Forced-flow membrane reactors configuration

When the catalyst is immobilized within the pores of an inert membrane (Figure 25.13b), the catalytic and separation functions are engineered in a very compact fashion. In classical reactors, the reaction conversion is often limited by the diffusion of reactants into the pores of the catalyst or catalyst carrier pellets. If the catalyst is inside the pores of the membrane, the combination of the open pore path and transmembrane pressure provides easier access for the reactants to the catalyst. Two contactor configurations—forced-flow mode or opposing reactant mode—can be used with these catalytic membranes, which do not necessarily need to be permselective. It is estimated that a membrane catalyst could be 10 times more active than in the form of pellets, provided that the membrane thickness and porous texture, as well as the quantity and location of the catalyst in the membrane, are adapted to the kinetics of the reaction. For biphasic applications (gas/catalyst), the porous texture of the membrane must favor gas-wall (catalyst) interactions to ensure a maximum contact of the reactant with the catalyst surface. In the case of catalytic consecutive-parallel reaction systems, such as the selective oxidation of hydrocarbons, the gas-gas molecular interactions must be limited because they are nonselective and lead to a total oxidation of reactants and products. For these reasons, small-pore mesoporous or microporous... 

Figure 4.3f shows a way of contact of the reactants on the catalytic membrane based on the forced flow of both reactants through the catalytic layer directly from one membrane side. Tliis configuration with respect to traditional reactors can offer an important improvement in the contact of reactants with the catalytic sites. Mass transfer from the gas phase to the liquid phase will occur in the same way as traditional reactors the liquid phase needs to be previously saturated with the gas reactant. The features of this last feeding configuration have been reported by Reif and Dittmeyer (2003) for both the catalytic nitrite reduction and the dechlorination of chloroform. 

Forced-flow-type hollow fibre polymeric membrane reactor operated in the (a) crossed-flow configuration (b) dead-end configuration. (Adapted from Macanas ef a/. Reprinted with permission from Elsevier, Copyright (2010).)... 

Temperature profiles, methane conversion, HRF and permeated flow are shown in Fig. 14.6. Figure 14.7 shows the membrane temperature profile and the permeation driving force along the reactor. Table 14.4 shows the permeation results and the product outcome, outlining that total hydrogen permeated is lower (26%) for the counter-current configuration. The calculated HRF and methane conversion ( CH4 ) in the counter-current flow... 

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