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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: A multichannel membrane microreactor for continuous selective oxidation of aniline by hydrogen peroxide on TS-1 nanoparticles was successfully demonstrated. The high surface area to volume ratio that can be attained in the microreactor (3000m2/m3) facilitates the selective removal of water by-product, which reduces the effect of catalyst deactivation during the reaction. An improvement in the product yield and selectivity towards azoxybenzene was also observed. Azobenzene was obtained as by-product and its formation was attributed to homogeneous reaction of nitrosobenzene with aniline. Increasing temperature was beneficial for both yield and selectivity, but beyond 340K, microreactor operation was ineffective due to bubble formation and hydrogen peroxide decomposition. [Copyright &y& Elsevier]

Abstract: Five silicalite-1 zeolite seeds of around 100nm, 600nm, 1.5μm, 3.0μm and 7.5μm were prepared. The preparation of porous α-alumina supports seeded using slip-casting technique and respective zeolite silicalite-1 membranes regrown by hydrothermal synthesis was investigated for different seed sizes. The effects of seed sizes on the formation of seed layers and zeolite membranes were studies in detail. It has been found that seed sizes have important effects on the formation of seed layers that determines the quality of regrown zeolite membranes. The seed layer and the regrown membrane from smallest seed (100nm) are most uniform and densest. With the increase of seed sizes (from 600nm to 3μm), the seed layers and the membranes become coarser and the intergrowth of the membranes becomes poorer. Increasing synthesis temperature favors improving the crystal intergrowth of the membrane, reducing the voids and changing the orientation of crystal growth. The zeolite particles with the size of 600nm and 1.5μm may act as seeds to form a continuous and uniform seed layer and membrane layer, whereas using zeolite seeds of 7.5μm, a continuous membrane cannot be obtained because of the formation of an incontinuous seed layer. [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]

Abstract: Sn-Beta zeolites were prepared by a rapid and clean steam-assisted conversion (SAC) method from dry stannosilicate gel. The amorphous gel was converted to highly crystalline Sn-Beta within 5h at mild reaction temperature of 453K. The properties of the as-prepared samples were characterized by XRD, SEM, FT-IR, UV–Vis, UV-Raman, ICP and N2 adsorption. A high gel conversion to BEA can be obtained with Sn4+ inserted in the zeolite framework. The SAC method was successfully used to produce pure silica Beta zeolite (Si/Sn=∞) to Sn-Beta zeolite with 3.8wt.% SnO2 (i.e., Si/Sn=83). The Sn-Beta prepared by SAC method is an efficient catalyst for Baeyer–Villiger (B–V) reaction of cyclohexanone to ε-caprolactone. [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]

Abstract: A monolayer of zeolite nanoparticles was deposited uniformly on SiO2 beads’ surface by a new seeding method based on the combined use of organic linker and dip-coating procedure. The seeds were transformed into a well-intergrown TS-1 zeolite film and characterizations by SEM and XRD indicated that the film has a preferred (011) orientation. EDXS, XPS and UV–vis spectroscopies confirmed the successful preparation of egg-shell TS-1/SiO2 catalysts. Thin shell catalysts (i.e., <11μm) were more active for styrene oxidation. Conversion reaction rate of 8.9mmolg−1 h−1 and turnover frequency of 28h−1 were obtained with aromatic aldehydes (i.e., benzaldehyde and phenyl acetaldehyde) being the main products. Greater mass transfer resistance made thick shell catalysts less efficient with lower specific conversion rate of 6.9mmolg−1 h−1 and turnover frequency of 25h−1. Also, the extra-framework titanium resulting from the longer synthesis led to poorer selectivity. Egg-shell TS-1/SiO2 catalyst beads were shown to be resistant to attrition and were easier to separate and recover from reaction. [Copyright &y& Elsevier]

Abstract: Pd membrane with excellent stability was prepared on macroporous α-Al2O3 tubes using a nanoporous Sil-1 zeolite as an intermediate support and diffusion barrier layer. The detailed microstructure of the composite membrane was examined by scanning electron microscopy and mapped by EDXS and EPMA to reveal a palladium membrane anchored by multi-legs Pd protrutions that penetrates through the interstices of the zeolite grains into the seed layer. This membrane architecture allowed the membrane to tolerate rapid and repeated cycling of gases, temperature and pressure over 300h without lost of permeance and selectivity. The zeolite layer contributed up to 25% of the transport resistance across the Pd–Sil-1 composite membrane and has a significant effect on the hydrogen permeance. [ABSTRACT FROM AUTHOR]

Abstract: Titanium silicalite-1 (TS-1) films were prepared on porous α-Al2O3 tubes using nanosized silicalite-1 (Sil-1) particles as seeds by hydrothermal treatment and a TS-1 catalytic membrane reactors (CMR) was reasonably designed and evaluated by phenol hydroxylation with hydrogen peroxide as oxidant. Some factors on influencing TS-1 film formation and catalytic properties were investigated and the TS-1 films were characterized by scanning electron microscope (SEM), transmission electron micrograph (TEM), X-ray diffractometer (XRD), FTIR, UV–vis and X-ray fluorescence (XRF). It was indicated that TS-1 films prepared from Sil-1 and TS-1 seeds were comparable in structure, morphology and reaction behavior. The crystallization time and times of TS-1 film had a strong effect on its morphology, thickness and orientation. However, the film thickness could be easily controlled by crystallization time and times. The Ti/Si ratio in synthesis solution intensely influenced the content of the titanium atoms incorporated as framework Ti that was correlated well with the activity. The maximum Ti (IV) incorporated corresponds to a Ti/Si ratio of approximately 0.02–0.03. A constant conversion for phenol hydroxylation was obtained with the film thickness of over 7.5μm. It is demonstrated that most of the reaction occurred in a shallow layer near the film due to the mass transfer effects in the TS-1 films. [Copyright &y& Elsevier]

Abstract: Titanium silicalite-1 (TS-1) zeolites and films supported on porous α-Al2O3 tubes were prepared using TS-1 and silicalite-1 (Sil-1) seeds by hydrothermal synthesis. The structure and catalytic properties of the TS-1 powders and films were characterized by SEM, XRD, FT-IR, UV–vis and styrene partial oxidation by hydrogen peroxide. The results showed that TS-1 prepared from Sil-1 seeds were as active as TS-1 from nucleated and TS-1 seeded syntheses, in spite of the concerns about nonuniformity and dilution caused by the use of pure silica Sil-1 seeds. The Ti atoms were successfully incorporated as tetra-coordinated titanium in the zeolite framework and the phenylacetaldehyde selectivity correlates well with the infrared band for Ti–O–Si of the TS-1. Reaction over TS-1 film indicates that reactions occurred at the topmost layer of the film due to the slow diffusion in the zeolite pores. [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]