DE102024131536B3 - METHOD FOR PRODUCING A NON-WOVEN MATERIAL SUITABLE FOR THE REMOVAL OF HARMFUL ANIONS FROM AQUEOUS SOLUTION, NON-WOVEN MATERIAL FOR THE REMOVAL OF HARMFUL ANIONS FROM AQUEOUS SOLUTION AND USE OF THE NON-WOVEN MATERIAL - Google Patents

Abstract

The invention relates to a method for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying its surface. The method according to the invention comprises the following steps:
a) Providing a nonwoven material selected from the group comprising polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone and polyvinylidene fluoride;
b) Applying a coating solution to the nonwoven material, wherein the coating solution contains polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent;
c) Treating the nonwoven material and the coating solution with electron beam radiation; and
d) Cleaning the modified nonwoven material.

Description

The invention relates to a method for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying a surface thereof.

Technological background

Due to the increasing anthropogenic input of micropollutants into water bodies, the effort required to obtain clean drinking water is constantly increasing. In particular, intensive agriculture (fertilization) introduces larger quantities of, for example, nitrate and nitrite ions into the water cycle, so that the limit values for nitrate (50 mg/L) [TrinkwV, 2023, p. 54] and nitrite (0.5 mg/L) [TrinkwV, 2023, p. 57] in water are frequently exceeded. In some cases, the limit values for nitrate/nitrite in drinking water can only be met by blending in less polluted water from other catchment areas.

If water needs to be freed from harmful anions, the current state of the art offers two possible methods. One is separation via the adsorption of the pollutants onto ion exchange resins; the other is membrane filtration using dense polymer membranes (nanofiltration, reverse osmosis). However, both methods are associated with problems.

The principle of an ion exchange material is based on the fact that ions are bound more strongly the greater their charge, and conversely, for identical charges, the larger the ionic radius. This makes it possible to significantly reduce the amount of one type of ion present in solution and replace it with another (non-disruptive/harmful) type of ion. However, the use of ion exchange resins has several disadvantages. Firstly, bacteria can easily colonize ion exchange systems, leading to additional water pollution. Furthermore, adsorption onto the ion exchange resins is non-specific, meaning that in addition to nitrate and nitrite ions, other ions dissolved in the water are also adsorbed. This also means that adsorption sites can be occupied by harmless substances, resulting in faster saturation of the material.

The use of nanofiltration and reverse osmosis membranes leads to the separation of substances according to molecular size, so that only very small molecules, water, and smaller salt ions can pass through the membranes. Due to the necessary small pore size of the membranes, this purification method is associated with high operating pressures of up to 40 bar to transport the water through the membrane. Consequently, a very high energy demand results when drinking water of high quantity and quality needs to be provided, and practical application is hampered by the high pressures. Since, as with the process using ion exchange resins, the water to be purified is almost completely desalinated, remineralization of the water by adding essential salts is necessary to obtain drinking water.

The state of the art describes various methods for modifying membranes. DE 10 2009 036 947 A1 This concerns a method for modifying polymer membranes, which involves directly modifying the membrane polymer with low molecular weight compounds using high-energy radiation. DE 10 2009 004 848 B3 describes a method for producing a microporous membrane on whose surface a polymer cross-linked by electron radiation is fixed.

The invention is therefore based on the objective of providing an alternative method for removing harmful anions from aqueous solution, the energy requirement of which is as low as possible and in which post-treatment of the treated water is avoided as far as possible.

Summary of the invention

1. a) Bereitstellen eines Vliesmaterials ausgewählt aus der Gruppe umfassend Polypropylen, Polyethylen, Viskose, Polyamid, Polylactid, Polyester, Polyethersulfon, Polysulfon und Polyvinylidenfluorid;
2. b) Auftragen einer Beschichtungslösung auf das Vliesmaterial, wobei die Beschichtungslösung Polyallylaminhydrochlorid (PAH) und/oder Polyhexamethylenbiguanid (PHMB) als Modifizierungsreagenz enthält;
3. c) Behandeln des Vliesmaterials und der Beschichtungslösung mit Elektronenstrahlung; und
4. d) Aufreinigen des modifizierten Vliesmaterials aus Schritt c).

This problem is solved by the inventive method for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying a surface thereof according to claim 1, and by the modified nonwoven material obtained according to claim 7. The manufacturing method comprises (in this order) the following process steps:

1. a) Providing a nonwoven material selected from the group comprising polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone and polyvinylidene fluoride;
2. b) Applying a coating solution to the nonwoven material, wherein the coating solution contains polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent;
3. c) Treating the nonwoven material and the coating solution with electron beam radiation; and
4. d) Cleaning the modified nonwoven material from step c).

Another aspect of the invention relates to the use of the modified nonwoven material for the removal of harmful anions from aqueous solution.

Further preferred embodiments of the invention can be found in the dependent claims and the following description.

Brief description of the character

The invention is explained in more detail below with reference to several exemplary embodiments and the accompanying drawing. The single figure shows, in a highly schematic form, the basic method for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying one of its surfaces.

Detailed description of the invention

The functions and possible variations of the invention are explained in more detail below using examples. However, the invention is not limited to these specific embodiments.

General aspects of the invention

1. a) Bereitstellen eines Vliesmaterials ausgewählt aus der Gruppe umfassend Polypropylen, Polyethylen, Viskose, Polyamid, Polylactid, Polyester, Polyethersulfon, Polysulfon und Polyvinylidenfluorid;
2. b) Auftragen einer Beschichtungslösung auf das Vliesmaterial, wobei die Beschichtungslösung Polyallylaminhydrochlorid (PAH) und/oder Polyhexamethylenbiguanid (PHMB) als Modifizierungsreagenz enthält; und
3. c) Behandeln des Vliesmaterials und der Beschichtungslösung mit Elektronenstrahlung; und
4. d) Aufreinigen des modifizierten Vliesmaterials aus Schritt c).

The inventive method for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying a surface thereof comprises the following steps:

1. a) Providing a nonwoven material selected from the group comprising polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone and polyvinylidene fluoride;
2. b) Applying a coating solution to the nonwoven material, wherein the coating solution contains polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent; and
3. c) Treating the nonwoven material and the coating solution with electron beam radiation; and
4. d) Cleaning the modified nonwoven material from step c).

The invention is based on the finding that an adsorbent coating can be produced on certain nonwoven materials by electron beam immobilization of special modification reagents, which makes it possible to remove various anions from aqueous solution via ionic interactions.

The resulting nonwoven materials exhibit a surprisingly high adsorption capacity for nitrate and nitrite ions, among other things, and are therefore particularly suitable for drinking water treatment. Furthermore, using the material as a filter fleece avoids high operating pressures, thus keeping the energy costs of the treatment process low.

The process for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying its surface comprises, in a first step, a) the provision of a nonwoven material suitable for the subsequent process steps. This material is a polymer from the group comprising polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone, and polyvinylidene fluoride. Polyethylene terephthalate (PET) is a particularly suitable polyester. The aforementioned polymers are especially suitable for electron beam immobilization because sufficiently high densities of functionalities are generated during electron beam treatment, and selective reaction with the added reagent is achieved. Furthermore, these materials are particularly suitable for drinking water treatment because they are stable in water.

The basis weight of the nonwoven material used is preferably in the range of 10 to 600 g/ ^m² , particularly preferably in the range of 20 to 500 g/ ^m² , and especially in the range of 100 to 300 g/ ^m² . Below a basis weight of 10 g/ ^m² , the nonwoven layer is very thin. This negatively affects the stabilization of the nonwoven material, so that it may be damaged by mechanical stress when used as a filter fleece. Above a basis weight of 600 g/ ^m² , the nonwoven layer is unnecessarily thick. Since the penetration depth of the modification is limited at the acceleration voltage used in the electron beam treatment, this represents an unnecessarily high material consumption. In addition, the greater thickness of the polymer layer can adversely affect the flexibility of the filter fleece, thus also limiting the filtration capacity for anions.

In a particularly preferred embodiment, polyethylene terephthalate (PET) with a basis weight in the range of 100 to 300 g/ ^m² , for example 200 g/ ^m² , is used. This embodiment is particularly suitable for a process for producing a modified nonwoven material for removing harmful anions from aqueous solution, since PET is, on the one hand, a relatively tear-resistant polymer and, on the other hand, absorbs very little water. With a basis weight of 200 g/ ^m², the layer thickness results in particularly suitable mechanical properties for use as a filter fleece.

In step b) of the process, a coating solution is applied to the nonwoven material, the coating solution containing polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent. In other words, the surface of the nonwoven material to be modified is wetted with the modifying reagent, for example, by immersing the nonwoven in a solution containing the modifying reagent. Alternatively, the solution can be sprayed on. In principle, any solvent can be used that sufficiently dissolves the modifying reagent, does not attack the nonwoven, and does not negatively affect the irradiation. Water is particularly suitable.

Polyallylamine hydrochloride (PAH; CAS 71550-12-4), polyhexamethylene biguanide (PHMB or polyhexanide; CAS 28757-47-3), or mixtures thereof are used as modification reagents. These compounds have proven suitable for electron beam immobilization. The concentration of the modification reagent used (or, if applicable, the total concentration of all modification reagents used) is preferably in the range of 0.05 to 20 wt.%, particularly preferably in the range of 0.1 to 10 wt.%, and especially in the range of 0.5 to 2 wt.%. A concentration lower than 0.05 wt.% of the modification reagent can have adverse effects on the filtration capacity of anions from aqueous solution, since a lower concentration of the modification reagent results in fewer functionalities being applied to the surface of the nonwoven material after electron beam immobilization. A concentration above 20 wt% may lead to undesirable side reactions between the molecules of the modifying reagent during electron beam treatment. The coating solution can be applied by immersion, spraying, and/or brushing.

In step c) of the process, the nonwoven material and the coating solution according to b) are treated with electron beam radiation. This immobilizes the modifying reagent according to b) on the nonwoven surface (electron beam immobilization). The radiation dose of the electron beam is preferably in the range of 20 to 600 kGy, particularly preferably in the range of 100 to 500 kGy, and especially in the range of 200 to 400 kGy. A radiation dose of less than 20 kGy of electron beam radiation has adverse effects on the removal of anions from aqueous solution, since below this radiation dose the immobilization of the modifying reagent on the nonwoven surface is incomplete and consequently fewer molecules of the modifying reagent are bound on the surface. A radiation dose above 600 kGy may lead to undesirable side reactions, in particular to the chemical decomposition of the modifying reagent. Irradiation causes PAH and PHMB to bind covalently to the polymeric nonwoven material. Reaction with both modifying reagents leads to polycationic structures on the surface of the nonwoven material. These polycationic structures have proven particularly suitable for the attachment of various anions.

In step d), the modified nonwoven material is then purified. This involves washing and drying the modified nonwoven material. In principle, any liquid that sufficiently dissolves the (unreacted) modifying reagent and does not attack the nonwoven can be used as a washing agent. According to a particularly preferred method, the modified nonwoven material is washed several times with deionized water and dried overnight at room temperature.

The single figure illustrates, in a highly schematic way, the previously described process for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying its surface. In step S1, a nonwoven material selected from the group comprising polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone, and polyvinylidene fluoride is provided. Subsequently, in step S2, a coating solution is applied to the nonwoven material, the coating solution containing polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent. After application, in step S3, the nonwoven material and the coating solution are treated with electron beam radiation. Finally, in step S4, the modified nonwoven material is purified.

Production of the modified nonwoven material

In the experiments described in more detail below, a nonwoven material made of polyethylene terephthalate (PET) with a basis weight of 200 g/ ^m² is provided.

In a subsequent process step, a coating solution is applied to the nonwoven material. This coating solution contains either polyallylamine hydrochloride (PAH) or polyhexamethylene biguanide (PHMB) as a modifying reagent. The coating solution is applied to the nonwoven material to be modified by immersing the material in the solution. Water is used as the solvent for the coating solution. The modifying reagent PAH or PHMB is present in concentrations ranging from 0.5% to 2% by weight (see Tables 1 to 4).

The modifying reagent is immobilized on the nonwoven material to be modified by treatment with electron beams. During electron irradiation, the modifying reagent binds to the surface of the nonwoven material. The energy dose of the electron beam is 200 kGy or 400 kGy (see Tables 1 to 4).

The modified nonwoven material is obtained after purification of the electron beam-treated nonwoven material. This purification step includes a washing process with a liquid and subsequent drying. The treated nonwoven material is washed several times with deionized water and dried in air at ambient temperature.

Investigation of the adsorber effect and other properties

Dynamic adsorption experiments are performed as examples to determine the adsorption activity of nitrate and nitrite ions on both unmodified and modified nonwoven materials. For this purpose, 10 mL and 50 mL of an aqueous solution containing either 10 ppm nitrate ions or 10 ppm nitrite ions are filtered through a nonwoven fabric with a surface area of 50 ^cm² at a flow rate of 3 mL/min. The residual concentration of nitrate and nitrite ions in the permeate is determined spectroscopically. The results for various (un)modified nonwoven materials are summarized in Tables 1 to 4 within the framework of experimental comparative studies.

The (un)modified nonwoven materials are further investigated with regard to their mechanical properties and functionality. Investigations using scanning electron microscopy (SEM), tensile tests, and mercury porosimetry show that the starting materials and modified nonwoven materials exhibit no measurable changes in nonwoven morphology, permeability, or porosity.

Experimental comparative study 1

Experimental comparative study 1 investigates the effects of the PAH concentration in the coating solution and the energy dose of the electron beam on the properties of the modified nonwoven material with regard to the removal of nitrate ions from aqueous solution. The residual amount of nitrate ions in the filtrate is determined after volumes of 10 mL and 50 mL, respectively. Table 1 shows the measurement results for the removal of nitrate ions from aqueous solution using a polyethylene terephthalate nonwoven material with a PAH-containing coating, treated with electron beams of varying energy doses. A PET nonwoven material, neither coated with a modifying reagent nor treated with electron beams, serves as the reference system. Table 1 fleece PAH Energy dose Nitrate elimination after 10 mL 50 mL [wt.%] [kGy] [%] [%] PET, 200 g/ ^m² - - 47 0 PET, 200 g/ ^m² 0.5 200 89 43 PET, 200 g/ ^m² 2 200 91 48 PET, 200 g/ ^m² 2 400 88 61

As can be seen, the nonwoven material is not suitable for filtering nitrate from aqueous solution without modification. Only through electron beam-induced binding of PAHs can nitrate ions be removed from aqueous solution to a significant extent.

In the case of a PET nonwoven material that was neither coated with PAH nor treated with electron beam radiation, the residual amount of nitrate in the permeate was reduced by 47% after filtration of 10 mL of a nitrate-containing aqueous solution. With a volume of 50 mL, the residual amount of nitrate in the permeate was not reduced (0%).

Investigations of the modified nonwoven materials show that, with a volume of 10 mL of a nitrate-containing aqueous solution, the reduction of nitrate ions remaining in the permeate is approximately 90%, independent of the PAH concentration in the coating solution and the energy dose of the electron radiation. This demonstrates, on the one hand, the suitability of these modified nonwoven materials for removing nitrate ions from aqueous solutions and, on the other hand, that the modified nonwoven materials are already largely optimized for the filtration of 10 mL of an aqueous nitrate solution, such that changes in the PAH concentration in the coating solution (0.5 and 2 wt%) as well as changes in the radiation dose (200 and 400 kGy) have only a negligible effect on the filtration capacity.

With a volume of 50 mL of a nitrate-containing aqueous solution, the suitability of the modified nonwoven materials for removing nitrate ions from aqueous solution becomes clear compared to the unmodified nonwoven material. While the amount of nitrate is not reduced in the latter case (0%), the modified nonwoven materials reduce the amount of nitrate in the respective permeate by 43 to 61%. It is found that the filtration capacity of the modified nonwoven material increases with increasing PAH concentration and increasing energy dose of the electron beam. The investigations show that the filter fleece with the highest filtration capacity in a 50 mL nitrate-containing aqueous solution is a PET nonwoven material treated with a coating solution containing 2 wt% PAH and electron beam radiation with an energy dose of 400 kGy.

Experimental comparative study 2

Experimental comparative study 2 investigates the effects of the PAH concentration in the coating solution and the energy dose of the electron beam on the properties of the modified nonwoven material with regard to the removal of nitrite ions from aqueous solution. The residual amount of nitrite ions in the filtrate is determined after volumes of 10 mL and 50 mL, respectively. Table 2 shows the measurement results for the removal of nitrite ions from aqueous solution using a polyethylene terephthalate nonwoven material with a PAH-containing coating, treated with electron beams of varying energy doses. A PET nonwoven material, neither coated with a modifying reagent nor treated with electron beams, serves as the reference system. Table 2 fleece PAH Energy dose Nitrite elimination after 10 mL 50 mL [wt.%] [kGy] [%] [%] PET, 200 g/ ^m² - - 41 1 PET, 200 g/ ^m² 0.5 200 87 34 PET, 200 g/ ^m² 2 200 88 45 PET, 200 g/ ^m² 2 400 88 68

As can be seen, the nonwoven material is not suitable for filtering nitrite from aqueous solution without modification. Only through electron beam-induced binding of PAHs can nitrite ions be removed from aqueous solution to a significant extent.

In the case of a PET nonwoven material that was neither coated with PAH nor treated with electron beam radiation, the residual amount of nitrite in the permeate was reduced by 41% after filtration of 10 mL of a nitrite-containing aqueous solution. With a volume of 50 mL, the residual amount of nitrite in the permeate was reduced only slightly (1%).

Investigations of the modified nonwoven materials show that, with a volume of 10 mL of a nitrite-containing aqueous solution, the reduction of nitrite ions remaining in the permeate is approximately 88%, independent of the PAH concentration and the energy dose of the electron beam. This demonstrates, on the one hand, the suitability of these modified nonwoven materials for removing nitrite ions from aqueous solutions and, on the other hand, that the modified nonwoven materials are already largely optimized for the filtration of 10 mL of a nitrite-containing aqueous solution, such that changes in the PAH concentration in the coating solution (0.5 and 2 wt%) as well as changes in the energy dose (200 and 400 kGy) of the electron beam have only a negligible effect on the filtration capacity of the modified nonwoven material.

In a 50 mL volume of nitrite-containing aqueous solution, the suitability of the modified nonwoven materials for removing nitrite ions from aqueous solution becomes clear compared to the unmodified nonwoven material. While the amount of nitrite is not reduced in the latter case (0%), the modified nonwoven materials reduce the amount of nitrite in the respective permeate by 34 to 68%. It is found that the filtration capacity of the modified nonwoven material increases with increasing PAH concentration and increasing energy dose of the electron beam. The investigations show that the filter fleece with the highest filtration capacity in a 50 mL volume of nitrite-containing aqueous solution is a PET nonwoven material treated with a coating solution containing 2 wt% PAH and electron beam radiation with an energy dose of 400 kGy.

Experimental comparative study 3

Experimental comparative study 3 investigates the effects of PHMB concentration in the coating solution and electron radiation energy dose on the properties of the modified nonwoven material with respect to the removal of nitrate ions from aqueous solution. The residual amount of nitrate ions in the filtrate is determined after volumes of 10 mL and 50 mL, respectively. Table 3 shows the measurement results for the removal of nitrate ions from aqueous solution using a polyethylene terephthalate nonwoven material with a PHMB-containing coating, treated with electron radiation of varying energy doses. A PET nonwoven material, neither coated with a modifying reagent nor treated with electron radiation, serves as the reference system. Table 3 fleece PHMB Energy dose Nitrate elimination after 10 mL 50 mL [wt.%] [kGy] [%] [%] PET, 200 g/ ^m² - - 47 0 PET, 200 g/ ^m² 0.5 200 89 3 PET, 200 g/ ^m² 2 200 89 2 PET, 200 g/ ^m² 2 400 91 7

As can be seen, the nonwoven material is not suitable for filtering nitrate from aqueous solution without modification. Only through electron beam-induced binding of PHMB can nitrate ions be removed from aqueous solution to a significant extent. In the case of a PET nonwoven material that was neither coated with PHMB nor treated with electron beam radiation, the residual amount of nitrate in the permeate was reduced by 47% after filtration of 10 mL of a nitrate-containing aqueous solution. At a volume of 50 mL, the residual amount of nitrate in the permeate was not reduced (0%).

Investigations of the modified nonwoven materials show that, with a volume of 10 mL of a nitrate-containing aqueous solution, the reduction of nitrate ions remaining in the permeate is approximately 90%, independent of the PHMB concentration and the energy dose of the electron radiation. This demonstrates, on the one hand, the suitability of these modified nonwoven materials for removing nitrate ions from aqueous solutions and, on the other hand, that the modified nonwoven materials are already largely optimized for the filtration of 10 mL of a nitrate-containing aqueous solution, such that changes in the PHMB concentration in the coating solution (0.5 and 2 wt%) as well as changes in the radiation dose (200 and 400 kGy) have only a negligible effect on the filtration capacity.

With a volume of 50 mL of a nitrate-containing aqueous solution, it was found that the PHMB-coated nonwoven materials were less effective than the PAH-coated nonwoven materials in removing nitrate ions from aqueous solution (see Tables 1 and 3). While the amount of nitrate was not reduced (0%) in the case of the unmodified nonwoven material, the modified nonwoven materials reduced the amount of nitrate in the respective permeate by 2 to 7%. It was also found that increasing the energy dose of the electron beam resulted in a slight improvement in the removal of nitrate ions from aqueous solution.

Experimental comparative study 4

Experimental comparative study 4 investigates the effects of PHMB concentration in the coating solution and electron radiation energy dose on the properties of the modified nonwoven material with respect to the removal of nitrite ions from aqueous solution. The residual amount of nitrite ions in the filtrate is determined after volumes of 10 mL and 50 mL, respectively. Table 4 shows the measurement results for the removal of nitrite ions from aqueous solution using a polyethylene terephthalate nonwoven material with a PHMB-containing coating, treated with electron radiation of varying energy doses. A PET nonwoven material, neither coated with a modifying reagent nor treated with electron radiation, serves as the reference system. fleece PHMB Energy dose Nitrite elimination after 10 mL 50 mL [wt.%] [kGy] [%] [%] PET, 200 g/ ^m² - - 41 1 PET, 200 g/ ^m² 0.5 200 87 1 PET, 200 g/ ^m² 2 200 85 4 PET, 200 g/ ^m² 2 400 86 5

As can be seen, the nonwoven material is not suitable for filtering nitrite from aqueous solution without modification. Only through electron beam-induced attachment of PHMB can nitrite ions be removed from aqueous solution to a significant extent.

In the case of a PET nonwoven material that was neither coated with PHMB nor treated with electron beam radiation, the residual amount of nitrite in the permeate was reduced by 41% after filtration of 10 mL of a nitrite-containing aqueous solution. With a volume of 50 mL, the residual amount of nitrite in the permeate was only slightly reduced (1%).

Investigations of the modified nonwoven materials show that, with a volume of 10 mL of a nitrite-containing aqueous solution, the reduction of nitrite ions remaining in the permeate is approximately 86%, independent of the PHMB concentration and the energy dose of the electron beam. This demonstrates, on the one hand, the suitability of these modified nonwoven materials for removing nitrite ions from aqueous solutions and, on the other hand, that the modified nonwoven materials are already largely optimized for the filtration of 10 mL of a nitrite-containing aqueous solution, such that changes in the PHMB concentration in the coating solution (0.5 and 2 wt%) as well as changes in the radiation dose (200 and 400 kGy) have only a negligible effect on the filtration capacity.

With a volume of 50 mL of a nitrite-containing aqueous solution, it was found that the PHMB-coated nonwoven materials were less effective than the PAH-coated nonwoven materials in removing nitrite ions from aqueous solution (see Tables 1 and 4). While the amount of nitrite was only slightly reduced (1%) in the case of the unmodified nonwoven material, a comparable reduction in the amount of nitrite in the respective permeate occurred with the modified nonwoven materials (1–5%). It was observed that increasing the energy dose of the electron beam resulted in a slight improvement in the removal of nitrite ions from aqueous solution.

When comparing the described nonwoven materials, a PET nonwoven material treated with a 2 wt% PAH solution and electron radiation with an energy dose of 400 kGy (see Tables 1 and 2) shows a significantly improved filtration capacity for nitrate and nitrite ions compared to the unmodified nonwoven material.

The electron beam-based modification equips the treated nonwoven material with an adsorber layer for anions. This nonwoven can be used to separate these anions from drinking water by being incorporated into a filter system, for example, in the form of a filter bag. The need for such a filter system arises from the increasing pollution of waterways with nitrate and nitrite inputs of anthropogenic origin.

The separation of nitrate/nitrite ions from the water to be filtered is more efficient and specific than, for example, with anion exchange resins. At the same time, the nonwoven material used presents only low hydrodynamic resistance, which allows for the use of low operating pressures. Consequently, the filter system can be operated without additional pumps or similar equipment if the water pressure is sufficient. Furthermore, the nonwoven material used reduces the risk of colonization by microorganisms such as bacteria, which can occur with anion exchange resins.

Regeneration of the adsorber material

After using the modified nonwoven material to remove, for example, nitrate and nitrite ions from aqueous solution, the materials can be cleaned by rinsing with a dilute saline solution, for example, with a concentration of 0.3 wt%. The excess chloride ions displace the adsorbed anions, allowing the nonwoven material to be used again to remove harmful anions from aqueous solution.

Reference symbol list

S1

Provision of a nonwoven material selected from the group comprising polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone and polyvinylidene fluoride

S2

Application of a coating solution to the nonwoven material, wherein the coating solution contains polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent.

S3

Treatment of the nonwoven material and the coating solution with electron beam

S4

Purification of the modified nonwoven material

Claims (9)

A process for producing a nonwoven material suitable for removing harmful anions from aqueous solution by modifying a surface thereof, comprising the following steps: a) providing a nonwoven material selected from the group consisting of polypropylene, polyethylene, viscose, polyamide, polylactide, polyester, polyethersulfone, polysulfone, and polyvinylidene fluoride; b) applying a coating solution to the nonwoven material, wherein the coating solution contains polyallylamine hydrochloride (PAH) and/or polyhexamethylene biguanide (PHMB) as a modifying reagent; c) treating the nonwoven material and the coating solution according to step b) with electron beam radiation; and d) purifying the modified nonwoven material from step c). Procedure according to Claim 1 , wherein the anions to be removed are selected from the group comprising nitrate and nitrite ions. Procedure according to Claim 1 or 2 , wherein the nonwoven material described in step a) has basis weights in the range of 10 to 600 g/m ² . Method according to one of the preceding claims, wherein the coating solution described in step b) contains 0.05 to 20 wt.% of the modification reagent. Method according to one of the preceding claims, wherein the electron radiation described in step c) has an energy dose in the range of 20 to 500 kGy. Method according to one of the preceding claims, wherein the purification in step d) provides for at least one washing process and a subsequent drying of the modified nonwoven material. Nonwoven material for removing harmful anions from aqueous solution, produced according to a process according to Claim 1 . Use of the nonwoven material according to Claim 7 for the removal of harmful anions from aqueous solution. Use of the nonwoven material according to Claim 7 , in which the modified nonwoven material is regenerated after the removal of harmful anions from aqueous solution by rinsing with a saline solution.