MXPA98007524A - Process for inhibiting polymerization during ladestilation of aromatic compounds of vin - Google Patents

Abstract

The present invention relates to a process for inhibiting the polymerization of a vinyl aromatic compound during the distillation of an aromatic vinyl compound comprising adding to the compound an effective amount of nitrous acid reaction product and a mine with the formula: wherein R and R, are hydrogen or an alkyl group with 1 to 18 carbon atoms

Description

"PROCESS FOR INHIBITING POLYMERIZATION DURING THE DISTILLATION OF VINYL AROMATIC COMPOUNDS" The present invention relates to a process for inhibiting the polymerization of vinyl aromatic compounds for example styrene, during the distillation of the compounds, by adding it to the aromatic compound of vinyl of a nitroso compound, for example N-nitroso-N '-di-3-pentyl-p-phenylneriamine. BACKGROUND Styrene is one of several aromatic vinyl compounds that has considerable commercial utility. Styrene is polymerized in polystyrene which is a plastic of many uses transparent, easily colorable and easy to manufacture. The efficiency of the polymerization process depends on the purity of the initial monomer. Since the processes for producing styrene and other vinyl aromatics will include various reaction products including benzene, toluene, etc., the mixture is distilled to remove these undesirable contaminants. Unfortunately, the temperatures required for distillation, typically 90 to 150 °, lead to the polymerization of the vinyl aromatics. In order to minimize or prevent the polymerization of the vinyl aromatic monomer, it is like adding a polymerization inhibitor to the distillation mixture. The technique presents several compounds that supposedly inhibit polymerization. US-A-4, 050, 993 presents the use of NN-Nitroso-methylaniline as a polymerization inhibitor. US-A-3, 988, 212 discloses the use of N-Nitrosodiphenylamine in combination with dinitro-o-cresol. US-A-4,013,580 discloses the use of N-Nitrosoaniline derivatives. US-A-4,341,600 presents the use of a mixture of dinitro-p-cresol and N-nitroso-diphenylamine. US-A-4, 654, 451 presents T-nitroso phenol substituted with antilo in combination with p-nitroso phenol. US-A-5, 034,156 present N-nitrosophenyl-hydroxylamine plus mono-methyl hydroquinone ether. US-A-5, 396, 004 discloses a phenylene diamine compound plus a hydroxylalkyl amine compound. US-A-5, 254-760 present l-oxy-2, 2,6,6,6-tetramethylpiperidine plus a nitroaromatic compound. US-A-4,929,778 discloses a phenylneriamine compound plus a sterically hindered phenol compound. US-A5, 312, 952 discloses the use of the reaction product of a C9-C or alkylphenol with sulfuric acid and functionally a nitro phenylnethylamine substituted by aryl or alkyl. WO9503263 presents 3, 5, di, 5345, butyl-4-hydroxy-NN-dimethyl benzylamine. EP-A-697386 presents 4-acetylamino-2, 2,6,6-tetramethyl piperidine N-oxyl in combination with 4-nitrosophenol. JP-A-0701910 discloses phosphite compounds-nitrosamine compounds or phenol compounds. JP-A.05310815 having the ammonium salt of N-nitrosophenyl hydroxylamine. JP-A-03149205 presents nitrssophenols plus dicycloexylammonium nitrate. JP-A-1226858 presenting the use of substituted nitrobenzene. US-A-4,967,027 presents p-nitroso phenol plus p-t-putil catechol. JP-A-59029624 which discloses the use of N-nitroso compound, for example, N-nitroso-diphenylamine and a catechol, for example, p-t-butylcatechol. In contrast to these compounds, a number of compounds which are particularly effective in inhibiting the polymerization of vinyl aromatic compounds in general and styrene in particular have now been discovered. These compounds are the N-nitroso derivatives of phenyl-diamine substituted or substituted by dialkyl having the following structure: But both mono and nitrous derivatives are useful as inhibitors. The compounds can be used by themselves or in combination with phenylenediamine.

COMPENDI The present invention relates to a process for inhibiting the polymerization of an aromatic vinyl compound during its distillation. One embodiment of the process involves adding to the vinyl aromatic compound an effective amount of the reaction product of nitric acid and an amine with the formula: (IV) wherein R and R are hydrogen or an alkyl group having 1 to 18 carbon atoms. Another embodiment is a process for inhibiting the polymerization of a vinyl aromatic compound during the distillation of the vinyl aromatic compound which comprises adding to the compound an effective amount of a nitrous compound a of: (I) (ID (IH) and mixtures thereof where R and R are hydrogen or an alkyl group with 1 to 18 carbon atoms.

Yet another embodiment is a process for inhibiting the polymerization of a vinyl aromatic compound during the distillation of the aromatic vinyl compound which comprises adding an effective amount of a mixture of inhibitory compounds having the structures I, II and IV: i I) < II),, | wherein R and R are hydrogen or an alkyl group having 1 to 18 carbon atoms. DETAILED DESCRIPTION The present invention relates to a process for inhibiting the polymerization of an aromatic vinyl compound during its distillation. The aromatic vinyl compounds to which the instant process is applicable include styrene, alpha-methylstyrene, divinylbenzene, divinyl toluene, divinylnaphthalene and polyvinylbenzene. The process generally involves adding an aromatic vinyl inhibitor compound during its distillation. The inhibitor compounds that can be used in the current process include nitroso compounds selected from a group consisting of structures, II, III and mixtures thereof. (i) (H) (III) N-Nitroso-diasuylphenylenediamine N 'N' -nitroso-diakisifenieno-N-phenyl, '-nitroso-i, 4- diammalnediamine diaminociclcexane The groups R and R1 can be hydrogen or an alkyl group with 1 to 18 carbon atoms. Illustrative of the alkyl groups that can be used are methyl, ethyl, propyl, butyl,. pentyl, optyl, decyl, sec-butyl, isopropyl and isopentyl. Included in structures I and II above are the o, m and p isomers. Preferred compounds encompassed within structures I and II are the following compounds having structures IA and IIA.

(I A) N-Nitroso-N, N '-di-3-pentyl-p-phenylenediamine or C - c c - c (II?: O N, N'-Nitroso-N, N '-di-3-pentyl-p-phenylenediamine Another nitroso compound that can be used as a polymerization inhibitor is N-phenyl, N'-nitroso-1,4-diaminocyclohexane having the structure III that appears next.

(III) The nitroso compounds are prepared by reacting nitrous acid with an amine. The amine used to obtain these compounds has structures (IV) and (V) that appear below.

(IV) NII (V) The reaction of nitrous acid with amine is well known in the art and is included here for the sake of the whole. In general, the amine is reacted with nitrous acid at a temperature of -10 ° C to 10 ° C. Nitrous acid can be added or can be generated in situ by adding sodium nitrite hydrochloric acid. In addition, in the case of a diamine, the amount of nitrous acid added will determine whether mono- or dinitroso compounds are obtained. However, even if a stoichiometric amount of 1: 1 of nitrous acid: amine is added, a mixture of the mono and dinitroso compounds can still be obtained. Therefore, the exact nature of the reaction product may not be known. The reaction product may include both mono- and dinitroso compounds together with the unreacted amine. In fact, the unreacted amine can act as a solvent for the nitroso compound. In a preferred embodiment, the amine is N, N '-di-3-pentyl-p-phenylene diamine which is represented by the structure (IVA) shown below, c- c c - c (VAT) The product of the reaction may contain the compounds IA, IIA and IVA.

It is, therefore, an embodiment of the present invention to use reaction products described above as the polymerization inhibitor. Alternatively, the pure components can be isolated and used either individually and in combination with each other. The separate components can be isolated by means well known in the art for example fractional crystallization, liquid chromatography and column chromatography. In order to adequately prevent the polymerization of the vinyl aromatics, an effective amount of the nitroso compound or mixtures thereof can be used. For the nitrous component having structures I and II, an effective amount varies from 1 to 1000 wt. ppm. If the nitrous component has structure (II) then the effective amount varies from 1 to 1000 ppm. When mixtures of the compounds (I), (II), and (IV) are used, the amounts of each component of the mixture vary as follows: compound 1 varies from 18 to 96 wt.%, Compound II varies from 2. at 50 wt% and compound IV varies from 2 to 80 wt%. The amount of the mixture that is added to the vinyl aromatic compound varies from 1 to 100 wt. ppm. The reaction compound of the amine and the nitrous acid can be used as found without further purification. Therefore, when the amine is represented by structure IV, the product of the reaction may include compounds I, II, IV plus other compounds and the amount of the product of the reaction that is added to the vinyl aromatic compound varies from 1 at 1000 wt. ppm. Having added the effective amount of the inhibitor to the mixture containing the aromatic vinyl compound, the mixture is distilled at a temperature of 65 to 150 ° C in normal distillation columns. The distillation temperature can be controlled by controlling the column pressure from 1 to 53 kPa. In addition, the inhibitor can be added to the aromatic vinyl compound in any convenient manner. In general, the inhibitor is added in liquid form by adding the required amount periodically or continuously to the intake of the distillation feed. In this regard, if the inhibitor is a solid, it is dissolved in a suitable solvent. As an illustration of solvents that can be used are toluene, benzene, gilenes, etc. Preferred solvents are ethylbenzene from the starting amine which allows easy separation of the purified vinyl aromatic compound. EXAMPLE 1 In a round-bottomed flask, 2.1 g of N, N'-di-3-pentyl-phenylenediamine obtained from UOPs denoted as UOP NO were placed. 5®. To this flask, which was cooled to 0 ° C, 50 ml was added. of hydrochloric acid solution composed of equal parts of water and concentrated hydrochloric acid. Then 12 ml of a 0.51 g solution of sodium nitrite was added over a period of 20 minutes. Any excess acid was then neutralized with a cooled solution of sodium hydroxide. The resulting mixture was poured into a separatory funnel to which 100 ml of ethyl ether was added. The organic phase was collected, dried and the ethyl ether was removed by the use of a rotary evaporator, the isolated product was a dark colored liquid which was identified as sample A. EXAMPLE 2 The following test procedure was applied to determine the ability of sample A to inhibit the polymerization of styrene. Five glass ampoules were filled with 5 g of styrene and 250 wt. ppm of sample A. Four ampoules were placed in an oil bath heated to 120 ° C. The fifth vial was analyzed to provide the initial amount of polymerization. One ampoule was removed in increments of one hour and the contents filtered to determine the amount of polystyrene formed. These results are presented below. The experiment was repeated, except that the amount of sample A was modified every hour to provide the results for 175, 125 and 72 wt. ppm. Dinitro-butyl-phenol (DNBP) and dinitrophenol (DNP) were also tested in the same manner to provide comparative examples and those results are also presented.

Polymerization inhibiting activity of several inhibitors The data shown in the table shows that the inhibitors of the present invention have higher activity than the inhibitors of the prior art. Instantaneous inhibitors have the same activity as DNBP or DNP but at one third of the concentration.

Claims (11)

1. CLAIMS 1. A process for inhibiting the polymerization of a vinyl aromatic compound during the distillation of a vinyl aromatic compound comprising adding to the compound an effective amount of a nitrous acid reaction product and an amine with the formula:

   where R and R are hydrogen or an alkyl group with 1 to 18 carbon atoms.
2. 2. The process of claim 1 wherein R and R are selected from a group consisting of hydrogen, methyl, ethyl, propyl, butyl, pentyl, sec-butyl, isopropyl and isopentyl.
3. 3. The process of claim 2 wherein the amine is
4. The process of claim 1 wherein the vinyl aromatic compound is selected from the group consisting of styrene, alpha-methyl styrene, divinylbenzene, vinyl toluene, vinylnaphthalene and pslivenylbenzene.
5. 5. A process for inhibiting the polymerization of a vinyl aromatic compound during the distillation of the vinyl aromatic compound comprising adding to the compound an effective amount of a nitroso compound selected from the group consisting of:

   (I) (II) (III) and mixtures thereof and R and R are hydrogen or an alkyl group with 1 to 18 carbon atoms.
6. 6. The process of claim 5 wherein the nitroso compound is a mixture of compound I and II.
7. The process of claim 5 wherein R and R are selected from a group consisting of hydrogen, methyl, ethyl, propyl, butyl, pentyl, sec-butyl, isopropyl and isopentyl.
8. 8. The process of claim 5 wherein the nitroso compound is:
9. 9. The process of claim 5 wherein the nitroso compound is added as a mixture of the inhibitory compounds with structures I, II and IV:

   wherein R and R are hydrogen or an alkyl group having 1 to 18 carbon atoms.

   (I) (H) (IV)
10. 10. The process of claim 9 wherein the amount of compound I ranges from 18 to 96% by weight, wherein amount II ranges from 2 to 50% by weight and the amount of compound IV ranges from 2 to 80% by weight.
11. 11. The process of claim 9 wherein compounds I, II and IV have structures IA, IIA, and IVA:

    c- c c - c (I?)

    0 c _ c

    (HA) 0

    C - C (VAT)

    EXTRACT The polymerization of the vinyl aromatics during the distillation of the yinyl aromatics is inhibited by adding to the vinyl aromatic compound, for example styrene, which distills a nitrous compound, for example, N-nitroso-N, N ' -di-3-pentyl-p-phenylenediamine.