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Graphical abstract Highlights • Olefin/paraffin separation processes with AgNO 3 solutions are investigated. • The evolution of absorption fraction and k L a along microchannel was investigated. • The evolution of bubble size along channel length was investigated. • The effect of ultrasound was investigated, achieving significant intensification. Abstract Ultrasound is an effective method to intensify gas-liquid processes as the oscillation energy is easily focused at the gas-liquid interface, which can induce strong interface oscillation and acoustic streaming. The combination of ultrasound and microreactor provides ideal control over the ultrasound field, making the energy efficiently utilized. In this study, characteristics of chemical absorption of C 2 H 4 from the mixture of C 2 H 6 /C 2 H 4 into AgNO 3 solutions under Taylor flow are investigated in a high-power ultrasonic microreactor. The effect of ultrasound on the bubble size reduction, absorption and mass transfer coefficient is presented and discussed. It is demonstrated that very large mass transfer coefficient with k L a and k L in the range of 7–42 s−1 and 0.00169–0.0225 m s−1 respectively are obtained, presenting significant intensification compared to absorption without ultrasound in the same reactor. [ABSTRACT FROM AUTHOR]

The nitration process of 2-ethylhexanol (2-EH) with mixed acid was studied in different capillary microreactors. The conversion of 2-EH and selectivity to 2-ethylhexyl nitrate (EHN) were investigated by varying reaction temperature, molar ratio of nitrate to 2-EH, residence time and water content in mixed acid. Under optimized conditions, the conversion of 2-EH and selectivity to EHN could be up to 99% in less than 10 seconds, indicating great potential of microreactors in process intensification. Moreover, with an assumption of homogeneous reaction, a kinetic model based on first order kinetics for nitric acid and 2-EH was proposed to determine both the apparent and intrinsic reaction kinetics. By taking into account the activity of solutes that depend on the acidity (M c ), the intrinsic kinetic was obtained, which is independent of the sulfuric acid concentration. The reaction model can well predict the conversion of 2-EH. [ABSTRACT FROM AUTHOR]

• Danckwerts mass transfer model is applied for absorption prediction. • Significant end effect is found in lab-scale experiments. • The effects of various parameters on the reactor volume are investigated. • Increasing the system pressure is very efficient to reduce the microreactor volume. Parametric analysis is presented for CO 2 absorption process using the Danckwerts mass transfer model, which enables an efficient target-oriented design of microreactors. Instead of trial-error evaluation over given reactors, this work provides a quantitative study on the effects of various parameters (i.e., flow rate, reaction rate, system pressure) on the reactor volume. It is found that increasing system pressure can significantly reduce the reactor volume, offsetting the disadvantage of microreactors with limited volume. This work also evaluates the end effect of lab-scale tests that results from the absorption in the connecting tube and the gas-liquid separator. With the theoretical approach, the end effect is shown to increase with the increase of the throughput, which is in accordance with experimental results. The amount of CO 2 absorbed in the end volume can be as large as 23 %∼47 % of the total CO 2 absorbed, indicating a rather serious end effect. [ABSTRACT FROM AUTHOR]

• The emulsification mechanism behind high-speed shearing was uncovered. • The effect of ultrasound and high-speed shearing on emulsification was studied. • The effect of recycling flow on reducing emulsion size was investigated. • A novel hybrid frequency strategy was proposed to produce nano-emulsion. The study first investigated the effects of individual ultrasound and high-speed shearing on emulsification, both obtaining emulsions with average sizes of approximately 1 μm. Subsequently, a combined strategy to utilize shearing instrument producing coarse emulsion for ultrasonic microreactor was proposed. Immiscible liquids were drawn into the stirring chamber by rotating paddles, where they underwent strong shearing and thorough mixing. The pre-mixed liquids were introduced into microchannel and subjected to further processing by oscillating cavitation bubbles. Through optimization of experimental parameters such as residence time and recycle ratio, the average emulsion size was significantly reduced to 522 nm. Finally, a dual-frequency strategy using ultrasound frequencies of 20 and 40 kHz consecutively further reduced the emulsion size to 307 nm. In comparison with conventional sonoreactors and high-pressure homogenizers, this dual-frequency approach demonstrated superior emulsification performance with less surfactant addition and energy input, indicating its high applicability on continuous emulsification process with proper design and optimization. [Display omitted] [ABSTRACT FROM AUTHOR]

• The mixing process of two miscible fluids in a T-micromixer was simulated by CFD. • The vortex structures were identified by different identification methods. • The mixing intensity and the segregation scale were quantitatively analyzed. • The mixing with the symmetric and asymmetric inlet conditions was compared. Based on the theory of Dean instability, the mixing process of two miscible fluids in a T-micromixer was investigated under symmetric and asymmetric inlet boundary conditions. The secondary vortex structures at selected cross-sections along the micromixer were obtained by CFD simulation and presented with different vortex identification methods. The mixing characteristics under the influences of vortices were qualitatively and quantitatively analyzed. The results demonstrate that four types of secondary vortex structures could be formed and developed in the micromixer, depending on the Dean number. For the symmetric inlet boundary condition, stable secondary vortex structures will increase the species contact areas, thus the engulfment Dean vortices provide much stronger mass transfer in the transversal direction compared with the asymmetric one. This study can provide an insight into the underlying vortex phenomena behind the mixing in a T-micromixer. [Display omitted] [ABSTRACT FROM AUTHOR]