EFFECT OF DISSOLVED INORGANIC SALTS ON THE VAPOR-LIQUID EQUILIBRIA AND ENTHALPY OF MIXING OF THE METHANOL-ETHYL ACETATE SYSTEM

The effect of three inorganic chloride salts, namely, sodium chloride, calcium chloride and zinc chloride on the vapor-liquid equilibria (VLE) and heat of mixing (h.o.m) of the methanol-ethyl acetate system has been investigated under the atmospheric conditions of 760 ± 3 mm Hg pressure. In the experimentation for VLE a Smith and Bonner type equilibrium still was used while in h.o.m. determination a calorimeter connected to a microprocessor-based control unit (MIPROC) which displays digitally the heat of mixing values in calories was employed. All the three salts dissolved to various concentration levels in the solvent mixture brought about a decrease in the azeotropic composition (expressed in terms of mole fraction of methanol) from 0.75 to values like 0.50, 0.37 and 0.18 depending upon the salt added and its concentration level. The salts sodium chloride and calcium chloride which are more soluble in methanol have been found to salt-in that component but with a peculiarity in that, in methanol-rich region the salting-in effect was substantial while in the methanol-lean region it is only marginal. The addition of salt zinc chloride which is more soluble in ethyl acetate results in an anomalous behaviour.

As for the salt effect on h.o.m., the addition of calcium chloride brought about a significant enhancement in the h.o.m values while the salts sodium chloride and zinc chloride (which could be added only to about 5% by weight concentration due to the experimental difficulties) entailed a decrease and lateral shift respectively in the h.o.m. values.

The VLE and h.o.m data which were found to be thermodynamically consistent have been correlated respectively by NRTL, Wilson and by a model similar to the Scatchard series type equation.     

STUDY OF THE PARAMETERS CONTROLLING THE ALTERNATING COPOLYMERIZATION OF METHYL METHACRYLATE AND STYRENE

The copolymerization of methyl methacrylate and styrene, in the presence of zinc chloride, was conducted in the aqueous phase. The zinc chloride acting as a complexing agent

Among the factors affecting the polymerization yield, we have; the level of complexing agents, the monomer ratio and the temperature

The polymers were characterized for their molecular weight (G.P.C.) and analyzed by N.MR, and D.T.A

A model taking into account the various parameters is proposed.     

ON THE DEVELOPMENT OF MULTIDIMENSIONAL TWO-FLUID MODELS FOR VAPOR/LIQUID TWO-PHASE FLOWS

The status of multidimensional two-fluid modeling of vapor/liquid two-phase flows is reviewed. In particular, a three dimensional two-fluid model is derived using ensemble averaging. It is proposed that realistic interfacial closure laws should:

• Be mathematically objective

• Lead to well-posed models

• Satisfy the second law of thermodynamics

• Agree with all relevant experimental data.

Unfortunately, most two-fluid models in use today do not satisfy these fundamental constraints.     

REACTIVE EXTRACTION OF SALICYLIC ACID AND D, L PHENYLALANINE IN A STIRRED CELL

Physical and reactive extractions of salicylic acid from the aqueous phase in a stirred cell were investigated theoretically and experimentally. A secondary amine, Amberlite LA 2, was used as the complexing agent for the acid

Reactive extraction of phenylalanine from the aqueous phase was investigated in the same way. For this, a quaternary amine, TOMAC, was used in which the chlorine ion was exchanged by the phenylalanine anion

Because of the instantaneous reaction in both cases, the mass transfer processes are diffusion-controlled. The concentration vs. time curves can be satisfactorily described by the two-film models. The reaction enhances the extraction considerably.     

SELECTIVITY STUDIES IN THE PHOTOCHLORINATION OF METHANE II: EFFECT OF THE RADIATION SOURCE OUTPUT POWER AND OUTPUT SPECTRAL DISTRIBUTION

The effect of the output power and output spectral distribution of the radiation energy fed to a photoreactor upon the reaction yield and selectivities is studied both theoretically and experimentally. The study aims at the analysis of these influences in a series reaction such as the photochlorination of methane where methylene chloride and eventually chloroform are the most valuable products. The computational model employed has been verified for a group of selected conditions by means of bench-sale experiments.

It is found that the chlorine conversion shows the expected square root dependence with respect to the Local Volumetric Rate of Energy Absorption (LVREA). This dependence, in a first approximation, can also be assigned to the effect of the radiation source output power upon yield. It is also found that by manipulating the amount of radiation power fed to the reactor it is possible to ascertain the operating conditions favoring the production of predetermined intermediate products (e.g., methylene chloride or chloroform).

It is concluded that the use of customized lamps especially designed for each particular product on the basis of feasible changes in the characteristics of the existing radiation sources will favor a selective and more economical production of some of the stable intermediates, i.e., lamp design is an important feature in any optimal process design.     

A MONTE-CARLO APPROACH TO THE INTERPRETATION OF BUBBLE PROBE SIGNALS IN FREELY BUBBLING FLUID BEDS†

The interpretation of the signals generated by a double probe may be done by the three characteristic times method:

t₁ the time duration of the pulses;

t₂ the time shift between the signals of the two probes;

t₃ the time interval between two pulses on one channel.

Each of these times is largely dispersed and the corresponding histograms may be constructed.

The present work is a trial to go over from the time histograms to physical properties of the bubbles combining a Monte-Carlo simulation and a flexible simplex optimisation procedure.

As a result, the percentage of oblique bubbles cutting just one level, the bubble size distribution, the average velocity-size relation, and the individual dispersion around it may be defined.

The procedure is finally applied to experimental results obtained with a light probe in a fluid bed of glass beads.     

THE CHARACTERIZATION OF MICROMIXING USING FAST MULTIPLE REACTIONS

Micromixing (mixing at the molecular scale) may be characterized by following fast, competitive, consecutive reactions having the following stoichiometry:

A + B → R (1)

R + B → S (2)

provided that reaction mechanism and kinetics are known. This paper includes many results obtained within the last five years, in particular (a) diffusion-reaction equations for a sheared lamina within which (1) and (2) occur, and (b) comparisons of this and other diffusion-reaction models with measured product distributions.     

CONTRIBUTION TO THE ANALYSIS OF THE SELECTIVITY OF GAS-LIQUID REACTIONS PART II: COMPARISON OF EXPERIMENTAL RESULTS WITH MODEL PREDICTIONS

The chlorination of paracresol is used in an experimental study of selectivity in gas-liquid contactors.

Experiments in a batch reactor show the influence on selectivity of the dimensionless numbers presented in Part I and involving competition between mass transfer and chemical reaction together with the hydrodynamics.

The extension of open reactor model presented in Part 1 to the batch reactor permits a comparison between theory and experiments and shows a good agreement     

THE ELECTRODEWATERING OF SEWAGE SLUDGES

Electrodewatering (EDW), the enhancement of conventional pressure filtration by an electric field, is an emerging technology with the potential to improve dewatering especially for difficult materials. CSIRO has many years of experience in EDW, ranging from bench scale tests to demonstration trials. A recent programme has investigated the applicability of EDW to aerobic wastewater treatment sludges which are particularly difficult to dewater using conventional equipment.

The bench scale filtration experiments produced cakes with solids contents of 35-46 wt% using EDW, compared with 24-30 wt% using pressure filtration alone. This paper : • describes how the dewatering results were achieved;

•identifies a relationship between moisture removal limits by EDW and the forms of water within the sludge;

•shows the results of preliminary attempts to mathematically model the EDW process     

DEVELOPMENT OF RANEY-TYPE LOW TEMPERATURE METHANOL SYNTHESIS CATALYSTS†

Catalysts prepared by caustic leaching of Cu—Zn—Al alloys are shown to have activities greater than those of a commercial copper-based catalyst.

Complete leaching of alloys containing 50 wt.% aluminium, with between 0 and 50 wt.% copper, and the balance zinc produced catalysts having a wide range of activities. The most active catalysts for methanol production were produced from alloys containing from 10 to 20 wt.% zinc.

The activities of catalysts prepared by the partial leaching of an alloy containing approximately 36% copper, 15% zinc and 48% aluminium were shown to pass through a maximum at a leaching time of 2.75 hours. This catalyst had more than double the activity of a commercial catalyst al reaction conditions similar to those employed industrially.     

KINETICS OF THE HYDROLYSIS OF ACRYLONITRILE TO ACRYLAMIDE OVER RANEY COPPER

Measurements of the kinetics of the hydrolysis of acrylonitrileover Raney copper catalysts have been made in the temperature range 40 to 100°C in a tubular reactor operated differentially with and without recycle and over concentration ranges of 0-25 weight percent acrylonitrile, 0-35 weight percent acrylamide and 40-99 weight percent water.

For the concentration range 0 to 7 wt. % acrylonitrile and 0 to 7 wt. % acrylamide, data were fitted by an adsorption model of the type

A + K,CA + KCCC and at higher concentrations by the powers law expression

The activation energy for the reaction was found to be 49.2kJmol^-1. Both models showed that the product acrylamide strongly inhibits the reaction.     

ON THE PERMEATION OF SOME GASES THROUGH THE LAMELLAE OF STATIC FOAMS. A PRELIMINARY APPROACH

Basing on the capillary method for the determination of foam bubble size, a method was proposed for establishing values of permeability coefficients of several gases. The permeability coefficients of He, Ar, H₂, N₂, CH₄ through the lamellae of static foam bubbles were preliminarily determined using this method.

A rough dependence of the N₂ permeability coefficient through the lamellae of static foam bubbles on the foam wetness and surfactant concentration was also found.

The results obtained lead to the conclusion that the Princen-Mason diffusion model of gas permeation through an isolated soap film was inadequate in the case of permeation through lamellae of bubbles forming a static foam.

A hypothesis that the gas permeation through the lamellae of a static foam is primarily caused by liquid convection in the lamellae core was put forward.     

THE EFFECT OF SUBSTRATE MASS TRANSFER LIMITATIONS IN AN IMMOBILIZED ENZYME MEMBRANE REACTOR

An unstirred ultrafiltration cell can be quite easily converted into an immobilized enzyme reactor. Indeed, if suitable amounts ofproteic solutions are fed and if the protein molecular weight exceeds the membrane cut off, gel precipitation occurs onto the active surface of the membrane because of concentration polarization phenomena. Two different gel formation procedures have been followed. Indeed, two different proteic solution have been injected, namely

1.a mixture of an inert protein and the enzyme

2.co-polymer obtained by co-cross-linking the enzyme and the inert protein.

Substrate mass transfer limitations which occur in the gel immobilized enzyme reactor have been considered. The relevance of mass transfer resistances upstream from the immobilized gel layer has been discussed together with the intrinsic enzyme kinetics.

A heterogeneous gel model has been proposed which adequately describes the experimental results. Effectiveness factor correlations of fairly general applicability have been also presented.     

STABILIZATION OF ZEOLITIC HYDROCRACKING CATALYST

The stability of a palladium-containing hydrocracking catalyst is improved by the ion exchange addition of zinc. The zinc appears to be uniformly distributed near the cracking sites where it effectively hydrogenates the coke precursors to minimize coking and maintain catalyst activity.

To be effective, the zinc ion exchange should be conducted at low pH to prevent zinc precipitation, and the catalyst should be reduced with H₂ prior to use. Incorporation of zinc has no effect on the initial activity of the hydrocracking catalyst     

THE INFLUENCE OF PRESSURE AND TEMPERATURE ON THE KINETICS OF VACUUM DRYING OF KETOPROFEN

This paper explores the influence of temperature and pressure on drying kinetics of 2-(3-benzoylphenil propionic acid) ketoprofen, in a vacuum dryer on laboratory scale, Experimentally determined relations between moisture content and drying rate vs time, were approximated with an exponential model. Model parameters were correlated with drying conditions (temperature, pressure) and defined by functions of their potentions.

From an energy balance of the process, a mathematical model for simulating dependence of sample temperature vs drying time, and moisture content of material, has been developed.

Simulation of the drying kinetics and sample temperature, by use of those functional dependencies shows good agreement with experimental results.     

RECIRCULATING REACTOR FOR THE STUDY OF MULTIPHASE KINETICS

A new laboratory reactor was set up to measure kinetic coefficients in a solid (catalyst)-liquid-gas reacting system.

The reactor consists of two parts: an absorber, where the liquid is partially saturated by the gas reactant and a reacting zone, where the liquid alone, containing the dissolved gas, flows through a fixed bed of catalyst.

The ricircle of the liquid in the absorber maintains a high concentration of the gas reactant in the liquid also in the zone of reaction, allowing the use of a high mass of catalyst (significative from a statistical point of view) and the achievement of sufficiently high conversion.

The tested reaction is the catalysed hydrogenation of ∝-metylstyrene: in order to consider a drastic situation and to verify the results with the literature data, the experimental conditions examined corresponded to very high chemical reaction rate (instantaneous reaction) at the surface of the pellets.

The tests were carried out with the reactor working both in batchwise and in continuous operative mode (steady state); the results show the reliability of the new reactor above all when the steady state operation is considered. For the use of the reactor in batchwise condition, the accumulation of the product inside the catalyst particles must be considered for an accurate measurement of the kinetic parameters,     

A KINETIC MODEL FOR THE PRODUCTION OF LIQUIDS FROM THE FLASH PYROLYSIS OF BIOMASS

A kinetically based prediction model for the production of organic liquids from the flash pyrolysis of biomass is proposed. Wood or other biomass is assumed to be decomposed according to two parallel reactions yielding liquid tar and ( gas + char) The tar is then assumed to further react by secondary homogeneous reactions to form mainly gas as a product

The model provides a very good agreement with the experimental results obtained using a pilot plant fluidized bed pyrolysis reactor

The proposed model is shown to be able to predict the organic liquid yield as a function of the operating parameters of the process, within the optimal conditions for maximizing the tar yields, and the reaction rate constants compare reasonably well with those reported in the literature     

HEAT AND MASS TRANSFER IN THE SHORT-TERM CONTACT OF THE MOIST MATERIALS WITH THE HEATING SURFACE

Compounded boundary-valued problem of the diffusion-filtering heat and mass transfer with arbitrary dimensions of the transfer potential vector was raised and solved based on the theory of short-term contact between the moist material and heat-transfer surface.

The boundary lines of the application of the short-term contact models were established.

The solution of the problem allows to select the directions of the intensification of the drying processes with short-term contact of the phases and to calculate various technological characteristics of the drying processes.     

THE SYNTHESIS AND EVOLUTION OF NETWORKS OF HEAT EXCHANGE THAT FEATURE THE MINIMUM NUMBER OF UNITS

An important problem in the design of chemical processes is that of bringing process streams from their temperatures of availability to the temperatures at which they are needed without undue cost. An important strategy for reducing the cost of doing this is heat recovery: Using the heat available from streams to be cooled to service streams to be heated.

In the absence of nonthermodynamic constraints, it is not difficult to assess the amount of heal recovery possible; and methods have been proposed (Linnhoff and Flower, 1978) that allow full heat recovery to be systematically obtained. The networks to which these methods lead are, however, more complex than necessary. Typically, therefore, those methods have been augmented with techniques for the evolutionary development of the initial network in order to simplify its structure, usually by minimizing the number of “matches” between streams.

The present work proposes a simple method for exploiting features of maximally simple networks (those that have as few “matches” as possible) in order to design, with greatly reduced effort, such a network that features a high (typically complete) degree of heat recovery. Further exploitation of those features allows a simple method of evolutionary development that makes it possible, in a very few evolutions, to improve the initial network as much as the data allow.

Unlike the other methods offered, the present ones are not hindered by the presence of nonthermodynamic constraints (practicality, safety, operability). Their generality and enhanced simplicity make them, more than any others, applicable in an industrial context. Although intended for application by hand, they lend themselves admirably to computer implementation, especially in an interactive mode.

These methods are demonstrated on the standard test examples and prove themselves powerful.     

APPLICATION OF TURBULENCE FUNDAMENTALS TO REACTOR MODELLING AND SCALEUP

Applications of the fundamentals of turbulent mixing become clear once those fundamentals are understood. The first article in this series presented those fundamentals, in order to show how to apply turbulent mixing fundamentals modelling and scaleup, this article covers the following topics:

1. reaction types and their interaction with mixing;

2. closure of the Reynolds equations for mixing and reactions;

3. application to complex geometries;

4. random coalescence-dispersion modelling;

5. application to complex chemistry.

The most difficult problem in applying our knowledge of turbulence to mixer modelling and scaleup is the choice of model complexity. The levels of model complexity available and how to apply them to various problems are presented following the introduction.