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WO2018164585A1 - Hydrophilic tfc membranes and a process for the preparation of such membranes - Google Patents

Hydrophilic tfc membranes and a process for the preparation of such membranes Download PDF

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Publication number
WO2018164585A1
WO2018164585A1 PCT/NO2018/050067 NO2018050067W WO2018164585A1 WO 2018164585 A1 WO2018164585 A1 WO 2018164585A1 NO 2018050067 W NO2018050067 W NO 2018050067W WO 2018164585 A1 WO2018164585 A1 WO 2018164585A1
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Prior art keywords
solution
support
process according
solvent
thin film
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PCT/NO2018/050067
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French (fr)
Inventor
Tom-Nils Nilsen
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Nilsen Tom Nils
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Priority claimed from NO20170560A external-priority patent/NO20170560A1/en
Application filed by Nilsen Tom Nils filed Critical Nilsen Tom Nils
Publication of WO2018164585A1 publication Critical patent/WO2018164585A1/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D69/00Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12Composite membranes; Ultra-thin membranes
    • B01D69/125In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
    • B01D69/1251In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction by interfacial polymerisation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D71/00Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06Organic material
    • B01D71/56Polyamides, e.g. polyester-amides
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2323/00Details relating to membrane preparation
    • B01D2323/36Introduction of specific chemical groups
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2325/00Details relating to properties of membranes
    • B01D2325/16Membrane materials having positively charged functional groups
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D53/00Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/228Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D61/00Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02Reverse osmosis; Hyperfiltration ; Nanofiltration

Definitions

  • the present invention is an improvement above presently known methods by preventing delamination.
  • the improvement is obtained by adjusting the contact angle between the HPS and the solution containing the first reactant by using solvents/solvent mixtures and/or solutes in order to administrate the first reactant into the pores of the HPS and without spontaneous rewetting of the surface of the HPS, optionally with formation of chemical bonds between the HPS and the IP film.
  • the method according to the invention produces membranes suitable for membrane processes like gas separation (GS), reverse osmosis (RO), nanofiltration (NF) and also osmotic processes including forward osmosis (FO) and pressure retarded osmosis (PRO).
  • GS gas separation
  • RO reverse osmosis
  • NF nanofiltration
  • FO forward osmosis
  • PRO pressure retarded osmosis
  • the invention thus further provides an improved TFC membrane, and method for gas separation, and method for nanofiltration, and method for desalination of water in RO, and method for concentrating/separating solutions using FO, and method for pressurization of saline water in PRO, the latter three methods comprising, but not restricted by, passing water through the improved membrane.
  • IP is a procedure used for rapid preparation of highly cross linked polymer thin films at room temperature. IP films are most commonly used as the rejection layer in separation
  • membranes e.g. for osmotic processes, chemical separations, desalination, sensor
  • IP proceeds through polymerization of two fast reacting intermediates at the interface between two immiscible liquid phases.
  • the relative diffusion rate of the two reactants determines the rate of polymerisation on each side of the polymer film formed.
  • the reaction is extremely fast and the instantaneously formed film at the interface leads to a dense layer that hinders diffusion of the amines and acid halides across the film, hence such films are typically very thin.
  • Continued polymerization takes place by the reactants diffusing through the dense film, leading to the formation of less dense layer on each side.
  • the reactants diffusion rates and their relative diffusion rate are dependent on the swelling capacity of the polymer by the solvents used and the solubility of the reactants in the solvent mixture inside the film.
  • the thickness of the formed film varies with the type of reactants, solvents, concentrations, and reaction time, ranging from 10 nanometres to several micrometres.
  • IP is frequently conducted on the surface of a
  • microporous support by first saturating the support with a water-based reagent and then bringing it into contact with a second reactant dissolved in an organic phase.
  • TFC membranes was first introduced by Cadotte (see US 4039440) and a further development of this (US 4277344) is still the main type of membrane used in RO and NF.
  • the RO process which relies on the semi-permeable character of a membrane to reject salt and let water pass is an efficient technique for desalination of seawater.
  • the development of TFC membranes was a major breakthrough in the field of membrane science and technology, allowing improvement of the solute separation ability and efficiency. TFC membranes are
  • TFC membranes have advantages over single-material asymmetric membranes in that the selective layer is formed in situ on a support membrane, so the chemistry and performance of the top barrier layer and the bottom porous support can be independently studied and optimized to maximize the overall membrane performance.
  • TFC RO membranes have become dominant in the market because they offer a combination of high flux and high selectivity over other types of RO membranes.
  • TFC RO membranes are based on polyamide thin films.
  • the PRO process also relies on the semi-permeable character of a membrane to reject salt and let water pass, but in this case the ability of the porous support membrane to let salt diffuse out is of crucial importance due to the opposite direction of the water flow and the salt flow. Also, the water resistance at the interface of the two membranes is crucial to the performance of a PRO membrane.
  • US 4277344 discloses a technique for preparing an aromatic polyamide film by IP on a porous support.
  • a porous polysulfone support is soaked in a solution of m- phenylenediamine (m-PDA) in water. After removal of excess m-PDA solution from the support, the support is soaked in a solution of trimesoyl chloride (TMC) dissolved in FREON (trichlorotrifluoroethane) .
  • TMC trimesoyl chloride
  • TFC membranes with improved water flux without reduced salt rejection are of interest and research has focused on improvement either through design and synthesis of new polymers forming thin films of the TFC membranes or by physical/chemical modification of the existing thin-films.
  • the fouling properties of TFC membrane is of special interest searching for the possibility of using hydrophilic supports.
  • TFC membranes are made by soaking a porous membrane in amine/water solution, as disclosed in US 4277344. The amine-soaked membrane is then soaked in a solution of an acid chloride in an organic solvent. When the two immiscible monomer solutions are brought into contact, the monomers partition across the liquid-liquid interface and react to form a polymer. As the reaction continues, polymer film is formed at the interface, and the film is usually very thin because the growing interfacial polymer behaves a barrier to diffusion of the monomers, and the polymerization levels off.
  • the IP method originally developed by Cadotte may be schematically described as:
  • hydrophilic supports are desirable because it gives higher water flux and improved fouling properties. There is a general prejudice in the art against using hydrophilic supports because of problems with delamination.
  • Still another mechanism for delamination may occur after the IP, and in use, by the process solution (e.g. water solution) having higher affinity to each of the two layers of the TFC than
  • the two layers have to each other.
  • the said solution may then penetrate in between the two surfaces, leading to delamination (alt. ii above).
  • the purpose of the present invention is to solve the problem of delamination on hydrophilic supports.
  • the inventor of the present invention has surprisingly found that delamination can be avoided, even on hydrophilic supports.
  • the present invention thus relates to a method for production of thin film composites (TFC) by interfacial polymerization (IP) on hydrophilic porous supports (HPS) avoiding delamination by adjusting the contact angle between the HPS and the solution containing the first reactant using solvents/solvent mixtures and/or solutes, in order to administrate the first reactant into the pores of the HPS and without spontaneous rewetting of the surface of the HPS, optionally with formation of chemical bonds between the HPS and the IP film.
  • TFC thin film composites
  • HPS hydrophilic porous supports
  • TFC membranes having improved water flux, salt rejection and fouling resistance.
  • the present inventor has found that by adjusting the contact angel between the amine solution and the HPS by adding other solvents and/or solutes to achieve a contact angel sufficiently high for the amine solution to enter the pores and sufficiently low to hinder/slow down capillary transport out of the pores. This way hindering a new film of solution to be reformed on the HPS surface after excess solution has been removed in the first place. Delamination by alt. (i) above will then be avoided.
  • the present inventor has developed a process to produce improved TFC membranes, which show very positive osmotic properties.
  • the membranes produced by the process of the invention can be formed on hydrophilic porous supports.
  • the membrane formed can be chemically bound to the microporous support, which addresses the problem that membranes of the prior art may experience delamination in some applications. Delamination by alternative (ii) above will then be avoided.
  • a first aspect of the present invention relates to a process for the preparation of a hydrophilic thin film composite membrane by interfacial polymerization (IP), characterized in that said process comprising:
  • the contact angle of the first solution with the support low enough to ensure that the solution fills the pores of the support.
  • the contact angle less than 80°.
  • the contact angle of the solution adjusted by adjusting the transport rate of the first solution out of the pores, after excess solution has been removed from the surface of the support, to avoid reforming of a film of first solution prior to adding a second solution.
  • first and second solutions are not miscible or mixing sufficiently slowly for an interface to form between the first and second solutions in the pore openings.
  • hydrophilic thin film composite membrane chemically in situ bond to the support by one of the reactants.
  • the hydrophilic thin film composite membrane in a polishing step or by adding ionic reactants to one of the reactant solutions, furnished with ionic groups.
  • ionic groups either pH dependent groups like organic acids or tertiary amines, or pH independent ionic groups like sulfonic acids or quaternary amines.
  • step (I) has either at least one of the reactants in step (I) or at least one of the reactants in step (II) at least three functional groups.
  • the support protic groups on the surface, preferably -OH, -NH and/or -NH 2 .
  • hydrophilic porous support a cellulose acetate, hydrolysed cellulose acetate, cellulose triacetate or hydrolysed cellulose triacetate.
  • hydrophilic porous support covalent bonds with the reactants of the first and/or second solution.
  • step (I) a polyfunctional amine or mixture of polyfunctional amines, preferably m-PDA and p-PDA and the solvent is a mixture of water and a glycol ether, and the second reactant added in step (II) is a polyfunctional acyl halide or mixtures of polyfunctional acid halides.
  • the second reactant added in step (II) selected from the group consisting of TMC, HTC and BTEC and the solvent being hydrophobic, preferably c-hexane or lamp oil.
  • the reactant in step (I) a polyfunctional acyl halide, reacting with the support and temporarily adjust the contact angle to be compatible with the solvent/solvent mixture being hydrophobic, preferably comprising c-hexane and/or lamp oil
  • the second reactant added in step (II) is polyfunctional amines, and the solvent/solvent mixture preferably comprising water and/or a glycol ether.
  • the reactant in step (I) selected from the group of TMC, HTC and MTEC reacting with the support and temporarily adjust the contact angle to be compatible with the solvent/solvent mixture being hydrophobic, preferably comprising c-hexane and/or lamp oil.
  • step (II) is the second reactant added in step (II) selected from the group of m-PDA and p-PDA and the solvent/solvent mixture preferably comprising water and/or a glycol ether.
  • a preferred embodiment comprises the solvent for the polyfunctional acyl halid diethylene glycol dimethyl ether, ethylene glycol dimethyl ether or diethylene glycol diethyl ether.
  • a preferred acidic group is organic acids, preferable added as acid halides that in contact with water form organic acids.
  • a preferred acidic group is sulfonic acid.
  • a preferred salt group is quaternary amines.
  • the present invention relates in a second aspect to a hydrophilic thin film composite membrane obtainable by a process described above and in the claims 1 to 23.
  • a third aspect of the present invention relates to the use of the thin film composite membrane obtained by the process described above and in the claims 1 to 23, in osmotic processes, reverse osmosis, gas separation and nanofiltration.
  • a forth aspect of the present invention relates to the use of the thin film composite membrane obtained by the process described above and in the claims 1 to 23, for the desalination of water comprising passing water through the thin film composite membrane.
  • a fifth aspect of the present invention relates to the use of the thin film composite membrane obtained by the process described above and in the claims 1 to 23, for the pressurization of saline water for power production comprising passing water through the thin film composite membrane.
  • TFC membrane is used herein to define the combination of a porous support on which is carried a thin film formed by IP of the polyfunctional amine and the polyfunctional acid halide compounds.
  • the film which forms is inherently very thin due to the rate at which these compounds react and the slow diffusion rate of the compounds through the film formed.
  • the thin film will be the limiting layer for transport rates, and is also called the separation membrane.
  • support is used herein as short name for hydrophilic porous support.
  • inert is used for solvents/solvent mixtures that do not react with the reactants nor the support.
  • contact angle is used herein as the angle between the solvent/solvent mixtures and the HPS where they meet.
  • HPS hydrophilic porous support
  • the delamination occurs because of rewetting of the HPS surface by capillary transport of the first added solution out of the pores before adding the second solution.
  • the rate of rewetting is given by the contact angle between the first solution and the HPS, and the size and size-distribution of the surface pores.
  • the rate of capillary transport is given by the Washburns equation (E. W. Washburn (1921). "The Dynamics of Capillary Flow”. Physical Review. 17 (3): 273), giving higher transport rate out of the pores at higher contact angle and larger pore radius.
  • a solution of a poly functional reactant is in a first step added to a hydrophilic porous support.
  • the polyfunctional reactant is dissolved in a solvent/solvent mixture, optionally added solute(s), with the contact angle between the support and the said solution is adjusted in a way that the said solution fills the pores, but avoid capillary transport out of the pores hindering reforming of a liquid film on the support after excess solution has been removed and before adding the second solution.
  • the first polyfunctional reactant solution and a solution of a second polyfunctional reactant are contacted at the surface of the support.
  • the two solutions are immiscible or mixing sufficiently slowly for an interface to form between the two solutions, on which IP may proceed with the two monomers, amines and acid halides.
  • the rate of mixing will depend on the miscibility of the two solutions and their viscosity, as well as the pores size, shape and the micro structure of the pore walls.
  • Chemical bonds may in situ be formed between the separation membrane and the support.
  • the contact angle of the (first) solution with the support being low enough to ensure that the solution fills the pores
  • the contact angle is less than 80°.
  • L The distance from the surface of the support membrane to the surface of first solution inside the pores after removing excess first solution from the surface of the support membrane
  • Contact angle between first solution and support membrane are experimentally adjusted are adjusted so no film of first solution is formed prior to adding a second solution, so as to avoid delamination of the separation membrane after it has been formed by interfacial polymerization.
  • the reaction product of the IP is a solid polymer film which is insoluble in both the first and the second solution. No specific reaction conditions are needed as the reaction is rapid and easy. Ambient temperature and pressure can be used.
  • IP HC1 will be a product that will slow down the reaction rate. It may be necessary to employ a base to neutralise HC1, e.g by buffering the amine solution to a pH of 7 to 13. Suitable buffers are well known in the art and include camphor sulfonic acid/triethyl amine.
  • membranes prepared by the present invention can exhibit a salt rejection in the order of 95 % and a water flux in the order of 2 x 10 "12 m /m 2 - s Pa in RO for a feed solution of 0.2 wt. % NaCl at a pressure difference of 10 x 10 5 Pa.
  • Hydrophilic porous support
  • the hydrophilic porous support used in the present invention is preferably a microporous support. It is generally formed of a polymeric material containing pore sizes which are permitting the passage of permeate at a sufficient rate. However, the porous support should not have pores which are so large that the membrane cannot tolerate the pressure at which the membrane will be used. If the pores are too large the high pressure will puncture the thin film.
  • the working pressure will depend on the process chosen. In practical terms the support membrane for a PRO process may have significantly larger pores than membranes intended for RO as the pressure in PRO processes usually are lower than in RO processes.
  • the pore size of the support will generally range from 1 to 100 nm.
  • the support is normally not strong enough to withstand the pressure in RO and osmotic processes like PRO, and reinforcement is needed.
  • the reinforcement may be provided by any suitable mean known in the art, such as a backing of polyamide web, non- woven polyamide or glass felt, or the reinforcement may be embedded in the support.
  • the thickness of the support itself is not critical to the present invention, however, the total thickness of support and reinforcement is important in PRO, and the total thickness of the support and
  • the hydrophilic character of the porous support membrane is of great importance to have as free flow as possible of permeate, and to have good fouling properties. If a hydrophobic support is used, pressure will be required at the inlet of the pores to overcome capillary forces for water and water solutions.
  • porous supports useful in the present invention include those having surfaces which can react with the acid halide, i.e. having -OH, - H- and/or -NH 2 groups.
  • the support is a cross-linked polymer or a cellulosic support such as cellulose acetate or triacetate, hydrolysed cellulose acetate or hydrolysed cellulose triacetate. Any cellulosic or polyetherimide (PEI) or indeed any hydrophilic support would be excellent.
  • the support may be functionalised to contain groups that will react with the acid halide and hence form actual covalent bond between the acid halide and the support.
  • the support may also inherently contain such groups. Suitable functional groups which can be introduced are amines, hydroxyls or other nucleophilic groups. Obviously, the concentration of acid halide should be large enough to leave enough acid halide to form the intended polymer film with the polyfunctional amine.
  • the hydrophilic porous support may be flat or hollow fibre, being reinforced or not, asymmetric or symmetric.
  • the polyfunctional amine provides one of the monomers needed for the IP reaction which occurs by contact between the first and second solution.
  • the polyfunctional amine will typically be of low molecular weight, e.g. less than 250 g/mol, essentially an amine having two or more amine functional groups.
  • the amine functional group is typically primary or secondary amines, however, the use of primary amines is preferred.
  • the use of tri functional (or more) amines is also contemplated, especially where the acid halide employed is not trifunctional or more.
  • the polyfunctional amine may be aromatic or aliphatic, e.g. cycloaliphatic.
  • Preferred polyfunctional amines are aromatic (e.g. m-phenylenediamine (m-PDA), p- phenylenediamine (p-PDA), 1,3,5-triaminobenzene, 1,3,4-triaminobenzene, 3,5- diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, and xylylenediamine) or aliphatic (e.g., ethylenediamine, propylenediamine, and tris(2-diaminoethyl)amine).
  • Cyclic compounds include piperazine or derivatives thereof such as 2-methylpiperazine, 2,5- dimethylpiperazine.
  • the preferred amine monomer is m-PDA.
  • the polyfunctional amine is dissolved in concentrations typically in the range of 0.05 to 20.0 weight percent, more favourable 0.5 to 6.0 weight percent.
  • the polyfunctional acid halide provides the other monomer needed for IP reaction which occurs by contacting the first and the second solution.
  • a monomer it will typically be of low molecular weight e.g. 300 g/mol, essentially an acid halide having three or more acid halide groups.
  • the use of two acid halides is also contemplated, especially where the amine employed is trifunctional or more.
  • the acid halides can be aromatic or aliphatic.
  • Diacid halides which may be used include oxalyl halide, succinyl halide, glutaryl halide, adipoyl halide, fumaryl halide, itaconyl halide, 1,2-cyclobutanedicarboxylic acid halide, isophthaloyl halide, terephthaloyl halide, 2,6-pyridinedicarbonyl halide, biphenyl-4,4- dicarboxylic acid halide, naphthalene- 1,4-dicarboxylic acid halide and naphthalene-2,6- dicarboxylic acid halide.
  • Preferred diacid halides in this invention are aromatic halides, particularly as exemplified by isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC).
  • More preferred acid halides include 5-isocyanatoisophthalic halide (ICIC), cyclohexane- 1,3,5 - tricarbonyl halide (HTC), 3,3,5,5-biphenyl tetraacyl halide (BTEC) and trimesoyl halide (TMC).
  • the preferred halide monomer in is trimesoyl chloride (TMC).
  • TMC trimesoyl chloride
  • the polyfunctional acid halide is dissolved in concentrations typically in the range of 0.01 to 10.0 weight percent, more favourable 0.05 to 3.0 weight percent.
  • the basic concept is to add ions to the membrane surface increasing the ionic load. By adding either positive or negative ions on to the membrane the salt rej ection will increase.
  • the ionic groups may be placed on the surface of the separation membrane after or during IP.
  • the ionic groups may be pH dependant such as carboxylic acids or tertiary amines, or pH independent ionic groups such as sulfonic acids or quaternary amines.
  • Carboxylic acids will be attached to the surface of the separation membrane as herein described when acid halides are added in excess in the second solution and hydrolysed to acids at reaction with water and as such is not considered a polishing step.
  • Sulfonic acids or quaternary amines may be attached to the membrane surface by any process giving free sulfonic acids or free quaternary amines.
  • Sulfonic acids may be attached to the excess acid halide groups after IP by substances containing protic groups such as -OH, -NH or - H 2 and at least one sulfonic group.
  • protic groups such as -OH, -NH or - H 2 and at least one sulfonic group.
  • examples of such substances are 8-hydroxyquinoline-5-sulfonic acid, 2-aminobenzenesulfonic acid, 3- aminobenzenesulfonic acid, 4-aminobenzenesulfonic acid aniline-2-sulfonic acid, aniline-3- sulfonic acid and aniline-4-sulfonic acid.
  • Tertiary and quaternary amines may be attached to the excess acid halide groups from the IP by substances containing at least one protic group like -OH, -NH or -NH 2 .
  • Alkyl groups may be CI - CI 8, preferably CI - C8.
  • the aryl groups may be unsubstituted or fully substituted, preferably unsubstituted to tri- substituted, the substituents preferably being inert to reactants in the system.
  • R may be the same or different from each other.
  • N may also be part of a ring structure, exemplified by pyrrolidine.
  • Alkyl groups may be C I - C I 8, preferably C I - C8.
  • the aryl groups may be unsubstituted or fully substituted, preferably unsubstituted to tri- substituted, the substituents preferably being inert to reactants in the system.
  • Preferred solvents for the polyfunctional amines may be water, dimethylsulfoxide (DMSO), dimethylformamide (DMF), di-methylethers, di-ethylethers, ethylmethyl-ethers and mixtures of the same. It is conventional in the art to use immiscible solvents in the first and second solution to ensure the formation of a boundary on which IP may occur, as described above.
  • the two solutions may be miscible, preferably having a rate of mixing sufficiently low for a boundary to be formed in the pore openings and exist for a sufficiently long time for IP to occur. Mixtures of water with the said solvents, particularly exemplified by diethylene glycol dimethyl ether (DEGM) will be preferred.
  • m-PDA (1) and TMC (2) from Alfa Aesar and camphorsulfonic acid (CSA) and triethylamine (TEA) from Alfa Aesa were used.
  • the bottles of m-PDA and TMC were flushed with argon gas after use to reduce decomposition.
  • the diethylene glycol dimethyl ether (DEGM) used as solvent was dried and stored over activated molecular sieves (4 A).
  • a hydrolyzed cellulose acetate (RC), nanofiltration membrane from HTI was used as the porous support in the example.
  • m-PDA m-Phenylene diamine
  • TMC Trimesoyl chloride
  • Reaction 1 The reaction of cellulose with trimesoyl chloride

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Abstract

The present invention relates to a method to produce thin film composite membranes by interfacial polymerisation on hydrophilic porous supports, in particular through the reaction of polyfunctional amines with polyfunctional acyl halides. The contact angle between the first solution and the support is sufficiently low for the said solution to fill the pores of the support, but sufficiently high to hinder the solution to leave the pores by capillary forces and reforming a film on the support after excess solution has been removed, before adding the second solution. To avoid delamination by water penetrating between the support and the thin film, cross links may be formed between the two layers.

Description

Title: Hydrophilic TFC membranes and a process for the preparation of such membranes
The present invention relates to a process for production of thin film composite (TFC) membranes by interfacial polymerization (IP) on hydrophilic porous supports (HPS), and TFC membranes produced by such a process.
The present invention is an improvement above presently known methods by preventing delamination. The improvement is obtained by adjusting the contact angle between the HPS and the solution containing the first reactant by using solvents/solvent mixtures and/or solutes in order to administrate the first reactant into the pores of the HPS and without spontaneous rewetting of the surface of the HPS, optionally with formation of chemical bonds between the HPS and the IP film.
The method according to the invention produces membranes suitable for membrane processes like gas separation (GS), reverse osmosis (RO), nanofiltration (NF) and also osmotic processes including forward osmosis (FO) and pressure retarded osmosis (PRO).
The invention thus further provides an improved TFC membrane, and method for gas separation, and method for nanofiltration, and method for desalination of water in RO, and method for concentrating/separating solutions using FO, and method for pressurization of saline water in PRO, the latter three methods comprising, but not restricted by, passing water through the improved membrane.
IP is a procedure used for rapid preparation of highly cross linked polymer thin films at room temperature. IP films are most commonly used as the rejection layer in separation
membranes, e.g. for osmotic processes, chemical separations, desalination, sensor
applications and encapsulation for drug delivery. IP proceeds through polymerization of two fast reacting intermediates at the interface between two immiscible liquid phases. The relative diffusion rate of the two reactants determines the rate of polymerisation on each side of the polymer film formed. The reaction is extremely fast and the instantaneously formed film at the interface leads to a dense layer that hinders diffusion of the amines and acid halides across the film, hence such films are typically very thin. Continued polymerization takes place by the reactants diffusing through the dense film, leading to the formation of less dense layer on each side. The reactants diffusion rates and their relative diffusion rate are dependent on the swelling capacity of the polymer by the solvents used and the solubility of the reactants in the solvent mixture inside the film. Hence, the thickness of the formed film varies with the type of reactants, solvents, concentrations, and reaction time, ranging from 10 nanometres to several micrometres.
To provide stability to the thin film, IP is frequently conducted on the surface of a
microporous support, by first saturating the support with a water-based reagent and then bringing it into contact with a second reactant dissolved in an organic phase. This type of
TFC membranes was first introduced by Cadotte (see US 4039440) and a further development of this (US 4277344) is still the main type of membrane used in RO and NF. The RO process which relies on the semi-permeable character of a membrane to reject salt and let water pass is an efficient technique for desalination of seawater. The development of TFC membranes was a major breakthrough in the field of membrane science and technology, allowing improvement of the solute separation ability and efficiency. TFC membranes are
characterized by an ultra-thin selective barrier layer laminated on a chemically different porous substrate, which is typically asymmetric, but not necessarily. The selective layer is the key component controlling the separation properties of the membrane, while the porous substrate gives the necessary mechanical strength. The porous support influences though the water and salt fluxes by its thickness, porosity and hydrophilic character. TFC membranes have advantages over single-material asymmetric membranes in that the selective layer is formed in situ on a support membrane, so the chemistry and performance of the top barrier layer and the bottom porous support can be independently studied and optimized to maximize the overall membrane performance. TFC RO membranes have become dominant in the market because they offer a combination of high flux and high selectivity over other types of RO membranes. At present, most commercial TFC RO membranes are based on polyamide thin films. The PRO process also relies on the semi-permeable character of a membrane to reject salt and let water pass, but in this case the ability of the porous support membrane to let salt diffuse out is of crucial importance due to the opposite direction of the water flow and the salt flow. Also, the water resistance at the interface of the two membranes is crucial to the performance of a PRO membrane.
Utilization of PRO in power generation (US 3906250 and US 4193267) has so far been limited by the poor performance of membranes.
US 4277344 (granted to Cadotte) discloses a technique for preparing an aromatic polyamide film by IP on a porous support. A porous polysulfone support is soaked in a solution of m- phenylenediamine (m-PDA) in water. After removal of excess m-PDA solution from the support, the support is soaked in a solution of trimesoyl chloride (TMC) dissolved in FREON (trichlorotrifluoroethane) .
Although the Cadotte membrane exhibits good flux and salt rejection, various approaches have been taken to further improve the water flux and the salt rejection of TFC RO membranes. In addition, other approaches have been taken to improve the resistance of said membranes to chemical degradation and the like. Many of these approaches have involved the use of various types of additives to the solutions used in IP. Despite the large amount of research which has been carried out in this area, there is still significant interest in developing more energy-efficient, contaminant selective, and fouling resistant TFC membranes for various applications. In particular, TFC membranes with improved water flux without reduced salt rejection are of interest and research has focused on improvement either through design and synthesis of new polymers forming thin films of the TFC membranes or by physical/chemical modification of the existing thin-films. The fouling properties of TFC membrane is of special interest searching for the possibility of using hydrophilic supports.
Developments in the field are described by S. Yu (Journal of Membrane Science, 342 (2009) pp. 313-320). Variation of polyacid halide compounds, to form polymer films resulted in membranes having higher water flux, but lower salt rejection relative to the fully aromatic composite. The chemical modification of diamine has also been studied with the same goal in mind. These modifications result in TFC membranes of enhanced water flux but
simultaneously accompanied by a considerable loss of salt rejection, or vice versa.
Additionally, other methods such as optimizing the formation of the thin-film by using solvent additives, or a catalyst, chemical modification of the aromatic polyamide thin-film after its formation, and/or treating the active skin layer of the membrane with ammonia or alkylamines have also been adopted to enhance water flux of the TFC RO membranes, but at the expense of the salt rejection.
Traditionally TFC membranes are made by soaking a porous membrane in amine/water solution, as disclosed in US 4277344. The amine-soaked membrane is then soaked in a solution of an acid chloride in an organic solvent. When the two immiscible monomer solutions are brought into contact, the monomers partition across the liquid-liquid interface and react to form a polymer. As the reaction continues, polymer film is formed at the interface, and the film is usually very thin because the growing interfacial polymer behaves a barrier to diffusion of the monomers, and the polymerization levels off. Thus, the IP method originally developed by Cadotte may be schematically described as:
A) Furnishing a polysulfone microporous support,
B) Coating, dipping or otherwise furnishing an amine comprising aqueous solution to the support such that it is essentially filled by this fluid,
C) Applying a halide comprising solution to the amine containing support, in which the halide solution is not miscible with water.
The use of hydrophilic supports is desirable because it gives higher water flux and improved fouling properties. There is a general prejudice in the art against using hydrophilic supports because of problems with delamination.
The inventor of the present patent application gives the following explanation for
delamination:
i) By capillary forces the solution comprising the first IP reactant reforms a film on the surface of the HPS after initial removing excess solution from the surface and prior to the addition of the second IP reactant. IP takes place on this liquid film, thus the resulting polymer has no contact with the HPS, and/or
ii) By water penetrating between the HPS and the separation membrane during preparation of the TFC or during use of the TFC.
When the support is too hydrophilic a water solution will lead to capillary transport out of the pores after excess water solution has been removed from the surface of the HPS, and forming a liquid film on the HPS. The film from the IP may then be formed on this film, and so be detached from the support, leading to delamination (alt. i above).
Still another mechanism for delamination may occur after the IP, and in use, by the process solution (e.g. water solution) having higher affinity to each of the two layers of the TFC than
Figure imgf000006_0001
the two layers have to each other. The said solution may then penetrate in between the two surfaces, leading to delamination (alt. ii above).
The purpose of the present invention is to solve the problem of delamination on hydrophilic supports.
The inventor of the present invention has surprisingly found that delamination can be avoided, even on hydrophilic supports. The present invention thus relates to a method for production of thin film composites (TFC) by interfacial polymerization (IP) on hydrophilic porous supports (HPS) avoiding delamination by adjusting the contact angle between the HPS and the solution containing the first reactant using solvents/solvent mixtures and/or solutes, in order to administrate the first reactant into the pores of the HPS and without spontaneous rewetting of the surface of the HPS, optionally with formation of chemical bonds between the HPS and the IP film.
Despite the large amount of research which has been conducted in this area, there is still a need for TFC membranes having improved water flux, salt rejection and fouling resistance. The present inventor has found that by adjusting the contact angel between the amine solution and the HPS by adding other solvents and/or solutes to achieve a contact angel sufficiently high for the amine solution to enter the pores and sufficiently low to hinder/slow down capillary transport out of the pores. This way hindering a new film of solution to be reformed on the HPS surface after excess solution has been removed in the first place. Delamination by alt. (i) above will then be avoided.
The present inventor has developed a process to produce improved TFC membranes, which show very positive osmotic properties. The membranes produced by the process of the invention can be formed on hydrophilic porous supports. In addition, the membrane formed can be chemically bound to the microporous support, which addresses the problem that membranes of the prior art may experience delamination in some applications. Delamination by alternative (ii) above will then be avoided.
More hydrophilic supports are generally wanted because of enhanced fouling resistance.
Summary of Invention
A first aspect of the present invention relates to a process for the preparation of a hydrophilic thin film composite membrane by interfacial polymerization (IP), characterized in that said process comprising:
(I) applying to a hydrophilic porous support a first solution comprising a first reactant having two or more functional groups and a solvent, and the contact angle of the solution with the support being sufficiently high to avoid capillary transport out of the pores after excess solution has been removed from the surface, and; (II) after removing excess first solution from the hydrophilic porous support, the said support is contacted, one sided or two sided, by a second solution comprising a second reactant with at least two functional groups and a solvent, and IP proceeds with the two monomers to form a thin film composite at the interface between the first and second solutions in the pore openings of the hydrophilic support.
In a preferred embodiment is the contact angle of the first solution with the support low enough to ensure that the solution fills the pores of the support.
In a preferred embodiment is the contact angle less than 80°.
In a preferred embodiment is the contact angle of the solution adjusted by adjusting the transport rate of the first solution out of the pores, after excess solution has been removed from the surface of the support, to avoid reforming of a film of first solution prior to adding a second solution.
In preferred embodiments is the first solution applied one sided or two sided.
In a preferred embodiment are the first and second solutions not miscible or mixing sufficiently slowly for an interface to form between the first and second solutions in the pore openings.
In a preferred embodiment is the hydrophilic thin film composite membrane chemically in situ bond to the support by one of the reactants.
In a preferred embodiment is the hydrophilic thin film composite membrane, in a polishing step or by adding ionic reactants to one of the reactant solutions, furnished with ionic groups. In a preferred embodiment are the ionic groups either pH dependent groups like organic acids or tertiary amines, or pH independent ionic groups like sulfonic acids or quaternary amines.
In a preferred embodiment has either at least one of the reactants in step (I) or at least one of the reactants in step (II) at least three functional groups.
In a preferred embodiment has the support protic groups on the surface, preferably -OH, -NH and/or -NH2.
In a preferred embodiment is the hydrophilic porous support a cellulose acetate, hydrolysed cellulose acetate, cellulose triacetate or hydrolysed cellulose triacetate.
In a preferred embodiment is the hydrophilic porous support an ultrafiltration
membrane.
In a preferred embodiment form the hydrophilic porous support covalent bonds with the reactants of the first and/or second solution.
In a preferred embodiment is the reactant in step (I) a polyfunctional amine or mixture of polyfunctional amines, preferably m-PDA and p-PDA and the solvent is a mixture of water and a glycol ether, and the second reactant added in step (II) is a polyfunctional acyl halide or mixtures of polyfunctional acid halides.
In a preferred embodiment is the second reactant added in step (II) selected from the group consisting of TMC, HTC and BTEC and the solvent being hydrophobic, preferably c-hexane or lamp oil.
In a preferred embodiment is the reactant in step (I) a polyfunctional acyl halide, reacting with the support and temporarily adjust the contact angle to be compatible with the solvent/solvent mixture being hydrophobic, preferably comprising c-hexane and/or lamp oil, and the second reactant added in step (II) is polyfunctional amines, and the solvent/solvent mixture preferably comprising water and/or a glycol ether. In a preferred embodiment is the reactant in step (I) selected from the group of TMC, HTC and MTEC reacting with the support and temporarily adjust the contact angle to be compatible with the solvent/solvent mixture being hydrophobic, preferably comprising c-hexane and/or lamp oil.
In a preferred embodiment is the second reactant added in step (II) selected from the group of m-PDA and p-PDA and the solvent/solvent mixture preferably comprising water and/or a glycol ether.
In a preferred embodiment comprises the solvent for the polyfunctional acyl halid diethylene glycol dimethyl ether, ethylene glycol dimethyl ether or diethylene glycol diethyl ether. In a preferred embodiment is IP film furnished with ionic groups achieved by copolymerization with the other monomers, or grafted on the IP film.
In a preferred embodiment are the ionic groups pH dependant groups, a preferred acidic group is organic acids, preferable added as acid halides that in contact with water form organic acids.
In a preferred embodiment are the ionic groups strong acids, a preferred acidic group is sulfonic acid.
In a preferred embodiment are the ionic groups organic salts, a preferred salt group is quaternary amines.
The present invention relates in a second aspect to a hydrophilic thin film composite membrane obtainable by a process described above and in the claims 1 to 23. A third aspect of the present invention relates to the use of the thin film composite membrane obtained by the process described above and in the claims 1 to 23, in osmotic processes, reverse osmosis, gas separation and nanofiltration. A forth aspect of the present invention relates to the use of the thin film composite membrane obtained by the process described above and in the claims 1 to 23, for the desalination of water comprising passing water through the thin film composite membrane.
A fifth aspect of the present invention relates to the use of the thin film composite membrane obtained by the process described above and in the claims 1 to 23, for the pressurization of saline water for power production comprising passing water through the thin film composite membrane.
Definitions
The term TFC membrane is used herein to define the combination of a porous support on which is carried a thin film formed by IP of the polyfunctional amine and the polyfunctional acid halide compounds. The film which forms is inherently very thin due to the rate at which these compounds react and the slow diffusion rate of the compounds through the film formed. In TFC membrane the thin film will be the limiting layer for transport rates, and is also called the separation membrane.
The term support is used herein as short name for hydrophilic porous support.
The term inert is used for solvents/solvent mixtures that do not react with the reactants nor the support.
The term contact angle is used herein as the angle between the solvent/solvent mixtures and the HPS where they meet.
The term «hydrophilic porous support)) (HPS) is used for support membranes that show delamination of the separation membrane when subjected to traditional interfacial
polymerization. The delamination occurs because of rewetting of the HPS surface by capillary transport of the first added solution out of the pores before adding the second solution. The rate of rewetting is given by the contact angle between the first solution and the HPS, and the size and size-distribution of the surface pores. The rate of capillary transport is given by the Washburns equation (E. W. Washburn (1921). "The Dynamics of Capillary Flow". Physical Review. 17 (3): 273), giving higher transport rate out of the pores at higher contact angle and larger pore radius.
Detailed Description
In this invention, a solution of a poly functional reactant is in a first step added to a hydrophilic porous support. The polyfunctional reactant is dissolved in a solvent/solvent mixture, optionally added solute(s), with the contact angle between the support and the said solution is adjusted in a way that the said solution fills the pores, but avoid capillary transport out of the pores hindering reforming of a liquid film on the support after excess solution has been removed and before adding the second solution.
In a second step the first polyfunctional reactant solution and a solution of a second polyfunctional reactant are contacted at the surface of the support. The two solutions are immiscible or mixing sufficiently slowly for an interface to form between the two solutions, on which IP may proceed with the two monomers, amines and acid halides. The rate of mixing will depend on the miscibility of the two solutions and their viscosity, as well as the pores size, shape and the micro structure of the pore walls.
Chemical bonds may in situ be formed between the separation membrane and the support.
By the phrase "the contact angle of the (first) solution with the support being low enough to ensure that the solution fills the pores" we mean that the contact angle is less than 80°.
By the phrases «the contact angle of the first solution with the support is sufficiently high to avoid capillary transport out of the pores after excess solution has been removed from the surface" and "the contact angle of the solution is adjusted by adjusting the transport rate of the first solution out of the pores, after removing excess solution from the surface of the support, to avoid reforming of a film of first solution prior to adding a second solution," we mean that the parameters in Washburns equation (E. W. Washburn (1921). "The Dynamics of Capillary Flow". Physical Review. 17 (3): 273):
L2 · 4η
t =
2r · tos(0) t = Time for first solution to move the distance L
L = The distance from the surface of the support membrane to the surface of first solution inside the pores after removing excess first solution from the surface of the support membrane
η_= Viscosity of first solution
r = Pore radius
Y = Surface tension between first solution and support membrane
φ = Contact angle between first solution and support membrane are experimentally adjusted are adjusted so no film of first solution is formed prior to adding a second solution, so as to avoid delamination of the separation membrane after it has been formed by interfacial polymerization.
The reaction product of the IP is a solid polymer film which is insoluble in both the first and the second solution. No specific reaction conditions are needed as the reaction is rapid and easy. Ambient temperature and pressure can be used. During IP HC1 will be a product that will slow down the reaction rate. It may be necessary to employ a base to neutralise HC1, e.g by buffering the amine solution to a pH of 7 to 13. Suitable buffers are well known in the art and include camphor sulfonic acid/triethyl amine.
We have shown that membranes prepared by the present invention can exhibit a salt rejection in the order of 95 % and a water flux in the order of 2 x 10"12 m /m2- s Pa in RO for a feed solution of 0.2 wt. % NaCl at a pressure difference of 10 x 105 Pa. Hydrophilic porous support
The hydrophilic porous support used in the present invention is preferably a microporous support. It is generally formed of a polymeric material containing pore sizes which are permitting the passage of permeate at a sufficient rate. However, the porous support should not have pores which are so large that the membrane cannot tolerate the pressure at which the membrane will be used. If the pores are too large the high pressure will puncture the thin film. The working pressure will depend on the process chosen. In practical terms the support membrane for a PRO process may have significantly larger pores than membranes intended for RO as the pressure in PRO processes usually are lower than in RO processes. The pore size of the support will generally range from 1 to 100 nm.
The support is normally not strong enough to withstand the pressure in RO and osmotic processes like PRO, and reinforcement is needed. The reinforcement may be provided by any suitable mean known in the art, such as a backing of polyamide web, non- woven polyamide or glass felt, or the reinforcement may be embedded in the support. The thickness of the support itself is not critical to the present invention, however, the total thickness of support and reinforcement is important in PRO, and the total thickness of the support and
reinforcement should not exceed 100 μπι for use in PRO.
The hydrophilic character of the porous support membrane is of great importance to have as free flow as possible of permeate, and to have good fouling properties. If a hydrophobic support is used, pressure will be required at the inlet of the pores to overcome capillary forces for water and water solutions.
Examples of porous supports useful in the present invention include those having surfaces which can react with the acid halide, i.e. having -OH, - H- and/or -NH2 groups. Most preferably the support is a cross-linked polymer or a cellulosic support such as cellulose acetate or triacetate, hydrolysed cellulose acetate or hydrolysed cellulose triacetate. Any cellulosic or polyetherimide (PEI) or indeed any hydrophilic support would be excellent. The support may be functionalised to contain groups that will react with the acid halide and hence form actual covalent bond between the acid halide and the support. The support may also inherently contain such groups. Suitable functional groups which can be introduced are amines, hydroxyls or other nucleophilic groups. Obviously, the concentration of acid halide should be large enough to leave enough acid halide to form the intended polymer film with the polyfunctional amine.
Chemical bonds between the support and the separation membrane provide more robust membranes, especially with respect to washing procedures. This is important in both RO and PRO membranes.
The chemical attachment also prevents delamination of the membrane from the support, a problem known in prior art composites. An alternative process for obtaining chemical bonds between the support and the separation membrane is described in Norwegian patent no. 335286 (Nilsen et al), differing from the present process by adding the poly acid halides dissolved in a hydrophilic solvent in a first step, and then adding polyamines dissolved in water in a second step. The final properties of the TFC membrane are achieved by a third step where poly acid halides are added dissolved in a hydrophobic solvent.
The hydrophilic porous support may be flat or hollow fibre, being reinforced or not, asymmetric or symmetric.
Polyfunctional Amine The polyfunctional amine provides one of the monomers needed for the IP reaction which occurs by contact between the first and second solution. As a monomer the polyfunctional amine will typically be of low molecular weight, e.g. less than 250 g/mol, essentially an amine having two or more amine functional groups. The amine functional group is typically primary or secondary amines, however, the use of primary amines is preferred. The use of tri functional (or more) amines is also contemplated, especially where the acid halide employed is not trifunctional or more. The polyfunctional amine may be aromatic or aliphatic, e.g. cycloaliphatic.
Preferred polyfunctional amines are aromatic (e.g. m-phenylenediamine (m-PDA), p- phenylenediamine (p-PDA), 1,3,5-triaminobenzene, 1,3,4-triaminobenzene, 3,5- diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, and xylylenediamine) or aliphatic (e.g., ethylenediamine, propylenediamine, and tris(2-diaminoethyl)amine). Cyclic compounds include piperazine or derivatives thereof such as 2-methylpiperazine, 2,5- dimethylpiperazine. The preferred amine monomer is m-PDA.
The polyfunctional amine is dissolved in concentrations typically in the range of 0.05 to 20.0 weight percent, more favourable 0.5 to 6.0 weight percent.
Polyfunctional Acid halide
The polyfunctional acid halide provides the other monomer needed for IP reaction which occurs by contacting the first and the second solution. As a monomer, it will typically be of low molecular weight e.g. 300 g/mol, essentially an acid halide having three or more acid halide groups. The use of two acid halides is also contemplated, especially where the amine employed is trifunctional or more. The acid halides can be aromatic or aliphatic.
Diacid halides which may be used include oxalyl halide, succinyl halide, glutaryl halide, adipoyl halide, fumaryl halide, itaconyl halide, 1,2-cyclobutanedicarboxylic acid halide, isophthaloyl halide, terephthaloyl halide, 2,6-pyridinedicarbonyl halide, biphenyl-4,4- dicarboxylic acid halide, naphthalene- 1,4-dicarboxylic acid halide and naphthalene-2,6- dicarboxylic acid halide. Preferred diacid halides in this invention are aromatic halides, particularly as exemplified by isophthaloyl chloride (IPC) and terephthaloyl chloride (TPC).
More preferred acid halides include 5-isocyanatoisophthalic halide (ICIC), cyclohexane- 1,3,5 - tricarbonyl halide (HTC), 3,3,5,5-biphenyl tetraacyl halide (BTEC) and trimesoyl halide (TMC). The preferred halide monomer in is trimesoyl chloride (TMC). The polyfunctional acid halide is dissolved in concentrations typically in the range of 0.01 to 10.0 weight percent, more favourable 0.05 to 3.0 weight percent.
Polishing step
For improving salt rej ection, the basic concept is to add ions to the membrane surface increasing the ionic load. By adding either positive or negative ions on to the membrane the salt rej ection will increase. The ionic groups may be placed on the surface of the separation membrane after or during IP. The ionic groups may be pH dependant such as carboxylic acids or tertiary amines, or pH independent ionic groups such as sulfonic acids or quaternary amines.
Carboxylic acids will be attached to the surface of the separation membrane as herein described when acid halides are added in excess in the second solution and hydrolysed to acids at reaction with water and as such is not considered a polishing step.
Sulfonic acids or quaternary amines may be attached to the membrane surface by any process giving free sulfonic acids or free quaternary amines.
Sulfonic acids may be attached to the excess acid halide groups after IP by substances containing protic groups such as -OH, -NH or - H2 and at least one sulfonic group. Examples of such substances are 8-hydroxyquinoline-5-sulfonic acid, 2-aminobenzenesulfonic acid, 3- aminobenzenesulfonic acid, 4-aminobenzenesulfonic acid aniline-2-sulfonic acid, aniline-3- sulfonic acid and aniline-4-sulfonic acid.
Tertiary and quaternary amines may be attached to the excess acid halide groups from the IP by substances containing at least one protic group like -OH, -NH or -NH2.
Examples of tertiary amines that may be attached to the acid halide surface are R3N (R= any chain such as alkyl, aryl, cyclic or branched and at least one chain contains at least one protic group like hydroxyl or amine). R may be the same or different from each other. N may also be part of a ring structure, exemplified by piperidine. Alkyl groups may be CI - CI 8, preferably CI - C8. The aryl groups may be unsubstituted or fully substituted, preferably unsubstituted to tri- substituted, the substituents preferably being inert to reactants in the system. Examples of quaternary amines that may be attached to the acid halide surface are salts of R4N+ (R= any chain such as alkyl, aryl, cyclic or branched and at least one chain contains at least one protic group like hydroxyl or amine). R may be the same or different from each other. N may also be part of a ring structure, exemplified by pyrrolidine. Alkyl groups may be C I - C I 8, preferably C I - C8. The aryl groups may be unsubstituted or fully substituted, preferably unsubstituted to tri- substituted, the substituents preferably being inert to reactants in the system.
Solvents
Preferred solvents for the polyfunctional amines, may be water, dimethylsulfoxide (DMSO), dimethylformamide (DMF), di-methylethers, di-ethylethers, ethylmethyl-ethers and mixtures of the same. It is conventional in the art to use immiscible solvents in the first and second solution to ensure the formation of a boundary on which IP may occur, as described above. In the present invention, the two solutions may be miscible, preferably having a rate of mixing sufficiently low for a boundary to be formed in the pore openings and exist for a sufficiently long time for IP to occur. Mixtures of water with the said solvents, particularly exemplified by diethylene glycol dimethyl ether (DEGM) will be preferred.
Preferred solvent for the polyfunctional acid halides, may be c-hexane, hydrocarbons (C5 - CI 4) and lamp-oil, or mixtures of the same. The solvent may be an aprotic and non-polar organic solvent, and may be aromatic or aliphatic. Preferred solvents for the acid halides in this invention are c-hexane and lamp oil. When the halides are added in the first solution, the contact angle between the support and the solution must be adjusted by adding a more hydrophilic solvent to the solution. Preferred solvents for adjusting the contact angle are di- methylethers, di-ethylethers, ethylmethyl-ethers and mixtures of the same. The resulting solution is preferably not miscible with the amine solution or having a rate of mixing with the amine solution sufficiently low as described above. Examples
Materials m-PDA (1) and TMC (2) from Alfa Aesar and camphorsulfonic acid (CSA) and triethylamine (TEA) from Alfa Aesa were used. The bottles of m-PDA and TMC were flushed with argon gas after use to reduce decomposition. The diethylene glycol dimethyl ether (DEGM) used as solvent was dried and stored over activated molecular sieves (4 A). A hydrolyzed cellulose acetate (RC), nanofiltration membrane from HTI was used as the porous support in the example.
Figure imgf000019_0001
(1) (2)
m-Phenylene diamine (m-PDA) Trimesoyl chloride (TMC)
Experimental
In example 1 hydrolysed CA membranes from HTI (originally an NF membrane) were soaked in a mixture of 80 % buffer and 20 % Diglyme containing 3,4 weight % m-PDA for 2 minutes. The buffer was 1 % CSA and 0,5 % TEA in water. Excess solution on the membrane surface was removed using paper tissues, and soaked in c-hexane containing 0, 15 weight % TMC for 1 minute. The membranes were washed in lamp oil and transferred to water via Diglyme. The ratio between water and Diglyme was established by testing reduction in capillary rice in a glass tube when adding Diglyme to water, and control that the same mixture resulted in an interface when contacting c-hexane. Table 1 : Formulations
Figure imgf000020_0003
Figure imgf000020_0001
Reaction 1 : The reaction of cellulose with trimesoyl chloride
Figure imgf000020_0002
Reaction 2: Schotten-Bauman reaction of PDA/MDA and TMC
Results
The membranes were tested for water flux in RO at 106 Pa with a NaCl concentration of 0.2 wt.%. The salt rejection was determined by conductivity measurements. Water flux: 2 10'12 mV- s-Pa
Retention: 95 %

Claims

Claims
1. A process for the preparation of a hydrophilic thin film composite membrane by interfacial polymerization (IP), characterized in that said process comprising: (I) applying to a hydrophilic porous support a first solution comprising a first reactant having two or more functional groups and a solvent, and the contact angle of the solution with the support being sufficiently high to avoid capillary transport out of the pores after excess solution has been removed from the surface, and;
(II) after removing excess first solution from the hydrophilic porous support, the said support is contacted, one sided or two sided, by a second solution comprising a second reactant with at least two functional groups and a solvent, and IP proceeds with the two monomers to form a thin film composite at the interface between the first and second solutions in the pore openings of the hydrophilic support.
2. A process according to claim 1, wherein the contact angle of the first solution with the support being low enough to ensure that the solution fills the pores of the support.
3. A process according to claim 1, wherein the contact angle of the solution is adjusted by adjusting the transport rate of the first solution out of the pores, after excess solution has been removed from the surface of the support, to avoid reforming of a film of first solution prior to adding a second solution.
4. A process as claimed in claim 1, wherein said first solution is applied one sided or two sided.
5. A process as claimed in claim 1, wherein the first and second solutions are not miscible or mixing sufficiently slowly for an interface to form between the first and second solutions in the pore openings.
6. A process as claimed in claim 1, wherein the hydrophilic thin film composite membrane chemically in situ is bond to the support by one of the reactants.
7. A process as claimed in claim 1, wherein the hydrophilic thin film composite membrane, in a polishing step or by adding ionic reactants to one of the reactant solutions, is furnished with ionic groups.
8. A process as claimed in claim 7, wherein said ionic groups are either pH dependent groups like organic acids or tertiary amines, or pH independent ionic groups like sulfonic acids or quaternary amines.
9. A process as claimed in claim 1 wherein either at least one of the reactants in step (I) or at least one of the reactants in step (II) has at least three functional groups.
10. A process according to any of the claims 1 to 9 wherein the support has protic groups on the surface, preferably -OH, - H and/or - H2.
11. A process according to any of the claims 1 to 10 wherein the hydrophilic porous support is cellulose acetate, hydrolysed cellulose acetate, cellulose triacetate or hydrolysed cellulose triacetate.
12. A process according to any of the claims 1 to 11 wherein the hydrophilic porous support is an ultrafiltration membrane.
13. A process according to any of the claims 1 to 12 wherein the hydrophilic porous support forms covalent bonds with the reactants of the first and/or second solution.
14. A process according to any of the preceding claims wherein the reactant in step (I) is a polyfunctional amine or mixture of polyfunctional amines, preferably m-PDA and p- PDA and the solvent is a mixture of water and a glycol ether, and the second reactant added in step (II) is a polyfunctional acyl halide or mixtures of polyfunctional acid halides.
15. A process according to claim 14, wherein the second reactant added in step (II) is selected from the group consisting of TMC, HTC and BTEC and the solvent being hydrophobic, preferably c-hexane or lamp oil.
16. A process according to any of the claims 1 to 13 wherein the reactant in step (I) is a polyfunctional acyl halide, reacting with the support and temporarily adjust the contact angle to be compatible with the solvent/solvent mixture being hydrophobic, preferably comprising c-hexane and/or lamp oil, and the second reactant added in step (II) is polyfunctional amines, and the solvent/solvent mixture preferably comprising water and/or a glycol ether.
17. A process according to claim 16, wherein the reactant in step (I) is selected from the group of TMC, HTC and MTEC reacting with the support and temporarily adjust the contact angle to be compatible with the solvent/solvent mixture being hydrophobic, preferably comprising c-hexane and/or lamp oil.
18. A process according to claim 17, wherein the second reactant added in step (II) is selected from the group of m-PDA and p-PDA and the solvent/solvent mixture preferably comprising water and/or a glycol ether.
19. A process according to any preceding claim wherein the solvent for the polyfunctional acyl halide comprises diethylene glycol dimethyl ether, ethylene glycol dimethyl ether or diethyl ene glycol diethyl ether.
20. A process according to any one of the preceding claims wherein the IP film is furnished with ionic groups achieved by copolymerization with the other monomers, or grafted on the IP film.
21. A process according to claim 20, wherein the ionic groups are pH dependant groups, a preferred group is organic acids, preferable added as acid halides that in contact with water form organic acids, and another preferred group is tertiary amines.
22. A process according to claim 20 wherein the ionic groups are strong acids, a preferred acidic group is sulfonic acid.
23. A process according to claim 20 wherein the ionic groups are organic salts, a preferred salt group is quaternary amines.
24. A hydrophilic thin film composite membrane obtainable by the process according to any one of claims 1 to 23
25. Use of the thin film composite membrane obtained by the process according to any one of claims 1 to 23 in osmotic processes, reverse osmosis, gas separation and nanofiltration.
26. Use of a thin film composite membrane obtained by the process according to any of the claims 1-23, for the desalination of water comprising passing water through the thin film composite membrane.
27. Use of a thin film composite membrane obtained by the process according to any of the claims 1-23 for the pressurization of saline water for power production comprising passing water through the thin film composite membrane.
PCT/NO2018/050067 2017-03-09 2018-03-09 Hydrophilic tfc membranes and a process for the preparation of such membranes WO2018164585A1 (en)

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