PEEK membranes and related methods and devices

Abstract

Porous polymeric filter membranes made using poly(ether ether ketone)-type polymers (PEEK), devices containing PEEK membranes, and related methods of preparing and using PEEK membranes are described.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This specification relates to porous polymeric filter membranes made using poly(ether ether ketone)-type polymers (PEEK), devices containing PEEK membranes, and related methods of preparing and using PEEK membranes. [Background technology]

[0002] Membrane filters and filter products are essential tools for modern industry, used to remove unwanted materials (e.g., pollutants, particulates, impurities) from useful fluid flows. Useful fluids processed using filters include, among others, water, liquid industrial solvents and process fluids, industrial gases used in manufacturing, and liquids with medical or pharmaceutical uses. The unwanted materials removed from the fluid can be impurities or contaminants in the form of solid particles, microorganisms, volatile organic substances, and chemical species contained in gaseous or liquid fluids. Generally, the fluid being processed or the processing conditions can pose a problem for the stability of the filter product; for example, the fluid may be one that chemically degrades the filter material, or the processing conditions may involve high temperatures, or both.

[0003] Filter membrane characteristics, such as chemical composition, size, dimensions, and physical properties (e.g., porosity, pore size), are related to measured performance characteristics (e.g., "bubble point," "flow time," retention, etc.). Within the current limits of these characteristic ranges, a filter can contain characteristics that provide a useful balance of size (e.g., thickness), porosity, and pore size for filtration performance (retention) when used with a particular type of fluid at a particular flow rate (flow time). Typical pore sizes are in the micron or submicron range, e.g., from about 0.001 micron to about 10 microns. Membranes with average pore sizes of about 0.001 to about 0.05 microns are sometimes classified as ultrafiltration membranes. Membranes with pore sizes of about 0.05 to 10 microns are sometimes classified as microporous membranes.

[0004] For commercial use, a filter membrane must also be able to efficiently and reliably perform its function as a filter, e.g., efficiently remove large amounts of impurities from a continuous flow of fluid passing through it. Filtration performance can be evaluated, for example, by flow time (FT) and retention. Flow time is a measure of the rate at which fluid flows through the filter membrane and must be sufficient to allow the filter membrane to be used commercially. Retention generally refers to the amount (in percent) of impurities removed from the flow of fluid through the filter membrane. Porosity, pore size, and bubble point can affect both flow time and retention. To improve retention, a membrane with smaller pores may be desirable, resulting in a higher bubble point and a longer (but still useful) flow time. Larger pore sizes may result in relatively lower retention, but shorter flow times and lower bubble points. For commercial use, a filter membrane must provide a good combination of flow time and filtration performance (e.g., as measured by retention).

[0005] Poly(oxy-1,4-phenyleneoxy-1,4-phenylene-carbonyl-1,4-phenylene), more commonly known as poly(ether ether ketone), or PEEK, has advantageous physical properties and chemical and thermal stability for many uses, including as a filter membrane. Its high melting point, high glass transition temperature, low solubility, and excellent chemical resistance make PEEK a popular material for use in harsh environment filtration applications. PEEK is stable at high temperatures (e.g., 300°C) and at room temperature in the presence of common organic solvents. PEEK is also relatively stable in hydrogen peroxide, acids, and bases, with the exception of high concentrations of strong acids.

[0006] Currently known techniques for manufacturing PEEK filter membranes are limited in the extent to which they can enhance and balance flow and retention properties. Processing PEEK into membrane structures using a non-solvent-induced phase separation (NIPS) process is difficult due to PEEK's high stability in organic and inorganic solvents. Attempts have been made to process PEEK using thermally induced phase separation (see U.S. Pat. No. 4,957,817), but the resulting porous structures may lack a highly desirable combination of flux, pore size, and morphology. Summary of the Invention

[0007] This specification relates to porous membranes made with poly(ether ether ketone), filtration devices containing the membranes, and methods for removing contaminants from liquid or gaseous fluids using the membranes and devices.

[0008] This specification also relates to a method for preparing porous PEEK membranes by forming a heated polymer-containing liquid (e.g., a "casting solution") containing PEEK in a non-solid form in an organic liquid, referred to as a "solvent." The solvent is non-polar and has a boiling point higher than the melting point of the PEEK polymer. The PEEK polymer contained in the heated solvent is in a non-solid form, e.g., molten or dissolved, and the heated casting solution is a homogeneous solution.

[0009] In exemplary methods, the membranes are formed according to a melt-casting process, such as a type of process known as "thermally induced phase separation" ("TIPS"). In these exemplary methods, the PEEK polymer is preferably a non-sulfonated form of the PEEK polymer, and the non-polar solvent of the casting solution is triphenylmethane.

[0010] Also, according to exemplary processes, porous PEEK polymer membranes can be prepared to exhibit a desirable or advantageous balance of physical and performance properties. In an exemplary method, the PEEK polymer material forming the porous membrane is dissolved at elevated temperature in a high-boiling, nonpolar solvent that becomes liquid upon heating. The polymer dissolved in the solvent forms a heated, homogeneous casting solution containing the polymer completely dissolved or melted in the solvent. The casting solution is then shaped, for example, by casting the heated casting solution onto a flat, smooth surface to form a thin film of the heated casting solution on the surface, or by another shaping technique, such as extrusion or forming a tubular membrane. After shaping, the casting solution is then cooled to induce a phase change in the PEEK polymer within the solution. The polymer forms a solidified, shaped polymer body (e.g., a porous flat film or a porous tubular body) comprising the solidified polymer material with small pores formed therein. The pores contain a portion of the original solvent, which is subsequently removed to leave the porous membrane.

[0011] Exemplary porous PEEK membranes can exhibit a desirable combination of flow and pore size (measured by bubble point), preferably an improved combination of high flow and high bubble point compared to porous PEEK membranes made by different methods.

[0012] Exemplary porous filter membranes can have an initial bubble point of at least 25, 30, or 40 pounds per square inch (psi) or more, an average bubble point of at least 25, 30, or 40 pounds per square inch (psi) or more (measured at 22 degrees Celsius using an HFE-7200 (3M)), or both. Preferred membranes can also have useful or relatively low (compared to other porous PEEK membranes) flow times in combination with the described bubble points, e.g., measured flow times of less than about 5,000 seconds or less than 4,000 seconds using IPA, and measured flow times of less than about 5,000 seconds, less than 4,000 seconds, or less than 3,000 seconds using water. The membranes also exhibit useful filtration properties, as measured by retention.

[0013] In one embodiment, the present invention uses isopropyl alcohol (500 milliliters) to 2 and a flow time of less than 10,000 seconds measured at a pressure of 14.5 psia; and an incipient bubble point of at least 25 pounds per square inch (psig) measured using an HFE-7200 at a temperature of 21 degrees Celsius.

[0014] In another aspect, the present invention relates to a method for preparing a porous polyetheretherketone membrane, the method comprising: preparing a combination comprising 20 to 40 weight percent of a polymer comprising polyetheretherketone and 60 to 80 weight percent of a solvent having a boiling point higher than the melting point of the polymer, based on the total weight of the combination; heating the combination to form a homogeneous casting solution; solidifying the polyetheretherketone of the casting solution to form a porous membrane; and removing the solvent from the porous membrane.

[0015] In yet another aspect, the present invention relates to a homogeneous polymer-containing liquid containing a polyetheretherketone polymer dissolved in a solvent, the liquid comprising, based on the total weight of the polymer-containing liquid, 20 to 40 weight percent of a polymer comprising polyetheretherketone; and 60 to 80 weight percent of a solvent having a boiling point higher than the melting point of the polyetheretherketone. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a method and system useful according to the present invention. [Figure 2A-2B] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figure 2C-2D] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figures 2E-2F] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figures 2G-2H] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figures 2I-2J] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figure 2K-2L] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figure 2M-2N] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figure 2O-2P] 13 is an image of a comparative PEEK membrane prepared using a polar solvent. [Figure 2Q-2R] 1 is an image of the porous PEEK membrane described. [Figure 2S-2T] 1 is an image of the porous PEEK membrane described. [Figure 3] Retention data for the listed filters and comparative filters are shown. [Figure 4] 1 shows test data for the degree of sulfonation of sample PEEK polymers. [Figure 5] 1 is an SEM image of the membrane described. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following description relates to methods for making porous filter membranes from poly(ether ether ketone) (PEEK). Exemplary methods include what is sometimes referred to as a melt-casting process, such as a method referred to as "thermally induced phase separation" ("TIPS"), further implemented according to the details described herein regarding the use of a non-polar solvent with a high boiling point (e.g., triphenylmethane) to dissolve the PEEK polymer.

[0018] According to an exemplary process, porous membranes made using PEEK polymer can be prepared to exhibit a desirable or advantageous balance of physical and performance properties. In an exemplary method, the PEEK polymer material forming the porous membrane is dissolved at elevated temperature in a high-boiling, non-polar solvent that becomes liquid upon heating. The polymer dissolved in the solvent forms a heated, homogeneous casting solution containing the polymer completely dissolved or melted in the solvent. The casting solution is then shaped, for example, by casting the heated casting solution onto a flat, smooth surface to form a thin film of the heated casting solution on the surface, or by another shaping technique, such as extrusion or forming a tubular membrane. After shaping, the casting solution is then cooled to induce a phase change in the PEEK polymer within the solution. The polymer forms a solidified, shaped polymeric body (e.g., a porous flat film or a porous tubular body) that includes the solidified polymeric material in the form of a solid polymer scaffold or matrix with a network of interconnected pores formed therein. When the polymer solidifies upon cooling, the original solvent of the casting solution remains within the pores and can then be removed, leaving a porous membrane.

[0019] The solvent of the casting solution includes (e.g., comprises, consists of, or consists essentially of) a nonpolar solvent having a high boiling point. A high boiling point is a boiling point at least higher than the melting point of the PEEK polymer, e.g., a boiling point of at least 340 degrees Celsius or at least 350 degrees Celsius. An example of such a nonpolar solvent having a high boiling point is triphenylmethane, which has a boiling point of 359 degrees Celsius. Optionally, the solvent may be a single type of solvent or a combination of two or more different chemical solvent materials, at least one of which is a nonpolar, high-boiling solvent. In exemplary casting solutions, the total amount of solvent in the casting solution is predominantly or entirely the nonpolar solvent having a high boiling point described above. For example, the total amount of solvent in the casting solution is made up of (comprises, consists of, or consists essentially of) at least 75, 90, 95, or 99 weight percent of a nonpolar solvent having a high boiling point, such as triphenylmethane.

[0020] In previous applications, polar organic solvents have been used to prepare PEEK solutions for casting and molding polymer membranes. See U.S. Patent No. 4,957,817. Solvents listed in the '817 patent include, among others, benzophenone (boiling point 379°C), diphenyl sulfone (boiling point 305°C), and dimethyl phthalate (boiling point 284°C). Membranes produced by these processes have physical and performance properties that can be improved on balance.

[0021] The PEEK membranes described above can be formed by dissolving PEEK in a solvent described above at an elevated temperature. The PEEK dissolved in the solvent can begin at room temperature as a solid particulate form of PEEK polymer, such as a powder, pellets, or other convenient or available physical form of PEEK polymer. Various PEEK polymer products are available from commercial sources, including those sold under the registered trademarks VICTREX® and VESTAKEEP® (manufactured by Evonik). Based on various factors, such as the molecular weight of the PEEK polymer, PEEK polymers may exhibit various physical properties, such as melting points. Exemplary commercially available PEEK polymers have melting points above 300°C, e.g., at least 320°C or 340°C. Victrex PEEK PF has a melting point of 343°C.

[0022] The PEEK polymer used to form the membrane can have a molecular weight that allows the polymer to be processed as described herein to produce a mechanically stable porous membrane useful as a filter membrane, with a flow and bubble point useful for that purpose. The molecular weight of the PEEK polymer can be determined by known methods, such as gel permeation chromatography (GPC) and size exclusion chromatography (SEC). Examples of PEEK polymers that may be useful in forming the membranes herein may have molecular weights in the range of greater than 70 or 75 Mw, up to 100 or 125 Mw or more. See Table 5.

[0023] PEEK polymers are also available in derivatized forms, including sulfonated forms, meaning that the polymer has been chemically modified to contain attached sulfonic acid (—SO3H) groups. In accordance with useful and preferred examples of the PEEK polymers described, the PEEK polymer may be underivatized, particularly non-sulfonated, i.e., not containing significant amounts of sulfonic acid groups. In certain examples, useful PEEK polymers may have a sulfonation level of less than 3 percent, e.g., less than 2 percent, or less than 1 percent.

[0024] The casting solution can contain a total amount of polymer that is predominantly or entirely PEEK polymer, for example, it can be made of (can comprise, consist of, or consist essentially of) at least 75, 90, 95, or 99 weight percent non-sulfonated PEEK polymer, based on the total polymer in the casting solution. Optionally, if desired, the casting solution can contain another type of polymer in combination with the PEEK polymer, although the useful casting solutions and porous membranes described can contain predominantly or entirely PEEK polymer, for example, non-sulfonated PEEK polymer. The PEEK polymer can be of a single type, for example, one PEEK polymer component having a single defined molecular weight and melting point, or it can be a blend of different types of PEEK polymers having different molecular weights and different melting points.

[0025] The relative amounts of polymer and solvent in the casting solution can be such that the heated casting solution can be formed, for example, by casting or extrusion followed by cooling to solidify the PEEK polymer and form a porous molded body (porous polymer body), which can then be further processed to form the described porous PEEK membrane by treating to remove the casting solution solvent from the porous polymer body. Exemplary casting solutions can contain 10 to 40 weight percent PEEK polymer and 60 to 90 weight percent solvent, based on the total weight of the casting solution or the total weight of the PEEK polymer and solvent; for example, 15 to 35 weight percent PEEK polymer and 65 to 85 weight percent solvent, based on the total weight of the casting solution or the total weight of the PEEK polymer and solvent; or 20 to 30 weight percent polymer and 70 to 80 weight percent solvent, based on the total weight of the casting solution or the total weight of the PEEK polymer and solvent. The casting solution contains mostly or entirely polymer and solvent, for example, at least 80, 90, 95, or 99 weight percent polymer and solvent, based on the total weight of the casting solution.

[0026] More specifically, a useful process can be based on a thermally induced phase separation process involving phase separation of the polymer from the solvent, induced by reducing the temperature of the heated casting solution after molding. According to such a method, a heated casting solution containing a polymer dissolved in a solvent becomes a homogeneous polymer solution while at elevated temperature during molding. The casting solution is characterized by having a temperature range over which the casting solution maintains the homogeneous solution of polymer dissolved in the solvent, and a second (lower) temperature range over which the casting solution phase separates, with the PEEK polymer remaining continuous within the solvent and becoming a solidified porous polymer body.

[0027] A useful or preferred temperature for the heated casting solution when prepared for the molding process can be above the melting point of the PEEK polymer, which can vary based on the characteristics of the PEEK polymer, such as molecular weight. Examples of useful temperatures for the casting solution can be at least 300 degrees Celsius, 320 degrees Celsius, 340 degrees Celsius, or 360 degrees Celsius. During heating, the PEEK completely dissolves (e.g., melts) in the solvent.

[0028] The heated casting solution can be formed into a desired shape, such as a thin sheet or hollow tube, by any useful method, such as casting, extrusion, or the like, and then reduced in temperature. In an exemplary method, the heated casting solution is formed into a thin, uniform film on a smooth, flat surface (the "casting surface"). The casting surface is maintained at a temperature lower than that of the heated casting solution, and contact between the heated casting solution and the casting surface reduces the temperature of the heated casting solution. By reducing the temperature of the heated casting solution from an elevated temperature (the "casting solution temperature") to a lower temperature (referred to as the "cooling temperature" or "forming temperature"), the heated casting solution separates into two phases: a continuous solid polymer phase in the form of a porous three-dimensional membrane structure (a porous polymer body) within a continuous solvent phase.

[0029] The temperature of the casting surface ("cooling temperature" or "molding temperature") is a temperature that is below the melting temperature of the PEEK polymer in the casting solution and below the temperature of the heated casting solution, for example, a temperature in the range of 20 to 280 degrees Celsius, or 40 to 250 degrees Celsius, or 80 to 220 degrees Celsius.

[0030] After the temperature of the heated casting solution is reduced and the dissolved polymer solidifies to form a solid polymer phase (porous polymer body) having a shaped porous membrane structure, the solvent from the casting solution can be removed from the pores of the shaped porous membrane structure, for example, by applying a different type of solvent ("washing solvent") to the membrane structure. The casting solution solvent can be removed from the porous polymer body by washing the porous polymer body with a washing solvent that is effective in removing the casting solution solvent. Optionally, multiple washing steps can be performed using two or more different solvents separately. Examples of useful washing solvents include nonpolar solvents, specific examples of which include ethyl acetate, dioctyl phthalate, and hydrofluoroether (HFE). The step of washing the porous polymer body to remove the casting solution solvent can be carried out at any useful temperature, for example, a temperature ranging from room temperature (22°C) to 100°C, e.g., 40-80°C.

[0031] Referring to Figure 1, an example system and sequence of process steps for carrying out the described method is shown. The method 100 includes steps including combining (102) a solvent and a polymer while mixing; heating (104) the solvent and polymer mixture to form a heated casting solution (120) containing (comprising, consisting of, or consisting essentially of) the solvent and the polymer; casting or otherwise shaping (106) the heated casting solution (120) to, for example, form a cast film (136) of the heated casting solution, and then solidifying the polymer in the cast film (136) from solution with the solvent into a solid polymer phase in the form of a formed porous polymer body 140 within the solvent; and then washing (108) the solvent from the formed porous polymer body 140. FIG. 1 shows a non-limiting example of useful steps of the described method; in other variations, the steps of a useful method for converting PEEK polymer dissolved in a heated casting solution 120 into a porous polymer body 140 may be carried out differently by shaping the heated casting solution, solidifying the polymer in the heated casting solution (e.g., by cooling), and then removing the solvent from the porous polymer body 140.

[0032] 1 , a polymer 110 containing (comprising, consisting essentially of, or consisting of) a non-sulfonated PEEK polymer is introduced (102) into a mixing vessel 112 along with a solvent 114 that is non-polar and has a high boiling point, as described. The solvent 114 and polymer 110 are mixed and heated (104) to form a heated casting solution (120) that includes the polymer in a molten form dissolved in the solvent. To form the heated casting solution (120), the combined polymer and solvent are heated to a temperature at which the solvent becomes liquid and the polymer melts or dissolves within the solvent to form a homogeneous heated casting solution (120).

[0033] The heated casting solution is then formed (106) into a desired shape, which may be a shape useful as a filter membrane, such as a sheet or tube. Forming step 106 can be performed by any useful method using useful equipment, such as extrusion or casting equipment and techniques. As shown, forming step 106 is performed by applying heated casting solution 120 onto a flat surface 130 (the "casting surface"), optionally with a "knife," "blade," or other leveling device 132 passed over the top of heated casting solution 120 while casting solution solvent 114 is still present, to level the casting solution and form a thin, uniform film 136 of heated casting solution 120.

[0034] When the heated casting solution is applied to the casting surface, the heated casting solution is applied while having a temperature above the melting temperature of the PEEK polymer, for example, at least 300 degrees Celsius, 320 degrees Celsius, or 340 degrees Celsius. Also, when the heated casting solution is applied to the casting surface, the temperature of the casting surface is below the melting temperature of the PEEK and below the temperature of the heated casting solution, a temperature that causes the polymer of the heated casting solution to solidify (e.g., solidify) or precipitate from solution to form a separate, continuous polymer phase contained in a solvent in the form of a solidified, solid porous polymer body 140 having a porous structure as described herein.

[0035] Examples of useful temperatures for the casting surface (e.g., 130) can be between room temperature and the temperature of the heated casting solution 120 when applied to the casting surface; for example, useful or preferred temperatures for the casting surface can range from 20 to 280 degrees Celsius, or from 40 to 250 degrees Celsius, or from 80 to 220 degrees Celsius. The temperature of the casting surface and the rate at which the heated casting solution cools upon contact with the casting surface can affect the physical characteristics and morphology of the porous membrane formed, including its porosity, pore size, and bubble point, which, individually and together, affect the filtration performance of the porous membrane as measured by flow time, retention, etc.

[0036] During the step of cooling the heated casting solution 120 to form the porous body 140, the casting solution solvent remains within the pores of the formed porous body 140. In a subsequent washing step (108), a washing solvent 134 can be used to wash the casting solution solvent 114 from the porous body 140.

[0037] Porous PEEK membranes prepared by the described methods can be useful as filter membranes by effectively removing unwanted contaminants or impurities from the fluid while allowing useful fluids to pass through the membrane in useful amounts and at useful flow rates to produce purified filtrate. The membranes are polymeric, porous, and have mechanical properties (e.g., sufficiently rigid yet flexible) that allow the membranes to be assembled and used in the form of filter products. Membranes have characteristics such as porosity, pore size, thickness, and composition (i.e., polymer makeup), which together contribute to the membrane's properties, including performance characteristics (e.g., retention, flow time, among others). The membrane should be sufficiently porous and have a suitable pore size to allow liquid fluids to pass through the membrane at a flow rate sufficient for the membrane to be used in commercial filtration applications while removing a significant amount (e.g., a percentage) of unwanted contaminants or impurities from the liquid.

[0038] Filter membranes are porous, possessing an "open pore" structure throughout the membrane's thickness and on two opposing surfaces, which allows for the desired flow of fluid (e.g., liquid) from one surface of the filter membrane through the thickness of the filter membrane to the other surface of the filter membrane. Along the membrane's thickness and between the two opposing surfaces is a cellular, three-dimensional void microstructure in the form of enclosed cells, i.e., "open cells" or "pores," which allows fluid to pass through the membrane's thickness. The open pores are referred to as openings, pores, channels, or passageways, and are largely interconnected between adjacent pores, allowing fluid to flow within, between, and through the membrane's thickness.

[0039] In exemplary membranes, the pores are distributed throughout the membrane thickness and arranged in a manner that can be considered asymmetric, slightly asymmetric, substantially symmetric, isotropic, uniform, etc., based on their position, shape, and size. Membranes in which pores of substantially uniform size are uniformly distributed throughout the membrane are often referred to as isotropic or "uniform." Anisotropic (also known as "asymmetric") membranes can be considered to have a morphology in which a pore size gradient exists across the membrane; for example, a membrane can have a structure with significantly larger pores at one membrane surface and significantly smaller pores at the other membrane surface. The term "asymmetric" is often used interchangeably with the term "anisotropic." The membranes described can be symmetric or asymmetric. A relatively higher cooling temperature of the casting surface can result in a more asymmetric morphology, while a relatively lower cooling temperature can result in a membrane with a relatively more symmetric morphology.

[0040] Certain exemplary membranes herein have a porous surface (air side) and a more closed surface (casting side), creating a slightly asymmetric structure. The majority of the membrane remains remarkably symmetric and uniform. The membrane may include a matrix wall structure with a high degree of tortuosity, as indicated by minimum pore size measurements, and elongated fibrous or fibrillar walls compared to the more spherical or rounded fused particles, as well as relatively high porosity. The matrix walls form highly tortuos pores defined by a matrix of elongated, connected strands (fibrils). This type of "fibrillated" matrix differs from matrix walls formed from particles that remain substantially in a "fused particle" morphology; the matrix is ​​defined by walls that exhibit a significantly rounded particle shape structure due to particles fusing at adjacent surfaces. The fused particle matrix may also have a lower porosity compared to the fibrillated matrix. See Table 4.

[0041] Exemplary membranes comprising fibrillated matrix walls defined by elongated strands can be characterized by factors including a porosity of at least 70 percent, e.g., a porosity in the range of 70 to 85 percent, a minimum pore size in the range of less than 200 nm, and a maximum pore size in the range of less than 800, 600, 200, or 100 nm.

[0042] Pore ​​characteristics of porous membranes can be measured by liquid-liquid porosimetry (or "porosimetry") techniques and instruments. These include pore structure, average pore size, maximum pore size, minimum pore size, pore area, and shape, e.g., "tortuosity."

[0043] In certain instances, membranes prepared using triphenylmethane as a solvent can have relatively high porosity, for example in the 80% range (e.g., 70-85%), with minimum pore sizes ranging from 30-100 nm, demonstrating high flexibility. The internal membrane structure of membranes prepared using triphenylmethane can be highly fibrillated with thin-walled fibers, as seen in Figure 5. This fibrillation differs from PEEK membranes made using diphenylsulfone or benzophenone (shown in SEM images (Figure 2C, Figure 2G)), which also have lower porosities of 66% and 67%.

[0044] The described membranes in thin film form can have any thickness dimension that allows the membrane to be effective for the desired use of the filter membrane. Examples of useful thicknesses of the thin film porous membranes herein can range from 10 to 300 microns, for example, from 50 to 200 microns.

[0045] Membranes can have a porosity that allows them to be effective as described herein, removing high levels of contaminants or impurities from the liquid while allowing a suitable flow rate of the liquid to pass through the membrane. Examples of useful membranes can have porosities of up to 80 percent, e.g., in the range of 60-80, e.g., 60-70 percent or 40-60 percent. As used herein, and in the field of porous bodies, the "porosity" (sometimes referred to as porosity) of a porous body is a measure of the void (i.e., "empty") space within the body as a percentage of the body's total volume, calculated as the ratio of the body's void volume to the body's total volume. A body with zero percent porosity is completely solid.

[0046] The size of the pores in the membrane ("pore diameter") (i.e., the average size of the pores throughout the membrane) can be sized in combination with the porosity and thickness of the membrane to provide a desired flow of liquid fluid through the membrane while achieving a desired high level of filtration (based on retention).

[0047] The pore size useful for a particular membrane may depend on factors such as the membrane thickness; the desired flow characteristics of the fluid through the membrane (e.g., flow rate or "flow time"); the desired level of filtration (e.g., as measured by "retention"); the particular type of fluid to be treated (filtered) by passing through the membrane; the particular contaminants to be removed from the fluid passing through the membrane; and other factors. In certain currently understood examples, useful pore sizes may range from about 10, 20, 30, or nanometers, or 0.05 microns to about 1, 3, 5, or 10 microns, e.g., sizes that may be classified as "microporous," "ultraporous," or "nanoporous." For purposes of this specification and claims, the term "microporous" may be used to refer to pores within any of these size ranges, including microporous and submicroporous sizes, to distinguish them from materials with larger pore sizes, i.e., materials that are considered "macroporous."

[0048] Membrane pore size can also be evaluated based on its correlation with a property known as the "bubble point," an understood characteristic of porous filter membranes. The bubble point corresponds to pore size, which can correspond to filtration performance, as measured, for example, by retention. Smaller pore sizes result in higher bubble points and often higher filtration performance (higher retention). However, higher bubble points typically also result in relatively higher resistance to flow through the porous material, resulting in longer flow times (lower flow rates for a given pressure drop).

[0049] Exemplary filter membranes herein can exhibit a combination of relatively high bubble points, good filtration performance, and desirable levels of flow, e.g., flow rates that enable the filter membranes to be used in commercial filtration processes. Exemplary membranes can have desirable combinations of bubble points and flow times compared to comparable PEEK membranes made by different methods, including methods using polar solvents. For example, PEEK membranes made as described herein can have a combination of relatively high bubble points and relatively short flow times, a combination of these properties that is more desirable than the bubble point and flow time combinations of PEEK membranes made using different solvents.

[0050] One method for determining the bubble point of a porous material involves immersing a sample of the porous material in a liquid with a known surface tension, applying gas pressure to one side of the sample, and gradually increasing the pressure. The minimum pressure at which gas flows through the sample is called the bubble point.

[0051] Exemplary porous filter membranes measured as described using the test methods described herein may have an initial bubble point of at least 25, 30, or 40 pounds per square inch (psi) or greater, and an average bubble point (measured at a temperature of 22 degrees Celsius using an HFE-7200 (3M)) of at least 25, 30, or 40 pounds per square inch (psi) or greater. The membranes also exhibit useful properties of flow time and retention, as described elsewhere herein.

[0052] In combination with a desired bubble point and filtration performance (e.g., as measured by retention), the described membranes can exhibit useful resistance to the flow of liquid through the membrane. Resistance to liquid flow can be measured in terms of flow rate or flow time (the reciprocal of flow rate). The described membranes can preferably have useful or relatively short flow times, preferably in combination with a relatively high bubble point and good filtration performance. An example PEEK membrane herein can have a measured flow time of less than about 10,000 seconds or less than 5,000 seconds (measured using IPA as described below), and a measured flow time of less than about 10,000, less than 5,000, or less than 4,000 seconds (measured using water as described below).

[0053] The level of effectiveness of a filter membrane in removing undesired substances (i.e., "contaminants") from a liquid can be measured in one way as "retention." Retention, in relation to the filtration performance of a filter membrane, generally refers to the total amount of impurities removed (in actual or during performance testing) from a fluid containing impurities relative to the total amount of impurities present in the fluid as it passes through the filter membrane. Thus, the "retention" value of a filter membrane is a percentage, with filters with high retention values ​​(high percentages) being relatively effective at removing particles from fluids, and filters with low retention values ​​(low percentages) being relatively less effective at removing particles from fluids.

[0054] In exemplary membranes prepared according to the present disclosure, the membranes may exhibit greater than 80, 90, or 95 percent retention at 1.0 percent monolayer coverage, e.g., 80-85 percent retention at 2.0, 3.0, or 4.0 percent monolayer coverage, as measured using the tests described in the Examples section at useful flow rates through the membrane. See Figure 3.

[0055] The described filter membranes may be useful for removing contaminants from a liquid by passing the liquid through the filter membrane to produce a filtered (or "purified") liquid, called a filtrate. The filtered liquid will contain reduced levels of contaminants compared to the contaminant levels present in the liquid before passing through the filter membrane.

[0056] The filter membranes described herein, or filters or filter components containing the filter membranes, can be useful in methods for filtering liquid chemicals to purify or otherwise remove undesired substances from the liquid chemicals, particularly for producing high-purity liquid chemicals useful in industrial processes requiring chemical inputs with very high levels of purity. Generally, the liquid chemicals can be any of a variety of useful commercially available materials, or liquid chemicals useful in any of a variety of different industrial or commercial applications. Particular examples of the filter membranes described can be used to purify liquid chemicals used in, or useful in, semiconductor or microelectronics manufacturing applications, such as filtering liquid solvents or other process solutions used in semiconductor photolithography processes (e.g., liquid photoresist solutions), wet etching or cleaning processes, spin-on-glass (SOG) formation processes, back surface antireflective coating (BARC) processes, etc.

[0057] Some specific, non-limiting examples of liquid solvents that can be filtered using the filter membranes as described include n-butyl acetate (nBA), isopropyl alcohol (IPA), 2-ethoxyethyl acetate (2EEA), xylene, cyclohexanone, ethyl lactate, gamma-butyrolactone, hexamethyldisilazane, methyl-2-hydroxyisobutyrate, methyl isobutylcarbinol (MIBC), n-butyl acetate, methyl isobutyl ketone (MIBK), isoamyl acetate, tetraethylammonium hydroxide (TMAH), propylene glycol monoethyl ether, propylene glycol methyl ether (PGME), 2-heptanone, cyclohexanone, sulfuric acid solutions (e.g., diluted), and propylene glycol monomethyl ether acetate (PGMEA).

[0058] The membrane can be included within a larger filter structure, such as a filter housing or filter cartridge used in a filtration system. The filtration system places the membrane in a liquid chemical flow path, for example, as part of a filter or filter cartridge, and passes at least a portion of the liquid chemical flow through the membrane, thereby removing a certain amount of impurities or contaminants from the liquid chemical. The membrane can be housed in any configuration between an inlet and an outlet, such as pleated, wound, etc. The filter or filter cartridge structure can include one or more of a variety of additional materials and structures that support the membrane within the filter and allow fluid to flow from the filter inlet, through the membrane, and through the filter outlet, thereby passing through the membrane as it passes through the filter. [Example]

[0059] These examples compare exemplary polymeric porous PEEK membranes made using three different polar solvents, as described in U.S. Pat. No. 4,957,917 (the '917 patent), with membranes prepared using the non-polar solvent triphenylmethane.

[0060] For comparison, the structural observation of the membranes is shown in SEM (scanning electron microscope) images, and the pore size, bubble point, and membrane filtration performance using liquid-liquid porosimetry are compared with the flux of IPA or water.

[0061] Three polar solvents were selected from U.S. Pat. No. 4,957,817, as shown in Table 1: TIFF2026501850000002.tif26170

[0062] Porous PEEK membranes were prepared using three different polar solvents as follows.

[0063] Preparation of the casting solution: Victrex 450 PF PEEK polymer was placed in a 20 ml borosilicate glass vial. A polar solvent was added to the vial to achieve the desired polymer concentration of between 5 and 40 weight percent based on the total weight of polymer and solvent. The vial was capped but not closed. The vial was placed in a preheated vial heater for 1 hour. The vial heater was heated to near the boiling point of the containing solvent, which is usually 10°C below the boiling point. The heating temperature for diphenyl sulfone was set to 320°C.

[0064] Film casting from casting solution: A smooth glass plate was placed on an Ecometer film applicator (model: 4340) and heated to 195°C. A casting knife (Model: BKY) with a set gap of 4 mil was heated to 300°C and placed on a glass plate. The casting solution was placed on a preheated glass plate and the film was cast at a casting knife speed of 30 millimeters per second. No other controls, such as environmental controls, were used. The film formed from the casting solution was removed from the glass plate and placed in acetonitrile for 15 minutes to remove the polar casting solution solvent.

[0065] Results for membranes made using diphenyl sulfone PEEK casting solutions were prepared using PEEK concentrations ranging from 20 to 50 weight percent in diphenyl sulfone (based on the total weight of PEEK and diphenyl sulfone). Membranes made with a PEEK concentration of 20 weight percent were brittle and prone to tearing. Membranes made with PEEK concentrations greater than 20 weight percent appeared to be mechanically more stable and were selected for flux and SEM analysis. SEM showed that membranes prepared using diphenyl sulfone under the same conditions as those used for the other solvents had a skin effect (no pores) on both surfaces, as seen in Figures 2A and 2B. Some membrane areas showed some flux but were too fragile to be tested for bubble point. Most of the membranes prepared using diphenyl sulfone as the solvent exhibited matrix walls in the form of spherical structures that were partially fused together (see Figures 2C and 2D). The non-fused regions between the particles formed the internal pore regions of the membrane, and therefore the internal pore size of the diphenyl sulfone membranes was large (see Table 2). This large pore size was not observed in the membranes fabricated using triphenyl methane.

[0066] Results for films prepared using benzophenone PEEK polymer concentrations ranging from 20 to 30 weight percent in benzophenone (based on the total weight of PEEK and benzophenone) were investigated. Membranes were cast and demonstrated sufficient mechanical strength. SEM showed a skin region (no pores) on one surface and an open surface on the other side (air side) for the sample made from 20 weight percent PEEK, as seen in Figures 2E and 2F. The difference between the mean flow pore size and the maximum pore size was approximately five times, suggesting that there were some areas of the closed membrane surface where large openings led to open cross-sectional areas, as seen in Figure 2H. The air side was completely open, suggesting that these membranes were essentially asymmetric. The sample containing 25 weight percent PEEK exhibited similar properties, with some small pores, or in this case defects, prominent. Heating the casting solution to near boiling point leads to loss of control of the casting conditions.

[0067] Increasing the polymer concentration from 20 to 25 percent for PEEK membranes made with benzophenone changes the membrane morphology, as seen in Figures 2L and 2H. At higher polymer concentrations, thicker fibers become more prominent and the membrane appears less fibrillated. The measurable flow time increased approximately 20-fold for the 25% PEEK membrane. In contrast, the PEEK membrane made with triphenylmethane is highly fibrillated and uniform across the entire cross section, as seen in Figure 2T. The casting side of the triphenylmethane PEEK membrane exhibits regular porosity, as seen in Figure 2R.

[0068] Results for membranes made using dimethyl phthalate As described in the '917 patent, a concentration of 5 weight percent PEEK in dimethyl phthalate (based on the total weight of PEEK and dimethyl phthalate) was selected. The boiling point of dimethyl phthalate was 284°C, the lowest of the solvents selected, but it was observed that the melting point temperature required for PEEK was at least 300°C. One attempt at membrane casting was made. The cast membrane was too small in size (sufficient for SEM analysis), and based on the SEM analysis, it was determined that this solvent would not be useful for producing meaningful membrane samples. The prepared samples were not large enough to perform performance testing. Cross-sections of the prepared samples showed irregular fibrillation and large pores in the cross-section (see Figures 2M, 2N, 2O, and 2P). The air side was open, and the casting side showed a skin layer (no pores), similar to PEEK membranes prepared using benzophenone or diphenylsulfone as solvents. In comparison, membranes prepared using triphenylmethane showed good surface porosity on both sides of the membrane and good fibrillation within the membrane.

[0069] Comparison - Results for membranes produced using triphenylmethane Membranes were prepared using a casting solution containing 20–30 weight percent PEEK in triphenylmethane (based on the total weight of PEEK and triphenylmethane). Membranes made with a 20 weight percent PEEK concentration were mechanically stable and were selected for flux and SEM analysis. SEM showed no skin layer on either surface; this is also visible in the SEM images, and pores are visible on both membrane surfaces. See Figures 2Q and 2R. Porosity measurements by liquid-liquid porosimetry and gravimetric measurements confirm the SEM observations, and triphenylmethane produces highly porous intrinsic films, as seen in Table 4.

[0070] Membrane performance comparison--Overview Table 2 below shows available membrane properties for PEEK membranes made with different polar solvents selected and indicated in Table 1. A membrane comparison of flow properties, bubble point, and pore size data is provided. Data that was not available due to mechanical instability or poor processability of the membrane during casting is marked NA (not available) in Table 2. Membranes prepared using diphenyl sulfone were not mechanically stable when the polymer concentration was less than 30 percent. Membranes obtained with a 40% PEEK concentration were stable enough to perform characterization. Table 2: Comparison of membrane performance of PEEK membranes prepared from various solvents. Membrane performance is shown in terms of IPA / water flux, bubble point (BP), and pore size.

[0071] Table 3 shows the best achievable membrane properties for Victrex 450 Pf PEEK membranes made with 20 percent and 23 percent PEEK using triphenylmethane as the solvent. Table 3: Best achieved data for PEEK 450 pf triphenylmethane membrane at different polymer concentrations. TIFF2026501850000004.tif41170

[0072] Table 4 shows a comparison of porosity between PEEK membranes fabricated using triphenylmethane, diphenylsulfone, and benzophenone. As shown, the membranes fabricated using triphenylmethane exhibited relatively high porosity, which is consistent with the SEM observations in Figure 2Q-TF. The membranes prepared using diphenylsulfone exhibited a high pore area, which corresponds to the observations noted in the SEM images, where rounded particles were observed, resulting in a loosely connected, open membrane structure. This open structure exists despite the PEEK-diphenylsulfone membranes being fabricated at high concentrations due to mechanical stability issues. Table 4 TIFF2026501850000005.tif39170

[0073] Table 5 below shows different molecular weight PEEK types from vendor Victrex ranging from 70k to >100k. TIFF2026501850000006.tif54170Table 5: Comparison of different PEEK grades manufactured by Victrex. The polymers are compared by melt viscosity, molecular weight, and percent crystallinity. It should be noted that the membrane prepared from Victrex 150 PF with a molecular weight of 72K was not mechanically stable.

[0074] Bubble Point Test To measure the mean bubble point, a sample flat sheet membrane is placed in a holder. Air is pressurized through the holder and the flow rate is measured as a function of pressure. A low surface tension fluid, HFE-7200 (3M), is then introduced to the membrane, wetting it. Air is pressurized through the holder and the air flow is measured as a function of pressure. The mean bubble point is the pressure at which the ratio of air flow through the wet membrane to the air flow through the dry membrane is 0.5. The test is performed at temperatures ranging between 20 and 22 degrees Celsius.

[0075] Coverage Test "Particle retention" or "coverage" refers to the percentage of the number of particles that can be removed from a fluid stream by a membrane placed in the fluid path of the fluid stream. The particle retention of a sample filter membrane disk can be measured by passing a feed solution of 0.1% Triton X-100 in water, sufficient to achieve a monolayer coverage of 1%, containing 8 ppm polystyrene particles with a nominal diameter of 0.03 microns (available from Duke Scientific G25B), through the membrane at a constant flow of 7 mL / min and collecting the permeate. The concentration of polystyrene particles in the permeate can be calculated from the absorbance of the permeate. The particle retention is then calculated using the following formula: TIFF2026501850000007.tif17170

[0076] The number (#) of particles required to achieve 1% monolayer coverage can be calculated using the following formula: TIFF2026501850000008.tif21170 formula, a = effective membrane surface area d p = particle diameter

[0077] As used herein, "nominal diameter" refers to the diameter of a particle as determined by photon correlation spectroscopy (PCS), laser diffraction, or optical or SEM microscopy. Typically, the calculated diameter, or nominal diameter, is expressed as the diameter of a sphere having the same projected area as a projected image of the particle. PCS, laser diffraction, and optical microscopy techniques are well known in the art. See, e.g., Jillavenkatesa, A., et al.; "Particle Size Characterization"; NIST Recommended Practice Guide; National Institute of Standards and Technology Special Publication 960-1; January 2001.

[0078] "Flow Time" Test (using isopropanol) The permeability ("flow") of isopropanol can be determined using an internal flow test. The membrane is placed in a holder with the first side facing upstream. Isopropanol is supplied to the sample at a specific pressure, i.e., 14.2 psi, at a temperature of 20-22 degrees Celsius for a predetermined time interval. The isopropanol flowing through the membrane is then collected and measured. The isopropanol permeability is calculated using the following formula: TIFF2026501850000009.tif12170 formula, V = volume of isopropanol collected t = collection time a = effective membrane surface area p = pressure drop across the membrane

[0079] Additionally, the flow time is 13.8 cm at 14.2 psi. 2 Flow time (T) is defined as the time it takes to collect 500 ml of fluid through a membrane with a surface area of ​​14.2 psi. Therefore, a given membrane surface area (a) can be used to collect a certain volume of IPA (V) for a certain time (t). Flow time (T) can be calculated using the following formula: TIFF2026501850000010.tif12170

[0080] The porosity of the membrane can be determined gravimetrically. First, the membrane is dried in an oven at 120°C for 5 minutes to determine the initial weight. Then, the membrane is placed in 100% IPA and immersed for 2 minutes. Excess IPA is removed from the surface, and the wet weight of the membrane is determined. The resulting porosity can be calculated as follows: TIFF2026501850000011.tif19170 formula, mass 湿潤 = mass of IPA wet film mass 乾燥 = mass of dry film ρ = density of IPA A 膜 = membrane area L 膜 = film thickness

Claims

1. Using isopropyl alcohol (500 ml), ２ and a flow time of less than 10,000 seconds measured at a pressure of 14.5 psia; and An initial bubble point of at least 25 pounds per square inch (psig) measured using an HFE-7200 at a temperature of 21 degrees Celsius A porous polyether ether ketone membrane having:

2. 10. The membrane of claim 1 having a porosity in the range of 70 to 85 percent.

3. Using isopropyl alcohol (500 ml), ２ and a flow time of less than 4,000 seconds measured at a pressure of 14.5 psia; and An initial bubble point of at least 30 psig as measured using an HFE-7200 at a temperature of 21 degrees Celsius 10. The membrane of claim 1, having

4. 10. The membrane of claim 1 having an average bubble point of at least 40 psig measured using an HFE-7200 at a temperature of 21 degrees Celsius.

5. The membrane of any one of claims 1 to 4, having a thickness in the range of 50 to 200 microns.

6. The membrane of claim 1 comprising a sheet.

7. 5. The membrane of claim 1, wherein the polyetheretherketone is not sulfonated.

8. 5. The membrane of any one of claims 1 to 4, wherein the polyetheretherketone has a molecular weight in the range of from greater than 75 Mw to 125 Mw.

9. 5. The membrane according to claim 1, comprising residual solvent with a boiling point higher than the melting point of the polyetheretherketone.

10. 10. The membrane of claim 9, wherein the residual solvent is triphenylmethane.

11. A filter product containing a membrane according to any one of claims 1 to 4.

12. A method for purifying a liquid, comprising passing the liquid through a membrane according to any one of claims 1 to 4.

13. 1. A method for preparing a porous polyetheretherketone membrane, comprising: For the total weight of the combination, 20 to 40 weight percent of a polymer comprising polyetheretherketone, and 60 to 80 weight percent of a solvent having a boiling point higher than the melting point of the polymer preparing a combination comprising heating the combination to form a homogeneous casting solution; coagulating the polyetheretherketone of the casting solution to form a porous membrane; and removing the solvent from the porous membrane; A method comprising:

14. 14. The method of claim 13, wherein the solvent has a boiling point of at least 320 degrees Celsius.

15. 14. The method of claim 13, wherein the solvent is triphenylmethane.

16. 16. The method of any one of claims 13 to 15, wherein the polyetheretherketone has a molecular weight in the range of from greater than 75 Mw to 125 Mw.

17. The membrane was then dried using isopropyl alcohol (500 ml) to a thickness of 13.5 cm. ２ 16. The method of any one of claims 13 to 15, having a membrane surface area of ​​0.01 to 0.10 mmHg and a flow time of less than 10,000 seconds measured at a pressure of 14.5 psia.

18. The method of any one of claims 13 to 15, wherein the membrane has a porosity in the range of 70 to 85 percent.

19. 16. The method of any one of claims 13 to 15, wherein the membrane has an initial bubble point of at least 25 psig as measured using an HFE-7200 at a temperature of 21 degrees Celsius.

20. 16. The method of any one of claims 13 to 15, wherein the membrane has an average bubble point of at least 40 psig measured using an HFE-7200 at a temperature of 21 degrees Celsius.

21. A homogeneous polymer-containing liquid comprising a polyetheretherketone polymer dissolved in a solvent, Based on the total weight of the polymer-containing liquid, 20 to 40 weight percent of a polymer comprising polyetheretherketone, and 60 to 80 weight percent of a solvent having a boiling point higher than the melting point of the polyetheretherketone; A homogeneous polymer-containing liquid comprising:

22. 22. The liquid of claim 21, wherein the solvent has a boiling point of at least 320 degrees Celsius.

23. 22. The liquid of claim 21, wherein the solvent is triphenylmethane.

24. 24. The fluid of any one of claims 21 to 23, wherein the polymer comprises at least 90 weight percent polyetheretherketone, based on the total weight of the polymer.

25. 24. A fluid according to any one of claims 21 to 23, wherein the polyetheretherketone has a molecular weight in the range of from 75 Mw to 125 Mw.

26. 24. The liquid of any one of claims 21 to 23, consisting essentially of a polymer and a solvent.

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