GB2207149A

GB2207149A - Improving solubility by electrodialysis

Info

Publication number: GB2207149A
Application number: GB08814638A
Authority: GB
Inventors: W A Fern; D E Sadler; G W Scott
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1987-07-21
Filing date: 1988-06-20
Publication date: 1989-01-25
Also published as: GB8814638D0; GB8717234D0

Abstract

A process for improving the solubility of a salt of an organic ionic dye or fluorescent brightening agent (FBA) with a first counter-ion, by exchanging the first counter-ion for a second counter-ion giving a salt of the dye FBA with improved solubility which comprises submitting a first aqueous solution or slurry of the salt of the dye or FBA with the first counter-ion to ion-exchange electrodialysis in conjunction with a second aqueous solution of a salt of the second counter-ion whereby at least a proportion of the first counter-ion in the first solution is replaced by the second counter-ion. The process may be conducted in electrodialysis cell 8 which has a dye compartment 10, replacement ion compartment 12, waste solution compartment 14, and two electrode compartments 16 and 18. The compartments are defined by cation permeable membranes 20, 22, 24 anion permeable membrane 26 and the walls of the cell. The process is especially useful for improving the solubility of anionic dyes, which are generally produced on a commercial scale in the form of their sodium salts, by at least partial replacement of the sodium ions by lithium or quaternary nitrogen (i.e. ammonium or substituted ammonium) ions. Improved solubility allows the preparation of higher strength liquid forms of the dyes. <IMAGE>

Description

Ion Exchange Process This specification describes an invention relating to a process for exchanging an ion of an aqueous solution of a water-soluble salt, especially the counter-ion in an aqueous solution of a salt of an ionic dye with an different counter-ion.

According to the present invention there is provided a process for improving the solubility of a salt of an organic ionic dye with a first counter-ion by exchanging the first counter-ion for a second counter-ion giving a salt of the dye with improved solubility which comprises submitting a first aqueous solution or slurry of the salt of the dye with the first counter-ion to ion-exchange electrodialysis in conjunction with a second aqueous solution of a salt of the second counter-ion whereby at least a proportion of the first counter-ion in the first solution is replaced by the second counter-ion.

The process is particularly useful for improving the solubility of water-soluble dyes in water and water-miscible solvents such as glycols and glycol ethers and esters.

The term dye includes fluorescent brightening agent (FBA) and examples of ionic dyes are anionic dyes such as direct dyes, acid dyes, cellulose reactive dyes, especially chlorotriazinyl reactive dyes, and stilbene FBAs and cationic dyes such as quaternary ammonium and phosphonium dyes. The ionic dye is preferably an anionic dye, and more especially a cellulose reactive dye or a direct dye carrying one or more, especially from 1 to 6, sulphonic acid groups.

In the case of anionic dyes the first counterion is preferably inorganic, especially an alkali metal such sodium or potassium or an alkaline earth metal, such as calcium. The second counter-ion is preferably a quaternary nitrogen ion or lithium ion and the second solution preferably comprises a salt of the quaternary nitrogen ion or lithium ion with an inorganic anion, such as chloride.The term quaternary nitrogen includes ammonium and substituted ammonium (NR+4) in which each R independently represents H or a short chain aliphatic group, especially C1 4-alkyl or C1#4-hydroxyalkyl. Examples of preferred second counterions are lithium, ammonium, and tetra(hydroxyethyl)- ammonium In the case of the replacement of a counter-ion of a salt of an anionic dye, the ion-exchange electrodialysis is conveniently performed in an electrodialysis cell. The cell conveniently comprises a stack of one or more dialysis units situated between anode and cathode compartments.Each dialysis unit comprises, in sequence, a dye compartment between two cation permeable membranes, a replacement ion compartment between a cation-permeable and an anion-permeable membrane and a waste compartment between an anion-permeable and a cation-permeable membrane. The cathode compartment is adjacent the dye compartment of the first unit in the cell and the anode compartment is adjacent the waste compartment of the last unit in the cell.

In operation, (i) the dye solution or slurry, either desalinated or containing electrolyte, is circulated through the dye compartment(s) (ii) the second solution, whose concentration is set at above that required for efficient passage of current and below that leading to significant transfer of the salt into the dye solution by osmosis, is circulated through the replacement ion compartment(s) and (iii) suitable electrolyte, e.g. dilute sodium sulphate, solutions are circulated through the waste compartment(s) and through the anode and cathode compartments.

On passing an electric current transversely across the compartments and membranes, the cations in the dye and replacement ion compartments are transferred through the cation permeable membranes towards the cathode and the anion of the second solution is transferred through the anion permeable membrane towards the anode.

In this way the first counter-ion in the first solution is progressively replaced by the second counter-ion from the second solution, thus rendering the dye more soluble, especially in water and water-miscible solvents. The unwanted first counter-ion and any electrolysis products formed at the electrodes are removed in the solutions passing through the waste and electrode compartments.

The process is especially suitable for the conversion of a sodium or potassium salt of an anionic dye into the lithium salt because it has been surprisingly found that cation-permeable membranes allow sodium and potassium ions to pass more rapidly than lithium ions and thus the lithium ions which are transferred into the dye compartment are less easily transferred onwards into the cathode compartment than the sodium or potassium ions originally present in the dye compartment.

In the case of a cat ionic dye the nature of the membranes and electrodes is reversed and the inorganic anion from the second solution is transferred into the dye compartment to replace the inorganic counter-ion of the original dye salt which is transferred into the anode compartment.

While the process is operable in a dialysis cell containing a single dialysis unit the cell preferably contains a plurality of such units particularly for industrial scale operation to provide efficient transfer of the counter ions.

Suitable materials for construction of the cation-permeable part of the cation-permeable membranes contain a negatively charged group such as sulponate, phosphonate or carboxylate, attached by a covalent bond to a base polymer, such as polystyrene, a perfluorinated polymer or a surface grafted co-polymer.

Suitable materials for construction of the anion-permeable part of the anion-permeable membrane contain a positively charged group, such as quaternary ammonium, attached by a covalent bond to a base polymer, such as polystyrene or a perfluorinated polymer.

The invention is further illustrated, with reference to the accompanying drawing, by the following examples in which all parts and percentages are by weight unless otherwise indicated.

General Procedure An electrodialysis cell (8), shown in the Figure, comprises a dye compartment (10), a replacement ion compartment (12) and a waste solution compartment (14) and two electrode compartments (16, 18) defined by three cation permeable membranes (20, 22, 24), and an anion permeable membrane (26), (NEOSEPTA CL-25T and NEOSEPTA AV-4T respectively, both from Tokuyama Soda) and the walls of the cell.

The cathode and anode compartments (16, 18) contain the cathode (28) and anode (30) respectively. Entry and exit ports (l0a, 10b, 12a, 12b, 14a, 14b, 16a, 16b, 18a, and 18b) are provided for circulation of liquids through the dye (10), replacement ion (12), waste (14), cathode (16) and anode (18) compartments respectively The area of each membrane is 70 cm .

In operation a desalinated solution or slurry of an anionic dye (as Na salt) was circulated through the dye compartment (10), a 5M aqueous solution of lithium chloride was circulated through the replacement ion compartment (12), a first 0.5M aqueous Na2SO4 solution was circulated through the waste compartment (14) and a second 0.5M aqueous Na SO, solution was circulated through the electrode compartments (16, 18).

Transfer of ions was induced by the application of an electric potential of 5v across the electrodes (28, 30). Progress of the ion exchange was monitored by sampling of the streams and determination of the concentration of sodium and lithium ions in the dye solution.

Example 1 An aqueous solution of Dye 1 containing 20.01% pure dye was circulated through the electrodialysis unit described in the General Procedure above. After 16 hours 96% of the sodium ions had been replaced by lithium ions and the solubility of the dye in water increased from 188 g/litre to 256 gilitre at 25 C.

Example 2 An aqueous solution of Dye 2 containing 12.81% pure dye was circulated through the elctrodialysis unit described in the General Procedure above. After 13.5 hours, 91.6% of the sodium ions had been replaced by lithium ions and the solubility of the dye in water increased from 233.7 gilitre to 331.6 gllitre at 25cm.

Example 3 An aqueous solution of Dye 3 containing 14.35% pure dye was circulated through the elctrodialysis unit described in the General Procedure above. After 12.5 hours 89% of the sodium ions had been replaced by lithium ions and the solubility of the dye in water increased significantly.

Dye 1 is 1-hydroxy-2-(2-sulphophenylazo)-8-(4-chloro-6- [ 2-methyl phenylamino ] -triazin-2-ylamino)-naphthalene-3,6-disulphonic acid.

Dye 2 is 2-chloro-4- (3-sulpho-4 [ 4-chloro-6-aminotriazin-2-yl- amino ] phenylamino)-6- (2, 4-disulpho-5- [ 1-ethyl-3-amido- 4-methyl-6-hydroxypyrid-2-on-5-ylazo ] phenylamino) triazine.

Dye 3 is 1-hydroxy-2-(2-sulphophenylazo)-8-(4-chloro-6- [ 2-carboxy 4-sulphophenylamino ] -triazin-2-ylamino)-naphthalene 3,6-disulphonic acid.

Claims

1. A process for improving the solubility of a salt of an organic ionic dye with a first counter-ion, by exchanging the first counter-ion for a second counter-ion giving a salt of the dye with improved solubility which comprises submitting a first aqueous solution or slurry of the salt of the dye with the first counter-ion to ion-exchange electrodialysis in conjunction with a second aqueous solution of a salt of the second counter-ion whereby at least a proportion of the first counter-ion in the first solution is replaced by the second counter-ion.

2. A process according to Claim 1 wherein the ionic dye is an anionic dye carrying from 1 to 6 sulphonic acid groups.

3. A process according to Claim 2 wherein the anionic dye is a cellulose reactive dye or a direct dye.

4. A process according to any one of Claims 1 to 3 in which the second counter-ion is lithium ion or a quaternary nitrogen ion.