Use of free radical scavengers to reduce fouling in high pressure polymerization processes

Abstract

Embodiments of a process for producing a high pressure ethylene-based polymer include polymerizing an ethylene monomer feed and optionally an additional comonomer feed via free radical polymerization at a pressure of at least 1000 atmospheres (atm) in the presence of a free radical scavenger to produce a high pressure ethylene-based polymer, wherein the radical scavenger comprises Structure 1: wherein: n may be 0 to 100; r1, R2 and R3 are each independently H, a (C1-C40) hydrocarbyl group, a (C1-C40) heterohydrocarbyl group, or an aromatic-containing moiety; and R4 to R8 are each independently H, OH, a (C1-C40) hydrocarbyl group, a (C1-C40) heterohydrocarbyl group, or an aromatic-containing moiety, provided that at least one of R4 to R8 must be OH. # imgabs0 #

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 411,354, filed on September 29, 2022, the entire disclosure of which is hereby incorporated by reference into this document. Technical Field

[0003] Embodiments described herein relate generally to high pressure polymerization processes, and specifically to the use of free radical scavengers to reduce fouling during high pressure polymerization. Background Art

[0004] One of the main reasons for reduced productivity in high pressure polymerization processes is fouling, for example, super compressor or preheater fouling. Therefore, there is a need for additives that eliminate reactor fouling but do not negatively affect the high pressure polymerization process or product. Summary of the invention

[0005] Embodiments of the present disclosure meet this need by using free radical scavengers that can reduce the amount of fouling without deleterious effects on the polymerization process or product properties.

[0006] According to at least one embodiment of the present disclosure, a method for producing a high-pressure ethylene-based polymer is provided. The method includes polymerizing an ethylene monomer feed and optionally an additional comonomer feed via free radical polymerization at a pressure of at least 1000 atmospheres (atm) in the presence of a free radical scavenger to produce a high-pressure ethylene-based polymer, wherein the free radical scavenger comprises structure 1:

[0007]

[0008] Wherein: n can be 0 to 100; R1, R2 and R3 are each independently H, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; and R4 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic-containing moiety, provided that at least one of R4 to R8 must be OH.

[0009] These and other embodiments are described in more detail in the detailed description that follows. DETAILED DESCRIPTION

[0010] Specific embodiments of the present application will now be described. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

[0011] The term "polymer" refers to a polymeric compound prepared by polymerizing monomers of the same or different types. Thus, the generic term polymer encompasses the term "homopolymer," which generally refers to a polymer prepared from only one type of monomer, and "copolymer," which refers to a polymer 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 generic term interpolymer includes copolymers or polymers prepared from more than two different types of monomers, such as terpolymers.

[0012] "Polyethylene" or "ethylene-based polymer" shall mean a polymer comprising greater than 50 mole % of units derived from ethylene monomers. This includes ethylene-based homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of ethylene-based polymers known in the art include, but are not limited to: 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 linear and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE). Ethylene-based polymers also encompass "ethylene copolymers," which are the polymerization reaction products of ethylene and one or more unsaturated carboxylic acid-containing monomers.

[0013] Embodiments are directed to a process for producing a high pressure ethylene-based polymer comprising polymerizing an ethylene monomer feed and optionally an additional comonomer feed via free radical polymerization at a pressure of at least 1000 atmospheres (atm) in the presence of a free radical scavenger to produce the high pressure ethylene-based polymer.

[0014] In embodiments, the polymer based on ethylene of high pressure is ethylene homopolymer, flame retardant low density polyethylene (LDPE). In other embodiments, the polymer based on ethylene of high pressure is the ethylene copolymer of the polymerization reaction product comprising ethylene and polar comonomer. In other embodiments, the polymer based on ethylene of high pressure is ethylene acid copolymer, which comprises the polymerization reaction product of ethylene and carboxylic acid comonomer. The comonomer containing carboxylic acid may include unsaturated monocarboxylic acid, such as acrylic acid, methacrylic acid or a combination thereof. In embodiments, based on the gross weight of the monomer present in the ethylene acid copolymer, the comonomer containing unsaturated carboxylic acid can be present in an amount of 5 wt % to 35 wt %, 12 wt % to 30 wt %, 15 wt % to 25 wt % or 21 wt % to 25 wt %. On the contrary, the ethylene content of ethylene acid copolymer is greater than 50 wt % or greater than 60 wt %. For example, the ethylene content of ethylene acid copolymer is 50 wt % to 95 wt %, 70 wt % to 88 wt %, 75 wt % to 85 wt % or 75 wt % to 79 wt %.

[0015] In embodiments, the free radical scavenger comprises structure 1:

[0016]

[0017] Wherein: n can be 0 to 100; R1, R2 and R3 are each independently H, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; and R4 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic-containing moiety, provided that at least one of R4 to R8 must be OH.

[0018] In other embodiments, n is 0 to 10, or preferably 0 to 5. In other embodiments, R1 is a C1-C6 olefin, preferably a C1-C3 olefin, or most preferably ethylene; and at least one of R2 and R3 is an aromatic-containing moiety. In other embodiments, at least one of R4 to R8 must be OH, and at least one of R4 to R8 must be a C1-C6 hydrocarbon group.

[0019] In other embodiments, the free radical scavenger comprises the following structure 2

[0020]

[0021] Wherein: m can be 0 to 100; R1 is H, (C1-C 40 ) hydrocarbon group, (C1-C 40) heteroalkyl, or an aromatic moiety; R4 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic-containing moiety, provided that at least one of R4 to R8 must be OH; R9 and R 10 Each independently is H, (C1-C 40 ) alkyl or (C1-C 40 ) heteroalkyl; and R 11 To R 14 are independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or containing aromatic moieties.

[0022] In other embodiments, m is 0 to 10, or preferably 0 to 5. In other embodiments, at least one of R4 to R8 must be OH, and at least one of R4 to R8 must be a C1-C6 hydrocarbon group. In other embodiments, R9 and R 10 At least one of is H or a C1-C6 hydrocarbon group, and R 11 To R 14 At least one of them is a C1-C6 hydrocarbon group.

[0023] In other embodiments, the free radical scavenger comprises the following structure 3

[0024]

[0025] Where: R1 is independently H, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; R5 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; R9 is H, (C1-C 40 ) alkyl or (C1-C 40 ) heteroalkyl; and R 11 To R 14 are independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or containing aromatic moieties.

[0026] In an embodiment, at least one of R5 to R8 and / or R 11 To R 14 In other embodiments, at least one of R5 to R8 is tert-butyl, at least one of R5 to R8 is methyl, or both conditions are met. In additional embodiments, R11 To R 14 At least one of them is tert-butyl, R 11 To R 14 In another embodiment, at least one of R5 to R8 is tert-amyl. In another embodiment, R 11 To R 14 At least one of the groups is a tert-amyl group.

[0027] In certain embodiments, the free radical scavenger comprises one or both of the following structures:

[0028]

[0029]

[0030] Various amounts are considered suitable for free radical scavengers. In an embodiment, the free radical scavenger is added at a concentration of 0.1 mol ppm to 5 ppm based on the amount of ethylene feed and optionally additional comonomer feed. In other embodiments, the free radical scavenger is added at a concentration of 0.1 mol ppm to 1 ppm, or 0.25 to 0.75 ppm, based on the amount of ethylene feed and optionally additional comonomer feed.

[0031] Additional additives are also contemplated for use in the process of the present invention. For example, polymerization may be carried out in the presence of a chain transfer agent. In embodiments, chain transfer agents include aliphatic hydrocarbons and olefins, ketones, aldehydes, and saturated aliphatic alditols. In one embodiment, the chain transfer agent includes propionaldehyde.

[0032] Free radical polymerization processes are generally known in the art. Typically, the process is carried out in a batch process or in a continuous manner at elevated temperature and pressure. Suitable reactors such as tubular reactors or autoclave reactors are familiar to those skilled in the art. In addition, compressor units upstream of the reactor and separator units downstream of the reactor are also familiar to those skilled in the art. The polymerization pressure may be in the range of at least 1000 atm (101.3 MPa or 1013.25 bar), 1000 atm to 5000 atm, 1200 atm to 4000 atm, or 1500 atm to 3500 atm. The polymerization temperature is typically in the range of about 70°C to about 380°C. All individual values ​​and subranges within the range of about 70°C to about 380°C are included herein and disclosed herein; for example, the polymerization temperature is in the range of 100°C to 300°C, or 150°C to 250°C.

[0033] In one or more embodiments, the high pressure ethylene-based polymer further comprises from 1 to 100 ppm of a free radical scavenger, from 10 to 100 ppm, or from 10 to 50 ppm of a free radical scavenger based on the weight of the high pressure ethylene-based polymer.

[0034] Test Method

[0035] Melt Index

[0036] Melt index is measured using 190°C / 2.16 kg conditions according to ASTM D1238-13 Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Platometer. Results are reported in grams eluted per 10 minutes (g / 10 min) or equivalently in decigrams per 1.0 minute (dg / 1 min.).

[0037] Total Dissolution Method

[0038] For this test, all samples used are in pellet form. About 1.0g ± 0.02g of resin is weighed into a clean 100mL glass bottle and the weight is recorded. A PTFE-coated stirring rod is added to the bottle. In a fume hood, 25mL of o-xylene is added to the bottle with an electronic pipette. The bottle is sealed with a crimp cap. The bottle is placed on a Gerstel robot, and the robot completes sample preparation. The sample is dissolved by placing the bottle on a heating / stirring plate for 30 minutes at 130°C. The solution is cooled on a 15-position stirrer for 15 minutes under stirring. After cooling for 15 minutes, 50mL of isopropanol is added to the bottle. The solution is stirred for another two hours. Turn off the stirrer and allow the solid particles to settle. Take out 1mL of solution and transfer to a 2-mL capped glass automatic sampling bottle. The automatic sampling bottle is placed in an LC automatic sampler for analysis. Samples and standard solutions are analyzed using reversed-phase liquid chromatography using a UV / Vis absorbance detector. The concentration in the extract is determined using an external standard calibration procedure.

[0039] Example

[0040] The following examples illustrate features of the present disclosure but are not intended to limit the scope of the present disclosure.

[0041] Example 1 - Reactor Fouling Test

[0042] Comparative Examples C1 and C2

[0043] In a 300 ml continuous reactor, ethylene and 1000 mol ppm of propionaldehyde were added at 7 lb / hr and both were pressurized to 30,000 psi using a compressor and valve. The reactor was heated to 100° C. (C1) or 140° C. (C2) to simulate the temperatures in the compressor and preheater section of an LDPE plant. Ethylene and propionaldehyde were allowed to flow through the reactor at this temperature for 18 hours. During the 18 hour process, all prepolymers formed were collected and weighed. At the end of 18 hours, the reactor was opened and the fouling level was checked.

[0044] Comparative Example C3 (BHT)

[0045] For Comparative Example C3, the same procedure as Comparative Example C2 was used, but butylated hydroxytoluene (BHT) was added to the propionaldehyde to give a final BHT concentration of 0.5 mol ppm in the reactor. BHT is a hindered phenol antioxidant commonly used in LDPE processes, but does not contain a (meth)acrylate substituent.

[0046] Embodiments I1 and I2 of the present invention

[0047] For Inventive Examples I1 and I2, the same procedure as in the Comparative Examples was used, except that Sumilizer GS (Structure 4) from Sumitomo Chemical was added to the propionaldehyde to give a final concentration in the reactor of 0.5 mol ppm. The reactor temperature was 100° C. for I1 and 140° C. for I2.

[0048] In addition, as shown in Table 1 below, the reactor fouling was measured for Comparative Examples C1-C3 and Inventive Examples I1-I2. As shown, each reactor was evaluated and ranked from 1-5, with 1 being the most fouled and 5 being completely clean. As shown below, Inventive Samples I1 and I2 produced reactors that were either completely clean (I1 = Rating 5) or clean (I2 = Rating 5) and had very little polymer collected on them, both of which indicate reduced fouling. In contrast, Comparative Samples C1 to C3 produced reactors with fouling ratings of 1 to 3, respectively, with at least 3 times the amount of polymer collected on the reactor, all of which indicate increased fouling.

[0049] Table 1

[0050]

[0051] Example 2 - Free Radical Scavenger Final Concentration

[0052] The following examples in Table 2 show how free radical scavengers are present in final polymer concentrations. In a 300 ml continuous reactor, ethylene was added at 25 lb / hr with about 400 mol ppm of propionaldehyde and both were pressurized to 28,000 psi using a compressor and valve. The reactor was heated to 270°C and operated adiabatically. Tert-butyl peracetate was added to produce 12% ethylene conversion in the reactor. Sumilizer GS is a free radical scavenger added to the reactor in the form of a solution in propionaldehyde at the levels shown in Table 2. In Table 2, free radical scavenger reactor feed concentrations and free radical scavenger feed / polymer produced are measured based on mass balances from pilot plant data. Free radical scavengers in the form of final polymers are measured by the total dissolution method.

[0053] Table 2

[0054] test A B C Free radical scavenger reactor feed concentration (mol ppm) 0.5 1.1 1.6 Free Radical Scavenger Feed / Polymer Produced (Mass ppm) 69 171 249 Free radical scavengers in final polymer (ppm by mass) 14 26 38

[0055] Obviously, modifications and variations are possible without departing from the scope of the present disclosure as defined in the appended claims.More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.

Claims

1. A method for producing a high pressure ethylene-based polymer, the method comprising: An ethylene monomer feed and optionally an additional comonomer feed are polymerized via free radical polymerization at a pressure of at least 1000 atmospheres (atm) in the presence of a free radical scavenger to produce the high pressure ethylene-based polymer, wherein the free radical scavenger comprises structure 1: Wherein: n can be 0 to 100; R1, R2 and R3 are each independently H, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; and R4 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic-containing moiety, provided that at least one of R4 to R8 must be OH.

2. The method according to claim 1, wherein the free radical scavenger comprises structure 2 in: m can be 0 to 100; R1 is H, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; R4 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic-containing moiety, provided that at least one of R4 to R8 must be OH; R9 and R 10 Each independently is H, (C1-C 40 ) hydrocarbon group, or (C1-C 40 ) heteroalkyl; and R 11 To R 14 are independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or containing aromatic moieties.

3. The method according to any preceding claim, wherein the free radical scavenger comprises structure 3 in: R1 is independently H, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; R5 to R8 are each independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or an aromatic moiety; R9 is H, (C1-C 40 ) hydrocarbon group, or (C1-C 40 ) heteroalkyl; and R 11 To R 14 are independently H, OH, (C1-C 40 ) hydrocarbon group, (C1-C 40 ) heteroalkyl, or containing aromatic moieties.

4. The method according to any preceding claim, wherein at least one of R5 to R8 and / or R 11 To R 14 At least one of them is tert-butyl or tert-pentyl.

5. The method of any preceding claim, wherein the free radical scavenger comprises one or both of the following structures:

6. A process according to any preceding claim, wherein the polymerisation occurs in the presence of a chain transfer agent.

7. The process of claim 6, wherein the chain transfer agent comprises aliphatic hydrocarbons and olefins, ketones, aldehydes and saturated aliphatic aldols.

8. The method of claim 6 or 7, wherein the chain transfer agent comprises propionaldehyde.

9. A process according to any preceding claim, wherein the free radical scavenger is added in a concentration of 0.1 mol ppm to 5 ppm, based on the amount of ethylene feed and optionally additional comonomer feed.

10. A method according to any preceding claim, wherein the additional comonomer comprises a polar monomer.

11. The method of any one of claims 1 to 10, wherein the high pressure ethylene-based polymer comprises low density polyethylene (LDPE).

12. A high pressure ethylene-based polymer produced by the process according to any preceding claim.

13. The high-pressure ethylene-based polymer according to claim 13, wherein the high-pressure ethylene-based polymer further comprises 1 ppm to 100 ppm of the free radical scavenger according to claims 1 to 12 based on the weight of the high-pressure ethylene-based polymer.

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