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There are few studies on the effects of spatial distribution of hydrodynamics on the micro-mixing in stirred reactors. In this work, a statistical approach is introduced to quantitatively assess the spatial distributions of hydrodynamic parameters, using the turbulent dissipation rate as an example. According to the results, the effects of impeller geometry and angular velocity on the turbulent dissipation rate can be well described in terms of the volume-averaged values and spatial distribution functions. In the present study, a more uniform distribution of the turbulent dissipation rate is achieved by the multiple impellers with an inclinational angle of 15° at the same rotational speed. However, increasing the inclinational angle can decrease the volume-averaged value. The cumulative percentage of area-averaged turbulent dissipation rate is well modeled by an exponential function. The effects of impeller types on the meso- and micro-mixing processes are also investigated. It is found that the micro-mixing process has more significant influences than the meso-mixing process in the bottom region and near the free surface. The effects of impeller types on the micro-mixing performance are further investigated using the Villermaux–Dushman reaction system, both experimentally and numerically. An empirical correlation that considers the spatial distribution of turbulent parameters for the reaction rate of I2 synthesis is proposed. The results show that the predictions of segregation index, which represents micro-mixing performance, are improved by a numerical model coupled with the new reaction rate model. [ABSTRACT FROM AUTHOR]

Stirred reactors are key equipment in production, and unpredictable failures will result in significant economic losses and safety issues. Therefore, it is necessary to monitor its health state. To achieve this goal, in this study, five states of the stirred reactor were firstly preset: normal, shaft bending, blade eccentricity, bearing wear, and bolt looseness. Vibration signals along x, y and z axes were collected and analyzed in both the time domain and frequency domain. Secondly, 93 statistical features were extracted and evaluated by ReliefF, Maximal Information Coefficient (MIC) and XGBoost. The above evaluation results were then fused by D-S evidence theory to extract the final 16 features that are most relevant to the state of the stirred reactor. Finally, the CatBoost algorithm was introduced to establish the stirred reactor health monitoring model. The validation results showed that the model achieves 100% accuracy in detecting the fault/normal state of the stirred reactor and 98% accuracy in diagnosing the type of fault. [ABSTRACT FROM AUTHOR]

The design of a controller for a chemical reactor was studied. Based on the inputoutput feedback linearization, the controller was designed for a situation where the output of the system is the concentration. The reaction in the reactor is of the firstorder type. First, the reactor is modeled and presented, and then a controller for this system is designed. The control system was implemented in Simulink MATLAB. The simulation results show that the designed controller is able to control the concentration in a wide range and its performance is desirable for changing either the disturbances or the set point. [ABSTRACT FROM AUTHOR]

In this paper, mechanical impeller mixing has been analyzed through CFD which has proven to be a useful method for simulating mixing before manufacturing the digester. In this work, simulations were done for five different digester designs for TS level of 12.1%. While the fifth digester was cylindrical, the other four were cubical in design with varying impeller diameters and the number of impellers. The power law model was used to resemble the sewage sludge as a non-Newtonian fluid. The modified versions of dead volume and uniformity index were used along with velocity gradient and mixing energy level to quantify the quality of mixing. An analysis of the temperature distributions during mixing and heating was done using a thermal study. The operating speed of 250 rpm was finalized after testing at continuously increasing speeds from 50 to 600 rpm for a flat blade type impeller. As per the thermal model, a 250-W heater raised the temperature by around 15 °C in just 10 min. It was found that cylindrical vessels worked better than cubical digesters and larger impellers also helped in improving the mixing. The cylindrical digester which achieved about 67% homogeneity at a mixing energy level of around 0.95 W/m3, was the optimum design among the investigated digesters.

This contribution describes the influence of turbulent flow conditions in the liquid and/or gas phase and directly in the phase interface, different flow patterns (axial/radial), volume‐specific power inputs, mass‐specific energy consumptions, as well as volume‐specific mass transfer coefficients on the gas hydrate formation, derived from an experimental investigation of five different reactor setups. The results correspond to all fields of gas hydrate research, especially actually discussed technical hydrate applications, like hydrate‐based desalination, gas storage, gas separation, biogas and green hydrogen handling, carbon dioxide deposition, new phase transfer materials, and even electrical power supply. Two main objectives, first, to determine favorable hydrate forming conditions in stirred systems to provide competitive hydrate formation processes, and second, the search for a concept to enable the transfer of experimental results, for example, from a stirred reactor to a pipeline system for inhibitor research, through the targeted adjustment of similar and comparable turbulent flow conditions in different reactor setups could be achieved. So far, the targeted formation of gas hydrates has been investigated essentially from the point of view of optimizing the formation conditions with regard to pressure and temperature as well as the addition of auxiliary materials and promoters. In addition, some studies consider different reactor types and setups, for example, spray reactors or bubble columns. In many publications, stirred and cooled pressure autoclaves are described, whereby the gas and the liquid phase are brought into contact with each other by mixing to a greater or lesser extent by an agitator, then forming a solid gas hydrate phase. Often missing in previous research work is a systematic approach for determining the influence of flow conditions on gas hydrate formation. Many different influencing factors in a stirred reactor system can strongly affect the kinetics and formation of gas hydrates, for example, stirrer type, rotational frequency, stirrer and reactor geometry, and filling level. This is the starting point of the present investigation that deals with the influence of the flow conditions on the formation of gas hydrates. Tests were performed in a stirred autoclave to measure the effects of different stirrer configurations. The results obtained contribute to the explanation of the hydrate formation mechanism and can be used to optimize the targeted production of gas hydrates in technical hydrate applications. A rapid, immediate, hydrate formation is advantageous and can be achieved by suitable flow conditions in stirred reactors, which is successfully proven within this study contribution. [ABSTRACT FROM AUTHOR]

The technology for producing artificial rutile by the reduction-rusting method has the advantages of high product quality and less slag. A computational fluid dynamics (CFD) method is used to simulate the solid-liquid suspension and gas-liquid dispersion characteristics in the stirred corrosion reactor. The results show that the maximum volume fraction difference of the solid phase in the reactor with an upward-lifting impeller is 0.02, and for the downforce type, it is 0.04. When the stirring speed is increased from 100 rpm to 150 rpm, the radial dispersion area of the gas phase is increased; after the six-inclined-blade disk turbine is selected as the lower impeller, the proportion of bubbles with a diameter less than 0.004 m in the reactor is increased from 26% to 45%. The content of metallic iron in the product of the corrosion reaction is 1.67% in the stirred reactor with a six-inclined-blade disk turbine as the lower impeller. [ABSTRACT FROM AUTHOR]

The solid-liquid flow field is established in the stirred reactor with baffles and draft tube. Mixing time and suspension quality of the flow field are studied. Based on the Eulerian multiphase flow model and RNG k−ε turbulence model, the CFD model is established for the simulation research. By comparing the experimental data of solid concentration distribution and mixing time with the simulated values, it is proved that the CFD model established can be used to study the flow field in the stirred reactor. The effects of stirring speed, liquid viscosity and solid particle size on mixing time and suspension quality are considered. With the increase of stirring speed, mixing time decreases, mixing uniformity is improved. Mixing time decreases first, then increases slightly with the increase of liquid viscosity, and the suspension quality is improved. When the solid particle size increases, mixing time increases rapidly, but the mixing uniformity becomes worse. [ABSTRACT FROM AUTHOR]

In this work, the absorption of CO2 using aqueous piperazine (PZ) solution have been investigated both experimentally and theoretically. The absorption experiments were carried out in a stirred batch contactor with two flat blades. The experimental data are obtained over the temperature range of 298–338 K and for the PZ concentration, CO2 partial pressure, and the stirrer speed in the range of 0.5–1.5 kmol/m3, 2.5-7.5 bar, and 0-300 rpm, respectively. The influences of each variable upon the absorption flux, removal efficiency, and loading of CO2 have been investigated. In addition, a model based on chemical equilibrium in the liquid phase is employed to evaluate the concentration of chemical species in the liquid phase. Evidence suggests that CO2 absorption flux, removal efficiency, and the loading increase with decreasing the temperature and increasing the stirrer speed. When PZ concentration is increased, the absorption flux and removal efficiency increase and CO2 loading reduce. Also by increasing PZ concentration from 0.5 to 1.5 M at a temperature of 388 K, absorption efficiency is increased from 70 % to 95 %. CO2 absorption flux was decreased from about 0.0175 to 0.01 mol/m2 s when CO2 loading was increased from 0.32 to 0.51.

The technology for producing artificial rutile by the reduction-rusting method has the advantages of high product quality and less slag. A computational fluid dynamics (CFD) method is used to simulate the solid-liquid suspension and gas-liquid dispersion characteristics in the stirred corrosion reactor. The results show that the maximum volume fraction difference of the solid phase in the reactor with an upward-lifting impeller is 0.02, and for the downforce type, it is 0.04. When the stirring speed is increased from 100 rpm to 150 rpm, the radial dispersion area of the gas phase is increased; after the six-inclined-blade disk turbine is selected as the lower impeller, the proportion of bubbles with a diameter less than 0.004 m in the reactor is increased from 26% to 45%. The content of metallic iron in the product of the corrosion reaction is 1.67% in the stirred reactor with a six-inclined-blade disk turbine as the lower impeller.

Bioreactors are essential tools for the development of efficient and high-quality cell therapy products. However, their application is far from full potential, holding several challenges when reconciling the complex biology of the cells to be expanded with the need for a manufacturing process that is able to control cell growth and functionality towards therapy affordability and opportunity. In this review, we discuss and compare current bioreactor technologies by performing a systematic analysis of the published data on automated lymphocyte expansion for adoptive cell therapy. We propose a set of requirements for bioreactor design and identify trends on the applicability of these technologies, highlighting the specific challenges and major advancements for each one of the current approaches of expansion along with the opportunities that lie in process intensification. We conclude on the necessity to develop targeted solutions specially tailored for the specific stimulation, supplementation and micro-environmental needs of lymphocytes' cultures, and the benefit of applying knowledge-based tools for process control and predictability. [ABSTRACT FROM AUTHOR]

Aiming at the mixing efficiency of non-Newtonian fluids in a mechanical stirred reactor, the flow field characteristics of non-Newtonian fluids in a mechanical stirred reactor were studied. The non-contact flow field measurement particle image velocimetry technique was applied to measure the flow field of non-Newtonian fluids in a four pitch blade turbine stirred reactor of experimental scale. The effects of different concentration and stirring speed on the flow field distribution in a mechanical stirred reactor were discussed and analyzed. The results indicate that the stirring speed not only affects the convection intensity between fluids, but also changes the flow field structure of fluids. Solution concentration has little influence on the flow field pattern, but it affects the size of the high velocity region in the lower part of the impeller and the maximum velocity of the fluid. [ABSTRACT FROM AUTHOR]

Highlights • A 3D CFD-PBM model developed to predict struvite formation in batch stirred reactor. • Includes hydrodynamic, thermodynamic, kinetic variables of struvite precipitation. • Crystal size distribution obtained from model matches experimental results. • Model will aid efficient reactor design for production of desired struvite crystals. Abstract A general model has been developed to elucidate the precipitation of struvite crystals in a batch stirred tank reactor. The model, which evaluates reactor performance, also predicts crystal size distribution (CSD) over time by considering the hydrodynamic, thermodynamic, and kinetic aspects of solution in the reactor. A Computational Fluid Dynamics (CFD) model was coupled with Population Balance Modeling (PBM) to model the growth of crystals in the reactor. A thermodynamic equilibrium model for struvite precipitation was consolidated with the reactor model. While the equilibrium model provided information on supersaturation development, the coupled CFD-PBM model captured the crystal growth kinetics and the influence of the reactor hydrodynamics on the overall process. Size distribution is crucial as it determines distinct grades of final struvite crystals, which are to be used as commercial fertilizer. In the simulation, the CFD flow field was solved through a Eulerian multiphase approach and RNG-k-ɛ turbulence model. The population balance equation was solved using a discretized form of the continuous partial differential equation, which transformed the continuous partial differential equation into finite ordinary differential equations as per size classes, which were then solved simultaneously. The growth rate, as a function of the supersaturation index (SI), was employed in the model through User Defined Function. The mean, standard deviation, and skewness of the model predicted CSD after 50 min were 20.81 μm, 9.61 μm, and 2.97, respectively and for the experimental CSD were 19.66 μm, 7.13 μm, and 2.46, respectively. The predicted peak-size percent fraction revealed a deviation from experimental results of 1.42%, 0.05%, 2.43%, 14.6%, 11.2%, 11.7%, 13.6%, and 14.2% at 0, 3, 10, 20, 30, 40, 50, and 60 min, respectively. [ABSTRACT FROM AUTHOR]

Highlights • DQMOM-IEM is adopted to investigate the mixing-sensitive Fenton oxidation process. • Molar concentrations expressions are deduced in terms of the resolved model scalar. • Space-time characteristics of the quenching process of Rhodamine B are captured. • Model predictions are in good agreement with experimental data. Abstract The direct quadrature method of moments combined with the interaction by exchange with the mean model (named as DQMOM-IEM) is applied to simulate the novel reactive-PLIF (planar laser induced fluorescence) experiment in an unbaffled stirred reactor. By using the mixture fraction and reaction progress variables, the descriptions of the Fenton reaction and oxidation reaction of Rhodamine B are formulated. The quenching of fluorescent signal can be visualized by solving the probability, probability weighted mixture fraction and reaction progress variables used in the two-environment DQMOM coupled with the IEM micro-mixing model. The effect of impeller speed on the mixing and reactions are revealed by the simulated dynamic processes. The predictions by DQMOM-IEM micro-mixing model agree well with the experimental data, suggesting that this model is an effective approach for numerical prediction of turbulent reactive flow in stirred reactors. [ABSTRACT FROM AUTHOR]

This paper presents the thermal analysis and mathematical modeling of a discontinuous agitation reactor. A data acquisition phase was implemented in terms of operation and utility of the agitation reactors. Subsequently, the concepts of thermodynamics, fluid mechanics, heat transfer and matter transport were applied to perform the respective thermal analysis and thus, determine the energy contained and transferred in the fluids used. In addition, a mathematical model was deduced in the EES software to examine its behavior, taking into account the operational variables subjected to various types of fluids. Finally, the physical-chemical environment of the reactor was simulated to validate the calculated data and compare them with the experimental values, relating the geometry of the equipment to the performance conditions and the specifications of the final product. [ABSTRACT FROM AUTHOR]

Pyrolysis of low density polyethylene (LDPE) by equilibrium fluid catalytic cracking (FCC) was studied in a stirred reactor under different process parameters. In this work, the effect of process parameters such as degradation temperature (420-510°C), catalyst/polymer ratio (0-60%), carrier gas type (H2, N2, ethylene, propylene, Ar and He), residence time and agitator speed (0-300 rpm) on the condensate yield (liquid, gas and coke) and product composition were considered. Reaction products were determined by GC analysis and shown to contain naphthenes (cycloalkanes), paraffins (alkanes), olefins (alkenes) and aromatics. Higher temperature and more catalyst amount enhanced LDPE cracking. The maximum “fuel like” condensed product yield was attained at 450°C and 10% catalyst, respectively and gaseous products increased with increases in temperature. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. Appropriate heat transfer (by stirring) increased the catalyst efficiency in a stirred reactor.

Struvite (MgNH4PO4·6H2O) crystallisation is a promising approach for phosphorus recovery from swine wastewater. Currently, intensive pig feeding has made heavy metals (HMs) extensive in swine wastewater; therefore, significant amounts of HMs have been detected in struvite recovery products. In this study, the HM residues in the struvite products recovered from stirred and fluidised bed reactors were investigated. The results showed that Zn, Mn, and Cu were the most abundant elements in swine wastewater (1,175.3±178.0, 745.4±51.5, and 209.3±54.4 μg L-1, respectively). The HMs, especially Zn (97.0%) and Cu (96.8%), were mainly distributed in the total suspended solids (TSS) of the swine wastewater. Redundancy analysis revealed that the HMs in the struvite products harvested from the fluidised bed reactor were mainly attributable to the aggregation of dissolved matters, because most TSS were elutriated through fluidisation. In contrast, the HMs in the struvite products harvested from the stirred reactor mainly originated from the TSS, which complexed with the HMs, and co-precipitated and settled with the struvite products. Furthermore, chemical fractionation of the HM species confirmed that the presence of HMs in the struvite products was mainly attributable to metal precipitation and organic aggregation. [ABSTRACT FROM AUTHOR]

In this study, pyrite was produced by hydrothermal precipitation from the reaction between FeSO4 and Na2S2O3 at high pressure and high temperature in a stirred reactor. The solid product was purified by means of solvent extraction to remove sulfur. Powder was characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermal analyses. Results indicated that pyrite was produced as nanostructure with high purity.

A fundamental study on the kinetics of uranium mineral bioleahing using Acidithiobacillus ferrooxidans has been carried out in stirred reactor (SR) and column reactor (CR). The four factors affecting uranium dissolution kinetic including aeration rate, pH, initial Fe 2+ concentration and temperature were selected to be optimized in SR. The aeration rate of 100 l/h pH of 1.8, initial Fe 2+ concentration of 4 g/l and temperature of 35 °C were determined as optimal conditions. To understand ferric and ferrous ions changes by biooxidation, chemical leaching at constant potential were conducted. Results showed that the electrochemical reaction controlled the overall uranium dissolution. By the progress of bioleaching, three stages of bioleaching were observed. The rate controlling is anodic uranium mineral decomposition in the first and second stages while in the third stage cathodic ferric reduction is rate controlling. By using SEM, EDX, XRD and BET analysis, the formation of K-jarosite layer over the residue particles confirmed and the increasing of porosity in the particles surface proved that diffusion of ions from layer was not limiting in uranium bioleaching. The modified kinetic model during bioleaching in SR was presented and developed in CR. Comparing the results, the semi-empirical model data are in good agreement with the experimental data for both uranium leaching and bioleaching in SR and CR. [ABSTRACT FROM AUTHOR]

In chemical engineering applications, it is not uncommon to encounter reactors featuring rotating parts. As these rotating parts are present in order to enhance processes such as chemical reactions and/or ensure homogeneity, it is essential to take them into account to perform predictive numerical simulations. This aspect can be particularly challenging, even more so when complex industrial geometries are to be treated. In this paper a numerical methodology for simulating unsteady granular flow in rotating geometries is presented. The method is based on splitting the domain into static and rotating parts. The information between rotating and static parts is passed by a non-conformal mesh matching technique. The presented methodology is validated numerically by comparing its results with other conventional methods. The method is then applied to an industrial scale problem. The applicability of the method and the way it may be used to investigate complex flow is demonstrated. Therefore this approach enables to consider the full geometry of complex reactors. It opens the door to further investigation, optimization and design of industrial scale chemical processes. [ABSTRACT FROM AUTHOR]

• Hydrate formation in a stirred reactor for water-methane systems is modeled. • The simulation results are validated using the experimental data. • Gas volume fraction and stirring rates of 0.4 and 900 RPM leads to the maximum formed hydrate. • Methane hydrate is formed mainly near the walls and around the stirrer blades. • Introduced CFD model can accurately predict the methane hydrate formation in the stirred reactor. Hydrate formation management in oil and gas industries needs a detailed understanding of hydrate formation phenomena in terms of dynamics and kinetics aspects. Stirred reactors are one of the popular experimental systems to study hydrate formation/dissociation in terms of kinetics and thermodynamics mechanisms. Various processes/systems such as gas hydrate formation and decomposition phenomena in oil and gas facilities are simulated using computational fluid dynamics (CFD). This research examines the hydrate formation in a stirred reactor for a water-methane system using the Eulerian multiphase flow model by employing CFD software (STAR CCM +). The developed numerical model incorporates the conservation equations of momentum, mass, and energy, where the hydrate equations, including mass transfer, hydrate kinetics, and heat of hydrate formation, are included in the governing equations. In this paper, the methane hydrate formation in the stirred reactor for the stirring rate of 300 RPM and volume fraction of 0.04 with a pressure of 5,500 kPa is simulated. Then, the simulation results are validated using the experimental data collected from the literature, resulting in an overall absolute average deviation percentage (AAD%) of 15.6 %. The influences of stirring rate (300 to 500 RPM), methane volume fraction (0.04 to 0.4), pressure (3,500 to 7,500 kPa), and subcooling (1.96 to 9.23 °C) are studied on the hydrate formation in the agitated reactor. The results reveal that the developed CFD model can predict the methane hydrate formation in the stirred reactor with acceptable precision. According to the simulation runs, methane hydrate is formed mainly near the walls and around the stirrer blades. In addition, an increase in subcooling, gas volume fraction, pressure, and stirring rate leads to more hydrate formation in the reactor with a constant temperature of 274.3 K. The maximum mass fraction of hydrate is observed for the case when the gas volume fraction and stirring rates are 0.4 and 900 RPM, respectively. However, the minimum value of methane hydrate is 0.092 g, where the volume fraction and impeller speed are 0.04 and 300 RPM. The findings of this study can help to further understand hydrate formation phenomena in oil and gas facilities. This model can provide oil and gas engineering sectors with effective strategies to control and manage gas hydrates. In addition, the proposed CFD model can be helpful for engineers and researchers in the petroleum industry to simulate hydrate formation in other complicated geometries in petroleum facilities. [ABSTRACT FROM AUTHOR]

Ozone absorption in water was investigated in a mechanically stirred reactor, using both the semi-batch and continuous mode of operation. A model for the precise determination of the volumetric mass transfer coefficient in open tanks without the necessity of the measurement the ozone concentration in the outlet gas was developed. It was found that slow ozone reactions in the liquid phase, including the decomposition of ozone, can be regarded as one pseudo-first order reaction. Under the examined operating conditions, the liquid phase was completely mixed, while mixing in a gas phase can be described as plug flow. The volumetric mass transfer coefficient was found to vary with the square of the impeller speed.

Ozone absorption in water was investigated in a mechanically stirred reactor, using both the semi-batch and continuous mode of operation. A model for the precise determination of the volumetric mass transfer coefficient in open tanks without the necessity of the measurement the ozone concentration in the outlet gas was developed. It was found that slow ozone reactions in the liquid phase, including the decomposition of ozone, can be regarded as one pseudo-first order reaction. Under the examined operating conditions, the liquid phase was completely mixed, while mixing in a gas phase can be described as plug flow. The volumetric mass transfer coefficient was found to vary with the square of the impeller speed. .

BACKGROUND Industrial processes are often operated in hot-sparged agitated reactors and the volumetric mass transfer coefficient ( kL a) is one of the most important parameters for design and scale-up of stirred tank reactors. In this work, the power consumption and volumetric mass transfer coefficient were studied under hot-sparged conditions. RESULTS The relative power demand ( RPD) increases remarkably with temperature according to a power law with an exponent of 0.44. kL a increases significantly with power consumption and superficial gas velocity according to power laws with exponents 0.56 and 0.28, respectively. However, the temperature has little influence on kL a, with a power law exponent of only 0.13 for a coalescent system, much smaller than the exponent of 1.64 for a non-coalescent system stirred by a similar triple-impeller. CONCLUSIONS In a hot-sparged coalescent system, an increase in temperature cannot enhance the mass transfer rate as it does in a non-coalescent system. As a practical guide to industrial applications, it is more effective to enhance the gas-liquid mass transfer by increasing the power consumption than by increasing the gas flow rate, especially when the gas flow rate is already very high. The empirical relationships between power consumption and kL a obtained in this work can provide helpful guidance for industrial design and operation of hot-sparged stirred reactors. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Agarose gel activation reaction, which is of great importance in preparing the carrier of the column packing material for blood purification, would be significantly influenced by the configuration and parameter of reactor. In order to optimize the structure design of the reactor and operating parameters of the process, the characteristics of suspension system composed of agarose gel, NaOH, water, 3-allyl bromide, and activated alumina were simulated numerically utilizing an Eulerian multiphase flow model and multi-reference frame (MRF) approach. The effect of impeller configuration was studied with three typical impellers, including Rushton disk turbine (DT), pitched blade downflow turbine (PBTD45), and pitched blade upflow turbine (PBTU45). The results showed that the optimum solid suspension was obtained using PBTD45 impeller with a diameter of 100mm and critical suspension speed of 570rpm in a 20L stirred reactor. In addition, the critical suspension speeds using the three impellers were calculated and the errors were all within the engineering allowance. Finally, the feasibility of scale-up design for agarose gel activation reactor was preliminarily discussed. The results would be useful to the optimization and scale-up of relevant reactor design. [ABSTRACT FROM AUTHOR]

Liquid-solid mass transfer behaviour of a rectangular stirred tank reactor lined with single screens and stacks of closely packed screens was studied in relation to catalytic and electrochemical reactor design by the electrochemical technique. Variables studied were impeller rotation speed, mesh number, and wire diameter of the screen, as well as physical properties of the solution, number of screens per stack, and impeller geometry. The rate of mass transfer increased with increasing impeller rotation speed and decreased with increasing screen mesh number and number of screens per stack. Radial flow turbine impellers produced higher rates of mass transfer than axial flow impellers. The data were correlated by dimensionless mass transfer equations. A comparison between the volumetric mass transfer coefficient at a stirred single-screen electrode and at a stirred flat plate electrode shows that the volumetric mass transfer coefficient at the single screen is higher than that at the flat plate by a factor ranging from 7.3-22.5, depending on the operating conditions. For screen stacks, the ratio between the stack volumetric mass transfer coefficient and the flat plate value ranges from 2-46 depending on the operating conditions. The importance of the present results in the design and operation of catalytic and electrochemical reactors used to conduct diffusion-controlled reactions was highlighted. The possibility of using screens as turbulence promoters to enhance the rate of heat transfer between the reactor wall and the surrounding cooling jacket was noted. [ABSTRACT FROM AUTHOR]

In this paper, the synthesis of iron pyrite nanoparticles (FeS 2 ) is investigated both experimentally and numerically through facile hydrothermal route in a laboratory-scale stirred autoclave reactor equipped with a 4-bladed 45° pitched-blade turbine (PBT) impeller. An elaborated CFD model is also adopted which accounts for the governing transport phenomena, namely mass, momentum, energy and species equations to investigate flow behavior as well as mixing patterns and chemical reactions for the synthesis of iron pyrite nanoparticles in the autoclave reactor. The iron pyrite reactor is described as an incompressible, single-phase, liquid mixing regime undergoing chemical reactions via integrating with an appropriate proposed kinetics model obtained experimentally. Power consumption and mixing time of the autoclave reactor are measured experimentally to assess the validity of the CFD model. Besides, the effect of temperature and reactant molar ratio as two important key parameters in the synthesis reaction is evaluated both numerically and experimentally, and the products in each scheme are characterized by X-ray diffraction (XRD) analysis. Both cold and reactive simulated results are in good agreement with experiments carried out in this work. Moreover, the reactive simulated results in conjunction with the XRD measurements illustrate that temperature is not an influential parameter in the synthesis of iron pyrite; whereas, an appropriate value of the reactants molar ratio is required to obtain a more purified product. The present developed CFD model is anticipated to help researchers in better understanding of the synthesis process, and to be useful as a bridge to the pilot-plant design in a cost-effective way. [ABSTRACT FROM AUTHOR]

In this semi batch pyrolysis study, the effect of different zeolite catalysts containing used FCC, HZSM-5 and mordenite on the degradation of virgin poly butadiene (PBR) were considered. The liquid, gas and coke yield as well as composition of liquid product as a function of different catalysts effect in the stirred reactor were compared. Main products obtained were light hydrocarbons within the gasoline range. The formation of aromatic products depended appreciably on the catalyst type and catalyst/polymer ratio. The results showed that C6 was main component of pyrolysis product with up to 32%. The results also showed that crosslink mechanism played an important role in the rubber pyrolysis. A huge number of double bonds in the PBR chains could prepare the proper media for crosslink mechanism in slow pyrolysis while flash pyrolysis followed the chain scission mechanism in the most times of degradation. Crosslink nets could increase the activation energy and the resistance against the chain scission degradation by difficult chain mobility and heat transfer. [ABSTRACT FROM AUTHOR]

Background and Aims Several studies have investigated the effectiveness of several proteolytic enzymes in free form as a treatment alternative to bentonite fining for wine stabilisation. This work tested the feasibility of stem bromelain, free or immobilised on a chitosan support, to reduce white wine protein haze potential. Methods and Results The kinetic behaviour of stem bromelain, in free form and covalently immobilised on chitosan beads, was studied in 12 unfined white table wines fortified with a tripeptide chromogenic substrate. The effectiveness of the protease on wine hazing potential was determined by treating the wines in a laboratory-scale stirred reactor, and the heat test was applied to evaluate the decrease in nephelometric turbidity units. Immobilised protease was active towards the synthetic substrate and in reducing hazing potential of the wine. The effect of wine components on bromelain proteolytic behaviour, as investigated by principal component analysis, was much more noticeable for the free enzyme (in decreasing order of importance: pH, total phenolic substances, free and total sulfur dioxide) than for the immobilised form. Conclusions An amount of 10 g/ L biocatalyst (bromelain immobilised on chitosan beads), after a 24-h treatment in a laboratory-scale stirred reactor, revealed a high capacity to reduce wine haze potential (approximately 70%), which was unaffected by wine composition. Significance of the Study Immobilised bromelain appears a suitable treatment alternative to bentonite fining for white wine haze stabilisation. [ABSTRACT FROM AUTHOR]

Pyrolysis of polypropylene (PP) with an equilibrium fluid catalytic cracking (FCC) catalyst in a stirred reactor was studied to produce “fuel like” hydrocarbons. The effect of process parameters such as degradation temperature, catalyst/polymer ratio (%), carrier gas type and stirrer rate on the condensed product yield and composition were determined. Reaction products were determined by GC analysis and shown to contain naphthenes, paraffins, olefins and aromatics. Temperature was shown to influence PP cracking. The addition of the catalyst has improved the economic viability of the process to produce light hydrocarbons. PP pyrolysis showed the maximum condensed product yields at 450 °C and 10% catalyst respectively. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. The results showed that reactive carrier gases can affect on the product yield and composition patently. Appropriate heat transfer – by stirring – can increase the catalyst efficiency in a stirred reactor. [ABSTRACT FROM AUTHOR]

The competitive production of chemicals requires bigger facilities with higher space-time yields, for which there is often no experience in terms of process and equipment design available. An economic operation is only possible if stable processes and robust equipment prevent failures, and if high safety standards warrant health and environmental protection. The present study uses mixing systems to show how these aims can be combined and implemented. [ABSTRACT FROM AUTHOR]

In this paper, kinetics of absorption of CO2in an aqueous ethylaminoethanol (EAE) and formulated solvent (aqueous blend of EAE and N-methyl-2-pyrrolidone (NMP)) was studied in a stirred cell reactor by using a fall in pressure technique. The reaction pathways for CO2–aqueous EAE system were comprehensively described using both zwitterion and termolecular mechanisms. The physico-chemical properties such as density (ρ) and viscosity (μ) of aqueous EAE and formulated solvent and the solubility () and diffusivity of CO2() in these solvents were estimated experimentally. The reactive absorption of CO2in an aqueous EAE was observed to be first order with respect to both CO2and EAE concentrations. Addition of NMP in aqueous EAE enhances theby 40%, which ultimately results into higher CO2absorption rates in formulated solvent (∼20% higher) compared to that of the aqueous EAE. Effect of concentration of EAE (0.5 to 2 kmol/m3) and temperature (303 to 318 K) on CO2absorption kinetics was studied in detail and it was realized that the rate of absorption of CO2in aqueous EAE and formulated solvent was significantly affected by the change in these parameters. The findings obtained during the temperature dependency study further indicates that the activation energy of the absorption of CO2in aqueous EAE (80.2 kJ/mol) was relatively lower in comparison with the activation energy of the absorption of CO2in formulated solvent (88.95 kJ/mol). The overall reaction of CO2with the formulated solvent could be regarded as the reaction of CO2with aqueous EAE in parallel with the reaction between CO2and aqueous NMP. [ABSTRACT FROM AUTHOR]

Abstract: A full-factorial designed experiment was completed to quantify the effect of temperature, wet CO2 density and brine Na–Ca–Cl salinity on the liquid-side mass transfer coefficient k L for the dissolution of CO2 into brine. The range of experimental conditions corresponds to those relevant to the surface dissolution approach to geologic storage of anthropogenic CO2. The measured range of k L was from 0.015 to 0.056cm/s. An empirical correlation was developed for k L as a function of temperature to wet CO2 density and NaCl salinity. Greater temperature and smaller NaCl salinity increase k L . There is an interaction effect between temperature and wet CO2 density, which increases or decreases k L depending on the value of each. CaCl2 salinity does not have a statistically significant effect on k L . Wet CO2 density was used as an independent variable, in the place of pressure, since it was found to play a critical role in the onset of gas entrainment. Geologic storage of CO2 via the surface dissolution method requires different operating conditions for different applications. Importantly, since the composition of brine varies between locations, the dependency of k L on NaCl salinity allows for location specific process design. [Copyright &y& Elsevier]

Abstract: The yield as well as molecular weight and composition of the condensed product generated from the HDPE was studied to gain insight into the role of temperature, equilibrium FCC catalyst, agitator speed and carrier gas on the pyrolysis products. Pyrolysis was done in a suite stirred bucchi stainless-steel autoclave reactor. The effect of process parameters such as degradation temperature, catalyst/polymer ratio (%), carrier gas type and stirrer rate on the condensed product yield and composition was determined. Reaction products were determined by GC analysis and shown to contain naphthenes (cycloalkanes), paraffins (alkanes), olefins (alkenes) and aromatics. The maximum “fuel like” condensed product yields were at 450°C and 10% catalyst, respectively. The influence of different types of carrier gasses with varied molecular weights and reactivity was studied. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. Appropriate heat transfer – by stirring – can increase the catalyst efficiency in a stirred reactor. It is demonstrated that the use of equilibrium FCC commercial catalyst under appropriate reaction conditions can have the ability to control both the condensed yield and carbon number distribution from HDPE degradation, and thus potentially decrease the process cost with more valuable hydrocarbons. [Copyright &y& Elsevier]

Solving process design, process optimization, safety analysis and other problems widely relies on mathematical models of the process. To solve problems related to mixing, detailed models such as compartment models or computational fluid dynamics (CFD) models are required. Compartment modelling generally uses four basic compartments: the mixer (M), the distributor (D), the perfectly mixed reactor and the ideal plug flow reactor (PFR). The main modelling tasks using compartment models are defining the structure of the compartment model and determining the parameters of the connections between the compartments. Hence, a qualitative approach was developed to support this identification process. Qualitative methods can be applied to analyse experimental data and to compress the information content of a time series. The primary goal of this study is to present an algorithm based on qualitative analysis that can be used to identify a compartment model structure based on the hydrodynamic measurement data of a stirred reactor. [ABSTRACT FROM PUBLISHER]

Abstract: This work concerns the controlled struvite formation (MgNH4PO4·6H2O) by precipitation as an alternative removal of phosphorus and, consequently, of ammonium from wastewater discharges. A new method, based on an integrated methodology, is proposed here for predicting and controlling struvite nucleation and growth rate. Experiments were conducted in an isothermal stirred batch reactor at a temperature of 25°C from a synthetic aqueous solution at different pH levels (8.5–9.6). The initial concentrations of Mg, PO4 and NH4 are fixed at 3mmol/L, then at 4mmol/L, with a molar ratio of Mg/NH4/PO4 equal to 1. Crystal size is determined by laser granulometry and morphometry. A population balance-based model coupled with a thermodynamic model predicts particle size distribution vs. experimental time using a reconstruction model. This approach is particularly numerically stable for the identification of nucleation and particle growth kinetics parameters that are used to predict crystal size distribution. The methodology is based on a thermodynamic model previously developed for which pH control and supersaturation constitute key parameters. The obtained results are of major importance for the design of struvite precipitation reactor, and for the development of crystal growth control methodology. [Copyright &y& Elsevier]

Abstract: An advanced study of a bioreactor system involving a Navier–Stokes based model has been accomplished. The model allows a more realistic impeller induced flow image to be combined with the Monod bioreaction kinetics reported previously. The time-course of gluconic acid production by Aspergillus niger strain is simulated at kinetic conditions proposed in the literature. The simulation is based on (1) a stepwise solution strategy resolving first the fluid flow field, further imposing oxygen mass transfer and bioreaction with subsequent analysis of flow interactions, and (2) a segregated solution of the model replacing the multiple iterations per grid cell with single iterations. The numerical results are compared with experimental data for the bioreaction dynamics and show satisfactory agreement. The model is used for assessment of the viscosity effect upon the bioreactor performance. A 10-fold viscosity rise results in 2-fold decrease of K L a and 25% decrease of the specific gluconic acid production rate. The model allows better understanding of the mechanism of the important bioprocess. [Copyright &y& Elsevier]

Abstract: In this paper a model of conventional and electrochemical bioleaching of high grade complex copper sulfide ores or flotation concentrates in isothermal stirred tank reactors is presented and compared to experimental data. Experiments were conducted in an electrobioreactor using a mixed culture of moderate thermophile microorganisms at pulp density 20% (w/v), leaching time 10days, stirring rate 600rpm and temperature 50°C. The behavior of conventional and electrochemical bioleaching processes was described with a combined reaction-based kinetic model. The model considers the effects of mineralogical composition of the feed, the properties of the initial solution, the presence of iron- and sulfur oxidizing microorganisms and both the passivation and electroreduction of chalcopyrite on the values of copper recovery, pH and redox potential during the processes. Comparing the values obtained from the integrated semi-empirical model with the experimental data showed that the model results are in good agreement with the real leaching data of copper recovery, ORP (oxidation reduction potential) and pH for the mentioned processes under different experimental conditions. [Copyright &y& Elsevier]

Abstract: The pyrolysis of linear low density polyethylene (LLDPE) by used fluid catalytic cracking (FCC) catalyst was studied in a stirred reactor to reach the appropriate transportation hydrocarbons. In this work, the effect of process parameters such as degradation temperature, catalyst/polymer ratio (%), carrier gas type and stirring rate on the condensed yield, product composition and residence time were considered. Product evaluation was performed by GC analyzer and paraffin, naphthene, olefin and aromatic plus carbon number and average molecular weight of the products were measured under different process parameters. Temperature and catalyst as the basic parameters show remarkable effect on the LLDPE cracking. The maximum transportation condensate yield reaches at 450°C and 20% catalyst respectively although increase of temperature and catalyst content, decrease the residence time patently. Based on the results, molecular weight and reactivity of the carrier gas as mass transfer factor also play a key role in the process. A decrease in molecular weight of the carrier gas led to increase the condensate yield and decrease the residence time. Meanwhile increasing of the carrier gas reactivity could increase the condensate hydrocarbons. Hydrogen as reactive and lower molecular weight carrier gas increases the condensed yield patently. The study showed that stirring rate as a function of heat transfer and temperature homogenizer also affects on the condensate hydrocarbons positively. The maximum condensate yield was found to occur at 50rpm although the residence time decreases with stirring rate increasing. [Copyright &y& Elsevier]

The waste materials from the carob processing industry are a potential resource for second-generation bioethanol production. These by-products are small carob kibbles with a high content of soluble sugars (45-50%). Batch and fed-batch Saccharomyces cerevisiae fermentations of high density sugar from carob pods were analyzed in terms of the kinetics of sugars consumption and ethanol inhibition. In all the batch runs, 90-95% of the total sugar was consumed and transformed into ethanol with a yield close to the theoretical maximum (0.47-0.50 g/g), and a final ethanol concentration of 100-110 g/l. In fed-batch runs, fresh carob extract was added when glucose had been consumed. This addition and the subsequent decrease of ethanol concentrations by dilution increased the final ethanol production up to 130 g/l. It seems that invertase activity and yeast tolerance to ethanol are the main factors to be controlled in carob fermentations. The efficiency of highly concentrated carob fermentation makes it a very promising process for use in a second-generation ethanol biorefinery. [ABSTRACT FROM AUTHOR]

Abstract: An explicit algebraic stress model (EASM) was used to simulate anisotropic turbulent flows in baffled stirred tanks equipped with a standard Rushton turbine. The quantitative predictions of velocity components, turbulence kinetic energy, Reynolds stresses and turbulence energy dissipation rate in the context of anisotropic turbulence were conducted to assess the comprehensive performance of the EASM. A lot of efforts have been made to ensure numerical stability during the calculations such as using a good initial flow field, manipulating source terms and adjusting under-relaxation factors. The predicted results were also compared with experimental data and other simulation results obtained using the standard k–ε model, algebraic stress model (ASM), Reynolds stress model (RSM) and large eddy simulation (LES). All the simulations were run with in-house codes. The simulation results show that agreement between the EASM predictions and experimental values is satisfactory. The EASM is consistently superior to the standard k–ε model when predicting both peak values and trend of variation in velocities and turbulence quantities. In comparison to the RSM, the EASM has almost the same predictive accuracy. The EASM is inferior to the LES on the prediction of turbulence kinetic energy. Nevertheless, the computational cost of the EASM is significantly lower than that of the LES, which is an obvious advantage in practical applications. [Copyright &y& Elsevier]

Abstract: The velvetbean caterpillar, Anticarsia gemmatalis Hübner (Lepidoptera: Noctuidae), is one of the main plagues for soybean crops. Velvetbean caterpillar larvae are susceptible to be infected by occlusion bodies of the baculovirus Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV), a biological insecticide. The insect cell line saUFL-AG-286 produces very high yields of occlusion bodies of AgMNPV in suspension cultures done in the low-cost serum-free medium UNL-10 in shake-flasks. However, its ability to adapt to conditions of industrial production in bioreactors was unknown. The aim of this study was to characterize the growth of saUFL-AG-286 cell cultures in UNL-10 medium, as well as its capability to replicate AgMNPV in two different bio-reactors at laboratory scale. The cell line was able to adapt to conditions that can be used at industrial scale, both in an airlift reactor and a stirred reactor, although the former was better than the last to support the cell growth. The infection with AgMNPV in the airlift reactor produced a high yield of occlusion bodies, with very low production of budded virus, the progeny used as inoculums. On the other hand, infection in the stirred reactor yielded high titers of budded virus. These results suggest that a feasible strategy for scaling-up the production of AgMNPV might involve the use of airlift reactors for the scaling-up of cell suspension cultures and the final production of occlusion bodies, while the scaling-up of the viral inoculums being carried out under conditions as those existing in stirred reactors. [Copyright &y& Elsevier]

Abstract: In this work, the hydrodynamics and mass transfer in a gas–liquid dual turbine stirred tank reactor are investigated using multiphase computational fluid dynamics coupled with population balance method (CFD–PBM). A steady state method of multiple frame of reference (MFR) approach is used to model the impeller and tank regions. The population balance for bubbles is considered using both homogeneous and inhomogeneous polydispersed flow (MUSIG) equations to account for bubble size distribution due to breakup and coalescence of bubbles. The gas–liquid mass transfer is implemented simultaneously along with the hydrodynamic simulation and the mass transfer coefficient is obtained theoretically using the equation based on the various approaches like penetration theory, slip velocity, eddy cell model and rigid based model. The CFD model predictions of local hydrodynamic parameters such as gas holdup, Sauter mean bubble diameter and interfacial area as well as averaged quantities of hydrodynamic and mass transfer parameters for different mass transfer theoretical models are compared with the reported experimental data of . The predicted hydrodynamic and mass transfer parameters are in reasonable agreement with the experimental data. [Copyright &y& Elsevier]