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Abstract: Two types of membrane reactors, the packed-bed membrane reactor (PBMR) and catalytic membrane reactor (CMR) were successfully miniaturized. Zeolites were incorporated as catalyst for reaction and membrane for separation. The membrane microreactors were tested for Knoevenagel condensation reaction between benzaldehyde and ethyl cyanoacetate to produce ethyl 2-cyano-3-phenylacrylate. Supra-equilibrium conversion and high product purity were obtained from selective removal of water during the reaction. A simple computation model was developed to simulate the reaction in the multichannel membrane microreactor using kinetic data from batch reaction, correlated data from membrane separation and published transport data. The influence of reactor geometry (i.e. channel width and membrane location), membrane separation and catalyst properties were evaluated and the results compared well with experimental data. The information provided by the model suggests several ways of improving the reactor performance. [Copyright &y& Elsevier]

Abstract: Mesoporous silica MCM-41 was successfully prepared by flow synthesis in a microreactor at shorter reaction times (i.e., minutes versus day) at high yield (i.e., 60% calcined sample) to give particles of more uniform size and shape compared to MCM-41 prepared by conventional batch synthesis. Magnetic iron oxide nanoparticles were incorporated and organic amines (i.e., propylamine and propyl diethylene amine) were grafted to obtain magnetic mesoporous catalysts for the Knoevenagel condensation reactions of benzaldehyde with ethyl cyanoacetate, ethyl acetoacetate and diethyl malonate. The incorporation of magnetic nanoparticles and large organic amines can hinder reactants access to the catalyst resulting in lower reactivity. NH2-magMCM-41 showed superb catalyst activity and selectivity for the all three Knoevenagel condensation reactions studied. The catalyst can be easily dispersed into solution and rapidly removed by a magnet for recovery and reuse. [Copyright &y& Elsevier]

Abstract: Freestanding Sil-1 and ZSM-5 micromembranes of Si/Al ratios ranging from 14 to ∞ were fabricated on silicon. The zeolite synthesis was adjusted to obtain micromembranes of similar microstructures (i.e., thickness, orientation, crystal grain size, morphology and intergrowth) and prepared membranes display comparable helium gas permeance. The low temperature removal of the organic TPA+ molecules by ozone enabled the preparation of low defect zeolite micromembranes that exhibit superb H2/nC4 (i.e., ≥100) and nC4/iC4 (i.e., ≥30) permselectivity ratios. The effects of aluminum content of the ZSM-5 micromembranes were investigated for single, binary and ternary gas permeation. Surface diffusion is important at low temperature and the single gas permeances of hydrogen, argon, nitrogen and methane were larger than Knudsen. The deviation from Knudsen increased with the Si/Al ratio and was largest for Sil-1. Propane–nitrogen separation in the zeolite micromembranes is mainly molecular sieving and display weak dependence on the aluminum content of the zeolite, where the separation of the ternary H2–CH4–CO2 mixture is by preferential adsorption and shows strong dependence on the Si/Al ratio of the zeolite. [Copyright &y& Elsevier]

Silicon-glass microreactors with TS-1 catalyst wall coatings were fabricated and used for 1-pentene epoxidation with hydrogen peroxide in continuous flow. Seeding of the microchannels before zeolite growth was necessary to obtain a small crystal size and a sufficient zeolite film thickness. Crystal size was further reduced by adjusting synthesis conditions and utilizing triethoxymethylsilane (TEMS) as a crystal growth inhibitor. Zeolite film morphology and crystal orientation did not show any significant effect on reactor performance. However, reaction rate was found to increase with decreasing TS-1 crystal size in the zeolite films and with increasing amount of tetrahedrally coordinated Ti(IV). Catalyst deactivation was observed, caused by the presence of organic compounds and Ti leaching from the microporous framework. [Copyright &y& Elsevier]

A ZIF-8/NaA composite membrane microreactor was fabricated on multi-channel stainless steel plate. NaA zeolite membrane was first introduced into the microchannel as a modification layer via a secondary growth. Subsequently, a layer of ZIF-8 membrane was grown over the NaA zeolite layer as a catalytic layer by using ZnO-induced synthesis method. Such ZIF-8/NaA composite membrane microreactor was applied in continuous flow Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate. Nearly 100% product yield was achieved in a short residence time under mild conditions. Importantly, no obvious deactivation was observed even after 50 h, indicating its excellent stability. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel Fe3O4@ZIF-8 core–shell microsphere is synthesized by a new facile method. [•] The microspheres are easily loaded/unloaded into/out a capillary microreactor. [•] The microreactor filled with the Fe3O4@ZIF-8 catalyst shows excellent performances. [Copyright &y& Elsevier]

Abstract: A catalytic layer of CsNaX zeolite film was deposited on quartz capillary tube by flow synthesis method under hydrothermal conditions. The procedure involved seeding of the capillary tube with zeolite nanocrystals followed by controlled zeolite regrowth and crystallization under flow conditions. The CsNaX capillary microreactor was employed in Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate. The sensitivity of the catalyst to water produced by the condensation reaction was remedied with the use of solvents. Ninety nine percent benzaldehyde conversions were obtained using a traditional solvent DMSO, but decreased with time as water accumulates and poisons the catalyst. Replacing the solvent with an ionic liquid (IL-BMIC) improves water absorption and the catalyst displayed better (i.e., >99%) and stable conversions. [Copyright &y& Elsevier]

New basic zeolite catalysts obtained by grafting amino groups onto NaX and CsNaX zeolites exhibit excellent catalytic activities for Knoevenagel condensation reaction between benzaldehyde and ethyl cyanoacetate (ECA), ethyl acetoacetate (EAA) and diethyl malonate (DEM). The CsNaX-NH2 catalyst also displays higher conversion compared to aminopropylated MCM-41. Knoevenagel condensation reaction in a CsNaX zeolite microreactor performed better than the traditional packed bed reactor (PBR) with an order of magnitude higher productivity (i.e. moles ethyl 2-cyano-3 phenylacrylate produced per hour for each gram catalyst). A nearly fourfold increase in reaction conversion was obtained for the microreactor when CsNaX-NH2 catalyst was used. A membrane microreactor was obtained by incorporating a water-selective, NaA membrane to the multi-channel microreactor. The selective removal of water byproduct during the reaction led to a 25% improvement in reaction conversion for both catalysts. [Copyright &y& Elsevier]

The performance of a membrane microreactor was tested and compared with that of a microreactor, a packed bed reactor (PBR) and a packed bed membrane reactor (PBMR) for the Knoevenagel condensation reaction of benzaldehyde and ethyl cyanoacetate to produce ethyl 2-cyano-3-phenylacrylate. Cs-exchanged NaX faujasite zeolite was used as the base catalyst for this equilibrium-limited reaction. Hydrophilic ZSM-5 membranes were employed in both the membrane microreactor and the PBMR for the selective removal of water byproduct from the reaction. The product yield per pass was low for the packed bed reactor. Higher yields were observed for the microreactor and PBMR, but the best performance belongs to the membrane microreactor, which displayed both supra-equilibrium conversion and better product purity. [Copyright &y& Elsevier]

Using a new fabrication method based on microelectronic fabrication and zeolite thin film technologies, MFI-type zeolites with engineered structures were incorporated as catalyst, membrane and structural material within the design architecture of a microreactor, membrane microseparator and microeletrochemical cell. Complex microchannel geometry and network (<5 μm), as well as zeolite arrays (<10 μm) were successfully fabricated onto highly orientated supported zeolite films. The zeolite micropatterns were stable even after repeated thermal cycling between 303 and 873 K for prolonged period of time. Blueprints for zeolite-based microchemical systems were presented, and test units were fabricated and the structural details of the microdevices’ architecture were analysed. [Copyright &y& Elsevier]