Cold model of a vibrated-bed microreactor capable of varying Peclet number at fixed weight hourly space velocity, providing a tool for simulating an important feature of the reaction kinetic scene in large catalytic fluid beds.

摘要

A cold-flow model of a vibrated-bed microreactor has been designed and tested with capability for varying the level of gas dispersion (characterized by axial Peclet number) at a fixed weight hourly space velocity (WHSV). A tool has thus been provided whereby an important feature (viz., gas dispersion) of the reaction kinetic scene in large catalytic fluid beds can be simulated on a microscale, using approximately 5 grams of catalyst.;The new microreactor exploits the coherent-expanded (C-E) vibrated-bed state, and is perhaps the first technical use of this state. The C-E state is achieved by subjecting a shallow layer of a fine powder to vertical sinusoidal vibration. The microreactor is charged with a powder, such as fluid catalytic cracking (FCC) catalyst, at a compacted depth of 1 mm, and is vibrated at ;An important object of the present research is to measure horizontal (axial) gas dispersion in a cold model (i.e., an unheated microreactor) by observing the residence time distribution of a tracer gas admitted as a pulse at microreactor inlet. Three mechanisms are responsible for axial gas dispersion. There is a diffusional exchange of gas between the interior and exterior of these packets of particles, and this exchange plays a greater role if the gas molecular diffusivity is large.;We have discovered a general correlation for axial gas dispersion, which incorporates these three mechanisms. The first mechanism displays a finite value at zero gas velocity, and increases in linear fashion with velocity. The second and third mechanisms, together, contribute 1.1 times the gas molecular diffusivity.;Discovery of this general correlation has led to design of a variable-length microreactor in which different levels of fluid-bed gas dispersion (i.e., different Peclet numbers) may be obtained at fixed WHSV simply by varying the length of the duct. (Abstract shortened by UMI.).