Hydrophobic membrane and membrane distillation method

Abstract

A membrane distillation process for treating organic liquids, a hydrophobic distillation membrane useful in the membrane distillation process, and a method for preparing the hydrophobic distillation membrane are described.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 010,831, filed April 16, 2020, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The following description relates to membrane distillation processes for treating organic liquids, hydrophobic membranes useful in membrane distillation processes, and methods for preparing hydrophobic membranes. [Background technology]

[0003] Membrane distillation is a specific type of distillation process that operates by distilling a liquid through a non-wetting porous membrane, a "distillation membrane," which is generally hydrophobic to prevent wetting of the membrane. Conventional distillation processes are carried out by vaporizing a liquid, for example, by heating, and then collecting the resulting vapor. Like conventional distillation processes, membrane distillation processes use thermodynamic forces (temperature difference and vapor pressure difference) to cause the evaporation of a liquid.

[0004] Membrane distillation, and the membranes used in membrane distillation, are primarily used to treat aqueous liquids, such as to purify water and desalinate seawater. The aqueous liquid and the water vapor derived from it come into contact with a porous hydrophobic membrane that has a surface energy that prevents it from being wetted by the aqueous liquid. Because the membrane is porous, water molecules in vapor form can pass through the membrane. Other molecules of the aqueous liquid that are less volatile, such as metal ions, that remain in the liquid phase do not pass through the membrane. As a result, the water from the aqueous liquid passes through the membrane in a relatively or highly purified form and is separated from the original liquid (e.g., saltwater).

[0005] The main application of membrane distillation is to purify water, for example, to desalinate seawater. In another application, membrane distillation has been described for treating aqueous solutions containing ammonia. See Duong et al., Water and Environmental Journal 28 (2013) pp. 425-434. See also Lawson et al., Membrane Distillation, J. Membrane Sci. 124 (1997) 1-25. Summary of the Invention

[0006] Many volatile organic liquids are used in industry and are required to be relatively or highly pure, free from specific levels of contaminants and impurities. One common type of volatile organic liquid supply commonly used is the type of organic liquid used as an organic cleaning liquid, an example of which is isopropyl alcohol. Isopropyl alcohol is widely used for cleaning and drying parts, filters, and wafer processing in the semiconductor industry. To be useful in this way, isopropyl alcohol should contain low levels of metals and low levels of non-volatile organic contaminants. Any of these types of contaminants can leave residue on the wafer surface when the isopropyl alcohol evaporates.

[0007] Dissolved metals and nonvolatile organic residues are often present in isopropyl alcohol and must be removed before use in certain semiconductor applications. One current technique for removing impurities is through treatment with ion exchange membranes. Negatively charged membranes can be effective in removing dissolved metals from liquids such as isopropyl alcohol. However, such membranes are only marginally effective in removing organic residues from isopropyl alcohol.

[0008] Membrane distillation is useful for separating a desired material from a feed liquid, thereby increasing the purity of the desired material. According to an example of a membrane distillation method described, a liquid feed composition ("liquid feed") containing a volatile organic liquid is processed by the membrane distillation method. This method uses a hydrophobic membrane, which refers to a porous distillation membrane having at least a hydrophobic surface. The liquid feed is placed in contact with the hydrophobic surface of the hydrophobic distillation membrane, but does not wet the hydrophobic surface. One or more volatile organic components of the liquid feed contact the hydrophobic membrane surface as a vapor and can pass through the membrane in vapor form. Less volatile or non-volatile components of the liquid feed remain in the liquid phase and do not pass through the membrane.

[0009] Hydrophobic distillation membranes have a hydrophobic or strongly hydrophobic surface to prevent the feed liquid from wetting the surface during processing.

[0010] As used herein, the "surface energy" (surface free energy) of a surface is considered to be equal to the surface tension of the liquid with the highest surface tension that wets the surface within 2 seconds of contact (see Example 3, Surface Energy Measurement) (also called the "Wetting Liquid Surface Tension" test or "Standard Liquid" test). Useful or preferred distillation membranes that are "hydrophobic" have a surface energy of less than 50, e.g., less than 40, 30, 20, 25, 22, 21, or 20 mN / m, as measured as the surface tension of the liquid with the highest surface tension that wets the surface within 2 seconds, as described in Example 4.

[0011] The hydrophobic surface is prepared by adding fluorinated groups to the surface of the base membrane. Before the fluorinated groups are added to the surface, the base membrane surface may be hydrophilic (e.g., having a surface energy of at least 47 or 50 mN / m).

[0012] As used herein, the term "base membrane" refers to a porous polymeric membrane that includes a surface to which a fluorinated material is applied to produce the described hydrophobic membrane. Useful or preferred base membranes may have a hydrophilic surface. The hydrophilic surface may be the result of the base membrane being prepared from a hydrophilic polymer, such as nylon, that renders the base membrane surface hydrophilic prior to adding fluorinated groups to the base membrane surface.

[0013] Alternatively, the base membrane having a hydrophilic surface may comprise a hydrophobic polymer such as a polyolefin (e.g., such that the membrane exhibits a surface energy of less than 40 mN / m) and be processed to increase the surface energy, e.g., hydrophilized. According to a specific example of a hydrophobic membrane and a method for producing a hydrophobic membrane, fluorinated groups are preferably not added to the membrane surface having a surface energy of less than 40 mN / m. However, the base membrane may also be made from a membrane comprising a hydrophobic polymer, e.g., a membrane exhibiting a surface energy of less than 40 mN / m and hydrophilized to increase the membrane's surface energy to more than 40 mN / m, e.g., at least 42, 47, 50, 60, or 70 mN / m.

[0014] As used herein, a membrane (e.g., a "base membrane") is considered to be "hydrophilic" if the membrane has a surface energy greater than 40 mN / m, e.g., greater than 50, 60, or 70 mN / m, measured as the surface tension of the highest surface tension liquid that wets the surface within 2 seconds.

[0015] In one aspect, the disclosure relates to a method for treating a liquid feed containing a volatile organic liquid, the method including providing a liquid feed containing a volatile organic liquid, contacting a stream of the liquid feed with a hydrophobic surface of a hydrophobic distillation membrane on a retentate side of the membrane, where the liquid feed does not wet the hydrophobic surface, passing the volatile organic liquid through the membrane as a vapor onto the permeate side of the membrane, and collecting the vapor on the permeate side of the membrane.

[0016] In another aspect, the present disclosure relates to a hydrophobic distillation membrane having a hydrophobic surface, the membrane comprising: a base membrane including a base membrane surface having a surface energy of at least 47 mN / m; and fluorinated groups attached to the base membrane surface to produce a hydrophobic surface having a surface energy of less than 47 mN / m.

[0017] In yet another aspect, the present disclosure relates to a method for preparing a hydrophobic distillation membrane, the method comprising providing a base membrane comprising a base membrane surface having a surface energy of at least 30 mN / m, and attaching fluorinated groups to the base membrane surface to reduce the surface energy to less than 25 mN / m. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 illustrates an exemplary system and method for membrane distillation as described. [Figure 2] FIG. 1 shows an example of a method for preparing a hydrophobic membrane herein. [Figure 3] FIG. 1 shows an example of a method for preparing a hydrophobic membrane herein. [Figure 4] FIG. 1 shows the surface tension of a mixture of methanol and water. [Figure 5] FIG. 1 illustrates an example of a vacuum membrane distillation process. [Figure 6] 1 shows the reduction of hydrocarbon impurities in an IPA solution by a single-layer porous polymer membrane prepared according to Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following description relates to a membrane distillation process that uses a hydrophobic membrane to separate components of a liquid feed. The present specification also relates to a hydrophobic membrane that includes a hydrophobic surface having fluorinated groups attached to the surface, and a method for preparing a hydrophobic membrane by attaching fluorinated groups to a porous membrane surface.

[0020] According to the described membrane distillation method, a liquid feed composition ("liquid feed") is generally a method using a hydrophobic membrane, which means a porous distillation membrane having at least a hydrophobic surface. The liquid feed contains at least one volatile organic liquid. The liquid feed contacts the hydrophobic surface of the hydrophobic distillation membrane ("hydrophobic membrane") but does not wet the hydrophobic surface. Volatile (vapor-forming) organic components of the liquid feed present at the interface between the liquid and the hydrophobic surface can pass through the membrane in vapor form, while less volatile or non-volatile components of the liquid feed remain in the liquid phase and do not pass through the membrane.

[0021] More specifically, the liquid feed stream contacts the hydrophobic surface of a hydrophobic distillation membrane on one side of the membrane (the retentate side). The surface energy of the membrane's hydrophobic surface is lower than the surface tension of the liquid feed. The liquid feed does not wet the hydrophobic surface, even under operating conditions that may include pressure and high temperature. At the interface between the membrane surface and the liquid surface, the liquid feed generates a vapor of the volatile organic liquid that is part of the liquid feed. The vapor is derived from one or more volatile components of the liquid feed, for example, a combination of one or more volatile organic liquids contained in the liquid feed. Because the liquid feed does not wet the membrane surface, vapor molecules of the volatile components of the liquid feed can enter the membrane pores and pass through the membrane as a vapor. Upon passing through the membrane to the other side of the membrane (the permeate side of the membrane), the vapor is collected. Nonvolatile components or components with lower relative volatility that are also present in the liquid feed and do not form a vapor do not pass through the membrane.

[0022] In comparison to previous membrane distillation methods that have been used to process aqueous liquids as liquid feeds and that involve passing water vapor through a porous hydrophobic distillation membrane, the methods described herein can be used to process liquid feeds that contain significant amounts of volatile organic liquids and can operate by passing organic vapors derived from the volatile organic liquids (as opposed to water vapor) through a hydrophobic distillation membrane.

[0023] Examples of useful or preferred liquid feed compositions may contain at least one volatile organic liquid in a substantial amount, e.g., at least 20 or 30 weight percent, e.g., up to or exceeding 40, 50, 60, 70, 80, 90, or 95 weight percent based on the total weight liquid feed. The liquid feed may contain a single type of volatile organic liquid in an amount within these ranges, e.g., a single type of organic solvent such as isopropyl alcohol. Alternatively, the liquid feed may contain two or more different types of volatile organic liquids in total amounts within these ranges, e.g., an organic solvent such as isopropyl alcohol combined with another organic solvent in a total amount within one of these ranges.

[0024] The term "volatile organic liquid" is used herein to include any organic compound that can be in liquid form and that forms a vapor, e.g., at room temperature, consistent with the meaning of the term in the chemical arts. Examples of volatile organic liquids include organic solvents that can be used to dissolve other substances (e.g., as a solvent to dissolve solutes), disperse other substances, form processing liquids or coatings, as a medium for chemical reactions, as a cleaning agent, and other known uses. Without limiting the present disclosure, organic liquids considered to be "volatile organic liquids" can have a boiling point (at atmospheric pressure) of less than 150°F (or 65.6°C), e.g., less than 130, 120, 100, 90, 80, or 70°F (54.4, 48.9, 37.8, 32.2, 26.7, or 21.1°C). Examples of boiling points of volatile organic liquids include 80.3°F (26.8°C) (isopropyl alcohol), 64.5°F (18.1°C) (methanol), 56.1°F (13.4°C) (acetone), 80.4°F (26.9°C) (benzene), and 111°F (43.4°C) (toluene).

[0025] Examples of specific types of volatile organic liquids include hydrocarbon compounds that generally contain one or more carbon atoms bonded to a hydrogen atom and any non-carbon, non-hydrogen substituents, such as oxygen, nitrogen, sulfur, or halogens. The compounds can be saturated or unsaturated (e.g., containing one or more double bonds). Examples include aromatic compounds such as benzene, turpentine, and toluene; saturated alkanes such as hexane and heptane; lower alcohols such as methanol, ethanol, butanol, and isopropanol; esters and ethers such as hydrofluoroethers and diethyl ether; ketones such as acetone and methyl ethyl ketone (MEK); amines; and nitrated and halogenated hydrocarbons such as tetrachloroethylene.

[0026] The volatile organic liquid contained in the liquid feed preferably has a surface tension (measured separately from the liquid feed) lower than the surface tension of water, e.g., lower than 50, 40, 30, 25, or 22 mN / m, measured at standard temperature and pressure conditions. Whether the volatile organic liquid contacts a surface in pure form or is part of the liquid feed, the volatile organic liquid should have a surface tension that prevents it from wetting the surface of the hydrophobic membrane used in the described membrane distillation method under non-operating conditions, i.e., conditions outside the membrane distillation process (e.g., at standard temperature and pressure). Furthermore, during the membrane distillation process, under operating conditions that may include high temperature, high pressure, or both, the volatile organic liquid should not wet the surface of the hydrophobic membrane used in the described membrane distillation method when the volatile organic liquid contacts a surface in pure form or when the volatile organic liquid is a component of the liquid feed.

[0027] The liquid feed may contain other organic or inorganic materials such as water, contaminants (e.g., dissolved metals, non-volatile organic residues, etc.), inorganic non-aqueous materials (e.g., solvents), such as liquid ammonia, acids, bases, etc. For example, the liquid feed may contain up to or more than 20, 40, or 50 weight percent water based on the total weight liquid feed.

[0028] The liquid feed has a surface tension that is lower than the surface tension of water. Depending on the composition of the liquid feed, the surface tension of the liquid feed can be less than 50, 40, 30, 25, 22, 21, or 20 mN / m, measured at standard temperature and pressure conditions.

[0029] Depending on the source and use (commercial application) of the liquid feed, for example, if the liquid feed is used in a commercial manufacturing process, the liquid feed may contain various types of impurities, such as dissolved metals, non-volatile organic residues, and other inorganic residues. As one example, the liquid feed may contain one or more dissolved metals in any amount, such as amounts ranging from 0.1 parts per billion (ppb) to 100 ppb. As another example, depending on the source and use of the liquid feed, it may contain any amount of non-volatile organic residues. The described membranes and methods may be used with liquid feeds containing amounts of non-volatile organic residues in the range of 0.1 to 10 weight percent, e.g., 0.5 to 1, 2, or 5 weight percent, based on the total weight liquid feed. In other applications, the liquid feed may contain substantially less non-volatile organic residues, e.g., amounts ranging from 1 or 10 to 5,000 parts per million (ppm), e.g., 50 or 100 to 1,000 or 2,500 ppm.

[0030] A specific example of a liquid feed composition that can be processed by the membrane distillation method described is an isopropyl alcohol cleaning solution of the type used for evaporative cleaning of semiconductor wafers. This type of liquid feed may contain a significant amount of isopropyl alcohol in combination with amounts of one or more dissolved metals, a certain amount of nonvolatile organic residue, and possibly a certain amount of water. The amount of isopropyl alcohol may be at least 40 or 50 weight percent, e.g., up to or exceeding 55, 60, 70, 80, 90, 95, 98, or 99 weight percent isopropyl alcohol, based on the total weight liquid feed. The amount of water may be less than 40 weight percent, e.g., less than 30, 20, 10, 5, 2, or 1 weight percent water, based on the total weight liquid feed. The one or more dissolved metals may be present in an amount of 0.1 parts per billion (ppb) to 100 ppb of total dissolved metal(s). Nonvolatile organic residues may be present in amounts ranging from 1 or 10 to 5,000 parts per million (ppm), for example, from 50 or 100 to 1,000 or 2,500 ppm, based on the total weight liquid feed.

[0031] Non-limiting examples of non-volatile organic residues that may be present in isopropyl alcohol cleaning solutions include non-polar C12 to C30 compounds, dodecene, diisopropylamine, tetramethylbenzidine, nonanol, amines (e.g., heptanamine, trimethylamine, N-N-diisopropylethylamine), ketones (e.g., 2-pentanone, acetone), alcohols (e.g., tert-butyl alcohol, ethanol), 3,3',5,5'-tetramethylbenzidine, and non-polar compounds (e.g., dodecene, and non-polar straight-chain hydrocarbons of C14 or greater).

[0032] According to one example of a method for treating a liquid supply in the form of an isopropyl alcohol cleaning solution (used in a wafer cleaning process), the cleaning solution contains dissolved metals, nonvolatile organic residues, and mostly isopropyl alcohol, e.g., at least 90, 95, 98, or 99 weight percent isopropyl alcohol, and is essentially water-free (e.g., less than 0.5 or 0.1 weight percent water). A stream of the isopropyl alcohol cleaning solution is contacted with the hydrophobic surface of a hydrophobic distillation membrane on one side of the membrane (the retentate side). The membrane's surface energy may be less than 22, 21, or 20 mN / m, which may be less than the surface tension of the isopropyl alcohol cleaning solution, which may be approximately 21 or 22 mN / m. The isopropyl alcohol cleaning solution may be heated (e.g., to a temperature in the range of 20 to 78 degrees Celsius) and may be under pressure while in contact with the surface of the hydrophobic membrane. Under these operating conditions, the isopropyl alcohol cleaning solution does not wet the contact surface of the hydrophobic membrane.

[0033] The isopropyl alcohol in the isopropyl alcohol wash solution exists in vapor form at the interface between the hydrophobic membrane surface and the liquid surface of the isopropyl alcohol wash solution. Because the isopropyl alcohol wash solution does not wet the membrane surface, the vapor isopropyl alcohol molecules enter the membrane pores and pass through the membrane as a vapor. The isopropyl alcohol vapor can be collected upon passing through the membrane to the opposite side (the permeate side of the membrane). Dissolved metals and nonvolatile organic components present in the isopropyl alcohol wash solution (liquid feed) on the retentate side of the membrane do not pass through the membrane and remain on the retentate side of the membrane.

[0034] 1 , an example membrane distillation apparatus 100 includes a body 110 containing a hydrophobic membrane 112. The body 110 defines a feed space 114 on a retentate side 116 (or "high pressure side") of the hydrophobic membrane 112 and a permeate space 118 on a permeate side 120 (or "low pressure side") of the hydrophobic membrane 112. A liquid feed inlet 122 is in fluid communication with the feed space 114 to allow the flow of an incoming liquid feed 130 (described herein) into the feed space 114.

[0035] At least the surface of the hydrophobic membrane 112 facing the retentate side 116 is sufficiently hydrophobic to prevent wetting of the surface by contact with the liquid feed 130. The membrane 112 may be in the form of a flat sheet, a hollow tubular membrane, or any other useful configuration. In the case of a membrane 112 in the form of a hollow tubular membrane, at least the outer wall of the membrane comprises the described hydrophobic surface, and the outer wall can be oriented toward the feed space 114 so as to contact the liquid feed 130 flowing therethrough, and the inner wall of the hollow tubular membrane can be positioned toward the permeate space 118.

[0036] The liquid feed 130 may be any liquid feed described herein, such as an isopropyl wash solution containing substantially only isopropyl alcohol, non-volatile organic residues, and one or more dissolved metals. The liquid feed 130 is contained within the feed volume 114 in a liquid form that does not wet the retentate side 116 of the hydrophobic membrane 112. However, isopropyl alcohol molecules 132 (or another volatile organic liquid component of the liquid feed) may be present in vapor form within the feed volume 114 at the interface between the retentate side 116 of the hydrophobic membrane 112 and a liquid surface (not specifically shown) of the liquid feed 130. The vapor-form isopropyl alcohol molecules 132 flow as a vapor through the pores 124 of the hydrophobic membrane 112.

[0037] The non-volatile organic residues, dissolved metals, or both (126) remain in the liquid phase of the liquid feed composition 130, are not present in vapor form, and do not pass through the hydrophobic membrane 112. The liquid feed 130 that flows across or past the membrane 112 through the feed space 114 and does not pass through the hydrophobic membrane 112 becomes the retentate 142 and exits the feed space 114 through the liquid feed outlet 150.

[0038] During operation, the liquid feed 130 enters the feed space 114 and contacts, but does not wet, the surface of the hydrophobic membrane 112 on the retentate side 116. When in contact with the hydrophobic surface of the hydrophobic membrane 112, without wetting the surface, the volatile organic liquid in the liquid feed 130 vaporizes, passes through the hydrophobic membrane 112 (see arrows), and forms gas molecules that exit the membrane in vapor form (molecular form) on the permeate side 124 of the hydrophobic membrane 112. The vapor of the volatile organic liquid (e.g., isopropyl alcohol molecules) 132 that passes through the permeate side 118 can be collected and treated as desired, such as by condensation.

[0039] If desired, the liquid supply 130 may be heated to a temperature that facilitates the migration of volatile organic vapors (e.g., isopropyl alcohol) through the hydrophobic membrane 112, for example, to a temperature in the range of 20 to 78 degrees Celsius.

[0040] Hydrophobic membranes include porous base membranes ("base membranes") that include a base membrane surface to which fluorinated groups have been added to reduce the surface energy of the base membrane surface, i.e., to increase the hydrophobicity and decrease the hydrophilicity of the surface. After the fluorinated groups have been added, the surface is hydrophobic or strongly hydrophobic, e.g., having a surface energy of less than 47, 30, 22, or 20 mN / m, as determined by a standard wetting fluid test.

[0041] According to certain specific exemplary embodiments, the base membrane surface is hydrophilic before the fluorinated groups are added, for example, the base membrane surface has a surface energy of at least 42 mN / m before the fluorinated groups are added.

[0042] A base membrane having a hydrophilic surface can be prepared by forming the base membrane from a hydrophilic polymer ("hydrophilic base polymer"), such as nylon. In such cases, when the hydrophilic polymer forms the base membrane and the base membrane surface, the surface can be hydrophilic, e.g., have a surface energy of at least 47 mN / m.

[0043] According to other exemplary embodiments, a base membrane comprising a hydrophilic surface can be produced from a membrane made of a hydrophobic polymer and initially having a hydrophobic surface (e.g., a surface exhibiting a surface energy of less than 40 mN / m) by treating the hydrophobic surface with a method that increases the surface energy of the hydrophobic surface. For example, a base membrane having a hydrophilic surface can be prepared by preparing a membrane from a hydrophobic polymer ("hydrophobic base polymer"), which initially comprises a membrane surface having a surface energy of less than 40 mN / m. The hydrophobic surface can be treated, for example, by known methods, to increase the surface energy of the membrane surface and make it more hydrophilic, producing a base membrane having a hydrophilic surface, e.g., a surface with a surface energy of greater than 40 mN / m, but made of an underlying hydrophobic polymer.

[0044] Methods for increasing the surface energy of a membrane surface are sometimes referred to as "hydrophilizing" the surface. According to the methods and membranes described, membrane surfaces that are initially hydrophobic, e.g., having a surface energy of less than 40 mN / m, can be treated (hydrophilized) to increase the surface energy to greater than 40 mN / m, e.g., at least 42, 47, 50, 60, or 70 mN / m. After the surface energy has been increased to this range, the membrane surface can be treated to add fluorinated groups to make the surface hydrophobic or strongly hydrophobic, e.g., to have a surface energy of less than 50, 47, 30, 22, or 20 mN / m.

[0045] An example method for making the described hydrophobic membrane is shown in Figures 2 and 3. Referring to Figure 2, a base membrane 20 is made of a hydrophilic polymer (e.g., nylon) and has a hydrophilic base membrane surface 30. In step (i), a fluorinated material 22 is chemically added to the hydrophilic surface 30 of the base membrane 20 to produce a hydrophobic surface 32 of the hydrophobic membrane 40(a).

[0046] Referring to FIG. 3 , membrane 20 is made from a hydrophobic polymer (e.g., polyolefin) and includes an initially hydrophobic membrane surface 30. In step (i), hydrophobic surface 30 is treated, or “hydrophilized,” to form a hydrophilic surface 34. The resulting base membrane 39 includes hydrophobic membrane 20 and a hydrophilic (“hydrophilized”) surface 34. In the next step (ii), a fluorinated material 38 is chemically added to the hydrophilic surface 34 of base membrane 39 to produce the hydrophobic surface 40 of hydrophobic membrane 40(b). The surface energy of a membrane surface is a well-known concept related to the wetting properties of the surface of a solid material. The surface energy of a membrane can be measured using standard tests, such as contact angle measurements of a drop of a standard test liquid with a known surface tension, among others. Surface energy is measured in units of force per unit length, e.g., mN / m. For membranes, a higher surface energy means the membrane is more hydrophilic (or less hydrophobic) and more easily wetted by liquids. A lower surface energy means that the membrane is less hydrophilic (or more hydrophobic) and less likely to be wetted.

[0047] Generally, useful or preferred hydrophobic membranes herein may have a hydrophobic surface that exhibits a surface energy that allows the membrane to be used in the described manner with a liquid feed containing a certain amount of volatile organic compounds, but the liquid feed does not wet the hydrophobic surface of the membrane. Examples of useful or preferred surface energies of the hydrophobic surface of the described hydrophobic membranes may be less than 50 mN / m, for example, less than 40, 30, 25, 22, 21, or 20 mN / m, as measured, for example, by a standard wetting liquid test.

[0048] All surface tension and surface energy values ​​reported herein are determined at room temperature unless otherwise specified. All surface energy values ​​reported herein are determined using standard liquid tests unless otherwise specified.

[0049] The hydrophobic membrane may be in the form of a "sheet" or "film" having two opposing major surfaces and a thickness between the two surfaces, at least one of which is hydrophobic as described herein. Alternatively, the hydrophobic membrane may be in the form of a hollow fiber tube having an inner hollow opening, an inner sidewall, an outer sidewall, and a thickness between the inner and outer sidewalls. At least one surface of the hollow fiber tube is hydrophobic as described herein, e.g., the surface of the outer sidewall.

[0050] The hydrophobic membrane may be selected to provide desired physical characteristics including porosity, pore size, bubble point, and thickness.

[0051] The hydrophobic membrane can have any thickness that enables it to function according to the methods herein. Useful or preferred thicknesses can range from 5 to 300 microns, e.g., 10 or 20 to 50, 100, or 200 microns, and these ranges are useful for various membrane configurations, including sheet membranes and hollow fiber tubular membranes.

[0052] Hydrophobic membranes can have any porosity that allows the membrane to be effective as described herein for use in membrane distillation processes. Exemplary porous membranes can have porosities ranging from 30 to 90 percent, for example, 40 to 80 percent (by volume). As used herein, and in the art of porous membranes, the "porosity" (sometimes referred to as porosity) of a porous membrane is a measure of the void (i.e., "empty") space within the membrane as a percentage of the membrane's total volume, calculated as the ratio of the membrane's void volume to the membrane's total volume. A body with zero percent porosity is a completely porous solid.

[0053] The porosimetry bubble point test is a test of a porous membrane that measures the pressure required to force air through the pores of the membrane after wetting the membrane with a particular liquid. The bubble point test is a well-known method for determining the pore size of a membrane. Useful or preferred hydrophobic membranes herein may have a porosimetry bubble point in the range of 5 to 200 pounds per square inch, as measured by the ethoxy-nonafluorobutane bubble point test [is this average?].

[0054] The hydrophobic membrane consists of a base membrane to which fluorinated groups are added to create a hydrophobic or strongly hydrophobic surface.

[0055] A variety of different polymers are available for forming the base membrane. These include hydrophilic polymers and hydrophobic polymers that can be hydrophilized before adding fluorinated groups. Non-limiting examples of polymers that can be used to prepare the base membrane include polyolefins (e.g., polypropylene, polyethylene, polyhaloolefins), polyesters, polyimides, polyetherimides, polysulfones, polyethersulfones, polycarbonates, regenerated cellulose, mixed cellulose esters, and agarose, as well as fluoropolymers, and other general and specific types of useful polymers.

[0056] More specific examples of hydrophobic polymers include polyethylene (e.g., ultra-high molecular weight polyethylene (UPE)), polypropylene, alpha-polyolefins, poly-3-methyl-1-butene, poly-4-methyl-1-butene, and copolymers of ethylene, propylene, 3-methyl-1-butene, or 4-methyl-1-butene with each other or with small amounts of other olefins, polyhaloolefins such as polytetrafluoroethylene, polyvinylidene fluoride, and copolymers thereof with other fluorinated or non-fluorinated monomers.

[0057] Suitable hydrophilic polymers include nylons, polyesters such as polyethylene terephthalate and polybutylene terephthalate, and related copolymers, any of which may be useful to form base membranes having surface energies of at least 47, 50, 60, 70, or 72 mN / m or more without being hydrophilized.

[0058] Fluorinated groups can be added to the surface of a base film having a surface energy of at least 42, 47, 50, 60, or 70 mN / m to reduce the surface energy of the surface to a hydrophobic or superhydrophobic level, for example, less than 42, 40, 30, 25, 22, or 20 mN / m.

[0059] Exemplary methods for attaching fluorinated groups to the base membrane surface include grafting techniques, in which the fluorinated groups are chemically bonded to the surface of the base membrane, as well as "gel polymerization" techniques, in which a cross-linked polymer network containing fluorinated groups is formed on the surface of the base membrane without the network being chemically bonded (chemically bonded) to the surface.

[0060] Examples of useful fluorinated groups include perfluoroalkyl groups, such as perfluorooctyl groups, perfluorohexyl groups, etc. Fluorinated groups can be derived from fluorinated monomers, such as fluorinated (e.g., perfluorinated) acrylates, such as perfluorooctyl acrylate. Examples of perfluoroacrylate monomers and methods for applying perfluoroacrylate monomers to porous membranes are also described in International (PCT) Patent Publication WO 2017 / 161241, the entire contents of which are incorporated herein by reference. The illustrated monomers include perfluoroacrylate monomers containing the perfluoro-alkyl groups perfluoro-propyl, perfluoro-butyl, perfluoro-sec-butyl, perfluoro-t-butyl, perfluoro-pentyl, perfluoro-hexyl, perfluoro-n-heptyl, perfluoro-octyl, perfluoro-nonyl, perfluoro-decyl, perfluoro-undecyl, perfluoro-dodecyl, perfluoro-tridecyl, perfluoro-tetradecyl, perfluoro-pentadecyl, perfluoro-hexadecyl, perfluoro-heptadecyl, perfluoro-octadecyl, perfluoro-nonadecyl, perfluoro-icosadecyl, perfluoro-2-methylbutyl, perfluoro-2-methylpentyl, perfluoro-2-ethylbutyl, perfluoro-3-methylpentyl, perfluoro-4-methylpentyl. According to the grafting technique, fluorinated groups can be chemically attached (i.e., grafted and covalently chemically bonded) to the polymer chains of the polymeric material forming the surface of the base membrane. For example, if the base membrane is made of nylon, the fluorinated groups are chemically bonded to the nylon polymer on the base membrane surface. The fluorinated groups can be derived from fluorinated monomers that become chemically bonded to the surface of the base membrane through a chemical reaction, including a UV-initiated reaction, between the fluorinated monomer and the polymeric surface of the base membrane. The fluorinated monomers react with the polymer on the base membrane surface to become chemically bonded. Optionally, the fluorinated monomers may be reacted in combination with one or more optional comonomers to form side chains attached to the polymeric material on the base membrane surface.The length of the side chain (ie, the number of fluorinated monomers and optional comonomers in the side chain) can be any useful length, for example, from 5 to 1000 monomers, or from 10 to 100 or 500 monomers.

[0061] According to a technique for forming a crosslinked polymer network coating on the surface of a porous membrane, sometimes referred to as the "gel polymerization technique," the polymer network is formed from a fluorinated monomer and a crosslinker, e.g., a monomer containing a bifunctional crosslinking molecule such as a bifunctional acrylate compound, which react to form a polymerized crosslinked coating in the presence of UV irradiation and a UV initiator.

[0062] A crosslinked polymer network coating containing fluorinated groups is formed on the surface of the membrane without the coating or the fluorinated groups chemically bonding to the membrane polymer. [Example]

[0063] Example 1: This example demonstrates the preparation of a surface modification solution containing a monomer and a crosslinker to form a coating and reduce the film surface energy.

[0064] In a typical experiment, a solution containing 0.72% Irgacure 651, 7% Zonyl TAN (perfluoroalkylethyl acrylate / ester perfluorohexylethyl acrylate copolymer), 1% hexanediol diacrylate crosslinker, and 91.28% decamethyltetrasiloxane was made at room temperature.

[0065] Example 2: This example demonstrates the preparation of a surface modification solution containing a monomer and a crosslinker to form a coating and increase the film surface energy.

[0066] In a typical experiment, a solution containing 0.4% Irgacure 2959, 7% dimethylacrylamide, 3% methylenebisacrylamide crosslinker, and 89.6% DI water was made at room temperature.

[0067] Example 3: This example demonstrates how a nylon membrane can be surface modified with a coating having polymerized and crosslinked Zonyl TAN polymer.

[0068] In a typical experiment, a sheet of nylon membrane (54 psi HFE bubble point, 175 microns thick) was immersed in the solution from Example 1 for 2 minutes. The membrane sheet was removed and placed between 1-mil polyethylene sheets. Excess solution was removed by rolling a rubber roller over the polyethylene / membrane sheet / polyethylene sandwich while it was lying flat on a table. The polyethylene sandwich was then taped to a transport unit that carried the assembly through a Fusion Systems broadband UV exposure lab unit, which emits radiation at wavelengths between 200 nm and 600 nm. The exposure time was controlled by the speed at which the assembly moved through the UV unit. In this example, the assembly moved through the UV chamber at 10 feet per minute. After exiting the UV unit, the membrane was removed from the sandwich and immediately placed in isopropyl alcohol (IPA) for 5 minutes. Following this cleaning procedure, the membrane was dried on a holder in an oven operating at 50°C for 10 minutes.

[0069] The membrane prepared according to this procedure was not wetted by 100% IPA (surface tension 21.7 dyne / cm) and hexane (surface tension 18.4 dyne / cm), but was wetted by 100% pentane, suggesting a membrane surface tension of 15.8 dyne / cm.

[0070] Example 4 - Surface Energy Measurements A liquid will wet a porous polymer membrane if the surface tension of the liquid is less than the surface free energy of the membrane. For purposes of this disclosure, when a membrane is placed in contact with the liquid with the highest surface tension in a series of inert (standard) liquids, the porous membrane will be wetted by the liquid and will spontaneously wick the liquid within 2 seconds without the application of external pressure. In a representative example, a series of inert (standard) liquids were prepared by mixing methanol and water in different mass ratios. The surface tensions of the resulting liquids are shown in Figure 4 (plotted using surface tension data published in Lange's Handbook of Chemistry, 11th edition).

[0071] A 47 mm disc of nylon membrane (54 psi HFE bubble point, 175 micron thickness) was placed in a beaker and contacted with inert liquids, one at a time. For each liquid, the time required for the membrane to spontaneously wick the liquid was recorded. As shown in Table 1, 15% methanol, with a surface tension of 51.83 mN / m, was the liquid with the highest surface tension, wetting the membrane within 2 seconds. Table 1 TIFF0007801244000001.tif39170

[0072] Example 5: This example demonstrates how a UPE membrane can be surface modified with a polymerized and crosslinked hydrophilic coating and a coating with Zonyl TAN polymer.

[0073] In a typical experiment, a sheet of asymmetric UPE membrane (121 psi HFE bubble point, 80 micron thickness) was immersed in the solution from Example 2 for 2 minutes. The membrane sheet was removed and placed between 1 mil polyethylene sheets. Excess solution was removed by rolling a rubber roller over the polyethylene / membrane sheet / polyethylene sandwich while it was lying flat on a table. The polyethylene sandwich was exposed to UV light with wavelengths ranging from 200 to 600 nm at a speed of 10 feet per minute. After exiting the UV unit, the membrane was removed from the sandwich and immediately placed in DI water, where it was washed by soaking for 5 minutes. The treated membrane sample was then washed in isopropyl alcohol for 5 minutes. Following this cleaning procedure, the membrane was dried on a holder in an oven operating at 50 °C for 10 minutes.

[0074] The surface energies of membranes prepared according to this procedure were tested as outlined in Example 4. The asymmetric membrane had a surface energy of 47.9 mN / m on the fine side (i.e., the side of the membrane with small pores) and 63.5 mN / m on the coarse side (i.e., the side of the membrane with large pores).

[0075] The membrane sheet was then immersed for an additional 2 minutes in a solution containing 1.08% Irgacure 651, 13% Zonyl TAN (perfluoroalkylethyl acrylate / ester perfluorohexylethyl acrylate copolymer), 1.9% hexanediol diacrylate crosslinker, and 84.02% decamethyltetrasiloxane. The membrane sheet was removed and placed between 1-mil polyethylene sheets. Excess solution was removed by rolling a rubber roller over the polyethylene / membrane sheet / polyethylene sandwich while it was lying flat on a table. The polyethylene was exposed to UV light with wavelengths ranging from 200 to 600 nm at a speed of 10 feet per minute. The membrane was then removed from the sandwich and immediately placed in 100% IPA water, where it was washed by immersing the membrane for 5 minutes. Following this cleaning procedure, the membrane was dried on a holder in an oven operating at 50°C for 10 minutes.

[0076] Both the fine and coarse sides of the membranes prepared according to this procedure were not wetted by 100% IPA (surface tension 21.7 mN / m) and hexane (surface tension 18.4 mN / m). The coarse side of the membrane (the side of the membrane with large pores) was wetted by 100% pentane (15.8 dynes / cm), but the fine side of the membrane (the side of the membrane with small pores) was not wetted by 100% pentane.

[0077] Example 6: This example demonstrates how a membrane distillation system such as that shown in Figure 5 can be used to purify a solution of IPA spiked with hydrocarbon model impurities (C7-C30).

[0078] A 500 g feed solution of 2 ppm concentration was prepared by adding 1 g of hydrocarbon standard (49451-U, 1000 ppm, Sigma) to isopropyl alcohol. The solution was heated to 45°C in the feed reservoir using an oil bath and pumped at a flow rate of 50 ml / min through a stainless steel cross flow cell containing the membrane from Example 5 and recycled back to the feed reservoir. A vacuum pump was used to pull a vacuum of 5 in Hg across the membrane in the flow cell, transporting the IPA vapor through two parallel condensers, collecting 1.33 g of condensed permeate.

[0079] The concentrations of hydrocarbon impurities in the feed and condensate samples were determined using a 7890B series GC system equipped with a 5977A MSD detector.

[0080] Figure 6 demonstrates that the concentration of hydrocarbons is reduced in the permeate, with removal efficiencies ranging from 19 to 70%.

[0081] Example 7 This example demonstrates how a UPE membrane can be surface modified with a coating having polymerized and crosslinked Zonyl TAN polymer.

[0082] In a typical experiment, a sheet of asymmetric UPE membrane (121 psi bubble point, 80 microns thick) was immersed for 2 minutes in a solution containing 1.08% Irgacure 651, 13% Zonyl TAN (perfluoroalkylethyl acrylate / ester perfluorohexylethyl acrylate copolymer), 1.9% hexanediol diacrylate crosslinker, and 84.02% decamethyltetrasiloxane. The membrane sheet was removed and placed between 1 mil polyethylene sheets. Excess solution was removed by rolling a rubber roller over the polyethylene / membrane sheet / polyethylene sandwich while it was lying flat on a table. The polyethylene sandwich was exposed to UV light with wavelengths ranging from 200 to 600 nm at a speed of 10 feet per minute. The membrane was then removed from the sandwich and immediately placed in 100% IPA water. The membrane was then washed by immersing it for 5 minutes. Following this washing procedure, the membrane was dried on a holder in an oven operating at 50 °C for 10 minutes.

[0083] The coarse side of the membrane (the side with the larger pores) was wetted with 95% methanol (23.6 mN / m surface energy), and the fine side of the membrane (the side with the smaller pores) was wetted with 90% methanol (24.4 mN / m).

[0084] Having thus described several exemplary embodiments of the present disclosure, those skilled in the art will readily appreciate that still other embodiments may be made and used within the scope of the appended claims. Many advantages of the present disclosure that are covered by this document have been set forth in the foregoing description. It will be understood, however, that the present disclosure is in many respects merely illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts, without exceeding the scope of the present disclosure. The scope of the present disclosure is, of course, defined in the language in which the appended claims are expressed.

Claims

1. 1. A method for treating a liquid feed containing a volatile organic liquid, comprising: providing a liquid feed containing a volatile organic liquid; contacting a liquid feed stream with a hydrophobic surface of the hydrophobic distillation membrane on a retentate side of the hydrophobic distillation membrane, wherein the liquid feed does not wet the hydrophobic surface; passing the volatile organic liquid as a vapor through a hydrophobic distillation membrane to a permeate side of the hydrophobic distillation membrane; collecting vapor on the permeate side of the hydrophobic distillation membrane; Including, The hydrophobic distillation membrane a polymeric base membrane comprising a polymeric base membrane surface having a surface energy of at least 47 mN / m; a cross-linked polymer containing fluorinated groups that coats the surface of the polymeric base membrane to create a hydrophobic surface; wherein the hydrophobic surface has a surface energy of less than 20 mN / m.

2. 10. The method of claim 1, wherein the polymeric base membrane comprises a hydrophobic polymer and a hydrophilized surface having a surface energy of at least 47 mN / m.

3. 3. The method of claim 1 or 2, comprising reducing the pressure on the permeate side of the hydrophobic distillation membrane relative to the retentate side of the hydrophobic distillation membrane.

4. The liquid feed comprises, based on the total weight of the liquid feed: less than 50% by weight of water, and At least 50% by weight of a volatile organic liquid having a surface tension of less than 50 mN / m contains, or Contains at least 60% by weight of isopropyl alcohol; or The method of claim 1 , comprising dissolved metals, non-volatile organic residues, or both.

5. A hydrophobic distillation membrane having a hydrophobic surface, a polymeric base membrane comprising a polymeric base membrane surface having a surface energy of at least 47 mN / m; a cross-linked polymer containing fluorinated groups that coats the surface of the polymer base membrane to create a hydrophobic surface; wherein the hydrophobic surface has a surface energy of less than 20 mN / m.

6. The polymer base film surface has a surface energy of at least 50 mN / m; The hydrophobic distillation membrane of claim 5.

7. 6. The hydrophobic distillation membrane of claim 5, wherein the hydrophobic surface is not wetted by 100 percent isopropyl alcohol at a temperature of 72 degrees Fahrenheit (22.2 degrees Celsius) and ambient pressure.

8. a porosity of 30 to 90 percent (by volume); or a thickness in the range of 5 to 300 microns, or a bubble point in the range of 5 to 200 pounds per square inch as measured by the Ethoxy-nonafluorobutane Bubble Point Test; or Two or three of these The hydrophobic distillation membrane of claim 5, having

9. The hydrophobic distillation membrane according to any one of claims 5 to 8, a retentate space on the retentate side of the hydrophobic distillation membrane; a permeate space on the permeate side of the hydrophobic distillation membrane; a liquid supply inlet in communication with the retentate space; a retentate outlet in communication with the retentate space; a permeate outlet communicating with the permeate space; A separation device comprising:

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