GB2179337A

GB2179337A - Process for purifying waste-waters

Info

Publication number: GB2179337A
Application number: GB08616244A
Authority: GB
Inventors: Rudolf Blattner; Wolfgang Petri
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1985-07-05
Filing date: 1986-07-03
Publication date: 1987-03-04
Also published as: GB8616244D0; CH663781A5; DE3622225A1

Abstract

The invention relates to the purification of waste-waters containing aromatic and/or aliphatic sulfonic acids by acid extraction with water-insoluble amines and subsequent extraction of the extracted organic phase which contains the sulfonic acids with an aqueous alkaline solution, in the temperature range from 30 DEG C to the boiling point of the aqueous phase, preferably from 50 DEG to 90 DEG C and, most preferably, from 60 DEG to 80 DEG C, and, after separation from the organic phase, either removing the resultant highly concentrated aqueous solution of sulfonic acids as obtained for suitable disposal, or separating the sulfonic acid salts in the form of the moist solid by crystallisation from the cooled solution, and recycling the aqueous re-extraction solution. The organic phase can be used once more for the extraction of the organic sulfonic acids.

Description

SPECIFICATION Process for purifying waste-waters The present invention relates to a processforthe purification of waste-waters polluted with aromatic and/or aliphatic sulfonic acids.

The July 1962 issue of "Chemie-lngenieur Technik" contains on pages 461-466 a reportof a lecture given by R. Kernin and A. Winger on the tech nologyofliquid ion exchangers atthe 87th Dechema Colloquium held on 27th October, 1961 in Frankfurt.

In this report it is said that amines or alkylphosphonic acids with a molecularweight of about 250 to 500 are suitable ion exchangers for, inter alia, waste-water treatment. Preferred am ines for treating wastewaters contaminated with sulfonic acid are waterinsoluble amines such as secondary and, most pre ferably,tertiaryamines,including in particular mix- turesoftrialkylaminesand mixtures of Csal kyls. The cited amines are commercially available anion exchangers, for example those known to the skilled person under the registered trademarks Amberlite~, Armeens or Hostarex~. The liquid ion exchanger method is comparable to the known solvent extraction.To the waste-water polluted with aromatic andi or aliphatic sulfonic acids is added - depending on the basicity ofthe amine employed - the amount of acid required for a complete extraction into the organic phase byformation of a pair of ions.

When equilibrium has been established, the pH of the treated aqueous phase should be > 3.

The aqueous phase is separated and the organic phase containing the extracted sulfonic acids is worked up by treating itwith an a"ueous alkaline solution.

This re-extraction in turn affords an organic phase which contains the regenerated water-insoluble amine and an aqueous phase containing the aromatic or aliphatic sulfonic acid salts.

The object is to perform the re-extraction such that a substantially concentrated aqueous solution ofthe sulfonic acids is obtained.

In obtaining this concentrated solution, a limitation is imposed by the fact that the sulfonic acid salts must be soluble in the indicated amount of water, otherwise precipitations that complicate the phase separation, or even make it impossible to effect, will result. It is therefore only possible to achieve a concentration uptothesaturation point in the aqueous medium of the sulfonic acid salts which it is desired to separate.

This shortcoming is overcome by the inventive feature of carrying out the re-extraction at elevated temperature in the rangefrom 30 Ctothe boiling pointof aqueous salt-containing phase. By this means it is possible to increase the concentration factor appreciably compared with performing the re-extraction at normal temperature. The highertemperatures furth- ermore effect a rapid, smooth phase separation owing to the reduced viscosity of the organic phase. The concentrated aqueous phase normally contains more than90%oftheorganicsulfonicacidsfromtheorigin- al mother liquor.Supersaturation causes the sulfonic acid salts to precipitate from the cooled, concentrated aqueous phase, and the precipitated salts are then removed by mechanical means (e.g. byfiltration). It is thereby possible to achieve a degree of concentration sufficient to obtain a moist solid. The cooled aqueous phase freed from the precipitated sulfonic acids can again be used for re-extraction. The concentrated solution, or the separated moist solid containing the sulfonic acid salts, is then conveyed to a suitable waste disposal facility, e.g. for incineration.

Accordingly, the present invention relates to a process for purifying waste-waters containing aromatic and/or aliphatic sulfonic acids by acid extraction with water-insoluble amines and subsequent reextraction from the sulfonic acid containing organic phase with an aqueous alkaline solution, which process comprises extracting the extracted organic phase, in the temperature range from 30"C to the boiling point of the aqueous phase, with an aqueous alkaline solution to give, as aqueous phase, a highly concentrated, substantially sa It-free, neutral orweakly alkaline solution and/or suspension of the sulfonic acids, which are separated from the organic phase for appropriate disposal.

Suitable aqueous alkaline solutions fortreating the organic phase may be solutions ofalkalines oralka line earths, for example of sodium, potassium, cal- cium or magnesium hydroxides, or aqueous ammonia solutions.

The concentration ofthe aqueous alkaline solution before the treatment of the extracted amine phase is conveniently so adjusted that the pH of the aqueous alkaline solution and/or suspension of the sulfonic acids afterthetreatment is inthe ra ng e from 7 to 8.

It is preferred to treat the extracted organic phase with an aqueous alkali, in particularwith aqueous sodium hydroxide. The preferred temperature range for the treatment is from 50' to 90"C, with the most preferred range being from 60' to 80 C. The treatment can also be carried outunderexcess pressure, where- bythe limits of the process, which are determined by the boiling pointofthemostreadilyvolatilecompo- nent, are expanded.Especially when using a mixture of an amine and a low boiling hydrocarbon (e.g. cyclohexane, mixture of Cs-Cghydrocarbons and the like) for performing the extraction, technical problems may arise during the re-extraction at elevated temperature if the boiling point of the azeotrope that formsisclosetoorbelowthetemperatureforthe re-extraction. In this case it is best to effect treatment under excess pressure. The separation ofthe aqueous alkaline solution and/or suspension ofthe sulfonic acids from the organic phase can be effected by precipitation or centrifugation.

After the separation of the organic phase, the aqueous alkaline solution and/or suspension ofthe sulfonic acids can be crystallised by cooling. A filter aid can also be added to the aqueous phase, for example sawdust or other cellulose derivatives, active charcoal, ground charcoal, silica gel ordiatomaceous earth. Combustible filter aids are preferred.Whereas the organic phase of the water-insoluble amines freed from aromatic and/or aliphatic sulfonic acids can be recycled, i.e. re-used for extracting wastewaters polluted with sulfonic acids, the separated aqueous phase is disposed of by e.g. filtering offthe precipitated salts or solids from the cooled aqueous solution and/or suspension of the sulfonic acids and conveying them to a suitable waste disposal facility or by incinerating them, and recycling the decontaminated aqueous phase. For incineration purposes it is advantageous to add a combustiblefilter aid to the aqueous phase.

Thefollowing Examplesfurtherillustratethepresent invention.

Example 1: a) Extraction into the organic phase 10 t of mother liquor resulting from the preparation of dinitrostilbenedisulfonic acid are adjusted with sulfuric acid to pH s0.5. With efficient stirring, kg of tri-n-octylamine are run in at room temperature.

After both phases have been thoroughly mixed for 10 minutes, stirring is discontinued and the phases are allowed to separate.

Upper phase: dark brown-black (= organic phase) Lower phase: pale yellow (= aqueous phase).

b) Re-extraction and concentration After separation ofthe aqueous phase, the organic phase is thoroughly mixed with 400 ml of dilute sodium hydroxide solution at 70'C (duration: about 10 minutes). The concentration of the sodium hydroxide solution is chosen such that the pH of the concentrate is 7-8 (almost complete extraction of the aromatic sulfonic acid from the extracted organic phase).

After discontinuing stirring, the mixture separates once more at70"C into 2 phases, the lower aqueous phase containing over 95% of the organic sulfonic acids from the original mother liquor (concentration ratio: c. 1:20).

The organic phase is used once more for extracting the waste-water.

Without a rise in temperature (e.g. 25'C), this concentration step results in the formation of precipitates which no longer permit a smooth phase separation as well as in an incomplete re-extraction. At room temperature, it is only possible to achieve a concentration ratioofupto 1 to5.

Example 2: The re-extraction is carried out as described in Example 1 b, but with 600 ml of dilute sodium hydroxide solution at 50 C. Concentration ratio: c. 1:15.

Example 3: Extraction is carried out as described in Example 1a, but with the addition of 600 g oftoluene to the amine phase. Re-extraction is carried out as in Example 1 b, but with 330 ml of dilute sodium hydroxidesolution at80'C. Concentration ratio: c.1 :25.

Example 4: Re-extraction is carried out as described in Example 3, exceptthat, after separation of the aqueous phase, this latter is cooled to < 30 C after the temperature has reached 70 C, whereupon some of the aromatic sulfonic acids precipitate and are isolated by filtration (or centrifugation). The mother liquor is bulked with NaOH (50 %) and water and subsequently used once more for carrying out reextraction at elevated temperature (e.g. 70"C).

Example 5: Re-extraction is carried out as described in Example 1 b. After separation ofthe organic phase at70'C, about 5 g ofsawdustare added as filter aid to the aqueous phase, which is then cooled to < 30 C.

The solids are isolated by filtration and the aqueous mother liquor is filtered back for re-extraction as in Example 4.

Example 6: Extraction into the organic phase is car ried out as described in Example 1 a, except that a mixture of 2000 g oftri-n-octylamine and 600 g of toluene are used. Advantages over Example 1: better mixing and accelerated phase separation.

In principle, the re-extraction can also be carried out by the counter-current method of extraction.

However, this is not necessary in the present instance owing to the high distribution coefficient ( > 100) of the sulfonic acid at pH > 7.

Claims

1. A process for purifying waste-waters containing aromatic and/or aliphatic sulfonic acids by acid extraction with water-insoluble amines and subsequent re-extraction from the sulfonic acid containing organic phase with an aqueous alkaline solution, which process comprises extracting the extracted organic phase in the temperature range from 30 Cto the boiling point of the aqueous phasewith an an aqueous alkaline solution to give, as aqueous phase, a highly concentrated, substantially salt-free, neutral or weakly alkaline solution and/or suspension ofthe sulfonic acids, which are separated from the organic phase for appropriate disposal.

2. A process according to claim 1, wherein the sulfonic acid containing organic phase is treated with an aqueous alkali.

3. A process acording to claim 2, wherein the sulfonic acid containing organic phase is treated with aqueous sodium hydroxide.

4. A process according to claim 1, wherein the sulfonic acid containing organic phase is treated in the temperature rangefrom 50 to90 C.

5. A process according to claim 4, wherein the sulfonic acid containing organic phase is treated in the temperature range from 60' to 90 C.

6. A process according to claim 1, wherein the sulfonic acid containing organic phase is treated under elevated pressure.

7. A process according to claim 1, wherein the concentration of the aqueous alkaline solution is adjusted such that the pH of the aqueous alkaline extract ofthe sulfonic acids after treatment is in the range from7to8.

8. Aprocessaccordingtoclaim 1,whereinthe aqueous alkaline solution and/or suspension ofthe sulfonic acids is allowed to crystallise by cooling after separation from the organic phase, and the aqueous solution freed from sulfonic acids is recycled to the extraction ofthe amine phase.

9. A process according to claim 1, wherein a filter aid is added to the aqueous alkaline solution and/or suspension of the sulfonic acids after separation from the organic phase.

10. A process according to claim 1, wherein the separation ofthe aqueous alkaline solution and/or suspension of the sulfonic acids from the organic phase is effected by centrifugation.

11. A process according to claim 1,whereina secondary ortertiary aliphatic amine of 20 to 30 carbon atoms is used for the extraction with a waterinsoluble amine.

12. A process according to claim 11 ,wherein a triisoctylamine is used for the extraction.

13. Aprocess according to claim 1 substantially as described with reference to any of the Examples.