PROCESS FOR THE PREPARATION OF ETHYLENE HOMOPOLYMERS OR COPOLYMERS IN A HIGH-PRESSURE REACTOR CONTROLLED BY A MODEL BASED PREDICTIVE CONTROLLER

摘要

Process for the preparation of ethylene homopolymers or copolymers in the presence of 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 one or more reaction zones, 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 if an ethylene homopolymers 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 if 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) if 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, if 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, method of controlling a process for the preparation of ethylene homopolymers or copolymers in a high-pressure reactor and method for transitioning from one grade to another in a process for the preparation of ethylene homopolymers or copolymers in a high-pressure reactor.