Substrate-inhibited enzyme reaction in a tubular reactor with axial dispersion

For a fixed set of physico-chemical parameters, an isothermal substrate-inhibited enzyme reaction in a tubular reactor with axial dispersion can give rise to multiple steady states. Criteria previously developed for non-isothermal reactions are applied to this case to develop analytic conditions which ensure uniqueness of steady states. The criteria compare well with values obtained from exact numerical calculations.     

Influence of flotation reagents on the wet grinding of quartz

A study has been made of the grinding of quartz in a porcelain laboratory ball mill as a function of pH and concentration of surfactants.In view of the grinding tests performed and the literature data on the surface properties of quartz, the grindability of quartz must be assumed to be dependent on surface charge; the grindability is a minimum under conditions of zeta-potential equal to zero. Extreme sensitivity of grinding to a concentration of Fe species has been found.     

Stability of the steady states and transient behavior for a non-isothermal bimolecular langmuir-hinshelwood reaction

The steady state stability and transient behavior of a catalytic reaction following the bimolecular Langmuir-Hinshelwood expression, phenomenologically adequate for carbon monoxide and hydrocarbon oxidation on noble metal catalysts, is describe. The corresponding steady state problem was discussed earlier. Some unique features of the isothermal and non-isothemal transient behavior with uniform initial conditions are identified.     

Simultaneous diffusion and chemical reaction in two-phase systems

An approximation is given for the case of simultaneous steady state diffusion and chemical reaction in a liquid—liquid system under such conditions that diffusion and chemical reaction are of the same order of magnitude in the two phases. The two-film model was adopted to represent the system, and results were plotted as variations of the enhancement factor with the diverse parameters affecting it. Comparison was made with an exact numerical solution, and the results show that the proposed approximation leads to small errors for low reaction rates, and gives a first approximation for the mass transfer rate for very rapid chemical reactions.     

Isothermal diffusion—reaction in a slab catalyst with bimolecular Langmuir-Hinshelwood kinetics: Connections with negative first-order kinetics

The problem of isothermal diffusion-reaction in a slab catalyst with bimolecular Langmuir—Hinshelwood kinetics is studied. Analytic solutions for the concentration profile and the catalytic effectiveness factor are reported for the full range of Thiele modulus values, in the limit of large adsorption inhibition constant. In this limit, connections with negative first-order kinetics are shown, and rather good explicit estimates of the region of multiple steady states are provided. Comparisons with numerical calculations are also made.     

Bubble dissolution with chemical reaction

The dissolution of an isolated stationary gas bubble, enhanced by a chemical reaction, in a large body of liquid is investigated. A theoretical model which properly accounts for the movement of the interface due to dissolution is formulated and solved using the method of finite differences. The finite difference results are used as a standard of comparison for the testing of various approximate solutions. These include a perturbation expansion, a quasi-stationary approximation and a quasi-steady approximation. The results of this work indicate that the quasi-steady approximation, which provides very simple analytical solutions, is an excellent one in the presence of a sufficiently rapid chemical reaction.     

Redox reaction of tri(2-deoxy-2-L-ascorbyl)amine. Formation of a persisting free radical species in water

Electrochemical studies showed that tri(2-deoxy-2-L-ascorbyl)amine ($\text{1}$), a new compound isolated as one of the products of reaction of dehydro-L-ascorbic acid with phenylalanine (with added L-ascorbic acid) in ethanol, is oxidized in aqueous solution in two reversible one-electron transfer steps, on mercury or platinum electrode. The first step occurs through the dianion, and its product is an unusually stable blue anion radical giving a characteristic ESR signal. The product of the second step of oxidation is labile and is slowly converted into the oxidized form of di(2-deoxy-2-L-ascorbyl)amine, presumably by hydrolysis with splitting of L-ascorbic acid.     

Metering of solids by a rotary valve feeder

The construction of a rotary vane-type solid feeder valve is described. It is shown that at low speeds the rate of solids flow through the valve is directly proportional to the rate of revolution. At higher speeds, the rate of increase of solid feed rate falls off until the rate becomes constant when the rate of solid flow through the rectangular orifice is limiting. The rate of flow through the valve is correlated by an equation that links the speed and geometry of the valve to the properties of the solid.     

The hydrogen electrode reaction characteristics of thin film electrodes of Ni-based hydrogen storage alloys

Film-type electrodes of hydrogen absorbing intermetallic compound and alloys, LaNi₅, Ni_0.11 Ti_0.89, Ni_0.50 Ti_0.50 and Ni_0.76 Ti_0.24 were prepared by a flash evaporation method. The hydrogen electrode reaction characteristics of the LaNi₅ and NiTi alloy films in 1 M NaOH are very similar to each other. The reaction proceeds via the Volmer-Tafel reaction route with mixed rate-determining characteristics. The exchange current densities of the constituent steps, as well as the overall reaction, are in the range of 10^?6 A cm^?2 (true). Surface analysis by an XPS technique has shown that La or Ti on the electrode surface exists as an electrocatalytically innert oxide of La₂O₃ or TiO₂. Close similarities of these electrodes with pure Ni electrodes indicate that Ni is responsible for the electrocatalytic activity. No synergistic effect is thus noticeable.     

Size distribution of droplets created by vapour condensation through a cooled pipe

The average droplet size and the size distribution of droplets created by passing vapour through a cooled pipe are studied. The idea of the existence of a Peclet number dependent upon the critical length, for which the non-uniformity of the droplet reaches a maximum, is logically proposed here and demonstrated by applying a relatively crude analysis. In spite of the use of a simplified model, the results also indicate that the droplet distribution follows a zero-order logarithmic normal distribution—fact that was experimentally determined by Davis and Nicolaon [3].     

Application of the reaction kinetics and dispersion model to gas-solid reactors for removal of sulfur dioxide from flue gas

The conversions of a reactive, micro-grained limestone were studied in terms of exposure time and concentration of sulfur dioxide in the flue gas. The rates of the sulfation reaction were correlated as a function of the conversion of calcium oxide to sulfate and concentration of sulfur dioxide in the gas phase. In comparison with active sodium carbonate the sulfation of limestone particles proceeds at the rate which is substantially lower than the sulfation rate of soda particles.The empirical kinetic equation developed in this study is further applied in a two-phase dispersion model of simplified non-ideal flow behavior of the gas and solid in the reactor. The model can serve a rational basis for the conceptual design of a suitable contacting apparatus. Numerical solutions of the model equations outline possibilities and limitations of the dry lime process for the removal of sulfur dioxide from hot flue gas.     

Study of interfacial kinetics for liquid-liquid systems—II: Intrinsic kinetics of the copper chelation reaction with an oxime-based reagent

The interfacial chelation of copper from copper sulfate-sulfuric acid solutions by the commerical oxime extractant LIX65N in toluene is studied using the liquid jet recycle reactor. The intrinsic initial rate of copper chelation by LIX65N is found to be represented in mol. cm^?2-sec^?1 by the expression R = $\text{1.22 × 10}{}^{\mathrm{?8}}\text{{Cu}{}^{\mathrm{2+}}\text{}[LIX65N]}\text{{H}{}^{\mathrm{+}}\text{} + 0.0288[LIX65N]}$ where {Cu²⁺} and {H⁺} are the cupric and hydrogen activities. The interfacial rate expression above is determined as free from diffusional contributions by using a numerical solution to model mass transfer with interfacial reaction in the LJRR. The above expression is selected on statistical and physical grounds from a set of models systematically generated from the most probable reaction pathways. The liquid jet technique has been shown to be an effective and accurate (±6% experimental error) technique for the study of liquid-liquid interfacial reactions.     

Photocatalysis in a slurry reactor

A series of experiments have been conducted on the photocatalytic reduction of methylene blue with zinc oxide catalyst in a slurry reactor. It is shown that by using a procedure involving separate experiments to determine the shielding effects of the suspended solid (inert solid of similar particle size with a standard actinometric solution) it is possible to identify experimentally the region in the reaction system where imperfect solids mixing influences the rate of reaction. The reactor employed here is also shown to provide a relatively simple means for kinetic measurements in photocatalytic reactions. The rate constants obtained in this study for methylene blue reduction were weakly dependent on zinc oxide concentration in the suspension. A value of 3·67 M^?1 sec^?1 at 0·1 wt.% ZnO at 31·9°C was obtained, where M is the molarity of the solution in methylene blue. This may be compared with 1·25 × 10⁴M^?1 sec^?1 reported by Yoneyama [14] for methylene blue reduction on a rutile crystal of titanium dioxide at room temperature, and 3·33 M^?1 sec^?1 for p-nitrosodimethylaniline reduction in a 0·1 wt. % ZnO suspension, also at room temperature[13].     

Verification of a model for estimating the void fraction in a three-component randomly packed bed

The void fraction in a three-component randomly packed bed was calculated from the authors' model, and the calculated values were compared with published experimental data for spherical and irregularly shaped particles and with results from computer simulations. Results from the model were in good agreement with simulated and published experimental data.     

Morphological characterization of reaction injection moulded (RIM) polyester-based polyurethanes

Characterization studies of reaction injection moulded (RIM) processed (in-situ polymerized) polyester-based segmented thermoplastic polyurethane have been performed utilizing various morphological techniques. The fast and exothermic urethane polymerization results in large temperature gradients in the mould which influence molecular weight and morphological structures. The present work is conducted to draw relationships between sample morphology and the processing conditions utilized to form the polymer.     

Experimental determination of axial dispersion coefficient in a bubble column

A new graphical method of finding axial dispersion coefficients in a bubble column is developed. This method requires only the area above an experimental curve, thus is simpler than the conventional method of curve fitting. The new method is used to find the dimensionless dispersion number in the bubble column and shows that the dispersion number decreases with column Reynolds number due to increasing coalescence of bubbles at higher gas flow-rates.