Couette Reactor Research Articles

Integrated Taylor–Couette Reactor Model for Heterogeneous Photocatalytic Degradation of AO7

Integrated Taylor–Couette Reactor Model for Heterogeneous Photocatalytic Degradation of AO7

Flow in a Taylor–Couette Reactor with Ribbed Rotors

This paper investigates the flow structure and flow pattern transition within a conical ribbed Taylor–Couette reactor (TCR), which is 4 mm in gap width and 200 mm in height, via particle image velocimetry (PIV) and numerical simulation methods. The effect of various parameters on the vortex structure and on flow transition, including the structural parameters of the ribs (rib spacing and rib width) and the operating parameters (Taylor number and axial Reynolds number), were investigated. Without axial flow, the ribbed TCR can control the flow structure while maintaining the symmetry of the flow field. Under certain conditions, a Taylor vortex pair can form between the ribs, with the down vortex rotating clockwise and the up vortex rotating counterclockwise. The axial dimension of the Taylor vortex can be controlled by adjusting the rib spacing, which can be summarized into four different conditions according to the size of the rib spacing. With axial flow, the axial Reynolds number greatly impacts the Taylor vortex structure within the ribbed TCR, and as the axial Reynolds number increases, the up vortex appears to be compressed and the down vortex appears to be stretched. The double vortex flow pattern between the ribs is eventually transformed into a single vortex. The critical axial Reynolds number for flow pattern transition is defined and correlated with the Taylor number and rib spacing. The results show that the critical axial Reynolds number is positively proportional to the Taylor number and is inversely proportional to rib spacing. The empirical correlation equation developed in this study shows strong predictive power and is validated using the experimental results. Overall, this study provides a comprehensive understanding of the flow structure and pattern transition within a ribbed TCR and lays the foundation for the further optimization of TCR design.

Micromixing Performance in a Taylor–Couette Reactor with Ribbed Rotors

The Taylor–Couette reactor (TCR) is becoming an increasingly significant topic in chemical industry. This study investigates the micromixing performance of a ribbed TCR with axial flow in the Villermaux–Dushman reaction system. The local micromixing mechanism of the ribbed TCR was analyzed, and the volume-averaged energy dissipation rate was calculated using CFD. The effects of operating parameters and rib structural parameters on micromixing performance were investigated. The results show that the introduction of ribs eliminates the high shear region between the vortex pairs, resulting in the strong micromixing region being situated on the inner and outer cylinder wall surfaces and the ribbed surface region. Smaller rib spacing, larger rib width, and rib height can strengthen micromixing and result in a smaller segregation index. Micromixing times of ribbed TCRs were calculated using the incorporation model, tm, in the range of 2.0 × 10−5 to 8.0 × 10−3. The results show that ribbed TCRs require a lower energy consumption to achieve a lower tm than other rotating reactors. A correlation equation between tm and five parameters was developed, with a correlation coefficient of 0.951. The accuracy of the volume-averaged energy dissipation rate obtained via CFD was verified through experimental analysis. The correlation between the micromixing time and the volume-averaged energy dissipation rate was established in a form that satisfies Kolmogorov’s turbulence theory for tm. To convert the volume-averaged energy dissipation rate into a local energy dissipation rate, a factor ϕ was introduced and solved using the engulfing diffusion model. This study provides insights into the design and optimization of ribbed TCRs.

An integrated system of a microreactor with a Taylor–Couette reactor for 2,2′‐dibenzothiazole disulfide synthesis

AbstractAn integrated microreaction system of a microreactor with a Taylor–Couette reactor (TCR) for continuous synthesis of 2,2′‐dibenzothiazole disulfide has been developed, so as to improve the process efficiency and the stability with solid product generation compared with the current batch process. The homogeneous oxidation with hydrogen peroxide catalyzed by phosphotungstic acid was applied. In the microreaction system, two feedstocks can be rapidly mixed through the microreactor; stable particle flow ability and high conversion can be achieved through the TCR, due to the flow characteristics of high shear stress and limited back‐mixing. Under the conditions of stable operation, the conversion can reach over 90%. The purity of the product is over 99%. The space–time yield can reach 160 g L−1 h−1, which is much higher than that in the batch reactor. The microreaction system is stable for long‐term running, which provides an effective design strategy for continuous flow processes with solid generation.

Effect of shear rate on the heterocoagulation between coal and quartz particles in a Taylor–Couette reactor

ABSTRACT Heterocoagulation between the valuable mineral and gangue particles is one of the significant factors that deteriorate flotation. To date, the effect of hydrodynamics on heterocoagulation is still ambiguous, so it is difficult to develop the inhibition method of mineral heterocoagulation based on flow field control. In the present work, the heterocoagulation experiments of the mixture of coal and quartz particles were carried out in a turbulent Taylor–Couette reactor, and the number of particles in the supernatant was measured to characterize heterocoagulation. It was found that the heterocoagulation between coal and quartz particles increased first then decreased with shear rate, which is due to the combined effects of shear rate on the collision of particles and the breakage of aggregates. The bubble loading of coal was measured to investigate the effect of heterocoagulation on true flotation. The results show that the bubble attachment of coal was mitigated after the heterocoagulation of quartz particles.

Flow Regimes in Two-Phase Hexane/Water Semibatch Vertical Taylor Vortex Flow

Optical-based experiments were carried out using the immiscible pair of liquids hexane and water in a vertically oriented Taylor–Couette reactor operated in a semibatch mode. The dispersed droplet phase (hexane) was continually fed and removed from the reactor in a closed loop setup. The continuous water phase did not enter or exit the annular gap. Four distinct flow patterns were observed including (1) a pseudo-homogenous dispersion, (2) a weakly banded regime, (3) a horizontally banded dispersion, and (4) a helical flow regime. These flow patterns can be organized into a two-dimensional regime map using the azimuthal and axial Reynolds numbers as axes. In addition, the dispersed phase holdup was found to increase monotonically with both the azimuthal and axial Reynolds numbers. The experimental observations can be explained in the context of a competition between the buoyancy-driven axial flow of hexane droplets and the wall-driven vortex flow of the continuous water phase.

Continuous Synthesis of Structurally Uniform Graphene Oxide Materials in a Model Taylor–Couette Flow Reactor

Graphene oxide (GO) has proven to be an invaluable material for a wide range of applications. The development of a bulk-scale continuous process to synthesize GO materials has become crucial. In this study, we used a model Taylor–Couette reactor with axial flow to transform the oxidation of graphite flakes into a continuous process. Efficient mixing of graphite and oxidizing agents was achieved via Taylor vortices, which remarkably shortened the duration of graphite oxide (GtO) synthesis from hours to minutes. Our results reveal that the level of oxidation increased at the Taylor vortex flow (TVF) regime and significantly decreased at other hydrodynamic flow regimes. More importantly, TVF regime resulted in structurally uniform GtO products. This confirms that the developed apparatus offers a robust method to synthesize high-quality, structurally uniform GtO in a continuous manner that can be used in numerous applications.

Influence of COM-peptides/proteins on the properties of flocs formed at different shear rates

Coagulation followed by floc separation is a key process for the removal of algal organic matter (AOM) in water treatment. Besides optimizing coagulation parameters, knowledge of the properties of AOM-flocs is essential to maximizing AOM removal. However, the impact of AOM on the floc properties remains unclear. This study investigated how peptides/proteins derived from the cellular organic matter (COM) of the cyanobacterium Microcystis aeruginosa influenced the size, structure, and shape of flocs formed at different shear rates (G). Flocs formed by kaolinite, COM-peptides/proteins and a mixture of the same were studied, and the effect of intermolecular interactions between floc components on floc properties was assessed. The coagulation experiments were performed in a Taylor–Couette reactor, with aluminum (Al) or ferric sulphate (Fe) utilized as coagulants. Image analysis was performed to gauge floc size and obtain data on fractal dimension. It was found that floc properties were affected by the presence of the COM-peptides/proteins and the coagulant used. COM-peptides/proteins increased floc size and porosity and widened floc size distributions. The Fe coagulant produced larger and less compact flocs than Al coagulant. Moreover, the decrease in floc size that occurred in parallel with increase in shear rate was not smooth in progress. A rapid change for the kaolinite-coagulant suspension and two rapid changes for the suspensions containing COM were observed. These were attributed to various intermolecular interactions between floc components participating in coagulation at different G. Based on the results obtained, shear rates suitable for efficient separation of flocs containing COM were suggested.

Morphological properties of flocs under turbulent break‐up and restructuring processes

Bentonite flocculation was performed in a Taylor–Couette reactor coupled with an in situ method of image acquisition and analysis. A hydrodynamic sequencing is imposed to perform successive cycles of flocculation and breakage. Depending on the shear rate applied during the breakage step, one or two cycles are needed after the first flocculation step to recover a full reversibility on both size and shape factors. The breakup step produces flocculi that are the building blocks for the next. The re‐flocculation steps produce smaller sizes and more regular shapes than the initial growth step. The floc size is calibrated by the turbulence as the radius of gyration is close to the Kolmogorov microscale whereas the floc structure is determined by flocculi aggregates. An analysis of the change of the flocs morphology, despite of their diversity, can also be achieved thanks to some relevant moments of the distributions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3706–3716, 2017

Homogeneously catalyzed hydroamination in a Taylor–Couette reactor using a thermormorphic multicomponent solvent system

In order to design an innovative continuous process for the conversion of the renewable β-myrcene, three methodical steps are shown in this paper to find a setup for the demanding homogeneously catalyzed hydroamination. First step is the theoretical and practical design of a suitable thermomorphic multicomponent solvent (TMS)-systems for recycling the catalyst system. The necessary phase equilibria were successfully investigated by modelling using the Perturbed Chain – Statistical Associating Fluid Theory (PC-SAFT) and measuring liquid–liquid equilibria of the ternary systems substrates/solvents mixtures at the separation temperature. In the next step the promising TMS-system was subsequently used to investigate the recycling of the catalyst in continuous operation. A Taylor–Couette reactor (TCR) was developed and modified for the application in homogeneous transition metal catalysis. The reactor was integrated in a miniplant setup and a continuous recycling of the catalyst phase as well as an efficient synthesis of the desired terpenyl amines is achieved in 3 complete cycles. The results show that the TCR is suitable for the hydroamination and generates high conversion and yields (XMyr=82%, YHA=80%). Recycling experiments were conducted successfully in the miniplant setup to show the long-term operation in a period of 24h.

An adaptive model for gas–liquid mass transfer in a Taylor vortex reactor

Gas–liquid Taylor–Couette flow devices have attracted interest for use as chemical and biological reactors, and consequently the accurate prediction of interphase mass transfer coefficients is crucial for their design and optimization. However, gas–liquid mass transport in these systems depends on many factors such as the local velocity field, turbulent energy dissipation rate, and the spatial distribution and size of bubbles, which in turn have complicated dependencies on process, geometric, and hydrodynamic parameters. Here we overcome these problems by employing a recently developed and validated Eulerian two-phase CFD model to compute local values of the mass transfer coefficient based upon the Higbie theory. This approach requires good estimates for mass transfer exposure times, and these are obtained by using a novel approach that automatically selects the appropriate expression (either the penetration model or eddy cell model) based upon local flow conditions. By comparing the simulation predictions with data from corresponding oxygen mass transfer experiments, it is demonstrated that this adaptive mass transfer model provides an excellent description for both the local and global mass transfer of oxygen in a semibatch gas–liquid Taylor–Couette reactor for a wide range of azimuthal Reynolds numbers and axial gas flow rates.

Application of a Taylor-Couette Reactor in Homogeneous Catalysis

New developments of synthesis routes in homogeneous catalysis often require a precise control of the reaction conditions in order to achieve optimal results. A precise control of the flow- and reactor behaviour can improve the performance of a catalytic system, e.g. by suppressing side- and consecutive reactions. The Taylor-Couette reactor (TCR) allows a precise control of the flow conditions combining the benefits of continuously stirred tank reactors (CSTR) and plug-flow reactors (PFR). A ribbed Taylor Couette reactor for the application in homogeneous catalysis was developed and tested in the continuous hydroamination of the renewable β-myrcene in miniplant-scale. The application of the atom-efficient hydroamination to terpenes allows the continuous production of terpenyl amines based on renewable resources. Catalyst recycling of the homogeneous transition metal catalyst was achieved by means of Thermomorphic Multicomponent Solvent (TMS)-systems. TMS-systems enable the realisation of the reaction under homogeneous conditions at elevated temperatures, but also allow a biphasic phase separation after the reaction. This way the homogeneous catalyst can be separated from the product phase and used again. Yields of the desired terpenyl amines of up to 87 % could be generated in a homogeneous toluene solution on a laboratory scale. The application of the TMS-system acetonitrile/n-heptane yielded 86 %, the TMS-system N,N-dimethylformamide/n-heptane generated 45 % of the desired hydroamination products. Both systems were then transferred into a continuously operated miniplant and realised using a Taylor-Couette reactor. The reactor performance was then validated and compared to the laboratory batch experiments. In the continuous miniplant experiments, the Taylor-Couette reactor could reproduce and even surpass the results of the batch experiments.

CFD simulation of shear flow and mixing in a Taylor–Couette reactor with variable cross-section inner cylinders

A Taylor–Couette (TC) reactor has been considered as a promising technology to produce uniform ultra-fine particles with controlled morphology and size because of its rather narrow shear rate distribution in comparison to a conventional stirred tank. However, small particles in the TC reactor are likely entrapped by the Taylor vortices and concentrated more in the core of the vortices, thus having an adverse or a positive impact on producing the uniformly fine particles. To mitigate this disadvantage, one approach is to adopt an inner cylinder with a variable cross-section through the proper design to obtain a non-constant gap between the inner and outer cylinders in the TC reactor. This study investigates the use of specific profiles of the cross section for the inner cylinder to deform the Taylor vortices, effectively reducing the regions of low velocity and shear rate in the TC reactor. The profiles are composed of a series of curves. The flow patterns and shear rate distributions in the modified TC reactors were investigated using CFD modelling. The sliding mesh method and the Reynolds stress model were employed in the simulation to account for highly turbulent rotating flows. The simulated results compared with those for the classical TC reactor clearly indicate that the regions of low shear rate are effectively reduced in the modified TC reactors because the Taylor vortices occurring in the gap becomes temporal-periodic with respect to the stationary outer cylinder. The obtained shear rate distributions are remarkably narrower than those of the classical TC reactor. It was revealed that the curvature of curves for the cross-section profiles can significantly affect the shear rate distributions, and there exists an optimal profile for the inner cylinder cross-section.

The LS-STAG immersed boundary method for non-Newtonian flows in irregular geometries: flow of shear-thinning liquids between eccentric rotating cylinders

This paper presents the extension of a well-established immersed boundary/cut-cell method, the LS-STAG method (Cheny and Botella in J Comput Phys 229:1043–1076, 2010), to non-Newtonian flow computations in 2D irregular geometries. One of the distinguished features of our IB method is to use level-set techniques in the cut-cells near the irregular boundary, where accurate discretization is of paramount importance for stability and accuracy of the computations. For this purpose, we present here an accurate discretization of the velocity gradients and shear rate in the cut-cells that fits elegantly in the framework of the velocity–pressure–stress staggered arrangement and the special quadratures developed previously for viscoelastic flows. After assessing the accuracy of the discretization on a benchmark solution for power-law fluids, the LS-STAG code is applied to the flow of various shear-thinning xanthan solutions in a wide-gap, non-coaxial, Taylor–Couette reactor for which rheological characterization, experimental flow measurements (PIV) and FLUENT simulations have recently been performed in our group. Our numerical investigation will give new insight on the flow patterns (onset, size and position of the recirculation zone) and will firmly correlate them to global flow properties such as shear-thinning index, generalized Reynolds number and torque ratio at the cylinders.

Preparation of NMC622 Cathode Materials Using a Cost Effective Circular Type Reactor for Li-Ion Battery Application

Li(Ni0.6Mn0.2Co0.2)O2 (NMC622) cathode materials have been recognized as the next generation cathode materials due to its higher capacity and lower raw material cost than commercialized cathode materials such as NMC532. Thus, many industrial companies have been made every effort to commercialize and apply the NMC622 to lithium ion battery system such as energy storage system (ESS). However, production cost of NMC622 still has been recognized as expensive material to be applied in the industrial field and it becomes main issues to be overcome. CSTR (Continuous Stirred Tank Reactor) has been widely applied in the industrial field to produce the NMC622 precursor but it has initial long stabilization time as well as low production efficiency. This is caused by the original limitation of CSTR such as the low mass transfer rate and required complete mixing zone to stabilize the system. Thus, in this study, we suggest the novel reactor system that shows the higher mass transfer rate as well as higher production rate than those of CSTR. Developed novel reactor system uses the taylor-couette flows to induce higher mass transfer rate and production efficiency with uniform particle size distribution.In this study, we synthesized NMC622 using taylor-couette reactor to understand the function and mechanism of the operation. The effect of operating parameters, i.e. pH, operating rpm, and feed retention time, in the taylor-couette reactor, was investigated thoroughly to evaluate the feasibility to produce NMC622 precursor. Produced precursors are characterized using SEM, XRD, ICP, FIB, PSA. Then, cathode materials are prepared and tested using a galvanostatic intermittent titration method (GITT) to understand the electrochemical properties. This study verified that taylor couette reactor is feasible process to be applied to the commercial NMC622 production.Acknowledgement - This work was supported by the Korea Institute of Energy Technology Evaluation and Planning under the Energy Technology Development Program (20132020101750)

A Study on the Production of NMC622 Cathode Materials Using a Novel Taylor-Couette Flow Reactor Process

Li(Ni0.6Mn0.2Co0.2)O2 (NMC622) cathode materials have been recognized as the next generation cathode materials due to its higher capacity and lower raw material cost than commercialized cathode materials such as NMC532. Thus, many industrial companies have been made every effort to commercialize and apply the NMC622 to lithium ion battery system such as energy storage system (ESS). However, production cost of NMC622 still has been recognized as expensive material to be applied in the industrial field and it becomes main issues to be overcome. CSTR (Continuous Stirred Tank Reactor) has been widely applied in the industrial field to produce the NMC622 precursor but it has initial long stabilization time as well as low production efficiency. This is caused by the original limitation of CSTR such as the low mass transfer rate and required complete mixing zone to stabilize the system. Thus, in this study, we suggest the novel reactor system that shows the higher mass transfer rate as well as higher production rate than those of CSTR. Developed novel reactor system uses the taylor-couette flows to induce higher mass transfer rate and production efficiency with uniform particle size distribution.In this study, we synthesized NMC622 using taylor-couette reactor to understand the function and mechanism of the operation. The effect of operating parameters, i.e. pH, operating rpm, and feed retention time, in the taylor-couette reactor, was investigated thoroughly to evaluate the feasibility to produce NMC622 precursor. Produced precursors are characterized using SEM, XRD, ICP, FIB, PSA. Then, cathode materials are prepared and tested using a galvanostatic intermittent titration method (GITT) to understand the electrochemical properties. This study verified that taylor couette reactor is feasible process to be applied to the commercial NMC622 production.

In situ characterization of floc morphology by image analysis in a turbulent Taylor–Couette reactor

Flocculation of bentonite was performed in a turbulent Taylor–Couette reactor under various shear rates. Image processing enabled to determine various morphological characteristics of individual flocs. Not only their mean values but also their distributions were studied under various hydrodynamic conditions. Relevant properties were selected. The temporal evolution of radius of gyration and circularity distributions was monitored during the flocculation process. Although size and shape are obviously correlated, this article points out that their dependency to hydrodynamics is different, showing that flocs of similar sizes produced under different hydrodynamic conditions exhibit different shapes. The sizes are calibrated by the turbulence as the double radius of gyration is close to Kolmogorov microscale, whereas the circularity seems correlated to the rotation speed. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2389–2403, 2014

The effect of shear rate on aggregate size distribution and structure at steady state: a comparison between a Taylor–Couette reactor and a mixing tank

The paper deals with the dependence of aggregate properties on the shear rate ( G ) at steady state. Aggregation of natural raw water and ferric sulphate was carried out in a laboratory Taylor–Couette reactor (TC) and continuous flow mixing tank (MT) with a paddle stirrer. Shear rates in the range of 20–350 s −1 were used. Methods of image and fractal analyses were used to determine the aggregate size and structure, respectively. It was found that the aggregate size decreased with increasing shear rate. There was a small difference in sizes of aggregates formed in TC and MT at G −1 , but at higher shear rates, almost no difference between TC and MT was observed. The D 2 fractal dimension increased with increasing shear rate indicating that aggregates became less porous and more compact. Moreover, a very close match in D 2 values was attained for both mixing devices. The D pf fractal dimension decreased with increasing shear rate meaning that aggregates were more regular at higher shear rates, but jagged on the surface with irregular shape at lower shear rates. In contrast to D 2 , aggregates formed in MT were much more irregular (jagged) than those formed in TC.

Fast and efficient nanoshear hybrid alkaline pretreatment of corn stover for biofuel and materials production

We report a fast and efficient nano-scale shear hybrid alkaline (NSHA) pretreatment method of lignocellulosic biomass. In this work, corn stover was pretreated in a modified Taylor–Couette reactor with alkali (sodium hydroxide) at room temperature for two minutes. Up to 82% of high cellulose content in the remaining solids was achieved with the novel NSHA pretreatment process. Compared with untreated corn stover, an approximately 4-fold increase in enzymatic cellulose conversion and a 5-fold increase in hemicellulose conversion were achieved. Compositional analysis proved significant removals of both lignin and hemicellulose after the NSHA pretreatment. SEM images revealed that the synergistic effect of NSHA pretreatment caused the severe disruption of biomass structure and exposure of cellulose microfibril aggregates in NSHA pretreated corn stover.

Simulation of Taylor–Couette reactor for particle classification using CFD

Dynamic characteristics about motion of Taylor vortex flow and separation of particles in Taylor–Couette reactor were investigated numerically and experimentally. Commercial computational fluid dynamics (CFD) program was used for calculation of the fluid dynamics of Taylor vortex flow and particle classification system. Gravitational and drag force balance affect the particles, when the Taylor–Couette reactor is vertically located. Thus, the particles movement depends on the size of particles and reactor operating conditions. When rotational speed of inner cylinder increases or the feed flow rate decreases, the axial moving velocity of the Taylor vortex decreases. In this study, the Taylor vortex moving velocity and moving region were determined for the various rotational speeds of the inner cylinder and inlet flow rates. To investigate the performance of particle classification, particles with various sizes injected at the center of reactor by Particle-tracking simulations. Then, the Taylor–Couette reactor applied as a crystallizer was proposed, which simultaneously classify the crystals.