WO2008125395A1 - Method for the removal of ions from mineral water and drinking water - Google Patents

Abstract

The invention relates to a method for the removal of ions from mineral water and drinking water by treatment with a water insoluble polymer based on basic N-vinyllactam.

Description

 Process for removing ions from mineral water and drinking water

description

The invention relates to the use of a polymer based on a basic vinylheterocycle having a pKa value of at least 3.8 as filter aid for removing ions from mineral water and drinking water. Furthermore, the invention relates to a process for the regeneration of the filter aid.

To improve the sensory quality of water, it is often necessary to remove ions. Furthermore, the removal of metal ions may also be required in view of the maximum levels specified in the relevant drinking and mineral water regulations.

From DE-A 1945749 is the removal of undesirable components such as metal ions from an aqueous medium by means of a polymeric sorbent containing basic or cationic groups, for example, base monomers modified copolymers based on ethylene and maleic anhydride. Specifically described beverage specific is the removal of small amounts of iron and copper from beer.

EP-A 88964 describes a process for the preparation of water-insoluble and only slightly swellable polymers of basic N-vinylheterocycles which can be used for the preparation of complexes with transition metals.

According to EP-A-4 38 713, polymers based on basic vinyl heterocycles are used for removing heavy metals from wine and wine-type beverages. The polymers should be able to be regenerated after treatment with dilute mineral acids.

From EP-A 642 521 it is known to remove aluminum ions from beverages such as wine, wine-type beverages or fruit juice.

In EP-A 781 787 is the use of water-insoluble and only slightly swellable polymers of basic N-vinyl heterocycles for the preparation of

Complexes with heavy metal ions are described. The complexes with heavy metal ions are said to serve to remove sulphurous compounds from wine and wine-like beverages.

According to RD 500031, crosslinked N-vinylimidazole and N-vinylpyrrolidone copolymers can be used as filter aids for removing metal ions in unspecified non-alcoholic beverages. For this purpose, the polymeri- be incorporated into filter materials such as diatomaceous earth or nonwoven materials.

However, the removal of ions from mineral or drinking water causes specific difficulties. On the one hand, the basic composition of useful or desired ions should be influenced as little as possible, especially for mineral waters, and on the other hand, a simple regenerability of the filter aid should be ensured for economic reasons.

The invention therefore an object of the invention to develop an improved method for the removal of ions from mineral water and drinking water. It was also an object to find an improved process for the regeneration of the corresponding filter aids, since the methods described so far only lead to inadequate results.

This object is achieved by a method for the removal of ions from mineral water and drinking water by treatment with a water-insoluble polymer, characterized in that as polymer insoluble in water, a polymer obtained from 50 to 99.5 wt .-% N-vinylimidazole Copolymerized from 0 to 49.5 wt .-% of another copolymerizable monomer and 0.5 to 10 wt .-%, based on the total amount of monomers, of a crosslinking monomer, is used.

The invention also provides a process for the regeneration of the filter aid, which is characterized in that the filter aid is subjected to at least one treatment step with acids and at least one treatment step with alkalis.

The preparation of the polymers used according to the invention is known per se and described in detail in EP-A 88964, EP-A 438713 and EP-A 642521 and reference is hereby expressly made to the disclosure of said documents.

Preferably, the polymer used contains 70 to 99.5 wt .-% N-vinylimidazole, 0 to 29.5 wt .-% of the copolymerizable monomer and 0.5 to 10 wt .-% of the crosslinking agent.

Copolymers of 50 to 99.5% by weight of N-vinylimidazole and N-vinylpyrrolidone as comonomer are also preferred. Preferred crosslinkers are N, N'-divinylimidazolidin-2-one. Very particular preference is given to a polymer of 90% by weight of N-vinylimidazole, 7% by weight of N-vinylpyrrolidone and 3% by weight of N, N'-divinylimidazoliin-2-one.

The data in% by weight refers to the total amount of monomers and crosslinkers.

Some of the polymers used according to the invention are commercially available, for example as Divergan® HM from BASF.

As already mentioned, the process is suitable for reducing the content of ions, which means according to the invention inorganic ions, it being possible to remove both cations and anions. It is possible to remove ions of metals and semimetals of the 3rd to 7th main group as well as the subgroups, selected lanthanides and actinides, in particular the elements mentioned below

3rd main group: B, Al, Ga, In, Tl

4th main group: Sn, Pb

5th main group: As, Sb, Bi, especially As

Main group: Se ₁ Te, Po, especially Se, Te 7. Main group: F, Br

1st subgroup: Cu, Ag, Au

2nd subgroup Zn, Cd, Hg

5. Subgroup: in particular vanadium

6. Subgroup: Cr, Mo, W 7. Subgroup: Mn, Tc

8. Subgroup: Fe, Co, Ni ,, Rh, Pd, Pt actinides: in particular U

Elements can exist in the form of their free anions and cations as well as in the form of complex oxo anions.

According to the invention, fluoride and bromide may be considered as free anions. As complex oxoanions, it is possible to remove main-group semimetallic elements such as, for example, borate, diborate or arsenate, as well as by-group metals such as chromate, molybdate or manganate.

As free cations, especially metal ions can be removed, in particular metal ions of the 1st, 2nd and 8th subgroup.

The treatment according to the invention for reducing the ion content consists in bringing the corresponding water into contact with the polymer for at least one minute, preferably at least one hour. The treatment can be carried out either at acidic, neutral or basic pH values. Which pH is most suitable for which type of ion can be determined by a person skilled in the art by a few simple experiments. The adjustment of the pH can be carried out with aqueous alkalis such as caustic soda or potassium hydroxide solution, or with the acids indicated below.

The treatment can be carried out batchwise by addition of the polymer to the water and separation or continuously. It can be carried out, for example, via a column filled with the polymer or a filter layer containing the polymer. The filter layer can be present in conventional filter devices.

Furthermore, the removal can also take place via a membrane containing the polymer. The polymer can be added to the beverage in the case of membrane-based filtration on the retentate or permeate side.

In the case of a batch process, the loaded filter aid can then be carried out with the aid of the customary solid / liquid separation devices. A separation via centrifugation is possible.

The use amount of the polymers as sorbent depends not only on the starting ion concentration and the desired final concentration, but also after the time available for the process and is in the range of 5 to 2500, preferably 10 to 250 g prolOO I aqueous liquid. As the application examples show, even after surprisingly short contact times, a significant reduction in the metal ion concentration takes place. However, longer residence times further increase the effectiveness of the polymers which can be used according to the invention.

Preferably, 1 to 1000 g of the polymer are used per 100 l of mineral or drinking water. The amount used depends, on the one hand, on the load of impurities and, on the other, on the type and geometry of the filter element used.

The treatment can be carried out at temperatures of 1 to 100 ⁰ C, preferably 1 to 40 ⁰ C. The treatment can take place at 0.1 to 0.9 MPa.

A regeneration of the sorbents (polymers) can be carried out by a process which is characterized in that the polymer loaded with ions is subjected to at least one treatment step with an alkali and at least one treatment step with an acid.

Suitable aqueous solutions are, in particular, sodium hydroxide solution or potassium hydroxide solution, particularly preferably sodium hydroxide solution. The concentration is usually 0.5 to 5 wt .-% solids base / 1, preferably 0.5 to 3.5 wt .-%. The treatment time depends on the amount of filter aid to be treated and the amount of contaminant loaded.

Suitable acids are mineral acids such as phosphoric acid, nitric acid, sulfuric acid or, in the case of glass appliances, also hydrochloric acid. Also suitable are citric acid, acetic acid or lactic acid. Usually, dilute acids are used.

It may also be advisable to carry out a washing step with cold or hot water at temperatures of from 1 to 100 ^° C., preferably from 1 to 40 ^° C., between the respective treatment steps with a lye and an acid.

Furthermore, for regeneration, a treatment with a complexing agent suitable for the ions mentioned can be carried out, for example with ethylenediaminetetraacetate.

The order of the treatment steps is arbitrary. It may depend on the starting pH or the type of ions to be removed.

Optionally, an enzymatic treatment of the filter aid can also be carried out for regeneration, if the treated water was contaminated with impurities of biological origin, which is understood to mean cell material according to the invention. Before treatment with an enzyme, the pH is usually adjusted to values <pH 7, preferably to pH 3.5 to 5.5.

The adjustment of the pH can be carried out, for example, with mineral acids such as phosphoric acid, nitric acid, sulfuric acid or, in the case of glass appliances, also with hydrochloric acid. Also suitable are citric acid or lactic acid.

In principle, the enzymes suitable are proteases, glucosidases, amylases or pectinases and all other enzymes which are capable of lysing cells or else mixtures of enzymes. Such enzymes or enzyme mixtures are commercially available. The enzymes are usually used in the form of aqueous solutions.

The appropriate amount of enzyme depends on the activity of the particular enzyme and the loading of the unfiltrate and the filter cake with impurities. The determination of the activity can be made by those skilled in the art by a few simple experiments by examining what amount of enzyme it takes to lyse a defined number of cells. Then, the dosage can be made depending on the turbidity or loading with cells. Subsequent to the enzymatic treatment, further treatment steps may be followed by an aqueous liquor or an acid. If desired, a washing step with cold or hot water can again take place between the enzymatic and the further treatment.

Optionally, following an enzyme treatment, a treatment step may be followed in which the filter medium is treated with an aqueous surfactant solution or surfactant dispersion. The concentration of surfactant, based on the total weight of the solution, may be from 0.01 to 4% by weight, preferably from 0.01 to 1.5% by weight. Suitable surfactants are both anionic and nonionic surfactants. It is also possible to use mixtures of surfactants.

Furthermore, an ultrasound treatment can also be carried out to remove biological contaminants.

The process according to the invention can be carried out both on an intact filter cake or a precoat layer or on a filter matrix, as well as on a disintegrated filter cake.

The treatment can take place at 0.1 to 0.9 MPa.

The process control usually takes place via temperature, time, pH and conductivity measurements.

A suitable treatment scheme for the regeneration can be carried out, for example, as follows:

Hot water rinsing, for example at 80 ^° C. rinsing with hot soda, for example in the range of 80 ^° C. rinsing with hot water, for example in the range of 80 ^° C., for example

Rinsing with cold water, for example at 13 to 15 ⁰ C rinsing with aqueous citric acid, for example at 13 to 15 ⁰ C, until the pH of the wash water is neutral

Rinsing with aqueous citric acid, for example at 13 to 15 ⁰ C.

With the aid of the method according to the invention, unwanted ions from mineral and drinking water can be removed in a simple manner, without negatively influencing the basic properties of the mineral or drinking water with regard to the content of desired ions or the conductivity. Furthermore, the regenerability is possible in a simple and economical manner. Examples

In the examples, a polymer of 90% by weight of N-vinylimidazole (VI), 7% by weight of N-vinylpyrrolidone (VP) and 3% by weight of N, N'-divinylimidazolidin-2-one was used Divergan® HM, Fa. BASF, is commercially available.

The element contents were determined either by atomic adsorption spectroscopy or by photometry according to customary methods. These are standard methods that are well known to the skilled person from the literature.

General rule:

The water sample was placed in a closable vessel and mixed with the stated amount of polymer. The vessel was sealed and the sample was treated with the polymer for a total of 60 minutes, the sample being stirred for 15 minutes, then sedimented for 45 minutes and then filtered off. The pH was adjusted with 1 mol of NaOH and 1 mol of phosphoric acid.

The commercially available standard solutions used each contained 1000 mg / l of the element to be removed.

The numerical values given under the respective pH values refer to mg / l.

Example 1: Iron

Standard solution: ammonium iron (II) sulphate hexahydrate

Example 2: Manganese

Standard solution: manganese (III) chloride

Example 3: Lead

Standard solution lead (II) nitrate

Example 4: Copper

Standard solution copper (II) sulfate

Example 5: Cadmium Standard Solution Cadmium (II) chloride

Beispiel 6: Zink

Example 6: Zinc

Standard solution zinc chloride

Example 7: Chromium Standard solution Chromium (III) chloride

Example 8: Bromide

Standard solution sodium bromide

Beispiel 9: Arsen

Example 9: Arsenic

Standard solution arsenic acid

Example 10

The treatment to remove uranium ions was performed in batch on a natural mineral water with a uranium content of 9 ug / l. The stated amount of polymer was weighed and stirred into a sample. The contact time was 1 h, of which the first 30 min with stirring. The treatment was carried out at 22 ⁰ C in a closed vessel, in order to bring about any change in the water by oxygen input or loss of carbon dioxide.

This made it possible to lower uranium levels below the World Health Organization recommended level of 2 μg / l. The conductivity of the mineral water was unchanged after treatment.

Example 1 1 regeneration

To determine the regenerability, the polymer was loaded in one case with copper ions, in the other case with iron ions.

The copper treatment was carried out with a solution containing 5 mg / l Cu ions. The iron treatment was carried out with a solution containing 1 mg / L of iron ions. The treatment with the respective solutions was carried out by the metal ion solution with 10 g / hl of the polymer were added. Subsequently, the solution was stirred for 15 min and then sedimented for 45 min. Thereafter, the polymer was filtered off through a filter. Subsequently, the adsorption of the respective metal on the polymer was determined on a sample.

For regeneration, the polymer was mixed with enough water to form a stirrable suspension, and then treated with 2 wt .-%, based on the suspension volume, of 1 molar HCl and 15 min. touched. Subsequently, the polymer was filtered off, re-suspended in water and treated with 2 wt .-%, based on the suspension volume of 1 mol sodium hydroxide solution, stirred for 15 min and filtered off again. Thereafter, the Polymerisatfilterkuchen was washed with water until the wash water had a pH of 7. The polymer thus treated was dried, again treated with the metal ion solution and regenerated. In total, 10 treatment cycles were performed. Even after the 10th regeneration, the polymer showed no capacity loss in the adsorption capacity to the metal.

Claims

claims 1. A process for the removal of ions from mineral water and drinking water by treatment with a water-insoluble polymer based on a basic N-vinyl lactam, characterized in that a water-insoluble polymer obtained from 50 to 99.5 wt .-% N- Vinylimidazole, 0 to 49.5 wt .-% of another copolymerizable monomer polymerized and 0.5 to 10 wt .-%, based on the total amount of monomers, of a crosslinking monomer, is used. 2. The method according to claim 1, characterized in that a polymer is used, which is obtained from with N-vinylpyrrolidione as a copolymerizable monomer. 3. The method according to claim 1 or 2, characterized in that a polymer of N-vinylimidazole, N-vinylpyrrolidone and N, N'-divinylimidazolidin-2-one is used. 4. The method according to any one of claims 1 to 3, characterized in that are removed as ions anions, complex oxo anions or cations of metals, semi-metals and halides. 5. The method according to any one of claims 1 to 4, characterized in that the treatment is carried out at acidic, neutral or basic pH values. 6. A process for the removal of ions from mineral water and drinking water by treatment with a water-insoluble polymer based on a basic N-vinyl lactam, characterized in that a water-insoluble polymer obtained from 50 to 99.5 wt .-% N- Vinylimidazole, copolymerized 0 to 49.5 wt .-% of another copolymerizable monomer and 0.5 to 10 wt .-%, based on the total amount of monomers, of a crosslinking monomer, is used, which by at least one treatment step with an alkali and at least one treatment step was regenerated with an acid. 7. The method according to claim 6, characterized in that caustic soda or potassium hydroxide are used as bases. 8. The method according to claim 6 or 7, characterized in that are used as acids, mineral acids, citric acid, acetic acid or lactic acid.