Process for the removal of inorganic salts

Details Process for the removal of inorganic salts Process for the removal of inorganic salts

1994-10-17

1996-01-16

Fortuna, Ana M.

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210651, 210641, 210644, 210654, B01D 6100

Patent

active

054845319

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for the removal of inorganic salts from aqueous solutions of organic salts or acids capable of micelle formation and, more particularly, to a process for the production of low-salt or salt-free solutions of anionic, cationic or amphoteric surfactants.


BACKGROUND OF THE INVENTION

Inorganic salts, such as sodium chloride or sodium sulfate or the like, can be formed as secondary products in the production of anionic, cationic or amphoteric surfactants and also nonionic surfactants. These inorganic salts can be troublesome in certain special applications, for example when any corrosion-promoting potential of the surfactant solution is to be strictly avoided or when salts influence the viscosity of the surfactant solution.
However, the removal of inorganic salts from organic acids or salts is difficult. For laboratory-scale and pilot-plant quantities, processes based on column chromatography may be applied or organic solvents may be used for precipitation. However, both processes are extremely complicated and do not always produce the required result.
Now, the problem addressed by the present invention was to provide an industrially workable process which would enable solutions of organic salts or acids capable of micelle formation to be freed from inorganic salts and also from other impurities incapable of micelle formation. In solving this problem, the invention makes use of the knowledge that, both in the ultrafiltration and in the reverse osmosis of solutions containing inorganic salts and organic salts or acids of the type mentioned, the inorganic salts pass over into the permeate while the organic salts or acids capable of micelle formation remain in the retentate. This is surprising insofar as the molecular weight of the organic salts or acids capable of micelle formation is lower than the cutoff molecular weight of the corresponding membranes, so that the expert had to assume that separation would not be possible in this case.
The surprising separation effect cannot be scientifically explained. However, it is assumed that secondary membrane formation and/or micelle formation are jointly responsible.


BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a process for the removal of inorganic salts from aqueous solutions of organic salts or acids capable of micelle formation, characterized in that the aqueous solutions are subjected to ultrafiltration or reverse osmosis and the organic salt or acids are recovered from the retentate.
In its broadest embodiment, the process according to the invention may be applied to surfactant solutions in which the surfactant concentration exceeds the critical micelle concentration, i.e. to surfactant solutions with a surfactant solids content of at least 1% by weight, preferably at least 10% by weight and more preferably at least 20% by weight. The upper limit to the surfactant solids content will be selected by the expert in such a way as to preclude any viscosity-related problems with the process. It may be at 40% by weight, 50% by weight and, in individual cases, at 60% by weight or 80% by weight. In a particularly preferred embodiment, solutions with a solids content of 10 to 50% by weight and, more particularly, 20 to 40% by weight are treated.
The process according to the invention is suitable for the substantial removal of salts from surfactant solutions. In addition, however, it may even be desirable instead of completely removing the salts merely to establish a defined residual salt content which is below the salt content of the starting product. Residual salt contents such as these are of interest when, in their subsequent use, the surfactant solutions are to be thickened by electrolytes and when products with a defined residual salt content are required to ensure the formulation remains consistent.


DETAILED DESCRIPTION OF THE INVENTION

The process according to the invention is suitable for organic salts or acids capable of micelle formation, i.e. anionic surfactants, c

REFERENCES:
patent: 4161447 (1979-07-01), Kosima
patent: 4436523 (1984-03-01), Hugelshofer et al.
patent: 4639319 (1987-01-01), Schellenberg et al.
patent: 5176834 (1993-01-01), Christian et al.
Rompp-Chemie-Lexikon, 9 edition, 1991 vol. 4, pp. 2769-2770.
Chem.-Ing. Tech. 57 (1985) Nr. 7, pp. 581-596.

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