Ion exchange membranes by UV initiated polymerization

文档序号：602568 发布日期：2021-05-04 浏览：8次中文

阅读说明：本技术 通过uv引发的聚合的离子交换膜 (Ion exchange membranes by UV initiated polymerization ) 是由乔治·顾萨瓦斯·哈德吉基里亚库西蒙·P·杜克斯迈克尔·J·肖于 2019-09-25 设计创作，主要内容包括：公开了生产离子交换膜载体的方法。该方法包括用带电荷的单体溶液使聚合物微孔基底饱和,所述带电荷的单体溶液包含至少一种官能单体、交联剂和有效量的至少一种光聚合引发剂；以及通过在有效地使至少一种官能单体交联并产生离子交换膜载体的条件下将饱和的聚合物微孔基底暴露于紫外光来使至少一种官能单体聚合。还公开了生产单价选择性离子交换膜的方法。该方法包括用带电荷的化合物层将离子交换膜载体的外表面官能化,干燥离子交换膜载体,以及将离子交换膜载体浸泡在包含酸或碱的溶液中持续有效地产生单价选择性离子交换膜的时间量。(A method of producing an ion exchange membrane support is disclosed. The method comprises saturating a polymeric microporous substrate with a charged monomer solution comprising at least one functional monomer, a crosslinking agent, and an effective amount of at least one photopolymerization initiator; and polymerizing the at least one functional monomer by exposing the saturated polymeric microporous substrate to ultraviolet light under conditions effective to crosslink the at least one functional monomer and produce the ion-exchange membrane support. Also disclosed is a method of producing a monovalent selective ion exchange membrane. The method includes functionalizing an outer surface of an ion exchange membrane support with a layer of a charged compound, drying the ion exchange membrane support, and soaking the ion exchange membrane support in a solution comprising an acid or a base for an amount of time effective to produce a monovalent selective ion exchange membrane.)

1. A method of producing an ion exchange membrane support comprising:

saturating a polymeric microporous substrate having a thickness between 25 μ ι η and 55 μ ι η with a charged monomer solution comprising at least one functional monomer, a crosslinker, and an effective amount of at least one photopolymerization initiator; and

polymerizing the at least one functional monomer by exposing the saturated polymeric microporous substrate to ultraviolet light at room temperature in a substantially oxygen-free environment for an amount of time effective to crosslink the at least one functional monomer and produce the ion-exchange membrane support.

2. The method of claim 1, wherein the at least one photopolymerization initiator comprises at least one of: 1-hydroxy-cyclohexylphenylketone, phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide, bisacylphosphine oxide, 2-hydroxy-2-methylpropiophenone, 2' -azobisisobutyronitrile and 2, 2-dimethoxy-2-phenyl-acetophenone.

3. The method of claim 2, wherein the effective amount is between about 2% w/w and 5% w/w.

4. The method of claim 2, wherein the effective amount is about 2% w/w and the amount of time effective to crosslink the at least one functional monomer is between about 20 seconds and about 30 seconds.

5. The method of claim 1, comprising producing a cation exchange membrane support, wherein the at least one functional monomer comprises at least one of: 2-sulfoethyl methacrylate (2-SEM), 2-acrylamido-2-methylpropanesulfonic Acid (AMPS), sulfonated glycidyl methacrylate, 3-sulfopropyl methacrylate, sodium 1-allyloxy-2-hydroxypropyl sulfonate, acrylic acid and methacrylic acid or their salts, sodium styrene sulfonate, styrene sulfonic acid, sulfonated vinylbenzyl chloride, sodium 1-allyloxy-2-hydroxypropyl sulfonate, 4-vinylbenzoic acid, trichloroacrylic acid, vinylphosphoric acid and vinylsulfonic acid.

6. The method of claim 1, comprising producing an anion exchange membrane support, wherein the at least one functional monomer comprises at least one of: methacrylamidopropyl trimethyl ammonium chloride; trimethyl ammonium ethyl methacrylate; quaternary ammonium salts of polyamines and vinyl aromatic halides; a quaternary ammonium salt formed by reacting a cyclic ether, a polyamine, and an alkyl halide; vinylbenzyltrimethylammonium chloride; trimethylammonium ethyl methacrylate chloride; 3- (acrylamidopropyl) trimethylammonium chloride; n, N', N "-pentamethyldiethylenetriamine di (vinylbenzyl chloride); glycidyl methacrylate/trimethylamine; and glycidyl methacrylate/N, N-dimethylethylenediamine reaction products.

7. The method of claim 1, further comprising functionalizing an outer surface of the ion exchange membrane support with a layer of charged compound, drying the functionalized ion exchange membrane support, and soaking the functionalized ion exchange membrane support in a solution comprising an acid or base for an amount of time effective to produce a monovalent selective ion exchange membrane.

8. The method of claim 1, wherein the ion exchange membrane has a permselectivity of at least 90% and less than 2 Ω -cm²The resistance of (2).

9. The method of claim 1, wherein the crosslinking agent comprises at least one of Divinylbenzene (DVB) and Ethylene Glycol Dimethacrylate (EGDM).

10. A method of producing an ion exchange membrane support comprising:

saturating a polymeric microporous substrate with a charged monomer solution comprising at least one functional monomer, a crosslinking agent, and an effective amount of at least one photopolymerization initiator; and

polymerizing the at least one functional monomer by exposing the saturated polymeric microporous substrate to ultraviolet light at an intensity effective to penetrate the substrate in a substantially oxygen-free environment for an amount of time effective to crosslink the at least one functional monomer and produce the ion-exchange membrane support.

11. The method of claim 10 comprising exposing the saturated polymeric microporous substrate to a solution having a mW/cm at about 2000²And about 2200mW/cm²The ultraviolet light of the intensity in between lasts for an amount of time between about 1 second and about 5 seconds.

12. The method of claim 10 comprising exposing the saturated polymeric microporous substrate to a solution having a molecular weight of at about 200mW/cm²And about 500mW/cm²The ultraviolet light of the intensity in between lasts for an amount of time between about 20 seconds and about 30 seconds.

13. The method of claim 10 comprising exposing the saturated polymeric microporous substrate to a solution having a molecular weight of at about 500mW/cm²And about 2000mW/cm²The ultraviolet light of the intensity in between lasts for an amount of time between about 5 seconds and about 20 seconds.

14. The method of claim 10 comprising exposing the saturated polymeric microporous substrate to ultraviolet light on a top surface and a bottom surface.

15. The method of claim 14, comprising exposing the saturated, polymeric microporous substrate to a solution having a concentration of about 200mW/cm on each of the top and bottom surfaces²And about 500mW/cm²Ultraviolet light of an intensity in between.

16. The method of claim 10, comprising pulsing the ultraviolet light.

17. The method of claim 16 comprising exposing the saturated polymeric microporous substrate to a solution having a mW/cm at about 2000²And about 2200mW/cm²Ultraviolet light of an intensity in between.

18. The method of claim 10, wherein the at least one photopolymerization initiator comprises at least one of: 1-hydroxy-cyclohexylphenylketone, phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide, bisacylphosphine oxide, 2-hydroxy-2-methylpropiophenone, 2' -azobisisobutyronitrile and 2, 2-dimethoxy-2-phenyl-acetophenone.

19. The method of claim 18, comprising exposing the saturated polymeric microporous substrate to ultraviolet light having a wavelength effective to photoinitiate the at least one photopolymerization initiator.

20. The method of claim 19, wherein the wavelength effective to photoinitiate the at least one photopolymerization initiator is between about 245nm and about 420 nm.

21. The method of claim 18, wherein the charged monomer solution comprises at least two photopolymerization initiators.

22. The method of claim 21, wherein each of the at least two photopolymerization initiators is configured to be initiated at a different wavelength of light.

23. A method of producing a monovalent selective ion exchange membrane comprising:

functionalizing an outer surface of the ion-exchange membrane support with a layer of a charged compound;

drying the functionalized ion exchange membrane support; and

soaking the functionalized ion exchange membrane support in a solution comprising an acid or a base for an amount of time effective to produce the monovalent selective ion exchange membrane.

24. The method of claim 23, comprising soaking the functionalized ion exchange membrane support in a solution comprising 1N NaOH for about 15 minutes.

25. The method of claim 23, further comprising rinsing the monovalent selective ion exchange membrane with water and conditioning the monovalent selective ion exchange membrane in a solution comprising 0.5M NaCl.

Technical Field

Aspects and embodiments disclosed herein relate generally to ion exchange membranes and, more particularly, to ion exchange membranes that are photoinitiated by UV photopolymerization.

SUMMARY

According to one aspect, a method of producing an ion exchange membrane support is provided. The method can include saturating a polymeric microporous substrate having a thickness between 25 μm and 55 μm with a charged monomer solution comprising at least one functional monomer, a crosslinking agent, and an effective amount of at least one photopolymerization initiator. The method can include polymerizing at least one functional monomer by exposing the saturated polymeric microporous substrate to ultraviolet light at room temperature in a substantially oxygen-free environment for an amount of time effective to crosslink the at least one functional monomer and produce the ion-exchange membrane support.

In some embodiments, the at least one photopolymerization initiator may include at least one of: 1-hydroxy-cyclohexylphenylketone, phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide, bisacylphosphine oxide, 2-hydroxy-2-methylpropiophenone, 2' -azobisisobutyronitrile and 2, 2-dimethoxy-2-phenyl-acetophenone (2, 2-dimethoxy-2-phenyl-acetophenone).

An effective amount may be between about 2% w/w and 5% w/w.

The effective amount can be about 2% w/w, and the amount of time effective to crosslink the at least one functional monomer can be between about 20 seconds and about 30 seconds.

The method may include producing a cation exchange membrane support. The at least one functional monomer may include at least one of: 2-sulfoethyl methacrylate (2-SEM), 2-acrylamido-2-methylpropanesulfonic Acid (AMPS), sulfonated glycidyl methacrylate, 3-sulfopropyl methacrylate, sodium 1-allyloxy-2-hydroxypropyl sulfonate, acrylic acid and methacrylic acid or salts thereof, sodium styrene sulfonate, styrene sulfonic acid, sulfonated vinylbenzyl chloride, sodium 1-allyloxy-2-hydroxypropyl sulfonate, 4-vinylbenzoic acid, trichloroacrylic acid, vinylphosphoric acid and vinylsulfonic acid.

The method may include producing an anion exchange membrane support. The at least one functional monomer may include at least one of: methacrylamidopropyl trimethyl ammonium chloride; trimethylammonium ethyl methacrylate; quaternary ammonium salts of polyamines and vinyl aromatic halides; a quaternary ammonium salt formed by reacting a cyclic ether, a polyamine, and an alkyl halide; vinylbenzyltrimethylammonium chloride; trimethylammonium ethyl methacrylate chloride; 3- (acrylamidopropyl) trimethylammonium chloride; n, N', N "-pentamethyldiethylenetriamine di (vinylbenzyl chloride); glycidyl methacrylate/trimethylamine; and glycidyl methacrylate/N, N-dimethylethylenediamine reaction products.

The method can include functionalizing an outer surface of an ion exchange membrane support with a layer of a charged compound, drying the functionalized ion exchange membrane support, and soaking the functionalized ion exchange membrane support in a solution comprising an acid or a base for an amount of time effective to produce a monovalent selective ion exchange membrane.

In some embodiments, the ion exchange membrane can have a permselectivity (premselectivity) of at least 90% and less than 2 Ω -cm²The resistance of (2).

The crosslinking agent may include at least one of Divinylbenzene (DVB) and Ethylene Glycol Dimethacrylate (EGDM).

According to another aspect, another method of producing an ion exchange membrane support is provided. The method can include saturating a polymeric microporous substrate with a charged monomer solution comprising at least one functional monomer, a crosslinking agent, and an effective amount of at least one photopolymerization initiator. The method can include polymerizing at least one functional monomer by exposing the saturated polymeric microporous substrate to ultraviolet light at an intensity effective to penetrate the substrate in a substantially oxygen-free environment for an amount of time effective to crosslink the at least one functional monomer and produce an ion-exchange membrane support.

In some embodiments, the method may include exposing the saturated polymeric microporous substrate to a solution having a molecular weight of at about 2000mW/cm²And about 2200mW/cm²The ultraviolet light of the intensity in between lasts for an amount of time between about 1 second and about 5 seconds.

In some embodiments, the method may include exposing a saturated polymeric microporous substrate to a solution havingAt about 200mW/cm²And about 500mW/cm²The ultraviolet light of the intensity in between lasts for an amount of time between about 20 seconds and about 30 seconds.

In some embodiments, the method may include exposing the saturated polymeric microporous substrate to a solution having a molecular weight of at about 500mW/cm²And about 2000mW/cm²The ultraviolet light of the intensity in between lasts for an amount of time between about 5 seconds and about 20 seconds.

The method can include exposing the saturated polymeric microporous substrate to ultraviolet light on the top and bottom surfaces.

In some embodiments, the method may include exposing the saturated polymeric microporous substrate to a solution having a surface area of about 200mW/cm on each of the top and bottom surfaces²And about 500mW/cm²Ultraviolet light of an intensity in between.

The method may include pulsing an ultraviolet light.

The method can include exposing a saturated polymeric microporous substrate to a solution having a molecular weight of at about 2000mW/cm²And about 2200mW/cm²Ultraviolet light of an intensity in between.

The method can include exposing a saturated polymeric microporous substrate to ultraviolet light having a wavelength effective to photoinitiate at least one photopolymerization initiator.

The wavelength at which the at least one photopolymerization initiator can be effectively photoinitiated is between about 245nm and about 420 nm.

The charged monomer solution may include at least two photopolymerization initiators.

In some embodiments, each of the at least two photopolymerization initiators may be configured to be initiated at a different wavelength of light.

According to yet another aspect, a method of producing a monovalent selective ion exchange membrane is provided. The method can include saturating a polymeric microporous substrate having a thickness between 25 μm and 55 μm with a charged monomer solution comprising at least one functional monomer, a crosslinking agent, and an effective amount of at least one photopolymerization initiator. The method can include polymerizing at least one functional monomer by exposing the saturated polymeric microporous substrate to ultraviolet light at room temperature in a substantially oxygen-free environment for an amount of time effective to crosslink the at least one functional monomer and produce the ion-exchange membrane support. The method can include functionalizing an outer surface of the ion-exchange membrane support with a layer of a charged compound. The method may include drying the functionalized ion exchange membrane support. The method can include soaking the functionalized ion exchange membrane support in a solution comprising an acid or a base for an amount of time effective to produce a monovalent selective ion exchange membrane.

The method may include soaking the functionalized ion exchange membrane support in a solution comprising 1N NaOH for about 15 minutes.

The method can further comprise rinsing the monovalent selective ion exchange membrane with water, and conditioning the monovalent selective ion exchange membrane in a solution comprising 0.5M NaCl.

The present disclosure contemplates all combinations of any one or more of the foregoing aspects and/or embodiments, as well as combinations with any one or more of the embodiments set forth in the detailed description and any examples.

Brief Description of Drawings

The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 is a representation of the thermal decomposition of AIBN;

FIG. 2 is a representation of the photolysis (UV) of 2, 2-dimethoxy-2-phenyl-acetophenone (DMPA);

FIG. 3 is a graph of the ultraviolet light absorption wavelength of a DMPA;

FIG. 4 is a representation of the chemical structure of bisacylphosphine oxide (BAPO);

FIG. 5 includes a representation of exemplary photopolymerization initiators and their effective initiation wavelengths;

FIG. 6 is a photograph of an ultraviolet curing apparatus;

FIG. 7 is a schematic view of an ultraviolet curing apparatus;

FIG. 8 is a schematic view of a timer for use with the UV curing apparatus of FIGS. 6 and 7;

FIG. 9A is a graph of the spectral distribution of light emitted by an ultraviolet lamp; and

fig. 9B is a photograph of a graph of light transmission of polyethylene.

Detailed Description

Embodiments disclosed herein provide ion exchange membranes and processes for making the same. The electrodialysis membranes described herein can generally combine low electrical resistance with high permselectivity. Their properties may make them highly effective in water desalination applications, in particular in seawater desalination. The ion exchange membranes described herein can be made by polymerizing one or more monofunctional ion generating monomers (monofunctional ionic monomers), optionally a neutral monomer, with at least one multifunctional monomer, in the pores of a porous substrate.

Ion exchange membranes are commonly used to transport cations or anions at an electrical potential or chemical potential. The ion exchange membrane may have negatively or positively charged groups attached to the polymeric material constituting the bulk of the membrane (bulk). The counter ion for each group generally functions as a transferable ion. The cation exchange membrane may have a fixed negative charge and mobile positively charged cations. Anion exchange membranes can have fixed positively charged groups and mobile negatively charged anions. The properties of the ion exchange membrane can be engineered by controlling the amount, type and distribution of the immobilized ionic groups. These membranes may be described as strong acid membranes, strong base membranes, weak acid membranes, or weak base membranes. Strong acid cation exchange membranes typically have sulfonic acid groups as the charged groups. Weak acid membranes typically have carboxylic acid groups that constitute fixed charged groups. Quaternary and tertiary amines can produce fixed positively charged groups in strong base anion exchange membranes and weak base anion exchange membranes, respectively.

Ion exchange membranes can be used for desalination of water by Electrodialysis (ED), as a power generation source in reverse electrodialysis, or as a separator in fuel cells. Thus, the water treatment system disclosed herein may be or may include a desalination system, a power generation system, or an electrodialysis reversal system. Other applications include the recovery of metal ions in the electroplating and metal processing industries and in the food and beverage industries. In other embodiments, the water treatment systems disclosed herein can be or can include metal ion recovery systems or food and beverage processing systems.

In certain exemplary embodiments, the ion exchange membranes disclosed herein may be used in groundwater treatment and/or in agricultural environments. The water treatment systems disclosed herein may be or may include groundwater treatment systems. The water treatment system disclosed herein may be or may include an agricultural irrigation runoff treatment system. The method may include treating groundwater. The method may include treating agricultural water runoff.

Electrodialysis desalinates water, typically under the power of a direct current voltage, by transferring ions and some charged organics through pairs of anion-and cation-selective membranes. The ED device may comprise an electrically conductive and substantially water impermeable anion-selective membrane and a cation-selective membrane arranged as opposite walls of the cell. Adjacent cells typically form a cell pair. The membrane stack may include many cell pairs, sometimes hundreds of cell pairs. An ED system may include many stacks. Each membrane stack typically has a DC (direct current) anode at one end of the stack and a DC cathode at the other end. At DC voltage, ions may move towards the electrode with the opposite charge.

The battery pair includes two types of batteries, a diluting battery and a concentrating battery. Each type of cell may be defined by opposing membranes. An exemplary cell pair may include a common cation transfer membrane wall and two anion transfer membrane walls forming two cells. That is, the first anion transfer membrane and the cation transfer membrane form a dilute cell, and the cation transfer membrane and the second anion transfer membrane form a concentrate cell. In dilute cells, cations typically pass through the cation transfer membrane facing the anode, but can be blocked by the paired anion transfer membrane of the concentrating cell in the direction facing the cathode. Similarly, anions can pass through the anion transfer membrane of the dilute cell facing the cathode, but can be blocked by an adjacent pair of cation transfer membranes facing the anode. In this way, salts in the dilute cells can be removed. In adjacent concentrating cells, cations may enter from one direction and anions may enter from the opposite direction. The flow in the stack may be arranged such that the dilute and concentrate streams remain separate. Thus, a desalted water stream may be produced from the dilute stream.

The lack of irrigation water of sufficient quality is detrimental to crop yield and may require selection of crop species with less demand. Newer irrigation methods that reduce the amount of water used using techniques such as drip irrigation may also result in unsustainable conditions due to the accumulation of salts and impurities in the soil by the water used for irrigation. As most of the water is utilized and evaporated by the crops, the salinity of the soil can rise to much higher concentrations than irrigation water. Irrigation conditions and soils with insufficient source water or insufficient rainfall for leaching the soil can result in soil salinity 4 to 5 times higher than the irrigation water itself. Furthermore, if the ground consists of relatively shallow impermeable ground layers, the irrigation water can raise the groundwater level. When high salt groundwater reaches the crop root level, the water can be detrimental to crop growth. Furthermore, saline soil (saline soil) can damage leafy crops due to water splashing from the soil surface. Furthermore, if the agricultural land is drained of brine, trace impurities in the soil such as selenium or boron, or residual contaminants from fertilizer use such as nitrates, can cause contamination of the effluent and cause difficulties in safe effluent control.

Irrigation water requirements also compete with potable drinking water for humans and non-contaminated water for livestock and wildlife. It is therefore often the case that a combined source of irrigation water and drinking water is required in agricultural areas. The films described herein may be used for agricultural irrigation water treatment.

Monovalent (univalent) selective membranes or monovalent (monovalent) selective membranes primarily transfer monovalent ions. Monovalent selective membranes can separate ions based on charge and/or size. Monovalent selective membranes can distinguish between monovalent and divalent ions. Monovalent selective cation transfer membranes can distinguish between ions having a charge of +1, such as sodium and potassium, and ions having a greater positive charge, such as magnesium and calcium. Thus, the monovalent selective cation exchange membranes described herein can selectively transport monovalent ions, such as sodium and potassium ions, while blocking the transport of divalent ions, such as calcium and magnesium ions. Similarly, monovalent selective anionic membranes can separate ions having a charge of-1, such as chloride, bromide, and nitrate ions, from ions having a greater negative charge. Thus, the monovalent anion exchange membranes described herein can selectively transport monovalent ions such as chloride and nitrate ions while blocking transport of divalent ions such as sulfate ions.

The ion exchange membranes disclosed herein can be used for treating brackish water and wastewater desalination. While ED is generally considered too expensive for seawater use, the ion exchange membranes disclosed herein can be effectively used for seawater desalination. Effective and efficient seawater desalination can be carried out at less than 1 omega-cm²E.g. less than 0.8 omega-cm²Or less than 0.5 ohm-cm²In the case of membrane resistance of (3). The ion exchange membranes disclosed herein can also provide an ion permselectivity of greater than 90%, such as greater than 95% or greater than 98%. Furthermore, the ion exchange membranes disclosed herein have a longer useful life as well as greater physical strength and chemical durability than comparable conventional ion exchange membranes. Finally, the ion exchange membranes disclosed herein can be manufactured at relatively low cost.

Thus, the ion exchange membranes disclosed herein can be used for Reverse Electrodialysis (RED). RED can be used to convert the free energy generated by mixing two aqueous solutions of different salinity into electrical energy. Generally, the greater the difference in salinity, the greater the potential for power generation. The water treatment systems disclosed herein may be or include RED systems. The methods disclosed herein may be used to generate electricity.

The ion exchange membranes disclosed herein may be used as Polymer Electrolyte Membranes (PEM). The PEM is a type of ion exchange membrane that can serve as both an electrolyte and a separator to prevent direct physical mixing of hydrogen from the anode and oxygen supplied to the cathode. The PEM may contain negatively charged groups, such as sulfonic acid groups, attached to or as part of the polymer comprising the PEM. Protons typically migrate through the membrane by jumping from one fixed negative charge to another to penetrate the membrane.

The membranes disclosed herein can generally include an ion exchange membrane support and a charged functionalized layer covalently bonded to the ion exchange membrane support. The ion exchange membrane support may include a polymeric microporous substrate and a crosslinked ion transfer polymer layer on a surface of the substrate. As an intermediate production step, the membrane support may additionally comprise an amine group layer covalently bound to the crosslinked ion transfer polymer layer. The charged functionalized layer is a positively charged functionalized layer comprising at least one of sulfonic acid groups, carboxylic acid groups, quaternary ammonium groups, and tertiary amine groups hydrolyzed to positively charged ammonium.

The films described herein may generally exhibit good mechanical strength. The mechanical strength may be sufficient to allow the film to withstand the stresses of a continuous film manufacturing process and be manufactured and sealed into the final film holding device or module without significant or hidden damage that may occur after a period of operation. Furthermore, the mechanical strength may be sufficient to provide high dimensional stability. When operating as a desalination plant, the membranes may typically exhibit minimal dimensional changes during cleaning, disinfection, or decontamination protocols, or during transportation or upon storage. High dimensional stability to changes in, for example, ion content or temperature of the fluid contacting the membranes can be provided so that during operation, changes in the distance between the membrane pairs that can lead to current inefficiencies are minimized. Dimensional changes during electrodialysis, which can cause stress in the constrained membrane, leading to membrane defects and poor performance, can also generally be minimized.

The films described herein may exhibit low electrical resistance. Generally, low resistance reduces the electrical energy required for desalination and reduces operating costs. Film resistivity (specific membrane resistance) is typically measured in Ω -cm. A more convenient engineering measure is omega-cm². Resistance can be measured by a resistance test procedure using a cell with two electrodes of known area in an electrolyte solution. Platinum or black graphite is commonly used for the electrodes. The resistance between the electrodes is then measured. A membrane sample of known area may be positioned between the electrodes in the electrolyte solution. The electrode does not contact the membrane. The resistance was then measured again with the membrane in place. The membrane resistance can then be estimated by subtracting the electrolyte resistance without the membrane from the test results with the membrane in place.

Resistance can also be measured by determining the voltage versus current curve in a cell having two well-stirred chambers separated by a membrane. Calomel electrodes can be used to measure the potential drop across the membrane. The slope of the potential drop versus current curve can be obtained by varying the voltage and measuring the current.

Electrochemical impedance may also be used for the calculation. In this method, an alternating current may be applied across the membrane. Measurements at a single frequency give data relating to the electrochemical properties of the membrane. By using frequency and amplitude variations, detailed structural information can be obtained.

The membranes described herein can have high permselectivity. Osmotic selectivity may generally refer to the relative transport of counterions to co-ions (co-ion) during electrodialysis. For a theoretically ideal cation exchange membrane, only positively charged ions will pass through the membrane, giving a permselectivity of 1.0. When membranes separate monovalent salt solutions of different concentrations, permselectivity can be found by measuring the potential across the membrane.

The ion exchange membranes disclosed herein can have reduced water permeation. Permeation of the dilute stream through membrane defects can reduce efficiency under the driving force of the osmotic pressure differential between the dilute and concentrate streams. Water infiltration can reduce current efficiency and the productivity of purified water by removing pure water. In seawater electrodialysis using membranes (thin membranes), water loss can be particularly severe because the high concentration difference between the concentrate (brine) side of the membrane and the pure water side of the membrane generally increases the osmotic driving force. Membrane defects can be particularly detrimental to operation, as high osmotic pressures will tend to force pure water through such defects and increase water loss, increasing power consumption.

The membranes disclosed herein may generally have a structure that allows for high permeability and low permeability flow of cations. Apparent permselectivity, as used herein, is the ratio of the transport rate of a counterion (cation) to a homoionic (anion). Conventional measured parameters do not indicate the rate of counter ion removal. In certain embodiments, the membranes disclosed herein can be engineered to control cation permeability.

Cation permeability can be controlled by the influence of the structure of the ions (molecular size and total charge) and the membrane microstructure. The membrane microstructure can hinder counter-ion permeability if the membrane is designed with relatively small pores. Relative terms may be considered to mean that the counterions encounter high resistance as a result of interaction with the membrane material as they traverse the channels that are slightly larger than their apparent diameter. The membrane may have a relatively low water content, tending to reduce the way counter ion permeability. The water content and effective pore size of the membrane can be engineered by balancing the content of hydrophilic monomers to increase the amount and nature of the counter ion permeability and crosslinking monomers. The crosslinking monomer may be selected to be either a hydrophobic monomer or a hydrophilic monomer.

The membranes disclosed herein may generally comprise an ion exchange membrane support. The ion exchange membrane support may include a polymeric microporous substrate and a crosslinked ion transfer polymer layer on a surface of the substrate. The membrane support may be produced by a process that includes selecting a suitable porous substrate and incorporating a crosslinked ion transfer polymer layer on the surface of the substrate.

The microporous membrane substrate may be made from polyolefins, polyvinylidene fluoride, or other polymers. One exemplary class of substrates includes thin polyolefin films. Another exemplary type of substrate is made from Ultra High Molecular Weight Polyethylene (UHMWPE). The microporous substrate may include microporous membranes of polypropylene, high molecular weight polyethylene, ultra high molecular weight polyethylene, or polyvinylidene fluoride. The substrate may typically have a thickness of less than about 155 μm, for example less than about 55 μm or less than about 25 μm.

Embodiments of the substrate film may have a porosity greater than about 45%, for example greater than about 60%. In certain embodiments, the base film may have a porosity of greater than about 70%. The base membrane may have a nominal pore size of from about 0.05 μm to about 10 μm, for example, from about 0.1 μm to about 1.0 μm or from about 0.1 μm to about 0.2 μm.

The film support may be produced by saturating charged monomers in the pores of the substrate. The functional monomer, crosslinker, and polymerization initiator can polymerize in the pores of the substrate to form a crosslinked charged polymer. In certain embodiments, the functional monomer may comprise an ion-generating monomer, such as a monofunctional ion-generating monomer. The crosslinking agent may include a multifunctional monomer. As used herein, the term ion generating monomer may generally refer to a monomeric species having at least one covalently attached charged group. The charged groups may be positively or negatively charged, as described in more detail below. Monofunctional monomers may generally refer to monomers having a single site for carrying out a polymerization reaction. Multifunctional monomers may generally refer to monomers that have more than one polymerization site and may thus form a networked polymer or a cross-linked polymer.

The process of polymerizing the crosslinked ion transfer polymer layer in the pores of the substrate may include saturating the substrate with a solution comprising a monofunctional ion-generating monomer, a multifunctional monomer, and a polymerization initiator. The process may include removing excess solution from the surface of the substrate while saturating the porous volume with solution and initiating polymerization. Polymerization may be initiated by the application of heat, Ultraviolet (UV) light, or ionizing radiation, optionally in the substantial absence of all oxygen. The process can be carried out to incorporate a crosslinked ion transfer polymer layer to substantially completely fill the pores of the substrate.

Thus, in certain embodiments, the membrane support may be produced by polymerization of one or more ion generating monomers, neutral monomers, and suitable crosslinker monomers. Exemplary neutral monomers are hydroxyethyl acrylate and hydroxymethyl methacrylate. Other neutral monomers are within the scope of the present disclosure. The ion-generating monomer can be selected to produce a cation exchange membrane or an anion exchange membrane.

The monomer mixture may be selected to engineer the crosslinked copolymer to produce a film having a desired balance of properties. For example, combining water soluble and/or swellable ion generating monomers with non-water swellable comonomers can produce copolymers with high content (degree) of ionic groups and reduced swelling in water. Such ion exchange membranes can be used for desalination. In particular, exemplary copolymers may have better physical strength in water and suffer less dimensional change in use due to changes in water ion content or temperature changes. Thus, exemplary ion exchange membranes may exhibit suitable mechanical strength, low electrical resistance, and high permselectivity, for example, for seawater electrodialysis.

Monomers containing negatively charged groups include the following as representative examples, but are not limited to such examples: sulfonated acrylic monomers suitable for providing cation exchange capacity, such as 2-sulfoethyl methacrylate (2-SEM), 2-propylacrylic acid, 2-acrylamido-2-methylpropanesulfonic Acid (AMPS), sulfonated glycidyl methacrylate, 3-sulfopropyl methacrylate, sodium 1-allyloxy-2-hydroxypropyl sulfonate, and the like. Other exemplary monomers are acrylic acid and methacrylic acid or their salts, sodium styrene sulfonate, styrene sulfonic acid, sulfonated vinylbenzyl chloride, sodium 1-allyloxy-2-hydroxypropyl sulfonate, 4-vinylbenzoic acid, trichloroacrylic acid, vinylphosphoric acid, and vinylsulfonic acid. Preferred monomers are 2-sulfoethyl methacrylate (2-SEM), styrene sulfonic acid and its salts, and 2-acrylamido-2-methylpropane sulfonic Acid (AMPS).

Cation exchange membrane embodiments described herein may have less than about 1.0 ohm-cm²E.g., less than about 0.5 ohm-cm²Of (c) is measured. Certain embodiments of the cation exchange membranes described herein can have a permselectivity of greater than about 95%, such as greater than about 99%. In some embodiments, the ionogenic monomer used to produce the cation exchange membrane may be 2-sulfoethyl methacrylate (2-SEM) or 2-acrylamido-2-methylpropanesulfonic Acid (AMPS) or may include 2-sulfoethyl methacrylate (2-SEM) or 2-acrylamido-2-methylpropanesulfonic Acid (AMPS). One exemplary crosslinker is ethylene glycol dimethacrylate. Other ion generating monomers and cross-linking agents are within the scope of the present disclosure.

Monomers containing positively charged groups include the following as representative examples, but are not limited to such examples: methacrylamidopropyl trimethyl ammonium chloride; trimethylammonium ethyl methacrylate; quaternary ammonium salts of polyamines and vinyl aromatic halides, such as 1, 4-diazabicyclo [2,2,2] octane bis (vinylbenzyl chloride) (quaternary ammonium salts of 1, 4-diazabicyclo [2,2,2] octane (DABCO) and piperazine divinyl chloride); or a quaternary ammonium salt formed by reacting a cyclic ether, a polyamine, and an alkyl halide, such as iodoethyldimethylethylenediamino 2-hydroxypropyl methacrylate (a quaternary ammonium salt formed by reacting Glycidyl Methacrylate (GMA) with N, N-dimethylethylenediamine and ethyl iodide); and vinylbenzyltrimethylammonium chloride. Other exemplary monomers for use in the anion exchange membrane include trimethylammonium ethyl methacrylate chloride, 3- (acrylamidopropyl) trimethylammonium chloride, N ', N "-pentamethyldiethylenetriamine bis (vinylbenzyl chloride) (quaternary ammonium salts of N, N', N" -pentamethyldiethylenetriamine and vinylbenzyl chloride), glycidyl methacrylate/trimethylamine, or glycidyl methacrylate/N, N-dimethylethylenediamine reaction product.

Anion exchange membrane embodiments described herein may have less than about 1.0 Ω -cm²E.g., less than about 0.5 ohm-cm²Of (c) is measured. In certain embodiments, the anion exchange membranes described hereinCan have a permselectivity greater than about 90%, such as greater than about 95%. In some embodiments, the ionogenic monomer used to produce the anion exchange membrane may be or may include trimethylammonium ethyl methacrylate chloride crosslinked with ethylene glycol dimethacrylate, or glycidyl methacrylate/N, N-dimethylethylenediamine reaction product crosslinked with ethylene glycol dimethacrylate, and the anion exchange membrane formed by reacting N, N ', N "-pentamethyldiethylenetriamine bis (vinylbenzyl chloride) (quaternary ammonium salts of N, N', N" -pentamethyldiethylenetriamine and vinylbenzyl chloride) or 1, 4-diazabicyclo [2,2 ″ -diazabicyclo [2,2]Octane bis (vinylbenzyl chloride) (1, 4-diazabicyclo [2, 2)]Octane (DABCO) and quaternary ammonium salts of vinylbenzyl chloride).

The charged monomer solution may comprise the functional monomer at a concentration of at least about 50 weight percent. For example, the charged monomer solution may comprise the functional monomer at a concentration between about 50 wt% and 75 wt%. The charged monomer solution can comprise the functional monomer at a concentration of about 50 wt%, about 55 wt%, about 60 wt%, about 65 wt%, about 70 wt%, or about 75 wt%.

The crosslinking agent may include at least one of Divinylbenzene (DVB) and Ethylene Glycol Dimethacrylate (EGDM). Multifunctional monomers comprising one or more ionic groups may be used. Without being limited by the examples, monomers such as 1, 4-divinylbenzene-3-sulfonic acid or salts thereof may be used. The degree of crosslinking may range from 2% to 60%. Polyfunctional monomers suitable for providing crosslinking with monomers containing negatively or positively charged groups include the following as representative examples, but are not limited to such examples: ethylene glycol dimethacrylate, 1, 3-butanediol diacrylate, 1, 4-butanediol dimethacrylate, 1, 4-butanediol diacrylate, 1, 6-hexanediol diacrylate, pentaerythritol triacrylate, tetraethylene glycol dimethacrylate, divinylbenzene, trimethylolpropane triacrylate, isophorone diisocyanate, glycidyl methacrylate, trimethylolpropane trimethacrylate, ethoxylated (n) bisphenol a di (meth) acrylate (n ═ 1.5, 2,4,6, 10, 30), ethoxylated (n) trimethylolpropane tri (meth) acrylate (n ═ 3, 6, 9, 10, 15, 20), propoxylated (n) trimethylolpropane triacrylate (n ═ 3, 6, 9, 10, 15, 20), 6) Vinylbenzyl chloride, glycidyl methacrylate, and the like.

Organic solvents may be used as reactant carriers. One class of useful solvents is dipolar aprotic solvents. Some examples of suitable solvents include dimethylacetamide, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide or-triamide, acetonitril, and acetone. The organic solvent may be used to solvate the ionic group-containing monomer and the water-insoluble monomer. An exemplary solvent is N-methylpyrrolidone. Other solvents that may be used are n-propanol and dipropylene glycol. Similar hydroxyl-containing solvents may be used in certain embodiments, such as alcohols, e.g., isopropanol, butanol, glycols such as various glycols, or polyols, such as glycerol. Other solvents are within the scope of the present disclosure. The solvents in question may be used alone or in combination. In some embodiments, a solvent may be used with water to increase the solubility of the ion-containing organic.

The substrate hole filling or saturation process may be performed at slightly elevated temperatures (e.g., above 40 ℃) to reduce air solubility. In other embodiments, the matrix pore filling or saturation process may be performed after a gentle vacuum treatment of the substrate sample immersed in the formulation solution (formulation solution). The substrate sample may be pre-soaked and then placed on a polyester or similar sheet and covered with a cover sheet. The soaked and coated substrate may be smoothed to remove air bubbles.

The method of producing a membrane may include saturating a polymeric microporous substrate with a charged monomer solution comprising at least one functional monomer and an effective amount of at least one polymerization initiator. The polymerization step may be initiated to polymerize the functional monomer.

Conventionally, the polymerization step is a thermal polymerization. The solution may contain a thermal initiator. Table 1 shows charged monomer solution formulations containing an exemplary thermal initiator, 2' -Azobisisobutyronitrile (AIBN). FIG. 1 is a representation of the thermal decomposition of AIBN.

Table 1: charged monomer solution formulations with thermal initiators

Material	Percent (%)	Weight (g)
			NMP	12.63	31.57
1-BuOH	8.84	22.11
			DPG	0.63	1.58
EGDM	15.41	38.51
			DVB	3.79	9.47
AA	1.26	3.15
			2-SEM	56.81	142.01
AIBN	0.64	1.60

For thermal polymerization, the soaked substrate may be heated in an oven at a temperature sufficient to initiate complete polymerization and for a time necessary to initiate complete polymerization. The soaked substrate may be placed on a heated surface at a temperature sufficient to initiate and complete polymerization and for a time necessary to initiate and complete polymerization. However, temperatures sufficient to initiate and complete polymerization are typically between 90 ℃ and 110 ℃, and sometimes as high as 120 ℃. The time required to initiate and complete polymerization at this temperature may be up to about 6 minutes or longer than about 6 minutes. Thus, the thermally induced energy requirements are high. Exposure to high temperatures for such long periods of time may cause thermal damage to the functional groups. In addition, the polymerization cannot be stopped quickly. The polymerization will generally continue until the substrate is cooled to a temperature at which polymerization ceases.

Polymerization by exposure to UV light can be carried out at room temperature in a short amount of time and can be initiated and stopped immediately. UV light initiation with a suitable polymerization initiator may be used. The method may include irradiating the assembly with UV light of an intensity sufficient to initiate and complete polymerization and for a time required to initiate and complete polymerization.

The method may include saturating the film with a solution comprising a photoinitiator without using a thermal initiator. Photoinitiators are molecules that absorb light of a particular wavelength and decompose into free radicals that initiate polymerization. Typically, UV initiators absorb UV light, which results in decomposition into free radicals that can attack the ion exchange monomer and induce polymerization. An exemplary photoinitiator is 2, 2-dimethoxy-2-phenyl-acetophenone (DMPA). Fig. 2 is a representation of UV decomposition of DMPA. The radicals resulting from the UV decomposition can be used for the polymerization of the ion-exchange membrane substrate. Table 2 is a charged monomer solution formulation containing the photoinitiator DMPA.

Table 2: charged monomer solution formulations with photoinitiators

Material	Percent (%)	Weight (g)
			NMP	12.63	31.57
1-BuOH	8.84	22.11
			DPG	0.63	1.58
EGDM	15.41	38.51
			DVB	3.79	9.47
AA	1.26	3.15
			2-SEM	56.81	142.01
DMPA	0.64	1.60

Charged monomer solution formulations can be prepared by combining all components (e.g., functional monomer and photoinitiator) and stirring for a time sufficient to achieve substantially complete dissolution. The charged monomer solution can be formulated to increase the transparency of a saturated substrate when exposed to UV light. Thus, in some embodiments, a saturated substrate may change color from translucent white to transparent. The increase in transparency may allow UV light to penetrate the substrate, enabling complete and uniform polymerization of the film carrier.

The charged monomer solution may be substantially free of any inhibitor. Inhibitors are typically added to the monomer solution containing the thermal initiator to improve stability during coating. The monomer solution comprising a photoinitiator disclosed herein may be substantially free of any inhibitor. One exemplary inhibitor is 4-Methoxyphenol (MEHQ). However, the charged monomer solution may be substantially free of any inhibitor.

The charged monomer solution may comprise at least one chain transfer agent to effect chain transfer polymerization. Chain transfer polymerization generally involves transferring the polymerization activity of a growing polymer chain to a chain transfer agent, monomer, polymer, or solution molecule. Chain transfer agents typically have at least one weak chemical bond, which facilitates the chain transfer reaction. Common chain transfer agents include mercaptans, such as dodecyl mercaptan (DDM), and halocarbons, such as carbon tetrachloride. One exemplary chain transfer agent is pentaerythritol tetrakis (mercaptopropionate) (PETMP). Other chain transfer agents may be included.

The microporous polymer substrate may be saturated with the stirred solution and exposed to UV light until complete polymerization occurs. In particularThe method may include irradiating the assembly with UV light of an intensity sufficient to initiate and complete polymerization. Thus, the method may include exposing the soaked substrate to UV light at an intensity effective to penetrate the substrate and to crosslink the at least one functional monomer and produce the ion-exchange membrane. The intensity can be about 200mW/cm²And 2200mW/cm²In the meantime. The intensity may be selected based on process conditions, such as, for example, the amount of time to complete the polymerization. The intensity may be selected based on substrate parameters, such as, for example, the thickness and/or transparency of the substrate. Thus, based on the amount of time of exposure, the intensity may be at about 200mW/cm²And 500mW/cm²Between about 500mW/cm²And 2000mW/cm²Between, or at about 2000mW/cm²And about 2200mW/cm²In the meantime.

In particular, the irradiation may be selected to a value sufficient to penetrate the substance. Attenuation of UV light may be considered and methods may be employed to reduce attenuation through the bulk of the substrate. Conventionally, UV cured films suffer from non-uniform curing due to ineffective irradiation through the bulk of the film. For example, a film having a thickness from 100 μm to 500 μm or not sufficiently translucent to UV light may not be irradiated by UV light having an intensity sufficient to penetrate the substrate. UV light may be attenuated and the effect lost, resulting in uneven curing and polymerization of the substrate. The methods disclosed herein may include exposing the soaked substrate to UV light at an intensity effective to penetrate the substrate and to crosslink the at least one functional monomer and produce an ion exchange membrane. In exemplary embodiments, the selected intensity of UV light can be combined with a soaked substrate having a thickness between 25 μm and 55 μm and being transparent to produce a good ion exchange membrane.

The method can include exposing the soaked substrate to UV light for an amount of time effective to crosslink the at least one functional monomer and produce the ion-exchange membrane support. As previously described, UV initiation can occur at a faster rate than thermal initiation. The increased polymerization rate can increase the overall manufacturing rate of the ion exchange membrane and reduce production costs.

The soaked substrate may be exposed to UV light for the time required to initiate and complete polymerization. Thus, the method can include irradiating the substrate for an amount of time effective to crosslink the at least one functional monomer and produce the ion-exchange membrane. The amount of time required to initiate and complete polymerization may be selected based on process conditions such as, for example, the intensity of UV light. The amount of time may typically be less than 1 minute. For example, the amount of time may be less than 30 seconds, less than 20 seconds, or less than 10 seconds. The amount of time may be, for example, between about 30 seconds and about 1 minute, between about 20 seconds and about 30 seconds, between about 5 seconds and about 20 seconds, between about 5 seconds and about 10 seconds, between about 3 seconds and about 5 seconds, or between about 1 second and about 5 seconds. Generally, greater strength may be associated with a lesser amount of time required to initiate and complete polymerization.

The conversion or polymerization rate can be increased by photopolymerizing the soaked substrate in an environment substantially free of oxygen or air. Oxygen may act as a polymerization inhibitor. In some embodiments, exposure to UV light may be performed in an environment saturated with an inert gas, such as nitrogen. The exposure to UV light may be performed in a chamber filled with nitrogen or another inert gas and substantially free of oxygen. In other embodiments, the soaked substrate may be placed between two membranes. Any bubbles can be removed from the soaked substrate. The membrane may be of any inert material. The overlying film may be any inert material as long as it is substantially transparent to UV light. The underlying film may be any inert material. In embodiments where the soaked substrate is exposed to UV light on the top and bottom surfaces, both the upper and lower films may be substantially transparent to UV light. The upper film may be, for example, polypropylene or polyethylene. The underlying film may be, for example, polyester or polyethylene.

In some embodiments, the method may include exposing the saturated polymeric microporous substrate to UV light on the top and bottom surfaces of the sheet. The irradiation from each UV light beam may be adjusted to provide an appropriate intensity, e.g., an intensity sufficient to penetrate a saturated or soaked substrate. Thus, the method may include immersing the substrate in the top and bottom surfacesEach having an exposure at 200mW/cm²And 500mW/cm²UV light of an intensity in between.

The method may include pulsing a UV light. The UV light may be pulsed in order to control the temperature of the substrate. It should be appreciated that exposure to UV light can raise the temperature of the substrate. As previously mentioned, high temperatures can promote damage to functional groups. Therefore, by pulsing the UV light, the temperature can be controlled and the functional groups can be protected. The amount of time sufficient to initiate and complete polymerization can be considered the total amount of time exposed to UV light. The pulses may comprise, for example, pulses of 1 second to 10 seconds. Each pulse may independently be, for example, 1 second, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, or 10 seconds. The pause may comprise a pause of, for example, 1 second to 10 seconds. The pulses and pauses of UV light may be the same or different. Each pause may be independently, for example, 1 second, 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, or 10 seconds. In some embodiments, the method may include monitoring the temperature of the soaked substrate or the area surrounding the soaked substrate. The UV light may be pulsed when a threshold temperature is detected, for example a temperature above 25 ℃ or above 30 ℃. The UV light may be applied continuously when a threshold temperature is detected, for example a temperature below 30 ℃ or below 25 ℃. Additionally, the length and amount of the UV pulse and/or pause may be selected when a threshold temperature is detected.

The photopolymerization may be carried out in the presence of one or more photoinitiators, for example two or more photopolymerization initiators. Exemplary photoinitiators such as DMPA absorb UV light in the wavelength range of about 250nm, as shown in fig. 3. At short wavelengths, better surface cure can be achieved when used at moderately high concentrations in the formulation. Another exemplary photoinitiator, bisacylphosphine oxide (BAPO), which absorbs UV light in the wavelength range between about 350nm and 420nm, may also be used. In particular, BAPO can provide better substrate penetration and better deep cure. Figure 4 is a representation of the chemical structure of BAPO. The photopolymerization initiator may include at least one of: 1-hydroxy-cyclohexylphenylketone, phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide, bisacylphosphine oxide, 2-hydroxy-2-methylpropiophenone, 2' -azobisisobutyronitrile and 2, 2-dimethoxy-2-phenyl-acetophenone.

In general, the UV light wavelength may be selected to correspond to a wavelength range in which the photopolymerization initiator is activated. The photopolymerization initiator may have a maximum absorption in the applied wavelength. The saturated polymeric substrate may be exposed to UV light having a wavelength effective to photoinitiate the at least one polymerization initiator. The wavelength range may be between 245nm and 420 nm. The wavelength range may be, for example, between 245nm and 300nm, between 300nm and 350nm or between 350nm and 420 nm.

Exemplary photopolymerization initiators and their effective wavelengths are shown in fig. 5. Briefly, photoinitiators such as 2-hydroxy-2-methylpropiophenone absorb light having wavelengths between 245nm and 331nm (i.e., at 245nm, 280nm, and 331 nm); photoinitiators such as BAPO absorb light having wavelengths between 295nm and 370nm (i.e., between 295nm and 370 nm); and photoinitiators such as 1-hydroxy-cyclohexyl-phenyl ketone absorb light having a wavelength between 246nm and 333nm, i.e. at 246nm, 280nm and 333 nm.

The charged monomer solution may be formulated to include two or more photopolymerization initiators configured to photoinitiate in different wavelength ranges. At shorter wavelengths (e.g., between 245nm and 300 nm), better surface cure can be achieved, and photoinitiators can be used at moderately high concentrations. At longer wavelengths (e.g., between 300nm and 420 nm), UV light generally provides better body penetration and better deep cure. The method may include exposing the soaked substrate to UV light in a first wavelength range and UV light in a second wavelength range. As previously described, the UV light may be pulsed in the first wavelength range for 1 second to 10 seconds. As previously described, the UV light may be pulsed in the second wavelength range for 1 second to 10 seconds. According to certain embodiments, the two or more photopolymerization initiators may have a synergistic effect in polymerizing the charged monomers.

In an exemplary embodiment, the method may include saturating the substrate with a solution comprising BAPO and 2-hydroxy-2-methylpropiophenone or 1-hydroxy-cyclohexyl-phenylketone to induce the change in wavelength with light.

The polymerization initiator may include a radical polymerization initiator. Free radical polymerization initiators that may be used include, for example, Benzoyl Peroxide (BPO), ammonium persulfate, 2 '-Azobisisobutyronitrile (AIBN), 2' -azobis (2-methylpropionamidine) dihydrochloride, 2 '-azobis [2- (2-imidazolin-2-yl) propane ] and dimethyl 2, 2' -azobis (2-methylpropionate).

The charged monomer solution may comprise a crosslinking agent and an effective amount of a photopolymerization initiator to induce crosslinking of the functional monomer. The effective amount may generally depend on process factors such as the type and concentration of the functional monomer, the type and concentration of the crosslinking agent, the type of photopolymerization initiator, the intensity of the ultraviolet light, the time of exposure to the ultraviolet light, and other factors that affect the intensity of the UV radiation, such as the distance from the ultraviolet light source, the blocking of light from the ultraviolet light source (e.g., by a filter), the precipitating compound in the charged monomer solution, and the like. For example, it has been found that certain photopolymerization initiators precipitate in charged monomer solutions over time. Thus, according to certain embodiments, the charged monomer solution may be prepared on the day of use. The charged monomer solution may be prepared within 5 days from use, within 4 days from use, within 3 days from use, within 2 days from use, or within 1 day from use. The charged monomer solution may be prepared at the point of use.

The effective amount may typically be between about 2% w/w and about 5% w/w. An effective amount may be, for example, about 1% w/w, about 2% w/w, about 3% w/w, about 4% w/w, about 5% w/w, or about 6% w/w. An effective amount of photopolymerization initiator may be about 2% w/w for an exposure time of about 20 seconds to 30 seconds. An effective amount of photopolymerization initiator may be about 5% w/w for an exposure time of about 1 second to 3 seconds. The effective amount of photopolymerization initiator may include one or more photopolymerization initiators, for example, two or more photopolymerization initiators. Any two photopolymerization initiators may be contained in the charged monomer solution in a ratio of between 2:1 and 1:2 of the first photopolymerization initiator to the second photopolymerization initiator.

A continuous test or manufacturing process may include saturating the porous substrate, initiating and completing polymerization, and washing or leaching unpolymerized material from the now-formed membrane support. The film may optionally be dried. The conditioning with saline solution can be done in a continuous immersion process, such as by a tank of saline solution, or by soaking a wound roll of film, or after the module is made.

If the monomer solution is formulated with a solvent that wets the substrate, the process can begin by feeding the substrate from a roll and through a tank of monomer formulation and removing excess solution. The soaked substrate can be assembled between two layers of plastic sheet fed from rollers and sandwiched between two rollers to remove air and produce a smooth multi-layer assembly. The removal of the bubbles can create an oxygen free environment. One exemplary sheet material is a polyethylene terephthalate film. Other sheet materials may be used. An alternative method of sheet material assembly may include running a saturated sheet through a UV source covered with an inert gas to create a substantially oxygen free environment.

The assembly may be treated with an ultraviolet lamp to initiate and complete polymerization. For example, the described three-layer assembly may be run on a conveyor belt and/or through a tunnel or other treatment device having an inlet and an outlet for the soaked substrate assembly with a UV light source on one or both sides of the assembly. In some embodiments, the method may include adjusting the speed of the substrate passing through the UV light source to control the amount of time exposed to the UV light. The cover sheet may be removed after polymerization. The now formed membrane support may be washed and optionally dried.

The membrane support may be treated with a solution comprising an acid or a base to form an ion exchange membrane. For example, the membrane support may be soaked in a solution comprising NaOH or another suitable base for an amount of time effective to functionalize the ion exchange membrane support and produce an ion exchange membrane. The amount of time may be, for example, between 10 minutes and 20 minutes, such as about 15 minutes. The solution may contain, for example, about 1.5N NaOH. The ion exchange membrane may be conditioned with a salt solution. The salt solution may comprise, for example, NaCl or another suitable salt. The salt solution may contain, for example, about 0.5M NaCl. The ion exchange membrane or membrane support may be rinsed with water and dried between, before and/or after the soaking and conditioning treatment.

The method can further include functionalizing an outer surface of the ion exchange membrane to produce a monovalent selective ion exchange membrane. In short, the ion-exchange membrane can be functionalized with a layer of charged compound. According to certain embodiments, the layer of charged compound may be chemisorbed to the ion-exchange membrane such that the charged compound is covalently bound to the membrane support. The charged compound layer may be chemisorbed by one or more intermediate layers, such as styrene or acrylic based intermediate layers having sulfonic acid groups bonded to a polymeric intermediate layer having amine groups (e.g., PEI or branched PEI). The styrene or acrylic based interlayer can provide stability to covalent bonds and increase membrane lifetime. The PEI or branched PEI may be selected to have a pore size sufficient to bind to the outer surface of the membrane without substantially penetrating the membrane substrate. In some embodiments, the branched PEI may have a molecular weight of at least 60,000 g/mol. Any intermediate layer may be polymerized by UV light with a suitable photopolymerization initiator, as described herein. The charged functional layer may then be bonded to the intermediate layer.

The ion exchange membranes disclosed herein have reduced water permeation. Polymers often swell in water due to charge repulsion from similar charges on the monomer units. This expansion can impede diffusion into the pores of the substrate and reduce the amount of charge that can be permanently placed in the substrate. The manufacturing process of the film typically involves long and repeated drying and soaking cycles, which tends to increase the manufacturing cost.

Efficiency is typically reduced by permeation of the dilute stream through a membrane defect under the driving force of the osmotic pressure differential. Water infiltration tends to reduce current efficiency and the productivity of purified water by removing pure water. In seawater electrodialysis applications using membranes, water loss is particularly visible because the high concentration difference between the concentrate (brine) and pure water sides of the membrane increases the osmotic driving force. Thus, membrane defects can be particularly detrimental to operations in seawater desalination, as high osmotic pressures tend to force pure water through such defects, and increase water loss and increase power consumption.

Anion exchange membranes produced by the UV-initiated processes disclosed herein can have a permselectivity of at least 90%, e.g., between 90% and 92%, at least 92%, between 92% and 94%, or at least 94%. The anion exchange membrane may have less than 1 Ω -cm²E.g. less than 0.7 omega-cm²Or less than 0.5 ohm-cm²The resistance of (2).

The cation exchange membrane produced by the UV-initiated process disclosed herein may have a permselectivity of at least 100%, e.g., between 100% and 102%, at least 102%, between 102% and 104%, or at least 104%. The cation exchange membrane may have less than 3 Ω -cm²E.g. less than 2 omega-cm²Or less than 1.5 ohm-cm²Or a smaller resistance.

In particular, the ion exchange membranes described herein can be stable enough to withstand organic contaminants, such as phenylalkynes, toluene, ethylbenzene, and xylenes, for extended periods of time when in use. Thus, the ion exchange membranes disclosed herein may be used to treat wastewater containing organic contaminants, such as produced water, groundwater, brackish water, brine, and seawater. The wastewater may comprise, for example, between about 100ppm to 1000ppm TDS. In certain embodiments, the wastewater may comprise, for example, between about 100ppm to 400ppm TDS, between about 400ppm to 600ppm TDS, or between about 600ppm to 1000ppm TDS. Furthermore, the cation exchange membranes disclosed herein can be used in agricultural water treatment where the use of water with high sodium content can damage the soil, but magnesium and calcium are beneficial.

The methods disclosed herein can be used to prepare both anion exchange membranes and cation exchange membranes. Certain functional monomers and crosslinking agents are disclosed. However, the present disclosure is not limited to the specific chemistries shown. For example, other functional monomers may be used. In addition, different crosslinking agents may be used with the mixture of crosslinking agents. Also, many different photoinitiators can be used.

Examples

The function and advantages of these and other embodiments will be better understood from the following examples. These examples are intended to be illustrative in nature and are not to be construed as limiting the scope of the invention.

Example 1: production of cation exchange membrane test specimen pieces

The following laboratory methods were used to study formulation and process effects by producing small coupons for resistivity and permselectivity testing. A 43mm diameter sample sheet of porous membrane substrate was die cut. Slightly larger disks (50mm or 100mm diameter) of clear polyester sheet were also die cut. A 105mm aluminum weigh boat (boat) was used to hold a set of coupons. The test piece was sandwiched between two polyester film disks.

First, a base coupon was thoroughly wetted with a monomer solution to make a test sample. This was done by adding the formulated solution to an aluminum boat and dipping a disk of polyester film having a substrate coupon laminated thereon into the solution so that the porous support was saturated. The saturated support was then removed from the monomer solution and placed on a piece of polyester film. For example, air bubbles are removed from the coupon by smoothing or pressing the coupon with a convenient tool such as a small glass rod or by hand. A second polyester disk was then laminated on top of the first coupon and smoothed to provide complete surface contact between the coupon and the underlying and overlying polyester film layers. A second porous substrate was then laminated on the above polyester film and the saturation, smoothing and addition of the cover layers of the polyester film were repeated to give a multilayer interlayer of two coupons and three protective polyester film layers. A typical experimental run will have a multilayer sandwich of 10 or more saturated base sample sheets. The edges of the aluminum boat are crimped down to hold the disk/sample plate assembly if desired.

The boat and assembly are then placed in a sealable bag, typically a zip-style polyethylene bag, and a low positive pressure of an inert gas, typically nitrogen, is added before the bag is sealed. The bag containing the boat and coupon assembly was placed in an oven at 80 ℃ for up to 30 minutes. The bag is then removed and cooled and the now reacted cation exchange membrane coupon is placed in a 0.5N NaCl solution at 40 ℃ -50 ℃ for at least 30 minutes, with a NaCl soak of up to 18 hours being found to be satisfactory.

Example 2: preparation of ion exchange membranes with photopolymerization initiators

An ultraviolet curing device as shown in the photograph of figure 6 and the diagram of figure 7 was used to polymerize the charged monomer layer of the ion-exchange membrane support. The curing device includes a shutter system as shown in fig. 8. The shutter is equipped with a timer that controls the amount of time that the shutter is exposed to UV light. The system also includes an on/off button for controlling the onset of exposure to UV light for a preset amount of time. The usable wavelength of the graph is between 250nm and 600 nm.

Conventional ion exchange membranes

A conventional ion exchange membrane was prepared in a similar manner to that described in example 1. In particular, the functional monomer is polymerized by thermal polymerization. Charged monomer formulations were prepared as described in tables 3-4. Anion exchange membranes and cation exchange membranes are prepared by selecting the appropriate functional monomer.

Table 3: conventional anion exchange charged monomer solution formulations

Table 4: conventional cation exchange charged monomer solution formulations

Photoinitiated ion exchange membrane-single photopolymerization initiator

Photoinitiated ion exchange membranes were prepared as described above for the thermally initiated ion exchange membranes except that the thermal initiator was replaced with 2% w/w of a single photopolymerization initiator. Specifically, a sample of 50g of the formulation of tables 3 and 4 was mixed with 1.0g of 2-hydroxy-2-methylpropiophenone (A), (B), (C), (1173, distributed by BASF, Ludwigshafen, Germany). The mixture was stirred sufficiently for at least 1 hour to allow complete dissolution of the photopolymerization initiator.

Photoinitiated ion exchange membranes-multiple photopolymerization initiators

The photo-initiated ion exchange membrane was prepared as described above for the single initiator photo-polymerization initiated ion exchange membrane except that the multiple photo-polymerization initiators were included at a total concentration of 2% w/w. In particular, charged monomersThe solution contained 2 parts by weight of 1-hydroxy-cyclohexylphenylketone (184, fromSpecialty Chemicals, Basel, Switzerland, distributed) and 1 part by weight of phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide (BAPO) ((B-BAPO)819, fromDistributed by Specialty Chemicals).

Initial tests conducted without a film on top of the substrate during exposure to UV light gave soft polymers that could have low molecular weight and incomplete conversion. This is a result of the action of oxygen. Oxygen acts as an inhibitor and prevents the achievement of high conversions. Therefore, it was decided that a film will be used to cover the top surface of the substrate during the experiment.

A substrate having a thickness of 20 μm(distributed by Entek, Newcastle upon Tyne, United Kingdom) was placed in the charged monomer solution and allowed to soak in the charged monomer solution for 5 minutes until the substrate was fully saturated. The saturated substrate was removed and laid flat on a piece of mylar (mylar). A piece of polyethylene was placed on top of the substrate and a roller was used to drain off excess solution and air bubbles. The substrate, positioned between the mylar and polyethylene, was transferred to a curing area and exposed to UV light. Using a sheet, e.g. for plastics (zip)) UV light transmissive polyethylene of the pouch. The light transmittance of polyethylene is indicated by its spectrum shown in the graphs of fig. 9A-9B.

Only the top side of the substrate is exposed to UV light. The substrate is exposed for a predetermined amount of time, which varies for the experiment. The shutter system was placed at a distance of 1 inch from the curing surface. All membranes, anionic and cationic, were prepared in a similar manner, varying only the time the sample was exposed.

Ion exchange membranes prepared at different UV exposure times were tested for permselectivity and electrical resistance.

The results of the anion exchange membrane preparation are summarized in table 5.

Table 5: results from testing of anion exchange membranes

The results show that an anion exchange membrane polymerized with a single photoinitiator and a mixture of initiators gives the best results when the exposure time is 30 seconds. The permselectivity values ranged from 92% to 94%, and the resistance values were acceptable. The permselectivity of the mixed initiator was 91.20% at 20 seconds of exposure.

The results of the cation exchange membrane preparation are summarized in table 6.

Table 6: results from testing of cation exchange membranes

The results show that cation exchange membranes polymerized with a single photoinitiator and a mixture of initiators give the best results with exposure times between 20 and 30 seconds. Ion exchange membranes show acceptable levels of water blocking and permselectivity of 102% -104%.

It was noted that the formulation containing the photoinitiator 2-hydroxy-2-methylpropiophenone showed signs of turbidity and precipitation after aging for 3 days. Observations indicate that photoinitiator formulations with 2-hydroxy-2-methylpropiophenone should be prepared or discarded on the day of consumption. It is hypothesized that the photoinitiator 2-hydroxy-2-methylpropiophenone reacts slowly with one or more of the component preparations that cause precipitation. However, the article containing 1-hydroxycyclohexylphenyl ketone and phenyl-bis (2,4, 6-trimethylbenzoyl) phosphine oxide was completely clear after aging for 5 days.

Thus, the results show acceptable properties of the prepared ion exchange membranes. It is expected that certain improvements will produce better results. The improvement comprises: reducing the distance between the UV lamp and the curing surface; removing added inhibitor from the solution, the inhibitor typically being added to improve stability during heat-initiated coating; increasing the photoinitiator concentration to compensate for possible consumption of free radicals by oxygen; modifying the formulation by incorporating additives such as additional monomers (e.g., a total concentration greater than 55 wt% or greater than 60 wt%) and chain transfer agents, which may have a synergistic effect on polymerization; and removing the glass filter currently present between the lamp and the curing surface to reduce UV attenuation and increase the intensity of light reaching the substrate.

The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term "more than one" refers to two or more items or components. The terms "comprising", "including", "carrying", "having", "containing" and "involving" are open-ended terms, i.e. meaning "including but not limited to", whether in the written description or in the claims and the like. Thus, use of such terms is intended to include the items listed thereafter and equivalents thereof as well as additional items. In relation to the claims, the only transitional phrases "consisting of and" consisting essentially of are respectively a closed transitional phrase or a semi-closed transitional phrase. The use of ordinal terms such as "first," "second," "third," and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Any feature described in any embodiment may be included in or substituted for any feature of any other embodiment. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Those of skill in the art will understand that the parameters and configurations described herein are exemplary and that the actual parameters and/or configurations will depend on the specific application in which the disclosed methods and materials are used. Those skilled in the art will also recognize, or be able to ascertain using no more than routine experimentation, equivalents to the specific embodiments disclosed.

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Ion exchange membranes by UV initiated polymerization

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