The invention relates to a reaction device which is used to study the behavior of a catalyst in the presence of reactants. The inventive device includes: various different mass flow regulators, which are used to supply a known controlled stream of gases, a pump which supplies the system with liquid reactants from a container, a hot box, wherein there have been placed a supply current evaporator and preheater, a valve which can be used to select the process path, a reactor into which the catalyst is introduced inside a furnace, a system which can be used to separate the liquid and gaseous products by cold condensation under pressure and which controls the pressure in the line of output gases, and a system for controlling the level in the decantation operation, the system being automated and computerized.