DE1117559B - Process for improving the odor and color fastness of aromatic dicarboxylic acid alkyl esters or mixtures thereof - Google Patents

Description

Process to improve the odor and color fastness of aromatic dicarboxylic acid alkyl esters The invention relates to a process to improve the properties of dicarboxylic acid esters used as plasticizers and synthetic lubricants are suitable.

According to the invention, alkyl dicarboxylates are obtained by treatment cleaned with ozone and subsequent reduction.

Esters that can be purified according to the invention are, for. B. the Diesters of aromatic dicarboxylic acids, such as phthalic acid with saturated aliphatic acids Alcohols with four or more carbon atoms in the molecule, e.g. B. butanols, nonanols and deans. Mixed esters of these acids, such as butyl octyl phthalate and mixtures of diesters the phthalic acid obtained by esterifying phthalic anhydride with a mixture of primary alcohols containing 7 to 9 carbon atoms can be obtained be cleaned by the method according to the invention.

The ozone used in the method of the present invention is preferred applied in the form of ozonated air. The discoloration occurs faster with increased Temperature. The ozone treatment is therefore preferably carried out at a temperature between 10 and 100 ° C.

After exposure to the ozone, the esters undergo a reductive treatment subject. This is done either by washing the esters with the aqueous solution a reducing agent or by treatment with hydrogen in the presence of hydrogenation catalysts, preferably Raney nickel. Washing is preferably done at room temperature or at a temperature of up to about 100 ° C. with a volume ratio of ester to aqueous Solution of the reducing agent from 20: 1 to 5: 1 carried out. The concentration the reducing agent used is not critical, but is preferred within 1 to 20 percent by weight. Suitable reducing agents are alkali sulfites and bisulfites, sulfur dioxide, sodium nitrite and hydrazine. Preferably with an aqueous solution of alkali sulfite or bisulfite, in particular with sodium sulfite or sodium bisulfite.

After the ozone treatment and before the reducing treatment the esters with an aqueous alkali solution, preferably an aqueous sodium, Potassium hydroxide solution, washed. The concentration of the alkali used is not crucial, but is preferably 1 to 20 percent by weight. Washing with Alkali is preferably carried out at a temperature between 20 and 100.degree. The volume ratio from ester to aqueous alkali is also not critical, but is preferred between 20: 1 and 5: 1.

After the reductive treatment, the esters are expediently preferred washed with water at a temperature between 10 and 100 ° C.

The volume ratio of ester to water is between 6: 1 and 2nd - 1st

After washing with water, the esters are suitably for example by suitable desiccants or heating in a vacuum and then Filter, dried.

The ozone treatment of the esters according to the invention can be carried out with others or cleaning methods applied after the ozone treatment. For example the esters can be washed with an aqueous alkali solution before the ozone treatment and passed through an adsorber with activated carbon after the ozone treatment. The product purified in this way can optionally be used for further decolorization of the esters treated again with ozone. the Esters can after washing Treated with alkali also with steam to remove any traces of free alcohol to remove. This will reduce the effects of the previous ozone and alkali treatment The improvement in the color of the esters achieved is not impaired.

The cleaning effect achieved by the method according to the invention can either be in improving the color of the esters or, in the case of esters with proportions high boiling point, in improving odor resistance by reducing the peroxide content of the ester is effected. Both effects can be used at the same time be achieved. The improved properties of the esters can be according to known Procedure to be established. For example, the color of the ester in one Lovibond tintometer can be measured. The peroxide content of the ester can, for. B. by iodometric titration or with ferrothiocyanate.

The invention is illustrated in the examples. The parts by weight listed have the same ratio to parts by volume as kilograms to liters. The color of the Unless otherwise noted, Ester was taken in a Lovibond tintometer Using a 15.2 cm cell to determine the peroxide content of the ester after that in "Industrial and Engineering Chemistry, Analytical Edition" (1947), Vol. 19, P.980, ferrothiocyanate method described was measured. Example 1 A sample of a mixture, which in the suppuration of phthalic anhydride with a mixture from primary alcohols containing 7 to 9 carbon atoms was obtained at a rate of 120 parts by volume per hour together with a stream of ozonated air with a Introduced into a reaction vessel at a rate of 7200 parts by volume per hour. The color of the esters before ozone treatment was 2.54 using a cell mm 12.1 yellow and 3.0 red. The reaction temperature was 25 ° C, the residence time in Reaction vessel 2 hours.

100 parts by volume of the pus sample pretreated in this way with a color of 1.5 yellow and 0.7 red were then mixed with 20 parts by volume of a 5% aqueous Washed sodium sulfite solution at 70 ° C. for 15 minutes. The mixture was allowed to settle and separated off as much of the aqueous phase as without any noticeable loss of the pus phase was possible. The pus phase was then stirred for 30 minutes at 98.degree washed with water, the ratio of ester to water being 4: 1 parts by volume.

After the mixture had settled, the aqueous phase was separated off, repeated washing with water and then separated the pus layer., dried and filtered. The color of the ester treated in this way was 0.5 yellow.

EXAMPLE 2 A sample of di-2-ethylhexyl phthalate was treated with ozone according to the procedure of Example 1, the ester feed rate being 120 parts by volume per hour and that of the ozonated air being fed in being 7200 parts by volume per hour. The temperature was kept at 25 ° C. The residence time in the reaction vessel was 1 hour. A portion of the ozone-treated ester sample was then washed with a 10% strength aqueous sodium hydroxide solution at 70 ° C. for 15 minutes. The ratio of ester to alkali was 10. 1. The mixture was then left to settle for 30 minutes, the ester and the aqueous phase being separated. As much of the aqueous phase was then separated off as was possible without noticeable loss of ester phase, and the residue of the mixture was washed with agitation with water at 98 ° C. for 30 minutes in a volume ratio of ester to water of 4: 1 and then settled for 30 minutes calmly. The aqueous phase was then separated off and the washing with water was repeated. Finally the ester layer was dried and filtered. A second portion of the ozone-treated ester sample was washed with a 5% aqueous sodium sulfite solution using the procedure of Example 1.

After steaming the two ester samples under reduced Pressure was used to measure the peroxide content. It was found that the sodium hydroxide solution washed sample of ozone-treated ester 2.5 - 10-s weight percent peroxide, In contrast, the sample washed with sodium sulfite solution was only 0.5-1 / 10-3 percent by weight contains active oxygen. Example 3 A sample of di-2-ethylhexyl phthalate was made treated with ozone according to the procedure of Example 1, the feed rate being of the ester 120 parts by volume per hour and that of the ozonated air 7200 parts by volume per hour. The reaction temperature was kept at 25 ° C. The dwell time in the reaction vessel was 1 hour.

65 parts by volume of the ozone-treated ester were given for 15 minutes 70 ° C with 13 parts by volume of a 5% sodium bisulfite solution and then with Water washed. The pus phase is separated off and treated with a 10% sodium hydroxide solution washed. In. in this way the peroxide concentration of the ester is 0.8-10 s Weight percent active oxygen decreased.

Another sample of the ozone-treated ester is tested with a 10% strength Washed sodium hydroxide solution according to Example 2. The peroxide concentration of this Sample is 2.2-10-s weight percent active oxygen. Example 4 A sample Di-2-ethylhexyl phthalate is treated with ozone according to the procedure of Example 1, the feed rate of the ester being 139 parts by volume per hour and that of the ozonated air was 24,000 parts by volume per hour. The temperature was at 20 ° C held. The residence time in the reaction vessel was 1 hour.

The ester treated with ozone was then treated with a 10% strength Washed sodium hydroxide solution as in Example 2. The peroxide concentration of the washed ester was 2.5-10% by weight active oxygen.

2000 parts by volume of this ester were in a hydrogen atmosphere moved with 20 parts by weight of Raney nickel for 3 hours at 80 ° C. The ester was then filtered and distilled with steam at a pressure of 100 mm. The peroxide concentration of Esters was made up to 0.3-10-s weight percent active oxygen reduced.

Example 5 A sample of a diester obtained by reacting Phthalic anhydride with a mixture of alcohols with 7 to 9 carbon atoms, was treated with ozone according to the procedure of Example 1. The feeding speed of the ester was 120 parts by volume per hour, that of the ozonated air was 7200 parts by volume per hour. The temperature was kept at 25 ° C; the residence time in the reaction vessel was 2 hours. According to iodometric titration, the peroxide content of the ester was Part of the ozone-treated ester was: 0.095 weight percent active oxygen with a 10% aqueous sodium hydroxide solution according to the method of the example 2 washed. Another part of the ester was with 10 parts by volume of a 10% aqueous hydrazine solution washed at 18 to 20 ° C for 30 minutes. Both parts were treated separately with steam at a pressure of 100 mm and measured the peroxide content. The peroxide content of the ester treated with aqueous sodium hydroxide was 4.1 10% by weight of active oxygen, of the hydrazine-treated ester 0.2 - 10-s% by weight of active oxygen.

Claims (7)

PATENT CLAIMS: 1. Process for improving the smell of aromatic Dicarboxylic acid alkyl esters or mixtures thereof, characterized in that one by the ester conducts ozone and the esters pretreated in this way then optionally before washing with water and after washing with an aqueous alkali solution either the reductive treatment by washing with an aqueous solution of a reducing agent or in a manner known per se, the action of hydrogen in the presence of a Subjects to hydrogenation catalyst. 2. The method according to claim 1, characterized in that that one carries out the passage of ozone at a temperature between 10 and 100'C. 3. The method according to claim 1 and 2, characterized in that the ozone in The form of ozonated air. 4. The method according to claim 1 to 3, characterized in that that washing is carried out with water at a temperature between 10 and 100 ° C and hereby maintains a volume ratio of ester to water between 6: 1 and 2: 1. 5. The method according to claim 1 to 3, characterized in that one washing with aqueous alkali solutions at a temperature between 20 and 100 ° C and here a volume ratio of ester to alkali solution between 20: 1 and 5 : 1 complies. 6. The method according to claim 1 to 3, characterized in that one when washing with the aqueous solution of a reducing agent, a volume ratio from ester to solution of the reducing agent between 20: 1 and 5: 1 and appropriate maintains a concentration of the reducing agent between 1 and 20 percent by weight. 7. The method according to claim 1 to 6, characterized in that there is used as the hydrogenation catalyst Raney nickel. Contemplated publications: USA. Patent No. 1,425,803;. British Patent No. 744 42l.