Tert-butanol co-solvents in production of ethylene acid copolymers

Abstract

Embodiments of the present disclosure relate to a process for producing an ethylene acid copolymer, the process comprising polymerizing a feed comprising an ethylene monomer, a comonomer comprising an unsaturated carboxylic acid, and a cosolvent by free radical polymerization at a pressure of at least 1000 atm to produce the ethylene acid copolymer, wherein the cosolvent comprises tert-butanol and wherein the cosolvent comprises less than 15% by weight 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 (at 190 DEG C, 2.16 kg).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 411,323, 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 ethylene acid copolymers, and specifically to the use of tert-butyl alcohol solvent to reduce phase separation and corrosion. Background Art

[0004] For 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. In addition, as the amount of acid in the polymer chain increases, phase separation can cause scaling and gelation problems. Therefore, methanol co-solvents are often used to reduce phase separation. However, large amounts of methanol may increase corrosion. In addition, methanol can act as a chain transfer agent to reduce the molecular weight capacity of the process.

[0005] Therefore, an alternative to methanol as a co-solvent is needed. Summary of the invention

[0006] Embodiments of the present disclosure meet this need by replacing methanol with a tert-butyl alcohol co-solvent which reduces phase separation and reduces polymer chain termination and corrosion. Additionally, another advantage is that the residual tert-butyl alcohol levels in the ethylene acid copolymer are non-reactive with any added base, thereby preventing the acid groups in the polymer chains from being ionomerized.

[0007] According to at least one embodiment of the present disclosure, a method for producing an ethylene acid copolymer is provided. The method comprises: polymerizing a feed comprising an ethylene monomer, a comonomer containing an unsaturated carboxylic acid, and a cosolvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce the ethylene acid copolymer, wherein the cosolvent comprises tertiary butyl alcohol and wherein the cosolvent accounts for less than 15% by weight of the feed, and wherein the ethylene acid copolymer has a melt index (I2) of less than 35 dg / min measured according to ASTM D1238 (at 190°C, 2.16 kg).

[0008] According to another embodiment, the process comprises 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) and a reaction temperature greater than 200° C. to produce the ethylene acid copolymer, wherein the cosolvent comprises tert-butyl alcohol and wherein the cosolvent comprises less than 15 weight percent of the feed.

[0009] These and other embodiments are described in more detail in the following figures and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a graphical representation of the cloud point data for Example 1; and

[0011] Figure 2 is a graphical representation of the cloud point data for Example 2; DETAILED DESCRIPTION

[0012] 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.

[0013] 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.

[0014] "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 both linear low density resins and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE).

[0015] "Ethylene acid copolymers" are the polymerization products of ethylene and monomers containing one or more unsaturated carboxylic acids.

[0016] Embodiments relate to a method for producing ethylene acid copolymers, the method comprising polymerizing a feed comprising ethylene monomer, a comonomer containing an unsaturated carboxylic acid and a cosolvent by free radical polymerization under a pressure of at least 1000 atmospheres (atm) to produce the ethylene acid copolymer. The cosolvent comprises tertiary butyl alcohol. The cosolvent may account for less than 15 weight % of the feed. In other embodiments, the cosolvent accounts for 5 weight % to 14 weight % or 7 weight % to 13 weight %.

[0017] In one or more embodiments, polymerization is carried out in the presence of a free radical initiator. Based on the weight of the feed, the usual amount of the free radical initiator is about 0.1 wt % to about 5 wt %, about 0.2 wt % to about 2 wt % or about 0.25 wt % to about 1 wt %. Based on the weight of the feed by weight, another usual amount of the free radical initiator can be about 50ppm to about 2,500ppm, about 100ppm to about 1,000ppm or about 150ppm to about 500ppm. The free radical initiator can be all added at the beginning of the reaction, or can be added continuously or in stages during the reaction (particularly when the monomer is so added). The example of a suitable free radical initiator includes peroxyesters, peroxides, persulfates, perborate, percarbonate, azo compounds, etc. Specific examples of suitable free radical initiators include hydrogen peroxide, tert-butyl peroctoate, tert-butyl peracetate, di-tert-butyl peroxide, lauroyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, 2,2'-azobis[2,4-dimethyl]valeronitrile, 2-(tert-butylazo)-2-methylbutyronitrile, 2-(tert-butylazo)-2-4-dimethylvaleronitrile, azobis(isobutyronitrile), azobis(methylbutyronitrile) (AMBN), tert-amyl peroxy-2-ethylhexanoate, and mixtures of any two or more thereof.

[0018] In one or more embodiments, the polymerization, which may be optionally performed with the above-mentioned free radical initiator, may be performed at a temperature of 230° C. or less, less than 220° C., or less than 210° C. In addition, the polymerization may be performed at a temperature ranging from 175° C. to 230° C., 200° C. to 230° C., or 210° C. to 230° C. In an exemplary embodiment, the polymerization may be performed at a temperature ranging from 175° C. to 230° C. using tert-butyl peroctanoate.

[0019] In alternative embodiments, the polymerization may be carried out at a temperature greater than 180° C., greater than 200° C., greater than 220° C., greater than 230° C., or greater than 240° C. In addition, the polymerization may be carried out at a temperature ranging from 230° C. to 280° C., 230° C. to 260° C., or 240° C. to 250° C. In an exemplary embodiment, the polymerization may be carried out at a temperature ranging from 230° C. to 280° C. using t-butyl peracetate.

[0020] In embodiments, the comonomer containing unsaturated carboxylic acid can comprise unsaturated monocarboxylic acid, such as acrylic acid, methacrylic acid or their combination.In embodiments, based on the gross weight of the monomer present in the ethylene acid copolymer, the comonomer containing unsaturated carboxylic acid can exist with the amount of 5 % by weight to 35 % by weight, 12 % by weight to 30 % by weight, 15 % by weight to 25 % by weight or 21 % by weight to 25 % by weight.On the contrary, the ethylene content of ethylene acid copolymer is greater than 50 % by weight or greater than 60 % by weight.For example, the ethylene content of ethylene acid copolymer is 50 % by weight to 95 % by weight, 70 % by weight to 88 % by weight, 75 % by weight to 85 % by weight or 75 % by weight to 79 % by weight.

[0021] In an embodiment, the ethylene acid copolymer may have a melt index (I2) of 1 dg / 10min to 2000 dg / 10min, 1 dg / 10min to 300 dg / 10min, 20 dg / 10min to 100 dg / 10min, 1 dg / 10min to 35 dg / 10min, 25 dg / 10min to 35 dg / 10min, 125 dg / 10min to 300 dg / 10min, 200 dg / 10min to 275 dg / 10min, or 250 dg / 10min to 275 dg / 10min measured according to ASTM D-1238 (190°C / 2.16Kg). In another embodiment, the ethylene acid copolymer has a melt index (I2) of less than 35 dg / min.

[0022] As mentioned above, the co-solvent may include tert-butyl alcohol. 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, supercritical ethylene can serve as a solvent and monomer for the polymerization of ethylene acid copolymers. The solvent may also include a hydrocarbon solvent, which may include but is not limited to mineral solvents, such as from mineral oil, normal paraffin solvents, isoparaffin solvents, cyclic solvents, etc. The hydrocarbon solvent may be, for example, selected from the group consisting of n-octane, isooctane (2,2,4-trimethylpentane), n-dodecane, isododecane (2,2,4,6,6,-pentamethylheptane) and other isoparaffin solvents. The solvent may be present in the mixture with less than 99% by weight, 5% by weight to 95% by weight, 5% by weight to 90% by weight, or 10% by weight to 90% by weight.

[0023] Free radical polymerization processes are generally known in the art. Typically, the process is carried out at elevated temperature and pressure in a batch process or in a continuous manner. 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. Note that some reactor designs use multiple zones to achieve efficient polymerization; the temperature ranges herein apply to any single zone in a multi-zone reactor.

[0024] In addition to the above components, additional additives such as inhibitors, chain transfer agents, free radical scavengers, etc. are also contemplated as part of the mixture fed to the reactor.

[0025] Test Method

[0026] Melt Index (190°C, 2.16kg, "I2") Test Method: Use ASTM D1238-13 "Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Platometer" using 190°C / 2.16 kilograms (kg) conditions. Report results in grams eluted per 10 minutes (g / 10min.) or equivalently decigrams per 1.0 minute (dg / 1min.).

[0027] Example

[0028] The following examples illustrate features of the present disclosure but are not intended to limit the scope of the present disclosure.

[0029] Cloud point experiment

[0030] The cloud point curve of each co-solvent was measured using an optical cell according to the experimental method disclosed in: Macromol. Chem. Phys., 2003, 204, 638–645. The cloud point is the temperature and pressure below which the solution phase separates. The experimental solution contained 10 wt% of an ethylene acid copolymer, a supercritical ethylene solvent, the co-solvents listed in various weight percentages in Table 1, and 0.5 wt% of a BHT (butylated hydroxytoluene) inhibitor. The solution was placed in an optical cell and heated to the desired temperature, which, as shown, ranged from 178°C to 240°C. The cell was then pressurized above the cloud point to ensure that it was in a single-phase (homogeneous) state. The pressure was then reduced until a cloud point was found. The optical cell was then heated to the next temperature point.

[0031] The ethylene acid copolymers used in the examples are prepared by standard free radical copolymerization methods, using high pressure, operating in a continuous manner. The ionomer is fed into the reaction mixture in a ratio related to the monomer reactivity and the required incorporation amount. In this way, a uniform, nearly random distribution of monomer units along the chain is achieved. Polymerization carried out in this way is well known and is described in U.S. Patent No. 4,351,931 (Armitage), which is hereby incorporated by reference. Other polymerization techniques are described in U.S. Patent No. 5,028,674 (Hatch et al.) and U.S. Patent No. 5,057,593 (Statz), which are hereby incorporated by reference.

[0032] Table 1 - Co-solvents

[0033] Co-solvent Boiling point at 1atm(℃) Methanol 64.7℃ Formic acid 100.8℃ Acetic acid 118℃ Pivalic acid 163.8℃ Tert-Butanol 117.7℃

[0034] Example 1

[0035] For Table 2 and Figure 1 In Example 1 shown in , the ethylene acid copolymer has 19 wt % methacrylic acid comonomer and a melt index (I2) of 60 g / 10 min. Different amounts of cosolvents were used, the amount of cosolvent being selected to be equimolar with 6 wt % methanol. As shown, the cloud point pressure values ​​at each temperature point are lower than methanol. As mentioned above, this is advantageous because phase separation does not occur at lower temperatures and pressures as in the case of methanol.

[0036] Table 2

[0037]

[0038] Example 2

[0039] For Table 3 and Figure 2Example 2 shown uses the same ethylene acid copolymer as Example 1, and adds 6 wt% of various co-solvents. Because tert-butyl alcohol has a molecular weight of 74.12 g / mol and methanol has a molecular weight of 32.04 g / mol, fewer moles of tert-butyl alcohol are present in the system at the same mass loading.

[0040] Table 3

[0041]

[0042] Example 3

[0043] Table 4

[0044]

[0045] Referring to Table 4, additional samples were treated with tert-butyl alcohol and methanol to show the increased molecular weight that can be achieved when using tert-butyl alcohol co-solvent relative to methanol co-solvent. As shown, Comparative Example 3 involves the production of 21.7 wt% MAA copolymer at 220°C and 27,000 psi. The resulting material has a melt index (I2) of about 117 g / 10 min. In contrast to that shown in Inventive Example 1, 13 wt% tert-butyl alcohol was required to achieve single-phase reactor operation for producing the same material, but the resulting melt index was significantly lower (~29). The lower melt index corresponds to a higher molecular weight, which indicates that tert-butyl alcohol provides less chain transfer effects by not undesirably terminating the polymer chain as methanol does. In addition, as shown in Inventive Example 2, clean reactor operation (very low fouling) and single-phase operation for 19 wt% MAA copolymer were achieved with 7 wt% tert-butyl alcohol at 248°C and 2,7000 psi.

[0046] Example 4 - Corrosion Data

[0047] For the corrosion study, tetradecane, carbon steel coupon, methacrylic acid and co-solvent (methanol or tert-butyl alcohol) were charged in a 40 mL glass bottle. The total mass in 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. Afterwards, the vial was cooled 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.

[0048] Table 6

[0049]

[0050] As shown for sample block samples 6 and 7, methanol or tert-butyl alcohol alone did not show significant corrosion (<1.0 mg mass loss) of the carbon steel sample block. As shown for sample block 1, the baseline of methacrylic acid alone showed a mass loss equal to 13.0 mg. This can be considered as normal background corrosion due to the fact that methacrylic acid is always present in the method. As shown for comparison sample block 2, the combination of methacrylic acid and methanol resulted in significantly increased corrosion. Two experiments of 2g methacrylic acid and 0.5g methanol (comparison sample block 2) and 2.0g methacrylic acid and 1.0g methanol (comparison sample block 3) produced 80mg and 95mg of sample block mass loss respectively. Although methanol itself is not corrosive, the combination with methacrylic acid significantly increases the corrosion of carbon steel. In contrast to the present invention sample block samples 4 and 5, tert-butyl alcohol and methacrylic acid combined to cause less corrosion, producing 20mg and 19mg of sample block mass loss respectively. Therefore, in addition to the other benefits of tert-butyl alcohol delivery, such as increased molecular weight, improved corrosion is achieved by replacing methanol as a co-solvent with tert-butyl alcohol.

[0051] Embodiments herein may include one or more aspects. According to a first aspect, a method for producing an ethylene acid copolymer, the method comprising polymerizing a feed comprising ethylene monomer, a comonomer containing an unsaturated carboxylic acid, and a cosolvent by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce the ethylene acid copolymer, wherein the cosolvent comprises tertiary butyl alcohol and wherein the cosolvent accounts for 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 measured according to ASTM D1238 (at 190°C, 2.16 kg).

[0052] A second aspect includes any of the preceding aspects, wherein the polymerization is conducted at a temperature less than or equal to 230°C.

[0053] A third aspect includes any of the preceding aspects, wherein the ethylene acid copolymer comprises 5 wt % to 35 wt %, or 12 wt % to 25 wt % of an unsaturated carboxylic acid-containing comonomer incorporated therein.

[0054] A fourth aspect includes any of the preceding aspects, wherein the ethylene acid copolymer has a melt index (I2) of 1 dg / min to 35 dg / min measured according to ASTM D-1238 (190° C. / 2.16 Kg).

[0055] A fifth aspect includes any of the preceding aspects, wherein the unsaturated carboxylic acid-containing comonomer includes acrylic acid, methacrylic acid, or a combination thereof.

[0056] A sixth aspect includes any of the preceding aspects, wherein the polymerization is carried out in the presence of a free radical initiator.

[0057] According to a seventh aspect, a method for producing an ethylene acid copolymer comprises polymerizing a feed comprising ethylene monomer, a comonomer containing an unsaturated carboxylic acid, and a cosolvent via 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 cosolvent comprises tert-butyl alcohol and wherein the cosolvent comprises less than 15 weight percent of the feed.

[0058] An eighth aspect includes the seventh aspect, wherein the polymerization is conducted at a temperature greater than 220°C, greater than 230°C, or greater than 240°C.

[0059] The ninth aspect includes the seventh aspect to the eighth aspect, wherein the ethylene acid copolymer has a melt index (I2) of 1 dg / min to 2000 dg / min measured according to ASTM D-1238 (190° C. / 2.16 Kg).

[0060] The tenth aspect includes the seventh to ninth aspects, wherein the ethylene acid copolymer comprises 5 to 35 wt%, or 12 to 25 wt%, of an unsaturated carboxylic acid-containing comonomer incorporated therein.

[0061] The eleventh aspect includes the seventh aspect to the tenth aspect, wherein the unsaturated carboxylic acid-containing comonomer comprises acrylic acid, methacrylic acid, or a combination thereof.

[0062] The twelfth aspect includes the seventh to eleventh aspects, wherein the polymerization is carried out in the presence of a free radical initiator.

[0063] The thirteenth aspect includes the first to sixth aspects, wherein the polymerization is carried out at a temperature of less than or equal to 230° C. in any reaction zone of a single zone or multi-zone reactor.

[0064] The fourteenth aspect includes aspects seven to eleven, wherein the polymerization is carried out at the reaction temperature in any reaction zone of a single zone or multi-zone reactor.

[0065] According to the fifteenth aspect, a method for producing an ethylene acid copolymer comprises polymerizing a feed comprising ethylene monomer, a comonomer containing an unsaturated carboxylic acid and a cosolvent by free radical polymerization in any reaction zone of a single zone or 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 cosolvent comprises tert-butyl alcohol and wherein the cosolvent accounts for less than 15 weight percent of the feed.

[0066] 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 an ethylene acid copolymer, the method comprising: A feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a cosolvent is polymerized by free radical polymerization at a pressure of at least 1000 atmospheres (atm) to produce the ethylene acid copolymer, wherein the cosolvent comprises t-butyl alcohol and wherein the cosolvent comprises less than 15 weight percent of the feed, and wherein the ethylene acid copolymer has a melt index (I2) of less than 35 dg / min as measured according to ASTM D1238 (at 190° C., 2.16 kg).

2. The method according to claim 1, wherein the polymerization is carried out at a temperature less than or equal to 230°C.

3. The method of any preceding claim, wherein the ethylene acid copolymer comprises 5 to 35 wt%, or 12 to 25 wt%, of an unsaturated carboxylic acid-containing comonomer incorporated therein.

4. The method according to any preceding claim, wherein the ethylene acid copolymer has a melt index (I2) of 1 dg / min to 35 dg / min measured according to ASTM D-1238 (190°C / 2.16 Kg).

5. The method of any preceding claim, wherein the unsaturated carboxylic acid-containing comonomer comprises acrylic acid, methacrylic acid, or a combination thereof.

6. A process according to any preceding claim, wherein the polymerisation is carried out in the presence of a free radical initiator.

7. A method for producing an ethylene acid copolymer, the method comprising: A feed comprising ethylene monomer, an unsaturated carboxylic acid-containing comonomer, and a cosolvent is polymerized 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 cosolvent comprises tert-butyl alcohol and wherein the cosolvent comprises less than 15 weight percent of the feed.

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 method according to claim 7 or 8, wherein the ethylene acid copolymer has a melt index (I2) of 1 to 2000 dg / min measured according to ASTM D-1238 (190°C / 2.16 Kg).

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

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

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

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

15. A method for producing an ethylene acid copolymer, the method comprising: A feed comprising ethylene monomer, a comonomer containing an unsaturated carboxylic acid, and a cosolvent is polymerized by free radical polymerization in any reaction zone of a single zone or 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 cosolvent comprises tert-butyl alcohol and wherein the cosolvent comprises less than 15 weight percent of the feed.

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