Narrow Results

A two-step microreactor for the preparation of Diphenyldimethoxysilane $({({\mathrm{\text{C}}}_6{\mathrm{\text{H}}}_5)}_2\mathrm{\text{Si}}{({\mathrm{\text{OCH}}}_3)}_2)$ is established. Diphenyldichlorosilane $({({\mathrm{\text{C}}}_6{\mathrm{\text{H}}}_5)}_2{\mathrm{\text{SiCl}}}_2)$ and methanol $({\mathrm{\text{CH}}}_3\mathrm{\text{OH}})$ are selected as reactants. A model is created to optimize the structure of the reaction domain of the microreactor. The optimization parameters are $P=3:4$, $R=1:1$, $L=70\mu \mathrm{\text{m}}$. The concentration of the products is compared when there are obstacles in the reaction domains and non-reaction domains. The model and optimization method are helpful in the design of microreactor.

In order to reduce the carbon emissions of fuel vehicles, hydrogen has received extensive attention as a new clean energy. In this paper, a packed-bed microreactor for hydrogen production from methanol steam is designed for use in hydrogen fuel cells. By considering the heating gas velocity in the heating tubes, the inlet temperature of the microreactor, the size and number of heating tubes, inlet pressure, pellet porosity and thermal conductivity, parameters such as methanol conversion rates and hydrogen concentration were evaluated. First, the rate at which the gas is heated has a great influence on the reaction results. Choosing a larger heating gas velocity leads to an increase in the temperature inside the microreactor, thereby increasing the CH₃OH conversion, resulting in a higher H₂ concentration at the outlet. Changing the inlet temperature of the microreactor affects the reaction speed, but has little effect on the H₂ concentration at the outlet. By studying the radius and number of heating tubes, we selected three different sets of data to compare the conversion rate of reactants and the concentration of products, and finally determined the optimal parameters as R = 4 mm and N = 8. Second, the inlet pressure has little effect on the H₂ concentration at the outlet, but has a significant effect on the reaction speed. Particle porosity has no effect on the reaction results. Finally, the larger the thermal conductivity, the higher the temperature in the microreactor, which is more conducive to the reaction.

Hydrogen has received widespread attention as a new clean energy in order to reduce the carbon emissions of fuel vehicles. This paper studies a tubular microreactor based on methanol steam reforming. Methanol and steam are mixed in proportion and the chemical reaction takes place in a porous catalytic bed. For heating purposes, hot gas from the burner penetrates the reactor bed through heating tubes. Energy is supplied through the heating tubes to drive the endothermic reaction system. The microreactor is enclosed in an insulated jacket. In this paper, parameters such as methanol conversion and hydrogen concentration are evaluated by considering microreactor materials, heating gas temperature and flow direction, heating tube distribution, pressure drop and reaction channel length. First of all, choosing a microreactor material with a smaller thermal conductivity can avoid excessive heat loss, and improve heat transfer performance. Increasing the heating gas temperature leads to an increase in the temperature of the reaction zone, thereby increasing the CH₃OH conversion rate and H₂ mass fraction. Changing the flow direction of the heating gas affects the reaction rate, but has little effect on the reaction result. Through the research on the distribution of the heating tubes, the results show that the hydrogen production rate is higher when the contact area between the heating tubes and the reaction zone is larger. Secondly, through the comparison of the data under different pressure drops, the best parameter $P=50$pa is obtained, and the CH₃OH conversion rate is 80.6% at this time. Finally, increasing the length of the reaction channel can make the reaction more complete. For example, when the reaction channel length $L=0.39$m, the CH₃OH conversion rate is as high as 83.7%.

In this paper, the monophasic catalytic reaction in the microreactor is studied. Several factors that may affect the catalytic reaction are discussed, including the pressure drop, the size of catalyst particles, and the channel structure. Finally, some important conclusions can be reached. The change of pressure drop has an effect on the reaction. For example, the C₃H₆ conversion rate is 62.88% when the pressure drop is 8atm, and the C₃H₆ conversion rate is 61.78% when the pressure drop is 11atm. The effect of the change particle radius is not obvious on the reaction. Enhancing the mixing of substances before entering the reaction domain is helpful to the catalytic reaction. There are different substances concentration in catalyst particles at different positions in microreactors. But from the surface to the inside of catalyst particles, the substances concentration has a clear change rule.

A simple glass capillary-microreactor for studying the epoxidation of cyclohexene is described in this paper. Reaction conditions were optimized to achieve high reaction yield. The microreactor is easy to fabricate, fast and easy way for reliable catalyst screening in studying homogeneous oxidation reactions. Four different catalysts (i.e. manganese(II) and copper(II) metal complexes of Schiff and reduced Schiff base ligands) were synthesized and used. The reaction products were monitored by gas chromatography/mass spectrometry. The reaction performance was compared with conventional (batch scale) reaction. In both cases, catalytic activities and the product yields were found to be relatively higher for the copper(II) complexes when compared with the conventional route.

Microreactor technology is a new concept of chemical synthesis for nanoparticle production. The "state of the art" in microreactor fabrication and its application to the synthesis of nanoparticles is reviewed. The microfluidic concepts, the materials and technologies for microreactor manufacture, with particular emphasis on polymers and microreplication techniques, and their application to the synthesis of various nanomaterials in microreactors are presented. The unique synthesis properties of various nanoparticles using a microfluidic process as well as broader impact in term of nanomaterials engineering, i.e., selectivity and monodispersity, reduced amount of chemicals, fast reaction, minimum cost, a better control of the process, minimum waste and reduced amounts of reaction byproducts and improved safety, are discussed in comparison with the traditional wet-chemical batch synthesis approach.

The present work deals with the investigation of the greener route for the production of silver nanoparticles using Raphanus sativus (R. sativus) bioextract in a continuous flow tubular microreactor. The parameters affecting the particle size and distribution were investigated. From the results obtained it can be inferred that the ascorbic acid (reducing agent) present in the R. sativus bioextract is responsible for the reduction of silver ions. At optimum condition, the particle size distribution of nanoparticles is found between 18nm and 39nm. The absorbance value was found to be decreased with an increase in the diameter of the microreactor. It indicates that a number of nuclei are formed in the micrometer sized (diameter) reactor because of the better solute transfer rate leading to the formation of large number of silver nanoparticles. The study of antibacterial activity of green synthesized silver nanoparticles shows effective inhibitory activity against waterborne pathogens, Shegella and Listeria bacteria.

In this paper, endeavor has been made to design and analyze different Y-type micromixers by characterizing the mixing and flow behavior in ultra-low Reynolds number region. The effects of different geometric and flow parameters on the mixing and pressure drop are studied through computational fluid dynamics (CFD) simulations using COMSOL Multiphysics software. The parameters investigated are obstacle geometry, obstacle arrangement, obstacle depth, aspect ratio (AR), entrance angle ($E_{\theta })$, Reynolds number (Re) and obstacle packing factor (OPF). The simulation results reveal that rectangular shaped obstacles in staggered arrangement gives the best mixing. Increasing obstacle depth and OPF increases both mixing and pressure drop whereas increasing entrance angle enhances mixing but has negligible effect on pressure drop. Also both the mixing and pressure drop performance enhances with decreasing AR and lower Reynolds number gives better mixing in the lower laminar flow region.

It is highly desirable to develop a phosphine-free recyclable heterogenous catalytic system without the use of expensive and air-sensitive basic phosphines for palladium-catalysed coupling reactions. Nano-palladium catalysts for example, in various stabilised forms have been extensively explored as potential alternatives to achieve a higher catalytic activity. In line with the great interest directed towards the development of microfabricated chemical systems for a variety of chemical and biological applications, we demonstrate here a microreactor based on microfluidic channels on glass chips for the continous flow organic synthesis using immobilised nano-palladium. The palladium colliods were immobilised on the inner-walls of the microchannels via an intermediate organosilane monolayer. The covalent attachment of colloidal palladium provides minimum leaching of the catalyst. The Suzuki coupling of an aryl halide and an organoboron has been used a model system to investigate the performance characteristics. The reaction affords an excellent yield, a higher turnover rate and the ease of catalyst recycling. Similarly, the approach can be applied to other palladium-catalysed syntheses, such as Heck-, Sonogashira-, and Stilles-type coupling reactions.