This invention describes gas-solid, liquid-solid and gas-solid-liquid processes in microchannels devices including such processes as heterogeneous catalysis, particle formation, particle attrition, particle separation and adsorption or desorption of selected species. Various processes can be enhanced by the unique properties of microchannels such as the predominance of laminar flow, high rates of shear, high rates of heat transfer and high rates of mass transfer. Also encompassed by this invention are methods for the introduction to and removal from microchannels of particle containing fluid streams.