Search

This paper reviews the design features and performance characteristics of semifluidized bed bioreactors. Both biofilm reactors and immobilized enzyme bioreactors have been analysed. Also, both two phase (liquid – solid) and three phase (gas – liquid – solid) operations are considered. Apart from the hydrodynamic parameters (semifluidization velocity, bed expansion ratio, height of packed section formed, fractional fluid holdups in both fluidized and packed sections), all other operating/system parameters affecting reactor performance such as axial dispersion, intrinsic kinetics of bioconversion (mostly nonlinear), the effectiveness factor and Thiele – type modulus have also been surveyed. The specific advantages and attractive features of these bioreactors have been highlighted based on data from successful case studies such as bioplastic synthesis, biodiesel manufacture, Xanthan gum production and aerobic waste water treatment with and without LPO (Liquid Phase Oxygen) utilization. [ABSTRACT FROM AUTHOR]

In the present work, a third-generation gamma transmission tomography system was used to evaluate the liquid distributions of a Raschig rings random packed column, at two different water flows: 2 and 6 l/min. For each water flow, the measurements were carried out at nine column heights. The liquid-gas holdup was determined by the reconstructed images. The distribution of the Raschig rings, as well as the position and the average accumulated amount of the water concentration among the Raschig rings were capable to be determined, even at low temporal resolution of the system of 8.8 h. The regions of accumulated water concentration were similar for the water flow velocities at 2 and 6 l/min. The average accumulated water concentration for 6 l/min was higher compared to 2 l/min. The spatial resolution of the tomography system determined by the modulation transfer function (MTF) analysis was of 1.45 mm. [ABSTRACT FROM AUTHOR]

The structure of many multiphase systems is governed by an energy that penalizes the area of interfaces between phases weighted by surface tension coefficients. However, interface evolution laws depend also on interface mobility coefficients. Having in mind some applications where highly contrasted or even degenerate mobilities are involved, for which classical phase field models are inapplicable, we propose a new effective phase field approach to approximate multiphase mean curvature flows with mobilities. The key aspect of our model is to incorporate the mobilities not in the phase field energy (which is conventionally the case) but in the metric which determines the gradient flow. We show the consistency of such an approach by a formal analysis of the sharp interface limit. We also propose an efficient numerical scheme which allows us to illustrate the advantages of the model on various examples, as the wetting of droplets on solid surfaces or the simulation of nanowires growth generated by the so-called vapor–liquid–solid method. [ABSTRACT FROM AUTHOR]

We summarize in this note a few theoretical and numerical results described with more details in the forthcoming paper [5] devoted to a new phase field model for approximating mean curvature flows. Our work is motivated by the simulation of multiphase mean curvature flows with possibly inhomogeneous surface tensions and mobility coefficients. The key aspect of our model is to incorporate the mobilities not in the phase field energy (which is conventionally the case) but in the metric which determines the gradient flow. We show the consistency of such approach by a formal analysis of the sharp interface limit. We also propose an efficient numerical scheme which allows us to illustrate the advantages of the model on various examples, as the wetting of droplets on solid surfaces or the simulation of nanowires growth generated by the so-called vapor-liquid-solid method. [ABSTRACT FROM AUTHOR]

Abstract: Colloidal coordination compounds in the sub‐micrometer range were synthesized from a chloro gold(I) carbene complex via the anti‐solvent procedure and stabilized by a surfactant shell of Tween 20. This compound was successfully applied as model system to monitor heterogeneous multiphase ligand substitution reactions at the solid–liquid interface. [ABSTRACT FROM AUTHOR]

In experiments and kinetic models it was shown that the reaction rate of the biphasic aqueous hydroformylation of 1-octene is linear dependent on the created interfacial area. This phenomenon is directly linked to the question whether the reaction takes place in the bulk phase and is mass transfer limitation or at the surface which would mean an increase of reaction space. To evaluate the place of reaction a mass transfer analysis has been carried out. No mass transfer limitation for the gaseous components carbon monoxide and hydrogen as well as the olefin 1-octene was determined for the aqueous catalyst phase by calculating the Hatta numbers. With this observation it is possible to exclude the mass transfer as a potential influence and hence the aqueous bulk as the place of reaction. Thus the reaction is most probably surface active. This can be either explained the increase in film volume fraction where non-polar substrate as well as polar catalyst complex is present or through an increased catalyst concentration at the surface through dipole moment fluctuations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 161-171, 2018 [ABSTRACT FROM AUTHOR]

The phase separation of liquid/liquid systems consisting of oil, water and amphiphilic molecules is a function of temperature and composition. The phase separation is fastest in liquid three phase systems, where the organic and aqueous excess phases are separated by a microemulsion middle phase. In this work, a detailed analysis of the relevant physical properties (density, rheology, interfacial tension) of the phases in combination with drop size distribution measurements and image analysis of the droplet interactions is performed using an endoscope measurement system. This methodology enables to directly quantify influencing effects of droplet size and droplet interactions on dispersion and phase separation processes. The duration and character of the separation process strongly depends on the droplet interactions (e.g. formation of multiple emulsions) of the dispersed phases. [ABSTRACT FROM AUTHOR]

The continuous hydrogenation of a mixture of L-arabinose and D-galactose over a Ru/C catalyst was investigated in a miniaturized packed-bed reactor. The reaction is one important step of the transformation of the naturally occurring hemicellulose arabinogalactan into valuable sugar alcohols. Process intensification was accomplished by reducing the reactor dimensions to a few millimeters; thus leading to better mass and heat transfer performance. The effects of temperature, pressure, and liquid flow rate on the yield and by-product formation are discussed. Based on a kinetic model derived from batch experiments, a model of the continuous reactor was developed and used for scale-up purposes. [ABSTRACT FROM AUTHOR]

The additive-free, biphasic aqueous hydroformylation of the long chain olefin 1-octene was investigated with the goal to derive a mathematical expression for the macro kinetic and to increase selectivity towards aldehydes while maintaining fast reaction rates. The influence of different important chemical parameters such as catalyst precursor, catalyst concentration, ligand excess, pH-value, salt concentration, temperature, gas pressure and gas composition was estimated. At 10 MPa and 373 K the highest rate of reaction with 41·10 –5 kmolm −3 s −1 was reached. An optimal compromise between high selectivity and activity was found at 8 MPa syngas pressure and 353 K reaction temperature. Selectivity was thus increased from 20% to 76% with octene isomers as the only by-products. The rate of reaction was linearly dependent on the created interfacial area as shown in previous publications. The optimised conditions were applied to other olefinic compounds with different structural characteristics. Obtained insights were used to establish a rate expression for this reaction, incorporating the interfacial area between organic substrate and aqueous catalyst phase. This novel approach helps to draw attention towards the aspect of procedural rate enhancement in homogeneous catalysis. [ABSTRACT FROM AUTHOR]

Gas-liquid flow is frequently investigated in microreactor research, but mainly focused on well-described Taylor-bubble flow. Dispersed flow featuring small bubbles results in increased specific surface-to-volume ratio and more stable flow in microchannels. The influence of local energy dissipation rate and channel geometry was investigated on gas-liquid dispersion in nozzles with hydraulic diameter from 0.25 to 0.5 mm. Resulting bubble diameter and its size distribution were examined. For systems with increased bubble coalescence, micronozzles can be switched in series to redisperse the flow for augmented mass transfer. The contribution will give a fundamental view on bubble generation, redispersion for dispersed gas-liquid systems in microstructured devices together with design and scale-up discussion. [ABSTRACT FROM AUTHOR]

El interés creciente de utilizar filtros activos de potencia para compensar las corrientes no sinusoidales producidas por las cargas no lineales ha aumentado el uso de la teoría instantánea de potencia reactiva. Sin embargo, esta teoría se puede aplicar solamente a los sistemas trifásicos de tres o cuatro conductores. Este artículo presenta una nueva definición de la potencia instantánea que puede ser aplicada a todos los sistemas polifásicos. Así, el concepto de producto tensorial es introducido para definir el tensor instantáneo de potencia y también la descomposición de la corriente en las componentes activas y reactivas sin importar el número de fases del sistema eléctrico. Finalmente, un análisis exhaustivo de casos prácticos se ha realizado a nivel de simulación, los cuales han permitido que el enfoque propuesto sea verificado.The use of the instantaneous reactive power theory is greater than before due to the increased interest to use active power filters to compensate the non-sinusoidal currents produced by nonlinear loads. However, this theory can only be applied to three-phase systems of three or four conductors. This paper presents a new definition of instantaneous power that can be applied to all multiphase systems. Thus, the concept of tensor product is introduced to define the instantaneous power tensor and also the current decomposition in active and reactive components regardless of the number of phases of the power system. Finally, an exhaustive analysis of practical cases has been carried out at a simulation level which verified the proposed approach.

The thermodynamically constrained averaging theory (TCAT) is a comprehensive theory used to formulate hierarchies of multiphase, multiscale models that are closed based upon the second law of thermodynamics. The rate of entropy production is posed in terms of the product of fluxes and forces of dissipative processes. The attractive features of TCAT include consistency across disparate length scales; thermodynamic consistency across scales; the inclusion of interfaces and common curves as well as phases; the development of kinematic equations to provide closure relations for geometric extent measures; and a structured approach to model building. The elements of the TCAT approach are shown; the ways in which each of these attractive features emerge from the TCAT approach are illustrated; and a review of the hierarchies of models that have been formulated is provided. Because the TCAT approach is mathematically involved, we illustrate how this approach can be applied by leveraging existing components of the theory that can be applied to a wide range of applications. This can result in a substantial reduction in formulation effort compared to a complete derivation while yielding identical results. Lastly, we note the previous neglect of the deviation kinetic energy, which is not important in slow porous media flows, formulate the required equations to extend the theory, and comment on applications for which the new components would be especially useful. This work should serve to make TCAT more accessible for applications, thereby enabling higher fidelity models for applications such as turbulent multiphase flows.

The procedural rate enhancement of a liquid-liquid gas reaction system by example of the biphasic hydroformylation of 1-octene in miniplant scale is presented. Different stirring techniques were applied on a lean reaction system without the use of chemical additives to increase the internal surface area. Reaction rates were doubled compared to standard laboratory stirring methods. While the reaction rate showed a logarithmic relation towards the rate of energy dissipation, it was nearly linearly related to the created interfacial area between organic and aqueous phase. Obtained results support the intensively discussed theory that the reaction takes place at the surface. This study also underlines the importance of procedural optimization in multiphase reactions. [ABSTRACT FROM AUTHOR]

Computational process models in combination with innovative design methodologies provide a powerful reactor design platform. Yet, model-based design is mostly done in a pure deterministic way. Possible uncertainties of the underlying model parameters, prediction errors due to simplifying assumptions regarding the reactor behavior and suboptimal realizations of the design along the reaction coordinate are in general not considered. Here we propose a systematic design approach to directly account for the impact of such variabilities during the design procedure. The three level design approach of Peschel et al. (2010) based on the concept of elementary process functions (EPF) serves as basis. The dynamic optimizations on each level are extended within a probabilistic framework to account for different sources of randomness. The impact of these sources on the performance prediction of a design is quantified and used to robustify the reactor design aiming at a more reliable performance and thus design prediction. The uncertainties of model parameters, non-idealities of the reactor behavior and inaccuracies in the design are included via statistical moments. By means of the sigma point method ( Julier and Uhlmann, 1996 ) random variables are mapped to the design objective space via the nonlinear process model. Importantly, this work introduces a full probabilistic orthogonal collocation approach, i.e. random and stochastic variables can be described. Whereas the former one relates to randomness independent on the reaction time (e.g. kinetic model parameters or initial conditions), the latter one describes stochasticity along the reaction time (e.g. fluctuating pressure or temperature control). As an example process the hydroformylation of 1-dodecene in a thermomorphic solvent system consisting of n -decane and N , N -dimethylformamide is considered. Our probabilistic EPF approach allows designing robust optimal reactors, which operate within an estimated confidence at their expected optimum considering almost any kind of randomness arising in the design procedure. An additional value is that with increased predictive power of the reactor performance its embedding in an overall process is strongly simplified. [ABSTRACT FROM AUTHOR]

Using prototype human synovial fluid, we have synthesized a calcium phosphate nanopowder consisting of two crystalline phases (whitlockite and carbonate-containing hydroxyapatite). The nanopowder was used to produce calcium phosphate (monetite) coatings on titanium substrates by microarc oxidation. It has been shown that, with increasing microarc oxidation voltage (from 200 to 300 V), the mass, thickness, roughness parameter, and Ca : P ratio of the coatings increase linearly. Increasing the voltage to 300 V and the calcium phosphate coating growth time to 10 min allows a single-phase coating up to 100 μm in thickness, consisting of monetite nanocrystals, to be produced on a metallic surface and its adhesion strength to be improved. [ABSTRACT FROM AUTHOR]

Selective benzene (BEN) hydrogenation to cyclohexene (CHE) has been studied in a complex four-phase system by using 2Ru/La2O3-ZnO as the catalyst. The catalyst is highly efficient (yield of desired cyclohexene=28 %) and stable for about five cycles. Characterizations reveal formation of La(OH)3 on the catalyst surface and formation of Zn(OH)3− during the reaction, which play a key role in the formation of CHE. For the first time, the reaction mixture can be observed in situ, showing the emulsion of this complicated four-phase system. The droplet size of the organic compound and the rate of hydrogenation are correlated with different stirring rates excluding mass transfer limitations. [ABSTRACT FROM AUTHOR]

The scarcity of fossil fuels affects the efficiency of established modes of cargo transport within the transportation industry. Extensive research is being carried out on improving the efficiency of existing modes of cargo transport, as well as developing alternative means of transporting goods. One such alternative method is using energy contained within fluid flowing in pipelines to transfer goods from one place to another. The present study focuses on the use of advanced numerical modelling tools to simulate the flow within hydraulic capsule pipelines (HCPs) transporting spherical capsules with an aim of developing design equations. "Hydraulic capsule pipeline" refers to the transport of goods in hollow containers ("capsules"), typically spherical or cylindrical in shape, which are carried along the pipeline by water. HCPs are used in mineral industries and have potential for use in oil and gas sectors. A novel modelling technique was employed to investigate various geometric and flow conditions within HCPs. Both qualitative and quantitative flow analyses were carried out on the flow of spherical capsules in an HCP for both onshore and offshore applications. Furthermore, based on the least-cost principle, an optimization methodology was developed for the design of single-stage HCPs. The input to the optimization model is the solid throughput required from the system, and the outputs are the optimal diameter of the HCPs and the pumping requirements for the capsule transporting system. [ABSTRACT FROM AUTHOR]

Tunable multiphase systems can be applied for the hydroformylation of long-chained olefins. These reaction systems enable highest yields and fastest separation processes under three phase operating conditions. However, little is known about the characteristic properties of these complex dispersions. In this study, a simplified model system consisting of water, 1-dodecene and a solvo-surfactant was analysed. The minimum aggregation concentration, interfacial tension, density and viscosity were determined. Additionally, the phase behaviour was investigated using conductivity measurements. The phase volume fractions under three phase conditions were analysed. An endoscope measurement technique was applied to determine the dispersion conditions and drop size distributions in a stirred tank as a function of composition and stirrer speed. [ABSTRACT FROM AUTHOR]

The study provides an extensive overview of on‐board integrated chargers for electric vehicles that are based on multiphase (more than three phases) machines and power electronics. A common attribute of all discussed topologies is that they do not require a charger as a separate device since its role is transferred to the already existing drivetrain elements, predominantly a multiphase machine and an inverter. The study demonstrates how additional degrees of freedom that exist in multiphase systems can be conveniently utilised to achieve torque‐free charging operation. Therefore, although three‐phase (or multiphase) currents flow through machines' stator windings, they do not generate any torque; thus the machines do not have to be mechanically locked. Cost and weight saving is achieved in this way, while the available space is increased. For each topology operating principles are explained, and its control elaborated in detail for both charging and vehicle‐to‐grid mode. Finally, the validity of theoretical considerations and control algorithms of some of the existing charging solutions is experimentally verified and experimental performance of all discussed topologies is compared. [ABSTRACT FROM AUTHOR]

Gas holdup was investigated in a gas–liquid and gas–liquid-solid reciprocating plate column (RPC) under various operation conditions. Aqueous carboxymethylcellulose (sodium salt, CMC) solutions were used as the liquid phase, the solid phase was spheres placed into interplate spaces, and the gas plase was air. The gas holdup in the RPC was influenced by: the vibration intensity, i.e., the power consumption, the superficial gas velocity, the solids content and the rheological properties of the liquid phase. The gas holdup increased with increasing vibration intensity and superficial gas velocity in both the two- and three-phase system. With increasing concentration of the CMC PP 50 solution (Newtonian fluid), the gas holdup decreased, because the coalescence of the bubbles was favored by the higher liquid viscosity. In the case of the CMC PP 200 solutions (non-Newtonian liquids), the gas holdup depends on the combined influence of the rheological properties of the liquid phase, the vibration intensity and the superficial gas velocity. The gas holdup in the three-phase systems was greater than that in the two-phase ones under the same operating conditions. Increasing the solids content has little influence on the gas holdup. The gas holdup was correlated with the power consumption (either the time-averaged or total power consuption) and the superficial gas velocity.

Gas holdup was investigated in a gas-liquid and gas-liquid-solid reciprocating plate column (RPC) under various operation conditions. Aqueous carboxymethyl cellulose (sodium salt, CMC) solutions were used as the liquid phase, the solid phase was spheres placed into interplate spaces, and the gas phase was air. The gas holdup in the RPC was influenced by: the vibration intensity, i.e., the power consumption, the superficial gas velocity, the solids content and the rheological properties of the liquid phase. The gas holdup increased with increasing vibration intensity and superficial gas velocity in both the two- and three-phase system. With increasing concentration of the CMC PP 50 solution (Newtonian fluid), the gas holdup decreased, because the coalescence of the bubbles was favored by the higher liquid viscosity. In the case of the CMC PP 200 solutions (non-Newtonian liquids), the gas holdup depends on the combined influence of the rheological properties of the liquid phase, the vibration intensity and the superficial gas velocity. The gas holdup in the three-phase systems was greater than that in the two-phase ones under the same operating conditions. Increasing the solids content has little influence on the gas holdup. The gas holdup was correlated with the power consumption (either the time-averaged or total power consumption) and the superficial gas velocity.

This brief review focuses on the work performed at the Chemical Reaction Engineering Laboratory (CREL) at Washington University, St. Louis, in using Computer Aided Radioactive Particle Tracking (CARPT) and Gamma Ray Computed Tomography (CT), in generating velocity and phase holdup profiles in different multiphase reactors. This data is used for validation of the Euler-Euler interpenetrating fluid model executed in the framework of FLUENT and CFDLIB. Data for holdup and velocity profiles, as well as for mixing parameters, obtained in liquid-solid and gas-solid risers, slurry bubble columns, and stirred tanks, are discussed. It is shown that Euler-Euler simulations are capable of predicting such data well for the cases studied. Extension of CARPT-CT to industrial systems is briefly discussed.

Micellar multiphase systems can be applied to enable reactions like the hydroformylation of long-chained olefins. These liquid/liquid systems combine advantages of homogenous catalysis like high and specific yield or mild reaction conditions with a fast phase separation process. In previous studies highest yields were observed in systems under three phase operation conditions whereby the reaction rate was a function of stirrer speed. Hence, dispersion conditions and drop size distributions need to be taken into consideration. In this study, micellar three phase systems were analysed using an endoscope measurement technique and image analysis in a stirred tank. A methodical approach to identify the respective phases and to clarify the dispersion conditions was found. The mean Sauter diameters were quantified as a function of the system composition. By applying abrupt changes of the stirrer frequency, the dynamic behaviour and coalescence effects were investigated. [ABSTRACT FROM AUTHOR]

A thermo-electromechanical formulation for the description of ionic electroactive polymers is derived within the framework of the Theory of Porous Media. The model consists of an electrically charged porous solid saturated with an ionic solution. The saturated porous medium is assumed to be incompressible. Different constituents following different kinematic paths are considered such as solid, fluid, anions, cations and free charges. The electromechanical and the electrodynamic field equations are discussed. Based on the second law of thermodynamics, a consistent model is developed. With respect to the closure problem of the model, the needed constitutive relations and evolution equations are presented. [ABSTRACT FROM AUTHOR]

This paper presents a multiphase continuation power flow (MCPF) methodology to perform voltage security analyses on unbalanced multiphase distribution systems. The proposed tool includes comprehensive models of most network components, and allows for explicit representation of neutral cables and grounding connections. The methodology has been validated through comparisons with a commercial software and with results available in the literature. Additional analyses are presented using the IEEE 4-bus, the Neutral-to-Earth (NEV) and the IEEE 8500 Test Systems. These systems have been developed to present several challenges to distribution systems analytical tools. In particular, the influence of the 3-phase transformer connections on the PV curves have been demonstrated and has been useful to stress the importance of a complete system representation. [ABSTRACT FROM PUBLISHER]

In this work, the theoretical field dependence of the magnetic entropy change far away from the transition is used to analyze the field dependence of composite materials formed by fcc La(Fe,Si) 13 and bcc α-Fe(Si) phases. A non-interacting phases approximation is followed in the analysis and results are in good agreement with microstructural data obtained from X-ray diffraction and Mössbauer spectroscopy. The range of validity of the approximation is estimated. It is concluded that the quadratic field dependence of magnetic entropy change is reached a few tens of kelvin above the transition temperature at 1.5 T. However, the linear dependence (characteristic of ferromagnets well below its Curie temperature) is only reached a few hundred kelvin below the transition. The results presented here can be used in the deconvolution of the contribution of impurities to the MCE signal in composites. [ABSTRACT FROM AUTHOR]

The incorporation of nano-sized sepiolite clays into thermoplastic starch/poly(butylene adipate- co -terephthalate) (TPS/PBAT) blends has been investigated with the goal of improving the matrix properties. TPS/PBAT nano-biocomposites were elaborated with two different proportions of the polymeric phases. The influence of the sepiolite nanoclays on the mechanical, thermal and structural properties of the corresponding blends was evaluated. SEM images confirmed the good dispersion of the sepiolite clay, with a low occurrence of small aggregates in the polymeric matrix. Wide-angle X-ray diffraction showed no significant alteration of the crystalline structures of PBAT and starch induced by the sepiolite clay. The addition of sepiolite slightly affected the thermal degradation of the nano-biocomposites; however, the mechanical tests revealed an increase in some mechanical properties, demonstrating that sepiolite is a promising nanofiller for TPS-based materials. [ABSTRACT FROM AUTHOR]

• Current knowledge on process design and enhancement with OBRs is reviewed. • Depending on the baffle geometries, additional design parameters may be needed. • Micromixing performance in OBRs still needs to be explored. • Parameters other than plug flow may be a priority depending on the process goal. • The implementation of OBRs is still challenging for some applications. The continuous oscillatory baffled reactor (OBR) is a particular type of tubular reactor, which has drawn increasing attention over the past few decades due to the benefits it provides in terms of intensification of heat and mass transfer, as well as equipment compactness compared with stirred tank reactors. This process enhancement is principally due to the interaction of the oscillatory flow with internal baffles and the consequent generation of transverse flows and eddies. Continuous OBRs are already applied in several industrial sectors, however these reactors present certain limitations in terms of operating conditions and the range of possible applications. This review presents and discusses the current knowledge on continuous OBR design guidelines, performance characterization and applications. It aims to guide the selection of the most appropriate continuous OBR design, as well as the characterization criteria, according to the type of application and final process objective. [Display omitted] [ABSTRACT FROM AUTHOR]

Cover Feature: Tunable Multi-Phase System for Highly Chemo-Selective Oxidation of Hydroxymethyl-Furfural (ChemSusChem 17/2022) HMF, multiphase systems, oxidation, Ru/C catalyst, selectivity control Keywords: HMF; multiphase systems; oxidation; Ru/C catalyst; selectivity control EN HMF multiphase systems oxidation Ru/C catalyst selectivity control 1 1 1 09/09/22 20220907 NES 220907 B The Cover Feature b shows the potential of multiphase liquid systems for the oxidation of 5-hydroxymethylfurfural (HMF) with tunable selectivity. [Extracted from the article]