Polymerization inhibitor for high-temperature ethylene distillation train
High-temperature stable antifoulant compositions with quinone methides and phenylenediamines address polymerization and fouling in ethylene fraction streams, effectively reducing gum formation and improving process efficiency.
Patent Information
- Application Number
- JP2025516174
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-09-19
- Filing Date
- 2023-08-30
- Publication Date
- 2025-09-04
AI Technical Summary
Conventional inhibitor chemicals are ineffective in high-temperature ethylene fractionation units, leading to polymerization, gum formation, and fouling, which adversely affect heat transfer efficiency and product yields.
The use of high-temperature stable antifoulant and antipolymerization compositions comprising quinone methides and/or phenylenediamines, optionally with hindered phenols, to inhibit polymerization and fouling in ethylene fraction streams.
The compositions effectively reduce polymerization, gum formation, and fouling in high-temperature ethylene fraction streams by reacting with thermally generated free radicals, enhancing reaction rates and inhibiting polymerization.
Smart Images
Figure 2025529537000001_ABST
Abstract
Description
[Technical Field]
[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Application No. 63 / 408,061, filed September 19, 2022, which is incorporated herein by reference in its entirety.
[0002] The disclosed technology relates to compositions and methods for inhibiting polymerization, gum formation, and fouling in ethylene fractional streams. More specifically, the disclosed technology relates to methods for inhibiting polymerization, gum formation, and fouling in high temperature ethylene fractional streams, comprising treating the high temperature ethylene fractional stream with a high temperature stable antifoulant and / or antipolymer composition comprising a quinone methide and / or a phenylenediamine. [Background technology]
[0003] Undesirable polymerization, also known as gum formation, can occur in the light-ends fractionation train of an ethylene plant, causing fouling that adversely affects heat transfer efficiency, fluid flow, and product yields, and can result in the production of significant amounts of "popcorn polymer." Most units can be effectively treated with conventional inhibitor chemicals such as 4-hydroxyTEMPO (or other stable free-radical chemicals), n,n-diethylhydroxylamine (or other hydroxylamines), butylated hydroxytoluene (or other phenolic antioxidants), and combinations thereof.
[0004] However, some units operate at higher than normal temperature conditions. These units cannot be treated with traditional inhibitor approaches because these traditional activators are ineffective. Another approach is required to inhibit polymerization, gum formation, and fouling in these atypical units. Summary of the Invention
[0005] The disclosed technology provides for the inhibition of polymerization, gum formation, and fouling in ethylene fraction streams using high temperature stable antifoulant and / or antipolymerization compositions comprising quinone methides and / or phenylenediamines.
[0006] Various aspects of the present disclosure relate to a high temperature stable composition for inhibiting polymerization in a high temperature ethylene fraction train, the composition comprising: an effective amount of the following formula: [ka] (R 1 , R 2 , and R 3 are independently selected from the group consisting of H, —OH, —SH, —NH2, alkyl, cycloalkyl, heterocyclo, and aryl. and an effective amount of one or more phenylenediamines, such as unsymmetrical phenylenediamines.
[0007] In various embodiments, the high temperature stable antifoulant or antipolymerization agent composition further comprises one or more hindered phenols.
[0008] Various aspects of the present disclosure further relate to a method of inhibiting polymerization in an ethylene fractionation stream, comprising administering an effective amount of a compound of the following formula: [ka] (R 1 , R 2 , and R 3 are independently selected from the group consisting of H, —OH, —SH, —NH2, alkyl, cycloalkyl, heterocyclo, and aryl. The method includes adding one or more quinone methides.
[0009] In various embodiments of the disclosed methods, the methods further comprise adding an effective amount of one or more phenylenediamines.
[0010] In various embodiments of the disclosed method, the method further comprises adding an effective amount of one or more hindered phenols.
[0011] Various aspects of the present disclosure further relate to a method for inhibiting gum formation and fouling in a high temperature ethylene fractionation train, comprising: [ka] (R 1 , R 2 , and R 3 are independently selected from the group consisting of H, —OH, —SH, —NH2, alkyl, cycloalkyl, heterocyclo, and aryl. The method includes adding one or more quinone methides.
[0012] In various embodiments of the disclosed methods, the methods further comprise adding an effective amount of one or more phenylenediamines.
[0013] In various embodiments of the disclosed method, the method further comprises adding an effective amount of one or more hindered phenols.
[0014] Those skilled in the art will appreciate that the drawings, described below, are for illustrative purposes only and are not intended to limit the scope of the present teachings in any way. [Brief explanation of the drawings]
[0015] [Figure 1] FIG. 1 shows the reduction in gum formation in liquid samples derived from a synthetic matrix consisting of 50% isoprene and 50% n-heptane after treatment with 20 ppm doses of various polymerization inhibitor chemicals, including various embodiments of the compositions of the disclosed technology. [Figure 2A]Figure 1 shows the reduction in gum formation in liquid samples derived from a synthetic matrix consisting of 50% isoprene and 50% n-heptane after treatment with 20 ppm of various polymerization inhibitor chemicals, including various thermally stressed and non-thermally stressed embodiments of the composition of the disclosed technology, and under conditions of N purging (complete removal of O ). [Figure 2B] Figure 1 shows the reduction in gum formation in liquid samples derived from a synthetic matrix consisting of 50% isoprene and 50% n-heptane after treatment with 20 ppm of various polymerization inhibitor chemicals, including various thermally stressed and non-thermally stressed embodiments of the compositions of the disclosed technology, and under N2 blanket (with residual dissolved O2) conditions. [Figure 2C] Figure 1 shows the reduction in gum formation in liquid samples derived from a synthetic matrix consisting of 50% isoprene and 50% n-heptane after treatment with 20 ppm of various polymerization inhibitor chemicals, including various thermally stressed and non-thermally stressed embodiments of the compositions of the disclosed technology, and under N2 blanket (with residual dissolved O2) conditions. [Figure 3] FIG. 1 shows the reduction in gum formation in liquid samples derived from a synthetic matrix consisting of 50% isoprene and 50% n-heptane after treatment with 10 ppm or 20 ppm doses of various polymerization inhibitor chemicals, including various embodiments of the compositions of the disclosed technology. DETAILED DESCRIPTION OF THE INVENTION
[0016] Approximate language, as used herein throughout the specification and claims, is applied to modify any quantitative expression that can be permissibly varied without resulting in a change in the basic function to which it may be related. Thus, values modified by terms such as "about" are not limited to the exact value specified. In at least some cases, approximation language may correspond to the precision of the instrument for measuring the value. Range limitations may be combined and / or interchanged, and such ranges specifically include all subranges set forth herein, unless otherwise indicated by context or language. Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to amounts of ingredients, reaction conditions, and the like used in the specification and claims should be understood to be modified in all instances by the term "about."
[0017] "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, or the subsequently identified substance may or may not be present, and that the description includes cases where the event or circumstance occurs or the substance is present, and cases where the event or circumstance does not occur or the substance is not present.
[0018] As used herein, the words "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements and may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
[0019] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
[0020] The disclosed technology provides compositions and methods for inhibiting polymerization, gum formation, and staining in ethylene fraction streams, the compositions comprising quinone methides and / or phenylenediamines.
[0021] The compositions and methods disclosed herein have been found to be effective in reducing undesired polymerization, gum formation, and staining in ethylene fractional streams. More specifically, the compositions and methods disclosed herein have been found to be effective in reducing undesired polymerization, gum formation, and staining in atypical, high-temperature ethylene fractional streams by applying high-temperature stable activators, such as quinone methides and / or phenylenediamines, optionally in combination with hindered phenols. Without being bound by theory, it is believed that the addition of one or more high-temperature stable activators to the atypical, high-temperature ethylene fractional stream inhibits free radical polymerization. It is believed that the quinone methide active may react with any thermally generated carbon-centered free radicals, while the phenylenediamine active may interact with thermally generated oxygen-centered free radicals and / or terminate alkyl radicals in the stream. Furthermore, it is believed that the optional hindered phenol active may enhance the reaction rate of the quinone methide active with the carbon-centered free radicals.
[0022] As used herein, the term "ethylene fractionation train" refers to a section of an ethylene plant that includes one or more fractionation units.
[0023] As used herein, the term "high temperature ethylene fractionation train" refers to an ethylene fractionation train that operates at a high temperature, such as between about 120°C and 160°C.
[0024] As used herein, the term "effective amount" refers to any amount of high temperature stable activator effective to inhibit polymerization, gum formation and fouling in the ethylene fraction stream.
[0025] In various embodiments of the disclosed technology, high temperature stable compositions for inhibiting polymerization, gum formation, and fouling in ethylene fractional streams are disclosed. In various embodiments, the high temperature stable compositions may comprise an effective amount of one or more high temperature stable activators. In some embodiments, the high temperature stable compositions may comprise any high temperature stable activator in an amount effective to inhibit polymerization, gum formation, and fouling in ethylene fractional streams. In other embodiments, the high temperature stable activator may comprise any activator effective to inhibit free radical polymerization in high temperature ethylene fractional streams.
[0026] In various embodiments, suitable high temperature stable activators have the formula (I): [ka] (R 1 , R 2 , and R 3 are independently selected from the group consisting of H, -OH, -SH, -NH2, alkyl, cycloalkyl, heterocyclo, and aryl. Quinone methides, alkyl-(3,5-di-tert-butyl-4-oxocyclohexane-2,5-dienylidene)cyano derivatives of quinone methides, alkyl-(3,5-di-tert-butyl-4-oxocyclohexane-2,5-dienylidene) acid derivatives of quinone methides, alkyl-(3,5-di-tert-butyl-4-oxocyclohexane-2,5-dienylidene) ester derivatives of quinone methides, 2,6-di-tert-butyl-4-(4-nitrobenzylidene)cyclohexa-2,5-dienone, di-tert-butyl-3-(4-nitrobenzylidene)cyclohexa-2,5-dienone, 2,6-di-tert butyl-4-(4-cyanobenzylidene)cyclohexa-2,5-dienone, 2,6-di-tert-butyl-4-(4-methoxybenzylidene)-cyclohexa-2,5-dienone, 2,6-di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxybenzylidene)-cyclohexa-2,5-dienone, 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)acetonitrile, 2,6-di-tert-butyl-4-(methoxymethylene)cyclohexa-2,5-dienone, phenylenediamines, hindered phenols, and combinations thereof.
[0027] In various embodiments, the high temperature stable composition may include one or more quinone methides of formula (I) and one or more phenylenediamines.
[0028] In various embodiments, the high temperature stable composition may include one or more quinone methides of formula (I), one or more phenylenediamines, and one or more hindered phenols.
[0029] In various embodiments, a suitable quinone methide has the formula (II): [ka] 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone.
[0030] In various embodiments, suitable phenylenediamines may include asymmetric phenylenediamines such as N-(1,4-dimethylpentyl)-N-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, or combinations thereof.
[0031] In various embodiments, suitable hindered phenols may include 2,6-di-tert-butylphenol, butylated hydroxytoluene, butylated hydroxyanisole, 2,4,6-tri-tert-butylphenol, 4,4′-methylenebis[2,6-bis(2-methyl-2-propanyl)phenol], or combinations thereof.
[0032] In various embodiments, the high temperature stable activator is present in the composition in an amount of from about 0.1 ppm to about 10,000 ppm, or about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, It may be present in an amount of 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or 10000 ppm, or from about 0.1 ppm to about 50 ppm, or from about 20 ppm to about 40 ppm, or any amount between these values.
[0033] In various embodiments, the high temperature stable composition may comprise one or more quinone methides of Formula (I) and one or more phenylenediamines in a ratio of between about 1:1 and 1:100, or 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or 1:100, or between about 1:2 and 1:10, or any ratio between any of these ratios.
[0034] In various embodiments, the high temperature stable activators of the disclosed technology may be used in a method for inhibiting polymerization in an ethylene fractionation train. In various embodiments, the high temperature stable activators may further be used in a method for inhibiting gum formation and fouling in a high temperature ethylene fractionation train. In various embodiments, the method may include adding an effective amount of one or more high temperature stable activators to the ethylene fractionation train.
[0035] In various embodiments, the method comprises adding to the ethylene fractionation stream an effective amount of a compound of formula (I): [ka] (R 1 , R 2 , and R 3 are independently selected from the group consisting of H, -OH, -SH, -NH2, alkyl, cycloalkyl, heterocyclo, and aryl. one or more quinone methides selected from the group consisting of alkyl-(3,5-di-tert-butyl-4-oxocyclohexane-2,5-dienylidene)cyano derivatives of quinone methides, alkyl-(3,5-di-tert-butyl-4-oxocyclohexane-2,5-dienylidene) acid derivatives of quinone methides, alkyl-(3,5-di-tert-butyl-4-oxocyclohexane-2,5-dienylidene) ester derivatives of quinone methides, 2,6-di-tert-butyl-4-(4-nitrobenzylidene)cyclohexa-2,5-dienone, di-tert-butyl-3-(4-nitrobenzylidene)cyclohexa-2,5-dienone, 2,6-di-tert-butyl The method may include adding 2,6-di-tert-butyl-4-(4-cyanobenzylidene)cyclohexa-2,5-dienone, 2,6-di-tert-butyl-4-(4-methoxybenzylidene)-cyclohexa-2,5-dienone, 2,6-di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxybenzylidene)-cyclohexa-2,5-dienone, 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)acetonitrile, 2,6-di-tert-butyl-4-(methoxymethylene)cyclohexa-2,5-dienone, or an effective amount of one or more phenylenediamines, one or more hindered phenols, or a combination thereof.
[0036] In various embodiments, the method may include adding to the ethylene fractionation train an effective amount of one or more quinone methides of formula (I) and an effective amount of one or more phenylenediamines.
[0037] In various embodiments, the method may include adding to the ethylene fractionation train an effective amount of one or more quinone methides of formula (I), an effective amount of one or more phenylenediamines, and an effective amount of one or more hindered phenols.
[0038] In various embodiments, a suitable quinone methide has the formula (II): [ka] 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone.
[0039] In various embodiments, suitable phenylenediamines may include asymmetric phenylenediamines such as N-(1,4-dimethylpentyl)-N-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, or combinations thereof.
[0040] In various embodiments, suitable hindered phenols may include 2,6-di-tert-butylphenol, butylated hydroxytoluene, butylated hydroxyanisole, 2,4,6-tri-tert-butylphenol, 4,4′-methylenebis[2,6-bis(2-methyl-2-propanyl)phenol], or combinations thereof.
[0041] In various embodiments of the methods of the disclosed technology, the high temperature stable activator is present in an ethylene fraction stream at a concentration of from about 0.1 ppm to about 10,000 ppm, or at a concentration of from about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 750, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 6000, 7500, 8000, 8000, 9000, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 6000, 75 ... It may be added in an amount of 50, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or 10000 ppm, or from about 0.1 ppm to about 50 ppm, or from about 20 ppm to about 40 ppm, or any amount between these values.
[0042] In various embodiments, the method may include adding one or more quinone methides of Formula (I) and one or more phenylenediamines in a ratio of about 1:1 to 1:100, or 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or 1:100, or in a ratio of about 1:2 to 1:10, or any ratio between any of these ratios. [Example]
[0043] The present technology is further described in the following examples, which should be considered as illustrative and should not be construed as narrowing the scope of the disclosed technology or limiting its scope to any particular embodiment.
[0044] Example 1 Exemplary inhibitor chemicals: BHT-2,6-di-tert-butylphenol PDA-1-N,N'-di-sec-butyl-p-phenylenediamine PDA-2-N-(1,4-dimethylpentyl)-N-phenyl-p-phenylenediamine QM base -4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone and 2,6-di-tert-butylphenol.
[0045] Thermally induced gumming tests were performed on a synthetic matrix consisting of 50% isoprene (stock inhibitor removed) and 50% n-heptane. The thermally induced gumming test consisted of treating a sample with 10 ppm or 20 ppm of the above inhibitor chemicals (or mixtures thereof), placing the sample in an autoclave, and blanketing or purging the sample with 400 psig nitrogen (three times), then placing the sample in a heated oil bath for four hours. The oil bath was heated to 140°C to replicate the high temperature operating conditions to be treated. After four hours of heating, the autoclave was cooled, vented, and the liquid sample removed.
[0046] The liquid sample was then transferred to a pre-weighed beaker and placed in a block heater. A stream of heated nitrogen was directed at the top of the liquid to force evaporation of the liquid phase. If any polymer (gum) had formed during the 4-hour heating phase, it would remain in the beaker after the liquid had evaporated. After 30 minutes, the beaker was cooled and weighed. The amount of gum was quantified in mg / 100 mL.
[0047] As shown in Figures 1 and 3 , among the various inhibitor chemicals tested, the addition of QM Base / PDA-2 and QM Base / PDA-2 / BHT mixtures to the samples significantly reduced gum formation compared to the untreated samples and the other chemicals.
[0048] Furthermore, as shown in Figures 2A-2C, the addition of QM Base and QM Base / PDA-2 mixtures to the samples significantly reduced gum formation compared to untreated samples as well as heat stress inhibitor chemicals under both O2-free (3x N2 purge) and low O2 (N2 blanket) conditions.
[0049] While embodiments of the disclosed technology have been described, it should be understood that the disclosure is not so limited and that modifications can be made without departing from the disclosed technology. The scope of the disclosed technology is defined by the appended claims, and all devices, processes, and methods that fall within the meaning of the claims, either literally or equitably, are intended to be embraced therein.
Claims
1. 1. A high temperature stable composition for inhibiting polymerization in a high temperature ethylene fraction train, comprising: An effective amount of the following formula: 【Chemical Formula 1】 (R １ , R ２ , and R ３ are independently H, —OH, —SH, or —NH ２ , alkyl, cycloalkyl, heterocyclo, and aryl). and one or more quinone methides of an effective amount of one or more phenylenediamines; 1. A high temperature stable composition comprising:
2. 10. The high temperature stable composition of claim 1 further comprising one or more hindered phenols.
3. The one or more quinone methides have the formula (II): 【Chemistry 2】 2. The high temperature stable composition of claim 1, comprising 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone of the formula:
4. 10. The high temperature stable composition of claim 1, wherein the one or more phenylenediamines comprise an asymmetric phenylenediamine.
5. 5. The high temperature stable composition of claim 4, wherein the unsymmetrical phenylenediamine is N-(1,4-dimethylpentyl)-N-phenyl-p-phenylenediamine.
6. 3. The high temperature stable composition of claim 2, wherein the one or more hindered phenols comprises 2,6-di-tert-butylphenol.
7. 10. The high temperature stable composition of claim 1, wherein the composition comprises the one or more quinone methides in an amount from about 1 ppm to about 10,000 ppm.
8. 8. The high temperature stable composition of claim 7, wherein the composition comprises the one or more quinone methides in an amount of from about 10 ppm to about 40 ppm.
9. 10. The high temperature stable composition of claim 1, wherein the composition comprises the one or more phenylenediamines in an amount from about 1 ppm to about 10,000 ppm.
10. 10. The high temperature stable composition of claim 9, wherein the composition comprises the one or more phenylenediamines in an amount of from about 10 ppm to about 40 ppm.
11. 3. The high temperature stable composition of claim 2, wherein the composition comprises the one or more hindered phenols in an amount of from about 0.1 ppm to about 10,000 ppm.
12. 12. The high temperature stable composition of claim 11, wherein the composition comprises the one or more hindered phenols in an amount of from about 0.1 ppm to about 40 ppm.
13. 1. A method for inhibiting polymerization in an ethylene fraction stream, comprising: An effective amount of the following formula: 【Chemistry 3】 (R １ , R ２ , and R ３ are independently H, —OH, —SH, or —NH ２ , alkyl, cycloalkyl, heterocyclo, and aryl). adding one or more quinone methides of method.
14. 14. The method of claim 13, further comprising adding an effective amount of one or more phenylenediamines.
15. 15. The method of claim 13 or 14, further comprising adding an effective amount of one or more hindered phenols.
16. The one or more quinone methides have the formula (II): 【Chemistry 4】 14. The method of claim 13, comprising 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone of the formula:
17. 15. The method of claim 14, wherein the one or more phenylenediamines comprise an asymmetric phenylenediamine.
18. 18. The method of claim 17, wherein the unsymmetrical phenylenediamine is N-(1,4-dimethylpentyl)-N-phenyl-p-phenylenediamine.
19. The method of claim 15, wherein the one or more hindered phenols comprise 2,6-di-tert-butylphenol.
20. 14. The method of claim 13, wherein the method comprises adding the one or more quinone methides in an amount from about 1 ppm to about 10,000 ppm.
21. 21. The method of claim 20, wherein the method comprises adding the one or more quinone methides in an amount of from about 10 ppm to about 40 ppm.
22. 15. The method of claim 14, wherein the method comprises adding the one or more phenylenediamines in an amount from about 1 ppm to about 10,000 ppm.
23. 23. The method of claim 22, wherein the method comprises adding the one or more phenylenediamines in an amount of from about 10 ppm to about 40 ppm.
24. 16. The method of claim 15, wherein the method comprises adding the one or more hindered phenols in an amount from about 0.1 ppm to about 10,000 ppm.
25. 25. The method of claim 24, wherein the method comprises adding the one or more hindered phenols in an amount of from about 0.1 ppm to about 40 ppm.
26. 14. The process of claim 13, wherein the ethylene fractionation train operates at an elevated temperature of from about 120°C to about 160°C.
27. The method of claim 13, wherein the polymerization is a free radical polymerization.
28. 1. A method for inhibiting gum formation and fouling in a high temperature ethylene fractionation train, comprising: An effective amount of the following formula: 【Chemistry 5】 (R １ , R ２ , and R ３ are independently H, —OH, —SH, or —NH ２ , alkyl, cycloalkyl, heterocyclo, and aryl). adding one or more quinone methides of method.
29. 30. The method of claim 28, further comprising adding an effective amount of one or more phenylenediamines.
30. 30. The method of claim 28, further comprising adding an effective amount of one or more hindered phenols.
31. The one or more quinone methides have the formula (II): 【Chemistry 6】 29. The method of claim 28, comprising 4-benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone of the formula:
32. 30. The method of claim 29, wherein the one or more phenylenediamines comprise an asymmetric phenylenediamine.
33. 33. The method of claim 32, wherein the unsymmetrical phenylenediamine is N-(1,4-dimethylpentyl)-N-phenyl-p-phenylenediamine.
34. 31. The method of claim 30, wherein the one or more hindered phenols comprise 2,6-di-tert-butylphenol.
35. 30. The method of claim 28, wherein the method comprises adding the one or more quinone methides in an amount from about 1 ppm to about 10,000 ppm.
36. 36. The method of claim 35, wherein the method comprises adding the one or more quinone methides in an amount of from about 10 ppm to about 40 ppm.
37. 30. The method of claim 29, wherein the method comprises adding the one or more phenylenediamines in an amount from about 1 ppm to about 10,000 ppm.
38. 38. The method of claim 37, wherein the method comprises adding the one or more phenylenediamines in an amount of from about 10 ppm to about 40 ppm.
39. 31. The method of claim 30, wherein the method comprises adding the one or more hindered phenols in an amount from about 0.1 ppm to about 10,000 ppm.
40. 40. The method of claim 39, wherein the method comprises adding the one or more hindered phenols in an amount of from about 0.1 ppm to about 40 ppm.
41. 30. The process of claim 28, wherein the ethylene fractionation train operates at a temperature of from about 120°C to about 160°C.