Avoiding segregation during the loading of a catalyst-inert powder mixture in a packed micro-bed

The optimal loading protocol of a microreactor (catalyst and inert: 0.1 mm, column: 2 mm internal diameter) with a catalyst-inert mixture is fundamentally different from that of a conventional lab-scale reactor (typical values: catalyst, 2 mm; inert, 0.2 mm; column, 10 mm internal diameter). This is shown to be due to segregation, occurring during loading. The following loading procedure has been used: premix the powders, funnel the mixture down, drop it within the reactor, and densify the bed. The average time a particle takes, from the mixing vial to reach its final position, depends on its properties, which in general results in an axially segregated bed. Radial segregation is observed for particles smaller than 60 mu m, as a result of electrostatic forces. This paper describes for each handling step how to minimise segregation during the loading of a catalyst-diluent solid mixture. This includes using a funnel with a low-friction and steep wall, minimising difference in velocity of particle-gravity flow, and adding more inert after the mixture, prior to the densification step. The term rho(p)d(p)(2) is shown to sufficiently predict segregation due to the velocity difference during gravity flow. Segregation can be observed relatively easily in a glass mock-up reactor. Optimising all the handling steps to minimise segregation results in a visually homogeneous bed. (C) 2009 Elsevier B.V. All rights reserved.