Improved multi-stage process for producing multi-modal ethylene polymer composition

Multi-stage polymerization process for the production of a multi-modal linear low density polyethylene in at least two staged reactors connected in series comprising at least (i) polymerizing in a first slurry phase stage ethylene monomers and optionally one or more alpha-olefine comonomers, in the presence of a Ziegler-Natta polymerization catalyst system to obtain a first polyethylene fraction component (A) (ii) polymerizing in a second gas or slurry phase stage ethylene monomers and one or more alpha-olefine comonomers, in the presence of a Ziegler-Natta polymerization catalyst system to obtain a second polyethylene fraction component (B), whereby the Ziegler-Natta polymerization catalyst system comprises 1) a solid procatalyst formed by contacting at least: a) a Mg-alcoholate complex of the formula (I): Mg(OR 1 ) 2-n (R 1 ) n , wherein each R 1 independently represents a C 1 -C 20 hydrocarbyl group and 0 ‰¤ n < 2 and may or may not be an integer; b) an aluminium compound of the formula (II) Al(R 2 ) m X 3-m , wherein each R 2 independently represents an alkyl of up to 6 carbon atoms; each X is independently a halogen; 0 ‰¤ m < 3 and m and may or may not be an integer c) a vanadium compound and a titanium compound in portions such as to provide a molar ratio of V:Ti from 10:90 to 90: 10 in order to yield the solid procatalyst and 2) one or more organometallic cocatalyst(s) of the formula (III) wherein each R is independently a C 1 -C 20 -alkyl group, 0 ‰¤ x ‰¤ 2; 1 ‰¤ y 5 3; 0 5 z 5 2 and x + y + z = 3; x, y and z may or may not be an integer, yielding a multi-modal polyethylene, whereby the process shows a reduced change of comonomer response with polymerization time and a more stable comonomer conversion with polymerization time compared to multi-stage processes using Ziegler-Natta catalysts with 100% Ti.