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,     

PRODUCTION OF ETHANOL WITH SACCHAROMYCES CEREVISIAE IN A CONTINUOUS REACTOR Note II: tests and modelling for a packed tubular reactor with immobilized yeasts

The biochemical production of ethanol has been studied in a packed tubular reactor with Saccharomyces Cerevisiae immobilized on wooden cubes.

The kinetics of the reaction was described in a previous paper. The experimental axial profiles for the substrate and product concentrations are compared with those calculated from a reactor model obtained by introducing the biochemical kinetic expression in the design equations. A good fit between the experimental and the calculated values could only be obtained by including a biological efficiency coefficient.

The reactor was kept in operation for 28 days to assess its technological reliability. It was found to be biologically stable. Its productivity was constant and comparable to that reported in the literature for similar reactors.     

A discussion of maximal extent of an isothermal reversible gas phase reaction in double-membrane reactors

The maximal reactant conversions in cocurrent isothermal double-membrane reactors are discussed theoretically, in comparison to single-membrane reactors. A method for calculation of the limiting conversion is proposed and demonstrated on the elementary reversible gas phase reaction A=B+C. Owing to the disturbing separation and reaction equilibrium, double-membrane reactor without sweep gas could provide complete conversion. When the sweep gas is introduced, large but not infinite sweep gas flow enables complete conversion. The criteria for approaching the limiting conversions are presented, in terms of values of dimensionless model parameters. To demonstrate the validity of the conclusion that double-membrane configuration is superior to the single-membrane configuration considering the maximal attainable conversion, the results of simulation of thermal water splitting are presented. As to the applicability of double-membrane reactor model that assumes reaction equilibrium, that approximation could be reasonable only when the maximal attainable conversion is lower than unity.     

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     

CHARACTERIZATION OF FLUIDIZED BED REACTORS WITH GAS TRACER MEASUREMENTS

In a steady state bench scale fluidized bed the decomposition reaction of NaHCO₃ was carried out. The residence times distributions, DRT, of carbon dioxide (the gaseous product) and non adsorbing argon (the reference tracer) were mass spectroscopically measured as a function of the bed temperature. By means of single-, two- and three-phase dispersion models as well as by a cell model, the DRT's were evaluated on line by a computer.

The steady state transverse and longitudinal concentration profiles of these tracers upstream from the plane source were also measured and evaluated by a dispersion model as well as by a counter current back mixing model. Comparison of the steady state and nonsteady state dispersion coefficient measurements indicate that the longitudinal gas mixing is only partially due to backmixing. The experimentally determined wake fractions agree well with those published in the literature. Since the adsorption rate of CO₂ on the pore surface area of the particles in the dense phase is high no interphase transfer from the interstitial gas of the dense phase into the bubble phase takes place.

The desorption of CO₂ and its return into the interstitial gas and than into the gas phase occurs only slowly and with an initial time lag. The on-line DRT can be used as a diagnostical technique for investigation of the reactor during its operation, if operation disturbances or breakdowns occur.     

APPLICATION OF UF TECHNOLOGY TO LARGE-SCALE SYNTHESIS OF GT 267-004, A SEQUESTRANT FOR C. DIFFICILE TOXIN

GT 267-004 is a nonabsorbed, nonantibiotic, high molecular weight anionic polymer that is undergoing clinical evaluation as a Clostridium difficile toxin sequestrant. The API is a mixed salt form that consists of approximately 30 to 50% potassium and 70 to 50% sodium as the counterions on the polymer.

The initial polymerization process results in an aqueous polymer solution with the polymer in the 100% sodium form. It also contains some oligomeric impurities. UF technology was applied in a novel way to convert the single-salt polymer to the mixed salt form and to simultaneously remove the oligomers below the required specification limits in a single-unit operation.

Experiments with a UF lab unit validated the concept of simultaneously performing ion exchange and purification. An appropriate amount of potassium chloride was added to the polymer solution to carry out the ion exchange considering the selectivity of the polymer for the potassium ion over the sodium ion. The resulting mixed salts in solution were removed using ultrafiltration membranes. The process produced the API in excellent purity.

The lab data were used to scale up the process to produce several hundred kg of the API. The engineering analysis of the large-scale UF operation was carried out to run the UF process in the cyclic mode and in the diafiltration mode. The UF operation was optimized with respect to time, water usage, operability, and the concentration of product solution required for the subsequent processing.

The optimized UF process was found to be a very cost-effective and time-efficient route to produce the new API.     

INTERPRETATION OF MICROMIXING EFFECTS ON FAST CONSECUTIVE-COMPETING REACTIONS IN SEMI-BATCH STIRRED TANKS BY A SIMPLE INTERACTION MODEL

A model is proposed for interpreting micromixing experiments in a semi-batch reactor. In these experiments, a fast consecutive-competing reaction system is used A + B → R, R + B → S, B being added either dropwise or as a pulse into an excess of A. A segregation index X_s = 2n_s/n_B0 is measured after completion of the reaction for various locations of the injection point. The macroscopic flow pattern is assumed to be known, essentially characterized by the recirculation time t_c. Micromixing then takes place within the cloud via a mechanism of interaction with the mean environment (IEM model, micromixing time t_m). Experimental results published by Barthole et al. (precipitation of barium sulphate) and Bourne et al. (diazo coupling) are successfully interpreted by this model. The influence of stirring speed, injection volume, concentration of species and mode of injection (pulse or dropwise) are especially well accounted for. This model provides a simple method for predicting the influence of mixing on selectivity in semi-batch reactors.     

METHODOLOGY FOR SENSITIVITY ASSESSMENT OF PETROLEUM FRACTIONATORS TO FEED COMPOSITION VARIATIONS

The environmental constraints coming into place on aromatics in petroleum products makes it necessary to develop an analytical technique that explicitly accounts for their effect. Furthermore, the multicomponent nature of petroleum fractions makes it difficult to analyze feed composition sensitivities without a large number of tests. This paper presents a convenient way to analyze the sensitivity or, as sometimes called, the switchabilily of petroleum fractionators. The technique depends on “lumping” all the paraffinics, naphthenic and aromatic components into three “pseudo components”: P, N and A.

Although this approach may appear simplistic, it is based on rigorous physical data. It, therefore, has a clear advantage over the traditional characterization methods. In addition, the method is inherently linked to the conventional TBP-Analysis of the ASTM type.

The utility of this technique is presented with an application to the sensitivity and switchability of a refinery stabilizer. Assuming fixed recovery of C₄ and C₅ in the bottom and overhead products, the various effects of feed variations on reflux, reboiler and condenser duties, and distillate product are demonstrated. Further, the effect on column temperature and composition profile is also analyzed.     

CHARACTERIZING FLUIDIZATION BY THE BED COLLAPSING METHOD

The fluidizing characteristic of a powder may be identified by studying the subsidence curve of a fully fluidized bed after abrupt termination of the fluid supply. The full bed collapsing process consists of three consecutive stages: a rapid initial stage for bubble escape, an intermediate stage of hindered sedimentation with constant velocity of solids descent, and a final decelerating stage of solids consolidation. For certain fluid-solid systems, either one or two of these stages may be missing. Mathematical models proposed for the individual stages and corroborated by high-speed cinematographic experimental measurements, led to the formulation of a dimensionless subsidence time Θ, correlating the physical properties of the solids and the fluid as well as the operating parameters to the fluidizing characteristic of the system. The larger the value of Θ, the smoother the fluidization.

For automatic determination of the subsidence behavior of a collapsing bed, an instrument using an optical-fiber projector-receiver set, for rapid tracking and recording of the subsiding bed surface, was developed. When the instrument output was fed into a microprocessor, the relevant parameters defining fluidizing characteristics were computed and displayed. By using this instrument, the fluidizing characteristics of binary mixtures of two closely sized powders were studied. For binary mixtures consisting of Geldart's Group A and Group B powders, fluidizing characteristics were noted to be intermediate between those of the two consistent components according to their relative proportions. When a Group C powder was added to either a Group A or Group B powder, however, the fluidizing characteristic of either component was found to be improved by the presence of the other, and there existed, in general, an intermediate composition with optimum fluidizing characteristic surpassing that of either of the constituents.     

COMPLETENESS THEOREM FOR A PRODUCT OF SELF-ADJOINT MATRICES

It is proven that the matrices AB and BA formed from the product a positive definite self-adjoint matrix A and a self-adjoint matrix B has real eigenvalues and a complete set of eigenvectors. If B is positive (negative) semidefinite the eigenvalues are greater (less) than or equal to zero. These properties have been useful in the analysis of multicomponent diffusion and distillation processes.     

A STUDY ON THE PERFORMANCE OF THE CATALYTIC POROUS-WALL THREE-PHASE REACTOR

A theoretical investigation of a catalytic porous-wall reactor in which gaseous and liquid reactants approach each other from opposite sides of the catalyst is undertaken. Equations for the annular liquid-channel are coupled with those for the catalytic wall and solved numerically and analytically using a simplified model. For the model reaction under study, the main design and operation parameters which affect reactor performance are the Thiele modulus, Peclet number, width of the liquid channel and the inlet concentration of the reactant in the liquid phase.

The effect of reactor configuration is peculiar to the cylindrical geometry because the thickness and relative location of the catalytic wall as well as the selection of the liquid and gas channels can influence the reactor performance. Thin-walled catalyst tubes have larger effectiveness factors and as the tube radius approaches that of the reactor, conversion in the reactor increases especially when the liquid is saturated with the gaseous reactant. Concentration of the liquid reactant in the feed has a significant effect if the reactant is depleted at some point inside the catalyst wall. Since the reaction zone width can be adjusted by changing the feed composition, this might have important implications with respect to selectivity.     

PERFORMANCES OF FILLED AND UNFILLED PTMSP MEMBRANES IN PERVAPORATION

The performances of filled and unfilled poly[l-(trimethylsily1(-I-propyne] (PTMSP) membranes have been investigated. The aims of this work are:

1) to describe through a mathematical model the performance decay which takes place during the pervaporation of organics from aqueous streams with PTMSP membranes;

2) to test and understand how the presence of adsorptive and non-adsorptive fillers acts to modify the performances of these membranes. So some criteria can be drawn to choose the right filler and its best concentration.

The interpretation of the experimental results with the filled membranes is accomplished by a model for the diffusion in a composite system that is constituted by the continuous polymeric phase with the dispersed filler particles.

It is concluded that the fillers hinder the decay of the flux and of the selectivity. Furthermore, in order to improve the performances, the filler must possess a high sorption selectivity accompanied by a favorable value for the ratio of the diffusivity of organics to that of the water.     

HEAT EFFECTS FOR PHYSICAL AND CHEMICAL ABSORPTION IN TURBULENT LIQUID FILMS

An eddy diffusivity model was used to describe simultaneous heat and mass transfer for chemical absorption in turbulent liquid films. For absorption accompanied by a first-order reaction an approximate expression for the mass transfer coefficient is derived and shown to be in excellent agreement with exact numerical calculations. An equation is developed for the temperature rise at the free surface due to both the heat of reaction and the heat of solution. Relationships are also developed for the concentration of the liquid phase product at the free surface and the depletion of the liquid phase reactant at the free surface.

The temperature rise at the free surface for gas absorption accompanied by an instantaneous reaction due to both the heat of solution and the heat of reaction was determined. An equation is also derived for the concentration of liquid phase product at the free surface for the case of an instantaneous reaction.     

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     

CONTROL OF A PULSED LIQUID-LIQUID EXTRACTION COLUMN BASED ON A MULTILEVEL SYSTEM OF AUTOMATA

This paper presents the real-time application of the learning control theory to the control of a chemical pilot plant: a pulsed liquid-liquid extraction column.

The behaviour of an agitated liquid-liquid extraction column can be related to random mechanisms such as the phenomena of droplets breakage and coalescence. Previous studies on hydrodynamic and mass transfer aspects showed that a pulsed liquid-liquid extraction column had an optimal behaviour for operating conditions close to flooding. These results led to choose the following strategy to control the column in its optimal behaviour zone:

- the measure of the conductivity of the liquid medium below the distributor which gives a good information about flooding, is the controlled variable

-the pulse frequency is the control action.

The learning control algorithm is based on a multilevel system of automata which operates in a random environment. By means of an evaluation unit of the performances of the column which generates either penalty (inaction) or reward on the basis of heuristic rules, the automaton chooses a value of the pulse frequency. This approach is essentially connected to artificial intelligence in so far as human knowledge on the plant is included in these rules.

This algorithm has been implemented on a microcomputer for control purposes. The experimental results presented show the good performances of the approach.     

ATMOSPHERIC CONTACT DRYING OF GRANULAR BEDS WETTED WITH A BINARY MIXTURE

When regarding the atmospheric contact drying of granular beds wetted with a liquid mixture, both the drying rate and the selectivity of the process, i.e. the change of moisture composition, are of interest. The batch drying of a free flowing ceramic substance, wetted with a 2-propanol-water mixture, is investigated in a rotary dryer with heated wall and air flow.

The theoretical analysis is based on physical models for heat and mass transfer, moisture migration and particle transport, which are presented in examples.

The experimental and theoretical results show that higher selectivities can be achieved by reducing the particle size because of the lower liquid-phase mass-transfer resistance. An increase of the rotational speed leads to a higher drying rate with slightly decreased selectivity if the particles are sufficiently small, since contact heat transfer is enhanced.     

Synthesis of cyclohexylcyclohexanone on bifunctional Pd faujasites Influence of the balance between the acidity and the metallic function

The transformation of cyclohexanone was carried out on a series of bifunctional PdHFAU catalysts with Pd contents between 0.1 and 0.5 wt.% and framework Si/Al ratios equal to 5, 20, 40 and 100, under the following conditions: flow reactor, 473 K, pressures of cyclohexanone and hydrogen equal to 0.17 and 0.83 bar, respectively. With all the catalysts, cyclohexylcyclohexanone, the formation of which requires successive steps of aldolization, dehydration and hydrogenation, is directly formed. The effect of the balance between the hydrogenating and acid functions of the catalysts (taken as the ratio between their activity for toluene hydrogenation and their number of protonic acid sites, A_H/B) on their activity, stability and selectivity is the one expected from a bifunctional catalytic process. The activity per protonic site first increases with A_H/B, then remains constant above a certain value of A_H/B (0.4 h⁻¹), the limiting step of cyclohexylcyclohexanone formation being then cyclohexanone aldolization. The selectivity to cyclohexylcyclohexanone as well as the stability increase with A_H/B remaining constant for A_H/B>1 h⁻¹. While a high selectivity to cyclohexylcyclohexanone is obtained, the catalyst stability is relatively poor due to the retention inside the zeolite micropores of polar tricyclic C₁₈ compounds.     

舒巴坦钠溶析结晶工艺优化

目前舒巴坦钠粗品的提纯采用还原成舒巴坦酸后再经反应结晶合成舒巴坦钠的方式，耗时耗力且所需药品、试剂种类较多，不节能环保。针对该问题，采用正交实验 L_{27} \left(3^{13}\right) 对舒巴坦钠的溶析结晶工艺进行优化，探明了6个因素6个交互作用对粒度、纯度以及两者的综合评分的影响，包括养晶时间（A）、溶析剂用量（B）、溶析剂中乙醇的体积分数（C）、溶析剂的滴加速率（D）、搅拌速率（E）、温度（F）以及养晶时间分别与溶析剂用量（A×B）、与溶析剂中乙醇的体积分数（A×C）的交互作用、溶析剂用量与溶析剂中乙醇的体积分数的交互作用（B×C），并得到了一组最优方案A ₂ B ₂ C ₁ D ₃ E ₃ F ₂。通过该方案可获得纯度x>97%，体积平均粒度D[4,3]≈290μm，质量收率约为84%的舒巴坦钠产品，并发现杂质舒巴坦青霉胺对舒巴坦钠的粒度分布有一定的影响。在解决原有问题的基础上，合适粒度分布的舒巴坦钠产品也可为后续制剂工艺提供方便。     

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.     

ACETIC ACID AS AN OXYGEN CARRIER BETWEEN TWO PHASES FOR EPOXIDATION OF OLEIC ACID

Acetic acid was found to be an effective oxygen carrier for epoxidation of oleic acid. The reaction model of oleic acid epoxidation in the two-phase reaction system was systematically analyzed and the rate determining step was experimentally identified.

The results indicated that the rate of oxidation of the unsaturated acid was independent of the concentration of oleic acid and depended on the mixing rate and the rate of formation peracetic acid which in turn depended on the concentration of acetic acid, strength of acid catalyst and the oxygen source, hydrogen peroxide. In the region of reaction control, the rate equation of epoxidation was found to be

$

where k = 2.98 × 10^-2 M^-2 min^-1 at temperature of 35^°C.