EP3554666A1

EP3554666A1 - Coated meshes and their use, especially for oil-water separation

Info

Publication number: EP3554666A1
Application number: EP17811296.7A
Authority: EP
Inventors: Friederike Fleischhaker; Sung Yeun Choi; Kai BERGNER; Stefanie RUNCK; Aron WOSYLUS
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2016-12-16
Filing date: 2017-12-07
Publication date: 2019-10-23
Also published as: EA201991326A1; WO2018108700A1

Abstract

The present invention refers to a method for the separation of a liquid mixture comprising water and a hydrophobic liquid, especially for oil-water separation, comprising the step of contacting the liquid mixture comprising the hydrophobic liquid and water with a hydrophilically coated mesh allowing water to pass through the mesh while at least part of the hydrophobic liquid remains on the mesh, wherein the mesh is a weave with a geometric pore size of less than 100 μηη having warp threads, the warp threads having a diameter dw, and shute threads, the shute threads having a diameter ds, wherein ds and dw differ by at least a factor of 1.1 and wherein the surface of the mesh is at least partly covered by a hydrophilic coating, the hydrophilic coating having a contact angle for water of less than 10°. The invention further relates to the hydrophilically coated mesh and its use.

Description

Coated meshes and their use, especially for oil-water separation

The present invention relates to methods for the separation of a liquid mixture comprising water, especially for oil-water separation, comprising the step of contacting a liquid mixture comprising at least one hydrophobic liquid and water with a hydrophilically coated mesh allowing water to pass through the mesh while at least part of the hydrophobic liquid remains on the mesh as well as such hydrophilically coated meshes and their use.

Oil-water separation is a worldwide challenge. Typical separation problems comprise the sepa- ration emulsions of crude oil and (formation) water, the separation of industrial oily waste water or separation in connection with the removal of oil spills.

It is known in the art to separate oil-water emulsions or other oil-water mixtures by the addition of chemical additives such as demulsifiers and/or deoilers. Examples of such demulsifiers are disclosed for instance in EP-A 0 264 841 , EP-A 0 499 068 or EP-A 0 267 517.

It is furthermore known to use materials which are capable of selectively absorbing organic solvents, including but not limited to oils. Examples comprise open-cell foams based on a mela- mine-formaldehyde modified with a hydrophobic coating such as disclosed in

WO 2007/1 10361 A1 or WO 2008/107439 A1. J. K. Yuan, X. G. Liu, O. Akbulut, J. Q. Hu, S. L. Suib, J. Kong, F. Stellacci, Nat. Nanotechnol. 2008, 3, 332 disclose superwetting nanowire membranes for selective absorption. Such membranes are obtained by coating nanowire membranes with silicones. It has also been suggested to use meshes for separation of oil and water. Meshes are widely known for various applications. Especially wire weaves can be used as suitable meshes. Examples are described in EP-A 1 418 261 , DE 10 2008 026 195 A1 , DE 10 2009 044 740, DE 20 2004 015 498 U1 or IE 2005 0665. However for oil-water separations coatings are required. L. Feng, Z. Y. Zhang, Z. H. Mai , Y. M. Ma, B. Q. Liu, L. Jiang, D. B. Zhu, Angew. Chem. 2004, 116, 2046 ; Angew. Chem. Int. Ed. 2004, 43 , 2012 disclose a super-hydrophobic and super- oleophilic coating mesh film for the separation of oil and water. The coating is performed by using a homogeneous emulsion comprising 50 % by wt. of water, 30 % by wt. of polytetrafluoro- ethylene (teflon), 10 % by wt. of polyvinylacetate as adhesive, 8 % by wt. of polyvinylalcohol as dispersant 2% dodecylbenzenesulfonate as surfactant. As shown in the cited document drops of water remain on the mesh and do not pass it while drops of diesel oil flow through the mesh.

However, the described hydrophobic/oleophilic oil-removing materials are easily fouled or clogged by oils. Thus the separation efficiency is drastically reduced after a limited number of uses. Additionally, adhered oils are hard to remove which results in secondary pollution during this cleaning process as well as in a waste of both, oil and oleophilic material. Z. Xue, S. Wang, L. Lin, L. Chen. M. Liu, L. Feng and L. Jiang, Adv. Mater. 2011, 23, 4270 - 4273 report about the manufacture of a superhydrophilic and underwater superoleophobic hy- drogel-coated steel mesh for oil-water separation. The steel mesh was coated with a radiation curable, aqueous composition of acryl amide, Ν,Ν'-methylenebisacrylamide as crosslinker, a photoinitiator and high molecular polyacrylamide (M_n = 3,000,000 g/mol) as adhesive agent and the coated mesh was cured with UV-light. The netting described has the opposite separation characteristics than the netting described by L. Feng et al. A drop of water can pass through the netting while oil remains on the netting. Such materials have the advantage that they are easy to clean, the equipment is reusable, the oil-phase can be processed after separation and the equipment is protected from oil-fouling. However, the polyacrylamide coating described by Xue et al. suffers from a lack of efficiency and stability with respect to the separation of crude oil - water emulsions. According to WO 2015/180872 A1 such meshes coated in the manner described do not separate sufficiently crude oil - water emulsions. Curable coating compositions are also described in WO 2015/180 873 A1 for oil-water separation using a plain weave mesh.

W. Zhang, Z. Shi, F. Zhang, X. Liu, J. Jin, and L. Jiang, Adv. Mater. 25, 2071 - 2076 disclose superhydrophobic and superoleophilic PVDF membranes for effective separation of water-in-oil emulsions with high flux. For the water-in-oil emulsions tested petroleum ether, toluene, isooc- tane and dichloromethane were used as oil phase. Emulsions of crude oil and water were not tested.

P. Kim, M. J. Kreder, J. Alvarenga and J. Aizenberg, Nano Lett, 2013, 13 (4), pp 1793-1799, disclose the use of γ-ΑΙΟΟΗ (Boehmite) with infiltrated perfluorated solvents to achieve an om- niphobic surface. Plain weave meshes for oil-water separation coated with hydrated aluminum oxides are described in WO 2015/180 872 A1 .

Even though the separation of liquid mixtures comprising water and hydrophobic liquids, especially oil-water mixtures, is known in the prior art there is a need for improved methods and separation means.

Thus an object of the present invention is to provide such methods and separation means.

This object is achieved by a method for the separation of a liquid mixture comprising water and a hydrophobic liquid, especially for oil-water separation, comprising the following step

• Contacting the liquid mixture comprising the hydrophobic liquid and water with a hydrophil- ically coated mesh allowing water to pass through the mesh while at least part of the hydrophobic liquid remains on the mesh, wherein the mesh is a weave with a geometric pore size of less than 100 μηη having warp threads, the warp threads having a diameter d_w, and shute threads, the shute threads having a diameter d_s, wherein d_s and d_w differ by at least a factor of 1 .1 and wherein the surface of the mesh is at least partly covered by a hydrophilic coating, the hydrophilic coating having a contact angle for water of less than 10°.

The object is also achieved by a hydrophilically coated mesh as defined herein. The coated mesh of the present invention can be used for the separation of water from a liquid mixture comprising water, especially for oil-water separation.

Thus another aspect of the present invention is the use of the coated mesh of the present invention for the separation of water from a liquid mixture comprising water and a hydrophobic liquid, especially for oil-water separation.

Another aspect of the present invention is a device for cross-flow filtration comprising a hydrophilically coated mesh of the present invention. Surprisingly it has been found that improvement of the aforementioned separation is possible by using a coated mesh with specific weaving characteristics.

The liquid mixture to be separated comprises water and a hydrophobic liquid. The term "hydrophobic liquid" as used herein encompasses any kind of organic liquids which is immiscible or only partially miscible with water. Accordingly a hydrophobic liquid is a single hydrophobic liquid substance or a mixture of two or more hydrophobic liquid substances. Examples of hydrophobic liquids include hydrocarbons, such as aliphatic and/or aromatic hydrocarbons, like n-hexane or n-dodecane, in particular hydrocarbons having a boiling point of more than 150 °C, and oil, like crude oil, mineral oils such as diesel oil, gasoline, heavy fuel oil, engine oil, like motor oil, vege- table oils such as coconut oil, tall oil or rape oil, or synthetic oils such as silicone oils.

In one preferred embodiment, the hydrophobic liquid is oil, especially crude or refined oil.

The liquid mixture of water and the hydrophobic liquid, like oil, shall include any kind of mixtures of the hydrophobic liquid (HL) and water comprising a HL phase and a water phase, including but not limited to HL-water emulsions or water-HL emulsions, in particular emulsions of oil, especially crude oil and water such as formation water or sea water.

In one preferred embodiment of the invention, the liquid mixture to be separated is a mixture of crude oil and water, in particular a mixture of crude oil and water.

Examples of specific water-oil separation processes include separation processes in course of oil production and oil refining, such as the separation of crude oil and water produced from an oil bearing formation, the separation of heavy oil from oil sands tailings or heavy oil obtained from steam assisted gravity drainage (SAGD) techniques, de-oiling of water, oil sludge dewater- ing or the removal of hydrocarbons from drilling fluids. Further examples comprise the separation of oil-water mixtures from tank bottoms at refineries or other storage facilities, collection points for disposable waste oils, waste from chemical factories, ballast water or the removal of oil spills.

The method according to the present invention for the separation of the liquid mixture comprises the step of contacting the liquid mixture with a hydrophilically coated mesh allowing water to pass through the mesh while at least part of the hydrophobic liquid remains on the mesh.

Accordingly water is at least partly separated off from the mixture resulting in a remaining mixture with increased fraction of hydrophobic liquid. Thus the term "separation" includes partial and full separation of water. In a preferred embodiment water is separated off to at least 50 % (v/v), more preferred to at least 60 %(v/v), even more preferred to at least 70 % (v/v), even more preferred to at least 75 % (v/v), even more preferred to at least 80 % (v/v), even more preferred to at least 85 % (v/v), even more preferred to at least 90 % (v/v), even more preferred to at least 95 % (v/v), even more preferred to at least 96 % (v/v), even more preferred to at least 97 % (v/v), even more preferred to at least 98 % (v/v), even more preferred to at least 99 % (v/v), even more preferred to at least 99.5 % (v/v), even more preferred to at least 99.9 % (v/v).

In order to separate the mixtures according to the process of the present invention the mixture may be pressed against the mesh. The force applied may simply be gravity forces but of course also elevated pressure may be applied. Due to the hydrophilic surface properties of the coated mesh, water may pass through the mesh while the passage of oil through the mesh is impeded so that at least part of the oil is retained on the mesh and may be removed from the mesh.

In one embodiment of the invention for the separation of the mixtures a separating device is used which at least comprises: a first chamber at least comprising an inlet for fluids and an outlet for fluids, wherein the first chamber is connected with a second chamber at least comprising an outlet for fluids and wherein furthermore the coated mesh according to this invention separates the first chamber from the second chamber. In a preferred embodiment the device is a device for cross-flow filtration.

Accordingly another aspect of the present invention is a device for cross-flow filtration comprising a hydrophilically coated mesh according to the present invention.

For separating the mixtures using the device described, the mixture to be separated is allowed to flow into the first chamber. A suitable pressure selected by the skilled artisan may be applied. Water or at least part of the water of the oil-water mixture passes through the mesh into the second chamber and may be recovered from the second chamber from the outlet of the second chamber. The hydrophobic liquid, like oil, or a mixture with decreased water content may be recovered from the outlet of the first chamber. The process may be continuous or discontinu- ous. In a preferred embodiment the process is a continuous cross-flow filtration. If one separating step is not sufficient to separate oil and water completely the separation step may be repeated using the same or another device. For example for separating a cascade of two or more of the devices described successively assembled may be used. As an example, a separator for the separation of the hydrophobic liquid, e.g. crude oil, and water may be used as described in WO 2015/180 872 A1 and which is equipped with meshes according to the present invention. A schematic representation of such a separator is shown in Fig. 1 . The separator is a cylinder shaped hollow body which at least comprises an inlet for an oil-water mixture, an oil bucket for separated oil, outlets for separated water and separated oil and furthermore a mist extractor and an outlet for separated gas. Meshes may be incorporated vertically (1 a) or almost vertically (1 b) into the separator at a location close to the inlet for the oil-water emulsion. A mesh (1 c) may also be incorporated horizontally. In such embodiment, the inlet for the oil-water emulsion is located above the mesh so that the mixture may be separated into oil and water under the influence of gravity. In order to hold back oil spills a mesh may fur- thermore be used as water weir (3) and/or in the mist extractor (2). Of course the skilled artisan may use meshes in an oil-water separator in another manner.

The mesh used in the separation of the mixture is a weave with a geometric pore size of less than 100 μηη having warp threads, the warp threads having a diameter d_w, and shute threads, the shute threads having a diameter d_s, wherein d_s and d_w differ by at least a factor of 1 .1 and wherein the surface of the mesh is at least partly covered by a hydrophilic coating, the hydro- philic coating having a contact angle for water of less than 10°

The threads are preferably made of metals such as steel, stainless steel, bronze, brass, or alu- minum or polymeric materials such as polyethylene, polypropylene, polyacrylamide, or polyeth- ersulfone or natural fibers such as cotton, cellulose or mixtures thereof, preferably made of metals (wires), more preferably stainless steel.

Preferably, the weave is a woven wire cloth, especially a zero aperture filter cloth. Accordingly, the shute and warp threads are shute and warp wires. Such wire cloths are known in the art. In contrast to plain weave with single wires of same diameter forming apertures, typically forming rectangular apertures, the wires are pressed closely together in zero aperture filter cloths (D.B. Purchas, K. Sutherland, Handbook of Filter Media, second edition (2002), chapter 6.2, Elsevier Sience Ltd., Oxford).

The weave according to the present invention is characterized by warp threads, the warp threads having a diameter d_w, and shute threads, also known as weft threads, the shute threads having a diameter d_s. Most commonly, meshes have warp and shute threads of same diameter, which are woven by alternating the shute thread over and under the warp threat (Plain weave).

However the weave according to the present invention has different diameters ds/dw (Dutch type weave). The diameters d_s and d_w differ by at least a factor of 1 .1. More preferable the diameters differ by at least a factor of 1 .3, even more preferably by at least 1.5, even more pref- erably at least 1 .8, even more preferably at least 2.0, even more preferably at least 2.2 and even more preferably at least 2.4.

In one embodiment of the present invention the diameter d_w is greater than ds. In another em- bodiment of the present invention ds is greater than d_w (Reverse Dutch weave). Reversed Dutch type weave is preferred.

According to the present invention several Dutch weaving types are possible. Preferably each shute thread crosses the warp threads by going over one and then under the next (Plain Dutch weave) or the shute thread passes over one or more warp threads and then under two or more warp threads (Twilled Dutch weave). Plain Dutch weave is more preferred.

Such weaves are commercially available. Examples are filter clothes, such as filter clothes of Haver & Boecker, Oelde, Germany. Examples are Minimesh SPW (single plain Dutch weave), Minimesh HIFLO (single plain Dutch weave), RPD HIFLO-S (reverse plain Dutch weave), DTW (twilled Dutch weave), BMT (twilled Dutch weave), BMT-ZZ (twilled Dutch weave), RPD (reverse plain Dutch weave), TRC (twilled reverse plain Dutch weave) and SPW (single plain Dutch weave). Preference is given to RPD HIFLO-S and RPD, even more preferred is RPD HIFLO-S.

The warp and shute (also called weft) threads may have different pattern. All patterns can be used as long as warp and shute threads are different in size as described herein. In case different warp and shute threads are used, diameters refer to the average diameter. It is clear to the practitioner in the art that due to the weaving process diameter of the threads can be changed slightly. Thus the diameters refer to the thread diameters used before weaving. Technical requirements and testing are described in DIN ISO 9044:2001 -09.

An exemplary weaving pattern is described in US 201 1/290 369 A1 . Accordingly, a wire cloth can be used comprising warp wires and shute (weft) wires crossing each other and interwoven by a weave pattern, said warp wires being formed in at least two different configurations to define warp wires of first and second types, wherein a length of the first type of warp wires deviates from a length of the second type of warp wires in relation to a particular length unit, wherein pores are formed in interstices between sections of two neighboring warp wires and crossing sections of two neighboring weft wires. Preferably, a longer one of the first and second types of the warp wires loops around the weft wires by substantially 360°, with confronting sections of two spaced-apart warp wires touching one another. The wire cloth can be treated by at least one process consisting of compacting and stabilization by thermal treatment, like calendaring or sintering. The first and second types of warp wires can have a waved configuration of different degrees to define warp wires of low waviness and warp wires of high waviness. For example the wave height of the warp wires of high waviness is a multiple of a wave height of the warp wires of low waviness. The warp wires of first and second types of warp wires can define an alternating pattern of low waviness and high waviness. The warp wires of first and second types of warp wires define in direction of the weft wires a pattern in which a number of warp wires of low waviness follow one another and a number of warp wires of high waviness follow one another. The warp wires of first and second types of warp wires can define in direction of the weft wires a pattern in which a number of warp wires of low waviness is different than a number of warp wires of high waviness. The weft wires can be placed in alternating vertically offset rela- tionship. The warp wires of first and second types of warp wires can have a same or different diameter. The warp wires of first and second types of warp wires can define a pattern in which the number of warp wires of first and second types of warp wires varies, with the weft wires woven substantially planar. Preferably the thread with the larger diameter has a diameter in the range from 0.02 mm to 0.3 mm, more preferably 0.03 mm to 0.2 mm, even more preferably 0.04 mm to 0.1 mm, even more preferably 0.05 mm to 0.09 mm, even more preferably 0.06 mm to 0.08 mm.

Preferably the thread with the smaller diameter has a diameter in the range from 0.01 mm to 0.2 mm, more preferably 0.01 mm to 0.1 mm, even more preferably 0.01 mm to 0.08 mm, even more preferably 0.01 mm to 0.05 mm.

Preferably the geometric pore size is less than 50 μηη, more preferably in the range of 1 μ to <50 μηη, even more preferably the pore size is in the range of 5 μηη to <50 μηη, even more pref- erably from 5 to 40 μηη. The geometric pore size can be determined using the so called glass bead test. Accordingly the pore size represents the largest geometrical determined pore size verified by the glass bead test, typically with a tolerance of 5%. In said test a suspension containing glass beads is passed through the mesh - the diameter of the largest bead passing through is considered as the geometric pore size.

In a preferred embodiment the mesh count is 1 15 to 380 MESH in one direction (warp or shute direction) and 325 to 850 MESH in the other direction (shute or warp direction). The dimension MESH refers to the number of apertures per English inch. Exemplary mesh counts are 850x380 (5, 10 or 15 μηη pore size), 640x200 (20 μηη pore size), 425x150 (25 or 30 μηη pore size), 325x1 15 (40 μηη pore size). Due to the different diameter of the shute and warp threads the number of meshes are also different with regard to warp and shute direction.

The hydrophilic coating has a contact angle for water of less than 10°, preferably less than 5°. The hydrophilic coatings described in the following are considered to fulfill this requirement. The contact angle can be measured by a contact angle goniometer. Surfaces with contact angles greater than 90° are typically designated as hydrophobic.

Preferably the hydrophilic coating having a contact angle for water of less than 10° comprises hydrated aluminum oxide or a hydrophilic polymer crosslinked by heat or radiation curing, pref- erably comprising hydrated aluminium oxide. Preferably, the hydrophilic coating has a thickness of 50 nm to 5000 nm, more preferably 50 nm to 2000 nm, even more preferably 50 nm to 500 nm, even more preferably 50 nm to 200 nm, even more preferably 100 nm to 200 nm or 50 nm to 150 nm. The hydrophilic coating having a contact angle for water of less than 10° comprising, preferably consisting of, hydrated aluminum oxide is described in WO 2015/180 872 A1 .

Accordingly the mesh to be used for the separation according to this invention comprises preferably a surface comprising hydrated aluminumoxide. "Hydrated aluminium oxides" include al- uminiumoxyhydroxides, such as a-AIOOH or y-AIOOH having a defined crystalline structure but also aluminumoxyhydroxides having a less defined structure, i.e. products being amorphous or having at least amorphous portions. "Hydrated aluminum oxides" may comprise besides aluminium ions also other metal ions such as for instance ferric ions being understood that usually at least 90 mol % of the metal ions present are aluminum ions.

Preferably, the surface of the mesh comprises γ-ΑΙΟΟΗ which is also known as Boehmite.

The thickness of layer of hydrated aluminum oxides on the surface of the mesh typically may be 50 nm to 500 nm, preferably 100 nm to 200 nm. The mesh according to the invention may be made by converting the surface of an aluminum mesh to a surface comprising hydrated aluminum oxides or by coating a mesh of another material, for instance a mesh of stainless steel with aluminum or aluminum compounds such as aluminum oxides and converting the coating to hydrated aluminum oxides. By modifying the surface of an unmodified mesh a surface-modified mesh comprising a surface comprising hydrated aluminumoxide, preferably γ-ΑΙΟΟΗ can be obtained. The modified surface provides hydrophilic, preferably superhydrophilic properties to the mesh thereby rendering it suitable for separation of a mixture of water with a hydrophobic liquid, such as oil. The term "superhydrophilic" means that the contact angle for oil is preferably > 150° while the contact angle for water is below < 5°. Such coating is suitable to provide a hydrophilic surface with a contact angle of less than 10°.

In a first embodiment of the invention a mesh as described above is coated with aluminum or aluminum oxide. Any technology for coating may be used. Examples of suitable coating tech- nologies include physical vapor deposition methods such as thermal evaporation, sputtering, electron beam evaporation techniques, or CVD technologies. Such techniques are known to the skilled artisan and are for example disclosed in Mahan, John E. "Physical Vapor Deposition of Thin Films" New York: John Wiley & Sons, 2000; Dobkin and Zuraw (2003) "Principles of Chemical Vapor Deposition"; or or Kluwer, Smith, Donald (1995) "Thin-Film Deposition: Princi- pies and Practice" McGraw-Hill.

Alternatively, aluminum layer can be deposited on the mesh using thin aluminum flakes. The thickness of aluminum flakes may be 5 nm to 500 nm, preferably 5 nm to 50 nm. When the mesh is immersed in the thin aluminum flake dispersion, the flakes wrap the thread and bind on the thread surface.

The thickness of the layer of aluminum or aluminum oxide is selected by the skilled artisan ac- cording to his/her needs and usually is from 50 nm to 500 nm, preferably 100 nm to 200 nm.

Layers of aluminum /aluminum oxide may also be coated onto the mesh by sol-gel methods followed by thermal treatment. Also such techniques are known to the skilled artisan and are for example disclosed in C. Jeffrey Brinker, George W. Scherer (Hrsg.) "Sol Gel Science. The Physics and Chemistry of Sol-Gel Processing. The Physics and Chemistry of Sol-gel Processing", Academic Press, Boston (1990) or Kim, Philseok; Kreder, Michael J.; Alvarenga, Jack; et al. NANO LETTERS Volume: 13 Issue: 4 Pages: 1793-1799 Published: APR 2013.

Optionally, the uncoated mesh may be precoated with an adhesion layer. Such an adhesion layer may be a layer of Cr or Ti which also may be applied by using by physical vapor deposition methods but also layers of other oxides may be possible. The thickness of such an additional coating may be from 1 to 20 nm, for example 3 to 10 nm.

In an additional step following the coating with aluminum or aluminum oxides the coating is con- verted into hydrated aluminum oxides, preferably γ-ΑΙΟΟΗ, by treating the coating with water, preferably deionized water, or water vapor at a temperature above room temperature, preferably more than 50°C and more preferably more than 95°C. In one embodiment the coated mesh may be put into boiling water. The duration of the treatment with water is selected by the skilled artisan according to his/her needs and may be from 10 to 40 min, preferably 15 to 30 min.

Alternatively, hydrated aluminum oxides can be directly formed on the mesh starting from soluble aluminum sources. Under the controlled pH and temperature, hydrated aluminum oxides can be deposited on the mesh by precipitation from the solution of such aluminum sources, like aluminates or aluminum salts. Said method is further described in B. Dash, I. N. Bhattacharya B. K. Mishra ..Precipitation and Dehydration of Hydrated Alumina", Lambert Academic Publishing (2014), or US 2 935 376 A.

The thickness of the layer of hydrated aluminum oxides on the surface of the mesh usually is from 50 nm to 1 μηη, preferably 100 nm to 500 nm.

The present invention also relates to a mesh comprising a surface comprising hydrated aluminum oxides, in particular a surface comprising γ-ΑΙΟΟΗ which is available by the methods of the first embodiment described above. In a second embodiment of the invention an aluminum mesh is used as starting material.

The mesh size may be chosen by the skilled artisan according to his/her needs. In particular, the mesh size may be from 10 μηη to 100 μηη, for example 40 μηη to 60 μηη. Further details of unmodified meshes to be used have been described above and we explicitly refer to the description. The surface of the mesh is converted into hydrated aluminum oxides, preferably γ- AIOOH by treating the mesh with water at a temperature above room temperature, preferably more than 50°C. In one embodiment the aluminum mesh may be put into boiling water for about 10 to 40 min, preferably 15 to 30 min.

The present invention also relates to a mesh comprising a surface comprising hydrated aluminum oxides, in particular a surface comprising γ-ΑΙΟΟΗ which is available by the method of the second embodiment described above.

The hydrophilic coating having a contact angle for water of less than 10° comprising, preferably consisting of, a hydrophilic polymer crosslinked by heat or radiation curing is described in WO 2015/180 873 A1. Accordingly in a first aspect a method of manufacturing a coated mesh is described in

WO 2015/180 873 A1 , wherein the method comprises coating a mesh with a curable coating composition and curing the coating by irradiation with UV comprising radiation and/or by annealing wherein the coating composition comprises at least · a polar solvent or solvent mixture,

• a hydrophilic coating precursor selected from the group of

o hydrophilic, monoethylenically unsaturated monomers, with the proviso that at least one of the monomers is (meth)acryl amide,

o preformed hydrophilic oligomers and

o preformed hydrophilic polymers,

• a hydrophilic crosslinker,

• a hydrophilic polymerization initiator, and

• a hydrophilic polymeric adhesion agent comprising acidic groups. Preferably the method comprises coating a mesh with a photochemically curable coating composition and curing the coating by irradiation with UV comprising radiation wherein the coating composition comprises at least

• a polar solvent or solvent mixture comprising at least 70 % by wt. of water relating to the total of all solvents used,

• at least one hydrophilic, monoethylenically unsaturated monomer, with the proviso that at least 50 % by wt. -relating to the total amount of all monomers used- is (meth)acryl amide,

• a hydrophilic crosslinker comprising at least two ethylenically unsaturated groups, · a hydrophilic photoinitiator, and

• a hydrophilic polymeric adhesion agent comprising acrylic acid. The coated mesh is available by coating an uncoated mesh with a curable coating composition followed by thermally and/or photochemically curing the coating. The coating provides hydrophilic surface properties to the mesh. Optionally, before coating the mesh a suitable pre-coating may be applied.

The curable coating composition may be a thermally and/or photocurable composition, preferably a photocurable composition. It provides hydrophilic, preferably superhydrophilic properties to the mesh coated with the formulation so that it may be suitable for oil-water separation. The term "superhydrophilic" means that the contact angle for an oil is > 150° while the contact angle for water is < 5°. Such coating is suitable to provide a hydrophilic surface with a contact angle of less than 10°.

The curable coating composition comprises at least a polar solvent, a hydrophilic coating precursor, a hydrophilic crosslinker, a hydrophilic initiator and a hydrophilic, polymeric adhesive agent.

The curable coating composition comprises at least a polar solvent. The polar solvent may be water or an organic solvent miscible with water. Examples of polar organic solvents miscible with water comprise alcohols such as methanol, ethanol, propanol, isopropanol or ketones such as acetone.

In a preferred embodiment of the invention, the solvent at least comprises water. Besides water one or more than one additional polar organic solvents solvent miscible with water as defined above may be used. In one embodiment, the solvent comprises at least 50 % by wt. of water relating to the total of all solvents, preferably at least 70 % by wt. of water, more preferably at least 85 % by wt., and most preferably only water is used as solvent.

The amount of polar solvent(s) in the curable coating composition may be selected by the skilled artisan according to his/her needs. Generally, the amount of polar solvent(s) is from 20 % by. wt. to 90 by wt., preferably 40 % by wt. to 60 by wt. % relating to the total of all components of the curable coating composition.

The coating precursors are hydrophilic components and are selected from the group of hydrophilic, polymerizable monomers, preformed hydrophilic oligomers and polymers. Oligomers and polymers themselves may also comprise polymerizable group.

The crosslinkable composition comprises at least one monoethylenically unsaturated, hydrophilic monomer with the proviso that at least one of the monomers is (meth)acrylamide, preferably acrylamide.

Preferably, the hydrophilic monomers, oligomers or polymers used are miscible with water in any ratio, but it is sufficient for execution of the invention that the components dissolve in the coating composition. In general, the solubility of the hydrophilic monomers in water at room temperature should be at least 50 g/l, preferably at least 100 g/l.

Besides (meth)acrylamide, preferably acrylamide other monoethylenically unsaturated mono- mers may be used as comonomers. Examples of such further monomers comprise monomers comprising COOH-groups such as (meth)acrylic acid, fumaric acid, itaconic acid, crotonic acid, or maleic acid, monomers comprising other acid groups such as vinylphosphonic acid, esters of hydroxyethyl or hydroxypropyl(meth)acrylate with (poly)phosphoric acid, allylphosphonic acid, 2- acrylamido-2-methylpropanesulfonicacid, or vinylsulfonic acid, hydrophilic (meth)acrylates, for instance amino(meth)acrylates or such as dimethylaminoethyl(meth)acrylate, dimethyla- minopropyl(meth)acrylate, 2-(2-dimethylaminoethyloxy)ethyl (meth)acrylate or ami- no(meth)acrylamides such as dimethylaminoethyl(meth)acrylamide or dimethylaminopro- pyl(meth)acrylamide, quaternized amino(meth)acrylates and quaternized ami- no(meth)acrylamides, hydroxyalkly(meth)acrylates, such as hydroxyethyl(meth)acrylate or hy- droxypropyl(meth)acrylate, hydroxyalkyl(meth)acrylamides such as such as hydroxyeth- yl(meth)acrylamide or hydroxypropyl(meth)acrylamide, ureidomethacrylate, oligo- or polyeth- yleneglycol(meth)acrylates and/or -(meth)acrylamides or methyl oligo- or methylpolyeth- yleneglycol(meth)acrylates and/or -(meth)acrylamides, vinyl- and allyl-substituted heteroaro- matic compounds, including vinyl- and allyl-substituted pyridines, pyrimidines, pyrroles and im- idazoles such as vinylpyrrolidone.

Preferably, a monomer mixture comprising at least 50 % by wt. of (meth)acrylamide, preferably acrylamide, more preferably at least 75 % by wt. of (meth)acryl amide, preferably acrylamide may be used. In one embodiment of the invention only (meth)acryl amide, preferably acrylamide is used as monomer.

Also preformed hydrophilic oligomers or hydrophilic polymers may be used. Examples of such preformed polymers or oligomers comprise homopolymers or copolymers of the monomers mentioned above such as polyacrylamide or polyvinylpyrrolidone. Further examples comprise polyethyleneglycol or polyethyleneimine.

The amount of monomers and/or oligomers and/or polymers in the curable coating composition may be from 2 % by wt. to 80 % by wt., preferably from 40 % by wt. to 60 % by wt. with respect to the total of all components of the coating composition.

In a preferred embodiment of the invention monomers are used as coating precursor.

The curing coating composition furthermore comprises at least one hydrophilic crosslinker, i.e. components comprising at least two polymerizable groups. For reacting with monoethylenically unsaturated monomers the precursor comprises at least two ethylenically unsaturated groups.

Preferably, the crosslinkers used are miscible with water in any ratio, but it is sufficient for execution of the invention that the components dissolve in the coating composition. In general, the solubility of the crosslinkers in water at room temperature should be at least 50 g/l, preferably at least 100 g/l.

Examples of suitable hydrophilic crosslinkers comprise water soluble multifunctional acrylates, - acrylamides such as oligoethyleneglycoldiacrylat.es or Ν,Ν'- methylene bis acrylamide. Such crosslinkers are particularly preferred if monomers are used in the coating composition.

If oligomeric or polymeric precursors are used also such crosslinkers may be used. In one embodiment they are used together with additional monomers.

The amount of crosslinkers in the coating composition may be selected by the skilled artisan according to his/her needs. Generally, the amount may be from 0.5 to 10 % by wt, preferably 0.5 to 5 % by wt. with respect to the total of all components of the coating composition. Hydrophilic initiators for initiating curing may be initiators for thermally initiating polymerization and/or photoinitiators. Preferably, photoiniators are used.

Preferably, the initiators used are miscible with water in any ratio, but it is sufficient for execution of the invention that the components dissolve in the coating composition.

Examples of photoinitiators comprise 2,2'-diethoxyacetophenone, mixtures of benzophenone and 2,2'-diethoxyacetophenone, oxy-phenyl-acetic acid 2-[2 oxo-2 phenyl-acetoxy-ethoxy]-ethyl ester and oxy-phenyl-acetic 2-[2-hydroxy-ethoxy]-ethyl ester, or phosphine oxides such as phenyl bis (2, 4, 6-trimethyl benzoyl) phosphine oxide. Of course a mixture of two or more initiators may be used.

Examples of thermal initiators comprise water soluble azo initiators or peroxo initiators.

The amount of initiators in the coating composition may be selected by the skilled artisan ac- cording to his/her needs. Generally, the amount may be from 0.5 to 7 % by wt., preferably 1 to 5 % by wt. with respect to the total of all components of the coating composition.

The curing composition furthermore comprises at least one hydrophilic polymeric adhesion agent. The polymeric adhesion agent comprises acidic groups.

Preferably, the adhesion agents used are miscible with water in any ratio, but it is sufficient for execution of the invention that the components dissolve in the coating composition.

Examples of such acidic groups comprise carboxylate -COOH groups, sulfonic acid groups - SO3H, or phophonic acid groups -P(0)(OH)2 groups. Preferably, the polymeric adhesion agent comprises at least carboxylate -COOH groups. The polymeric adhesion agent may in particular comprise monoethylenically unsaturated monomers comprising acidic groups, preferably -COOH groups. Examples of suitable polymeric adhesion agents comprise polyacrylic acid or homopolymers or copolymers of fumaric acid, itaconic acid, crotonic acid, maleic acid, methacrylic acid and acrylic acid. Preferably, the adhe- sion agent comprises at least (meth)acrylic acid, preferably acrylic acid.

In one preferred embodiment of the invention polyacrylic acid is used, preferably polyacrylic acid having a weight average molecular weight M_w of more than 1 ,000,000 g/mol, for example 1 ,000,000 g/mol to 5,000,000 g/mol.

The amount of adhesion agents in the coating composition may be selected by the skilled artisan according to his/her needs. Generally, the amount may be from 0.1 to 5% by wt., preferably 0.2 to 2 % by wt. with respect to the total of all components of the coating composition. The curing composition may of course comprise further components. Such further components may be used modifying and/or fine-tuning the properties of the coating.

The coating components are made by mixing all components of coating composition. In the method according to the invention an uncoated mesh which optionally might have been precoated is coated with the curing coating composition described above. Such coating may be performed by dipping an uncoated mesh into the coating composition. In another embodiment the coating composition may be sprayed onto the uncoated mesh. The thickness of the coating may be selected by the skilled artisan according to his/her needs. In one embodiment it may be from 0.5 μηη to 2 μηη.

After coating the mesh with the curable coating composition the film is crosslinked.

In case of compositions comprising photoinitiators crosslinking is started by irradiating the meshs comprising an uncured coating with UV- or UV/VIS - radiation, for instance with a radia- tion of about 365 nm. In case of compositions comprising thermal initiators crosslinking is started by annealing the mesh coated with an uncured coating.

The process of coating the uncoated mesh may comprise additional steps. The mesh may be cleaned in an additional step before coating. Such a cleaning step may comprise removing organic impurities from a metal mesh using organic solvents such as acetone. The mesh may be precoated with adhesion agents before coating it with the curable composition. Examples of suitable adhesion agents comprise in particular the polymeric adhesion agents as described above.

In the preferred embodiment, the curing coating composition comprises at least a polar solvent or solvent mixture comprising water in an amount of at least 70 % by wt. of water relating to the total of all solvents used. Preferably, the amount of water is at least 85 % by wt., and more preferably only water is used as solvent.

As a further component, the preferred curing coating composition comprises at least one hydro- philic, monoethylenically unsaturated monomer, with the proviso that at least 50 % by wt. relating to the total amount of all monomers used is (meth)acryl amide, preferably acrylamide. Preferably at least 75 % by wt. of (meth)acryl amide, preferably acrylamide may be used, and most preferably only (meth)acryl amide, preferably acrylamide is used as monomer. Suitable hydro- philic comonomers which may be used besides (meth)acrylamide have already been described above.

As a further component, the preferred curing coating composition comprises at least a hydro- philic crosslinker comprising at least two ethylenically unsaturated groups. Examples of such crosslinkers have already been described above.

As a further component, the preferred curing coating composition comprises at least a hydro- philic photoinitiator. Examples of such photoinitiators have already been described above.

As a further component, the preferred curing coating composition comprises at least one hydro- philic polymeric adhesion agent comprising (meth)acrylic acid, preferably acrylic acid. In one preferred embodiment the adhesion agent comprises polyacrylic acid, preferably polyacrylic acid having a weight average molecular weight M_w of more than 1 ,000,000 g/mol, for example 1 ,000,000 g/mol to 5,000,000 g/mol. The thickness of the curing coating may be selected by the skilled artisan according to his/her needs. In one embodiment it may be from 0.5 μηη to 2 μηη.

The coated meshes can be used for the separation of water from a liquid mixture comprising water and a hydrophobic liquid, especially for oil-water separation. Thus the coated meshes may be used waste in water treatment, water purification, or in oil/gas industry.

List of figures:

Fig. 1 : Schematic representation of an oil-water separator equipped with meshes Fig. 2: Schematic representation of the testing device for the meshes

Examples:

Example 1

1 ) Meshes used meshes Mesh description Haver & Boecker Minimesh^® RPD HIFLO-S (Reverse Plain Dutch weave)

1

Pore size: 5 μηι, MESH 850x380, d_s:d_w ^« 2.5

Haver & Boecker Minimesh^® RPD HIFLO-S (Reverse Plain Dutch weave)

2

Pore size: 15 μηι, MESH 850x380, d_s:d_w ^« 2.5

Haver & Boecker Minimesh^® RPD HIFLO-S (Reverse Plain Dutch weave)

3

Pore size: 25 μηι, MESH 425x150, d_s:d_w * 2.5

Haver & Boecker Plain weave mesh, VA 200-25

C1

Pore size: 25 μηι, MESH 500, d_s:d_w * 1

Haver & Boecker Plain weave mesh, VA 160-25

C2

Pore size: 38 μηι, MESH 400, d_s:d_w ^« 1

Haver & Boecker Plain weave mesh, VA 130-30

C3

Pore size: 50 μηι, MESH 325, d_s:d_w * 1

2) Coating of meshes

The meshes as specified in item 1 ) were cut into pieces with a size 6 cm x 6 cm. The resulting metal grid pieces were cleaned with acetone, deionized water and again acetone and dried with air.

The cleaned metal grid pieces were coated with 100 nm Al by thermal evaporation according to processes well known to the skilled artisan. Details are disclosed in K.S. Sree Harsha, "Princi- pies of Vapor Deposition of Thin Films", Elsevier, 2006; R.GIang "Vacuum Evaporation", Handbook of Thin Film Technology, McGraw-Hill, ΝΥ,ρ 1 -130, 1970, I. A. Blech "Step Coverage by Vapor Deposited Thin Aluminum Films", Solid StateTechnology, p123, 1983.

In a following step the Al layer was converted into aluminum oxyhydroxide by putting the coated grids into boiling deionized water for 30 min. All contact angles of the hydrophilically coated meshes are below 10°.

3) Separation of mixture of water and hydrophobic liquid The coated grids as specified in item 2) were trimmed and mounted in a filter holder (d = 47mm) as illustrated in Fig. 2. Accordingly, 500ml (250ml hydrophobic liquid and 250ml water as further specified below) of the mixture was poured into the filtration setup formed by the filter cloth (2), which is positioned between a funnel (1 ) and support base (3) and secured by clamp (4). Any liquid passing through the mesh was collected using a beaker (not shown in Fig. 2). The volume of hydrophobic liquid that was not held back by the grid, i.e. collected in the beaker was measured. For each test mixture a freshly-prepared grid was used. All tests were performed at room temperature.

The following test mixtures of water and hydrophobic liquid (all Vol-%A/ol.-%) were used:

(i) Hexane/Water (HW), (ii) Hexane/ Brine (18 wt.-% salt) (HB),

(iii) Dodecane/ Brine (18 wt.-% salt) (DB),

(iv) Motor oil / Brine (18 wt.-% salt) (MB), and

(v) Crude oil (oilfield in Northern Germany) / Brine (18 wt.-% salt) (CB).

The water phase was colored blue for better visibility with methylene blue. The percentage of oil phase (vol-% relating to the total volume of oil used for the test) that is not held back by the mesh and passes through the mesh is listed in Tables 1 and 2. Since at least three reproduction experiments were performed per mesh and mixture a range may be provided.

Table 1 Percentage (vol%) of the hydrophobic phase of the tested mixtures that passes the corresponding filter clothes (1 - 3) in comparison with the plain weave meshes (C1 - C3). Blank boxes: no measurements were performed

Example 2 Boehmite coated filter clothes

Minimesh^® RPD HIFLO-S, DTW-S, and RPD-S weaves (all Haver & Boecker) with 20 · m of pore size were coated with aluminum oxyhydroxide as described in Example 1. Separation test was carried out as described in Example 1.

Table 2 Percentage (vol%) of the hydrophobic phase of the tested mixtures that passes the responding various types of filter clothes with 20 μηη of pore size Example 3 Boehmite coating using Aluminum flakes

A stainless steel (1 .4404) mesh, Minimesh^® RPD HIFLO-S (Haver & Boecker) with 20 μηι, 10 μηη and 5 μηη of pore size were cleaned as described in Example 1 . The cleaned filter cloth was immersed in 0.2 wt.-% aluminum flake dispersion made of Metasheen® 41 (BASF) and /- propanol for 1 minute. After 3 times immersion, the coated filter clothes were dried at room temperature on the bench for overnight. In a following step, the Al layer was converted into aluminum oxyhydroxide by putting the coated filter clothes into boiling deionized water for 30 min. Separation test was carried out as described in Example 1.

Table 3 Percentage (vol%) of the hydrophobic phase of the tested mixtures that passes the responding filter clothes (Minimesh® RPD HIFLO-S) . Example 4 Boehmite coated filter clothes using Aluminum flakes

Minimesh^® RPD HIFLO-S, DTW-S, and RPD-S (Haver & Boecker) with 20 · m of pore size were coated with aluminum oxyhydroxide as described in Example 3. Separation test was car- ried out as described in Example 1.

Table 4 Percentage (vol%) of the hydrophobic phase of the tested mixtures that passes the responding various types of filter clothes with 20 μηη of pore size Example 5 Direct Boehmite coating on the filter clothes

A stainless steel (1 .4404) mesh, Minimesh^® RPD HIFLO-S (Haver & Boecker) with 20 μηι, 15 μηη and 10 · m of pore size were cleaned as described in Example 1.

The cleaned filter cloth was immersed in 1 L of Dl water. Using 0.5M NaOH solution, pH raised to 9.7. Hydrated alumina precipitation was carried out at 60°C and pH 9.7 using 4.6w% Sodium Aluminate solution and 7w% HCI solution.

The coated filter cloth was washed with Dl water in a sonication bath for 10 s and dried at room temperature.

Separation test was carried out as described in Example 1.

Table 5 Percentage (vol%) of the hydrophobic phase of the tested mixtures that passes the responding filter clothes (Minimesh® RPD HIFLO-S). Example 6 Hydrophilic polymer coating on the filter clothes

A stainless steel (1 .4404) mesh, Minimesh^® RPD HIFLO-S (Haver & Boecker) with 20 μηι, 10 μηη and DTW-S, and RPD-S (Haver & Boecker) with 20 · m of pore size were cleaned as de- scribed in Example 1 .

For polymer coating, the hydrogel precursor solution was prepared with 25 g acrylamide, 25 g acrylic acid, 1.5 g Ν,Ν'-methyl-bis acrylamide (crosslinking agent), 1 .0g 2,2'- diethoxyacetophenon (photoinitiator), and 0.5 g polyacrylamide (Mw = 2,000,000 g/mole, adhesive agent ) dissolved in 94 g deionized water.

The cleaned meshes were damped with the hydrogel precursor, then cured under UV-light (365 nm).

Separation test was carried out as described in Example 1 .

Table 6 Percentage (vol%) of the hydrophobic phase of the tested mixtures that passes the responding filter clothes.

Claims

Patent Claims

A hydrophilically coated mesh, wherein the mesh is a weave with a geometric pore size of less than 100 μηη having warp threads, the warp threads having a diameter d_w, and shute threads, the shute threads having a diameter d_s, wherein d_s and d_w differ by at least a factor of 1 .1 and wherein the surface of the mesh is at least partly covered by a hydrophilic coating, the hydrophilic coating having a contact angle for water of less than 10°.

The mesh of claim 1 , wherein the threads are made of metals such as steel, stainless steel, bronze, brass, or aluminum or polymeric materials such as polyethylene, polypropylene, polyacrylamide, or polyethersulfone or natural fibers such as cotton, cellulose or mixtures thereof, preferably made of metals.

The mesh of claim 1 or 2, wherein the weave is a wire cloth.

The mesh of any of claims 1 to 3, wherein each shute thread crosses the warp threads by going over one and then under the next or the shute thread passes over one or more warp threads and then under two or more warp threads, preferably each shute thread crosses the warp threads by going over one and then under the next.

The mesh of any of claims 1 to 4, wherein d_s and d_w differ by at least a factor in the range of 1 .2.

The mesh of any of claims 1 to 5, wherein d_s > d_w-

The mesh of any of claims 1 to 6, wherein the thread with the larger diameter has a diameter in the range from 0.02 mm to 0.3 mm and/or the thread with the smaller diameter has a diameter in the range from 0.01 mm to 0.2 mm.

The mesh of any of claims 1 to 7, wherein the weave has a geometric pore size of less than 50 μηη.

The mesh of any of claims 1 to 8, wherein the hydrophilic coating has a contact angle for water of less than 5°.

10. The mesh of any of claims 1 to 9, wherein the hydrophilic coating having a contact angle for water of less than 10° comprises hydrated aluminum oxide or a hydrophilic polymer crosslinked by heat or radiation curing, preferably comprising hydrated aluminium oxide. 1 1 . The mesh of any of claims 1 to 10, wherein the hydrophilic coating has a thickness of less of 50 nm to 5000 nm.

12. Method for the separation of a liquid mixture comprising water and a hydrophobic liquid, especially for oil-water separation, comprising the following step

• Contacting the liquid mixture comprising the hydrophobic liquid and water with a hydrophilically coated mesh of any of claims 1 to 1 1 allowing water to pass through the mesh while at least part of the hydrophobic liquid remains on the mesh.

13. The method of claim 12, wherein the hydrophobic liquid is oil.

14. Use of the coated mesh of any of claims 1 to 1 1 for the separation of water from a liquid mixture comprising water and a hydrophobic liquid, especially for oil-water separation.

15. A device for cross-flow filtration comprising a hydrophilically coated mesh of any of claims 1 to 1 1.