Solvent management via two-phase ethylene feed to second reactor to increase ethylene-based polymer output

Abstract

Embodiments of a dual reactor solution polymerization process include: introducing a first feed comprising an ethylene monomer, optionally hydrogen, optionally a C3-C12 alpha-olefin comonomer, and a hydrocarbon solvent into a first polymerization reactor to produce a first reactor product comprising an ethylene-based polymer via solution polymerization at a temperature of 100 DEG C to 225 DEG C; and introducing the first reactor product and a two-phase second feed comprising an ethylene monomer, a hydrocarbon solvent, optionally hydrogen, and optionally a C3-C12 alpha-olefin comonomer to a second polymerization reactor to produce an ethylene-based polymer via solution polymerization, wherein the weight ratio of the sum of hydrocarbon solvent plus comonomer in the two-phase second feed to ethylene monomer is 0.1 to 2.0.

Description

[0001] Cross-references to Related Patent Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 404,744, filed on September 8, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This specification relates generally to ethylene-based polymers and, in particular, to improved polymerization processes involving a two-phase ethylene feed. Background Art

[0004] The solution polymerization process used to produce ethylene-based polymers (e.g., LLDPE) utilizes a hydrocarbon solvent in its reactor to carry out a single liquid-phase polymerization reaction. This solvent serves the multi-purpose of dissolving the polymer and ethylene gas, thereby providing a single liquid-phase environment for the polymerization reaction while removing some of the heat of reaction. The polymer concentration exiting the reactor section, or viewed another way, the amount of solvent used to produce each product, determines the maximum overall polymer production rate, as the plant's throughput is limited by the total solvent devolatilization capacity of the back-end equipment. Therefore, any process improvement that reduces solvent usage will help increase the plant's overall capacity.

[0005] Traditionally, ethylene monomer is dissolved in a solvent and comonomers and fed as a single liquid feed stream to ensure consistent reactor feed. However, this single liquid feed requires a large amount of solvent to completely dissolve the fresh ethylene. As a result, reactor polymer concentration is limited, and therefore plant capacity is also limited.

[0006] Therefore, there is a continuing need for improved polymerization processes that can increase the production of ethylene-based polymers. Summary of the Invention

[0007] Embodiments of the present disclosure address this need for increased production of ethylene-based polymers by utilizing a two-phase ethylene feed stream in a solvent feed stream to feed the second reactor. Without being limited by theory, this two-phase feed injection technique increases overall polymer concentration, reduces overall solvent loading, and subsequently helps increase productivity of existing dual-reactor polymerization systems.

[0008] According to one embodiment, a dual-reactor solution polymerization method is provided. The dual-reactor solution polymerization method comprises: reacting a monomer comprising ethylene, optionally one or more C3-C 12A first feed of an α-olefin comonomer, optionally hydrogen, and a hydrocarbon solvent is introduced into a first polymerization reactor to produce a first reactor product comprising an ethylene-based polymer via solution polymerization at a temperature of 100° C. to 225° C.; and the first reactor product and a feed comprising ethylene monomer, a hydrocarbon solvent, and optionally one or more C3-C 12 A two-phase second feed of an α-olefin comonomer and optionally hydrogen is introduced into a second polymerization reactor to produce an ethylene-based polymer via solution polymerization, wherein the weight ratio of the sum of the hydrocarbon solvent and comonomer in the two-phase second feed to the ethylene monomer is 0.1 to 2.2.

[0009] Additional features and advantages will be set forth in the following detailed description, and in part will become apparent to those skilled in the art from that description or learned by practicing the embodiments described herein, including the drawings, the following detailed description, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of the present invention's tandem dual-reactor polymerization process according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0011] The specific embodiments of the present application will now be described. However, the present disclosure can be implemented in different forms and should not be construed as being limited to the embodiments set forth in the present disclosure. On the contrary, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

[0012] definition

[0013] The term "polymer" refers to a polymeric compound prepared by polymerizing monomers (whether of the same or different types). Thus, the general term polymer encompasses the term "homopolymer," which is typically used to refer to polymers prepared from only one type of monomer, as well as "copolymer," which refers to polymers prepared from two or more different monomers. As used herein, the term "interpolymer" refers to a polymer prepared by the polymerization of at least two different types of monomers. Thus, the general term "interpolymer" includes copolymers, and polymers prepared from more than two different types of monomers, such as terpolymers.

[0014] "Polyethylene" or "ethylene-based polymer" shall mean a polymer comprising greater than 50% by weight of units derived from ethylene monomer. This includes polyethylene homopolymers or copolymers (meaning units derived from ethylene and one or more comonomers). Comonomers may include olefin comonomers as well as polar comonomers. Common forms of polyethylene known in the art include low density polyethylene (LDPE); linear low density polyethylene (LLDPE); ultra low density polyethylene (ULDPE); very low density polyethylene (VLDPE); single-site catalyzed linear low density polyethylene, including both linear low density resins and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE).

[0015] The term "LLDPE" includes resins made using a Ziegler-Natta catalyst system, as well as resins made using single-site catalysts, including but not limited to dual metallocene catalysts (sometimes referred to as "m-LLDPE") and constrained geometry catalysts; and resins made using post-metallocene, molecular catalysts. LLDPE includes linear, substantially linear, or heterogeneous polyethylene copolymers or homopolymers. LLDPE includes less long chain branching than LDPE and comprises substantially linear ethylene polymers, which are further defined in U.S. Pat. No. 5,272,236, U.S. Pat. No. 5,278,272, U.S. Pat. No. 5,582,923, and U.S. Pat. No. 5,733,155; homogeneously branched linear ethylene polymer compositions, such as those in U.S. Pat. No. 3,645,992; heterogeneously branched ethylene polymers, such as those prepared according to the process disclosed in U.S. Pat. No. 4,076,698; and / or blends thereof (such as those disclosed in U.S. Pat. No. 3,914,342 or U.S. Pat. No. 5,854,045).

[0016] The terms "comprising," "including," "having," and their derivatives are not intended to exclude the presence of any additional components, steps, or procedures, whether or not specifically disclosed. For the avoidance of any doubt, all compositions claimed through use of the term "comprising" may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless stated to the contrary. In contrast, the term "consisting essentially of excludes from the scope of any subsequently recited component, step, or procedure, except those that are not essential to operability. The term "consisting of excludes any component, step, or procedure not specifically recited or listed.

[0017] The embodiments of the present disclosure relate to Figure 1The dual reactor solution polymerization system 5 and method shown in FIG. The method comprises: reacting a mixture containing ethylene monomer, optionally one or more C3-C 12 A first feed 10 of an α-olefin comonomer, optionally hydrogen, and a hydrocarbon solvent is introduced into a first polymerization reactor 40 to produce a first reactor product 47 comprising an ethylene-based polymer via solution polymerization at a temperature of 100° C. to 225° C.; in other embodiments, the temperature may be 100° C. to 205° C., 120° C. to 180° C., or 150° C. to 180° C. Subsequently, the first reactor product 47 and a feed comprising ethylene monomer, a hydrocarbon solvent, optionally hydrogen, and optionally one or more C3-C 12 A two-phase second feed 48 of alpha-olefin comonomer is fed to a second polymerization reactor 50 to produce an ethylene-based polymer 65 via solution polymerization.

[0018] The two-phase second reactor feed 48, comprising a gas phase and a liquid phase, has a weight ratio of the sum of the hydrocarbon solvent and comonomer to the ethylene monomer of 0.1 to 2.2, 0.6 to 1.6, 0.8 to 1.2, or 1.0 to 1.2. Without being limited by theory, a weight ratio above 2.2 can produce a single liquid phase feed, which results in a significantly lower reactor polymer concentration. In an embodiment, the two-phase second feed comprises 7 to 100% by volume of a gas phase, or 7 to 60% by volume of a gas phase. In one or more embodiments, the two-phase second reactor feed can be introduced into the reactor at a temperature of 10°C to 100°C, 15°C to 80°C, or 15°C to 60°C, or 20°C to 80°C, or 20°C to 60°C. Without being limited by theory, the ratio of the sum of the hydrocarbon solvent and comonomer to the ethylene monomer can increase the saturation temperature, so a two-phase second reactor feed having a higher ratio (i.e., closer to 2) can be associated with a higher temperature, such as 50°C to 100°C. Without further being limited by theory, a two-phase second reactor feed at a temperature at or below 100°C enables operation with less gelation in the reactor.

[0019] A variety of reactors are considered suitable for use in the polymerization system 5. In one embodiment, the first polymerization reactor 40, the second polymerization reactor 50, or both comprise loop reactors. Alternatively, the first polymerization reactor 40, the second polymerization reactor 50, or both comprise continuous stirred tank reactors.

[0020] Refer again Figure 1 , the first feed 10 can be a single-phase liquid feed. In one or more embodiments, the weight ratio of the sum of the hydrocarbon solvent and comonomer in the first feed 10 to the ethylene monomer is greater than 2.2 to 10, 4 to 8, or 4 to 6.

[0021] A variety of hydrocarbon solvents are considered suitable for use in system 5. In one or more embodiments, the hydrocarbon solvent comprises an aromatic hydrocarbon solvent, an aliphatic hydrocarbon solvent, or a mixture thereof.

[0022] In addition, it is believed that a variety of catalysts are suitable for use in the first polymerization reactor 40 and the second polymerization reactor 50. These catalysts may include Ziegler-Natta catalyst systems, single-site and multi-site catalysts (including but not limited to double metallocene catalysts, constrained geometry catalysts, post-metallocene catalysts, molecular catalysts, bisphenylphenoxy catalysts and heterogeneous Ziegler-Natta catalysts). In an embodiment, the first polymerization reactor 40 can use a bis-phenyl-phenoxy catalyst. In other embodiments, the second polymerization reactor 50 can utilize a heterogeneous Ziegler-Natta catalyst.

[0023] In other embodiments, the polymerization system may include additional polymerization reactors downstream of the first polymerization reactor 40 and the second polymerization reactor 50. These reactors may be loop reactors, continuous stirred tank reactors, tubular flow reactors, plug flow reactors, tubular reactors, or combinations thereof.

[0024] Test Method

[0025] density

[0026] Samples for density measurement were prepared according to ASTM D 1928. Polymer samples were pressed at 190°C and 30,000 psi for three minutes, then at 21°C and 207 MPa for one minute. Measurements were made using ASTM D792, Method B, within one hour of sample pressing.

[0027] Melt index (I2)

[0028] Melt index or I2 (grams / 10 minutes or dg / min) is measured according to ASTM D 1238, Condition 190°C / 2.16 kg, Procedure B.

[0029] Example

[0030] The embodiments will be further illustrated by the following examples.

[0031] Six samples were produced: Comparative Example A, which included a single liquid phase feed to the second reactor; and Inventive Examples 1-4, which included a 2-phase vapor-liquid feed to the second reactor.

[0032] Comparative Example A and Inventive Examples 1-4 were prepared via solution polymerization in a dual series loop reactor system according to U.S. Patent No. 5,977,251 in the presence of a first catalyst system (CAT 1) as described below in Table 1 in the first reactor and a second catalyst system (CAT 2) as described below in Table 1 in the second reactor. Inventive Example 4 was similarly prepared via solution polymerization in a dual series loop reactor system according to U.S. Patent No. 5,977,251 in the presence of a first catalyst system (CAT 3) as described below in Table 1 in the first reactor and a second catalyst system (CAT 4) as described below in Table 1 in the second reactor.

[0033]

[0034]

[0035] In Comparative Example A (left column of Table 2), a second reactor solvent plus comonomer to ethylene ratio of 2.4 was used to maintain a single liquid phase feed at a 40°C feed temperature.

[0036] Table 2

[0037]

[0038]

[0039]

[0040] In contrast, Inventive Example 1 utilizes a lower second reactor solvent plus comonomer to ethylene ratio of 1.23, placing the second reactor feed in a two-phase gas-liquid state. This results in a 9.5% increase in productivity compared to the design capacity of Comparative Example A, which does not increase the solvent ratio. At the same time, the total amount of solvent required for the two-phase feed formulation remains within the maximum total solvent processing constraint. Inventive Examples 2-4 also have second reactor solvent to ethylene ratios of 2.2 or less and also demonstrate improved productivity compared to the design capacity of Comparative Example A.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Therefore, this specification is intended to cover modifications and variations of the various embodiments described herein, provided that such modifications and variations fall within the scope of the appended claims and their equivalents.

Claims

1. A dual-reactor solution polymerization method comprising: The monomer comprising ethylene, optionally one or more C3-C 12 introducing a first feed of an alpha-olefin comonomer, optionally hydrogen, and a hydrocarbon solvent into a first polymerization reactor to produce a first reactor product comprising an ethylene-based polymer via solution polymerization at a temperature of 100° C. to 225° C.; as well as The first reactor product and a two-phase second feed are introduced into a second polymerization reactor to produce an ethylene-based polymer via solution polymerization, wherein the two-phase second feed temperature is 10° C. to 100° C. and comprises ethylene monomer, a hydrocarbon solvent, optionally hydrogen, and optionally one or more C3-C 12 an alpha-olefin comonomer, wherein the weight ratio of the sum of the hydrocarbon solvent and comonomer to ethylene monomer in the two-phase second feed is from 0.1 to 2.

2.

2. The process of claim 1, wherein the weight ratio of the sum of the hydrocarbon solvent and comonomer to ethylene monomer in the two-phase second feed is from 0.6 to 1.

6.

3. The process of claim 1, wherein the two-phase second feed comprises a liquid phase and a gas phase.

4. The process of claim 2, wherein the two-phase second feed comprises 7% to 98% by volume of the gas phase.

5. The process according to any preceding claim, wherein the two-phase second feed comprises C3-C 12 α-olefin comonomer.

6. The process of any preceding claim, wherein the first polymerization reactor, the second polymerization reactor, or both comprise a loop reactor.

7. A process according to any preceding claim, wherein the first feed is a single-phase liquid feed.

8. The process according to any preceding claim, wherein the weight ratio of the sum of the hydrocarbon solvent and comonomer to ethylene monomer in the first feed is from greater than 2.2 to 10.

9. The method according to any preceding claim, wherein the hydrocarbon solvent comprises an aromatic hydrocarbon solvent, an aliphatic hydrocarbon solvent, or a mixture thereof.

10. An ethylene-based polymer produced by the process of any one of the preceding claims.

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