摘要:

The kinetics of reduction with hydrogen of thin, dense strips of NiO in the 230-452°C temperature range were measured by the thermogravimetric technique. Pure hydrogen gas at 1 atm was used as the reducing agent. The fractional conversion-time curves were sigmoid-shaped, indicative of the autocatalytic nature of the reduction process. As relatively thin (54 μm thick) specimens were employed, the pore-diffusion of gases offered only negligible resistance. The topochemical-reaction-rate constant kc, deduced from the measured rates using nominal surface area, is found to be given by

ISSN:0098-6445    

DOI:10.1080/00986449708936666

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A model for polymer dissolution in mixed solvents has been developed with the purpose of explaining the hitherto unexplained maximum in the dissolution rate with the solvent composition. The variation of the interface concentration of both the solvents and the dissolution rate with the composition of the non-solvent in the dissolution medium is predicted. The model predicts an increase in dissolution rate with an increase in low molecular weight non-solvent content of the dissolution medium. However, further increase in the non-solvent content, decreases the dissolution rate. The relative role of kinetic and thermodynamic quality of the solvent is shown to be the reason for this unusual behaviour. The model also predicts reduction in swelling with an increase in non-solvent content of the dissolution medium. The implications of the work in designing mixed solvent systems for microlithography to meet the goal of maximum dissolution rate with minimum swelling are discussed.

ISSN:0098-6445    

DOI:10.1080/00986449708936667

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A diffusion model is developed to simulated the behavior of mass transport of the solute in the emulsion liquid membrane. The solute is allowed to react reversiblely with the internal reagent, and the effective diffusivity of the solute in membrane phase is dependent on local solute concentration in membrane phase. A numerical solution is presented for the non-linear equations of this model. The results are compared with those of two previous models, and it is found that the Modified Diffusion Model represents more accurately than other earlier models.

ISSN:0098-6445    

DOI:10.1080/00986449708936668

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This work aims at giving a first insight of non-Newtonian fluid flow through synthetic foams.

ISSN:0098-6445    

DOI:10.1080/00986449708936669

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this work the Johnson-Segalman fluid model is employed to investigate the combined effects of elasticity and shear thinning on the load bearing capacity of lubricants under isothermal conditions. A dimensional analysis, using characteristic lubricant properties and realistic bearing operating conditions, yields a simplified set of equations for the stresses and the balance of mass and momentum. A perturbation solution to these equations gives the stresses, velocities and pressure as second order expansions in the powers of Weissenberg number, We.

ISSN:0098-6445    

DOI:10.1080/00986449708936670

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Experimental investigations were carried out in model external-loop airlift reactors. Two reactors of laboratory scale (riser liquid height ranged between 1.16-1.56 m, riser diameter 0.03 m, AD/ARratio between 0.111-1,000, total liquid volume VT= (1.189-2.446).10−3m3) and pilot-plant scale (riser liquid height of 4.4 and 4.7 m, respectively, riser diameter 0.200 m, AD/ARratio of 0.1225 and 0.040 m, total liquid volume, VT= (0.144-0.170) m3) were used.

ISSN:0098-6445    

DOI:10.1080/00986449708936671

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Particle concentration and particle size distributions have been measured for two-phase (solid/air) turbulent coaxial jets using the Laser Diffraction Method (LDM) and a tomography data transform technique. Effects of velocity ratio, particle loading ratio, and particle size on the dispersions of gas and particles were determined. Experimental results show that the gas disperses much more rapidly than the particles and particle dispersion decreases with increasing in particle size. Increasing velocity ratio significantly increases gas dispersion, while effects of other variables are less significant. The mean particle size at the jet edge is about 15-20% smaller than that at the jet centerline. The turbulent Schmidt number Scpfor two-phase turbulent coaxial jets ranges from 1.4 to 1.5.

ISSN:0098-6445    

DOI:10.1080/00986449708936672

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An investigation was undertaken involving the extraction equilibrium of phenol from an aqueous solution using trioctylamine sulfate salt (TOA salt)/trioctylamine (TOA) as the extractant. The purpose of using trioctylamine as the organic solvent is to increase the total capability of phenol extraction as well as to avoid the use of other organic solvents. In order to prevent the formation of a second phase from the reaction of trioctylamine and sulfuric acid, 1-octanol in an appropriate amount was added to make the organic solution homogeneous. Equilibrium distribution coefficients (Kd) in the extraction of phenol by TOA salt/TOA were measured for various operating conditions. The equilibrium distribution coefficient of phenol (Kd) between two phases decreased with increasing the initial concentration of phenol, thereby decreasing the initial concentration of sulfuric acid, and subsequently increasing the volume ratio of aqueous phase to organic phase. We recommended that the extraction is carried out at low temperature. A higher value of Kdup to 800 was obtained in using trioctylamine sulfate/trioctylamine as the extractant for equal volume ratio of aqueous phase to organic phase.

ISSN:0098-6445    

DOI:10.1080/00986449708936673

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A priori design of catalysts is not yet possible. Such task would demand unavailable scientific knowledge of the correlations among synthesis parameters and resulting solid state and surface structures, on the one hand, and among those atomic-level structural details and their catalytic functions, on the other hand. To avoid testing every possible combination, therefore, the applied chemist or chemical engineer must identify empirical correlations underlying the existing experimental data base.

ISSN:0098-6445    

DOI:10.1080/00986449708936674

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The catalytic reforming of methane by steam is an important industrial process that produces H2, CO and CO2, thus chemically transforming natural gas, coal gas and light hydrocarbon feedstocks to synthesis gas or hydrogen fuel. Methane-steam reforming may consist of a number of reactions depending on the reforming catalyst, operating conditions and feedstock composition, The typical industrially desirable reactions are the reverse of methanation (CH4+ H2O = CO + 3H2) and the water-gas shift (CO + H2O = CO2+ H2). Both reactions are equilibrium limited and the composition of the mixture that exits the reformer is in accordance with the one calculated thermodynarmically. Removal of reaction products at the reactor exit by means of selective membrane permeation can offer improved CH4conversions and CO2and H2yields, assuming the subsequent utilization of the reject streams by a second methane-steam reformer. We numerically investigated the feasibility of a system of two tubular methane-steam reformers, in series with an intermediate permselective polyimide membrane permeator, as means of improving the overall CH4conversion and the H2, CO2yields over conventional methane-steam reforming equilibrium reaction-separation schemes that are currently in industrial practice. The unique feature of the permselective polyimide separator is the simultaneous removal of H2and CO2versus CH4and CO from the reformed streams. The utilized 6FDA-3,3′, 5,5′-TMB aromatic polyimide was reportedly characterized [10] and found to exhibit superior permselective properties compared with other polyimides of the same or different dianhydride sequence. Conversion and yield of the designed reactor-membrane permeator reforming system can be maximized by optimizing the permselective properties of the membrane material and the design variables of the reactors and the permeator. Product recovery and purity in the permeate stream need to be compromised to overall enhance methane conversion and product yield. The operating variables that were varied to investigate their effect on the magnitude of conversion and yield included the inlet pressure of the first reformer, the temperature of both reformers, and the permeator dimensionless Pe' number (variation of the first two variables results to a drastic change in the composition of the reformed stream that enters into the permeator). The numerical results show that the new reformer-membrane permeator cascade process can be more effective (it can offer increased CH4conversions and H2, CO2yields) than conventional equilibrium methane-steam reforming reaction-separation processes currently in practice.

ISSN:0098-6445    

DOI:10.1080/00986449708936675

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor