CH664371A5 - METHOD FOR PRODUCING MOST SALT-FREE AQUEOUS SOLUTIONS OF IONIC DYES. - Google Patents

Description

DESCRIPTION

The preparation of stable aqueous solutions of anionic dyes which contain little or practically no foreign salts has been described in the literature, in particular in many patents. A distinction can be made between methods which prevent the formation of foreign salts from the outset or those in which the salts formed are subsequently removed.

Diazotization with nitric acid esters (DAS 21 44 420) or intermediate isolation of diazonium salts (US 41 18 182, DOS 29 49 517) enable e.g. a direct synthesis of dye solutions free of inert salts. Subsequent removal of inert salts is possible, for example, by precipitation and isolation of the color acid and its dissolution with bases such as lithium hydroxide or alkanolamines, if only in a few cases. Other desalination methods are salt precipitation using solvents (DOS 31 23 236), phase separation processes (US 37 19 703, DOS 30 45 377), Donnan dialysis (EP 97 125), reverse osmosis (DAS 22 04 725, DOS 33 01 870 , DOS 31 48 878, EP 88 727, EP 59 782) or electrodialysis (JP-OS 55 923, 1973).

Electrodialysis (ED) is a suitable method to separate inorganic salts from aqueous solutions. It is also used to desalt organic chemicals such as water-soluble carboxylic acids, amino acids, polymers, pharmaceuticals or organic waste solutions [overview: A. Weissberger, B.W. Rossiter ed., Physical Methods of Chemistry, Part II B / Electrochemical Methods, in Techniques of Chemistry Vol. I, Part II B, 393 ff., Wiley-Inter-science, New York (1971)].

However, electrodialysis is usually not suitable, completely selectively different ions, e.g. separate organic (valuable product) from inorganic ions. From case to case, special measures must be taken (e.g. pH adjustment) to achieve the desired separation. Naturally, the separation of ions of very different molecular weights works best, whereas the separation of small ions such as H®, Li®, Na®, R® or Cl®, N03, SO40 from only slightly larger organic ions (MG - 300) Problems, but is also possible. However, in the case of dye ions in particular, disturbances often occur because the dyes interact strongly with the membranes. Such disorders have been studied in detail in methyl orange and Congo red (E. Korngold, Proceedings of the Fifth Int. Symp. On Fresh Water from the Sea, Vol. 3, 33; A. Delyannis, E. Delyannis ed., Athens 1976). The work shows that the interaction of ionic dyes with different membranes is not only a change in permselectivity and membrane tension, but that water splitting occurs.

"Water splitting" in electrodialysis means (unlike in electrolysis) dissociation of H2O in H® and OH® in the membranes. This feared effect leads to extreme pH shifts not only on the surface of the membranes, but also between the individual chambers of an ED cell; this can trigger subsequent reactions, such as the formation and precipitation of metal hydroxides or even the destruction of the (anion) exchange membrane.

Korngold was able to show that these effects occur in very low concentrations (1500 ppm); Apparently, larger dye molecules have less effect than smaller ones. Smaller, i.e. Low molecular weight ionic (substances) can be found in almost all dye solutions that come from manufacturing. Water splitting also occurs when the concentration of inorganic electrolytes is too low.

Japanese Laid-Open Application 55 923/1973 (AS 79/12 937) describes that water-soluble direct dyes of the azo series and water-soluble fluorescent dyes can be freed from inorganic salts by electrodialysis; the above-mentioned difficulties are also observed there and avoided by carrying out the electrodialysis at 40 to 50 ° C. and adding a solubilizer to the solution.

Both measures have disadvantages, because an ED cell should generally not be continuously subjected to a thermal load of 40 to 50 ° C, since the service life of the membranes already decreases significantly at these temperatures. A temperature of 40 to 50 ° is also prohibitive for thermally sensitive products. The addition of large amounts of solubilizer (in the application, on average, more solubilizer than pure dye is used, is expensive, pollutes the environment and, in higher concentrations, also drastically reduces the lifespan of the membranes. In addition, the removal of the solubilizer after electrodialysis is very expensive The procedure described cannot be used for reactive dyes because of their sensitivity.

It has now surprisingly been found that largely salt-free aqueous solutions of ionic dyes can be prepared by electrodialysis if the flow rate of the diluate is chosen to be lower than that of the concentrate.

It should be noted that the preliminary literature describes precisely the reverse distribution of the flow velocity; Despite the sparse information in JA-OS 55 923/1973 about the implementation of electrodialysis, it is stated that the liter capacity in the diluate cells is 50% higher than in the concentrate cells. H. Strathmann's work (separation of molecular mixtures with the aid of synthetic membranes, Steinkopf, Darmstadt 1979, p. 86) also points in the same direction by recommending the highest possible flow rate for the diluate cells.

The method according to the invention surprisingly avoids both the concentration polarization on the membranes as a result of depletion of inorganic salts in the diluate and disturbances caused by the ionic dye molecules themselves; it also does not need an environmentally harmful «solution mediator». It is therefore - particularly for the chemically very sensitive reactive dyes - an extremely gentle method for desalination.

Electrodialysis can be carried out in commercially available electrodialysis systems, using commercially available ion exchangers, for example membranes “Selemion” ® from Asahi Glass or membranes “Neosepca” ® from Tokuyama Soda. The electrodialysis temperature can

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664 371

see - 10 to 80 ° C, in particular between 15 and 40 ° C for sensitive dyes.

The flow rate in the concentrate and diluate is set so that the pumped quantities in the diluate are chosen to be smaller than in the concentrate. The absolute quantities are of minor importance, they generally remain within the limits specified by the apparatus manufacturers, generally in the lower range of the specified flow rate, for example at <5 cm / s, while in the concentrate a range> 5 cm / s is usually set becomes; this driving style also has an energy-saving side effect: energy for pump performance is saved. In this way, current densities of 0.01 A / dm2 to 6 A / dm2 are achieved with a voltage per sub-cell of 2 V. The depletion of the salt content can be 90%, in many cases 99%.

The method is illustrated by the following examples, but is not limited to them:

example 1

44 parts of a saline, water-moist press cake of the dye of the structure

is checked gradually. The electrodialysis was stopped when the final chloride value was <0.01% in the solution.

ED duration: 27 h, material yield:> 99.5%, residual chloride-5 content- (dye pure): <0.1%.

The desalted dye solution has a pure dye content of 26% and is buffered dry by adding 2% Na2HP04 calculated on dye to a pH of 8.5.

The buffered dye solution shows excellent storage stability. After a rapid aging test of 3 d at 60 ° C, the color strength and pH are practically unchanged. After freezing the dye solution at -20 ° C and thawing it, the solution can also be used without restrictions.

15 With 3 parts of this desalted solution, dye baths, padding liquors and printing pastes were prepared in a known and customary manner, which, applied and fixed to cotton in the manner customary for reactive dyes, gave blue dyeings and prints which were just as vivid 20 as those which with the appropriate use of dye baths of the same concentration, padding liquors or printing pastes with 1 part of a powder formulation containing 78% by weight of pure dye.

25 Example 2

33 parts of a saline, water-moist press cake of the dye of the structure

Na salt

CL

with a pure dye content of 50% are dissolved in 56 parts of demineralized water (demineralized) at about 35 ° C. The dye solution is then subjected to electrodialysis at a temperature of about 35 ° C. and a pH of 8.0.

The apparatus consists of an ED cell and three circuits. Each of these circuits is equipped with a magnetic centrifugal pump, a heat exchanger and a storage container (1 to 10 1) and connected to the ED cell via polyethylene hoses.

The ED cell has 2 platinum electrodes, each 0.35 dm2. The electrode compartments are separated from the adjacent concentrate compartments by Nafion® cation exchange membranes (company Ionics). Between the electrode rooms there are 6 concentrate and 5 diluate rooms in an alternating arrangement. The rooms are alternately separated by Selemion-AMV membranes (Asahi Glass) and Sele-mion-CMV membranes (Asahi Glass). All membranes have an active area of 0.37 dm2. The membrane spacing of 2 mm is achieved by installing PVC frames, which also have the inlet and outlet arrangements via which the circuits are connected.

The apparatus is equipped with direct current supply, temperature, pH and conductivity measurement as well as N2 flushing.

The circuits of the electrodialysis apparatus were loaded with the following solutions:

Electrolyte: 75 parts 5% NaîSCU solution; Concentrate: 75 parts of 0.5% NaCl solution; Diluate: 100 parts of dye solution.

At about 35 ° C, the solutions were pumped around and electrodialysed. The flow rates for diluate and concentrate were 1000 parts / h and 2000 parts / h, respectively. The initial current of about 2 A drops with the progress of desalination, which can be determined analytically by e.g. Chloride determination f— (s ° 3 "^ r - (ö)

35

CH

(Na salt)

so3s so3H

with a pure dye content of 54% are dissolved in 67 parts of demineralized water at about 35 ° C. The dye 40 solution is then subjected to electrodialysis at a temperature of about 35 ° C. and a pH of 8.0. The apparatus and test procedure correspond to example 1.

Electrolyte: 46 parts of 5% Na2SÛ4 solution

Concentrate: 50 parts of 0.5% NaCl solution 45 Diluate: 100 parts of dye solution.

The flow rates were 1000 parts / h in the diluate and 4000 parts / h in the concentrate.

At an initial current of 2 A, dialysis was carried out for 35 h until the chloride value of the solution was practically zero. 50 Residual chloride content (pure dye): <0.1%.

The desalted dye solution has a pure dye content of 19% and a pH of 8.0.

After testing according to Example 1, 4 parts of this desalted solution gave the same results as with 1 part 55 of a powder formulation containing 76% by weight of pure dye.

Example 3

100 parts of a salt-containing reaction solution of the dye 60 fes of the formula

-S02-NH

W5 ° r

NH_

CL

CuPc

']

—11.8

J> 2NH2] ÌSH 1-7

Na salt

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with a pure dye content of 6% are subjected to electrodialysis at a temperature of 20 to 25 ° C and a pH of 6.5 until the residual chloride content is below 0.1%. The apparatus, test procedure and parts by volume of the test use correspond to example 1. The desalted dye solution has a pure dye content of 7.5% and is buffered dry by adding 5% NaìHP04 calculated on dye to a pH of 7.0.

In order to obtain a desired pure dye content of 12%, part of the dye solution is sprayed with a pure dye content of 50% and dissolved in 85 parts of demineralized water at 20 to 25 ° C. The dye solution is then subjected to electrodialysis at a temperature of 20 to 25 ° C. and a pH of 7.0 until the residual chloride content is below 0.1%. The apparatus, test procedure and parts by volume of the test operation correspond to example 1.

The desalted dye solution has a pure dye content of 8.5% and is buffered by adding 2% Na2HP04 dry to dye to a pH of 7.5.

In order to achieve a desired pure dye content of 21.5% with a pure dye content of 30%, 20 to 25 ° C are dissolved in 80 parts of demineralized water. The dye solution is then subjected to electrodialysis at a temperature of 20 to 25 ° C. and a pH of 9.0 until the residual chloride content is below 0.1%. The apparatus, test procedure and parts by volume of the test operation correspond to example 1.

The desalted dye solution has a pure dye content of 8.5% and a pH of 7.0.

To achieve a desired pure dye content of 19%

NaO-S

- 3rd

has a pH of 7.2, an MEK of 3.69 and a (Cl®) concentration of 1.9%.

The mass extinction coefficient MEK is calculated from the extinction at 513 and 535 nm of the VIS spectrum in dilute aqueous solution, measured in a 1 cm cuvette, and the concentration C of the measurement solution in g / 1 according to the equation

MEK = [E (535 nm) + E (513 nm)] / 2xc.

Concentrated drying and the powder concentrate obtained proportionately added to the solution.

After testing according to Example 1, the same good results were achieved with 3 parts of this desalted solution as with 1 part 5 of a powder formulation containing 36% by weight of pure dye.

Example 4

15 parts of a saline, water-moist press cake io of the dye of the formula

Gate*

odeï CNä "SsLzì

.CT3 "

obtained, the dye solution is concentrated by means of circulation evaporation.

After testing according to Example 1, the same good results were achieved with 3 parts of this desalted solution as with 1 part 25 of a powder formulation containing 64.5% by weight of pure dye.

Example 5

20 parts of a saline, water-moist press cake 30 of the dye of the structure

Cl

40 obtained, the dye solution is concentrated by means of vacuum evaporation.

After testing according to Example 1, the same good results were achieved with 3 parts of this desalted solution as with 1 part of a powder formulation 45 containing 57% by weight of pure dye.

Example 6

An aqueous solution of the raw dye of the formula

-NH

-NH

2nd

995 parts of this solution were electodialysed according to Example 1 in an analog system, an ED cell with 60 diluate and 61 concentrate chambers being used. The current density was initially 3 A / dm2, but fell to 0.3 A / dm2 in the course of 65 dialysis, the ED temperature was 22-25 °, the flow rate in the diluate was 1500 parts / h, in the concentrate 2500 parts / h, the current yield of electrodialysis (based on chloride) was 91%, the material yield was

M «

-Mnh

(Na salt)

5

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almost quantitative (> 99%), the degree of desalination was 95%.

860 parts of desalted dye solution with a pH of 7.1, an MEK of 4.26 and a [Cle] concentration of <0.1% were obtained. Hue and color purity were unchanged. By distilling off water in a water jet vacuum at a bottom temperature of 50 ° C., 36 parts of a concentrated, low-viscosity dye solution with an MEK of 10.2 were obtained. After three days' storage at - 20 ° C and + 60 ° C at normal temperature, the solution was still usable, whereby the pH value of the warm sample had dropped to 5.9.

Explanation of the drawing:

The electrodialysis cell, the diagram of which can be seen in the figure, is connected via polyethylene hoses to three separate circuits which supply the cell with the concentrate (1), the diluate (2) and the electrolyte (3) from storage containers. The cell has two platinum electrodes (4), each 0.35 dm2. The electrode compartments (5) are separated from the adjacent concentrate compartments (6) by cation exchange membranes (7), which are commercially available under the name ®Nafion. There are six concentrate rooms s (6) and five diluate rooms (8) in an alternating arrangement between the electrode rooms. The rooms are alternately separated from each other by cation exchange membranes (9), which are commercially available under the name ®Selemion CMV or anion exchange membranes (10), which are available commercially under the name ®Selemion AMV io. The membranes have an active area of 0.37 dm2 and are attached by a PVC frame so that they are 2 mm apart. The inlet and outlet arrangements via which the circuits are connected are also attached to the frame. Each of the three circuits is equipped with a magnetic centrifugal pump and a heat exchanger. The apparatus is equipped with direct current supply, temperature, pH and conductivity measurement as well as with nitrogen flushing.

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1 sheet of drawings

Claims (3)

664 371 1. Process for the preparation of largely salt-free aqueous solutions of ionic dyes by electrodialysis, characterized in that the flow rate of the diluate (= solution to be treated) is chosen to be lower than that of the concentrate. 2. The method according to claim 1, characterized in that with the help of electrodialysis> 90% of the inorganic foreign ions are removed. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that the flow rate in the diluate is more than 15% lower than in the concentrate.