Process for controlling an ethylene polymerization process

A method for controlling a slurry polymerization for the preparation of polyethylene which is carried out in a series of polymerization reactors having a first polymerization reactor and one or more subsequent polymerization reactors, where the polyethylene is formed in polymerization reactors comprising, as slurry, a suspension of particulate polyethylene in a suspension medium comprising a diluent by contacting a Ziegler-type catalyst, ethylene, and either hydrogen or, as comonomer(s), one or more C3 to C10 alpha-olefins or hydrogen and one or more C3 to C10 alpha-olefins at a reactor temperatures from 60° C. to 95° C. and a reactor pressures from 0.15 MPa to 3 MPa,

• where the Ziegler-type catalyst is fed to the first polymerization reactor and a diluent, ethylene, and either hydrogen or one or more C3 to C10 alpha-olefins or hydrogen and one or more C3 to C10 alpha-olefins are fed to each of the polymerization reactors and slurry is withdrawn from each of the polymerization reactor, and
• where the polymerization reactor each have a reactor slurry section comprising the slurry and a reactor vapor section comprising a vapor comprising ethylene, diluent, and either hydrogen or one or more C3 to C10 alpha-olefins or hydrogen and one or more C3 to C10 alpha-olefins,
• the method comprising:
• a) withdrawing vapor from the reactor vapor section of the first polymerization reactor;
• b) analyzing the vapor to determine its composition;
• and
• c) calculating thereof, based on the pressure within the first polymerization reactor, values for the partial pressure of ethylene, for the partial pressure ratio of hydrogen to ethylene and for the partial pressure ratios of the one or more comonomers to ethylene;
• d) maintaining the flow rate of the ethylene to the first polymerization reactor at a constant level;
• e) adjusting the flow rate of the Ziegler-type catalyst to the first polymerization reactor to maintain the ethylene partial pressure at a targeted ethylene partial pressure;
• f) either adjusting the flow rate of hydrogen to the first polymerization reactor to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio;
• or adjusting the flow rates of the one or more comonomers to the first polymerization reactor to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios;
• or adjusting both the flow rate of hydrogen to the first polymerization reactor to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio and adjusting the flow rates of the one or more comonomers to the first polymerization reactor to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios;
• h) withdrawing vapor from the reactor vapor section of the one or more subsequent polymerization reactors,
• i) analyzing the vapor to determine its composition;
• and
• j) calculating thereof, based on the pressure within the subsequent polymerization reactor, values for the partial pressure of ethylene, for the partial pressure ratio of hydrogen to ethylene and for the partial pressure ratios of the one or more comonomers to ethylene;
• k) maintaining the flow rate of the ethylene to the one or more subsequent polymerization reactors at a constant level;
• and
• l) either adjusting the flow rate of hydrogen to the one or more subsequent polymerization reactors to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio;
• or adjusting the flow rates of the one or more comonomers to the one or more subsequent polymerization reactors to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios;
• or adjusting both the flow rate of hydrogen to the one or more subsequent polymerization reactors to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio and adjusting the flow rates of the one or more comonomers to the one or more subsequent polymerization reactors to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios.

A process for the preparation of polyethylene in a slurry polymerization which is carried out in a series of polymerization reactors having a first polymerization reactor and one or more subsequent polymerization reactors, by contacting, in a suspension medium comprising a diluent, ethylene, a Ziegler-type catalyst and either hydrogen or, as comonomer(s), one or more C3 to C10 alpha-olefins or hydrogen and one or more C3 to C10 alpha-olefins at a reactor temperature from 60° C. to 95° C. and a reactor pressure from 0.15 MPa to 3 MPa,

• where the Ziegler-type catalyst is fed to the first polymerization reactor and a diluent, ethylene, and either hydrogen or one or more C3 to C10 alpha-olefins or hydrogen and one or more C3 to C10 alpha-olefins are fed to each of the polymerization reactors and slurry is withdrawn from each of the polymerization reactor, and
• where the polymerization reactor each have a reactor slurry section comprising the slurry and a reactor vapor section comprising a vapor comprising ethylene, diluent, and either hydrogen or one or more C3 to C10 alpha-olefins or hydrogen and one or more C3 to C10 alpha-olefins,
• wherein the polymerization is controlled by a method comprising:
• a) withdrawing vapor from the reactor vapor section of the first polymerization reactor;
• b) analyzing the vapor to determine its composition;
• and
• c) calculating thereof, based on the pressure within the first polymerization reactor, values for the partial pressure of ethylene, for the partial pressure ratio of hydrogen to ethylene and for the partial pressure ratios of the one or more comonomers to ethylene;
• d) maintaining the flow rate of the ethylene to the first polymerization reactor at a constant level;
• e) adjusting the flow rate of the Ziegler-type catalyst to the first polymerization reactor to maintain the ethylene partial pressure at a targeted ethylene partial pressure;
• f) either adjusting the flow rate of hydrogen to the first polymerization reactor to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio;
• or adjusting the flow rates of the one or more comonomers to the first polymerization reactor to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios;
• or adjusting both the flow rate of hydrogen to the first polymerization reactor to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio and adjusting the flow rates of the one or more comonomers to the first polymerization reactor to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios;
• h) withdrawing vapor from the reactor vapor section of the one or more subsequent polymerization reactors,
• i) analyzing the vapor to determine its composition;
• and
• j) calculating thereof, based on the pressure within the subsequent polymerization reactor, values for the partial pressure of ethylene, for the partial pressure ratio of hydrogen to ethylene and for the partial pressure ratios of the one or more comonomers to ethylene;
• k) maintaining the flow rate of the ethylene to the one or more subsequent polymerization reactors at a constant level;
• and
• l) either adjusting the flow rate of hydrogen to the one or more subsequent polymerization reactors to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio;
• or adjusting the flow rates of the one or more comonomers to the one or more subsequent polymerization reactors to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios;
• or adjusting both the flow rate of hydrogen to the one or more subsequent polymerization reactors to maintain the hydrogen/ethylene partial pressure ratio at a targeted hydrogen/ethylene partial pressure ratio and adjusting the flow rates of the one or more comonomers to the one or more subsequent polymerization reactors to maintain the comonomer/ethylene partial pressure ratios at targeted comonomer/ethylene partial pressure ratios.