A. Renken

Micro process engineering : a comprehensive handbook

VOLUME I: Fundamentals, Operations and Catalysts FLUID DYNAMICS IN MICROCHANNELS Multiphase Flow Microfluidic Networks Boiling and Two-Phase Flow in Microchannels Microscale Flow Visualization Modeling of Microfluidic Devices MIXING IN MICROSYSTEMS Characterization of Mixing and Segregation in Homogeneous Flow Systems Passive and Active Micromixers Mixing and Contacting of Heterogeneous Systems HEAT/MASS TRANSFER Heat Transfer in Homogeneous Systems Transport Phenomena in Microscale Reacting Flows Fluid-Fluid and Fluid-Solid Mass Transfer MICROSTRUCTURED DEVICES FOR PURIFICATION AND SEPARATION PROCESSES Extraction Capillary Electrochromatography MICROSTRUCTURED REACTORS Homogeneous Reactions Heterogeneous Multiphase Reactions Photoreactors Microstructured Reactors for Electrochemical Synthesis VOLUME II: Devices, Reactions and Applications MICROREACTOR DESIGN, FABRICATION AND ASSEMBLY Silicon and Glass Microreactors Metallic, Steel, Ceramic and Plastic Microreactors BULK AND FINE CHEMISTRY Liquid- and Liquid-Liquid-Phase Reactions - Aliphatic Substitution Reactions Liquid- and Liquid-Liquid-Phase Reactions - Aromatic Substitution Reactions Liquid- and Liquid-Liquid-Phase Reactions - Addition and Elimination Liquid- and Liquid-Liquid-Phase Reactions - Coupling Reactions Liquid- and Liquid-Liquid-Phase Reactions - Oxidations and Reduction Gas-Liquid-Phase Reactions: Substitution Gas-Liquid-Phase Reactions: Addition Gas-Liquid-Phase Reactions: Reduction Gas-Liquid-Phase Reactions: Miscellaneous Reactions POLYMERIZATION Free Radical Polymerization Living Radical Polymerization Cationic Polymerization Polycondensation FUNCTIONAL MATERIALS Organic Particles and Pigments Inorganic Particles Polymer Particles Microencapsulates, Proteins and Lipids/Vesicles Oil-in-Water and Water-in-Oil Emulsions Double, Triple and Complex Multilayered Emulsions Microreactor Applications in the Consumer Goods Industry FUEL PROCESSING Application and Operation of Microreactors for Fuel Conversion Steam Reforming Partial Oxidation CO Clean-Up: Water Gas Shift and Methanation Reactions CO Clean-Up: Preferential Oxidation VOLUME III: System, Process and Plant Engineering MICROREACTOR SYSTEMS DESIGN AND SCALE-UP Structured Multi-Scale Process Systems Design and Engineering - The Role of Microreactor Technology in Chemical Process Design Reaction and Process System Analysis, Miniaturization and Intensification Strategies Principles and Guidelines for Selection of Microstructured Devices for Mixing and Reaction Catalyst Development, Screening and Optimization SENSING, ANALYSIS, AND CONTROL Microtechnology and Process Analytics Optical In-Line Spectroscopy in Microchemical Processes On-Line Monitoring of Reaction Kinetics in Microreactors Using Mass Spectrometry and Micro-NMR Spectroscopy Automation and Control of Microprocess Systems MICROREACTOR PLANTS: CASE STUDIES Industrial Microreactor Process Development up to Production Microreactor Plant for the Large-Scale Production of a Fine Chemical Intermediate: A Technical Case Study Development and Scale-Up of a Microreactor Pilot Plant Using the Concept of Numbering-Up Microstructures as a Tool for Production in the Tons per Hour Scale ECONOMICS AND ECO-EFFICIENCY ANALYSES The Economic Potential of Microreaction Technology Life Cycle Assessment of Microreaction Technology Versus Batch Technology - A Case Study Exergy Analysis of a Micro Fuel Processing System for Hydrogen ald Electricity Production - A Case Study

In-situ surface and gas phase analysis for kinetic studies under transient conditions. The catalytic hydrogenation of CO2

Transient measurement techniques are applied for the kinetic investigation of the reaction mechanism of the carbon dioxide methanation, using diffuse reflectance infrared spectroscopy and mass spectrometry. The coupled information of the surface intermediates and the gas phase components time evolution leads to accurate identification of spectator species on the surface. Reaction intermediates, carbon monoxide and formates have been identified. The former is a key intermediate, and its hydrogenation leads to methane formation. The latter is fixed on the support, in equilibrium with a active formate species on the interface metal-support. A reaction mechanism is proposed including the formation step of the formates through a carbonate species.

Kinetics and mechanism of the reduction of nitric oxides by H2 under lean-burn conditions on a Pt–Mo–Co/α-Al2O3 catalyst

The kinetics and the mechanism of the selective reduction of nitric oxides (NOx) by hydrogen is studied on a trimetallic Pt–Mo–Co/a-Al2O3 catalyst under oxidising conditions. This system is interesting in view of an exhaust gas control of power plants or lean-burn cars. It can be shown that the NO dissociation is the crucial step, dominating the overall reaction behaviour and that it depends on temperature and on the partial pressure of H2. With increasing temperatures the reaction reveals an autocatalytic behaviour resulting in bistability and hysteresis. At higher temperatures, where no bistability is found, the NO/H2 as well as the competing O2/H2 reaction occur only above a certain critical partial pressure of H2. The kinetics of the NO/H2/O2 reaction are established using a modified Langmuir–Hinshelwood model (T=142°C–160°C, yO2>4%) which takes into account the critical H2 partial pressure. The model describes the experimental data within ±15%. The determined activation energies are: 63 kJ/mol for the NOx consumption, 77 and 45 kJ/mol for the N2 and N2O formation, respectively, and 130 kJ/mol for the O2/H2 reaction. Adsorption enthalpies are determined to -59 kJ/mol for the adsorption of H2, -77 kJ/mol for the adsorption of NO and -97 kJ/mol for the adsorption of O2. An interesting feature of the reaction is the enhancement of the NO/H2 reaction by oxygen for low partial pressures of O2. This appears to be the first study where a promoting effect of oxygen for the NO/H2 reaction is found on a platinum supported catalyst.

A fourier transform infrared spectroscopic study of C02 methanation on supported ruthenium

Diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy has been used to study in situ, the low-temperature (T < 200°C) methanation of CO2 over Ru on TiO2 supports and on Al2O3. For 3.8% Ru/TiO2, the reaction exhibits an activation energy (Ea) of 19 kcal/mol, is 0.43 ± 0.05 (approximately one-halt) order in H2 concentration, and essentially independent of C02 concentration. At 110°C, 40% of the available metal sites are occupied by CO (Qco = 0.4), a known methanation intermediate. In contrast to Ru/TiO2, Ru/Al2O3, despite having the same Ea and Qco = 0.2, is 15 times less active. Batch catalyst screening experiments showed no dependence of methanation activity on adsorbed CO (COa) formation rate (as modeled by HCOOH dehydration) or on Qco. In view of this, and the fact that CO dissociation is known to be structure-sensitive, heterogeneity in the active sites is invoked to reconcile the data. The high Ru dispersion on TiO2 is believed to contribute to the enhanced activity over this support. Adsorbed CO2 and H2 react, possibly at the metal-support interface, to form COa via rapid equilibration of the reverse water-gas shift reaction, in which HCOOH (and/or HCOO- ion) play a major role. According to this view, the COa and HCOO-a intermediates seen by FTIR represent accumulated reservoirs en route to CH4, in which the COa hydrogenation step is rate-controlling. An interesting synergy occurs for mixtures of Ru/anatase and Ru/rutile, the former being a better catalyst for CO. supply while the latter is more effective in COa hydrogenation.

Pd/SiO2 catalysts: synthesis of Pd nanoparticles with the controlled size in mesoporous silicas

Synthesis of Pd nanoparticles with controlled size (d(Pd) = 1-3.6 nm) was carried out within the pores of the mesoporous HMS and SBA-15 silicas. Pd was ion-exchanged on non-calcined silicas, prepared by solvent extraction of the templates. A high concentration of silanol groups on the mesopore surface allowed attaining Pd loading up to 4.4. wt.%. The Pd/HMS and Pd/SBA-15 were characterised by chemical analysis, XRD, N2 adsorption-desorption and transmission electron microscopy (TEM) methods. The materials possess a high SSA and narrow pore size distribution. Introduction of Pd nanoparticles in HMS resulted in a progressive loss of the regularity in the mesoporous structure. On the contrary, all Pd/SBA-15 composites retained the original well-ordered 2D hexagonal structure of SBA-15. The thick walls of the SBA-15 framework are accounted for the higher stability observed. The TEM investigations confirmed that the Pd nanocrystals were located within the SBA-15 mesoporous framework channels. The particle size did not exceed the mesopore diameter (2-6 nm) at Pd loading of 0.1-4.4wt.%. Pd clusters were found to be resistant against sintering during air-calcination (550 degreesC, 4h). The catalyst 2.1%Pd/SBA-15 used in methane combustion at 520 degreesC demonstrated stable activity during 6h on stream.

Periodic operation of catalytic reactors—introduction and overview

A review, with 89 refs., is presented on the subject of periodic operation of catalytic reactors by compn. forcing. Possible objectives of this mode of reactor operation are increased conversion, improved selectivity, reduced catalyst deactivation and insight into mechanisms of reactor models. Several forcing strategies may be used: manipulating one or more reactant concns., or interspersing pulses of inerts between pulses of reactants. These strategies are distinct from the variables in periodic operation, i.e., frequency, wave shape, amplitude, and phase lag. Lab.-scale equipment for periodic forcing makes use of single reactors along with the control of reactant and/or diluent flows. On an industrial scale, two catalyst beds are used, each operating with different feeds under different conditions. Catalyst transfers between the beds. A large literature has developed over the 25 yr since periodic operation was first proposed. [on SciFinder (R)]

Fourier transform infrared spectroscopic study of carbon dioxide methanation on supported ruthenium

Diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy has been used to study in situ, the low-temperature (T < 200°C) methanation of CO2 over Ru on TiO2 supports and on Al2O3. For 3.8% Ru/TiO2, the reaction exhibits an activation energy (Ea) of 19 kcal/mol, is 0.43 ± 0.05 (approximately one-halt) order in H2 concentration, and essentially independent of C02 concentration. At 110°C, 40% of the available metal sites are occupied by CO (Qco = 0.4), a known methanation intermediate. In contrast to Ru/TiO2, Ru/Al2O3, despite having the same Ea and Qco = 0.2, is 15 times less active. Batch catalyst screening experiments showed no dependence of methanation activity on adsorbed CO (COa) formation rate (as modeled by HCOOH dehydration) or on Qco. In view of this, and the fact that CO dissociation is known to be structure-sensitive, heterogeneity in the active sites is invoked to reconcile the data. The high Ru dispersion on TiO2 is believed to contribute to the enhanced activity over this support. Adsorbed CO2 and H2 react, possibly at the metal-support interface, to form COa via rapid equilibration of the reverse water-gas shift reaction, in which HCOOH (and/or HCOO- ion) play a major role. According to this view, the COa and HCOO-a intermediates seen by FTIR represent accumulated reservoirs en route to CH4, in which the COa hydrogenation step is rate-controlling. An interesting synergy occurs for mixtures of Ru/anatase and Ru/rutile, the former being a better catalyst for CO. supply while the latter is more effective in COa hydrogenation.

Structured combustion catalysts based on sintered metal fibre filters

Novel efficient structured combustion catalysts based on sintered metal fiber filters (MFF) were developed. To increase sp. surface area (SSA), metal fibers were coated by crack-free porous oxide films of SiO2, Al2O3, porous glass, and mesoporous SBA-15 silica. The composite materials presented uniform open macrostructure of the non-treated MFF filters and were suitable supports for deposition of catalytically active phases (Pd, Pt, and Co3O4). These catalysts were tested in hydrocarbon (CH4, C3H8) combustion. Co3O4 supported on MFF without any coating (6.8% Co3O4/MFF) was the most active for propane total oxidn. At the same time in methane combustion the activity of this catalyst was relatively low. Pd supported on the MFF coated by mesoporous SBA-15 film (0.5% Pd/SBA-15/MFF) demonstrated the highest activity in methane total oxidn. due to the high palladium dispersion. The SBA-15 film supported on MFF provided the highest dispersion of the deposited noble metals (Pd, Pt) with an av. particle size .apprx.2.0 nm. The metal nanoparticles formed within the mesopore channels were stable against sintering during calcination and the particle diam. was obsd. not to exceed the diam. of the silica pores. These catalysts did not undergo deactivation under reaction conditions at temps. up to 500 Deg. On the contrary, the Pd supported on MFF coated by the microporous SiO2 and Al2O3 films, prepd. by sol-gel technique, suffered from metal sintering during the calcination step and also during reaction, demonstrating strong catalyst deactivation. The catalytic filters are suitable materials for assembling different multiple layers to obtain structured catalytic beds with the compn./concn. gradients of active component in the axial direction. The enhanced overall catalytic performance was obsd. in adiabatic catalytic reactor during propane combustion due to a synergy of the 0.5% Pd/SBA-15/MFF and the 0.5% Pt/SBA-15/MFF catalytic layers assembled in the appropriate order forming gradient catalytic bed. [on SciFinder (R)]

Hydrogen production by catalytic cracking of methane over nickel gauze under periodic reactor operation

The catalytic cracking of methane over nickel gauze is proposed as an attractive alternative for the prodn. of CO-free hydrogen. The catalyst deactivates due to intensive coke deposition. Therefore, the reactor was operated periodically with the reaction followed by the catalyst regeneration by burning of coke in oxidative atm. The optimal reaction performance was found to consist of reaction periods of 4 min followed by 4 min regeneration periods. [on SciFinder (R)]

Three-phase nitrobenzene hydrogenation over supported glass fiber catalysts: reaction kinetics study

The catalytic properties of Pd and Pt supported on woven glass fibers (GF) were investigated in the three-phase hydrogenation of nitrobenzene (NB). Over all catalysts, a 100 % yield of aniline was attained. The catalytic activity for the best catalysts was two times higher than the activity of commercial Pt/C catalyst traditionally used for liquid‐phase hydrogenation. The intrinsic reaction kinetics were studied and a reaction scheme is suggested. The direct formation of aniline from NB was observed over Pd/ GF with traces of intermediates. Four intermediate products were detected during aniline formation over Pt/GF: nitrosobenzene, phenylhydroxylamine, azoxybenzene, and azobenzene. The Eley-Rideal kinetic model fits the experimental data well. The parameters of the model were determined as a function of initial NB concentration and hydrogen pressure. Pt and Pd supported on GF in woven fabrics are suggested as suitable materials for reactors with a structured catalytic bed in multiphase reactor performance.