Preparation of stable anionic dyestuff solutions: pressure permeation of crude dye in solution of lithium or ammonium salt

DETAILED DESCRIPTION We claim: 1.
Process for the preparation of stable aqueous solutions of anionic dyestuffs by pressure permeation of feed solutions of the crude dyestuffs, characterized in that the feed solution for the pressure permeation is prepared by stirring an optionally dried presscake of the crude dyestuff or a suspension of the crude dyestuff into an electrolyte solution containing 0.
1 to 20% by weight of lithium salts or ammonium salts of organic or inorganic acids.
2.
Process according to claim 1, characterized in that lithium salts and trialkylammonium salts of the formula ##STR9## K=0 to 2 L=0 to 3 M=0 to 3 K+L+M=3 n=1 to 4 of nitric acid, carbonic acid and citric acid are used.
3.
The process according to claim 1, wherein the anionic dyestuff is a reactive dyestuff.
4.
The process according to claim 1, wherein the anionic dyestuff is an anionic fluorescent whitening agent.
5.
The process according to claim 1, wherein the feed solution for the pressure permeation is prepared by stirring the optionally dried presscake of the crude dyestuff or the suspension of the crude dyestuff into an electrolyte solution containing 0.
5 to 5% by weight of lithium salts or ammonium salts or organic or inorganic acids.
6.
The process according to claim 1, wherein the crude dyestuff is dissolved in the electrolyte solution in a higher concentration than would be possible to dissolve the crude dyestuff in water.




Description:
The present invention relates to a process for the preparation of highly concentrated aqueous solutions of anionic dyestuffs, in particular reactive dyestuffs.
To obtain stable concentrated aqueous solutions of dyestuffs and fluorescent whitening agents, it is often necessary to greatly diminish the salt content, such as obtained after synthesis and isolation.
In industry, this is predominantly done by pressure permeation, in which salt-containing permeate is discharged through a semipermeable membrane and replaced by deionized water.
In many cases, this is followed by a concentration step, in which only permeate is discharged but no water is added