What is proposed is a process for preparation and distillative workup of diphenylmethane diisocyanate (MDI), proceeding from a benzene-comprising feedstream, in which, in a catalytic hydrogenation of nitrobenzene to aniline, steam is raised at two different pressure levels, which partly or completely covers the energy demand for the overall process, by using two fluidized bed reactors of identical design, of which a first fluidized bed reactor is operated with an aniline load for which the fluidized bed reactors have been designed and provides steam at a first, lower pressure level, and a second fluidized bed reactor is operated with a load lowered with respect to the first fluidized bed reactor to such an extent that the second fluidized bed reactor affords steam at the higher pressure level.