Compositions and methods for inhibiting vinyl aromatic monomer polymerization

IS 2 170 784 T3

DESCRIPTION

Compositions and methods for inhibiting the polymerization of vinyl aromatic monomers. Field of the invention

This invention relates to compositions and methods for the inhibition of the unwanted polymerization of vinyl aromatic monomers during processing.

Background of the invention

Common industrial methods for styrene production generally include separation and purification processes such as distillation to remove unwanted impurities. Unfortunately, purification processes performed at elevated temperatures result in a higher rate of unwanted polymerization. Distillation is generally done under vacuum to reduce monoomer loss. The presence of oxygen, although virtually excluded in styrene distillation, also promoted the polymerization of the monomer.

This polymerization not only results in loss of the desired monomer end product, but also in loss of production efficiency due to polymer formation and / or polymer agglomeration in the process equipment. The thermal polymerization of the styrene monoomer results in normal (ie, linear) polymer formation. This resulting polystyrene polymer is characterized by its glassy and transparent appearance and by its solubility in styrene monoomer and many organic solvents.

Summary of the invention

The present invention provides methods for inhibiting the polymerization of vinylaromaotic monoomers, such as styrene, and compositions consisting of synergistic combinations of actives.

According to the present invention, a method is provided to inhibit the polymerization of vinylaromaotic monoomers in an oxygen-free vinylaromaotic monomer processing system that consists of adding an effective polymerization-inhibiting amount of a dinitrophenol compound, a hydroxylamine compound, and a compound of phenylenediamine.

The hydroxylamine compound acted as a polymerization inhibitor compound and the phenylenediamine compound acted as a catalyst to accelerate the reaction between the hydroxylamine compound and free radicals present in the monomer system.

Description of related art

Compounds that are generally marketed to inhibit the polymerization of vinyl aromatic monoomers are those of the dinitrophenolic type. For example, US Patent No. 4,105,506 to Watson et al. Teaches the use of 2,6-dinitro-p-cresol as a polymerization inhibitor for vinyl aromatic compounds. US patent N^°4,466,905 to Butler et al. Teaches that a combination of 2,6-dinitro-p-cresol and p-phenylenediamines inhibited polymerization in a distillation column when oxygen is present. US patent N^° 4,774,374, by Abruscato et al., Teaches compositions and processes for the inhibition of the polymerization of vinylaromaotic compounds using an oxygenated product that is formed by the reaction of a Naryl-N'-alkyl-p-phenylenediamine with oxygen. US patent N^° 4,720,566 to Martin teaches methods and compositions for inhibiting acrylonitrile polymerization in a slaking tower, not excluding oxygen, using a hydroxylamine compound and a phenyl-p-phenylenediamine compound.

Czech Patent No. 163,428 teaches a method for stabilizing styrene and divinylbenzene using 2,4-dinitro-orthocresol and diethylhydroxylamine. European patent application N^° 0 240 297 teaches the use of this combination to inhibit styrene polymerization. These publications discuss systems at lower temperatures and higher oxygen contents. However, the use of diethylhydroxylamine is problematic in styrene purification processes since it has a boiling point of between 125^°C and 130^°C at 760 mm Hg, which is similar to styrene and can transfer with styrene during purification processing.

Different inhibitory compositions have been used in styrene and other vinyl aromatic monomers to inhibit unwanted polymerization. Other agents used include sulfur, p-benzoquinone, phenylenediamines, tert-butylpyrocatechol, phenothiazine, hydroxylamines, nitro compounds, and inhibited phenols. However, many of these compounds have disadvantages such as high toxicity, instability, danger of explosion at elevated temperature, or insufficient efficacy under processing conditions (ie, the inhibitor needs oxygen to be effective). The present inventor has discovered an original composition for inhibiting the polymerization of vinyl aromatic monomers that avoids these problems associated with known inhibitors.

EP-A-0 594 341 discloses a method and composition for inhibiting the polymerization of vinyl aromatic monomers under distillation conditions. The composition consists of a combination of a phenylenediamine compound and a hydroxylamine compound.

US-A-4,466,905 discloses a composition to prevent polymerization of vinyl aromatic compounds, the composition of which may include 2,6-dinitro-p-cresol and a phenylenediamine.

EP-A-0 240 297 discloses a method for inhibiting the polymerization in the presence of oxygen of a vinyl aromatic compound by using a substitute hydroxylamine having a boiling point higher than that of the vinyl aromatic compound and a dinitrophenol.

Detailed description of the invention

As mentioned above, the present invention refers to methods for the inhibition of the polymerization of vinyl aromatic monoamers in an oxygen-free vinyl aromatic monoomer processing system, which consist of adding a combination of a dinitrophenol compound, a hydroxylamine compound and a hydroxylamine compound. phenylenediamine compound a

ES 2 170 784 T3 monomers.

The method of the present invention proves to be effective in inhibiting the polymerization of vinylaromatic monomers under monomer processing conditions. These processing conditions include, but are not limited to, the purification and distillation processes of vinylaromatic monoemers.

Vinylaromaetic monomers that can be treated with the present invention include, but are not limited to, styrene, bromostyrene, divinylbenzene, and α-methylstyrene. The compositions of the present invention are especially effective in inhibiting the polymerization of styrene monoomers.

The expression "oxygen-free processing conditions" proposes to define the substantially oxygen-free conditions under which vinylaromatic monoemers, especially styrene, are processed. These conditions, exemplified by the distillation and purification processes, generally have less than 2 parts per million parts of oxygen present present and preferably less than 1 part per million parts of styrene.

Preferably, the dinitrophenol compounds have the structure

<img file="ES2170784T3_D0001.tif" />

wherein R3 is hydrogen or C1 to C12 alkyl.

The hydroxylamine compounds useful in the present invention preferably have the formula:

^R4 ^\

N-OH ^/^R5 wherein R4 and R5 are the same or different product and are hydrogen, or alkyl, aryl, alkaryl, aralkyl, or hydroxyalkyl groups and preferably have between three and twenty carbon atoms. In one representation, R4 is H and R5 is C6 alkyl to C20 alkyl. The preferred hydroxylamine compound is bis (hydroxypropyl) hydroxylamine (HPHA).

Preferably, the useful phenylenediamine compounds in this invention have the form:

<img file="ES2170784T3_D0002.tif" />

wherein R6, R7, R8 and R9 are the same or different product and are hydrogen, or alkyl, aryl, alkaryl or aralkyl groups having from one to twenty carbon atoms. The preferred phenylenediamine compound are N, N'-di-sec-butyl p-phenylenediamine and N-phenyl-N '- (1,4-dimethylpentyl) -p-phenylenediamine.

The compositions of the present invention are shown to be effective in inhibiting the polymerization of vinylaromatic monomers during oxygen-free processing. The compositions of the invention offer improved activity in each separate component in styrene monomers that undergo distillation and purification processes at elevated temperatures. Styrene is usually processed at a temperature between 95 and 125 ° C. The compositions of the present invention are particularly effective in higher temperature styrene monomer processing systems (&gt; 110^°C).

The total amount of dinitrophenol compound, hydroxylamine compound and phenylenediamine compound used in the methods of the present invention is the amount that is sufficient to inhibit polymerization and will vary according to the conditions under which the vinyl aromatic monoemer is processed and exposed to high temperatures. Generally, at higher processing temperatures and higher monoomer contamination, larger amounts of the polymerization inhibitor composition will be required.

Preferably, the total amount of the composition added to the vinyl aromatic monoomer ranges from 1 to 10,000 parts per million parts of the monoer. Most preferably, the treatment variation is between 5 parts and 500 parts of the composition per million parts of monoemer.

Preferably, the weight ratio of the dinitrophenol hydroxylamine compound and phenylenediamine compound ranges from 1: 9 to 9: 1, with a weight ratio of 1: 1: 1 being preferred.

The compositions used in the present invention can be added to the vinyl aromatic monomer following any conventional method, either as separate and individual ingredients or as a combination of ingredients. It is preferable that they are added as a unique treatment composition.

IS 2 170 784 T3

The compositions used in the method of the present invention can be added to the vinyl aromatic monomer, either as a dispersion or as a solution using the appropriate liquid carrier or solvent. Any solvent compatible with each of the ingredients of the composition and with the aromatic vinyl monoomer can be used.

Therefore, it is possible to produce a more effective vinyl aromatic monoomer polymerization inhibitory treatment than that obtained by using each compound separately when measured at comparable treatment levels. This improved activity allows the concentration of each of the ingredients to be reduced, so that the total amount of polymerization inhibitor required, especially at higher processing temperatures, can be reduced.

The preferred composition used in the method of the invention uses bis (hydroxypropyl) hydroxylamine and N, N'-di-sec-butyl-p-phenylenediamine with 4,6-dinitro-o-cresol and 2-sec-butyl-4, 6-dinitrophenol, respectively.

The invention will now be further described with reference to several specific examples, which should only be understood as illustrative and not as limiting the scope of the invention.

Examples

In order to evaluate the best inhibition of polymerization of the compositions of the invention and to demonstrate the best activity of each composition, a styrene polymerization test was carried out.

Uninhibited styrene (5 ml) was placed in a test tube with the correct amount of treatment. The tube was closed with a septum and argoon was boiled through the liquid at 15 ml / min. for 3 minutes. The tubes were then placed in an oil bath heated to 120 ° C for 2 hours. The amount of polystyrene formed was determined by the precipitation of methanol. The results of this test are given in Table I.

TABLE I

Styrene polymerization test Uninhibited styrene

120 ° C

<td>Treatment</td><td>Dose (ppm)</td><td>Percentage polymer</td>

<td>White</td><td> —— 23,30</td><td></td>

<td>DNOC</td><td> 300</td><td> 2,15</td>

<td>DNBP</td><td> 300</td><td> 1,77</td>

<td>PDA</td><td> 300</td><td> 21,06</td>

<td>HPHA</td><td> 300</td><td> 17,96</td>

<td>PDA: HPHA: DNOC</td><td> 100:100:100</td><td> 1,38</td>

<td>PDA: HPHA: DNOC</td><td> 75:150:75</td><td> 1,78</td>

<td>PDA: HPHA: DNOC</td><td> 50:150:100</td><td> 1,23</td>

<td>PDA: HPHA: DNBP</td><td> 100:100:100</td><td> 1,02</td>

<td>PDA: HPHA: DNBP</td><td> 50:150:100</td><td> 0,79</td>

DNOC is 4,6-dinitro-o-cresol

DNBP is 2-sec-butyl-4,6-dinitrophenol PDA is N, N'-di-sec-butyl-p-phenylenediamine HPHA is bis- (hydroxypropyl) hydroxylamine

These test results demonstrate the best inhibition of polymerization of the three-component combination of DNOC / DNBP, HPHA and PDA. Unexpected results in a range of 1: 1: 1 to 1: 3: 2 were noted in inhibiting styrene polymerization at higher styrene processing temperatures (120^°C).

Uninhibited styrene (100 mL) was placed in a three-necked flask incorporating a bubbler, septum, and condenser. The appropriate treatment was added and the solution was boiled argoon at 10 ml / min for 10 minutes. Then, with continuous injection of argon vapor, the flask was immersed in an oil bath heated to 120^°C. Samples (0.5 mL) were taken every 30 minutes and the polymer formed was determined by the precipitation of methanol. The results of this test are presented below.

Table II reports on the efficacy of the composition used in the method of the present invention in inhibiting styrene polymerization.

TABLE II

Styrene polymerization test

Uninhibited styrene

120^°C

Treatment: PDA / HPHA / DNBP in a ratio of 200: 200: 100 ppm

<td>Time (h)</td><td>% Polymer</td>

<td> 1</td><td> 0,07</td>

<td> 2</td><td> 0,31</td>

<td> 3</td><td> 0,49</td>

<td> 4</td><td> 1,10</td>

PDA is N, N'-di-sec-butyl-p-phenylenediamine HPHA is bis- (hydroxypropyl) hydroxylamine DNBP is 2-sec-butyl-4,6-dinitrophenol

Even when this invention has been described in relation to specific embodiments thereof, it is evident that those skilled in the art will be able to find many other forms and modifications of this invention. The appended claims and this invention should, in general, be construed as points covering all forms and logical modifications that may occur within the actual scope of the present invention.