Tert-butanol cosolvent in the formation of ethylene acid copolymers

Abstract

Embodiments of the present disclosure are directed to a process for producing an ethylene acid copolymer, comprising polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a cosolvent via free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce an ethylene acid copolymer, wherein the cosolvent comprises tert-butanol, and the cosolvent constitutes less than 15 wt. % of the feed, and wherein the ethylene acid copolymer has a melt index (I2) of less than 35 dg / min as determined according to ASTM D1238 (190°C, 2.16 kg).

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 411,323, filed September 29, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] FIELD OF THE INVENTION Embodiments described herein relate generally to ethylene acid copolymers, and specifically to the use of tert-butanol solvent to reduce phase separation and corrosion. [Background technology]

[0003] In ethylene acid copolymers, phase separation within the free radical solution mixture is problematic because it can limit the incorporation of the acid into the polymer. Furthermore, as the amount of acid in the polymer chain increases, phase separation can cause fouling and gel problems. Therefore, methanol cosolvents are traditionally used to reduce phase separation. However, high amounts of methanol can increase corrosion. Furthermore, methanol can function as a chain transfer agent, reducing the molecular weight capability of the process.

[0004] As a result, there is a need to replace methanol as a co-solvent. Summary of the Invention

[0005] Embodiments of the present disclosure fulfill this need by replacing methanol with a tert-butanol co-solvent, which can reduce phase separation and reduce polymer chain termination and corrosion. Yet another advantage is that residual tert-butanol levels in ethylene acid copolymers are non-reactive with any added base, thus preventing ionomerization of acid groups in the polymer chains.

[0006] According to at least one embodiment of the present disclosure, there is provided a method for producing an ethylene acid copolymer, the method comprising polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a cosolvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce an ethylene acid copolymer, the cosolvent comprising tert-butanol, the cosolvent comprising less than 15 wt% of the feed, and the ethylene acid copolymer having a melt index (I2) of less than 35 dg / min as determined according to ASTM D1238 (190°C, 2.16 kg).

[0007] According to another embodiment, the method comprises polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a co-solvent via free radical polymerization at a pressure of at least 1000 atmospheres (atm) and a reaction temperature greater than 200°C to produce an ethylene acid copolymer, wherein the co-solvent comprises tert-butanol, and the co-solvent comprises less than 15 wt% of the feed.

[0008] These and other embodiments are described in more detail in the figures and detailed description that follow. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graphical plot of the cloud point data for Example 1. [Figure 2] 1 is a graphical plot of the cloud point data for Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE INVENTION Certain 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, whether of the same or different types. Thus, the general term polymer generally encompasses the term "homopolymer," which refers to a polymer prepared from only one type of monomer, as well as the term "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 polymerization of at least two different types of monomers. Thus, the general 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 containing more than 50 mole percent units derived from ethylene monomers. This includes ethylene-based homopolymers or copolymers (meaning the units are derived from two or more comonomers). Common forms of ethylene-based polymers 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 (m-LLDPE), including both linear and substantially linear low-density resins, medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0013] "Ethylene acid copolymer" is the polymerization reaction product of ethylene and one or more unsaturated carboxylic acid-containing monomers.

[0014] An embodiment is directed to a process for producing an ethylene acid copolymer, comprising polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a cosolvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce the ethylene acid copolymer. The cosolvent comprises tert-butanol. The cosolvent may comprise less than 15 wt. % of the feed. In other embodiments, the cosolvent comprises 5-14 wt. %, or 7-13 wt. %.

[0015] In one or more embodiments, the polymerization is carried out in the presence of a free radical initiator. Typical amounts of the free radical initiator are about 0.1% to about 5%, about 0.2% to about 2%, or about 0.25% to about 1% by weight based on the weight of the feed. Other typical amounts of the free radical initiator can be about 50 ppm to about 2,500 ppm by weight, about 100 ppm to about 1,000 ppm by weight, or about 150 ppm to about 500 ppm by weight based on the weight of the feed. The free radical initiator may be added all at the beginning of the reaction or may be added continuously or in stages during the reaction (especially if the monomer is added in this manner). Examples of suitable free radical initiators include peroxyesters, peroxides, persulfates, perborates, percarbonates, azo compounds, and the like. Specific examples of suitable free radical initiators include hydrogen peroxide, tert-butyl peroctoate, tert-butyl peracetate, di(t-butyl)peroxide, lauroyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, 2,2'-azobis[2,4-dimethyl]pentanenitrile, 2-(t-butylazo)-2-methylbutanenitrile, 2-(t-butylazo)-2-4,dimethylpentanenitrile, azobis(isobutyronitrile), azobis(methylbutyronitrile) (AMBN), tert-amylperoxy 2-ethylhexanoate, and mixtures of any two or more thereof.

[0016] In one or more embodiments, the polymerization, which may optionally be carried out using the free radical initiators described above, may be carried out at a temperature of up to 230° C., less than 220° C., or less than 210° C. Additionally, the polymerization may be carried out at a temperature ranging from 175 to 230° C., or from 200 to 230° C., or from 210 to 230° C. In an exemplary embodiment, the polymerization may utilize t-butyl peroctoate at a temperature ranging from 175 to 230° C.

[0017] In alternative embodiments, the polymerization may be carried out at temperatures greater than 180° C., greater than 200° C., greater than 220° C., greater than 230° C., or greater than 240° C. Additionally, the polymerization may be carried out at temperatures ranging from 230 to 280° C., or from 230 to 260° C., or from 240 to 250° C. In an exemplary embodiment, the polymerization may utilize t-butyl peracetate at a temperature ranging from 230 to 280° C.

[0018] In embodiments, the unsaturated carboxylic acid-containing comonomer may include an unsaturated monocarboxylic acid, such as acrylic acid, methacrylic acid, or a combination thereof. In embodiments, the unsaturated carboxylic acid-containing comonomer may be present in an amount of 5% to 35%, 12% to 30%, 15% to 25%, or 21% to 25% by weight, based on the total weight of the monomers present in the ethylene acid copolymer. Conversely, the ethylene content of the ethylene acid copolymer may be greater than 50% or greater than 60% by weight. For example, the ethylene content of the ethylene acid copolymer may be 50% to 95%, 70% to 88%, 75% to 85%, or 75% to 79% by weight.

[0019] In embodiments, the ethylene acid copolymer may have a melt index (I2) of 1 to 2000 dg / 10 min, 1 to 300 dg / 10 min, 20 to 100 dg / 10 min, 1 to 35 dg / 10 min, 25 to 35 dg / 10 min, 125 to 300 dg / 10 min, 200 to 275 dg / 10 min, or 250 to 275 dg / 10 min, as measured according to ASTM D-1238 (190°C / 2.16 Kg). In another embodiment, the ethylene acid copolymer has a melt index (I2) of less than 35 dg / min.

[0020] As mentioned above, the co-solvent may include tert-butanol. In addition to the co-solvent, the feed may also include a solvent. In one embodiment, the solvent may include supercritical ethylene. In this case, the supercritical ethylene may function as both a solvent and a monomer for the polymerization of the ethylene acid copolymer. The solvent may also include a hydrocarbon solvent, including, but not limited to, mineral solvents derived from mineral oil, normal paraffinic solvents, isoparaffinic solvents, and cyclic solvents. The hydrocarbon solvent may be selected from the group consisting of, for example, n-octane, isooctane (2,2,4-trimethylpentane), n-dodecane, isododecane (2,2,4,6,6-pentamethylheptane), and other isoparaffinic solvents. The solvent may be present in the mixture at less than 99% by weight, 5% to 95% by weight, 5% to 90% by weight, or 10% to 90% by weight.

[0021] Free radical polymerization processes are generally known in the art. Generally, the process is conducted at high temperature and pressure, either in a batch process or a continuous mode. Suitable reactors, such as tubular reactors or autoclave reactors, are well known to those skilled in the art. Additionally, compressor units upstream of the reactor and separator units downstream of the reactor are also well known to those skilled in the art. The polymerization pressure can be at least 1000 atm (101.3 MPa or 1013.25 bar), 1000 to 5000 atm, 1200 to 4000 atm, or 1500 to 3500 atm. The polymerization temperature typically ranges from 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 ranges from 100°C to 300°C, or from 150°C to 250°C. It should be noted that some reactor designs use multiple zones to achieve effective polymerization, and the temperature ranges herein are applicable to any individual zone in a multi-zone reactor.

[0022] In addition to the above components, additional additives such as inhibitors, chain transfer agents, radical scavengers, etc. are also contemplated as part of the mixture fed to the reactor.

[0023] Test Method

[0024] Melt Index (190°C, 2.16 kg, "I2") Test Method: ASTM D1238-13, Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer, using the condition 190°C / 2.16 kilograms (kg). Results are reported in grams dissolved per 10 minutes (g / 10 min) or the equivalent in decigrams per 1.0 minute (dg / 1 min). [Example]

[0025] The following examples illustrate features of the present disclosure but are not intended to limit the scope of the disclosure.

[0026] Cloud point experiment

[0027] Using an optical cell, the cloud point curve for each cosolvent was measured according to the experimental method published in Macromol. Chem. Phys., 2003, 204, 638-645. The cloud point is the temperature and pressure below which a solution undergoes phase separation. The experimental solutions contained 10 wt. % ethylene acid copolymer, supercritical ethylene solvent, various weight percents of the cosolvents listed in Table 1, and 0.5 wt. % BHT (butylated hydroxytoluene) inhibitor. The solutions were placed in the optical cell and heated to the desired temperature, which ranged from 178 to 240 °C, as shown. The cell was then pressurized above the cloud point to ensure the cell was in the single-phase (homogeneous) regime. The pressure was then reduced until the cloud point was found. The optical cell was then heated to the next temperature point.

[0028] The ethylene acid copolymers utilized in the examples were prepared by standard free-radical copolymerization methods operating in a continuous mode using high pressure. Monomers are fed to the reaction mixture in a ratio related to the reactivity of the monomers and the desired incorporation. In this manner, a uniform, nearly random distribution of monomer units along the chain is achieved. Polymerization in this manner is well known and is described in U.S. Pat. No. 4,351,931 (Armitage), which is incorporated herein by reference. Other polymerization techniques are described in U.S. Pat. No. 5,028,674 (Hatch et al.) and U.S. Pat. No. 5,057,593 (Statz), both of which are incorporated herein by reference.

[0029] [Table 1]

[0030] Example 1

[0031] For Example 1, shown in Table 2 and Figure 1, the ethylene acid copolymer contained 19 wt% methacrylic acid comonomer and had a melt index (I2) of 60 g / 10 min. Various cosolvent amounts were utilized, with the amount of cosolvent chosen to be equimolar to 6 wt% methanol. As shown, the cloud point pressure values ​​at each temperature point were lower than methanol. As noted above, this is advantageous because there is no phase separation at lower temperatures and pressures, as occurs with methanol.

[0032] [Table 2]

[0033] Example 2

[0034] In Example 2, shown in Table 3 and Figure 2, the same ethylene acid copolymer as in Example 1 was used with various cosolvents added at 6 wt %. Because tert-butanol has a molecular weight of 74.12 g / mol and methanol has a molecular weight of 32.04 g / mol, there are fewer moles of tert-butanol in the system at the same mass loading.

[0035] [Table 3]

[0036] Example 3

[0037] [Table 4]

[0038] Referring to Table 4, additional samples were treated with tert-butanol and methanol to demonstrate the increase in molecular weight achievable when using a tert-butanol cosolvent versus a methanol cosolvent. As shown, Comparative Example 3 involved the production of 21.7 wt. % MAA copolymer at 220°C and 27,000 psi. The resulting material had a melt index (I2) of approximately 117 g / 10 min. In contrast, as shown for Inventive Example 1, 13 wt. % tert-butanol was required to achieve single-phase reactor operation for the production of the same material, yet the resulting melt index was significantly lower (approximately 29). The lower melt index corresponds to a higher molecular weight, indicating that tert-butanol provides less chain transfer effects by not undesirably terminating polymer chains as methanol does. Furthermore, as shown in Inventive Example 2, clean reactor operation (very low fouling) and single-phase operation for a 19 wt% MAA copolymer was achieved at 248°C and 2,7000 psi with 7 wt% tert-butanol.

[0039] Example 4 - Corrosion Data

[0040] For corrosion testing, 40 mL glass vials were filled with tetradecane, carbon steel coupons, methacrylic acid, and a co-solvent (methanol or tert-butanol). The total mass in the vial, excluding the mass of the carbon steel coupon, was equal to 10 g. The vials were heated to 100 °C for 7 days. After that, the vials were allowed to cool to ambient temperature, and the carbon steel coupons were removed. The amount of corrosion was determined by mass balance / weight loss of the carbon steel coupons and is provided in Table 6.

[0041] [Table 5]

[0042] As shown for coupon sample 6 and coupon sample 7, methanol or tert-butanol alone do not significantly corrode the carbon steel coupons (less than 1.0 mg mass loss). As shown for coupon 1, the baseline for methacrylic acid alone shows a mass loss equal to 13.0 mg. This can be considered normal incidental corrosion resulting from the fact that methacrylic acid is always present in the process. For comparative coupon 2, the combination of methacrylic acid and methanol results in a significant increase in corrosion. Two experiments with 2 g of methacrylic acid and 0.5 g of methanol (comparative coupon 2) and 2.0 g of methacrylic acid and 1.0 g of methanol (comparative coupon 3) resulted in coupon mass losses of 80 mg and 95 mg, respectively. While methanol itself is not corrosive, its combination with methacrylic acid dramatically increases corrosion to carbon steel. In contrast, tert-butanol, in combination with methacrylic acid, resulted in less corrosion, resulting in a coupon mass loss of 20 mg and 19 mg, respectively, as shown in Inventive Coupon Sample 4 and Inventive Coupon Sample 5. Thus, by replacing methanol with tert-butanol as a co-solvent, improved corrosion was achieved in addition to other benefits that tert-butanol provides (e.g., increased molecular weight).

[0043]

[0010] According to a first aspect, there is provided a method for producing an ethylene acid copolymer, the method comprising: polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a cosolvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce an ethylene acid copolymer, the cosolvent comprising tert-butanol, the cosolvent comprising less than 15 wt% of the feed, and the ethylene acid copolymer having a melt index (I2) of less than 35 dg / min as determined according to ASTM D1238 (at 190°C and 2.16 kg).

[0044] A second embodiment includes any of the preceding embodiments, wherein the polymerization is carried out at a temperature of 230° C. or less.

[0045] A third embodiment includes any preceding embodiment, wherein the ethylene acid copolymer comprises from 5% to 35%, or from 12% to 25%, by weight of an unsaturated carboxylic acid-containing comonomer incorporated into the ethylene acid copolymer.

[0046] A fourth embodiment includes any preceding embodiment, wherein the ethylene acid copolymer includes a melt index (I2) of 1 to 35 dg / min, as measured according to ASTM D-1238 (190°C / 2.16 Kg).

[0047] A fifth embodiment includes any preceding embodiment, wherein the unsaturated carboxylic acid-containing comonomer includes acrylic acid, methacrylic acid, or a combination thereof.

[0048] A sixth embodiment includes any preceding embodiment, wherein the polymerization is carried out in the presence of a free radical initiator.

[0049] According to a seventh aspect, there is provided a process for producing an ethylene acid copolymer, comprising polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a co-solvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) and a reaction temperature greater than 200° C. to produce the ethylene acid copolymer, wherein the co-solvent comprises tert-butanol, and the co-solvent constitutes less than 15 wt % of the feed.

[0050] An eighth embodiment includes the seventh embodiment, wherein the polymerization is carried out at a temperature greater than 220°C, greater than 230°C, or greater than 240°C.

[0051] A ninth embodiment includes the seventh or eighth embodiment, wherein the ethylene acid copolymer has a melt index (I2) of 1 to 2000 dg / min, as measured according to ASTM D-1238 (190°C / 2.16 Kg).

[0052] A tenth embodiment includes the seventh through ninth embodiments, wherein the ethylene acid copolymer comprises from 5% to 35%, or from 12% to 25%, by weight of an unsaturated carboxylic acid-containing comonomer incorporated into the ethylene acid copolymer.

[0053] An eleventh embodiment includes the seventh through tenth embodiments, in which the unsaturated carboxylic acid-containing comonomer includes acrylic acid, methacrylic acid, or a combination thereof.

[0054] A twelfth embodiment includes the seventh through eleventh embodiments, wherein the polymerization is carried out in the presence of a free radical initiator.

[0055] A thirteenth embodiment includes the first through sixth embodiments, wherein the polymerization is carried out in a single-zone reactor or in any reaction zone of a multi-zone reactor at a temperature that is 230° C. or less.

[0056] A fourteenth embodiment includes the seventh through eleventh embodiments, wherein the polymerization is carried out in a single-zone reactor or in any reaction zone of a multi-zone reactor at the reaction temperature.

[0057] According to a fifteenth aspect, there is provided a process for producing an ethylene acid copolymer, comprising polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a co-solvent by free radical polymerization in a single-zone reactor or in any reaction zone of a multi-zone reactor at a pressure of at least 1000 atmospheres (atm) and a reaction temperature greater than 180° C. to produce the ethylene acid copolymer, wherein the co-solvent comprises tert-butanol, and the co-solvent constitutes less than 15 wt. % of the feed.

[0058] It will be apparent that modifications and variations are possible without departing from the scope of the present disclosure, as defined in the appended claims. More specifically, while certain aspects of the present disclosure have been identified herein as preferred or particularly advantageous, it is not intended that the present disclosure be necessarily limited to these aspects.

Claims

1. 1. A process for producing an ethylene acid copolymer, comprising: polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a co-solvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce said ethylene acid copolymer, wherein said co-solvent comprises tert-butanol, and said co-solvent comprises less than 15 wt% of said feed; The ethylene acid copolymer has a melt index (I) of less than 35 dg / min, as determined according to ASTM D1238 (190°C, 2.16 kg). ２ ).

2. 10. The method of claim 1, wherein the polymerization is carried out at a temperature of 230°C or less.

3. 3. The method of claim 1 or 2, wherein the ethylene acid copolymer comprises from 5 to 35 weight percent, or from 12 to 25 weight percent, of an unsaturated carboxylic acid-containing comonomer incorporated into the ethylene acid copolymer.

4. The ethylene acid copolymer has a melt index (I) of 1 to 35 dg / min when measured according to ASTM D-1238 (190°C / 2.16 Kg). ２ 4. The method according to claim 1, wherein

5. The method of any one of claims 1 to 4, wherein the unsaturated carboxylic acid-containing comonomer comprises acrylic acid, methacrylic acid, or a combination thereof.

6. The method of any one of claims 1 to 5, wherein the polymerization is carried out in the presence of a free radical initiator.

7. 1. A process for producing an ethylene acid copolymer, comprising:

1. A process comprising: polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a co-solvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) and a reaction temperature above 200°C to produce said ethylene acid copolymer, wherein said co-solvent comprises tert-butanol, and wherein said co-solvent comprises less than 15 wt% of said feed.

8. 8. The method of claim 7, wherein the polymerization is carried out at a temperature greater than 220°C, greater than 230°C, or greater than 240°C.

9. The ethylene acid copolymer has a melt index (I) of 1 dg / min to 2000 dg / min, as measured in accordance with ASTM D-1238 (190°C / 2.16 Kg). ２ 9. The method of claim 7 or 8, wherein

10. 10. The method of any one of claims 7 to 9, wherein the ethylene acid copolymer comprises from 5% to 35%, or from 12% to 25% by weight of an unsaturated carboxylic acid-containing comonomer incorporated into the ethylene acid copolymer.

11. The method of any one of claims 7 to 10, wherein the unsaturated carboxylic acid-containing comonomer comprises acrylic acid, methacrylic acid, or a combination thereof.

12. The method of any one of claims 7 to 11, wherein the polymerization is carried out in the presence of a free radical initiator.

13. 10. The process of claim 1, wherein the polymerization is carried out in a single-zone reactor or in any reaction zone of a multi-zone reactor at a temperature that is 230°C or less.

14. 8. The process of claim 7, wherein the polymerization is carried out at the reaction temperature in a single-zone reactor or in any reaction zone of a multi-zone reactor.

15. 1. A method for producing an ethylene acid copolymer, 1. A process comprising: polymerizing a feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a co-solvent by free radical polymerization in a single-zone reactor or in any reaction zone of a multi-zone reactor at a pressure of at least 1000 atmospheres (atm) and a reaction temperature above 180° C. to produce said ethylene acid copolymer, wherein said co-solvent comprises tert-butanol, and said co-solvent comprises less than 15 wt % of said feed.

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