Charles H. Byers

Effect of solvent on the homogeneous precipitation of titania by titanium ethoxide hydrolysis

Abstract A method has been developed for studying and controlling the growth of colloidal titania by titanium ethoxide hydrolysis in ethanol, 1-butanol, and tert-butyl alcohol. Particle growth was followed from approximately 0.02 to 1.0 μm by dynamic laser-light scattering. Evaluation of the particle growth kinetics indicated that growth was controlled by surface phenomena and that the type of precipitate formed was affected by the solvent. Electron microscopy showed that monodisperse spherical particles were formed in the solvents ethanol and 1-butanol. The precipitate that was formed in tert-butyl alcohol had no regular shape and was characteristic of uncontrolled homogeneous precipitation.

High-capacity pressurized continuous chromatograph

Abstract Multicomponent liquid chromatographic separations have been achieved by using a slowly rotating annular bed of sorbent material. The feed material is continuously introduced at a stationary point at the top of the bed, and eluent is allowed to flow everywhere else around the annulus. The rotation of the sorbent bed causes the separated components to appear as helical bands, each of which has a characteristic, stationary exit point; hence the separation process is truly continuous. The concept has been developed primarily on a 279-mm-diam by 0.6-m-long device with a 12.7-mm-wide annulus. The effects of annulus width and diameter have been studied using the same device with annulus widths up to 114.3 mm. With this largest width, approximately 96% of the area available within the outer cylinder is devoted to the rotating sorbent bed. Further annulus-width studies have been pursued on units with 89- and 445-mm diameters. These geometric extensions to the basic concept allow extremely large capacity i...

Continuous Chromatographic Separation of Fructose, Mannitol and Sorbitol

Abstract The separation of mixtures of fructose, mannitol and sorbitol by continuous annular chromatography on Dowex 50W-X8 has been investigated. Distribution and mass transfer coefficients of the three substances were obtained by batch chromatography. The influence of feed concentration and flow rate on these parameters were discussed. The separation was simulated numerically and compared with experimental data. With this procedure, the separation of mixtures of fructose, mannitol and sorbitol by continuous annular chromatography (CAC) was calculated in advance, using only batch data. Additionally, the influence of rotation rate, column loading, eluent flow rate and feed concentration on the resolution of the individual peaks were investigated. With these results, the operation parameters for an industrial application of the CAC for this separation problem were determined.

Probing the early-stage/rapid processes in hydrolysis and condensation of metal alkoxides

Understanding and control of the early-stage sol-gel reaction processes involving metal alkoxides are important to many advanced materials development and applications. In this work, Fourier transform infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS) were coupled with a specially designed, rapid flow-through mixing cell for monitoring such processes. The rapid, early-stage hydrolysis and condensation of zirconium n-butoxide in ethanol were chosen as the basis for a model system. FTIR was used to study soluble-species reaction kinetics, while the SAXS technique monitored in situ the solid-phase particle formation/growth (i.e., the nucleation and aggregation kinetics of polymeric clusters/particles). Monitoring the reactions and cluster/particle growth within a millisecond time regime was achieved. In addition, key parameters such as reaction time, concentration of base (i.e., quarternary tetramethyl ammonium hydroxide), temperature, water concentration, and alkoxide concentration were fully investigated in a continuous flow-through reactor.

Small-angle x-ray scattering studies of early-stage colloid formation by thermohydrolytic polymerization of aqueous zirconyl salt solutions

Early-stage processes involving the polymerization of zirconium species in aqueous solutions at elevated temperatures ({approximately}100{degree}C) as well as colloid formation were studied. Small-angle x-ray scattering (SAXS) data were analyzed via Guinier, {open_quotes}longrods,{close_quotes} and Porod plots to determine particle growth kinetics and morphology. Our SAXS data suggest that zirconium tetramers and octamers polymerize into larger clusters and elongated-rod-(or needle)-shaped primary particles, which have a length of a few nanometers and a radius of gyration of cross section between 4 and 5 {Angstrom}. Cube-shaped particles are aggregates of the needlelike primary particles. The transition from zirconium tetramer to a colloidal sol particle follows a mass-fractal growth (1{lt}fractal dimension, D{lt}3). {copyright} {ital 1999 Materials Research Society.}

Separation of metals by continuous annular chromatography with step elution

Abstract A continuous annular chromatograph (CAC) was used to separate dilute aqueous mixtures of iron and chromium salts using Dowex 50W-X8 as the sorbent. While an isocratic separation of the two species could be easily obtained, this mode of operation resulted in excessive dilution of the products. Introduction of a step in eluent concentration, however, permitted a much more efficient separation of the two metals. Separation of Fe3+ and Cr3+remained nearly complete but elution of the more strongly retained species (Cr3+) occurred over a much narrower angle and dilution of the product streams was significantly reduced or even eliminated in some cases. A theoretical model was developed to describe the operation of the continuous annular chromatograph with step elution. With the inclusion of significant dispersive factors (axial dispersion and film mass transfer resistance), the solution of the model equations provided an excellent prediction of the experimental CAC data. Similar improvements to the CAC ...

Mass Transport from Single Droplets in Imposed Electric Fields

Electric field effects on mass transfer involving droplets in a 2-ethyl-hexanol medium are studied. Single water droplets are observed under the influence of both steady and pulsed electric fields. Droplet oscillations result in the latter case, enhancing the continuous phase mass transfer coefficient. These data are compared with results from both nonoscillating mass transfer and theoretical models. 8 refs., 8 figs.

Preparative desalting of bovine serum albumin by continuous annular chromatography

Bovine serum albumin (BSA) was continuously desalted from alkaline salts (a mixture of sodium phosphate, sodium chloride and potassium chloride) using a size-exclusion gel as the stationary phase. An annular chromatograph was used to achieve a continuous mode of operation and therefore a reasonable throughput. Distribution and mass transfer coefficients of the substances as well as bed properties were obtained by batch chromatography. These separations were simulated mathematically applying an approximate linear chromatographic theory. It was shown experimentally and theoretically that the BSA and the salt solution could be recovered continuously in a purity higher than 98%. The influence of rotation rate on the resolution of the individual peaks was investigated.

Wall effects on flow past fluid spheres at finite Reynolds number : wake structure and drag correlations

Abstract Following the pioneering works of Leal and coworkers, a detailed report is made on the dynamics of recirculating wakes that form at finite Reynolds number Re due to vorticity accumulation at the rear of a fluid sphere that is either suspended in a tube by an upflowing fluid ( the fluidized drop problem ) or falling in a tube ( the falling drop problem ). The axisymmetric, steady flow of a Newtonian fluid past the fluid sphere is determined by finite element analysis using a consistent penalty formulation. By way of example, the flow past a fluid sphere that is falling in a tube for which the ratio of the tube radius to the drop radius 1 λ = 5 undergoes remarkable transitions when the ratio of the viscosity of the drop to that of the ambient fluid, κ, varies over a narrow range. When κ ≤ 2.75, no wake forms behind the sphere as Re increases. When 3 ≤ κ Re = Re c (1) , grows, and eventually disappears as Re rises above a certain amount Re c (2) . Remarkably, when κ = 3, these critical Reynolds numbers are as low as Re c (1) = 51 ± 1 and Re c (2) = 77 ± 1. When κ ≥ 10, it is shown by using as many as 46,000 velocity degrees of freedom that the detached eddy attaches to the drop when Re exceeds a critical value, Re ≥ Re c ∗ , which was heretofore unknown. Whereas only a single, large-primary-eddy is present inside the drop when Re c ∗ , a second but much smaller-secondary-eddy also forms inside the drop upon attachment. Two new correlations are developed that account for the effects of a tube wall and finite fluid inertia on drag for fluidized and falling droplets. Moreover, in contrast to related correlations of others for fluid spheres that are placed in an infinite expanse of ambient fluid, the new correlations are valid over the entire range of Reynolds numbers considered.

The synthesis of metal hydrous oxide particles by multiphase electrodispersion

Abstract A multiphase electrodispersion precipitation reactor called the electric dispersion reactor (EDR) was developed to synthesize ultrafine particles for the production of precursor powders of advanced ceramic materials. A pulsed electric field is employed to create dispersions of micrometer- and submicrometer-scale conducting (aqueous-based) drops in non-conducting (organic) liquids. Species initially dissolved in the organic phase diffuse into the aqueous droplets containing the other reagents. Reaction ensues, leading immediately to precipitation and gelation in the aqueous droplets. The EDR has produced 0.1–5 μm particles of silica, alumina, zirconia, yttria, and composite hydrous oxide particles from metal alkoxide and metal salt precursors. Also considered is the application of the EDR to the control and modification of the morphological characteristics of these particles, with illustrative examples.