Process for the polymerization and copolymerization of ethylene, using a gas injection device

Claim 1

In a process for the polymerisation or copolymerisation of ethylene in a reactor at a pressure greater than 1,000 bars, which process includes cooling the reactor effluent comprising a mixture of polymer and monomer between a pressure-reduction valve located downstream from the reactor and a separator operating at 200 to 500 bars, separating polymer from monomer in the separator and recycling separated monomer to the reactor, the improvement comprising: (A) injecting fresh monomer into the reactor effluent between the valve and the separator at a temperature lower than that of the reactor effluent and at a pressure below that of the separator using a gas injection device comprising at least one assembly comprising (1) a convergent ejection nozzle of throat cross-section S 1 substantially at the downstream end of said nozzle, through which arrives at a flow rate Q, motive fluid consisting of reactor effluent; (2) a convergent mixing zone which said fluid enters after passing through said ejection nozzle to be mixed with the monomer injected, which is supplied at a flow rate q, said mixing zone at its upstream end having a larger cross-section than S 1 ; and (3) a diffuser of throat cross-section S 3 constituting the downstream end of said mixing zone, wherein the ratio Q/S 1 is between 0.20 and 1.35 t/hr.mm 2 and the ratio (q+Q)/S 3 is between 0.1 and 0.3 t/hr.mm 2 , the pressure of said fluid entering said ejection nozzle being higher than the pressure of said separator and between about 400 and 2,500 bars and the pressure of said injected monomer being not greater than 180 bars whereby the pressure of the fluid is brought down to the pressure of the separator; and (B) substantially all of said fresh monomer for the polymerization process being supplied by its injection into the reactor effluent using said gas injection device.