N-(2’-Hydroxyethyl)-2-pyrrolidone solution of polyarylsulfone polymer for membrane preparation and its use

Abstract

The present invention relates to a solution comprising a polyarylsulfone polymer selected from the group of polyethersulfone and polysulfone, N-(2'-hydroxyethyl)-2-pyrrolidone, a process for producing their membranes, and the use of these membranes for separation processes.

Description

Technical Field

[0001] The present invention relates to a solution comprising a polyarylsulfone polymer selected from the group of polyethersulfone and polysulfone, N-(2'-hydroxyethyl)-2-pyrrolidone, a process for producing their membranes, and the use of these membranes for separation processes.

Background Art

[0002] Polyarylsulfone polymers, such as polysulfone (i.e., commercially available under the trade names: Ultrason® S, Udel®) and polyethersulfone (i.e., commercially available under the trade names: Ultrason® E, Veradel®, Sumicaexel®), are high-performance polymers used in various technical applications due to their mechanical properties as well as their chemical and thermal stability. One of the main technical applications of polyarylsulfone polymers is their use as raw materials for producing polymer membranes, such as dialysis membranes or ultrafiltration membranes. Polymer membranes are used in separation processes and are widely utilized, for example, in medical applications, food technology, biotechnology, the pharmaceutical industry, and water treatment.

[0003] In J.G. Wijmans et.al., Eur. Polym. J., 1983, Vol. 19, No. 12, pp. 1143-1146, it is pointed out that polyarylsulfone polymers have limited solubility in many common solvents. In particular, polysulfone concentrated solutions in various solvents tend to be turbid and precipitation occurs.

[0004] WO 2019 / 042749 A1 pamphlet discloses a process for manufacturing a membrane by contacting a polymer solution containing a polymer, a first solvent, and a co-solvent with a coagulant. N-methylpyrrolidone and N-ethylpyrrolidone are claimed as the first solvent. Polyvinylpyrrolidone is used as a water-soluble polymer. Further, the membrane obtained by this process is disclosed. The post-treatment of the membrane includes an oxidation step with sodium hypochlorite. The manufacture of the membrane from the polymer solution is further described in WO 2015 / 056145 A1 pamphlet.

[0005] WO 2017 / 220386 A1 pamphlet discloses the use of an N-acetylmorpholine solution of polysulfone for the production of an ultrafiltration membrane. Polyvinylpyrrolidone is used as a water-soluble polymer. If no water-soluble polymer is added, the resulting membrane has no water permeability. The post-treatment of the membrane includes an oxidation step using sodium hypochlorite.

[0006] WO 2021 / 191043 pamphlet describes the use of N-n-butyl-2-pyrrolidone as an alternative solvent for various polymers including polyarylsulfone polymers. The use of the above solution in combination with a water-soluble polymer in membrane production is also described. Various grades of polyvinylpyrrolidone are used as the water-soluble polymer. The post-treatment of the membrane includes an oxidation step using sodium hypochlorite.

[0007] EP 2021 / 082449 specification describes a solution containing at least one sulfone polymer and N-tert-butyl-2-pyrrolidone as an alternative solvent. The use of the above solution in combination with a water-soluble polymer in membrane production is also described. Combinations of various grades of polyvinylpyrrolidone are used as the water-soluble polymer. The post-treatment of the membrane includes an oxidation step using sodium hypochlorite.

[0008] In the above prior art, during the post-treatment of the membrane, for example, an additional oxidation step using sodium hypochlorite is required.

[0009] In S. Munari et.al., Desalination, 1988, Vol. 70, pp. 265-275, the preparation of microporous polysulfone membranes from a casting solution of polysulfone, a solvent, and polyvinylpyrrolidone as an additive solvent is described. N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone are cited as common solvents. It has been pointed out that due to the low molecular mass of the polymer, the polysulfone solution is characterized by low viscosity, and as a result, it is difficult to cast. To overcome this problem, it has become common to add high molecular weight polyvinylpyrrolidone to the polysulfone solution. In this experiment, N,N-dimethylacetamide, which is classified as a highly concerned chemical substance in the European Union, is used as the solvent. The post-treatment of the membrane consists of washing with water.

[0010] U.S. Patent Application Publication No. 2005 / 0170183A1 describes a molded body having substituents characterized by various formulas bonded to its surface. The molded body contains a polyaryl ether, and the polyaryl ether may be, among others, a polyaryl sulfone polymer (for example, polyethersulfone). For example, the preparation of a molded body in the form of a membrane or film from an N,N-dimethylacetamide solution or a dimethyl sulfoxide solution of polyethersulfone is described. Regarding the formation of the membrane, the use of poly(ethylene glycol) in the solution is further mentioned.

[0011] Functionalization of an easily prepared molded body (film or membrane) is carried out by treating the molded body in a heterogeneous reaction with an aqueous H2SO4 solution containing a drug and a carbonyl compound. As an example of the drug, N-(2'-hydroxyethyl)-2-pyrrolidone is mentioned. That is, N-(2'-hydroxyethyl)-2-pyrrolidone is not used as a solvent, but as a reagent for modifying the insoluble molded body.

[0012] European Patent Application Publication No. 3756753A1 discloses a combination of pyrrolidone-based solvents for film formation as an alternative to conventionally used solvents. This combination includes 2-pyrrolidone and N-alkyl-2-pyrrolidones, especially N-n-butyl-2-pyrrolidone. As the film-forming polymer, a polyarylsulfone polymer is described, and the polymer is used in combination with a water-soluble polymer, and the aqueous solution polymer is a mixture of polyvinylpyrrolidone and poly(ethylene glycol).

[0013] In C. Kahr et al., Polymer 2020, Vol. 186, 122071, membrane formation by non-solvent-induced phase separation using various solvents is described. N-methylpyrrolidone and N,N-dimethylacetamide as conventional solvents are compared with 2-pyrrolidone and N,N-dimethylacetamide as alternative solvents. Polyvinylpyrrolidone and poly(ethylene glycol) with different concentrations and molecular weights are applied in all four solvent systems. Not only the membrane properties but also the viscosity of the polymer solution are considered.

[0014] Generally, there is a continuing need for solvents suitable to replace currently used solvents in specific applications. One desire is for a solvent with fewer problematic toxicity profiles compared to conventionally used solvents such as N-methyl-2-pyrrolidone. For sulfone polymer solutions, the solvent desirably enables a solution that is free of turbidity and has a high sulfone polymer content. Also, solutions further containing water-soluble polymers need to be stable and transparent as these factors affect the pore structure and in turn the quality of the membranes obtained from these solutions. Solvents conventionally used to make membranes result in low-viscosity polymer solutions that are difficult to cast, so there is also a need for solvent systems that result in more viscous polymer solutions. Further, solvents utilized for membrane formation by non-solvent induced phase inversion need to exhibit complete miscibility with water used as the coagulant. For membranes obtained using these polymer solutions, it is important that at least the same standard of membrane quality, and preferably even better membrane quality, is achieved. In particular, the water permeability of such membranes is desirably as high as possible and there are few visible defects or macrovoids in the cross-section of the membrane. A further requirement is acceptable mechanical stability and thereby longer membrane life.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] It was an object of the present invention to find a solvent with low toxicity concerns, readily available, that dissolves polyaryl sulfone polymers, results in a solution with low turbidity and high viscosity, thereby enabling easy preparation of membranes. It was a further object of the present invention to provide, as simply as possible, a membrane preparation process based on these solutions, for example by avoiding time-consuming and / or dangerous post-treatment of the membranes. It was a further object of the present invention to provide membranes exhibiting improved membrane performance.

MEANS FOR SOLVING THE PROBLEMS

[0016] The inventors have found that the above objects are (a) A polyarylsulfone polymer containing the repeating unit of formula 1 [Chemical formula] and a polysulfone polymer containing the repeating unit of formula II [Chemical formula] Or a polyarylsulfone polymer selected from the group of their mixtures, wherein the weight average molecular weight M w of the polyarylsulfone polymer is in the range of 40,000 to 105,000 g / mol, and the polyarylsulfone polymer contains at least 95% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer and (b) N-(2'-hydroxyethyl)-2-pyrrolidone Surprisingly, it has also been found that it can be achieved by a solution containing

Embodiments for Carrying Out the Invention

[0017] Polyarylsulfone polymer The polyarylsulfone polymer contains at least 95% by weight (weight percent), preferably at least 97% by weight, more preferably at least 98% by weight, and particularly preferably at least 99% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer.

[0018] The polyarylsulfone polymer is a polymer containing -S(=O)2- units in the polymer. The -S(=O)2- units are also referred to as sulfonyl units.

[0019] The polyarylsulfone polymer contains aromatic groups. In addition to 1,4-phenylene units, the polyarylsulfone polymer can also contain units based on minor isomers such as 1,2-phenylene units and 1,3-phenylene units.

[0020] The polyarylsulfone polymer contains end groups such as Cl-, OH-, MeO-, tert-butyl-, or aryl groups at the polymer chain ends. Various chain ends can contain various end groups. The polyarylsulfone polymer generally contains end groups in an amount of 0.02 to 1% by weight (% by weight), preferably 0.03 to 0.8% by weight, based on the total weight of the polyarylsulfone polymer.

[0021] The polyarylsulfone polymer contains less than 5% by weight, preferably less than 3% by weight, more preferably less than 2% by weight, and particularly preferably less than 1% by weight, of additional chemical groups not represented by the repeating units of Formulas I and II, based on the total weight of the polyarylsulfone polymer. These additional chemical groups are usually the above-mentioned end groups or minor aromatic isomers.

[0022] Examples of polyethersulfone polymers containing the repeating unit of Formula I include Ultrason® E grades available from BASF SE such as Ultrason® E2020P, Ultrason® E3010, Ultrason® E6020P, or Ultrason® E7020P.

[0023] Examples of polysulfone polymers containing the repeating unit of Formula II include Ultrason® S grades available from BASF SE such as Ultrason® S3010 or Ultrason® S6010.

[0024] The weight average molecular weight M of the polymer w is based on the total mass of molecules having a specific molecular mass. For this value, larger molecules, i.e., molecules with a larger mass, contribute more than smaller molecules, i.e., molecules with a smaller mass. M w and its determination method are well known in the art. M wFor example, it can be determined by gel permeation chromatography (GPC) using a suitable column (stationary phase), solvent (liquid phase), and detector (e.g., by refractive index or UV). These chromatography units need to be calibrated using standard polymers (e.g., polystyrene) with known molecular weights. Considering the detector signal and calibration curve, the attached computer system calculates a chromatogram representing the molecular weight distribution of each sample. The molecular weight distribution indicates the number of those molecules relative to the molar mass of the molecules present in the sample. M w and the number average molecular weight M n are obtained by computer analysis. M n is based on the number of molecules having a specific mass. Using these two values, the polydispersity index (PDI = M w / M n ), which is a measure of the breadth of the molecular weight distribution, can also be calculated.

[0025] When the polyarylsulfone polymer is measured by gel permeation chromatography (GPC) with the eluent being tetrahydrofuran (THF) and the standard being polystyrene (PS), it shows a weight average molecular weight value M w in the range of 40,000 to 105,000 g / mol, preferably 45,000 to 100,000 g / mol and more preferably 50,000 to 95,000 g / mol. When measured by GPC with the eluent being THF and the standard being PS, the preferred polyethersulfone polymer containing the repeating unit of formula I shows a weight average molecular weight value in the range of 40,000 to 100,000 g / mol, preferably 48,000 to 90,000 g / mol, and the preferred polysulfone polymer containing the repeating unit of formula II shows a weight average molecular weight value in the range of 45,000 to 70,000 g / mol, preferably 53,000 to 60,000 g / mol.

[0026] Preferred polyarylsulfone polymers exhibit a polydispersity index of from 2 to 5, preferably from 2.5 to 4.7. Preferred polyethersulfone polymers containing the repeating unit of Formula I exhibit a PDI value of from 2.5 to 3.6, preferably from 2.7 to 3.4, and preferred polysulfone polymers containing the repeating unit of Formula II exhibit a PDI value of from 3.8 to 4.7, preferably from 4 to 4.5.

[0027] Glass transition temperature T g is the temperature range in which the polymer chain segments become mobile and the sample reversibly transitions from a solid amorphous region to a more flexible, softer state. The glass transition temperature and methods for its determination are well known in the art. It can be determined, for example, by differential scanning calorimetry (DSC) by measuring the heat capacity as a function of temperature and thereby changing the temperature at a constant rate (e.g., 10 K / min). Generally, the sample is first cooled and then heated at the same rate. The glass transition temperature can be obtained from the acquired diagram by geometric or computer analysis.

[0028] Preferred polyarylsulfone polymers exhibit a glass transition temperature of from 160 to 250 °C, preferably from 170 to 240 °C, more preferably from 180 to 230 °C, measured by differential scanning calorimetry (DSC) at a heating rate of 10 K / min in accordance with ISO 11357-1 (2017) and 11357-2 (2020).

[0029] The viscosity number (reduced viscosity, VN) correlates with the molecular weight of the polymer and can be measured on a 1 wt% polymer solution dissolved in N-methylpyrrolidone based on ISO 1628-5 (1998). Thereby, the elution time (t) of a defined volume of the polymer solution in a Ubbelohde 1C capillary is related to the flow-down time (t0) of the pure solvent and is then normalized with the polymer concentration (c in g / ml) according to Equation 1.:

Equation

[0030] The viscosity number is expressed in g / ml. Preferred polyarylsulfone polymers exhibit a viscosity number of 40 to 130 g / ml, preferably 50 to 120 g / ml, and most preferably 60 to 110 g / ml, based on a 1 wt% polymer solution dissolved in N-methylpyrrolidone according to ISO 1628-5 (1998).

[0031] Solvent The solution of the present invention contains N-(2'-hydroxyethyl)-2-pyrrolidone (CAS-No. 3445-11-2), which is commercially available on an industrial scale, as a solvent. This solvent is a protic solvent and has a lower concern for toxicity compared to various frequently used aprotic pyrrolidone derivatives such as N-methyl-2-pyrrolidone, which is classified as "may damage fertility. May cause harm to the fetus." according to the hazard and harmful information of GHS (Globally Harmonized System of Classification and Labelling of Chemicals). The polyarylsulfone polymer and the mixture of the polyarylsulfone polymer and the water-soluble polymer can be well dissolved in N-(2'-hydroxyethyl)-2-pyrrolidone, resulting in a transparent solution showing a surprisingly high viscosity. Both transparency and minimum viscosity are required conditions for preparing high-quality films from such solutions.

[0032] Solution The solution of the present invention contains, based on the total weight of the solution, preferably 50 to 99 wt%, more preferably 55 to 95 wt%, particularly preferably 60 to 90 wt%, most particularly preferably 65 to 85 wt%, and most preferably 70 to 80 wt% of N-(2'-hydroxyethyl)-2-pyrrolidone.

[0033] The solution of the present invention contains, based on the total weight of the solution, 1 to 50 wt%, preferably 5 to 45 wt%, more preferably 7 to 40 wt%, particularly preferably 10 to 35 wt%, and most particularly preferably 12 to 25 wt% of the polyarylsulfone polymer.

[0034] Water-soluble polymer The solution of the present invention can further contain a water-soluble polymer, i.e., a polymer that is easily soluble in water and gives a transparent solution at a concentration of at least 10 g per 100 g of water at 21°C. These water-soluble polymers act as viscosity modifiers because they affect the solution viscosity. Furthermore, these water-soluble polymers act as pore-forming agents in the membrane preparation process, thus having a great influence on the membrane properties. Generally, the water-soluble polymer that fills the formed pores is removed in the post-treatment step of membrane preparation. This step includes various washing and / or oxidation steps and can remove the water-soluble polymer that leaves empty pores after removal. In addition to other parameters, the type and molecular weight of the polymer greatly affect the effort required to remove the water-soluble polymer during the post-treatment of the membrane.

[0035] Preferably, the water-soluble polymer is generally selected from the group of polyvinylpyrrolidone and poly(alkylene oxide) or mixtures thereof, having a number-average molar mass M n of at least 250 g / mol. More preferably, the water-soluble polymer is selected from the group of polyvinylpyrrolidone, poly(ethylene oxide), poly(propylene oxide), and poly(ethylene oxide) / poly(propylene oxide)-block-copolymers or mixtures thereof, having a number-average molar mass M n of at least 250 g / mol. Particularly preferably, the water-soluble polymer is selected from the group of polyvinylpyrrolidone and poly(ethylene oxide) or mixtures thereof, having a number-average molar mass M n of at least 250 g / mol, and in the case of polyvinylpyrrolidone, the solution viscosity is characterized in that the K value measured according to the method of Fikentscher described in Cellulosechemie 13, 1932 (58) by Fikentscher is 12 or more. The K value is determined by measuring the viscosity of the polymer solution known in the art described by Fikentscher. A very particularly preferred water-soluble polymer has an M of at least 250 g / mol nand a polyvinylpyrrolidone having a solution viscosity characterized by a K value of 12 or more determined according to the method described in Cellulosechemie 13, 1932 (58) by Fikentscher.

[0036] The solution preferably contains 0.1 to 15% by weight, more preferably 2 to 10% by weight, and particularly preferably 3 to 7% by weight of a water-soluble polymer based on the total weight of the solution.

[0037] More preferably, the solution contains 0.1 to 15% by weight, preferably 2 to 10% by weight, and more preferably 3 to 7% by weight of a water-soluble polymer selected from the group consisting of water-soluble polyvinylpyrrolidone and water-soluble poly(alkylene oxide) or mixtures thereof, based on the total weight of the solution.

[0038] Particularly preferably, the solution contains 0.1 to 15% by weight, preferably 2 to 10% by weight, and more preferably 3 to 7% by weight of a water-soluble polymer selected from the group consisting of water-soluble polyvinylpyrrolidone, water-soluble poly(ethylene oxide), water-soluble poly(propylene oxide), and water-soluble poly(ethylene oxide) / poly(propylene oxide)-block-copolymer or mixtures thereof, based on the total weight of the solution.

[0039] Most particularly preferably, the solution contains 0.1 to 15% by weight, preferably 2 to 10% by weight, and more preferably 3 to 7% by weight of a water-soluble polymer selected from the group consisting of water-soluble polyvinylpyrrolidone and water-soluble poly(ethylene oxide) or mixtures thereof, based on the total weight of the solution.

[0040] Most preferably, the solution contains 0.1 to 15% by weight, preferably 2 to 10% by weight, and more preferably 3 to 7% by weight of water-soluble polyvinylpyrrolidone based on the total weight of the solution.

[0041] Additional solvent: The solution of the present invention may further contain an additional solvent, i.e., one or more additional solvents or a mixture thereof. The additional solvent is a compound that dissolves only polyarylsulfone polymers selected from the group consisting of polyethersulfone containing repeating units of formula I, polysulfone polymers containing repeating units of formula II, or mixtures thereof, at a low concentration of 1 g of polyarylsulfone polymer per 100 g of additional solvent at 21°C. In the membrane preparation process, the additional solvent affects the solvent exchange rate and the rate of the precipitation process, and thus controls membrane properties such as pore size and number.

[0042] Preferably, the additional solvent is water, C1-C4 alkanol, C2-C8 alkanediol, oligo(alkylene glycol), and C3-C 12It is selected from the group of alkanetriols or mixtures thereof. More preferred additional solvents are methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol, di(ethylene glycol), tri(ethylene glycol), tetra(ethylene glycol), propane-1,2-diol, di(propylene glycol), tri(propylene glycol), tetra(propylene glycol), propane-1,3-diol, butane-1,2-diol, butane-1,3-diol, butane-1,4-diol, butane-2,3-diol, pentane-1,2-diol, pentane-1,3-diol, pentane-1,4-diol, pentane-1,5-diol, pentane-2,3-diol, pentane-2,4-diol, hexane-1,2-diol, hexane-1,3-diol, hexane-1,4-diol, hexane-1,5-diol, hexane-1,6-diol, hexane-2,5-diol, heptane-1,2-diol, heptane-1,7-diol, octane-1,8-diol, octane-1,2-diol, hexa-1,5-diene-3,4-diol, neopentyl glycol, 2-methylpentane-2,4-diol, 2,4-dimethylpentane-2,4-diol, 2-ethylhexane-1,3-diol, 2,5-dimethylhexane-2,5-diol, 2,2,4-trimethylpentane-1,3-diol, pinacol, glycerol, butane-1,2,3-triol, butane-1,2,4-triol, pentane-1,2,3-triol, pentane-1,2,4-triol, pentane-1,2,5-triol, hexane-1,2,3-triol, hexane-1,2,4-triol, hexane-1,2,6-triol, hexane-1,3,4-triol, hexane-1,3,5-triol, hexane-1,3,6-triol, hexane-1,4,5-triol, trimethylolmethane, 1,1,1-trimethylol ethane, 1,1,1-trimethylol propane, or mixtures thereof.

[0043] Preferably, the solution contains an additional solvent in an amount of 0.1 to 20% by weight, more preferably 1 to 15% by weight, particularly preferably 2 to 13% by weight, and most particularly preferably 5 to 12% by weight, based on the total weight of the solution.

[0044] Cosolvent In addition to N-(2'-hydroxyethyl)-2-pyrrolidone, the solution of the present invention may contain a further solvent specified herein as a cosolvent. In the process of membrane preparation, the cosolvent affects the rate of the precipitation process and thus controls membrane properties such as pore size and number.

[0045] Preferred cosolvents are solvents that are readily miscible with N-(2'-hydroxyethyl)-2-pyrrolidone in any ratio. More preferably suitable cosolvents are, for example, high-boiling ethers, esters, ketones, asymmetric halogenated hydrocarbons, anisole, gamma-valerolactone, N,N-dimethylformamide, dimethyl sulfoxide, dihydrolevoglucosenone, methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate, sulfolane, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-n-butyl-2-pyrrolidone, N-tert-butyl-2-pyrrolidone, N,N-dimethyl-2-hydroxypropanamide, and N,N-diethyl-2-hydroxypropanamide. Particularly preferred cosolvents are gamma-valerolactone, N-tert-butyl-2-pyrrolidone, and N-n-butyl-2-pyrrolidone.

[0046] In a preferred embodiment, at least 10% by weight, more preferably at least 50% by weight, particularly preferably at least 80% by weight, and most particularly preferably at least 90% by weight of the total weight of all solvents in the solution is N-(2'-hydroxyethyl)-2-pyrrolidone.

[0047] In a more preferred embodiment, no cosolvent is used in the solution and N-(2'-hydroxyethyl)-2-pyrrolidone is the only solvent used.

[0048] Preparation of the Solution The solution of the present invention can be easily prepared by combining the various components of the solution. Generally, there is no specific order for adding the various components. Thus, the solution of the present invention can be prepared by combining all the components, namely, the polyarylsulfone polymer, N-(2'-hydroxyethyl)-2-pyrrolidone, and, if necessary, further components such as a water-soluble polymer, an additional solvent, or a co-solvent, and dissolving all the compounds according to any process known in the art.

[0049] The dissolution process can be supported or accelerated, for example, advantageously, by raising the temperature of the mixture and / or by mechanical operations such as stirring, shaking, sonication (e.g., by using a sonication bath).

[0050] In a preferred embodiment under stirring at 60°C, first, the polyarylsulfone is dissolved in N-(2'-hydroxyethyl)-2-pyrrolidone, and then the water-soluble polymer and the additional solvent are added and stirred until a clear solution is obtained.

[0051] The solution of the present invention generally exhibits a viscosity of 0.1 to 150 Pa·s, preferably 0.5 to 75 Pa·s, particularly preferably 1 to 50 Pa·s, and most preferably 2 to 30 Pa·s, measured at 60°C at 5 to 100 rpm (revolutions per minute) using a Brookfield Viscometer DV-I Prime equipped with an RV6 spindle from Brookfield Engineering Laboratories, Inc. (Middleboro, USA). The shear rate, i.e., the number of revolutions per minute, is generally selected according to the viscosity of the sample. Usually, low-viscosity samples are measured at a higher shear rate, and high-viscosity samples are measured at a lower shear rate.

[0052] High solution viscosity is beneficial for the casting process during membrane preparation since it results in better film quality as demonstrated by the solutions of the present invention. Further, in the case of high viscosity solutions, it is generally not necessary to use high molecular weight water-soluble polymers to (further) increase the viscosity during membrane preparation.

[0053] The measure of turbidity is nephelometric turbidity units (NTU) measured using a calibrated nephelometer or turbidimeter, which represents the amount of light reaching a detector on the side of the light beam after scattering from the sample. The solutions of the present invention preferably exhibit a turbidity of 0 to 2 NTU, more preferably 0 to 1 NTU, and particularly preferably 0 to 0.9 NTU when measured using a turbidimeter 2100AN (Hach Lange GmbH, Duesseldorf, Germany) utilizing an 860 nm filter at 60°C.

[0054] Since low turbidity of the solution avoids macrovoids and defects in the membrane that would affect the balance between the pure water permeability coefficient and the molecular weight cut-off, low turbidity of the solution is an essential condition for preparing high-quality membranes and thus high-performance membranes.

[0055] Membrane Preparation The inventors have further found a process for preparing a membrane using a solution comprising the following (a) to (c). (a) A polyarylsulfone polymer selected from the group consisting of a polyethersulfone containing a repeating unit of formula I and a polysulfone containing a repeating unit of formula II, or a mixture thereof, wherein the weight average molecular weight M w of the polyarylsulfone polymer is in the range of 40,000 to 105,000 g / mol, and the polyarylsulfone polymer contains at least 95% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer, (b) N-(2'-hydroxyethyl)-2-pyrrolidone, and (c) A water-soluble polymer.

[0056] In the context of the present invention, the membrane is preferably understood to be a semi-permeable structure capable of separating two fluids, or a semi-permeable structure capable of isolating molecular and / or ionic components or particles from a liquid. The membrane acts as a selective barrier that can allow some particles, substances or chemicals to pass through while retaining others. The membrane can have various shapes such as a flat sheet, a spiral wound, a pillow, a tube, a single bore hollow fiber or a multi-bore hollow fiber.

[0057] Separation using the membrane can be carried out in various ways, for example, by pressure, by a concentration gradient, or by a gradient such as an electric potential gradient or a temperature gradient. Examples of pressure-driven operations are microfiltration, ultrafiltration, or nanofiltration, or reverse osmosis operations. Examples of concentration-based operations are dialysis or forward osmosis. A good overview is described in WO 2017 / 045985 pamphlet or M. Ulbricht, Polymer 47 (2006), pp. 2217-2262, which is incorporated herein by reference. A preferred membrane is an ultrafiltration membrane.

[0058] The membrane can be prepared by various methods such as polymer phase separation (phase inversion), sol-gel method, interfacial reaction, stretching, extrusion, track etching, microfabrication, etc.

[0059] Preferably, the membrane according to the present invention is prepared by liquid non-solvent induced phase separation (NIPS) comprising the following steps: (a) Preparing a solution comprising a polyarylsulfone polymer selected from the group consisting of a polyethersulfone comprising a repeating unit of formula I, a polysulfone comprising a repeating unit of formula II, or a mixture thereof, N-(2'-hydroxyethyl)-2-pyrrolidone, and a water-soluble polymer, wherein the weight average molecular weight M w of the polyarylsulfone polymer ranges from 40,000 to 105,000 g / mol, and the polyarylsulfone polymer comprises at least 95% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer. b1) shaping the polymer solution into a specific shape, such as a fibrous shape, a tubular shape, or a flat sheet shape, by methods such as extrusion of the polymer solution, or film preparation from the polymer solution, or casting the polymer solution; b2) solidifying the shape formed in step b1) by exposing the polymer solution to a coagulant.

[0060] Step (a) The solution of step a) conforms to the above-mentioned polymer solution. Preferably, the solution further contains the above-mentioned additional solvent and / or co-solvent. The preparation of the solution of step a) can be carried out as described above.

[0061] In a preferred embodiment, the solution of step a) contains 5-45% by weight of a polyarylsulfone polymer, 55-95% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone, and 1-15% by weight of a water-soluble polymer, based on the total weight of the solution.

[0062] In a more preferred embodiment, the solution of step a) contains 10-35% by weight of a polyarylsulfone polymer, 60-90% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone, and 2-10% by weight of a water-soluble polymer, based on the total weight of the solution.

[0063] In one embodiment, the solution may be degassed and / or heated before proceeding to the next step.

[0064] Steps b1) and b2) Steps b1) and b2) can be carried out continuously, i.e., not as separate steps. For example, when continuously extruding the polymer solution into a coagulation bath, or in separate steps, for example, first forming a polymer film and then transferring it to the coagulation bath after a specific drying time.

[0065] The formed polymer solution still contains a polyarylsulfone polymer, a solvent, a water-soluble polymer, etc. The phase separation of the polymer and the solvent has not yet started or been completed, that is, the polymer has not yet completely solidified. In the case of forming by extrusion, the polymer solution is formed into a fibrous or tubular shape. In the case of shape processing by film formation or casting, the polymer solution is made into a flat sheet shape.

[0066] The exposure of the formed polymer solution to the coagulant (step b2) can be carried out, for example, in a coagulation bath containing the coagulant. It is desirable that the polyarylsulfone polymer has a low solubility in the coagulant, that is, it is desirable that it is less than 1 g of polyarylsulfone polymer per 100 g of coagulant at 21 °C.

[0067] Contact with the coagulant induces non-solvent-induced demixing of the homogeneous polymer solution, and as a result, the polymer solidifies and a membrane is formed in the respective geometric shapes of the polymer solution. The structure and morphology of the membrane depend strongly not only on the nature and presence of various compounds present in the solution, but also on the process parameters used herein. The water-soluble polymer and the additional solvent mainly have two functions: on the one hand, adjusting the viscosity of the solution at a high level to facilitate film formation by, for example, casting, and on the other hand, functioning as a pore former that strongly determines the performance characteristics of the membrane.

[0068] Suitable coagulants are, for example, liquid water, water vapor, and mixtures of water and alcohols, co-solvents, and / or the solvent of the solution of the present invention, that is, N-(2'-hydroxyethyl)-2-pyrrolidone. Suitable alcohols are, for example, C1-C4 alkanols, C2-C8 alkanediols, oligo(alkylene glycols), C3-C 12 monoalcohols, diols or triols selected from the group of alkanetriols, or poly(ethylene oxide) having an M of 100-1000 g / mol n is.

[0069] Suitable co-solvents are selected from, for example, high-boiling ethers, esters, ketones, asymmetric halogenated hydrocarbons, anisole, gamma-valerolactone, N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, dihydrolevoglucosenone, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-n-butyl-2-pyrrolidone, N-tert-butyl-2-pyrrolidone, N,N-dimethyl-2-hydroxypropanamide, and N,N-diethyl-2-hydroxypropanamide. Preferred co-solvents are gamma-valerolactone, N-tert-butyl-2-pyrrolidone, and N-n-butyl-2-pyrrolidone.

[0070] Preferably, the coagulant is a mixture containing liquid water and the solvent N-(2'-hydroxyethyl)-2-pyrrolidone, or a mixture containing liquid water and an alcohol, such as poly(ethylene oxide) having M n with a molecular weight of 100 to 1000 g / mol, and / or a mixture containing liquid water and a co-solvent. More preferably, the coagulant is a mixture containing liquid water and the solvent N-(2'-hydroxyethyl)-2-pyrrolidone. The coagulant may contain 10 to 90% by weight of water and 90 to 10% by weight of alcohol and / or co-solvent or the solvent N-(2'-hydroxyethyl)-2-pyrrolidone based on the total weight of the coagulant, preferably 30 to 70% by weight of water and 70 to 30% by weight of alcohol and / or co-solvent or the solvent N-(2'-hydroxyethyl)-2-pyrrolidone. Generally, the total amount of all components of the coagulant amounts to 100%.

[0071] Further details of process steps a) and b) depend on the desired geometric structure of the membrane and the production scale, including laboratory scale or commercial / industrial scale.

[0072] In a preferred process, a flat sheet membrane is prepared. This process is: (a) Preparing a solution comprising a polyarylsulfone polymer selected from the group consisting of a polyethersulfone containing a repeating unit of formula I, a polysulfone containing a repeating unit of formula II, or a mixture thereof, N-(2'-hydroxyethyl)-2-pyrrolidone, and a water-soluble polymer, wherein the weight-average molecular weight M w of the polyarylsulfone polymer is in the range of 40,000 to 105,000 g / mol, and the polyarylsulfone polymer contains at least 95% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer; b1) Preparing a polymer film from the solution of step a) by applying the solution of step a) to a substrate; b2) Exposing the polymer film to a coagulant and comprising.

[0073] Step a) The solution of step a) conforms to the above-mentioned polymer solution. Preferably, the solution further contains the above-mentioned additional solvent and / or co-solvent. The preparation of the solution of step a) can be carried out as described above.

[0074] In a preferred embodiment, the solution of step a) contains 5 to 45% by weight of the polyarylsulfone polymer, 55 to 95% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone, and 1 to 15% by weight of the water-soluble polymer based on the total weight of the solution.

[0075] In a more preferred embodiment, the solution of step a) contains 10 to 35% by weight of the polyarylsulfone polymer, 60 to 90% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone, and 2 to 10% by weight of the water-soluble polymer based on the total weight of the solution.

[0076] The solution is preferably prepared while being stirred at a temperature of 20 to 100 °C, preferably 40 to 90 °C, more preferably 50 to 70 °C. The ready solution is usually degassed for 2 to 24 hours, preferably 6 to 20 hours, more preferably 10 to 14 hours. Next, the solution is preferably reheated at a temperature of 20 to 100 °C, preferably 40 to 90 °C, more preferably 50 to 70 °C for 1 to 4 hours, preferably 1.5 to 3 hours.

[0077] Step b1) The preparation of the polymer film from the solution of the present invention can be carried out, for example, by casting, or other methods such as rolling, spraying, etc. Preferably, for example, using a casting knife and optionally an automatic coater, at a temperature of 40 to 90 °C, preferably 50 to 70 °C, on a substrate, preferably a polymer substrate (for example, a polymer film from biaxially oriented poly(ethylene terephthalate), for example, the trademark Hostaphan®), a glass substrate, or a metal substrate (for example, a metal conveyor belt). It can be carried out by casting.

[0078] In a preferred embodiment, the polymer film is produced by casting using a casting knife with a diameter of 100 to 500 μm, more preferably 200 to 400 μm.

[0079] Step b2) Generally, the polymer film is left stationary for 5 to 150 seconds, preferably 10 to 100 seconds, more preferably 20 to 60 seconds, and then applied to a coagulation bath containing the above-mentioned coagulant. The immersion is carried out at 10 to 50 °C, preferably 15 to 40 °C, more preferably 20 to 30 °C for 3 to 20 minutes, preferably 5 to 15 minutes. Next, the film is peeled off from the substrate and generally post-treated.

[0080] In an even more preferred process, a non-flat sheet film is prepared. This process is: (a) Preparing a solution comprising a polyarylsulfone polymer selected from the group consisting of a polyethersulfone containing a repeating unit of formula I, a polysulfone containing a repeating unit of formula II, or a mixture thereof, N-(2'-hydroxyethyl)-2-pyrrolidone, and a water-soluble polymer, wherein the weight average molecular weight M w of the polyarylsulfone polymer is in the range of 40,000 to 105,000 g / mol, and the polyarylsulfone polymer contains at least 95% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer; (b) Continuously shaping and demixing the solution into a non-flat shape and inducing a certain degree of solidification of the shaped solution by directly exposing the solution of step (a) to a coagulant. It includes.

[0081] Step (a) The solution of step (a) conforms to the above-mentioned polymer solution. Preferably, the solution further contains the above-mentioned additional solvent and / or co-solvent. The preparation of the solution of step (a) can be carried out as described above.

[0082] In a preferred embodiment, the solution of step (a) contains 5 to 45% by weight of the polyarylsulfone polymer, 55 to 95% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone, and 1 to 15% by weight of the water-soluble polymer based on the total weight of the solution.

[0083] In a more preferred embodiment, the solution of step (a) contains 10 to 35% by weight of the polyarylsulfone polymer, 60 to 90% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone, and 2 to 10% by weight of the water-soluble polymer based on the total weight of the solution.

[0084] The solution is preferably prepared while being stirred at a temperature of 20 to 100 °C, preferably 40 to 90 °C, more preferably 50 to 70 °C. The prepared solution is usually degassed for 2 to 24 hours, preferably 6 to 20 hours, more preferably 10 to 14 hours. Next, the solution is preferably reheated at a temperature of 20 to 100 °C, preferably 40 to 90 °C, more preferably 50 to 70 °C for 1 to 4 hours, preferably 1.5 to 3 hours.

[0085] Step b) Shaping the solution of step a) into a non-flat shape can be achieved, for example, by extruding the solution through an extrusion nozzle to obtain, for example, a fibrous shape. To maintain the desired shape, the polymer solution is generally extruded directly into a coagulation bath containing the above-mentioned coagulant, thereby inducing demixing of the polymer and the solvent, so that the polymer is solidified into the desired shape. For example, if one or more additional hollow needles are present in the extrusion nozzle and a solution of the coagulant is further injected through them inside the developing fiber, a single or multiple tubular shapes can be obtained as described below.

[0086] Preferred membranes showing a non-flat shape are hollow fiber membranes (single-hole hollow fibers or porous hollow fibers). They can be prepared by various spinning techniques, such as melt spinning, dry spinning, or wet spinning. Thus, the solution obtained in step a) above is extruded through an extrusion nozzle (also called a spinneret) containing the required number of hollow needles (step b). The coagulant is injected into the polymer extruded through the hollow needles during extrusion molding. With this setup, the extruded polymer membrane becomes a hollow cylindrical shape, and parallel continuous channels extending in the extrusion direction are formed within the extruded polymer. Preferably, the porous structure on the outer surface of the extruded membrane is formed by contacting the outer surface of the extruded hollow polymer fibers with a mild coagulant such as water vapor, and the shape is fixed even without an active layer, i.e., a highly porous filtration layer, on the outer surface. Subsequently, the membrane is brought into contact with the coagulant. Process parameters such as extrusion speed, temperature, nozzle shape, type of coagulant, and concentration affect not only the shape and thickness of the membrane but also the pore size and distribution, and thus the performance of the membrane, and can be used to control these. The hollow fiber membranes can optionally be wound into rolls and / or bundled into bundles of hollow fibers.

[0087] The membranes prepared by the above procedure are generally post-treated by a washing step and / or an optional oxidation step.

[0088] In one embodiment, the membrane prepared by the above process (steps a - b) is exposed to a solution containing an oxidation-active component after an optional washing step. In this case, the solution containing the oxidation-active component is preferably an aqueous solution. To remove the oxidizing agent, washing is performed after the oxidation step. For example, water-soluble oxidizing agents such as sodium hypochlorite or halogen, especially chlorine in a concentration range of 500 - 5000 ppm by weight, more preferably 1000 - 4000 ppm by weight, and particularly preferably 1500 - 3500 ppm by weight based on the total weight of the oxidation aqueous solution, are preferred.

[0089] To remove the water-soluble polymer and form pores, not only washing but also oxidation is carried out. Washing may follow oxidation in some cases, or vice versa. Similarly, oxidation and washing may be carried out simultaneously in one step. The membrane is oxidized using a chlorite solution or chlorine gas at 20 - 90 °C, preferably 35 - 80 °C, more preferably 50 - 70 °C, pH 9 - 10, preferably 9.3 - 9.7, for 0.5 - 4 hours, preferably 1 - 3 hours, more preferably 1.5 - 2.5 hours, and is preferably subsequently washed with water. Washing with water is usually carried out in a water bath for 2 - 24 hours, preferably 4 - 20 hours, more preferably 8 - 16 hours, and generally carried out 1 - 5 times, preferably 3 times with water at 20 - 90 °C, preferably 35 - 80 °C, and more preferably 50 - 70 °C. In a further step, the membrane is usually washed with a sodium bisulfite solution, preferably using an aqueous sodium bisulfite solution of 0.1 - 1 wt%, preferably 0.3 - 0.7 wt%, more preferably 0.4 - 0.6 wt%.

[0090] When the solution of the present invention based on N-(2'-hydroxyethyl)-2-pyrrolidone is used for membrane preparation, it is preferable not to perform post-oxidation treatment. As described above, since the solution of the present invention has a high viscosity, there is no need to use a high molecular weight water-soluble polymer to increase the viscosity. Instead, a low molecular weight water-soluble polymer that does not need to be removed by post-oxidation treatment can be used.

[0091] Furthermore, a membrane prepared using the solution of the present invention comprising a polyarylsulfone polymer selected from the group consisting of a polyethersulfone containing a repeating unit of formula I and a polysulfone containing a repeating unit of formula II, or a mixture thereof, N-(2'-hydroxyethyl)-2-pyrrolidone, and a water-soluble polymer, wherein the weight average molecular weight M w of the polyarylsulfone polymer is in the range of 40000 - 105000 g / mol, and a membrane has been found in which the polyarylsulfone polymer contains at least 95 wt% of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer.

[0092] As described above, the preparation of the membrane preferably includes the following steps (a) Preparing a solution comprising a polyarylsulfone polymer selected from the group consisting of a polyethersulfone containing a repeating unit of formula I, a polysulfone containing a repeating unit of formula II, or a mixture thereof, N-(2'-hydroxyethyl)-2-pyrrolidone, and a water-soluble polymer, wherein the weight-average molecular weight M w of the polyarylsulfone polymer is in the range of 40,000 to 105,000 g / mol, and the polyarylsulfone polymer contains at least 95% by weight of the repeating units of formula I and II based on the total weight of the polyarylsulfone polymer b1) shaping the polymer solution into a specific shape, such as a fibrous shape, a tubular shape, or a flat sheet shape, by a method such as extrusion of the polymer solution, or preparation of a film from the polymer solution, or casting the polymer solution b2) solidifying the shape formed in step b1) by exposing the polymer solution to a coagulant

[0093] Preferably, the solution used for forming the membrane further contains the above-mentioned additional solvent and / or co-solvent. The preparation of the solution in step a) can be carried out as described above. Usually, the membrane is post-treated by various washing and / or oxidation steps as described above

[0094] In addition, the performance of the membrane can be specified by its pure water permeability coefficient (PWP) and its fractional molecular weight. The PWP indicates the permeability coefficient of various membranes for pure water according to the following formula (Equation 2) depending on the membrane area, the applied pressure, and the permeation experiment time: [Number] PWP: pure water permeability coefficient [kg / bar h m 2 m: mass of permeated water [kg] A: membrane area [m 2 ​​P: Pressure [bar] t: Time of the permeation experiment [h].

[0095] To achieve a high flux, the membrane according to the present invention preferably has, with respect to ultrafiltration membranes, a PWP of more than 100 kg / h·m 2 ·bar, more preferably more than 125 kg / h·m 2 ·bar, and particularly preferably more than 150 kg / h·m 2 ·bar, and with respect to nanofiltration membranes, preferably has a PWP of more than 25 kg / h·m 2 ·bar, more preferably more than 50 kg / h·m 2 ·bar, particularly preferably more than 100 kg / h·m 2 ·bar.

[0096] The pure water permeability coefficient of the membrane is determined before determining its molecular weight cut-off in order to avoid limitations of the permeation value due to pore clogging / fouling by the polymer used for the determination of the molecular weight cut-off.

[0097] The weight average molecular weight cut-off (MWCO) of the membrane is the molecular weight of the poly(ethylene oxide) standard of the lower limit weight average molecular weight (M w ) that is retained by the membrane by at least 90%. It is generally expressed in kilodaltons (kDa). For example, an MWCO of 18.4 kDa means that poly(ethylene oxide) with M w of 18.4 kDa or more is retained by at least 90%. The MWCO of the membrane according to the present invention is usually 2 to 200 kDa, preferably 10 to 200 kDa, and more preferably 10 to 100 kDa for ultrafiltration membranes, and the upper limit of MWCO for nanofiltration membranes is less than 10 kDa, and the lower limit of MWCO is preferably at least 5 kDa, more preferably at least 3 kDa, and particularly preferably at least 2 kDa.

[0098] The membrane of the present invention can be used in any kind of separation process of gas or liquid mixtures, such as purification of drinking water, treatment of industrial wastewater or municipal wastewater, desalination of seawater or brackish water, dialysis, purification of pharmaceuticals, plasmolysis, and water treatment applications such as food processing.

[0099] In a general embodiment of the process of the present invention for preparing a flat sheet membrane, a polyethersulfone containing a repeating unit of formula I and having a weight average molecular weight of 48,000 to 90,000 g / mol is mixed with N-(2'-hydroxyethyl)-2-pyrrolidone and polyvinylpyrrolidone having at least 12 K values. The various polymers are used in amounts such that the resulting solution contains 10 to 35 wt% polyethersulfone and 2 to 10 wt% polyvinylpyrrolidone. To facilitate dissolution of the polymers, the mixture is heated with stirring at a temperature of 50 to 70 °C until a homogeneous and transparent viscous solution is obtained. Next, the solution is degassed for 10 to 14 hours and reheated at 50 to 70 °C for 1.5 to 3 hours. Subsequently, the solution is cast at a temperature of 50 to 70 °C onto a glass plate having a casting knife with a diameter of 200 to 400 μm. After allowing the resulting film to stand for 20 to 60 seconds, it is placed in an aqueous coagulation bath containing 30 to 70 wt% water and 70 to 30 wt% N-(2'-hydroxyethyl)-2-pyrrolidone at 20 to 30 °C for 5 to 15 minutes. After removing the glass substrate, the membrane is transferred to a water bath at room temperature and left for 8 to 16 hours, then washed three times with water at 50 to 70 °C and stored in a wet state.

[0100] In a general embodiment of the process of the present invention for preparing a hollow fiber membrane, a polysulfone containing a repeating unit of formula II and having a weight average molecular weight of 53,000 to 60,000 g / mol is N-(2'-hydroxyethyl)-2-pyrrolidone and a number average molecular weight M of at least 250 g / mol nIt is mixed with poly(ethylene oxide) shown. Various polymers are used in amounts such that the resulting solution contains 10 to 35% by weight of polyethersulfone and 2 to 10% by weight of poly(ethylene oxide). To facilitate the dissolution of the polymer, the mixture is heated with stirring at a temperature of 40 to 90 °C until a homogeneous and transparent viscous solution is obtained. Next, the solution is degassed for 10 to 14 hours and then reheated at 40 to 90 °C for 1.5 to 3 hours. Next, the solution is subjected to a wet spinning process at 50 to 70 °C and extruded through an extrusion nozzle (spinneret). The bore fluid, i.e., the aforementioned coagulation liquid, injected into the polymer extruded through the hollow needle contains 20 to 30% by volume of water and 70 to 80% by volume of the solvent N-(2'-hydroxyethyl)-2-pyrrolidone. The obtained fibers are immersed in a coagulation bath containing water, wound around a coil winder, and subsequently exposed to an aqueous solution containing 1500 to 3500 ppm by weight of NaOCl at 50 to 70 °C and pH 9.3 to 9.7 for 1 to 3 hours. Thereafter, the membrane is washed with water at 50 to 70 °C and washed once with an aqueous solution of sodium bisulfite at 0.4 to  0.6% by weight. The membrane is stored in a wet state.

[0101] It has been found that the solvent N-(2'-hydroxyethyl)-2-pyrrolidone easily dissolves polyarylsulfone polymers, resulting in a solution with low turbidity.

[0102] The use of N-(2'-hydroxyethyl)-2-pyrrolidone shows various advantages compared to other solvents, especially other pyrrolidone derivatives:

[0103] First of all, N-(2'-hydroxyethyl)-2-pyrrolidone is easily available and has less concern about toxicity compared to, for example, frequently used N-methylpyrrolidone.

[0104] Secondly, the solution of the present invention obtained shows high viscosity, which leads to better film quality and is beneficial for the casting process during membrane preparation.

[0105] Thirdly, due to the high viscosity of the solution, there is no need to use a high molecular weight water-soluble polymer to increase the viscosity during membrane preparation. Instead, the high viscosity solution allows the use of a water-soluble polymer with a relatively low K value or molecular weight value. This type of polymer does not require an oxidation step and can be removed from the resulting membrane by simple washing with water. Thus, advantageously, one of the process steps can be avoided, making it possible to avoid the use of potentially dangerous chemicals (and the necessary additional washing steps).

[0106] Fourthly, it has been further found that by using the solution of the present invention containing a low molecular weight water-soluble polymer, regardless of the presence or absence of an oxidation treatment, a membrane having an advantageous balance between the pure water permeability coefficient and the molecular weight cut-off is obtained, and thus improved membrane performance is provided compared to membranes known in the art.

Examples

[0107] Abbreviations and compounds used in the examples: DMAc N,N-dimethylacetamide DMSO Dimethyl sulfoxide DSC Differential scanning calorimetry GPC Gel permeation chromatography HEP N-(2’-hydroxyethyl)-2-pyrrolidone MWCO Molecular weight cut-off NMP N-methyl-2-pyrrolidone NTU Nephelometric turbidity unit PEO Poly(ethylene oxide) PWP Pure water permeability TBP N-tert butyl-2-pyrrolidone 2P 2-pyrrolidone Agnique® AMD3L N,N-dimethyl-2-hydroxypropanamide (N,N-dimethyl lactamide) Hereinafter abbreviated as "AMD3L" Ultrason® E3010, having an intrinsic viscosity of 66 ml / g (measured in a 1 wt% polymer solution dissolved in N-methylpyrrolidone according to ISO 1628-5 (1998)), a glass transition temperature of 225 °C (in accordance with DSC, 10 K / min, ISO 11357-1 (2017) and 11357-2 (2020)); molecular weight M w 58,000 g / mol (eluent THF, GPC with PS standards), and M w / M n = 3.3, a polyethersulfone abbreviated as "E3010" Ultrason® E6020P, having an intrinsic viscosity of 81 ml / g (measured in a 1 wt% polymer solution dissolved in N-methylpyrrolidone according to ISO 1628-5 (1998)); a glass transition temperature of 225 °C (in accordance with DSC, 10 K / min, ISO 11357-1 (2017) and 11357-2 (2020)); molecular weight M w 75,000 g / mol (eluent THF, GPC with PS standards), and M w / M n = 3, a polyethersulfone abbreviated as "E6020P", Ultrason® E7020P, having an intrinsic viscosity of 100 ml / g (measured in a 1 wt% polymer solution dissolved in N-methylpyrrolidone according to ISO 1628-5 (1998)); a glass transition temperature of 225 °C (in accordance with DSC, 10 K / min, ISO 11357-1 (2017) and 11357-2 (2020)); molecular weight M w 92,000 g / mol (eluent THF, GPC with PS standards), and M w / M n = 3.0, a polyethersulfone abbreviated as "E7020P" Luvitec® K90, having a molecular weight M of 1,000,000 - 1,500,000 w and a solution viscosity characterized by a K value of 90 measured according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)), a polyvinylpyrrolidone abbreviated as "K90" Luvitec® K85, having a molecular weight M of 1,100,000 g / mol wPolyvinylpyrrolidone abbreviated as "K85" having a solution viscosity characterized by a K value of 85 measured according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) Luvitec® K30 with a molecular weight M of 44,000 to 540,000 w Polyvinylpyrrolidone abbreviated as "K30" having a solution viscosity characterized by a K value of 30 measured according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) Luvitec® K25 with a molecular weight M of 28,000 to 340,000 w Polyvinylpyrrolidone abbreviated as "K25" having a solution viscosity characterized by a K value of 25 measured according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) Luvitec® K17 with a molecular weight M of 7,000 to 11,000 w Polyvinylpyrrolidone abbreviated as "K17" having a solution viscosity characterized by a K value of 17 measured according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) Luvitec® K12 with a molecular weight M of 2,000 to 3,000 w Polyvinylpyrrolidone abbreviated as "K12" having a solution viscosity characterized by a K value of 12 measured according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) Pluriol® E400 with a number average molecular weight M of 400 g / mol calculated from the OH number according to DIN53240 n Poly(ethylene oxide) abbreviated as "PEO400"

[0108] Measurement of solution turbidity The turbidity of the polymer solution was measured with a turbidimeter 2100AN (Hach Lange GmbH, Duesseldorf, Germany) using an 860 nm filter at 60 °C and expressed in nephelometric turbidity units (NTU).

[0109] Measurement of solution viscosity The viscosity of the polymer solution was measured using a Brookfield viscometer DV-I Prime (Brookfield Engineering Laboratories, Inc., Middleboro, USA) with an RV6 spindle at 60 °C and 5 - 100 rpm. The shear rate used varied depending on the viscosity of the solution and is shown in the following table.

[0110] Measurement of water permeability of the membrane Using ultrapure water (salt-free water filtered by a Millipore UF-system), the pure water permeability coefficient (PWP) of the membrane was tested at 23 °C and a water pressure of 1 bar using a pressure cell with a diameter of 74 mm. The pure water permeability coefficient (PWP) was calculated as follows (Equation 2):

Number

[0111] Measurement of MWCO of the membrane In subsequent tests, a high molecular weight poly(ethylene oxide) standard solution was used as the feed solution filtered by the membrane at a pressure of 0.15 bar. The molecular weight of the permeate of each poly(ethylene oxide) standard used was determined by GPC measurement of the feed solution and the permeate.

[0112] Examples 1 - 17: Viscosity and turbidity of polyarylsulfone polymer solutions dissolved in various solvents ​​The polymer solution of the present invention using various polyarylsulfone polymers at a predetermined concentration of 20% by weight was prepared by mixing within 30 minutes at speeds of 200, 800, and 1200 rpm using a SpeedMixer® DAC600.1 Vac-P (Hauschild & Co. KG, Hamm, Germany). For comparison, corresponding solutions were prepared using other solvents following the same procedure. The solution viscosity and turbidity were measured at 60°C following the above procedure. The results are summarized in Table 1.

[0113] [Table 1]

[0114] From the data summarized in Table 1, it can be seen that the solution of the present invention using N-(2'-hydroxyethyl)-2-pyrrolidone as a solvent at a predetermined concentration of polyarylsulfone polymer exhibits a significantly higher viscosity level compared to the corresponding solutions (comparative examples) based on other solvents. This is effective even when changing the type of polyarylsulfone polymer. A higher solution viscosity is advantageous because it promotes the process steps of film casting and results in a better film. Furthermore, the solution turbidity of the solution of the present invention is at a low level required to obtain a high-quality membrane. The higher the turbidity level, the more defects may occur in the membrane and the lower the separation performance of the membrane. The turbidity is at a similar level compared to the solutions (comparative examples) based on other solvents.

[0115] Preparation of Membrane - General Procedure The amounts shown in this general procedure are general ranges, and the exact amounts for each experiment are described in Tables 2 and 4 - 7. Into a three - necked flask equipped with a magnetic stirrer, as shown in Tables 2 and 4 - 7, 65 or 81 g of a solvent, 15 - 19 g of Ultrason® polymer, 4 - 8 g of Luvitec® polyvinylpyrrolidone or poly(alkylene oxide) (e.g., Pluriol® E400) were added. The mixture was heated with gentle stirring at 60 °C until a homogeneous, transparent, viscous solution, commonly referred to as a solution, was obtained. The solution was degassed at room temperature overnight.

[0116] Thereafter, the membrane solution was reheated at 60 °C for 2 hours and cast onto a glass plate at 60 °C using a casting knife (300 microns) with an Erichsen coating machine (Coatmaster 510, Erichsen GmbH & Co KG, Hemer, Germany) operating at a speed of 5 mm / s. Before immersing the membrane film in an aqueous coagulation bath consisting of a mixture of the same solvent and water in a weight ratio of 40:60 as used in the preparation of the above - mentioned polymer solution for 10 minutes at 25 °C, it was allowed to stand for 30 seconds. After peeling the membrane from the glass plate, the membrane was exposed to either post - treatment A or post - treatment B.

[0117] Post - treatment A (including only the washing step and not the oxidation step) The membrane was washed three times with water at 60 °C.

[0118] Optional post - treatment B (oxidation and washing steps) The membrane was transferred to a water bath at 60 °C, pH 9.5, containing a 2000 ppm NaOCl solution for 2 hours. Next, the membrane was washed with water at 60 °C and once with a 0.5 wt% solution of sodium bisulfite to remove active chlorine.

[0119] After post - treatment, the membrane was stored in a wet state.

[0120] Examples 18 - 20: Solutions with adjusted viscosities, and membranes with and without post - oxidation treatment Both the polymer solution of the present invention and the comparative polymer solution were prepared according to the above-described procedure using the types and amounts of polymers shown in Table 2. The amount of the water-soluble polymer was kept constant. The type of the water-soluble polymer was selected so that the adjusted solution exhibited a target viscosity of 16 to 17 Pa·s.

[0121] According to the above-described method, the viscosity and turbidity were measured. From all these solutions, two membranes were prepared in each case according to the above-described procedure, where in one case only washing with water as a post-treatment (post-treatment A), and in the other case an oxidative post-treatment with NaOCl and washing with a sodium bisulfite solution (post-treatment B). For each membrane, the pure water permeation coefficient and the fractional molecular weight were determined according to the above-described method. The results are summarized in Table 3.

[0122]

Table 2

[0123]

Table 3

[0124] From these experiments, it can be seen that for a given amount of the water-soluble polymer, in the case of the solution of the present invention containing the polyarylsulfone polymer Ultrason® E6020P and N-(2'-hydroxyethyl)-2-pyrrolidone, a water-soluble polymer with a lower K value (see above by Fikentscher) brings about the target solution viscosity, while in the case of other solvents, a water-soluble polymer with a higher K value is required. This is because the viscosity contribution of N-(2'-hydroxyethyl)-2-pyrrolidone in the solvent of the present invention is high. Since the K value is a measure of the molar mass, solvents other than N-(2'-hydroxyethyl)-2-pyrrolidone require a water-soluble polymer with a higher molar mass to obtain the same target viscosity. A specific viscosity level is required to obtain a high-quality film by casting.

[0125] A further advantage in the case of N-(2’-hydroxyethyl)-2-pyrrolidone results from the fact that low molecular weight water-soluble polymers can be removed from the obtained membranes by simple washing with water. In this case, post-oxidation treatment is not necessary, but in the case of other solvents, if post-oxidation treatment is carried out, high molecular weight water-soluble polymers can be significantly removed. In the case of N-(2’-hydroxyethyl)-2-pyrrolidone, the obtained membranes exhibit a high pure water permeability coefficient in combination with a low fractional molecular weight even if post-oxidation treatment is not carried out, while membranes obtained from other solutions exhibit a low PWP and a high MWCO. In the case of other solvents, post-oxidation treatment results in a high PWP but also a rather high MWCO at the same time.

[0126] Examples 21 to 48: Various water-soluble polymer solutions and their various membranes without post-oxidation treatment According to the above procedure, various membranes were prepared. In so doing, various water-soluble polymers, namely, various grades of polyvinylpyrrolidone or poly(ethylene oxide) (PEO400) were used. According to the above procedure, the viscosity and turbidity of the polymer solutions before the casting step were determined. The membranes were post-treated only by washing with water (post-treatment A). According to the above method, the PWP and MWCO of the obtained membranes were analyzed. The results are summarized in Tables 4 to 7.

[0127] [Table 4]

[0128] [Table 5]

[0129] [Table 6]

[0130] [Table 7]

[0131] From Tables 4 to 7, it can be seen that the solution of the present invention based on N-(2'-hydroxyethyl)-2-pyrrolidone exhibits a higher solution viscosity compared to the corresponding NMP solution. Therefore, the solution of the present invention is better suited for casting films. If the obtained film is only washed with water without performing post-oxidation treatment, in the case of N-(2'-hydroxyethyl)-2-pyrrolidone, the obtained film shows an advantageous balance of PWP and MWCO, but in the case of NMP, the PWP value becomes extremely low, which is not suitable for an effective separation procedure.

Claims

1. A solution comprising: (a) a polyethersulfone containing a repeating unit of Formula 1 【Chemical 1】 and a polysulfone containing a repeating unit of Formula II [Chemical Formula 2] A polyarylsulfone polymer selected from the group of them or their mixtures, wherein the weight average molecular weight M of the polyarylsulfone polymer ｗ is in the range of 40,000 to 105,000 g / mol, and the polyarylsulfone polymer contains at least 95% by weight of repeating units of formulas I and II based on the total weight of the polyarylsulfone polymer and (b) N-(2'-hydroxyethyl)-2-pyrrolidone A solution containing the same.

2. The solution according to claim 1, wherein the solution contains 50 to 99% by weight of N-(2'-hydroxyethyl)-2-pyrrolidone based on the total weight of the solution.

3. The solution according to claim 1 or 2, wherein the solution contains 1 to 50% by weight of a polyarylsulfone polymer based on the total weight of the solution.

4. The solution according to any one of claims 1 to 3, containing a water-soluble polymer showing a solubility in at least 10 g of water per 100 g of water at 21°C.

5. The solution according to claim 4, wherein the solution contains 0.1 to 15% by weight of a water-soluble polymer based on the total weight of the solution.

6. The solution according to claim 4 or 5, wherein the water-soluble polymer is selected from polyvinylpyrrolidone, poly(alkylene glycol) or a mixture thereof.

7. The solution according to any one of claims 1 to 6, wherein the polyarylsulfone polymer contains an additional solvent that dissolves at a concentration of less than 1 g of the polyarylsulfone polymer per 100 g of the additional solvent at 21°C.

8. The solution according to claim 7, wherein the solution contains 0.1 to 20% by weight of the additional solvent based on the total weight of the solution.

9. The additional solvent is water, C １ -C ４ alkanols, C ２ -C ８ alkanediols, oligo(alkylene glycols), and C ３ -C １２ The solution according to claim 7 or 8, selected from the group consisting of alkanetriols or mixtures thereof.

10. The solution according to any one of claims 1 to 9, showing a solution viscosity of 4 to 150 Pa·s measured at 60°C and 5 to 100 rpm (revolutions per minute) using a Brookfield Viscometer DV-I Prime with an RV6 spindle.

11. The solution according to any one of claims 1 to 10, showing a solution turbidity of 0 to 1 NTU (nephelometric turbidity unit) determined with a turbidimeter using a filter of 860 nm at 60°C.

12. A method for preparing a membrane using the solution according to any one of claims 4 to 11.

13. The following steps: a) preparing a solution according to any one of claims 4 to 11; and b1) preparing a polymer film from the solution in step a) by applying the solution in step a) to a substrate; and b2) exposing the polymer film to a coagulant The method according to claim 12, comprising the steps of.

14. The following steps: a) preparing a solution according to any one of claims 4 to 11; b) continuously shaping and demixing the solution into a non-flat shape and inducing a certain solidification of the shaped solution by directly exposing the solution of step a) to a coagulant; The method according to claim 12, comprising:

15. Use of a membrane according to any one of claims 12 to 14 for the purification of drinking water, the treatment of industrial or municipal wastewater, the desalination of seawater or brackish water, dialysis, the purification of pharmaceuticals, plasmolysis, and food processing.

Images