SEPARATION OF PHENOLS FROM DILUTE AQUEOUS SOLUTION BY USE OF TRI-o-OCTYL PHOSPHINE OXIDE AS EXTRACTANT

ABSTRACT

Trioctyl phosphine oxide (TOPO) is examined as an extractant for phenol and other phenolic compounds. Equilibrium distribution coefficients have been measured for extraction of phenol, dihydroxybenzenes, and trihydroxybenzenes by solvents composed of TOPO in various diluents. Results are interpreted in terms of a model based upon complexation stoichiometry, allowing for solvation of uncomplexed solute as well. TOPO is a strong complexant for all the phenolic solutes studied. The nature of the diluent has a significant effect upon distribution coefficients, and in the case of an alcohol diluent reduces the distribution coefficient for phenol considerably.

The degree of complexation remains appreciable at temperatures which would be used for regeneration of phenol by distillation. This makes it necessary to use a diluent boiling at least 70°C to 80°C higher than the boiling point of phenol, which is 182°C. Regeneration studies are reported for isobutyl heptyl ketone, dimethyl naphthalene, and a mixture of dimethylnaphtahlaene and n-octadecane as diluents. Extraction with TOPO will be most worthy of consideration for feed concentrations of phenol equal to 3000 ppm or less, or for extraction of di- and trihydroxybenzenes.     

THE BULK AND SURFACE STRUCTURE OF γ-ALUMINA

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.     

OPTIMAL DESIGN OF MULTIPLE BATCH UNITS WITH FEEDSTOCK/PRODUCT STORAGES

This article derives an analytical solution for determining the optimal size of the multiple batch unit plant with storage units. The total cost to be minimized consists of the setup cost of the batch processing units, the inventory holding cost of feedstock/product storage and the capital cost of the batch and storage units. A novel approach, which is called the PSW(Periodic Square Wave) model, is applied to represent the material flows among the batch and storage units. The PSW model presumes that the material flow between unit and storage is a periodic square shaped wave. The resulting optimal batch size has similar characteristics to the classical economic lot sizing model such as EOQ or EPQ model in the sense that the batch size is determined as the balance between setup and inventory holding cost. However, the influence of inventory holding cost of the PSW model is different from that of EOQ/EPQ model. The EOQ/ EPQ model includes only the product inventory holding cost while the PSW model includes all inventory holding costs around the batch unit.

The PSW model is suitable for analyzing interlinked batch-storage system and is more accurate rather than EOQ/EPQ model. The optimal lot size of the PSW model is much smaller than that of EOQ/EPQ model as shown at an example. This is quite a remarkable result considering that the EOQ/EPQ model has been widely used over the last half century.     

GENERALIZED PREDICTIVE CONTROL OF A PULSED LIQUID-LIQUID EXTRACTION COLUMN

This paper deals with the application of a general predictive controller to a pulsed liquid-liquid extraction column. The control purpose is to maintain the column in its optimal behaviour zone in spite or flowrates and physical properties of solvent and solute fluctuations. The complex dynamics of the column is modeled by a low order linear discrete model with time varying parameters which are recursively identified. Based on these estimates, the control policy is adapted on line.

The obtained results illustrate the successful application of such an adaptive algorithm.     

DEVELOPMENT OF ANN MODEL FOR NON-LINEAR DRYING PROCESS

ABSTRACT

This paper presents an application of artificial neural network (ANN) technique to develop a model representing the non-linear drying process. The air heat plant (AHP), an important component in drying process is fabricated and used for building the ANN model. An optimal feed forward neural network topology is identified for the air heating system set-up. The training sets are obtained from experimental data. Back propogation algorithm with momentum factor is used for training. The results show that the back propogation ANN can learn the functional mapping between input and output. The advantages of ANN model developed for AHP is highlighted. The developed model can be used for control purposes.     

CONDENSATION-SORPTION OF WATER HISTORY WITH A CUBIC SPECIMEN OF WOOD

ABSTRACT

Depending on the temperature, moisture of the surrounding atmosphere may condensate or not. A piece of wood may thus be in contact either with liquid water during the night for a given time, or with air during daylight at a given relative humidity. A sorption-desorption history of moisture may thus occur, with a moisture content in the wood which may vary to a high extent below or beyond the fiber saturation point. A model based on a finite difference model is able to describe the process : the kinetics of the sorption-desorption history is in good agreement with the experiments ; moreover, a fuller insight into the nature of the process is gained with the profiles of moisture content in various places of the wood sample.     

OPTIMIZATION OF SINGLE-ZONE DRYING OF POLYMER SOLUTION COATINGS TO AVOID BLISTER DEFECTS

ABSTRACT

The optimal conditions for drying polymer-solvent coatings result from a trade-off between minimizing the residual solvent level and creating defects. Blistering defects can be caused by boiling the solvent within the coating. In this paper, we use a detailed drying model with automated constrained optimization to find optimal drying conditions for prototypical coatings that minimize the residual solvent without blistering the coating. The drying oven is assumed to have a single zone with fixed residence time. The optimal drying conditions include the oven air temperature and substrate-side and coating-side heat transfer coefficients The latter are constrained to physically reasonable values. According to our results, the optimal coating-side heat transfer coefficient is always equal to or greater than the optimal substrate-side heat transfer coefficient.     

AN APPROACH FOR ESTIMATION OF CRITICAL POINTS OF WATER SORPTION ISOTHERMS OF FOODS

Abstract

The problem of optimal storage conditions of dry foods with sigma-shaped Water Sorption Isotherm is investigated. It is assumed that the optimal value of water activity, A_o, corresponds to the critical points of the isotherm where its local slope (the first derivative) has a minimum value. Two approaches were tested. In the first one the experimental data were fitted by the modified GAB/BET model and the optimal point was calculated by differentiation of the resulting equation. In regression the second approach estimates of local slope of the isotherm between adjacent experimental points was calculated. The data were fitted by the proposed empirical model for the first derivative of the sigma-shaped isotherm. Then, the minimum value of the first derivative was computed. Comparative analysis of both methods based on experimental moisture sorption data for pistachio nuts at 10, 20 and 30°C revealed that the relative error in the optimal point by the second method is less than that by the first one.     

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

ABSTRACT

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.     

DESIGN OF BATCH GRAPE DRYERS

ABSTRACT

The mathematical model describing the batch operation of industrial dryers with trucks and trays is presented and analysed for the case of grape dehydrators. The optimum flowsheet configuration and operation conditions for the specific mode of operation and type of dryer employed, are sought and verified by appropriate formulation of design and optimization strategies. The optimization objective is the total annual cost of the plant, subject to constraints imposed by the operation of the dryer, thermodynamics, and construction reasoning. The decision variables were the number of trucks and the drying air stream conditions involving temperature and humidity. The MINLP nature of the design problem required mathematical programming techniques for its solution. The optimization was carried out for a wide range of production capacities, and the optimal points were evaluated in each case. A characteristic design study was presented in order to demonstrate the effectiveness of the proposed approach.     

STEAM DRYING OF WOOD CHIPS IN PNEUMATIC CONVEYING DRYERS

ABSTRACT

A model for a pneumatic conveying dryer is presented. Although the main emphasis is put on superheated steam drying of wood chips, it can be used for other porous materials as well

The model includes a comprehensive two-dimensional model for the drying of single wood chips which accounts for the main physical mechanisms occurring in wood during drying. The external drying conditions in a pneumatic conveying dryer were calculated by applying the mass, heat and momentum equations for each incremental step in dryer length. A plug flow assumption was made for the dryer model and the single particle and dryer models were solved in an iterative manner. The non-spherical nature of wood chips were accounted for by measuring the drag and heat transfer coefficients

Model calculations illustrate the complex interactions between steam, particles and walls which occur in a flash dryer. The drying rate varies in a very complex manner through the dryer. The internal resistance to mass transfer becomes very important in The drying of less permeable wood species such as spruce. Two effects were observed as the particle size was increased: firstly the heat transfer rate decreased, and secondly the residence time increased. To some extent, these effects compensate for each other, however, the net result is that larger chips have a higher final moisture content.     

COMPARISON OF SUPERHEATED STEAM AND AIR OPERATED SPRAY DRYERS USING COMPUTATIONAL FLUID DYNAMICS.

ABSTRACT

In this paper a numerical simulation of a spray dryer using the computational fluid dynamics (CFD) code Fluent is described. This simulation is based on a discrete droplet model and solve the partial differential equations of momentum, heat and mass conservation for both gas and dispersed phase.

The model is used to simulate the behaviour of a pilot scale spray dryer operated with two drying media : superheated steam and air Considering that there is no risk of powder ignition in superheated steam, we choosed a rather high inlet temperature (973 K). For the simulation, drop size spectrum is represented by 6 discrete droplets diameters, fitting to an experimental droplets size distribution and all droplets are injected at the same velocity, equal to the calculated velocity of the liquid sheet at the nozzle orifice.

It is showed that the model can evaluate the most important features of a spray dryer : temperature distribution inside the chamber, velocity of gas, droplets trajectories as well as deposits on the walls. The model predicts a fast down flowing core jet surrounded by a large recirculation zone. Using superheated steam or air as a drying medium shows only slight differences in flow patterns. Except for the recirculation which is tighter in steam.

The general behaviour of droplets in air or steam are quite the same : smallest droplets are entrained by the central core and largest ones are taken into the recirculation zone. In superheated steam, the droplets penetrate to a greater extent in the recirculation zone. Also, they evaporate faster. The contours of gas temperature reflect these differences as these two aspects are strongly coupled. In both air and steam there is a “cool” zone which is narrower in steam than in air. Finally, the panicle deposit problem seems to be more pronounced in air than in steam.

Adding to the inherent interest in using superheated steam as a drying medium, the model predicts attractive behaviour for spray drying with superheated steam. In particular. under the conditions tested with the model, a higher volumetric drying rate is obtained in superheated steam.     

KINETICS OF THE CLAY ROOFING TILE CONVECTION DRYING

ABSTRACT

Kinetics of the convection drying process of flat tile has been investigated experimentally in an industrial tunnel dryer. Several velocities of wet tile movement through the dryer were tested to obtain maximum allowable drying rate curve. As there are various models to describe the kinetics of convection drying, finding a model that would fairly well approximate the kinetics of the whole drying process was part of the research. Especially the polynomial and exponential models were tested.

It was found that exponential model of the type: B(t) = (a-B_e. EXP(?bt²) +B_et (?dB(t)/dt) = 2bt(B(t)?B_e significantly correlates the kinetics of the whole tile drying process.

Applying the maximum allowable drying rate curve obtained for flat tile in the first period of drying, a grapho–analytic model for the optimal conducting of the process has been developed.     

Synthesis of Rice Processing Plants. III. Sensitivity Analysis

Abstract

An optimal process flowsheet for a rice processing plant has been developed. The optimization problem was formulated as a Mixed-Integer Nonlinear Programme, MINLP, consisting of a vector of binary and continuous variables. The set of optimum decision variables including the number of drying, cooling, and tempering units, temperature and relative humidity of drying air, drying time, cooling time, and tempering time were determined as the solution of the MINLP problem. Six objective functions were investigated as performance criteria. A sensitivity analysis of each model parameter was conducted to determine its influence on the optimal flowsheet. The MINLP approach is an efficient tool for optimization and the simplified models were adequate for use at the synthesis stage. The solution is insensitive to uncertainty in the models. However, due to the nonconvex nature of MINLPs, the solution was found to depend on the initial starting values, especially for the maximum profit flowsheet.     

A Preliminary Study on Strategies for Optimal Fluid-Bed Drying

ABSTRACT

The degradation of product quality during convective drying depends on the temperature and water concentration history of the panicles and drying time. For improving product quality in combination with acceptable operation costs, optimal control of the operation variables is required.

In this preliminary study the relevance of dynamic optimal operations for batch-wise fluid-bed drying is explored by simulation. Optimal trajectories of operation variables were calculated for a pilot-plant installation by using a model which concerned the drying history of the panicles and the product quality (inactivation of biological active components). The applied objective function was based on an economic criterion combining product quality and operation costs.

Although the advances for the chosen pilot-plant application are moderate, in future studies the potentials and relevance of dynamic optimal operations for drying will be quantified for installations on industrial scale.     

AN ANALYSIS OF CELLULAR FLOW OBSERVED ON THE INTERFACE OF A PARTIALLY FORMED DROPLET†

In [16], during an experiment designed to model the internal circulation of a forming droplet, secondary surface flows were observed on the droplet interface.

After summarizing the experimental results of [16], we present one possible mechanism, based on the surface surfactant mass transport equation of Levich and the surface stress-strain boundary conditions at a free surface, that provides a good qualitative explanation of the origins and the nature of the secondary motion observed in [16]. The critical hypotheses in this mechanism are that the normal component of ihe vorticity at the free surface is determined primarily by the components of the velocity field tangential to the level lines of the surface surfactant density, near the maxima and minima of that density function and that the normal component of the fluid stress does not vanish at such points.

The consequent analysis of the mass transport equation in the interface shows that the resulting surface motion may be viewed as arising from a resonance phenomenon analogous to the forced vibrations of a spring at resonance.

The effects of adsorbtion-desorbtion and surface dilational viscosity may be incorporated in this mechanism. A method for the experimental measurement of surface dilational viscosities is proposed.     

SOLIDS TRANSPORTATION MODEL OF AN INDUSTRIAL ROTARY DRYER

ABSTRACT

A complete simulation model has been developed for an industrial rotary dryer to account for the heat and mass exchange between the solids and the gas. This simulator is mainly composed of three models: solids transportation model, furnace model, and gas model. The solids transportation model is the modified Cholette-Cloutier model It consists of a series of interactive reservoirs which are subdivided into an active and a dead compartments to account for the characteristic extended tail of the residence time distribution (RTD) curves observed in industrial dryers.

To expand the validity of the model, experiments have been performed in an industrial rotary dryer to obtain RTD curves under different mineral concentrate and gas flow rates. This paper describes these experiments and presents the variation of the average residence time and model parameters as function of solids and gas flow rates.     

VACUUM CONTACT DRYING OF SELECTED BIOTECHNOLOGY PRODUCTS

ABSTRACT

The paper is mainly concentrated on investigations of the vacuum contact drying of the following biomaterials: (1) beer yeast, (2) whey and its components: proteinaceous liquid, lactose, post-lactose liquid, (3) saturated solution of the citric acid, (4) post-fermentation broth of the fodder antibiotic bacitracin. The investigations of vacuum contact drying process in which dried material adheres closely to a hot surface were performed. In order to make possible the determination of optimal process parameters the measurements were performed for various constant temperatures of the hot surface, total pressures in vacuum chamber and layer thickness of biomaterials.

The effective thermal properties for dry layers of selected biomaterials depending on temperature and total pressure were also experimentally determined.

A mathematical model of the vacuum contact drying for most intensive regime of its performance i.e. boiling one was presented. It will enable the process simulation and estimation of the dryers efficiency depending on process parameters.

In addition, investigations of beer yeast viability depending on the hot surface temperature and the total pressure were performed.     

Comparison study of schemes for separation of intermediate isotope components

ABSTRACT

This paper uses the Q-cascade model to investigate the separation performance of eight schemes, comprising variations of two single-cascades and two double-cascades, to separate an intermediate isotope component. Optimization determines the relationship between the minimum relative total flow and concentration for different concentration requirements of the intermediate component. The results show that single-cascade schemes are not efficient. Rather, the optimal scheme is a double-cascade scheme that uses a three-stream cascade and a cascade with two feeds and an intermediate withdrawal. The successful optimization of all schemes indicates that this approach can be generalized to optimize various multistep separation processes.     

EXHAUST EMISSIONS OF PAHs OF PASSENGER CARS

Exhaust emissions of 16 PAHs, listed by the U.S. Environmental Protection Agency (USEPA) as priority pollutants, are measured using a vehicle bench on a sample of passenger cars. Thirteen gasoline vehicles and 17 diesel vehicles are tested, complying with ECE 1504 to Euro 3 emission standards, according to three real-world driving cycles based on European driving behavior (2 urban and 1 motorway). HPLC with fluorometric detection is used for their quantification.

The effect of cold or hot start is put to the fore with the short urban INRETS cycle.

The particle and gas-phase distribution is studied for all the vehicles and the hot driving cycles.

In this study, the cars' emissions are shown to be reduced, according to the legislative level (Euro-1, 2, 3 …). The majority of volatile PAHs is mainly observed in the gas phase whereas the less volatile and carcinogenic PAHs are especially adsorbed on particles.