GB2088857A

GB2088857A - Process for Purifying Dihydroxydiphenyl Sulfone

Info

Publication number: GB2088857A
Application number: GB8132785A
Authority: GB
Original assignee: TOKAI ELECTRO CHEMICAL CO; Tokai Denka Kogyo KK
Current assignee: TOKAI ELECTRO CHEMICAL CO; Tokai Denka Kogyo KK
Priority date: 1980-10-31
Filing date: 1981-10-30
Publication date: 1982-06-16
Also published as: JPS5829946B2; JPS5777665A; DE3141454A1; GB2088857B

Abstract

Dihydroxydiphenyl sulfone contaminated with a colored substance is decolorized by dissolving it in a solvent, adding a reducing agent to the resulting solution to decolorize the solution, and subsequently precipitating and separating crystals of the decolorized sulfone.

Description

SPECIFICATION Process for Purifying Dihydroxydiphenyl Sulfone This invention relates to a process for purifying dihydroxydiphenyl sulfone (hereinafter referred to as "bisphenol-S".

As the process for preparing bisphenol-S there are generally known a process wherein phenol is reacted with a sulfonating agent such as a concentrated sulfuric acid, a fuming sulfuric acid or a sulfuric anhydride, and a process wherein phenol is reacted with phenolsulfonic-acid.

However, since those reactions are all carried out for a long period of time under high temperatures of 1400 to 2500C, the byproduction of a tarry substance of reddish or dark brown is unavoidable. Besides, this tarry substance closely resembles the main product, bisphenol-S, in point of solubility in various solvents, so its separation is very difficult and this causes coloration of the final product.

Bisphenol-S has a heat resistance, resistance to oxidation and stability to light which are based on the uniqueness of its diphenyl sulfone linkage, and because of these characteristics bisphenol-S is increasingly being used as a substitute for bisphenol-A in the field of engineering plastics such as polyester, epoxy and polycarbonate resins.

However, resin products prepared from bisphenol-S containing impurities, particularly a colored substance, are colored yellowish brown and lose transparency, so that the application field as plastics is limited. As a raw material for the production of engineering plastics, therefore, a pure bisphenol-S not containing a colored substance is requested.

Heretofore, as the method of purifying a colored bisphenol-S there has been proposed a method (as described in the working examples of Japanese Patent Publications Nos. 5274/63 and 36264/76) wherein bisphenol-S containing a colored substance is dissolved in methanol or an alkaline aqueous solution and then an active carbon is added into the solution to adsorb off the colored substance. According to such an adsorptive removal using an active carbon, however, the colored substance in the solution cannot thoroughly be removed, so the solution of bisphenol-S still presents purplish red, and the whiteness of bisphenol-S crystallized and recovered from the solution is not considered to be fully satisfactory.

Japanese Patent Laying Open Print No.

111045/75 discloses a purifying method for bisphenol-S wherein a colored bisphenol-S is dissolved in an aqueous phenol solution to allow the colored substance to be extracted into the phenol layer and thereafter the bisphenol-S dissolved in the water layer is crystallized and recovered. However, an industrial application of this method involves many difficulties, for example, it is necessary that the concentration of phenol and that of bisphenol-S in the solution as well as the solution temperature be controlled fairly exactly.

Furthermore, Japanese Patent Publication No.

3005/67 proposes a purifying method for bisphenol-S wherein bisphenol-S containing a colored substance is dissolved in water and then an aliphatic higher alcohol is added followed by heating to above 1 200C and stirring under pressure to allow the colored substance to be extracted into the alcohol layer. But in order to fully extract off the colored substance it is necessary to make stirring for a long period of time at a high temperature and under pressure, and therefore this method is not suitable for industrial application.

This invention provides an improved process for preparing bisphenol-S having a high degree of whiteness from bisphenol-S containing a colored substance.

The process of the invention comprises dissolving in a solvent bisphenol-S containing a colored substance, adding a reducing agent to render the solution colorless and thereafter precipitating and separating crystals of the decolorized bisphenol-S. In this operation, if a chelating agent is also present, the purification effect can be further improved.

By way of illustrating the solvent used in the invention, mention may be made of lower aliphatic alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol and isopropyl alcohol, lower aliphatic carboxylic acids such as formic acid, acetic acid and propionic acid, lower aliphatic ketones such as acetone and methyl ethyl ketone, lower aliphatic esters such as ethyl acetate and methyl acetate, dimethylformamide, di methyl sulfoxide, N-methylpyrrolidone-2, and alkaline aqueous solutions.

Essentially, any reducing agent may be used in the invention provided it has a reducing action, and particularly sodium dithionite, sodium formaldehyde sulfoxylate, sodium hydroboride and thiourea dioxide are preferred. The amount of the reducing agent to be used differs according to the coritent of a colored substance in bisphenol-S, but if it is added in an amount of 0.1 to 5 percent by weight based on the weight of bisphenol-S, it can fully show its effect.

The temperature condition in the decolorizing operation with a reducing agent differs according to the kind of reducing agent used, but in order to perform the decolorizing operation effectively in a short time, it is preferable that the solution be heated to a temperature ranging from 400C to the boiling point of the solvent.

In this invention it is preferable that a chelating agent be present during the treatment with the reducing agent. In case a metallic reaction vessel is used in the preparation of bisphenol-S, a sulfonating agent sometimes causes the metal to be partially dissolved out into the product, and by this reason orsome other reason, metal ions as an impurity are often mixed into a crude bisphenol-S.

In such a case, the addition of a chelating agent is effective. To exemplify the chelating agent used in the invention, mention may be made of nitrolotriacetic acid, ethylene-diaminetetraacetic acid and diethylenetriaminepentaacetic acid. The amount of these chelating agents to be used range from 0.01% to 1.0% by weight based on the weight of bisphenol-S, in which they can fully show their effect.

As to the method for precipitating bisphenol-S from solution after decolorization, there may be chosen a method suitable for the solvent used from among conventional methods such as cooling, concentration and neutralization.

In working the process of this invention, the dissolving in solvent of bisphenol-S containing a colored substance, the decolorizing treatment with a reducing agent and the precipitation of crystals may be carried out under any of the following conditions-reduced pressure, normal pressure and under pressure, but generally normal pressure is sufficient.

For the separation of precipitated crystals, there may be used conventional methods such as filtration by suction, pressure filtration and centrifugal separation.

Working examples of this invention will be given hereinunder for more detailed illustration of the invention, but it is to be understood that the invention is not limited thereto. In coloration degree of bisphenol-S shown in the working examples is in terms of Hazen Unit Colour measured by an APHA meter.

Comparative Example 100 g of bisphenol-S containing a colored substance was added to 1 kg of a 2% aqueous caustic soda solution heated to 500C and was dissolved therein with stirring. Then 0.5 g of an active carbon was added, and after a further stirring for 10 minutes while maintaining the temperature at 500 C, the active carbon was filtered off. The filtrate was neutralized to pH 4.0 with sulfuric acid and cooled, then the precipitated crystals were filtered off and dried.

Example 1 100 g of bisphenol-S containing a colored substance was added to 1 kg of a 2% aqueous caustic soda solution heated to 500C and was dissolved therein with stirring, then 0.5 g of sodium dithionite was added and stirring was made for 10 minutes while maintaining the temperature at 500C, and thus decolorization was effected. Thereafter, the decolorized solution was neutralized to pH 4.0 with sulfuric acid and cooled, then the precipitated crystals were filtered off and dried.

Example 2 1. In the method of Example 1,0.5 g of thiourea dioxide was used in place of sodium dithionite.

Example 3 in the method of Example 1,0.5 g of sodium formaldehyde suifoxylate was used in place of sodium dithionite.

Example 4 In the method of Example 1 0.1 g of sodium ethylene-diaminetetraacetate was used together with sodium dithionite.

Example 5 100 g of bisphenol-S containing a colored substance was added to 1 kg of methyl alcohol heated to 600C and was dissolved therein with stirring, then 0.5 g of sodium dithionite was added and stirring was made for 10 minutes while maintaining the temperature at 600C, and thus decolorization was effected. Thereafter, the decolorized solution was cooled to room temperature and the precipitated crystals were filtered off and dried.

Table 1 below shows Hazen Unit Colour of the decolorized bisphenol-S obtained in the Comparative Example and Examples 1-5.

Table 1 Hazen Unit Sample Colour Bisphenol-S containing a colored substance (untreated product) 250 Comparative Example 90 Example 1 30 Example 2 25 Example 3 30 Example 4 20 Example 5 20

Claims

1. A process for purifying dihydroxydiphenyl sulfone, which process comprises dissolving in a solvent dihydroxydiphenyl sulfone containing a colored substance, adding a reducing agent to the resulting solution to decolorize the solution, and subsequently precipitating and separating crystals of the decolorized dihydroxydiphenyl sulfone.

2. A process according to Claim 1, in which said decolorizing operation is performed in the presence of a chelating agent.

3. A process according to Claim 2, in which said chelating agent is selected from nitrolotriacetic acid, ethyienediaminetetraacetic acid and diethylenetriaminepentaacetic acid.

4. A process according to Claim 1, 2 or 3, in which said reducing agent is selected from sodium dithionite, sodium formaldehyde sulfoxylate, sodium hydroboride and thiourea dioxide.

5. A process according to any one of Claims 1 to 4, in which said solvent is an alkaline aqueous solution.

6. A process according to any one of Claims 1 to 5, in which said decolorizing operation is performed at a temperature above about 400C and below the boiling point of the solvent.

7. A process for decolorizing dihydroxydiphenyl sulfone, the process comprising contacting dihydroxydiphenyl sulfone containing a colored substance with a reducing agent, said dihydroxydiphenyl sulfone being in solution in a solvent therefor, and thereafter precipitating and separating crystals of decolorized dihydroxydiphenyl sulfone.

8. A process as claimed in Claim 1 or Claim 7, substantially as hereinbefore described with particular reference to the Examples.

9. A process as claimed in Claim 1 or Claim 7, substantially as illustrated in any one of Examples 1 to 5.

1 0. Decolorized dihydroxydiphenyl sulfone when prepared by the process claimed in any one of the preceding claims.