Catalytic composition and process for oligomerizing ethylene, in particular to 1-hexene

A catalytic composition comprising a mixture of:

• at least one chromium carboxylate;
• at least one free carboxylic acid comprising one or more carboxylate anions identical or different from carboxylate anions of said at least one chromium carboxylate;
• at least one aryloxy compound of an element M selected from the group consisting of magnesium, calcium, strontium and barium, with general formula M(RO)2-nXn in which RO is an aryloxy radical containing 6 to 80 carbon atoms, X is a halogen atom or a hydrocarbyl radical containing 1 to 30 carbon atoms and n is a whole number that can take the values 0 or 1;
• and
• at least one hydrocarbylaluminum compound selected from the group consisting of tris(hydrocarbyl)-aluminum compounds, chlorinated or brominated hydrocarbylaluminum compounds with general formula AlR′mY3-m, in which R′ is a hydrocarbyl radical containing 1 to 6 carbon atoms, Y is a chlorine or bromine atom and m is a number from 1 to 3, and aluminoxanes;
• wherein the proportion of free carboxylic acid with respect to the chromium is such that the mole ratio of the free acid to the chromium metal is greater than 0.4:1 and less than 3.0:1.