Reactor for chemical reactions which are carried out in triphasic systems (liquid, gas, solid) which includes a bottom head into which the reagent gas is fed, through an inlet nozzle; one or more superimposed thermal exchange sections, each of these sections being immersed in the corresponding synthesis sections; a head containing outlet nozzles for discharging the suspension and outlet nozzles for discharging the non-reacted gas and a group of inclined transversal diaphragms for separating the particles of liquid and/or solid drawn therein.