Membrane microreactors zeolite membranes

The following are some of the reasons that microreactors can be be used (i) reduced mass and heat transfer limitations, (ii) high area to volume ratio, (iii) safer operation, and (iv) ease of seating up by numbering out. The advantages of scaling down zeolite membranes are that it could be easier to create defect-free membranes and... 

The application of zeolite membranes in microreactors is still in an early stage of development, and suffers sometimes from unexpected problems arising from template removal [70]. However, several application examples of zeolite membranes in microstructured devices have been demonstrated yielding similar advantages as were to be expected from experiences on the macroscale. Because of the high surface to volume ratio of microreactors, the application of zeolite membranes in these systems has great potential. 

Gavriilidis, a., Yeung, K. L., Design and fabrication of zeolite-based microreactors and membrane microseparators, Micropor. Mesopor. Mater. 42 (2001)... 

The efforts and advances during the last 15 years in zeolite membrane and coating research have made it possible to synthesize many zeolitic and related-type materials on a wide variety of supports of different composition, geometry, and structure and also to predict their transport properties. Additionally, the widely exploited adsorption and catalytic properties of zeolites have undoubtedly opened up their scope of application beyond traditional separation and pervaporation processes. As a matter-of-fact, zeolite membranes have already been used in the field of membrane reactors (chemical specialties and commodities) and microchemical systems (microreactors, microseparators, and microsensors). 

Lai SM, Ng CP, Martm-Aranda R, Yeung KL. Knoevenagel condensation reaction in zeolite membrane microreactor. Micropor Mesopor Mater 2002 66(2-3) 239-252. 

Lau W N, Yeung K L, Zhang X F and Martin-Arand R (2007), Zeolite membrane microreactors and their performance , Stud Surf Sci Catal, 170,1460-1465. 

Following the principles of process intensification, there has been recently a growing interest in integration of unit operations by merging a microreactor vrith a membrane separation unit. The concept of membrane microreactors is applied in biocatalysis [97,98], and chemical catalysis where various catalysts can be attached to the membrane pores (zeolites [99], carbon nanofibers as support [100], metals [101]) (Figure 9.25). 

Lau, W.N., Zhang, X.F., Yeung, K.L., and Martin-Aranda, R. (2005) Zeolite membrane microreactor for fine chemical synthesis. Stud. Surf. Sci. Catal., 158, 1335-1342. 

Among the many classes of microreactor which have been used in organic phototransformation, we will limit our discussion only on molecular-sieve zeolites, Nafion membranes, vesicles, and low-density polyethylene films. 

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 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. 

Oxidation of Aliphatic Compounds. - A general review of the use of supra-molecular systems as microreactors for photochemical reactions contains a section dealing with the photosensitized oxidation of alkenes included in zeolites, nation membranes and vesicles. Particular consideration is given to the possibility of controlling the form and environment of the sensitizer and substrate so that the reaction selectively follows an energy-transfer or an ET pathway. The same authors have also provided a more substantial review on the same theme. Recent developments in relation to the stereochemistry and mechanism of the ene photooxygenation of alkenes by O2 have also been reviewed. ... 

Knoevenagel condensation between carbonyl compounds and methylene malo-nic esters on a CsNaX zeolitic coating in a microreactor demonstrated an order of magnitude higher productivity as compared with a traditional packed-bed reactor while the selectivity remained the same in both reactors [107,108]. A nearly fourfold increase in reaction conversion was obtained for the microreactor when NH2 modified CsNaX zeolitic coatings were apphed [109]. The conversion was further improved when zeolitic coatings were grown onto a stainless steel membrane (0.2 pm pores) inserted in a microreactor [110]. 

Currently, the membranes incorporated in MMRs are mainly zeolite and Pd-based dense metal ones. Incorporation of these membranes in microreactors can be achieved using one of the preparation methods described in previous chapters. 

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