Membrane microreactors reactions

Lai SM, Ng CP, Martin-Aranda R, and Yeung KL. Knoevenagel condensation reaction in zeohte membrane microreactor. Micropor Mesopor Mater 2003 66(2-3) 239-252. 

Lai SM, Martin-Aranda R, Yeung KL (2003) Knoevenagel condensation reaction in a membrane microreactor. Chem Commun 22 218-219... 

Membrane microreactor Fabrication methods Thickness (nm) Reaction Temperature (°C) Catalyst Membrane function References... 

Scheme for membrane microreactors for multiphase reactions, that is, gas-liquid reactions (left), a PSS supported dense PDMS gas-permeable membrane with CNFs as a catalyst support (right). (Aran eta ., 2011) (Copyright permission 2011 Elsevier). 

Ye S Y, Tanaka S, Esashi M, Hamakawa S, Hanaoka T and Miznkami F (2005), Thin palladium membrane microreactor with porons silicon support and their application in hydrogenation reaction , Solid-State Sensors, Actuators and Microsystems, 2005. Digest of Technical Papers. Transducers 05. The 13th International Conference, 2,2078-2082. 

Noel T, Hessel V. Membrane microreactors gas-liquid reactions made easy. ChemSusChem 2013 6(3) 405-7. 

A microfluidic reaction system has also been used for the production of prodrugs. A multichannel membrane microreactor was fabricated and tested for Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate to produce a-cyanocinnamic acid ethyl ester, a known intermediate for the production of an antihypertensive drug [9]. Knoevenagel condensations of carbonylic coiiqtounds and malonic esters yield several important key products such as nitriles used in anionic polymerization, and the a,p-unsaturated ester intermediates employed in the synthesis of several therapeutic drugs that include niphendip-ine and nitrendipine. Unlike most condensation reactions. 

Besides, gas-liquid reactions can be performed within a membrane microreactor where membrane serves for product separation and thereby limits product inhibition [100]. In this version, the fabrication and operation of new hybrid membrane microreactors for gas-liquid-solid reactions is described. The reactors consist of porous stainless steel tubes onto which carbon nanofibers (CNFs) are grown as catalyst support (Figure 9.26). CNFs have high surface area, so they can be efficiently used as a catalyst support. 

Nitrite reduction in water is tested as a model reaction. It is shown that nitrite reduction proceeds by both catalytic reduction (with Pd and H2) and by the reactor material itself (i.e., by Fe on CNFs). Eventually, the latter effect will exhaust in time and the reaction will still proceed with the immobilized Pd-catalyst on the CN Fs and the membrane-assisted supply of hydrogen. Results proved that the porous metallic membrane microreactors with carbon nanofibers are suitable materials for the reduction of nitrite and the reactor design is very promising for the multiphase microreactor technologies [lOOj. 

Lai, S.M., Ng, C.R, Martin-Aranda, R. and Yeung, K.L. (2003) Knoevenagel condensation reaction in zeolite membrane microreactor. Microporous and Mesoporous Materials, 66,239-252. 

Jani, J.M., Can Aran, H., Wessling, M. and Lammertink, R.G.FI. (2012) Modeling of gas-liquid reactions in porous membrane microreactors. Journal of Membrane Science, AimiQ, 57-64. 

Lai S M, Ng C P, Martin-Aranda R and Yeung K L (2003), Knoevenagel condensation reaction in zeolite membrane microreactor , Micropor Mesopor Mat, 66, 239-252. 

The authors developed a multi-layered microreactor system with a methanol reforma- to supply hydrogen for a small proton exchange membrane fiiel cell (PEMFC) to be used as a power source for portable electronic devices [6]. The microreactor consists of four units (a methanol reformer with catalytic combustor, a carbon monoxide remover, and two vaporizers), and was designed using thermal simulations to establish the rppropriate temperature distribution for each reaction, as shown in Fig. 3. 

Another example for microreactor-controlled selectivity in the reaction of olefin with x02 can be found in the photosensitized oxidation of DPB in ZSM zeolite [160], Nafion membranes [161], and vesicles [163], In homogeneous solution, ZSM zeolite, and Nafion membranes, the oxidation of DPB with 02 yielded the [2 + 4] reaction product, endoperoxide 6, as the unique product (Figs. 15 and 18). In sharp contrast, in vesicle medium, the oxidation produced the aldehydes 1 and 2 ([2 + 2] reaction) in quantitative yield as described in Section III.B.l (Fig. 

The field of chemical process miniaturization is growing at a rapid pace with promising improvements in process control, product quality, and safety, (1,2). Microreactors typically have fluidic conduits or channels on the order of tens to hundreds of micrometers. With large surface area-to-volume ratios, rapid heat and mass transfer can be accomplished with accompanying improvements in yield and selectivity in reactive systems. Microscale devices are also being examined as a platform for traditional unit operations such as membrane reactors in which a rapid removal of reaction-inhibiting products can significantly boost product yields (3-6). 

The benefits of the use of micromembranes for the selective removal of one or more products during reaction have been demonstrated for equdibrium-limited reactions [289]. For example, the performance of hydrophilic ZSM-5 and NaA membranes over multichannel microreactors prepared from electro-discharge micromachining of commercial porous stainless steel plates was studied by Yeung et al. in the Knoevenagel condensation [290,291] and andine oxidation to azoxybenzene [292]. For such kind of reactions, the zeolite micromembrane role consists of the selective removal of water, which indeed yields higher conversions, better product purity, and a reduction in catalyst deactivation in comparison to the traditional packed bed reactor. 

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