An-Najah Staff

The preparation of dilute aqueous silicone oil emulsions has been investigated with particular attention to the effect of oil viscosity (0.49–350mPa s), impeller selection (equal diameter Sawtooth and pitched blade turbines) and the method of addition of the oil. Emulsification was found to be sensitive to how the oilwas added to the vessel with narrower drop size distributions and smaller Sauter mean diameters, d32, obtained when the oil was injected into the impeller region. The equilibrium values were also attained in a shorter time with the equilibrium d32 ∝We−0.6. For addition of the oil to the surface the relationship was weaker with equilibrium d32 ∝We−0.4. The viscosity group was particularly useful in describing the behaviour of equilibrium particle sizes for different viscosity oils and also for viscosity changes arising from different process temperatures. An unexpected result is that the Sawtooth impellor proved to be more energetically efficient at drop break-up producing smaller droplets than the Pitched Bade Turbine. This result is particularly interesting since the power number for the latter is larger and therefore for equivalent operating conditions should produce smaller drop sizes. We suggest that one possible reason is that the local shear rates for the Sawtooth impellor are larger. Another possible reason is that the Sawtooth geometry provides more points where the local shear rates are high. © 2008 Elsevier B.V. All rights reserved.

1. Introduction It is well-accepted that local shear, elongation and necking are very important aspects of drop formation as are the physical properties of the fluids involved. Hence a successful design depends on developing amechanistic understanding of how the equipment selection, process strategy and material properties interact to affect the resulting microstructure (e.g. particle size) and hence the performance of the products. Typically two approaches are adopted:
• Scale-up at geometric similarity and constant tip speed.
• Scale-up at equal specific power input. Scale-up on the basis of geometric similarity and constant tip speed assumes that the relevant shear that produces the limiting drop size occurs in the agitator region where the velocity gradients are the steepest. These are assumed to scale with the peripheral velocity of the impeller and the approach generally works
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The preparation of concentrated aqueous silicone oil emulsions has been investigated with particular attention to the effect of the dispersed-phase volume fraction ϕ
from 0.01 to 0.5 for a wide range of oil viscosities (50 to 1000 cSt). Oil was added on the top surface of a 6-L vessel. Drop size distribution and Sauter mean diameter, d32, measurements were carried out over 24 h mixing time. Emulsification was found to be relatively sensitive to the oil phase viscosity, ld, for the same
ϕ yielding a narrower drop size distribution for low oil viscosity (50 cSt) and a wider drop size distribution for the highly viscous oil (1000 cSt). For the same
, increasing ld resulted in increasing d32. The equilibrium d32 was found to be well correlated to the viscosity number by d32 D
0
026  V0
204 i for
= 0.5. For the same oil viscosity, d32 was found to increase with increasing
. A multiregression of d32 with both
and Vi for various silicone oil viscosity grades was successfully correlated by d32
9
6
0
069V0
216 i with a regression coefficient (R2) of 0.975. This shows a very weak dependence of the equilibrium d32 on
. Keywords: Dispersed-phase volume fraction, Drop size distribution, Liquid-liquid dispersion, Silicone oil, Surfactant Received: January 22, 2009; revised: March 23, 2009; accepted: April 27, 2009 DOI: 10.1002/ceat.200900038 1 Introduction Liquid–liquid dispersion is one of the most complex of all mixing operations. Agitating two immiscible liquids results in the dispersion of one phase in the other in the form of small droplets with drop size distributions whose characteristics depend on the equipment and the operating conditions. It is virtually impossible to make dispersions of uniform drop size, because of the wide range of properties and flow conditions. The knowledge of the resulting drop size distribution characteristics or, more exactly, the evolution of this distribution with changes of external energy input is of major importance. A large amount of work can be found in the literature concerning the prediction of drop size distributions in turbulent liquid-liquid dispersions in stirred vessels. Most of them use the concept of a turbulent energy cascade to predict the maximum stable diameter,

Ultradispersed metal oxide nanoparticles have applications as heterogeneous catalysts for organic reactions. Their catalytic activity depends primarily on their surface area, which in turn, is dictated by their size, colloidal concentration and stability. This work presents a microemulsion approach for in situ preparation of ultradispersed copper oxide nanoparticles and discusses the effect of different microemulsion variables on their stability and highest possible time-invariant colloidal concentration (nanoparticle uptake). In addition, a model which describes the effect of the relevant variables on the nanoparticle uptake is evaluated. The preparation technique involved solubilizing CuCl2 in single microemulsions followed by direct addition of NaOH. Upon addition of NaOH, copper hydroxide nanoparticles stabilized in the water pools formed in addition to a bulk copper hydroxide precipitate at the bottom. The copper hydroxide nanoparticles transformed with time into copper oxide. After reaching a time-independent concentration, mixing had limited effect on the nanoparticle uptake and particle size. Particle size increased with increasing the surfactant concentration, concentration of the precursor salt, and water to surfactant mol ratio; while the nanoparticle uptake increased linearly with the surfactant concentration, displayed an optimum with R and a power function with the concentration of the precursor salt. Surface areas per gram of nanoparticles were much higher than literature values. Even though lower area per gram of nanoparticles was obtained at higher uptake, higher surface area per unit volume of the reverse micellar system was attained. A model based on water uptake by Wisor type II microemulsions, and previously used to describe iron oxide nanoparticle uptake by the same microemulsions, agreed well with the experimental results.

Nanoparticles serve the need for advanced materials with specific chemical, physical, and electronic properties. These properties can be attained by manipulating the particle size. Consequently, size control has been recognized as a key factor for selecting a nanoparticle preparation technique. (w/o) Microemulsions, or reverse micelles, have been successfully used to prepare wide variety of nanoparticles with controlled sizes. Studies showed that adjusting microemulsion and/or operation variables provides a key to controlling nanoparticle size and polydispersity. The effect of a given variable, however, relies heavily on the reactant addition scheme. The mixing of two microemulsions scheme has been widely used in the literature, and the effect of microemulsion and operation variables on intermicellar nucleation and growth was detailed. The single microemulsions reactant addition scheme, on the other hand, enables intramicellar nucleation and growth, and therefore, may lead to a different response. Moreover, studies on nanoparticle preparation using the single microemulsions scheme involved more of reactive surfactants and introduced the concept nanoparticle uptake, which pertains to the maximum colloidal concentration of nanoparticles that can be stabilized in a microemulsion system. This review looks into the mechanisms controlling nanoparticle formation and compares literature trends reported for the effect of microemulsion and operation variables on the nanoparticle size and polydispersity for the single microemulsions reactant addition scheme. Moreover, it sheds some light on nanoparticle uptake and its significance.

Ultradispersed catalysts significantly enhance rates of reaction and mass transfer by virtue of their extended and easy accessible surface. These attractive features were exploited in this study to effectively capture H2S(g) from an oil phase by ultradispersed sorbents. Sorption of H2S(g) from oil phases finds application for scavenging H2S(g) forming during heavy oil extraction and upgrading. This preliminary investigation simulated heavy oil by (w/o) microemulsions having 1-methyl-naphthalene; a high boiling point hydrocarbon, as the continuous phase. H2S(g) was bubbled through the microemulsions which contained the ultradispersed sorbents. The type and origin of sorbent were investigated by comparing in situ prepared FeOOH and commercial α-Fe2O3 nanoparticles as well as aqueous FeCl3 and NaOH solutions dispersed in the (w/o) microemulsions. The in situ prepared FeOOH nanoparticles captured H2S(g) in a chemically inactive form and displayed the highest sorption rate and capacity. Temperature retarded the performance of FeOOH particles, while mixing had no significant effect.