摘要:

AbstractInterfacial activity between liquid reaction injection molding (RIM) reactants was observed using light microscopy. Diisocyanates were brought into contact with various diols and diamines in a thin (250 μm) gap. A dynamic phenomenon, rapidly producing a well‐mixed, intermaterial phase, was discovered. It was revealed that the rate of growth of this newly formed region was dependent on both the rate of reaction and the physical properties of the initially formed product species at the reaction interface. Spontaneous interfacial mixing also occurred without chemical reaction when a reaction product was dissolved in “capped” contacting reactant liquids. It is believed that strong interfacial intermolecular forces, inducing flow through the polymerization product layer formed immediately upon reactant contact, are responsible for the initial explosiveness of this microscopic process. The range of eventual thicknesses of the mixed, interfacial region (100–800 μm) for various typical RIM systems indicates that this microscopic subprocess may be significant to the fate of the overal

ISSN:0001-1541    

DOI:10.1002/aic.690340702

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA new thermodynamic model is presented for aqueous solutions of polar nonelectrolytes. The model is based on solute aggregation in an aqueous lattice, which is inferred from spectroscopic, thermodynamic, and physiochemical data. The adjustable model parameters have physical meaning, and are less intercorrelated and temperature‐dependent than are the parameters in other models such as the UNIQUAC and NRTL equations, which apply to a more general class of solutions. The model describes observed extrema in the activity coefficients of aqueous solutions, thus pointing out that the behaviors of aqueous and non‐aqueous solutions are fundamentally different, and that aqueous solutions cannot be well described with nonaqueous solution models over the whole concentration range. The two‐parameter form of the new model can better predict binary vapor‐liquid equilibria from liquid‐liquid equilibrium data than other two‐parameter models, and gives better predictions of ternary liquid‐liquid equilibrium using only binary data. It is also shown that the model can be used to describe aqueous solutions of water‐s

ISSN:0001-1541    

DOI:10.1002/aic.690340703

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAn analytical study of the electrophoretic motion of two freely‐suspended, nonconducting spheres with thin electrical double layers is presented using a method of reflections. The particles may differ in radius and/or in zeta potential at the surface, and they are oriented arbitrarily relative to the direction of applied electric field. Corrections to Smoluchowski's equation due to particle interactions are determined in a power series of 1/r12up to 0(r −712), wherer12is the center‐to‐center distance between the particles. It is found that the electrophoretic particles do not interact with one another when they have equal zeta potentials. For the specific case of spheres with identical radii, our results agree well with the exact calculations using bipolar coordinates. Based on a microscopic model, the results for two particles are used to find the effect of volume fractions of particles of each type on the mean particle velocities in a bounded dispersion. Of particular interest is the electrophoresis of a suspension of particles with arbitrary size distribution but with identical zeta potentials, in which the sole factor influencing the mean particle velocity is the volume fraction of all particles. In general, the effect of particle interactions on electrophoresis is much weaker than that on sedi

ISSN:0001-1541    

DOI:10.1002/aic.690340704

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractReaction mechanism and rates were determined from 803 to 1,073 K for the carbochlorination of Al2O3and of Al, Si and Fe‐mixed oxides using Cl2and C slurried in a stirred melt of NaCl—AlCl3. Alumina chlorination rates of 0.33–2.0 × 10−8kmol/s were obtained using C:melt weight ratios between 1:21 and 1:42. The reaction rate was proportional to C loading at temperatures below 923 K, while gas‐liquid mass transfer was rate‐controlling at higher temperatures. Carbochlorination of the combined oxides in coal fly ash at 923 K and oxide conversions less than about 50% was also gas‐liquid mass‐transfer‐controlled. At higher conversions, dissolution became the rate‐controlling factor. A 40% (molar) AlCl3melt was more effective than a 48% AlCl3melt for the selective chlorinati

ISSN:0001-1541    

DOI:10.1002/aic.690340705

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe recent theory for pore volume diffusion in porous media (Bhatia, 1985, 1986) is further extended to include surface diffusion with adsorption‐desorption phenomena proceeding at finite rates. The short‐range memory effects, previously discussed in terms of a correlation between successive pores traversed, are included here and are found to be important for surface diffusion as well. A tortuosity for surface diffusion is defined and found to be larger than 3, in the range of 5 to 7, because of internal correlation effects in the random network structure examined. Under conditions of gradients in pore surface area it is shown that the surface transport equation is\documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{\partial(S_0 C_{s0})}}{{\partial t}} = \nabla _x \cdot S_0 D_{se}\nabla _x C_{s0} + S_0[k_a C_0(M - C_{so}) - (k_d + k_s)C_{so}] $$\end{document}and the relation between the effective surface diffusivityDseand the pore structure parameters is derived. The equation for pore volume diffusion requires further justification when adsorption‐desorption occurs at finite rates, and is also derived

ISSN:0001-1541    

DOI:10.1002/aic.690340706

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractDiffusion flux models are developed for isobaric diffusion of a multicomponent gas mixture in pore networks of distributed pore size and length constructed by arranging pore segments around the bonds of a lattice of constant coordination number. Eigenvalue‐eigevector analysis is used to decompose the dusty‐gas model equations, written for each pore segment in the network, into a set of independent single‐species diffusion problems, each of which is then treated by combining the effective medium theory for resistor networks with the smooth field approximation (Burganos and Sotirchos, 1987). Results for a ternary mixture diffusing in a porous slab show that direct application of the smooth field approximation underestimates significantly the mass transport resis

ISSN:0001-1541    

DOI:10.1002/aic.690340707

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThis work follows the global input/output linearization approach for the design of control systems for nonlinear plants of Kravaris and Chung. A robust nonlinear state feedback is proposed for uncertainties considered as a class of bounded perturbations to the state model. A Liapunov‐based approach is used to guarantee uniform ultimate boundednes

ISSN:0001-1541    

DOI:10.1002/aic.690340708

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe rate of dissolution of sphalerite is shown to be directly proportional to the concentration of substitutional iron impurity in the solid. This is attributed to the formation of a narrow impurity band within the forbidden band gap of the sphalerite. The impurity band is of irond‐orbital origin. The transfer of electrons between thisd‐orbital band and the oxidant is energetically more favorable than the transfer of electrons between the valence band and the oxidant. A fundamental model combining the electronic structure of sphalerite and semiconductor electrochemistry is presented. An equation is derived that describes the rate of dissolution as being first order for the concentration of iron in the solid and half‐order for the concentration of the oxidant. This is in agreement with the experimental evi

ISSN:0001-1541    

DOI:10.1002/aic.690340709

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractA new liquid membrane separation technique for gas mixtures has been developed: feed and sweep gases flow through the lumen of two different sets of hydrophobic microporous hollow fibers while a liquid on the shell side acts as the membrane. This membrane is identified as the contained liquid membrane (CLM). Major shortcomings of immobilized liquid membrane techniques are eliminated. The novel separation device is identified as the hollow fiber contained liquid membrane (HFCLM) permeator. Experimental studies are made with different CO2‐N2feed mixtures and a pure helium sweep stream, with special emphasis on model landfill gas purification. Either pure water or an aqueous solution of K2CO3is used as membrane. The effects of several variables on the performance of the HFCLM permeator have been studied. A three‐component permeation model, incorporating axial pressure drop, is developed for binary mixture separation in a HFCLM permeator having a sweep gas stream. The experimental data show good agreement with the theoretical predicti

ISSN:0001-1541    

DOI:10.1002/aic.690340710

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe performance of the industrial HCN synthesis Andrussow reactor on a Pt gauze catalyst is simulated using rate equations for 13 simultaneous unimolecular and bimolecular surface reactions. Individual rates have been determined experimentally for reactants, intermediates, and products on polycrystalline Pt, and the model therefore contains no adjustable parameters except for reactant flux limits. Predicted selectivities of HCN formation agree quite well with those observed in commercial reactors, and a distinct optimum with feed composition is obtained near that observed experimentally. In addition, behaviors are predicted at compositions, pressures, and temperatures inaccessible to the commercial reactors. Both isothermal and nonisothermal situations are examined. Questions concerning the validity of models, reactant flux limits, and the decoupling of simultaneous surface reactions are considered.

ISSN:0001-1541    

DOI:10.1002/aic.690340711

出版商:American Institute of Chemical Engineers    

年代:1988

数据来源: WILEY