Engineered interphase design

Although the Internet has made information more readily accessible, the typical tight time frame for the development of optimal interphase design requires one to have a more practical source of basic information on a nearby bookshelf. Research scientists and technical service engineers alike will benefit from this handbook of pertinent and up-to-date information on polypropylene-based materials. 

Optimal reactor design is critical for the effectiveness and economic viability of AOPs. The WAO process poses significant challenges to chemical reactor engineering and design, due to the (i) multiphase nature of WAO reactions (ii) temperatures and pressures of the reaction and (iii) radical reaction mechanism. In multiphase reactors, complex relationships are present between parameters such as chemical kinetics, thermodynamics, interphase/intraphase intraparticle mass transport, flow patterns, and hydrodynamics influencing reactant mass transfer. Complex models of WAO are necessary to take into account the influence of catalyst wetting, the interface mass-transfer coefficients, the intraparticle effective diffusion coefficient, and the axial dispersion coefficient. " ... 

This article attempts to unify the vast hterature on PTC chemistry with a comprehensive review of kinetic studies and mathematical modeling of PTC systems, which necessarily involve the role of intraphase and interphase mass transport. This coupling of knowledge from chemistry with engineering should prove useful in developing rational methods of reactor design and scale-up for commercial PTC applications. 

Step 1. Reactants enter a packed catalytic tubular reactor, and they must diffuse from the bulk fluid phase to the external surface of the solid catalyst. If external mass transfer limitations provide the dominant resistance in this sequence of diffusion, adsorption, and chemical reaction, then diffusion from the bulk fluid phase to the external surface of the catalyst is the slowest step in the overall process. Since rates of interphase mass transfer are expressed as a product of a mass transfer coefficient and a concentration driving force, the apparent rate at which reactants are converted to products follows a first-order process even though the true kinetics may not be described by a first-order rate expression. Hence, diffusion acts as an intruder and falsifies the true kinetics. The chemical kineticist seeks to minimize external and internal diffusional limitations in catalytic pellets and to extract kinetic information that is not camouflaged by rates of mass transfer. The reactor design engineer must identify the rate-limiting step that governs the reactant product conversion rate. 

The authors would like to thank the Office of Naval Research (ONR) for their financial support (grant number N00014-95-1-0340). We would also like to thank the members of the Designed Interphase Group (DIG) for their support, in particular Dr J S Riffle in Chemistry, Dr R Davis and Norman Broyles in Chemical Engineering and Dr S Davis who is now at Kodak. 

Finally, pressure-pulsed-CVI (P-CVI) has recently been presented as a means of engineering, at the micrometer (or even nanometer) scale, either the interphase or the matrix. Based on this technique, multilayered selfhealing interphases and matrices (combining crack-arrester layers and glass-former layers) have been designed and produced, through a proper selection of chemical composition of the layers [539]. 

Yu, Z., Brisson, J. and Ait-Kadi, A. (1994) Prediction of Mechanical Properties of Short Kevlar Fiber-Nylon-6,6 Composites, Polymer Composites, 15(1), 64-73. Karian, H.G. (1996) Designing Interphases for Mega-Coupled Polypropylene Com X)sites, Plastics Engineering, 52(1), 33-5. 

Figure 7.2. Schematic drawing of the two principal methodologies in designing multiscale composite structures, i.e., the top-bottom engineering approach and the bottorrirup approach observed in natural composites with the emphasis on the role of interphase phenomena at various length and time scales [169]...

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