Process for coating small solids

摘要

The present invention is directed to processes and apparatus useful for fluidizing small particulate solids having a diameter of less than about 50 microns in average particle size, and at least partially enveloping these small solids with a coating material or a precursor thereto. The basic apparatus of this invention comprises: a cross-current multi-stage fluid bed reactor having N fluid beds in flow communication with one another, wherein N>2; means for introducing small solid particles to a bed selected from the N beds of the reactor; means for introducing a fluidizing gas to the N beds of the reactor, thereby promoting a flow of the small solid particles from the first bed through bed #N of the multi-stage fluid bed reactor; means for introducing a coating material or a precursor thereto, to one or more of the N beds of the reactor; means for distributing the coating material or precursor thereto throughout the cross-section of the reactor beds containing the same; means for controlling the residence or contact time of the small articulate solids in the beds containing the coating material or the precursor thereto, such that the small particulate solids therein are at least partially enveloped by the coating material or precursor thereto; and one or more exit means for removal of the fluidizing gas and the small solid particles at least partially enveloped by coating material or precursor thereto.