SK457489A3 - Method for attaining alpha-methylstyrene, having a polymerisation quality, from cumene oxidation products - Google Patents

Description

(57) Annotation:

Polymer-grade α-methylstyrene is obtained by treating the by-product from the process of oxidizing cumene to phenol and acetone, i.e. j. α-methylstyrene fraction containing cumene, acetophenone, tert-butylbenzene, α-methylstyrene dimers, phenol and α-methylstyrene. The alpha-methylstyrene waste fraction with a higher content of amethystyrene is first subjected to extraction with aqueous alkaline solutions and then rectified to a separation of cumene and volatile substances such as α-methylstyrene, rectification to a separation of tert-butylbenzene, and less acetophenone and other. substances such as α-methylstyrene with simultaneous stabilization by the specified substances.

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Process for obtaining polymerization quality α-methylstyrene from cumene oxidation products

Technical field

The invention relates to a process for obtaining polymerization-grade α-methylstyrene for the production of ABS resins by treating mixtures of liquid cumene oxidation products.

BACKGROUND OF THE INVENTION

A number of technologies that produce polymers with increased temperature resistance and which are applied to a variety of end products require a permanent α-methylstyrene

The usual process for preparing polymer-grade α-methylstyrene is that the crude cumene is dehydrogenated at temperatures of 400 to 600 ° C in the presence of catalyst and water vapor, separating the hydrogen, light hydrocarbons of the reaction mixture and then isolating α- Polymerization grade methylstyrene. These procedures are described e.g. in C.J. Pavlova Vydelenieje is also a purification of monomers according to Sintetic rubber, Khimija Leningrad (1989).

A disadvantage of the known processes for the preparation of α-methylstyrene is, inter alia, an increase in the acetophenone content of the rectification obtained by α-methylstyrene, which has a negative effect on the light stability of the polymer prepared from this α-methylstyrene.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention provides a process for obtaining α-methylstyrene polymerization grade for the production of ABS resin from a by-product of the process of oxidizing cumene to phenol and acetone, i.

α-methylstyrene fraction containing 50 to 99.5 wt.

% α-methylstyrene, 0.01 to 10 wt. phenol or other impurities by a complex process for isolating α-methylstyrene. This method consists in extracting the α-methylstyrene fraction and subsequently two-stage rectification under the indicated conditions. The α-methylstyrene resin is treated by extraction with a sodium or potassium hydroxide solution having a concentration of 0.1 to 45% by weight in a ratio of 1: 0.1 to 1: 100 to the crude α-methylstyrene fraction at temperatures of 5 to 100 °. C reduces the initial phenol concentration from 0.01 to 1.5 wt. to a maximum content of 50 ppm in the α-methylstyrene fraction.

The treated α-methylstyrene fraction is further subjected to a two-stage rectification process to separate α-methylstyrene from the less volatile and more volatile species. The rectification of α-methylstyrene can be carried out in columns operating at a pressure of 8 to 100 kPa and having a number of trays of 22 to 30 and a reflux ratio R i. the reflux of liquid L and distillate D at a height of R = 2.5 to 5 so that the final concentration of α-methylstyrene is at least 97.5% by weight. and the acetophenone concentration did not exceed 50 ppm. The product of the second stage of rectification is preferably simultaneously stabilized directly in the column, the stabilizer being added in the final rectification phase to the rectified mixture or to the distillate or boiling liquid. The stabilizer in an amount of 5 to 2000 ppm may be a substance selected from the group of tert-butylpyrocatechin, pyrocatechin, resorcinol, hydroquinone, α-nitroso-β-naphthol, p-nitrosophenol and p-methoxyphenol. The stated working parameters of extraction and subsequent rectification were experimentally confirmed.

Further details that may enhance the advantages of the invention are, for example, an extraction stage with a higher aqueous phase ratio or the inclusion of a countercurrent extractor and this leads to a further reduction of impurities such as phenol, acetone in raffinate and thus further influence the quality of the target monomer.

In the next rectification step, higher pressures, practically in the range of from 8 to 100 kPa, can be used as compared to the rectification of styrene, due to the low purity of the thermopolymerization. For a real rectification column with a given number of actual trays, the pressure increase is accompanied by a slight increase in the mass transfer coefficient between the liquid and vapor phases with a significantly greater effect than the simultaneous reduction in relative volatility under the given conditions. This improves the separation of the mixture due to the increased separation capacity of the column.

The following is an example of processing a by-product from the process of oxidizing cumene to phenol and acetone by converting it into polymerization grade α-methylstyrene according to the invention. The conditions illustrate the whole invention but do not limit its scope.

DETAILED DESCRIPTION OF THE INVENTION

Example 1 α-Methylstyrene fraction with 95.1 wt. % α-methylstyrene, 1.7 wt. % cumene, 2.2 wt. % tert-butylbenzene, 0.5 wt. % acetophenone, 0.2 wt. % phenol and 0.3 wt. unidentified components were subjected to a single-step extraction with 0.5% NaOH solution. in a weight ratio of 1: 2 at 20 ° C.

At the outlet of the extractor, a raffinate of 95.2 wt. % tert-butylbenzene, 1.7 wt. % cumene, 2.2 wt. % tert-butylbenzene, 0.5 wt. acetophenone, 15 ppm phenol, 0.04 wt. water and 0.31 unidentifiable components.

The resulting raffinate was subjected to rectification in the first stage in a 22 theoretical floor column operating at a reflux ratio of R = 3.3 at a head pressure of 6 to 3 kPa and at a bottom of the column 14 to 18 kPa and a boiling temperature of 100 to 120 ° C and a column head temperature of 80-87 ° C at which less volatile than α-methylstyrene was separated from the compound mixture. The final distillate contained 96.18 wt. % α-methylstyrene, 1.99% wt. % cumene, 1.78 wt. tert-butylbenzene, 10 ppm acetophenone, 15 ppm phenol and 0.05 wt. water.

This distillate was subjected to the next stage of rectification, in the same column as above, but at a reflux ratio of R = 4, at which a portion of the more volatile compounds than α-methylstyrene was separated and at the same time stabilized the boiling liquid tert-butylpyrocatechin at 20 ppm . The resulting boiling liquid having a composition of 97.8 wt. % α-methylstyrene, 0.5 wt. % cumene, 1.64 wt. tert-butylbenzene, 10 ppm acetophenone, 15 ppm phenol, and 13 ppm tert-butylpyrocatechin are monomeric α-methylstyrene usable directly for the production of ABS resins.

After three days of storage in an inert atmosphere at 23 ° C, an acetophenone concentration of 16 ppm, i. without a visible change.

It is evident from the example that undesirable impurities can be removed from the α-methylstyrene fraction as a byproduct in the production of phenol by oxidation of cumene by the above process, respectively reduced to values satisfying the requirements for monomeric α-methylstyrene for the preparation of ABS resins.

Example 2

Purification of the crude α-methylstyrene fraction of the same composition as in Example 1 was carried out as in Example 1, except that the raffinate was differently stabilized.

The stabilization method and the results obtained for the acetophenone content immediately after rectification and after 3 days of storage under the same conditions as in Example 1 are given in the following table:

Table 1 - method of stabilization and acetophenone content of the product

No. experiment process stabilization *) Used stabilizer title dose Acetophenone content after rectification Acetophenone content after 3 days of storage 1 1 - - 36 211 2 2 pyrocatechol 1500 18 27 3 2 Rezorcfn 30 15 42 4 3 hydroquinone 50 45 45 5 3 p-methoxyphenol 100 32 36 6 4 p-nitrosophenol 10 33 38 7 3 and B-nitroso-naphthol 20 28 31

- unstabilized

- a stabilizer added after extraction before the first rectification

- a stabilizer added after the 1st rectification

- a stabilizer dosed after the 2nd rectification

The results obtained show that the process according to the invention yields a product with satisfactory parameters and shelf life. Failure to meet the stabilizer dosing condition (Experiment No. 1 - Comparative) results in an undesirable increase in acetophenone content during storage.

It is an advantage of the process according to the invention that a product is obtained having properties suitable for the production of polymers and with sufficient shelf life for industrial use.

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Claims (5)

A process for obtaining polymerization quality α-methylstyrene from an α-methylstyrene fraction containing 50 to 99.5 wt. % α-methylstyrene, 0.01 to 10 wt. phenol or other impurities, characterized in that the mixture is subjected to extraction with a solution of NaOH or KOH in a concentration of 0.1 to 45% by weight, in a weight ratio of caustic to α-methylstyrene of 1: 0.1 to 1: 100, at the raffinate obtained is further purified by rectification in columns operating at a pressure of from 8 to 100 kPa, with a number of trays of 22 to 30, the reflux ratio of the liquid to the distillate being 2.5 to 5. Process according to claim 1, characterized in that the maximum permissible concentrations of undesirable impurities in the polymerization-quality α-methylstyrene are less than 50 ppm for phenol and the minimum α-methylstyrene content is greater than 97.5% by weight. Process according to claims 1 to 2, characterized in that 5 to 2000 ppm of tert-butylpyrocatechin, pyrocatechin, resorcinol, hydroquinone, α-nitroso-β-naphthol, p-nitrosophenol and p-methoxyphenol are added as stabilizers. The method according to claims 1, 2 and 3, characterized in that the stabilizer is added in the final rectification phase to the rectified mixture or to the distillate or to the boiling liquid. Method according to claims 1, 2, 3 and 4, characterized in that the rectification steps are two, wherein in the first step the components are removed more volatile and in the second step.