Catalyst composition pre-formation unit for preparing a catalyst composition for oligomerization of ethylene

A method of making a catalyst composition for the oligomerization of ethylene, comprising:

• preparing, in a first vessel having a first gas inlet, in a first solvent, a first solution by mixing a co-catalyst and a modifier, wherein the co-catalyst is selected from trialkyl aluminum, alkyl aluminum sesquichloride, dialkyl aluminum chloride, or alkyl aluminum dichloride, and wherein the modifier is selected from ammonium or phosphonium salts of the formula [H4E]X, [H3ER]X, [H2ER2]X, [HER3]X or [ER4]X or HX or RX wherein E is N or P, X is Cl, Br or I and R is alkyl, cycloalkyl, acyl, aryl, alkenyl, alkynyl or the corresponding bridging di-, tri- or multi-units, or ammonium or phosphonium salts based on cyclic amines;
• adding a chromium compound and a ligand from a second vessel having a second gas inlet to the first solution to obtain a second solution;
• and
• optionally mixing the second solution for 10 seconds to 5 hours, in a mixing unit;
• wherein the first vessel, the second vessel, and the mixing unit are at least partly within a temperature controlled enclosure.