Iodide Iodate Reaction Research Articles

Two-stage microreactor with intensely swirling flows: Comparison of three methods of liquids feeding

A two-stage microreactor with intensely swirling flows (MRISF-2) allows to perform effectively two subsequent reactions in synthesis of nanosized particles. Micromixing quality plays crucial role in ultrafast co-precipitation reactions, and depends both on the specific energy dissipation rate and on the geometry of the reactor as well as the solutions feeding manner. Solutions in MRISF-2 could be supplied by different ways: through the upper and/or lower tangential inlet pipes and through the central (axial) inlet pipe. This paper is aimed to compare experimentally and numerically three ways of liquid solutions feeding in MRISF-2 with objective to find the conditions of the highest specific energy dissipation rate. The best method of solutions supplying was found experimentally and confirmed numerically: one solution is supplied tangentially, the other through the central inlet pipe. The average specific energy dissipation rate for this method is 1.7 and 6.0 times higher compared to supply through two upper tangential inlet pipes and upper + lower tangential inlet pipes, respectively. This advantage was confirmed by measurements of segregation index Xs by use of iodide-iodate reaction technique. Good agreement between experimental and numerical simulation results for energy dissipation rate was found for all studied cases.

Micro-mixing enhancement in a Taylor-Couette reactor using the inner rotors with various surface configurations

This study investigates the effects of various inner cylinder configurations on micromixing and fluid dynamics within a Taylor-Couette (TC) reactor using the inner cylinders with different surface designs, including the traditional smooth-surfaced rotor cylinder. The four innovative inner cylinders were specifically designed with axial corrugations (N40 and N80) and three-dimensional rough surfaces (NZ40 and NZ80). Micromixing efficiency was assessed experimentally using the iodide-iodate reaction as a probe. To further understand the impact of the rotors' surface structures on micromixing, computational fluid dynamics (CFD) modelling was utilized to analyse the fluid dynamics within the TC reactor. An incorporation model was employed to calculate the micromixing time. The experimental findings reveal that the segregation index decreases with increasing rotation speed for all inner cylinders. Besides, NZ80′s micro-mixing efficiency surpasses that of its counterparts, NZ40, N40, and N80. The CFD modelling results underscore the significant influence of the inner cylinder's surface configuration on the turbulence dissipation rate and volume probability distribution, which are likely to contribute positively to the micromixing efficiency within the TC reactor. Furthermore, the empirical correlations obtained have been established to understand the micro-mixing time within TC reactors using different rotating cylinders.

Energy Dissipation Rate and Micromixing in a Two-Step Micro-Reactor with Intensively Swirled Flows.

The influence of the hydrodynamics (flow rates Q, specific energy dissipation rate ε) on the micromixing in a two-step microreactor with intensively swirled flows (MRISF-2) was studied experimentally. Three methods of liquid input into the reactor were compared: (i) through the upper tangential and axial nozzles (TU1, Ax); (ii) through two upper tangential nozzles (TU1, TU2); (iii) through the upper and lower tangential nozzles (TU1, TL2). Segregation index Xs used as a measure of micromixing level was determined by means of iodide iodate reaction method. The Bernoulli equation for a device with two inputs and one output was derived to assess the energy consumption. It was revealed that in MRISF-2 up to 99.8-99.9% of input energy is dissipated, i.e., transformed into liquid element deformations thus resulting in better micromixing. For each of three liquid inputs, the dependence ε = f(Q) could be fairly approximated by an exponent ε = A1Qn1, with n1 ≈ 3.0. For connection (TU1, TU2) the dependence Xs = f(ε) falls linearly for Q > 2 L/min, but for the low flow rates (Q ≈ 1 L/min) there is an unusually small Xs value; the effect of good micromixing is caused by the kinetic energy concentrated in a small volume of liquid near the neck. The best behavior in terms of micromixing was achieved for the (TU1, Ax) connection scheme: the level of Xs ≈ 0.01 for ε ≈ 30 W/kg, and comes down with growing ε to Xs ≈ 0.002 for ε ≈ 30,000 W/kg. These values are 50 and 250 times lower compared to the mixing in a lab glass with a magnetic stirrer, as shown in our previous work. The parameters of dependencies Xs=A3εn3 were found for (TU1, Ax) and (TU1, TL2).

Feasibility study on micromixing intensification in a spinning disk reactor utilizing heterogeneous surface wettability

The micromixing intensification of reactor is the research hotspot in process intensification filed. In this work, the micromixing intensification of spinning disk reactor (SDR) was studied by utilizing heterogeneous surface wettability for the first time. Several partial hydrophobic modified disks were designed and employed to realize the heterogeneous surface wettability. The micromixing performance of SDR was evaluated by iodide-iodate reaction system. Results showed that micromixing efficiency of SDR with partial hydrophobic modified disk was higher than that of non-modified disk. The wettability of liquid inlet zone on the disk surface had a significant influence on results. Hydrophobic modified zone was more crucial in comparison with the modified area. The values of XS maximally decreased by 49.9% in SDR with partial hydrophobic modified disk compared to the non-modified disk. This preliminary study provided a feasible path for micromixing intensification in SDR by utilizing heterogeneous surface wettability, displaying considerable application prospects.

Intensification of micromixing efficiency in a spinning disk reactor: Experimental investigation

Spinning disk reactor (SDR) exhibits excellent performance for liquid-liquid micromixing. For traditional SDR, there is still much room to intensify micromixing efficiency through structure design of disk surface and pre-mixer type. In this work, SDR consisted of a spinning disk and a pre-mixer. Three kinds of baffles on the disk were designed for enhancing disturbance of liquid film. Besides, two types of pre-mixers were adopted in the SDR for improving micromixing environment. The iodide-iodate reaction was employed as working system. Compared with other kinds of baffles, the radial baffle exhibited better micromixing efficiency. The incorporation model was adopted to determine the corresponding micromixing time of SDR with radial baffle which reduced about 60% than that of SDR with smooth disk. Pre-mixer could also enhance the micromixing efficiency of SDR, especially at relatively low rotational speed. Considering different rotational speed requirements, suitable intensification mode was proposed for improving micromixing performance of SDR.

Green synthesis of sub 10 nm silver nanoparticles in gram scale using free impinging jet reactor

In this paper we report controlled synthesis of sub 10 nm silver nanoparticles at 30 g/day at room temperature condition using a green protocol using a free impinging jet reactor. The focus is on impingement of low velocity liquid jets to ensure process completion in the film. Identical liquid jets of 400-micron diameter with low Weber number (We = 10–40) were impinged at different approach angles (90°–150°) to explore mixing characteristics using iodide-iodate reaction system. The regime showed monotonic improvement in silver nanoparticle mean size and polydispersity with increase in We. The smallest and most uniform (5.2 ± 0.9 nm) particles could be synthesized at We = 40. The study also establishes the horizontal component of jet velocity as a parameter to control mixing and particle size. Under identical reaction condition a free impinging jet reactor outperformed two other continuous reactors viz. a spinning disc reactor and a spinning disc spinning bowl reactor in terms of mean particle size.

Alternative Kinetic Model of the Iodide–Iodate Reaction for Its Use in Micromixing Investigations

The Villermaux–Dushman method, one of the most extensively used test reaction systems for micromixing characterization, has been widely criticized for years due to uncertainties regarding the incomplete dissociation of sulfuric acid and the proposed kinetic study by Guichardon et al. In this work, a renewed study of the kinetics of the iodide–iodate reaction is presented, using perchloric acid to avoid issues concerning incomplete acid dissociation. The experimental results are in good agreement with the fifth-order rate law for the iodide–iodate reaction. The reaction rate coefficient strongly depends on the ionic strength and can be modeled with a Davies-like equation. When implemented in the incorporation model, the kinetic model presented in this study can be used to estimate micromixing times that are in line with the theoretical engulfment time. This is observed in two different reactors with low and high intensities of mixing: an unbaffled stirred vessel and a rotor–stator spinning disk reactor. The results from the latter are also compared with the second Bourne reaction, giving very similar micromixing times. The kinetic model presented in this study in combination with strong monoprotic acids is suggested as an alternative to characterize micromixing behavior.

Micromixing efficiency in a rotating foam stirrer reactor with various reactor configurations and liquid viscosities

AbstractBACKGROUNDThe rotating foam stirrer reactor (RFSR) has shown its high mass transfer efficiency. Nevertheless, its micromixing efficiency, which is one of the significant parameters, still needs more comprehensive study for its better application and optimization. This work therefore employed the iodide–iodate reaction system to analyze the micromixing efficiency in an RFSR, and the effects of reactor configuration and liquid viscosity on micromixing efficiency were investigated.RESULTSThe results show that high micromixing efficiency can be achieved when the feed location is at the outer edge of the rotor. Solid foam with low pores per linear inch (ppi) and equipping baffles on the reactor wall can also considerably improve the micromixing efficiency. The results further reveal that the micromixing efficiency decreased with increasing liquid viscosity. Micromixing times in an RFSR with various configurations, estimated based on the incorporation model, ranged from 2.1 × 10−4 to 2.0 × 10−2 s. The minimum value is smaller than that of many conventional reactors and is competitive with that of some novel reactors. In addition, a correlation to predict the micromixing time based on the average energy dissipation rate was developed, which agreed well with experimental values.CONCLUSIONThis study indicates that the RFSR has excellent micromixing efficiency and also provides fundamental information for optimization of the RFSR and its application in process industries. © 2019 Society of Chemical Industry

Mixing efficiency of a rotor-stator spinning disc extractor

In this work, the mixing efficiency of a rotor-stator spinning disc extractor (RSSDE) is presented. The micromixing efficiency of RSSDE is studied, with the iodide-iodate reaction as working system. The influence of the various operating conditions (e.g. rotational speed, liquid viscosity, volume flow rate, concentration of acid and rotor-stator distance) on micromixing efficiency (characterized by segregation index XS) is investigated. It is found that the XS decreases with the rise of rotational speed, the reduction of rotor-stator distance and the concentration of acid and liquid viscosity. Based on the incorporation model, the estimated micromixing times are in the range of 10−5–10−4 s, which is less than that of other tank mixing and rotating devices. In addition, the residence time of liquid in the rotor-stator cavity is researched to describe the effect of independent variables, like rotational speed, volumetric flow rate, rotor-stator distance, and liquid viscosity, with the help of electrical conductance technique. Besides, the corresponding correlation is also established to predict the residence time. The calculation result shows good coincidence with the experimental data, with a deviation within 20%.

Micromixing efficiency in a rotating packed bed with non-Newtonian fluid

Micromixing performance of reactors has great influence on fast reactions such as polymerization, pharmaceutical and crystallization applications. In this work, based on Villermaux–Dushman iodide–iodate reaction system, an experimental investigation of micromixing with non-Newtonian fluid (CMC solution) in a rotation packed bed (RPB) was carried out. And a two-dimensional RPB Computational Fluid Dynamics (CFD) model coupled with shear-thinning rheological property was developed. Both experimental and numerical results indicated that increasing rotational speed could dramatically improve the micromixing performance due to the shear-thinning behavior in the RPB. Especially, the CMC concentration was an important factor that should be carefully considered, which showed quite different impacts on micromixing efficiency with liquid flow rate. In addition, based on incorporation model and experimental results, the micromixing time of the RPB with non-Newtonian fluid was determined as 4.1 × 10−4 s–1.9 × 10−3 s. This fundamental research had guiding significance for practical operations of RPBs when processing non-Newtonian fluids.

Micromixing performance and the modeling of a confined impinging jet reactor/high speed disperser

In order to get a better micromixing performance, an intensification reactor that couples a confined impinging jet reactor and high speed disperser (CIJR-HSD) was designed. The influences of operating and structural parameters on the micromixing performance were investigated by using the iodide-iodate reaction system. The results showed that the segregation index decreased with the increase of both the rotational speed and the number of rotors; whilst there was little influence due to both inlet flow rate and the presence of packing. The coupling distance between the centre of the CIJR and the first rotor of the HSD also had a non-negligible effect on segregation index. The micromixing time was determined by the Engulfment model, and could also be evaluated by the energy dissipation model based on fluid energy transformation. It was found that the micromixing time for the CIJR-HSD device was in the range of 0.1–0.3 ms, while that for a single CIJR was in the range of 0.35–0.5 ms.

Investigation of micromixing and precipitation process in a rotating packed bed reactor with PTFE packing

A rotating packed bed (RPB) reactor plays an important role in process intensification of micromixing and mass transfer. However, the commonly used stainless steel wire mesh packing suffers from serious corrosion in various chemical processes. Polytetrafluoroethylene (PTFE) material, which is well-known for its excellent anticorrosion property, was employed as packing in the RPB reactor. Micromixing efficiency of the RPB reactor with PTFE packing was studied experimentally by adopting the iodide-iodate reaction system. Results showed that the micromixing efficiency of the RPB reactor with PTFE packing was better than that with the conventional stainless steel wire mesh packing. The micromixing time (tm) was calculated using an incorporation model based on the experimental data. Furthermore, the RPB reactor with PTFE packing was applied to a precipitation process for the preparation of magnesium hydroxide (Mg(OH)2) nanoparticles. The obtained Mg(OH)2 nanoparticles have small size and narrow particle size distribution, which indicates that the RPB reactor with PTFE packing is a promising reactor for preparing small size nanoparticles with its excellent micromixing efficiency.

Flow characteristics and micromixing modeling in a microporous tube-in-tube microchannel reactor by CFD

Micromixing performance in reactor is one of the key factors for fast reaction systems, such as fine chemicals, pharmaceutical and crystallization. In this work, a three-dimensional CFD model was developed for analyzing flow characteristics and micromixing efficiency in microporous tube-in-tube microchannel reactor (MTMCR). PDF transport model based on Lagrangian Monte Carlo method and a modified Finite-rate/Eddy dissipation model were used to build micromixing model, respectively. The effects of Reynolds number and flow ratio on micromixing efficiency were studied using Villermaux–Dushman iodide–iodate reaction system. The segregation index XS is used to quantify the micromixing performance. The results showed that XS decreased with the increasing of Re and the decreasing of flow ratio R, and simulated values agreed well with published experimental data. Based on the modified Finite-rate/Eddy dissipation model, the parallel competing reaction system was analyzed by taking into account mixing-controlled and kinetic-controlled factors, which explained how this model worked. Moreover, porous diameter and width of annular channel were optimized to improve the micromixing efficiency of MTMCR, and the optimal values were 20μm and 250μm, respectively.

Geometrical improvement of inline high shear mixers to intensify micromixing performance

The micromixing performance of two inline high shear mixers (HSMs) was studied using the iodide-iodate reaction system, considering the effects of rotor speeds, flux ratios, viscosities and fluid concentrations. The segregation index (Xs) was adopted to assess the micromixing performance. It is indicated that the value of Xs decreases with the increase of rotor speed and the flux ratio of two feed solutions. The dual rows ultrafine-teethed HSM exhibits the poorer micromixing performance at low rotor speeds, comparing with the single-row blade-screen HSM. Then we modified the geometric configurations of the teethed HSM with the aid of computational fluid dynamics (CFD) analysis, including the modification of the clamp nut with blades and the addition of a liquid distributor, and reevaluated the micromixing performance in the modified HSM in order to improve mixing in the reactor. The results indicate that the fluid dispersion and turbulence intensity in the inlet region of the HSM play an important role in enhancing the micromixing level, the liquid distributor can greatly improve the micromixing performance of the dual rows ultrafine-teethed HSM and the estimated micromixing time can reach 10−5s. The results obtained here will provide much insight for the applications of the inline HSMs and other reactors in the field of intensifying fast chemical reaction.

Micromixing efficiency of a novel helical tube reactor: CFD prediction and experimental characterization

A novel helical tube reactor (HTR) consisting of a pre-mixer and a helical tube was designed for mixing and reaction process intensification. The pre-mixer was used to adjust and change the premixing behavior between the involved reactants, which eventually determines the environment for micromixing. Two types of pre-mixers, co-current flow pre-mixer (CCM) and cross-flow pre-mixer (CRM), were employed and their mixing performance was studied by computational fluid dynamics (CFD) simulations. Results revealed that the CRM has better mixing performance than the CCM, suggesting that the predicted micromixing efficiency of the HTR consisting of the CRM (CRM-HTR) may be better than that comprising the CCM (CCM-HTR). Furthermore, the iodide–iodate reaction system was used separately to characterize the micromixing efficiency of the HTR comprising the different types of pre-mixers, and the results are in agreement with those of CFD which predicted better micromixing performance in the CRM-HTR than the CCM-HTR. Additionally, the effects of feed position and initial dispersion size of acid solution, volumetric flow ratio, and viscosity on micromixing efficiency of the CRM-HTR were investigated. A comparison between the CRM-HTR and a straight tube reactor (CRM-TR) with a length equivalent to that of the CRM-HTR revealed that CRM-HTR has better micromixing efficiency. Moreover, the effects of curvature ratio and number of turns on micromixing efficiency of the CRM-HTR were also conducted. The results demonstrated that the curvature ratio had an important influence on the micromixing. This work shows that the novel CRM-HTR has great potential for chemical reaction process intensification.

Computational Fluid Dynamics Analysis of the Micromixing Efficiency in a Rotating-Packed-Bed Reactor

Micromixing in rotating-packed-bed (RPB) reactors is of great significance for their process-intensifying performance. On the basis of the iodide–iodate reaction system, a two-dimensional computational framework of RPB was developed to investigate the micromixing efficiency in a RPB. The volume-of-fluid multiphase model, laminar finite-rate model, and the Reynolds stress model were adopted to simulate the volumetric fraction of the liquid phase, the concentration distributions, and the effects of rotating speed and liquid flow velocity on the micromixing performance of a RPB. The computational fluid dynamics results showed that the micromixing and reaction processes occurred mainly in the inlet region of RPB packing, which further confirmed the end effect of the packing. An increase of the rotating speed and liquid flow velocity could remarkably enhance the micromixing efficiency in a RPB. On the basis of the incorporation model, the micromixing time in a RPB was estimated as 0.05−0.30 ms, indicating a re...

The influence of feeding location on the micromixing performance of novel large-double-blade impeller

The large-double-blade impeller has a broad application prospects in rapid reactions of viscous systems. In syrup aqueous solution with viscosity of 0.8 Pa s, the influence of feeding location on the micromixing performance of the novel large-double-blade impeller was studied experimentally by adopting the iodide–iodate reaction system, and the distribution of energy dissipation rate in the stirring vessel was obtained by numerical simulation method for the micromixing based on standard E model and eddy-dissipation-concept (EDC) model. The results of simulation agreed well with the experimental data, both of which showed that the feeding location has an important effect on the micromixing performance. Feeding in the blade area is more favorable to reducing by-products and improving micromixing quality than in other areas under the same conditions for its comparatively large local energy dissipation rate. These results provide useful guidelines for the optimal design and operation of the novel large-double-blade impeller in rapid reactions of viscous system.

Micromixing Efficiency Enhancement in a Rotating Packed Bed Reactor with Surface-Modified Nickel Foam Packing

Micromixing, the mixing at the molecular scale, is believed to play a substantial role in many industrial processes. In this work, a novel surface-modified nickel foam packing (SNP) loaded in a rotating packed bed (RPB) reactor was first proposed to improve the micromixing efficiency studied by adopting the iodide–iodate reaction as a working system. Experimental results showed that the RPB reactor with the SNP presented better micromixing efficiency, compared to the RPB reactor with the nonmodified nickel foam packing (NNP) or traditional stainless steel wire mesh packing (SWP). It could be found that the segregation index (XS) decreased as the rotational speed and liquid flow rate each increased, while it increased with increasing acid concentration and volumetric ratio. Moreover, the micromixing time (tm) was calculated using an incorporation model based on the experimental data. Compared with NNP or SWP, the minimum tm value of SNP (tm = 3.28 ms) is less than that of NNP (tm = 5.68 ms) or SWP (tm = 8....

Micromixing characteristics in a gas–liquid–solid stirred tank with settling particles

The parallel-competing iodide–iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3m diameter. The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils, identified as HEDT+2WHD. Nitrogen and glass beads of 100μm diameter and density 2500kg·m−3 were used as the dispersed phases. The micromixing could be improved by sparging gas because of its additional potential energy. Also, micromixing could be improved by the solid particles with high kinetic energy near the impeller tip. In a gas–solid–liquid system, the gas–liquid film vibration with damping, due to the frequent collisions between the bubbles and particles, led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing. A Damping Film Dissipation model is formulated to shed light on the above micromixing performances. At last, the micromixing time tm according to the incorporation model varied from 1.9ms to 6.7ms in our experiments.

Micromixing efficiency in a T-shaped confined impinging jet reactor

Confined impinging jet reactor (CIJR) offers advantages for chemical rapid processes and has become an important new reactor used in the chemical industry. The micromixing efficiency in a T-shaped CIJR for two tubes of inner diameter of 3mm was studied by using a parallel competing iodide–iodate reaction as the working system. In this work, the effects of different operating conditions, such as impinging velocity and acid concentration, on segregation index were investigated. In addition, the effects of the inner nozzles diameter and the distance L between the jet axis and the top wall of the mixing chamber on the micromixing efficiency were also considered. It is concluded that the best range of L in this CIJR is 6.5–12.5mm. Based on the incorporation model, the estimated minimum micromixing time tm of CIJR approximately equals to 2×10−4s. These experimental results indicate clearly that CIJR possesses a much better micromixing performance compared with the conventional stirred tank (micromixing time of 2×10−3 to 2×10−2s). Hence, it can be envisioned that CIJR has more promising applications in various industrial processes.