Microchemical Processes Research Articles

Study on liquid–liquid two-phase mass transfer characteristics in the microchannel with deformed insert

In this work, the liquid–liquid two-phase mass transfer characteristics in the microchannel with deformed insert were studied. The experiment used di-(2-ethylhexyl) phosphoric acid/kerosene-Cu 2+ as the mass transfer evaluation system. The effects of some key factors such as the total flow velocity, channel inner diameter, channel length, insert diameter, extractant concentration on the extraction efficiency and mass transfer coefficient were systematically investigated. Compared with a simple microreactor, the liquid–liquid mass transfer enhancement effect of the insert was quantitatively analyzed. The study found that the regular deformation of insert could cause fluid interface deformation and promote flow state chaos, effectively increasing the mass transfer rate. And the enhancement effect of the insert was more significant at high flow velocities. The highest mass transfer coefficient in the microchannel with deformed insert was 7.886 s –1 , the enhancement factor could reach 4.17. And only needed 0.095 s to approach the extraction equilibrium. The deformed center insert exhibited an effective liquid–liquid mass transfer enhancement effect, which can be used as a micro-chemical process enhancement method to be applied in the fields of higher throughput mass transfer and chemical synthesis, and at the same time provide ideas for development and structural optimization of microreactors.

Microdispersion of Gas or Water in an Anthraquinone Working Solution for the H2O2 Synthesis Process Intensification

The Reidl–Pfleiderer process intensification for H2O2 synthesis is urgently required. Microdispersion technique is becoming one of the highest promising ways, but the microdispersion rules of gas or liquid in the anthraquinone working solution have not been mentioned until now. This study employs an observation platform to investigate the microdispersion performances of hydrogen, oxygen, or water in the anthraquinone working solution to provide reliable data for developing new microchemical processes. The influence of two-phase flow rate, viscosity, and channel size on bubble size in a circular microchannel was studied. A specific surface area higher than 20 000 m2/m3 was obtained when the channel size was 150 μm. A unified mathematical prediction model for the gas–liquid and liquid–liquid microdispersion was developed, and it can be used for the future practical industrial system process intensification.

Liquid-liquid dispersion and flow characteristics in a miniaturized annular rotating device

Liquid-liquid microchemical processes suffer from the problems of small handling capacity and large pressure drops. In particular, process intensification is highly required for high phase ratios of the dispersion phase to the continuous phase and high- viscosity conditions. In this study, we reported a novel microdispersion device named miniaturized annular rotating device (m-ARD), which is a novel microdispersion device with a large handling capacity, small pressure drop, and relatively narrow droplet distribution, even at a low phase ratio of the continuous phase to the dispersion phase and under high-viscosity conditions. Various parameters were studied to determine the dispersion of the generated droplets and the flow pattern, average droplet diameter, pressure drop, and hold-up of the dispersion phase. Two typical droplet generation routes, namely, dripping and jetting, and typical flow patterns, i.e., helical and annular flows were also obtained. Transition maps of the droplet generation route and flow pattern were constructed. The average droplet diameter and handling capacity were up to 380 μm and 30 mL/min, respectively. A small pressure drop was observed in the m-ARD. Furthermore, two dimensionless equations were developed to calculate the average droplet diameter and hold-up of the dispersion phase. This work provides a promising dispersion technology for the process intensification of liquid–liquid mass transfer and reactions.

Kinetics of microwave liquid-phase desorption with chemical dissociation: SO2 desorption of basic aluminum sulfate desulfurization rich liquid

BackgroundReaction kinetics was an important tool for quantitative expression of micro-chemical processes. In this study, a kinetic evaluation method of microwave liquid-phase desorption mechanism was established, which was of great value to reveal the non-thermal effect of microwave desorption. MethodsDesorption kinetics of basic aluminum sulfate (aluminum base) desulfurization rich liquid were monitored with a microwave simultaneous cooling system. The effect of microwave power on its chemical reaction was investigated by linear and nonlinear regression analysis. Significant findingsThe kinetic analysis showed that the pre-exponential factor and activation energy decreased with the increase of microwave power, and the dependence on microwave power was more consistent with the first-order linear model and the second-order polynomial model. At the same temperature, the microwave desorption rate was 1.3–2.6 times that of water bath thermal desorption. At the same desorption reaction rate, the microwave desorption temperature was 10 K–20 K lower than that of thermal desorption. Compared with thermal desorption, although the reaction order did not change under different microwave power, the pre-exponential factor and activation energy decreased, and the reaction rate constant was about 1.1–2.1 times that of the same temperature.

Interfacial evolution and dynamics of liquid bridge during droplet coalescence in rectangular microchannels: Effect of aspect ratio

BackgroundDroplet coalescence in rectangular microchannel is universally applied in microchemical process, however, the effect of aspect ratio on interfacial evolution and dynamics of coalesced droplets has not yet been elucidated. MethodsProcess of coalescence in microchannels with different aspect ratios was recorded by visualization technology, and the interfacial evolution of liquid bridge was investigated experimentally. FindingsThe evolution of neck width could be divided into two stages: dispersed phase controlling stage and continuous phase controlling stage, and the neck evolution conforms to power law in the both two stages. However, the exponents in the two stages are different under various flow rate ratios of two phases and aspect ratios of rectangular microchannels. There exists a turning point between the two stages. The neck width at turning point increases linearly with the two-phase flow rate ratio, and the arrival time of turning point decreases exponentially with the increase of flow rate ratio.

Design and evaluation of a 3D multi-manifold micromixer realized by a double-Archimedes-screw for rapid mixing within a short distance

Recent developments in 3D micromixers promise to accomplish satisfactory mixing for applications in microchemical process, biomicrofluidic analyses, μ-TAS, etc. However, the complicated 3D architecture employed to ensure thorough mixing might reduce fluid circulation due to the space for fluid flowing becomes narrow. In this study, we developed a single 3D multi-manifold micromixer composed of a double-Archimedes-screw for rapidly mixing within a short distance. Archimedes screw is well known for its fluid circulation under stable flow. The mixing strategy is based on split-and-recombination for increasing the interfacial area, and the 3D flow rotation for generating omnidirectional momentum-changes during the fluid propagation. With the spiral conformation, the Archimedes-screw micromixer (ASM) can substantially enhance fluid circulation. Numerical simulations used to help to design the optimal screw-turn show that satisfactory mixing efficiency can achieve at the distance of approximately twice the microchannel width. The ASM characteristics, such as pressure loss, ratio of cross-sections, and Reynolds number (Re) were evaluated. Experimental demonstration by an ASM fabricated by two-photon stereolithography showed mixing result in good agreement with the simulation findings.

Separation of nanoparticles via surfing on chemical wavefronts.

The separation of micro and nanoscale colloids is a necessary step in most biological microassay techniques, and is a common practice in microchemical processing. Chemical waves are frequently encountered in biochemical systems driven far from equilibrium. Here, we put forward a strategy for separating small suspending colloids by means of their surfing on substrate chemical wavefronts. The colloids with catalytic activities sensitive to the substrates are activated to show self-propulsion and consequently exhibit a chemotactic response to the traveling wavefronts, which results in their spontaneous separation from the multicomponent complex mixture via self-diffusiophoresis. The dynamics of the process is analyzed through a particle-based simulation. In addition, it is found that separation can be carried out according to particle size. The mechanisms underpinning the chemical and physical separation processes are discussed, and the dependencies on the reaction rate constant and particle size are presented. The results may prove relevant for further experimental and theoretical studies of separation in complex active environments.

Highly mono-dispersed liquid crystal capsules with core–shell structure

Microfluidics have driven innovations in various fields including biology, soft-matter, and micro-chemical processes. Microfluidic systems provide a unique research environment for micro-scale liquid droplets. Especially encapsulated liquid crystal (LC) droplet fabrication, which can provide a considerable advancement for the relevant fundamental study and applications. We demonstrate the fabrication of uniform sized LC droplets using a microfluidic device system with a T-shaped junction micro-channel. The droplet size can be controlled by changing the flow rate of two immiscible fluids. Also, by adjusting the device’s geometrical structure, a desired droplet size can be obtained. The principle of generation of the droplet and the factors that determine the size of the droplet are theoretically briefly explained. These produced LC droplets were encapsulated by the complex coacervation method. The thickness of the fabricated capsule shell was about 1 μm. The texture transition of the encapsulated mono-dispersed droplets driven by in-plane field shows their potential for various applications, such as various fields of display and biotechnology.

An easily fabricated three-dimensional threaded lemniscate-shaped micromixer for a wide range of flow rates.

Mixing fluid samples or reactants is a paramount function in the fields of micro total analysis system (μTAS) and microchemical processing. However, rapid and efficient fluid mixing is difficult to achieve inside microchannels because of the difficulty of diffusive mass transfer in the laminar regime of the typical microfluidic flows. It has been well recorded that the mixing efficiency can be boosted by migrating from two-dimensional (2D) to three-dimensional (3D) geometries. Although several 3D chaotic mixers have been designed, most of them offer a high mixing efficiency only in a very limited range of Reynolds numbers (Re). In this work, we developed a 3D fine-threaded lemniscate-shaped micromixer whose maximum numerical and empirical efficiency is around 97% and 93%, respectively, and maintains its high performance (i.e., >90%) over a wide range of 1 < Re < 1000 which meets the requirements of both the μTAS and microchemical process applications. The 3D micromixer was designed based on two distinct mixing strategies, namely, the inducing of chaotic advection by the presence of Dean flow and diffusive mixing through thread-like grooves around the curved body of the mixers. First, a set of numerical simulations was performed to study the physics of the flow and to determine the essential geometrical parameters of the mixers. Second, a simple and cost-effective method was exploited to fabricate the convoluted structure of the micromixers through the removal of a 3D-printed wax structure from a block of cured polydimethylsiloxane. Finally, the fabricated mixers with different threads were tested using a fluorescent microscope demonstrating a good agreement with the results of the numerical simulation. We envisage that the strategy used in this work would expand the scope of the micromixer technology by broadening the range of efficient working flow rate and providing an easy way to the fabrication of 3D convoluted microstructures.

Validation of daily increments and a marine‐entry check in the otoliths of sockeye salmon Oncorhynchus nerka post‐smolts

Juvenile sockeye salmon Oncorhynchus nerka that were reared and smolted in laboratory conditions were found to produce otolith daily increments, as well as a consistently visible marine-entry check formed during their transition to salt water. Field-collected O. nerka post-smolts of an equivalent age also displayed visible checks; however, microchemistry estimates of marine-entry date using Sr:Ca ratios differed from visual estimates by c. 9 days suggesting that microstructural and microchemical processes occur on different time scales.

Chinese archaeological artefacts: Microstructure and corrosion behaviour of high-leaded bronzes

Metallographic features of ancient bronze artefacts often hide peculiar micro-chemical processes and corrosion behaviours, which are worth to be studied as they can provide conservators and archaeologists with valuable tools and information. It is widely documented that Chinese bronzes were cast and the way to adjust their properties was to change the alloy composition. In particular, addition of lead, which is insoluble in the bronze matrix, results in the formation of inclusions or globules, which undergo oxidation processes leading to their conversion into corrosion products. The mechanisms through which this occurs were still poorly investigated. The present work was conducted to further study the corrosion behaviour of high-leaded bronze, especially focusing on the behaviour of lead globules. To this aim, a collection of Chinese archaeological bronzes, showing intermediate steps of degradation, were selected and investigated. The use of combined microscopy-based, molecular and elemental, analytical techniques allowed the characterization as well as the precise location of corrosion products, thus enabling us to propose a degradation pathway basing on thermodynamic data provided by Pourbaix diagram. The achieved results will be useful for researchers involved in these kinds of studies to better interpret data obtained.

Transport Phenomena in Chaotic Laminar Flows

In many important chemical processes, the laminar flow regime is inescapable and defines the performance of reactors, separators, and analytical instruments. In the emerging field of microchemical process or lab-on-a-chip, this constraint is particularly rigid. Here, we review developments in the use of chaotic laminar flows to improve common transport processes in this regime. We focus on four: mixing, interfacial transfer, axial dispersion, and spatial sampling. Our coverage demonstrates the potential for chaos to improve these processes if implemented appropriately. Throughout, we emphasize the usefulness of familiar theoretical models of transport for processes occurring in chaotic flows. Finally, we point out open challenges and opportunities in the field.

Development of multistage distillation in a microfluidic chip

Although there has been a lot of work on the development of microchemical processing systems such as micro-reactors and micro-sensors, little attention has been paid to micro-separation units, and in particular, microscale distillation. In this paper, various silicon-glass microscale distillation chips with different channel configurations were fabricated and tested. A temperature gradient was setup across the chip by heating and cooling the two ends. The feed was located at the middle of the microchannel. Arrays of micropillars were incorporated in order to guide the liquid flow. It was found that the separation performance was promoted by increasing the length of the microchannel. However, this created an imbalance of the liquid flows at the two sides of the microchannel and caused flooding. This hydrodynamic limitation was addressed by incorporating micropillars on both sides of the channel. The most efficient microdistillation chip consisted of a microchannel with 600 microns width and 40 cm length. Experimental results showed high efficiency for the separation of a 50 mol% acetone-water mixture when the heating and cooling temperature were 95 °C and 42 °C respectively. The concentrations of acetone were 3 mol% in the bottom stream and 95 mol% in the distillate, which was equivalent to at least 4 equilibrium stages at total reflux conditions. Furthermore, a 50 mol% methanol-toluene mixture was separated into nearly pure toluene in the bottom stream and 75 mol% methanol in the distillate. The performance of the microdistillation unit was reproducible in repeated tests.

A model for transport phenomena in a cross-flow ultrafiltration module with microchannels.

Cross-flow ultrafiltration of macromolecular solutions in a module with microchannels is expected to have the advantages of fast diffusion from the membrane surface and a high ratio of membrane surface area to feed liquid volume. Cross-flow ultrafiltration modules with microchannels are expected to be used for separation and refining and as membrane reactors in microchemical processes. Though these modules can be applied as a separator connected with a micro-channel reactor or a membrane reactor, there have been few papers on their performance. The purpose of this study was to clarify the relationship between operational conditions and performance of cross-flow ultrafiltration devices with microchannels. In this study, Poly Vinyl Pyrrolidone (PVP) aqueous solution was used as a model solute of macromolecules such as enzymes. Cross-flow ultrafiltration experiments were carried out under constant pressure conditions, varying other operational conditions. The permeate flux decreased in the beginning of each experiment. After enough time passed, the permeate flux reached a constant value. The performance of the module was discussed based on the constant values of the flux. It was observed that the permeate flux increased with increasing transmembrane pressure (TMP) and feed flow rate, and decreased with an increase of feed liquid concentration. A model of the transport phenomena in the feed liquid side channel and the permeation through the membrane was developed based on the concentration and velocity distributions in the feed side channel. The experimental results were compared with those based on the model and the performance of the ultrafiltration module is discussed.

1208 スラグ流生成/分離システムの構築(アクチュエータのためのマイクロナノプロセス,一般講演)

Recently, in the field of microchemical process, the study of process using slug flow is attractive. Slug flow is the flow in which two types of liquids appear alternately as a striped pattern, promoting chemical reaction. So far, T/Y shaped flow channel is commonly used to form slug flow. However it is difficult to change slug length, which depends on the characteristics and flow rate of the fluids. Three-port electro magnetic microvalve, which can change slug length without depending on the characteristics and flow rate of the fluids, has been developed in this research. Moreover, the device consisting of hydrophobic/hydrophilic plates has been developed as a separator which separates slug flow into two liquids. Furthermore, the separating process of slug flow has been realized with it. As a result of the experiments separating water/oil slug flow, the separating rate is 100%, respectively.

Numerical and experimental mixing studies in a MEMS-based multilaminated/elongational flow micromixer

Improvement of mixing quality in microchannel mixers or reactors has been recognized as a relevant technical issue critical to the development and application of integrated microchemical processing systems. Silicon micro- electro mechanical systems (MEMS) technology was successfully used to fabricate a novel multichannel micromixer. This improved micromixer design basically used the mechanisms of fluid multilamination, elongational flow, and geometric focusing for mixing enhancement. The fabricated triple-stack (Pyrex™/silicon/Pyrex™) multilaminated/elongational flow micromixer (herein referred to as MEFM-4) was evaluated for its mixing performance using residence time distribution (RTD) measure in conjunction with UV–vis absorption spectroscopy detection technique. Using a semi-empirical model and the so-called convolution–deconvolution theorem, a model description of the experimental RTD data was obtained for the flow/mixing unit. This result was compared with numerical RTD predictions based on computational fluid dynamics (CFD) simulations. The simulation results are in good agreement with the experimental data, especially in the low flow-rate range (Reynolds number <13 in this study). However, as expected, the accuracy of the CFD simulations is generally limited at higher flow rates (high Peclet number) because of unavoidable numerical diffusion. This paper describes the efficient design, fabrication and characterization of an effective microchannel mixer for microchemical systems’ applications.

Sensor Location for Effective Fault Diagnosis in Micro Chemical Processes

It is clear from worldwide research that micro chemical processes (MCPs) offer a unique approach to the spatial and temporal control of chemical reactions. The well-known advantages of MCPs are often counterbalanced by serious faults such as channel blockage and catalyst deterioration. To realize stable long-term operation of MCPs, it is necessary to develop a monitoring system that can detect and diagnose these faults. In this work, a physical model-based process monitoring system for a tubular microreactor is developed. A state space model is derived by using the orthogonal collocation method, and the extended Kalman filter is used as an observer. The optimal sensor locations are determined so that unknown parameters such as catalyst effectiveness can be estimated most accurately. In addition, the validity of the conventional observability measures in solving the sensor location problems of MCPs is assessed.

Advanced chemical processing using microspace

A paradigm shift is required in chemical processing for the environmentally benign production of high quality products. To bring production systems in concert with this paradigm to reality, a new processing concept based on strict reaction control must be established. Presently, microchemical processes are expected to significantly contribute to the realization of such production systems. In a microspace, viscous force, surface tension, conduction heat transfer, and molecular diffusion become dominant. In addition, we can easily and precisely control the contact time, shape and size of the interface between fluids and so on. In this paper, studies dealing with reactions and unit operations conducted in microspace were surveyed and distinguished achievements were summarized along with the unique concepts they were based upon. The promising direction in science and technology for future microreaction technology is also discussed.

Toward autonomous control of microreactor system for steam reforming of methanol

Since the introduction of microchemical systems (MCS) in the last decade, it has been recognized that one of the most crucial challenges is the implementation of an appropriate control strategy. A novel study in realizing a controllable miniature chemical plant for a small-scale hydrogen source for fuel cells is presented. Catalytic steam reforming (SR) reaction of a methanol–water mixture was the model reaction studied. A microscaled reactor, sensors and actuators, were successfully prepared and integrated by using microelectromechanical systems (MEMS) technology. Microfabricated system components were then interconnected with a comprehensive control algorithm which could form the basis for an eventual autonomous, self-contained system. MCS represent a concept wherein precisely microfabricated fluid passages and reaction zones are integrated with sensors and actuators. Having an appropriate control strategy for the entire system of MCS is therefore a significant technical challenge. Although numerous MEMS-based examples of sensors and actuators exist for control of pressure, temperature and flow, there are few cases where these components have been combined with chemical reaction units and control algorithms into MCS. In this study, control of temperature and flow allows the hydrogen production rate to be modulated in a suitable fashion to support proton exchange fuel cell operation as a model. The reaction characteristics with temperature and flow changes, cold start-up behavior and the response to rapid changes in hydrogen demand were investigated. The control scheme implemented showed potential for autonomous control of fuel processing and other microchemical processing applications.

Data-based and model-based blockage diagnosis for stacked microchemical processes

One of the critical problems in the operation of microchemical processes is blockage in microchannels. Therefore, a process monitoring system which can detect and diagnose blockage is indispensable for effective and stable operation of microchemical processes. In the present research, two types of diagnosis systems, a data-based blockage diagnosis system (DB-BDS) and a model-based blockage diagnosis system (MB-BDS), are proposed. To realize efficient diagnosis for various degrees of blockage, the proposed DB-BDS uses the ratios of temperature differences between normal and abnormal operating conditions at one sensor to those at the other sensor. On the other hand, MB-BDS, which uses simple physical models of the process, diagnoses blockage by calculating the correlation coefficients between the prepared temperature distribution vectors and the actual temperature distribution vector when blockage is detected. The performance of the proposed systems is evaluated with their applications to a stacked microreactor. DB-BDS and MB-BDS are applied to various types of blockage, i.e., various locations and degrees. The results show that both DB-BDS and MB-BDS can diagnose the blockage location successfully even when blockage degree is less than 10%.