HK1238196B - Sorbens for binding metals, production thereof and use thereof for the binding of metals - Google Patents

Description

The present invention relates to an adsorbent suitable for binding metals from solutions, the production of a corresponding adsorbent, as well as the use of the adsorbent for binding metals from solutions.

The removal or recovery of metals, especially heavy metals, from industrial wastewaters, for example, in electroplating operations, from catalyst residues in the petrochemical or pharmaceutical industry, from mine water, for instance, from mines, or from the remediation of heavy metal contaminated soils, is becoming an increasingly important task, since heavy metals, in particular, either have harmful effects on the environment and also their recovery represents an economic interest. That is, on one hand environmental aspects are in the foreground, on the other hand the availability of valuable metals, whose availability is increasingly questionable or whose prices are rising, is of great interest. Another important application field of sorbents for the removal, recovery or reclamation of metals, or heavy metals, is the separation of these in drinking water treatment as well as in seawater desalination. Similarly, the separation of heavy metals from concentrated salt solutions, such as those used in chlor-alkali electrolysis or similar processes, is of great interest.

M. Chanda et al., Reactive Polymers 1995, 25(1), pages 25-36 discloses an adsorbent used for binding uranium and iron ions from solutions, comprising a porous silica gel coated with polyethyleneimine as a support material. The polyethyleneimine is further cross-linked with glutaraldehyde.

Previously known phases/adsorbents often lack sufficient binding capacity for the aforementioned application areas to bind the metals adequately, for example, from highly concentrated or low-concentration solutions or strongly acidic solutions, especially in the presence of alkali or alkaline earth metal ions. Furthermore, previously known phases often do not exhibit stability across the entire pH range from pH 0 to pH 14. Another disadvantage of many previously known phases is that although the desired metal can be bound, it cannot usually be recovered easily or at all from the used adsorbent. Due to the generally unsatisfactory binding capacity of known adsorbents/phases, a large volume of adsorbent/phase is often required, making the metal-binding processes very laborious and cost-inefficient. Moreover, due to the generally low binding capacity of known metal-binding adsorbents, the process often needs to be carried out multiple times in order to provide metal-free water, for example, as drinking water.

That is why the object of the present invention is to provide a new sorbent that does not exhibit the above-mentioned disadvantages, partially or entirely. In particular, it is an object of the present invention to provide a sorbent having a high binding capacity for metals, especially heavy metals and noble metals, per gram or per milliliter. Preferably, the sorbent provided according to the invention is particularly sanitizable with sodium hydroxide, or allows for the easy recovery of the metals. Another object of the present invention is to provide a sorbent which still exhibits a relatively high binding capacity for metals even under acidic conditions.

Furthermore, the volume of the sorbent used for metal binding should be reduced compared to known metal-binding sorbents from the prior art.

The object of the present invention is solved by a sorbent according to claim 1.

In a further embodiment of the present invention, it is preferred that the concentration of amino groups of the sorbent, determined by titration, is at least 800 µmol/mL, more preferably at least 1000 µmol/mL, even more preferably at least 1200 µmol/mL, and most preferably at least 1500 µmol/mL of sorbent. The upper limit of the concentration of amino groups of the sorbent according to the invention, determined by titration, is limited by spatial feasibility or the maximum possible density of the arrangement of the amino groups within the polymer containing the amino groups, and is at most 4000 µmol/mL, more preferably 3000 µmol/mL, and most preferably 2500 µmol/mL. The concentration of amino groups of the sorbent determined by titration refers to the concentration obtained according to the analytical methods specified in the example section of this application, using breakthrough measurement with 4-toluenesulfonic acid.

Furthermore, it is preferred that the sorbent according to the invention has a ratio of the mass of the polymer containing amino groups to the total pore volume of the porous support material of greater than or equal to 0.1 g/mL, more preferably greater than or equal to 0.125 g/mL, even more preferably greater than or equal to 0.15 g/mL, and most preferably greater than or equal to 0.20 g/mL. Again, there are physical limits for the upper bound of this ratio, but preferably no more than 0.5 g/mL, more preferably no more than 0.4 g/mL, and most preferably no more than 0.3 g/mL.

The mass of the polymer containing amino groups can be determined according to DIN 53194 by the increase in tap density compared to the support material. The total pore volume [V] of the porous support material can be determined by the solvent absorption capacity (SAC) of the porous support material. Similarly, the pore volume [Vol.-%] can also be determined. In each case, this refers to the volume of the freely accessible pores of the support material, since only this can be determined by the solvent absorption capacity. The solvent absorption capacity indicates what volume of a solvent is required to completely fill the pore space of one gram of dry sorbent (preferably the stationary phase). Here, pure water or aqueous media as well as organic solvents such as dimethylformamide can be used as solvents. If the sorbent increases its volume when wetted (swelling), the amount of solvent used is automatically recorded. To measure the SAC, a precisely weighed amount of dry sorbent is wetted with an excess of a good-wetting solvent, and any excess solvent in the interparticle volume is removed by centrifugation. The solvent within the pores of the sorbent remains. The mass of the retained solvent is determined by weighing and converted into volume using the density. The SAC of a sorbent is reported as volume per gram of dry sorbent (mL/g).

The coating of the amino-group-containing polymer on the porous support material preferably exists in the form of a hydrogel. This is particularly because the amino-group-containing polymer exhibits the aforementioned high concentration of amino groups. A hydrogel, as used herein, refers to a polymer containing a solvent (preferably water), but which is soluble in the solvent, whose molecules are chemically, for example, through covalent or ionic bonds, or physically, for example, by entanglement of the polymer chains, connected into a three-dimensional network. Due to built-in polar (preferably hydrophilic) polymer components, they swell in the solvent (preferably water) with considerable volume increase, without losing their structural integrity. From the prior art, it is known that hydrogels may partially lose their properties irreversibly when dried. However, the hydrogels in the present application do not lose their properties, since they are chemically and mechanically stabilized by the porous support material. The amino-group-containing coating is particularly present as a hydrogel in the inventive sorbent when this is swollen in a solvent, i.e., particularly during the use described below for binding metals from solutions.

The porous carrier material is preferably a mesoporous or macroporous carrier material. The average pore size of the porous carrier material is preferably in the range of 6 nm to 400 nm, more preferably in the range of 10 to 300 nm, and most preferably in the range of 20 to 150 nm. A pore size within the specified range is important to ensure that the binding capacity is sufficiently high. In the case of too small a pore size, the amino group-containing polymer on the surface of the porous carrier material may clog the pores, and the inner volume of the pores will not be filled with an amino group-containing polymer. Furthermore, it is preferred that the porous carrier material has a pore volume in the range of 30 to 90 vol.%, more preferably from 40 to 80 vol.%, and most preferably from 60 to 70 vol.%, each value being based on the total volume of the porous carrier material.

The average pore size of the porous carrier material can be determined by the mercury intrusion method according to DIN 66133.

The porous support material can include or consist of an organic polymer, an inorganic material, or a composite material composed of organic polymers and inorganic materials.

To provide a sorbent that exhibits high sorbent stability over a pH range from 0 to 14, it is preferred that the porous support material be an organic polymer.

Preferably, the organic polymer for the porous support material is selected from the group consisting of polyalkyl, preferably with an aromatic unit in the side chain (that is, bound to the polyalkyl chain), polyacrylate, polymethacrylate, polyacrylamide, polyvinyl alcohol, polysaccharides (e.g., starch, cellulose, cellulose esters, amylose, agarose, sepharose, mannan, xanthan, and dextran), as well as mixtures thereof. Most preferred is the organic polymer polystyrene or a derivative of polystyrene, preferably a copolymer of polystyrene (or a derivative of polystyrene) and divinylbenzene. If the organic polymer carries an aromatic unit, this is preferably sulfonated. In a very particularly preferred embodiment of the present invention, the organic polymer is a sulfonated cross-linked poly(styrene-co-divinylbenzene) or a derivative thereof.

Is the porous support material an inorganic material, or does it comprise an inorganic material, the inorganic material is preferably an inorganic metal oxide, selected from the group consisting of silicon dioxide, aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, fluorosil, magnetite, zeolites, silicates (e.g., diatomite), mica, hydroxyapatite, fluoroapatite, metal-organic frameworks, ceramics, glass, porous glass (e.g., Trisoperl), metals, e.g., aluminum, silicon, iron, titanium, copper, silver and gold, graphite and amorphous carbon. In particular, the inorganic porous support material is silicon dioxide or aluminum oxide, particularly silicon dioxide. The silicon dioxide is preferably silica gel.

In particular, for reasons of use in a wide pH range, especially in the basic range, the porous support material is preferably an organic polymer.

The porous support material used according to the invention can have a homogeneous or heterogeneous composition, and therefore particularly includes materials composed of one or more of the above-mentioned materials, for example in multi-layered compositions.

The porous support material is preferably a particulate material with an average particle size in the range of 5 to 2000 µm, more preferably in the range of 10 to 1000 µm. The porous support material can also be a sheet-like or fibrous material, such as a membrane or a foam. Thus, the outer surface of the porous support material can be flat (flakes, films, discs, membranes, fibrous or non-fibrous fabrics) or curved (either concave or convex: spherical, granular, (hollow) fibers, tubes, capillaries).

As mentioned above, the porous support material is coated with a polymer containing amino groups, which consists of individual polymer chains or comprises them. The polymer chains are preferably covalently linked to each other. The amino group-containing polymer is preferably not covalently linked to the surface of the porous support material.

The use of a non-covalently surface-bound cross-linked polymer as an amino-group-containing polymer on the porous support material has the following three advantages: (1) flexibility of the polymer, since it is not covalently bound to the surface of the porous support material; (2) the cross-linking of the amino-group-containing polymer ensures that the film remains on the surface of the porous support material and does not get lost during the use of the sorbent; (3) the thickness of the amino-group-containing polymer can be chosen relatively large on the support material when the polymer is not covalently bound to the support material.

A sufficient flexibility and permeability of the amino-group-containing polymer is important so that several of the amino groups can adopt a conformation that allows the metals to be bound coordinatively multiple times.

The high metal-binding capacity of the sorbents according to the invention, or of those produced by the aforementioned methods according to the invention, was surprising for the inventors for the following reasons: Despite the nearly complete filling of the pores of the support material with the amino-group-containing polymer, the pores remain accessible for metals due to the permeability of the polymer, resulting in the sorbent according to the invention having a high metal-binding capacity. This was all the more surprising as polymer standards from inverse size-exclusion chromatography do not show any accessibility or permeability. This was even observed for the smallest standards with a molecular weight of 450 Da to over 90%. In contrast to conventional chromatographic sorbents and metal-binding sorbents, which are based on the principle of surface functionalization, it was surprisingly found that the high metal-binding property...that the present invention utilizes the entire volume of the polymer responsible for binding, and not only its surface; that is, the amino group-containing polymer forms together with the metal-containing solvent a so-called hydrogel, in which the polymer network exhibits nanoporosity. This leads to the fact that the metal-binding capacity is not only determined by the surface of the support material, but by the volume of the applied polymer. The high metal-binding capacity of the sorbents according to the invention, or of the sorbents produced according to the invention, is due to the formation of chemical complexes between groups of the amino group-containing polymer and the metals to be bound. These groups can themselves be amino groups, or they can be residues,which exhibit Lewis base properties and are bound to the polymer containing amino groups (as described below). This leads, for example, to the advantage of high salt tolerance or binding capacity in acidic environments compared to conventional ion exchangers. In parallel with the formation of chemical complexes through which metals are bound, the phase also has a very high binding capacity for anions, such as sulfate, phosphate, nitrite, nitrate, chromate, arsenate, etc.

The amino-group-containing polymer on the 10 sorbent according to the invention is selected from polyvinylamine, polyallylamine and polylysine. Among these, polyvinylamine and polyallylamine are preferred, with polyvinylamine being particularly preferred.

According to a preferred embodiment of the sorbent according to the invention, the amino-group-containing polymer has a crosslinking degree of at least 2%, based on the total number of crosslinkable groups in the amino-group-containing polymer. More preferably, the crosslinking degree is in the range of 2.5 to 60%, more preferably in the range of 5 to 50%, and most preferably in the range of 10 to 40%, each time based on the total number of crosslinkable groups in the amino-group-containing polymer. The crosslinking degree can be adjusted by using the desired amount of crosslinking agent. It is assumed that 100 mol% of the crosslinking agent reacts and forms crosslinks. This can be verified by analytical methods such as MAS NMR spectroscopy and quantitative determination of the amount of crosslinking agent relative to the amount of polymer used.This method is preferred according to the invention. However, the degree of crosslinking can also be determined by IR spectroscopy with respect to, for example, C-O-C or OH vibrations using a calibration curve. Both methods are analytical standard methods for an expert in this field. If the degree of crosslinking is above the specified upper limit, the polymer coating of the polymer containing amino groups is not flexible enough and results in a lower metal-binding capacity. If the degree of crosslinking is below the specified lower limit, the polymer coating is not sufficiently stable on the surface of the porous support material.

The crosslinking agent has two, three, or more functional groups, through the binding of which to the polymer, crosslinking occurs. The crosslinking agent used for crosslinking the amino-group-containing polymer is preferably selected from the group consisting of dicarboxylic acids, tricarboxylic acids, urea, bis-epoxides or tris-epoxides, diisocyanates or triisocyanates, and dihaloalkylenes or trihaloalkylenes, wherein dicarboxylic acids and bis-epoxides are preferred, such as terephthalic acid, biphenyldicarboxylic acid, ethylene glycol diglycidyl ether, and 1,12-bis-(5-norbornen-2,3-dicarboximido)-decandioic acid, with ethylene glycol diglycidyl ether and 1,12-bis-(5-norbornen-2,3-dicarboximido)-decandioic acid being more preferred. In one embodiment of the present invention, the crosslinking agent is preferably a linear, conformationally flexible molecule with a length between 4 and 20 atoms.

The preferred molecular weight of the amino-group-containing polymer of the sorbent according to the invention is preferably in the range of 5,000 to 50,000 g/mol, which particularly applies to the polyvinylamine used.

The sorbent according to the invention can, in another embodiment, also have organic residues that are bound to the amino-group-containing polymer and exhibit the property of a Lewis base. In this case, it is particularly preferred that the organic residue is bonded to an amino group of the amino-group-containing polymer. It is especially preferred that the amino group to which the organic residue is bonded represents a secondary amino group, so that it still exhibits sufficient Lewis basicity without being sterically hindered.

In a further embodiment, the present invention also relates to a method for producing the sorbent according to claim 7.

In the inventive method for producing a sorbent, the porous support material provided in step (a) is one that is mentioned above in connection with the inventive sorbent. The preferred embodiments mentioned there apply equally here.

In step (b) of the inventive method, a non-crosslinked amino-group-containing polymer is preferably used, as listed above in connection with the amino-group-containing polymer of the inventive sorbent. The preferred embodiments mentioned there apply equally here.

The pore-filling method in step (b) of applying the amino-group-containing polymer to the porous support material in the inventive method has the advantage over conventional impregnation methods that a larger amount of amino-group-containing polymer can be applied to the porous support material, thereby increasing the metal-binding capacity. This leads to the surprising advantages mentioned above.

Under the pore-filling method, one generally refers to a specific coating process in which a solution containing an amino-group-containing polymer is applied to the porous support material in an amount corresponding to the total volume of the pores of the porous support material. In this process, the total volume of the pores of the porous support material is determined in step (b), that is, during the first application, as described above.

In step (c) of the inventive method, the solvent used for the pore-filling method is preferably removed by drying the material at temperatures in the range of 40°C to 90°C, more preferably in the range of 50°C to 70°C, and most preferably in the range of 50°C to 60°C. In this process, drying is particularly carried out at a pressure in the range of 0.01 to 1 bar, more preferably at a pressure in the range of 0.1 to 0.5 bar.

It is an essential step of the inventive method for producing an adsorbent that, after drying or removing the solvent from the first step of applying by the pore-filling method, steps (b) and (c) of applying a polymer containing amino groups to the porous support material by the pore-filling method are repeated. For this purpose, the total volume of the pores is determined by differential weighing of the wet and dry materials after step (b), which is available for the repeated application of the amino group-containing polymer to the porous support material. In a further embodiment of the inventive method, it is also preferred that steps (b) and (c) are repeated at least twice. Before the second repetition of steps (b) and (c), the total pore volume available for the pore-filling method is again determined by differential weighing of the wet and dry materials. The repetition of steps (b) and (c) is preferably carried out in the stated order.

After the steps of applying the amino-group-containing polymer, in a step (e), the amino-group-containing polymer is cross-linked, preferably by means of the cross-linking agents specified in connection with the sorbent according to the invention. All the features mentioned above in connection with the sorbent according to the invention regarding cross-linking also apply to the method according to the invention for production.

Furthermore, it is preferred that no cross-linking of the amino-group-containing polymer occurs between the multiple steps of applying the amino-group-containing polymer onto the porous support material by means of a pore-filling method.

It is preferable that the removal of the solvent used in the pore-filling method is carried out by drying in a tray dryer, as this step can be significantly accelerated in this way.

In a further embodiment, in the inventive method, steps (b) and (c) are repeated before step (e) as many times as necessary to ensure that the concentration of amino groups of the sorbent determined by titration after step (e) is at least 600 µmol/mL, more preferably at least 800 µmol/mL, even more preferably at least 1000 µmol/mL, and most preferably at least 1200 µmol/mL, each value being based on the total volume of the sorbent. The upper limits of the concentration of the amino groups of the sorbent specified above in connection with the inventive sorbent also represent the preferred upper limits in the inventive process.

In a further embodiment of the inventive method, it is preferred that the ratio of the mass of the amino-group-containing polymer to the total volume of the pores of the porous support material after step (d) is greater than or equal to 0.1 g/mL, more preferably greater than or equal to 0.125 g/mL, and most preferably greater than or equal to 0.15 g/mL. The upper limit of this ratio is preferably at most 0.5 g/mL, more preferably at most 0.4 g/mL, and most preferably at most 0.3 g/mL.

In the pore-filling method of step (b) of the inventive process, a solvent is preferably used for the amino-group-containing polymer, which is capable of dissolving the amino-group-containing polymer. The concentration of the amino-group-containing polymer in the solvent used for the pore-filling method in step (b) of the inventive process is preferably in the range of 5 g/L to 200 g/L, more preferably in the range of 10 g/L to 180 g/L, and most preferably in the range of 30 to 160 g/L. A concentration below the specified lower limit has the disadvantage that steps (b) and (c) would have to be performed too frequently in order to achieve the desired amino-group concentration of the sorbent determined by titration, which ensures sufficient metal-binding capacity. A concentration above the specified upper limit does not guarantee that the polymer can sufficiently penetrate into the pores of the porous support material.

In a further embodiment of the inventive method, it is preferred that in a step (f)—preferably after step (e)—an organic group having the property of a Lewis base is bound to the amino-group-containing polymer. In particular, it is preferred that the organic group is bound to the amino groups of the amino-group-containing polymer. Furthermore, it is advantageous that after binding the organic group, the amino groups are present as secondary amino groups, so that their Lewis basicity is not lost and no steric hindrance occurs for the binding of the amino groups to the metals. An organic group having the property of a Lewis base refers particularly to groups that can form a complex bond with the metal to be bound.

Organic residues that act as Lewis bases are, for example, those containing heteroatoms with lone electron pairs, such as N, O, P, As, or S.

All the preferred embodiments mentioned above in connection with the inventive sorbent apply to the same extent to the sorbent produced by the inventive method, or to the components used in the inventive process.

Another embodiment of the present invention relates to the use of an adsorbent for binding metals from solutions according to claim 12.

In the solutions from which metals are to be bound, the invention may relate to concentrated or dilute aqueous or non-aqueous, acidic, basic or neutral solutions.

In the present application, the metals are preferably metals that are present in ionic form or as metal-ligand coordination compounds in ionic form in the aforementioned solutions. The metals are preferably complex-forming metals, i.e., metals that can form metal-ligand coordination bonds. More preferred are transition metals or rare earth metals; even more preferred are noble metals or rare earth elements. Particularly preferred are the metals copper, nickel and chromium.

In a further embodiment of the inventive use, the solutions from which the metals are to be bound are solutions having a salt content of alkali metal ions of at least 5 g/l.

Furthermore, the solutions from which the metals are to be bound are preferably aqueous solutions, in particular also an acidic aqueous solution with a pH value of ≤ 5, more preferably ≤ 4, and even more preferably ≤ 3.

For the binding of metals from solutions, the metal-containing solutions are brought into contact with the sorbent according to the invention. This can, for example, take place in a classical column. In this case, the sorbents according to the invention can also be present as mixtures of different sorbents developed for the binding of various metals. This is usually achieved by attaching different organic groups to the polymer containing amino groups.

In analog fashion, the contact between the sorbent according to the invention and the metal-containing solution can also be carried out in batch mode, i.e., without passing the solution through a vessel containing the sorbent, but rather in the form of swelling the sorbent in the solution.

The present invention will now be explained with reference to the following figures and examples, which are to be considered only as exemplary:

Figures:

Figures 1 and 2: Fig. 1 and 2 show the comparison of the isotherms of the sorbents from Example 1 and Comparative Example 1 during the binding of copper from aqueous solutions according to Example 2. Figure 3: Fig. 3 shows the metal-binding capacity of the sorbent from Example 1 for the metals copper, nickel, and chromium as a function of the metal concentration according to Example 3. Figure 4: Fig. 4 shows the amount of absorbed copper [g] per amount of sorbent [kg] in the presence of different concentrations of NaCl according to Example 4. Figures 5 and 6: Fig. 5 and 6 show the time course from Example 5 for the uptake of copper by a sorbent from Example 1. Figure 7: Fig. 7 shows the binding capacity for copper after regeneration of the sorbent after various cycles according to Example 6. Figure 8: Fig. 8 shows the comparison of copper binding of multi-coated sorbents with a single-coated sorbent according to Example 7.

Example section: Analytical methods:

Determination of the concentration of amino groups of an adsorbent using breakthrough measurement with p-toluenesulfonic acid (titration analysis): The dynamic anion exchange capacity is determined using a column packed with the test stationary phase. Initially, all exchangeable anions in the column are exchanged against trifluoroacetate. Then, the column is washed with an aqueous reagent solution of p-toluenesulfonic acid until this solution exits the column at the same concentration as it entered (breakthrough). The amount of p-toluenesulfonic acid bound by the column is calculated from the concentration of the p-toluenesulfonic acid solution, its flow rate, and the area of the breakthrough in the chromatogram. The determined amount of p-toluenesulfonic acid indicates the concentration of amino groups of the adsorbent.

The dynamic anion exchange capacity for p-toluenesulfonic acid in water is referenced to the phase volume and reported in millimoles per liter (mM/L).

Example 1: Preparation of an inventive sorbent:

200 g of a sulfonated polystyrene/divinylbenzene support material (average pore size 30 nm) are weighed into a vessel. This material has a pore volume determined by the WAK of 1.48 mL/g. In the first coating, the pore volume should be filled to 95%. The polymer solution for coating is prepared. 165.3 g of a polyvinylamine solution (solid content 12.1 wt.-%) are diluted with 108 g of water. The pH of the solution is adjusted to 9.5 using 7 ml of concentrated hydrochloric acid. The polymer solution is added to the support and mixed for 3 hours on an overhead shaker. Subsequently, the coated support is dried for 48 hours at 50°C in a vacuum oven at 25 mbar. The material has 197,7 g of water was lost through drying. The material is coated for the second time. For this purpose, 165.0 g of polyvinylamine solution (solid content 12.1 wt.-%) is adjusted to a pH value of 9.5 with 6.8 mL of concentrated HCl and diluted with 20 g of water. The polymer solution is added to the carrier and mixed for 3 hours on an overhead shaker. Subsequently, the coated carrier is dried for 48 hours at 50°C in a vacuum oven at 25 mbar. The material lost 181.2 g of water through drying. The material is coated for the third time. For this purpose, 165.2 g of polyvinylamine solution (solid content 12.1%) is adjusted to a pH value of 9.5 with 7.1 mL of concentrated HCl.5 is added and diluted with 5 g of water. The polymer solution is added to the carrier and mixed for 3 hours on an overhead shaker. Subsequently, the phase is dried in a vacuum oven at 50°C and 25 mbar until constant weight is achieved.

The material was coated in 3 steps with a total of 0.20 g PVA per mL pore volume.

The dried material was suspended in 1.5 L isopropanol in a double-jacket reactor and cross-linked with 24.26 g ethylene glycol diglycidyl ether at 55°C over 6 hours.

The coated material is washed with the following solvents: 600 mL isopropanol, 3600 mL 0.1 M HCl, 1800 mL water, 1800 mL 1 M NaOH, 1800 mL water, 1800 mL methanol.

Subsequently, the material is dried. Yield: 275 g of dried material.

Analysis: The concentration of amino groups determined by titration is 963 µmol/mL.

Comparison Example 1: Production of a conventional adsorbent:

The conventional sorbent is a 2-aminoethylthioethyl-modified silica gel ((Si)-CH2-CH2-S-CH2-CH2-NH2) with a particle size of > 45 µm (manufacturer Phosphonics, supplier Sigma-Aldrich, order number: 743453-10G; 0.8–1.3 mmol/g loading).

The modification can be carried out by reacting silica gel with 3-mercaptopropyltrimethoxysilane and subsequently reacting it with ethylimine.

Example 2: Use of the sorbents prepared according to Example 1 and Comparative Example 1 for binding copper from aqueous solutions:

In order to obtain isotherms in Figures 1 and 2, the following procedure was carried out: 10 samples of about 100 mg of the sorbent were accurately weighed and each was incubated for at least 1.5 hours with different aqueous Cu(II) solutions (as CuSO4) of varying concentrations. The sorbent was filtered off, and the Cu(II) concentration in solution was determined photometrically. From the remaining copper concentration, the amount of bound copper was calculated, and the isotherm was created.

From the comparison of the isotherms in Figures 1 and 2, it is evident that the inventive sorbent exhibits a significantly higher binding capacity than the conventional sorbent. From the approximated rectangular isotherms for the inventive sorbent, it is apparent that it shows a very strong binding without an actual equilibrium establishment. This allows for the nearly complete removal of heavy metals from highly diluted solutions.

Example 3: Use of the sorbent produced according to Example 1 for binding the three transition metals nickel, copper, and chromium from a solution:

Each of 10 samples of a defined amount of the sorbent is accurately weighed and incubated for at least 1.5 hours with different aqueous metal solutions of varying concentrations. The sorbent is then filtered off, and the metal concentration in solution is determined photometrically or using a metal determination method by Hach-Lange (preferably photometrically). The amount of bound metal is calculated from the remaining metal concentration, and the isotherm is created.

As shown in Figure 3, the sorbent according to the invention binds metals such as nickel (∼70 mg/g sorbent), copper (∼120 mg/g sorbent), and chromium (∼80 mg/g sorbent) to a large extent. The same was also demonstrated for solutions containing the metals palladium, lead, and iridium.

Example 4: Use of the sorbent produced according to Example 1 for binding metals from solutions with a high salt content:

5 samples of approximately 100 mg of the sorbent are accurately weighed and incubated with solutions of Cu (as CuSO4·5H2O = 50 mg/ml water) for at least 0.5 h. The solutions contain 0 M NaCl, 0.01 M NaCl, 0.1 M NaCl, 0.5 M NaCl, and 1 M NaCl. Subsequently, the sorbent is filtered off, and the copper concentration in the filtrate is determined photometrically. The amount of bound copper is calculated from the remaining metal concentration, and the isotherm is created.

As can be seen from Figure 4, even at concentrations of up to 1 M sodium chloride, the binding capacity of copper remains above 100 mg Cu/g sorbent. This indicates that it involves a non-ionic binding mechanism, which clearly differs from "conventional" ion exchangers.

There is no competition for binding sites of copper with sodium that remains uncomplexed. Therefore, the binding capacity for copper is maintained.

This property allows the use of the phase in the treatment of drinking water, surface water, mine water, wastewater, seawater desalination plants, chlor-alkali electrolysis, etc., where the ubiquitous and highly excessive alkali and alkaline earth metals must not cause disturbances.

Example 5: Binding rate of an adsorbent produced as in Example 1:

Samples weighing approximately 100 mg of the phase are accurately weighed and incubated with a Cu solution (as CuSO4·5H2O = 50 mg/ml water) for the specified period. Subsequently, the sorbent is filtered off, and the copper concentration in the filtrate is determined photometrically. The amount of bound copper is calculated from the remaining metal concentration.

Figures 5 and 6 show the binding of copper from solutions over time. After about 90 minutes, all binding sites of the sorbent are occupied by copper. No change in concentration is observable even after 48 hours.

Example 6: Reusability of the sorbent produced according to Example 1:

1 g of the sorbent from Example 1 is weighed and treated as follows: 1. Washing with 1 M NaOH (3 × 5 ml) 2. Washing with water (3 × 5 ml) 3. Addition of 50 ml Cu (as CuSO4·5H2O, 50 mg/ml) 4. Incubation for 90 minutes 5. Filtration 6. Determination of copper concentration in the filtrate (spectrophotometrically) and calculation of the amount of bound copper 7. Repetition of the procedure

As shown in Figure 7, the copper binding capacity remains unaffected after 10 cycles of regeneration and reuse of the sorbent (except for cycles 5 and 6), even after treatment with 5 M HCl and 1 M NaOH.

Example 7: Comparison of multiple-coated sorbents with a single-coated sorbent: Production of a simply coated sorbent on a silicate support:

100 g of AGC Kieselgel D-50-120A (average pore size 12 nm) are weighed into a vessel. This material has a pore volume determined by the WAK of 1.12 mL/g. The polymer solution for coating is prepared. 79.6 g of a polyvinylamine solution (solid content 11.3 wt.%) are diluted with 20 g of water. The pH of the solution is adjusted to 9.5 using 3 ml of concentrated hydrochloric acid. The polymer solution is added to the support and mixed on a sieve machine for 6 hours. Subsequently, the coated support is dried for 48 hours at 50°C in a vacuum drying oven at 25 mbar.

The material was coated with 0.08 g of PVA per mL of pore volume.

The dried material was suspended in 0.5 L isopropanol in a double-jacket reactor and cross-linked with 3.64 g ethylene glycol diglycidyl ether at 55°C over 6 hours.

The coated material is washed with the following solvents: 400 mL isopropanol, 1200 mL 0.1 M HCl, 400 mL water, 800 mL of 0.5 M triethylamine in water, 600 mL water, 600 mL methanol.

Subsequently, the material is dried. Yield: 108.0 g of dried material.

Analysis: The concentration of amino groups determined by titration is 593 µmol/mL.

Production of a double-coated sorbent on a silicate support:

250 g of AGC D-50-120A silica gel (average pore size 12 nm) are weighed into a vessel. This material has a pore volume determined by the WAK of 1.12 mL/g. The polymer solution for coating is prepared. 200 g of a polyvinylamine solution (solid content 11.3 wt.%) are diluted with 60 g of water. The pH of the solution is adjusted to 9.5 using 7.5 ml of concentrated hydrochloric acid. The polymer solution is added to the support and mixed for 6 hours on the sieve machine through vibration. Subsequently, the coated support is dried for 48 hours at 50°C in a vacuum oven at 25 mbar. The material lost 230 g of water during drying. The material is coated a second time. For this purpose, 200 g of polyvinylamine solution (solid content 11.3 wt.%) are adjusted to a pH of 9.5 with 6.8 mL of concentrated HCl and then diluted with 23 g of water. The polymer solution is added to the support and again mixed for 6 hours on the sieve machine through vibration. Subsequently, the coated support is dried for 48 hours at 50°C in a vacuum oven at 25 mbar.

The material was coated with 0.16 g of PVA per mL of pore volume.

The dried material was suspended in 1.5 L isopropanol in a double-jacket reactor and cross-linked with 18.2 g ethylene glycol diglycidyl ether at 55°C over 6 hours.

The coated material is washed with the following solvents: 1000 mL isopropanol, 3000 mL 0.1 M HCl, 1000 mL water, 2000 mL of 0.5 M triethylamine in water, 1500 mL water, 1500 mL methanol.

Subsequently, the material is dried. Yield: 308 g of dried material.

Analysis: The concentration of amino groups determined by titration is 1254 µmol/mL.

Production of a tri-layer coated sorbent on a silicate support:

250 g of AGC D-50-120A silica gel (average pore size 12 nm) are weighed into a vessel. This material has a pore volume determined by the WAK of 1.12 mL/g. The polymer solution for coating is prepared. 199 g of a polyvinylamine solution (solid content 11.3 wt.-%) are diluted with 60 g of water. The pH value of the solution is adjusted to 9.5 using 7.6 ml of concentrated hydrochloric acid. The polymer solution is added to the support and mixed for 6 hours on a sieve shaker by vibration. Subsequently, the coated support is dried for 48 hours at 50°C in a vacuum oven at 25 mbar. The material lost 231 g of water during drying.The material is coated for the second time. For this purpose, 200 g of polyvinylamine solution (solid content 11.3 wt.%) are adjusted to a pH value of 9.5 with 7.0 mL concentrated HCl and diluted with 24 g water. The polymer solution is added to the carrier and mixed again for 6 hours on the sieve machine by vibration. Subsequently, the coated carrier is dried for 48 hours at 50°C in a vacuum oven at 25 mbar. The material has lost 210 g of water through drying. The material is coated for the third time. For this purpose, 199 g of polyvinylamine solution (solid content 11.3 wt.%) are adjusted to a pH value of 9.5 with 7.0 mL concentrated HCl.5 is added and diluted with 4 g of water. The polymer solution is added to the carrier and mixed again for 6 hours on the sieve machine using vibration. Subsequently, the coated carrier is dried for 48 hours at 50°C in a vacuum drying oven at 25 mbar.

The material was coated with 0.24 g of PVA per mL of pore volume.

The dried material was suspended in 1.5 L isopropanol in a double-jacket reactor and cross-linked with 27.3 g ethylene glycol diglycidyl ether at 55°C over 6 hours.

The coated material is washed with the following solvents: 1000 mL isopropanol, 3000 mL 0.1 M HCl, 1000 mL water, 2000 mL of 0.5 M triethylamine in water, 1500 mL water, 1500 mL methanol.

Subsequently, the material is dried. Yield: 330 g of dried material.

Analysis: The concentration of amino groups determined by titration is 1818 µmol/mL.

Figure 8 clearly shows that the binding capacity of the double- and triple-coated sorbent increases drastically compared to the single-coated sorbent.

Comparative Example 2: Preparation of an adsorbent according to Example 2 of DE 10 2011 107 197 A1:

As a basis for the sorbent, Amberchrom CG1000S from Rohm & Haas is used. This material is sulfonated as follows: 165 mL of concentrated H2SO4 is placed into a temperature-controlled 250 mL reactor. Then, 30.0 g of the support material is added to the sulfuric acid, and the weighing bottle is rinsed three times with 20 mL of concentrated sulfuric acid each. After adding the support material, the suspension is stirred and heated to 80°C. After 3 hours of reaction time, the suspension is drained from the reactor and distributed into two 150 mL syringes. The sulfuric acid is suctioned off, and the phase is then successively washed with 200 mL of diluted (62%) sulfuric acid, 125 mL of water, 175 mL of methanol, 125 mL of water, and finally with 175 mL of methanol. The phase is then dried by suction and subsequently dried under vacuum at 50°C. The water uptake capacity or pore volume of the resulting sulfonated polystyrene is determined by weighing the dried, sulfonated polystyrene, adding the same volume of water, and then centrifuging off the excess water. The water located in the pores remains in place.

To coat the polystyrene, an aqueous polyvinylamine solution is prepared, which consists of polyvinylamine with an average molecular weight of 35,000 g/mol. The pH is adjusted to 9.5. The amount of polyvinylamine corresponds to 15% of the polystyrene to be coated, and the volume of the solution amounts to 95% of the determined pore volume of the polystyrene. The polyvinylamine solution is then added together with the polystyrene into a tightly closed PE bottle and shaken for 6 hours on a sieve shaker at high frequency. Sufficient mixing must be ensured. After the procedure, the polyvinylamine solution has penetrated into the pores of the polystyrene. Subsequently, the polystyrene is dried at 50°C in a vacuum oven until a constant weight is achieved.

For the crosslinking of polyvinylamine, the coated polystyrene is taken up in three times its volume of isopropanol and then mixed with 5% diethyleneglycol diglycidyl ether, based on the number of amino groups of the polyvinylamine. The reaction mixture is stirred for six hours in the reactor at 55°C. Subsequently, it is transferred to a glass filter funnel and washed with two bed volumes of isopropanol, three bed volumes of 0.5 M TFA solution, two bed volumes of water, four bed volumes of 1 M sodium hydroxide solution, and finally eight bed volumes of water.

Analysis: The concentration of amino groups determined by titration is 265 µmol/mL.

Claims (12)

1. Sorbent, comprising a porous support material coated with a crosslinked amino group-containing polymer, wherein the concentration of the amino groups of the sorbent determined by titration is at least 600 µmol/mL, based on the total volume of the sorbent, and wherein the amino group-containing polymer is selected from polyvinylamine, polyallylamine and polylysine, wherein the concentration of the amino groups of the sorbent is determined by means of breakthrough measurement with 4-toluenesulphonic acid, as described in the "Analytical methods" section of the description.
2. Sorbent according to claim 1, wherein the ratio of the mass of the amino group-containing polymer to the total volume of the pores of the porous support material is greater than or equal to 0.1 g/mL, wherein the mass of the amino group-containing polymer is determined by the increase in the tamped density compared with the support material according to DIN 53194, and wherein the total volume of the pores of the porous support material is determined by the solvent absorption capacity of the porous support material, wherein the solvent absorption capacity, reported in the unit g (organic solvent)/ mL (dry sorbent), is measured by thoroughly wetting an exactly weighed quantity of dry sorbent with an organic solvent such as for example dimethylformamide and removing excess solvent from the inter-particle volume by centrifugation, determining the mass of the retained solvent by weighing and converting it into the volume via the density of the organic solvent.
3. Sorbent according to claim 1 or 2, wherein the pore volume of the porous support material lies in the range from 30 to 90 vol.-%, based on the total volume of the porous support material, wherein the pore volume is determined in the same way as the total volume of the pores of the porous support material in claim 2.
4. Sorbent according to one of claims 1 to 3, wherein the porous support material has an average pore size in the range from 6 nm to 400 nm, wherein the average pore size of the porous support material is determined by the pore filling method with mercury according to DIN 66133.
5. Sorbent according to one of claims 1 to 4, wherein the porous support material comprises an organic polymer, an inorganic material or a composite material of organic polymer and inorganic material.
6. Sorbent according to one of claims 1 to 5, wherein the amino group-containing polymer is present not covalently linked with the porous support material.
7. Process for the production of a sorbent according to one of claims 1 to 6, which comprises the following steps:

   (a) provision of a porous support material;

   (b) application of an amino group-containing polymer onto the porous support material by a pore filling method, wherein the amino group-containing polymer is selected from polyvinylamine, polyallylamine and polylysine;

   (c) removal of the solvent used in the pore filling method;

   (d) repetition of steps (b) and (c); and

   (e) crosslinking of the amino group-containing polymer,

   wherein the steps (b) and (c) are repeated before the step (e) sufficiently often that the concentration of the amino groups of the sorbent determined after step (e) by titration is at least 600 µmol/mL, based on the total volume of the sorbent, wherein the concentration of the amino groups of the sorbent is determined by means of breakthrough measurement with 4-toluenesulphonic acid, as described in the "Analytical methods" section of the description.
8. Process according to claim 7, wherein the ratio of the mass of the amino group-containing polymer to the total volume of the pores of the porous support material after step (d) is greater than or equal to 0.1 g/mL, wherein the mass of the amino group-containing polymer and the total volume of the pores of the porous support material are determined in the same way as in claim 2.
9. Process according to one of claims 7 or 8, wherein step (c) is performed at a temperature in the range from 40 to 80°C and/or a pressure in the range from 0.01 bar to 1 bar.
10. Process according to one of claims 7 to 9, wherein the concentration of the amino group-containing polymer in the solvent used for the pore filling method in step (b) lies in the range from 5 g/L to 200 g/L.
11. Process according to one of claims 7 to 10, wherein in a step (f) an organic residue which has the nature of a Lewis base is bound onto the amino group-containing polymer.
12. Use of a sorbent according to one of claims 1 to 6 for binding metals from solutions.