DE3714107A1 - Process for eliminating residual hydrogen peroxide from aqueous solutions - Google Patents

Abstract

A process is described for eliminating residual hydrogen peroxide from aqueous solutions, in particular from bleaching baths, the aqueous hydrogen peroxide solution being reacted with at least 0.3 mol of cyanamide per mol of H2O2 in alkaline medium. In this manner, the H2O2 contents are virtually completely degraded without polluting the waste water.

Description

The present invention relates to a method for Removal of residual hydrogen peroxide from aqueous Solutions, in particular from bleaching baths in dyeing processes.

When dyeing cellulose fibers such. B. Cotton and Linen is used to bleach and close the fiber hydrophilize to the color yield and fastness of the Optimal coloring. The bleaching treatment will usually done with hydrogen peroxide.

In conventional dyeing processes, the fiber is usually bleached in an oxidizing manner at temperatures of 80 to 90 ° C. The bleached fiber is then rinsed thoroughly with water to remove the residual oxidizing agent. The removal of the H ₂ O ₂ is necessary because in many reactive dyes the fixation of the dye on the fiber in an oxidizing medium is adversely affected. The fiber treated in this way can then be dyed with reactive dyes.

From DE-OS 32 31 608 it is known that by adding of thio compounds such as e.g. B. thiosulfate, Thioglycolic acid, thiourea and its derivatives as well Thiocyanate etc. in the bleaching bath the rest still in the bleach removed remaining hydrogen peroxide can be.

The removal of the remaining H ₂ O ₂ has the advantage that the rinsing process can be saved. In this way, a considerable reduction in costs can be achieved by saving water, energy and the time required for flushing or emptying.

The disadvantage of the proposed method is Risk of additional wastewater pollution insufficient degradation of the thio compounds used (e.g. thioureas), which causes difficulties in Discharge into sewage treatment plants.

The present invention was therefore based on the object a process for removing residual hydrogen peroxide from aqueous solutions, especially from bleaching baths develop, which the disadvantages of the state the technology does not have, but a quick and effective removal of excess Hydrogen peroxide allows without wastewater to charge.

This object was achieved according to the invention by reacting the aqueous hydrogen peroxide solution with at least 0.3 mol of cyanamide per mol of H ₂ O ₂ in an alkaline medium.

Surprisingly, it has been shown that one using the method according to the invention Can remove hydrogen peroxide almost completely.

According to the present invention, the aqueous hydrogen peroxide solution is reacted with cyanamide, at least 0.3 mol of cyanamide per mole of H ₂ O _{2 being} required for complete removal of the H ₂ O ₂ .

The molar ratio of cyanamide is preferred: To view hydrogen peroxide from 1: 3 to 4: 1. It is of course also possible to have a larger excess Use cyanamide, but this is pure not recommended for economic reasons. Otherwise does not interfere with any excess cyanamide, because it is under the reaction conditions of the invention is broken down to urea and as such neither the Coloring negatively affects wastewater problems.

The cyanamide can be used both as a solid and in the form an aqueous solution, for example with solid concentrations from 10 to 60% by weight can be used.

In the context of the present invention, it is also possible instead of the cyanamide, its water-soluble salts such as e.g. B. use sodium hydrogen cyanamide.

The reaction of the cyanamide with hydrogen peroxide should in an alkaline medium, preferably between pH 9 and pH 14. Has been particularly advantageous a pH range of 10.5 to 12.5 was found. The The optimal pH range can be set using the usual basic substances.

The reaction temperature should be between 20 and 100 ° C, preferably between 70 and 90 ° C to a quick To allow removal of the hydrogen peroxide.

The addition of the cyanamide to the bleach baths during the The dyeing process expediently takes place after completion the bleaching process and before adding the dyes, the use of cyanamide not only on pure natural or artificial cellulose fibers is limited, but also in blends with synthetic fibers can be applied.  

By adding the cyanamide, the hydrogen peroxide content of the aqueous solution is virtually completely reduced after a few minutes, so that only small amounts of H ₂ O _{2 can} be detected using the customary test methods.

In this way it is possible to pre-rinse to do without the coloring without it subsequent dyeing process leads to a loss of quality. Another advantage of the method according to the invention is the low wastewater pollution caused by the Degradation of the excess cyanamide to urea is accomplished.

The following examples are intended to explain the invention in more detail without, however, restricting it thereto.

example 1

A bleaching bath with the following composition

5 g / l hydrogen peroxide (30%) 1.3 g / l sodium hydroxide (100%) 2 g / l sodium silicate 1 g / line of alkali salt-EDTA complex 1 g / l of a surfactant Ethoxylate base

was heated to 90 ° C and then with stirring 44 g of 50% cyanamide solution are added.

After a reaction time of approx. 10 minutes, was on H₂O₂ checked. The usual test methods showed that the H₂O₂ content was <30 ppm.

Example 2

With a fleet ratio of 1:10 you treat unbleached cotton initially in a corresponding Bleaching bath described in Example 1 for 1 hour at 90 ° C.

After the bleaching process is complete, the bathroom is emptied and rinse the material thoroughly with cold water.

Now dye the cotton in at 70 ° C for 1 hour a dye bath with the composition:

100 g / l sodium chloride 20 g / l sodium carbonate 3 g / l reactive dye labeled Reactive Blue 5 (Cl 61210)

with a fleet ratio of 1:10.  

After dyeing, the material is rinsed and washed with soap washed.

The color obtained is bright and medium Intensity.

Example 3

The bleaching process is repeated as in Example 2 however, after the bleaching process is complete, without the bath to empty, add the components of the dye bath and colors at 70 ° C for one hour.

The blue color obtained is less intense and shows a slight gray tinge.

Example 4

After bleaching the cotton according to Example 2, one gives at 90 ° C 2 g of 50% cyanamide solution and cools 70 ° C.

At this temperature, the dyeing process according to Example 2 carried out.

A coloration is obtained which is identical to that in Example 2 is achieved.

If you take 4 g instead of 2 g cyanamide solution, then so too no discernible difference in color, d. H. Excess cyanamide does not affect the color negative.  

Example 5

If you take Reactive Blue 5 instead of the blue dye a red one, namely Reactive Red 4 (Cl 18 105) and works according to Examples 2 to 4, it is the same Behavior related to hue and intensity too watch like Reactive Blue.

Claims (5)

1. A method for removing residual hydrogen peroxide from aqueous solutions, in particular from bleaching baths, characterized in that the aqueous hydrogen peroxide solution is reacted with at least 0.3 mol of cyanamide per mol of H ₂ O ₂ in an alkaline medium. 2. The method according to claim 1, characterized in that that the molar ratio of cyanamide: hydrogen peroxide 1: 3 to 4: 1. 3. The method according to claims 1 and 2, characterized characterized in that instead of the cyanamide whose water-soluble salts are used. 4. The method according to claims 1 to 3, characterized characterized in that the implementation at a pH from 9 to 14, preferably 10.5 to 12.5, makes. 5. The method according to claims 1 to 4, characterized characterized in that the reaction temperature 20 to 100 ° C, preferably 70 to 90 ° C, is.