High-temperature Flow Reactor Research Articles

High-Temperature Boc Deprotection in Flow and Its Application in Multistep Reaction Sequences.

A simplified Boc deprotection using a high-temperature flow reactor is described. The system afforded the qualitative yield of a wide variety of deprotected substrates within minutes using acetonitrile as the solvent and without the use of acidic conditions or additional workups. Highly efficient, multistep reaction sequences in flow are also demonstrated wherein no extraction or isolation was required between steps.

Nucleophilic aromatic substitution of heterocycles using a high-temperature and high-pressure flow reactor

We report herein a high-temperature and high-pressure continuous-flow protocol to carry out nucleophilic aromatic substitution (SNAr) of heterocycles with nitrogen nucleophiles. Utilizing the Phoenix Flow Reactor™ in parallel with Design-of-Experiment software enabled rapid optimization of the SNAr protocol. This protocol facilitated efficient synthesis of a broad range of 2-aminoquinazolines, and was extended to 2-aminoquinoxalines and 2-aminobenzimidazoles.

Speciation data for fuel-rich methane oxy-combustion and reforming under prototypical partial oxidation conditions

Non-catalytic partial oxidation (POX) of hydrocarbon fuels is an important process for producing syngas. Quantitative experimental data under the demanding conditions relevant for POX reactions, e.g. long residence times, rich stoichiometries and high temperatures, respectively, are rare in literature. Here, the DLR high-temperature flow reactor setup was used to obtain a unique experimental data set for validation of reaction models and general understanding of fuel-rich hydrocarbon chemistry. A systematic experimental speciation data set for rich methane conditions with relevance to partial oxidation/gasification processes is presented. Both fast oxidation and slow reforming reactions are considered here. Quantitative data is obtained in the DLR high temperature flow reactor setup with coupled molecular beam mass spectrometry (MBMS) detection. Five test case scenarios are investigated, featuring rich methane conditions (ϕ=2.5) for the temperature range from 1100–1800K under atmospheric conditions. CO, CO2 and acetylene in two different amounts is added to the system for systematic analysis for addressing phenomena related to partial oxidation. The new experimental database includes quantitative species profiles of major and intermediate species and is available as Supplemental material. The experimental data is compared with results from a 0D modeling approach using the GRI 3.0, USC-II, Chernov and a reduced model based on the full Chernov mechanism. The comparisons reveal significant differences in the model predictions among themselves and with respect to the experimental data, underlining the relevance of this unique data set for further mechanism development and/or optimization.

An atmospheric pressure high-temperature laminar flow reactor for investigation of combustion and related gas phase reaction systems.

A new high-temperature flow reactor experiment utilizing the powerful molecular beam mass spectrometry (MBMS) technique for detailed observation of gas phase kinetics in reacting flows is presented. The reactor design provides a consequent extension of the experimental portfolio of validation experiments for combustion reaction kinetics. Temperatures up to 1800 K are applicable by three individually controlled temperature zones with this atmospheric pressure flow reactor. Detailed speciation data are obtained using the sensitive MBMS technique, providing in situ access to almost all chemical species involved in the combustion process, including highly reactive species such as radicals. Strategies for quantifying the experimental data are presented alongside a careful analysis of the characterization of the experimental boundary conditions to enable precise numeric reproduction of the experimental results. The general capabilities of this new analytical tool for the investigation of reacting flows are demonstrated for a selected range of conditions, fuels, and applications. A detailed dataset for the well-known gaseous fuels, methane and ethylene, is provided and used to verify the experimental approach. Furthermore, application for liquid fuels and fuel components important for technical combustors like gas turbines and engines is demonstrated. Besides the detailed investigation of novel fuels and fuel components, the wide range of operation conditions gives access to extended combustion topics, such as super rich conditions at high temperature important for gasification processes, or the peroxy chemistry governing the low temperature oxidation regime. These demonstrations are accompanied by a first kinetic modeling approach, examining the opportunities for model validation purposes.

Catalytically active magnetic nanoparticles in the Cu-O system

Cu-O nanoparticles 11 to 215 nm in average size have been prepared by a levitation-jet process in a He flow with air additions and characterized by scanning electron microscopy, X-ray diffraction, BET measurements, vibrating-sample magnetometry, and optical spectroscopy in the UV, visible, and IR spectral regions. The nanoparticles were pseudospherical in shape and consisted predominantly of Cu2O and CuO. Magnetization measurements showed that the nanoparticles exhibited soft-magnetic ferromagnetic behavior (up to 0.06 A m2/kg in terms of maximum magnetization). The nanoparticles were also investigated in a high-temperature air flow reactor as a promising catalytic material for propane oxidation to CO2. In the case of two-phase nanoparticles, the total conversion temperature was found to decrease by 70 K as the nanoparticle size decreased from 110 to 51 nm, with a minimum temperature of 450 K for single-phase Cu2O particles 29 nm in size. The increase in catalytic activity seems to be related to the behavior of localized electron states on the CuO/Cu2O interface, which are responsible for the room-temperature ferromagnetism of the nanoparticles.

Role of the Filters in the Formation and Stabilization of Semiquinone Radicals Collected from Cigarette Smoke.

The fractional pyrolysis of Bright tobacco was performed in nitrogen atmosphere over the temperature range of 240 - 510 °C in a specially constructed, high temperature flow reactor system. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the free radicals in the initially produced total particular matter (TPM) and in TPM after exposure to ambient air (aging). Different filters have been used to collect TPM from tobacco smoke: cellulosic, cellulose nitrate, cellulose acetate, nylon, Teflon and Cambridge. The collection of the primary radicals (measured immediately after collection of TPM on filters), the formation and stabilization of the secondary radicals (defined as radicals formed during aging of TPM samples on the filters) depend significantly on the material of the filter. A mechanistic explanation about different binding capability of the filters decreasing in the order: cellulosic < cellulose nitrate < cellulose acetate < nylon ~ teflon is presented. Different properties were observed for the Cambridge filter. Specific care must be taken using the filters for identification of radicals from tobacco smoke to avoid artifacts in each case.

Fe2O3 nanoparticle mediated molecular growth and soot inception from the oxidative pyrolysis of 1-methylnaphthalene

While it is well documented iron oxide can reduce soot through burnout in the oxidative regions of flames, it may also impact molecular growth and particle inception. The role of Fe2O3 nanoparticles in mass growth of soot from 1-methylnapthalene (1-MN) was studied in a dual-zone, high-temperature flow reactor. An iron substituted, dendrimer template was oxidized in the first zone to generate ∼5nm Fe2O3 nanoparticles, which were seeded into the second zone of the flow reactor containing 1-MN at 1100°C and ϕ=1.4–5.0. Enhanced molecular growth in the presence of Fe2O3 nanoparticles resulted in increased yields of polycyclic aromatic hydrocarbons (PAH) and soot compared to purely gas-phase reactions of 1-MN at identical fuel–air equivalence ratios. This also resulted in an increase in soot-number concentration and a slight shift to smaller particles with increasing addition (from no addition to 3mM) of Fe2O3. Introduction of Fe2O3 nanoparticles resulted in the formation of stabilization of environmentally persistent free radicals (EPFRs), including benzyl, phenoxyl, or semiquinone-type radicals as well as carbon-centered radicals, such as cyclopentadienyl or a delocalized electron in a carbon matrix. At the high concentrations in the flow reactor, these resonance-stabilized free radicals can undergo surface-mediated, radical–radical, molecular growth reactions which may contribute to molecular growth and soot particle inception.

ChemInform Abstract: Highyl Efficient Thermal Cyclization Reactions of Alkylidene Esters in Continuous Flow to Give Aromatic/Heteroaromatic Derivatives.

AbstractGould—Jacobs and Conrad—Limpach‐type thermal cyclization and benzannulation reactions are investigated from readily prepared functional precursors using a high pressure and high temperature flow reactor system with very short residence times.

Sintering kinetics and mechanism of vitreous nanoparticles

The sintering of vitreous nanoparticle doublets is investigated numerically by a volume of fluid method coupled to Hamaker summation and experimentally by a high-temperature sintering flow reactor as well as by doublet shape analysis in the transmission electron microscope. In particular, the characteristic differences between nanoparticulate and bulk sintering are studied. The sintering mechanism of vitreous nanoparticles is determined to be viscous flow with interparticle van der Waals interactions acting as additional driving force. The early stages of the nanoparticle sintering kinetics are inversely proportional to the square of the particle size, instead of an indirect proportionality to the first order of the particle size for the entire bulk process. The transition between nanoparticulate and bulk sintering is localised to primary particle diameters of approx. 200–300 nm.

Development of Micro-Flow Hydrothermal Monitoring Systems and Their Applications to the Origin of Life Study on Earth

Continuous extensive studies on thermophilic organisms have suggested that life emerged on hydrothermal systems on primitive Earth. Thus, it is well known that hydrothermal reactions are, therefore, very important to study fields deeply related to the origin-of-life study. Furthermore, the importance of hydrothermal and solvothermal systems is now realized in both fundamental and practical areas. Here, our recent investigations are described for the development of real-time and in situ monitoring systems for hydrothermal reactions. The systems were primarily developed for the origin-of-life study, but it was also applicable to fundamental and practical areas. The present techniques are based on the concept that a sample solution is injected to a narrow tubing flow reactor at high temperatures, where the sample is rapidly heated up in a very short time by exposure at to a high-temperature narrow tubing flow reactor with a very short time scale. This enables millisecond to second time-scale monitoring in real time and/or in situ at temperatures of up to 400°C. By using these techniques, a series of studies on the hydrothermal origin-of-life have been successfully carried out.

Impact of torrefaction on syngas production from wood

Torrefaction is a way to treat biomass before transportation or thermochemical conversion. It can be used to increase the energy content of wood or to facilitate grinding. The purpose of this paper was to quantify the impact of such a treatment on the behaviour of wood during gasification by steam at high temperature to produce syngas. The aspects of both gas yields and reaction kinetics were considered. Beechwood was submitted both to light torrefaction and severe torrefaction, using a specially designed crossed fixed bed reactor. The initial wood and the torrefied woods were first characterised, then gasified in a new laboratory high-temperature entrained flow reactor (HT-EFR) at 1400 °C for 2 s in an atmosphere containing 20 vol% steam in N 2. The syngas produced was then analysed. The experiments were modelled using a thermo-dynamical equilibrium approach. It was confirmed that torrefaction decreased the O/C ratio. The quantity of syngas produced increased with the severity of the torrefaction. The equilibrium approach describes the results satisfactorily. Gasification experiments carried out at a lower temperature – 1200 °C – indicated that the chars from torrefied woods are less reactive towards steam than the char from wood.

Radicals from the Oxidative Pyrolysis of Tobacco

The fractional, oxidative pyrolysis of Bright tobacco was performed in an oxygen/nitrogen atmosphere containing from 0 to 20.4% of O2 over the temperature range of 200–510 °C in a specially constructed, high-temperature flow reactor system. The effect of the temperature and the concentration of oxygen in the reaction atmosphere on the generation of free radicals from Bright tobacco and two major components of Bright tobacco (polyphenols and cell wall biopolymers) were studied. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze for free radicals in the initially produced total particular matter (TPM) and in the gas phase. Two types of radicals were observed in the initially produced TPM: type I radicals characterized by a five-line EPR spectrum with an apparent g-value of ∼2.0064 that was tentatively assigned to a tyrosyl radical formed at lower temperatures from the cell wall biopolymer fraction of tobacco, and type II radicals characterized by a single-line EPR spectrum with g-factor ...

Nanoparticle synthesis completed with in situ catalyst preparation performed on a high-pressure high-temperature continuous flow reactor

The present communication reports a three-way strategy on utilizing a newly developed continuous high-pressure, high-temperature micro-fluidic reactor to synthesize and modify nanoparticles (NPs) and produce catalytically relevant materials in one flow. Well-defined platinum nanoparticles have been synthesized within a few seconds and in a highly controlled fashion. By changing the applied temperature, flow rate and the type of solvent, the size and the surface morphology of the resulting nanoparticles was changed and tuned on-the-fly. It was also shown that the primarily synthesized NPs can be successfully modified further by using them as seeds in the same flow from where they were formed, by applying the seeded growth method, which resulted in increased particle size and the formation of well-defined but randomly distributed shapes. Furthermore, after synthesizing, the Pt nanoparticles were adsorbed onto the surface of well-known support materials in the same flow to provide in situ production of commercially relevant Pt/SiO2 catalysts. The in situ prepared catalytically active materials were tested in the hydrogenation of cinnamaldehyde and showed high activity.

Formation of the Secondary Radicals from the Aging of Tobacco Smoke

The fractional pyrolysis of Bright tobacco was performed in a nitrogen atmosphere over the temperature range of 240−510 °C in a specially constructed, high-temperature flow reactor system. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the free radicals in the initially produced total particular matter (TPM) and in TPM after exposure to atmospheric, dry- or water-saturated air (argon). When the initially produced TPM was allowed to age, the formation of secondary radicals with an EPR g value of 2.0053 ± 0.0003 was observed. The rate of the formation of these radicals was found to depend dramatically upon the presence of water vapor in the exposure atmosphere. The secondary radicals were nearly undetectable in the water-saturated atmosphere and increased significantly by decreasing the water concentration by partial evacuation or purging with a dry air/argon atmosphere. The EPR spectra and the conditions of the formation of the observed secondary radicals were consistent with many aspects of oxygen-centered, semiquinone radicals formed from hydroxylated aromatic molecules, including hydroquinones and catechols, chemisorbed to metals or other electron-acceptor sites in the TPM. In conjunction with previous studies of primary radicals produced prior to aging of the tobacco, we believe that semiquinone-type radicals are largely produced in aged tobacco smoke and are at much lower concentrations in primary tobacco smoke.

Methane Partial Oxidation Catalyzed by Platinum and Rhodium in a High-Temperature Stagnation Flow Reactor

A series of measurements investigating the partial oxidation chemistry of methane and oxygen over platinum and rhodium foils was performed in a stagnation flow reactor at a pressure of 30 Torr. Pro...

Precursors of Radicals in Tobacco Smoke and the Role of Particulate Matter in Forming and Stabilizing Radicals

Known constituents of tobacco (cellulose, pectin, lignin, protein, chlorogenic acid, and rutin) were subjected to fractional pyrolysis over the temperature range of 240−510 °C in a specially constructed, high-temperature flow reactor system. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze for free radicals in the initially produced total particulate matter (TPM) and in TPM that was allowed to age with exposure to air and light. The TPM formed during pyrolysis of cellulose, pectin, and rutin did not contain any radicals, whereas radicals in the TPM of protein, lignin, and chlorogenic acid increased with increasing pyrolysis temperature. The nature of the EPR spectra of the initially formed radicals (primary radicals) depended on the chemical structure of the constituent and temperature of pyrolysis. New types of free radicals were observed after exposure of the TPM to light and air (secondary radicals), but the nature of the EPR spectra was remarkably similar for all constituents. Only chlorogenic acid produced TPM in which the concentration of radicals decreased with exposure to air. Mixtures of the constituents, proportional to their abundance in tobacco leaves, represented the yield of radicals in TPM at temperatures above 375 °C reasonably well, but not below this temperature, suggesting that (1) another, untested constituent in tobacco is responsible for radical formation or that (2) TPM from tobacco contains additional constituents that promote radical stabilization and/or formation.

Gd 2O 3:Eu 3+ phosphor particles processed through aerosol route

In this work, the influence of the Eu 3+ luminescence center concentration on the structural, morphological and spectroscopic properties of powders obtained by an aerosol method was studied. In the method, gadolinium and europium nitrate solutions were ultrasonically aerosolised and fed into a high-temperature (up to 1200 °C) tubular flow reactor to control the aerosol decomposition. During decomposition, the aerosol droplets undergo evaporation/drying, precipitation and thermolysis in a single-step continuous process. Spherical, solid, agglomerate-free, submicron-sized particles with the crystallite sizes below 20 nm have been obtained. In order to control the particle crystal structure and to establish the conditions for the stabilization of the low-temperature gadolinia cubic phase, process parameters such as synthesis temperature, droplet/particle residence time and annealing temperatures were varied. The particle morphology, phase and chemical structure were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and EDS. Structural changes (crystallite size and microstrains) after powders thermal treatment were carried out using the Koalariet-XFit program as the profile-matching tool. The results obtained and the mechanisms for ultrafine phosphor particle generation are discussed in terms of precursor chemistry, process parameters and luminescence properties.

Reactor system for the study of high-temperature short-time sintering of nanoparticles

A high-temperature short residence time flow reactor system has been realized for the investigation of the gas phase sintering kinetics of nanoparticles separated from all other synthesis mechanisms, e.g., chemical reaction, nucleation, coagulation and condensation. Major components are a hot-wall tubular reactor for the production of unsintered aggregates consisting of spherical primary particles in the size range 10–80 nm and a sintering reactor for the investigation of the sintering kinetics at well-defined temperature and residence time history. Therefore, rapid heating and quenching of the particles at the beginning and at the end of the reaction zone, respectively, is maintained. Main parameters in the sintering reactor are: temperatures up to 1873 K and residence times in the range 8–1000 ms. The reactor conditions are characterized by temperature profile measurements with a newly constructed suction thermocouple probe and by computational fluid dynamics simulations of the residence time distributions. Exemplary results of the sintering of silica nanoparticles obtained by transmission electron microscopy analysis are presented.

CS2 Formation in the Claus Reaction Furnace: A Kinetic Study of Methane−Sulfur and Methane−Hydrogen Sulfide Reactions

Improving the understanding of reaction kinetics of CS2 formation in the Claus plant front-end reaction furnace (RF) is a key step in developing strategies to reduce CS2 formation and, consequently, the environmental impact of Claus plants. Specifically, experiments were carried out in a high-temperature flow reactor with pressures of 101−150 kPa, temperatures of 800−1250 °C, and residence times of 90−1400 ms to study the kinetics of CH4−S2 and CH4−H2S reactions; these conditions are typical of those encountered in the Claus RF. The reaction between methane and sulfur was found to be very rapid, resulting in complete consumption of sulfur in less than 100 ms at 1100 °C with formation of CS2 and H2S as the primary sulfur-containing products. At higher temperature (>1000 °C), the produced H2S decomposes with a proportional increase in CS2 formation. A simple rate expression for CS2 formation was obtained, and a kinetic model was developed to describe H2S formation/consumption in the CH4−S2 system. In the CH...

Aerosol processing of fine Ag:(Bi,Pb)2223 composite particles

This paper represents an attempt in the obtaining of metal–ceramic composite precursor powders in the Ag:Bi-based superconductor system with uniform distribution of comprised phases through spray pyrolysis method. The process involves aerosol formation ultrasonically (800 kHz) from the urea-modified nitrates precursor solution (for the fixed cation ratio Bi:Pb:Sr:Ca:Cu=1.8:0.2:2:2:3 and for the Ag fraction of 20 wt.%) and control over the aerosol decomposition united with self-combustion of droplets in a high-temperature tubular flow reactor in the temperature range up to 820 °C. Following the initial attempts in providing of the 2223 phase high contents, particles were additionally calcined for 2 h in air and oxygen, at 825 and 810 °C respectively. Structure, morphology and compositional stoichiometry of synthesized powders were followed in accordance to various analysis methods (XRD, DTA, SEM and EDS).