Patent ID: 8710160
Filing Date: 2014-04-29
Classification: C08F

Abstract:
1. A process for the preparation of ethylene homopolymers or copolymers in the presence of a free-radical polymerization initiator at from 100° C. to 350° C. and pressures in the range of from 160 MPa to 350 MPa in a high-pressure polymerization unit comprising a high-pressure reactor with at least one reaction zone, to each of which free-radical polymerization initiator is fed, which is controlled by a model based predictive controller carrying out the steps: a) feeding target values for density and melt flow rate (MFR) of the ethylene homopolymer to be prepared as setpoint ranges to the controller when an ethylene homopolymer is prepared or feeding target values for density, MFR and copolymer composition of the ethylene copolymer of to be prepared as setpoint ranges to the controller when an ethylene copolymer is prepared; b) measuring data in the high-pressure polymerization unit and calculating by means of a model based on these data a value for the density of the ethylene homopolymer or copolymer currently prepared in the high-pressure reactor; c) independently of step b), measuring data in the high-pressure polymerization unit and calculating by means of a model based on these data a value for the MFR of the ethylene homopolymer or copolymer currently prepared in the high-pressure reactor; d) when an ethylene copolymer is prepared, independently of steps b) and c), measuring data in the high-pressure polymerization unit and calculating by means of a model based on these data a value for the copolymer composition of the ethylene copolymer currently prepared in the high-pressure reactor; e) feeding the calculated values for the density, for the MFR and, when an ethylene copolymer is prepared, for the copolymer composition as controlled variables to the controller; and f) measuring data in the high-pressure polymerization unit and calculating by means of the controller based on these measured data, the setpoint ranges fed in step a) and the values calculated in steps b), c) and d) as outputs setpoint ranges for manipulated variables of the high-pressure polymerization unit including setpoint ranges for feeding the free-radical polymerization initiator, wherein the calculation of the setpoint ranges for feeding the free-radical polymerization initiator is repeated at least every 3 minutes.