Aerosol Flow Reactor Research Articles

Study of the dispersion behaviour of l-leucine containing microparticles synthesized with an aerosol flow reactor method

l-leucine containing particles having salbutamol sulphate or sodium chloride as a main component have been produced by an aerosol flow reactor method. In the method, aqueous solute droplets were transferred into a heated laminar flow reactor where droplet drying took place. The geometric number mean diameter (GNMD) of the produced particles varied between 0.50 and 1.01 μm. Amino acid l-leucine, due to its surface-active nature in water, formed the outer layer of the initial droplet and in the product composite salbutamol and NaCl powders. The morphology of the amorphous salbutamol particles changed from spherical to wrinkled and that of the crystalline NaCl particles from faceted to rounded but fractured due to incorporated l-leucine. These powders mixed with coarse lactose powder were tested in a novel deagglomeration apparatus where they experienced continuous turbulent flows with jet flow rates from 15 to 90 l/min intended to disperse powder agglomerates. In general, the incorporation of l-leucine improved dispersion efficiency as well as decreased dependence on dispersing flow rate of all the powders. The influence of l-leucine was observed particularly at low flow rates: The particle number concentration of the dispersed NaCl particles increased ∼ 19 times and that of the salbutamol particles ∼ 12 times with 20 wt.% of l-leucine at a flow rate of 15 l/min. Added l-leucine affected the dispersion of salbutamol particles more than that of NaCl particles due to different particle surface. Moreover, the salbutamol- l-leucine agglomerates were reduced to the primary particles at high flow rates. This was not observed for the NaCl- l-leucine agglomerates. Fine particle fractions (FPF, D ≤ 5 μm) of NaCl- l-leucine and salbutamol- l-leucine composite particles at a flow rate of 60 l/min increased, respectively, from 0.14 to 0.29 and 0.19 to 0.39 with increasing l-leucine content. Commercial micronized salbutamol powder gave an FPF of 0.15.

Attenuated Total Reflection Fourier Transform Infrared Spectroscopy to Investigate Water Uptake and Phase Transitions in Atmospherically Relevant Particles

In this study, attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy is used to investigate water uptake and phase transitions for atmospherically relevant particles. Changes in the ATR-FT-IR spectra of NaCl, NH(4) NO(3), (NH(4))(2)SO(4), Ca(NO(3))(2), and SiO(2) as a function of relative humidity (RH) are presented and discussed. For these various particles, water can (1) become adsorbed on the particle surface; and/or (2) become absorbed in the particle structure to form a hydrate salt; and/or (3) become absorbed by the particle to form a liquid solution. Spectral features and analyses that distinguish these various processes are discussed. For the salts that do undergo a solid to liquid phase transition (deliquescence), excellent agreement is found between the measurements made here with ATR-FT-IR spectroscopy, a relatively simple, inexpensive, and readily available analytical tool, compared to more expensive, elaborate aerosol flow reactor systems using tandem differential mobility analyzers. In addition, for particles that adsorb water, we show here the utility of coupling ATR-FT-IR measurements with simultaneous quartz crystal microbalance (QCM) measurements. This coupling allows for the quantification of the amount of water associated with the particle as a function of relative humidity (f(RH)) along with the spectroscopic data.

Fractal growth modelling of [formula omitted] nanoparticles

The kinetics of iodine oxide aerosol production and growth was studied in an aerosol flow reactor by the photolysis of I 2 in an excess of O 3 , at a temperature of 295 K and a total pressure of 1 atm. The time-resolved evolution of the particle size distribution was fitted using a model which assumes that the initial period of particle growth (in the free molecular flow regime) is dominated by collision-coalescence, maintaining spherical shape and compact structure. This leads to the formation of primary particles of about 3 nm radius, which trigger fractal (agglomerative) growth in the transition regime resulting in particle aggregates characterised by lower mass fractal dimensions ( D f ) in the range 2.2–2.5. Enhancement of the particle pair collision kernels due to competing van der Waals and hydrodynamic forces is treated within the model. The densities of the fractal aggregates are lower than that of the bulk material, recently identified as I 2 O 5 [Saunders, R. W., & Plane, J. M. C. (2005). Formation pathways and composition of iodine oxide ultrafine particles. Environmental Chemistry, 2, 299], as a result of internal void space within the aggregate structures.

Rapid nickel oxalate thermal decomposition for producing fine nickel metal powders

Abstract The global kinetics for the thermal decomposition of nickel oxalate within an aerosol flow reactor are studied by developing a one-dimensional particle phase model that describes the particle behavior within the reactor. The solid precursor is nickel oxalate with an average particle size of 12 μm. The particles are large enough in size for the gravitational force to cause slip between the particle and fluid phases, thus the particles pass through the reactor slightly faster than the gas phase. The particle residence times for the kinetic study range from 2–6 s for reactor temperatures of 695–767 K. First-order kinetics best fit the experimental conversion data. The decomposition reaction is interpreted as instantaneous nucleation of nano-sized product nickel, followed by two-dimensional growth of these nuclei, controlled by diffusion of product carbon dioxide.

Co‐synthesis of H2 and ZnO by in‐situ Zn aerosol formation and hydrolysis

AbstractSimultaneous synthesis of H2 and ZnO nanoparticles is investigated by steam‐hydrolysis of Zn vapor in a hot‐wall aerosol flow reactor with separated evaporation, cooling, and reaction zones. Superheated Zn vapor was carried by Ar into a tubular, quartz reactor where it was mixed and quenched by a superheated, equimolar H2O/Ar stream, resulting in Zn/ZnO nanoparticles and H2. The Zn(g) vapor was generated by electric heating of a Zn crucible whose weight was continuously monitored and compared to H2 production rate. The reactor was operated at 1 bar and 573–1273 K: above and below the Zn saturation vapor pressure suppressing and allowing, respectively, Zn aerosol formation by condensation taking place in parallel with the omnipresent ZnO formation by gas phase or surface hydrolysis of Zn. The process yielded up to 90% H2 conversion and nanoparticles with Zn and ZnO mean crystallite sizes of 100 and 40 nm, respectively, containing up to 80 wt % ZnO. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Low Pressure Aerosol Flow Reactor

In this work we report the development of a novel low pressure aerosol flow reactor for the determination of the kinetic parameters of fast heterogeneous processes. The experimental apparatus consists of a spray atomizer to introduce aerosols into a low pressure zone; a fast flow reactor for kinetic measurements and an IR spectrometer and mass spectrometer for concentration measurements. The surface area distribution and number density of the aerosol particles are determined from their infrared spectra and the decay kinetics are determined by monitoring the disappearance rates of the gas phase species (with a mass spectrometer) as a function of the aerosol properties. We report the application of this apparatus to the investigation of the uptake of acetone by liquid water aerosols (0.1–20 μ m diameter) at room temperature and a pressure of 35 Torr. These measurements yielded a value of the mass accommodation coefficient, α, of 3.6 − 2 + 3.1 × 10 − 3 .

A Scalable Turbulent Mixing Aerosol Reactor for Oxide-Coated Silicon Nanoparticles

A new, turbulent flow aerosol reactor is described that enables synthesis of uniformly sized aerosol nanoparticles during a residence time of a few milliseconds. The short residence time allows processing of high number concentration aerosols, in excess of 10^9 cm^(-3), to be processed with minimal coagulation, leading to an aerosol throughput approaching 10^(11) particles cm^(-3) s^(-1). Turbulent mixing speeds thermal and chemical transport beyond diffusional limits inherent in laminar flow reactors, providing the thermal energy to drive chemical reactions, coalescence, densification, and crystallization of particles. With enhanced transport, residence time in the reactor can be reduced, thus limiting coagulate particle growth while maintaining a high throughput of nonlayered or multilayered aerosol particles. The turbulence that enables rapid mixing is generated by dissipation of kinetic energy supplied to the reactor by high velocity gas jets. The apparatus described here increased the throughput by a factor of 100 above previous laminar flow reactors, and the induced fast mixing enables scale-up to much higher throughput. Characterization of particles by differential mobility analysis and transmission electron microscopy confirmed uniformity in size and composition.

Generation of Submicron Arizona Test Dust Aerosol: Chemical and Hygroscopic Properties

This article describes a submicron dust aerosol generation system based on a commercially available dust disperser intended for use in laboratory studies of heterogeneous gas–aerosol interactions. Mineral dust particles are resuspended from Arizona Test Dust (ATD) powder as a case study. The system output in terms of number and surface area is adjustable and stable enough for aerosol flow reactor studies. Particles produced are in the 30–1000 nm size range with a lognormal shape of the number size distribution. The particles are characterized with respect to morphology, electrical properties, hygroscopic properties, and chemical composition. Submicron particle elemental composition is found to be similar for the particle surface and bulk as revealed by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES), respectively. A significant difference in chemical composition is found between the submicron aerosol and the ATD bulk powder from which it was generated. The anionic composition of the water-soluble fraction of this dust sample is dominated by sulfate. Resuspended dust particles show, as expected, nonhygroscopic behavior in a humid environment. Small hygroscopic growth of about 1% (relative change in mobility diameter) was observed for 100 nm particles when the relative humidity (RH) was changed from 12 to 94%. Particles larger than 100–200 nm shrank about 1% once exposed to RH > 90%. This was interpreted as a restructuring of the larger agglomerates of dust to particles of smaller mobility diameter, under the influence of water vapor.

H2 production by Zn hydrolysis in a hot‐wall aerosol reactor

AbstractA novel process for hydrogen generation from water at high conversion is presented that is based on zinc hydrolysis as part of the two‐step water‐splitting thermochemical cycle of Zn/ZnO redox reactions. It encompasses formation of Zn nanoparticles by steam‐quenching a Zn(g) flow followed by in situ hydrolysis. The process is experimentally demonstrated at the laboratory scale using a tubular aerosol flow reactor featuring a Zn‐evaporation, a mixing and a reaction zone. In the reaction zone, operated at and just below the Zn(g) saturation temperature, Zn particles were formed and hydrolyzed with chemical conversion of up to 70%. The onset of H2 formation is traced to ZnO formation by surface growth along the reactor axis using X‐ray diffraction and microscopic analyses of Zn and ZnO particles collected on the reactor walls and effluents. © 2005 American Institute of Chemical Engineers AIChE J, 2005

In situ formation and hydrolysis of Zn nanoparticles for [formula omitted] production by the 2-step ZnO/Zn water-splitting thermochemical cycle

The production of solar hydrogen via the Zn/ZnO water-splitting thermochemical cycle consists of a 1st-step solar endothermic dissociation of ZnO and a 2nd-step non-solar exothermic hydrolysis of Zn. We report on a novel combined process for the efficient execution of the second step that encompasses the formation of Zn nanoparticles followed by their in situ hydrolysis for H 2 generation. The advantages of using Zn-nanoparticles are three-fold: (1) their inherent high specific surface area augments the reaction kinetics, heat transfer, and mass transfer; (2) their large surface to volume ratio favors complete or nearly complete oxidation; and (3) their entrainment in a gas flow allows for simple, continuous, and controllable feeding of reactants and removal of products. This combined process is experimentally demonstrated using a tubular aerosol flow reactor featuring Zn-evaporation, steam-quenching, and Zn / H 2 O -reaction zones. When the Zn-evaporation zone was operated at 1023 K and the Zn / H 2 O reaction zone was operated continuously just below the Zn(g) saturation temperature, Zn particles of 69 nm average crystallite size were formed and in situ hydrolyzed by up to 83% degree of chemical conversion, while the H 2 yield reached up to 70% after a single pass of H 2 O of 0.85 s residence time.

Size-Resolved Kinetic Measurements of Aluminum Nanoparticle Oxidation with Single Particle Mass Spectrometry

Aluminum nanoparticles are being considered as a possible fuel in advanced energetic materials application. Of considerable interest therefore is a knowledge of just how reactive these materials are, and what the effect of size on reactivity is. In this paper we describe results of size resolved oxidation rate using a recently developed quantitative single particle mass spectrometer (SPMS). Aluminum nanoparticles used were either generated by DC Arc discharge or laser ablation, or by use of commercial aluminum nanopowders. These particles were oxidized in an aerosol flow reactor in air for specified various temperatures (25-1100 degrees C), and subsequently sampled by the SPMS. The mass spectra obtained were used to quantitatively determine the elemental composition of individual particles and their size. We found that the reactivity of aluminum nanoparticles is enhanced with decreasing primary particle size. Aluminum nanoparticles produced from the DC Arc, which produced the smallest primary particle size (approximately 19 nm), were found to be the most reactive (approximately 68% aluminum nanoparticles completely oxidized to aluminum oxide at 900 degrees C). In contrast, nanopowders with primary particle size greater than approximately 50 nm were not fully oxidized even at 1100 degrees C (approximately 4%). The absolute rates observed were found to be consistent with an oxide diffusion controlled rate-limiting step. We also determined the size-dependent diffusion-limited rate constants and Arrehenius parameters (activation energy and pre-exponential factor). We found that as the particle size decreases, the rate constant increases and the activation energy decreases. This work provides a quantification of the known pyrophoric nature of fine metal particles.

04/02741 Rapid solar-thermal dissociation of natural gas inan aerosol flow reactor: Dahl, J. K. et al. Energy, 2004, 29, (5–6), 715–725

04/02741 Rapid solar-thermal dissociation of natural gas inan aerosol flow reactor: Dahl, J. K. et al. Energy, 2004, 29, (5–6), 715–725

Nanoparticles containing ketoprofen and acrylic polymers prepared by an aerosol flow reactor method

The purpose of this study was to outline the effects of interactions between a model drug and various acrylic polymers on the physical properties of nanoparticles prepared by an aerosol flow reactor method. The amount of model drug, ketoprofen, in the nanoparticles was varied, and the nanoparticles were analyzed for particle size distribution, particle morphology, thermal properties, IR spectroscopy, and drug release. The nanoparticles produced were spherical, amorphous, and had a matrix-type structure. Ketoprofen crystallization was observed when the amount of drug in Eudragit L nanoparticles was more than 33% (wt/wt). For Eudragit E and Eudragit RS nanoparticles, the drug acted as an effective plasticizer resulting in lowering of the glass transition of the polymer. Two factors affected the preparation of nanoparticles by the aerosol flow reactor method, namely, the solubility of the drug in the polymer matrix and the thermal properties of the resulting drug-polymer matrix.

Influence of the solvent composition on the aerosol synthesis of pharmaceutical polymer nanoparticles

Spherical, Eudragit L100 polymer nanoparticles with and without a ketoprofen drug were prepared by a novel aerosol flow reactor method. In this method, the polymer solution is sprayed to form nanosized droplets followed by the evaporation of a solvent. A purpose of the work was to explore the effect of solvent, solvent mixture, and co-solute (ketoprofen) on the formation of polymer particle, and particularly on particle morphology. The solvents used, i.e. ethanol, THF, toluene, and water, were selected according to their vapor pressure and dissolution capability for the polymer. At the polymer concentration range from 0.2 to 1.5 g/l of the starting solution, the geometric number mean diameters (GMD) of the particles increased from 75 to 130 nm and from 65 to 100 nm from the solutions of ethanol and THF, respectively. Particle morphology was observed by a scanning electron microscope (SEM). Particles changed from collapsed to irregular via spherical shape in the course of the decreasing solubility of the polymer in the medium. This is critically dependent on the solvent evaporation rate as well as the solute solubility, i.e. fast evaporative removal of solvent results in collapsed particles whereas low solubility results in irregular particles. Interplay between the vapor pressure of the solvents and the polymer solubility in the medium made possible to prepare particles with more complicated structures such as shriveled and blistery structures. The particle morphology as detected by SEM did not change when 10 wt.% of ketoprofen was added to the precursor solution.

04/01115 Sensitivity analysis of the rapid decomposition of methane in an aerosol flow reactor: Dahl, J. et al. International Journal of Hydrogen Energy, 2004, 29, (1), 57–65

04/01115 Sensitivity analysis of the rapid decomposition of methane in an aerosol flow reactor: Dahl, J. et al. International Journal of Hydrogen Energy, 2004, 29, (1), 57–65

A numerical investigation of aerosol dynamics in a wall-less reactor

This paper describes a numerical investigation of aerosol formation during silane decomposition in a wall-less reactor. The wall-less reactor is amenable to numerical investigation because the homogeneous chemical reactions leading to the formation of solid particles are isolated from heterogeneous effects, such as occur at the walls of a laminar flow aerosol reactor. The flow/heat transfer and gas-phase chemical kinetics are simulated utilizing separate one-way coupled models. The aerosol dynamics model is based on a simplified sectional model originally developed by Okuyama et al. This model is modified to allow for the simulation of particle growth via condensation. Simulations have been performed which indicate that particle growth via condensation may be an important process. Additionally, the effects of total reactor pressure, temperature and inlet silane concentration on the dynamics of the aerosol population have been investigated. Conditions which result in the formation of larger and more numerous particles have been identified.

Overall Kinetics of Heterogeneous Elemental Mercury Reactions on TiO2 Sorbent Particles with UV Irradiation

The kinetics of gas-phase elemental mercury (Hg0) oxidation on titania particle surfaces in the presence of UV irradiation was established. Overall reaction orders with respect to the gas-phase mercury concentration (α) and the UV intensity (β) were found to be 1.4 ± 0.1 and 0.35 ± 0.05 for the differential bed reactor, whereas values of α and β were 1.1 ± 0.1 and 0.39 for the aerosol flow reactor (AFR). While the values are similar, the AFR results are more representative of the practical sorbent process. In the low-temperature range ( 110 °C), an increase of the temperature resulted in a decrease of the overall reaction rate, indicating an adsorption-controlled process.

Polymeric drug nanoparticles prepared by an aerosol flow reactor method.

Our purpose was to study the possibility of using a novel method, namely, aerosol flow reactor method, for the preparation of drug-containing nanoparticles with varying amounts of drug and polymer. The physical properties of the prepared nanoparticles were analyzed. The nanoparticle size distributions were measured using differential mobility analyzer. The structure of the prepared nanoparticles was assessed by x-ray diffraction, differential scanning calorimetry, and electron microscopy. Drug release from the nanoparticles was analyzed. The spherical particles produced showed a unimodal and lognormal size distribution, and the geometric number mean size of the nanoparticles could be varied between 90 and 200 nm. When the amount of drug in the polymeric matrix was small, the nanoparticles had a homogeneous, amorphous structure. Drug crystals were formed when the amount of drug was increased over the solubility limit of the drug into the polymer. The amounts of drug and polymer controlled the drug release from the nanoparticles. The aerosol flow reactor method was found to be able to produce homogeneous amorphous matrix-type nanoparticles that can directly be collected as dry powder.

Rapid solar-thermal dissociation of natural gas in an aerosol flow reactor

A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to hy drogen (H 2) and carbon black at high rates. Concentrated sunlight approaching 10 kW heats a 9.4 cm long×2.4 cm diameter graphite reaction tube to temperatures ~2000 K using a 74% theoretically efficient secondary concentrator. Pure methane feed has been dissociated to 70% for residence times less than 0.1 s. The resulting carbon black is 20–40 nm in size, amorphous, and pure. A 5 million (M) kg/yr carbon black/1.67 M kg/yr H 2 plant is considered for process scale-up. The total permanent investment (TPI) of this plant is $12.7 M. A 15% IRR after tax is achieved when the carbon black is sold for $0.66/kg and the H 2 for $13.80/GJ. This plant could supply 0.06% of the world carbon black market. For this scenario, the solar-thermal process avoids 277 MJ fossil fuel and 13.9 kg-equivalent CO 2/kg H 2 produced as compared to conventional steam-methane reforming and furnace black processing.

Preparation of cobalt nanoparticles by hydrogen reduction of cobalt chloride in the gas phase

Cobalt nanoparticles were produced by the hydrogen reduction of cobalt chloride vapor in a multistage tubular aerosol flow reactor. Reaction zone temperature, preheating temperature, mole fractions of CoCl 2 and H 2, and residence time were considered as key process variables for the control of particle size and size distribution. Ranging from 50 to 78 nm in average diameter, cobalt nanoparticles with narrow size distributions were synthesized throughout our experiments. All of the considered process variables affected the particle size and size distribution in the synthesis of cobalt nanoparticles. As the reaction zone temperature and the CoCl 2 mole fraction increased, the average particle diameter increased. But the average particle diameter decreased as the residence time of reactants increased.