摘要:

AbstractThe combined phenomena of SiO2particle generation and deposition were analyzed theoretically and experimentally in a tubular flow reactor. The deposition tube was directly connected to a high‐temperature tube furnace reactor by a flange and the deposition characteristics of SiO2particles were measured. The SiCl4conversion and deposition efficiencies were calculated, solving the mass and energy balance equations and the aerosol dynamic equation in the tubular flow reactor. Effects of process variables such as furnace set temperature, inlet SiCl4concentration and total gas‐flow rate were examined. Experimental results agreed closely with theoretical prediction. Effects of natural convection are significant at low gas‐flow rate. Tube wall temperature profiles inside the deposition tube were proposed for uniform coating of SiO2particles. The study shows that the tube furnace reactor can be used to coat the inside wall of the deposition tube with ultrafine particles uniformly by adjusting tube wall temperature pro

ISSN:0001-1541    

DOI:10.1002/aic.690431312

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe chemical reaction mechanism and fine particle generation during atmospheric pressure chemical vapor deposition with the tetraethylorthosilicate/ozone system were studied experimentally and theoretically for a flow‐type vertical‐tube reactor. For the thermal decomposition of ozone, numerical simulations obtained using reaction rate constants for a batch reactor explained experimental results well. The activation energy of chemical reaction between TEOS and the oxygen radical, O· was evaluated from the particle generation rate (2.18 × 105J/mol). Particle population balance equations, based on the simplified reaction coagulation model, were coupled with equations for the thermal decomposition of ozone and chemical transformations of TEOS and solved numerically. Calculation results for particle number concentration and size agreed with experimental results for temperatures below 430 K. For temperatures above 430 K measured concentrations agreed well with calculated values, but measured sizes were significantly smaller than calculated sizes. Thermal desorption spectra from particles generated at 423 K revealed a peak from C2H4at ∼ 800 K, presumably from ethoxy groups. This emission explains, at least in part, the observed decrease in particle size at high tempe

ISSN:0001-1541    

DOI:10.1002/aic.690431313

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractExperiments were conducted to test the theory of nucleation‐controlled growth of spherical particles in a turbulent jet. Dibutyl phthalate (DBP) particles were formed in a bench‐scale jet apparatus with nozzle diameters 0.235 cm and 0.375 cm. Size distributions and number concentrations of the particles were measured at different DBP vapor concentrations, jet velocities, and positions. There is evidence that the DBP particle nucleation was confined to the shear layer of the jet and that the particles grew by condensation as they moved away from the nozzle. Trends in the data suggest that for low rates of particle formation in jets, the final aerosol concentration can be predicted from simple scaling l

ISSN:0001-1541    

DOI:10.1002/aic.690431314

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractVapor‐phase synthesis of ultrafine TiO2particles was investigated experimentally in the simultaneous hydrolysis and oxidation of TiCl4. Experiments were made for the control of particle size, size distribution and phase composition of ultrafine TiO2particles with the preheating of reactants. The molar ratio of H2O/TiCl4was adopted as a variable for the control of particle size and size distribution in various reaction systems such as TiCl4–H2O, TiCl4–H2O–O2, and TiCl4–H2O–air. As the molar ratio of H2O/TiCl4increased from 2 to 12, the average particle size decreased from 45 nm to 19 nm, and the rutile content of TiO2powders increased from 21% to 54% in the TiCl4–H2O system. Changes in the average particle size were the same in the TiCl4–H2O–O2system as in the TiCl4–H2O system, but particle‐size distributions were narrower in the TiCl4–H2O–O2system. The same tendencies of average particle size, size distribution and rutile content were also found in the TiCl4–H2O–air system. A high production rate of ultrafine TiO2particles was obtained at the condition of high mole fraction of TiCl4and low gas‐flow rate in the presence of water va

ISSN:0001-1541    

DOI:10.1002/aic.690431315

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractParameters and/or processes responsible for the stability of catalyst supports and ceramic membranes are discussed. Two major parameters/processes were identified which are responsible for the stability of sol‐gel derived nanostructured oxides at elevated temperatures. They are metastable‐to‐stable phase transformation and structure and packing of primary particles within the aggregate. Based on these observations, strategies to develop thermostable nanostructured oxides for high‐temperature membrane and catalyst applications are discussed by taking titania and titania‐alumina nanocomposites as

ISSN:0001-1541    

DOI:10.1002/aic.690431316

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractAsymmetric membranes consisting of palladium, ruthenium and platinum deposited on the surface or inside the pores (average size, 200 nm) of a tubular alumina membrane were prepared by the chemical vapor deposition (CVD) technique. Sublimation and decomposition temperatures of their acetylacetonato complexes used as metal sources for CVD were important factors in preparing the membranes selected for hydrogen separation. Among the membranes prepared by CVD, the palladium membrane gave the highest flux of hydrogen and was about 1.6 times higher than a dense palladium membrane with a thickness of 4.5 μm prepared by an electroless plating technique. The hydrogen permeation through the membranes prepared by CVD are related to the surface diffusion of spillover hydrogen

ISSN:0001-1541    

DOI:10.1002/aic.690431317

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractMordenite (MOR) and ferrierite (FER) membranes without any pinhole and crack were synthesized by a vapor‐phase transport method. The permeance of H2, He, CH4, N2, O2and CO2was determined at 290–400 K, which showed minimum with increasing temperatures for most cases. In the parallel diffusion model was proposed, molecules adsorbed in a micropore are assumed to diffuse in parallel through the central region of the pore and along the wall region of the pore. This parallel diffusion model accounts for the effect of pore size of MOR and FER on the permeation and expresses the experimental data well. The interaction between gas molecules and pore walls are evaluated for each

ISSN:0001-1541    

DOI:10.1002/aic.690431318

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractA series of ion‐conducting perovskites of the form [La1‐xAx] [Co0.2Fe0.8] O3‐δ(x = 0.4, 0.6 for A = Sr; × = 0.8 for A = Ba) were investigated for their use as a catalytic membrane for the oxidative coupling of methane (OCM). A‐site cations consisting of La0.4Sr0.6and La0.2Ba0.8produce materials with the highest oxygen fluxes and result in C2+selectivities of 50% at 1,098 K, which are significantly higher than those achieved with a powdered catalyst in a packed‐bed reactor configuration. Selectivities in these materials appear to be limited by high oxygen ion recombination rates that compete for oxygen with the desired coupling reaction(s). The results also indicate that oxygen fluxes are not limited by diffusion, but by surface exchange rates at the oxygen‐lean side of the membrane. The study on stability of these materials showed that all three perovskites could be reduced in a pure methane or ethane stream at 1,023 K, but they were totally stable under reaction conditions where oxyg

ISSN:0001-1541    

DOI:10.1002/aic.690431319

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe partial oxidation of methane to synthesis gas (syngas, CO + H2) was performed in a mixed‐conducting perovskite dense membrane reactor at 850°C, in which oxygen was separated from air and simultaneously fed into the methane stream. Steady‐state oxygen permeation rates for La1‐xA′xFe0.8Co0.2O3‐δperovskite membranes in nonreacting air/helium experiments were in the order of A′x= Ba0.8>Ba0.6>Ca0.6>Sr0.6. Deep oxidation products were obtained from a La0.2Ba0.8Fe0.8Co0.2O3–δdisk‐shaped membrane reactor without catalyst, with a 4.6% CH4inlet stream. These products were further reformed to syngas when a downstream catalytic bed was added. Packing the 5% Ni/Al2O3catalyst directly on the membrane reaction‐side surface resulted in a slow fivefold increase in O2permeation, and a fourfold increase in CH4conversion. XRD, EDS, and SEM analyses revealed structure and composition changes on the membrane surfaces. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was oper

ISSN:0001-1541    

DOI:10.1002/aic.690431320

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractDense intermetallic and ceramic (alumina based) coatings can be formed in situ during simultaneous combustion synthesis and densification in the field of centrifugal forces. Both microstructure and composition of alumina‐based coatings formed during alumino‐thermal reduction of oxides can be altered by an introduction of additives such as ZrSiO4, SiO2, Na2CrO4, and carbon. The activation energy and frequency factor for the Ni‐Al reacting system consisting of equal atomic amounts of Ni and Al powders with an average particle size of 5 μm were measured using a nonisothermal technique, which were equal to 1.05 × 105J/mol and 1.017 × 108s−1, respectively. A mathematical model of in‐situ densification of a single‐phase combustion product (NiAl) in the field of centrifugal forces was develope

ISSN:0001-1541    

DOI:10.1002/aic.690431321

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY