DE1767584C3 - Neutralization of ion exchanger regenerates - Google Patents

Description

When an ion exchanger is regenerated, the regenerant generally does not become complete consumed. A regeneration liquid is therefore produced which, in the case of a cation exchanger, has not yet been used Contains acid and, in the case of an anion exchanger, still unused base. These liquids are referred to below as regenerates. Different types of water are now used to desalination of water Combinations of cation and anion exchange filters that sequentially remove the water to be desalinated flows through. During the regeneration of these ion exchanger filters, both acidic and alkaline regenerates that may not be released directly as waste water. The regenerates have to go to at least be neutralized beforehand. So far, the alkaline and the acidic have been used for this purpose Regenerates neutralized against each other, optionally with the addition of further bases or acids, if one of the two regenerates was present in a stoichiomelric excess. Special neutralization vessels are required for this with appropriate dosing and control devices.

The mutual neutralization of the regenerates has already been carried out on ion exchangers. For this purpose one used z. B. a weakly acidic cation exchanger in the hydrogen form. Above The alkaline regenerate is filtered through this exchanger, whereby the exchanger changes to the salt form and is absorbed neutral eluate is obtained. The exchanger is returned to the hydrogen form with the aid of the acidic regenerate, a neutral (salt-containing) eluate being obtained. This method requires one special ion exchange filter.

The present application relates to a process for the neutralization of ion exchanger regenerates from a water treatment plant, in which acid and alkaline regenerates are alternately filtered through a weak ion exchanger, which is characterized in that the weak ion exchanger filter used is one which is used at the same time in the desalination plant for water treatment is used as a working filter. In this mode of operation, in addition to the actual regenerates, the washing water that accumulates after the regeneration when rinsing the exchanger with water is passed over the weak ion exchanger
Surprisingly, it has been found that the above-described neutralization of the exchanger eluates and wash water can also be carried out with the help of the weakly basic or weakly acidic ion exchanger working in a desalination circuit, without reducing the capacity, precipitating or damaging ion exchangers which act as working filters and neutralization filters comes. It is only necessary to dimension the installed amount of the double-acting exchanger so large that its capacity is sufficient for the working cycle and in addition to absorbing the alkalis and acids present in the regenerates. The operation of the present invention can be represented as follows:

^Fa "'
Weakly acidic exchanger as a working and

Neutralization filter

During the working cycle, the solution to be desalinated is passed through a filter arrangement

weakly acidic cation exchanger,
strongly acidic cation exchanger
and

one or more anion exchangers performed.
After the end of the loading process, the weakly acidic cation exchanger still contains enough exchangeable hydrogen ions that the free alkalis in the regenerates and washing water produced during the regeneration of the anion exchangers of the desalination plant are bound when passing over the weakly acidic exchanger and the initially alkaline solutions are removed the weakly acidic exchanger run off neutralized.

Subsequently, the weakly acidic exchanger becomes both that from the strongly acidic cation exchanger draining regenerate as well as the washing water are supplied. The free acid contained therein must be Weakly acidic exchanger so largely converted into the hydrogen form that this after the now The following loading of the desalination plant is used to neutralize the for the next regeneration of the Anion exchanger containing free alkalis necessary hydrogen ions. The ones from the regenerates and wash water of the strongly acidic cation exchanger flowing off the weakly acidic exchanger are also neutralized.

Case 2

Weakly basic exchanger as a working and
Neutralization filter

During the working cycle, the solution to be desalinated is passed through a filter arrangement
one or more cation exchangers,
a weakly basic anion exchanger
guided. This can be followed by further anion exchangers, depending on the desalination requirements.

After the end of the loading process, the weakly basic anion exchanger still contains enough acid-binding capacity that the accumulating in the desalination plant after the regeneration of the cation exchangers Regenerate and wash water present free acids when passing over the weak basic anion exchanger are bound and the initially acidic solutions from the

run off weakly basic anion exchanger neutralized.

The weakly basic anion exchanger is then given the necessary for its regeneration Amount of alkali supplied. This can be from pure, freshly prepared solution or from the processes and Wash water of a downstream, strongly basic anion exchanger, depending on the circuit of the Desalination plant. The free alkalis contained in the solution must be sufficient for the Weakly basic anion exchanger so largely converted into the hydroxide form that this after Now the following loading of the desalination plant still for the neutralization of the next regeneration the free acid produced by the cation exchanger has the necessary acid-binding capacity. From Regenerates and wash water flowing off the weakly basic anion exchanger from the regeneration the anion exchangers are also neutralized.

The regenerates neutralized in this way via weakly dissociated cations or anion exchangers and washing water from a desalination circuit have a pH value that is particularly close to the neutral point, if the regenerates and wash water are opposite to the direction of flow that occurs during loading prevails, feeds the ion exchange bed. In addition, with this procedure, the for Neutralization used weakly dissociated ion exchangers during the desalination period independently fully functional from random fluctuations in the amount of acid and alkali to be neutralized.

If desired, the neutralized wastewater can can be buffered to a pH value of 6.5 - 7 by adding 1 - 1.5 parts by volume of raw water.

Claims 2 and 3 contain preferred embodiments of the method according to Claim 1.

All exchangers with acidic groups can be used as weakly acidic cation exchangers. whose pH value is below 6. In particular, resins based on crosslinked polymers are used which through copolymerization of monomers with one or more olefinic double bonds, for example of acrylic acids, their esters or nitriles on the one hand and divinylbenzene on the other hand have been received. These exchangers have very good stability over the entire pH range. If the resins mentioned contain a sponge structure which has been produced during the manufacture of the resins, so these resins also have excellent resistance to constant change from acidic to alkaline environment and the associated changes in volume.

All exchangers serve as weakly basic anion exchangers for the purposes of the inventions described with basic groups whose pH is above 7.5. Condensation products are preferably used from amines and formaldehyde or epichlorohydrin sawie resins obtained by interpolymerization of Monomers with one or more olefinic double bonds, for example of styrene on the one hand and divinylbenzene on the other hand, with the introduction of primary, secondary, tertiary or quaternary amino groups are constructed. These resins can retain 0-50% of their total capacity on quaternary groups. A spongy structure of the resin framework is also an advantage here.

example

An ion exchange system, consisting of three filters connected in series (1350 liters of a weakly acidic cation exchanger, 1350 liters of a strongly acidic cation exchanger, 1400 liters of a weakly basic anion exchanger) desalinates 440 m ³ of raw water between two regenerations , 4 ° d, a total hardness of 13.5 ° d and a carbonate hardness of 1 l ° d.

The hourly throughput is 22 m ³ . The desalinated water has an average conductivity of 3-10μ5 / ατι (after trickling out of the released carbonic acid).

At the beginning of the regeneration, 85 kg of 100% NaOH are filtered through the anion exchanger in the form of a 4% solution at a specific load of 5 parts by volume per hour. The displacement of the lye and the washing out of the exchanger provide about 10 m ^{3 of} washing water. Lye and wash water are filtered directly through the weakly acidic cation exchanger.

The cation exchangers are then regenerated as a composite by adding 146.4 kg of 100% HCl in Form of a 6% solution with a specific load of 5 parts by volume per hour over the strongly acidic cation exchanger and then directly via the weakly acidic cation exchanger filtered. Displacement and wash water are passed through the exchanger in the same direction.

The regenerates and wash water filtered through the weakly acidic cation exchanger are all neutralized (pH 5.5 - 6.5).

Claims (3)

Patent claims: 1. Process for the neutralization of ion exchange regenerates from a water treatment plant, in which one alternates acid and alkaline regenerates over a weak ion exchanger filters, characterized in that a weak ion exchange filter is used those used at the same time as a working filter in the desalination plant for water treatment is used 2. The method according to claim 1, wherein instead of the entire regenerate only the unused Portions of the regenerate are passed through a weak ion exchanger. 3. The method according to claim 1 and 2, wherein the solutions to be neutralized opposite to Direction of flow, which is maintained during the loading in the desalination cycle, into the bed of the weak ion exchanger are introduced.