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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]

Abstract: The influence of different additives to V2O5/TiO2 catalyst for the gas phase partial oxidation of toluene was investigated in a microchannel reactor, where well-controlled reaction conditions were provided without heat and mass transfer influence. It was found that K-doping decreased the catalyst selectivity for benzaldehyde and benzoic acid. The addition of Sb promoted the selectivity but inhibited the catalyst activity greatly. The modification with Ag remarkably improved the catalyst performance in terms of increasing benzaldehyde and benzoic acid selectivity along with an increased activity. With Ag modified V2O5/TiO2 as catalyst and pure oxygen as oxidant, the total selectivity of benzaldehyde and benzoic acid reached over 80% with the toluene conversion above 10%. The maximum space–time yield of 4.82kgh−1 L−1 has been achieved, calculated on the basis of the channel volume. [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]

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]

Highlights: [•] Shear stress plays an important role in determining bubble length in squeezing regime. [•] A correlation was developed to address the effect of μL and jTP on bubble length. [•] Bubble frequency reaches a maximum with an increase of the gas–liquid flow ratio. [•] Cross-sectional shape of Taylor bubbles is close to square at low Ca. [Copyright &y& Elsevier]

Abstract: The present study deals with pressure effects on the hydrodynamic characteristics of gas–liquid two phases within a T-junction microchannel. The operating pressure is in the range of 0.1∼5.0MPa. Nitrogen and de-ionized water are selected as the test fluids. The gas Weber numbers vary from 1.37×10−5 to 3.46 at atmospheric pressure and from 1.70×10−3 to 70.32 at elevated pressure, respectively. The liquid Weber numbers are in the range of 3.1×10−3∼4.9. The operating pressure plays an important role in gas–liquid two phases flow. Seven typical flow patterns such as bubbly flow, slug flow, unstable slug flow, parallel flow, slug-annular flow, annular flow, and churn flow are observed. Based on the force analysis of the gas and liquid phase in microchannel, the formation mechanisms of flow patterns are discussed at great length, and the flow pattern maps are divided into five regions using We GS and We LS as coordinates. These results are beneficial for future investigation to understand gas–liquid two-phase mass transfer and reaction characteristics in microchannel at elevated pressure. [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: Ethylene is essential material for the petrochemical industry. Ethylene production via catalytic dehydration of ethanol over TiO2/γ-Al2O3 catalysts in multi-microchannel reactors is reported in this paper. The physicochemical properties of these catalysts are characterized by X-ray diffraction (XRD) and FT-IR spectrum. The effects of operation parameters, such as ethanol concentration, reaction temperature and liquid hourly space velocity, have been investigated experimentally. The reaction results indicate that the catalysts doped with TiO2 have high ethanol conversion of 99.96% and ethylene selectivity of 99.4%. Ethylene yield of 26g/(gcat h) can be achieved, which provides very favorable foundation for the process intensification and miniaturization of the ethylene production process using bioethanol. [Copyright &y& Elsevier]