Assessing mixing uniformity in microreactors via in-line spectroscopy

Mixing behavior is critical for enhancing the selectivity of fast chemical reactions in microreactors.A high Reynolds number(Re)improves the mixing rate and selectivity of the reactions,but some exceptions of increasing side product yield with the higher Re have been reported.This study investigated the mixing uniformity in microreactors with in-line UV-vis spectroscopy to clarify the relationship between reaction selectivity and chaotic mixing with the higher Re.A colorization experiment of thymolphthalein in an acidic solution was conducted with an excess acid amount to the base to indicate a non-uniformly mixed region.Non-uniformity significantly increased with Re.At the same time,the degree of mixing,which was measured by a usual decolorization experiment,showed that the mixing rate increased with Re.The in-line analysis of the Villermaux-Dushman reaction during the mixing clarified that side product yield significantly increased with Re at around 300 and then decreased at around 1100.These results suggest the compensation effect between the mixing uniformity and mixing rate on the selectivity of the mixing-sensitive reactions.Faster mixing,characterized by a larger Re,can disturb mixing uniformity and,in some cases,decrease reaction selectivity.

Enhancement of liquid-liquid micromixing performance in curved capillary microreactor by generation of Dean vortices

Micromixing efficiency is an important parameter for evaluating the multiphase mass transfer performance and reaction efficiency of microreactors.In this work,the novel curved capillary reactor with different shapes was designed to generate Dean flow,which was used to enhance the liquid-liquid micromixing performance.The Villermaux-Dushman probe reaction was employed to characterize the micromixing performance in different curved capillary microreactors.The effects of experiment parameters such as liquid flow rate,inner diameter,tube length,and curve diameter on micromixing performance were systematically investigated.Under the optimal conditions,the minimum value of the segmentation factor XS was 0.008.It was worth noting that at the low Reynolds number(Re<30),the change of curved shape on the capillary microreactor can significantly improve the micromixing performance with XS reduced by 37.5%.Further,the correlations of segment index XS with dimensionless factor such as Reynolds number or Dean number were developed,which can be used to predict the liquid-liquid micromixing performance in capillary microreactors.

An efficient microreactor with continuous serially connected micromixers for the synthesis of superparamagnetic magnetite nanoparticles

A new microreactor with continuous serially connected micromixers(CSCM)was tailored for the coprecipitation process to synthesize Fe_(3)O_(4) nanoparticles.Numerical simulation reveals that the two types of CSCM microchannels(V-typed and U-typed)proposed in this work exhibited markedly better mixing performances than the Zigzag and capillary microchannels due to the promotion of Dean vortices.Complete mixing was achieved in the V-typed microchannel in 2.7 s at an inlet Reynolds number of 27.Fe_(3)O_(4) nanoparticles synthesized in a planar glass microreactor with the V-typed microchannel,possessing an average size of 9.3 nm and exhibiting superparamagnetism,had obviously better dispersity and uniformity and higher crystallinity than those obtained in the capillary microreactor.The new CSCM microreactor developed in this work can act as a potent device to intensify the synthesis of similar inorganic nanoparticles via multistep chemical precipitation processes.

Kinetics measurement of ethylene-carbonate synthesis via a fast transesterification by microreactors

High-purity ethylene carbonate(EC)is widely used as battery electrolyte,polycarbonate monomer,organic intermediate,and so on.An economical and sustainable route to synthesize high-purity ethylene carbonate(EC)via the transesterification of dimethyl carbonate(DMC)with ethylene glycol(EG)is provided in this work.However,this reaction is so fast that the reaction kinetics,which is essential for the industrial design,is hard to get by the traditional measuring method.In this work,an easy-to-assemble microreactor was used to precisely determine the reaction kinetics for the fast transesterification of DMC with EG using sodium methoxide as catalyst.The effects of flow rate,microreactor diameter,catalyst concentration,reaction temperature,and reactant molar ratio were investigated.An activity-based pseudohomogeneous kinetic model,which considered the non-ideal properties of reaction system,was established to describe the transesterification of DMC with EG.Detailed kinetics data were collected in the first 5 min.Using these data,the parameters of the kinetic model were correlated with the maximum average error of 11.19%.Using this kinetic model,the kinetic data at different catalyst concentrations and reactant molar ratios were predicted with the maximum average error of 13.68%,suggesting its satisfactory prediction performance.

Study of Macro-Mixing in a Microreactor

The transfer rate between fluids in a microreactor is directly influenced by the mixing within the reactor, which subsequently impacts the reaction rate. This paper investigates the flow behavior and macro-mixing performance in a microreactor. First, the flow performance of the Ehrfeld Miprowa microreactor is studied. Cold experiments are conducted to examine fundamental flow laws and verify the accuracy of the chosen computational fluid dynamics simulation model.Subsequently, macro-mixing performance in the microreactor, both with and without internal components, is investigated through both experiment and simulation. A bromocresol violet–NaOH–H2SO4 system is utilized in the macro-mixing experiments, which explore the effects of flow rate and internal components on macro-mixing. The Navier–Stokes equation is adopted as the computational model for macro-mixing simulations, which also consider the mass transfer and diffusion of tracer. The simulation results are in good agreement with the experimental results. Both experimental and simulation results demonstrate that the presence of internal components in the microreactor enhance its macro-mixing performance.

Gas–liquid flow mass transfer in a T-shape microreactor stimulated with 1.7 MHz ultrasound waves

This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas–liquid flow in a T-shape microreactor with a diameter of 800 μm. A 1.7 MHz piezoelectric transducer(PZT) was employed to induce the vibration in this microreactor. Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO_2 absorption into water and Na OH solution. The approach of absorption of CO_2 into a 1 mol·L^(-1) Na OH solution was used for analysis of interfacial areas. With the help of a photography system, the fluid flow patterns inside the microreactor were analyzed. The effects of superficial liquid velocity, initial concentration of Na OH, superficial CO_2 gas velocity and length of microreactor on the mass transfer rate were investigated. The comparison between sonicated and plain microreactors(microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on kLa and interfacial area at various operational conditions. For the microreactor length of 12 cm, ultrasound waves improved kLa and interfacial area about 21% and 22%, respectively. From this study, it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate. This study suggests a new enhancement technique to establish high interfacial area and kLa in microreactors.

Microreactor for the Catalytic Partial Oxidation of Methane

Fixed-bed reactors for the partial oxidation of methane to produce synthetic gas still pose hotspot problems. An alternative reactor, which is known as the shell-and-tube-typed microreactor, has been developed to resolve these problems. The microreactor consists of a 1 cm outside-diameter, 0.8 cm insidediameter and 11 cm length tube, and a 1.8 cm inside-diameter shell. The tube is made of dense alumina and the shell is made of quartz. Two different methods dip and spray coating were performed to line the tube side with the LaNixOy catalyst. Combustion and reforming reactions take place simultaneously in this reactor. Methane is oxidized in the tube side to produce flue gases （CO2 and H2O） which flow counter-currently and react with the remaining methane in the shell side to yield synthesis gas. The methane conversion using the higher-loading catalyst spray-coated tube reaches 97% at 700 ℃, whereas that using the lower-loading catalyst dip-coated tube reaches only 7.78% because of poor adhesion between the catalyst film and the alumina support. The turnover frequencies （TOFs） using the catalyst spray-and dip-coated tubes are 5.75×10^-5 and 2.24×10^-5 mol/gcat· s, respectively. The catalyst spray-coated at 900 ℃ provides better performance than that at 1250 ℃ because sintering reduces the surface-area. The hydrogen to carbon monoxide ratio produced by the spray-coated catalyst is greater than the stoichiometric ratio, which is caused by carbon deposition through methane cracking or the Boudouard reaction.

Gas-liquid-liquid slug flow and mass transfer in hydrophilic and hydrophobic microreactors

Gas-liquid-liquid three-phase slug flow was generated in both hydrophilic and hydrophobic microreactors with double T-junctions.The bubble-droplet relative movement and the local mass transfer within the continuous slug and the dispersed droplet were investigated.It was found that bubbles moved faster than droplets under low capillary number(Ca),while droplets moved faster upon the increase of Ca due to the increased inertia.For the first time,we observed that the increased viscosity of droplets fastened the droplet movement.The mass transfer in the continuous slug was dominated by convection,leading to nearly constant global mass transfer coefficient(k_(L)a);while that in the dispersed droplet was dominated by diffusion,resulting in k_(L) decreasing along the channel.Such features are analogical to the corresponding gas-liquid or liquid-liquid two-phase slug flow,but the formation of bubble-droplet clusters caused by relative movement lowered the absolute mass transfer coefficient.These results provide insights for the precise manipulation of gas-liquid-liquid slug flow in microreactors towards process optimization.

Integrated UV-based photo microreactor-distillation technology toward process intensification of continuous ultra-high-purity electronic-grade silicon tetrachloride manufacture

Ultra-high-purity silicon tetrachloride(SiCl4)is demanded as an electronic-grade chemical to meet the stringent requirements of the rapidly developing semiconductor industry.The high requirement for ultra-high-purity SiCl4 has created the need for a high-efficient process for reducing energy consumption as well as satisfying product quality.In this paper,a mass of production technology of ultra-high-purity SiCl4 was successfully developed through chlorination reaction in the ultraviolet(UV)-based photo microreactor coupled with the distillation process.The influences of key operational parameters,including temperature,pressure,UV wavelength and light intensity on the product quality,especially for hydrogen-containing impurities,were quantified by the infrared transmittance of Fourier transform infrared spectroscopy(FT-IR)at 2185 cm^-1and 2160 cm^-1indicating that chara cteristic vib rational modes of Si-H bonds,as well as the operating conditions of distillation were also investigated as key factors for metal impurities removing.The advanced intensification of SiCl4 manufactured by the integration of photo microreactor and distillation achieves the products with superior specifications higher than the standard commercial products.

Conceptual design and neutronic analysis of a megawatt-level vehicular microreactor based on TRISO fuel particles and S-CO_(2) direct power generation

With global warming,the demand for diversified energy sources has increased significantly.Transportable microreactors are important potential supplements to the global power market and are a promising development direction.This paper describes a 5 MW integrated long-life S-CO_(2)cooled vehicular microreactor(VMR)design based on tristructural isotropic(TRISO)fuel particles that aims to provide electricity for industrial power facilities,remote mines,and remote mountainous areas that are not connected to central power grids.First,to facilitate transportation,flexible deployment,and simplified operation and maintenance requirements,the VMR core and auxiliary system were designed to be reasonably small and as simple as possible.Second,the TRISO fuel particles used in the proposed VMR offer excellent properties,such as high inherent security and nonproliferation,which are vital for reactors in remote areas.In addition,a long core lifetime was achieved using the compact core design and enhanced fuel loading capacity,which is challenging when using TRISO as fuel.Finally,to make the VMR economically competitive in terms of improved neutron performance and fuel efficiency compared to similar designs,large-size TRISO particles and tube-in-duct fuel assembly were utilized and different core configurations were schemed and simulated to obtain the design that best satisfied the proposed criteria.The lifetime and burnup in the final optimized VMR were satisfactory at 21 years and43.9 MWd/kgU,respectively,with an adequate shutdown margin and excellent safety parameters to ensure safe operation.

Hydrogenation Behavior of Hydrogen Peroxide in a Microreactor

The hydrogenation of hydrogen peroxide is an unwanted side reaction in the direct synthesis of hydrogen peroxide and remains a problem to solve.The mechanism of this reaction has been studied with batch reactors but the slow heat and mass transfer in batch reactors hindered the understanding of its intrinsic kinetics.In this study,a microreactor is employed to investigate the parameters that influence the hydrogenation reaction,including flow rate,channel length,hydrogen pressure,solvent composition,and initial hydrogen peroxide concentration.The activity of different catalysts was compared and the hydrogenation law was confirmed,providing guiding information to better control the hydrogenation process.

Study on Performance of Laminated Porous Metal Fiber Sintered Felt as Catalyst Support for Methanol Steam Reforming Microreactor

In this study, the laminated porous metal fiber sintered felt(PMFSF) functioning as catalyst support was used in a cylindrical methanol steam reforming(MSR) microreactor for hydrogen production. The PMFSF was fabricated by the low temperature solid-phase sintering method using metal fibers such as copper fibers and aluminum fibers which are obtained by the multi-tooth cutting method. The two-layer impregnation method was employed to coat Cu/Zn/Al/Zr catalyst on the PMFSF. The effect of fiber material, uniform porosity and gradient porosity on the performance of methano steam reforming microreactor was studied by varying the gas hourly space velocity(GHSV) and reaction temperature. Our results showed that the loading strength of porous copper fiber sintered felt(PCFSF) was better than porous aluminum fiber sintered felt(PAFSF). Under the same reaction conditions, the PCFSF showed higher methanol conversion and more H_2 output than PAFSF. Moreover, the gradient porosity(Type 5: 90%×80%×70%) of PMFSF used as the catalyst support in microreactor demonstrated a best reaction performance for hydrogen production.

High-efficiency and safe synthesis of tonalid via two Friedel-Crafts reactions in continuous-flow microreactors

Tonalid,an important fragrance ingredient with widespread applicatio n,was synthesized via two FriedelCrafts reactions,which were catalyzed by AlCl_(3).The traditional tonalid production was conducted in batch stirring tank reactors,suffering from low production capacity and the safety hazard of temperature runaway.To solve these problems,the continuous-flow technologies were developed for the highefficiency and intrinsically safe synthesis of tonalid in microreactors.Catalyst AlCl_(3)was neatly homogenized in proper solvents by forming complex with reactant,which was a necessary step for the continuous synthesis in microreactors.Several reaction conditions,including reactant molar ratio,catalyst concentration,temperature,and microchannel hydrodynamic diameter,were investigated for the two Friedel-Crafts reactions in micro reactors.At optimized conditions,the yields of the two Friedel-Crafts reactions were 44.15%and 97.55%,respectively.In comparison with the batch reactors,the reaction times of these two reactions could both be reduced by nearly two thirds in microreactors at the similar yield.

Computational fluid dynamics simulation and experimental study on mixing performance of a three-dimensional circular cyclone-type microreactor

Microchannels enable the fast and efficient mixing of multiphase fluids.In this study, a millimeter-scale three-dimensional(3D) circular cyclone-type microreactor was designed for the mixing.The flow characteristics and mixing intensity were simulated by computational fluid dynamics simulations at a flow rate range of 12–96 m L/min using a water/ethyl acetate system.In the 3D variable-diameter structure,the microreactor induced paired opposite vortices and abruptly changed the local pressure to achieve a stable turbulent effect within the theoretical range of laminar flow.Tracer injection simulations indicated that sufficient mixing units successfully promote fluid dispersion.Diazo-coupling experiments showed a segregation index of X_S= 0.00,039 within a residence time of 9 s.Extraction experiments on the nbutanol/succinic acid/water system showed that the 3D circular cyclone-type microreactor achieved 100%extraction efficiency(E) in 4.25 s, and the overall volume mass transfer coefficient(K_La) reached 0.05–1.5s^(-1) in 12–96 m L/min.The isolated yield of the phase transfer alkylation and oxidation reactions in the 3D circular cyclone-type microreactor achieved 99% within 36 s, which was superior to the coil microreactor and batch reactor.

Two-step continuous flow process of sodium tanshinone ⅡA sulfonate using a 3D circular cyclone-type microreactor

A sustainable and practical process is presented for the direct synthesis of sodium tanshinone IIA sulfonate(STS).Our approach was inspired by the well-established and industrially applied batch synthetic route for STS production.We constructed a telescoped two-step continuous flow platform.This involved a continuous tanshinone IIA sulfonation and in-line salt formation.For the setup,we constructed a 3D circular cyclone-type microreactor using femtosecond laser micromachining.Compared to the 68%yield for 2 h in batch,the two-step continuous flow had an STS yield of 90%,achieved for a total residence time of<3.0 min under optimal conditions.The proposed continuous flow method vastly simplified the operation and improved procedural safety,while significantly reducing the required acid content and wastewater production.

Continuous synthesis of dolutegravir sodium crystals using liquid-gas heterogeneous microreactor

In this work, a liquid-gas heterogeneous microreactor was developed for investigating continuous crystallization of dolutegravir sodium(DTG), as well as revealing reaction kinetics and mixing mechanism with 3-min data acquisition. The reaction kinetics models were established by visually recording the concentration variation of reactants over time in the microchannel via adding pH-sensitive fluorescent dye. The mixing intensification mechanism of liquid-gas flow was quantified through the fluorescent signal to indicate mixing process, demonstrating an outstanding mixing performance with a mixing time less than 0.1 s. Compared with batch crystallization, continuous synthesis of dolutegravir sodium using liquid-gas heterogenous microreactor optimizes crystal distribution size, and successfully modifies the crystal morphology in needle-like habit instead of rod-like habit. The microreactor continuous crystallization can run for 5 h without crystal blockage and achieve D90 of DTG less than 30 μm. This work provides a feasible approach for continuously synthesizing dolutegravir sodium, and can optimize the existing pharmaceutical crystallization.

基于温度原位监测的微反应器在HNS微流道制备过程中的应用

针对含能材料微流道制备过程中缺乏温度原位监测手段的问题,提出一种集成薄膜温度传感器的微反应器系统;微反应器由包含薄膜温度传感器的玻璃基片与包含微流道的硅基片键合组成;微流道的上游、中游、下游分别放置了3个温度传感器,以实现微反应过程中高空间分辨率的温度测量;基于该微反应器,搭建了六硝基茋(HNS)连续化微流道制备系统,实时监测了HNS微纳米化及球形化过程中的温度变化。结果表明,微反应器具有精度高、耐腐蚀、可观测的优点;HNS微纳米化是一个放热反应,流体最大温升为6.4℃,由于HNS的逐渐析出,流体中的固体含量增大,流速变慢,流体温度的分布发生变化;在HNS球形化过程中,两相流体的混合是一个放热过程,流体最大温升为2.3℃;微流道中游处的温度明显高于上游与下游,说明当液滴流动至中游时,HNS微球已经制备完成。

CTAB/SDBS水基囊泡相磁流体制备及稳定性研究

以阳离子表面活性剂十六烷基三甲基溴化胺(CTAB)和阴离子表面活性剂十二烷基苯磺酸钠(SDBS)为原料复配自发形成囊泡相,并以其为微反应器,Fe^(2+)和Fe^(3+)在囊泡内发生反应,得到平均粒径为20m的Fe_(3)O_(4)纳米晶囊泡分散液作为水基磁流体。采用广角X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电镜(TEM)、扫描电镜(SEM)、磁滞回线(VSM)等对合成的Fe_(3)O_(4)纳米晶以及磁流体进行分析表征。结果表明,以合适的阴阳离子表面活性剂获得的囊泡相为微反应器形成的水基囊泡相磁流体,在室温稳定性优良,静置60h其稳定性系数仍然可达97%。在磁场反复作用后,囊泡相水基磁流体仍具有良好的稳定性,其中的Fe_(3)O_(4)纳米粒子颗粒均匀,具有超顺磁性特征,磁饱和度达到59emu/g。

Layer-by-layer fabrication of montmorillonite coating immobilizing Cu_(2)O nanoparticles for continuously catalyzing glycerol to dihydroxyacetone

Microreactors are increasingly used for green and safe chemical processes owing to their benefits of superior mass and heat transfer,increased yield,safety,and simplicity of control.However,immobilizing catalysts in microreactors remains challenging.In this investigation,a technique for creating Cu_(2)O/montmorillonite catalyst coating,using electrostatic attraction for layer-by-layer self-assembly,was proposed.The montmorillonite film's morphology and thickness could be efficiently regulated by adjusting the degree of exfoliation and surface charge of montmorillonite,alongside layer-by-layer coating times.The Cu_(2)O nanoparticles were immobilized using the flow deposition approach.The resulting Cu_(2)O@montmorillonite-film-coated capillary microreactor successfully transformed glycerol into dihydroxyacetone.The conversion of glycerol and product selectivity could be controlled by adjusting the molar ratio of reactants,temperature,residence time,and Cu_(2)O loading.The maximum glycerol conversion observed was 47.6%,with a 27%selectivity toward dihydroxyacetone.The study presents a technique for immobilizing montmorillonite-based catalyst coatings in capillary tubing,which can serve as a foundation for the future application of microreactors in glycerol conversion.

微反应器内环酯类锂电池添加剂合成研究进展

锂电池电解液添加剂是一类在锂电池中用量不大,但对改善锂电池高低温性能,提高使用寿命和循环次数等方面发挥重要作用的高附加值电子化学品。随着锂电池等下游应用长期向好地发展,添加剂的需求量不断增长,但传统的釜式反应器由于传递性能不佳导致产品质量稳定性较差且污染严重。微反应器在微米尺度对流体有着高效分散和混合的优势,能显著提高生产效率、降低生产成本,在锂电池添加剂合成方面受到越来越广泛的关注。本文结合微反应器优异的传递性能,系统综述了微反应器在环酯类锂离子电池电解液添加剂合成中的应用进展,并对添加剂的微化工合成领域的研究方向进行了展望。