Filtration System

Abstract

A filtration system is provided that includes a first vessel, a second vessel, and a separating layer. The first vessel is configured to receive a liquid phase. The second vessel is in fluid communication with the first vessel and configured to receive a permeate of the liquid phase. The separating layer separates the first vessel and the second vessel. The separating layer is porous, the pores being capable of filtering the liquid phase. The separating layer comprises a graphitic material, a cross-linking agent, and a polymer coating.

Description

[Technical field]

[0001] The present disclosure relates to the field of filtration systems and methods for filtering liquid phases, mixtures, suspensions or solutions. [Background technology]

[0002] Filtration systems are currently used in various industries in purification processes to recover a retentate or to remove contaminants and recover a purified liquid phase. Filtration systems can have semi-permeable filtration membranes and can therefore be used in osmosis or reverse osmosis systems. Osmosis systems can be used, for example, in dialysis or salt water purification. Filtration systems can generally be classified based on the pore size of the filtration membrane (e.g., microfiltration, nanofiltration, ultrafiltration and reverse osmosis). For example, microfiltration can filter out bacteria and suspended solids, but not viruses or ions. Ultrafiltration has a separating layer with a pore size of about 0.01 microns that can filter out bacteria, suspended solids, and some larger viruses. Nanofiltration has a separating layer with a pore size of about 1 nm that generally filters out most organic molecules, most viruses, most organic matter, as well as some salts and larger ions. For example, nanofiltration can remove divalent ions from water that make it hard. Reverse osmosis has a separation layer with a pore size of about 0.1 nm and can essentially remove all dissolved and suspended contaminants from water, even monovalent ions. In other words, reverse osmosis can be used to desalinate water. Improvements in filtration systems are desired to achieve a better balance of permeability and selectivity, as well as better resistance to heat and abrasive chemicals. Specifically, it would be advantageous to identify new materials that can function as the separation layer of these filtration systems in order to achieve the desired improvements. Summary of the Invention

[0003] Surprisingly, the inventors have discovered that the use of graphitic materials in combination with cross-linking agents and polymers in the separation layers of filtration systems can provide improved filtration systems. Compared to conventional separation layers such as separation membranes, the separation layers of the present invention, which comprise graphitic materials, cross-linking agents, and polymer coatings, are more robust and have better mechanical properties. The separation layers of the present invention are also easily adaptable (e.g., can be manufactured with different pore sizes) to modify the balance of permeability and selectivity depending on the filtration application. The separation layers of the present invention provide improved resistance to heat and abrasive chemicals compared to conventional separation membranes. Thus, the separation layers of the present invention can generally achieve a longer life cycle than conventional separation layers, making them more desirable in larger industrial facilities. The separation layers of the present invention also provide increased liquid flow rates through the separation layers compared to conventional separation layers, while maintaining high rejection of the retentate of interest.

[0004] In one aspect, a filtration system is provided that includes a first vessel configured to receive a liquid phase; a second vessel in fluid communication with the first vessel and configured to receive a permeate of the liquid phase; and a separation layer separating the first vessel and the second vessel, the separation layer having pores for filtering the liquid phase and comprising a graphitic material, a cross-linking agent, and a polymer coating.

[0005] In some embodiments, the graphitic material is selected from the group consisting of graphite, graphene, graphite oxide, graphene oxide, reduced graphene oxide, reduced graphite oxide, and functionalized counterparts thereof.

[0006] In some embodiments, the filtration system is an ultrafiltration system and the pores have a size between 0.005 and 0.09 μm.

[0007] In some embodiments, the filtration system is a nanofiltration system and the pores can have dimensions between 0.5 and 5 nm.

[0008] In some embodiments, the filtration system is a reverse osmosis filtration system and the pores can have a size of less than 0.5 nm.

[0009] In some embodiments, the filtration system is a pervaporation filtration system and the pores can have a size less than 0.5 nm.

[0010] In some embodiments, the filtration system further comprises a porous support substrate that is at least partially covered by the separating layer.

[0011] In some embodiments, the porous support substrate comprises a material selected from the group consisting of polypropylene, polystyrene, polyethylene, polyethylene oxide, polyethersulfone, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, polydimethylsiloxane, polyester, cellulose, cellulose acetate, cellulose nitrate, polyacrylonitrile, fiberglass, quartz, alumina, ceramic, carbon, metal, silver, polycarbonate, nylon, aramid, and polyetheretherketone.

[0012] In some embodiments, the porous support substrate is a spiral filtration module, a porous sheet wound into one of a hollow porous tube, or a flat porous plate.

[0013] In some embodiments, the porous support substrate has an average pore size of from 0.01 μm to 50 μm, preferably from 0.1 μm to 5 μm.

[0014] In some embodiments, the separating layer comprises multiple monolayers and / or multilayers.

[0015] In some embodiments, the multiple monolayers and / or multilayers are linked together by crosslinking with a crosslinking agent.

[0016] In some embodiments, the separating layer comprises crosslinks between the graphitic material and the polymer formed by a crosslinking agent.

[0017] In some embodiments, the graphitic material is present in the separating layer at a concentration of 5-95 wt %, preferably 50-80 wt %.

[0018] In some embodiments, the polymer is present in the separating layer at a concentration of .about.95 wt %.

[0019] In some embodiments, the polymer is selected from the group consisting of glycols, cellulose ethers, polyvinyl alcohols, polyethyleneimines, polyacrylic acids, polyurethanes, polyepoxides polyisocyanates, polyvinyl acetates, polyacrylates, polymelamines, polyureas, and copolymers thereof.

[0020] In some embodiments, the cross-linking agent is present in the separating layer at a concentration of 1-20 wt %, preferably 1-10 wt %.

[0021] In some embodiments, the crosslinking agent is selected from the group consisting of aldehydes, isocyanates, aziridines, bisacrylamides, carbodiimides, silicon chelates, zirconium chelates, titanium chelates, polyamines, polycarboxylates, polyepoxides, polyisocyanates, polyaziridines, polyvalent metal ions, polyanhydrides, borates, alkylated melamines, alkylated ureas, polyisocyanates, and phosphates.

[0022] In some embodiments, the system further comprises a means for applying pressure within the first vessel to drive flow of the liquid phase from the first vessel to the second vessel.

[0023] In a further aspect, there is provided a composition comprising 50-80 wt % of a graphitic material having a plurality of layers; 10-49 wt % of a polymer; and 0.1-10 wt % of a crosslinking agent selected from a titanium chelate, a zirconium chelate, a dialdehyde, a polyisocyanate, or a polyaziridine.

[0024] In some embodiments, the crosslinking agent is a titanium or zirconium chelate, such as titanium(IV) oxide bis(2,4-pentanedionate).

[0025] In some embodiments, the cross-linking agent is a dialdehyde, such as glyoxal or glutaraldehyde.

[0026] In some embodiments, the crosslinker is a polyisocyanate or a polyaziridine, preferably a polyaziridine such as trimethylolpropane tris(2-methyl-1-aziridinepropionate).

[0027] In some embodiments, the polymer comprises hydroxyl, amine, carboxyl and / or epoxy groups.

[0028] In some embodiments, the polymer is selected from polyvinyl alcohol, hydroxypropyl cellulose, polyacrylic acid, glycols, cellulose ethers, polyethyleneimines, polyurethanes, polyepoxides, and copolymers thereof.

[0029] In some embodiments, the graphitic material has a thickness of from 5 nm to 50 μm.

[0030] In some embodiments, the graphitic material is selected from the group consisting of graphite, graphene, graphite oxide, graphene oxide, reduced graphene oxide, and reduced graphite oxide or functionalized counterparts thereof.

[0031] In some embodiments, the polymer and crosslinker are present in a weight ratio of polymer to crosslinker of 1:100 to 10:1.

[0032] Numerous additional features and combinations thereof relating to improvements of the present invention will be apparent to those of skill in the art upon reading this disclosure. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a schematic diagram of a filtration system according to one embodiment of the present disclosure.

[0034] [Diagram 2] FIG. 2 is a schematic diagram of an exemplary reverse osmosis filtration system according to one embodiment of the present disclosure.

[0035] [Diagram 3] FIG. 3 is a schematic diagram of an exemplary pervaporation filtration system or membrane distillation system according to one embodiment of the present disclosure.

[0036] [Figure 4] FIG. 4 is a schematic diagram of an exemplary dead-end filtration system according to one embodiment of the present disclosure.

[0037] [Diagram 5] FIG. 5 is a schematic diagram of a cross-flow filtration system according to one embodiment of the present disclosure.

[0038] [Figure 6] FIG. 6 is a schematic diagram showing cross-linking between a graphitic material and a polymer.

[0039] [Figure 7] FIG. 7 is a schematic diagram showing cross-linking between a graphitic material, a polymer and a cross-linking agent.

[0040] [Figure 8]Figure 8 shows the mass of permeate (deionized water) across a reduced graphite oxide (rGO) membrane (1) and a graphene oxide-polymer composite (GOPC) (2) as a function of time.

[0041] [Figure 9A] FIG. 9A is a graph showing the permeate mass passing and flux through a GOPC membrane for a 5 wt % lignin solution.

[0042] [Figure 9B] FIG. 9B is a graph showing the permeate mass passing and flux through the rGO membrane for a 5 wt % lignin solution.

[0043] [Figure 10] FIG. 10 is a graph showing the mass permeate as a function of time for 20 cycles of filtration through a GOPC membrane.

[0044] [Figure 11] FIG. 11 is a graph of lignin rejection as a function of filtration cycles.

[0045] [Figure 12] FIG. 12 is a photograph of the membrane after the wet adhesion test.

[0046] [Figure 13] FIG. 13 is a photograph of the film after the dry adhesion test.

[0047] [Figure 14A] FIG. 14A is a photograph of the membrane before the dry peel test.

[0048] [Figure 14B] FIG. 14B is a photograph of the strongly crosslinked membrane after the dry peel test.

[0049] [Figure 14C] FIG. 14C is a photograph of the non-crosslinked membrane after the dry peel test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] Referring to FIG. 1, a filtration system 1 is provided having a first vessel 10 containing a liquid phase 11 requiring filtration. The filtration system 2 has a second vessel 12 in fluid communication with the first vessel 10. The second vessel 12 receives a filtrate 13 of the liquid phase 11 to be filtered. The liquid phase 11 is filtered through a separation membrane 15, optionally supported on a porous substrate 16. The separation membrane 15 is porous to allow the liquid phase 11 and organisms, particles, molecules, and / or ions having dimensions less than the pore dimensions to pass through to the second vessel 12. The separation layer comprises, consists essentially of, or consists of a graphitic material, an optional basecoat layer, a crosslinker, a polymer coating. The basecoat layer is an optional adhesion layer that can be disposed on a substrate to improve adhesion of the graphitic material to the substrate. In some embodiments, the thickness of the separation layer or graphitic material is between 5 nm and 50 μm.

[0051] The term "graphitic material" as used herein refers to a material selected from one or more of graphene, graphite, graphene oxide, graphite oxide, reduced graphene oxide, and reduced graphite oxide. The term "graphitic oxide material" as used herein refers to a material selected from one or more of graphene oxide, graphite oxide, reduced graphene oxide, and reduced graphite oxide.

[0052] Graphite is a type of graphite that is made up of sp 2Graphene is a crystalline form of carbon formed by stacking two-dimensional lattices of graphene-hybridized carbon. In its thinnest manifestation, a single layer of the hexagonal crystal structure of graphite is called graphene. Depending on the context, structures having a hexagonal crystal structure with up to 10 layers, and in some cases up to 100 layers, may continue to be called graphene, and the boundary between graphite and graphene may be blurred. In this specification, structures having up to 10 layers of graphene are called graphene, and structures having more than 10 layers of graphene are called graphite. Perhaps due to the difference in thickness between the two, particles of graphite are commonly referred to as "flakes" and particles of graphene as "sheets". Thus, in some embodiments, the separating layer comprises multiple monolayers and / or multilayers of graphene.

[0053] Graphite oxide is a compound containing various proportions of carbon, oxygen, and hydrogen. The mass fraction of carbon is generally about 45%, and according to the general definitions used herein, the typical carbon to oxygen ratio can be 1.8-2.9. The inherent functional groups of graphite oxide include hydroxyl, epoxide, carbonyl, carboxylic acid, and organic sulfate. Graphene oxide is also a compound of similar proportions of carbon, oxygen, and hydrogen as graphite oxide, so the materials are similar. Reduced graphite oxide and reduced graphene oxide are similar to their graphite oxide and graphene oxide counterparts except for the fact that they have gained an electron (indicating a reduced oxidation state), and their reduction is generally achieved by chemical, thermal, photo, hydrothermal reduction, or a combination of various reduction methods. Maximum reduction of graphene oxide results in graphene, whereas maximum reduction of graphite oxide results in graphite. Similar to the definitions adopted above, the expressions graphene oxide or reduced graphene oxide are used herein to refer to structures having up to 10 layers, and the expressions graphite oxide or reduced graphite oxide are used to refer to structures having more than 10 layers.

[0054] A graphitic material, such as a graphitic oxide-like material, may be mixed with one or more other active materials in a formulation and then formed into a layer. One or more layers may be used or formed in a stacked, flat structure. Manufacturing techniques include solvent casting followed by doctor blade, roller coating, vacuum filtration, pressure filtration, and the like. Typically, the formulation contains all the "active materials" in a solvent, and the solvent evaporates leaving only the active materials in the layer. The one or more active materials forming the remaining layer are collectively referred to herein as the (final) chemical composition. In an exemplary embodiment, a graphitic oxide-like material is preferred over a graphitic material. The concentration of the graphitic oxide-like material in the resulting chemical composition may be, for example, at least 60 wt%, preferably 70 wt%, and more preferably 75 wt%, in which case the layer may be referred to as a graphitic oxide layer. The graphitic material may be a single layer of such a chemical composition or successive layers that may be stacked together. The successive layers may be of the same chemical composition or different materials.

[0055] Chemically functionalized graphitic materials are those that are chemically modified to bear foreign chemical groups, either through covalent bonds or non-covalent bonds such as π-π interactions.

[0056] In some embodiments, the separation layer is a graphene oxide-polymer composite (GOPC) and comprises (a) graphene oxide and its derivatives, (b) a polymer coating, and (c) a chemical crosslinker. The amount of graphene oxide and its derivatives in the resulting GOPC separation membrane is preferably 50% to 80% by weight, but may be 5% to 95% by weight. The amount of polymer in the resulting GOPC separation membrane may be 0.1% to 95% by weight, 1% to 95% by weight, 1% to 75% by weight, or 5% to 95% by weight. The amount of crosslinker in the resulting GOPC separation membrane may be 0.1% to 75% by weight, 0.5% to 70% by weight, 5% to 60% by weight, or 1% to 20% by weight, preferably in the range of 1% to 10%. In some embodiments, the GOPC layer can be chemically, thermally, or photothermally reduced to introduce additional stability or hydrophobicity for certain separation applications when more hydrophobic fluids are used or higher film stability is desired. The molecular weight cut-off of the GOPC separation layer can be adjusted by the weight ratio of graphene oxide to polymer, the graphene oxide flake size, and the content and type of crosslinker. Other examples of graphitic materials suitable for the separation layer of the present disclosure include, but are not limited to, pristine graphene, graphene nanoplatelets (GNPs), or turbostratic graphene synthesized via exfoliation methods.

[0057] In some embodiments, the hydroxyl, carboxyl, ketone, and epoxy groups of the graphitic material in the separation layer (e.g., when the graphene oxide sheets are the graphitic material) are chemically modified to other functional groups, including, but not limited to, chloroformate, amine, acryl, and thiol groups.

[0058] In some embodiments, the graphitic material is single or multi-layer graphite oxide (GO) or reduced graphite oxide (rGO) sheets with particle sizes ranging from 10 nm to 500 μm, preferably 1 μm to 50 μm. The particle size distribution of the GO / rGO sheets can be directly related to the density of the material.

[0059] In some embodiments, the separating layer preferably comprising GOPC may have a thermal stability limit greater than about 70° C. In some embodiments, for example, the separating layer comprising GOPC may have a thermal stability limit of at least about 286 (L / (m 2 ) with deionized water at room temperature. 2 In some embodiments, the molecular weight cut off of the separating layer, preferably comprising GOPC, ranges from about 100 Daltons to about 1000 Daltons.

[0060] The separation layer of the present disclosure can have various pore sizes to perform ultrafiltration, nanofiltration, pervaporation filtration, membrane distillation, and reverse osmosis filtration. The separation system of the present disclosure can be configured as dead-end filtration (or dead-end filtration) or cross-flow filtration. In one embodiment, the filtration system is an ultrafiltration system. The separation layer of the ultrafiltration system can have pores of 0.005-0.09 μm, 0.005-0.02 μm, or about 0.01 μm. As used herein, the term "about" can be interpreted as ±5%, ±10% ±15%, or ±20%. In one embodiment, the filtration system is a nanofiltration system. The separation layer of the nanofiltration system can have pores of 0.5-5 nm, 0.5-2 nm, or about 1 nm.

[0061] In one embodiment, the filtration system 1 can be a reverse osmosis filtration system, as illustrated in FIG. 2. The separation layer of the reverse osmosis filtration system can have pores of less than 0.5 nm, less than 0.25 nm, or about 0.1 nm. Referring to FIG. 2, the reverse osmosis filtration system generally further comprises a means 17 for applying pressure to the first vessel 10 to drive the flow of the liquid phase 11 from the first vessel 10 to the second vessel 12. The means 17 can be, for example, a lever or a piston, or the pressure can be applied indirectly using a vacuum pump or the like that applies a pressure difference between the first vessel 10 and the second vessel 12. The means 17 for applying pressure to the first vessel 10 can also be used for ultrafiltration, nanofiltration, and other types of filtration, although in different structures. The means 17 is useful for facilitating filtration, especially when the pore size of the separation layer is small (e.g., less than 10 μm).

[0062] In one embodiment, the filtration system 1 can be a pervaporation filtration or membrane distillation system, as illustrated in FIG. 3. The separation layer of the pervaporation filtration system or membrane distillation system can have pores of less than 0.5 nm, less than 0.25 nm, or less than 0.1 nm. Referring to FIG. 3, the pervaporation filtration system or membrane distillation system has a feed 18 of liquid phase 11 passing across separation layer 15, which then becomes retentate 19. The second vessel 12 receives a permeate 13 of the liquid phase 11 passing across separation layer 15. A vacuum 20 or negative pressure can be applied to the second vessel 12 to drive the flow and gasification of the liquid phase across separation layer 15. In the embodiment illustrated in FIG. 3, the permeate 13 is a gas phase. Thus, in the pervaporation filtration system, the feed 18 of the liquid phase 11 comprising the solute can be concentrated, and a concentrated retentate 19 can be obtained.

[0063] In one embodiment, the filtration system can be dead-end filtration, as illustrated in Figure 4. In dead-end filtration, the liquid phase 11 is typically stagnant and adjacent to a separating layer 15. Pressure 14 can be applied to drive a flow of the liquid phase 11 across separating layer 15 to a second vessel 12.

[0064] In one embodiment, the filtration system can be cross-flow filtration, as illustrated in Figure 5. In such an embodiment, the liquid phase 11 flows across a separating layer 15, and at least a portion of the liquid phase 11 passes through the separating layer 15 into the second vessel. Cross-flow filtration is particularly suited to concentrating the liquid phase.

[0065] The separation layer comprises a polymer coating. The polymer coating typically covers at least a portion of the graphitic material, and preferably substantially covers the graphitic material. The polymer is also crosslinked with the graphitic material. FIG. 6 is an exemplary schematic diagram of crosslinking that may occur between a polymer and functional groups of graphite oxide. In some embodiments, the polymer comprises one or more functional groups, including, but not limited to, hydroxyl, carboxyl, ketone, epoxy, chloroformate, amine, acrylic, and thiol groups. Representative polymers include, but are not limited to, polyethylene glycol (PEG), cellulose ethers, polyvinyl alcohol (PVA), polyethyleneimine (PEI), polyacrylic acid (PAA), polyurethane (PU), polyepoxide polyvinylpyrrolidone (PVP), polyisocyanate, polyvinyl acetate, polyacrylate, polymelamine, polyurea, and copolymers thereof. The cellulose ether can be selected from the group consisting of carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), methylcellulose (MC), hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC). In some preferred embodiments, the polymer is selected from the group consisting of glycols, cellulose ethers, polyvinyl alcohols, polyethyleneimines, polyacrylic acids, polyurethanes, polyepoxides, and copolymers thereof.

[0066] In some embodiments, the polymer is 5 wt% to 95 wt% of the separating layer and the graphitic material is 5 wt% to 95 wt% of the separating layer. The type of polymer and the amount of polymer affect the pore size of the separating layer. In general, without wishing to be bound by theory, increasing the polymer content relative to the graphitic material increases the porosity and decreasing the polymer content decreases the porosity.

[0067] In some embodiments, the polymer is or includes a UV-curable polymer, and accordingly, a photoinitiator is included. For example, the polymer can be a UV-curable polyurethane or polyvinyl acetate. In such embodiments, the concentration of the polymer can range from 1 to 49 wt%. Having a UV-curable polymer allows for post-treatment of the GO coating to increase the stability of the GO on the substrate. The UV treatment preferably removes some oxygen, making the coating more stable in the aqueous phase. If the coating is composed of a multilayer sheet (a stack of sheets), the UV treatment is effective in reducing the interlayer distance compared to a non-UV treated coating. The UV-curable polymer also improves adhesion to the substrate. Alternatively, a thermosetting polymer can be used.

[0068] Finally, the separation layer also comprises a chemical crosslinker. The chemical crosslinker can form crosslinks with the graphitic material and with the polymer. For example, as shown in Figure 7, the chemical crosslinker can form crosslinks with the functional groups of the graphite oxide and with the functional groups of the polymer. In some embodiments, the chemical crosslinker is selected from aldehydes (e.g., dialdehydes), isocyanates, aziridines, bisacrylamides, carbodiamides (e.g., polycarbodiamides), silicon chelates, zirconium chelates, titanium chelates, polyamines, polycarboxylates, polyepoxides, polyisocyanates, polyaziridines, polyvalent metal ions, polyanhydrides, borates, phosphates, alkylated melamines, alkylated ureas, polyisocyanates, and combinations thereof.

[0069] In some embodiments, the crosslinking agent is or includes a titanium chelate and / or a zirconium chelate. For example, the crosslinking agent can be titanium(IV) oxide bis(2,4-pentanedionate). These chelates can form bonds with hydroxyl and carboxyl groups and act to crosslink these sites. They act as catalysts in esterification reactions. They improve water stability, adhesion, and hardness.

[0070] In some embodiments, the crosslinking agent is or includes an aldehyde, such as a dialdehyde. For example, the crosslinking agent can be glyoxal or glutaraldehyde. These crosslinking agents can form bonds with hydroxyl and carboxyl groups, acting to crosslink these sites. They can control the length of the crosslinks, improving water stability, adhesion, and hardness. They can also be used to control the pore size. For example, increasing or adding the content of aldehyde crosslinking agents can reduce the pore size of the separation layer.

[0071] In some embodiments, the crosslinker is or includes a carbodiamide, such as polycarbodiamide. For example, the crosslinker can be polycarbodiamide, N,N'-diisopropylcarbodiimide. These crosslinkers can react with carboxylic acid groups to crosslink. They improve water stability, adhesion, and hardness. They can also be used to adjust pore size. For example, increasing or adding the carbodiamide crosslinker content can reduce the pore size of the separation layer.

[0072] In some embodiments, the crosslinking agent is or includes a polyisocyanate. In some embodiments, the polyisocyanate is present at a concentration of 0.1 to 75% by weight. The polyisocyanate can have a functionality of greater than 2, preferably greater than 3. For example, the crosslinking agent can be hexamethylene diisocyanate (HDI), methylene diphenyl diisocyanate (MDI), and / or block-HDI. These crosslinking agents can form bonds with hydroxyl and carboxyl functional groups and act to crosslink these sites. They can be used to control the length of the crosslinks. They also improve water stability, adhesion, and hardness. They can control the pore size and promote faster crosslinking reactions. For example, increasing or adding the polyisocyanate crosslinking agent content can reduce the pore size of the separation layer. Polyisocyanates can form inter- and intra-sheet covalent urethane bonds (R-NH-C(O)-) between GO and crosslinkers via reaction of the isocyanate groups with hydroxyl groups on GO, or similarly, can form inter- and intra-sheet covalent urethane bonds (R-NH-C(O)-) between GO and crosslinkers via reaction of the isocyanate groups with carboxylic acid groups on GO.

[0073] In some embodiments, the crosslinking agent is or includes a polyamine. For example, the crosslinking agent can be polyetheramine and / or 1,2-diaminoethane. These crosslinking agents can react with carboxylic acid functional groups to crosslink. They can improve water stability, adhesion, and hardness. They can also adjust the pore size and promote faster crosslinking reactions. For example, increasing or adding the content of polyamine crosslinking agent can reduce the pore size of the separation layer.

[0074] In some embodiments, the crosslinking agent is or includes a polyepoxide. For example, the crosslinking agent can be triglycidyl-2 aminophenol. These crosslinking agents can react with carboxylic acid functional groups to crosslink. They can improve stability in water, adhesion, and hardness. They can also adjust the pore size and promote faster crosslinking reactions. For example, increasing or adding the content of polyepoxide crosslinking agent can reduce the pore size of the separation layer.

[0075] In some embodiments, the crosslinker is or includes polyaziridine. For example, the crosslinker can be trimethylolpropane tris(2-methyl-1-aziridinepropionate). These crosslinkers can react with carboxylic acid functional groups to crosslink. They improve water stability, adhesion, and hardness. They can also adjust the pore size and promote faster crosslinking reactions. For example, increasing or adding the polyaziridine crosslinker content can reduce the pore size of the separation layer.

[0076] In some embodiments, the crosslinker is or includes an alkylated melamine and / or urea crosslinker. These crosslinkers can have a functionality greater than 2, preferably greater than 3. These crosslinkers can form inter- and intrasheet covalent ether bonds (-O-R3-N(R1)-R2-O-, where R3 and R2 are C1-C6 alkyl groups) between GO and the crosslinker due to the reaction of the alkylated amino groups with hydroxyl groups on the GO.

[0077] In some embodiments, the separating layer comprises a crosslinker at a concentration of 0.1-75 wt%, 1-70 wt%, 3-65 wt%, 5-60 wt%, 1-20 wt%, 1-17.5 wt%, 1-15 wt%, 1-10 wt%, 2-20 wt%, 4-20 wt%, 5-20 wt%, 2-17.5 wt%, 4-15 wt%, or 4-10 wt%.

[0078] The present disclosure further provides a composition consisting of or comprising: (a) 50-80 wt% graphitic material having a plurality of layers; (b) 10-49 wt% polymer; and (c) 0.1-10 wt% crosslinker selected from titanium chelates, zirconium chelates, dialdehydes, polyisocyanates, or polyaziridines. In some embodiments, the crosslinker concentration is 0.2-10 wt%, 0.5-10 wt%, or 1-10 wt%. The composition is particularly suitable for use as a separating layer in filtration systems and methods of performing filtration. The titanium chelates, zirconium chelates, dialdehydes, and polyaziridines crosslinkers are as described above; the polymers are as described above; and the graphitic material is as described above. In some embodiments, the composition includes a polymer and a crosslinker in a weight ratio of polymer to crosslinker of 1:100 to 10:1, 4:1 to 2:1, 3.5:1 to 2.5:1, or about 3:1. In one non-limiting, exemplary embodiment, the composition includes PVA as the polymer and a dialdehyde as the crosslinker. In such embodiments, the weight ratio of PVA to dialdehyde can be 4:1 to 2:1, 3.5:1 to 2.5:1, or about 3:1.

[0079] Returning to FIG. 1, in some embodiments, the filtration system optionally includes a support substrate 16. Thus, in some embodiments, the filtration device has (a) a porous support substrate, and (b) a GOPC separation layer deposited on at least a portion of the porous support substrate. The GOPC separation layer can include multiple monolayer and multilayer graphene oxide sheets, and each graphene oxide sheet can be linked to adjacent polymer chains via chemical crosslinkers, as previously shown in FIGS. 6 and 7. The addition of polymers can strongly adhere the GOPC layer to the substrate, and the crosslinks between GO-polymer and GO sheets provide good stability of the GOPC during the separation process. As previously mentioned, the support substrate is optional. Thus, in some embodiments, the filtration device includes only a GOPC layer without the use of a porous support substrate. In such cases, the GOPC layer functions as a free-standing separation layer.

[0080] In some embodiments, the porous support substrate comprises a material selected from polypropylene, polystyrene, polyethylene, polyethylene oxide, polyethersulfone (PES), polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, polydimethylsiloxane, polyester, cellulose, cellulose acetate, cellulose nitrate, polyacrylonitrile, fiberglass, quartz, alumina, ceramic, carbon, metal, silver, polycarbonate, nylon, Kevler or other aramids, polyetheretherketone, woven and non-woven synthetic or natural fibrous products.

[0081] In some embodiments, the form of the porous support substrate includes a porous sheet configured to be wound into a spiral filtration module, a hollow porous tube / fiber, and a flat porous plate. The porous support substrate can have an average pore size ranging from 0.01 μm to 50 μm, preferably 0.1 to 5 μm.

[0082] The separation layer and porous substrate described herein can be produced or manufactured by various processes. In an exemplary method for manufacturing the separation layer, a precursor solution of GOPC is first prepared by mixing graphene oxide, polymer, chemical crosslinker and solvent. The precursor solution of GOPC is then deposited on a supporting porous substrate using flexographic printing, spin coating, dip coating, doctor blade coating, slot die coating method, or spray coating, allowing for a roll-to-roll manufacturing process. The thickness of the dried GOPC can be from 5 nm to 50 μm, depending on the coating method.

[0083] As an example, the graphene oxide-polymer composite separation layer of the present disclosure can be used to concentrate, remove and purify a variety of substances, including, but not limited to, inorganic salts, lignin, lactose, humic acid and fulvic acid.

[0084] In one embodiment, a method is provided for concentrating black liquor using the reverse osmosis filtration system described herein. The black liquor can include lignin, sodium sulfate, sodium carbonate, sodium hydrosulfide, sodium thiosulfate, sodium hydroxide, hemicellulose, methanol, organic acids, and water. In one example, the separating layer has a flow rate of at least about 5 L / (m2) at room temperature when in weak black liquor. 2 ·hr·bar) at 70°C in dilute black liquor, and at least about 10 L / (m 2 100% lignin is rejected by the GOPC separator membrane. In some embodiments, at least 99% of the lignin is rejected by the graphene oxide membrane.

[0085] In some embodiments, at least a portion of the sodium sulfate, sodium carbonate, sodium hydrosulfide, sodium thiosulfate, and sodium hydroxide are rejected by a separating layer (e.g., a GOPC separating layer) of the present disclosure. In some embodiments, at least 90% of the sodium sulfate, sodium carbonate, sodium hydrosulfide, sodium thiosulfate, and sodium hydroxide are rejected by a separating layer (e.g., a GOPC separating layer) of the present disclosure.

[0086] In one embodiment, a method is provided for filtering milk to remove lactose using the filtration system described herein (e.g., a GOPC separating layer in a reverse osmosis system). Milk generally comprises lactose, fat, protein, minerals, and water. In some embodiments, the separating layer (e.g., a GOPC separating layer) of the present disclosure has a flow rate of at least about 25 L / (m2) at room temperature using commercially available milk (containing about 5 wt. % lactose). 2 100 MPa (100 MPa) 100 MPa (100 MPa) 100 MPa (100 MPa) 15 ...

[0087] In one embodiment, a method is provided for removing humic and fulvic acids from drinking water using a filtration system described herein (e.g., a GOPC separating layer in a reverse osmosis system). The separating layer (e.g., a GOPC separating layer) of the present disclosure is capable of filtering at least about 2.5 L / (m) of an aqueous solution containing 4 wt. % humic acid and 1 wt. % fulvic acid at room temperature. 2 100 MPa (100 MPa) ...

[0088] In one embodiment, a method for desalination of seawater is provided using the filtration system described herein (e.g., a GOPC separating layer in a reverse osmosis system). The seawater may comprise sodium chloride, magnesium chloride, sodium sulfate, calcium chloride, potassium chloride, sodium bicarbonate, and other trace inorganic salts. The separating layer (e.g., a GOPC separating layer) can be used to desalinate seawater (including a salinity of about 3.5 wt%) at a rate of at least about 200 L / (m) at room temperature. 2 100 MPa (100 MPa) can be obtained. In some embodiments, at least a portion of the inorganic salts are rejected by the separating layer (e.g., a GOPC separating layer). In some embodiments, using seawater (containing a salinity of about 3.5 wt%), at least 90% of the inorganic salts are rejected by the separating layer (e.g., a GOPC separating layer) at room temperature.

[0089] In one embodiment, a method is provided for concentrating lithium from brine using a separation layer of the present disclosure (e.g., a GOPC separation layer in a pervaporation, forward osmosis, reverse osmosis, or membrane distillation system). Using the GOPC separation described herein can result in a 20-fold faster concentration rate and approximately a 10-fold smaller plant footprint.

[0090] The filtration systems described herein, and in particular the GOPC separating layers, can also be used to separate oil from emulsified water.

[0091] Working Example

[0092] GOPC separation layers containing PVA polymer and zirconium chelate crosslinker with PES support substrate were fabricated by the following protocol: 1) 2 wt% GO solution and 1 wt% PVA solution were provided; 2) 8 g of GO solution and 24 g of DI water were mixed in an overhead mixer for 10 min; 3) 10 g of PVA solution was added; 4) pH titration was performed with 10 wt% NaOH solution until pH 7.5-8; 5) 25 μL of zirconium chelate was added to the solution and mixed for another 10 min; 6) PES membrane (0.22 μm pore size) was wetted with deionized (DI) water; 7) The prepared solution was coated with a 20 μm wire-bar; and 8) the coated PES membrane was dried in a convection oven at 100 °C.

[0093] A GOPC separation layer containing HPMC polymer and glyoxal crosslinker with a polypropylene support substrate was fabricated by the following protocol: 1) 2 wt% GO solution and 1 wt% HPMC solution were provided; 2) 8 g GO solution and 24 g DI water were mixed in an overhead mixer for 10 min; 3) 10 g HPMC solution was added; 4) 0.2 g glyoxal was added to the solution and mixed for another 10 min; 5) a polypropylene (PP) membrane was plasma treated; 6) a PP membrane (0.2 μm pore size) was wetted with DI water; 7) the prepared solution was coated onto the PP membrane with a 20 μm wire-bar; and 8) the coated PP membrane was dried in a convection oven at 100 °C.

[0094] The GOPC separation layer containing a PVA polymer and a glyoxal crosslinking agent with a PES support substrate was manufactured according to the following protocol: 1) A 2 wt% GO solution and a 1 wt% PVA solution were provided. 2) 8 g of the GO solution and 24 g of DI water were mixed with an overhead mixer for 10 minutes. 3) 10 g of the PVA solution was added. 4) 0.2 g of glyoxal was added to the solution and mixed for an additional 10 minutes. 5) The PES membrane was subjected to plasma treatment. 6) The PES membrane (with a pore size of 0.22 μm) was wetted with DI water. 7) The prepared solution was coated with a 20-μm wire-bar. 8) The coated PES membrane was dried in a convection oven at 80°C. 9) The oven-dried and coated PES membrane was immersed in a 25 wt% glyoxal solution. And 10) The coated PES membrane was then dried in a convection oven at 100°C.

[0095] Reduced graphene oxide rGO was prepared according to the following protocol. 1) A 2 wt% GO solution, a 1 wt% PVA solution, and a 20 wt% ascorbic acid (AA) solution were provided. 2) All of these were placed in a 50-mL glass beaker. 3) The contents of the beaker were mixed with a magnetic stirring plate for 15 minutes. 4) The PES membrane (with a pore size of 0.22 μm) was wetted with DI water. 5) The prepared solution was coated with a 20-μm wire-bar. 6) Then, it was dried in a convection oven at 80°C for 15 minutes. And 7) Finally, it was sandwiched between two pieces of parchment paper and heat-pressed at 80°C for 15 minutes under a pressure of 0.7 MPa.

[0096] The flow of the permeate of the GOPC separation layer and the rGO separation layer, both having a PES support substrate and a PVA polymer, was compared using a dead-end filtration configuration. The permeate flow used was DI water at room temperature (20°C). The pressure was set to 50 PSI with compressed air. A motor with a propeller was installed directly above the separation layer to perform stirring (120 PRM). The results are shown in Figure 8. GOPC was significantly higher than rGO, at 286 L / m 2 / hour / bar compared to 8.47 L / m 2 / hour / bar.

[0097] The fluxes of GOPC and rGO were further evaluated in comparison to a 5 wt% lignin solution at 20° C. The filtration parameters are shown below in Table 1. The results are shown in Figures 9A and 9B. [Table 1]

[0098] The results obtained in this example are compared with membranes from the prior art and are shown in Table 2 below. [Table 2]

[0099] The performance of GOPC was carried out at 60°C with 5 wt% lignin solution with the same parameters as provided above (Table 1). More specifically, a cycle test (20 cycles) was carried out to evaluate the performance of GOPC in continuous use. The feedstock was replenished after each cycle. The permeated filtrate was collected for further experiments. The results are shown in Figure 10. After 20 cycles, no significant change in filtration flow rate was observed during the 20 cycle test. This result suggests the potential antifouling properties of the separation layer of the present invention (especially GOPC).

[0100] The filtered solution was analyzed by laser transmission using 0.01 wt% lignin, 0.02 wt% lignin and 0.05 wt% lignin as references, and the results are shown in Figure 11. The GOPC over 20 cycles achieved 99.9% rejection of lignin.

[0101] The effect of polyisocyanate crosslinker on adhesion under wet conditions was investigated. Figure 12 shows the adhesion test results, which indicate that the strongly crosslinked membrane has significantly higher adhesion than the non-crosslinked membrane (without crosslinker). The membrane coupon (or coupon) was fully immersed in 10 wt% NaOH solution in a PET jar. The jar was placed on a laboratory shaker and agitated at 200 rpm for 5 hours. After the test, the non-crosslinked membrane showed peeling (white areas), while the strongly crosslinked membrane showed no peeling, which is comparable to the two commercial membranes below (Toray UTC-73HA RO membrane and DOW NF90NF membrane). Dry adhesion test was also performed on the same membranes. Figure 13 shows the results, which indicate that the strongly crosslinked membrane has better dry adhesion than all other tested membranes. 3M Scotch tape was applied to each of the membrane coupons on the coated side and peeled off by hand. Figures 14A-14C show the dry peel test results using a protocol according to ASTM D3359. The coated layer was cut into 1 mm x 1 mm squares using a laser marker and a similar tape test was performed using 3M Scotch tape. Before and after images were taken and processed into grayscale images (left) and contrast-enhanced images (right) to more clearly identify the areas of delamination. The strongly crosslinked membrane maintained most of the coated area (shown as black squares) in Figure 14B, whereas in Figure 14C, almost all of the black squares of the non-crosslinked membrane were gone and replaced by white squares representing the delaminated areas after the test.

Claims

1. 1. A filtration system comprising: a first vessel configured to receive a liquid phase; a second vessel in fluid communication with the first vessel and configured to receive the liquid phase permeate; and a separating layer separating the first container and the second container, the separating layer having pores for filtering the liquid phase and comprising a graphitic material, a cross-linking agent and a polymer coating; A filtration system comprising:

2. 2. The filtration system of claim 1, wherein the graphitic material is selected from the group consisting of graphite, graphene, graphite oxide, graphene oxide, reduced graphene oxide, reduced graphite oxide, and functionalized counterparts thereof.

3. 3. The filtration system of claim 1 or 2, wherein the filtration system is an ultrafiltration system.

4. 4. The filtration system of claim 3, wherein the pores have a size between 0.005 and 0.09 μm.

5. 3. The filtration system of claim 1 or 2, wherein the filtration system is a nanofiltration system.

6. The filtration system of claim 5, wherein the pores have a size between 0.5 and 5 nm.

7. 3. The filtration system of claim 1 or 2, wherein the filtration system is a reverse osmosis filtration system.

8. The filtration system of claim 7 , wherein the pores have a dimension of less than 0.5 nm.

9. 3. The filtration system of claim 1 or 2, wherein the filtration system is a pervaporation filtration system or a membrane distillation system.

10. 10. The filtration system of claim 9, wherein the pores have a dimension of less than 0.5 nm.

11. The filtration system of any one of claims 1 to 10, further comprising a porous support substrate at least partially covered by the separating layer.

12. 12. The filtration system of claim 11, wherein the porous support substrate comprises a material selected from the group consisting of polypropylene, polystyrene, polyethylene, polyethylene oxide, polyethersulfone, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, polydimethylsiloxane, polyester, cellulose, cellulose acetate, cellulose nitrate, polyacrylonitrile, fiberglass, quartz, alumina, ceramic, carbon, metal, silver, polycarbonate, nylon, aramid, polyetheretherketone, woven and nonwoven fibrous products.

13. 13. The filtration system of claim 11 or 12, wherein the porous support substrate is a porous sheet, a hollow porous tube, or a flat porous plate that is wound into a spiral filtration module.

14. Filtration system according to any one of claims 11 to 13, wherein the porous support substrate has an average pore size of from 0.01 μm to 50 μm, preferably from 0.1 μm to 5 μm.

15. Filtration system according to any one of claims 1 to 14, wherein the separating layer comprises a plurality of monolayers and / or multilayers.

16. 16. The filtration system of claim 15, wherein the plurality of monolayers and / or multilayers are bonded together by cross-linking with a cross-linking agent.

17. 17. The filtration system of any one of claims 1 to 16, wherein the separating layer comprises cross-links between the graphitic material and the polymer formed by a cross-linking agent.

18. Filtration system according to any one of the preceding claims, wherein the graphitic material is present in the separating layer at a concentration of 5 to 95 wt%, preferably 50 to 80 wt%.

19. Filtration system according to any one of claims 1 to 18, wherein the polymer is present in the separating layer at a concentration of 5 to 95 wt %.

20. 20. The filtration system of any one of claims 1 to 19, wherein the polymer is selected from the group consisting of glycols, cellulose ethers, polyvinyl alcohols, polyethyleneimines, polyacrylic acids, polyurethanes, polyepoxides, polyisocyanates, polyvinyl acetates, polyacrylates, polymelamines, polyureas, and copolymers thereof.

21. Filtration system according to any one of the preceding claims, wherein the cross-linking agent is present in the separating layer at a concentration of 1 to 20 wt%, preferably 1 to 10 wt%.

22. 22. The filtration system of any one of claims 1 to 21, wherein the cross-linking agent is selected from the group consisting of aldehydes, isocyanates, aziridines, bisacrylamides, carbodiimides, silicon chelates, zirconium chelates, titanium chelates, polyamines, polycarboxylates, polyepoxides, polyaziridines, polyvalent metal ions, polyanhydrides, borates, alkylated melamines, alkylated ureas, polyisocyanates and phosphates.

23. 23. The filtration system of any one of claims 1 to 22, further comprising means for applying pressure in the first vessel to drive flow of the liquid phase from the first vessel to the second vessel.

24. 50-80 wt % of a graphitic material comprising a plurality of layers; 10 to 49 wt % of a polymer; and 0.1-10 wt % of a crosslinker selected from a titanium chelate, a zirconium chelate, a dialdehyde, a polyisocyanate, or a polyaziridine; A composition comprising:

25. 25. The composition of claim 24, wherein the crosslinking agent is a titanium chelate, a zirconium chelate.

26. The composition of claim 25, wherein the crosslinking agent is titanium(IV) oxide bis(2,4-pentanedionate).

27. 25. The composition of claim 24, wherein the crosslinking agent is a dialdehyde.

28. 28. The composition of claim 27, wherein the crosslinking agent is glyoxal or glutaraldehyde.

29. 25. The composition of claim 24, wherein the crosslinker is a polyaziridine or a polyisocyanate.

30. The composition of claim 29, wherein the crosslinking agent is trimethylolpropane tris(2-methyl-1-aziridine propionate).

31. The composition according to any one of claims 24 to 30, wherein the polymer comprises hydroxyl, amine, carboxyl and / or epoxy groups.

32. The composition according to any one of claims 24 to 31, wherein the polymer is selected from polyvinyl alcohol, hydroxypropyl cellulose, polyacrylic acid, glycols, cellulose ethers, polyethyleneimines, polyurethanes, polyepoxides and copolymers thereof.

33. The composition of any one of claims 24 to 32, wherein the graphitic material has a thickness of from 5 nm to 50 μm.

34. 34. The composition of any one of claims 24 to 33, wherein the graphitic material is selected from the group consisting of graphite, graphene, graphite oxide, graphene oxide, reduced graphene oxide, and reduced graphite oxide.

35. The composition of any one of claims 24 to 34, wherein the polymer and crosslinker are present in a weight ratio of polymer to crosslinker of from 1:100 to 10:1.

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