# US 2019/0244682 A1 · Methods and Systems for Operating a High Pressure Ethylene Polymerization Unit

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- Number: US 2019/0244682 A1
- Document ID: US20190244682A1
- Status: Published application
- Kind: A1
- Application number: 16/311,214
- Filed: 2017-04-20
- Published: 2019-08-08
- Earliest claimed: 2016-06-30
- Assignees: ExxonMobil Chemical Patents Inc.
- Applicants: ExxonMobil Chemical Patents Inc.
- Inventors: Steven R. De Ceuster; Ludo W.J. Alen; Daniel E. Milam
- Web page: https://patentgrep.com/patent/US20190244682A1

## CPC

- G16C 20/10: Analysis or design of chemical reactions, syntheses or processes
- C08F 2/01: characterised by special features of the polymerisation apparatus used
- C08F 110/02: Ethene
- C08F 210/02: Ethene
- C08F 218/08: Vinyl acetate
- C08F 2400/04: High pressure, i.e. P > 50 MPa, 500 bars or 7250 psi
- C08F 2500/01: High molecular weight, e.g. >800,000 Da.
- G05B 15/00: Systems controlled by a computer (G05B13/00, G05B19/00 take precedence; automatic controllers with particular characteristics G05B11/00)
- G05B 19/418: Total factory control, i.e. centrally controlling a plurality of machines, e.g. direct or distributed numerical control [DNC], flexible manufacturing systems [FMS], integrated manufacturing systems [IMS] or computer integrated manufacturing [CIM]
- G16C: COMPUTATIONAL CHEMISTRY; CHEMOINFORMATICS; COMPUTATIONAL MATERIALS SCIENCE
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)

## Abstract

Disclosed are high-pressure polymerization methods and systems using optimized operation sequence logic established at least partly from an analysis of a database containing data of previous operations. The optimized operation sequence logic and collected current process and system data are used to automate the operation of a high pressure ethylene polymerization process and unit.

## Claims

### Claim 1

A method for operating a high pressure ethylene polymerization unit, comprising
(I) collecting data from previous operations;
(II) building a database including the collected data of previous operations;
(III) analyzing the database;
(IV) establishing an optimized operation sequence logic;
(V) collecting current data of a current operation; and
(VI) conducting the current operation according to the optimized operation sequence logic and current data.

### Claim 2 (depends on 1)

The method of claim 1, wherein in step (IV) includes establishing computer coding embodying the optimized operation sequence logic.

### Claim 3 (depends on 1)

The method of claim 1, wherein step (VI) is conducted at least partly by using an automated computer system.

### Claim 4 (depends on 1)

The method of claim 1, which includes a process of starting up a reactor in the ethylene polymerization unit comprising at least steps (IV), (V), and (VI).

### Claim 5 (depends on 4)

The method of claim 4, wherein the optimized operation sequence logic in step (IV) considers at least the following process variables:
(a) whether the reactor comes out of a short or prolonged shutdown length of time of a reactor shutdown;
(b) whether the shutdown occurred while a vinyl acetate (VA) grade of polyethylene was being produced;
(c) whether an oxygen analyzer check is needed;
(d) whether a reactor pressure test is needed;
(e) whether compressor cylinders are changed during the shutdown; and
(f) whether the shutdown was an emergency shutdown or a controlled shutdown.

### Claim 6 (depends on 4)

The method of claim 4, wherein the optimized operation sequence logic in step (IV) of the process of starting up the reactor comprises the step of taking reactor points in service.

### Claim 7 (depends on 5)

The method of claim 5, wherein the optimized operation sequence logic further comprises before implementing the step of taking reactor points in service deciding on whether to carry out one or more of the following steps and their sequences:
(a) reviewing and confirming startup data by operator;
(b) checking valve positions;
(c) starting secondary compressor;
(d) operator confirming secondary compressor started;
(e) checking extruder parameters and setting Jacket Water Systems (JWSs), preheaters, and purge gas purification unit (PGPU) flows;
(f) starting modifier flow;
(g) ramping to target reactor pressure and flushing all initiator pumps;
(h) setting compressor constraints and reducing modifier flow;
(i) checking that quench line is free;
(j) waiting for JWS to reach target and checking that extruder line is free; and
(k) setting offgas pressure, high pressure separation (HPS) level, and low pressure separation (LPS) level.

### Claim 8 (depends on 6)

The method of claim 6, wherein the optimized operation sequence logic further comprises after the step of taking reactor points in service the step of adjusting compressor constraints and reducing JWS temperature.

### Claim 9 (depends on 4)

The method of claim 4, wherein the optimized operation sequence logic in the reactor start-up uses a means for a procedural operations sequence.

### Claim 10 (depends on 4)

The method of claim 4, wherein the optimized operation sequence logic pauses operation when one of the following conditions occurs: (a) point loss; (b) oxygen detected; (c) low steam pressure; (d) modifier flow deviation from desired flow;
(e) back pressure alarm while a reactor point is being taken in service; and (f) activation of interlocks.

### Claim 11 (depends on 1)

The method of claim 1, wherein the method comprises a process of switching the operation from conditions optimized for producing a first product to conditions optimized for producing a second product, the process comprising at least steps (IV), (V), and (VI), and the optimized operation sequence logic in step (IV) of the switching starts from the beginning of the production of the final batch of the first product to the end of the production of the first batch of the second product.

### Claim 12 (depends on 11)

The method of claim 11, wherein the optimized operation sequence logic in the step of switching comprises adjusting one or more of initiator, reactor pressure, reactor temperature, modifier material, modifier flow, and JWS temperature control.

### Claim 13 (depends on 11)

The method of claim 11, wherein at least one of the following applies:
(a) the first product is an ethylene-vinyl acetate copolymer; and the second product is an ethylene homopolymer;
(b) the first product is an ethylene homopolymer, and the second product is an ethylene-vinyl acetate copolymer;
(c) the first product is a high-density polyolefin, and the second product is a medium-density polyolefin; and
(d) the first product is a medium-density polyolefin, and the second product is a high-density polyolefin.

### Claim 14 (depends on 10)

The method of claim 10, wherein the optimized operation sequence logic pauses normal operation when one of the following conditions occurs: (a) point loss; (b) back pressure alarm; (c) rod loading constraints on high pressure compressor; and (d) modifier flow deviation from desired flow.

### Claim 15 (depends on 10)

The method of claim 10, wherein the optimized operation sequence logic in the grade transition uses a means for a procedural operations sequence.

### Claim 16 (depends on 1)

The method of claim 1, wherein the method comprises a process of defouling the reactor starting from when average conversion from the beginning of the previous defouling cycle exceeds real-time conversion, the process comprising at least steps (IV), (V), and (VI).

### Claim 17 (depends on 16)

The method of claim 16, wherein optimized operation sequence logic in step (IV) of the process of defouling the reactor comprises: (a) from the JWS at the beginning of the reactor to that at the end of the reactor, increasing jacket water systems temperatures to a defouling target temperature; (b) keeping all temperatures at their respective defouling target for a period of time; and (c) decreasing the temperatures to a recipe value, from the beginning to the end of the reactor.

### Claim 18 (depends on 17)

The method of claim 17, wherein the defouling target temperature is between about 180° C. and about 200° C.

### Claim 19 (depends on 17)

The method of claim 17, wherein the period of time is determined by calculating defouling degree based on a correlation of JWS temperatures to light-off temperatures.

### Claim 20 (depends on 19)

The method of claim 19, wherein the correlation is a linear correlation until defouling starts.

### Claim 21 (depends on 20)

The method of claim 20, wherein the reactor defouling is stopped upon the moment when deviation from the linear correlation stops increasing.

### Claim 22 (depends on 17)

The method of any of claim 17, wherein the recipe value in step (c) is below 90° C.

### Claim 23 (depends on 1)

The method of claim 1, the method comprising a process of defouling the recycle implementing at least steps (IV), (V), and (VI), wherein:
the process comprises automatically increasing and decreasing temperatures of coolers for each train, and changing modifier control and reactor peak temperature.

### Claim 24 (depends on 1)

The method of claim 1, wherein the method comprises a process of packing a modifier for the reactor implementing at least steps (IV), (V), and (VI), wherein:
the process comprises automatically injecting an amount of modifier after a start-up.

### Claim 25 (depends on 24)

The method of claim 24, wherein step (IV) includes determining the amount of modifier according to (a) required concentration of the modifier for a particular grade; and (b) total amount of the modifier and VA remaining in the unit.