A method for charging a catalyst into a reactor (40) comprising a separation loop (21), comprising the following steps: a) filling the reactor (40) with a solvent S1; b) filling the separation loop (21) with said solvent S1; c) causing said solvent S1 to move in the synthesis reactor (40) and the separation loop (21); d) heating the reactor (40) to a temperature of 100° C. or less; e) injecting an inert gas into the bottom of the reactor (40); f) mixing said catalyst with a solvent S2 in a vessel (30) in order to obtain a liquid/solid mixture; g) increasing the pressure in the vessel (30) then sending the liquid/solid mixture to the reactor (40); h) withdrawing said solvent S1 and/or S2.