11: Microwave-Assisted Enzymatic Reactions
Figure Scheme 11.1 Synthesis of butyl butyrate between butanol and ethyl butyrate.
Figure Scheme 11.2 Regioselective esterification of methyl-α-d-glucopyranoside.
Figure Scheme 11.3 Resolution of racemic 1-phenylethanol.
Figure Scheme 11.4 Synthesis of butyl butyrate.
Figure Scheme 11.5 Synthesis of galacto-oligosaccharides (GOS) from lactose using β-galactosidase from
Kluyveromyces lactis
(free and immobilized).
Figure Scheme 11.6 Transesterification of methyl acetoacetate with an alcohol ROH.
Figure Scheme 11.7 Ring-opening polymerization of ϵ-caprolactone.
Figure Scheme 11.8 Synthesis of propylene glycol monolaurate from 1,2-propanediol and lauric acid.
Figure Scheme 11.9 Synthesis of styrene oxide by lipase-catalyzed formation of perlauric acid.
Figure Scheme 11.10 Synthesis of
n
-butyl diphenyl methyl mercapto acetate.
Figure Scheme 11.11 Synthesis of isoniazide using lipase as a catalyst.
Figure Scheme 11.12 Lipase-catalyzed transesterification reaction of methyl acetoacetate.
Figure Scheme 11.13 Synthesis of citronellyl acetate from citronellol and vinyl acetate.
Figure Scheme 11.14 Esterification reaction of oleic acid by Novozym 435.
Figure Scheme 11.15 Synthesis of isoamyl myristate by Novozym 435 in solvent-free system.
Figure Scheme 11.16 Reagents and conditions: (i) acetone, 4 Å molecular sieves, Novozym 435, 45–60 °C, stirring, 18–24 h. (ii) Acetone, 4 Å molecular sieves, Novozym 435, microwave irradiation, 45–60 °C, stirring, 120–160 s. (iii) Novozym 435, 4 Å molecular sieves, 45–60 °C, microwave irradiation, 75–105 s. R = oleic, stearic, linoleic, α-linolenic, eicosapentaenoic (EPA), docosahexaenoic acids (DHAs), or their esters.
Figure 11.1 Experimental setup for lipase-catalyzed methyl benzoate transesterification under microwave heating. (1) CEM microwave reactor, (2) glass slurry reactor, (3) glass stirrer, (4) Remi's lab stirrer, (5) computer control unit, and (6) Remi's speed regulator.
Figure Scheme 11.17 Novozym 435 catalyzed synthesis of
n
-hexyl benzoate.
Figure Scheme 11.18 Lipase-catalyzed synthesis of ethyl 2-(4-aminophenyl)acetate.
Figure Scheme 11.19 Resolution of (
R
,
S
)-2-octanol by the immobilized PSL.
Figure Scheme 11.20 Lipase-catalyzed kinetic resolution of racemic secondary alcohols.
Figure Scheme 11.21 Dynamic kinetic resolution of 1-phenylethylamine.
Figure Scheme 11.22 Enzyme-catalyzed kinetic resolution of
rac
-1-phenylethanol.
Figure Scheme 11.23 Lipase-catalyzed kinetic resolution of (
R
,
S
)-1-(1-naphthyl)ethanol.
Figure Scheme 11.24 Enzymatic resolution of dl-(±)-3-phenyllactic acid.
Figure Scheme 11.25 Lipase-catalyzed transesterification of (
R
/
S
)-1-phenylpropagyl alcohol with vinyl acetate.
Figure 11.2 Dipole movement across α-helices and interaction with microwave radiation.
Figure 11.3 Illustrations of water-induced superheating mechanism: (a) the free or immobilized enzyme particle is surrounded by a layer of water molecules while the bulk hydrophobic solvent is dry; and (b) the enzyme particle is surrounded by a layer of water molecules while the bulk solvent contains a small amount of dispersed water.
Figure 11.4 Comparison of time-dependent BSA digestion under conventional and microwave heating illustrated using the PyMOL software. The tryptic peptides obtained after a 5-min heating period at 37 °C are shown in red while additional fragment generated after 16 h at 37 °C are highlighted in blue.
Chapter 12: Effects of Microwave Activation in Hydrogenation–Dehydrogenation Reactions
Figure 12.1 Cyclohexane dehydrogenation on a Pd/TiO
2
catalyst (flow conditions, 0.5 h
−1
).
Chapter 13: Hydrogen Evolution from Organic Hydrides through Microwave Selective Heating in Heterogeneous Catalytic Systems
Figure 13.1 Cartoon illustrating the dehydrogenation of tetralin occurring on the Pt/AC (platinum supported on activated carbon) catalyst subjected to microwave heating.
Figure 13.2 Conversion of tetralin to hydrogen gas and naphthalene during the dehydrogenation reaction under reflux conditions using microwave heating (MW power, 320 W) and conventional heating with a heat mantle at a temperature of 207 °C.
Figure 13.3 Correlation of (•) tetralin conversion and (□) average temperature from the tetralin dehydrogenation with 0.2 g of Pt/AC subjected to microwave irradiation for 60 min.
Figure 13.4 Models illustrating the temperature differences between tetralin and the Pt/AC catalytic system under microwave heating: (a) at a low ratio of the catalyst to tetralin and (b) at a high ratio of the catalyst to tetralin.
Figure 13.5 Experimental setup in the dehydrogenation of tetralin on a single-pass fixed-bed reactor involving a 2.45-GHz single-mode microwave apparatus.
Figure 13.6 (a) Dependence of the conversion of tetralin to hydrogen gas and naphthalene over the Pt/AC catalyst surface on reaction temperature under microwave heating and conventional heating with a mantle heater. (b) Dependence of conversion of tetralin over Pt/AC catalyst on feed flow rate of tetralin under microwave heating and conventional heating at a reaction temperature of 207 °C and a microwave power output of 90–170 W.
Figure 13.7 Model of heat transfer direction: (a) Under microwave heating (MWH):
T
catalyst
>
T
surrounding
, heat transfers from the catalyst to the surrounding matter; mass also transfers in the same direction because of the coupling vector. (b) Under classical convection heating (CH):
T
catalyst
<
T
tetralin
, heat transfers from the surrounding matter to the catalyst.
Figure 13.8 The state of the sintering of a catalyst after ceramics heater and microwave heating.
Figure 13.9 Dependence of the conversion of methylcyclohexane to hydrogen gas and toluene over the Pd/AC catalyst under microwave heating and conventional heating with a ceramics heater (temperature, 340 °C) [28].
Figure 13.10 Relation between the Pt/AC particle temperatures and bulk temperatures. (a) Simulation image and (b) plot of temporal change on Pt/AC particle temperatures and bulk temperatures.
Figure 13.11 Temperature distribution for lengthwise location of Pd/AC catalyst in the reactor with and without methylcyclohexane. (a) Microwave heating, (b) conventional heating with a ceramic heater, (c) temperature distribution for a reactor containing Pd/AC catalysts without methylcyclohexane under microwave heating (MWH) and conventional heating (CH). From Ref. [28].
Figure 13.12 (a) Sketched image and (b) photograph of the conventional microwave reactor and microwave Dewar-like vacuum reactor.
Figure 13.13 (a) Sketched image and dimensions of the double-walled reactor and (b) actual photograph of the microwave Dewar-like vacuum vessel.
Chapter 14: Microwave-Stimulated Oil and Gas Processing
Figure 14.1 Arrhenius plots (
k
is the overall ethane conversion apparent rate constant): 1 – VSbO
x
microwave, 2 – VSbO
x
thermal, 3 – VMoNbO
x
microwave, 4 – VMoNbO
x
thermal, 5 – VMoO
x
microwave, 6 – VMoO
x
thermal.
Chapter 15: Algal Biomass Conversion under Microwave Irradiation
Figure 15.1 The descriptions of microwave and induction ovens and their thermal histories.
Figure 15.2 Saccharification rate and glucose selectivity of the hydrothermal hydrolysis of maltose (top) and cellobiose (bottom) by using microwave (MW) and induction heating (IH) as a function of severity parameter (log
R
0
).
Figure Scheme 15.1 Proposed degradation mechanism of disaccharides by hydrothermal hydrolysis using (a) microwave and (b) induction heating.
Figure 15.3 The effects of electrolytes on hydrothermal hydrolysis of cellobiose: (a) effect of concentration of NaCl (cellobiose 200 mg/100 ml, reaction temperature 200 °C, reaction time 5 min with 4 min of heating up time). (b) Arrhenius plot of hydrothermal hydrolysis of cellobiose with and without addition of NaCl (0.17 M). (c) Effects of monovalent and divalent cations (0.17 M) on hydrothermal hydrolysis of cellobiose.
Figure 15.4 Effects of polyoxometalate cluster and microwave irradiation on hydrolysis of corn starch and Avicel cellulose: (a) comparison of microwave (MW) and induction heating (IH) on yields of reducing sugar and glucose and (b) comparison of POMs and strong cation exchange resins on microwave energy consumption.
Figure 15.5
Ulva meridionalis
.
Figure 15.6 Typical chemical structures of algal hydrocolloids of green, brown, and red algae: (a) ulvan, (b) rhamnan sulfate, (c) alginates, and (d) carrageenans.
Figure 15.7 Effects of reaction temperature on polyoxometalate cluster (2 mM) and microwave irradiation on hydrolysis of
Ulva meridionalis
.
Figure 15.8 Effects of polyoxometalate cluster and microwave irradiation on hydrolysis of
Ulva meridionalis
: (a) comparison of POMs (PW; phsophotungstic acid, SiW; silicotungstic acid, PMo; phosphomolybdic acid), HCl, and H
2
SO
4
on yields of neutral sugar, reducing sugar, and uronic acids, (b) size exclusion chromatograms of the hydrolysates, and (c) comparison of microwave and induction heating.
Figure 15.9 Temperature dependency of the dielectric spectra of native (a) sodium alginates, (b) κ-carrageenans, (c) corn starch, and (d)
Citrus
pectin in water (2.0 wt%). The dashed lines represent relative permittivity, whereas the solid lines represent the loss factors.
Figure Scheme 15.2 Preparation procedures of partially reduced (a) sodium alginate [31] and (b) desulfated carrageenan [32a]. Their effects on the degree of substitution and compositions of counter cations of (c,d) sodium alginates and (e-f) κ-carrageenan. The desulfation procedures was conducted according to Nakagawa
et al
. [32b].
Figure 15.10 Dependency of the dielectric spectra on acidic functional groups of (a) sodium alginates, (b) κ-carrageenan in water (2.0 wt%). The dashed lines represent relative permittivity, whereas the solid lines represent loss factors. DW; distilled water.
Figure 15.11 Correlations between tan
δ
(
ϵ
″/
ϵ
′) at 2.45 GHz with other physical properties of hydrocolloids in water including (a) conductivity (
σ
), (b) pH, (c) nonfreezing water, (d, e) viscosity, and (f) energy efficiency.
Chapter 16: Microwave-Assisted Lignocellulosic Biomass Conversion
Figure 16.1 Bioethanol production from lignocellulosic biomass by separate hydrolysis and fermentation (SHF) process.
Figure 16.2 Conceptual image of multi-mode continuous flow microwave reactor.
Figure 16.3 Photograph of the multi-mode continuous flow microwave reactor with a 4.9 kW microwave generator.
Figure 16.4 Conceptual image of direct-irradiation continuous flow microwave reactor.
Figure 16.5 Measured permittivity characteristics of ethylene glycol at 2.45 GHz (
ϵ
r
′: real part of relative permittivity,
ϵ
r
″: imaginary part of relative permittivity).
Figure 16.6 Power density distribution in the cross section of the direct-irradiation continuous flow microwave reactor at the ethylene glycol temperatures of (a) 25 °C and (b) 80 °C.
Figure 16.7 A photograph of the first prototype of direct-irradiation continuous flow microwave reactor with three 1.2 kW microwave generators.
Figure 16.8 Photograph of the second prototypes of direct-irradiation continuous flow microwave reactor with three 5 kW microwave generators.
Figure 16.9 Conceptual image of pilot-plant-scale continuous flow microwave reactor.
Figure 16.10 Measured permittivity characteristics of woody biomass slurry and distilled water at 2.45 GHz (
ϵ
r
′: real part of relative permittivity,
ϵ
r
″: imaginary part of relative permittivity).
Figure 16.11 Simulation model of the pilot-plant-scale continuous flow microwave reactor. Absorbing boundary was set at the top and bottom planes of the metal pipe.
Figure 16.12 Power absorption distribution in the cross section of the designed pilot-plant-scale continuous flow microwave reactor at the slurry temperatures of (a) 40 °C and (b) 80 °C.
Figure 16.13 Photograph of the pilot-plant-scale continuous flow microwave reactor.
Figure 16.14 Microwave heating characteristics by the pilot-plant-scale continuous flow microwave reactor.
Chapter 18: Oxidative and Reductive Catalysts for Environmental Purification Using Microwaves
Figure 18.1
n
-Pentane oxidation over N-150 and G-3A under microwave irradiation (MW) and conventional heating (CH) measured with increasing (dotted line) and decreasing (full line) temperature; •: N-150 MW, ○: N-150 CH, ▴: G-3A MW, ▵: G-3A CH; 800 ppm
n
-pentane in air, GHSV: 1000 h
−1
.
Figure 18.2 Acetaldehyde oxidation over N-150 and G-3A under microwave irradiation (MW) and conventional heating (CH) measured with increasing (dotted line) and decreasing (full line) temperature; •: N-150 MW, ○: N-150 CH, ▴: G-3A MW, ▵: G-3A CH; 1400 ppm CH
3
CHO in air, GHSV: 9000 h
−1
.
Figure 18.3 NO
x
reductive reaction over G-3A under microwave irradiation (full line) and conventional heating (dotted line) measured with decreasing temperature; •: 630 ppm NO–2.6% H
2
O in He, GHSV: 4800 h
−1
, ▴: 630 ppm NO–5% O
2
–2.6% H
2
O in He, GHSV: 4800 h
−1
, ▪: 1600 ppm NO–6000 ppm CH
4
–3% H
2
O in He, GHSV: 4800 h
−1
.
Figure 18.4 AMF 3D-height images of G-3A used for NO
x
reductive reactions under microwave irradiation (a) and conventional heating (b).
Chapter 19: Microwave-/Photo-Driven Photocatalytic Treatment of Wastewaters
Figure 19.1 (a) Photograph of an integrated microwave/photoreactor system having a single-mode applicator and (b) schematic of the system and a typical plot (inset) of the change of temperature with irradiation time for an aqueous TiO
2
dispersion under microwave irradiation.
Figure 19.2 Visual comparison of color fading in the degradation of RhB solutions (0.05 mM) subsequent to being subjected to various degradation methods for 150 min. From left to right: initial RhB solution; RhB subjected to photoassisted degradation (UV); RhB subjected to integrated microwave-/photo-assisted degradation (UV/MW); and RhB subjected to thermal- and photo-assisted degradation (UV/CH).
Figure 19.3 (a) Decrease in total organic carbon (TOC) in the decomposition of RhB solution (initial TOC concentration, 18.6 mg l
−1
; 30 ml) by MW (without TiO
2
), UV (60 mg), UV/CH (60 mg), and UV/MW (30 mg); (b) temporal evolution of the decrease in TOC during the degradation of RhB solution (0.050 mM, 30 ml) at a radiance of 0.3 and 2.0 mW cm
−2
; (c) decrease in TOC values for the influence of different added gases on the degradation of RhB (0.050 mM); (d) decrease in TOC for RhB solutions (0.050 mM, 30 ml) with TiO
2
loading (30 mg) by the UV/MW method (microwave applied power at 150, 225, and 300 W); and (e) temporal evolution of the formation of NH
4
+
ions in the decomposition of RhB (0.050 mM) using the UV, UV/CH, and UV/MW methods; the radiance was 0.3 mW cm
−2
.
Figure Scheme 19.1 Proposed initial mechanistic steps in the degradation of RhB dye by the UV and UV/MW methods.
Figure 19.4 The
in situ
observation of the pH dependence of the zeta-potential on the TiO
2
particle surface (P25): (a) photograph of the experimental setup, (b) under UV irradiation alone, and (c) under simultaneous UV/MW irradiation.
Figure 19.5 (a) Schematic illustration of the microwave-assisted photoreactor (MPR) coupled to a cooling system in the microwave multi-mode applicator. (b) Temporal decrease in the concentration of bisphenol-A (BPA: 0.050 mM) during its decomposition in aqueous media by photoassisted oxidation (UV), by the microwave-/photo-assisted oxidation (UV/MW) method, and by the integrated microwave-/photo-assisted degradation under cooling conditions (UV/MW/Cool).
Figure 19.6 (a) Temporal changes of the temperature and (b) decrease in methylene blue (MB) concentrations by the UV and by the integrated UV/MW protocols with 2.45 and 5.8-GHz microwaves in the presence of TiO
2
.
Figure 19.7 Setup used to generate
•
OH radicals in water alone under MW irradiation, in an aqueous TiO
2
dispersion by MW irradiation alone, and by the UV and UV/MW methods.
Figure 19.8 (a) Image and (b) photograph of the nanosecond transient diffuse reflectance spectroscopic system.
Figure 19.9 Cartoon depicting the influence of microwave radiation on a Vo-ST01 particle.
Figure 19.10 (a) Photograph of small MDELs and (b) the experimental setup of a small MDEL device in a single-mode microwave apparatus.
Figure 19.11 Time profiles of the extent of the photoassisted defluorination of perfluorooctanoic acid (PFOA) in aqueous solutions in the photoreactor containing the 20 MDELs systems.
Figure 19.12 Water sterilization equipment used to sterilize natural water (accumulated rain water) samples using the solar cells located on the right-hand side of the photograph and the TiO
2
-coated MDELs (150 pieces) [32] Copyright 2014 by S. Horikoshi and N. Serpone.