Studies in solid-solid reactions: Autocatalysis in the reduction of cuprous chloride by silicon

Reaction between silicon solid cuprous chloride constitutes a major step in preparing the catalyst for the manufacture of chlorosilanes. Experimental results on this reaction are reported. Data are analyzed based on the observed autocatalytic nature of the reaction. Rate constants activation energies for both the steps-non-catalytic and autocatalytic—are obtained. Finally, the effect of various process parameters on the reaction rate is discussed.     

Kinetics of the reaction between steam and the basal plane of graphite

The gold decoration/transmission electron microscopy technique has been used to measure the rate of removal of carbon atoms from the basal plane of gra processes have been determined: removal of edge atoms surrounding the monolayer etch pits, and abstraction of carbon atoms within the basal plane which for edge carbon removal ranges from 0.02 at 600°C to 26 atom/atom active site/s at 900°C. The activation energy of 52 kcal/mole is close to the val of the saturated basal atoms (with 3 sp² bonds) may be expressed in terms of the probabilities of successful collisions of O atoms which are fo for both CO₂ and CH₂O reactions, are of the order of 10^?10 in the above temperature range. Comparison of the two reaction oxygen and water is the species responsible for basal atom abstraction.The gasification of graphite by steam is immensely anisotropic. At 23 torr H₂O the turnover frequency in the prismatic or edge directions, {10$\text{1}$0} and {11$\text{2}$0} faces, is higher than that on the basal {0001} plane by a factor of 4 × 10¹⁰ at 900°C and 4 × 10¹² at 700°C.     

Modelling of the pressure swing air seperation process

A theoretical analysis is given of the separation of oxygen and nitrogen in air by a single column pressure swing gas separation process. The problem treated includes changes in mass flow due to adsorption. The findings are compared with data obtained using molecular sieve adsorbent.     

Mixing and fast chemical reaction—VI: Extension of the reaction zone

Work reported earlier[1, 3] as well as here indicates that mixing at the molecular scale (micromixing) takes place by molecular diffusion in fluid elements, which are simultaneously undergoing laminar deformations. Whereas simple shear was considered before, the present analysis describes diffusion and reaction in regions deformed by extensional flow. After outlining various simple types of extension, results in the literature[4,7] are quoted, which were obtained from observations on the diffusion of heat spots in turbulent air. These indicated stretching motions in two directions with a corresponding shrinkage in the third. Direct application of these findings to diffusion in the direction of shrinkage leads to predictions of th product distribution from competitive, consecutive reactions. Without fitting any parameters, these predictions agree quite well with the distributions of two dyestuffs produced by two diazo coupling reactions. Insufficient fluid mechanical information is available to enablea more accurate comparison; matters requiring further study are listed.     

Modelling forced periodic operation of catalytic reactors

The kinetic adsorption/desorption or AD models used to predict product selectivities obtained through forced-feed concentration cycling have been re-examined. Selectivity improvement results from model structure and nonlinear rates of reaction. The relaxed-steady state bound to periodic operation was found to be predictable from steady state rates for the kinetic model used. Adsorption/desorption models predict no rate improvement for periodic operation. Also they fail to predict experimental observations that are now fairly extensive.     

Mixing and fast chemical reaction—VII Deforming reaction zone model for the CSTR

Earlier work on batch reactors indicated that the final stage of homogenisation to the molecular scale (micromixing) occurs by molecular diffusion in deforming fluid elements. The product distribution of, for example, consecutive, competitive reactions is sensitive to concentration gradients at the molecular scale (segregation). Such reactions may be used as reactive tracers to throw light on the behaviour of small fluid elements. Moreover an understanding of micromixing allows the selectivity of fast, multiple reactions to be better controlled. This paper describes two ways of applying the unsteady-state equations for diffusion and reaction within a shrinking fluid element to determine the steady-state concentrations in a CSTR. The iterative model is more economical in computer time than the dynamic model and applies to fast reactions (i.e. when the time for diffusion and reaction is a small fraction of the mean residence time). It described well the measured effects on the product distribution of varying the volumetric feed rati the stoichiometric ratio and of changing the operating mode from semicontinuous to continuous. When the initial size of the deformable fluid element is identified with the Kolmogoroff microscale and a reasonable estimate of shear rate is introduced, a highly satisfactory prediction of experimental resu knowing the kinematic viscosity and the power consumption of the stirrer, becomes possible.     

A kinetic study of the reaction between terephthalic acid and ethylene oxide in a nonsolvent system

Kinetics of the reaction between terephathalic acid and ethylene oxide, catalysed by triethylamine, was studied in a high-pressure reactor without using solvent. This reaction was carried out at a temperature range of 80–100°C and at a pressure range of 10–15 Kg/cm² beyond the corresponding vapor pressure of ethylene oxide. Effects of temperature, catalyst concentration, mole ratio of ethylene oxide to terephthalic acid, particle size of terephthalic acid, pK value of the tertiary amine and stirrer speed were experimentally investigated on the yield of bis(2-hydroxyethyl) terephthalate and reaction rates. It was found that the bulk reaction of terephthalic acid with ethylene oxide occurred in the liquid phase. Based on experimental results a reaction mechanism to synthesize bis(2-hydroxyethyl) terephthalate from terephthalic acid and ethylene oxide in a nonsolvent system was proposed, and rate constants were obtained with a model based on this proposed reaction mechanism. The activation energy of the reaction was found to be between 3.67–8.28 kcal/mole in the temperature range of 80–95°C.     

Modelling and parametric sensitivity of an annular photoreactor with complex kinetics

This paper reports the behaviour of a continuous annular reactor irradiated with a tubular ultraviolet source placed at its axis, and analyzes the case of a chemical reaction occurring in the homogeneous phase with complex kinetics. The reacting system is analyzed without resorting to the kinetic steady state hypothesis, thus allowing the computation of concentration profiles for the intermediate activated species.Three different models of radiation sources are considered: the line source model with emission in parallel planes, the line source model with sphericaWe have investigated and evaluated the influence of all significant parameters of the system on the reactant, intermediate species and product concentr     

Computer-generation of reaction paths and rate equations in the thermal cracking of normal and branched paraffins

Reaction networks for the thermal cracking of hydrocarbons and the associated rate equations are generated by computer using an approach based upon Boolean relation matrices.     

Dynamic modeling and reaction invariant control of pH

A systematic treatment of the dynamics and control of acid-base reactions is presented. A state model consisting of mass balances for the species present is formed. Through a linear transformation of the concentration vector a new model is set up. The state vector of this model is partitioned into a reaction invariant and a reaction variant part. The model is thus split into two parts, one describing the physical properties of the reactor system independent of chemical reactions, the other describing the chemical reactions.For fast acid-base reactions the reaction invariant part of the model is sufficient to define the thermodynamic state of the system. The reaction rate vector is thus eliminated from the model. In this case the reaction variant part of the model consists of a static equation, relating pH to the reaction invariant state variables.The model obtained provides a sound basis for design of control loops for feedback and feedforward control of pH. As a direct application a new scheme for adaptive control of pH is proposed.     

Oscillatory and chaotic behaviour of a forced exothermic chemical reaction

An exothermic reaction takes place in a continuous stirred reactor, the cooling temperature of which is varied with time. It is shown that with an increase in the amplitude of the forcing that quasiperiodic behaviour occurs, followed by a sequence of period doubling bifurcations leading to chaos. Furthermore, multiple oscillatory states can arise, where both states are periodic or one state periodic and the other chaotic.     

Integration of combustion reaction systems

When integrating the mass and energy balances with a stiff integrator, such as LSODE (Hindmarsh, [1]), absolute error tolerances are inefficient during the initiation of free radicals, loss of precision in evaluating the algebraic mass balances can lead to numerical instability, and integrator stall can occur when species decay to depletion with a sub-first-order kinetic model. To improve reliability and efficiency, asymptotic expansions ar patched with the combustion model. When loss of precision exceeds some heuristic measure, the state variables of the differential equations (concentrations of the basic species) are reselected in order that the largest concentrations are computed by the algebraic mass balances.     

The effect of chemical reaction on the breakup of liquid jets

Linear stability analysis predicts that a chemical reaction occurring at or near a liquid jet interface may strongly influence its breakup into droplets. Jet length is shown to depend primarily on the site of the reaction (at the interface or in one of the bulk phases), the transfer rates of the various species, and the interfacial tension dependence on composition and secondarily on a number of other factors. Experiments with silicone oil jets (containing various carboxylic acids) in water (containing a range of concentrations of sodium hydroxide) confirm qualitatively the principal predictions of the analysis.     

Mixing and fast chemical reaction—II: Diffusion-reaction model for the CSTR

Of several possible representations of inhomogeneity in mixtures and of its influence on chemical reactions, a diffusion-reaction formulation has been developed here to model the mixing-dependent product distributions leaving a CSTR. (A similar treatment of competitive, consecutive reactions in a batch reactor was given earlier[20]). The reactions reported in Parts I and III are conducted using a much larger volume of alkaline, 1-naphthol (A) solution than of diazo salt solution (B). Partial segregation is thus visualised as a dispersion of quiescent, spherical B-rich zones, into which A diffuses and within which all reactions occur. Unsteady-state diffusion-reaction equations thus characterise the concentration changes within these zones. These have been solved numerically with boundary conditions etc. characteristic of the CSTR. In addition to the dimensionless variables determining the product distribution in the chemical regime, a further group (similar to the Thiele modulus and theta number) has a dominant effect in the mixed, diffusional-chemical regime. As various variables are changed, the model predicts effects on the product distribution, which are readily understood.     

Mass transfer with heterogeneous and first order homogeneous reaction using the film theory

The problem of mass transfer with both first order irreversible homogeneous and an arbitrary heterogeneous reaction has been analyzed using the film theory, subject to the assumption of a linear profile of reactant between the bulk phase and the heterogeneous reaction surface. The enhancement factor is shown to depend on the product of two dimensionless groups. One is analogous to the usual group arising from mass transfer and first order irreversible reaction, and the other is a Damköhler number which describes the transport of the reactant to and reaction on the surface. The result is discussed in the context of solubilization of an insoluble liquid amphiphile by an aqueous surfactant solution. A maximum in the flux enhancement is observed because of the resistances associated with transport of the reactant species to the reaction surface.     

Mixing and fast chemical reaction-V: Influence of diffusion within the reaction zone on selectivity

The competitive, consecutive reations A + B = R, R + B = S are considered to occur within spherical or planar zones, initially containing only the reagent B and into which the reagent A diffuses. Depending upon whether B is immobile or can diffuse within the reaction zone, so will different distributions of the products R and S be obtained. These distributions have been computed by numerically integrating the diffusion-reaction equations. When B diffuses, less S is formed and increasing the volume ratio α = V_A/V_B of the reagent solutions also causes less S to be formed, provided that the mixing modulus is constant. The latter trend has been confirmed by conducting the coupling of 1-naphthol (A) and diazotised sulphanilic acid (B) at α = 10, 50 and 100. The product distributions were predicted well without fitting any constants by a model postulating a gradually thinning, planar reaction zone within which also B diffused.     

Effectiveness factor and selectivity estimation for a parallel reaction system

The case of double parallel reaction scheme taking place in a porous catalytic pellet is analyzed. Effectiveness factor expressions for both reactions are derived after matching asymptotic solutions strictly valid for small and large values of the Thiele moduli.It is assumed that the kinetics of both reactions follow a general irreversible power law model, that isothermal conditions prevail and that external mApproximate results in terms of effectiveness factors compare fairly well with exact results obtained by numerical integration of the differential equa     

Gas absorption with photochemical reaction

Gas-liquid reactions can be activated by high energy radiations (photons). When gas absorption is accompanied by pseudo-first order reaction further enhancement in the specific rate of absorption can be realised for situations where either the reactive species in the liquid phase is activated or the dissolved solute gas is activated.     

Transient diffusion and reaction of ions in an electrostatic double-layer: Application to the response of potentiometric electrodes

The transport equations for unsteady diffusion and simultaneous chemical reaction in an electrostatic double-layer in series with a mass transfer boundary layer have been solved. The results are presented in terms of the transient response of a potentiometric electrode, and show hysteresis and non-first-order behavior associated with the transport phenomena in the double-layer. The double-layer effects can be reduced and even eliminated in the presence of chemical reaction, which provides an alternate mechanism for ion transport within the double-layer.