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Liquid properties, such as, surface tension and viscosity are important parameters as they control gas-liquid mass transfer in bioprocesses. An oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) was considered to evaluate its potential for mass transfer performance in non-pure gas-liquid systems. The effect of surface tension and viscosity on the volumetric ( k L a) and liquid-side mass transfer coefficients (k L), interfacial area, (a), gas holdup (ε G) and bubbles' dynamics were investigated under different operational conditions (oscillation amplitude (x 0) and frequency (f) and superficial gas velocity (u g)). Two liquid phases, ethanol and sucrose aqueous solutions covering a range of surface tension and viscosity values were used. For the bubble size distribution (BSD) measurements an image analysis technique was used. A Design of Experiment (DoE) methodology was implemented in this work to establish the relation of x 0 , f , u g , surface tension and viscosity with k L a. According to the results, changes in the liquid properties and operational conditions showed marked effects on bubble's size and mass transfer. However, surface tension and viscosity had no significant influence on ε G , contrary to the reported for common contactors, where ε G increased in the presence of ethanol and decreased at moderate/high viscosities. Moreover, it was found that increasing the oscillatory movement notably improved k L , and k L a (2–6-fold), either in ethanol or sucrose solutions, compared to common reactors, even with moderate power consumption (∼ 105 W m−3). This improvement resulted from the bubbles' breakage, which originates bubbles with small and approximately the same size (homogeneous regime) enhancing a , instead, lower oscillations resulted in large bubbles (heterogeneous regime). The results demonstrate that the OFR-SPC can ensure outstanding mass transfer rates, with potential and feasibility for use in gas-liquid bioprocesses, where mass transfer and liquid properties are important. [Display omitted] • Mass transfer in the OFR-SPC was higher than in the conventional gas-liquid contactors, with moderate power consumption. • An increase in oscillatory conditions improves mass transfer. • For viscous medium, an oscillation increase originates a modal BSD, compared to bubble column. • Higher oscillations decrease k L in the presence of ethanol, in opposite to sucrose solutions. • The addition of ethanol or sucrose barely affected gas holdup in the OFR-SPC face to common gas-liquid contactors. [ABSTRACT FROM AUTHOR]

Antibubbles are ephemeral objects composed of a liquid core encapsulated by a thin gas shell immersed in a liquid bulk. The gas shell thickness evolves in time, driven by two contributions: gravitational drainage and gas–liquid mass transfer. The low density contrast between the antibubble and the bulk, as well as its weak deformability constitute advantages that are used to measure the mass transfer coefficient (MTC) in a so-called antibubble column, in a time-resolved fashion. Shells made with pure air give low data reproducibility. Consequently, perfluorohexane, a low-solubility gas, was mixed to air to enforce gas desorption from the bulk and obtain reliable data. MTC obtained with various surfactants and concentrations are found to deviate from the Frössling correlation built for fully rigid interfaces: higher MTC are consistent with partially rigid interfaces due to a partial coverage of surfactants along a so-called spherical cap, while lower MTC are consistent with an additional resistance to the transfer of mass due to the presence of surfactants forming a monolayer at high concentration. Finally, the advantages in terms of control and compactness of an antibubble column as compared to a bubble column for liquid–gas mass transfer are demonstrated. Specifically, an antibubble is shown to transfer dozens of times more mass than a bubble that would initially carry the same amount of gas. Antibubbles are therefore shown to provide a new, time-resolved, way to measure MTC, as well as promising route to enhance liquid–gas transfers in multiphase reactors. • Time-resolved mass transfer coefficient measurement using antibubble. • Results and discussion for different types and concentrations of surfactants. • An antibubble is shown to exchange 30x more mass than a bubble of equivalent radius. • Technical description and theoretical predictions for the mass transfers are provided. [ABSTRACT FROM AUTHOR]

Non‐fossil fuels are urgently needed for maritime and inland shipping applications to mitigate the sector's adverse impact on the global climate. This study investigates the performance of potassium borohydride (KBH4) as an alternative, carbon‐free energy carrier on the basis of detailed process simulations of the overall energy storage cycle in Aspen Plus®. After optimizing the individual on‐board and off‐board process steps, the feasibility of installing a KBH4‐based energy supply system on board of an inland‐waterway cargo vessel is evaluated and critical process steps are highlighted along with current research challenges. [ABSTRACT FROM AUTHOR]

In general, multiphase reactors with different configurations are used in various industries, a fluidized bed reactor has found extensive application in wastewater treatment and other biochemical processes. For the design and development of three-phase fluidized bed reactors, knowledge of the hydrodynamic parameters such as bed voidage is essential. In this paper, an attempt has been made using water, glycerol with different concentrations, and mono ethanolamine as Newtonian liquid and different concentrations of carboxy methyl cellulose as non-Newtonian liquids and seven different particles to study the effect of fundamental and operating variables on bed voidage in a three-phase fluidized bed. The dependency of the bed voidage on various parameters such as the gas and liquid flow rates, particle size and shape, and the physical and rheological properties of liquids are analyzed. The bed voidage increases with fluid flow rates and decreases with an increase in particle diameter and sphericity and it increases with an increase in the viscosity of Newtonian liquids and fluid consistency index of non-Newtonian liquids. On the basis of the experimental results, a generalized correlation has been developed to predict bed voidage in a fluidized bed using Newtonian and non-Newtonian liquids. The experimental results showed good agreement with those predicted according to the developed correlation, with a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

Horizontal stirred bed reactors are widely used in the commercial manufacturing of polypropylene. However, a comprehensive understanding of the particle dynamics in horizontal stirred bed reactors remains elusive, primarily due to the lack of detailed experimental data. In this work, we studied the influence of operating parameters on the particle flow dynamics in a laboratory-scale horizontal stirred bed reactor using single-photon emission radioactive particle tracking. The results show that the general solids flow behavior is strongly affected by both the agitator rotation speed and reactor fill level. Operation at low rotation speed and low fill level results in solids flow with poor radial and circumferential distribution due to internal bed circulation. On the contrary, at increased rotation speeds and fill levels, solids motion throughout the bed is continuous resulting in excellent solids distribution. The solids circulation was found to increase for both an increase in rotation speed and reactor fill level. The axial dispersion coefficient, on the other hand, shows a linear relation with the rotation speed, but no conclusive relation between the axial dispersion coefficient and the reactor fill level was found. • A horizontal stirred bed reactor is studied using radioactive particle tracking. • The flow pattern, solid circulation, and axial dispersion are analyzed. • Fill level and rotation speed have a significant influence on the particle dynamics. [ABSTRACT FROM AUTHOR]

In Part I of this review article, the significance of DME as fuel and the various types of catalysts used for different feedstocks were considered. However, the industrial processes using a variety of reactor configurations affect the overall capex and opex. The production of syngas, irrespective of the source, is the first step in DME synthesis, which is then followed by conversion into DME using a battery of reactors and separators. A critical analysis is presented and future scope outlined. [ABSTRACT FROM AUTHOR]

Heterogeneous non-catalytic gas-solid reactors are commonly used in the production of chemicals, metals and metal oxides, for example, rotary drum reactor for producing quick lime; blast furnace, a moving bed reactor for producing iron, etc. Industrial processes involve multicomponent mixtures of solids as most of the naturally occurring materials such as minerals are multicomponent in nature. Generally the raw materials are heterogeneous and their physical and chemical characteristics vary from one source to another. The solid particles are also usually moist, the moisture content varying from season to season. The physico-chemical phenomena that take place in these reactors include flow of gases through porous media, heat transfer between the gases, solids, equipment and the environment, evaporation and condensation of moisture, reactions between gases and solids and within a single phase, melting and solidification depending on the temperatures inside the reactor, etc. The flow of particles is also of great importance especially in rotary drum and moving bed reactors. General features of the mathematical models for non-catalytic reactors are described along with models for the phenomena mentioned above. Case studies from the iron and steel industry on model-based optimization of production of direct reduced iron in a rotary kiln and induration of wet iron ore pellets on a moving packed bed reactor are discussed here.

This chapter describes the mass transfer characteristics in gas/water/organic solvent systems. The ability of an organic solvent (called NAP, i.e., Non Aqueous Phase) to influence the gas transfer of solutes (Volatile Organic Compounds, VOCs, or oxygen) from the gas phase to the aqueous phase and to affect the gas/liquid interface and the volumetric mass transfer coefficient K L a is considered. The objective of the chapter is to summarize the current knowledge in the comprehension of mass transfer mechanisms. The influent parameters and the possible mass transfer mechanisms are described. Theoretical mass transfer enhancements that could be reached are quantified and compared with experimental data. Moreover, new insights based on the "Equivalent Absorption Capacity" concept are given. Coupled with the ɛ-NTU method, this concept could be used for the determination of the overall mass transfer coefficient K L a in multiphasic gas/water/NAP systems. [ABSTRACT FROM AUTHOR]

This article discusses the use of a multi‐cyclone separator, which is a simplified form of a degassing hydrocyclone, in the separation of sweeping nitrogen bubbles and dissolved oxygen from water. The motion of the nitrogen bubbles and mass transfer of dissolved oxygen is discussed. It was observed that the Sauter mean diameter and gas volume in the swirling flow region as well as the total gas holdup increased as the volumetric ratio of gas to liquid flow increased. Almost all bubbles were found to exit through the gas outlet, indicating optimum performance of the bubble‐separation process. The multi‐cyclone separator was found to achieve good performance for the mass transfer of oxygen from water to nitrogen. This work is important in predicting the destination of bubbles and dissolved gas in swirling flow. © 2018 American Institute of Chemical Engineers AIChE J, 65: 215–223, 2019 [ABSTRACT FROM AUTHOR]

Gas fermentation has emerged as a technologically and economically attractive option for producing renewable fuels and chemicals from carbon monoxide (CO) rich waste streams. LanzaTech has developed a proprietary strain of the gas fermentating acetogen Clostridium autoethanogenum as a microbial platform for synthesizing ethanol, 2,3‐butanediol, and other chemicals. Bubble column reactor technology is being developed for the large‐scale production, motivating the investigation of multiphase reactor hydrodynamics. In this study, we combined hydrodynamics with a genome‐scale reconstruction of C. autoethanogenum metabolism and multiphase convection–dispersion equations to compare the performance of bubble column reactors with and without liquid recycle. For both reactor configurations, hydrodynamics was predicted to diminish bubble column performance with respect to CO conversion, biomass production, and ethanol production when compared with bubble column models in which the gas phase was modeled as ideal plug flow plus axial dispersion. Liquid recycle was predicted to be advantageous by increasing CO conversion, biomass production, and ethanol and 2,3‐butanediol production compared with the non‐recycle reactor configuration. Parametric studies performed for the liquid recycle configuration with two‐phase hydrodynamics showed that increased CO feed flow rates (more gas supply), smaller CO gas bubbles (more gas–liquid mass transfer), and shorter column heights (more gas per volume of liquid per time) favored ethanol production over acetate production. Our computational results demonstrate the power of combining cellular metabolic models and two‐phase hydrodynamics for simulating and optimizing gas fermentation reactors. Gas fermentation has emerged as a technologically and economically attractive option for producing renewable fuels and chemicals from carbon monoxide (CO) rich waste streams. LanzaTech has developed a proprietary strain of the gas fermentating acetogen Clostridium autoethanogenum as a microbial platform for synthesizing ethanol, 2,3‐butanediol, and other chemicals. [ABSTRACT FROM AUTHOR]

Continuous flow chemistry is a rapidly developing branch in organic and drugs synthesis, whereas it is common practice in heterogeneous catalysis for base chemicals production. Heterogeneously catalysed synthetic protocols are being developed and can take advantage of the reaction and reactor engineering experience at the macro-scale, provided that suitable models are applied to the micro- and meso-reactors in use. The main process parameters that define possible mass, heat and momentum transport limitations in heterogeneous catalytic reactors are reviewed. Specific models applying such concepts to microreactors are proposed. Finally, examples are reported of heterogeneously catalysed reactions carried out in microreactors for different applications. [ABSTRACT FROM AUTHOR]

In this study, a cylindrical stainless-steel column with dimensions of 250 cm in height and 16.2 cm in diameter was employed to investigate how fluid properties influence phase distribution within slurry bubble columns. The research focused on various superficial gas velocities and operating pressures. Data collection was carried out using single-source Computed Tomography and overall gas holdup. The gas holdup was found to be directly proportional to both the superficial gas velocity and the operating pressure. Results revealed that both liquid properties and operating pressure have a considerable impact on flow regime transition. Interestingly, when comparing water to Therminol LT, higher gas holdup measurements were observed when water was used, displaying a relative difference of approximately 29% in the bubbly flow regime under ambient conditions. The effect of liquid properties on holdup profiles became more pronounced at high pressures. For example, under higher pressure conditions, Therminol LT exhibited a higher gas holdup rate due to its lower viscosity and surface tension, leading to an increased rate of bubble breakup. While the influence of physical properties on the solids' holdup profile was relatively less significant, it remained noteworthy when compared to its impact on the gas holdup profile. • Hydrodynamics of a slurry bubble column reactor operating at mimicked Fischer-Tropsch (FT) reaction conditions. • Non-invasive gamma ray computed tomography measurement technique. • Effect of liquid phases on phases distribution was studied at different superficial gas velocities, operating pressures. • Findings can be utilized as a benchmarking tool for CFD and phenomenological modeling. [ABSTRACT FROM AUTHOR]

In the present work, it is studied for the first time the use of an oscillatory flow reactor provided with smooth period constrictions (OFR-SPC) in gas-liquid mass transfer process when a solid phase is present. The superficial gas velocities ( u G ), solids loading (calcium alginate beads: 0–15% (v/v)) and the oscillatory conditions (frequency and amplitude) effects on volumetric liquid side mass transfer coefficient ( k L a ) are experimentally evaluated. The liquid-side mass transfer coefficient, k L , and the specific interfacial area, a , are studied individually. The results show that k L a increases with both superficial gas velocity and oscillatory conditions, in two and three-phase systems, the oscillatory conditions being the ones with the highest impact on the gas-liquid mass transfer process. The presence of solids seems to have a negligible influence on k L a in all experimental conditions for the range of solids loading studied. This behavior was not observed in other reactors where a negative solids (calcium alginate beads) influence on the mass transfer process was verified. Globally, the results show the importance of hydrodynamic phenomena on the mass transfer process in two and three-phase systems, indicating OFR-SPC as a good alternative to the conventional reactors, especially when a third phase is present. [ABSTRACT FROM AUTHOR]

Kinetic studies were conducted for the aerobic oxidation of 2-mercaptoethanol (2-ME) and 4-fluorobenzenethiol (4-FBT) catalyzed by cobalt(II) phthalocyanines: H16PcCo, F16PcCo, and F64PcCo, each exhibiting a metal center subject to increasing Lewis acidity and steric hindrance. The experiments were performed in a reaction-limited, isothermal, bench-scale, batch reactor, with thiol concentrations measured using GC/FID. Conversions of 2-ME to 2-hydroxyethyl disulfide and 4-FBT to 4-fluorophenyl disulfide in excess of 90% were achieved. Kinetic analyses suggest that the substrate binding and electron transfer are directly related to the Lewis acidity and steric bulkiness of catalyst molecules. Substrate binding was found to be the slow step for thiol oxidations catalyzed by H16PcCo. The rate-determining step for thiol oxidations, catalyzed by F16PcCo and F64PcCo, is the expulsion of the thiyl radical (RS•) from the catalyst molecule. [ABSTRACT FROM PUBLISHER]

While treating the industrially produced wastes through various processes such as physical, chemical, biological and radiation processes have been implemented on various scales and is the focus of various studies and development, the trend of minimizing and/or eliminating the pollutions at the source via developing and selecting proper catalytic multiphase reactors is worth to be given proper attention and consideration which is the focus of this manuscript beside outlining the processes used for treating the wastes. In order to achieve such goal in minimizing the wastes, these multiphase reactors must be well understood, studied, scaled up and designed. This can be only achieved by developing and implementing advanced measurement and computing techniques which have been developed in our research laboratory and are briefly outlined here with selected results. [ABSTRACT FROM AUTHOR]

[Display omitted] • k L a in OFR-SPC was higher (up to 5-fold) than in conventional gas-liquid contactors, with moderate power consumption. • An increase in oscillatory conditions improved gas-liquid mass transfer and decreased bubble size. • k L and a were not affected below the electrolyte transition concentration in the OFR-SPC. • Gas holdup and bubble size were not affected below the electrolyte transition concentration in the OFR-SPC. In bioprocesses, the microorganisms' growth is ruled by physical, chemical, and biological conditions being the electrolyte concentration one of the most important parameters to control. In this study, the effect of three electrolytes (HCl, NaOH, NaCl) in aqueous solutions on the volumetric (k L a) and liquid-side (k L) mass transfer coefficients and bubbles' dynamics in an oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) under different operational conditions (oscillation amplitude, x 0 and frequency, f and superficial gas velocity, u g) were studied. Electrolyte concentrations below and above the transition concentration (c t) of bubbles coalescence were evaluated. The results showed insignificant inhibition of bubble coalescence, regardless of electrolyte kind and concentration. Also, no significant variations were found in k L a , k L , ε G , and d 32 values compared with water. The three electrolytes behave similarly. Moreover, contrary to the widespread consensus in which the presence of electrolytes below the c t in aqueous systems reduces k L , in the present study in the OFR-SPC the k L results were identical to pure systems and higher than common gas-liquid contactors. According to the results, k L a was improved by increasing the oscillatory conditions and u g. The results indicate that oscillations and u g govern the hydrodynamics and mass transfer changes in aqueous electrolyte solutions. These results suggest that efficient mass transfer rates (up to 5-fold higher face to bubble columns and airlift) can be achieved with moderate power consumption, 100 W m−3, and, hence, enabling the OFR-SPC with potential for bioprocesses, replacing bubble columns and airlift bioreactors. [ABSTRACT FROM AUTHOR]

The study of local hydrodynamic properties of three-phase bioreactors in biotechnology processes is of great importance, mainly because of the complex interaction between bioreactor and microorganisms. However, classical techniques used for measuring local hydrodynamic properties such as single needle probes are mainly limited to two-phase flows. In this work it was developed and validated a new system, based on the customization of an optical probe initially designed in LEGI. The necessity of a new system was due to the agglomeration of the solid-phase (spent grains which are used as the micro-organisms carrier for the targeted application) around the optical tip, which influences the measurements. This new system allows for the measurement of the main local gas-phase properties in a complex gas–liquid–solid mixture. The new system was first validated for air–water system in an internal loop gas-lift reactor and then applied to a spent grains–air–water mixture at low solid load in an internal gas lift reactor. In addition, experiments using complementary techniques (as high speed camera and PIV) were performed that allowed for the validation of the new system and the explanation of possible physical mechanisms that are underlying on this multiphase system. The system developed has the potential for improvement and use in several biotechnology applications. [ABSTRACT FROM AUTHOR]

In the present work the superficial gas velocities ( u G ) and the oscillatory conditions (frequency and amplitude) effects on the gas–liquid mass transfer process in a novel oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) are experimentally evaluated. The liquid-side mass transfer coefficient, k L , and the specific interfacial area, a , are studied individually. The specific interfacial area is obtained using the new automatic image analysis technique developed by Ferreira et al. (2012). The experimental results of volumetric liquid side mass transfer coefficient ( k L a ), Sauter mean diameter ( d 32 ) and gas holdup ( ε G ), and the calculated values of a and k L , are correlated with the superficial gas velocity and the power density ( P / V ), in order to be used in scale-up processes and in comparisons with the literature. The results show that k L a increases with both superficial gas velocity and oscillatory conditions, the last ones having the highest impact on the mass transfer process. The increase in the oscillation motion (frequency and amplitude) results in bubble size reduction (from ∼7 mm, without oscillation, to ∼1 mm, with oscillation), in bubble average residence time increase and, consequently, in a increase. A k L increase with d 32 decrease is observed, showing the importance of hydrodynamic phenomena on k L , specially, when very low bubbles sizes are presented in oscillatory flow reactors. [ABSTRACT FROM AUTHOR]

The quest for transition to clean energy sources and intensified chemical processes has led to growing interest in microwave-heated reactors. Microwave generated from renewable electricity is a clean energy source and can intensify chemical processes with its unique heating characteristics, especially selective heating. Selective microwave heating creates a temperature differential between phases in a multiphase reactor, allowing a new paradigm in process intensification. Numerous studies have demonstrated the potential of microwaves to achieve process intensification. Nevertheless, detailed explanations for the observations are lacking primarily due to the unavailability of accurate temperature measurements. This perspective article discusses the significant challenges hindering the development and deployment of microwave multiphase reactors and the opportunities for further research. Structured reactors, such as monoliths, are emphasized as a canonical setup for experiments and modeling. [Display omitted] • Status of microwave-assisted process intensification is presented. • Recent advancements in microwave multiphase reactors are presented. • Major challenges hindering the development of microwave reactors are discussed. • Crucial research needs for rapid deployment of microwave reactors are analyzed. • Role of microwave heated monoliths as a canonical setup is explored. [ABSTRACT FROM AUTHOR]

Heterogeneous non-catalytic gas-solid reactors are commonly used in the production of chemicals, metals and metal oxides, for example, rotary drum reactor for producing quick lime; blast furnace, a moving bed reactor for producing iron, etc. Industrial processes involve multicomponent mixtures of solids as most of the naturally occurring materials such as minerals are multicomponent in nature. Generally the raw materials are heterogeneous and their physical and chemical characteristics vary from one source to another. The solid particles are also usually moist, the moisture content varying from season to season. The physico-chemical phenomena that take place in these reactors include flow of gases through porous media, heat transfer between the gases, solids, equipment and the environment, evaporation and condensation of moisture, reactions between gases and solids and within a single phase, melting and solidification depending on the temperatures inside the reactor, etc. The flow of particles is also of great importance especially in rotary drum and moving bed reactors. General features of the mathematical models for non-catalytic reactors are described along with models for the phenomena mentioned above. Case studies from the iron and steel industry on model-based optimization of production of direct reduced iron in a rotary kiln and induration of wet iron ore pellets on a moving packed bed reactor are discussed here. [ABSTRACT FROM AUTHOR]

Abstract: The hydrodynamics of binary mixture of polydisperse particles in a turbulent fluidized bed was investigated by experiment and numerical simulation in this paper. A computational fluid dynamics model (CFD) coupled with population balance model (PBM) was developed, which combined the advantage of CFD model and PBM. The CFD model is applied to simulate the flow field and PBM is used to represent the particle size distribution (PSD). The effects of particle attrition and aggregation on particle behaviors were also considered. The model was validated by comparing simulation results with experimental data. Furthermore, five cases with different types of polydispersity, involving a continuous PSD of single component, a binary mixture of continuous PSDs without much difference between predominant sizes, a binary mixture of continuous PSDs with significant difference between predominant sizes, a continuous PSD of single component undergoing attrition and a continuous PSD of single component undergoing aggregation, were tested. The mixing behavior of polydisperse binary mixture in the turbulent fluidized bed was also obtained numerically. The results showed that the model was effective in describing the mixing behavior of binary mixture of polydisperse particles. In the binary mixture of particles with PSDs of minor difference system, the large particles first sink down into the small particle layer along the wall, and then along the central axis. However, for the binary mixture of which PSDs are with significant difference, the large particles go into the small particle layer along the central axis first. [Copyright &y& Elsevier]

Highlights: [•] Solid circulation is constructed in the ICFB with the formations of three local rolls. [•] Solid cycle time shows a log-normal probability distribution pattern. [•] Enlarging the fluidizing velocity in the RC or HEC reduces the solid cycle time. [•] Large residence time of solid phase appears in the two corners of the bed. [•] Increasing the baffle incline angle or gap height reduces solid residence time in HEC. [ABSTRACT FROM AUTHOR]

Abstract: This study provides new insights into fluid catalytic cracking (FCC) riser reactor from multi-scale viewpoint. The problem of simultaneous intraparticle molecule transfer and reaction, particle kinetics, and gas–solid flow in polydisperse FCC riser reactors was considered. A multi-scale CFD method was developed for constructing a multi-scale model to solve this problem. The multi-scale model consisted of a two-phase CFD model incorporating a single-particle model and a population balance model. The main flow field distribution parameters within the catalyst particles and reactors as well as the solid particle size distribution (PSD) could be calculated simultaneously based on intraparticle transfer and reaction using these models. The single-particle and multi-scale models were first verified and evaluated. Based on the validated models, intraparticle transfer limitations and/or flow fields in two size-scale FCC riser reactors were predicted. The simulations demonstrated three different reaction zones in FCC risers, and more elaborate mass, heat, and momentum transfer behaviors could be obtained. The simulations also demonstrated that particle kinetics (i.e., breakage and aggregation) have obvious influences on the FCC flow field in FCC risers; these effects have not been observed in conventional CFD models. [Copyright &y& Elsevier]

Abstract: Two-fluid model combined with Energy-Minimization Multi-Scale (EMMS) drag model has been accepted as an effective method to simulate the hydrodynamics of heterogeneous gas–solid flow in circulating fluidized beds. In the EMMS drag model, a drag correlation obtained from homogeneous fluidization and/or packed bed, denoted as traditional drag correlation, is necessary to describe the homogeneous gas–solid interactions within three (dilute-phase, dense-phase and inter-phase) sub-systems. In this article we study the effects of different traditional drag correlations on the effective inter-phase drag force of clustered gas–solid flow within the framework of EMMS drag model, and their consequent effects on CFD results. It was shown that due to the proper consideration of meso-scale structural effect, CFD results using the EMMS drag model are in a reasonable agreement with experimental data (including radial and axial solid concentration profiles and root mean square of local solid concentration), and are slightly affected by different inputting traditional drag correlations. Present conclusion is quite different from the one obtained in previous studies, where coarse grid simulation with traditional drag correlation failed to predict the hydrodynamics of CFB risers and was sensitive to the traditional drag correlation used. Therefore, the EMMS drag model appears as an advantage over traditional drag correlations, since it is not only insensitive to the empirical input, but also gives much better agreement with experiments. [Copyright &y& Elsevier]

Highlights: [•] Styrene absorption into water/silicone oil mixtures was investigated. [•] Mixtures were considered pseudo-homogeneous phases. [•] Oil addition hindered the mass transfer rate compared to the air/water system. [•] An apparent decrease in KLa values due to silicone oil addition was observed. [•] It is questionable to study the change in KLa in terms of silicone oil addition. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxygen mass transfer performance of unbaffled stirred tanks is presented. [•] Unbaffled vessels appear able to satisfy the oxygen demand of animal cell cultures. [•] Influence of impeller geometry on oxygen mass transfer performance is investigated. [ABSTRACT FROM AUTHOR]

Highlights: [•] The DEM–CFD model is developed to describe flow and reaction in a MTO FBR. [•] Particles are modeled by the DEM and gas by the Navier–Stokes equations. [•] The combined model incorporates a lumped kinetics for the MTO process. [•] The combined model also incorporates some key heat transfer equations. [•] The simulation results capture the major features of MTO process well in FBR. [ABSTRACT FROM AUTHOR]

A novel phenomenological discrete bubble model was developed and tested for prediction of the hydrodynamic behavior of the dense phase of a 3D gas-solid cylindrical fluidized bed. The mirror image technique was applied to take into account the effects of the bed wall. The simulation results were validated against experimental data reported in the literature that were obtained by positron emission particle tracking. The time-averaged velocity profiles of particles predicted by the developed model were found to agree well with experimental data. The initial bubble diameter had no significant influence on the time-averaged circulating pattern of solids in the bed. The model predictions clearly indicate that the developed model can fairly predict the hydrodynamic behavior of the dense phase of 3D gas-solid cylindrical fluidized beds. [ABSTRACT FROM AUTHOR]

Highlights: [•] Flow regimes for a gas–liquid flow in a packed bed mini reactor were identified. [•] Gas–liquid–solid mass transfer coefficients of this reactor were investigated. [•] Mass transfer increased with raised superficial gas or liquid velocity. [•] A correlation for the estimation of mass transfer coefficients was developed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a coupled model based on a direct concurrent multi-scale approach incorporating a single particle model and a two-phase CFD model was developed to predict the effects of intraparticle transfer on the flow field and main composition distributions of a catalytic reaction to convert methanol to olefins (MTO) in a fluidized bed reactor (FBR). A single particle model was first constructed to describe the individual intraparticle molecular diffusion and reaction kinetics, while a CFD model characterized the gas–solid flow field in the FBR. Because the grid cells generated in the CFD model were too small compared with the size of the FBR, no distributions were considered in a single grid. In this case, all catalyst particles inside each small computational cell for the CFD model experienced the same external conditions, thus ensuring the effective coupling of the two models. This was validated by comparing the above assumption with simulation results and with experiment results. On the basis of the coupled model, the intraparticle transfer limitation and the flow field in the FBR were predicted numerically. The simulated results indicated that the intraparticle transfer limitation did exist and had significant effects on the reactor flow field. This model is expected to be useful in predicting the intraparticle transfer limitation in FBRs. [Copyright &y& Elsevier]

In the present work, two different models (micro-scale and meso-scale) were developed to investigate the heat transfer between the gas and liquid phases in the trickle flow regime of a packed bed reactor. In the micro-scale model, a simplified description of bed geometry, known as the double-slit model, was implemented to study the effects of different operating parameters, in terms of gas and liquid Reynolds, Prandtl and Eötvös numbers, on the interfacial Nusselt number. In the meso-scale model, the Volume-of-Fluid (VOF) approach was used to simulate trilobe, cylindrical and spherical catalyst shapes and accurately predict the effects of interface morphology and bed geometry on interfacial heat transfer. To validate the implemented methods, a simple packed bed reactor with spherical catalysts was developed to experimentally investigate the interfacial heat transfer of co-current, downward gas–liquid film flows. The results obtained from CFD simulations and experimental data were in agreement and accurately predicted bed reactor temperature profiles with a mean relative error of 2.15%. In both the micro- and meso-scale models, an increase in the Reynolds and Prandtl numbers increased the interfacial Nusselt number; whereas, an increase in dimensionless groups of the liquid phase or the Eötvös number caused the opposite effect. Finally, a new correlation was proposed that evaluated the gas–liquid Nusselt number in the trickle flow regime with a standard deviation of 7.19% compared to results acquired using the micro-scale model. [ABSTRACT FROM AUTHOR]

Abstract: Turbulence intensity, or hydromechanical stress, is a controlling parameter in many industrially relevant processes. Especially fermentation processes are often characterized by intense aeration and agitation, operating conditions for which the measurement of turbulence intensity is extremely difficult. Since the maximum stable drop diameter in a break-up controlled dispersion is directly correlated with turbulence intensity, the measurement of drop sizes can enable an indirect access to the intensity of turbulence under such operating conditions. This work presents the constraints and the development of a method for the measurement of maximum stable drop size in aerated liquid–liquid dispersions in stirred tanks for the purpose of characterizing turbulence intensity. Continuous and dispersed phase properties were selected to achieve a break-up controlled dispersion with negligible coalescence. This was accomplished mainly by applying a dilute dispersion, a low ionic strength and by incorporating a dispersed phase, paraffin oil, with a negative spreading coefficient. The negative spreading coefficient prevents coalescence due to drop–bubble interactions for aerated operating conditions. It was demonstrated that the off-line measured drop size distributions are representative for the conditions in the bioreactor and are not altered by sample handling. The sampling and measurement procedure was found to be highly reproducible with a standard deviation for the maximum stable drop size for independent experiments of approximately 10%. Relevant constraints for the application of the method in large-scale experiments were discussed and accounted for during method development to allow a later application in production scale equipment. [Copyright &y& Elsevier]

The effect on gas-liquid mass transfer of dispersing an oil phase in water in an aerated stirred tank is not predictable, because the mechanisms involved are not well understood. To try to elucidate these mechanisms, a set of experiments was carried out that included: (i) measurement of the effect of oil addition on gas dispersion properties, (ii) quantification of mass transfer of two solutes (heptane and oxygen) with very different solubilities in the liquid phases, and (iii) variation of the spreading characteristics of the oil phase, which consisted of mixtures of dodecane and heptane in varying concentrations. It was found that in the case of heptane mass transfer, when the oil spreading coefficient S changes from negative to positive, the outlet gas becomes practically saturated, corresponding to a several-fold increase in mass transfer coefficient. In the case of oxygen mass transfer, the effect of S is not as dramatic, but it is also quite significant. For a spreading oil phase (S > 0), the mass transfer coefficient decreases upon trace oil addition, going through a minimum as oil holdup increases, and then increasing steadily. In the case of a non-spreading oil phase, mass transfer coefficient initially increases with oil holdup increase, going through a maximum and then decreasing. Comparison between mass transfer coefficients for the two solutes indicates that kLa for heptane is larger than that of oxygen by a margin not explainable through the difference in diffusivities, which is evidence for a difference in transfer paths/mechanisms. A physical interpretation compatible with these results is offered. [ABSTRACT FROM AUTHOR]

Abstract: The gas distribution between the dilute (bubble) and dense (emulsion) phases of a fluidized bed is studied locally and globally in the bubbling regime for mixtures composed of sand and different weight fractions of biomass (2–16%). The dilute phase has been characterized by analyzing the pressure and voidage signals. A suite of pressure transducers was used to measure pressure fluctuations at different locations along the bed. A reflective optical probe measured local voidage signals and was placed at different radii (0

Abstract: Design and analysis of photoreactors is significantly more challenging than conventional reactors due to participation of radiation in chemical reactions. This problem is further compounded in case of photocatalytic reactors because of presence of photocatalytic particles, which not only produce complex light scattering effects but, in case of slurry systems, also act as an additional phase, the hydrodynamics of which is essential to characterize for evaluating the phase distribution of photocatalyst particles without which it is not possible to calculate the light intensity distribution. This then necessitates the use of a computational fluid dynamics (CFD)-based simulation approach which can simultaneously take into account the hydrodynamics of multiple phases, light intensity distribution and reaction kinetics. This paper presents a sequential review of all steps for CFD simulations of photocatalytic reactors. The hydrodynamic modeling has been considered first with an emphasis on the Eulerian–Eulerian model because of its ability to handle large-scale photocatalytic reactor systems with only relatively moderate computational resources. This has been followed by a review of lamp emission models, which in CFD models are used as boundary conditions for solving the radiation transport equation (RTE). Before discussing the kinetics of photocatalytic reactors, a review of numerical models for solving the RTE has also been presented for both slurry and immobilized reactor systems. Finally, the paper discusses important factors for setting up the boundary conditions for CFD modeling of photocatalytic reactors. [Copyright &y& Elsevier]

Abstract: The problem of modeling a class of two-phase moving-bed tubular gasification reactors by means of a lumped (finite-dimensional) representation is addressed in this paper. A model is designed, as simple as possible, in the light of a specific – experimental, equipment, operation, monitoring or control – design task and the uncertainty of the underlying kinetics and transport parameters. First, the enforcement of quasi-steady state (QSS) gas-phase assumptions and stoichiometric considerations followed by spatial finite-difference approximation plus interpolation leads to a representation of the tubular reactor as a train of N continuous stirred tank reactors (CSTRs). Then, the number of tanks and their volumes are chosen according to the modeling objective. The proposed approach is illustrated with a case example, studied before with experiments and PDE-based simulations, finding that the dynamics of the tubular reactor can be modeled with three CSTRs (9-ODE). [Copyright &y& Elsevier]

Abstract: Numerical simulations of turbulent immiscible liquid–liquid mixing processes in cylindrical stirred tanks driven by a Rushton turbine are carried out based on an Eulerian–Eulerian approach using in-house codes. An isotropic standard k−ε turbulence model and an anisotropic two-phase explicit algebraic stress model (EASM) are used for flow field simulations. Quantitative comparisons of the homogenization curve and mixing time predicted by the EASM are conducted with reported experimental data and other predictions by the standard k–ε model and large eddy simulation (LES). The comparisons show that the EASM predictions are in satisfactory agreement with experimental data and better than the k–ε model ones. The variation of the continuous phase mixing time with impeller speed can be an effective method to determine the critical impeller speed for complete dispersion of oil phase. The key features of the complex liquid–liquid mixing processes in stirred tanks have been successfully predicted by the EASM, which can be an alternative tool for practical engineering applications with economical computational cost and good accuracy. [Copyright &y& Elsevier]

Abstract: Gas–liquid flows with solid catalyst particles are encountered in many applications in the chemical, petrochemical, pharmaceutical industries, etc. Most commonly, two reactor types are applied for large scale in the industry. They are slurry bubble column and trickle bed reactors. Both of these types of reactors have some disadvantages limiting their efficiencies. To overcome these disadvantages, a novel reactor type, micro-structured bubble column (MSBC), is proposed. In the MSBC, the micro-structuring of catalytic material is realized by introducing a static mesh of thin wires coated with catalyst inside the column. Wires also serve the purpose of cutting the bubbles, which in turn results in high interfacial area and enhanced interface dynamics. The static catalytic mesh also ensures lower cost by avoiding filtration of catalyst particles. Numerical formulation of the described reactor is based on the 3-D discrete bubble model (DBM) presented in the previous works of Darmana et al. (2005, 2007). The extended version of DBM presented here introduces wires in the existing model and studies their effect on liquid and bubble dynamics. Bubbles and wires are represented by spherical and cylindrical markers, respectively; and the liquid flow-field is solved in the Eulerian gird cells. An improved drag correlation for bubbles in dense (up to 50%) swarm flow is also incorporated in the model. The model implementation and results are verified for a wide spectrum of parameters from the data available from the previous studies, analytical results and experimental findings. Our results show that the model is able to predict the hydrodynamic behavior and bubble dynamics, including the cutting of bubbles through wire mesh, very well. [Copyright &y& Elsevier]

This work investigates structured catalytic packings in a bubble-point reactor in which the reaction and flash occur simultaneously. A three-dimensional (3D) computational fluid dynamics (CFD) model was used to determine the optimum operating conditions and to examine the reactor performance when traditional catalyst pellets were replaced with BeiHua (BH) structured catalytic packings for benzene alkylation with propylene. It was found that the optimum operating conditions were a reaction temperature of 160°C and a molar ratio of benzene to propylene in the feed of 4.0. In this work, we also explored the relationship between the geometric configuration and the reactor performance. The momentum transfer (pressure drop), heat transfer (Nu number), mass transfer (Sh number), propylene conversion, cumene selectivity, and effectiveness factor were determined for different geometric configurations, which included changes in the corrugation angle, ratio of the packing height to the diameter, and ratio of the areas of the reaction to open-channel regions. Two new types of transition or wave-like structures (30–45–30° and 45–30–45°), which resulted in a higher propylene conversion, cumene selectivity, and effectiveness factor, were adopted. Furthermore, the applicability of this new technology for benzene alkylation with propylene was verified in a pilot plant. [ABSTRACT FROM AUTHOR]

Abstract: Fluorine doped SrTiO3 photocatalysts were prepared by spray pyrolysis with varying fluorine content, and were employed for the first time for hydrogen evolution from aqueous methanol solution under visible light irradiation. The doped fluorine ions were substituted for 6-coordinated oxygen ions in the lattice of SrTiO3, which led to the generation of extra electrons and oxygen deficiencies. The doping of fluorine resulted in the partial transformation of the band gap structure of SrTiO3 to Sr(Ti4+ 1−x Ti3+ x )O3−x F x , by reducing Ti4+ to Ti3+ to compensate for the charge balance in the host lattice. The doping of fluorine contributed to the photocatalytic activity for hydrogen evolution by forming an acceptor level by Ti3+ from the conduction band to the valence band, generating the free electrons in the lattice structure, discarding the hydroxyl group on the surface and increasing the BET surface area and pore volume of the photocatalyst. The hydrogen evolution rate exhibited a maximum value of 464.1μmolg−1 h−1 (QE=0.74%) with induction period of 1h, when the amount of fluorine content doped into SrTiO3 was 4.0mol%. [Copyright &y& Elsevier]

Abstract: This work deals with the transfer and reaction performances for the alkylation of benzene with propylene to produce cumene over monolith catalysts by means of the combination of experiments and computational fluid dynamics (CFDs). A three-dimensional (3D) mathematical model was established to identify the geometric configuration–performance relation so as to provide a comprehensive comparison of momentum transfer (pressure drop), heat transfer (Nu number), mass transfer (Sh number), and reaction performances (i.e. propylene conversion, cumene selectivity, and effectiveness factor) among monolith catalysts with five kinds of channel shapes (i.e. circle, hexagon, square, rectangle, and regular triangle). The objective of this work is to address the cogently interesting issues as to (i) whether or not monolith catalysts can improve the transfer and reaction performances for the alkylation of benzene with propylene in comparison with the traditional pellet catalyst or even structured catalytic packing; (ii) which kind of channel shape is optimum from the viewpoint of chemical reaction engineering; and (iii) how much energy can be reduced in the actual process consisting of a gas–liquid–solid bubble-point reactor and two distillation columns. It was found that monolith catalyst exhibits the lower pressure drop, higher cumene selectivity and higher effectiveness factor; and regular triangle or rectangle channel is optimum when considering pressure drop and cumene selectivity together. Furthermore, the advantages of monolith catalyst can lead to the lowest energy consumption for the whole process. [Copyright &y& Elsevier]

Abstract: We performed Direct Numerical Simulation (DNS) of an exothermic gas-phase reaction under laminar flow condition in a 2-D packed bed reactor with random distribution of cylindrical particles of 2.9mm diameter. The reaction used in this work is of Arrhenius type between Ethylene and Oxygen with Ethylene Oxide as a product. The gas flows into the reactor as a mixture of Ethylene and Oxygen. The simulations show that there is a region in the reactor with high reaction rate where basically all heat is produced. There is a large temperature gradient in this region in the radial direction and in the other parts of the reactor there is no temperature gradient in the radial direction. There is not a big convection term in the radial direction in the modeled packed bed. This rather small convection in the radial direction is the result of the arrangement of the particles. CFD simulations provide useful data on the flow field and radial convective term inside the packed beds which can be used for the improvement and further optimization on the design and operation of the packed bed reactors. [Copyright &y& Elsevier]

Abstract: The main objective of this study was to investigate the catalytic activity of three low cost materials (sepiolite, red volcanic rock and iron shavings) during the Fenton-like process on the treatment of simulated and actual olive mill wastewaters. Among the catalysts screened, iron shavings (ZVI) was the most promising, as it was the catalytic material that attained the best performance. Besides it as the advantage of being a waste of iron processing industry, not needing any modification before use. Since the Fenton's reaction efficiency is dependent on ZVI and H2O2 concentrations and as well as initial pH, the effect of these parameters was analyzed in batch tests for a synthetic phenolic effluent treatment. From the results it was concluded that the most interesting removals (94% of TPh, 54% of COD and 60% of TOC) were reached using [ZVI]=40g/L, [H2O2]=35mM and pH=3. This effectiveness was confirmed when Fenton's peroxidation under the same conditions was applied to an actual olive mill wastewater (OMW). The impact of this methodology over the effluents biodegradability and toxicity was still grasped. Furthermore, the stability of ZVI under continuous conditions was also tested when applied to both the synthetic phenolic effluent and real OMW treatments in a fixed bed reactor using the H2O2 load and pH optimized in batch reaction; high activity was still observed after 168h of operation of the column when synthetic phenolic effluent was treated, since TPh, TOC and COD removals remained about 73%, 39% and 44%, respectively. These results show that ZVI can be used as low cost catalytic material in Fenton reaction for the treatment of OWM in batch or continuous reaction with high catalytic stability. [Copyright &y& Elsevier]

Abstract: A dynamic simulation model for the novel toluene gas removal chemical-absorption process based on the photo-Fenton reaction has been developed. It can predict the unsteady- and steady-state performance of a bubble column reactor for photo-Fenton degradation of toluene in a waste gas. In modeling, reaction kinetics in the liquid phase and gas–liquid mass transfer were combined with the tanks-in-series model for nonideal mixing in the gas and liquid phases. The rate equations for Fenton reagents (Fe ions and H2O2), OH radical and the intermediates were included besides those for toluene in the gas and liquid phases. The iron redox cycle generating hydroxyl radical is a key process in the photo-Fenton process. In the simulation model, therefore, the iron redox cycling was taken into account. Experiments for toluene gas photo-Fenton degradation in a semi-batch bubble column were conducted to elucidate the reaction kinetics and to verify the capability of the proposed dynamic simulation model. The proposed simulation model could satisfactorily represent the rather complicated dynamic changes of toluene concentrations in the gas and liquid phases, hydrogen peroxide, iron ions and intermediates during the course of the photo-Fenton process controlled by the iron redox cycle, which was established firstly by the Fenton reaction with the presence of H2O2 and subsequently by the UV light and dissolved oxygen after the complete consumption of H2O2. [Copyright &y& Elsevier]