Design of feed segments in microreactors: Influences of arrangements and shapes of segments on product composition for multiple reactions

In many microreactors, reactant flows are split into many lamination segments and then fed into the reactor to enhance mixing efficiency. This feeding method is applied since mixing in microreactors is mainly driven by diffusion because of low Reynolds and thus the mixing time is proportional to the square of diffusion length. The mixing efficiency of reactants greatly influences the product composition for multiple reactions. In most multiple reaction systems, fast mixing is effective to improve yield and selectivity of desired products. Thus, relations among design factors for the feed segments, mixing efficiency, and product composition of multiple reactions are important to establish a design method of microreactors using this feeding method to produce desired products at high yield and selectivity. We studied influences of the design factors for the segments on mixing efficiency and product composition for a multiple reaction system by using CFD simulations. The design factors studied were arrangements, aspect ratio of the rectangular cross section, and cross-sectional shapes of feed segments at the reactor inlet. The results showed that the cross-sectional arrangements and shapes that enable reactants to diffuse to every direction are effective to fasten mixing and improve yield of the desired product. The mixing efficiency is also improved with increase in the aspect ratio when the cross-sectional area of the segment is fixed. This result indicated that the direction that has shorter diffusion length affects greatly the average mixing efficiency on the plane perpendicular to the axial direction. Consequently, the influence of the diffusion direction and that length to each direction are important when we consider the effect of design factors on the yield and selectivity of desired product of multiple reactions.