Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
POLYOLEFIN PREPARATION PROCESS
Document Type and Number:
WIPO Patent Application WO/2019/086987
Kind Code:
A1
Abstract:
This invention relates to a solution polymerization process that allows two different types of polyethylene to be produced at the same time. The different polyethylenes may have substantially different densities.

Inventors:
BROWN, Stephen (59 Cranbrook Crescent SE, Calgary, Alberta T3M 2C3, T3M 2C3, CA)
Application Number:
IB2018/058027
Publication Date:
May 09, 2019
Filing Date:
October 16, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
NOVA CHEMICALS (INTERNATIONAL) S.A. (Avenue de la Gare 14, 1700 Fribourg, 1700, CH)
International Classes:
C08F2/06; C08F6/00; C08F10/00
Domestic Patent References:
WO2017108951A12017-06-29
Foreign References:
CA3004181A12017-06-29
US6160060A2000-12-12
US20090163643A12009-06-25
US4803259A1989-02-07
US4105609A1978-08-08
US4731438A1988-03-15
US4379882A1983-04-12
US6180730B12001-01-30
US6479624B22002-11-12
US6479274B12002-11-12
US7741993B12010-06-22
US4686289A1987-08-11
US7226989B22007-06-05
US5080845A1992-01-14
US5589555A1996-12-31
US5637659A1997-06-10
US5554775A1996-09-10
US5434116A1995-07-18
Download PDF:
Claims:
CLAIMS

1 . An integrated solution polymerization process comprising

i. forming a compound ethylene stream by compressing ethylene in a single compressor;

ii. dividing said compressed ethylene stream into a first ethylene feed stream and a second ethylene feed stream;

iii. injecting said first ethylene feed stream, a hydrocarbon solvent, a first catalyst system, optionally one or more C3 to C12 alpha olefins and optionally hydrogen into a first polymerization reaction train operating at a first temperature and first pressure to produce a first ethylene polymer solution;

iv. injecting said second ethylene feed stream, a hydrocarbon solvent, a second catalyst system, one or more C3 to C12 alpha olefins and optionally hydrogen into a second polymerization reaction train operating at a second temperature and second pressure to produce a second ethylene polymer solution; v. directing said first ethylene polymer solution to a first polymer separation unit operation to produce a first liquid stream containing said first solvent and unreacted monomer and a crude first ethylene polymer;

vi. directing said second ethylene polymer solution to a second polymer separation unit operation to produce a second liquid stream containing said second solvent and unreacted monomer and a crude second ethylene polymer;

vii. directing said first liquid stream and said second liquid stream to a single distillation unit;

viii. finishing said crude first ethylene polymer in a finishing operation containing a pellet extruder and a pellet stripper; and

ix. finishing said crude second ethylene copolymer in a second finishing operation containing a devolatilizing extruder, with the proviso that said second finishing extruder does not include a pellet stripper.

2. The process of claim 1 wherein said first reactor train contains three reactors in series.

3. The process of claim 2 wherein said first reactor train includes a first mixed reactor; a second mixed reactor and a tubular reactor in series.

4. The process of claim 1 wherein said second reactor train includes a first mixed reactor, a second mixed reactor and a tubular reactor in series.

5. The process of claim 1 wherein said pellet stripper uses steam as a stripping agent.

6. The process of claim 1 wherein said devolatilizing extruder uses steam as a stripping agent.

7. An integrated solution polymerization plant that is capable of the

simultaneous production of two different types of polyethylene, comprising

1 ) a single ethylene compressor;

2) a first solution polymerization reactor train;

3) a second solution polymerization reactor train;

4) a first solution separation unit operation that communicates with said first solution polymerization reaction train and separates a first crude polymer stream from a first liquid stream containing solvent and unreacted monomer;

5) a second solution separation unit operation that communicates with said second solution polymerization reactor train and separates a second crude polymer stream from a second liquid stream containing solvent and unreacted monomer;

6) a single distillation unit operation wherein said first liquid stream and said second liquid stream are distilled;

7) a first finishing operation containing a pellet extruder and a pellet stripper; and

8) a second finishing unit operation containing devolatilizing extruder, with the proviso that said second finishing unit operation does not contain a pellet stripper.

Description:
POLYOLEFIN PREPARATION PROCESS

TECHNICAL FIELD

This invention relates to a solution polymerization process that allows two different types of polyethylene to be produced at the same time. The different polyethylenes may have substantially different densities.

SUMMARY OF THE INVENTION

In an embodiment, this invention provides

an integrated solution polymerization process comprising

i. forming a compressed ethylene stream by compressing ethylene in a single compressor;

ii. dividing said compressed ethylene stream into a first ethylene feed stream and a second ethylene feed stream;

iii. injecting said first ethylene feed stream, a hydrocarbon solvent, a first catalyst system, optionally one or more C3 to C12 alpha olefins and optionally hydrogen into a first solution polymerization reactor train operating at a first temperature and first pressure to produce a first ethylene polymer solution;

iv. injecting said second ethylene feed stream, a hydrocarbon solvent, a second catalyst system, one or more C3 to C12 alpha olefins and optionally hydrogen into a second solution polymerization reactor train operating at a second temperature and second pressure to produce a second ethylene polymer solution; v. directing said first ethylene polymer solution to a first polymer separation unit operation to produce a first liquid stream containing said first solvent and unreacted monomer and a first crude ethylene polymer;

vi. directing said second ethylene polymer solution to a second polymer separation unit operation to produce a second liquid stream containing said second solvent and unreacted monomer and a second crude ethylene polymer;

vii. directing said first liquid stream and said second liquid stream to a single distillation unit;

viii. finishing said first crude ethylene polymer in a finishing operation containing a pellet extruder and a pellet stripper; and

ix. finishing said second crude ethylene polymer in a second finishing operation containing a devolatilizing extruder, with the proviso that said second finishing operation does not include a pellet stripper. In a further embodiment, this invention provides an integrated solution polymerization plant that is capable of the simultaneous production of two different types of polyethylene, comprising

1 ) a single ethylene compressor;

2) a first solution polymerization reactor train;

3) a second solution polymerization reactor train;

4) a first solution separation unit operation that communicates with said first solution polymerization reaction train and separates a first crude polymer stream from a first liquid stream containing solvent and unreacted monomer;

5) a second solution separation unit operation that communicates with said second solution polymerization reactor train and separates a second crude polymer stream from a second liquid stream containing solvent and unreacted monomer;

6) a single distillation unit operation wherein said first liquid stream and said second liquid stream are distilled;

7) a first finishing operation containing a pellet extruder and a pellet stripper; and

8) a second finishing unit operation containing devolatilizing extruder, with the proviso that said second finishing unit operation does not contain a pellet stripper.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a process flow diagram of a non-limiting embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In Figure 1 , a single compressor C1 provides compressed ethylene for all polymerization reactors used in this invention - and this is an essential element of this invention. In an embodiment, the ethylene compressor provides a compressed ethylene stream at a pressure of from 5 to 45 MPa, in some cases 7 to 35 MPa or 7 to 20 MPa.

As an overview: the first ethylene product is produced using elements numbered 1 1 to 34 in Figure 1 ; and the second ethylene product is produced using elements numbered 1 1 ' to 30'; 32 and 35. In Figure 1 , the use of a number (such as 1 1 ) and a number' (such as 1 1 ') is used to indicate that many common technology elements may be used to produce both the first ethylene product and the second ethylene product (i.e. in the embodiment shown in Figure 1 ; 1 1 is substantially the same as 1 1 '; 12 is substantially the same as 12', etc.). An element that does not have both of a number and a corresponding number' can be used to identify important features of this invention:

a) a common distillation system is used (shown as 32 in Figure 1 );

b) the finishing system for the first ethylene polymer uses a pelletizing extruder 33 and a pellet stripper 34; and

c) the finishing system for the second ethylene polymer uses a devolatilizing extruder (35).

In an embodiment, the process of this invention uses common feed purification system and a common control room for both product streams - i.e. the same feed purification system and the same control room are used to produce both the first ethylene product and the second ethylene product.

An embodiment of the invention that may be used to prepare the first ethylene polymer is now described with reference to Figure 1 .

The term "reactor train" is commonly used by those skilled in the art to refer to a reactor system that contains more than one reactor.

In Figure. 1 , solvent 1 1 , ethylene 12 and optional alpha olefin 13 are combined to produce reactor feed RF1 , which is injected into reactor 21 .

Alternative embodiments include the independent (separate) injection feed streams into reactor 21 , i.e. independent injection of solvent 1 1 , ethylene 12 and optional alpha olefin 13. Feed streams may be heated or cooled, the upper limit on reactor feed stream temperatures may be 90°C; in other cases 80°C and in still other cases 70°C; the lower limit on reactor feed stream temperatures may be -20°C; in other cases -10°C and in still other cases 0°C. A variety of solvents are suitable for solution polymerization processes. Non-limiting examples include linear or branched C5 to C12 alkanes. Non-limiting examples of alpha olefin include 1 - butene, 1 -pentene, 1 -hexene and 1 -octene. Catalyst is injected into reactor 21 through line 14. The catalyst used is not especially important to the success of this invention, non-limiting examples of suitable catalyst are described below.

Optionally hydrogen 15 may be injected into reactor 21 ; in general, hydrogen is added to terminate propagating polymer chains, i.e. as an agent to control the molecular weight of the ethylene polymer produced. Reactor feed streams, 1 1 -13 and 1 1 '-13' may be heated or cooled, the upper limit on reactor feed stream temperatures may be 90°C; in other cases 80°C and in still other cases 70°C. The lower limit on reactor feed stream temperatures may be -20°C; in other cases -10°C and in still other cases 0°C.

The reactor train shown in Figure 1 for the preparation of the first ethylene polymer includes two reactors, reactor 21 and reactor 22. The shape, design or the number of the reactor(s) is not particularly important to the success of this invention. For example, unstirred or stirred spherical, cylindrical or tank-like vessels could be utilized, as well as recirculating loop reactors or tubular reactors. As shown in Figure 1 , fresh feeds are also injected into reactor 22. Solvent 16, ethylene 17 and optional alpha olefin 18 are combined to produce reactor feed RF2 which is injected into reactor 22. Catalyst is injected into reactor 22 through line 19. Optionally hydrogen 20 may be injected into reactor 22.

Depending on the catalyst employed and the ethylene polymer produced, the operating temperature of reactor 21 and 22 can vary over a wide range. For example, the upper limit on reactor temperature may be 300°C, in some cases 280°C, and in other cases 260°C; and the lower limit on reactor temperature may be 80°C, in some cases 100°C, and in other cases 125°C. Typically, reactor 22 (the second reactor) is operated at a slightly higher temperature than reactor 21 ; e.g. reactor 22 is typically 5°C to 25°C hotter than reactor 21 . The reactor residence time is typically less than 15 minutes, and in some cases less than 10 minutes. The operating pressure of reactor 21 and 22 can vary over a wide range. For example, the upper limit on reactor pressure may be 45 MPa, in some cases 30 MPa, and in other cases 20 MPa; and the lower limit on reactor pressure may be 3 MPa, in some cases 5 MPa, and in other cases 7 MPa.

The continuous solution polymerization reactors 21 and 22, shown in Figure 1 , produce stream 23 which contains an ethylene polymer in a single liquid phase solution (or two liquid phases). Stream 23 may also contain unreacted ethylene, active catalyst, deactivated catalyst, optional unreacted alpha olefin, optional unreacted hydrogen and light-end impurities if present. Tank 24 contains a catalyst deactivator dissolved, or slurried, in a solvent; non-limiting examples of suitable solvents include linear or branched C5 to C12 alkanes. The catalyst deactivator substantially stops the polymerization reaction, by changing the active catalyst into an inactive form. Suitable deactivators are well known in the art, non-limiting examples include: amines (e.g. U.S. Patent No. 4,803,259 to Zboril et al.); alkali or alkaline earth metal salts of carboxylic acid (e.g. U.S. Patent No. 4,105,609 to Machan et al.); water (e.g. U.S. Patent No. 4,731 ,438 to Bernier et al.);

hydrotalcites, alcohols and carboxylic acids (e.g. U.S. Patent No. 4,379,882 to Miyata); or a combination thereof (U.S. Patent No. 6,180,730 to Sibtain). In general, the catalyst deactivator is added in the minimal amount required to substantially deactivate the catalyst and quench the polymerization reaction. A minimal amount of catalyst deactivator minimizes cost and minimizes the amount of un-reacted catalyst deactivator present in process streams.

Injection of the catalyst deactivator into the process produces a deactivated reactor solution, stream 25. Stream 25 passes through pressure let down device 26, heat exchanger 27, pressure let down device 28 and enters a V/L separator 29; V/L denotes "vapor/liquid". Prior to entering the V/L separator, the deactivated reactor solution may have a maximum temperature of 300°C, in some cases 290°C and in other cases 280°C; while the minimum temperature of the deactivated reactor solution prior to entering the V/L separator could be 150°C, in some cases 200°C and in other cases 220°C. Prior to entering the V/L separator, the deactivated reactor solution may have a maximum pressure of 40 MPa, in some cases 25 MPa, and in other cases 15 MPa; while the minimum pressure could be 1 .5 MPa, in some cases 5 MPa, and in other cases 6 MPa.

In the V/L separator two streams are formed: a first crude ethylene polymer stream 30, comprised of an ethylene polymer rich solvent, deactivated catalyst and optional alpha olefin, and; a gaseous overhead stream 31 comprised of ethylene, solvent, oligomers, optional alpha olefins, optional hydrogen and light-end impurities if present. The V/L separator may be operated over a relatively broad range of temperatures and pressures. For example, the maximum operating temperature of the V/L separator may be 300°C, in some cases 285°C, and in other cases 270°C; while the minimum operating temperature of the V/L separator may be 100°C, in some cases 140°C and in other cases 170°C. The maximum operating pressure of the V/L separator may be 20 MPa, in some cases 10 MPa, and in other cases 5 MPa; while the minimum operating pressure of the V/L separator may be 1 MPa, in some cases 2 MPa, and in other cases 3 MPa. In Figure 1 , 100% of the gaseous overhead stream 31 is sent to a distillation train 32 via line FL1 , while first crude ethylene polymer stream 30 is sent to the first finishing unit operation. The first finishing unit operation includes a pelletizing extruder 33 and a pellet stripper 34.

Turning now to a description of the preparation of the second ethylene polymer product. The words used to describe numerals 1 1 to 30 (inclusive) may also be used to describe numerals 1 1 ' to 30'.

For clarity, the description of numbers 1 1 ' to 30' is provided below.

In Figure 1 , solvent 1 1 ', ethylene 12' and optional alpha olefin 13' are combined to produce reactor feed RF1 ', which is injected into reactor 21 '.

Alternative embodiments include the independent (separate) injection feed streams into reactor 21 ', i.e. independent injection of solvent 1 1 ', ethylene 12' and optional alpha olefin 13'. Feed streams may be heated or cooled, the upper limit on reactor feed stream temperatures may be 90°C; in other cases 80°C and in still other cases 70°C; the lower limit on reactor feed stream temperatures may be -20°C; in other cases -10°C and in still other cases 0°C. A variety of solvents are suitable for solution polymerization processes. Non-limiting examples include linear or branched C5 to C12 alkanes. Non-limiting examples of alpha olefin include 1 - butene, 1 -pentene, 1 -hexene and 1 -octene. Catalyst is injected into reactor 21 ' through line 14'. The catalyst used is not especially important to the success of this invention, non-limiting examples of suitable catalyst are described below.

Optionally hydrogen 15' may be injected into reactor 21 '; in general, hydrogen is added to terminate propagating polymer chains, i.e. as an agent to control the molecular weight of the ethylene polymer produced.

The reactor train shown in Figure 1 for the preparation of the second ethylene polymer includes two reactors, reactor 21 ' and reactor 22'. The shape, design or the number of the reactor(s) is not particularly important to the success of this invention. For example, unstirred or stirred spherical, cylindrical or tank-like vessels could be utilized, as well as recirculating loop reactors or tubular reactors. Reactor trains including three reactors in series are known. One common reactor train design includes a first mixed reactor and a second mixed reactor in series. Another common design uses a first mixed reactor, a second mixed reactor and a tubular reactor in series. As shown in Figure 1 , fresh feeds are also injected into reactor 22'. Solvent 16', ethylene 17' and optional alpha olefin 18' are combined to produce reactor feed RF2' which is injected into reactor 22'. Catalyst is injected into reactor 22' through line 19'. Optionally hydrogen 20' may be injected into reactor 22'.

Depending on the catalyst employed and the ethylene polymer produced, the operating temperature of reactor 21 ' and 22' can vary over a wide range. For example, the upper limit on reactor temperature may be 300°C, in some cases 280°C, and in other cases 260°C; and the lower limit on reactor temperature may be 80°C, in some cases 100°C, and in other cases 125°C. Typically, reactor 22' (the second reactor) is operated at a slightly higher temperature than reactor 21 '; e.g. reactor 22' is typically 5°C to 25°C hotter than reactor 21 '. The reactor residence time is typically less than 15 minutes, and in some cases less than 10 minutes. The operating pressure of reactor 21 and 22 can vary over a wide range. For example, the upper limit on reactor pressure may be 45 MPa, in some cases 30 MPa, and in other cases 20 MPa; and the lower limit on reactor pressure may be 3 MPa, in some cases 5 MPa, and in other cases 7 MPa.

The continuous solution polymerization reactors 21 ' and 22', shown in Figure

1 , produce stream 23' which contains an ethylene polymer in a single liquid phase solution (or two liquid phases). Stream 23' may also contain unreacted ethylene, active catalyst, deactivated catalyst, optional unreacted alpha olefin, optional unreacted hydrogen and light-end impurities if present. Tank 24' contains a catalyst deactivator dissolved, or slurried, in a solvent; non-limiting examples of suitable solvents include linear or branched C5 to C12 alkanes. The catalyst deactivator substantially stops the polymerization reaction, by changing the active catalyst into an inactive form. Suitable deactivators are well known in the art, non- limiting examples include: amines (e.g. U.S. Patent No. 4,803,259 to Zboril et al.); alkali or alkaline earth metal salts of carboxylic acid (e.g. U.S. Patent No. 4,105,609 to Machan et al.); water (e.g. U.S. Patent No. 4,731 ,438 to Bernier et al.);

hydrotalcites, alcohols and carboxylic acids (e.g. U.S. Patent No. 4,379,882 to Miyata); or a combination thereof (U.S. Patent No. 6,180,730 to Sibtain). In general, the catalyst deactivator is added in the minimal amount required to substantially deactivate the catalyst and quench the polymerization reaction. A minimal amount of catalyst deactivator minimizes cost and minimizes the amount of un-reacted catalyst deactivator present in process streams.

Injection of the catalyst deactivator into the process produces a deactivated reactor solution, stream 25'. Stream 25' passes through pressure let down device 26', heat exchanger 27', pressure let down device 28' and enters a V/L separator 29'. Prior to entering the V/L separator, the deactivated reactor solution may have a maximum temperature of 300°C, in some cases 290°C and in other cases 280°C; while the minimum temperature of the deactivated reactor solution prior to entering the V/L separator could be 150°C, in some cases 200°C and in other cases 220°C. Prior to entering the V/L separator, the deactivated reactor solution may have a maximum pressure of 40 MPa, in some cases 25 MPa, and in other cases 15 MPa; while the minimum pressure could be 1 .5 MPa, in some cases 5 MPa, and in other cases 6 MPa.

In the V/L separator two streams are formed: a second crude ethylene polymer stream 30', comprised of an ethylene polymer rich solvent, deactivated catalyst and optional alpha olefin, and; a gaseous overhead stream 31 ' comprised of ethylene, solvent, oligomers, optional alpha olefins, optional hydrogen and light- end impurities if present. The V/L separator may be operated over a relatively broad range of temperatures and pressures. For example, the maximum operating temperature of the V/L separator may be 300°C, in some cases 285°C, and in other cases 270°C; while the minimum operating temperature of the V/L separator may be 100°C, in some cases 140°C and in other cases 170°C. The maximum operating pressure of the V/L separator may be 20 MPa, in some cases 10 MPa, and in other cases 5 MPa; while the minimum operating pressure of the V/L separator may be 1 MPa, in some cases 2 MPa, and in other cases 3 MPa. In Figure 1 , 100% of the gaseous overhead stream 31 ' is sent to a distillation train 32 via line FL1 ', while second crude ethylene polymer stream 30' is sent to the second finishing unit operation. The second finishing unit operation includes a

devolatilizing extruder 35 and does not include a pellet stripper.

Alternative Embodiments of Polymer Separation Units

In Figure 1 , the first polymer separation unit (V/L separator) is indicated by a single number (29) and the second polymer separation unit is similarly indicated by a single number (29'). However, this is not intended to require that one or both of these polymer separation units consists of only a single separation vessel. To the contrary, it is well known to use 2 or more vessels in the polymer separation unit. In addition, only a single preheater (27) is shown upstream of the first polymer separation unit (29) and, likewise, only a single preheater (27') is shown upstream of the second polymer separation unit (27'). However, it is known to add heat in the polymer separation unit. For example, U.S. Patent 6,479,624 (Wepner et al.) illustrates a vessel that contains a heat exchanger (to add heat to the polymer melt) that is located on top of, and within, a polymer devolatilization vessel.

The present invention does not require that the first polymer separation unit is the same as the second polymer separation unit and it will be recognized by those skilled in the art that many combinations of vessels, operating at different pressures and temperatures; with or without a stripping agent (a 'stripping agent' may be steam, or an inert gas, non-limiting examples include, nitrogen, carbon dioxide or hydrocarbons) and with or without additional heat being added are possible.

One illustrative (non-limiting) example would include the V/L separator described above in combination with the heated devolatilization vessel of U.S. Patent 6,479,274 (Wepner et al.).

Embodiments of Finishing Operations

Embodiments of First Finishing Unit Operation

The first "crude" ethylene polymer is converted into a finished polyethylene product in a unit operation that contains a conventional extruder (equipped with a pellet cutter) and a pellet stripper.

For clarity, the term "crude" is simply intended to convey the fact that the "crude" ethylene polymer is not yet a finished/final product.

The crude first ethylene polymer will typically exist in a molten form. The first finishing unit operation of this embodiment uses a conventional extruder to convert the molten material into extruded pellets. Pellet extruders are well known to those skilled in the art and it is not intended to restrict the present invention to any particular design of extruder.

The extrudate is typically passed through a die and cutter at the exit of the extruder. The die typically produces strands of polyethylene that are cut into short lengths (about 0.2 to 0.8 cm) to form "pellets" having a cylindrical shape. The strand extrusion/cutting operation is often cooled with a water bath, resulting in pellets that are water wet.

The pellets generally contain residual Volatile Organic Compounds (VOC), for example residual solvent and comonomer. Accordingly, the water wet pellets are then directed to a "pellet stripper" to reduce the level of VOC. Pellet strippers are also known to those skilled in the art but are less commonly employed than pellet extruders. A stripping agent (e.g. steam, or an inert gas) is typically used to assist the pellet stripping process.

One common embodiment of a pellet stripper uses a countercurrent flow of steam - i.e. the pellets are added to the top of the pellet stripper and steam is introduced at the bottom of the pellet stripper. In an embodiment, the steam may be introduced at serial locations along the length of the pellet stripper. A description of a suitable pellet stripper is provided in U.S. Patent 7,741 ,993 (Airhart).

Embodiments of Second Finishing Unit Operation

The second crude ethylene polymer is converted into a finished polyethylene product in a second unit operation that uses a devolatilizing extruder. The devolatilizing extruder provides two functions in a single apparatus, namely:

i) it reduces the level of VOC (i.e. it devolatilizes the crude ethylene polymer); and

ii) it produces an extruded product (which extruded product is typically cut into pellets to produce the final finished product).

Devolatilizing extruders of many different designs are known. It is not intended to limit the present invention to any particular type of devolatilizing extruder. In general, devolatilizing extruders are well suited for finishing ethylene copolymers having a melt index, \∑, of from 0.5 to 15 grams per 10 minutes (as determined by ASTM D1238 at a temperature of 190°C using a load of 2.16 kg) and comparatively low density (especially from 0.89 to 0.915 g/cc). Suitable examples of devolatilizing extruders are disclosed in U.S. Patents 4,686,289; 7,226,989; and 5,080,845.

Production Rates of First and Second Ethylene Polymers

It should be noted that the production rates of the first polymer stream may be substantially different from the production rates of the second polymer stream. This enables optimization of production rates of the different products according to market demand.

In an embodiment, the first polymer stream may be produced at a rate of from 10 to 70% of the overall production rate with the second polymer stream being produced at a rate of from 90 to 30% of the overall production rate at a given point in time. Thus, the ethylene flows in 12 or 12' may differ, i.e. the actual flow rate of 12 may be substantially greater than (or substantially less than) the flow rate of 12' at a given point in time.

Similarly, the embodiment shown in Figure 1 illustrates the use of the two reactors in series. It is also contemplated that one (or both) of the ethylene products may be prepared using, for example, a single reactor - or more than two reactors. Catalyst Embodiments

The catalysts suitable for use in the present invention are not particularly limited. The invention can be used with any single site catalyst (SSC), Ziegler- Natta catalyst, chromium catalyst or any other organometallic catalyst capable of polymerizing olefins in a solution process. Generally, the catalyst components may be premixed in the process solvent or fed as separate streams to each reactor. In some instances premixing catalyst components may be desirable to provide a reaction time for the catalyst components prior to entering the reaction. Such an "in line mixing" technique is described in a number of patents in the name of DuPont Canada Inc (e.g. U.S. Pat. No. 5,589,555, issued Dec. 31 , 1996).

The term "Ziegler-Natta catalyst" is well known to those skilled in the art and is used herein to convey its conventional meaning. Ziegler-Natta catalysts are suitable for injection through lines 14 and 19 and 14' and 19' in Figure 1 . Ziegler- Natta catalyst systems comprise: at least one transition metal compound wherein the transition metal is selected from groups 3, 4 or 5 of the Periodic Table (using lUPAC nomenclature), non-limiting examples include TiCI 4 and titanium alkoxides (Ti(ORi) 4 ) where Ri is a lower Ci -4 alkyl radical; and an organoaluminum

component, which is defined by (AI(X') a (OR2)b(R3)c), wherein, X' is a halide

(preferable chlorine), OR2 is an alkoxy or aryloxy group; R3 is a hydrocarbyl (preferably an alkyl having from 1 to 10 carbon atoms) and a, b, or c are each 0, 1 , 2 or 3 with the provisos, a+b+c=3 and b+c=1 . As will be appreciated by those skilled in the art, conventional Ziegler Natta catalysts frequently incorporate additional components. For example, an amine or a magnesium compound or a magnesium alkyl such as butyl ethyl magnesium and a halide source (which is typically a chloride, e.g. tertiary butyl chloride). The Ziegler-Natta catalyst may also include an electron donor, e.g., an ether such as tetrahydrofuran, etc. Such components, if employed, may be added to the other catalyst components prior to introduction to the reactor or may be directly added to the reactor. The Ziegler Natta catalyst may also be "tempered" (i.e. heat treated) prior to being introduced to the reactor (again, using techniques which are well known to those skilled in the art and published in the literature). There is a large amount of art disclosing these catalyst and the components and the sequence of addition may be varied over broad ranges.

Single site catalysts are also suitable catalysts for injection through lines 14 and 19 and 14' and 19' in Figure 1 . The term "single site catalyst" refers to a catalyst system that produces homogeneous ethylene polymers; which may or may not contain long chain branching. There is a large amount of art disclosing single site catalyst systems, a non-limiting example includes the bulky ligand single site catalyst of the formula: (L) n -M-(Y) P wherein M is selected from the group consisting of Ti, Zr, and Hf; L is a monoanionic ligand independently selected from the group consisting of cyclopentadienyl-type ligands, and a bulky heteroatom ligand containing not less than five atoms in total (typically of which at least 20%, preferably at least 25% numerically are carbon atoms) and further containing at least one heteroatom selected from the group consisting of boron, nitrogen, oxygen, phosphorus, sulfur and silicon, said bulky heteroatom ligand being sigma or pi-bonded to M; Y is independently selected from the group consisting of activatable ligands; n may be from 1 to 3; and p may be from 1 to 3, provided that the sum of n+p equals the valence state of M, and further provided that two L ligands may be bridged.

Non-limiting examples of bridging groups include bridging groups containing at least one Group 13 to 16 atom, often referred to as a divalent moiety such as, but not limited to, at least one of a carbon, oxygen, nitrogen, silicon, boron, germanium and tin atom or a combination thereof. Preferably the bridging group contains a carbon, silicon or germanium atom, most preferably at least one silicon atom or at least one carbon atom. The bridging group may also contain substituent radicals, including halogens.

Some bridging groups include but are not limited to a di Ci-6 alkyl radical (e.g. alkylene radical for example an ethylene bridge), di Ce-ιο aryl radical (e.g. a benzyl radical having two bonding positions available), silicon or germanium radicals substituted by one or more radicals selected from the group consisting of Ci-6 alkyl, Ce-ιο aryl, phosphine or amine radical which are unsubstituted or up to fully substituted by one or more Ci-6 alkyl or Ce-ιο aryl radicals, or a hydrocarbyl radical such as a Ci-6 alkyl radical or a Ce-ιο arylene (e.g. divalent aryl radicals); divalent Ci-6 alkoxide radicals (e.g. --CH2CHOHCH2--) and the like.

Exemplary of the silyl species of bridging groups are dimethylsilyl, methylphenylsilyl, diethylsilyl, ethylphenylsilyl or diphenylsilyl compounds. Most preferred of the bridged species are dimethylsilyl, diethylsilyl and methylphenylsilyl bridged compounds.

Exemplary hydrocarbyl radicals for bridging groups include methylene, ethylene, propylene, butylene, phenylene and the like, with methylene being preferred.

Exemplary bridging amides include dimethylamide, diethylamide, methylethylamide, di-t-butylamide, diisoproylamide and the like.

The term "cyclopentadienyl", frequently abbreviated as "Cp", refers to a 5- member carbon ring having delocalized bonding within the ring and typically being bound to the active catalyst site, generally a group 4 metal (M) through r|5 - bonds. The cyclopentadienyl ligand may be unsubstituted or up to fully substituted with one or more substituents selected from the group consisting of C1-10 hydrocarbyl radicals in which hydrocarbyl substituents are unsubstituted or further substituted by one or more substituents selected from the group consisting of a halogen atom and a Ci -4 alkyl radical; a halogen atom; a Ci-e alkoxy radical; a Ce-ιο aryl or aryloxy radical; an amido radical which is unsubstituted or substituted by up to two Ci-e alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals; silyl radicals of the formula -Si-(R)3 wherein each R is independently selected from the group consisting of hydrogen, a Ci-e alkyl or alkoxy radical, and Ce-ιο aryl or aryloxy radicals; and germanyl radicals of the formula -- Ge~(R)3 wherein R is as defined above.

Typically, the cyclopentadienyl-type ligand is selected from the group consisting of a cyclopentadienyl radical, an indenyl radical and a fluorenyl radical where the radicals are unsubstituted or up to fully substituted by one or more substituents selected from the group consisting of a fluorine atom, a chlorine atom; Ci-4 alkyl radicals; and a phenyl or benzyl radical which is unsubstituted or substituted by one or more fluorine atoms.

If none of the L ligands is a bulky heteroatom ligand then the catalyst could be a bis-Cp catalyst (a traditional metallocene) or a bridged constrained geometry type catalyst or tris-Cp catalyst. If the catalyst contains one or more bulky heteroatom ligands the catalyst would have the formula:

(D)m

(L)n - M - (Y)p

wherein M is a transition metal selected from the group consisting of Ti, Hf and Zr; D is independently a bulky heteroatom ligand (as described below); L is a monoanionic ligand selected from the group consisting of cyclopentadienyl-type ligands; Y is independently selected from the group consisting of activatable ligands; m is 1 or 2; n is 0, 1 or 2; p is an integer; and the sum of m+n+p equals the valence state of M, provided that when m is 2, D may be the same or different bulky heteroatom ligands.

For example, the catalyst may be a bis(phosphinimine), or a mixed phosphinimine ketimide dichloride complex of titanium, zirconium or hafnium.

Alternately, the catalyst could contain one phosphinimine ligand or one ketimide ligand, one "L" ligand (which is most preferably a cyclopentadienyl-type ligand) and two "Y" ligands (which are preferably both chloride).

The preferred metals (M) are from Group 4 (especially titanium, hafnium or zirconium). In one embodiment the catalysts are group 4 metal complexes in the highest oxidation state.

Bulky heteroatom ligands (D) include but are not limited to phosphinimine ligands (PI) and ketimide (ketimine) ligands.

The phosphinimine ligand (PI) is defined by the formula:

R21

I

R21 - P = N -

R21

wherein each R21 is independently selected from the group consisting of a hydrogen atom; a halogen atom; C1-20, preferably C1-10 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom ; a Ci-e alkoxy radical; a C6-10 aryl or aryloxy radical; an amido radical; a silyl radical of the formula: -Si- (R22K wherein each R22 is independently selected from the group consisting of hydrogen, a Ci-e alkyl or alkoxy radical, and Ce-ιο aryl or aryloxy radicals; and a germanyl radical of the formula: -Ge-(R22)3, wherein R22 is as defined above. The preferred phosphinimines are those in which each R21 is a hydrocarbyl radical, preferably a C1-6 hydrocarbyl radical.

Suitable phosphinimine catalysts are Group 4 organometallic complexes which contain one phosphinimine ligand (as described above) and one ligand L which is either a cyclopentadienyl-type ligand or a heteroatom ligand.

As used herein, the term "ketimide ligand" refers to a ligand which:

(a) is bonded to the transition metal via a metal-nitrogen atom bond;

(b) has a single substituent on the nitrogen atom (where this single substituent is a carbon atom which is doubly bonded to the N atom); and

(c) has two substituents Subi and Sub2 (described below) which are bonded to the carbon atom.

Conditions a, b and c are illustrated below:

\ /

C

N

metal

where the substituents Subi and Sub2 may be the same or different and may be further bonded together through a bridging group to form a ring. Exemplary substituents include hydrocarbyls having from 1 to 20 carbon atoms, preferably from 3 to 6 carbon atoms, silyl groups (as described below), amido groups (as described below) and phosphido groups (as described below). For reasons of cost and convenience it is preferred that these substituents both be hydrocarbyls, especially simple alkyls and most preferably tertiary butyl.

Suitable ketimide catalysts are Group 4 organometallic complexes which contain one ketimide ligand (as described above) and one ligand L which is either a cyclopentadienyl-type ligand or a heteroatom ligand.

The term bulky heteroatom ligand (D) is not limited to phosphinimine or ketimide ligands and includes ligands which contain at least one heteroatom selected from the group consisting of boron, nitrogen, oxygen, phosphorus, sulfur and silicon. The heteroatom ligand may be sigma or pi-bonded to the metal.

Exemplary heteroatom ligands include silicon-containing heteroatom ligands, amido ligands, alkoxy ligands, boron heterocyclic ligands and phosphole ligands, as all described below. Silicon containing heteroatom ligands are defined by the formula:

-(Y)SiRxRyRz wherein the - denotes a bond to the transition metal and Y is sulfur or oxygen. The substituents on the Si atom, namely R x , R y and R z , are required in order to satisfy the bonding orbital of the Si atom. The use of any particular substituent R x , R y or R z is not especially important to the success of this invention. It is preferred that each of R x , R y and R z is a C1-2 hydrocarbyl group (i.e. methyl or ethyl) simply because such materials are readily synthesized from commercially available materials.

The term "amido" is meant to convey its broad, conventional meaning. Thus, these ligands are characterized by (a) a metal-nitrogen bond; and (b) the presence of two substituents (which are typically simple alkyl or silyl groups) on the nitrogen atom.

The terms "alkoxy" and "aryloxy" are also intended to convey their conventional meanings. Thus, these ligands are characterized by (a) a metal oxygen bond; and (b) the presence of a hydrocarbyl group bonded to the oxygen atom. The hydrocarbyl group may be a C1-10 straight chained, branched or cyclic alkyl radical or a Ce-13 aromatic radical where the radicals are unsubstituted or further substituted by one or more Ci- 4 alkyl radicals (e.g. 2,6 di-tertiary butyl phenoxy).

Boron heterocyclic ligands are characterized by the presence of a boron atom in a closed ring ligand. This definition includes heterocyclic ligands which also contain a nitrogen atom in the ring. These ligands are well known to those skilled in the art of olefin polymerization and are fully described in the literature (see, for example, U.S. Patent Nos. 5,637,659; 5,554,775; and the references cited therein).

The term "phosphole" is also meant to convey its conventional meaning. Phospholes are cyclic dienyl structures having four carbon atoms and one phosphorus atom in the closed ring. The simplest phosphole is C 4 PH 4 (which is analogous to cyclopentadiene with one carbon in the ring being replaced by phosphorus). The phosphole ligands may be substituted with, for example, C1-20 hydrocarbyl radicals (which may, optionally, contain halogen substituents);

phosphido radicals; amido radicals; or silyl or alkoxy radicals. Phosphole ligands are also well known to those skilled in the art of olefin polymerization and are described as such in U.S. Patent No. 5,434,1 16 (Sone, to Tosoh). The current invention also contemplates the use of chromium catalysts that are also well known in the art. The term "chromium catalysts" describes olefin polymerization catalysts comprising a chromium species, such as silyl chromate, chromium oxide, or chromocene on a metal oxide support such as silica or alumina. Suitable cocatalysts for chromium catalysts, are well known in the art, non-limiting examples include trialkylaluminum, alkylaluminoxane, dialkoxyalkylaluminum compounds and the like.

INDUSTRIAL APPLICABILITY

A solution polymerization process enables the production of two different types of ethylene copolymers at the same time. The copolymers may have substantially different densities. The copolymers are useful in the preparation of a wide variety of flexible packaging and molded products.