Process for preparing polyethylene

• US 7,402,635 B2
• Filed: 07/22/2003
• Issued: 07/22/2008
• Est. Priority Date: 07/22/2003
• Status: Expired due to Fees

• Current Assignee: Fina Technology, Inc. (Totalenergies Se)
• Original Assignee: Fina Technology, Inc. (Totalenergies Se)
• Inventors: Noll, Patrick
• Primary Examiner(s): Teskin; Fred M
• Application Number:
  US10/625,711
• Publication Number:
  US 20050020784A1
• Time in Patent Office: 1,827 Days
• Field of Search: 526/59, 526/60, 526/61, 526/64, 700/269, 700/31, 700/34, 700/30, 422/105, 422/132, 706/21, 706/906
• US Class Current: 526/64
• CPC Class Codes: B01J 19/0006 Controlling or regulating processes controlling or regulating in general G05
• CPC Class Codes: B01J 19/2435 Loop-type reactors
• CPC Class Codes: B01J 2219/00191 Control algorithm
• CPC Class Codes: B01J 2219/00243 Mathematical modelling
• CPC Class Codes: C08F 10/02 Ethene
• CPC Class Codes: C08F 2/00 Processes of polymerisation
• CPC Class Codes: C08F 2/14 Organic medium
• CPC Class Codes: C08F 210/14 Monomers containing five or more carbon atoms
• CPC Class Codes: C08F 210/16 Copolymers of ethene with alpha-alkenes, e.g. EP rubbers
• CPC Class Codes: C08F 2400/02 Control or adjustment of polymerization parameters
• CPC Class Codes: G05B 13/048 using a predictor
• CPC Class Codes: G05B 17/02 electric
• CPC Class Codes: Y10S 706/906 Process plant

Abstract

Disclosed is process for producing polyethylene using a slurry loop reactor. The process includes using a mathematical model to predict a plurality of process control parameters based on the desired product properties and reactor characteristics and controlling the process using the predicted process control parameters. Also disclosed is a process controller programmed with the model and a method for optimizing the configuration of a loop reactor using the model.

Claims

1. A process for producing polyethylene using a loop reactor comprising:

using a mathematical model to predict a plurality of process control parameters based on desired product properties and reactor characteristics and controlling the process using the predicted process control parameters;

wherein variables used to prepare the mathematical model include a plurality of variables selected from the group consisting of;

ethylene flow into reactor, ethylene flow out of reactor, isobutane flow into reactor, isobutane flow out of reactor, hexene flow into reactor, hexene flow out of reactor, hexene conversion in reactor, hydrogen flow into reactor, hydrogen flow out of reactor, hydrogen conversion in reactor, polymer flow out of reactor, liquid flow out of reactor, total mass flow into reactor, total mass flow out of reactor, total volume flow out of reactor, catalyst flow into reactor, catalyst flow out of reactor, concentration of ethylene in the reactor liquid, concentration of hexene in the reactor liquid, concentration of hydrogen in the reactor liquid, temperature of reactor, pressure of reactor, weight concentration of solids in a reactor slurry, volume concentration of solids in a reactor slurry, weight concentration of solids in a settling leg solids bed, number of settling legs, reactor volume, settling leg diameter, settling leg height, bulk density of reactor polymer, density of reactor polymer, density of reactor liquid, density of reactor slurry, residence time of reactor solids, catalyst activity, catalyst productivity, catalyst diameter, catalyst feed factor, catalyst activity factor, terminal velocity of settling polymer, polymer settling rate, rate of polymer leaving reactor that is not part of the settling leg solids bed, rate of slurry leaving reactor that is part of the settling leg solids bed, rate of slurry leaving reactor that is not part of the settling leg solids bed, viscosity of reactor liquid, density of catalyst, polymer diameter, Archimedes number for polymer settling in settling leg, Reynolds number for polymer settling in settling leg, acceleration due to gravity, cross sectional area of a settling leg occupied by polymer, and cross sectional area of a settling leg; and

wherein the variables used to prepare the mathematical model are;

polymer flow out of the reactor, liquid flow out of the reactor, concentration of ethylene in the reactor liquid, temperature of the reactor, pressure of the reactor, weight concentration of solids in the reactor slurry, reactor volume, settling leg diameter, settling leg height, bulk density of the reactor polymer, density of the reactor polymer, and density of the catalyst.

4. The process of claim 1, wherein the model is displayed in a spreadsheet.

6. The process of claim 1, further comprising the steps of:

using sensors in the reactor to provide inputs to a PID controller;

using another controller to receive data from said PID controller; and

reprogramming the PID controller with the other controller, based upon the inputs from the reactor sensors.

7. The process of claim 6, wherein a plurality of PID controllers are used to receive inputs from the reactor sensors, and wherein the PID controllers are reprogrammed based upon the inputs from the reactor sensors and the other PID controllers.

8. The process of claim 1, wherein said mathematical model is incorporated into logic circuits of a controller.

10. The process of claim 1, wherein said mathematical model is created with a Fortran or C++ computer program.

2. A process for producing polyethylene using a loop reactor comprising:

using a mathematical model to predict a plurality of process control parameters based on desired product properties and reactor characteristics and

controlling the process using the predicted process control parameters;

wherein variables used to prepare the mathematical model include a plurality of variables selected from the group consisting of;

ethylene flow into reactor, ethylene flow out of reactor, isobutane flow into reactor, isobutane flow out of reactor, hexene flow into reactor, hexene flow out of reactor, hexene conversion in reactor, hydrogen flow into reactor, hydrogen flow out of reactor, hydrogen conversion in reactor, polymer flow out of reactor, liquid flow out of reactor, total mass flow into reactor, total mass flow out of reactor, total volume flow out of reactor, catalyst flow into reactor, catalyst flow out of reactor, concentration of ethylene in the reactor liquid, concentration of hexene in the reactor liquid, concentration of hydrogen in the reactor liquid, temperature of reactor, pressure of reactor, weight concentration of solids in a reactor slurry, volume concentration of solids in a reactor slurry, weight concentration of solids in the settling leg solids bed, number of settling legs, reactor volume, settling leg diameter, settling leg height, bulk density of reactor polymer, density of reactor polymer, density of reactor liquid, density of reactor slurry, residence time of reactor solids, catalyst activity, catalyst productivity, catalyst diameter, catalyst feed factor, catalyst activity factor, terminal velocity of settling polymer, polymer settling rate, rate of polymer leaving reactor that is not part of the settling leg solids bed, rate of slurry leaving reactor that is part of the settling leg solids bed, rate of slurry leaving reactor that is not part of the settling leg solids bed, viscosity of reactor liquid, density of catalyst, polymer diameter, Archimedes number for polymer settling in settling leg, Reynolds number for polymer settling in settling leg, acceleration due to gravity, cross sectional area of a settling leg occupied by polymer, and cross sectional area of a settling leg; and

wherein the variables used to prepare the mathematical model are;

polymer flow out of the reactor, liquid flow out of the reactor, concentration of ethylene in the reactor liquid, temperature of the reactor, pressure of the reactor, weight concentration of solids in the reactor slurry, reactor volume, settling leg diameter, settling leg height, bulk density of the reactor polymer, density of the reactor polymer, density of the catalyst, concentration of hexene in the reactor liquid, concentration of hydrogen in the reactor liquid, hexene conversion in the reactor, and hydrogen conversion in the reactor.

5. The process of claim 2, wherein the model is displayed in a spreadsheet.

9. The process of claim 2, wherein said mathematical model is incorporated into logic circuits of a controller.

11. The process of claim 2, wherein said mathematical model is created with a Fortran or C++ computer program.

3. A process for designing a configuration of a loop reactor used to produce polymers comprising:

using a mathematical model to predict a plurality of process control parameters based on desired product properties and reactor characteristics and controlling the process using the predicted process control parameters, where variables used to prepare the mathematical model are selected from the group consisting of;

mass balance of the reactor contents, reactor geometry, catalyst kinetics, and settling phenomena in an outlet settling leg, which is used to determine relationships between inlet feed rates and reactor geometry on production conditions; and

wherein variability is decreased by 70% in comparison to a conventional PID controller.

12. A process for producing polyethylene using a loop reactor comprising:

using a mathematical model to predict a plurality of process control parameters based on desired product properties and reactor characteristics and controlling the process using predicted and actual process control parameters;

wherein the mathematical model includes settling leg data and a plurality of variables selected from the group consisting of;

13. The process of claim 12, wherein the mathematical model includes formulas selected from the group consisting of:

mass balance of a reactor, determined by;

T_iw−

(L_o+P_o)=0, where;

P_o is polymer flow out of the reactor, L_o is liquid flow out of the reactor, and T_iw is total mass flow into the reactor;

mass flows in an outlet liquid based upon outlet concentrations and hydrogen flow, determined by;

14. The process of claim 12, wherein it is assumed that HDPE is produced from monomers consisting of ethylene and hexene, and where ethylene feed into the reactor is calculated from a mass balance of ethylene around the reactor, using:

E_i{E_o+[P_o−

(H_i−

H_o)]}=0 or E_i=E_o+[P_o−

(H_i−

H_o)], where;

E_i is ethylene flow into the reactor,

E_o is ethylene flow out of the reactor,

P_o is polymer flow out of the reactor,

H_i is hexene flow into the reactor, and

H_o is hexene flow out of the reactor.

15. The process of claim 12, wherein it is assumed that HDPE is produced from monomers and where HDPE production kinetics are assumed to be first-order for ethylene concentration in a liquid and catalyst flow rate, wherein kinetic rate is determined by:

P_o=kc_oC_Eτ

_S.

16. The process of claim 13, where catalyst activity is determined by: