Method for manufacturing charged ultrafiltration membranes and use thereof in dairy applications

Abstract

The charged ultrafiltration membrane is synthesized by thermal-initiated free radical polymerization of sodium p-styrenesulfonate in pores of an ultrafiltration precursor membrane. The resulting graft chain of the charged UF membrane provides a significant negative charge to maintain almost complete protein interception at significantly higher flux.

Description

[0001] Citation of Related Applications

[0002] This application was filed as a PCT international patent application on July 6, 2023, and claims the benefit and priority of U.S. Provisional Patent Application No. 63 / 359,228 filed on July 8, 2022, the disclosure of which is incorporated herein by reference in its entirety. Background of the Invention

[0004] The present invention generally relates to the use of ultrafiltration membranes for separating aqueous streams containing proteins, sugars and minerals. The proteins are retained by the membrane, while sugars, minerals and water permeate through the membrane. SUMMARY OF THE INVENTION

[0006] This summary is provided to introduce a selection of concepts further described herein in a simplified form. This summary is not intended to identify required or essential features of the claimed subject matter. This summary is also not intended to be used to limit the scope of the claimed subject matter.

[0007] Consistent with various aspects of the present invention, disclosed herein is a method for manufacturing an ultrafiltration membrane, which may include (a) contacting a precursor membrane comprising polyethersulfone (PES) and / or polysulfone (PSF) with an aqueous solution comprising sodium styrene sulfonate and a free radical initiator and (b) curing the precursor membrane to form the ultrafiltration membrane, wherein the ultrafiltration membrane has sulfonated polystyrene bound in the pores of the ultrafiltration membrane and / or bound on the outer surface of the ultrafiltration membrane.

[0008] Ultrafiltration membranes are also included herein. Typically, the ultrafiltration membrane may include (I) polyethersulfone (PES) and / or polysulfone (PSF) membranes and (II) sulfonated polystyrene incorporated in the pores of the ultrafiltration membrane and / or incorporated on the outer surface of the ultrafiltration membrane. More commonly, the ultrafiltration membrane further includes a mechanical support layer positioned below the membrane (and attached to the membrane). The mechanical support layer may include polypropylene (PP) or polyester (PET), such as nonwoven PP or PET.

[0009] According to other aspects of the present invention, ultrafiltration modules and milk separation systems are provided herein. A representative ultrafiltration module may include: (1) an inlet for a feed stream (e.g., a dairy product such as whole milk or skim milk), (2) any of one or more ultrafiltration membranes disclosed herein, the ultrafiltration membrane having any suitable configuration, such as a hollow fiber configuration, a tubular configuration, or a spiral wound configuration, (3) a first outlet for a UF retentate stream, and (4) a second outlet for a UF permeate stream. A representative milk separation system may include: (A) any of one or more ultrafiltration modules disclosed herein, (B) a nanofiltration module, and (C) a reverse osmosis module.

[0010] Also included herein are methods for making a dairy composition. One such method may include: (i) ultrafiltration of a milk product using any of the ultrafiltration membranes disclosed herein (or any of the ultrafiltration modules disclosed herein) to produce a UF permeate fraction and a UF retentate fraction, (ii) nanofiltration of the UF permeate fraction to produce a NF permeate fraction and a NF retentate fraction, (iii) subjecting the NF permeate fraction to a reverse osmosis step to produce a RO permeate fraction and a RO retentate fraction, and (iv) combining at least two of the UF retentate fraction, the RO permeate fraction, the RO retentate fraction, and a fat-rich fraction to form the dairy composition.

[0011] The above summary and the following detailed description all provide examples and are intended to be illustrative only. Therefore, the above summary and the following detailed description should not be considered restrictive. Further, in addition to those features or variations described herein, other features or variations may also be provided. For example, certain aspects may be directed to various feature combinations and sub-combinations described in the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following drawings constitute part of this specification and are included to further illustrate certain aspects of the present invention. The present invention can be better understood by referring to these drawings in conjunction with the detailed description and examples.

[0014] Figure 1 is a scanning electron microscope (SEM) image of a precursor film comprising a PSF top layer and a bottom mechanical support layer.

[0015] Figure 2 A graphic representation of polystyrene bound in the pores of an ultrafiltration membrane is given.

[0016] Figure 3 A representative schematic diagram of the diffusion of the aqueous reaction solution into the pores of the precursor film before curing is given.

[0017] Figure 4 Bar graphs showing the water permeability of the precursor membranes and ultrafiltration membranes described in Examples 1-5 are presented.

[0018] Figure 5-6 Bar graphs showing protein rejection for the precursor membranes and ultrafiltration membranes described in Examples 1-5 are presented.

[0019] Figure 7 These are photographs of the modified PS35 ultrafiltration membrane of Example 5 absorbing methylene blue dye at 100°C at different curing times (cooking times).

[0020] definition

[0021] In order to more clearly define the terms used herein, the following definitions are provided. The following definitions apply to the present disclosure unless otherwise stated. If a term is used in the present disclosure, but the term is not clearly defined in this article, the definition from the 2nd edition (1997) of IUPAC Chemical Terminology (IUPAC Compendium of Chemical Terminology, 2nd Ed (1997)) can be applied, as long as the definition does not conflict with any other disclosure or definition used herein, or any claim that can apply the definition is unclear or invalid. If any definition or usage provided by any file incorporated by reference herein conflicts with the definition or usage provided herein, the definition or usage provided herein shall prevail.

[0022] The various features of the subject matter are described herein so that combinations of different features can be envisioned within a particular aspect. For each and every aspect and / or feature disclosed herein, all combinations that do not adversely affect the systems, compositions, processes, and / or methods described herein are contemplated, regardless of whether a particular combination is explicitly described. In addition, unless otherwise expressly stated, any aspect and / or feature disclosed herein can be combined to describe an inventive system, composition, process, and / or method consistent with the present invention.

[0023] In the present disclosure, although compositions, methods and systems are often described with the term "comprising" various materials or steps or components, the compositions, methods and systems may also "consist essentially of" or "consist of" the various materials or steps or components, unless otherwise specified.

[0024] Unless otherwise specified, the terms "a", "an" and "the" are intended to include plural substitutions, such as at least one (at least one). For example, a disclosure of "an ultrafiltration membrane" is intended to include one or more than one (one or more than one) ultrafiltration membranes, unless otherwise specified.

[0025] In the methods of the present disclosure, the terms "combining" and "contacting" include combining or contacting materials in any order, in any manner, and for any length of time, unless otherwise specified. For example, the materials can be blended, mixed, treated, impregnated, etc.

[0026] Several types of scopes are disclosed in the present invention.When disclosing or claiming any type of scope, it is intended to disclose or declare each possible number that this scope can reasonably cover respectively, including the endpoint of described scope and the combination of any sub-range and sub-range included therein.For example, in various aspects of the present invention, the aqueous reaction solution in step (a) can include 1 to 25 % by weight of sodium styrene sulfonate.By disclosing that aqueous solution includes 1 to 25 % by weight of sodium styrene sulfonate, its purpose is to state that weight percent can be any amount in described scope, and for example, any scope or combination of 1 to 25 % by weight scope can be included, such as 2 to 20 % by weight sodium styrene sulfonate or 5 to 15 % by weight sodium styrene sulfonate etc..Equally, all other scopes disclosed herein should be explained in a manner similar to this example.

[0027] In general, an amount, size, formulation, parameter, range, or other quantity or characteristic is "about" or "approximately," whether or not explicitly stated as such. Whether or not modified by the term "about" or "approximately," the claims include equivalents to the stated quantities or characteristics.

[0028] Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the typical methods, devices, and materials are described herein.

[0029] All publications and patents mentioned herein are incorporated herein by reference in their entirety for the purpose of describing and disclosing, for example, the constructs and methodologies that are described in the publications and patents, which might be used in connection with the present description. DETAILED DESCRIPTION OF THE INVENTION

[0031] Disclosed herein are: an ultrafiltration membrane comprising a polyethersulfone (PES) and / or polysulfone (PSF) membrane and sulfonated polystyrene bound in the pores of the ultrafiltration membrane and / or bound on the outer surface of the ultrafiltration membrane; a method for producing the ultrafiltration membrane; an ultrafiltration module comprising a plurality of the ultrafiltration membranes; a milk separation system comprising a plurality of the ultrafiltration modules; and a method for manufacturing a dairy composition using the ultrafiltration membrane and the ultrafiltration module.

[0032] Ultrafiltration (UF) membranes are typically described by their molecular weight cutoff (MWCO, the molecular weight or size of molecules retained by the membrane). For example, to separate and concentrate proteins in a dairy plant, an ultrafiltration membrane may have a MWCO of 10 kDa, such that at least 90% of material with a molecular weight greater than 10,000 Daltons is retained (retentate), while lower molecular weight species pass through (permeate).

[0033] The object of the present invention is to produce an ultrafiltration membrane that maintains a high level of protein retention, but is achieved at a higher total flux. Thus, the membrane will retain the same amount of protein at a higher throughput. For example, the charged ultrafiltration membrane disclosed herein can retain the same level of protein as a standard 10 kDa MWCO ultrafiltration membrane, but with a significantly higher flux (e.g., 20% to 70% higher). This is achieved by modifying a precursor PES or PSF membrane with a bound sulfonated polystyrene functional group to form a charged polymer membrane that retains proteins based on molecular size and charge.

[0034] This purpose is mainly aimed at dairy applications, such as milk-based beverages and related products, as their major component is protein. However, the methods, techniques, membranes, etc. described herein are not limited to milk or dairy applications, but can also be applied to non-alcoholic and alcoholic beverages, generally but not limited to beer, wine, water, wastewater treatment, juice, oats, almonds / nuts, peas, rice, seeds, grains and other plant material processing, as well as end-use applications and products based on these materials.

[0035] Another object of the present invention is to use a free radical polymerization process instead of a cationic polymerization process that creates ionic bonds between polymer chains and precursor films to form a charged polymeric film. Although any curing method can be used, in some aspects, a thermal curing of the free radical polymerization process using a thermal initiator is used to form a charged UF membrane.

[0036] Yet another object of the present invention is to form charged polymer membranes in a simple synthesis scheme with a limited number of process steps, and in this case, by direct use of sodium styrene sulfonate. In addition, glycerol can be included in the aqueous reaction solution along with the sodium styrene sulfonate to promote and maintain wetting of the matrix membrane and pores.

[0037] Although the present invention is described in detail with reference to ultrafiltration (UF) membranes and methods of making the same, the methods and techniques disclosed herein are also applicable to microfiltration (MF) membranes, as well as nanofiltration (NF) and reverse osmosis (RO) and forward osmosis (FO) membranes, and thus, MF membranes having an incorporated sulfonated polystyrene portion are contemplated herein - as well as NF and RO and FO membranes.

[0038] In addition to the food processing applications described above, other non-limiting uses of charged membranes (e.g., charged UF membranes, charged MF membranes) may include bacteria removal, virus removal, fermentation processes, ion exchange, separation of rare elements, and separation of charged paint particles, among other end-use applications.

[0039] Ultrafiltration membrane

[0040] Various methods for making ultrafiltration membranes are provided herein. For example, the method for making an ultrafiltration membrane may include the following steps (or consist essentially of the following steps, or consist of the following steps): (a) contacting a precursor membrane comprising polyethersulfone (PES) and / or polysulfone (PSF) with an aqueous solution comprising sodium styrene sulfonate and a free radical initiator, and (b) curing the precursor membrane to form the ultrafiltration membrane, wherein the ultrafiltration membrane has sulfonated polystyrene bound in the pores of the ultrafiltration membrane and / or bound on the outer surface of the ultrafiltration membrane.

[0041] Generally, the features of any of the methods disclosed herein (e.g., the composition of the PES polymer, PSF polymer, aqueous solution, curing process, and the temperature and time conditions for performing any step, etc.) are described independently herein, and these features can be combined in any combination to further describe the disclosed methods. In addition, unless otherwise stated, other process steps may be performed before, during, and / or after any of the steps listed in the methods disclosed herein. In addition, any ultrafiltration membrane produced according to any of the disclosed methods is within the scope of the present disclosure and is included herein.

[0042] Now referring to step (a), any suitable precursor membrane comprising polyethersulfone (PES) polymer material and / or polysulfone (PSF) polymer material can be utilized. Typically, the pure water permeability of precursor PES and PSF membranes is at least 20% higher than that of standard 10 kDa MWCO PES membranes. Prior to contact with the aqueous reaction solution in step (a), the precursor membrane can be fully wetted, partially dried or fully dried, and contain or do not contain glycerol. The precursor membrane can be unsupported or supported, and when supported, is typically on a PP or PET nonwoven material.

[0043] The aqueous solution in step (a) comprises monomers, typically sodium styrene sulfonate and a free radical initiator. Although not limited thereto, the aqueous solution generally comprises 1 to 25% by weight of sodium styrene sulfonate in one aspect, 2 to 20% by weight of sodium styrene sulfonate in another aspect, and 5 to 15% by weight of sodium styrene sulfonate in another aspect. The amount of sodium styrene sulfonate present in the aqueous solution in step (a) may generally be limited by the desired amount diffused into the pores or the desired degree of reaction. For example, too much grafted polymer may be formed, resulting in excessive flux loss.

[0044] Likewise, the amount of the free radical initiator in the aqueous solution is not particularly limited. Typical ranges include, but are not limited to, 0.1 to 5 wt %, 0.2 to 4 wt % or 0.5 to 2.5 wt % of the free radical initiator based on the weight of the aqueous solution. The amount of the free radical initiator can generally depend on the amount of sodium styrene sulfonate present in the solution, the type of curing used in step (b), and the current temperature, etc.

[0045] Any suitable free radical initiator may be used in aqueous solution, but the type of initiator may depend on the type of curing used in step (b). For thermal curing, a representative and non-limiting example of a suitable curing agent is potassium persulfate, which is advantageously both heat activated and water soluble. Other suitable alternatives include sodium persulfate and ammonium persulfate, both of which are water soluble. Water-insoluble initiators such as azobisisobutyronitrile (AIBN) may also be used, but are usually used together with a suitable cosolvent (typically a water soluble alcohol).

[0046] Optionally, the aqueous solution may further comprise glycerol. While not wishing to be bound by theory, the presence of a small amount of glycerol in the aqueous solution is beneficial for improving pore wetting and preventing pore drying, typically from as little as 0.1 wt % up to and including 15-20 wt %. More commonly, when glycerol is used, the aqueous solution comprises 0.2 to 8 wt %, 0.5 to 5 wt %, or 3 to 15 wt % glycerol.

[0047] Step (a) can be carried out at any suitable temperature, such as 10°C to 90°C, 20°C to 70°C, 15°C to 55°C, 20°C to 45°C or 20°C to 30°C, although not limited thereto. In these and other aspects, these temperature ranges are also meant to include situations where step (a) is carried out at a series of different temperatures, rather than at a single fixed temperature, wherein at least one temperature falls within the respective ranges. There is no particular limitation on the pressure at which step (a) is carried out, but it can be at high pressure (e.g., 5 psig to 100 psig), at atmospheric pressure or at any suitable subatmospheric pressure. In some cases, step (a) is carried out at atmospheric pressure, thereby eliminating the need for pressure vessels and their associated costs and complexity. Step (a) can be carried out for any period of time, which is sufficient to diffuse and / or wick the aqueous solution into the pores of the precursor film. Illustrative and non-limiting time periods include a wide range of time periods, such as 10 sec to 6 hr, 10 sec to 2 min, 15 sec to 5 hr, 30 sec to 2 hr, 1 min to 24 hr, 1 min to 1 hr, 5 min to 6 hr, 15 min to 5 hr or 30 min to 2 hr, but are not limited to these time periods. Other suitable temperature, pressure and time ranges will be readily apparent from this disclosure.

[0048] Any suitable vessel or container can be used for step (a), as long as the vessel or container can contact (e.g., immerse) the precursor film in the aqueous solution, for example, for a period of time sufficient to allow the aqueous solution to diffuse and / or wick into the pores of the precursor film. Step (a) can be performed batchwise or continuously.

[0049] In one aspect of the invention, the precursor film may be dry before step (a), while in another aspect, the precursor film may be wet before step (a), and in yet another aspect, the precursor film may be dry before step (a) but additionally wetted in water before step (a).

[0050] After step (a) has been carried out - the precursor film has been contacted with the aqueous solution - but before step (b), the precursor film may be partially dried. In particular, before step (b), excess water may be removed from the precursor film. The precursor is only partially dried so that an appropriate amount of water (as well as sodium styrene sulfonate monomer and initiator) remains in the pores.

[0051] Referring now to step (b), the precursor membrane is cured to form the ultrafiltration membrane, whereby the ultrafiltration membrane comprises sulfonated polystyrene bound in the pores of the ultrafiltration membrane and bound on the outer surface of the ultrafiltration membrane. The sulfonated polystyrene used herein comprises substituted styrene moieties, for example, methylated polystyrene groups.

[0052] Any suitable curing method can be used in step (b), such as placing the precursor film under UV radiation (UV light initiation) or electron beam radiation. However, it is determined herein that the precursor film can be conveniently cured with heat. Therefore, in one aspect of the invention, the curing in step (b) can include placing the precursor film at an elevated temperature, which typically falls within the range of 70 to 200°C, although not limited thereto. Other suitable temperature ranges include 70 to 150°C, 95 to 180°C, or 80 to 130°C. In these and other aspects, these temperature ranges are also meant to include situations where thermal curing is performed at a range of different temperatures, rather than at a single fixed temperature, wherein at least one temperature falls within the respective ranges. The maximum curing temperature can generally depend on the melting point or softening point of the polyethersulfone (PES) and / or polysulfone (PSF) used for the precursor film and the melting point or softening point of any support layer (e.g., which can be PP-based or PET-based).

[0053] In one aspect, after step (b), the ultrafiltration membrane can be rinsed with water, which can be carried out at the same location as step (b), or can be carried out at a separate location. In another aspect, after step (b), the ultrafiltration membrane can be rinsed with water, contacted with an aqueous glycerol solution, and then dried.

[0054] In accordance with various aspects of the present invention, the precursor membrane and the ultrafiltration membrane may also include a mechanical support layer positioned below (and attached to) the respective membranes. This additional layer typically occurs before step (a). The mechanical support layer may be made of any suitable material, but is typically PP-based or PET-based, such as non-woven PP or non-woven PET. As described above, the curing temperature in step (b) may vary, depending on the composition of the mechanical support layer and its melting or softening temperature. For a wider pH range during use of the membrane, PP may typically be used as the support layer.

[0055] Also included herein are ultrafiltration membranes that may comprise (I) polyethersulfone (PES) and / or polysulfone (PSF) membranes, and (II) sulfonated polystyrene bound in the pores of the ultrafiltration membrane and / or bound on the outer surface of the ultrafiltration membrane. These ultrafiltration membranes may be produced according to any of the methods and processes described herein. In addition, the ultrafiltration membrane may comprise, and typically comprises, a mechanical support layer positioned below (and attached to) the membrane. As described above, suitable PP or PET nonwoven materials are typically used as the mechanical support layer. Photos of representative precursor membranes are shown in FIG. Figure 1 , which has a top layer of PES or PSF and a bottom mechanical support layer of PP or PET. Typically, these layers are interconnected so that the 2-layer configuration does not delaminate. Figure 2 Polystyrene is shown bound in the pores of an ultrafiltration membrane (the sulfonic acid or sulfonate groups are not explicitly shown, only the polystyrene grafts).

[0056] In one aspect, the disclosed ultrafiltration membranes may be characterized in that their water permeability is at least 20% higher than the water permeability of a 10 kDa molecular weight cutoff (MWCO) membrane, and in some cases, at least 25%, at least 30%, at least 40%, at least 50%, at least 100%, or at least 200% higher. Additionally or alternatively, the ultrafiltration membranes disclosed herein may be characterized in that their water permeability is at least 120 L / m 2 -hr-bar, such as at least 150, at least 200, at least 250, at least 300, at least 500 or at least 1000 L / m 2 -hr-bar. The water permeability test is further described in the subsequent examples.

[0057] In one aspect, the disclosed ultrafiltration membrane may be characterized in that the percent rejection of lactalbumin is greater than or equal to the percent rejection of lactalbumin of a 10 kDa MWCO membrane, typically exceeding 90% in practice. Additionally or alternatively, the ultrafiltration membrane disclosed herein may be characterized in that, for a second 5 ml (10 ml) and a third 5 ml (15 ml) sample increment, the percent rejection of lactalbumin is at least 90%, and in some cases, at least 92% or at least 95%. The lactalbumin rejection test is further described in the subsequent embodiments.

[0058] To determine if the sulfonated polystyrene graft is not covalently bound in the pores of the membrane, the membrane can be subjected to a high concentration brine extraction, which will disrupt the electrostatic interactions for the cationic polymeric material. The extract can then be analyzed by UV-Vis, which has a peak in the 270 - 300 nm range (the aromatic rings of the sulfonated polystyrene can be identified in this nm range). This indicates that the graft is leaching from the membrane, which is unacceptable for food applications because the graft may end up in the product stream. In contrast, an ultrafiltration membrane (with covalently attached sulfonated polystyrene) will have no absorbance in this wavelength range due to covalent bonding.

[0059] Systems and processes using ultrafiltration membranes

[0060] The disclosed UF membranes, which contain sulfonated polystyrene bound in the pores of the UF membrane and / or bound on the outer surface of the UF membrane, can be used in a variety of devices, systems and processes. One such device is an ultrafiltration module, which can include: (1) an inlet for a feed stream, (2) one or more of any of the ultrafiltration membranes disclosed herein, the ultrafiltration membrane having any suitable configuration, such as a hollow fiber configuration, a tubular configuration or a spiral wound configuration, (3) a first outlet for a UF retentate stream, and (4) a second outlet for a UF permeate stream. The feed stream entering the ultrafiltration module through the inlet can be any suitable dairy product, such as whole milk or skim milk, but is not limited thereto. Typically, the ultrafiltration module employs multiple ultrafiltration membranes, for example, in a spiral wound configuration.

[0061] A representative milk separation system may include: (A) one or more than one of the ultrafiltration modules disclosed herein, (B) a nanofiltration module, and (C) a reverse osmosis module. Other milk separation systems included herein may include: one or more than one of the ultrafiltration modules disclosed herein, a nanofiltration module, and a forward osmosis module; alternatively, one or more than one of the ultrafiltration modules disclosed herein and a nanofiltration module; alternatively, one or more than one of the ultrafiltration modules disclosed herein and a reverse osmosis module; or alternatively, one or more than one of the ultrafiltration modules disclosed herein and a forward osmosis module. Typically, the milk separation system employs a plurality of ultrafiltration modules.

[0062] Also provided herein is a method for making a dairy composition, wherein an ultrafiltration membrane is used. Exemplary methods may include: (i) ultrafiltration of a milk product using any of the ultrafiltration modules disclosed herein (or any of the ultrafiltration modules disclosed herein) to produce a UF permeate fraction and a UF retentate fraction, (ii) nanofiltration of the UF permeate fraction to produce a NF permeate fraction and a NF retentate fraction, (iii) a reverse osmosis step of the NF permeate fraction to produce a RO permeate fraction and a RO retentate fraction, and (iv) combining at least two of the UF retentate fraction, the RO permeate fraction, the RO retentate fraction, and a fat-rich fraction to form the dairy composition. For example, in one aspect, the dairy composition may contain at least a UF retentate fraction and a RO retentate fraction, and in another aspect, the dairy composition may contain at least a UF retentate fraction, a RO retentate fraction, and a fat-rich fraction (cream). Example

[0063] The present invention is further illustrated by the following examples, which should not be interpreted in any way as limiting the scope of the present invention. After reading this specification, those of ordinary skill in the art can associate various other aspects, modifications and their equivalents without departing from the spirit of the present invention or the scope of the appended claims.

[0064] The general procedure for preparing ultrafiltration membranes is as follows. First, a 4.70 cm diameter precursor membrane sample (which is polyethersulfone (PES) or polysulfone (PSF)) with a nominal MWCO in the range of 10-20 kDa is force-wetted with water - membrane side up - in a closed flow cell at 90 psig for the specified time. For precursor membranes with a nominal 10-20 kDa MWCO, the time duration is 2 min.

[0065] The precursor membrane was removed from the enclosed cell and submerged and soaked in an aqueous reaction solution containing ~15.87 wt % sodium styrene sulfonate, ~0.79 wt % potassium persulfate, and ~83.33 wt % deionized (DI) aqueous solution containing 5 vol % glycerol at ambient temperature and pressure for 1 hr. A representative schematic of the diffusion of the aqueous reaction solution into the pores of the precursor membrane is shown in Figure 3 Diffusion is one mechanism for the monomer to enter the pores, while another mechanism is the wicking of the aqueous reaction solution into the open, dry pores. The dry pores can also be partially filled with glycerol from the drying process.

[0066] After 1 hr, the impregnated membrane was removed from the solution and placed face up on a polypropylene mesh on top of a glass plate, which was placed in a ~100°C oven and heat cured for 1 hr. After the cured ultrafiltration membrane was removed from the oven and cooled, the membrane was placed in DI water and forced to rinse for 2 min at 90 psig in a closed flow cell. Next, the ultrafiltration membrane was immersed and soaked in a 5 volume % glycerol DI water solution for 30 min, removed from the glycerol solution and dried.

[0067] Precursor membranes were obtained from Solecta, Inc. and are summarized in Table 1, along with ultrafiltration membranes prepared with bound sulfonated polystyrene groups.

[0068] Table 1

[0069]

[0070] The pure water permeability of the membranes of Examples 1-5 was measured on a dedicated device with a stainless steel membrane holder. The water permeability was measured after the 2-min peak at 90 psig. Process flux and protein retention tests were performed on Examples 1-5 using an AMICON stirred cell. Protein retention studies were performed on whey protein isolate in deionized water at a feed concentration of 548 ppm. Solute concentrations were measured by UV-Vis spectrophotometry at 279 nm.

[0071] Figure 4 The results of water permeability tests of the precursor membranes and modified ultrafiltration membranes of Examples 1-5 are summarized. The flux was measured using a stainless steel closed cell fed by a stainless steel tank pressurized with compressed air. The feed pressure was initially increased sharply to 90 psig for 2 min to ensure complete wetting of the membrane. Flux data were collected by measuring 5 pressures with a pressure difference of 5 psig, the measurement time was 60 sec, and each pressure measurement was repeated three times. The permeabilities of the precursor membranes of Example 1 (PE10), Example 2 (PE20C), and Example 4 (PS35C) were Figure 4The permeabilities are shown as a single bar in the figure, while for Example 3 (PE20) and Example 5 (PS35), the permeabilities before immersion / reaction (precursor membrane) and after immersion / reaction (charged ultrafiltration membrane) are shown.

[0072] The PE20 and PS35 membranes of Examples 3 and 5 had much higher pure water permeabilities before reaction / immersion. However, after reaction / immersion, the permeability of the PE20 membrane of Example 3 was much lower than that of the PE10 membrane of Example 1. Figure 4 The data in show the effect of sulfonated polystyrene incorporated into the pores on the pore size of the membrane, thus causing a reduction in water permeability.

[0073] Surprisingly, even after reaction / immersion, the PS35 membrane of Example 5 maintained a fairly high water permeability—much higher than that of the PE10 membrane of Example 1 and with a surprising water permeability of over 300 L / m 2 -hr-bar high water permeability.

[0074] Figure 5-6 The results of whey protein retention for the precursor membranes and modified ultrafiltration membranes of Examples 1-5 are summarized. The protein retention (%) of various membranes was determined using whey protein isolate in deionized (DI) water. The retention studies were performed using a closed AMICON stirred cell filled with ~50 mL of whey protein solution, with the agitator set to 3 and an applied pressure of 50 psig. The whey protein inlet concentration was 548 ppm, and the permeate was collected in batches to distinguish between protein retention after the initial burst (the first 5 ml increment) and membrane surface fouling. Protein concentration was determined by UV-visible spectrophotometry at 279 nm.

[0075] The protein retention percentages of the precursor membranes of Example 1 (PE10), Example 2 (PE20C) and Example 4 (PS35C), and the protein retention percentages of the modified / charged ultrafiltration membranes of Example 3 (PE20) and Example 5 (PS35) were calculated by Figure 5-6 Each bar represents a 5 ml increment of permeate, so the second bar represents the second 5 ml increment of permeate collected from the 50 ml feed volume (total 10 ml of permeate), and the third bar represents the third 5 ml increment of permeate collected from the 50 ml feed volume (total 15 ml of permeate).

[0076] For all membranes tested containing 548 ppm of whey protein infusion, whey protein separation retention was quite high. For the second and third increments, all whey protein retention percentages were over 90% except for the unmodified precursor membrane of Example 4 (PS35C). Figure 5The retention of the first 5 ml of the permeate after the reaction (Example 3 - PE20) was lower than that of the control membrane (Example 2 - PE20C). The retention percentage of the subsequent permeate fractions (next two 5 ml of permeate) of Example 3 (PE20) was not significantly different from that of Example 1 (10 kDa MWCO PE10).

[0077] Unexpectedly, for the second and third increments, the percent retention of whey protein for the PS35 membrane of Example 5 after reaction / immersion was over 98% - a significant improvement in protein retention compared to Example 4. In addition, the modified PS35 ultrafiltration membrane had comparable to slightly better protein retention than the unmodified PE10 membrane of Example 1 at all sample increment data points.

[0078] Another method used to confirm successful modification of the precursor membrane is dye adsorption. Positively charged dyes are adsorbed by negatively charged membranes through electrostatic interactions. Figure 7 The photographs showing the absorption of methylene blue dye by the modified PS35 ultrafiltration membrane of Example 5 at different curing times (cooking times) at 100°C are shown. The methylene blue dye is retained by the sulfonated polystyrene bound in the pores of the membrane. Washing or rinsing the modified membrane with water does not remove the sulfonated polystyrene portion from the pores of the membrane.

Claims

1. A method for manufacturing an ultrafiltration membrane, the method comprising: (a) contacting a precursor membrane comprising polyethersulfone (PES) and / or polysulfone (PSF) with an aqueous solution comprising sodium styrene sulfonate and a free radical initiator; and (b) curing the precursor membrane to form the ultrafiltration membrane, wherein the ultrafiltration membrane has the sulfonated polystyrene bound in the pores of the ultrafiltration membrane and / or bound on the outer surface of the ultrafiltration membrane.

2. The method of claim 1, wherein the precursor film is dried prior to step (a).

3. The method of claim 1, wherein the precursor film is wet prior to step (a).

4. The method of claim 1, wherein the precursor film is dry prior to step (a), and is wetted in water prior to step (a).

5. The method according to any one of the preceding claims, wherein the aqueous solution further comprises glycerol.

6. The method according to any one of the preceding claims, wherein the aqueous solution further comprises 0.1 to 20 wt%, 0.2 to 8 wt%, 0.5 to 5 wt% or 3 to 15 wt% glycerol.

7. The method according to any one of the preceding claims, wherein the aqueous solution comprises 1 to 25 wt%, 2 to 20 wt% or 5 to 15 wt% sodium styrene sulfonate.

8. The method according to any one of the preceding claims, wherein the aqueous solution comprises 0.1 to 5 wt%, 0.2 to 4 wt% or 0.5 to 2.5 wt% of the free radical initiator.

9. The method of any one of the preceding claims, wherein the free radical initiator comprises potassium persulfate, sodium persulfate, ammonium persulfate, or any combination thereof.

10. A method according to any preceding claim, wherein step (a) is carried out for a time sufficient to allow the aqueous solution to diffuse and / or wick into the pores of the precursor film.

11. A method according to any one of the preceding claims, wherein the precursor film is partially dried prior to step (b).

12. The method according to any one of claims 1 to 11, wherein the curing in step (b) comprises subjecting the precursor film to an elevated temperature in the range of 70 to 200°C.

13. The method of any one of claims 1-11, wherein curing in step (b) comprises subjecting the precursor film to UV radiation or electron beam radiation.

14. The method according to any one of claims 1 to 13, wherein the ultrafiltration membrane is rinsed with water after step (b).

15. The method according to any one of claims 1 to 13, wherein after step (b) the ultrafiltration membrane is rinsed with water, contacted with an aqueous glycerol solution, and dried.

16. A method according to any one of the preceding claims, wherein the precursor membrane and the ultrafiltration membrane comprise a mechanical support layer positioned beneath (and attached to) the respective membrane.

17. An ultrafiltration membrane prepared by the method of any preceding claim.

18. An ultrafiltration membrane, comprising: (I) polyethersulfone (PES) and / or polysulfone (PSF) membranes; and (II) Sulfonated polystyrene bound in the pores of the ultrafiltration membrane and / or bound on the outer surface of the ultrafiltration membrane.

19. The membrane of claim 18, wherein the ultrafiltration membrane comprises a mechanical support layer positioned beneath (and attached to) the membrane.

20. The membrane of any one of claims 17-19, wherein the ultrafiltration membrane is characterized in that the water permeability is at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least 100% or at least 200% greater than the water permeability of a 10 kDa molecular weight cutoff (MWCO) membrane.

21. The membrane of any one of claims 17-20, wherein the ultrafiltration membrane is characterized by a water permeability of at least 120, at least 150, at least 200, at least 250, at least 300, at least 500, or at least 1000 L / m 2 -hr-bar.

22. The membrane of any one of claims 17-21, wherein the ultrafiltration membrane is characterized by a whey protein retention percentage greater than or equal to that of a 10 kDa MWCO membrane.

23. The membrane of any one of claims 17-22, wherein the ultrafiltration membrane is characterized by a retention percentage of whey protein of at least 90%, at least 92% or at least 95% for the second 5 ml (10 ml) and third 5 ml (15 ml) sample increments.

24. The membrane of any one of claims 17-23, wherein the ultrafiltration membrane is characterized by a -1 The wave number (in cm -1 ) has a FTIR transmittance of less than 100%.

25. The membrane of any one of claims 17-24, wherein the high saline concentration extract of the ultrafiltration membrane has no absorbance when measured by UV-Vis at 270-300 nm.

26. An ultrafiltration module, comprising: (1) an inlet for a feed stream; (2) one or more ultrafiltration membranes according to any one of claims 17 to 25, wherein the ultrafiltration membrane has a hollow fiber configuration, a tubular configuration or a spiral wound configuration; (3) a first outlet for a UF retentate stream; and (4) A second outlet for the UF permeate stream.

27. A milk separation system, comprising: (A) one or more than one ultrafiltration module according to claim 26; (B) Nanofiltration module; and (C) Reverse osmosis module.

28. A method for producing a dairy composition, the method comprising: (i) ultrafiltration of a milk product using an ultrafiltration membrane according to any one of claims 17 to 25 (or a module according to claim 26) to produce a UF permeate fraction and a UF retentate fraction; (ii) nanofiltering the UF permeate fraction to produce a NF permeate fraction and a NF retentate fraction; (iii) subjecting the NF permeate fraction to a reverse osmosis step to produce a RO permeate fraction and a RO retentate fraction; and (iv) combining at least two of the UF retentate fraction, the RO permeate fraction, the RO retentate fraction and the fat-rich fraction to form the dairy composition.

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