Process for stabilizing the performances of a catalyst for Fischer Tropsch reaction

A process for maintaining the stability of the performances of a catalyst for Fischer-Tropsch reaction carried out in a slurry bubble column reactor, wherein a solid phase, consisting of a metal cobalt-based catalyst in finely subdivided form, is dispersed in a continuous liquid phase consisting of hydrocarbons, and is kept in suspension by a gaseous phase consisting of synthesis gas, which passes through said liquid phase, in the form of bubbles, comprising:

• a. in the reaction start-up phase, regulating the operative variables, among which, prevalently, the flow-rate of the synthesis gas, so that the PH2O/PH2 ratio between the partial water pressure (PH2O) generated during the reaction, and the partial hydrogen pressure (PH2) gradually increases from 0.4 to 0.8 (without substantially exceeding these limits) for a period of time not shorter than 100-150 hrs and not longer than 200-300 hrs;
• b. in the reaction start-up phase, regulating the operative variables, among which, prevalently, the flow-rate of the synthesis gas, so that the PH2O/Z ratio gradually increases from 0.4 to 0.8 (without substantially exceeding these limits) for a period of time not shorter than 100-150 hrs and not longer than 200-300 hrs, wherein Z is given by the following equation:
• Z=P0·(T/T1)4·e−(K2/t·K3))
• wherein
• P0=1 bar
• T1=100° C.
• T=temperature inside the reactor, in ° C.
• K2=constant equal to 7745 K·nm
• t=temperature inside the reactor as K
• K3=average diameter of the catalyst pores;
• and
• c. at the end of the start up, maintaining the PH2O/PH2 and PH2O/Z ratios substantially the same as, or lower than 0.8, by operating on the same operative parameters of the two phases previously described.