REMOVING METAL IONS WITH A MEMBRANE BASED ON ANIONIC POLYARYLENE ETHERSULFONE AND A CATIONIC POLYMER WITH AMINO GROUPS

Abstract

The present invention relates to a method for removing metal ions from an aqueous system comprising a step of filtering the aqueous system through a loaded membrane which contains a carrier membrane based on a polyarylene ethersulfone which carries anionic groups, and a cationic polymer which is a polymer comprising primary and/or secondary amino groups. The invention further relates to a loaded membrane which contains a carrier membrane based on a polyarylene ethersulfone which carries anionic groups, and a cationic polymer which is a polymer comprising primary and/or secondary amino groups.

Claims

1. A method for removing metal ions from an aqueous system comprising a step of filtering the aqueous system through a loaded membrane which contains a carrier membrane based on a polyarylene ethersulfone which carries anionic groups, and a cationic polymer which is a polymer comprising primary and/or secondary amino groups.

2. The method according to claim 1 where the cationic polymer is polyethyleneimine, polyethyleneimine-polyvinylalcohol, poly-L-lysine, diethylaminoethyl-dextran, chitosan, polyetheramine, and polymers based on vinylamine.

3. The method according to claim 1 or 2 where the anionic groups are sulfonate, carboxylate, or phosphonate groups.

4. The method according to any of claims 1 to 3 where the carrier mebrane is based on a) a sulfonated polyarylene ethersulfone; b) a carboxylated polyarylene ethersulfone; or c) a carrier polymer obtainable by reacting at least one aromatic dihalide (M1a), a dialkali metal salt of at least one aromatic diol (M2a), and at least one anionic monomer, where the anionic monomer is a sulfonated monomer selected from sulfonated aromatic dihalide (M1b) and/or sulfonated aromatic diol (M2b), and/or a carboxylic monomer selected from aromatic diols which carry a carboxylate group (M2c).

5. The method according to claim 4 where the sulphonated monomers are of the general formulae M1b and M2b ##STR00015## where Ar is divalent aromatic residue, Hal is F, Cl, Br or I, n and m independently are 0, 1 or 2, provided that n and m are not simultaneously 0, and the aryl groups of M1a and M2a may carry at least one C.sub.1-C.sub.4 alkyl group.

6. The method according to claim 4 where the carboxylic monomer is of the general formula M2c ##STR00016## where R.sub.1 is a divalent alkyl residue which carries a —CO.sub.2H group.

7. The method according to any of claims 1 to 6 where 0.1 to 40 mol %, preferably 0.3 to 30 mol %, and in particular 0.5 to 25 mol % of the repeating units of the polyarylether sulfone carry at least one anionic group.

8. The method according to any of claims 1 to 7 where the metal ions are selected from Ca, Mg, Al, Cu, Ni, Pb, Zn, Sb, Co, Cr, Cd, Hg, Po, Ra, Rn, Th, U, Pu, Sr, Cs, Pm and/or Ag.

9. The method according to any of claims 1 to 8 where the carrier membrane has a molecular weight cut-off from 20,000 to 200,000 Da, and the loaded membrane has a molecular weight cut of below 20,000 Da.

10. The method according to any of claims 1 to 9 where the loaded membrane is an ultrafiltration membrane.

11. The method according to any of claims 1 to 10 where the loaded membrane has a pure water permeability from 20 to 500 LMH/bar.

12. The method according to any of claims 1 to 11 where the carrier membrane has a pure water permeability from 200 to 1000 LMH/bar.

13. The method according to any of claims 1 to 12 further comprising a step of regenerating the loaded membrane after the filtering step by a treatment with an oxidation agent or a strong acid, and a subsequent step of a treatment with the cationic polymer.

14. A loaded membrane as defined in any of claims 1 to 13 which contains a carrier membrane based on a polyarylene ethersulfone which carries carboxylate groups, and a cationic polymer which is a polymer comprising primary and/or secondary amino groups, where the carrier mebrane is based on a carrier polymer obtainable by reacting at least one aromatic dihalide (M1a), a dialkali metal salt of at least one aromatic diol (M2a), and at least one anionic monomer, where the anionic monomer is a carboxylic monomer selected from aromatic diols which carry a carboxylate group (M2c).

15. The loaded membrane according to claim 14 where the carboxylic monomer is of the general formula M2c ##STR00017## where R.sub.1 is a divalent alkyl residue which carries a —CO.sub.2H group.

16. The loaded membrane according to claim 14 or 15 where the loaded membrane is an ultrafiltration membrane, and where the PWP is from 20 to 500 LMH/bar.

Description

EXAMPLES

[0125] PPSU-1: A polyphenylenesulfone (PPSU) with a viscosity number (ISO 307, 1157, 1628; in 0.01 g/mol phenol/1,2 orthodichlorobenzene 1:1 solution) of 71 and a glass transition temperature (DSC, 10° C./min; according to ISO 11357-1/-2) of 220° C. [0126] PVP-1: A polyvinylpyrrolidone with a solution viscosity characterised by the K-value of 90, determined according to the method of Fikentscher. [0127] PEI-1: Aqueous polyethyleneimine solution with a concentration of 99% (ISO3251), a viscosity number >200000 mPa*s (ISO 2555) and an average molecular weight of 25000 g/mol (GPC). [0128] PEI-2: Aqueous polyethyleneimine solution (FG) with a concentration of 99% (ISO3251), a viscosity number of 5000 mPa*s (ISO 2555) and an average molecular weight of 800 g/mol (GPC).

Example 1—Synthesis of Anionic Polymer “DPAcoPPSU-11.2”

[0129] In a 4 l vessel equipped a with stirrer, Dean-Stark-trap, nitrogen inlet and temperature control 585.8 g (2.04 mol) of dichlorodiphenyl sulfone, 335.2 g (1.80 mol) of dihydroxydiphenyl and 57.2 g (0.20) of bis-4,4-(4-hydroxyphenyl)valeric acid were dissolved, under nitrogen, in 1538 ml of N-methylpyrrolidone and mixed with 317 g (2.30 mol) of anhydrous potassium carbonate. The reaction mixture was firstly heated at 180° C., for 1 h at a pressure of 300 mbar, the water of reaction and N-methylpyrrolidone being continuously distilled off, and then reacted for 6 h at 190° C. After adding 1462 ml of N-methylpyrrolidone, the inorganic constituents were filtered off. Basic groups were neutralized by adding 300 ml of glacial acetic acid and the polymer was then isolated by precipitation in water. After three extractions with water, the product was dried under reduced pressure at 140° C., giving a white powder (DPAcoPPSU-11.2).

[0130] The proportion of units having acid groups was determined using .sup.1H-NMR as 11.2 mol % and the viscosity number of the product was 66.3 ml/g.

Example 2—Synthesis of Anionic Polymer “DPAcoPPSU-17”

[0131] In a 4 l vessel equipped a with stirrer, Dean-Stark-trap, nitrogen inlet and temperature control 585.8 g (2.04 mol) of dichlorodiphenyl sulfone, 316.6 g (1.70 mol) of dihydroxydiphenyl and 85.9 g (0.30 mol) of bis-4,4-(4-hydroxyphenyl)valeric acid were dissolved, under nitrogen, in 1538 ml of N-methylpyrrolidone and mixed with 331.7 g (2.40 mol) of anhydrous potassium carbonate. The reaction mixture was firstly heated at 180° C., for 1 h at a pressure of 300 mbar, the water of reaction and N-methylpyrrolidone being continuously distilled off, and then reacted for 6 h at 190° C. After adding 1462 ml of N-methylpyrrolidone, the inorganic constituents were filtered off. Basic groups were neutralized by adding 300 ml of glacial acetic acid and the polymer was then isolated by precipitation in water. After three extractions with water, the product was dried under reduced pressure at 140° C., giving a white powder (DPAcoPPSU-17).

[0132] The proportion of units having acid groups was determined using .sup.1H-NMR as 17 mol % and the viscosity number of the product was 61.3 ml/g.

Example 3—Synthesis of Anionic Polymer “DPAcoPPSU-20.6”

[0133] In a 4 l vessel equipped a with stirrer, Dean-Stark-trap, nitrogen inlet and temperature control 582.9 g (2.03 mol) of dichlorodiphenyl sulfone, 297.9 g (1.60 mol) of dihydroxydiphenyl and 114.5 g (0.40 mol) of bis-4,4-(4-hydroxyphenyl)valeric acid were dissolved, under nitrogen, in 1538 ml of N-methylpyrrolidone and mixed with 345.5 g (2.50 mol) of anhydrous potassium carbonate. The reaction mixture was firstly heated at 180° C., for 1 h at a pressure of 300 mbar, the water of reaction and N-methylpyrrolidone being continuously distilled off, and then reacted for 6 h at 190° C. After adding 1462 ml of N-methylpyrrolidone, the inorganic constituents were filtered off. Basic groups were neutralized by adding 300 ml of glacial acetic acid and the polymer was then isolated by precipitation in water. After three extractions with water, the product was dried under reduced pressure at 140° C., giving a white powder (DPAcoPPSU-20.6).

[0134] The proportion of units having acid groups was determined using .sup.1H-NMR as 20.6 mol % and the viscosity number of the product was 61.7 ml/g.

Example 4—Synthesis of Anionic Polymer “sPPSU-2.4”

[0135] In a 4 l vessel equipped a with stirrer, Dean-Stark-trap, nitrogen inlet and temperature control, a reaction mixture was provided, by suspending 580.1 g (2.02 mol) of 4,4′-dichlorodiphenylsulfone (DCDPS), 335.2 g (1.80 mol) of 4,4′-dihydroxybiphenyl (DHB), 45.7 g (0.2 mol) bisphenol A, 14.7 g (0.03 mol) of 4,4′-dichlorodiphenylsulfone-3,3′-disulfonic acid disodium salt and 293 g (2.12 mol) of potassium carbonate nitrogen atmosphere in 1250 ml of N-methylpyrrolidone. The reaction mixture was heated to 190° C. under stirring and kept at 190° C. for 6 h, during which nitrogen was purged through the reaction mixture at 30 I/h. Subsequently, 1750 ml of N-methylpyrrolidone was added and the reaction mixture was cooled down to 60° C. under nitrogen. The reaction mixture was filtered and precipitated in water comprising g 100 ml HCl (2 M). The precipitated product was extracted with hot water for 20 h at 85° C. and dried at 120° C. for 24 h under reduced pressure to obtain the sulfonated polyphenylene sulfone (sPPSU-2.4).

[0136] The proportion of units having acid groups was determined using+1-NMR as 2.4 mol % and the viscosity number of the product was 77.0 ml/g (1 wt/vol-% solution in N-methylpyrrolidone at 25° C.).

Example 5—Synthesis of Anionic Polymer “sPPSU-2.1”

[0137] In a 4 l vessel equipped a with stirrer, Dean-Stark-trap, nitrogen inlet and temperature control, a reaction mixture was provided, by suspending 580.1 g (2.02 mol) of 4,4′-dichlorodiphenylsulfone (DCDPS), 335.2 g (1.80 mol) of 4,4′-dihydroxybiphenyl (DHB), 45.7 g (0.2 mol) bisphenol A, 14.7 g (0.03 mol) of 4,4′-dichlorodiphenylsulfone-3,3′-disulfonic acid disodium salt and 293 g (2.12 mol) of potassium carbonate nitrogen atmosphere in 1250 ml of N-methylpyrrolidone. The reaction mixture was heated to 190° C. under stirring and kept at 190° C. for 6 h, during which nitrogen was purged through the reaction mixture at 30 I/h. Subsequently, 1750 ml of N-methylpyrrolidone was added and the reaction mixture was cooled down to 60° C. under nitrogen. The reaction mixture was filtered and precipitated in water comprising g 100 ml HCl (2 M). The precipitated product was extracted with hot water for 20 h at 85° C. and dried at 120° C. for 24 h under reduced pressure to obtain the sulfonated polyphenylene sulfone (sPPSU-2.1).

[0138] The proportion of units having acid groups was determined using .sup.1H-NMR as 2.1 mol % and the viscosity number of the product was 75.2 ml/g (1 wt/vol-% solution in N-methylpyrrolidone at 25° C.).

Example 6—Preparation of Carrier Membrane

[0139] Into a three-neck flask equipped with a magnetic stirrer there were added 65 ml of N-methylpyrrolidone, 6 g PVP-1, 10 g 1,2-propandiol and 19 g of one of the polymers from the Examples 1 to 5. The mixture was heated under gentle stirring at 60° C. until a homogeneous clear viscous solution was obtained. The solution was degassed overnight at room temperature. After that the membrane solution was reheated at 60° C. for 2 hours and casted onto a glass plate with a casting knife (300 microns) at 60° C. using an Erichsen Coating machine operating at a speed of 5 mm/min. The membrane film was allowed to rest for 30 seconds before immersion in a water bath at 25° C. for 10 minutes to coagulate the polymers to form the carrier membrane.

[0140] Workup of the membrane: After the membrane had detached from the glass plate, the membrane was carefully transferred into a water bath for 12 h. Afterwards the membrane was transferred into a bath containing 2500 ppm NaOCl at 50° C. for 4.5 h to remove polyvinylpyrrolidone. The membrane was then washed with water at 60° C. and one time with a 0.5 wt.-% solution of sodium bisulfite to remove active chlorine. After several washing steps with water the membrane was stored wet until characterization as described in Example 7.

Example 7—Characterization of Carrier Membrane

[0141] The membranes prepared in Example 6 including the corresponding Comparative Membrane based on PPSU-1 were characterized. The results are summarized in Table 1.

[0142] The pure water permeation (PWP in kg/h*m.sup.2*bar) of the membranes was tested using a pressure cell with a diameter of 60 mm using ultrapure water (salt-free water, filtered by a Millipore UF-system). In a subsequent test, a solution of different PEG-Standards was filtered at a pressure of 0.15 bar. By GPC-measurement of the feed and permeate, the molecular weight cut-off (MWCO in kDa) of the membranes were determined.

TABLE-US-00001 TABLE 1 Pure water permeation (PWP) and molecular weight cut-off (MWCO) of membranes PWP MWCO Carrier Membrane Based on polymer [kg/h * m.sup.2 * bar] [kDa] Example 7.1 DPAcoPPSU-11.3 390 26 Example 7.2 DPAcoPPSU-17.0 465 30 Example 7.3 DPAcoPPSU-20.6 385 16 Example 7.4 sPPSU-2.4 310 25 Example 7.5 sPPSU-2.1 410 30 Comparative 7.6 PPSU-1 540 17

Example 8—Loading of Membranes with Cationic Polymers

[0143] The membranes prepared in Example 6 and characterized in Example 7 were stored in 0.1 N sulfuric acid for 15 min, then rinsed with water until neutral and subsequently stored for 15 min in an aqueous coating solution, which contained 5 wt % of a cationic polymer as listed in Table 2. Finally the sample was rinsed until the washing water is pH neutral. The results of the characterization are summarized in Table 2.

[0144] The data demonstrated that different cationic polymer can be flexible loaded to the carrier membrane, and that the loaded membranes have a high quality regarding PWP and MWCO.

TABLE-US-00002 TABLE 2 Pure water permeation (PWP) and molecular weight cut-off (MWCO) of membranes Carrier Cationic PWP MWCO Membrane Based on polymer polymer [kg/h*m.sup.2*bar] [kDa] Example 8.1 DPAcoPPSU-11.3 PEI-2 70 2.9 Example 8.2 DPAcoPPSU-17.0 PEI-1 100 14 Example 8.3 DPAcoPPSU-20.6 PEI-2 60 8 Example 8.4 sPPSU-2.4 PEI-2 110 15 Example 8.5 sPPSU-2.1 PEI-1 280 29 Comparative 8.6 PPSU-1 PEI-2 540 17

Example 9—Regenerating the Loaded Membrane

[0145] The loaded membranes, which were prepared in Example 8, were transferred into a bath containing 2500 ppm NaOCl at 50° C. for 4.5 h to remove the coating. The membrane was then washed with water at 60° C. and after several times rinsing with water the membrane was stored wet until characterization as summarized in Table 3.

[0146] The data demonstrated that the PWP and MWCO after regeneration is in the similar range as the original carrier membrane (cf Table 1). Thus, it was shown that the loaded membrane can be regenerated and optionally stored during the conventional membran washing steps, such as chemical back wash cycles.

TABLE-US-00003 TABLE 3 Pure water permeation (PWP) and molecular weight cut-off (MWCO) of membranes Cationic PWP MWCO Example Based on polymer polymer [kg/h*m.sup.2 * bar] [kDa] Example 9.1 DPAcoPPSU-11.3 PEI-2 640 23 Example 9.2 DPAcoPPSU-17.0 PEI-1 660 26 Example 9.3 DPAcoPPSU-20.6 PEI-2 530 17 Example 9.4 sPPSU-2.4 PEI-2 320 30 Example 9.5 sPPSU-2.1 PEI-1 400 33 Comparative 9.6 PPSU-1 PEI-2 525 17

Example 10—Metal Ion Binding Capacity of Loaded Membrane

[0147] Metal ion concentrations of the loaded membranes prepared in Example 8 in aqueous solutions were determined with a photometer NOVA 60 Spectroquant® (Merck KGaA) using the test sets for copper (0.05-8.00 mg/I Cu; No. 1.14553.0001) and nickel (0.1-6.00 mg/I Ni; No. 1.14554.0001).

[0148] Circular membrane specimen of 7.4 cm diameter (43 cm.sup.2) was punched out and stored in 4.16 ppm solution of CuSO.sub.4 or 5.18 ppm NiSO.sub.4 aqueous solution. After 60 minutes the concentration was estimated again and the metal ion binding capacity calculated.

[0149] The data demonstrated that the loaded membranes allow not only the filtration with a MWCO as analyzed in Table 2, but in addition the removal of metal ions.

TABLE-US-00004 TABLE 4 Metal ion binding capacity of loaded membranes Cationic Cu (II) Ni (II) Example Based on polymer polymer [mg/m.sup.2] [mg/m.sup.2] Example 10.1 DPAcoPPSU-11.3 PEI-2 29 11 Example 10.2 DPAcoPPSU-17.0 PEI-1 7 17 Example 10.3 DPAcoPPSU-20.6 PEI-2 24 13 Example 10.4 sPPSU-2.4 PEI-2 13 4 Example 10.5 sPPSU-2.1 PEI-1 19 17 Comparative 10.6 PPSU-1 PEI-2 <1 1