Synergistic combination for inhibiting polymerization

Description

FIELD OF INVENTION

[0001] The disclosed technology generally described hereinafter provides for a synergistic composition for inhibiting polymerization of unsaturated polymerizable monomers, and more specifically, a synergistic composition for polymerization inhibition of acrylic acid or methacrylic acid.BACKGROUND OF THE INVENTION

[0002] A major problem with the manufacturing of unsaturated polymerizable monomers is the polymerization of said monomers. In the absence of efficient polymerization inhibitors or dispersants, the undesired polymerization during manufacturing causes many problems, like fouling or blocking of the equipment, which will reduce the run time or increase cost to clean the system. Thus, an efficient polymerization inhibitor or dispersant is preferred to keep the manufacturing smooth and safe.

[0003] There are many types of polymerization inhibitors or dispersants for this application, including phenols, hydroquinone, phenothiazine, copper salts, manganese salts, stable free radicals, like 4-hydroxy-(2,2,6 6-tetramethylpiperidin-1-yl)oxyl (or 4-hydroxy TEMPO), etc. Such inhibitors or dispersants can be used alone, or in combination, to inhibit polymerization. However, new inhibitors or dispersants with better inhibition efficiency are desired. US 4814493 discloses a process for the production of CI-C8 alkyl acrylate by the reaction of a C I-C8 alkyl alcohol with acrylic acid in the presence of esterification catalysts and soluble manganese or cerium ions. US 4507495 discloses a process of producing ethyl acrylate by the reaction of ethylene and acrylic acid in the presence of sulfuric acid. Using phenolic type inhibitors, soluble manganese or cerium salts. JP 2001348359 discloses a method comprises using. in a refining column as poly merization inhibitors N-nitrosophenylhydroxylamine or a salt in combination with a manganese salt compound and / or phenothiazine compound. EP 2398832 discloses a polymerization inhibitor composition and a method of inhibiting polymerization of distillable monomers in liquid and evaporated / condensed phases with the polymerization inhibitor composition. US 2010130766 discloses a method for inhibiting polymerization of (meth)acrylic acid a step of inhibiting polymerization of (meth)acrylic acid and / or the ester thereof by using a solution of a dialkyldithiocarbamic acid copper salt dissolved in an organic solvent. US5371280 discloses polymerization inhibitors against polymerization of vinyl compounds. The inhibitors may comprise joint use of a coppers salt and a manganese salt.SUMMARY OF THE INVENTION

[0004] The disclosed technology generally described hereinafter provides for a composition and method for a synergistic polymerization inhibitor as set out in the appended claims. In some embodiments, the composition comprises a copper compound, and a manganese compound.

[0005] In some embodiments, the copper compound is a copper salt selected from the group consisting of copper (II) acetate, copper (II) oxide, copper (II) sulfate, copper (II) chloride, copper (II) dithiocarbamate, copper (II) formate, copper (II) propionate, and copper (II) oleate. In some embodiments, the manganese compound is a manganese salt selected from the group consisting of manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) acetylacetonate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, tricarbonyl (methylcyclopentadienyl) manganese, cyclopentadienyl manganese tricarbonyl, or combinations thereof.

[0006] In some embodiments, the copper compound is at least 100 ppm. In some embodiments, the manganese compound is at least 100 ppm. The copper compound is between about 0.01 wt% and about 50 wt%. The manganese compound is between about 0.01 wt% and about 50 wt%.

[0007] The claimed composition comprises a copper compound or a manganese compound; and a cationic polymer.

[0008] In some embodiments, the copper compound is a copper salt selected from the group consisting of copper (II) acetate, copper (II) oxide, copper (II) sulfate, copper (II) chloride, copper (II) dithiocarbamate, copper (II) formate, copper (II) propionate, and copper (II) oleate. In some embodiments, the manganese compound is a manganese salt selected from the group consisting of manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) acetylacetonate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, tricarbonyl (methylcyclopentadienyl) manganese, cyclopentadienyl manganese tricarbonyl, or combinations thereof.

[0009] In some embodiments, the cationic polymer has molecular weight greater than 500. In some embodiments, the cationic polymer comprises a plurality of repeating units, and wherein at least 20%of the repeating units are positively charged. In some embodiments, the cationic polymer is [Al(OH) n Cl 3-n ] m , where n = 1.0 to 2.5, m ≤ 20.

[0010] In some embodiments, the cationic polymer is selected from the group consisting of a polydiallyldialkylammonium salt, a polymer formed from an amine and epihalohydrin or dihaloalkane, an epichlorohydrin-dialkylamine polymer, an epichlorohydrin-dialkylamine-ethylenediamine polymer, a polymer formed from a vinyltrialkylammonium salt, a polyaluminum salt, a polymer of dialkylaminoalkyl (meth) acrylates, a polymer of dialkylaminoalkyl (meth) acrylamides, a poly[2-(acryloyloxy) ethyl]trimethylammonium salt, or a polymethacryloxyethyltrimethylammonium salt.

[0011] In some embodiments, the copper compound or manganese compound in the composition is at least 100 ppm, and the cationic polymer is at least 100 ppm. In some embodiments, the copper compound or manganese compound is between about 0.01 wt% and about 50 wt%. In some embodiments, the cationic polymer is between about 0.01 wt% and about 90 wt%.

[0012] In yet another aspect of the disclosed technology (disclosed but not claimed), a synergistic polymerization inhibitor composition is provided. The composition comprises a phenothiazine, and a manganese compound.

[0013] In some embodiments, the manganese compound is a manganese salt selected from the group consisting of manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) acetylacetonate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, tricarbonyl (methylcyclopentadienyl) manganese, cyclopentadienyl manganese tricarbonyl, or combinations thereof.

[0014] In some embodiments, the phenothiazine is at least 100 ppm and the manganese compound is at least 100 ppm. In some embodiments, the phenothiazine is between about 0.01 wt% and about 80 wt%. In some embodiments, the manganese compound is between about 0.01 wt% and about 50 wt%.

[0015] In yet another aspect of the disclosed technology, a method for inhibiting polymerization of unsaturated polymerizable monomers is provided. The method comprises adding a synergistic polymerization inhibitor composition to a monomer manufacturing system or component thereof, the composition comprising, a copper salt and a manganese salt.

[0016] In some embodiments, the monomer is methacrylic acid, and the synergistic polymerization inhibitor composition inhibits methacrylic acid polymerization. In some embodiments, the monomer is an acrylate, and the synergistic polymerization inhibitor composition inhibits acrylate polymerization. In some embodiments, the monomer is a methacrylate, and the synergistic polymerization inhibitor composition inhibits methacrylate polymerization. In some embodiments, the monomer is an acrolein, and the synergistic polymerization inhibitor composition inhibits acrolein polymerization. In some embodiments, the monomer is an acrylonitrile, and the synergistic polymerization inhibitor composition inhibits acrylonitrile polymerization.

[0017] In some embodiments, the synergistic polymerization inhibitor composition is at least 10 ppm. In some embodiments, the synergistic polymerization inhibitor composition is about 10 wt%.

[0018] In yet another aspect of the disclosed technology, a method for inhibiting polymerization of unsaturated polymerizable monomers is provided. The method comprises adding a synergistic polymerization inhibitor composition to a monomer manufacturing system or component thereof, the composition comprising, a copper salt or a manganese salt, and a cationic polymer.

[0019] In some embodiments, the monomer is methacrylic acid, and the synergistic polymerization inhibitor composition inhibits methacrylic acid polymerization. In some embodiments, the monomer is an acrylate, and the synergistic polymerization inhibitor composition inhibits acrylate polymerization. In some embodiments, the monomer is a methacrylate, and the synergistic polymerization inhibitor composition inhibits methacrylate polymerization. In some embodiments, the monomer is an acrolein, and the synergistic polymerization inhibitor composition inhibits acrolein polymerization. In some embodiments, the monomer is an acrylonitrile, and the synergistic polymerization inhibitor composition inhibits acrylonitrile polymerization.

[0020] In some embodiments, the synergistic polymerization inhibitor composition is at least 10 ppm. In some embodiments, the synergistic polymerization inhibitor composition is about 10 wt%.

[0021] In yet another aspect of the disclosed technology, a method for inhibiting polymerization of unsaturated polymerizable monomers is provided. The method comprises adding a synergistic polymerization inhibitor composition to a monomer manufacturing system or component thereof, the composition comprising, a phenothiazine and a manganese salt.

[0022] In some embodiments, the monomer is methacrylic acid, and the synergistic polymerization inhibitor composition inhibits methacrylic acid polymerization. In some embodiments, the monomer is an acrylate, and the synergistic polymerization inhibitor composition inhibits acrylate polymerization. In some embodiments, the monomer is a methacrylate, and the synergistic polymerization inhibitor composition inhibits methacrylate polymerization. In some embodiments, the monomer is an acrolein, and the synergistic polymerization inhibitor composition inhibits acrolein polymerization. In some embodiments, the monomer is an acrylonitrile, and the synergistic polymerization inhibitor composition inhibits acrylonitrile polymerization.

[0023] In some embodiments, the synergistic polymerization inhibitor composition is about 10 wt%. In some embodiments, the synergistic polymerization inhibitor composition is at least 10 ppm.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] These and other features of the disclosed technology, and the advantages, are illustrated specifically in embodiments now to be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: FIG. 1 is a graph providing results of an illustrative embodiment of the disclosed technology; and FIG. 2 is a graph providing results of an illustrative embodiment of the disclosed technology. DETAILED DESCRIPTION

[0025] The disclosed technology generally described hereinafter provides for a synergistic composition for inhibiting polymerization of unsaturated polymerizable monomers, such as, but not limited to acrylic acid, methacrylic acid, acrylates, acrolein, and / or acrylonitrile monomers. More specifically, the disclosed technology provides a synergistic composition for polymerization inhibition of acrylic acid and / or methacrylic acid.

[0026] With the disclosed synergistic compositions and methods, manufacturers involving the aforementioned monomers allow systems to keep running for a longer time before a maintenance shutdown is needed, which will increase productivity and also reduce the cost to clean the equipment. This technology also reduces the safety risk from uncontrolled polymerization of the aforementioned monomers, such as, but not limited to acrylic acid, methacrylic acid, acrylates, methacrylates, acrolein, and / or acrylonitrile monomers.

[0027] The present technology provides for a synergistic polymerization inhibitor composition. In some embodiments, the synergistic polymerization composition comprises a copper compound and a manganese compound. These compounds can either be soluble or insoluble in water.

[0028] In some embodiments, the copper compound is a copper salt, and the manganese compound is a manganese salt. In some embodiments, the copper compound is selected from, but not limited to, copper (II) acetate, copper (II) oxide, copper (II) sulfate, copper (II) chloride, copper (II) dithiocarbamate, copper (II) formate, copper (II) propionate, copper (II) oleate, or combinations thereof. It should be understood by one skilled in the art that the copper compound can be selected from any copper (II) compounds that provide a similar effect.

[0029] In some embodiments, the copper compound is at least 100 ppm. In other embodiments, the copper compound is at least 200 ppm, and in other embodiments, at least 500 ppm. In some embodiments, the copper compound is less than 500,000 ppm, and in other embodiments, the copper compound is less than 100,000 ppm. In some embodiments, the copper compound is in the range between about 500 ppm and about 100,000 ppm.

[0030] In some embodiments, the copper compound is between about 0.01 wt% and about 50 wt%. In other embodiments, the copper compound is between about 0.02 wt% and 20 wt%, and in other embodiments, between about 0.05 wt% and 10 wt%.

[0031] In some embodiments, the manganese compound is selected from, but not limited to, manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, or combinations thereof. It should be understood by one skilled in the art that the manganese compound can be selected from any manganese (II) compounds that provide a similar effect.

[0032] In some embodiments, the manganese compound is at least 100 ppm. In other embodiments, the manganese compound is at least 200 ppm, and in other embodiments, at least 500 ppm. In some embodiments, the manganese compound is less than 500,000 ppm, and in other embodiments, the manganese compound is less than 100,000 ppm. In some embodiments, the manganese compound is between about 500 ppm and about 100,000 ppm.

[0033] In some embodiments, the manganese compound is between about 0.01 wt% and about 50 wt%. In other embodiments, the manganese compound is between about 0.02 wt% and 20 wt%, and in other embodiments, between about 0.05 wt% and 10 wt%.

[0034] In yet another aspect of the present technology, a synergistic polymerization inhibitor composition is provided. The synergistic polymerization inhibitor composition comprises a copper compound or a manganese compound, and a cationic polymer. In some embodiments, the synergistic polymerization inhibitor composition comprises a copper compound and a cationic polymer. In other embodiments, the synergistic polymerization inhibitor composition comprises a manganese compound and a cationic polymer.

[0035] In some embodiments, the synergistic polymerization inhibitor composition comprises a copper compound, wherein the copper compound comprises copper (II) acetate, copper (II) oxide, copper (II) sulfate, copper (II) chloride, copper (II) dithiocarbamate, copper (II) formate, copper (II) propionate, copper (II) oleate, or combinations thereof.

[0036] In some embodiments, the manganese compound comprises manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, or combinations thereof.

[0037] In some embodiments, the cationic polymer comprises a polydiallyldialkylammonium salt, a polymer formed from an amine and epihalohydrin or dihaloalkane, an epichlorohydrin-dialkylamine polymer, an epichlorohydrin-dialkylamine-ethylenediamine polymer, a polymer formed from a vinyltrialkylammonium salt, a polyaluminum salt, a polymer of dialkylaminoalkyl (meth) acrylates, a polymer of dialkylaminoalkyl (meth) acrylamides, a poly [2-(acryloyloxy) ethyl] trimethylammonium salt, a polymethacryloxyethyltrimethylammonium salt, or combination thereof. In other embodiments, the cationic polymer is selected from, but not limited to, the group consisting of a polydiallyldialkylammonium salt, a polymer formed from an amine and epihalohydrin or dihaloalkane, an epichlorohydrin-dialkylamine polymer, an epichlorohydrin-dialkylamine-ethylenediamine polymer, a polymer formed from a vinyltrialkylammonium salt, a polyaluminum salt, a polymer of dialkylaminoalkyl (meth) acrylates, a polymer of dialkylaminoalkyl (meth) acrylamides, a poly [2-(acryloyloxy) ethyl] trimethylammonium salt, a polymethacryloxyethyltrimethylammonium salt, or a combination thereof. In some embodiments, the cationic polymer is [Al(OH) n Cl 3-n ] m , where n = 1.0 to 2.5, m ≤ 20.

[0038] In some embodiments, the cationic polymer has a molecular weight greater than 500. In some embodiments, the cationic polymer comprises a plurality of repeating units. In such embodiments, at least 20%of the repeating units are positively charged, in other embodiments, at least 50%are positively charged, and in other embodiments, at least 80%are positively charged.

[0039] In some embodiments, the synergistic polymerization inhibitor composition comprises at least 100 ppm of the copper salt, and at least 100 ppm of the cationic polymer. In some embodiments, the copper salt or manganese salt is between about 0.01 wt% and about 50 wt%. In some embodiments, the cationic polymer is between about 0.01 wt% and about 90 wt%.

[0040] In yet another aspect of the present technology, a synergistic polymerization inhibitor composition comprising a phenothiazine and a manganese salt is provided.

[0041] In some embodiments, the manganese salt comprises manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) acetylacetonate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, tricarbonyl (methylcyclopentadienyl) manganese, cyclopentadienyl manganese tricarbonyl, or combinations thereof.

[0042] In some embodiments, the phenothiazine is at least 100 ppm and the manganese salt is at least 100 ppm. In some embodiments, the phenothiazine is between about 0.01 wt% and about 80 wt%, in some embodiments, between about 0.02 wt% and about 50 wt%, and in other embodiments, between about 0.05 wt% and 20 wt%.

[0043] In some embodiments, the manganese salt is between about 0.01 wt% and about 50 wt%, in some embodiments, between about 0.02 wt% and about 20 wt%, and in other embodiments, between about 0.05 wt% and 10 wt%.

[0044] In yet another aspect of the present technology, a method for inhibiting the polymerization of unsaturated monomers is provided. In some embodiments, a method for inhibiting the polymerization of acrylic acid and methacrylic acid is provided. It should be understood by one skilled in the art that the present method can inhibit polymerization of other unsaturated polymerizable monomers, such as, but not limited to, acrylates, methacrylates, acrolein, and / or acrylonitrile monomers.

[0045] The method comprises adding a synergistic polymerization inhibitor composition to an acrylic acid or similar monomer manufacturing system or component thereof. Examples of such manufacturing systems and components include, but are not limited to, monomer absorption columns, monomer distillation columns, and / or monomer purification columns. In some embodiments, the synergistic polymerization inhibitor is added to a crude monomer stream. In some embodiments, the synergistic polymerization inhibitor is added to a monomer-solvent mixed stream. In other embodiments, the synergistic polymerization inhibitor is added to a crude methacrylic acid or acrylic acid stream.

[0046] In some embodiments, the synergistic polymerization inhibitor composition of the present method comprises a copper salt and a manganese salt. The synergistic polymerization inhibitor composition inhibits the polymerization of acrylic acid, methacrylic acid, acrylates, methacrylates, acroleins, and / or acrylonitriles.

[0047] In some embodiments, the synergistic polymerization inhibitor composition of the present method is at least 10 ppm of the crude monomer stream. In some embodiments, the crude monomer stream is an acrylic acid or methacrylic acid stream. In other embodiments, the synergistic polymerization inhibitor composition is present at about 10 wt%of the crude monomer stream.

[0048] In yet another aspect of the present technology, a method for inhibiting the polymerization of unsaturated monomers is provided. In some embodiments, a method for inhibiting the polymerization of methacrylic acid is provided. The method comprises adding a synergistic polymerization inhibitor composition to monomer manufacturing system or component thereof. In some embodiments, the monomer manufacturing system is a methacrylic acid manufacturing system or component thereof, where the composition comprises, a copper salt or a manganese salt, and a cationic polymer.

[0049] In some embodiments, the synergistic polymerization inhibitor composition concentration is at least 10 ppm of the crude monomer stream. In some embodiments, the synergistic polymerization inhibitor composition is about 10 wt%of the crude monomer stream.

[0050] In yet another aspect of the present technology, a method for inhibiting methacrylic acid is provided. The method comprises adding a synergistic polymerization inhibitor composition to a methacrylic acid manufacturing system or component thereof, the composition comprising, a phenothiazine and a manganese salt.

[0051] In some embodiments, the synergistic polymerization inhibitor composition is at least 10 ppm of the crude monomer stream. In other embodiments, the synergistic polymerization inhibitor composition is about 10 wt%of the crude monomer stream.EXAMPLES

[0052] The present invention will be further described in the following examples, which should be viewed as being illustrative and should not be construed to narrow the scope of the invention or limit the scope to any particular invention embodiments.

[0053] Acrylic acid polymerization inhibition was tested through the induction time test, by heating acrylic acid with or without inhibitors in a hot oil bath and measuring the time before the mixture turns cloudy or loses flowability. For example, flowability can be determined by gel formation and / or increased viscosity. Water or other solvent (such solvents can include, but are not limited to toluene, methyl isobutyl ketone, or ethyl acetate) can be added into acrylic acid to test. The test can be performed in an inert gas atmosphere (i.e. nitrogen, or argon gas) , or in air or oxygen. The time before the mixture turns cloudy or gelled (i.e. loses flowability) was recorded as induction time, where the longer induction time indicates better efficiency to inhibit polymerization.

[0054] In the following examples, a standardized test condition was set to: heat 20 mL distilled acrylic acid, and 1 mL deionized water in a testing bottle immersed in a hot oil bath set at 140°C, and inhibitors for testing were added into the mixture and well mixed before the testing bottle been immersed in the hot oil bath. 50 mL / min air bubbling were kept throughout the entire process. The time that the mixture turns from clear to cloudy or gelled was recorded as induction time.A. Synergistic Combination of Copper Salt and Manganese Salt

[0055] It was determined that the synergistic combination of manganese (Mn) salt (e.g. manganese (II) acetate) and copper (Cu) salt (e.g. copper (II) acetate) performed much better than the single use of each metal salt alone. This synergistic composition also performed significantly better than current inhibitors in the market used for acrylic acid manufacturing. For example, such inhibitors include, but are not limited to, hydroquinone (HQ), phenothiazine (PTZ), MEHQ, 4-OH TEMPO, copper dithiocarbamate, nitrosobenzene, and / or manganese acetate.

[0056] Table 1 provides the testing results of the synergistic combination of manganese salt and copper salt. EXP 1-9, 12 and 18-20 are reference examples. Table 1 shows the significant improvement on polymerization inhibition from the synergistic combination of Mn and Cu salts. EXP. 1 was a blank control without any inhibitor addition. EXP. 9 contained a widely used combination of three inhibitors, (hydroquinone (HQ) , phenothiazine (PTZ) and copper dithiocarbamate salt (CB) ) . TABLE 1. Inhibitor Induction Time Test in Acrylic AcidEXP.HQ a< (ppm)PTZ b< (ppm)Mn (II)° (ppm)Cu (II) d< (ppm)Cationic polymer e< (ppm)Induction Time (mins)126 f< 2426347142262659274366165976310128107597102 g< 164107102 g< 50 (Cat. A)38811710250 (Cat. A)381122 g< 50 (Cat. A)215137102 g< 25 (Cat. A)316147102 g< 50 (Cat. B)458157102 g< 50 (Cat. C)333167102 g< 50 (Cat. D)49617710250 (Cat. A)803187102649191026552071022650a. Hydroquinone concentration in solution based on acrylic acid amount b. Phenothiazine concentration in solution based on acrylic acid amount c. Mn salt concentration in solution based on acrylic acid amount (added as manganese acetate) d. Cu salt concentration in solution based on acrylic acid amount (added as copper acetate) e. Cationic polymer concentration in solution based on amount of acrylic acid f. Without any additives g. Cu salt was added as copper dibutyldithiocarbamate instead of copper acetate

[0057] The results in EXP. 2-7 in Table 1 demonstrate that the combination of Mn and Cu compounds (i.e. salts) provide a synergistic effect and has superior performance than the market used inhibitors as in EXP. 9, or the single metals when used alone (EXP. 2 &3) .B. Synergistic Combination of Copper / Manganese Salt and Cationic Polymer

[0058] EXP. 10-17 in Table 1 demonstrated that the synergistic combination of copper or manganese salt and a cationic polymer provided significantly better polymerization inhibition than current inhibition products in the market used for acrylic acid manufacturing. Examples of such cationic polymers tested include polydiallyldimethylammonium chloride, polymer from epichlorohydrin-dimethylamine-ethylenediamine, polyallumium chloride, and polymer from epichlorohydrin-dimethylamine. (See Table 2 below. ) TABLE 2. Illustration of cationic polymersCat. Apolydiallyldimethylammonium chlorideCat. Bpolymer from epichlorohydrin-dimethylamine-ethylenediamineCat. Cpolyalumium chlorideCat. Dpolymer from epichlorohydrin-dimethylamine C. Synergistic Combination of Phenothiazine (PTZ) and Manganese Salt

[0059] Reference EXP. 17-20 in Table 1 demonstrated that the combination of PTZ and manganese compound provided significantly better polymerization inhibition than current inhibition products in the market used for acrylic acid manufacturing.

[0060] The scope of the disclosed technology is defined by the appended claims.

Claims

1. A synergistic polymerization inhibitor composition, the composition comprising: a copper compound or a manganese compound, wherein the copper compound or manganese compound is between about 0.01 wt% and about 50 wt%; and a cationic polymer, wherein the cationic polymer is between about 0.01 wt% and about 90 wt%.

2. The composition as recited in claim 1, wherein the copper compound is a copper salt selected from the group consisting of copper (II) acetate, copper (II) oxide, copper (II) sulfate, copper (II) chloride, copper (II) dithiocarbamate, copper (II) formate, copper (II) propionate, copper (II) oleate, or combinations thereof.

3. The composition as recited in claim 1, wherein the manganese compound is a manganese salt selected from the group consisting of manganese (II) acetate, manganese (II) oxide, manganese (II) sulfate, manganese (II) chloride, manganese (II) dithiocarbamate, manganese (II) acetylacetonate, manganese (II) formate, manganese (II) propionate, manganese (II) oleate, tricarbonyl (methylcyclopentadienyl) manganese, cyclopentadienyl manganese tricarbonyl, or combinations thereof.

4. The composition as recited in claim 1, wherein the cationic polymer comprises a plurality of repeating units, and wherein at least 20% of the repeating units are positively charged.

5. The composition as recited in claim 1, wherein the cationic polymer is [Al(OH)nC3-n]m, where n = 1.0 to 2.5, m ≤ 20.

6. The composition as recited in claim 1, wherein the cationic polymer is selected from the group consisting of a polydiallyldialkylammonium salt, a polymer formed from an amine and epihalohydrin or dihaloalkane, an epichlorohydrin-dialkylamine polymer, an epichlorohydrin-dialkylamine-ethylenediamine polymer, a polymer formed from a vinyltrialkylammonium salt, a polyaluminum salt, a polymer of dialkylaminoalkyl (meth) acrylates, a polymer of dialkylaminoalkyl (meth) acrylamides, a poly [2- (acryloyloxy) ethyl] trimethylammonium salt, or a polymethacryloxyethyltrimethylammonium salt.

7. The composition as recited in claim 1, wherein the copper compound or manganese compound in the composition is at least 100 ppm, and the cationic polymer is at least 100 ppm.

8. A method for inhibiting polymerization of unsaturated polymerizable monomers, the method comprising: adding a synergistic polymerization inhibitor composition to a monomer manufacturing system or component thereof, the composition comprising, a copper salt or a manganese salt, and a cationic polymer.

9. The method as recited in claim 8, wherein the monomer is methacrylic acid, and the synergistic polymerization inhibitor composition inhibits methacrylic acid polymerization.

10. The method as recited in claim 8, wherein the monomer is an acrylate, and the synergistic polymerization inhibitor composition inhibits acrylate polymerization.

11. The method as recited in claim 8, wherein the monomer is a methacrylate, and the synergistic polymerization inhibitor composition inhibits methacrylate polymerization.

12. The method as recited in claim 8, wherein the monomer is an acrolein, and the synergistic polymerization inhibitor composition inhibits acrolein polymerization.

13. The method as recited in claim 8, wherein the monomer is an acrylonitrile, and the synergistic polymerization inhibitor composition inhibits acrylonitrile polymerization.