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The effects of ultrasound on the hydrodynamic and mass transfer behaviors of immiscible liquid–liquid two‐phase flow was investigated in a domestic ultrasonic microreactor. Under ultrasonic irradiation, cavitation bubble was generated and underwent violent oscillation. Emulsification of immiscible phases was initiated by virtue of oscillating bubbles shuttling through the water/oil interface. The pressure drop was found to decrease with increasing ultrasound power, with a maximum decrement ratio of 12% obtained at power 30 W. The mass transfer behavior was characterized by extraction of Rhodamine B from water to 1‐octanol. An enhancement factor of 1.3–2.2 on the overall mass‐transfer coefficient was achieved under sonication. The mass transfer performance was comparable to passive microreactor at similar energy dissipation rate (61–184 W/kg). The extraction equilibrium was reached under a total flow velocity 0.01 m/s and input power 20 and 30 W, exhibiting its potential use in liquid‐liquid extraction process. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1412–1423, 2018 [ABSTRACT FROM AUTHOR]

Intensification of liquid mixing was investigated in domestic fabricated ultrasonic microreactors. Under the ultrasonic field, cavitation bubbles were generated, which undergo vigorous translational motion and surface oscillation with different modes (volume, shape oscillation, and transient collapse). These cavitation phenomena induce intensive convective mixing and reduce the mixing time from 24-32 s to 0.2-1.0 s. The mixing performance decreases with the channel size, due to the weaker cavitation activity in smaller channel. The energy efficiency is comparable to that of the conventional T-type and higher than the Y-type and Caterpillar microreactors. Residence time distribution was also measured by a stimulus-response experiment and analyzed with axial dispersion model. Axial dispersion was significantly reduced by the ultrasound-induced radial mixing, leading to the increasing of Bo number with ultrasound power. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1404-1418, 2017 [ABSTRACT FROM AUTHOR]

Ultrasonic microreactors were used to intensify gas-liquid mass-transfer process and study the intensification mechanism. Fierce surface wave oscillation with different modes was excited on the bubble. It was found that for slug bubbles confined in smaller microchannel, surface wave oscillations require more ultrasound energy to excite due to the confinement effect. Cavitation microstreaming with two toroidal vortices was observed near the oscillating bubble by a streak photography experiment. Surface wave oscillation at the gas-liquid interface increases the specific surface area, while cavitation microstreaming accelerates the interface renewal and thus improves the individual mass-transfer coefficient. With these two reasons, the overall mass-transfer coefficient was enhanced by 3-20 times under ultrasonication. As for gas-liquid flow hydrodynamics, ultrasound oscillation disturbs the bubble formation process and changes the initial bubble length and pressure drop. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1294-1307, 2016 [ABSTRACT FROM AUTHOR]

The combination of ultrasound and microreactor is an emerging and promising area, but the report of designing high-power ultrasonic microreactor (USMR) is still limited. This work presents a robust, high-power and highly efficient USMR by directly coupling a microreactor plate with a Langevin-type transducer. The USMR is designed as a longitudinal half wavelength resonator, for which the antinode plane of the highest sound intensity is located at the microreactor. According to one dimension design theory, numerical simulation and impedance analysis, a USMR with a maximum power of 100 W and a resonance frequency of 20 kHz was built. The strong and uniform sound field in the USMR was then applied to intensify gas–liquid mass transfer of slug flow in a microfluidic channel. Non-inertial cavitation with multiple surface wave oscillation was excited on the slug bubbles, enhancing the overall mass transfer coefficient by 3.3–5.7 times. [ABSTRACT FROM AUTHOR]

The hydrodynamics of single-phase liquid flow with relatively high fluid viscosities in a microchannel was investigated experimentally. The results showed that the conventional theory could predict the single-phase flow with high fluid viscosities in microchannels. Furthermore, the effect of viscosity on the slug flow of two immiscible liquid phases in a microchannel was studied with high-speed imaging techniques. It was found that a higher dispersed-phase viscosity quickened the flow pattern transition from slug flow to parallel flow and resulted in smaller slugs. A modified capillary number representing the mutual effects of the viscosities of the continuous phase and the dispersed phase was proposed for predicting the slug sizes in microchannels. [ABSTRACT FROM AUTHOR]

The development of highly efficient processes for the cycloaddition of CO2 with epoxides to produce five-membered cyclic carbonates is a very attractive topic. In this work, the cycloaddition of propylene oxide (PO) and CO2 to give propylene carbonate (PC) is studied in a microreactor using a HETBAB ionic liquid catalyst. The microreactor performance is evaluated by studying the effects of different operating conditions, including reaction temperature, operating pressure, residence time, molar ratio of CO2/PO, and the catalyst concentration in PO. The process characteristics of the reaction concerning the gas–liquid mass transfer and the intrinsic kinetics perspectives are discussed. The results show that the residence time can be dramatically reduced from several hours in a conventional stirred reactor to about 10 s in a microreactor. The yield of PC at 3.5 MPa can reach 99.8% at a residence time of 14 s. The turnover frequency (TOF) value varies in the range of 3000 to 14 000 h−1 compared to 60 h−1 in the conventional stirred reactor. The space time yield (STY) or the overall reaction rate ranges from 650 to 4500 gprod. (gcat. h)−1, which is much larger than the value [ca. 19 gprod. (gcat. h)−1] for the conventional stirred reactor. To some extent, the present study has also demonstrated the concept of ‘Novel Process Windows’. [ABSTRACT FROM AUTHOR]

The miscible liquid-liquid two phases based on Taylor flow in microchannels was investigated by high-speed imaging techniques and Villermaux/Dushman reaction. The mixing based on Taylor flow was much better compared with that without introducing gas in microchannels, even the ideal micromixing performance could be obtained under optimized superficial gas and liquid velocities. In the mixing process based on Taylor flow, the superficial gas and liquid velocities affected the lengths and the velocities of Taylor bubble and liquid slug, and finally the micromixing performance. The formation process of Taylor flow in the inlets, the initial uniform distribution of reactants and the internal circulations in the liquid slug, and the thin liquid films all improved the mixing performance. Furthermore, a modified Peclet number that represented the relative importance of diffusion and convection in the mixing process was proposed for explaining and anticipating micromixing efficiency. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1660-1670, 2012 [ABSTRACT FROM AUTHOR]

It is indispensable to remove CO at the level of less than 50 ppm in H2-rich feed gas for the proton exchange membrane (PEM) fuel cells. In this paper, catalyst with high activity and selectivity, and a microchannel reactor for CO preferential oxidation (PROX) have been developed. The results indicated that potassium on supported Rh metal catalysts had a promoting effect in the CO selective catalytic oxidation under H2-rich stream, and microchannel reactor has an excellent ability to use in on-board hydrogen generation system. CO conversion keeps at high levels even at a very high GHSV as 500 000 h-1, so, miniaturization of hydrogen generation system can be achieved by using the microchannel reactor. [Copyright &y& Elsevier]

Abstract: Methanol oxidation reforming is an important reaction in the process of hydrogen generation for PEMFC. In this paper, we report the wall coated catalysts in a microchannel reactor for methanol oxidation reforming. The preparation method of the wall coating catalyst was studied in detail, i.e., the sol–gel and solution-coating techniques. To prepare the catalysts for methanol oxidation reforming, the washing-coating layer of CuZnAl was prepared by the sol–gel technique, and then the active layer was coated on it by solution-coating technique with emulsion colloid containing Pd–ZnO particles. Both the supporting layer and catalyst on the stainless steel foils were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The formed wash-coating layer with ordered arrays of petaloid microcrystallites in layer surface and Pd–Zn alloy crystal phase can be clearly observed. The reaction experimental results indicated that the catalyst prepared have high activity and relatively high stability. [Copyright &y& Elsevier]

Abstract: Gas phase partial oxidation of toluene over V/Ti oxide catalysts has been successfully performed in a microchannel reactor, which provides very good mass and heat transfer conditions. With the elimination of hot spots, which are known as the most negative factors for partial oxidation of hydrocarbons, steady and uniform reaction conditions can be achieved in the catalyst bed by using the microreactor. Since the best performance of the catalysts might be exploited, the selectivity of partial oxidation products of toluene has remarkably increased compared to the traditional packed fixed-bed reactor, even without the bother of modifying the catalysts, diluting the reactants or catalysts with inert contents to avoid hot spots or improve the diffusion and mixing. Furthermore, in virtue of its inherent safety features, when using pure oxygen as oxidant, the reactions were handled safely within the explosion limits in the microreactor. With TiO2 carried V2O5 as catalysts, the total selectivity of benzaldehyde and benzoic acid reaches around 60%, and the toluene conversion is about 10%. The conversion can go up without violent decline of selectivity, unlike most fixed bed reactors. Space time yield of 3.12kgh−1 L−1 calculated on the basis of the channel volume has been achieved. The influence of operating conditions has been investigated in detail in the microreactor. [Copyright &y& Elsevier]

The synergistic effects of gas agitation and ultrasound on mass transfer between immiscible liquids were investigated in an in-house made ultrasonic microreactor. With the introduction of inert gas (N 2 ), a three-phase slug flow with slug bubbles either dispersed in continuous aqueous phase or encapsulated in oil plugs was observed. Under ultrasound irradiation, slug bubbles underwent surface wave oscillation and induced agitation in microchannel. In addition, microbubbles were generated by acoustic cavitation, oscillating intensely and resulting in the formation of O/W emulsion. Bubble oscillation (i.e., slug bubbles and microbubbles) as well as emulsification promoted liquid-liquid mass transfer significantly. Extraction of vanillin from aqueous solution to toluene was employed to demonstrate the mass transfer enhancement. Compared with silent operation, both mass transfer coefficient and extraction efficiency were largely improved by the combined use of gas agitation and ultrasound. With gas flow velocity being 0.005–0.083 m/s at fixed ultrasound power of 30 W, the overall mass transfer coefficients ranged from 0.047 s −1 to 0.429 s −1 , which was 2.33–17.20 times larger than the corresponding liquid-liquid two-phase process without ultrasound irradiation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Process of CO2 absorption by MEA solutions was analyzed in microchannel reactors. [•] Effects of relevant parameters on the process were evaluated. [•] k 1 for CO2 reaction with MEA was successfully determined under ambient pressure. [•] An Arrhenius-type equation was obtained for k 1 for CO2 absorption in microchannel. [Copyright &y& Elsevier]

Abstract: This paper concerns an experimental investigation into the flow pattern transition and break-up mechanism of liquid film in single-channel falling film microreactors. Three major flow patterns were observed to be ‘corner rivulet flow’, ‘falling film flow with dry patches’, and ‘complete falling film flow’. The critical flow rate associated with the transition between each flow pattern was determined. Hysteresis was found, as the critical flow rate was higher when the flow pattern shifted from ‘falling film flow with dry patches’ to ‘complete falling film flow’ than it was when the flow pattern shifted in the opposite direction. There existed a minimum wetting flow rate (MWF) in order to the complete falling film flow pattern to be present. MWF was observed to increase with the width or depth of microchannel and could not be well predicted by traditional falling film correlations. Based on the obtained data, an empirical correlation has been proposed for the prediction of MWF in falling film microreactors, where the influence of fluid physical properties and channel dimension is revealed. [Copyright &y& Elsevier]

Abstract: In this work, the influence of surface properties on the flow characteristics and mass transfer performance of two immiscible liquids are investigated in the opposed and cross-flow configuration microchannels, as the volumetric flux ratio is far <1. For visually identifying flow patterns in transparent PMMA microchannels, dyed de-ionized water and kerosene are selected as test fluids. To investigate the mass transfer characteristics in stainless steel microchannels, water–succinic acid–n-butanol is chosen as a typical system. Reynolds number varied between 11 and 275. Only at low ReM numbers, the dispersed phase flow pattern can occur in the opposed T-shaped PMMA microchannel before surface modification. At higher ReM numbers, only the continuous phase flow pattern (parallel flow) is observed before and after surface modification. Moreover, the fluctuation amplitude after surface modification is larger than before surface modification at the opposed T-junction. To eliminate the effects of the sampling intervals and separation process of oil–water two phases on mass transfer performance, one new testing method is established by manufacturing the novel oil–water separator based on the principle of siphon. For the conditions applied during the study, the overall volumetric mean mass transfer coefficients range from 0.19 to 11.96s−1, which are one or three orders of magnitude higher than those in typical conventional large scaled contactors. [Copyright &y& Elsevier]

Abstract: T-type microchannel reactors were used to prepare monodispersed nanocrystals of barium sulfate and boehmite. The size of barium sulfate is strongly dependent on the velocity of the reactants in the channel. High velocity is beneficial for producing small particles. The concentration of reactants also affects the size. Boehmite was prepared by neutralization of NaAlO2 and Al2(SO4)3. Changing the proportion of NaAlO2 and Al2(SO4)3 will lead to different pH values which determine the phase of alumina. High efficiency of micromixing is the key factor of the purity of the alumina morphology. Na2CO3 was used to adjust pH at given value during aging process. Aging is indispensable for the amorphous alumina to crystallize to boehmite. Raising the age temperature would reduce the time the crystallization need. The morphology and purity were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). [Copyright &y& Elsevier]

Abstract: This study showed that a ZnO–Cr2O3/CeO2–ZrO2/Al2O3 (Zn–Cr) catalyst was a promising catalyst for hydrogen production from methanol due to its high stability and selectivity. There was no significant deactivation of the catalyst over 300min of continuous operation when water was introduced into the feed. In the absence of water, the catalyst deactivated rapidly due to coke formation. The addition of water into the feed changed the route of methanol conversion and improved its rate. In order to investigate the pathway of CO formation, three reactions, i.e. decomposition of methanol (DM), steam reforming of methanol (SRM) and water gas-shift (WGS), were studied in this paper. The results showed that CO and CO2 were produced through the DM reaction and SRM reaction, respectively. The WGS and reverse WGS reactions were negligible. Adding H2 and CO in the feed did not influence the process behavior of the SRM reaction. The addition of CO2 and H2O into the feed decreased the yield of CO2. [Copyright &y& Elsevier]