Carboxylic acid cosolvents in the formation of ethylene acid copolymers.

Abstract

Embodiments of the present disclosure relate to a process for producing an ethylene acid copolymer, comprising polymerizing ethylene monomer and an unsaturated carboxylic acid-containing comonomer via free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce an ethylene acid copolymer, wherein the ethylene monomer and the unsaturated carboxylic acid-containing comonomer are in a mixture with at least one saturated carboxylic acid cosolvent, the at least one saturated carboxylic acid cosolvent having a boiling point of less than 237° C. at a pressure of 1 atm and present in the mixture in an amount of 1 to 25 wt %.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to U.S. Patent Application No. 63 / 304,890, entitled "CARBOXYLIC ACID COSOLVENTS IN THE PRODUCTION OF ETHYLENE ACID COPOYMER," filed January 31, 2022, the entire contents of which are incorporated by reference into this disclosure.

[0002] FIELD OF THEINVENTION FIELD OF THE DISCLOSURE Embodiments described herein relate generally to ethylene acid copolymers, and specifically to the use of saturated carboxylic acid co-solvents to reduce phase separation. [Background technology]

[0003] For ethylene acid copolymers, phase separation within the free radical solution mixture is problematic as it can limit the incorporation of acid into the polymer. Furthermore, as the amount of acid in the polymer chain increases, phase separation can cause fouling and gel problems. Thus, methanol co-solvents are traditionally used to reduce phase separation. However, high amounts of methanol can increase corrosion. Furthermore, methanol can act as a chain transfer agent to reduce the molecular weight capacity 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 meet this need by replacing methanol with a saturated carboxylic acid co-solvent, which can reduce phase separation and reduce polymer chain termination and corrosion.

[0006] According to at least one embodiment of the present disclosure, there is provided a method for producing an ethylene acid copolymer, comprising polymerizing ethylene monomer and an unsaturated carboxylic acid-containing comonomer via free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce an ethylene acid copolymer, wherein the ethylene monomer and the unsaturated carboxylic acid-containing comonomer are in a mixture with at least one saturated carboxylic acid cosolvent, the at least one saturated carboxylic acid cosolvent having a boiling point of less than 237° C. at a pressure of 1 atm and present in the mixture in an amount of 1 to 25 wt %.

[0007] These and other embodiments are described in more detail in the figures and detailed description that follow. [Brief description of the drawings]

[0008] [Figure 1] 1 is a graph of cloud point data for Example 1. [Diagram 2] 1 is a graph of cloud point data for Example 2. [Diagram 3] 1 is a graph of cloud point data for Example 3. [Figure 4] 1 is a graph of cloud point data for Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 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.

[0010] The term "polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or different types. Thus, the generic term polymer generally includes 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 generic term interpolymer includes copolymers or polymers prepared from more than two different types of monomers, such as terpolymers.

[0011] "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 that 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).

[0012] "Ethylene acid copolymer" is the polymerization reaction product of ethylene and one or more unsaturated carboxylic acid containing monomers.

[0013] An embodiment relates to a method for producing an ethylene acid copolymer, comprising polymerizing ethylene monomer and an unsaturated carboxylic acid-containing comonomer via free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce an ethylene acid copolymer. The ethylene monomer and the unsaturated carboxylic acid-containing comonomer are in a mixture with at least one saturated carboxylic acid cosolvent. The saturated carboxylic acid cosolvent has a boiling point of less than 237° C. at a pressure of 1 atm and is present in the mixture in an amount of 1 to 25 wt %.

[0014] Ethylene Acid Copolymer 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 monomers present in the ethylene acid copolymer. Conversely, the ethylene content of the ethylene acid copolymer is greater than 50% by weight, or greater than 60% by weight. For example, the ethylene content of the ethylene acid copolymer is 50% to 95%, 70% to 88%, 75% to 85%, or 75% to 79% by weight. In embodiments, the ethylene acid copolymer may have a melt index (I2) measured according to ASTM D-1238 (190° C. / 2.16 Kg) of 1 to 2000 dg / 10 min, 10 to 100 dg / 10 min, 20 to 80 dg / 10 min, or 1500 to 2000 dg / min.

[0015] solvent The mixture may further include at least one solvent. In one embodiment, the solvent includes supercritical ethylene. The solvent may also include a hydrocarbon solvent, which may include, but is not limited to, mineral solvents, such as from mineral oil, normal paraffinic solvents, isoparaffinic solvents, cyclic solvents, and the like. 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, 5-95% by weight, 5-90% by weight, or 10-90% by weight.

[0016] Co-solvents As discussed above, the co-solvent comprises one or more saturated carboxylic acids having a boiling point below 237° C. at 1 atm pressure. Without being bound by theory, these lower boiling saturated carboxylic acids reduce the possibility of phase separation while also reducing corrosion and chain termination. Suitable co-solvents may include formic acid, acetic acid, propanoic acid, 2-methylpropanoic acid, butyric acid, pentanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, pivalic acid (2,2-dimethylpropanoic acid), hexanoic acid, 2,3-dimethylbutanoic acid, 3,3-dimethylbutanoic acid, 2,3-dimethylpentanoic acid, heptanoic acid, cyclohexane carboxylic acid, and combinations thereof. In one embodiment, the saturated carboxylic acid co-solvent comprises pivalic acid, acetic acid, or combinations thereof. The co-solvent may be present in the mixture in an amount ranging from 1 to 25% by weight, 1 to 20% by weight, 3 to 20% by weight, or 5 to 15% by weight.

[0017] Free radical polymerization processes are generally known in the art. Generally, the process is carried out at high temperature and pressure, either in a batch process or in a continuous mode. Suitable reactors, such as tubular reactors or autoclave reactors, are well known to those skilled in the art. In addition, 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 in the range of 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 is typically in the range of about 70°C to about 380°C. All individual values ​​and subranges in 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.

[0018] In addition to the components described above, additional additives such as initiators, inhibitors, chain transfer agents, and the like are also contemplated as being part of the mixture fed to the reactor.

[0019] Test Method Melt Index (190°C, 2.16 kg, "I2") Test Method: ASTM D 1238-13, Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer, using the following 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). EXAMPLES

[0020] The following examples illustrate features of the present disclosure but are not intended to limit the scope of the disclosure.

[0021] Cloud Point Experiment The optical cell was used to measure the cloud point curve for each co-solvent according to the experimental method published in Macromol. Chem. Phys., 2003, 204, 638-645. The cloud point is the temperature and pressure below which the solution phase separates. The experimental solutions contained 10 wt% ethylene acid copolymer, supercritical ethylene solvent, the co-solvents listed in Table 1 at various weight percentages, and 0.5 wt% BHT (butylated hydroxytoluene) inhibitor. The solutions were placed in the optical cell and heated to the desired temperature, which was in the range of 178-240°C as shown. The cell was then pressurized above the cloud point to ensure it 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.

[0022] The ethylene acid copolymers utilized in the examples were prepared by standard free radical copolymerization methods using high pressure and operating in a continuous mode. Monomers are fed to the reaction mixture in a ratio related to the reactivity of the monomers and the amount desired to be incorporated. In this way, a uniform and approximately 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.

[0023] [Table 1]

[0024] Example 1 For Example 1 shown in Table 2 and Figure 1, the ethylene acid copolymer contained 19 wt% methacrylic acid comonomer and a melt index (I2) of 60 g / 10 min. Various co-solvent amounts were utilized, with the amount of co-solvent selected to be equimolar to 6 wt% methanol. As shown, the cloud point pressure values ​​at each temperature point were significantly lower than methanol, especially as the amount of saturated carboxylic acid increased. As discussed above, this is advantageous since there is no phase separation at lower temperatures and pressures, as is the case with methanol.

[0025] [Table 2]

[0026] Example 2 For Example 2, shown in Table 3 and Figure 2, the same ethylene acid copolymer was used as in Example 1, with various co-solvents added at 3 wt %. As shown in comparison to Example 1, even lower amounts of co-solvents reduced the cloud point of the solution.

[0027] [Table 3]

[0028] Example 3 For Example 3, shown in Table 4 and Figure 3, the same ethylene acid copolymer as Examples 1 and 2 was used with various co-solvents added at 6 wt%. As shown in comparison to Example 1, even lower amounts of co-solvents reduced the cloud point of the solution. Furthermore, at a temperature of about 194°C, the cloud point is significantly lower for the same concentration of pivalic acid as methanol.

[0029] [Table 4]

[0030] Example 4 For Example 4 shown in Table 5 and Figure 4, an ethylene acid copolymer having 22 wt% methacrylic acid comonomer and a melt index (I2) of 25 dg / min was used with various co-solvents added at 6 wt%. As shown, even with the incorporation of more methacrylic acid, there is still a reduced cloud point of the solution due to the saturated carboxylic acid co-solvent.

[0031] [Table 5]

[0032] Corrosion Data For the corrosion test, a 40 mL glass vial was filled with tetradecane, carbon steel coupons, methacrylic acid, and pivalic acid. The total mass inside the vial, excluding the mass of the carbon steel coupon, was equal to 10 g. The vial was heated to 100° C. for 7 days. After that, the vial was allowed to cool to ambient temperature and the carbon steel coupon was removed. The amount of corrosion was determined by mass balance / weight loss of the carbon steel coupon and is provided in Table 6.

[0033] [Table 6]

[0034] The results showed that methanol or pivalic acid alone did not show any significant corrosion of the carbon steel coupons (<2.0 mg mass loss). The baseline with only methacrylic acid showed a mass loss equal to 13.0 mg. This can be considered normal background corrosion resulting from the fact that methacrylic acid is always present in the process. The combination of methacrylic acid and methanol results in significantly increased corrosion. Two experiments with 2 g methacrylic acid and 0.5 g methanol and 2.0 g methacrylic acid and 1.0 g methanol resulted in coupon mass losses of 80 mg and 95 mg, respectively. Methanol itself is not at all corrosive, but only the combination with methacrylic acid (as currently implemented in the process) dramatically increased corrosion to the carbon steel. Pivalic acid resulted in less corrosion in combination with methacrylic acid compared to methanol, with two experiments resulting in coupon mass losses of 26 mg and 32 mg, respectively. Thus, the data demonstrated that improved corrosion was achieved by replacing methanol with pivalic acid as a co-solvent, in addition to the other benefits that pivalic acid provides.

[0035] 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, although certain 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 those aspects.

Claims

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

1. A process comprising: polymerizing ethylene monomer and an unsaturated carboxylic acid-containing comonomer via free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce said ethylene acid copolymer, said ethylene monomer and unsaturated carboxylic acid-containing comonomer being in a mixture with at least one saturated carboxylic acid cosolvent, said at least one saturated carboxylic acid cosolvent having a boiling point of less than 237° C. at a pressure of 1 atm and present in said mixture in an amount of 1 to 25 weight percent.

2. The method of claim 1 , wherein the ethylene acid copolymer comprises from 5 to 35 weight percent, or from 12 to 30 weight percent, of an unsaturated carboxylic acid-containing comonomer incorporated therein.

3. The ethylene acid copolymer has a melt index (I ) of 1 to 2000 dg / min, measured according to ASTM D-1238 (190° C. / 2.16 Kg). ２ 3. The method of claim 1 or 2, comprising:

4. The method of any one of claims 1 to 3, wherein the unsaturated carboxylic acid-containing comonomer comprises acrylic acid, methacrylic acid, or a combination thereof.

5. The method of any one of claims 1 to 4, wherein the at least one saturated carboxylic acid co-solvent comprises pivalic acid, acetic acid, formic acid, or a combination thereof.

6. An ethylene acid copolymer comprising the polymerization reaction product of ethylene monomer and a carboxylic acid comonomer, the ethylene acid copolymer comprising greater than 20 weight percent acid comonomer and a melt index (I2) of 1 to 2000 dg / min as measured in accordance with ASTM D-1238 (190°C / 2.16 Kg).

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