Kinetics of oxidation of pseudocumene in the vapor phase

The kinetics of pseudocumene oxidation in the vapor phase with tin vanadate as catalyst have been studied over the following ranges of the variables: Oxygen concentration, 0.909 to 2.857 mole/m³; pseudocumene concentration, 0.071 to 0.125 mole/m³; temperature, 260 to 320°C; space time, 22.5 to 90 × 10⁴ g. catalyst/mole sec. Oxidation-reduction models have been found to describe the kinetics adequately. The mechanism is found to remain the same throughout the temperature range covered.     

Kinetics of absorption of oxygen in aqueous solutions: (1) acidic chromous chloride, (2) acidic titanous chloride and (3) ammoniacal cuprous chloride

The kinetics of absorption of oxygen in aqueous solutions of acidic chromous chloride and ammoniacal cuprous chloride were studied in a stirred cell. Both these reactions were found to be very fast and the theory of gas absorption accompanied by fast pseudo-m^th order reaction was used to analyse the results. The kinetics of absorption of oxygen in aqueous acidic solutions of titanous chloride were investigated in a bubble column where the reaction was found to be free from diffusional resistance.The reaction between oxygen and chromous chloride was found to be first order with respect to oxygen and second order with respect to chromous ion. The value of the third order rate constant for 2·0 M HCl solution was found to be 2·7 × 10¹² (cm³/g mole)² sec^?1 at 30°C.The oxidation of titanous chloride was observed to be zero order with respect to titanous ion and first order with respect to oxygen. The value of the first order rate constant was found to be 8·6 × 10^?3 sec^?1. It has been suggested that in this case hydrolysis precedes the oxidation and it is likely that the reaction of oxygen with the hydrolysed product is the rate controlling step.The absorption of oxygen in aqueous ammoniacal cuprous chloride was found to be third order; first order with respect to each species, namely Cu⁺, oxygen and free ammonia. The value of the third order rate constant was found to be 7·5 × 10¹⁰ (cm³/g mole)² sec^?1. The higher value of the rate constant compared to that for oxidation of acidic solutions of curpous chloride indicates that the presence of a complexing agent such as ammonia increases the rate of absorption of oxygen substantially.     

The Role of Mass Transfer in the Kinetics of Chemical Oxidation of Anthracine Slurry to Anthraquinone in a Batch Stirred Tank Reactor

The kinetics of chemical oxidation of anthracine powder by acidified dichromate in a batch agitated vessel stirred by a 45° four pitched blade turbine impeller was studied under different conditions. Variables studied were impeller rotation speed, solution physical properties and temperature. The rate of anthracine oxidation was found to increase with temperature according to the Arrhenius equation with an activation energy of 3.98 cal/mole. The rate of anthracine oxidation was found to increase with 0.56 power of impeller rotation speed. The value of the activation energy and the sensitivity of the rate of oxidation to stirring lend support to the diffusion‐controlled nature of the reaction. The data were correlated by the equation: Sh = 0.5 · 10^–3 Sc^0.33 · Fr^0.33 Implication of the above equation for the operation of industrial reactors was noted.     

用序贯法对反应速率模型中的参数作精确估算

对一个确定的模型,不仅要确定参数的估算值,还必须了解其可靠性。为了缩小参数的不定性,降低参数间的相关性,以扩大模型拟合的适定性和准确度,本文讨论了参数精确估算的序贯设计过程。 文内还详细讨论了精估参数的实验设计准则——最小联合置信容积准则和形状准则,以及序贯设计的实用价值。以氨合成为例,用序贯法精确估算了反应速度模型中的参数。这一模型是在序贯判别过程中选定的。把精估结果用于拟合大型生产过程的实测数据,得到了满意的结果。     

Absorption of chlorine in aqueous solutions of phenols and aromatic sulfonic acids

The kinetics of absorption of Cl₂ in aqueous solutions of phenol, o-chlorpophenol, p-chlorpophenol, p-nitrophenol, m-aminophenol-hydrochloride, ptoluenesulfonic acid and m-nitrobenzenesulfonic acid, at 30°C, was studied in a model stirred contactor, with a plane liquid interface and independent stirrers for gas and liquid phases. A laminar jet apparatus was also used to study the kinetics of chlorination of aqueous p-toluenesulfonic acid and m-aminophenol-hydrochloride. All the reactions were found to be first order in Cl₂ and first order in the dissolved organic substance. The values of second order rate constants at 30°C varied from about 1.1 x 10⁶ to 5.7 x 10⁹ cm³/g mole sec for phenolic substances and from 1.1 x 10⁶ to 3.5 x 10⁶, cm³/g mole sec for the sulfonic acids.Chlorination of o- and p-chlorophenol in aqueous buffered solutions was analysed on the basis of absorption of Cl₂ followed by two parallel fast pseudo-first order reactions, where the hydrolysis of Cl₂, catalysed by buffer anion, and the chlorination of chlorophenol were found to occur in the liquid film.Measurements of the effective interfacial area and the liquid-side mass transfer coefficient were made in a mechanically agitated contactor and a bubble column by using some of these chlorination reactions.     

Absorption of 2-butene and 2-methyl-2-butene in aqueous solutions of sulphuric acid

The kinetics of absorption of 2-butene in aqueous solutions of sulphuric acid was studied in a stirred cell in the range of acid concentration from 70·2 per cent w/w (11·5 g mole/l.) to 80·2 per cent w/w (14·56 g mole/l.). The absorption was found to conform to fast pseudo-first order mechanism. The pseudo-first order reaction rate constant at 28°C was found to vary from about 500 to 3·8 × 10⁶ sec^?1 over the above concentration range.The absorption of 2-methyl-2-butene (isoamylene) in aqueous solutions of sulphuric acid was also found to conform to fast psuedo-first order mechanism, in the range of acid concentration from 61·5 per cent w/w (9·395 g mole/l.) to 75 per cent w/w (12·845 g mole/l.). The pseudo-first order reaction rate constant at 30°C was found to vary from about 4·2 × 10⁵ to 2·2 × 10⁸ sec^?1 over the above concentration range.     

Using a statistical multiresponse method of experimental design in a reaction network study

A statistical design method for multiresponse models was used in an experimental study of a reaction network. The study involved the vanadia-catalysed oxidation of o-xylene using a recirculation reactor. Concentrations of reactants and temperature were used as operating variables, and the concentrations of products were the measured responses. The published design procedure was modified by conducting several runs after each design evaluation to reduce computing costs while retaining the benefits of statistical design and analysis. This enabled network analysis to be conducted efficiently to the limits of the equipment, and pointed the way to improved estimates of the parameters.     

Absorption of carbon dioxide in ethylenediamine solutions i. absorption kinetics and equilibrium

The chemical absorption of carbon dioxide by a laminar jet of ethylenediamine has been studied at 25.5°C under pseudo-first-order kinetic conditions. The reaction was found to be second-order with a rate constant of 1.0 x 10⁵ 1/g. mole sec. Equilibrium calculations at 18°C indicate that the partial pressure of carbon dioxide is very low, even over highly carbonated ethylenediamine solutions. The effects of amine concentration and carbonation ratio on the physical solubility and diffusivity of carbon dioxide in solution were inferred from corresponding results for nitrous oxide     

Sodium bisulfite-initiated polymerization of methyl methacrylate in aqueous medium in the presence of the metal oxides CuO and MnO2

Sodium bisulfite-initiated polymerization of methyl methacrylate (MMA) in water medium was carried out in the absence and in the presence of cupric oxide and manganese dioxide using various initiator concentrations at various temperatures ranging from 30° to 60°C. It seems that the metal oxide–water interface plays an important role, as it has been found that both oxides accelerate the rate of polymerization. Cupric oxide was found to be more effective than manganese dioxide. The cupric oxide was found to have nearly the same catalytic effect as the cuprous oxide, and manganese dioxide was found to be somewhat more effective than titanium dioxide. The initial rate of polymerization increased from 2.3 × 10^?5 mole/(l.sec) to 3.4 × 10^?4 mole/(l.sec) and to 6.6 × 10^?5 mole/(l.sec) when the metal oxide concentration increased from 0 to 3 g/l. in case of cupric oxide and manganese dioxide, respectively. The initial rate of polymerization increased from 3.7 × 10^?4 mole/(l.sec) to 4.2 × 10^?4 mole/(l.sec) and from 7.2 × 10^?5 to 2.2 × 10^?4 mole/(l.sec) when the temperature was raised from 30° to 60°C in the presence of cupric oxide and manganese dioxide, (9 g/l.), respectively. Both the rate of polymerization and the number-average molecular weights were found to increase with increase the monomer concentration; the rate values were higher while the number-average molecular weights were lower in case of cupric oxide than in case of manganese dioxide. For example, the rate of polymerization increased from 2 × 10^?5 mole/(l.sec) to 8.1 × 10^?5 mole/(l.sec) and from 1.9 × 10^?5 mole/(l.sec) to 6.9 × 10^?5 mole/(l.sec); and the number-average molecular weight increased from 0.7 × 10⁵ to 2.2 × 10⁵ and from 1.5 × 10⁵ to 4.9 × 10⁵ in the presence of cupric oxide and manganese dioxide (10 g/l.), respectively, when the monomer concentration was increased from 23.5 g to 94 g/1. water. The apparent energy of activation for the polymerization of methyl methacrylate in water medium between 40° and 50°C was found to be 0.8 and 4.3 kcal/mole when using cupric oxide and manganese dioxide (9 g/l.), respectively.     

Oxidation of propane over a diesel exhaust catalyst

The oxidation of propane, over a concentration range of 0.30 to 1.04 mole % in air was investigated over a commercial diesel exhaust catalyst consisting of CuO, Cr₂O₃ and Pd supported on Al₂O₃. The rate of reaction was correlated by a first order, irreversible rate function; the resulting pre-exponential factor and activation energy were 3.15 × 10⁷ cc/g-sec and 21.3 kcal/gmole, respectively. At high temperatures the reaction rate became influenced by pore diffusion. A temperature of 675°K was required to obtain 50% propane conversion. It was concluded that this catayst is unsuitable for catalytic mufflers on diesel buses since the measured value of diesel exhaust temperatures at the cataytic muffler inlet is significantly less than 675°K.     

Oxidation of Benzene to Maleic Anhydride in a Fluidized Bed Reactor

In this project, the selective oxidation of benzene to maleic anhydride (MAN) was studied. Gas phase catalytic oxidation of benzene was carried out in a laboratory scale fluidized bed reactor on six different types of catalysts, which have different compositions. Effects of temperature, flow rates of benzene and air and catalyst type on the reaction selectivity were investigated at atmospheric pressure. The experiments were performed over a temperature range of 325 to 400 °C, a space‐time (W/F_A0) range from 11.28 × 10⁵ to 31.9 × 10⁵ g s mol^–1, and benzene/air mole ratio changes between 0.0109 and 0.0477. It was seen that conversion of benzene to MAN increased with increasing temperature for the catalysts supported by silica gel, aluminum oxide and titanium oxide. From the results it was found that conversion increased with increasing flow rate of air. When the comparison of the catalysts were made, it could be said that catalysts supported by silica gel showed higher MAN conversions. So it can be concluded that catalysts supported by silica gel were more suitable catalysts for benzene oxidation to MAN in a fluidized bed reactor.     

MULTIRESPONSE MODELING OF THE OXIDATION OF NAPHTHALENE OVER A VANADIA CATALYST

The oxidation of naphthalene was studied over an industrial vanadium pentoxide (V₂O₅) catalyst which was promoted by potassium sulphate. Multi-response data were obtained at 335, 350, 365 and 380°C for oxygen to naphthalene mole ratios from 47:1 to 3:1. The data were fitted to the two-step Redox and Steady State Adsorption (SSAM) Models using multiple-response non-linear regression techniques.

In this, the first reported study of the application of multi-response techniques to modeling of naphthalene oxidation, certain inadequacies in the two-step models have been found. In particular, negative activation energies were obtained for the oxidation of naphthalene and 1,4-naphthoquinone in the formation of phthalic anhydride. An activation energy of 146 kJ.mol^-1 was obtained for the rate of oxidation of the catalyst. The overall process of naphthalene oxidation was highly temperature-sensitive over the range of temperatures investigated as evidenced by an effective activation energy of 125 kJ.mol^-1.     

A SEQUENTIAL PROCEDURE FOR PRECISE ESTIMATION OF PARAMETERS IN KINETIC MODEL

For a determined mathematical model,it is not only necessary to obtain the estimates of parameters,but also their reliabilites.The present work deals with a sequential statistical design strategy for anexperimental program to obtain precise parameter estimetes for a nonlinear kinetic model.It aims at de-creasing the indeterminatness of the parameter estimates,in reducing the correlation between parameterestimates,and in inceasing the adequacy and accuracy of the model.The paper discusses the experimental design criterion for precise parameter estimates-the minimun vol-ume design criterion and the spherical shape design criterion,and the practical value of a sequential statis-tical design strategy.At last,an example was performed to precise estimate the parameters in the kinetic model of ammoniasynthesis reaction which was selected as being adequate in the previous work.Comparison of the results from the industrial unit and the corresponding values calculated with themodel using the estimates of parameters reveals the reasonable reliability of the model.     

The Adsorption of a Polystyrene-b-Polyisoprene Block Copolymer at the n-Hexadecane/Air Interface

Surface-tension measurements were used to investigate the surface adsorption and micellisation of a polystyrene-b-polyisoprene block copolymer in n-hexadecane which is a selectively bad solvent for polystyrene. Measurements were made over a range of concentrations (1.29–2.88)x10^?4 mol dm^?3 and temperatures 25–40°C. The block copolymer was found to be positively adsorbed at the n-hexadecane/air interface. The linearity of plots of γ against In c just below the critical micelle concentration (c.m.c.) indicated an approximately constant surface concentration. The area per block copolymer molecule at the surface had an average value of 4.1 nm². A plot of In (c.m.c.) against T^?1 gave a value for the standard enthalpy of micellisation of -41.9.3.0 kJ per mole of copolymer chains. The standard entropy contribution (-TΔSΔ) to the standard free energy of micellisation was found to be 19.7.3.0 kJ mol^?1. These thermodynamic values are in good agreement with results obtained earlier for this system by light scattering and calorimetry.     

An analysis of reverse osmotic characteristics of American-standard type tubular module

Reverse osmosis experiments were carried out with a TM-5-14 tubular module to obtain its reverse osmotic characteristics. Analysis of the data based on the general equations proposed by Ohya and Sourirajan (5) gives membrane characteristic constants, A = 0.845 x 10^?6 g·mole H₂O/cm²·atm·s, and (D_AM/ kδ) = 1.38 x 10^-5cm/sec. The experimental data of mass transfer coefficients agree well with the equation proposed by Linton and Sherwood (7).     

Analysis of irreversible oxidation wave of adsorbed CO at Pt(1 1 1), Pt(1 0 0) and Pt(1 1 0) electrodes

The oxidation wave of CO preadsorbed at 50 mV on Pt(1 1 1), (1 0 0) and (1 1 0) electrodes in phosphate buffer solution of pH 3 was observed as a function of the sweep rate. The sweep rate dependence of the peak current and peak potential, as well as the form of the wave, were examined on the basis of the Gilman mechanism that the electron transfer from a complex consisting of CO and oxygen containing species is the rate-determining step. An electron transfer step from CO itself was excluded. The peak current and peak potential analyses and the wave simulation gave the same value for f, the change in the interaction energy during the formation of the activated complex from the reactants. f was sweep-rate and surface-structure dependent. The nature of f was discussed.Nomenclature symmetry factor - reversible work required to bring an adsorbed species from its standard state - µ electrochemical potential - electrode potential referred to the reversible hydrogen electrode - _p peak potential - _1/2 width at half height of the oxidation wave - (a) adsorbed state - f() mutual interaction energy of the activated complex inRT units - f(R) mutual interaction energy of the reactants in RT units - f f() –f(R) - i oxidation current density, mA cm^–2 - i _p peak current, mA CM^–2 - k rate constant - Q ₀ electric charge, mCcm^–2 - v sweep rate, m Vs^–1 This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribuion to electrochemistry.     

An analysis of reverse osmotic characteristics of ROGA-4000 spiral-wound module

Reverse osmosis experiments were carried out with a ROGA-4000 Spiral-Wound module to obtain its reverse osmotic characteristics. Analysis of the data based on the general equations proposed by Ohya and Sourirajan (10) gives membrane characteristic constants, A = 1.24 × 10^-6 g mole H·₂O/cm²·atmsec, and (D_AM /kδ) = 2.3 × 10^-5 cm/sec, which show the membrane belongs to the CA-NRC-18 type family. The experimental data of mass-transfer coefficients always show about 35% lower values than the theoretical value of laminar flow between flat parallel membranes proposed by Kimura and Sourirajan (12).     

Sequential statistical design strategy in a kinetic study of propylene oxidation

A sequential design strategy was used to direct an experimental kinetic study of propylene oxidation over bismuth molybdate. Two statistical criteria were used to design experiments. The first is a joint criterion for the dual problem of model discrimination and parameter estimation which was proposed by Hill et al. (1968), but which to the best of our knowledge has not been tested in an experimental program. Using this joint criterion design, it was demonstrated that both the objectives of model discrimination and precise parameter estimation were effectively accomplished. After model discrimination had been achieved, a design strategy for further improvement in parameter precision was found, as expected, to be effective for that purpose.     

Investigation of water electrolysis by spectral analysis. I. Influence of the current density

The potential (or current) fluctuations observed under current (or potential) control during gas evolution were analysed by spectral analysis. The power spectral densities (psd) of these fluctuations were measured for hydrogen and oxygen evolution in acid and alkaline solutions at a platinum disk electrode of small diameter. Using a theoretical model, some parameters of the gas evolution were derived from the measured psd of the potential fluctuations, such as the average number of detached bubbles per time unit, the average radius of the detached bubbles and the gas evolution efficiency. The influence of the electrolysis current on these parameters was also investigated. The results of this first attempt at parameter derivation are discussed.Nomenclature b Tafel coefficient (V^–1), Equation 46 - C electrode double layer capacity (F) - e gas evolution efficiency (%) - f frequency (Hz) - f _p frequency of the peak in the psd _v and _i (Hz) - F Faraday constant, 96 487 C mol^–1 - l electrolysis current (A) - J electrolysis current density (mA cm^–2) - k slope of the linear potential increase (V s^–1), see Fig. 1 - n number of electrons involved in the reaction to form one molecule of the dissolved gas - r _b radius of a spherical glass ball (m) - r _e radius of the disk electrode (m) - R _e electrolyte resistance () - R _p polarization resistance () - R _t charge transfer resistance () - u ₁ distribution function of the time intervals between two successive bubble departures (s^–1) - v _g mean volume of gas evolved per unit time (m³ s^–1) - v _t gas equivalent volume produced in molecular form per unit time (m³ s^–1) - V ₀ gas molar volume, 24.5×10^–3 m³ at 298 K - x ₀ time pseudoperiod of bubbles evolution (s) - Z electrode electrochemical impedance () Greek characters _e dimensionless proportional factor (Equation 19) - slope of log /logJ and loge/logJ curves - number of bubbles evolved per unit time (s^–1) - _a activation overpotential (V) - _ci concentration overpotential of reacting ionic species (V) - _cs concentration overpotential of dissolved molecular gas (V) - _ohm ohmic overpotential (V) - _t total overpotential (V) - v parameter characteristic of the gas evolution pseudoperiodicity, Equation 13 (s^–1) - time constant of the double layer capacity change (s) - _v power spectral density (psd) of the potential fluctuations (V² Hz^–1) - _i power spectral density (psd) of the current fluctuations (A² Hz^–1) Special symbols spatial average of the overpotential _j over the electrode surface - time averaged value of - _j fluctuation of around - <> mean value of the total overpotential jump amplitude due to a bubble departure - <I> mean value of the current jump amplitude due to a bubble departure Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.