Method of copolymerization in suspension of ethylene with straight-chain alpha-olefins to obtain low-density copolymers

Claim 1

A method of copolymerization in suspension of a liquid aliphatic hydrocarbon reaction medium containing 6 to 8 carbon atoms, gaseous ethylene and at least one alpha-olefin having 3 to 8 carbon atoms to obtain copolymers having a density below 0.940 g/ml, wherein copolymerization is carried out in the presence of a Ziegler catalyst carried on a solid, microspheroidal product obtained by spray drying a solution of magnesium chloride in ethanol or a mixture of ethanol and a higher boiling point solvent and having high catalytic activity, characterized in that: (a) the gaseous ethylene, at least one alpha-olefin and catalyst are introduced into the reaction medium and a first reaction step is carried out at a temperature between 45° and 65° at a pressure of 2 to 6 bars for 20 seconds to 30 minutes, (b) the resulting copolymer suspension is then subjected to a second reaction step which is carried out at a temperature between 50° and 80° C. and at a pressure of 5 to 25 bars for between 1 and 3 hours, wherein the reaction medium is supplied with ethylene and alpha-olefin and, if required, with further quantities of solvent but not with further quantities for catalyst, (c) the amount of alpha-olefin supplied during the first step is adjusted so as to maintain the concentration of alpha-olefin in the reaction medium at between 4% and 7% by weight, (d) the amount of alpha-olefin supplied during the second reaction step is adjusted so as to maintain the concentration of alpha-olefin in the reaction medium at between 15% and 20% by weight, (e) the copolymer obtained from the hydrocarbon suspension is recovered by conventional separation means and the product is dried without any process for destroying or eliminating the catalyst.

Claim 2

A method of copolymerization in suspension of a liquid aliphatic hydrocarbon reaction medium containing 6 to 8 carbon atoms, gaseous ethylene and at least one alpha-olefin having 3 to 8 carbon atoms to obtain copolymers having a density below 0.940 g/ml, wherein copolymerization is carried out in the presence of a Ziegler catalyst carried on a solid, microspheroidal product obtained by spray drying a solution of magnesium chloride in ethanol or a mixture of ethanol and a higher boiling point solvent and having high catalytic activity, characterized in that: (a) the gaseous ethylene, at least one alpha-olefin and catalyst are introduced into the reaction medium and a first reaction step is carried out at a temperature between 45° and 65° at a pressure of 2 to 6 bars for 20 seconds to 30 minutes, (b) the resulting copolymer suspension is then subjected to a second reaction step which is carried out at a temperature between 50° and 80° C. and at a pressure of 5 to 25 bars for between 1 and 3 hours, wherein the reaction medium is supplied with ethylene and alpha-olefin and, if required, with further quantities of solvent but not with further quantities for catalyst, (c) the amount of alpha-olefin supplied during the first step is adjusted so as to maintain the concentration of alpha-olefin in the reaction medium at between 4% and 7% by weight, (d) the amount of alpha-olefin supplied during the second reaction step is adjusted so as to maintain the concentration of alpha-olefin in the reaction medium at between 15% and 20% by weight, (e) the copolymer obtained from the hydrocarbon suspension is recovered by conventional separation means and the product is dried without any process for destroying or eliminating the catalyst.