GB2341178A

GB2341178A - Process for the separation of dichlorophenol isomers

Info

Publication number: GB2341178A
Application number: GB9918381A
Authority: GB
Inventors: M M Behramkamdin; T Chandiran; P C Joseph; P K Gawas; T S Dakorwala
Original assignee: Gharda Chemicals Ltd
Current assignee: Gharda Chemicals Ltd
Priority date: 1998-09-02
Filing date: 1999-08-05
Publication date: 2000-03-08
Anticipated expiration: 2019-08-05
Also published as: GB2341178B; GB9918381D0

Abstract

This invention discloses a process for the separation of 2,5-dichlorophenol and 2,4-dichlorophenol mixture by a method which involves the treatment of the dichlorophenol mixture with aqueous ammonia solution under specified conditions.

Description

2341178 PROCESS FOR THE SEPARATION OF DICHLOROPH NOL ISOMERS This

invention relates to a new and improved process for the selective recovery of a specific chlorinated dichlorophenol isomer from a mixture of chlorinated dichlorophenol isomers. In particular, this invention relates to a method for the separation of 2,4 dichlorophenol and 2,5-dichlorophenol when both isomers are contained in a mixture by means of a cost effective method.

Both 2,4-dichlorophenol and 2,5-dichlorophenol have a high degree of commercial value as intermediates for the preparation of agrochemicals. The 2,4-dichlorophenol is of particular value as an intermediate in the production of 2,4-D, whilst 2,5-dichlorophenol is useful in the manufacture of 3,6-dichloro-2-methoxybenzoic acid.

Hydrolysis of 1,2,4-trichlorobenzene with caustic in methanol for 3-5 hours at 140-1800C gives as major products a mixture of 80-82%, 2,5-dichlorophenol, 12-15%, 2,4 dichlorophenol and 5%, 3,4-dichlorophenol. The mixture of 2,4-dichlorophenol and 2,5-dichlorophenol can be readily separated from 3,4-dichlorophenol by fractional distillation. The 2,4-dichlorophenol and 2,5 dichlorophenol separation by fractional distillation is difficult due to the close boiling points of these two isomers. The fractional crystallisation of the 2,4 dichlorophenol and 2,5-dichlorophenol gives 2,5 dichlorophenol and a eutectic mixture of the isomers.

Various methods of separation of 2,4-dichlorophenol and 2,5-dichlorophenol are known to the art, for example:

(i) The selective sulfonation of 2,5-dichlorophenol using oleum, followed by separation and desulfonation as in US-A-3412145 (1968), (ii) Preferential extraction of organic solutions with C02- 2- 0 P04 3- 1 & B03 3-, salts of Group I and II metals in a packed column as per Ger. Offen. 2060844 (1969), (iii) Adduct formation with urea, followed by filtration and breaking up of the adduct by boiling with water as in US-A- 3,462,498 (1965), and (iv) Counter-current extraction with Na2C02/NaOH in an apparatus having 5 theoretical stages as in Proc. Int.

Solv. Extn. Conf., 1974, 1, 983-94.

All of these methods are too cumbersome, less economical and too environmentally taxing to be implemented on a commercial scale.

It is therefore an objective of the present invention to provide a method which is cost effective and which generates low effluent volumes during the separation of 2,4dichlorophenol and 2,5-dichlorophenol.

In this method of the present invention the 2,4 dichlorophenol and 2,5-dichlorophenol isomers are separated by utilising a difference in the acidity of, as well as the differential solubility of, the ammonium salts of 2,4 dichlorophenol and 2,5-dichlorophenol in water. The method can be operated in a batch process or, with suitable recycling, as a continuous process.

The mixture of the dichlorophenols - either in the eutectic or any other mixture of 2,5-dichlorophenol and 2,4-dichlorophenol - is first converted into their ammonium salts using aqueous ammonia. The temperature at which the dichlorophenol isomers and the aqueous ammonia are reacted can vary from 20-50"C, the preferred range of temperature being 25-400C. The ammonium salts of the dichlorophenols which are precipitated out by the treatment with aqueous ammonia are enriched with salt of 2,4-dichlorophenol, while the filtrate is enriched with the salt of 2,5 dichlorophenol. The 2,4-dichlorophenol enriched ammonium salt solid can be either repeatedly crystallised from water to obtain pure 2,4-dichlorophenol ammonium salt or else boiled with water to remove the ammonia and recover the dichlorophenol. One can then use fractional crystallisation to obtain 2,4-dichlorophenol of the required purity. From the filtrate ammonia is removed by boiling the solution, and then the dichlorophenol layer is separated. The dichlorophenol obtained is further fractionally crystallised to obtain pure 2,5 dichlorophenol. The residual dichlorophenol mixture left after the fractional crystallisation out of 2,4 dichlorophenol and 2,5-dichlorophenol which will be approaching the eutectic composition can be recycled again for the ammonia treatment step.

The following Examples serve to illustrate the process for the separation of 2,4-dichlorophenol from 2,5 dichlorophenol in accordance with the present invention.

EXAMPLE 1

A liquid dichlorophenol mixture weighing 163 gm and containing 49% 2,4-dichlorophenol and 51% 2,5 dichlorophenol is added to 465 ml of 1.5N NH3 solution over 2 hr. at 40-450C. The reaction mixture was gradually cooled to 300C, seeded with 2,4-dichlorophenol and gradually cooled to 280C, and then filtered to obtain 99 gm of solid containing 90 gm of dichlorophenol. The filtered solid was washed with aqueous ammonia. A sample analysis by HPLC showed a ratio of 72.3: 27.7; 2,4 dichlorophenol to 2,5 dichlorophenol. A sample of the filtrate was acidified and worked-up to recover a dichlorophenol mixture, which on HPLC analysis showed a ratio of 25.6 73.3; 2,4 dichlorophenol to 2,5.dichlorophenol.

EXAMPLE 2

The solid obtained in Example 1 was slurried in 100 ml of water and the slurry was heated to ref lux and ammonia removed. The ammonia liberated was scrubbed and recycled, whilst the residue after ammonia removal was cooled to 400C and a 88 gm dichlorophenol layer separated out; the aqueous layer being recycled back to the process. The separated dichlorophenol layer was then recycled for further ammonia treatment as in Example 1.

The filtrate and its wash liquor of Example 1 were combined and boiled to remove ammonia. The ammonia liberated was scrubbed and recycled, while the residue was subsequently cooled to 400C and a 68 gm dichlorophe nol layer separated out; the aqueous layer being recycled back in the process. The separated dichlorophenol layer was fractionally crystallised to obtain 33 gm of 2,5 dichlorophenol of 98% purity. The eutectic mixture obtained was recycled for ammonia treatment as in Example 1. - EXAMPLE 3

A liquid dichlorophenol mixture weighing 1000 gm and containing 42.5% of 2,4-dichlorophenol, 54.6% of 2,5 dichlorophenol and 0.9% of 3,4-dichlorophenol was added to 2670 ml of 1.6 N NH3 solution over 2 hr. at 40-450C. The reaction mixture was gradually cooled to 300C and seeded with 2,4-dichlorophenol. The seeded reaction mixture was gradually cooled to 280C and then filtered to obtain 710 9m of wet solid containing 627 gm of dichlorophenol. A sample analysis by HPLC showed 53.9% of 2,4-dichlorophenol, 45.1% of 2,5-dichlorophenol and 0.92% of 3,4-dichlorophenol. The combined filtrate and its wash liquor were boiled and the evolved ammonia scrubbed to obtain 320 gm, of dichlorophenol, the analysis of a sample of which showed 27.2% of 2,4-dichlorophenol, 72.1% of 2,5-dichlorophenol and 0.73% of 3,4dichlorophenol.

The 710 gm of solids obtained after filtration were treated again with 725 ml of 1.4 N ammonia solution at 450C for 1 hr and cooled slowly with seeding to 25'C and filtered to recover 345 gm of solids containing 314 gm of dichlorophenol. A sample analysis showed 84.1% of 2,4 dichlorophenol, 15.5% of 2,5-dichlorophenol and 0.37% of 3,4-diqhlorophenol. The filtrate and its wash liquor were combined and ammonia boiled off to leave 258 gm of dichlorophenol, the analysis of a sample of which showed 21.06% of 2,4-dichlorophenol, 78.08% of 2,5-dichlorophenol and 0.85% of 3,4-dichlorophenol.

The 345 gm of solids were added to 350 ml water and heated to 600C, slowly cooled to 280C with seeding, and then centrifuged to obtain 214 gm of solids containing 196 gm of 2,4-dichlorophenol of 97.3% purity. The dichlorophenol obtained from the centrifugate was recycled for ammonia treatment as in Example 1.

Claims

1. A process for the separation of 2,4-dichlorophenol and 2,5-dichlorophenol mixtures of eutectic composition and other compositions, which comprises treating the mixture with aqueous ammonia, in an amount of less than one mole per mole based on the total dichlorophenol mixture, to obtain a 2,4-dichlorophenol enriched ammonium salt solid phase and a 2,5-dichlorophenol enriched ammonium salt liquid phase and then recovering the dichlorophenols, preferably by boiling in water.

2. A process as claimed in claim 1 wherein ammonia and water are recovered and recycled in the process for subsequent use.

3. A process as claimed in claim 1 or claim 2 wherein the 2,4-dichlorophenol rich phase either as its ammonium salt or as the free phenol is recycled for further separation and the 2,5-dichlorophenol rich phase is crystallised to recover pure 2,5-dichlorophenol.

4. A process as claimed in any one of claims 1 to 3 wherein selective crystallisation of the 2,4-dichlorophenol ammonium salt from water is performed to obtain 2,4 dichlorophenol of a purity of at least 97% by weight.

5. A process as claimed in any one of claims 1 to 4 wherein the dichlorophenol mixtures obtained from the filtrate or centrifugate after crystallisation and removal of 2,5-dichlorophenol and 2,4-dichlorophenol are treated again with ammonia for further separation.

6. A process as claimed in claim 1 substantially as hereinbefore described.

7. A process as claimed in claim 1 substantially as hereinbefore described in any one of the specific Examples.

Amendments to the claims have been filed as follows 2 CLAIMS 1. A process for the separation of 2,4-dichlorophenol and 2,5-dichlorophenol from a mixture containing the two dichlorophenols, which comprises treating the mixture with aqueous ammonia, in an amount of less than one mole per mole based on the total dichlorophenol mixture, to obtain 2,4-dichlorophenol enriched ammonium salt solid phase and 2,5-dichlorophenol enriched ammonium salt liquid phase and then recovering the dichlorophenols.

2. A process is claimed in claim 1 wherein the dichlorophenols are recovered by boiling in water.

3. A process as claimed in claim 1 or claim 2 wherein ammonia and water are recovered and recycled in the process for subsequent use. 4. A process as claimed in any one of claims 1 to 3 20 wherein the 2,4- dichlorophenol rich phase either as its ammonium salt or as the free phenol is recycled for further separation and the 2,5-dichlorophenol rich phase is crystallised to recover pure 2,5-dichlorophenol. 25 5. A process as claimed in any one of claims 1 to 4 wherein selective crystallisation of the 2,4-dichlorophenol ammonium salt from water is performed to obtain 2,4dichlorophenol of a purity.of at least 97% by weight. 30 6. A process as claimed in any one of claims 1. to 5 wherein the dichlorophenol mixtures obtained from the filtrate or centrifugate after crystallisation and removal of 2,5-dichlorophenol and 2,4-dichlorophenol are treated again with ammonia for further separation. 35 q 7. A process as claimed in claim 1 substantially as hereinbefore described.

8. A process as claimed in claim 1 substantially as hereinbef ore described in any one of the specific Examples.