A State-of-the-Art Review of Mixing in Microfluidic Mixers

Microreaction technology is one of the most innovative and rapid developing fields in chemical engineering, synthesis and process technology. Many expectations toward enhanced product selectivity, yield and purity, improved safety, and access to new products and processes are directed to the microreaction technology. Microfluidic mixer is the most important component in microfluidic devices. Based on various principles, active and passive micromixers have been designed and investigated. This review is focused on the recent developments in microfluidic mixers. An overview of the flow phenomena and mixing characteristics in active and passive micromixers is presented, including the types of physical phenomena and their utilization in micromixers. Due to the simple fabrication technology and the easy implementation in a complex microfluidic system, T-micromixer is highlighted as an example to illustrate the effect of design and operating parameters on mixing efficiency and fuid flow inside microfluidic mixers.

Efficient fixation of CO_(2) into propylene carbonate with [BMIM]Br in a continuous-flow microreaction system

Utilization of carbon dioxide(CO_(2)) is of great significance in the development of CO_(2) absorption and the solution of greenhouse gas effect.Highly efficient conversion of CO_(2) into cyclic carbonate with green catalysts is essential for the more sustainable expansion of CO_(2) fixation.Traditional batch reactor is limited by low efficiency, high cost and low security. Meanwhile, continuous flow system showcased a myriad of virtues, including shortening the residence time from hours to seconds, and decreasing reaction temperature, and possessing the nature of easy industrial scale-up. In this paper, a continuous-flow microreaction system was developed to synthesis propylene carbonate(PC) from propylene oxide(PO) and CO_(2) using 1-butyl-3-methylimidazolium bromide([BMIM]Br) as catalyst. By observing the flow patterns inside microreaction system, the effects of reaction temperature, molar fraction of catalyst, operating pressure, residence time, molar ratio of CO_(2)/PO as well as recycling performance of catalyst on the overall performances were comprehensively evaluated into details. Under different reaction conditions,the flow patterns were set to vary between slug flow and annular flow. The results showed that the yield of propylene carbonate(PC) can reach99.7% at 140℃ and 3.0 MPa with the residence time of 166 s, while the recycling performance of the designed system greatly conforms the future trend of green chemistry.

Continuous, homogeneous and rapid synthesis of 4-bromo-3-methylanisole in a modular microreaction system

4-Bromo-3-methylanisole is mainly used to synthesize black fluorane dye(2-anilino-3-methyl-6-dibutylaminofluorane, ODB-2), which is one of the most important heat and pressure-sensitive dyes in the manufacture of thermal papers. Compared to the industrial heterogeneous batch process, a continuous homogeneous bromination technology in a modular microreaction system has been developed, and 4-bromo-3-methylanisole has been successfully prepared through high-selective mono-bromination of 3-methylanisole with Br2 solution in CHCl3. In optimal conditions, the content of bis-brominated byproducts can be controlled less than 0.5%,which is superior to the industrial standard with 99.5% 3-methylanisole conversion at very short residence time and mild reaction temperature.

A circular microreaction method to the safe and efficient synthesis of 3-methylpyridine-N-oxide

3-Methylpyridine-N-oxide is an essential intermediate in the preparation of 2-chloro-5-methylpyridine,which can be used to synthesize nicotine insecticides such as imidacloprid and acetamiprid.The traditional method of production of 3-methylpyridine-N-oxide is catalytic oxidation of 3-methylpyridine in semi-batch reactors.Due to strong exothermic reaction and explosive property of 3-methylpyridine,the reaction efficiency and safety is low using batch technology.Therefore,the development of a safer and efficient 3-methylpyridine-N-oxide production process is very necessary in industrial production.In this paper,microreaction systems were introduced into the preparation of 3-methylpyridine-N-oxide.The comparison of three different methods(traditional semibatch method,co-current microreaction method,and circular microreaction method)showed that the circular microreaction method was the most applicable,with relative higher product yield(~90%),less side reaction and better reaction control.

Microreaction Technology for Synthetic Chemistry

Microreaction technology as an emerging tool for synthetic chemistry has been extensively applied in academic and industrial researches. Normally, synthetic chemists used to running reactions in the classical glassware for cen turies are unfamiliar and unaccustomed to use microreaction tech no logy for routine synthetic work. This review tries to give a general introduction of the capabilities of microreaction tech no logy.

Synthesis of mesoporous silica microspheres by a spray-assisted carbonation microreaction method

A novel spray-assisted carbonation microreaction method for the synthesis of mesoporous silica microspheres is reported.The synthetic process comprises the preparation of a silica sol via a carbonation reaction,rapid gelation at high temperature,and subsequent rapid solvent evaporation by spray drying.The carbonation microreaction was conducted in a membrane dispersion microreactor,in the presence of sodium silicate and carbon dioxide reactants.The as-synthesized silica microspheres exhibit a uniform mesostructure,excellent dispersity,and a narrow particle size distribution,with average diameters of 1-2 μm,Brunauer-Emmett-Teller surface areas of 300-1149m2/g,and total pore volumes of 0.21-1.82 cm3/g.Relatively low concentrations of the silicate species and well-controlled silica condensation rates are responsible for the formation of the observed spherical morphology.The synthetic process is of significant practical importance as a result of using low-cost raw materials,and because of the excellent controllability and process stability displayed.Furthermore,this rapid and flexible method may be extended to the synthesis of various silica materials and their composites.