MXPA99000630A - Inhibitor of polimerizac - Google Patents

Abstract

A monomer composition, stabilized against premature polymerization, comprising: a) an ethylenically unsaturated monomer or polymerizable monomer mixture by initiation of free radicals, and b) an effective amount, sufficient to inhibit premature polymerization of component (a) of a mixture of: 8) 1 99% by weight, based on the total weight of the components (i) and (ii) of a mixture of at least one aromatic amine and at least one organic acid in a molar ratio of 10: 1 at 1:10, and ii) 99 to 1% by weight based on the total weight of components (i) and (ii) of at least one radical compound.

Description

POLYMERIZATION INHIBITOR DESCRIPTION OF THE INVENTION This invention relates to free radical scavengers for use as or in connection with olefin polymerization inhibitors, particularly but not exclusively for polymerization inhibition of vinyl aromatics. Olefinic compounds such as butadiene, acrylic monomers, styrene and other aromatic vinyl compounds have a strong tendency to polymerize on storage or heating. High temperature techniques such as distillation during separation and purification processes and the industrial production of these olefinic compounds are commonly used. Although free radical scavengers have been used to avoid olefin polymerization, there is a requirement for more efficient scrubbers which can be used at lower concentrations or scrubbers which are more efficient at the same concentrations as currently used. Lower concentrations are economical, less toxic and are environmentally beneficial. The most efficient compositions are economical, giving reduced waste and / or prolongation of the active life of the olefin. Various compounds and compositions have been used as free radical scavengers to avoid or reduce unwanted polymerization of olefinic compounds during high temperature processes. These inhibitors have given several degrees of success. In a typical process an olefinic compound can be contacted with the inhibitor before distillation or other processing. However, the amount of the polymer formed during such processing can be substantially higher than desired, leading to economic losses. In other cases it may be possible to achieve economically desirable low levels of polymerization but only by use of economically unacceptable amounts of the inhibitor. Sulfur has been widely used as a polymerization inhibitor but has led to difficulties in handling and disposal for sulfur-free inhibitors, referred to NSIs. SU-A-819078 discloses the use of butyl-4-oxi-N, N-dimethylbenzylamine 3.5-diteracy in combination with an aliphatic carboxylic acid of C? 0-C2o- However the concentrations of this particular NSI are large enough (500 to 2200 ppm) that much of the NSI is not consumed in a typical process. This results in non-economic amounts of residual NSI that are present in the effluent or waste from the process. EP-A-550754 discloses a polymerization inhibitor by vinyl compounds which combine a reaction product of 4- (dimethylamino) methyl-2,6-bis (tert-butyl) phenol with an inorganic or carboxylic acid in the weight ratio 1 to 15: 3. WO95 / 03263 describes the reduction in the amount of this NSI for use in combination with air. However, it is not desirable to introduce air into many high temperature processes involving olefinic compounds. First there is an economic cost associated with ensuring a supply of the required amount of air. Second, a safety hazard is frequent due to the introduction of air into the stream of a hot olefinic compound due to the risk of oxidation, fire or an explosion. The use of stable free radicals to inhibit polymerization by purifying other free radicals has been described. GM Burnett, Mechanism of Polymer Reactions, Interscience, New York 1954, 76, states that a spherically hindered nitroxyl radical, 2, 2, 6, 6-tetramethylpyperidinyl-l-oxyl (referred to as TEMPO) is effective against carbon-centered radicals . The use of stable free radicals as scrubbers is observed by EG Rozantsev, Free Nitroxil Radicáis, Plenan Press, 1970, 105. The practical utility of nitroxyl radicals as scrubbers to avoid polymerization in GB 1127127 and BG 1218456 is described. It has restricted the high cost of stable free radicals its commercial use and a requirement remains for economic means to avoid or control the polymerization. US 4670132 discloses that certain stable free radicals can be used as polymerization inhibitors under certain conditions at levels less than 700 parts per billion. However, such low use ratios are not of general applicability. It has now been found that a free radical scavenging composition that includes an aromatic amine in combination with an organic acid and a stable free radical compound is effective without the economic disadvantages of the compositions previously described. According to a first aspect of the present invention a monomer composition, stabilized against premature polymerization, comprises: a) a monomer or ethylenically unsaturated mixture of monomers polymerizable by initiation of free radicals, and b) an effective amount, sufficient to inhibit premature polymerization of component (a) of a mixture of: (i) 1 to 99% by weight, based on the total weight of components (i) and (ii) of a mixture of at least one aromatic amine and at least one organic acid in a molar ratio of 10: 1 to 1:10 , and (ii) 99 to 1% by weight based on the total weight of components (i) and (ii) of at least one stable radical compound. The compositions according to this invention exhibit a synergistic effect since the efficiency of inhibition is greater than that of the two components. Preferred monomers are vinyl aromatic compounds for example styrene, methylstyrene, vinyltoluene or divinylbenzene or aliphatic vinyl compounds including acrylonitrile, acrylic acid, methacrylic acid, acrylate esters, methacrylate esters, butadiene and butenes. The invention is particularly applicable in the inhibition of polymerization of styrene during distillation, purification or storage. In preferred compositions the weight of component i) is 50 to 99% and the weight of component ii) is 50 to 1%. In particularly preferred embodiments of the invention the weight of component i) is 67 to 99% and the weight of component ii) is 33 to 1%. The percentages and other amounts in this specification are by weight unless otherwise indicated. Percentages and other proportions are selected at 100% total. The molar ratio of the at least the aromatic amine to the at least organic acid is 3: 1 to 1: 3. In preferred embodiments of the invention the aromatic amine has the formula (1) wherein Q is O or S or N-Z and wherein at least one R is an alkylamine of structure (2) -XK / 2 in which Y, Z are the same or different and comprise branched or straight chain alkyl of Cx 3 C9 or hydrogen and in which X is either a covalent or alkylene bond of Ci to C4, and wherein each remaining R is independently benzyl, branched or straight chain alkyl of Cx to C4 or hydrogen with the proviso that two or more R's may be connected to form one or more rings. Q is preferably oxygen. X is preferably methylene. Y and Z are preferably methyl. R1 and R5 are preferably tertiary butyl. A preferred amine has Y and Z as methyl and R2 and R4 as hydrogen. Preferred amines include benzylamine and benzylamine derivatives, for example 3,5-tertiarybutyl-4-hydroxybenzylamine, anilines and phenylenediamines, for example N, N-dimethyl-1,4-phenylenediamine 3,5-ditertiarybutyl-4-oxy, N, N-dimethylbenzylamine 3, 5-ditertiarybutyl-4-oxy-N, N-diethylbenzylamine N, N-dimethyl-2, 6-diterciaributyl-4-aminophenol 1,4-phenylenediamine N, N-dimethyl-4-aminothiophenol N, N'-bis- (1,4-dimethylpentyl) -1,4-phenylenediamine. In preferred embodiments of the invention, the organic acid is a carboxylic acid. Particularly effective are C6 to C22 carboxylic acids, preferably Cs to C18 saturated or unsaturated. These can be substituted with groups inert to attack by nitroxyl radicals. Straight or branched chain acid may be employed. They are convenient for handling branched chain acids which are liquid at room temperature. The stable radical compound is preferably a sterically hindered nitroxyl of the formulas (3) O) Where R is hydrogen, alkyl or aryl and T is a group required to form a ring and wherein two or more T groups can be linked by a linking E group. Preferred nitroxyl compounds can be selected from: l-oxyl-2, 2,6,6-tetramethylpiperidine, 1-oxyl-2, 2,6,6-6-tetramethylpiperidin-4-ol, l-oxyl-2, 2 , 6,6-tetramethylpiperidin-4-one, l-oxyl-2, 2, 6,6-tretramethylpiperidin-4-yl acetate, 2-ethylhexanoate of 1, oxyl -2, 2,6,6-tetramethylpiperidin-4-yl, stearate of 1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl, benzoate of 1, oxyl-2, 2,6,6-tetramethylpiperidin-4-yl, 4-tert-butylbenzoate of 1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl, bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) succinate, bis (1) sebacate , oxyl-2, 2,6,6-tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) sebacate, bis (1, oxyl-2 adipate , 2, 6, 6-tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2, 6,6-tetramethylpiperidin-4-yl) n-butylmalonate, bis (1, oxyl-2, 2-phthalate. , 6,6-tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) isophthalate, bis (1, oxyl-2, 2, 6,6 terephthalate -tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl), N, N'bis (1-oxyl-2, 2,6,6-tetramethylpiperidine hexahydroterephthalate) -4-yl) adipamine, N- (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) caprolactam, N- (1 -oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) ) -dodecyl succinimide 2,4, 6 -tris- (N-butyl-N- (1-oxyl-2, 2, 6,6-tetramethylpiperidin-4-yl) -s-triazine, and 4, 4"-ethylenebis (1 -oxyl-2, 2,6,6-tetramethylpiperidin-3-one), 4-acetylamino-2,2,6,6-tetramethylpiperidin-N-oxyl More preferably, the compound of the component b) is l-oxyl-2, 2,6,6-tetramethylpiperidin-4-ol, or bis (1-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) sebacate According to a second aspect of the present invention a process for inhibiting the premature polymerization of an aromatic or aliphatic vinyl compound during distillation, purification or storage, comprises the step of incorporating therein an effective inhibitory amount, sufficient to prevent premature polymerization during distillationpurification or storage of a mixture of (i) 1 to 99% by weight, based on 1 total weight of components (i) and (ii), of a mixture of at least one aromatic amine and at least one organic acid in a molar ratio of 10: 1 to 1:10 and (ii) 99 to 1% by weight, based on the total weight of components (i) and (ii), of at least one stable radical compound . Preferred processes of this invention use a stabilizing composition which is synergistic in nature, ie it uses half the concentration of component a) together with half the concentration of component b) to produce a greater stabilizing efficiency than the which can be achieved using either component a) or b) alone. Preferred processes according to this invention employ stabilizing compositions as described above with reference to the first aspect of this invention. The effective amount of the polymerization inhibitors employed can vary over a wide range depending on the particular olefinic compound and the distillation or other purification conditions employed. Preferably the total amount of an aromatic amine and an aliphatic carboxylic acid and a stable free radical is from 1 ppm to 2000 ppm based on the weight of the olefinic compound. For most olefinic compounds the mixture of components a) and b) is from 5 to 1000 ppm. Larger amounts of the inhibitor are required at higher temperatures. During the distillation of olefinic mixtures the temperature of the heat exchanger can be up to about 150 ° C. Since the boiling points of the various aromatic amines of component a) and of the various stable free radicals b) are different, the compounds which have the desired boiling points can be easily selected. The compositions of this invention which inhibit the polymerization of the olefinic compound are also suitable for protecting the sections of the heat exchanger of a distillation column or the compressor sections before entering the distillation column. The polymerization inhibitor in the olefinic compound can be introduced to be protected by any conventional method. This can be added as a concentrated solution in a suitable solvent. Since the solubilities of the various aromatic amines of component a) of the various organic acids of component a) and of the various stable free radicals of component b) are different, the compounds which have the desired solubilities can be easily selected. Components a) and b) can be injected separately into the distillation train together with the incoming feed, or through separate entry points provided there is an efficient distribution of the inhibitors. The inhibitors are gradually removed during the distillation operation. Consequently it is generally necessary to maintain the appropriate amount of the inhibitor mixture in the distillation apparatus by adding inhibitors during the course of the distillation process. Such addition can be carried out either on a generally continuous basis or this can consist of intermittently charging the inhibitor in the distillation system in order to maintain the concentration of the inhibitor in excess of the minimum required level. The amine and the carboxylic acid can be added separately at different entry points in the process stream. The present invention allows the distillation and purification of olefinic compounds in manufacturing plants to operate more economically compared to the prior art processes due to the higher efficiency with or without the presence of oxygen. This allows uses of lower inhibitors with minimal polymer formation. The present invention also allows the storage of olefinic compounds for prolonged periods of time at ambient or elevated temperatures with or without the presence of oxygen using economically beneficial amounts of the purifying composition to minimize polymer formation. The present invention is further described by way of example but not in any limiting sense. Examples 1 to 3 Commercial grade styrene is washed with dilute caustic soda solution to remove the storage stabilizer, tert-butylcatechol. The styrene is then washed with water to remove the excess alkali, after which it is dried in anhydrous sodium sulfate before use as follows; The inhibitor and styrene (sufficient to form the total weight of the mixture at 200 g) are charged to a fixed 250 ml round bottom flask with an overhead stirrer, thermometer, spray tube and condenser cooled with water (see diagram below) ). The agitator starts. Then apply the nitrogen spray (200 ml min "1) through the reaction mixture, then heat the reaction mixture to 100 ° C using an oil bath, and stir at this temperature for 2 hours. samples are removed and analyzed for polystyrene content using a spectrophotometric method at 420 nm.The method of analysis is based on the American standard test method D2121 and a calibration is made using authentic polystyrene in styrene solutions of known concentrations by weight. In a controlled experiment, with no inhibitor present, much more than 30,000 ppm (limit of quantification) of polystyrene is formed.The levels of the polymer obtained with several inhibitors are shown in the following table.The mixtures of inhibitors are considerably more effective in reducing the amount of the polymer formed that any of the components are when any of the components are used when they are used individually in the total proportion of the concentration of the inhibitor. This clearly demonstrates that an unexpected synergistic effect occurs in the inhibition of styrene polymerization in the absence of air using both an aromatic aliphatic amine carboxylic acid inhibitor and a stable free radical inhibitor together as compared using either the inhibitor alone to twice its concentration found in the combination.

A is the radical 4-hydroxy-2, 2,6,6,6-tetramethyl-piperidinyl-1-oxyl. B is 3, 5-diterciaributil-4-oxy, N, N-dimethylbenzylamine in combination with stearic acid (molar ratio 1: 1.5). Examples 4 to 6 The procedure of Examples 1 to 3 is repeated with a test temperature higher than 115 ° C and instead of a nitrogen spray an air spray (4 ml min x) is applied. these tests; A is the radical 4-hydroxy-2, 2,6,6,6-tetramethyl-piperidinyl-1-oxyl. B is 3, 5-diterciaributil-4-oxy-N, N-dimethylbenzylamine in combination with stearic acid (molar ratio 1: 1.5). There is a clear synergistic inhibition effect in the polymerization of styrene in the presence of air. When a mixture of two inhibitor compounds are used together compared to using either the inhibitor alone at twice its concentration used in the combination. Examples 7 to 9 The procedure of Examples 1 to 3 is repeated and a spray of air (4 ml min "1) is applied instead of a nitrogen spray.

A is the radical 4-hydroxy-2, 2,6,6-tetramethyl-piperidinyl-1-oxyl.

C is 3,5-di-tertiarybutyl-4-oxy-N, N-dimethylbenzylamine in combination with stearic acid (molar ratio 1: 3). Examples 10 to 12 The procedure of Examples 7 to 9 is repeated but the time at 100 ° C is 1 hour instead of two hours.

A is the radical 4-hydroxy-2, 2,6,6,6-tetramethyl-piperidinyl-1-oxyl. D is 1,4-phenylenediamine in combination with stearic acid (molar ratio 1: 1.5). Examples 13 to 15 The procedure of Examples 4 to 6 is repeated but the time at 115 ° C is one hour instead of two hours.

A is the radical 4-hydroxy-2, 2,6,6,6-tetramethyl-piperidinyl-1-oxyl. E is N, N-bis- (1,4-dimethylpentyl) -1,4-phenylenediamine in combination with stearic acid (molar ratio 1: 1.5).

Examples 16 to 21 The procedure of Examples 1 to 3 is repeated but a molar equivalent amount of capric / caprylic acid is used instead of stearic acid without any significant difference in the results. Examples 22 to 24 The procedures of Examples 4 to 6 are repeated but a molar equivalent amount of capric / caprylic acid is used instead of stearic acid without any significant difference in the results. Examples 25 to 27 The procedures of Examples 7 to 9 are repeated B is 3, 5-diterciaributil-4-oxy-N, N-dimethylbenzylamine in combination with stearic acid (molar ratio 1: 1.5) F is diterciaributilo nitroxide.

Claims (14)

1. CLAIMS 1. A monomer composition, stabilized against premature polymerization, characterized in that it comprises: a) an ethylenically unsaturated monomer or mixture of monomers polymerizable by initiation of free radicals, and b) an effective amount, sufficient to inhibit the premature polymerization of the component ( a) of a mixture of: (i) 1 to 99% by weight, based on the total weight of components (i) and (ii) of a mixture of at least one aromatic amine and at least one organic acid in one molar ratio of 10: 1 to 1:10, and (ii) 99 to 1% by weight based on the total weight of components (i) and (ii) of at least one stable radical compound. wherein the aromatic amine has the formula (1) (wherein Q is O or S or N-Z and wherein at least one R is an alkylamine of structure (2) -XN 'C / 2 in which Y, Z are the same or different and comprise branched or straight chain alkyl of Ci to C9 or hydrogen and wherein X is either a covalent or alkylene bond of Ci to C4, and wherein each remaining R is independently benzyl, branched or straight chain alkyl of Cx to C4 or hydrogen with the proviso that two or more Rs may be connected to form one or more rings); wherein the organic acid is a carboxylic acid; and wherein the stable radical compound is a spherically hindered nitroxyl of formula 3 O) (wherein R is hydrogen, alkyl or aryl and T is a group required to form a ring and wherein two or more T groups can be linked by a linking E group).
2. 2. A composition according to claim 1, characterized in that the weight of the component (i) is 50 to 99% and the weight of the component (ii) is 50 to 1%.
3. 3. A composition according to claim 2, characterized in that the weight of the component (i) is 67 to 99% and the weight of the component (ii) is 33 to 1%.
4. 4. A composition according to any preceding claim, characterized in that the molar ratio of the aromatic amine to organic acid is 3: 1 to 1: 3.
5. 5. A composition according to claim 1, characterized in that Q is oxygen.
6. 6. A composition according to claim 1 or 5 characterized in that X is methylene.
7. 7. A composition according to any of claims 1, 5 or 6, characterized in that Y and X are methyl.
8. 8. A composition according to any of the preceding claims, characterized in that the amine is selected from N, N-dimethyl-1,4-phenylenediamine 3,5-diterciaributyl-4-oxy, N, -dimethylbenzylamine 3, 5-diterciaributil 4-oxy-N, N-diethylbenzylamine N, N-dimethyl-2,6-diterciaributyl-4-aminophenol 1,4-phenylenediamine N, N-dimethyl-4-aminotiofenol N, N "-bis- (1, 4-dimethylpentyl) -1,4-phenylenediamine 9. A composition according to claim 1, characterized in that the organic acid is a C6 to C22 carboxylic acid 10. A composition according to claim 1, characterized in that the acid organic is a C6 to C18 carboxylic acid 11. A composition according to claim 1, characterized in that the nitroxyl compound is selected from: l-oxyl-2, 2,6,6-tetramethylpiperidine, 1 -oxyl-2, 2,6,6-tetramethylpiperidin-4-ol, 1-oxyl -2,6,6,6-tetramethylpiperidin-4 -one, l-oxyl-2 acetate , 2, 6, 6-tretramethylpiperidin-4-yl, 2-ethylhexanoate 1, oxyl-2, 2,6,6-tetramethylpiperidin-4-yl, stearate 1, oxyl-2, 2,6,6-tetramethylpiperidin -4-yl, benzoate of 1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl, 4-tert-butylbenzoate of 1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl, bis-succinate (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) sebacate, bis (1, oxyl) sebacate -2, 2, 6, 6-tetramethylpiperi4in-4-yl), bis (l, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) adipate, bis (1, oxyl-2) n-butylmalonate. , 2, 6,6-tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl) phthalate, bis (1, oxyl-2, 2, 6, 6 isophthalate) -tetramethylpiperidin-4-yl), bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4-yl), hexahydroterephthalate of bis (1, oxyl-2, 2,6,6,6-tetramethylpiperidin-4) -yl), N, N "bis (l-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) adipamin, N- (1-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) ) caprolactam, N- (1-oxyl-2, 2,6,6-tetramethylpiperidin-4-yl) -dodecyl-succinimide 2,4,6-tris- (N-butyl-N- (l-oxyl-2, 2, 6,6-tetramethylpiperidin-4-yl) -s-triazine, and 4,4'-ethylenebis (1-oxyl-2, 2,6,6-tetramethylpiperidin-3-one), 4-acetylamino 2, 2, 6 , 6-tetramethylpiperidin-N-oxyl 12. A composition according to claim 1, characterized in that the nitroxyl is 1-oxyl- 2, 2, 6, 6-tetramethylpiperidin-4-ol, or bis (l-oxyl sebacate - 2,2,6,6-tetramethylpiperidin-4-yl) 13. A process for inhibiting polymerization prematurely of an aromatic or aliphatic vinyl compound during distillation, purification or storage, characterized in that it comprises the step of incorporating therein an effective inhibitory amount, sufficient to prevent premature polymerization, during the distillation, purification or storage of a mixture of (i) 1 to 99% by weight, based on 1 total weight of components (i) and (ii), of a mixture of at least one aromatic amine and at least one organic acid in a molar ratio of 10 : 1 to 1:10 and (ii) 99 to 1% by weight, based on the total weight of components (i) and (ii), of at least one stable radical compound. Wherein the aromatic amine, the organic acid and the radical compound are as defined in claim 1. 1. A process according to claim 13, characterized in that the mixture is selected to provide a composition according to any of claims 1 to 12. 15. A process according to the claim 13 or 14