An internal static mixing system such as a disperser of mesh wire or expanded metal co-knit with a multi filament material selected from inert polymers, catalytic polymers, catalytic metals or mixtures in combination with a vertical reactor having a reaction zone and the disperser disposed in said reaction zone, particularly for carrying out paraffin alkylation using acid catalyst is disclosed. In an embodiment, a geographic definition, specifying a geographic area, is received. The frame has two frame elements forming openings and at least one frame intermediate element arranged between them.