Manufacture of ethylene homopolymers and copolymers

Claim 1

In a process for the continuous manufacture of ethylene homopolymers or of copolymers of ethylene with up to 15 mole %, based on the ethylene, of α-monooelefins of 3 to 8 carbon atoms, by catalytically polymerizing the monomer or monomers at from 60° to 115° C. and at ethylene partial pressures of from 1 to 40 bars in an alkane hydrocarbon of 4 to 6 carbon atoms, which is liquid under the polymerization conditions and is a solvent for the monomer or monomers but a non-solvent for the polymer formed, the polymer being isolated by (a) discharging, from the polymerization chamber, a mixture essentially consisting of polymer, alkane hydrocarbon and monomer or monomers, (b) bringing the mixture from stage (a) to from 1.1 to 3 bars and to from 20° to 120° C., to form a gaseous phase, essentially consisting of the monomer or monomers and alkane hydrocarbon, the constituents of which phase are recycled to the polymerization chamber, and a solid phase essentially consisting of polymer with from 0.1 to 8 percent by weight, based on the weight of the polymer, of alkane hydrocarbon adhering thereto, and (c) flushing the solid phase from stage (b) at from 1 to 2 bars, and at from 20° to 130° C., with an amount of nitrogen which is from 1 to 30 times the amount by volume of the polymer, to form a solid phase consisting of substantially pure polymer, which is separated off as such, and a gaseous phase consisting essentially of alkane hydrocarbon and nitrogen, the improvement comprising: (d) adjusting the gaseous phase from stage (c) to from 1.1 to 40 bars above atmospheric pressure and lowering the temperature to the point that two phases form, namely a gaseous phase essentially consisting of nitrogen, which can, if desired, be combined with the nitrogen for stage (c), and a liquid phase essentially consisting of alkane hydrocarbon, and (e) separating the liquid phase from stage (d) into two portions, by evaporating from 2 to 50 percent by volume of the liquid phase at from 1 to 3 bars to form the first portion, which is combined with the gaseous phase from stage (c), and recycling the remaining amount of the liquid phase, as the second portion which may or may not be in the gaseous state in an intermediate stage, to the polymerization chamber.