Showing papers in "Chemical Engineering & Technology in 2006"

Enhancement of Thermal Conductivity with CuO for Nanofluids

Abstract: The enhancement of the thermal conductivity of ethylene glycol in the presence of copper oxide (CuO) is investigated. CuO nanofluids are prepared in a two-step method. No surfactant is employed as a dispersant. The volume fraction of CuO nanoparticles suspended in ethylene glycol liquid is below 5 vol.-%. The crystalline phases of the CuO powders are measured with x-ray diffraction patterns (XRD). CuO nanoparticles are examined using scanning electron microscopy (SEM) to determine their microstructure. The thermal conductivities of the CuO suspensions are measured by a modified transient hot wire method. The viscosity was measured with a viscosity instrument. The results show that CuO nanofluids with low concentrations of nanoparticles have considerably higher thermal conductivities than the identical ethylene glycol base liquids without solid nanoparticles. The thermal conductivity ratio improvement for CuO nanofluids is approximately linear with the volume fraction of nanoparticles. For CuO nanoparticles at a volume fraction of 0.05 (5 vol-.%) thermal conductivity was enhanced by up to 22.4 %. CuO nanofluids thus have good potential for effective heat transfer applications.

Polymorphism of Active Pharmaceutical Ingredients

Abstract: Different polymorphs of the same active pharmaceutical ingredient (API) display distinct physical properties, such as melting point, solubility, dissolution rate, hygroscopicity, or stability. The ability to successfully produce and reproduce specific stable polymorphs is intricately correlated with the efficiency and speed of drug development, the robustness of manufacturing process, and - ultimately - the stability and quality of APIs. This paper focuses on eight case study examples of interesting polymorphic transformations observed in the course of the regular API development process. Through extensive physicochemical characterization, using multiple analytical techniques, the phenomena observed could be elucidated and proper measures recommended to reduce the risk of unexpected polymorphic transformations.

Soot in Diesel Combustion Systems

Abstract: Diesel soot, one of the major environmental pollutants, is the finer particle produced during the high temperature pyrolysis or combustion of diesel fuel. Advances in the understanding of soot formation in diesel combustion systems during the recent decades are surveyed in this paper. It is universally accepted that soot formation steps can be summarized as (1) formation of molecular precursors of soot, (2) nucleation or inception of particles from heavy polycyclic aromatic hydrocarbon molecules, (3) mass growth of particles by addition of gas phase molecules, (4) coagulation via reactive particle-particle collisions, (5) carbonization of particulate material, and, finally, (6) oxidation of polycyclic aromatic hydrocarbons and soot particles. Several mathematical models of diesel soot formation available in the related literature are offered in this review, which are Hiroyasu's model, Moss' model, Tesner's model, Lindstedt's model, and detailed soot formation models. Experimental and numerical studies currently play an important role in exploring the diesel soot formation mechanism. The success of such studies relies on the development of both diagnostic techniques to increase the quality of experiments and mathematical models for numerical simulations.

Flow and Heat Transfer Prediction in a Corrugated Plate Heat Exchanger using a CFD Code

Abstract: The purpose of this study is to explore the potential of using a general purpose CFD code to compute the characteristics of the flow field, and of the heat transfer augmentation in conduits with corrugated walls, encountered in commercial plate heat exchangers (PHE). The CFD code is used to simulate the performance of a PHE model comprised of stainless steel plates, following a herringbone design and assembled for single-pass countercurrent flow. The code is validated by comparing the numerical results with experimental data on pressure drop and overall temperature differences acquired for the countercurrent flow of water at both sides of the model PHE. The limited data published in the literature are also in fairly good agreement with the results of the present study. It is shown that the CFD code is an effective and reliable tool for studying the effect of various geometrical configurations on the optimum design of a PHE.

Rotor-Stator and Disc Systems for Emulsification Processes

Abstract: Emulsions now find a wide range of applications in industry and daily life. In the pharmaceutical industry lipophilic active ingredients as well as many nutritional products such as vitamins are often formulated in the dispersed phase of oil-in-water emulsions. Emulsions can be produced with different mechanical emulsification techniques. In the following review, the process of rotor-stator systems and disc systems are compared to other popular mechanical emulsification systems. On the basis of experimental results from the authors' laboratory, a discontinuous gear-rim dispersing system, discontinuous disc system, and a continuous high pressure system are compared with regard to their attainable mean droplet diameter and drop size distribution in an oil-in-water emulsion. It can be shown that dissolver discs with a very simple geometry attain very small mean droplet diameters and a very narrow droplet size distribution, comparable to the emulsions obtained with established rotor-stator systems such as gear-rim dispersers.

Hydrodynamics and Mixer‐Induced Bubble Formation in Micro Bubble Columns with Single and Multiple‐Channels

Abstract: A hydrodynamic characterization of an industrially used gas-liquid contacting microchannel device is discussed, viz. the micro bubble column of IMM. Furthermore, similar characterization of a gas-liquid flow microchip of TU/e, with two tailored mixer designs, is used to solve fundamental issues on hydrodynamics, and therefore, to achieve further design and operating optimization of that chip and the IMM device. Flow pattern maps are presented in a dimensionless fashion for further predictions on new fluidic systems for optimum single-channel multiphase operation. Bubble formation was investigated in the two types of mixers and pinch-off and hydrodynamic decay mechanisms are observed. The impact of these mechanisms on bubble size, bubble size distributions, and on the corresponding flow patterns, i.e., the type of mixer design, can be decisive for the flow pattern map and thus, may be used to alter flow pattern maps. The bubble sizes and their distribution were improved for the tailored designs, i.e., smaller and more regular bubbles were generated. Finally, the impact of multi-channel distribution for gas and liquid flow is demonstrated. Intermediate flow patterns such as slug-annular flow, also found for single-phase operation, and the simultaneous coexistence of flow regimes are presented, with the latter providing evidence of flow maldistribution.

Raman spectroscopy - a powerful tool for the quantitative determination of the composition of polymorph mixtures : Application to CaCO3 polymorph mixtures

Abstract: Raman spectroscopy is an ideal method for identifying polymorphs, because it provides excellent fingerprint spectra specific to each crystal structure. Currently, Raman spectroscopy is successfully used for the quantitative polymorphic analysis of calcium carbonate only in the case of binary mixtures. When a third polymorph is present in the mixture, errors in the quantitative determination increase due to the difficulty in discriminating the different phases in the Raman spectra. In the present work, a new method is developed for mixtures containing more than two polymorphs and tested in the case of vaterite, aragonite, and calcite mixtures of different compositions. It is proved that Raman spectroscopy is a powerful, accurate, and reliable technique for quantitative determination of polymorph mixtures of calcium carbonate. The method can be used for other compounds exhibiting multiple polymorphs.

An Electrochemical Model of a Solid Oxide Steam Electrolyzer for Hydrogen Production

Abstract: An electrochemical model was developed to simulate the J-V characteristics of a solid oxide steam electrolyzer (SOSE) used for hydrogen production. Activation, concentration, and ohmic overpotentials were considered as the main factors for voltage loss. The Butler-Volmer equation, Fick's model, and Ohm's law were applied to determine the overpotentials of a SOSE cell. The simulation results were compared with experimental data from the literature and good agreement was obtained. Additionally, parametric modeling analyses were conducted to study how the operating temperature and gas composition affected the electrical characteristics. It was found that the voltage loss could be reduced by increasing the operating temperature and steam molar fraction. It was also observed that an anode-supported SOSE cell exhibited a higher hydrogen production efficiency than electrolyte-supported and cathode-supported cells. The electrochemical model can be used to perform further analysis in order to further understand the principles of SOSE hydrogen production, and to optimize SOSE cell and system designs.

Effect of Raw Materials on Properties of Activated Carbons

Abstract: Activated carbon can be produced from a large variety of raw materials, basically by two methods, physical and chemical activation or a combination of both. The adsorption properties of activated carbon vary with the feed materials used and the way of activation. Production cost may be lowered by choosing a cheap raw material and performing a suitable production process. Agricultural and forestry residues, or generally, biomass residue wastes could be used as suitable raw materials for the production of activated carbon. In the present work, different agricultural residues such as hard shells of apricot stones, almond, walnut and hazelnut shells, rice hulls and residues of liquorices were used as precursors. The activation was performed using phosphoric acid under the same conditions. The results showed that at the selected experimental conditions, the type of biomass as well as the final activation temperature, heating rate and impregnation rate of the chemical agent had the greatest influence on the quality of activated carbon. The quality of activated carbon was evaluated in terms of the iodine number reflecting the surface area. According to the results, activated carbon from the hard shells of apricot stones had the best adsorption properties and the largest surface area.

Experimental and CFD Simulation Study for the Wetting of a Structured Packing Element with Liquids

Abstract: The hydrodynamics of liquid flow in packed columns affects the column performance from the point of view of heat and mass transfer. The interfacial and the specific wetted areas are decisive in this case. The complex three-dimensional liquid flow on a single structured and flat packing element of Rombopak 4M was investigated. It consists of four connected wavy inclined plates in an X-shape configuration. The geometric characteristics of the packing were related to the fluid mechanics of the liquid distribution. CFD simulation results for different cell sizes and flow rates, obtained using the VOF (volume of fluid) model, are presented as being capable of describing this complex geometry. With the help of the CFD simulation and the experimental results from Rombopak 4M, correlations from the literature describing the interfacial and wetted area and liquid holdup in packed columns were adjusted to describe the hydrodynamic performance of Rombopak 4M.

Precipitation of L‐Glutamic Acid: Determination of Nucleation Kinetics

Abstract: This work presents a new procedure to determine the nucleation kinetics during the reactive precipitation of an organic substance. The new method has been applied to the pH-shift precipitation of L-glutamic acid upon mixing of an aqueous monosodium glutamate solution with hydrochloric acid. The induction time has been measured precisely in a stirred batch reactor by the combination of two in-situ measurement techniques, namely ATR-FTIR spectroscopy (attenuated total reflection Fourier Transform technique) and Focused Beam Reflectance Measurement (FBRM). It is shown that ATR-FTIR is a suitable tool to measure the concentrations of the different L-glutamic acid ions, and can be used to determine the starting time of the process when the desired supersaturation is established in the reactor. The onset of particle formation is detected through FBRM. The precipitated polymorph is identified using in-situ Raman spectroscopy and Particle Vision & Measurement (PVM). Finally, the induction time is used together with the independently measured growth kinetics to determine the nucleation rate.

VOF-Simulation of the Lift Force for Single Bubbles in a Simple Shear Flow

Abstract: Bubbles in shear flows experience a lift force, causing them to migrate sideways while they are rising. This lateral migration is investigated in numerical simulations, which are carried out with an extended version of the highly parallelized code FS3D, employing an advanced Volume-of-Fluid method. The movement of single bubbles in linear shear flows is simulated to obtain the magnitude of the lift force - expressed by the lift force coefficient C L - for various bubble diameters and material data. Simulation results are in good agreement with experiments for medium liquid phase viscosities. An investigation of the dynamic pressure on the bubble surface explains why large bubbles migrate in the opposite direction compared to small bubbles.

Heterogeneously Catalyzed Esterification of FFAs in Vegetable Oils

Abstract: The production of methyl esters (biodiesel) from free fatty acids (FFAs) contained in vegetable oils was studied using a heterogeneous acid catalyst. The feedstock was a by-product of a vegetable oil refinery. The experiments were performed in a batch reactor, in a temperature range of 363.15–393.15 K, with an initial molar ratio of methanol to FFAs of 6.6/1, while the catalyst mass was fixed at 2 wt % of the total vegetable oil mass. A technical kinetic model has been developed which accounts for the reversible esterification reaction. Kinetic parameters were determined by fitting experimental data to the model.

Factors Affecting the Polymorphic Outcome of Glycine Crystals Constrained on Patterned Substrates

Abstract: The primary goal of crystallization process is to generate particles with controlled size, shape and solid form, and the desired chemical purity. Many different types of approaches including molecular level strategies have been devised and employed to control the final structure of crystals. One promising approach is the utilization of self-assembled monolayers (SAMs) as templates. Recently, we reported that single glycine crystals can nucleate on patterned metallic square islands, with the size and morphology of the particles controlled by the dimensions of the islands or the concentration of the solution. Herein, the effect of the solution concentration on the polymorphic outcome of glycine crystals confined to hydrophilic metallic islands is investigated. Furthermore, we examine how variations in the solvent evaporation rate can impact the polymorph distribution of glycine.

Inferential Estimation of Polymer Melt Index Using Sequentially Trained Bootstrap Aggregated Neural Networks

Abstract: The inferential estimation of a polymer melt index in an industrial polymerization process using aggregated neural networks is presented in this paper The difficult-to-measure polymer melt index is estimated from easy-to-measure process variables, and their relationship is estimated using aggregated neural networks The individual networks are trained on bootstrap re-samples of the original training data by a sequential training algorithm In this training method, individual networks, within a bootstrap aggregated neural network model, are trained sequentially The first network is trained to minimize its prediction error on the training data In the training of subsequent networks, the training objective is not only to minimize the individual networks' prediction errors but also to minimize the correlation among the individual networks Training is terminated when the aggregated network prediction performance on the training and testing data cannot be further improved Application to real industrial data demonstrates that the polymer melt index can be successfully estimated using an aggregated neural network

Effect of High Pressure Processing on the Extraction of Lycopene in Tomato Paste Waste

Abstract: The effect of high pressure processing on the extraction of lycopene in tomato paste waste was studied. The experimental results show that high pressure processing did not destroy the molecular structure of lycopene. The extraction yield of lycopene obtained by high pressure processing for 1 min was higher than that obtained with solvent extraction for 30 min. These excellent results for the extraction by high pressure processing are promising for the future extraction of lycopene from tomato paste waste.

Effects of Draft Tubes on Particle Velocity Profiles in Spouted Beds

Abstract: The vertical particle velocity profiles in a full-column cylindrical conical spouted bed, with or without a draft tube, are measured using a fibre optic probe system. The profiles have different characteristics for a draft tube spouted bed (DTSB) than for a conventional spouted bed (CSB). The spout of a CSB consists of a central flow where particle velocities fit exponential distributions, and a boundary layer where particle velocities are nearly uniform. The spout of a DTSB has no boundary layer and its radial particle velocity profiles are approximately linear. The particle velocities in the spout of a DTSB increase when superficial gas velocity increases, draft tube diameter decreases, or when entrainment height decreases. A kinematic model has been used to simulate the granular flow in the annulus of a CSB and DTSB, and they are compared with the experiments. The particle velocities in the annulus of a DTSB are much lower than that of a CSB. Their radial profiles are also different with a CSB. The dependence of particle velocities in the annulus of a DTSB on superficial gas velocity, draft tube diameter, and entrainment height are also discussed. One concludes that the draft tube diameter and entrainment height are two key factors for the solid circulation rate of a DTSB.

Capillary Filling Flows inside Patterned-Surface Microchannels

Abstract: Capillary flows inside microchannels with patterned-surfaces are investigated theoretically and numerically. The surface energy method is used to derive an equivalent contact angle (ECA) model for small capillary number flows. The SIMPLE algorithm using a volume of fluid (VOF) method is adopted to investigate the flows in those microchannels. The flow characteristics such as the liquid front shapes and the evolution of the liquid lengths are obtained. The numerical results reveal that capillary flows in a patterned-surface microchannel still follow the traditional capillary theories. The ECA model is confirmed by the numerical results. It indicates that the capillary flows inside the patterned-surface microchannels can be estimated by means of the homogeneous-surface microchannels with the equivalent contact angle. The ECA model provides a good criterion for the total wettability of a patterned-surface microchannel, as well.

Optimization of Fischer-Tropsch Synthesis using Neural Networks

Abstract: Fischer-Tropsch synthesis is an important chemical process for the production of liquid fuels and olefins Optimization of hydrocarbon products such as diesel and gasoline produced by Fischer-Tropsch synthesis usually requires the knowledge of the complex polymerization mechanism and the kinetic parameters associated with it in order to optimize production The Fischer-Tropsch reaction mechanism is still not fully understood, making optimization a hard task In this work, a neural network was used in substitution to the reaction mechanism to optimize diesel and gasoline production based on few experimental data for the reaction The neural network has yielded satisfactory predictions of the product distribution (with prediction errors lower than 5 %) and the optimum operating conditions for gasoline and diesel production were found for a commercial iron based catalyst

Detailed 3D modeling of mass transfer processes in two-phase flows with dynamic interfaces

Abstract: A model is presented which allows a priori computation of mass transfer coefficients for bubbles (droplets) rising in quiescent Newtonian fluids. The proposed model is based on the front tracking technique and explicitly accounts for the bubble-liquid mass transfer process. The dissolved species concentration in the liquid phase is computed from a species conservation equation while the value of the concentration at the interface is imposed via an immersed boundary technique. Simulations are carried out to demonstrate the capabilities of the model to predict bubble shape, flow field as well as transport of a species from the bubble to the liquid phase.

An Optimization of Capital and Operating Alternatives in a NGL Recovery Unit

Abstract: A natural gas liquids (NGL) recovery unit currently in operation has been simulated and compared with a real unit. Optimized operating conditions have been determined, in which the objective function is based on cost analysis. Following this, different turboexpansion processes have been analyzed and the best flow sheet selected, based on capital analysis and operating limitations. Parameter optimization of the entire modified plant has been performed using an advanced genetic algorithm program, to determine optimal operating conditions. The best revamping alternative is a turboexpander-exchanger process, in which case the profit is increased by 28 %.

Hydrodynamics in a RDC Extractor: Single and Two‐Phase PIV Measurements and CFD Simulations

Abstract: The single and two-phase flow field of a rotating disc contactor (RDC) extraction column is simulated with the help of computational fluid dynamics (CFD). The simulations were validated by particle image velocimetry (PIV) measurements. The single phase setup was used to test different turbulence models, and a 2D and 3D grid approach. For the two-phase simulations, a 2D computational grid and the Euler-Euler model was used. The two-phase PIV measurements are possible when using an iso-optical system, where the refractive indices of both liquid phases are identical.

Membranes in biotechnology

Abstract: Membranes have become an integral part of biotechnological processes. They have proved to be useful tools for the retention of biocatalysts in industrial biotransformations. This paper describes the development of membrane reactors and the application of membrane-based processes in biotransformations. Membrane systems for substrate dosing (e.g., aeration), catalyst retention (e.g., ultrafiltration), product separation (e.g., pervaporation), and salt removal (electrodialysis) from solutions are dealt with. The use of membranes in bioelectrochemistry is also discussed.

Formation and Growth of Crystal Bridges in Bulk Solids

Abstract: Solidification and caking of bulk solids often occurs during storage or while being transported to the customer. To investigate the formation and growth of solid bridges between two discrete particles, the modification of the contact region between these two particles stored in a climatic chamber is examined. The effect of load, temperature, relative humidity, and storage time on the formation of a bridge is analyzed. The objective is to describe the behavior of crystalline or salt-like granules under real storage conditions.

Separation of Ethylene Glycol/Water Mixtures using NaA Zeolite Membranes

Abstract: Inorganic membranes and particularly zeolite membranes are usually used for the dehydration of organic solvents by pervaporation (PV). This work reports an experimental study on the PV dehydration of ethylene glycol (EG)/water mixtures using commercial nanoporous NaA zeolite membranes. The concentration range investigated (C EG > 70 wt%) was selected according to existing industrial requirements. The recirculation flow rate was kept at a value of 1.5 L/min. The fluxes and separation factors were monitored as the dehydration proceeded. In addition, the activation energy of permeation (E a ) was calculated. The effect of temperature was investigated in the range 50-70 °C. The results obtained demonstrated the successful performance of the membrane for the dehydration of EG/ water mixtures. It was observed that at 70 °C and with 70 wt % initial EG concentration, larger fluxes and separation factors could be obtained, i.e., 0.94 kg m -2 h -1 and 1177, respectively. The Pervaporation Separation Index (PSI) of the membrane was found to be high compared to that of polymeric membranes.

Basic study of adhesion of several alumina-based washcoats deposited on stainless steel microchannels

Abstract: The adhesion of several washcoats deposited on stainless steel microchannels was investigated by performing a mechanical test (drop test) after application-oriented tests, temperature cycling, and water exposure. For this study alumina washcoats (γ-Al 2 O 3 ) and washcoats of commercially available alumina-based catalyst powders (Pt/Al 2 O 3 , Rh/Al 2 O 3 ) were used. The deposited washcoats showed very good adhesion not only for fresh samples but also after the application-oriented tests.

Microwave heating : A new approach of simulation and validation

Abstract: Currently the distribution of microwave processes in industrial applications is sparsely spread. Reasons for this are, in particular, the inhomogeneous heating patterns and the lack of optimization potential, due to the lack of possibilities for simulation of coupled electromagnetic and thermal processes. In this work two commercial software packages have therefore been coupled to simulate local and time specified temperature distributions of microwave treated samples. The results are validated by the sophisticated magnetic resonance imaging (MRI) technique, in order to avoid the problems of measuring temperature distributions in microwave fields. This method of measurement is non-invasive, shows high 3D spatial and time resolutions, and does not influence the electromagnetic field.

Utilization of Focused Beam Reflectance Measurement in the Control of Crystal Size Distribution in a Batch Cooled Crystallizer

Abstract: Controlling crystal size distribution (CSD) is important to downstream processing and to product quality. The distribution can be characterized by a mean or dominant size and the spread about the mean or dominant size. The development of tools leading to the control of the distribution in a batch crystallizer is the main topic of the present study. An experimentally based control scheme was implemented for batch cooling crystallization of paracetamol from ethanol solutions. Estimates of the CSD in the batch crystallizer were obtained by applying a model of the octahedral paracetamol crystals to a chord length distribution (CLD) obtained from focused beam reflectance measurement (FBRM) and Lasentec software. The model estimates showed reasonably good agreement with results obtained from sieve analyses performed at the end of the runs.

Efficiencies of Sieve Tray Distillation Columns by CFD Simulation

Abstract: A 3-D two-fluid CFD model in the Eulerian-Eulerian framework was developed to predict the hydrodynamics and heat and mass transfer of sieve trays. Interaction between the two phases occurs via interphase momentum and heat and mass transfer. The tray geometries are based on the large rectangular tray of Dribika and Biddulph and FRI commercial-scale sieve tray of Yanagi and Sakata. In this work a CFD simulation is developed to give predictions of the fluid flow patterns, hydraulics, and mass transfer efficiency of distillation sieve trays including a downcomer. The main objective has been to find the extent to which CFD can be used as a design and prediction tool for real behavior, concentration and temperature distributions, and efficiencies of industrial trays. Despite the use of simple correlations for closure models, the efficiencies obtained are very close to experimental data. The results show that values of point efficiency vary with position on the tray because of variation of affecting parameters, such as velocities, temperature and concentration gradients, and interfacial area. The simulation results show that CFD can be used as a powerful tool in tray design and analysis, and can be considered as a new approach for efficiency calculations and as a new tool for testing mixing models in both phases. CFD can be used as a “virtual experiment” to simulate tray behavior under operating conditions.

Prediction of the Removal Efficiency of a Novel Two‐Stage Hybrid Scrubber for Flue Gas Desulfurization

Abstract: Emission of SO 2 from various industrial sources occurs in varying concentrations and quantities. The operation of scrubbers as SO 2 control devices is getting more and more attention as pollution control regulations are tightened. Experimental investigations on the scrubbing of SO 2 in a novel two-stage hybrid (spray-cum-bubble column) scrubber using water and dilute sodium alkali are reported. Empirical and semi-empirical correlations are developed for the prediction of the performances of the bubble and the spray sections in terms of various pertinent variables of the system for water and alkaline scrubbing, respectively. The contribution of the mass transfer enhancement factor towards the removal of SO 2 has been exploited while developing the semi-empirical correlation for the prediction of performance in alkaline scrubbing. The predicted values are in excellent agreement with the experimental values. Finally, the operating features of the scrubber and design aspects are discussed in order to develop our understanding for practical applications.