Showing papers in "Chemical Engineering and Processing in 2007"

The physicochemical properties of spray-dried watermelon powders

Abstract: A study was conducted using Buchi mini spray dryer B-191 to produce spray-dried watermelon powders using two different maltodextrin concentrations (3% and 5%) as the encapsulating agent and four different inlet temperatures (145 °C, 155 °C, 165 °C and 175 °C). The spray-dried watermelon powders were analysed for moisture content, dissolution, water activity, colour, lycopene and β-carotene. Results demonstrated that as inlet temperature increased, the moisture content and dissolution decreased. However, there were no significant changes in the water activities of the spray-dried powders for all the inlet temperatures investigated. Colormetric analyses showed that the L * , a * , b * , hue and chroma values changed with the inlet temperatures. The results were well correlated to the lycopene and β-carotene contents of the spray-dried powders.

An overview of simultaneous strategies for dynamic optimization

Abstract: Simultaneous approaches for dynamic optimization problems are surveyed and a number of emerging topics are explored. Also known as direct transcription, this approach has a number of advantages over competing dynamic optimization methods. Moreover, a number of industrial applications have recently been reported on challenging real-world applications. This study provides background information, summarizes the underlying concepts and properties of this approach, discusses recent advances in the treatment of discrete decisions and, finally, illustrates the approach with two process case studies.

A review of intensification of photocatalytic processes

Abstract: Photocatalysis is an attractive technology with potential applications in various disciplines, such as chemical synthesis, environmental technology and medicine, and receives an impressive amount of exposure in the open literature. However, industrial implementation remains limited due to scale up problems and the design of photoreactors. In this paper an overview is presented of recent advances in the design and application of novel reactors and devices. Two issues are essential: photon transfer limitations and mass transfer limitations (in the case of liquid phase reactions). In the field of mass transfer optimisation, spinning disc reactors, monolithic reactors and microreactors have been investigated for their use in photocatalysis. Significant advances are reported compared to conventional reactors. Studies focusing on performance improvement by optimising photon transfer, however, remain limited. While optical fibers and LEDs have been explored, major breakthroughs are still lacking. More focus on the introduction of a multitude of micro- or even nanoscale light emitting sources close to the catalyst particles is likely to be the way forward.

Thermal processing and quality: Principles and overview

Abstract: The food processing industry has matured over the years with an impressive record on safety and a vibrant marketplace for new product development. Consumer demands for high-quality products has inspired researchers and the food industry to explore alternative methods as replacement for traditional processing methods. The food industry is poised to adopt cost effective technologies that offer better quality and safe products. Given the impressive safety record associated with traditional systems, one may be tempted to conclude that there is little room for advancement and innovation to meet current consumer demands. Process optimization will continue to evolve to enhance quality and overall energy utilization either in traditional or novel systems. The need for efficient operations will certainly drive system automation, control and monitoring systems that can handle complex mathematical routines in real-time. Such systems would certainly require vigorous validation and verification for industry to embrace them. It truly sounds illogical for industry to re-evaluate existing process schedules based on studies that demonstrate non-linearity of survival curves. However, the need to optimize quality and operating costs could potentially prompt re-evaluating existing systems to capture additional benefits. New processing concepts such as the application of variable retort temperature have received attention from processing experts and promises to improve both the economy and quality of thermally processed foods.

Reactive distillation: The front-runner of industrial process intensification - A full review of commercial applications, research, scale-up, design and operation

Abstract: Most industrial scale reactive distillations (presently more than 150), operated worldwide today at capacities of 100–3000 ktonnes/y, and are reported in this paper. Most of these plants started up less than 15 years ago. The drivers, processes, systems, scale-up methods and partner collaborations for this rapid invasion of a new process intensified technique are explained in this paper. The business drivers are (a) economical (prosperity): variable cost, capital expenditure and energy requirement reduction. In all cases these are reduced by 20% or more, when compared to the classic set-up of a reactor followed by distillation. (b) Environmental (planet): lower emissions to the environment. In all cases carbon dioxide and diffusive emissions are reduced and (c) social (people): improvements on safely, health and society impact are obtained by lower reactive content, lower run away sensitivity and lower space occupation. These industrial reactive distillation systems comprise homogeneous and heterogeneous catalysed, irreversible and reversible reactions, covering large ranges of reactions, notably hydrogenations, hydrodesulfurisation, esterifications and etherification. Various commercial methods for packing heterogeneous catalyst in columns are now available. The systems comprise amongst others: multiple catalyst systems, gas and liquid internal recycle traffic over these catalyst systems, separation, mass flow, and enthalpy exchange. These are integrated optimally in a single vessel, a characteristic feature of process intensification. The scale-up methods applied from pilot plants to commercial scale are brute force and modelling. Technology providers CDTECH and Sulzer Chemtech have used these scale-up methods successfully. Barriers perceived and real have also been removed by these companies. Chemical manufacturing companies have also developed their own specific reactive distillations by their own research and development. These companies, both on their own and in consortia, also developed heuristic process synthesis rules and expert software to identify the attractiveness and technical feasibility of reactive distillation. Heuristic rules and expert software will be presented and supported by examples. Academic research also produced design methods to identify the feasibility of reactive distillation, to determine the feed locations, to select packing types, to sequence columns optimally and also produced methods to design, optimise and control the columns with steady state and dynamic simulation models. The rapid commercial scale implementation of reactive distillation by co-operation of partners in research, scale-up, design and reliable operation can also be seen as a model for rapid implementation of other process intensification techniques in the chemical industry.

High intensity pulsed electric fields applied for food preservation

Abstract: Preservation of liquid foods by high intensity pulsed electric fields (PEF) is an interesting alternative to traditional techniques like thermal pasteurization. Based on the underlying mechanism of action, in this paper the crucial process parameters electrical field strength, total pulse energy input and treatment temperature were investigated experimentally. Inactivation studies were performed with three bacteria ( E. coli, Bacillus megaterium, Listeria innocua ) and one yeast ( Saccharomyces cerevisiae ). Stainless steel and carbon electrodes have been tested to investigate their applicability as electrode material. Simulating the influence of cell size and orientation as well as the presence of agglomerations or insulating particles indicated that the applied field strength has to be increased above the critical one to achieve product safety. It was found that temperatures higher than 40 °C can strongly increase the lethality of the PEF process. In this way also small cells like Listeria are easily affected by pulsed fields even at a field strength as low as 16 kV cm −1 . In addition, heating of the product prior to PEF has the advantage that most of the required process energy can be recovered using heat exchangers. Exemplary, such a process is analyzed by an enthalpy balance.

Evaluation of iron oxide and aluminum oxide as potential arsenic(V) adsorbents

Abstract: Iron (Fe 2 O 3 ) and aluminum oxide (Al 2 O 3 ) were found to be good and inexpensive adsorbents for As(V) removal in drinking water despite their relatively small surface area. The experimental results for this study suggest that by careful selection of the relative concentration of arsenic, pH, and dosages of Fe 2 O 3 and Al 2 O 3 , As(V) removal efficiency as high as 99% can be achieved. At lower pH ( 2 O 3 and Al 2 O 3 and the initial concentration of As(V), over 95% of As(V) adsorption was observed within a contact time of 20–60 min. The adsorption of As(V) on Fe 2 O 3 and Al 2 O 3 , like that on other nonporous adsorbents, is mainly controlled by the surface area. The adsorption of As(V) on Fe 2 O 3 and Al 2 O 3 was found to follow the Langmuir isotherm between the pH values of 5 and 9. The maximum As(V) uptake values at pH 6 – the optimal pH value for adsorption – using Fe 2 O 3 and Al 2 O 3 , were calculated as 0.66 mg/g and 0.17 mg/g, respectively. No significant variation in the uptake of As(V) on Fe 2 O 3 as compared with Al 2 O 3 was observed at different pH values. The initial sorption rate of Fe 2 O 3 is higher than that of Al 2 O 3 . All these factors make Fe 2 O 3 a better adsorbent than Al 2 O 3 . Fe 2 O 3 is a useful and effective adsorbent for POE (pint of entry) and POU (point of use) water treatment systems, such as small-scale commercial or individual home water treatment systems. Even though the adsorption capacities of Fe 2 O 3 and Al 2 O 3 for As(V) are quite low compared with those of other absorbents, their low cost makes them useful adsorbents. They may be very useful in arsenic removal from water in endemic areas such as China, India, and Bangladesh.

MHD flow and mass transfer of an electrically conducting fluid of second grade in a porous medium over a stretching sheet with chemically reactive species

Abstract: An analysis is carried out to study the flow, chemical reaction and mass transfer of a steady laminar boundary layer flow of an electrically conducting fluid of second grade in a porous medium subject to a transverse uniform magnetic field past a semi-infinite impermeable stretching sheet. The governing partial differential equations are converted into ordinary differential equations by a similarity transformation and an analytical solution for this flow is utilized, whereas the concentration profiles are obtained numerically for higher-order reactions. The variations of dimensionless surface concentration and dimensionless surface concentration gradient as well as mass transfer characteristics with various parameters are graphed and tabulated. Our numerical computations show that the effect of destructive chemical reaction is to diminish the concentration boundary layer. This phenomenon is quite the opposite when a generative reaction is present.

Determination of kinetic and equilibrium parameters of the batch adsorption of Cr(VI) onto waste acorn of Quercus ithaburensis

Abstract: The efficiency of waste acorn of Quercus ithaburensis (WAQI) as an adsorbent for removing Cr(VI) ions from synthetic wastewater has been studied. Batch adsorption experiments were carried out as a function of pH, adsorbent mass, Cr(VI) ion concentration, agitation rate and temperatures. Maximum metal sorption was found to occur at initial pH 2.0. The adsorption capacity of WAQI was found to be 31.48 mg g−1 for initial Cr(VI) concentration of 400 mg L−1 at 25 °C. Batch adsorption models, based on the assumption of the pseudo first-order, pseudo second-order mechanism and Elovich equation were applied to examine the kinetics of the adsorption. The results showed that kinetic data were followed fitting the pseudo second-order model than the pseudo first-order and Elovich equation. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated. The adsorption process was found to be endothermic and spontaneous. The results were analyzed by the Langmuir, Freundlich, Dubinin–Radushkevich (D–R), Temkin, Frumkin, Harkins–Jura, and Smith equation using linearized correlation coefficient at different temperature. The characteristic parameters for each isotherm have been determined. Models and the isotherm constant were evaluated depending on temperature. Langmuir and Freundlich equation is found to best represent the equilibrium data for Cr(VI) ions–waste acorn systems.

Determination of chondroitin sulfate from different sources of cartilage

Abstract: Cartilage is produced as a by-product from slaughter house and fishery industries in Thailand. The enzymatic extraction of chondroitin sulfate followed the method of Nakano et al. [T. Nakano, H.H. Sunwoo, X. Li, M.A. Price, S.S. Jeong, Study of sulfated glycosaminoglycans from porcine skeletal muscle epimysium including analysis of iduronosyl and glucoronosyl residues in galactosaminoglycan fractions, J. Agric. Food Chem. 44 (1996) 1424–1434] and the sulfate glycosaminoglycans (GAGs) assay [W.R. Farndale, D.J. Buttle, A.J. Barrett, Improved quantitation and discrimination of sulphated glycosaminoglycans by use of dimethylmethylene blue, Biochim. Biophys. Acta 883 (1986) 173–177] was employed to determine the content of chondroitin sulfate in cartilage of shark fin, ray, crocodile and chicken keel. Identification of types of chondroitin sulfate through FTIR spectroscopy KBr pellet technique was carried out. The results indicated that chicken keel, crocodile hyoid and sternum cartilage are the most promising potential sources of chondroitin sulfate. The value ranges from 11.55 to 14.84 g/100 g of dried cartilage, calculated as chondroitin-4-sulfate. Identification of dried chondroitin sulfate extracts from investigated cartilages show the existence of both chondroitin-4-sulfate and chondroitin-6-sulfate.

Freeze drying of pharmaceuticals in vials: Influence of freezing protocol and sample configuration on ice morphology and freeze-dried cake texture

Abstract: In pharmaceutical freeze-drying processes, the freezing step is a key-step because it fixes the morphology of the frozen material and, by the way, the final morphology of the freeze-dried material. It is the most difficult step to control, as it concerns the nucleation processes and it is also a damaging step with respect to the biological activity loss of pharmaceutical proteins. In this paper, we have reported original data obtained with a BSA (bovine serum albumin) based formulation used to stabilize pharmaceutical proteins during their freeze-drying process. Morphological characteristics of the ice crystals just after the freezing step were determined for different freezing protocols. Mean diameters and size distributions of the ice crystals have been determined by a direct optical microscopy method in cold chamber for different freezing parameters: size and type of vials (moulded or tubing), height of filling, vial right sectional surface area, shelf loading temperature. It was observed that the ice crystals sizes distributions depended not only on the freezing rates (well known result) but also on the vial size and type and also on the filling height. It was observed that moulded vials or higher values of filling height reduced the morphology heterogeneities resulting from large supercooling degrees and gave more homogeneous ice crystal size distributions. This behaviour was explained by the decrease of the supercooling effects which generally led to larger and non-homogenous distributions. Moreover, a convenient annealing treatment could homogenize and increase notably the mean ice crystals sizes. Water vapour mass transfer resistances data during the sublimation step were also determined and correlated to the experimental values of the mean ice crystals diameters which affected directly the dried layer permeability. These data were interpreted by the mass transfer laws of molecular diffusion theory (Knudsen regime).

Modeling reaction kinetics of petroleum coke gasification with CO2

Abstract: Kinetics characteristics of petroleum coke gasification with CO2 at 1248–1323 K and 0.1 MPa were studied using a pressurized thermogravimetric analyzer (TGA). It is shown that gasification rate increases with increasing conversion and then decreases after reaching a peak value around x = 0.3. The poor initial porosity is the main reason of the occurrence of maximal gasification rate. A normal distribution function model was proposed to fit the kinetics data. Results show it can describe well the variation of gasification rate at different temperatures. Relationship between the parameter rm in the model and temperature T obeys to the Arrhenius law. Activation energy of petroleum coke CO2 gasification is 198 kJ mol−1 and the reaction order is 0.54–0.88 in the investigated temperature range, which are in accordance with reported data.

Esterification of acetic acid with ethanol: Reaction kinetics and operation in a packed bed reactive distillation column

Abstract: The reaction kinetics of the esterification of acetic acid with ethanol, catalyzed both homogeneously by the acetic acid, and heterogeneously by Amberlyst 15, have been investigated. The reactions were carried out at several temperatures between 303.15 and 353.15 K and at various starting reactant compositions. Homogeneous and heterogeneous reactions have been described using the models proposed by Popken et al. [T. Popken, L. Gotze, J. Gmehling, Reaction kinetics and chemical equilibrium of homogenously and heterogeneously catalyzed acetic acid esterification with methanol and methyl acetate hydrolysis, Ind. Eng. Chem. Res. 39 (2000) 2601–2611]. These models use activities instead of mole fractions. Activity coefficients have been calculated using ASOG [K. Kojima, K. Tochigi, Prediction of Vapor–liquid Equilibria by the ASOG Method, Elsevier, Tokyo, 1979] and UNIFAC (Aa. Fredenslund, J. Gmehling, P. Rasmussen, Vapor–liquid Equilibria Using UNIFAC. A Group Contribution Method, Elsevier, Amsterdam, 1977] methods. A packed bed reactive distillation column filled with Amberlyst 15 has been employed to obtain ethyl acetate. The influence of feed composition and reflux ratio have been analyzed.

Freeze-drying of acerola (Malpighia glabra L.)

Abstract: Several quality parameters, such as water activity (aw), glass transition temperature (Tg), Vitamin C content, shrinkage and rehydration capacity were investigated for the freeze-drying of acerola fruits. The variation of temperature with time at different positions of the samples was measured during the freezing of samples, performed prior to the freeze-drying. Drying kinetic curves were obtained for different types of samples. The extent of shrinkage after freeze-drying was investigated and related to the glass transition temperature, Tg. The variation of water activity (aw) along the drying and sorption isotherms was obtained for different freezing techniques. It was observed that freeze-dried acerola fruits can be easily reconstituted, and important nutritional parameters are well preserved after the process. They may be considered as a good source of Vitamin C, whose content was best preserved for freeze-drying of fruits at an intermediary stage of ripening.

Removal of copper ions from aqueous solutions by dried sunflower leaves

Abstract: In the present work, the potential use of dried sunflower leaves to remove copper ions from aqueous solutions was evaluated. Kinetic data and equilibrium sorption isotherm were measured in batch conditions. The influence of some parameters such as: contact time, initial metal concentration, initial pH of solution and copper salt nature on the metal removal kinetics has been studied. Copper uptake was time contact, initial copper concentration, initial pH solution and copper salt type dependent. The sorption of copper increased as contact time, initial metal concentration, initial pH of solution increased. Maximum copper sorption was found to occur at around initial pH 5–6. Three simplified kinetic models including a first-order equation, pseudo-second-order and second-order equations were selected to follow the sorption process. The process follows a pseudo-second-order kinetics. Langmuir and Freundlich models were used to describe sorption equilibrium data at natural pH of solution. Results indicated that the Langmuir model gave an acceptable fit to the experimental data than the Freundlich equation. Maximum copper uptake obtained was q m = 89.37 mg/g (1.41 mmol/g).

About a correlating equation for predicting pressure drops through packed beds of spheres in a large range of Reynolds numbers

Abstract: This work aims at validating and extending the applicability of an existing correlating equation for predicting pressure drop through packed beds of spheres. A new set of data points out its use for bed geometric aspect ratio D / d part in the range 3.8–14.5, in the case of dense packings. The case of loose packings is also discussed using literature data. As a conclusion, a correlation is proposed for predicting pressure drops through fixed beds of spheres (dense and loose packings) for large ranges of Reynolds numbers (∼10 Re part D / d part

Experimental studies on heat transfer and friction factor characteristics of turbulent flow through a circular tube fitted with helical screw-tape inserts

Abstract: Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with full-length helical screw element of different twist ratio, and increasing and decreasing order of twist ratio set have been studied with uniform heat flux under turbulent flow conditions. The Reynolds number was varied from 2700 to 13 500. The experimental data obtained are compared with those obtained from plain tube published data. The maximum Nusselt number for the twist of 1.95 was obtained. The performance of the helical twist insert was compared with the twisted tape performance reported in the literature and found that it is better than twisted tape performance. The heat transfer augmentation for helical twist of increasing and decreasing order twist were also presented. The empirical correlations developed relating twist ratio and Reynolds number, are fitting the experimental data within ±13% and ±15% for Nusselt number and friction factor, respectively. The performance evaluation study has been presented to check the potential of using the helical twist insert.

The influence of microwave energy delivery method on strength reduction in ore samples

Abstract: Recent work has shown for the first time that high electric field strength microwave energy can facilitate comminution of ores, at energy inputs considered economically viable. However, due to difficulties in measuring stress formation inside a solid being exposed to microwave energy, the accuracy of a suggested thermal stress weakening mechanism has not been quantified. It is thought that microwave induced differential thermal expansion of certain mineral phases is sufficient to cause stresses that exceed the strength of the material. This study simulated this proposed weakening mechanism using a quasi-static thermo-mechanical 2D model of a simplified pyrite/calcite system formulated in commercial finite difference numerical modelling software. The effects of microwave power density and exposure time on simulated uniaxial compressive strength are quantified. Power densities expected in both continuous wave and pulsed microwave applications are examined, and the work concludes that pulsed treatment is more effective for weakening rocks. The paper makes recommendations as to the future operating requirements of microwave equipment for the most effective weakening at economic energy inputs.

Toward an understanding of the motion and mass transfer with chemically reactive species for two classes of viscoelastic fluid over a porous stretching sheet

Abstract: In this paper, we endeavour to give a numerical analysis of momentum and mass transfer characteristics in two viscoelastic fluid flows influenced by a porous stretching sheet, namely, second-grade and second-order non-Newtonian fluids by assigning both positive and negative values to the principal governing viscoelastic dimensionless parameter λ 1 . By means of suitable similarity transformations on the non-linear governing partial differential equations, we obtain several selected numerical solutions for non-dimensional concentration profiles and mass transfer characteristics. Graphs and tables are presented with a view to analyze the behaviour of the solution with changes in the governing dimensionless parameters of the problem. New results are obtained which show how the concentration distributions and mass transfer characteristics vary with suction/injection, viscoelasticity and magnetic field. Comparisons are given between the two aforementioned viscoelastic fluid flows and opposite trends with respect to the influence of viscoelasticity are observed.

Inactivation of naturally occurring microorganisms in tomato juice using pulsed electric field (PEF) with and without antimicrobials

Abstract: The combination of different hurdles such as moderately high temperatures (<50 °C), antimicrobial compounds and pulsed electric field (PEF), to reduce naturally occurring microbes in tomato juice was explored. The microbial count decreased with the increase in pulse number and treatment temperature at constant field strength. At field strength of 80 kV/cm, 20 pulses, 50 °C, and in the presence of nisin (100 U/mL), there was about 4.4 log reductions in microbial counts. There was significant difference (P < 0.05) in the reduction of microbial count when the temperature was increased from 45 to 50 °C. There was no Vitamin C reduction due to the treatment. Treated juice, without aseptically filled, was stored at 4 °C for 28 days without any significant microbial growth. Enzyme polygalacturonase was unaffected by PEF, but the activity of pectin methyl esterase was reduced by 55%. Antimicrobials such as clove oil and mint extract provide large microbial decay at low concentration and mild heat without PEF.

Hybrid separation processes—Combination of reactive distillation with membrane separation

Abstract: In this paper, the modelling, simulation and process analysis for a hybrid separation process, the combination of reactive distillation with membrane separation, is presented. The application is illustrated by the heterogeneously catalysed n-propyl propionate synthesis from 1-propanol and propionic acid. The membrane module is located in the distillate stream of the reactive distillation column in order to selectively remove the produced water without use of entrainers. Key aspects for the theoretical description of reactive distillation processes are discussed. For the stand-alone reactive separation process, the simulation results with a non-equilibrium model are in good agreement with experimental data obtained in a pilot-scale column. Additionally, a comparison of the most common modelling depths, namely the non-equilibrium model with Maxwell–Stefan equations, the equilibrium model taking into account reaction kinetics and the equilibrium model assuming chemical equilibrium, is presented. Vapour permeation experiments using Sulzer Pervap™ 2201(D) have been performed in a pilot-scale membrane plant in order to determine the separation characteristics for the dewatering of the non-ideal binary 1-propanol–water mixture. A first process analysis of the combined unit operations shows the influence of structural and operational parameters on the performance of the feasible hybrid process.

Ionic liquid synthesis in a microstructured reactor for process intensification

Abstract: Ionic liquids (IL) are the focus of growing interest over the last few years due to their low vapour pressure being beneficial for replacing common organic solvents with high vapour pressure. IL synthesised via alkylation are produced in batch or semi-batch stirred tank reactors. The reaction is highly exothermic and the kinetics was shown to be fast. The heat management during the reactor operation is a crucial point leading to high quality IL product and avoiding thermal runaway. This study reports the use of a microstructured reactor (MSR) system for the production of ethylmethylimidazole ethylsulfate by a solvent-free alkylation reaction. A combination of MSR and two tubular capillary reactors operating at two different cooling temperatures has been proposed. The save and stable operation of this reactor system is proven experimentally rendering the IL of high quality. The specific reactor performance was about 4 kgm−3 s−1 being ca. 3 orders of magnitude higher as compared to more traditional reactors.

Optimization of combined cycle power plants using evolutionary algorithms

Abstract: This paper deals with the application of an evolutionary algorithm to the minimization of the product cost of complex combined cycle power plants. Both the design configuration (process structure) and the process variables are optimized simultaneously. The optimization algorithm can choose among several design options included in a superstructure of the power plant such as different gas turbine systems available at the market, up to three pressure levels for steam generation in the heat-recovery steam generator, supplementary firing, steam reheat, parallel arrangement of heat exchangers in the gas path, and steam injection into the gas turbine. For the assumptions and simplifications made in this study, a 240 MW combined cycle power plant with a large gas turbine (150 MW), a two-pressure heat recovery steam generator with a reheater but without supplementary firing is favored from an economic viewpoint. A detailed exergy analysis of selected intermediate solutions and the final optimal design identifies the magnitude, location and causes of the thermodynamic inefficiencies.

On the modelling of population balance in isothermal vertical bubbly flows - average bubble number density approach

Abstract: To model the spatial evolution of the geometrical structure of the gas bubbles in isothermal vertical bubbly flow conditions, the population balance approach has been employed and merged with the three-dimensional two-fluid model. The population balance is realized by incorporating an average bubble number density transport equation into a commercial computational fluid dynamics (CFD) code ANSYS CFX 10. The coalescence and breakage effects of the gas bubbles are formulated according to the bubble coalescence by random collision driven by turbulence and wake entrainment while for bubble breakage by the impact of turbulent eddies. Three models representing these coalescence and breakage mechanisms proposed by Wu et al. [1] , Hibiki and Ishii [2] and Yao and Morel [3] are assessed. Local radial distributions of the five primitive variables in bubbly flows: void fraction, Sauter mean diameter, interfacial area concentration, and gas and liquid velocities, are compared with two experimental data of Liu and Bankoff [4] , [5] and Hibiki et al. [6] . Close agreements between the predictions and measurements demonstrated the capability of the average bubble number density transport equation in modelling bubbly flow conditions.

The validity domain of hybrid models and its application in process optimization

Abstract: Hybrid modeling is an attractive approach for processes, whose underlying physical phenomena, such as chemical reactions or heat and mass transfer, are not fully understood. A hybrid model combines a rigorous model part that represents available process knowledge with empirical model parts describing unknown phenomena. One of the key advantages of hybrid models over empirical models is its ability to extrapolate beyond the identification data domain, which is valuable in many applications such as process optimization and control. However, the validity domain of hybrid models is not universal and should be checked during model application to prevent misleading conclusions. This paper, therefore, presents two complementary validity criteria for hybrid models: the convex hull criterion checks, whether each empirical model part only interpolates the data encountered during model identification; the confidence interval criterion calculates confidence intervals for the hybrid model prediction. These criteria can be added as validity constraints to an optimization problem, as is demonstrated in a case study on a steady-state optimization of an ethylene glycol production process.

WGS reaction in a membrane reactor using a porous stainless steel supported silica membrane

Abstract: Water gas shift reaction for hydrogen production was studied in a catalytic membrane reactor using a supported silica membrane at 220–290 °C temperature and 2–6 bar pressure ranges. A CO conversion higher than the thermodynamic equilibrium of a traditional reactor was obtained. The best result, 95% CO conversion, was achieved at 4 bar and 280 °C. The membrane was also characterized in terms of permeance and selectivity by means of permeation tests carried out before and after reaction. In addition, permeance and separation factor were also measured during the reaction. Permeance of all species (H2: 9.7–29; CO: 0.3–1.1; CO2: 0.4–1.5 nmol/m2 s Pa), selectivity (H2/CO, H2/CO2 and H2/N2) ranging from 15 to 40 and separation factors (H2/CO = 20–45), showed no dependence on the related permeation driving force. Differences between selectivity and separation factor were registered. Furthermore, no inhibition effects of other gases on the hydrogen flux were observed. The membrane was prepared by the soaking roller procedure depositing a silica layer on a stainless steel support with an intermediate γ-alumina layer. The membrane reactor allowing selective hydrogen permeation presents a good performance exceeding also the equilibrium conversion of a traditional reactor.

Development of stickiness of whey protein isolate and lactose droplets during convective drying

Abstract: The stickiness development of droplets of whey protein isolate (WPI), lactose and their mixture solutions was determined using an in situ stickiness testing device at 24, 65 and 80 degrees C. Stainless steel, Teflon, glass and polyurethane probes were used. At room temperature, the presence of 0.5-1% (w/w) WPI greatly lowered the observed tensile strength of water and lactose solutions due to surface adsorption and led to a weakening of the cohesive strength. At elevated temperatures, lactose droplets remained sticky showing cohesive failure until the surface was completely covered with a thin crystal layer. WPI droplets formed a thin, smooth skin immediately on coming in contact with drying air. This surface became non-sticky early in the course of drying due to the transformation of the surface to a glassy state. The skin forming and surface active nature of WPI was exploited to minimize the stickiness of honey in a pilot scale spray drying trial. Replacement of 5% (w/w) maltodextrin with WPI raised the powder recovery of honey solids from 28% to 80% in a pilot scale drying test. At elevated temperature the magnitude of stickiness on probe materials was in the order of glass > stainless steel > polyurethane > Teflon. The Teflon surface offered the lowest stickiness both at low and high temperatures making it a suitable material to minimize stickiness through surface coating. (c) 2006 Elsevier B.V. All rights reserved.

The reaction engineering approach to modelling the cream and whey protein concentrate droplet drying

Abstract: Spray drying is the key process of the manufacturing of dairy powders. There have been a series of studies published previously on both modeling the drying characteristics of a single milk droplet and the dryer wide simulations incorporating computational fluid dynamics (CFD). In CFD simulations, it is desirable to track a large number of particles of different sizes to represent the size distribution effect. It is desirable to have an accurate yet simple model for correlating the drying rate of a single droplet, which does not require the solution of the partial differential equations. In this study, an aqueous cream and whey protein concentration solution was dried in droplet form and the appropriate reaction engineering approach (REA) model parameters obtained. The REA model predictions were compared with experimental results. Good agreement was achieved. The change of diameter of the droplet during drying was measured experimentally and compared with the model results also. The comparison between the drying characteristics of the high protein product and the high fat product reveals one aspect of compositional influence, for which the REA model has not yet been refined sufficiently to account fully. The laboratory measurements on compositional effects need to be conducted more extensively and accurately in future studies.

Efficient optimization of simulated moving bed processes

Abstract: Simulated moving bed (SMB) chromatography is attracting more and more attention since it is a powerful technique for complex separation tasks. Nowadays, more than 60% of preparative SMB units are installed in the pharmaceutical and in the food industry [SDI, Preparative and Process Liquid Chromatography: The Future of Process Separations, International Strategic Directions, Los Angeles, USA, 2002. http://www.strategic-directions.com ]. Chromatography is the method of choice in these fields, because often pharmaceuticals and fine-chemicals have physico-chemical properties which differ little from those of the by-products, and they may be thermally instable [J. Kinkel, M. Schulte, R. Nicoud, F. Charton, Simulated moving bed (SMB) chromatography: an efficient method for performing large-scale separation of optical isomers, Chiral Eur. 95 (1995) 121–132; J. Strube, A. Jupke, A. Epping, H. Schmidt-Traub, M. Schulte, R. Devant, Design, optimization and operation of chromatographic processes in the production of enantiomerically pure pharmaceuticals, Chirality 11 (1999) 440–450]. In these cases, standard separation techniques as distillation and extraction are not applicable [S. Imamoglu, Simulated moving bed chromatography (SMB) for applications in bioseparation, Adv. Biochem. Eng. Biotechnol. 76 (2002) 211–231]. The use of the SMB technology leads to more efficient operations in terms of dilution and adsorbent utilization than the classical batch separation. Optimization of SMB processes is still a challenging task, particularly when a rigorous first-principles process model is used. SMB processes exhibit strong non-linear behavior and they are of periodic nature. Additionally, their hybrid, non-steady and non-ideal characteristics have to be taken into account. Model-based optimization strategies are therefore of great importance for research and practice. In this article, we report new efficient numerical approaches for the solution of the dynamic optimization problem arising from SMB processes [A. Toumi, Optimaler Betrieb und Regelung von Simulated Moving Bed Prozessen, Dissertation, Fachbereich Bio und Chemieingenieurwesen, University of Dortmund, 2004]. They have been developed in the software package MUSCOD-II [D. Leineweber, Efficient reduced SQP methods for the optimization of chemical processes described by large sparse DAE models, Dissertation, vol. 613, VDI Reihe 3, Verfahrenstechnik, VDI Verlag, 1999], a recent implementation of the direct multiple shooting method where the optimal state trajectory and the corresponding operating parameters are determined simultaneously [H. Bock, K. Plitt, A multiple shooting algorithm for direct solution of optimal control problems, in: Proceedings of the 9th IFAC World Congress Budapest, Pergamon Press, 1984, pp. 243–247; H. Bock, Randwertproblemmethoden zur Parameteridentifizierung in Systemen nichtlinearer Differentialgleichungen, Dissertation, Bonner Mathematische Schriften, 1987, p. 183]. Numerical results show excellent performance for a benchmark enantiomer separation. Finally, the ability to solve the non-linear programs quickly also enables us to consider more challenging operating regimes like VARICOL [P. Adam, R. Nicoud, M. Bailly, O. Ludemann-Hombourger, Process and device for separation with variable-length chromatographic columns, US Patent 6,413,419 (2002)] and PowerFeed [Z. Zhang, M. Mazzotti, M. Morbidelli, PowerFeed operation of simulated moving bed units: changing flow-rates during the switching interval, J. Chromatogr. A 1006 (2003) 87–99].

Separation of proteins and lactose from dairy wastewater

Abstract: Fractionation of dairy wastewater into lactose-enriched and protein-enriched streams using ultrafiltration membrane technique was examined. Three membranes of MWCO of 3, 5 and 10 kDa of regenerated cellulose material were used to determine the efficiency of the process. The performance was determined under various processing conditions that include the operating temperature and transmembrane pressure across the membrane and the concentration of lactose in the feed solution. The experiments were initially conducted with a made-up solution of (i) pure lactose and then (ii) lactose solution with protein. Finally the experiments were performed with dairy wastewater supplied by a local dairy processing plant. It was found that the 3, 5 and 10 kDa membranes provided 70–80%, 90–95% and 100% recovery of lactose in permeate, respectively from made-up solution of pure lactose. The 10 kDa membrane results showed a 100% recovery of lactose from wastewater sample. At temperatures higher than the room temperature the lactose recovery was higher by a minimum of 5% and a maximum of 20% for 3 kDa membrane. An increase in transmembrane pressure increased the permeate flux which increased the percent of lactose being recovered. The addition of protein to the made-up lactose solution or using waster sample as feed did not decrease the percent of lactose being recovered even at transmembrane pressure of 1 bar. The 10 kDa membrane showed approximately 60–95% rejection of protein, the percentage being low at lower transmembrane pressures (less than 2.0 bars) and high at higher transmembrane pressures (greater than 2.5 bar). Other experiments conducted with wastewater showed that the permeate flux decreased slightly over a period of 25 min showing that fouling was not significant. In conclusion the most effective membrane to produce fractions: one with lactose-enriched (as permeate) and protein-enriched (retentate) from made-up solution as well as from dairy wastewater is 10 kDa.