WO2017220363A1

WO2017220363A1 - Process for removing arsenic compounds from aqueous systems

Info

Publication number: WO2017220363A1
Application number: PCT/EP2017/064238
Authority: WO
Inventors: Martin Heijnen; Peter Berg; Martin Weber; Jia Le LOW; Natalia Widjojo; Claudia Staudt; Marc Rudolf Jung
Original assignee: Basf Se
Priority date: 2016-06-20
Filing date: 2017-06-12
Publication date: 2017-12-28

Abstract

Use of a membrane M, comprising at least one sulfonated polyarylene ether A for removing arsenic compounds AS from aqueous systems, said membrane M being an ultrafiltration or microfiltration membrane with a molecular weight cutoff of at least 2,500 Da.

Description

Process for removing arsenic compounds from aqueous systems

The present invention is directed to the use of membranes M comprising at least one sulfonated polyarylene ether A for removing arsenic compounds AS from aqueous systems, said mem- brane M being an ultrafiltration or microfiltration membrane with a molecular weight cutoff of at least 2,500 Da.

Different types of membranes play an increasingly important role in many fields of technology. In particular, methods for treating water rely more and more on membrane technology.

There is a need for membranes with improved separation characteristics. In particular, it is desirable to have membranes capable of removing metal ions like arsenic compounds from water.

The following documents disclose alternative methods for removing arsenic compounds from water:

Saad et al., Water SA 2013, 39, 257 - 264;

Awual, M. R. A.; Jyo, A. Water Research 2009, 43, 1229 - 1236;

Awual, M. R. A.; Shenashen, M. A.; Yaita, T.; Shiwaku, H.; Jyo, A. Water Research 2012, 46, 5541 - 5550;

An, B.; Steinwinder, T. R.; Zhao, D. Y. Water Research 2005, 39, 4993 - 5004.

It was therefore an objective of the present invention to provide membranes with good permeabilities and rejection performance that are capable of removing arsenic compounds from aqueous systems.

These objectives have been solved by using membranes M comprising at least one sulfonated polyarylene ether A for removing arsenic compounds AS from aqueous systems. In another form the object was solved by a use of a membrane M comprising at least one sulfonated polyarylene ether A for removing arsenic compounds AS from aqueous systems, wherein said membrane M is an ultrafiltration or microfiltration membrane with a molecular weight cutoff of at least 2,500 Da.

In the context of this application, a membrane shall be understood to be a thin, semipermeable structure capable of separating two fluids or separating molecular and/or ionic components or particles from a liquid. A membrane acts as a selective barrier, allowing some particles, substances or chemicals to pass through, while retaining others.

"Aqueous systems" in this context shall mean solutions, dispersions or other mixtures with water. Preferably aqueous systems of arsenic compounds AS are solutions of arsenic compounds AS in water. When reference is made herein to a sulfonated polymer or to the presence of a sulfonic acid group in a polymer or a molecule, this shall include such sulfonic acid groups -SO3H as well as salts of sulfonic acid like sodium sulfonates. In the context of this application, a "sulfonated" molecule carries at least one sulfonate residue of the type -SO3H, or the corresponding metal salt form thereof of the type -S03^"M⁺, like an alkali metal salt form with M = Na, K or Li.

"Partially sulfonated" or "partly sulfonated" in the context of the present invention refers to a pol- ymer or monomer, wherein merely a certain proportion of the monomeric constituents is sulfonated and contains at least one sulfo group residue. I shall be understood that in the context of this application "sulfonated polyarylene ether A" are partly sulfonated.

Membranes M comprise as the main component or as an additive at least one partly sulfonated polyarylene ether A. In one embodiment, membranes M comprise as the main component or as an additive at least one partly sulfonated polysulfone, partly sulfonated polyphenylenesulfone and/or partly sulfonated polyethersulfone. In one embodiment, membranes M comprise as the main component or as an additive at least one partly sulfonated polyphenylenesulfone.

Suitable sulfonated polyarylene ethers A are known as such to those skilled in the art and can be derived from polyarylene ether units of the general formula I

with the following definitions: t, q: each independently 0, 1 , 2 or 3,

Q, T, Y: each independently a chemical bond or group selected from -0-, -S-, -SO2-, S=0,

C=0, -N=N-, -CR^aR^b- where R^a and R^b are each independently a hydrogen atom or a Ci-Ci2-alkyl, Ci-Ci2-alkoxy or C6-Ci8-aryl group, where at least one of Q, T and Y is not -0-, and at least one of Q, T and Y is -SO2-, and

Ar, Ar¹: each independently an arylene group having from 6 to 18 carbon atoms, wherein the aromatic moieties are partly sulfonated.

Optionally the aromatic rings as contained independently of each other may be further substituted.

The term "sulfonated" means that such sulfonated arylene moieties contain a sulfonate -SO3^" group or sulfonic acid group -SO3H bound to an aromatic ring. In one embodiment, sulfonated polyarylene ether A comprise non-sulfonated and sulfonated repeating units wherein said sulfonated repeating units are contained in said sulfonated polyarylene ether A in a number average molar proportion of 0.1 to 20 mole-%, based on the sulfonated polyarylene ether A.

In one embodiment, 0.1 to 20 mole% of the aromatic rings, calculated as 6 membered rings, of sulfonated polyarylene ether A are sulfonated. More preferably, 0.3 to 10 mol%, even more preferably 0.5 to 5 mole% and especially 1 to 3.5 mol% of the aromatic moieties of sulfonated polyarylene ether A are sulfonated. The content of sulfonated aromatic rings in sulfonated polyarylene ether A can be determined using ¹³C NMR spectroscopy. In one embodiment, sulfonated polyarylene ether A comprise non-sulfonated and sulfonated monomers and wherein said sulfonated monomers, calculated as 3,3'-disodiumdisulfonate-4,4'- dichlorodiphenylenesulfone, are comprised in copolymer C in an amount of 0.25 to 10 % by weight, preferably 0.5 to 7.5 % by weight. The content of sulfonated monomers in copolymer C can be determined by FT-IR spectroscopy as described in the experimental section.

In one embodiment, sulfonated polyarylene ether A comprise non-sulfonated and sulfonated monomers and wherein said sulfonated monomers, calculated as 3,3'-disodiumdisulfonate-4,4'- dichlorodiphenylenesulfone, are comprised in sulfonated polyarylene ether A in an amount of 0.25 to 10 % by weight, preferably 0.5 to 7.5 % by weight.

Suitable sulfonated polyarylene ether A can be provided by reacting at least one starting compound of the structure X-Ar-Y (M1 ) with at least one starting compound of the structure HO- Ar¹-OH (M2) in the presence of a solvent (L) and of a base (B), where

Y is a halogen atom,

- X is selected from halogen atoms and OH, preferably from halogen atoms, especially F, CI or Br, and

Ar and Ar¹ are each independently an arylene group having 6 to 18 carbon atoms. For making copolymer C, starting materials (M1 ) or (M2) of both are partly sulfonated.

If Q, T or Y, with the abovementioned prerequisites, is a chemical bond, this is understood to mean that the group adjacent to the left and the group adjacent to the right are bonded directly to one another via a chemical bond. Preferably, Q, T and Y in formula (I), however, are independently selected from -O- and -SO2-, with the proviso that at least one of the group consisting of Q, T and Y is -SO2-.

When Q, T or Y are -CR^aR^b-, R^a and R^b are each independently a hydrogen atom or a C1-C12- alkyl, Ci-Ci2-alkoxy or C6-Ci8-aryl group.

Preferred Ci-Ci2-alkyl groups comprise linear and branched, saturated alkyl groups having from 1 to 12 carbon atoms. Particularly preferred Ci-Ci2-alkyl groups are: Ci-C6-alkyl radicals such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, 2- or 3-methylpentyl and longer-chain radicals such as unbranched heptyl, octyl, nonyl, decyl, undecyl, lauryl, and the singularly or multiply branched analogs thereof.

Useful alkyl radicals in the aforementioned usable Ci-Ci2-alkoxy groups include the alkyl groups having from 1 to 12 carbon atoms defined above. Cycloalkyl radicals usable with preference comprise especially C3-Ci2-cycloalkyl radicals, for example cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclopropylmethyl, cyclopropylethyl, cyclopropylpropyl, cyclobutylmethyl, cyclobutylethyl, cyclpentylethyl, -propyl, -butyl, -pentyl, -hexyl,

cyclohexylmethyl, -dimethyl, -trimethyl.

Ar and Ar¹ are each independently a C6-Ci8-arylene group. Proceeding from the starting materials described below, Ar is preferably derived from an electron-rich aromatic substance which is preferably selected from the group consisting of hydroquinone, resorcinol,

dihydroxynaphthalene, especially 2,7-dihydroxynaphthalene, and 4,4'-bisphenol. Ar¹ is preferably an unsubstituted C6- or Ci2-arylene group.

Useful C6-Ci8-arylene groups Ar and Ar¹ are especially phenylene groups, such as 1 ,2-, 1 ,3- and 1 ,4-phenylene, naphthylene groups, for example 1 ,6-, 1 ,7-, 2,6- and 2,7-naphthylene, and the arylene groups derived from anthracene, phenanthrene and naphthacene.

Preferably, Ar and Ar¹ in the preferred embodiments of the formula (I) are each independently selected from the group consisting of 1 ,4-phenylene, 1 ,3-phenylene, naphthylene, especially 2,7-dihydroxynaphthalene, and 4,4'-bisphenylene. Units present with preference within the polyarylene ether are those which comprise at least one of the following repeat structural units la to lo:

In addition to the units la to lo present with preference, preference is also given to those units in which one or more 1 ,4-dihydroxyphenyl units are replaced by resorcinol or dihydroxy- naphthalene units. Particularly preferred units of the general formula I are units la, Ig and Ik, wherein Ig is most preferred. It is also particularly preferred when the sulfonated polyarylene ether are formed essentially from one kind of units of the general formula I, especially from one unit selected from la, Ig and Ik, wherein Ig is most preferred. In a particularly preferred embodiment, Ar = 1 ,4-phenylene, t = 1 , q = 0, T = SO2 and Y = SO2. Such polyarylene ethers are referred to as polyether sulfone (PESU).

In another particularly preferred embodiment, Ar = 1 ,4-biphenylene, t = 0, q = 0 and Y = SO2. Such polyarylene ethers are referred to as polyphenylene sulfones (PPSU).

Suitable sulfonated polyarylene ethers A preferably have a mean molecular weight Mn (number average) in the range from 2000 to 70000 g/mol, especially preferably 5000 to 40000 g/mol and particularly preferably 7000 to 30000 g/mol. The average molecular weight of the sulfonated polyarylene ether A can be controlled and calculated by the ratio of the monomers forming the sulfonated polyarylene ether A, as described by H.G. Elias in "An Introduction to Polymer Science" VCH Weinheim, 1997, p. 125.

Suitable starting compounds are known to those skilled in the art and are not subject to any fundamental restriction, provided that the substituents mentioned are sufficiently reactive within a nucleophilic aromatic substitution.

Preferred starting compounds are difunctional. "Difunctional" means that the number of groups reactive in the nucleophilic aromatic substitution is two per starting compound. A further criterion for a suitable difunctional starting compound is a sufficient solubility in the solvent, as explained in detail below.

Preference is given to monomeric starting compounds, which means that the reaction is preferably performed proceeding from monomers and not proceeding from prepolymers. The starting compound (M1) used is preferably a dihalodiphenyl sulfone. The starting compound (M2) used is preferably 4,4'-dihydroxydiphenyl sulfone or 4,4'-dihydroxybiphenyl. For making sulfonated polyarylene ethers A, starting materials (M1 ) or (M2) of both are partly sulfonated. Suitable starting compounds (M1 ) are especially dihalodiphenyl sulfones such as 4,4'-di- chlorodiphenyl sulfone, 4,4'-difluorodiphenyl sulfone, 4,4'-dibromodiphenyl sulfone, bis(2- chlorophenyl) sulfones, 2,2'-dichlorodiphenyl sulfone and 2,2'-difluorodiphenyl sulfone, particular preference being given to 4,4'-dichlorodiphenyl sulfone and 4,4'-difluorodiphenyl sulfone.

Preferably starting compound (M1 ) is a mixture of unsulfonated dihalodiphenyl sulfones (M1 u) such as 4,4'-dichlorodiphenyl sulfone and sulfonated dihalodiphenyl sulfones (M1 s) such as 3,3'-disodiumdisulfonate-4,4'-dichlorodiphenylenesulfone. Preferably sulfonated dihalodiphenyl sulfones (M1 s) is comprised in said mixture in a molar content of 0.1 to 20 mole-%, preferably 0.5 to 10 mol% and even more preferably 1 to 7.5 mol%, based on the amount f (M1 u) and (M1 s).

In one embodiment, starting compound (M1 ) is a mixture of an unsulfonated dihalodiphenyl sulfones (M1 u) and a sulfonated dihalodiphenyl sulfones (M1 s) that is the sulfonation product of a dihalodiphenyl sulfones that is different from the dihalodiphenyl sulfone used as (M1 u). For example, starting compound (M1 ) can be a mixture of 4,4'-dichlorodiphenyl sulfone (M1 u) and 3,3'-disodiumdisulfonate-4,4'-dichlorodinaphthylenesulfone (M1 s).

Preferably, starting compound (M1 ) is a mixture of an unsulfonated dihalodiphenyl sulfone (M1 u) such as 4,4'-dichlorodiphenyl sulfone and a sulfonated dihalodiphenyl sulfone (M1 s) that is the sulfonation product of the same dihalodiphenyl sulfone used as (M1 u). For example, starting compound (M1 ) can be a mixture of 4,4'-dichlorodiphenyl sulfone (M1 u) and 3,3'-di- sodiumdisulfonate-4,4'-dichlorodiphenylenesulfone (M1 s).

Preferred compounds (M2) are accordingly those having two phenolic hydroxyl groups. Phenolic OH groups are preferably reacted in the presence of a base in order to increase the reactivity toward the halogen substituents of the starting compound (M1 ).

Preferred starting compounds (M2) having two phenolic hydroxyl groups are selected from the following compounds:

- dihydroxybenzenes, especially hydroquinone and resorcinol;

- dihydroxynaphthalenes, especially 1 ,5-dihydroxynaphthalene, 1 ,6- dihydroxynaphthalene, 1 ,7-dihydroxynaphthalene, and 2,7-dihydroxynaphthalene;

- dihydroxybiphenyls, especially 4,4'-biphenol and 2,2'-biphenol;

- bisphenyl ethers, especially bis(4-hydroxyphenyl) ether and bis(2-hydroxyphenyl) ether; - bisphenylpropanes, especially 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3-methyl-4- hydroxyphenyl)propane and 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;

- bisphenylmethanes, especially bis(4-hydroxyphenyl)methane;

- bisphenyl sulfones, especially bis(4-hydroxyphenyl) sulfone;

- bisphenyl sulfides, especially bis(4-hydroxyphenyl) sulfide;

- bisphenyl ketones, especially bis(4-hydroxyphenyl) ketone;

- bisphenylhexafluoropropanes, especially 2,2-bis(3,5-dimethyl-4- hydroxyphenyl)hexafluoropropane; and

- bisphenylfluorenes, especially 9,9-bis(4-hydroxyphenyl)fluorene; 1 ,1 -Bis(4-hydroxyphenyl)-3,3,5-trimethyl-cyclohexane (bisphenol TMC).

An especially preferred starting compound (M2) is 4,4'-dihydroxybiphenyl. It is preferable, proceeding from the aforementioned aromatic dihydroxyl compounds (M2), by addition of a base (B), to prepare the dipotassium or disodium salts thereof and to react them with the starting compound (M1 ). The aforementioned compounds can additionally be used individually or as a combination of two or more of the aforementioned compounds. Hydroquinone, resorcinol, dihydroxynaphthalene, especially 2, 7-dihydroxynaphthalene, bisphenol A, dihydroxydiphenyl sulfone and 4,4'-bisphenol are particularly preferred as starting compound (M2).

However, it is also possible to use trifunctional compounds. In this case, branched structures are the result. If a trifunctional starting compound (M2) is used, preference is given to 1 ,1 ,1 - tris(4-hydroxyphenyl)ethane.

In another form the polyarylene ether A is free of triphenylphosphine oxide and halogenated derivatives of triphenylphosphine oxide (e.g. 4,4'-difluoro-triphenylphosphine oxide).

The ratios to be used derive in principle from the stoichiometry of the polycondensation reaction which proceeds with theoretical elimination of hydrogen chloride, and are established by the person skilled in the art in a known manner.

In another form the polyarylene ether A is free of zwitterions, such as 4-(2-hydroxyethyl)-1 - piperazine ethane sulfonic acid; piperazine-Ν,Ν'- bis (2-ethanesulfonic acid); 3-(N-morpholino) propane sulfonic acid; or ((cholamido propyl) dimethyl ammonio) -1 - propane sulfonate. A zwitterion is usually an electrically neutral compound that carries formal positive and negative charges on different atoms. In another form the polyarylene ether A is free of polyalkylene oxide, such as polyethylene oxide, or polyethylene oxide polypropylen oxide block or random copolymer.

In another form the polyarylene ether A is free of an amide group. The molar (M1 )/(M2) ratio in this embodiment is from 0.75 to 1.25, especially from 0.80 to 1 .15, most preferably from 0.90 to 1.1.

In one embodiment the molar (M1 )/(M2) ratio in this embodiment is from 1.003 to 1 .15 or from 1 .01 to 1 .1 . In one embodiment the molar (M1 )/(M2) ratio in this embodiment is from 0.85 to 0.997 or from 0.9 to 0.99. Alternatively, it is also possible to use a starting compound (M1 ) where X = halogen and Y = OH. In this case, the ratio of halogen to OH end groups used is preferably from 0.75 to 1.2, especially from 0.85 to 1.15, most preferably 0.90 to 1.1.

Alternatively, it is also possible to use a starting compound (M1 ) where X = halogen and Y = OH. In this case, the ratio of halogen to OH end groups used is preferably from 1 .003 to 1 .2, especially from 1.005 to 1 .15, most preferably 1 .01 to 1 .1.

Preferably, the conversion in the polycondensation is at least 0.9, which ensures a sufficiently high molecular weight.

In a less preferred embodiment, sulfonated polyarylene ether A is prepared by sulfonation of readily prepared unsulfonated polyarylene ethers like polysulfone, polyphenylenesulfone, or pol- yethersulfone.

Sulfonated polyarylene ether A in one embodiment comprises from 0.01 to 15 % by weight, preferably 0.1 to 10 % by weight, more preferably 0.5 to 5 % by weight and even more preferably 1 to 3.5 % by weight of sulfonic acid groups calculated as -SO3H, as determined by FT-IR. In one embodiment, membranes M comprise as its main component or as an additive at least one unsulfonated polyarylene ether P. Unsulfonated polyarylene ethers P can in principle have the same structure as sulfonated polyarylene ethers A with the difference that unsulfonated polyarylene ether P does not bear any sulfonate groups. Preferably unsulfonated polyarylene ether P is selected from polysulfone, polyphenylenesulfone, or polyethersulfone, or mixtures thereof. Especially preferably unsulfonated polyarylene ether P is polyphenylenesulfone.

Preferably sulfonated polyarylene ether A is comprised in membranes M in an amount of 0.1 to 100 % by weight. In one embodiment, membranes M comprise 0.1 to 99.9 % by weight of unsulfonated polymer P and 0.1 to 100 % by weight of sulfonated polyarylene ether A. In one embodiment, membranes M comprise 80 to 99 % by weight of unsulfonated polymer P and 1 to 20 % by weight of sulfonated polyarylene ether A. In one embodiment, membranes M comprise 0.1 to 20 % by weight of unsulfonated polymer P and 80 to 99.9 % by weight of sulfonated polyarylene ether A.

In one embodiment, membranes M comprise 80 to 100 % by weight of sulfonated polyarylene ether A. In another embodiment, membranes M comprise 90 to 100 % by weight of sulfonated polyarylene ether A. In another embodiment, membranes M comprise 70 to 100 % by weight of sulfonated polyarylene ether A. In another embodiment, membranes M comprise 60 to 100 % by weight of sulfonated polyarylene ether A. In another embodiment, membranes M comprise 50 to 100 % by weight of sulfonated polyarylene ether A.

In one embodiment, membranes M comprise 80 to 100 % by weight of sulfonated polyarylene ether A und no unsulfonated polymer P.

Preferably, membranes M comprise sulfonated polyarylene ether A in an amount that lead to a content of sulfonic acid groups calculated as -SO3H in membrane M of 0.1 to 10 % by weight, preferably 2.5 to 5 % by weight (determined by FT-IR). For example, membranes M can be ultrafiltration (UF) membranes or microfiltration (MF) membranes. These membrane types are generally known in the art and are further described below. Preferably, Membranes M have a molecular Weight Cutoff (MWCO) as determined according to the procedure given in the experimental section of higher than 2500 Da, preferably higher than 5000 Da. In one embodiment, membranes M have a MWCO of higher than 10,000 Da.

It is an unexpected result of the present invention that arsenic compounds AS can be retained by membranes with a MWCO above the molecular weight of such arsenic compounds. UF membranes are normally suitable for removing suspended solid particles and solutes of high molecular weight (expressed by the MWCO as determined according to the procedure given in the experimental section), for example above 2500 Da, preferably above 5000 Da. In particular, UF membranes are normally suitable for removing bacteria and viruses. UF membranes normally have an average pore diameter of 2 nm to 50 nm, preferably 5 to 40 nm, more preferably 5 to 20 nm.

UF membranes M comprise as the main component or as an additive at least one partly sulfonated polyarylene ether A at least one partly sulfonated polysulfone, partly sulfonated poly- phenylenesulfone and/or partly sulfonated polyethersulfone. In one embodiment, UF membranes comprise as the main component or as an additive at least one partly sulfonated poly- phenylenesulfone.

"Arylene ethers", "Polysulfones", "polyethersulfones" and "polyphenylenesulfones" shall include block polymers that comprise blocks of the respective arylene ethers, polysulfones, polyethersulfones or polyphenylenesulfones as well as other polymer blocks.

In one embodiment, UF membranes comprise as the main component or as an additive at least one block copolymer of at least one arylene ether and at least one polyalkylene oxide. In one embodiment, UF membranes comprise as the main component or as an additive at least one block copolymer of at least one polysulfone or polyethersulfone and at least one polyalkylene oxide like polyethylene oxide. In one embodiment, UF membranes comprise further additives like polyvinyl pyrrolidones or polyalkylene oxides like polyethylene oxides. In a preferred embodiment, UF membranes comprise as major components polysulfones, poly- phenylenesulfone or polyethersulfone in combination with additives like polyvinylpyrrolidone.

In one preferred embodiment, UF membranes comprise 99.9 to 50% by weight of a combination of polyethersulfone and 0.1 to 50 % by weight of polyvinylpyrrolidone. In another embodiment UF membranes comprise 95 to 80% by weight of polyethersulfone and 5 to 20 % by weight of polyvinylpyrrolidone. In one embodiment of the invention, UF membranes M are present as spiral wound membranes, as pillows or flat sheet membranes. In another embodiment of the invention, UF membranes are present as tubular membranes. In another embodiment of the invention, UF membranes are present as hollow fiber membranes or capillaries. In yet another embodiment of the invention, UF membranes are present as single bore hollow fiber membranes. In yet another embodiment of the invention, UF membranes are present as multibore hollow fiber membranes.

Multiple channel membranes, also referred to as multibore membranes, comprise more than one longitudinal channels also referred to simply as "channels".

In a preferred embodiment, the number of channels is typically 2 to 19. In one embodiment, multiple channel membranes comprise two or three channels. In another embodiment, multiple channel membranes comprise 5 to 9 channels. In one preferred embodiment, multiple channel membranes comprise seven channels. In another embodiment the number of channels is 20 to 100.

The shape of such channels, also referred to as "bores", may vary. In one embodiment, such channels have an essentially circular diameter. In another embodiment, such channels have an essentially ellipsoid diameter. In yet another embodiment, channels have an essentially rectan- gular diameter. In some cases, the actual form of such channels may deviate from the idealized circular, ellipsoid or rectangular form.

Normally, such channels have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 0.05 mm to 3 mm, preferably 0.5 to 2 mm, more preferably 0.9 to 1 .5 mm. In another preferred embodiment, such channels have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) in the range from 0.2 to 0.9 mm. For channels with an essentially rectangular shape, these channels can be arranged in a row.

For channels with an essentially circular shape, these channels are in a preferred embodiment arranged such that a central channel is surrounded by the other channels. In one preferred embodiment, a membrane comprises one central channel and for example four, six or 18 further channels arranged cyclically around the central channel.

The wall thickness in such multiple channel membranes is normally from 0.02 to 1 mm at the thinnest position, preferably 30 to 500 μηη, more preferably 100 to 300 μηη. Normally, hollow fiber membranes M have an essentially circular, ellipsoid or rectangular diameter. Preferably, membranes according to the invention are essentially circular. In one preferred embodiment, membranes M have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 2 to 10 mm, preferably 3 to 8 mm, more preferably 4 to 6 mm.

In another preferred embodiment, membranes M have a diameter (for essentially circular diam- eters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 2 to 4 mm.

In one embodiment the rejection layer is located on the inside of each channel of said multiple channel membrane.

In one embodiment multibore membranes are designed with pore sizes between 0.2 and 0.01 μηη. In such embodiments the inner diameter of the capillaries can lie between 0.1 and 8 mm, preferably between 0.5 and 4 mm and particularly preferably between 0.9 and 1 .5 mm. The outer diameter of the multibore membrane can for example lie between 1 and 26 mm, pre- ferred 2.3 and 14 mm and particularly preferred between 3.6 and 6 mm. Furthermore, the multibore membrane can contain 2 to 94, preferably 3 to 19 and particularly preferred between 3 and 14 channels. Often multibore membranes contain seven channels. The permeability range can for example lie between 100 and 10000 L/m²hbar, preferably between 300 and 2000 L/m²hbar. Typically multibore membranes of the type described above are manufactured by extruding a polymer, which forms a semi-permeable membrane after coagulation through an extrusion nozzle with several hollow needles. A coagulating liquid is injected through the hollow needles into the extruded polymer during extrusion, so that parallel continuous channels extending in extrusion direction are formed in the extruded polymer. Preferably the pore size on an outer surface of the extruded membrane is controlled by bringing the outer surface after leaving the extrusion nozzle in contact with a mild coagulation agent such that the shape is fixed without active layer on the outer surface and subsequently the membrane is brought into contact with a strong coagulation agent. As a result a membrane can be obtained that has an active layer inside the channels and an outer surface, which exhibits no or hardly any resistance against liquid flow. Herein suitable coagulation agents include solvents and/or non-solvents. The strength of the coagulations may be adjusted by the combination and ratio of non-solvent/solvent. Coagulation solvents are known to the person skilled in the art and can be adjusted by routine experiments. An example for a solvent based coagulation agent is N-methylpyrrolidone. Non-solvent based coagulation agents are for instance water, iso-propanol and propylene glycol.

MF membranes are normally suitable for removing particles with a particle size of 0.1 μηη and above.

MF membranes normally have an average pore diameter of 0.05 μηη to 10 μηη, preferably 0.1 μηη to 5 μηη.

Microfiltration can use a pressurized system but it does not need to include pressure. MF membranes can be capillaries, hollow fibers, flat sheet, tubular, spiral wound, pillows, hollow fine fiber or track etched. They are porous and allow water, monovalent species (Na+, CI-), dissolved organic matter, small colloids and viruses through but retain particles, sediment, algae or large bacteria.

Microfiltration systems are designed to remove suspended solids down to 0.1 micrometers in size, in a feed solution with up to 2-3% in concentration.

In another embodiment of the invention, MF membranes M comprise as the main component at least one polyarylene ether, at least one polysulfone, polyphenylenesulfone and/or polyethersul- fone.

MF membranes M comprise as the main component or as an additive at least one partly sulfonated polysulfone, partly sulfonated polyphenylenesulfone and/or partly sulfonated polyether- sulfone. In one embodiment, MF membranes M comprise as the main component at least one partly sulfonated polyphenylenesulfone.

In one embodiment, MF membranes M comprise as the main component or as an additive at least one block copolymer of at least one arylene ether and at least one polyalkylene oxide. In one embodiment, MF membranes comprise as the main component or as an additive at least one block copolymer of at least one polysulfone or polyethersulfone and at least one polyalkylene oxide like polyethylene oxide.

In one embodiment of the invention, membranes M are present as spiral wound membranes, as pillows or flat sheet membranes. In another embodiment of the invention, membranes Mare present as tubular membranes. In another embodiment of the invention, membranes Mare present as hollow fiber membranes or capillaries. In yet another embodiment of the invention, membranes M are present as single bore hollow fiber membranes. In yet another embodiment of the invention, membranes M are present as multibore hollow fiber membranes.

Hollow fiber membranes having more than one channel are also referred to a multibore membranes or multichannel or multiple channel membranes.

Multiple channel membranes, comprise more than one longitudinal channels also referred to simply as "channels".

In a preferred embodiment, the number of channels is typically 2 to 19. In one embodiment, multiple channel membranes comprise two or three channels. In another embodiment, multiple channel membranes comprise 5 to 9 channels. In one preferred embodiment, multiple channel membranes comprise seven channels. In another embodiment the number of channels is 20 to 100. The shape of such channels, also referred to as "bores", may vary. In one embodiment, such channels have an essentially circular diameter. In another embodiment, such channels have an essentially ellipsoid diameter. In yet another embodiment, channels have an essentially rectangular diameter. In some cases, the actual form of such channels may deviate from the idealized circular, ellipsoid or rectangular form.

Normally, such channels have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 0.05 mm to 3 mm, preferably 0.5 to 2 mm, more preferably 0.9 to 1 .5 mm. In another preferred embodiment, such channels have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) in the range from 0.2 to 0.9 mm.

For channels with an essentially rectangular shape, these channels can be arranged in a row.

The wall thickness in such multiple channel membranes is normally from 0.02 to 1 mm at the thinnest position, preferably 30 to 500 μηη, more preferably 100 to 300 μηη.

Normally, hollow fiber membranes M have an essentially circular, ellipsoid or rectangular diame- ter. Preferably, membranes M are essentially circular.

In one preferred embodiment, hollow fiber membranes M have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 2 to 10 mm, preferably 3 to 8 mm, more preferably 4 to 6 mm.

In another preferred embodiment, hollow fiber membranes M have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 2 to 4 mm.

In one embodiment the rejection layer is located on the inside of each channel of said multiple channel membrane. In one embodiment the rejection layer is located on the outside of said multiple channel membrane. In one embodiment multibore membranes are designed with pore sizes in the rejection layer between 0.2 and 0.01 μηη. In such embodiments the inner diameter of the capillaries can lie between 0.1 and 8 mm, preferably between 0.5 and 4 mm and particularly preferably between 0.9 and 1 .5 mm. The outer diameter of the multibore membrane can for example lie between 1 and 26 mm, preferred 2.3 and 14 mm and particularly preferred between 3.6 and 6 mm. Furthermore, the multibore membrane can contain 2 to 94, preferably 3 to 19 and particularly preferred between 3 and 14 channels. Often multibore membranes contain seven channels. The permeability range can for example lie between 100 and 10000 L/m²hbar, preferably between 300 and 2000 L/m²hbar.

Manufacturing of membranes M, especially of ultrafiltration membranes M, often includes non- solvent induced phase separation (NIPS). In the NIPS process, the polymers used as starting materials, i.e. at least one sulfonated polyarylene ether A and optionally unsulfonated polymers P are dissolved in at least one solvent S together with any further additive(s) used. In a next step, a porous polymeric membrane is formed under controlled conditions in a coagulation bath. In most cases, the coagulation bath contains water as coagulant, or the coagulation bath is an aqueous medium, wherein the matrix forming polymer is not soluble. The cloud point of the polymer is defined in the ideal ternary phase diagram. In a bimodal phase separation, a micro- scopic porous architecture is then obtained, and water soluble components (including polymeric additives) are finally found in the aqueous phase.

In case further additives are present that are simultaneously compatible with the coagulant and the matrix polymer(s), segregation on the surface results. With the surface segregation, an en- richment of the certain additives is observed. The membrane surface thus offers new (hydro- philic) properties compared to the primarily matrix-forming polymer, the phase separation induced enrichment of the additive of the invention leading to antiadhesive surface structures.

A typical process for the preparation of a solution to prepare membranes M comprises the fol- lowing steps: a) providing a dope solution D comprising at least one sulfonated polyarylene ether A and optionally unsulfonated polymer P and at least one solvent S, a2) optionally heating the mixture until a viscous solution is obtained; typically temperature of the dope solution D is 5-250 °C, preferably 25-150 °C, more preferably 50-90 °C,

a3) optionally stirring of the solution/suspension until a mixture is formed within 1 -15 h, typically the homogenization is finalized within 2 h,

a4) optionally removing gases dissolved or present in the solution by applying a

vacuum, b) Casting the membrane dope in a coagulation bath to obtain a membrane structure. Optionally the casting can be outlined using a polymeric support (non-woven) for stabilizing the membrane structure mechanically.

In one embodiment a process for the preparation of a solution to prepare membranes M comprises the following steps: a) providing a dope solution D comprising at least one sulfonated polyphenylenesulfone A and optionally unsulfonated polymers P and at least one solvent S, a2) adjusting the temperature of the mixture until a viscous solution is obtained; typically temperature of the dope solution D is 5-250 °C, preferably 25-150 °C, more preferably 50-90 °C,

a3) stirring of the solution/suspension until a mixture is formed within 1 -15 h, typically the homogenization is finalized within 2 h,

a4) removing gases dissolved or present in the solution by applying a vacuum,

Casting the membrane dope in a coagulation bath to obtain a membrane structure. Optionally the casting can be outlined using a polymeric support (non-woven) for stabilizing the membrane structure mechanically. In one embodiment, hollow fiber membranes or multibore membranes (multichannel hollow fiber membranes) are manufactured by extruding a polymer, which forms a semi-permeable membrane after coagulation through an extrusion nozzle with several hollow needles. A coagulating liquid is injected through the hollow needles into the extruded polymer during extrusion, so that parallel continuous channels extending in extrusion direction are formed in the extruded poly- mer. Preferably the pore size on an outer surface of the extruded membrane is controlled by bringing the outer surface after leaving the extrusion nozzle in contact with a mild coagulation agent such that the shape is fixed without active layer on the outer surface and subsequently the membrane is brought into contact with a strong coagulation agent. As a result a membrane can be obtained that has an active layer inside the channels and an outer surface, which exhib- its no or hardly any resistance against liquid flow. Herein suitable coagulation agents include solvents and/or non-solvents. The strength of the coagulations may be adjusted by the combination and ratio of non-solvent/solvent. Coagulation solvents are known to the person skilled in the art and can be adjusted by routine experiments. An example for a solvent based coagulation agent is N-methylpyrrolidone. Non-solvent based coagulation agents are for instance water, methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec.-butanol, iso-butanol, n-pentanol, sec.-pentanol, iso-pentanol, 1 ,2-ethanediol, ethylene glycol, diethylene glycol, triethylene glycol, propyleneglycol, dipropyleneglycol, glycerol, neopentylglycol, 1 ,4-butanediol, 1 ,5-pentanediol, pentaerythritol. Optionally processes according to the invention can be followed by further process steps. For example such processes may include c) oxidative treatment of the membrane previously obtained, for example using sodium hypochlorite.

In case membranes M are subjected to an oxidative treatment, dope solution D preferably com- prises 1 to 20 % by weight of polyvinylpyrrolidone or polyethyleneoxide, preferably polyvinylpyrrolidone, based on the total amount of sulfonated polyarylene ether A and unsulfonated polymers P. It is assumed that through this oxidative treatment, pores are generated in the membrane. Processes according to the invention may further comprise d) washing of the membrane with water.

This invention is further directed to processes for removing arsenic compounds AS from aque- ous systems using membranes M comprising at least one sulfonated polyarylene ether A. Such processes for removing arsenic compounds AS from aqueous systems comprise subjecting aqueous systems to a filtration using membranes M comprising at least one sulfonated polyarylene ether A. According to the invention, membranes M are used for removing arsenic compounds AS.

Arsenic compounds AS are preferably ionic. Arsenic compounds AS are preferably compounds comprising arsenic in the oxidation state +V. Preferably, arsenic compounds AS are arsenates.

According to the invention, membranes M are used to remove arsenic compounds AS from aqueous systems. In one embodiment, membranes M allow for a removal of more than 70, preferably more than 90 or 99 % by weight of all arsenic compounds AS from aqueous systems.

Such aqueous systems can for example be industrial waste water, especially mining water, waste water from oil wells or power plants, municipal waste water, sea water, brackish water, fluvial water, surface water or drinking water.

In one embodiment, membranes M are used in a water treatment step prior to the desalination of sea water or brackish water. Membranes M can be used for rehabilitation of mines, homogeneous catalyst recovery, desalting reaction processes.

Uses of membranes M according to the invention allows for easy, economical and efficient treatment of water or aqueous systems. Membranes M have excellent separation characteris- tics, for example with respect to the pure water permeability and the molecular weight cut-off. Furthermore, membranes M have very good dimensional stabilities, high heat distortion resistance, good mechanical properties and biocompatibility. They can be processed and handled at high temperatures, enabling the manufacture of membranes and membrane modules that are exposed to high temperatures and are for example subjected to disinfection using steam, water vapor or higher temperatures, for example above 100°C of above 125 °C. Membranes M show excellent properties with respect to the decrease of flux through a membrane over time and their fouling and biofouling properties. Membranes M are easy and economical to make. Membranes M have a long lifetime. Examples

Abbreviations

Dl water deionized water

PWP pure water permeability

TMP trans-membrane pressure

MWCO molecular weight cut-off

PEG polyethyleneglycol

PPSU polyphenylenesulfone

Example S1 : Synthesis of sulfonated PPSU

In a 4 I HWS-vessel with stirrer, Dean-Stark-trap, nitrogen-inlet and temperature control, 577.21 g (2,01 mol) dichlorodiphenylsulfone (DCDPS), 372.42 g (2.00 mol) 4,4^'-dihydroxybi- phenyl (DHDPS), 14.86 g (0.030) mol 3, 3^'-di-sodiumdisulfate-4,4 ^'-dichlorodiphenylsulfone (sDCDPS) und 293.01 g (2.12 mol) potassium carbonate (particle size 36,2 μηη) were suspended under nitrogen atmosphere in 2000 ml NMP. Under stirring the mixture was heated up to 190°C. 30 l/h nitrogen was purged through the mixture and the mixture was kept at 190°C for 6 h. After that time 1000 ml NMP were added to cool down the mixture. Under nitrogen the mixture as allowed to cool down below 60°C. After filtration the mixture was precipitated in water which contained 100 ml 2m HCI. The precipitated product was extracted with hot water (20 h at 85°C) and dried at 120°C for 24 h under reduced pressure.

Viscosity number: 90.2 ml/g (1 wt.-/vol% solution in N-methylpyrrolidon at 23°C). Viscosity number was measured according to ISO 1628 at 23°C using 0.01 g polymer dissolved in 1 ml NMP.

The content of the sDCDPS-containing units was determined by IR-spectroscopy as 1.5 mol-%. Method to determine content of sulfonated units was as follows: Samples were dissolved in di- methylformamide to prepare a thin film on a KBr-window. The content of sDCDPS-based units was determined by taking the ratio between the signal intensity in the FT-IR-spectra at 1028 cm- ¹ to 1008 cm-¹ and correlate the ratio with a calibration curve for samples having a content of sDCDPS-based units between 0.25 and 20 mol%.

Examples 1 to 3: Preparation of membranes

A solution containing 17,5 wt% sPPSU obtained according to example S1 and 4 wt% Polyvi- nylpyrrolidone with a solution viscosity characterised by the K-value of 90, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) (PVP K90 BASF SE) was prepared in N-Methylpyrrolidone (NMP) as solvent. After stirring the mixture for 10 h at 50°C, the solution was degassed for 12 h. Using a suitable spinning equipment, the solution was spun into a multibore hollow fiber, having 7 capillaries of 0.9 μηη diameter and an outer di- ameter of 4 mm. During spinning the solution was kept at 50°C while the precipitation bath (water) was kept at 20°C. The fabricated fibers were left in water overnight to ensure complete removal of the solvent. Subsequently the fibers were treated with a solution NaOCI-solution having a concentration of 2000 ppm active Chlorine at 60°C for 2 h. After this time the fibers were washed three times with distilled water. The characteristics of the membranes obtained in examples 1 to 3 are summarized in Table 1 .

Examples 4 to 6: Performance tests

The membranes obtained from Examples 1 to 3 were tested as follows:

For performance test of the membranes from sulfonated PPSU obtained according to example S1 , deionized water was pumped through the multibore hollow fiber membranes for 30 min with a trans-membrane pressure (TMP) of 0.4 bar and the pure water permeability (PWP) was taken.

Sodium arsenate dibasic heptahydrate solution (2 ppm) was then pumped through the fiber for 1 -4 h with TMP of 0.4 bar and the feed, permeate were collected for As (V) determination using ICP-OES.

For performance test of membranes, deionized water was pumped through the fiber for 30 min with a trans-membrane pressure (TMP) of 0.4 bar and the pure water permeability (PWP) was taken by measuring the mass of the permeate within a fixed time. Polyethylene glycol solution (1000 ppm) with molecular weight 2,000, 3,000, 4,000, 6,000, 8,000, 10,000, 12,000, 20,000 and 100,000 was then pumped through the fiber for 15 min with TMP of 0.15 bar and the feed, permeate were collected for molecular weight cut-off (MWCO) determination.

For ion rejection test of the membranes, a solution containing metal/contaminant ion

[Na2HAs04] (concentration of 2.0 ppm, pH of 7) was pumped through the fiber for 1-7.5 h. Both feed and permeate solutions were analyzed for the reduction in As (V) concentration over time using Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) to calculate the metal ion rejection, r = 100———— The ion solution permeability was also collected. Dl water with pH adjustment to 1 , followed by pure deionized water was then pumped through the fiber for a total of 30 min to regenerate the membrane. The second PWP was taken and the flux recovery was calculated from the ratio between the first and second PWP.

For regeneration studies, deionized water with pH adjustment to 1 was pumped through the membrane followed by a solution containing metal/contaminant ion [Na2HAs04] (concentration of 2.0 ppm, pH of 7) to investigate the change in rejection after regeneration.

The results are given in tables 1 to 4.

Table 1 :

Example Characteristics Performance test

Pure water MWCO / Da Ion solution Metal ion rejection / % permeability permeability

/ LMH bar¹ / LMH bar¹

1 186.78 7 000 185.8 87.85 ± 0.31

2 226.71 7 000 209.03 78.73 ± 1 .12

3 173.71 7 000 172.1 1 79.54 ± 6.79 Table 2: As (V) rejection results of membrane obtained in example 1

Table 3: As (V) rejection results of membrane obtained in example 2

Table 4: As (V) rejection results of membrane obtained in example 3

Time /

min Feed concentration / ppm Permeate concentration / ppm Rejection / %

0 2.054 0.278 86.46

2 2.054 0.312 84.83

4 2.054 0.312 84.79

6 2.054 0.307 85.06

8 2.054 0.31 1 84.86

10 2.054 0.309 84.98

15 2.054 0.307 85.06

20 2.054 0.319 84.47

50 2.054 0.336 83.66

60 2.054 0.355 82.73 Time /

min Feed concentration / ppm Permeate concentration / ppm Rejection / %

90 2.054 0.394 80.80

120 2.054 0.432 78.97

150 2.054 0.462 77.50

180 2.1 1 1 0.610 71.1 1

210 2.1 1 1 0.737 65.08

240 2.1 1 1 0.639 69.72

270 2.078 0.721 65.30

300 2.078 0.696 66.48

330 2.078 0.688 66.89

360 2.078 0.699 66.34

390 2.078 0.687 66.95

420 2.078 0.692 66.69

450 2.078 0.695 66.52

Claims

A use of a membrane M comprising at least one sulfonated polyarylene ether A for removing arsenic compounds AS from aqueous systems, wherein said membrane M is an ultrafiltration or microfiltration membrane with a molecular weight cutoff of at least 2,500 Da.

The use according to claim 1 , wherein sulfonated polyarylene ether A is comprised in membrane M in an amount of 80 to 100 % by weight.

The use according to any of claim 1 to 2, wherein said at least one sulfonated polyarylene ether A is selected from polysulfones, polyethersulfones, polyphenylenesulfone or mixtures thereof.

The use according to any of claim 1 to 3, wherein said at least one sulfonated polyarylene ether A is a sulfonated polyphenylenesulfone.

The use according to any of claims 1 to 4, wherein in sulfonated polyarylene ether A 0.1 to 20 mole% of the aromatic rings, calculated as 6 membered rings, of sulfonated polyarylene ether A are sulfonated.

The use according to any of claims 1 to 5, wherein said membrane M is a hollow fiber membrane having one or more channels.

The use according to any of claims 1 to 6, wherein said membrane M is a single bore hollow fiber membrane or a multibore membrane having 7 channels.

The use according to any of claims 1 to 7, wherein said membrane M has been prepared by coagulating a dope solution D comprising at least one sulfonated polyaryleneether A in a coagulant.

The use according to any of claim 8, wherein said membrane M has been prepared by a process including the following steps:

a) providing a dope solution D comprising at least one sulfonated polyarylene ether A and at least one solvent S, and

b) casting the membrane dope in a coagulation bath to obtain a membrane structure.

The use according to any of claim 9, wherein said process further comprises the following step:

c) oxidative treatment of the membrane obtained in steps a) and b).

1 1 . The use according to any of claims 1 to 10, wherein arsenic compounds AS are selected from compounds comprising arsenic in the oxidation state +V. 12 The use according to any of claims 1 to 1 1 , wherein arsenic compounds AS are arsenates.

The use according to any of claims 1 to 12, wherein the at least one sulfonated poly- arylene ether A is derived from polyarylene ether units of the general formula I

with the following definitions:

t, q: each independently 0, 1 , 2 or 3,

Q, T, Y: each independently a chemical bond or group selected from -0-, -S-, -SO2-,

S=0, C=0, -N=N-, -CR^aR^b- where R^a and R^b are each independently a hydrogen atom or a Ci-Ci2-alkyl, Ci-Ci2-alkoxy or C6-Ci8-aryl group, where at least one of Q, T and Y is not -0-, and at least one of Q, T and Y is -SO2-, and

14. The use according to claim 13, wherein Ar = 1 ,4-phenylene, t = 1 , q = 0, T = SO2 and Y SO2, or wherein Ar = 1 ,4-biphenylene, t = 0, q = 0 and Y = SO2.

15. The use according to claims 1 to 14, wherein membranes M are used for removing arsenic compounds AS from industrial waste water, municipal waste water, sea water, brackish water, fluvial water, surface water or drinking water, mining water.