The physical size, or mesh size, of a carbon must be considered in relation to the flow rate in the system it is to be used. Naturally, the smaller the carbon’s mesh size, the greater its resistance to flow. Thus, it is usual to select the smallest mesh size carbon that will satisfy the pressure drop limitations of the system.
Ash content is less important except where the carbon is used as a catalyst support since certain constituents of the ash may interfere or destroy the action of precious metal catalysts. Ash content also influences the ignition point of the carbon—this may be a major consideration where adsorption of certain solvents is concerned.
The density of carbon is, of course, of great importance to many users in estimating the weight required to fill a vessel.