Patent ID: 6723805
Filing Date: 2004-04-20
Classification: C08F,Y10S

Abstract:
A process for the controlled production of polyethylene and its copolymers in gas phase fluidized reactor(s), isolated or combined, under polymerization conditions, in the presence of hydrogen, oxygen, inert diluent(s) and chromium catalyst, wherein said process comprises the steps of:a) In the laboratory, periodically testing the MFR1, MFRR and the density of a resin; b) establishing the desired values or limits for the set of CVs and CCVs which comprises production rate, MFR1, MFRR and the density of the resin, catalyst productivity, opening of a temperature control valve, monomer partial pressure and superficial velocity of the gas in the reactor; c) determining, in real time, the value of the variables cited in item b), the properties of the resin having their value continuously inferred with the aid of mathematical models d) establishing limits for the set of MVs which comprises flow rate of catalyst, ratio between the concentrations of one or more comonomers and ethylene, ratio between the flow rates of one or more comonomers and ethylene, temperature of the fluidized bed, ratio between the flow rates of oxygen and ethylene, ratio between the flow rates of hydrogen and ethylene, flow rate of a recycle stream, flow rate of inert diluent(s) and opening of a purge valve; e) establishing limits for the variation rate of the variables of item d); f) using process mathematical models, simultaneously calculating the values which should be assumed under a stationary regimen by the variables cited in item d), considering that the level of the fluidized bed as well as the reactor pressure will be kept at constant values, so that the desired values set forth in b) will be reached without violating the limits established in items b) and d); g) determining the sequence of adjustments, to be effected during a pre determined period of time, so that the variables cited in d) reach the desired values calculated in item f) considering the dynamics and the importance of each of the variables cited in b) as well as the constraints established in e); h) adjusting the flow rates of catalyst, comonomer(s), cooling water, oxygen, hydrogen, inert diluent(s), the flow rate of the recycle stream and the opening of the purge valve so as to satisfy the previous items; and i) based on the lab tests, periodically correcting the value which is inferred for the properties of the resin.