CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 63/071,527 filed August 28, 2020, which is hereby incorporated by reference.

FIELD

[0002] The present invention relates generally to membranes and methods for separating contaminants from water, and more specifically to membranes and methods useful in desalination.

BACKGROUND

[0003] Along with technology development, industrialization that significantly contributed for welfare of mankind has also caused alarming global water demand. Water purification has been a challenging problem in the present world. There is a crucial need to improve water treatment technologies in a more energy efficient manner and alleviate stress to water resources.

[0004] Membrane technology is a potential candidate for feasible and economic water purification; however, while membranes have demonstrated good salt rejections, they have generally suffered from restricted flux across the membrane. There is a critical need to overcome the limitation of flux for desalination process using membranes.

SUMMARY

[0005] Embodiments of this disclosure relate to membranes useful in processes for the separation contaminates from water, processes of producing such membranes and processes of using such membranes. Thus, the membranes are useful in the separation of salts from water, for example the desalination of saline water such as produced water from an oil or gas well.

[0006] Accordingly, one aspect of this disclosure provides for a separation membrane for water desalination, the separation membrane comprising a microfiltration membrane having zinc oxide layers deposited thereon. The microfiltration membrane is an alumina (AI2O3) membrane. The alumina can be a-alumina, and in some instances the microfiltration membrane can consist of or consist essentially of a-alumina.

[0007] The microfiltration membrane has a pore size of from about 100 nm to about 1000 nm, and more typically from 150 nm to 500 nm. The microfiltration membrane can have a porosity of from about 10% to about 75%, or more typically from about 20% to about 50%.

[0008] In the above embodiments of this aspect, the separation membrane can have a Zn/Al ratio of at least 0.001, or optionally, at least 0.02 or at least 0.04. In embodiments, the ratio can be up to 0.12, or in some cases higher.

[0009] Generally, the zinc oxide layers will be deposited in multiple layers (such as by an atomic layer deposition process) each having a thickness of about 1 nm or less, or optionally of about 0.5 nm or less or of 0.3 nm or less. For example, there can be from about 4 to about 200 zinc oxide layers on the microfiltration membrane for a total zinc oxide thickness of from about 0.4 nm to about 200 nm. More typically, there will be from about 8 to about 150 zinc oxide layers or from 16 to 130 zinc oxide layers. Also, more typically the total thickness of the deposited layer will be from about 1 nm to about 175 nm, from about 2 nm to about 150 nm or from 60 nm to 130 nm.

[0010] Generally, the separation membrane will have a water flux of greater than 100 L m' ² h' ¹ , or greater than 120 L m' ² h' ¹ . While the separation can have a water flux of at least 160 L m' ² h' ¹ , more typically it will have a water flux of from 100 L m' ² h' ¹ to 160 L m' ² h' ¹ . For example, the separation membrane has a water flux at least 120 L m' ² h' ¹ , of at least 140 L m' ² h" or of at least 150 L m' ² h' ¹ . The separation membrane has a salt rejection of at least 95%, and can have a salt rejection of at least 98% or at least 99%.

[0011] The process of this disclosure typically comprises producing one of the above membranes by providing a microfiltration membrane; depositing multiple zinc oxide layers onto the microfiltration membrane in a chamber by an atomic layer deposition process operating on alternating steps of a first gaseous precursor and a second gaseous precursor; purging the chamber between the alternating steps; continuing the process until from about 4 to about 200 zinc oxide layers are on the microfiltration membrane so as to produce the separation membrane, wherein each layer has a thickness of about 1 nm or less.

[0012] In the process, the alternating steps can be carried out at a temperature from 50 °C to 300 °C, but more typically will be carried out from about 70 °C to about 200 °C, or from 150 °C to 200 °C, and at a pressure of less than 1 torr, or less than 0.5 torr.

[0013] In some of the embodiments, the process will deposit zinc oxide layers having a thickness of about 0.5 nm or less or of 0.3 nm or less. Additionally, in some of the embodiments there are from about 8 to about 150 zinc oxide layers deposited on the microfiltration membrane, and optionally from 16 to 130 zinc oxide layers.

[0014] Processes of this disclosure typically comprises desalinating of saline water by: providing one of the above described separation membranes; exposing a first side of the separation membrane to saline water; establishing a pressure differential across the membrane from the first side of the separation membrane to an opposing second side of the separation membrane so as to produce desalinated water on the opposing second side.

[0015] Among other applications, the process can be effective in removing salt contaminants from produced water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings included with this application illustrate certain aspects of the embodiments described herein. However, the drawings should not be viewed as exclusive embodiments. The subject matter disclosed herein is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will be evident to those skilled in the art with the benefit of this disclosure.

[0017] FIG. 1 is a schematic diagram of an atomic layer deposition (ALD) process suitable for use in producing the current separation membranes. [0018] FIG. 2 is a schematic diagram of a vacuum-assisted flow-through desolation process which can use the current separation membrane.

[0019] FIG. 3 shows images of Scanning Electron Microscope (SEM) micrographs of surface morphology for an a-alumina membrane before and after ZnO ALD.

[0020] FIG. 4 shows Energy Dispersive X-ray analyses (EDX) mapping of an a-alumina membrane before and after ZnO ALD.

[0021] FIG. 5A is a graph plotting ZN/A1 ratio versus the number of ALD cycles for an a-alumina membrane.

[0022] FIG. 5B is a graph of the mass of the a-alumina membrane versus the number of ALD cycles.

[0023] FIG. 6 is a graph of water contact angle of the a-alumina membrane with then number of ZnO ALD cycles.

[0024] FIG. 7 is a graph of water flux and ion rejection across the a-alumina membrane with the number of ZnO ALD cycles.

[0025] FIGS. 8A and 8B are graphs of ion concentration on a membrane surface (feed side) as a function of the number of desalination experiments for a membrane with cleaning (FIG. 8A) and without cleaning (FIG. 8B) in between desalination experiments.

[0026] FIG. 9 is images of EDX elemental mapping. In FIGS. 9(a-d) the images show Ca ²⁺ ion for the membrane with: FIG. 9(a) feed side with cleaning, FIG. 9(b) feed side without cleaning, FIG. 9(c) permeate side with cleaning, and FIG. 9(d) permeate side without cleaning; and FIGS. 9(e) and 9(h) show Na ⁺ ion for the membrane with: FIG. 9(e) feed side with cleaning, FIG. 9(f) feed side without cleaning, FIG. 9(g) permeate side with cleaning, and FIG. 9(h) permeate side without cleaning.

[0027] FIGS. 10A and 10B are graphs showing the concentration profiles of Na ⁺ (FIG. 10A and Ca ²⁺ (FIG. 10B) ions along the membrane cross-sections after seven desalination experiments with and without the cleaning process. DETAILED DESCRIPTION

[0028] The present disclosure may be understood more readily by reference to this detailed description as well as to the examples included herein. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments and examples described herein. However, those of ordinary skill in the art will understand the embodiments and examples described herein can be practiced without these specific details. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein.

[0029] In the description, component ratios will typically be reported as decimals; for example, 1.0 represents a ratio of 1 : 1 of a first component to a second component, and 0.5 represents a ratio of 1 :2 of the first component to the second component. Also, in the description, the term “atoms” may refer to neutrally charged atoms or to ions. For example, those skilled in the art will realize that generally salts will dissolve in water into their component ions but at times such ions may be referred to herein as atoms.

[0030] The membranes and processes described herein are useful in water purification. More specifically, the membranes are useful in the desalination of saline water. Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts. The salts can be mainly sodium chloride, but more generally may include other salts such as halide salts, sulfates, and borates, for example. Common ions in saline water include chloride, sodium, sulfates, magnesium, calcium and potassium, among others. The salt concentration is usually expressed in parts per thousand (ppt) or parts per million (ppm). “Saline water” as used herein generally includes all levels of non-zero salt concentration. Typically, as used herein, “saline water” will include relatively fresh water (500 ppm up to 1000 ppm); slightly saline water (around 1,000 to 3,000 ppm (0.1-0.3%)), moderately saline water (3,000 to 10,000 ppm (0.3-1%)); highly saline water 10,000 to 35,000 ppm (1-3.5%), and brines (above 35,000 ppm and typically about 35,000 ppm to about 260,000 ppm (26%)). For any embodiments, “saline water” be restricted to slightly saline water and saltier waters. The saline water herein includes, for example, seawater and produced water. Produced water is water that comes out of the well with the crude oil during crude oil production or natural gas production. Produced water contains soluble and non-soluble oil/organics, suspended solids, dissolved solids, and/or various chemicals used in the production process.

[0031] The current disclosure is directed at the use of membrane technology for feasible and economic water purification. While especially useful for removal of ions from various salts dissolved in the water, it has potential for removal of other impurities also. Membrane technology is attractive for water purification because it does not require additives, thermal energy, and media regeneration. It offers a chemically robust desalination option and improves the economics of desalination because the theoretical energy requirements are less than thermal alternatives.

[0032] The membranes of this disclosure not only demonstrate excellent performance in terms of salt rejections, but also have enhanced flux over prior-art membrane separation systems. Salt rejection refers to the quantity of salt removed during processing of saline water by the membrane. Flux refers to the movement of molecules across a membrane: in this case, flux is defined by the rate of diffusion or transport of water across the membrane.

[0033] Accordingly, in one aspect, the present disclosure relates to systems and processes for desalinating of saline water. The systems and processes utilize a separation membrane comprising a microfiltration membrane having zinc oxide thereon. Generally, the separation membrane of this disclosure will have a water flux of greater than 100 L m' ² h' ¹ , or greater than 120 L m' ² h' ¹ . While the separation can have a water flux of at least 160 L m' ² h' ¹ , more typically it will have a water flux of from 100 L m' ² h' ¹ to 160 L m' ² h' ¹ . For example, the separation membrane can have a water flux at least 140 L m' ² h' ¹ , or can have a water flux of at least 150 L m' ² h' ¹ . The separation membrane has a salt rejection of at least 95%, and can have a salt rejection of at least 98%, at least 99% or at least 99.5%.

[0034] The microfiltration membrane is a porous alumina (AI2O3) membrane. Currently, membranes composed of a-alumina are preferred, and in some instances, the microfiltration membrane can consist of or consist essentially of a-alumina. The microfiltration membranes of this disclosure have a pore size of from about 100 nm to about 1000, and more typically from 150 nm to 500 nm. The microfiltration membrane can have a porosity of from about 10% to about 75%, or more typically from about 20% to about 50%. [0035] The above described microfiltration membranes have the zinc oxide deposited on thereon as one or more zinc oxide layers to form the separation membrane of this disclosure. As further described below, the zinc oxide layers generally will be deposited in multiple layers each having a thickness of about 1 nm or less, or optionally of about 0.5 nm or less, or of 0.3 nm or less. As will be realized, each layer will be non-zero in thickness (>0 nm). Typically, a layer can be at least 0.1 nm, at least .05 nm or at least 0.1 nm. For example, there can be from about 4 to about 200 zinc oxide layers on the microfiltration membrane for a total zinc oxide thickness of from about 0.4 nm to about 200 nm. More typically, there will be from about 8 to about 150 zinc oxide layers or from 16 to 130 zinc oxide layers. Also, more typically the total thickness of the deposited layer will be from about 1 nm to about 175 nm, from about 2 nm to about 150 nm or from 60 nm to 130 nm.

[0036] The resulting separation membrane will generally have a Zn/Al ratio of at least 0.001. More typically, the Zn/Al ratio will be at least 0.01, at least 0.02, or at least 0.04. Generally, the Zn/Al ratio will be no greater than 0.15, but more typically no greater than 0.14, or no greater than 0.12. For example, the Zn/Al ratio can be from .005 to .015, or from .01 to 0.14, or from 0.04 to 0.12.

[0037] Those skilled in the art will realize from the above that the resulting separation membrane will have a pore size smaller than the pristine microfiltration membrane due to the layering of zinc oxide. For example, the pore size reduction can be about 50 nm or less depending on the number of layers. However, it is generally preferred that the pore size of the resulting separation membrane remains in about the same size range as for the pristine microfiltration membrane, i.e. about 100 nm to about 1000 nm, or more preferably about 150 nm to about 500 nm.

[0038] The above-described membrane can be produced by depositing multiple zinc oxide layers onto the microfiltration membrane in a chamber by an atomic layer deposition (ALD) process operating on alternating steps of a first gaseous precursor and a second gaseous precursor. The chamber is purged between the alternating steps.

[0039] ALD is a chemical vapor deposition process that is based upon surface limiting chemical reactions between precursors and a substrate. ALD method is suitable for depositing film with controllable thickness even at sub-nanometer scale. It operates on alternating, selflimiting chemical reactions between gaseous precursors and a solid surface to deposit thin films in a layer-by-layer fashion. Because the self-terminating surface reactions along with gaseous diffusion of precursor molecules induce conformal and uniform coating, ALD is well suited for catalyst synthesis and surface fabrications. ALD with metal oxides like ZnO and AI2O3 increase the hydrophilicity of the membrane surface, which makes ALD useful for water desalination.

[0040] For example, FIG.l illustrates a suitable ALD process that was used for the Examples. The ALD process of FIG. 1 uses the following mechanism:

ZnfLjH;;}? 4- H2O Cgi — * ZnO - 2C3H4 (g i

During the ALD process, an a-alumina membrane is exposed to a first precursor of diethylzinc, Zn(C2H5)2, which results in zinc being deposited on the membrane. Next the system is purged to remove and then water is introduced as the second precursor so as to produce a ZnO layer on the membrane. The system is purged again and the process can be repeated for a predetermined number of cycles (4, 8, 16, 64, and 128) to coat one or more thin layers of ZnO with a film on the membrane. In between the dosing of each precursor, the chamber is purged with N2 to ensure that the precursors did not react in vapor phase but rather at the surface of the alumina membranes.

[0041] In the current process, the alternating steps can be carried out at a temperature from 50 °C to 300 °C, from about 70 °C to about 200 °C or from 150 °C to 200 °C, and at a pressure of less than 1 torr, or less than 0.5 torr. The ALD process is continued until from about 4 to about 200 zinc oxide layers are on the microfiltration membrane so as to produce the separation membrane.

[0042] As will be realized from the above discussion on the separation membrane, the thickness of each layer is generally 1 nm or less, or optionally of about 0.5 nm or less, or of 0.3 nm or less. Generally, it is preferred that there be from about 8 to about 150 zinc oxide layers deposited on the microfiltration membrane, and more preferably from 16 to 130 zinc oxide layers, or from 32 to 120 zinc oxide layers deposited. For example, the total thickness of the deposited layer typically can be from about 1 nm to about 175 nm, from about 2 nm to about 150 nm or from 40 nm to 100 nm.

[0043] The separation membrane can be used in any suitable process which places the saline water in contact with the membrane, generally with a pressure differential across the membrane. For example, a first side of the separation membrane can be exposed to saline water, and a pressure differential established across the membrane from the first side of the separation membrane to an opposing second side of the separation membrane so as to produce desalinated water on the opposing second side. For example, the process can utilize vacuum-assisted flow- through. The pressure differential generally can be around 1 atm. For example, the pressure differential can be at least about 0.5 atm, at least 0.75 atm or at least 1 atm, and the pressure differential can be up to about 5 atm, up to about 3 atm or up to 2 atm. Under such conditions, the water portion of the mixture will pass through the membrane and the ions will be held back by the membrane, or not pass through. As will be appreciated, such membranes generally have two surfaces with a large surface area in comparison with the edges or thickness of the membrane. The positioning of the membrane is described in relation to these two large-area surfaces.

[0044] In some cases, it can be helpful to periodically clean the separation membrane that is used in desalination. The cleaning removes ions which become deposited on the separation membrane by the desalination. For example, the separation membrane can be immersed in an ultrasonication bath. Generally, the ultrasonication bath can be at room temperature. Ultrasonic membrane cleaning uses high-frequency sound waves to agitate the aqueous solution which further acts on retained ion inside tortuous pores of the membrane surface. In some applications, it can be advantageous to calcine the separation membrane prior to the ultrasonication bath, such as calcining in stagnant air at from about 350 °C to 650 °C for from about 1 h to about 5 h.

[0045] EXAMPLES

[0046] The membranes, their manufacture and their use can be better understood with reference to the following examples. The examples illustrate specific embodiments consistent with the present disclosure but do not limit the scope of the disclosure or the appended claims. Concentrations and percentages are by weight unless otherwise indicated. [0047] Membrane Synthesized by Atomic Layer Deposition Process

[0048] A thin layer of ZnO was coated on the a-alumina membranes (1 in. diameter, 1 mm thickness, -200 nm pore size, and -25% porosity from Coorstek) by ALD. The ZnO film was formed through the following mechanism:

[0049] The procedure was carried out using the ALD unit (OkYay Tech, Ankara, Turkey). During the ALD process, the chamber was maintained at 170 °C with a baseline pressure of -200 millitorr. To achieve the homogeneous coating, membranes were initially stabilized inside the chamber for 30 min prior to deposition. Using N2 as the gas carrier, sequential dosing of DI (deionized) water and diethylzinc, Zn(C2Hs)2, (Strem Chemicals Inc., >95%, Newburyport, MA, USA) was then conducted at different number of cycles (4, 8, 16, 64, and 128) to coat a thin layer of ZnO with a film thickness of -2 A per cycle. In between the dosing of each precursor, the chamber was purged with N2 to ensure that the precursors did not react in vapor phase but rather at the surface of the alumina membranes. FIG. 1 shows the schematic diagram of the ALD process.

[0050] Membrane Desalination Tests

[0051] The set-up for vacuum-assisted flow-through desalination process/system 10 is illustrated in FIG. 2. The ZnO ALD membrane 12 was attached to a bell-shaped glass tube 14 with an epoxy adhesive, and with the ALD treated surface facing out of the bell-shaped tube. The membrane was immersed in the salty solution 16 with the ALD treated surface facing the salty solution. Pressure difference between the two sides of the membrane creates the driving force for bulk motion of salty water across the membrane. The other side of the glass tube was connected to the vacuum pump 18 (1400B-01, WELCH-ILMVAC, Denver Gardner, Laguna Hills, CA, USA) which maintained vacuum in the permeate side and the pressure differential of -1 atm across the membrane. The pressure differential across the membrane was monitored by a pressure gauge 20. All the equipment (vertical glass tube, cold trap and vacuum pump) was connected with plastic tubing, and the vacuum tightness of the assembly and all connections was verified. The salty solution (0.3 wt%) in the feed side was prepared by mixing 3 g of salt (Sigma Aldrich, St. Louis, MO, USA) in 1000 g of DI water. The weight percentage of different ions in the salty water solution was Na ⁺ : 0.08, Mg ²⁺ : 0.01, S ²⁺ : 0.02, Cl“: 0.15, K ⁺ : 0.003, and Ca ²⁺ : 0.003. All desalination experiments were performed for ~1 h at room temperature. Water passed through the membrane in liquid form; and then due to vacuum 28 on the permeate side, evaporation takes place at room temperature. Evaporation at the permeate side of the membrane caused the purification of the salty water, leaving extremely salty water on top of the permeate side of the membrane. The evaporated water 22 was then condensed into clean liquid water 26 in the cold trap 24 and the amount was measured for calculation of water flux. All membranes were dried at 70 °C overnight in an oven before permeation test.

[0052] The desalination performance was evaluated in terms of water flux, which is defined as follows: where V (L) is the volume of permeate, A (m ² ) is effective membrane area, t (h) the time of operation under transmembrane pressure (AP) = P/ - P _/; = ~1 atm. The ion rejection was calculated as follows: where C/is the ion concentration in the feed side and C _P is the ion concentration in the permeate side.

[0053] Membrane Characterization

[0054] Scanning Electron Microscope (SEM) micrographs were used to examine the growth of ZnO ALD on the membranes. FEI Quanta 600F field emission SEM (FEI, Hillsboro, OR, USA) attached with EDX Unit (Energy Dispersive X-ray Analyses) and EVEX nanoanalysis System IV (EVEX Inc., Princeton, NJ, USA) were used to investigate the morphology and chemical elements of membrane surface and cross-section. The surface of the sample was scanned by accelerating a beam of fine focused electron under maximum potential difference of 20 kV. For SEM images, samples were first coated by gold layer (thickness of 200-300 A) and then analyzed. For EDX analysis, samples were not coated and directly used for elemental analysis. In order to investigate the effect of fouling, both the feed and permeate side of the membranes were analyzed to observe the concentration of the retained ions before and after desalination tests. Elemental analysis by inductively coupled plasma (ICP) mass spectroscopy was used to measure the ion concentration in feed and permeate solution after desalination experiment. In order to measure the contact angle, DI water (2 pL) was dropped on the membrane surface at room temperature. Contact angles were measured using a goniometer (Rame-Hart model 250) between water-air interface and substrate surface. The left contact angle (9i) and right contact angle (02) of the water drop (most of the time the value of 0i and 62 were close) were measured, and the average of three contact angles measurements (each for left and right side) was taken to be the final contact angle. The same measurement was done at three different positions on the membrane.

[0055] Results

[0056] FIG. 3 shows the SEM micrographs of surface morphology for the a-alumina membrane before and after ZnO ALD: FIG. 3(a) is the pristine membrane; FIG. 3(b), 3(c), 3(d), 3(e), and 3(f) are ZnO ALD membranes with 8, 16, 32, 64 and 128 ALD cycles, respectively. Before and after ZnO ALD, no significant change in membrane morphology was observed with SEM images.

[0057] FIG. 4 shows the EDX elemental mapping of the membrane before and after ZnO ALD: FIG. 4(a) is the pristine membrane; FIG. 4(b), 4(c), 4(d), 4(e), and 4(f) are ZnO ALD membranes with 8, 16, 32, 64 and 128 ALD cycles, respectively. With successive ZnO ALD cycles (~2 A/cycle), the ZnO film was found to be more continuous, uniform and dense. The EDX elemental mapping of the membrane surface showed the presence of Zn uniformly coated and distributed on the membrane surface. This indicates that the ZnO film was efficiently grown on the membrane surface without any apparent effect of diffusion limitations.

[0058] The content of Zn and Al were measured at different number of ALD cycles using

EDX spectroscopy. The oxygen-free EDX composition analysis has a permeation depth of ~1 pm. The number of ZnO ALD cycles changed Zn/Al ratio. FIG. 5 A shows that the Zn/Al ratio on the membrane side is increased from 0 (pristine membrane) to 0.11 (after 128 ZnO ALD cycles). The elemental analysis shows that the Zn/Al ratio increased gradually after each successive ZnO ALD, which indicates the growth of ZnO film on the membrane surface during the ALD process. [0059] In FIG. 5B, the mass gain of the ZnO ALD membrane was monitored with successive ZnO ALD cycles (4-128 cycles). With increasing ALD cycles, the mass of the ZnO ALD membrane increased, which is due to more ZnO deposition on the membrane. In the initial ALD cycles, ZnO is supposed to deposit as isolated particulates on the surface of the membrane. Further ALD cycles resulted in the outgrowth of ZnO particulates previously formed from nuclei, which might cover the membrane external surface and limit the probability for the precursor (diethylzinc) to enter the pores. Thus, in the higher number of ALD cycles (>20), the mass gain rate was relatively slower compared to that of the lower ALD cycle number (<20).

[0060] With increasing the number of ZnO ALD cycles, the membranes are expected to have increased affinity for water. In FIG. 6, the hydrophilicity of the membranes before and after ZnO ALD was determined by measuring the water contact angle (CA). It was observed that the water contact angle continuously decreased from 101.2° to 93.8° as the number of ZnO ALD increased from 4 to 128, which indicated that ZnO ALD led to a progressively increased hydrophilicity of the membranes.

[0061] ZnO ALD Membrane Performance

[0062] ZnO ALD membranes were used for the vacuum flow-through evaporation technique. Salty water passed through the ZnO ALD membrane in liquid form. Due to the vacuum in the permeate side, it reaches the evaporation state at room temperature, and the water on top of the membrane (permeate side) is evaporated. Over time, highly concentrated salty water was left on top of the permeate side of the membrane, as shown in FIG. 2. In the case of pervaporation, the size of the membrane pore is relatively small (<10 nm) and water transports through the membrane as vapor. However, in the vacuum flow-through evaporation, the size of the membrane pore is relatively larger (-200 nm), and there is a bulk movement of water across the membrane in liquid form.

[0063] FIG. 7 shows detailed results for water flux and ion rejection rate for the pristine AI2O3 membrane and the ZnO ALD-treated membrane. The pristine membrane without ALD showed water flux of 117 L m ^-2 h ^-1 , and it dropped to 92 L m ^-2 h ^-1 with successive desalination tests. This was because with successive desalination tests, membranes pores were covered with different salts from the salty feed water and it eventually led to fouling and thus decreases membrane flux.

[0064] In contrast, the ZnO ALD membrane showed gradual increase of water flux with increasing number of ALD cycles. With increasing the number of ALD cycles, the hydrophilicity of the membrane increased, which further causes the increase in water flux. The maximum water flux leveled off at 169 L m ^-2 h ^-1 after 128 ZnO ALD cycles. The water flux of the ZnO ALD membrane (169 L m ^-2 h ^-1 ) is found to be -83% higher than that achieved by the pristine membrane (92 L m ^-2 h ^-1 ) after equal number of desalination experiments were performed. With increasing ZnO ALD cycles, the membrane surface became more hydrophilic, which is supported by the contact angle results. However, ion rejection did not vary much by the ZnO ALD. For both the pristine membrane and ZnO ALD membranes, salt rejection values were >99.9%. This is because the desalination mechanism from vacuum-flow through evaporation is the same in both cases. Overall, the ZnO treated membrane exhibited very good salt rejection and better water flux than pristine membrane.

[0065] Effect of Ultrasonic Membrane Cleaning

[0066] Experiments were performed to investigate the effect of ultrasonic cleaning on membrane fouling, which is the major limitation in all membrane operations. To investigate the cleaning process, two pristine membranes were used for desalination experiments at the same conditions. After each cycle of desalination experiments, only one of the membranes was cleaned. After each step of desalination experiment, the membrane was detached from a bellshaped glass tube. The tested membrane was calcined in stagnant air at 550 °C for 3.5 h to remove the remaining epoxy adhesive. The calcined membrane was immersed in an ultrasonication bath at room temperature for 30 min. Ultrasonic membrane cleaning uses high- frequency sound waves to agitate the aqueous solution which further acts on retained ion inside tortuous pores of the membrane surface.

[0067] After desalination experiments, cleaned and uncleaned membranes were analyzed with EDX in order to measure the retained ion concentrations on the surface and cross-section of the membranes. FIGS. 8A and 8B show the results of EDX analysis of the membrane surface (feed side). FIGS. 8 A and 8B show graphs of ion concentration on a membrane surface (feed side) as a function of the number of desalination experiments for a membrane with cleaning (FIG. 8A) and without cleaning (FIG. 8B) in between desalination experiments.

[0068] The cleaned membrane showed much lower concentration of retained ion concentration (0.01-0.03%) compared to that of the uncleaned membrane (3-8%).

[0069] FIG. 9 shows EDX elemental mapping of Ca ²⁺ ion for membrane in the: FIG. 9(a) feed side with cleaning, FIG. 9(b) feed side without cleaning, FIG. 9(c) permeate side with cleaning, FIG. 9(d) permeate side without cleaning, Na ⁺ ion for membrane in the FIG. 9(e) feed side with cleaning, FIG. 9(f) feed side without cleaning, FIG. 9(g) permeate side with cleaning, and FIG. 9(h) permeate side without cleaning.

[0070] EDX elemental mapping (FIG. 9(a-d)) showed that Ca ²⁺ ion had lower ion concentration for cleaned membranes than for uncleaned membranes. Ca ²⁺ ion concentration had a relatively small value of ~0.11 wt% for the membrane feed side. For the uncleaned membranes, the amount of salts on the surface accumulated and the concentration of retained ion was higher (0.45 wt%) for the membrane feed side. It was found that the cleaning process between desalination experiments helped in removing the ions retained on the membrane surface and inside the tortuous pore channels.

[0071] FIG. 9(e-h) also demonstrated that Na ⁺ ion showed slightly higher concentration for the uncleaned membrane (0.15 wt% for membrane side) than for cleaned membrane (0.10 wt% for membrane side). The concentration was slightly higher for Ca ²⁺ when compared to Na ⁺ . This can be explained by the higher hydrated ion radius of the Ca ²⁺ (0.41 nm) in comparison to Na+ (0.36 nm), which allowed more retention of Ca ²⁺ ions in the tortuous pores and thus more concentration of Ca ²⁺ in comparison to Na ⁺ .

[0072] Because salty water flows across the membrane during desalination experiments, deposition of salt occurs in the tortuous pore channels along the membrane cross-section. To investigate this, the spatial distribution of the metal ions along the cross-sections of the used membranes was measured with EDX spectroscopy. FIGS. 10A and 10B shows the concentration profiles of Na ⁺ and Ca ²⁺ ions along the cross-sections of the cleaned and uncleaned membranes after seven desalination tests. Na ⁺ ions are shown in FIG. 10A and Ca ²⁺ ions in FIG. 10B. [0073] Along the whole thickness of the membrane, it was observed that the cleaned membrane showed lower concentration for both Ca ²⁺ and Na ⁺ ions than the uncleaned membrane. This can be attributed to the cleaning procedure (both calcining and ultrasonication), which helped in removing the retained ions from the tortuous pores. Thus, membranes without cleaning showed higher concentrations of tihe retained ions.

[0074] As will be apparent from the above disclosure, the separation membranes of this disclosure have good salt retention and superior water flux when compared to prior art membranes. Compared to vacuum flow-through evaporation (170 L m ^-2 h ^-1 ), the water flux values obtained by conventional desalination methods have been reported to be lower (~50 L m ^-2 h ^-1 ). Therefore, the vacuum assisted evaporation technique successfully achieved water flux almost three times higher than with the conventional desalination techniques. This implies that the vacuum flow through evaporation technique can intensify the desalination process.

[0075] In the above examples, ZnO was deposited on macroporous a-alumina membrane via atomic layer deposition (ALD) to improve water flux by increasing their hydrophilicity and reducing mass transfer resistance through membrane pore channels. It was observed from contact angles measurements that the membrane hydrophilicity was enhanced with increasing ZnO ALD cycles. Desalination with ZnO ALD membranes was conducted by a vacuum-assisted ‘flow- through’ evaporation method. Due to the high driving forces for water transport in the vacuum assisted method, there was bulk transport of water through the membrane, and then successive evaporation caused both extremely high-water flux (-170 L m ^-2 h ^-1 ) and high purification of salty water (>99.5%). The vacuum-assisted ‘flow-through’ technique of the ZnO ALD membrane showed over three times higher water flux than those of pervaporation and membrane distillation. It was also shown that ultrasonic membrane cleaning had considerable impact on reducing the membrane fouling. By investigating the EDX spatial distribution of the metal ions along the cross-section and surface of the used membranes, the cleaned membranes showed lower concentration for both Ca ²⁺ and Na ⁺ ions than the uncleaned membranes. In combination with the ZnO ALD membrane, the vacuum-assisted ‘flow-through’ evaporation offers a superior technique for desalination and water purifications. [0076] As can be seen from the above example, the membranes of this disclosure have high salt rejection and have high water flux. Additionally, the membranes are stable, allow for regeneration while retaining good performance, and work under severe environmental conditions.

[0077] The following numbered paragraphs represent non-limiting embodiments of the current disclosure.

[0078] 1. A separation membrane for water desalination, the separation membrane comprising a microfiltration membrane having zinc oxide deposited thereon.

[0079] 2. The separation membrane of paragraph 1, wherein the microfiltration membrane has a pore size of from about 100 nm to about 1000 nm.

[0080] 3. The separation membrane of paragraphs 1 or 2, wherein the microfiltration membrane has a porosity of from about 10% to about 75%.

[0081] 4. The separation membrane of paragraphs 1, 2 or 3, wherein the zinc oxide has a thickness of from about 0.4 nm to about 200 nm.

[0082] 5. The separation membrane of any of the above numbered paragraphs, wherein the zinc oxide is deposited on the microfiltration membrane by an atomic layer deposition process such that the zinc oxide is deposited as from about 4 to about 200 zinc oxide layers each having a thickness of about 1 nm or less.

[0083] 6. The separation membrane of any of the above numbered paragraphs, wherein the separation membrane has a water flux of at least 140 L m' ² h' ¹ and has a salt rejection of at least 95%.

[0084] 7. The separation membrane of any of the above numbered paragraphs, wherein the microfiltration membrane is an AI2O3 membrane.

[0085] 8. The separation membrane of paragraph 7, wherein the microfiltration membrane consists essentially of a-alumina. [0086] 9. The separation membrane of paragraphs 7 or 8, wherein the microfiltration membrane has a pore size of from 150 nm to 500 nm.

[0087] 10. The separation membrane of paragraphs 7, 8 or 9, wherein the separation membrane has a Zn/Al ratio of at least 0.02.

[0088] 11. The separation membrane of paragraphs 7, 8, 9 or 10, wherein the zinc oxide has a thickness of from about 1 nm to about 175 nm, and wherein the zinc oxide is deposited on the microfiltration membrane by an atomic layer deposition process such that the zinc oxide is deposited as from about 8 to about 150 zinc oxide layers each having a thickness of about 0.5 nm or less.

[0089] 12. The separation membrane of paragraph 11, wherein there are from 16 to about

130 zinc oxide layers.

[0090] 13. The separation membrane of paragraphs 11 or 12, wherein the separation membrane has a water flux of at least 150 L m' ² h' ¹ and has a salt rejection of at least 98%.

[0091] 14. A separation membrane for water desalination, the separation membrane comprising: a microfiltration membrane wherein the membrane comprises AI2O3; and zinc oxide deposited on the microfiltration membrane to a thickness of from about 1 nm to about 175 nm, wherein the zinc oxide is deposited on the microfiltration membrane by an atomic layer deposition process in from 16 to 130 zinc oxide layers, wherein each zinc oxide layer is 0.3 nm or less, and wherein the separation membrane has a pore size of from about 150 nm to about 500 nm, a Zn/Al ratio of at least 0.04, a water flux at least 160 L m' ² h' ¹ and a salt rejection of at least 99%.

[0092] 15. The separation membrane of paragraph 14, wherein the microfiltration membrane comprises a-alumina.

[0093] 16. The separation membrane of paragraph 15, wherein the microfiltration membrane consists essentially of a-alumina. [0094] 17. A process for the production of a separation membrane comprising a microfiltration membrane having one or more zinc oxide layers thereon, the process comprising: providing the microfiltration membrane; depositing multiple zinc oxide layers onto the microfiltration membrane in a chamber by an atomic layer deposition process operating on alternating steps of a first gaseous precursor and a second gaseous precursor; purging the chamber between the alternating steps; and continuing the process until from about 4 to about 200 zinc oxide layers are on the microfiltration membrane so as to produce the separation membrane, wherein each layer having a thickness of about 1 nm or less.

[0095] 18. The process of paragraph 17, wherein the first gaseous precursor is Zn(C2Hs)2 and the second gaseous precursor is H2O.

[0096] 19. The process of paragraphs 17 or 18, wherein the alternating steps are carried out at a temperature from 50 °C to 300 °C and at a pressure of less than 1 torr.

[0097] 20. The process of paragraphs 17, 18 or 19, wherein the microfiltration membrane has a pore size of from about 25 nm to about 1000 nm.

[0098] 21. The process of paragraph 20, wherein the microfiltration membrane has a porosity of from about 10% to about 75%.

[0099] 22. The process of any of paragraphs 17, 18, 19, 20 or 21, wherein the microfiltration membrane is an AI2O3 membrane.

[00100] 23. The process of any of paragraphs 17, 18, 19, 20, 21 or 22, wherein each of the zinc oxide layers have a thickness of about 0.5 nm or less.

[00101] 24. The process of paragraph 23, wherein there are from about 8 to about 150 zinc oxide layers deposited on the microfiltration membrane.

[00102] 25. A process for the production of a separation membrane comprising a microfiltration membrane having one or more zinc oxide layers thereon, the process comprising: providing an a-alumina microfiltration membrane having a pore size of from 100 nm to 300 nm and a porosity of from about 20% to about 50%; depositing multiple zinc oxide layers onto the microfiltration membrane in a chamber by an atomic layer deposition process operating on alternating steps of a first gaseous precursor and a second gaseous precursor, wherein the alternating steps are carried out at a temperature from 70 °C to 200 °C and at a pressure of less than 0.5 torr; purging the chamber between the alternating steps; and continuing the process until from about 16 to about 130 zinc oxide layers are on the microfiltration membrane so as to produce the separation membrane, wherein each layer having a thickness of about 0.3 nm or less.

[00103] 26. A process for the desalinating of saline water, the process comprising: providing a separation membrane comprising an AI2O3 microfiltration membrane having zinc oxide deposited thereon, wherein the zinc oxide is deposited on the AI2O3 microfiltration membrane by an atomic layer deposition process in one or more zinc oxide layers wherein each zinc oxide layer is 1 nm or less, and wherein the membrane has a Zn/Al ratio of at least 0.001, a pore size from about 100 nm to about 1000 nm, a water flux of at least 140 L m-2 h-1 and has a salt rejection of at least 95%; exposing a first side of the separation membrane to saline water; and establishing a pressure differential across the membrane from the first side of the separation membrane to an opposing second side of the separation membrane so as to produce desalinated water on the opposing second side.

[00104] 27. The process of paragraph 26, wherein the pressure differential is from about 0.5 torr to about 5 torr.

[00105] 28. The process of paragraphs 26 or 27, wherein the saline water is a produced water.

[00106] 29. The process of paragraphs 26, 27 or 28, wherein the microfiltration membrane has a pore size of from 150 nm to 500 nm.

[00107] 30. The process of paragraphs 26, 27, 28 or 29, wherein the microfiltration membrane consists essentially of a-alumina. [00108] 31. The process of any of paragraphs 26, 27, 28, 29 or 30, wherein the separation membrane has a Zn/Al ratio of at least 0.02.

[00109] 32. The process of any of paragraphs 26, 27, 28, 29, 30 or 31, wherein the zinc oxide has a thickness of from about 0.4 nm to about 200 nm.

[00110] 33. The process of paragraph 32, wherein there are from about 4 to about 200 zinc oxide layers deposited on the microfiltration membrane.

[00111] 34. The process of paragraph 32 or 33, wherein the separation membrane has a water flux at least 150 L m-2 h-1 and has a salt rejection of at least 98%.

[00112] 35. A process for the desalinating of saline water, the process comprising: providing a separation membrane comprising an a-alumina microfiltration membrane having zinc oxide deposited thereon to a thickness of from about 1 nm to about 175 nm, wherein the zinc oxide is deposited on the a-alumina microfiltration membrane by an atomic layer deposition process in from 16 to 130 zinc oxide layers with each layer being 0.3 nm or less, so as to have a Zn/Al ratio of at least 0.04, wherein the separation membrane has a pore size from about 150 nm to about 500 nm, a water flux of at least 160 L m-2 h-1 and has a salt rejection of at least 99%; exposing a first side of the separation membrane to saline water; and establishing a pressure differential of from 0.5 torr to 2 torr across the membrane from the first side of the separation membrane to an opposing second side of the separation membrane so as to produce desalinated water on the opposing second side.

[00113] 36. The process of paragraph 35, wherein the saline water is a produced water.

[00114] Therefore, the present compositions and methods are well adapted to attain the ends and advantages mentioned, as well as those inherent therein. The particular examples disclosed above are illustrative only, as the present treatment additives and methods may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative examples disclosed above may be altered or modified, and all such variations are considered within the scope and spirit of the present treatment additives and methods. While compositions and methods are described in terms of “comprising,” “containing,” “having,” or “including” various components or steps, the compositions and methods can also, in some examples, “consist essentially of’ or “consist of’ the various components and steps. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.