Membrane microreactors MMRs

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. 

Membrane microreactor Membrane is integrated with the microreactor having a characteristic length of <1 mm MMR... 

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). 

When the membrane is integrated in a microreactor having a characteristic length of <1 mm, it is called an MMR. For EMRs, an external electrical circuit is necessary for reactions to proceed. Electrical power can be co-generated with the production of chemicals in the EMRs. 

A distinctive feature of microreactors is the microchannels for fluid flow. MMRs are mainly characteristic of such microchannels with anchored catalysts for reactions and miniature membranes to perform separation, which are formed on the porous ceramic or metal supports. Based on the configuration and architecture of the reactor, MMRs can be classified into two categories plate type and tubular type. 

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. 

Wan et al. [39] investigated the selective oxidation of aniline by hydrogen peroxide to azoxybenzene in a multi-channel MMR, with or without water removal, employing TS-1 nanozeolite as catalyst. The reaction was conducted at different residence times and temperatures. A hydrophilic ZSM-5 membrane was used to remove water selectively from the reaction mixture by membrane pervaporation. The results indicate that catalyst deactivation was reduced during the reaction. An improvement in the product yield and selectivity toward azoxybenzene was also observed. Increasing temperature was beneficial for both yield and selectivity, but beyond 340 K, microreactor operation was ineffective due to bubble formation and hydrogen peroxide decomposition. 

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