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Multiphase Systems (multiphase + system)

Distribution by Scientific Domains

Chemistry	63%
Polymers and Materials Science	27%

Selected Abstracts

Multiphase Systems for the Recycling of Alkoxycarbonylation Catalysts

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006
Jeroen J., M. de Pater
Abstract This review evaluates the various multiphasic systems that have been developed for catalyst recycling in the context of alkoxycarbonylation of alkenes and alkynes. Immobilization of the catalyst on an insoluble support, such as silica, alumina, clay or a polymer, as well as immobilization in the inorganic phase of several liquid/liquid biphasic systems (aqueous/organic, ionic liquid/organic, fluorous/organic or supercritical CO2/organic) has been described. In several cases detailed information on the efficiency of catalyst separation and recycling is available. Most of the work was focused on the alkoxycarbonylation reactions of alkenes, for which several efficient methods for catalyst recycling were demonstrated. The recycling of catalyst through specific precipitation from supercritical CO2 or selective dissolution in a fluorous phase, has received only scant attention but offers many opportunities for further improvement. [source]

Mesh adaptation and transfer schemes for discrete fracture propagation in porous materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2007
Stefano Secchi
Abstract This paper presents a numerical procedure for cohesive hydraulic fracture problems in a multiphase system. The transient problem of crack nucleation and/or advancement, with the ensuing topological changes, is solved by successive remeshing and projection of the field variables required in the time marching scheme. The projection is directly applied to the nodal vector of the previous step and is performed by means of a suitable mapping operator which acts on nodal forces and fluxes. This hence ensures ,a priori' the local fulfilment of the balance equations (equilibrium and mass conservation). The resulting procedure is computationally simple; however checks have to be made on its capability of conserving strain energy of the system. The latter property together with the accuracy of the solution is heuristically assessed on the basis of numerical benchmarks. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Multiphase approximation for small-angle scattering

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2010
Dragomir Tatchev
The two-phase approximation in small-angle scattering is well known and is still the dominant approach to data analysis. The intensity scattered at small angles is proportional to the second power of the difference between the scattering densities of the two phases. Nevertheless, scattering contrast variation techniques are widely used, and they are obviously suitable for multiphase systems or systems with gradually varying scattering density, since if no parasitic scattering contributions are present the scattering contrast variation would only change a proportionality coefficient. It is shown here that the scattered intensity at small angles of a multiphase system can be represented as a sum of the scattering of two-phase systems and terms describing interference between all pairs of phases. Extracting two-phase scattering patterns from multiphase samples by contrast variation is possible. These two-phase patterns can be treated with the usual small-angle scattering formalism. The case of gradually varying scattering density is also discussed. [source]

Magnetic Multi-Functional Nano Composites for Environmental Applications

ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009
Jie Dong
Abstract A novel concept is proposed to synthesize a new class of composites featuring magnetic, molecular sieve and metallic nanoparticle properties. These multi-functional materials have potential applications as recyclable catalysts, disinfectants and sorbents. The magnetic property enables effective separation of the spent composites from complex multiphase systems for regeneration and recycle, safe disposal of the waste and/or recovery of loaded valuable species. The zeolite molecular sieve provides a matrix which supports a remarkably new, simple, efficient and economical method to make stable, supported silver nanoparticles by silver ion exchange and controlled thermal reduction. The silver nanoparticles generated in this way have excellent properties such as high reactivity and good thermal stability without aggregation, which act as nano reactors for desired functionality in a wide range of applications. Magnetic component (Fe3O4), molecular sieve matrix (zeolite) and silver nanoparticles generated by ion exchange followed by controlled reduction, together form this unique novel composite with designed functions. It represents a practically operational, economical, sustainable and environmentally friendly new advanced functional material. This paper focuses on the novel synthesis and characterization of the composite, with an example of applications as sorbents for the removal of vapor-phase mercury from the flue gas of coal-fired power plants. [source]

Multiphase approximation for small-angle scattering

Magnetic emulation of microgravity for earth-bound multiphase catalytic reactor studies,Potentialities and limitations

AICHE JOURNAL, Issue 5 2009
Faïçal Larachi
Abstract A method is proposed to generate Earth-bound artificial microgravity in a controlled facility capable of emulating lunar/Martian gravity or microgravity for experiments on passive/reactive catalytic multiphase flows. Its applicability was illustrated for trickle beds where flowing gas and liquid experience artificial microgravity inside the bore of a superconducting magnet generating large gradient magnetic fields to compensate for gravity. Artificial gravity is realized by commuting into apparent gravity acceleration the magnetization force at work on common "chemical engineering" non-magnetic fluids. The scaling property to be matched and maintained invariant in multiphase systems to achieve magnetic mimicry is phasic mass magnetic susceptibility. Hydrodynamic (liquid holdup, wetting efficiency, pressure drop) as well as catalytic reaction (conversion and selectivity) measurements were obtained. The main finding is a proof that magnetic fields affect reactor outcomes exclusively via hydrodynamic phenomena making them appealing proxies for emulating non-terrene reactor applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Measuring bubble, drop and particle sizes in multiphase systems with ultrasound

AICHE JOURNAL, Issue 11 2004
A. H. G. Cents
Abstract A technique is developed for measurement of bubble, droplet and particle-size distributions in multiphase systems, based on the propagation speed and attenuation of ultrasound. The measurement of the size distribution of the dispersed phase in multiphase systems was desired to analyze the mass-transfer mechanism in gas-liquid-liquid and gas-liquid-solid systems. To obtain this information, both the ultrasonic velocity and the attenuation coefficient of tone-burst signals are determined for a large frequency range (typically 100 kHz , 100 MHz). From these parameters, the size distributions and the volume fraction of the different dispersed phases can be determined using a scattering model. It was shown that the interfacial area can be determined very accurately, however, for the exact size distribution of the gas bubbles in the used size range (1,3 mm) an independent gas holdup determination is required. Experiments were performed in gas-liquid, solid-liquid, and gas-liquid-solid systems. The results showed good agreement of the particle-size distribution compared to a commercial laser-scattering analyzer, both with and without gas bubbles present. Furthermore, a good agreement between the scattering model and the experiments was found in the systems that contained gas bubbles, but these results should be validated using for instance, a digital camera technique. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2750,2762, 2004 [source]

Studies on nylon-6/EVOH/clay ternary composites

POLYMER COMPOSITES, Issue 1 2006
N. Artzi
Nylon-6 (Ny-6)/EVOH blends are interesting host multiphase systems for incorporation of low clay contents. The Ny-6/EVOH blend is a unique system, which tends to chemically react during melt-mixing, affecting thermal, morphological and mechanical properties of the ternary systems containing clay. The addition of clay seems to interrupt the chemical reaction between the host polymers at certain compositions, leading to lower blending torque levels when clay is added. A competition between Ny-6 and EVOH regarding the intercalation process takes place. Ny-6 seems to lead to exfoliated structure, whereas EVOH forms intercalated structure, as revealed from XRD and TEM analyses, owing to thermodynamic considerations and preferential localization of the clay in Ny-6. Hence, the ternary systems have combined intercalated and delaminated morphology or complete exfoliated morphology depending on blend composition and clay content. Selective extraction experiments (gel content) indicate the formation of chemical reaction between the Ny-6 and EVOH, and give an indirect indication of the polymer content residing in the galleries. The thermal properties of the polymers were found to be affected by the occurrence of chemical reaction, the level of intercalation and exfoliation and plasticizing effect of the low molecular weight onium ions treating the clay. Of special interest is the increased storage modulus attained upon the addition of only 1.5 wt% clay. POLYM. COMPOS. 27:15,23, 2006. © 2005 Society of Plastics Engineers [source]

Relative viscosity models and their application to capillary flow data of highly filled hard-metal carbide powder compounds

POLYMER COMPOSITES, Issue 1 2005
Tomas Honek
The rheological behavior of highly filled polymer systems used in powder injection molding (PIM) technology strongly influences the final properties of the products. In this study, the capillary flow data of multi-component polymer binders,based on polyethylene, paraffin, ethylene-based copolymers, and polyethylene glycol,compounded with three various hard-metal carbide powders were employed. The rheology of such highly filled (up to 50 vol%) multiphase systems is necessarily a complex phenomenon characterized by strain dependent, non-Newtonian properties complicated by flow instabilities and yield. Over 15 mathematical models proposed for highly filled systems were tested, some of them calculating the maximum filler loading. Due to the complex structure of the filler (irregular shape, particle size distribution) and a multi-component character of the binder, the applicability of these models varied with the powder-binder systems studied. However, the particular values of maximum loadings are in good accordance with the predictions based on powder characteristics. Simple modification of Frankel-Acrivos model to the systems containing unimodal hard-metal carbide powders with particles of an irregular shape and broad particle size distribution gave precise agreement between experimental data and model prediction. POLYM. COMPOS., 26:29,36, 2005. © 2004 Society of Plastics Engineers. [source]

Semi-Empirical Equations for the Residence Time Distributions in Disperse Systems , Part 1: Continuous Phase

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2004
J.-H. Ham
Abstract Residence time distributions (RTD) are often described on the basis of the dispersion or the tanks in series models, whereby the fitting is not always good. In addition, the underlying ideas of these models only roughly characterize the real existing processes. Two semi-empirical equations are presented based on characteristic parameters (mean, minimum, maximum residence time) and on an empirical exponent to permit better fitting. The determination of the parameters and their influence on the RTD are discussed. The usefulness of the models is shown in this first part for single-phase systems and for the continuous phase of multiphase systems using data from literature for laminar and turbulent flows in different apparatuses. A comparison with the results of other models is also done. [source]