An Experimental Study of the Synthesis of Ultrafine Titania Powder in Plasmachemical Flow-Type Reactor

2014 ◽  
Vol 12 (1) ◽  
pp. 377-396 ◽  
Author(s):  
E. V. Kartaev ◽  
V. P. Lukashov ◽  
S. P. Vashenko ◽  
S. M. Aulchenko ◽  
O. B. Kovalev ◽  
...  
Keyword(s):  
Crystal Lattice ◽  
Reaction Zone ◽  
Gas Flow ◽  
Flow Reactor ◽  
Powder Synthesis ◽  
New Approach ◽  
Titania Powder ◽  
Reactor Length ◽  
Powder Properties ◽  
Chloride Method

Abstract Methods for controlling the synthesis of the submicron (including nanosized) powder of titanium dioxide (titania, TiO2) in a setup with a plasmachemical flow reactor were investigated. The synthesis of titania particles from gaseous titanium tetrachloride (TiCl4) in the plasmachemical reactor by the chloride method was experimentally studied. The processes of formation and growth of particles depending on the type of the plasma-forming gas, flow rates of TiCl4; and the quenching gas (air), reactor length, and mean-mass temperature in the reaction zone were considered. When using nitrogen as heat-carrying gas, a new approach of titania powder synthesis based on combining of reaction zone and quenching zone has been applied. Under these non-equilibrium conditions and substantial temperature gradients, this method enabled us to synthesize reproducibly ultrafine titania powders (30–50 nm) with a high content (80–87%) of metastable anatase crystal lattice. The results reveal that the powder properties can be efficiently controlled, i.e., one setup can produce titania with a required particle size and a type of the crystal lattice: anatase (A) or rutile (R). The experimental data are found to agree well with the results of numerical calculations.

scholarly journals Preparation of isocyanates by carbamates thermolysis on the example of butyl isocyanate

2019 ◽  
Vol 58 (4) ◽  
pp. 40-47
Author(s):  
Ratmir R. Dashkin ◽  
◽  
Dmitry A. Gordeev ◽  
Khusrav Kh. Gafurov ◽  
Sergey N. Mantrov ◽  
...  
Keyword(s):  
Gas Phase ◽  
High Performance ◽  
Gas Flow ◽  
Flow Reactor ◽  
Packed Column ◽  
Biologically Active ◽  
Dibutyltin Dilaurate ◽  
Reaction Products ◽  
Uv Detector ◽  
Laboratory Setup

Butyl isocyanate is widely distributed as a precursor for the production of a number of biologically active substances: fungicides, preservatives, insecticides, personal care products, etc. Nowadays, there are a number of methods for the preparation of isocyanates, which can be divided into liquid phase and gas phase. One of the perspective methods for the production of isocyanates is the thermolysis of carbamate and/or the actions of various reaction activating agents, accompanied by the elimination of alcohol, but this process is reversible, which greatly complicates its use in industry. The paper presents the results of studies of non-catalytic thermal decomposition of N-alkylcarbamates with the formation of alkylisocyanates on the example of butylisocyanate in the gas phase, flow reactor in a wide temperature range (200 to 450 °C). In addition, a series of experiments was carried out using a catalyst, dibutyltin dilaurate, in order to reduce the thermolysis temperature and increase the yield of the final product. To implement the isocyanate production process, an experimental laboratory setup, consisting of a gas flow meter (argon) regulator, a packed column (for heating) and a sorption solution tank, was developed and tested. The thermolysis of N-n-butylcarbamate was carried out in two variations: the preparation of an individual n-butylisocyanate and the passage of reaction products through a sorption solution linking the n-butyl isocyanate to N-n-butyl-N '-(1-phenylethyl)urea, which allows to estimate the yield of the target n-butylisocyanate without additional losses. The analysis of the obtained substances was carried out by high performance liquid chromatography with a UV detector (target product) and a mass detector (analysis of by-products). According to the results of research, a modification of the laboratory facility was proposed, as well as n-butylisocyanate was obtained with a yield of 49% on the basis of a new technique.

Flow Structure and Heat Transfer in Stagnation Flow CVD Reactor

2010 ◽  
Author(s):  
Nasir Memon ◽  
Yogesh Jaluria
Keyword(s):  
Heat Transfer ◽  
Flow Structure ◽  
Atmospheric Pressure ◽  
Gas Flow ◽  
Flow Reactor ◽  
Chemical Vapor ◽  
Design Parameters ◽  
Stagnation Flow ◽  
Inlet Length ◽  
The Impact

An experimental study is undertaken to investigate the flow structure and heat transfer in a stagnation flow Chemical Vapor Deposition (CVD) reactor at atmospheric pressure. It is critical to develop models that predict flow patterns in such a reactor to achieve uniform deposition across the substrate. Free convection can negatively affect the gas flow as cold inlet gas impinges on the heated substrate, leading to vortices and disturbances in the normal flow path. This experimental research will be used to understand the buoyancy-induced and momentum-driven flow structure encountered in an impinging jet CVD reactor. Investigations are conducted for various operating and design parameters. A modified stagnation flow reactor is built where the height between the inlet and substrate is reduced when compared to a prototypical stagnation flow reactor. By operating such a reactor at certain Reynolds and Grashof numbers it is feasible to sustain smooth and vortex free flow at atmospheric pressure. The modified stagnation flow reactor is compared to other stagnation flow geometries with either a varied inlet length or varied heights between the inlet and substrate. Comparisons are made to understand the impact of such geometric changes on the flow structure and the thermal boundary layer. In addition, heat transfer correlations are obtained for the substrate temperature. Overall, the results obtained provide guidelines for curbing the effects of buoyancy and for improving the flow field to obtain greater film uniformity when operating a stagnation flow CVD reactor at atmospheric pressure.

A New Modeling Approach to Reacting Dispersed Flow in Smelting Cyclones

2000 ◽  
Author(s):  
M. Modigell ◽  
M. Weng
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Gas Flow ◽  
Equilibrium Calculation ◽  
New Approach ◽  
Reaction Progress ◽  
Numeric Simulation ◽  
Thermodynamic Equilibrium Calculation ◽  
Simulation Results ◽  
Comparison With Experimental Data

Abstract The present paper proposes a new approach to analyse the conversion of complexly composed particles that are dispersed in a cyclone gas flow at high temperatures. The numeric simulation of flow field and particle trajectories is coupled with a thermodynamic equilibrium calculation which describes the particle reaction progress. First simulation results and the comparison with experimental data are shown in this paper.

scholarly journals Oxidative Dehydrogenation of Propane over Vanadium-Containing Faujasite Zeolite

Molecules ◽  
2020 ◽  
Vol 25 (8) ◽  
pp. 1961 ◽  
Author(s):  
Małgorzata Smoliło ◽  
Katarzyna Samson ◽  
Ting Zhou ◽  
Dorota Duraczyńska ◽  
Małgorzata Ruggiero-Mikołajczyk ◽  
...  
Keyword(s):  
Oxidative Dehydrogenation ◽  
Gas Flow ◽  
Flow Reactor ◽  
Fixed Bed ◽  
Oxidative Dehydrogenation Of Propane ◽  
Reaction Products ◽  
Promising Alternative ◽  
Vis Spectroscopy ◽  
Gas Flow Reactor ◽  
Faujasite Zeolite

Oxidative dehydrogenation (ODH) of light alkanes to olefins—in particular, using vanadium-based catalysts—is a promising alternative to the dehydrogenation process. Here, we investigate how the activity of the vanadium phase in ODH is related to its dispersion in porous matrices. An attempt was made to synthesize catalysts in which vanadium was deposited on a microporous faujasite zeolite (FAU) with the hierarchical (desilicated) FAU as supports. These yielded different catalysts with varying amounts and types of vanadium phase and the porosity of the support. The phase composition of the catalysts was confirmed by X-ray diffraction (XRD); low temperature nitrogen sorption experiments resulted in their surface area and pore volumes, and reducibility was measured with a temperature-programmed reduction with a hydrogen (H2-TPR) method. The character of vanadium was studied by UV-VIS spectroscopy. The obtained samples were subjected to catalytic tests in the oxidative dehydrogenation of propane in a fixed-bed gas flow reactor with a gas chromatograph to detect subtract and reaction products at a temperature range from 400–500 °C, with varying contact times. The sample containing 6 wt% of vanadium deposited on the desilicated FAU appeared the most active. The activity was ascribed to the presence of the dispersed vanadium ions in the tetragonal coordination environment and support mesoporosity.

Influence of the Time-Temperatur-Profile on Powder Characteristics of Nanocrystalline Anatase (TiO2) produced by Chemical Vapor Synthesis

2007 ◽  
Vol 1056 ◽  
Author(s):  
Ruzica Djenadic ◽  
Sankhanilay Roy Chowdhury ◽  
Marina Spasova ◽  
Andreas Gondorf ◽  
Erdal Akyildiz ◽  
...  
Keyword(s):  
Gas Flow ◽  
Flow Reactor ◽  
Chemical Vapor ◽  
Titanium Isopropoxide ◽  
Degree Of Crystallinity ◽  
Chemical Vapor Synthesis ◽  
Nanocrystalline Particles ◽  
Powder Characteristics ◽  
Gas Flow Reactor ◽  
Nanocrystalline Anatase Tio2

ABSTRACTChemical Vapor Synthesis (CVS) is the conversion of molecular species into nanocrystalline particles by chemical reactions in a gas flow reactor. Pure anatase nanoparticles are generated in a hot wall reactor from titanium isopropoxide using different time-temperature-profiles. The time-temperature-profile (T(t)-profile) in the gas phase of the reactor has a profound influence on the particle characteristics such as particle microstructure and surface chemistry and, therefore, on the quality of the powder consisting of nanocrystalline particles. In this study a simple reaction-coagulation-sintering model (CVSSIN) was used to predict influence of the T(t)-profile on the powder characteristics. The as-synthesized anatase powders show a very high degree of crystallinity, primary particle of about 10 nm sizes and a low degree of agglomeration.

Influence of gas flow rate and reactor length on NO removal using pulsed power

2001 ◽  
Vol 29 (4) ◽  
pp. 592-598 ◽  
Author(s):  
T. Namihira ◽  
S. Tsukamoto ◽  
D. Wang ◽  
H. Hori ◽  
S. Katsuki ◽  
...  
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Pulsed Power ◽  
Gas Flow Rate ◽  
No Removal ◽  
Reactor Length

A New Approach to Gas Flow in Capillary Systems

1953 ◽  
Vol 57 (1) ◽  
pp. 35-40 ◽  
Author(s):  
R. M. Barrer
Keyword(s):  
Gas Flow ◽  
New Approach

scholarly journals Synthesis of Silicon Nanoparticles in a Novel CO2 Laser Pyrolysis Reactor With an Elongated Reaction Zone

2020 ◽  
Author(s):  
Seok-Ho Maeng ◽  
Hakju Lee ◽  
Seongbeom Kim
Keyword(s):  
Reaction Zone ◽  
Large Scale ◽  
Gas Flow ◽  
Silicon Nanoparticles ◽  
Nanoparticle Synthesis ◽  
Average Diameter ◽  
Laser Pyrolysis ◽  
Pyrolysis Reactor ◽  
The Masses ◽  
Focusing Lens

Abstract We demonstrated silicon nanoparticle synthesis using a novel CO2 laser pyrolysis reactor. The reactor was designed to have an elongated reaction zone more than 10 times longer than conventional laser pyrolysis systems. Such elongation was achieved by aligning the laser beam and precursor gas stream. SiH4 gas was used to synthesize the silicon nanoparticles. The yield of the nanoparticles was 40.9%, as calculated by comparing the masses of the synthesized nanoparticles and precursor gas used. Silicon nanoparticles synthesized by using a typical reactor with identical gas flow rate conditions and without a focusing lens had a nanoparticle yield of 1.7%, which was far smaller than for the new reactor. The average diameter of as-synthesized silicon nanoparticles was 26.7 nm. Considering that high power CO2 lasers are often used for large scale nanoparticle production by laser pyrolysis, our proposed reactor serves as a proof of concept that demonstrates its potential for large scale nanoparticle synthesis.

Aerosol synthesis of AlN by nitridation of aluminum vapor and clusters

1995 ◽  
Vol 10 (3) ◽  
pp. 512-520 ◽  
Author(s):  
Sotiris E. Pratsinis ◽  
Guizhi Wang ◽  
Siddhartha Panda ◽  
Theresa Guiton ◽  
Alan W. Weimer
Keyword(s):  
Crystallite Size ◽  
Flow Rate ◽  
Gas Flow ◽  
Flow Reactor ◽  
Gas Flow Rate ◽  
Surface Areas ◽  
Specific Surface Areas ◽  
Reactor Temperature ◽  
Direct Nitridation ◽  
Increasing Temperature

Aluminum nitride (AlN) powders were produced in an aerosol flow reactor by direct nitridation of aluminum vapor with ammonia and nitrogen in flowing argon. In the presence of excess NH3, pure AlN powders were obtained from 1400 to 1873 K. These powders had higher specific surface areas than commercially available AlN powders. The effects of reactor temperature and gas flow rate on AlN purity, yield, and grain and crystallite size were investigated. The BET grain diameter of AlN increased as the process temperature increased, indicating sintering controlled particle formation and growth. Both the crystallite size and the BET grain size of pure AlN powders slightly decreased as ammonia flow rate was increased. Increasing temperature and flow rate increased the AlN yield.

Origin of the multi-exponential decay dynamics in light-emitting silicon nanocrystals

2004 ◽  
Vol 832 ◽  
Author(s):  
Cécile Reynaud ◽  
Olivier Guillois ◽  
Nathalie Herlin-Boime ◽  
Gilles Ledoux ◽  
Friedrich Huisken
Keyword(s):  
Exponential Decay ◽  
Silicon Nanocrystals ◽  
Gas Flow ◽  
Flow Reactor ◽  
Particle Density ◽  
Nanocrystalline Silicon ◽  
Light Emitting ◽  
Stretched Exponential ◽  
Film Density ◽  
Exponential Law

ABSTRACTLight-emitting silicon nanocrystals (nc-Si) have attracted much interest due to their importance for optoelectronic devices. Electron hole recombination in a quantum confined system is generally considered as the theoretical frame explaining the photoluminescence (PL) origin. However, there is still a living debate, in particular regarding the PL decay dynamics. The decay is not single exponential and decay curves described by a stretched exponential law were systematically reported for all types of nanocrystalline silicon. The origin of this multi-exponential decay is often attributed to migration effects of the excitons between nanocrystals. In contrast to these approaches, the absence of carrier hopping has been demonstrated experimentally in porous silicon. In order to elucidate this question, specific samples were prepared, consisting in deposits made from gas phase grown silicon nanocrystals with different particle density. The nanoparticles were synthesized by laser pyrolysis of silane in a gas flow reactor, extracted as a supersonic beam, size-selected, and deposited downstream as films of variable densities by changing the deposition time. The nanoparticle number densities were determined by atomic force microscopy. Time-resolved photoluminescence measurements on these films were carried out as a function of the film density and at different PL wavelengths. The reported results showed photoluminescence properties independent of the film density. Even in the very low density film (∼4*109 particles/cm2) where nanoparticles are completely isolated from each other, the decay kinetics corresponds to a multi-exponential law. This means that exciton migration alone cannot explain the stretched exponential decay. Its origin must be linked to an intrinsic characteristic of the nc-Si particle. In this paper, the experimental results are described in more details and compared to the theoretical predictions available in the frame of the quantum confinement model. Then, the possible origins of the multi-exponential character of the decay dynamics is discussed, and the particular properties of the PL in indirect band-gap semiconductors emphasized.

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