Membrane microreactors fabrication

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

Abstract Process intensification (PI) is the future direction for the chemical and process industries and in this chapter, two key technologies to achieve this are discussed microreactors and so-caUed membrane microreactors (MMRs).There is great potential to enhance the overall efficiency of microreactors by integrating them with membrane technologies to make MMRs and there are tremendous opportunities for the application of MMRs in many fields. This chapter reviews microreactor design, fabrication and apphcations as well as materials for micromembranes (MM). The integration of MMs with microreactors and the applications of the resulting MMRs are then discussed. 

Further gas-phase studies include the work of Maria et al., who used an isothermal differential microreactor to study the dehydrogenation of cyclohexane and its methyl derivatives [25]. Ye et al. fabricated a Pd membrane microreactor from a silicon wafer using surface and bulk micromachining to study the hydrogenation of 1-butene [19]. 

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. 

When the membrane tube is reduced in diameter to a certain level, that is, ID < 1 mm, it becomes a hollow fiber and the fiber lumen may take on the effect of a microchannel on the fluid flow. The catalyst can be coated on the inner surface of the hollow fiber or impregnated inside the porous wall, while the separation is achieved by the porous hollow fiber itself or by the membrane formed on the outer surface of the hollow fiber, as shown in Figure 8.5. Such catalytic hollow fiber membranes can easily be fabricated into MMRs, called hollow fiber membrane microreactors (HFMMRs). 

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

The process of wet-chemical etching of single-crystalline silicon was the first process suitable for the mass fabrication of micromechanical components [53]. Simple geometric structures like grooves, channels or membranes have been incorporated in microreactor components such as pumps, valves, static mixers and (most often) analytical devices. Bonding processes, either thermally or... 

Besides the synthesis of bulk polymers, microreactor technology is also used for more specialized polymerization applications such as the formation of polymer membranes or particles [119, 141-146] Bouqey et al. [142] synthesized monodisperse and size-controlled polymer particles from emulsions polymerization under UV irradiation in a microfluidic system. By incorporating a functional comonomer, polymer microparticles bearing reactive groups on their surface were obtained, which could be linked together to form polymer beads necklaces. The ability to confine and position the boundary between immiscible liquids inside microchannels was utilized by Beebe and coworkers [145] and Kitamori and coworkers [146] for the fabrication of semipermeable polyamide membranes in a microfluidic chip via interfacial polycondensation. 

The small dimensions in microreactors imply the presence of laminar flow. This type of flow makes it easier to extract chemical kinetic parameters and fully characterize phenomena. The correct incorporation of the active catalyst onto the surface of the membrane is one of the important aspects of catalytic microreactors. Drott et al. (1997) investigated the use of porous silicon as a carrier matrix in microstructured enzyme reactors. The matrix was created by anodization and the fabrication of the microreactor used flow-through silicon cell comprising 32 channels of 50 pm wide, 250 pm deep and separated by 50 pm. The aim was to increase the surface area on which the enzymes (glucose oxidase) could be coupled. Comparisons were made with the classical non-porous reference device and the glucose turnover rates. The results showed that when compared with the reference reactor the enzyme activity increased 100-fold. 

Cui, T., Fang, J., Zheng, A., Jones, F., Reppond, A. (2000). Fabrication of microreactors for dehydrogenation of cyclohexane to benzene. Sensors and Actuators B Chemical, 71,228—231. Dittmeyer, R., Hollein, V., Daub, K. (2001). Membrane reactors for hydrogenation and dehydrogenation processes based on supported palladium. Journal of Molecular Catalysis A, 173, 135-184. 

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