WO2017135822A1 - Preparation of inorganic tight nanofiltration membranes - Google Patents

Preparation of inorganic tight nanofiltration membranes Download PDF

Info

Publication number
WO2017135822A1
WO2017135822A1 PCT/NL2017/050069 NL2017050069W WO2017135822A1 WO 2017135822 A1 WO2017135822 A1 WO 2017135822A1 NL 2017050069 W NL2017050069 W NL 2017050069W WO 2017135822 A1 WO2017135822 A1 WO 2017135822A1
Authority
WO
WIPO (PCT)
Prior art keywords
membrane
layer
precursor
process according
membranes
Prior art date
Application number
PCT/NL2017/050069
Other languages
French (fr)
Inventor
Ran SHANG
Sebastiaan Gerard Jozef HEIJMAN
Louis Cornelis RIETVELD
Original Assignee
Technische Universiteit Delft
Technologiestichting Stw
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Technische Universiteit Delft, Technologiestichting Stw filed Critical Technische Universiteit Delft
Publication of WO2017135822A1 publication Critical patent/WO2017135822A1/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/024—Oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0041—Inorganic membrane manufacture by agglomeration of particles in the dry state
    • B01D67/00416—Inorganic membrane manufacture by agglomeration of particles in the dry state by deposition by filtration through a support or base layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0072—Inorganic membrane manufacture by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/28—Pore treatments
    • B01D2323/283—Reducing the pores
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2323/00—Details relating to membrane preparation
    • B01D2323/42—Details of membrane preparation apparatus
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/027—Nanofiltration

Definitions

  • the present invention is in the field of a preparation of inorganic tight nanofiltration (NF) membranes with a cutoff ⁇ 450 Da and with high water permeability using atomic layer deposition, a membrane obtained with said process, and applications of such membranes.
  • NF inorganic tight nanofiltration
  • Inorganic membranes also called ceramic membranes
  • Advantages of inorganic membranes are that they have a high mechanical strength, a high chemical and thermal resistance, a long lifetime, and they are
  • the inorganic membranes can be classified in three types: inorganic microfiltration membranes with a pore size ranging from about 0.1 to 10 urn) inorganic
  • nanofiltration membranes are made having an MWCO ranging from 450 Da to 1000 Da.
  • an inorganic nanofiltration membrane with a MWCO of 200 Da could be produced via a sol-gel method.
  • Inorganic membranes that are made of zeolite can be fabricated using a zeolite crystallization method.
  • a zeolite membrane has ultra-micropores ranging from 0.3 to 0.7 nm (MWCO ⁇ 200 Da) .
  • MWCO ⁇ 200 Da ultra-micropores
  • their water permeability is very low (0.8-2.7 *10 -11 l/ ⁇ m 2 *s*Pa) ) since they are produced with a thick zeolite crystallized layer of 5-50 micrometers.
  • membranes To be applied for e.g. water treatment such membranes must have a high water permeability, i.e. a water
  • the sol-gel method multilayer coating for fabrication of the inorganic tight nanofiltration is adopted and a sintering process is normally needed for coating of each layer which normally is time- consuming (12-24 hours) .
  • the sol-gel method is also energy consuming because each cycle requires wetting, drying and sintering at 473-1474 °K (200-1200 °C) .
  • a single layer coating may results in pin-holes or cracks in the final top- layer, while multiple layer coating typically leads to an excessive thick top-layer.
  • such a thick top-layer shows high water resistance, i.e. low water permeability. Therefore, an inorganic tight nanofiltration membrane with MWCO ⁇ 450 Da, yet with a high water permeability, has not been fabricated using the sol-gel method so far.
  • the zeolite membranes typically have a very thick top- layer, which results in extremely low water permeability.
  • the top layer of this multi-layer structure was a niesoporous ⁇ 2 layer with a thickness of 250 nm and a mean pore size of 5 nm. After coating this multi-layer structure, a polymeric gel was formed and finally dried for 1 h at room temperature. These membranes had a MWCO of 480 Da. The membrane top-layer had a thickness of only 50 nm
  • nanofiltration membranes with an MWCO of 200 Da via the sol- gel methods.
  • One of the membranes was made of a Y-AI 2 O 3 intermediate layer and an anatase (Ti0 2 ) top-layer. It showed a water permeability of 1.11 ⁇ ⁇ "8 1 rrf 2 s '1 Pa "1 , but showed a low corrosion resistance compared to e.g. Ti0 2 membranes.
  • the other inorganic nanofiltration membrane consisted of an anatase intermediate ultra-filtration (UF) -membrane support modified with an optimized anatase top-layer obtained by a very slow drying process. For such a tight nanofiltration membrane the permeability is strongly reduced (0.56 *10 ⁇ 5 1 rrf
  • Titania (Ti0 2 ) layers obtained by a single dip-coating procedure showed an average thickness of about 0.5 ⁇ . Therefore, a second dipping procedure had to be used to increase the membrane thickness up to about 1 ⁇ .
  • Li and Wang disclosed a method for continuously
  • the method includes a flow type ALD reactor, in which the precursors are exposed to the
  • the method also includes a short exposure/purging time which are 0.01-1 s and 0-60 s, respectively. Based on this method a ceramic microflitration membrane can be
  • BSA bovine serum albumin
  • Patent US8518845 B2 discloses a method which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate using ALD.
  • Patent application EP1884578 Al discloses that ALD can be used to narrow the pore diameter by coating atomic layers on the pore walls and the pores was specified to be 40 ⁇ S0 nm in diameter.
  • EP 2 138 222 (Al) recites a method which can be used for pore size reduction, defect repair and in general for
  • infiltration method can be applied at temperatures of 200-300 °C, using available sealing technologies.
  • a microporous membrane which contains defects with a low selectivity, is modified to a microporous and/or nanoporous membrane of high selectivity. Membranes without defects and with pore sizes less than 1 nm, but still larger than 0.5 ran, are formed.
  • inorganic membranes which are highly selective to permeation of hydrogen by temporarily forming a carbon barrier in the pores of a porous substrate, followed by chemical deposition of S1O 2 , B 2 O 3 , T1O 2 , I 2 O 3 and mixtures thereof in the pores, followed by removal of the carbon barrier.
  • Suitable porous substrate are glass or Al 2 0 3 .
  • pore size inorganic membranes such as metal oxides, metal carbides, metal nitrides and cermets.
  • Mean pore diameters of below about 1.0 nm can be achieved.
  • the pore size of the membrane is progressively reduced in a controlled manner to deposit one or more layers of an inorganic compound on the pore walls, by exposing the membrane to the vapour of an inorganic precursor compound. Water vapour, oxygen, or vapours containing one or more oxygen ligands are further used to hydrolyse the deposited material to the inorganic membrane .
  • the membrane permeability for hydrogen gas is considered to be relatively low (in the order of 1 cm 3 / (cm 2 min 100 kPa) .
  • the water permeability of such membranes was not determined and is expected to be much lower than the said hydrogen
  • the present invention therefore relates to an improved process for preparation of inorganic tight nanofiltration (NF) membranes with a cut-off ⁇ 450 Da and with high water permeability using atomic layer deposition, which solves one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing
  • NF inorganic tight nanofiltration
  • the invention relates to a process for the preparation of inorganic tight nanofiltration (NF) membranes with a cut-off ⁇ 450 Da and with high water
  • NF tight nanofiltration
  • present membranes are especially suited for (use in) membranes for liquids, such as water.
  • liquid is used in its usual meaning being a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure.
  • a flow-through ALD reactor for fabrication of a ceramic nanofiltration (NF) membrane is provided.
  • a novel operational procedure of this flow-through type ALD reactor with 3 inlets (or outlets) is also provided to fabricate ceramic NF with high water permeability.
  • a tubular porous substrate may be placed in the holder with three in-/outlets.
  • reactant vapours precursors
  • a purging gas passes through the tube either from inside to outside or from outside to inside of the tube.
  • the present innovative design allows controlled growth of homogeneous layers in the pores of the tubular membrane, such as metal oxide layers, such as TiC> 2 . At the same time deposition growth is limited to the outside or inside surface of the porous tube. A benefit of this method is a minimized loss of porosity and water permeability of the fabricated membranes.
  • a process to fabricate high water permeable ceramic NF membranes using a plasma-enhanced ALD is provided.
  • a substrate disc-shape is placed in a vacuum reaction chamber.
  • the first precursor e.g. T1CI 4 , is
  • the second precursor e.g. O 2
  • the second precursor e.g. O 2
  • the second precursor e.g. O 2
  • a single layer of in this case Ti-oxide is coated on the surface and in the pores of the substrate.
  • ALD atomic layer deposition
  • nanofiltration membrane has pores that are one magnitude smaller than the pores in ultrafiltration membranes. As a result it has been found at least cumbersome to coat the nanopores of the nanofiltration membranes and specifically to coat pore walls, which is found to be a crucial step to tailor the pore size of a nanofiltration membrane.
  • inorganic tight nanofiltration membranes are produces by modifying an
  • inorganic membrane with MWCO of 480 Da using atomic layer deposition methods.
  • the MWCO decreases rapidly with the pore size, for instance a pores size of 5 nm corresponds to an MWCO of approximately 10 4 Da, whereas a pore size of 0.8 nm corresponds to 480 Da.
  • the 480 Da membrane may be fabricated using the same method that is described in Puhlfiir (see above). By coating homogeneous atomic layers of e.g. T1O 2 on the pore wall of the 480 Da inorganic membrane, a membrane with tighter pores is produced, while the thickness of the top-layer will be increased by less than 0.5 nm only.
  • a contact time may be applied (e.g. 0.5 minute, 1 minute, 10 minutes, 20 minutes, 60 minutes, and 120 minutes) between precursors (e.g.
  • a flow-through ALD reactor for fabrication of ceramic NF membrane is provided.
  • a flow-through ALD reactor has been reported by Kemell (see above)
  • the present inventors designed an innovative flow-through ALD reactor that can hold a ceramic tubular membrane (Figure 1).
  • Flow rates applied in the reactor and in the present process are typically in the order of 10 "6 -1 m 3 / (m 2 skPa) ⁇ @ 40 °C) , such as 10 "4 -0.5 m 3 /(m 2 skPa), e.g. 10 ⁇ -0.2 m 3 / (m 2 skPa) .
  • the pressure in the present system is typically 50-1000 kPa (0.5- 10 bar), such as 100-500 kPa.
  • the convection flow rate is typically controlled by mass flow controllers. This
  • a benefit of this method is a minimized loss of porosity and water permeability of the fabricated membranes.
  • the produced membrane sacrifices its porosity which results in a low water permeability.
  • the produced membranes have a higher porosity and water permeability compared to these that produced using the prior art methods such as given above (see e.g. experimental results) .
  • a porous substrate having nanopores is provided, preferably a ceramic substrate, such as a monolithic membrane with feed channels, as indicated above.
  • the ceramic substrate may be selected from tubular membranes, flat plate membranes, fibre membranes, and
  • the initial pore size is smaller than 5.0 nm, preferably smaller than 3 nm, more preferably smaller than 2 nm, even more preferably smaller than 1.5 nm, such as smaller than 1 nm.
  • a pore size (or likewise MWCO) of a nanofiltration membrane is estimated using MWCO with empirical pore size-MWCO correlations, such as specified by Van der Bruggen and Vandecasteele in "Modelling of the retention of uncharged molecules with nanofiltration” Water Research 36(5) 1360-1368 (2002) or by Shang et al . in
  • the MWCO is determined using a series of non-charged polymers with each a specific molecular weight (Da) and identifying which of the species still can pass through the pores thereby identifying the MWCO.
  • polyethylene glycol (PEG) polymers are typically used, typically a series of 2-50 PEG polymers, such as 5-10 PEG polymers.
  • Actual pore sizes of micro- and ultrafiltration membranes can also be determined by electron microscopy, such as scanning electron microscopy and preferably transmission electron microscopy.
  • Suitable crystalline and non-crystalline ceramic materials are selected from titanates, zirconates, and silicon comprising materials.
  • MWCO molecular Weight Cut-Off
  • R is the rejection, cF the feed concentration of a solute and cP the permeate concentration of this solute.
  • a mixture of dextranes or polyethylene glycols (PEG) covering a broad molecular weight range around the expected MWCO is used.
  • An example of MWCO determination is given in J. Membrane Science, 87 (1994), 35- 46. Tests are carried out in a standardized cell, with
  • the MW distributions of feed and permeate may be determined using Gel Permeation Chromatography (GPC) .
  • GPC Gel Permeation Chromatography
  • one or more atomic layers are deposited, typically 1-30 layers, such as 1-10 layers, preferably 1-5, such as 2-3 or 4 layers.
  • metal comprising layers are deposited, such as metal oxide layers, metal nitride layers, and metal sulphide layers.
  • carbon may be deposited, such as in the form of graphene.
  • the materials are formed via deposition of at least one precursor, typically a vapour, and thereafter an optional reaction between the deposited precursor with a further precursor, such as with an oxygen source precursor, such as water, which may be referred to as a reactant.
  • the atomic layers are deposited on the pore walls of the NF membrane, contrary to prior art methods. Such is achieved by flowing the at least one precursor through the porous
  • Flowing typically relates to diffusive flowing, i.e. by active and/or passive diffusion.
  • a top-layer of the substrate and a support layer of the substrate are provided with a metal source precursor, and (iv) an oxygen source precursor is provided to the surface of the top layer only.
  • the precursors flow over either inside or outside surface of the tubular
  • the advantage of the present process is that the excessive chemical deposition in the micropores is prevented; this is considered a key to fabricate tight NF membranes with high water permeability, as loss of water permeability is prevented.
  • the present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.
  • the substrate is an inorganic nanofiltration membrane with an MWCO of 300-1000 Da, preferably 400-750 Da, such as 500-600 Da. It has been found that a size expressed in an MWCO (Da) can be converted (or coincides) with a size in nm.
  • the substrate pore size therefore relates to 0.7-1.0 nm, such as 0.8-0.9 nm. So one can start with an inorganic membrane that is available on the market with a relatively small pore size and provide atomic layers on the pore walls. Therewith the pore diameter can be reduced by 0.04-0.4 nm.
  • an organic or inorganic precursor is used, wherein the metal is selected from Li, B, C, Mg, Ca, V, Cr, Fe, Co, Ni, Cu, Mo, Al, Si, Ti, Zr, Zn, W, and combinations thereof, preferably an Al, Ti, Zr or W metal source.
  • a metal source precursor is used, preferably TiCl 4 ,
  • titanium, tungsten, and aluminium type layers, respectively, and likewise oxides thereof, can be deposited.
  • the at least one metal precursor comprises a further moiety, wherein the further moiety is selected from halides, alkyls,
  • cyclopentadienyls alkoxides, ⁇ -diketonates, amides, imides, sylils, amidinates, and heterocyclic moieties.
  • moieties are chloride, methyl, methylcyclopentadienyl , 1, 3-cyclohexadiene, ethoxy, acteylactenonato, diethylamide, tert-butylimido, N, ' -diisopropyl-acetamidinato,
  • oxygen peroxide, water, ammonia, a fluoride, a chloride, ozone, hydrogen, nitrogen, nitrogen oxide, phosphohydride, ethoxy, methoxy, and combinations thereof, is used. It is preferred to use an oxygen source precursor, such as deionized water.
  • an oxygen source precursor is deionized water.
  • oxide comprising layers can be deposited.
  • deposition is carried out at a temperature between 373 °K and 573 °K and/or at a (partial) pressure of 1-10 5 Pa. So at an elevated temperature and/or at a wide range of pressures atomic layers are deposited. These boundary conditions give the best results in terms of homogeneity, control of layer thickness, completion of deposition, etc.
  • the vapour pressure of the metal source precursor that conveyed to the reactor is typically lower than 4000 Pa (about 30 Torr) , preferably 650-1300 Pa (about 5-10 Torr) .
  • a pore size is reduced by 0.04-0.4 ran.
  • a top-layer of the substrate and a support layer of the substrate are provided with a metal source precursory during a period of 0.1-30 s, preferably 0.2-10 s, more preferably 1- 5 s .
  • an oxygen source precursor is provided to the surface of the top layer only, such as deionized water, during a period of 0.1-120 sec, preferably 1-60 sec, more preferably 2-30 sec.
  • the membrane is purged with an inert gas, such as nitrogen, preferably during a period of 1-10 min, more preferably 2-8 min, even more preferably 5-7 min.
  • an inert gas such as nitrogen
  • steps (i)- ⁇ v) are repeated 1-30 times, preferably 2-10 times, such as 3, 4 or 5 times.
  • an MWCO is tailored by a number of deposition layers to a value of 10-450 Da, preferably 20-300 Da, more preferably 30-200 Da, such as 50-100 Da.
  • a variety of metal oxide layers is provided therewith forming a stack of layers, the metal oxides being selected from Al oxides, Ti oxides, and W oxides, such as AI2O3, Ti0 2 , and WO x .
  • the above-mentioned tungsten-containing metal source precursors are used to coat tungsten oxide (WO x ) on a stack of layers, the metal oxides being selected from Al oxides, Ti oxides, and W oxides, such as AI2O3, Ti0 2 , and WO x .
  • an extra benefit is that the produced inorganic tight nanofiltration membranes are negatively charged.
  • the negatively charged tight nanofiltration membrane can reject ions more effectively from water or wastewater compared to a non-charged membrane, thanks to an electrostatic repulsion effect .
  • the present invention relates to an inorganic NF membrane obtainable by the present process.
  • the present membrane may therefore be characterized in a molecular weight cut-off size of ⁇ 450 Da, preferably ⁇ 400 Da, more preferably ⁇ 300 Da, even more preferably ⁇ 250 Da, such as ⁇ 200 Da or ⁇ 150 Da, and having a water permeability of more than 1.39 *10 ⁇ 8 l/(m 2 *s*Pa) (5 1/ (m 2 *h*bar) , preferably more than 2.78 *10 ⁇ 8 l/(m 2 *s*Pa), such as more than 5.56 *10 ⁇ 8 1/ (m 2 *s*Pa) .
  • pore sizes are obtained. These values are confirmed by experiments. Such differentiates the present membrane over the above cited prior art.
  • the membranes with smaller pore sizes have a somewhat lower water permeability compared to membranes with relatively large pore sizes .
  • a pore size is smaller than 1 nm.
  • the present membrane has a (negative) layer for rejecting divalent or trivalent ions, typically rejecting cations, such as metal ions.
  • the present membrane has a (negative) layer for rejecting divalent or trivalent ions, typically rejecting cations, such as metal ions.
  • the surface of the membrane has an increased negative charge, preferably by coating with an oxide, such as tungsten oxide. Therewith ion rejection is enhanced.
  • the present invention relates to a use of a membrane according to the invention in fluid treatment, such as water or waste-water treatment, drinking water production, and industrial water production.
  • the present invention relates to a reactor 100 for performing a process according to the
  • a reactor chamber 50 comprising a reactor chamber 50, at least two temperature resistant insulators 31 spaced apart and provided at an inside of the reaction chamber, a first insulator located at a first part of the reactor chamber and a second insulator located at a second part of the reactor chamber, wherein the insulator preferably is an o-ring, at least one inlet 41 for a precursor purge comprising a first valve 11, at least one outlet 42 for a precursor purge comprising a second valve 12, at least one outlet 43 for a precursor purge comprising a third valve 13, wherein the second valve and third valve, respectively, are located to direct a precursor to both the top-layer and support-layer part of a membrane or to the top layer thereof only, and wherein the insulators position the membrane.
  • prior art reactor designs may not suffice, and hence the present improved reactor is provided, intended especially for carrying out the present process.
  • Figures 1 shows certain aspects of the present reactor.
  • Figures 2a, b show flow types.
  • Figs. 2c, d show schematics of ALD.
  • Figure 3a, c show a monolithic ceramic membrane (fig. 3a prior art ⁇ with supply channels of 0.5-2 mm.
  • Figure 4 shows a working principle of a nanofilter.
  • Figures 2a show flow types.
  • Figures 2a Prior Art
  • FIG. 2b both show schematics of a filtration layer 22 located at an outward side of a ceramic nanofiltration membrane.
  • a support layer 21 of the NF membrane is shown.
  • arrows indicate a flow of precursor chemicals.
  • the precursor chemicals pass by and come in contact with only the outer surface of the substrate, including filtration layer (top layer) and the outer surface of the support layer.
  • the flow of precursor chemicals penetrates the top layer of the NF- membrane. Therewith the diffusion of precursor chemicals into the top layer, i.e. the membrane pores, is facilitated and the coating in the membrane pore can be conducted in a reproducible and controllable manner.
  • an intermediate layer 23 may be present .
  • Fig. 2c shows a schematic representation of the present membrane with a small number of atomic layers deposited (e.g. 3) represented by a thin black line 24.
  • Fig. 2d shows a schematic representation of the present membrane with a somewhat larger number of atomic layers deposited (e.g. 6) represented by a thicker black line 24.
  • Figure 3a shows an example of a monolithic ceramic membrane 60 (prior art) with supply channels 70 of 0.5-2 mm.
  • the supply channels are provided in three circular band (19 in total) . It is noted that a number of supply channels could be smaller than 19, but coals also easily exceed a few hundred.
  • the channels are ordered in a hexagonal fashion with respect to a top surface of the membrane. In between bands a free space of 1-10 mm is provided, having no channels. A diameter of the cylindrical membrane filter is from 1-10 cm.
  • Fig. 3b shows an enlargement of a channel section of the pore in fig. 3a.
  • the electron microscope image shows a top Ti0 2 layer 22 of about 0.1 nm, an intermediate AI2O3 layer 23 of about 0.5 nm, and a ceramic support layer 21. In the very top a channel is still visible.
  • Fig. 3c shows an actual cross-section of a membrane, such as that of fig. 3a.
  • FIG 4 shows a working principle of a nanofilter 60.
  • Supply channel 70 are provided through which a contaminated fluid flows, in the example water comprising oil
  • the present invention includes a method to fabricate inorganic tight nanofiltration membranes which can be used e.g. for water and wastewater treatment. This type of
  • a coating of 1-10 layers of metal oxide molecules is homogeneously deposited on a pore wall of a porous substrate, which is an inorganic nanofiltration membrane with MWCO of 450-1000 Da (pore size of 0.8-1.0 nm) , using atomic layer deposition.
  • the metal oxide is formed by a metal source precursor and an oxygen source precursor.
  • the metal source precursor is Titanium Tetrachloride (TiCl 3 ⁇ 4 ) or titanium isopropoxide (Ti (OCH (CH 3 ) 2 ) ) or trimethylaluminum
  • the oxygen source precursor is deionized water.
  • the coating is carried out at a temperature of 373 °K, 473 °K, and 573 °K, respectively. During this process, the diameter of the original pores in the inorganic nanofiltration
  • nanofiltration membrane (substrate) could be carried out in traditional ALD reactors.
  • a novel reactor ( Figure 1) and novel processes are developed to fabricate the inorganic tight nanofiltration membranes.
  • the substrate is loaded in the reactor 50.
  • Two high temperature resistant O-rings 31 are placed to separate the reaction chamber into two parts: a top-layer 22 exposed chamber (connected with valves 11 and 13) and support layer 21 exposed chamber (connected with the valve 12) .
  • the vapours can either be conveyed through the top layer and support layers
  • the present invention also includes a new operation procedure of atomic layer deposition for fabrication of the above mentioned inorganic tight nanofiltration membranes.
  • the procedures are described as followed ( Figure 1):
  • Step 1 open valves 11 and 12; close valve 13; the vapour of the metal source precursor (precursor 41) is penetrated through the substrate 20 from the top-layer 21 to the support layer 20; the exposure time is between 0.1s and 30 s, e.g. depending on a thickness of a layer to be
  • Step 2 (optional) : close valves 11, 12 and 13; wait for 0.5 to 120 min.
  • Step 3 open valves 11, 12; and close valve 13; purge with inert gas (such as nitrogen gas) for 1 to 10 min.
  • inert gas such as nitrogen gas
  • Step 4 open valves 11 and 13; close valve 12; the vapour of the oxygen source precursor (precursor 2) is conveyed via the channels to the surface of the top layer 22; the exposure time is between 1 and 30 min.
  • Step 5 open valves 11 and 12; close valve 13; purge with inert gas (such as nitrogen gas) for 1 to 10 min.
  • inert gas such as nitrogen gas
  • Step 6 to coat another atomic layer of metal oxide, repeat the Steps 1 to 5.
  • the metal precursor is introduced to the membrane substrate using a flow-through approach (Fig. 2b).
  • the metal precursors can react with the entire surface and the pore walls more rapidly compared to the sweep-flow approach (fig. 2a).
  • the purging gas is applied using the flow-through approach as well.
  • the purging can be much more complete within a shorter time, compared to the sweep-flow approach, to avoid overgrowth deep-inside of the membrane support layer.
  • the oxygen source precursor is introduced to the membrane substrate using the sweep-flow approach.
  • the metal oxide layer can be more located in the filtration layer to reduce the pore size in the filtration layer of the ceramic NF membrane.
  • the support layer can still remain with a

Landscapes

  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

The present invention is in the field of a preparation of inorganic tight nanofiltration membranes with a cut-off <450 Da and with high water permeability using atomic layer deposition, a membrane obtained with said process, and applications of such membranes. Inorganic membranes (also called ceramic membranes) are used in water and wastewater treatment as an alternative to polymeric membranes. Advantages of inorganic membranes are that they have a high mechanical strength, a high chemical and thermal resistance, a long lifetime, and they are recyclable as raw ceramic material.

Description

Title: Preparation of inorganic tight nanofiltration membranes
FIELD OF THE INVENTION
The present invention is in the field of a preparation of inorganic tight nanofiltration (NF) membranes with a cutoff <450 Da and with high water permeability using atomic layer deposition, a membrane obtained with said process, and applications of such membranes.
BACKGROUND OF THE INVENTION
Inorganic membranes (also called ceramic membranes) are used in water and wastewater treatment as an alternative to polymeric membranes. Advantages of inorganic membranes are that they have a high mechanical strength, a high chemical and thermal resistance, a long lifetime, and they are
recyclable as raw ceramic material. Based on the pore size of the membranes, the inorganic membranes can be classified in three types: inorganic microfiltration membranes with a pore size ranging from about 0.1 to 10 urn) inorganic
ultrafiltration membranes with a molecular weight cut-off {MWCO} ranging from about 103 to 106 Da, which coincides with pore sizes ranging from 0.001 to 0.1 μπι; and the inorganic nanofiltration membranes with a MWCO ranging from 100 to 1000 Da) .
At present inorganic tight nanofiltration membranes, i.e. with an MWCO <450 Da, that still have good water
permeability, i.e. larger than 1.39 *10~8 l/(m2*s*Pa) (5
1/ (m2*h*bar) , have not been commercially fabricated. Using a traditional sol-gel method commercial inorganic
nanofiltration membranes are made having an MWCO ranging from 450 Da to 1000 Da. In the laboratory scale, an inorganic nanofiltration membrane with a MWCO of 200 Da could be produced via a sol-gel method.
Inorganic membranes that are made of zeolite can be fabricated using a zeolite crystallization method. Such a zeolite membrane has ultra-micropores ranging from 0.3 to 0.7 nm (MWCO <200 Da) . However, their water permeability is very low (0.8-2.7 *10-11 l/{m2*s*Pa) ) since they are produced with a thick zeolite crystallized layer of 5-50 micrometers.
Therefore, zeolite membranes that could be used for water treatment have not been commercialized yet.
To be applied for e.g. water treatment such membranes must have a high water permeability, i.e. a water
permeability larger than 1.39 *10"8 l/{m2*s*Pa). No proper method has been proposed to fabricate such type of membranes. Some disadvantages of prior art methods are detailed below. By using the traditional sol-gel method, it is hard to produce an inorganic tight nanofiltration membranes with a well-defined specific pore size (MWCO) . Therein, firstly a polymeric sol is normally required to dip-coat a top-layer (filtration layer) of micropores. It requires ultrafine sol particles around 1-2 nm in size. The smallest MWCO so far via this method is 200 Da. Secondly, in the sol-gel method, multilayer coating for fabrication of the inorganic tight nanofiltration is adopted and a sintering process is normally needed for coating of each layer which normally is time- consuming (12-24 hours) . The sol-gel method is also energy consuming because each cycle requires wetting, drying and sintering at 473-1474 °K (200-1200 °C) . A single layer coating may results in pin-holes or cracks in the final top- layer, while multiple layer coating typically leads to an excessive thick top-layer. In addition such a thick top-layer shows high water resistance, i.e. low water permeability. Therefore, an inorganic tight nanofiltration membrane with MWCO <450 Da, yet with a high water permeability, has not been fabricated using the sol-gel method so far.
The zeolite membranes typically have a very thick top- layer, which results in extremely low water permeability.
Some prior art documents recite fabrication of NF membranes, as indicated below.
Tsuru, Wada et al. in "Silica-zirconia membranes for nanofiltration . " Journal of Membrane Science 149(1}: 127-135. (1998) fabricated silica-zirconia nanofiltration membranes via colloidal sol-gel methods. Four colloidal sol solutions of different colloidal diameters were prepared for the coating. The authors firstly coated the colloidal sol of a relatively bigger colloidal diameter on the substrate as an intermediate layer and then coated the colloidal sol of smaller colloidal diameter as a top-layer. By choosing different colloidal diameters of sol solutions at a final coating stage, membranes of different MWCO between 200 and 1000 Da were fabricated. Pure water permeabilities ranged from O.lSxlO^8 to 1.5*10~8 1 rrf2 s"1 Pa-1, which is considered very low. So the fabricated tight nanofiltration membrane
(larger than 200 Da) has a relatively low water permeability, contrary to prevailing polymeric tight nanofiltration
membranes which have a water permeability of 1.39-1.94 χΐθ"8
1 rrf2 s_1 Pa-1 (1000 times or more larger) .
PuhlfurB, Voigt et al. in " icroporous Ti02 membranes with a cut off <500 Da.", Journal of Membrane Science 174(1): 123-133 (2000) fabricated Ti02 membranes by a polymeric sol- gel technique on top of a tubular ceramic multi-layer
support. The top layer of this multi-layer structure was a niesoporous ΊΊΟ2 layer with a thickness of 250 nm and a mean pore size of 5 nm. After coating this multi-layer structure, a polymeric gel was formed and finally dried for 1 h at room temperature. These membranes had a MWCO of 480 Da. The membrane top-layer had a thickness of only 50 nm
approximately. In this case, a water permeability of 5.56 xlO-8 1 rrf2 s_1 Pa"1 was achieved, which is acceptable.
Van Gestel, Vandecasteele et al . in "Alumina and titania multilayer membranes for nanofiltratio : preparation,
characterization and chemical stability." Journal of Membrane Science 207(1): 73-89 (2002) produced 2 inorganic
nanofiltration membranes with an MWCO of 200 Da via the sol- gel methods. One of the membranes was made of a Y-AI2O3 intermediate layer and an anatase (Ti02) top-layer. It showed a water permeability of 1.11 χΐθ"8 1 rrf2 s'1 Pa"1, but showed a low corrosion resistance compared to e.g. Ti02 membranes. The other inorganic nanofiltration membrane consisted of an anatase intermediate ultra-filtration (UF) -membrane support modified with an optimized anatase top-layer obtained by a very slow drying process. For such a tight nanofiltration membrane the permeability is strongly reduced (0.56 *10~5 1 rrf
2 s'1 Pa-1) . The low water permeability was a result of their thick coating layers. Titania (Ti02) layers obtained by a single dip-coating procedure showed an average thickness of about 0.5 μιη. Therefore, a second dipping procedure had to be used to increase the membrane thickness up to about 1 μπι.
Li, Yang et al. in "Modification of ceramic membranes for pore structure tailoring: The atomic layer deposition route.", Journal of Membrane Science 397-398(0): 17-23 (2012) and Nangmenyi, Lin et al. in "Experimental investigation of inorganic nanofiltration membranes prepared by atomic layer deposition and sol-gel methods for saltless water
softening.", International Journal of Environmental
Technology and Management 16(1-2): 21-33 (2013) applied atomic layer deposition to macroporous inorganic substrates, respectively, in order to narrow the pores. Li claims to have succeeded in narrowing the pore size from 50 nm to about 6.8 nm after 600 cycles of atomic layer deposition. The water permeability decreased from 0.47 *10"8 1/ (m2*s*Pa) to 0.032 *10"8 1/ (m2*s*Pa) .
Nangmenyi et al. in "Experimental investigation of inorganic nanofiltration membranes prepared by atomic layer deposition and sol-gel methods for salt less water
softening.", International Journal of Environmental
Technology and Management, 16(1-2), 21-33 (2013) claimed that they have made an inorganic nanofiltration by narrowing the macropores in the substrate to micropores, but the MWCO was not measured by the authors. They did also not mention the number of cycles that had been applied to the macroporous substrate to produce the so-called nanofiltration . They reported that the water permeability was decreased from 13.8 *10"5 l/(m2*s*Pa) for the undeposited membrane to
approximately 5.0 *10~5 1/ (m2*s*Pa) for the produced claimed nanofiltration membranes. These reported results however are not convincing and seem inconsistent. It is noted that the claimed nanofiltration has an extremely high water
permeability, which is (still) one third of the water
permeability of the macroporous undeposited membrane. It is observed that in a given coating process no new pores will be created; as a consequence a nanofiltration membrane that has been coated is expected to have had a water permeability that is approximately two orders of magnitude {i.e. 100 times) lower than the undeposited macroporous membrane. However, as reported by Nangmenyi the produced ultrafiltration membrane is claimed to have already a water permeability that is only one order of magnitude lower than the undeposited macroporous membrane. Nangmenyi did not give any explanation on the above results which are therefore considered atypical. In addition no details of the procedure of atomic layer deposition was given .
Li and Wang disclosed a method for continuously
precisely adjusting bore diameter of ceramic film in patent application CN102491777 A, as well as in Li, Wang et al. in "Method for continuously precisely adjusting bore diameter of ceramic film." 2012). The method includes a flow type ALD reactor, in which the precursors are exposed to the
substrate. The method also includes a short exposure/purging time which are 0.01-1 s and 0-60 s, respectively. Based on this method a ceramic microflitration membrane can be
modified to a ceramic ultrafiltration membrane, evidenced by a significantly improved bovine serum albumin (BSA)
rej ection .
Patent US8518845 B2 discloses a method which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate using ALD.
Patent application EP1884578 Al discloses that ALD can be used to narrow the pore diameter by coating atomic layers on the pore walls and the pores was specified to be 40~S0 nm in diameter.
However, the aforementioned patent documents and
publication do not include a method for fabrication of ceramic nanofiltration membranes, which have a very small pore size and are able to reject divalent ions. The
aforementioned ALD methods will not be applicable when the pore size is too small.
EP 2 138 222 (Al) recites a method which can be used for pore size reduction, defect repair and in general for
improving of the separation properties of microporous and nanoporous membranes. A chemical vapour (CVD type)
infiltration method can be applied at temperatures of 200-300 °C, using available sealing technologies. A microporous membrane, which contains defects with a low selectivity, is modified to a microporous and/or nanoporous membrane of high selectivity. Membranes without defects and with pore sizes less than 1 nm, but still larger than 0.5 ran, are formed.
US 5,503,873 (A) recites a CVD method of forming
inorganic membranes which are highly selective to permeation of hydrogen by temporarily forming a carbon barrier in the pores of a porous substrate, followed by chemical deposition of S1O2, B2O3, T1O2, I2O3 and mixtures thereof in the pores, followed by removal of the carbon barrier. Permeation
selective layers thusly formed have an increased permeance of hydrogen. Suitable porous substrate are glass or Al203.
US 6,649,255 (Bl) recites a method for producing
extremely small pore size inorganic membranes, such as metal oxides, metal carbides, metal nitrides and cermets. Mean pore diameters of below about 1.0 nm can be achieved. The pore size of the membrane is progressively reduced in a controlled manner to deposit one or more layers of an inorganic compound on the pore walls, by exposing the membrane to the vapour of an inorganic precursor compound. Water vapour, oxygen, or vapours containing one or more oxygen ligands are further used to hydrolyse the deposited material to the inorganic membrane .
The above three patent documents use only a relatively simple flow through approach or exposure in a chamber. The do not provide membranes with good selectivity and high
permeability, amongst others. In addition the approach may lead to excessive chemical deposition in the micropores; such may be beneficial to gas separation, but it is found to lead to a dramatic loss of water permeability. However, the membrane permeability for hydrogen gas is considered to be relatively low (in the order of 1 cm3/ (cm2 min 100 kPa) . The water permeability of such membranes was not determined and is expected to be much lower than the said hydrogen
permeability. It is noted that water permeability is not reported in the patents.
Kemell et al. in "Coating of highly porous fibre
matrices by atomic layer deposition", Chem. Vapour
Deposition, Wiley, Vol. 14, No. 11/12, (1-11-2008), p. 347- 352 recite atomic layer deposition in a coating of a porous 0.5 mm thick metal fibre matrix, which is different from a membrane. A1203 films are deposited with various processes. The coatings are to protect the fibres against
electrochemical corrosion and thermal oxidation. Further a metallic Ir film may be deposited in view of catalytic properties. When a selective membrane is made via this method, all the pores in the porous substrate are narrowed, resulting in significant loss of porosity and loss of water permeability.
The present invention therefore relates to an improved process for preparation of inorganic tight nanofiltration (NF) membranes with a cut-off <450 Da and with high water permeability using atomic layer deposition, which solves one or more of the above problems and drawbacks of the prior art, providing reliable results, without jeopardizing
functionality and advantages.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome one or more limitations of the devices of the prior art and at the very least to provide an alternative thereto.
In a first aspect, the invention relates to a process for the preparation of inorganic tight nanofiltration (NF) membranes with a cut-off <450 Da and with high water
permeability of above 5 *10"5 1/ (m2*h*Pa) (1.39 *10"8
1/ (m2*s*Pa) ) , combined with a good selectivity, using atomic layer deposition according to claim 1, an inorganic tight nanofiltration (NF) membrane obtainable by said process according to claim 15, use of said membrane according to claim 20, and a reactor for said process according to claim 21. The present membranes are especially suited for (use in) membranes for liquids, such as water. The term "liquid" is used in its usual meaning being a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure.
A flow-through ALD reactor for fabrication of a ceramic nanofiltration (NF) membrane is provided. A novel operational procedure of this flow-through type ALD reactor with 3 inlets (or outlets) is also provided to fabricate ceramic NF with high water permeability. A tubular porous substrate may be placed in the holder with three in-/outlets. In an example reactant vapours (precursors) pass either through the inside or the outside surface of the tube, while a purging gas passes through the tube either from inside to outside or from outside to inside of the tube. One of the significant
drawbacks of the prior art methods is that purging in the micropores cannot be completed, or otherwise purging should last very long. An insufficient purging in the pores is found to result in excessive deposition in the pores, and
therefore, results in a significantly decreased water
permeability. The present innovative design allows controlled growth of homogeneous layers in the pores of the tubular membrane, such as metal oxide layers, such as TiC>2. At the same time deposition growth is limited to the outside or inside surface of the porous tube. A benefit of this method is a minimized loss of porosity and water permeability of the fabricated membranes.
Furthermore, a process to fabricate high water permeable ceramic NF membranes using a plasma-enhanced ALD is provided. In an example a substrate disc-shape is placed in a vacuum reaction chamber. The first precursor, e.g. T1CI4, is
provided to the surface of the substrate and a purging process is followed to remove excessive, non-reacted
precursor. Thereafter, the second precursor, e.g. O2, is dosed in the reaction chamber followed with plasma exposure and another purging. A single layer of in this case Ti-oxide is coated on the surface and in the pores of the substrate. By repeating the above described coating cycle, thicker layers are coated and the pore size of the substrate is reduced accordingly.
It is well-known and widely reported that one of the drawbacks of plasma-enhanced ALD is the reduced conformality or step coverage when the substrates have surface structures of high aspect ratio or very high surface areas. However, the present process of using plasma-enhanced ALD for microporous membrane coating limits the deposition to a small depth that is near the pore openings. Deep penetration of coated layer into the microporous substrates is avoided, and therefore, the fabricated ceramic NF membranes have low filtration resistance and high water permeability. To apply atomic layer deposition (ALD) for tailoring the pore size of nanofiltration membranes has been found a big step and a challenge up to now. As mentioned above a
nanofiltration membrane has pores that are one magnitude smaller than the pores in ultrafiltration membranes. As a result it has been found at least cumbersome to coat the nanopores of the nanofiltration membranes and specifically to coat pore walls, which is found to be a crucial step to tailor the pore size of a nanofiltration membrane.
With respect to ALD and CVD techniques some important differences are present. In ALD the precursors are separated in time, whereas in CVD they are applied at the same time. A result is that CVD can not coat thin layers; typically CVD is limited to depositing layers of 1 nm or more. CVD is applied in the past for ceramic membrane coating, but only for gas separation membranes, because a membrane is formed with a too high resistance for water applications.
In an example of the present process inorganic tight nanofiltration membranes are produces by modifying an
inorganic membrane with MWCO of 480 Da using atomic layer deposition methods. In this respect it is noted that in the nano-size domain the MWCO decreases rapidly with the pore size, for instance a pores size of 5 nm corresponds to an MWCO of approximately 104 Da, whereas a pore size of 0.8 nm corresponds to 480 Da. The 480 Da membrane may be fabricated using the same method that is described in Puhlfiir (see above). By coating homogeneous atomic layers of e.g. T1O2 on the pore wall of the 480 Da inorganic membrane, a membrane with tighter pores is produced, while the thickness of the top-layer will be increased by less than 0.5 nm only.
Innovatively, after the introduction of the metal source precursor and before the purging, a contact time may be applied (e.g. 0.5 minute, 1 minute, 10 minutes, 20 minutes, 60 minutes, and 120 minutes) between precursors (e.g.
titanium tetrachloride) and membrane pores, as well as an extremely long purging time to ensure complete clearance of the remaining precursors. By using this method it has been found that the precursors are able to attach in the membrane pores, so that the atomic layers are deposited in the membrane pores, thereby reducing the pore size. Outside the membrane pores deposition may take place as well.
Furthermore, a flow-through ALD reactor for fabrication of ceramic NF membrane is provided. Although a flow-through ALD reactor has been reported by Kemell (see above), the present inventors designed an innovative flow-through ALD reactor that can hold a ceramic tubular membrane (Figure 1). Flow rates applied in the reactor and in the present process are typically in the order of 10"6-1 m3/ (m2skPa) {@ 40 °C) , such as 10"4-0.5 m3/(m2skPa), e.g. 10~ -0.2 m3/ (m2skPa) . The pressure in the present system is typically 50-1000 kPa (0.5- 10 bar), such as 100-500 kPa. The convection flow rate is typically controlled by mass flow controllers. This
innovative design allows controlled growth of homogeneous layers in the filtration layer of the tubular membrane, such as metal oxide layers, such as T1O2- A benefit of this method is a minimized loss of porosity and water permeability of the fabricated membranes.
In the present invention only a few cycles of coating (i.e. 1-10 cycles, such as 2-5 cycles, e.g. 3 or 4 cycles) are needed for fabrication of a tight nanofiltration
membrane. It has been found that when an excessive amount of coating layers is applied to the membrane pores, the produced membrane sacrifices its porosity which results in a low water permeability. By using the method proposed in this invention, the produced membranes have a higher porosity and water permeability compared to these that produced using the prior art methods such as given above (see e.g. experimental results) .
Further advantages are that no wetting/drying sintering cycles are required. Also an easy control and scale up to large modules of the present process is provided.
In the present process first a porous substrate having nanopores is provided, preferably a ceramic substrate, such as a monolithic membrane with feed channels, as indicated above. The ceramic substrate may be selected from tubular membranes, flat plate membranes, fibre membranes, and
combinations thereof. The initial pore size is smaller than 5.0 nm, preferably smaller than 3 nm, more preferably smaller than 2 nm, even more preferably smaller than 1.5 nm, such as smaller than 1 nm. Typically a pore size (or likewise MWCO) of a nanofiltration membrane is estimated using MWCO with empirical pore size-MWCO correlations, such as specified by Van der Bruggen and Vandecasteele in "Modelling of the retention of uncharged molecules with nanofiltration" Water Research 36(5) 1360-1368 (2002) or by Shang et al . in
"Hydraulically irreversible fouling on ceramic MF/UF
membranes: Comparison of fouling indices, foulant composition and irreversible pore narrowing", Separation and Purification Technology 147 303-310 (2015) . The MWCO is determined using a series of non-charged polymers with each a specific molecular weight (Da) and identifying which of the species still can pass through the pores thereby identifying the MWCO. In this respect polyethylene glycol (PEG) polymers are typically used, typically a series of 2-50 PEG polymers, such as 5-10 PEG polymers. Actual pore sizes of micro- and ultrafiltration membranes can also be determined by electron microscopy, such as scanning electron microscopy and preferably transmission electron microscopy. Suitable crystalline and non-crystalline ceramic materials are selected from titanates, zirconates, and silicon comprising materials.
The Molecular Weight Cut-Off (MWCO) value often is used by membrane manufacturers to characterize their porous ultrafiltration membranes. It is a typical permeation-related membrane characteristic. The value is typically defined as the molecular weight (MW) which is rejected for 90%. The rejection is typically defined as
R = (cF - cP)/cF = 1 - (cP/cF) where R is the rejection, cF the feed concentration of a solute and cP the permeate concentration of this solute. In view of variables preferably a mixture of dextranes or polyethylene glycols (PEG) covering a broad molecular weight range around the expected MWCO is used. An example of MWCO determination is given in J. Membrane Science, 87 (1994), 35- 46. Tests are carried out in a standardized cell, with
standard conditions for the measurements. PEG polymers of for instance 104 Da, 2000 Da, 1000 Da, 800 Da, 600 Da, 500 Da, 400 Da, 300 Da, and 100 Da. After the permeation experiment is carried out, the MW distributions of feed and permeate may be determined using Gel Permeation Chromatography (GPC) . By calculating the rejection for each MW using the equation mentioned before, the rejection as a function of MW can be determined in a single permeation experiment. The molecular weight where the rejection is 90% now easily can be verified.
In addition one or more atomic layers are deposited, typically 1-30 layers, such as 1-10 layers, preferably 1-5, such as 2-3 or 4 layers. Typically metal comprising layers are deposited, such as metal oxide layers, metal nitride layers, and metal sulphide layers. In this respect also carbon may be deposited, such as in the form of graphene. In view thereof the materials are formed via deposition of at least one precursor, typically a vapour, and thereafter an optional reaction between the deposited precursor with a further precursor, such as with an oxygen source precursor, such as water, which may be referred to as a reactant. The atomic layers are deposited on the pore walls of the NF membrane, contrary to prior art methods. Such is achieved by flowing the at least one precursor through the porous
substrate and sequentially by introducing a reactant in vapour form {which reacts with the first precursor e.g. to form metal oxide) to the surface of the top-layer of the substrate. Flowing typically relates to diffusive flowing, i.e. by active and/or passive diffusion.
Also (i) first a top-layer of the substrate and a support layer of the substrate are provided with a metal source precursor, and (iv) an oxygen source precursor is provided to the surface of the top layer only.
In an example of the present process the precursors flow over either inside or outside surface of the tubular
substrate, while the purging gas flows through the tube
(either from inside to outside, or from outside to inside) . The advantage of the present process is that the excessive chemical deposition in the micropores is prevented; this is considered a key to fabricate tight NF membranes with high water permeability, as loss of water permeability is prevented.
The present invention provides a solution to one or more of the above mentioned problems and overcomes drawbacks of the prior art.
Advantages of the present description are detailed throughout the description.
DETAILED DESCRIPTION OF THE INVENTION
In an exemplary embodiment of the present process the substrate is an inorganic nanofiltration membrane with an MWCO of 300-1000 Da, preferably 400-750 Da, such as 500-600 Da. It has been found that a size expressed in an MWCO (Da) can be converted (or coincides) with a size in nm. The substrate pore size therefore relates to 0.7-1.0 nm, such as 0.8-0.9 nm. So one can start with an inorganic membrane that is available on the market with a relatively small pore size and provide atomic layers on the pore walls. Therewith the pore diameter can be reduced by 0.04-0.4 nm.
In an exemplary embodiment of the present process as a metal source an organic or inorganic precursor is used, wherein the metal is selected from Li, B, C, Mg, Ca, V, Cr, Fe, Co, Ni, Cu, Mo, Al, Si, Ti, Zr, Zn, W, and combinations thereof, preferably an Al, Ti, Zr or W metal source.
In an exemplary embodiment of the present process a metal source precursor is used, preferably TiCl4,
Ti (OCH (CH3) 2) 4 , WFe, W0C14, or Al2Me6. Therewith titanium, tungsten, and aluminium type layers, respectively, and likewise oxides thereof, can be deposited.
In an exemplary embodiment of the present process the at least one metal precursor comprises a further moiety, wherein the further moiety is selected from halides, alkyls,
cyclopentadienyls, alkoxides, β-diketonates, amides, imides, sylils, amidinates, and heterocyclic moieties. Examples of such moieties are chloride, methyl, methylcyclopentadienyl , 1, 3-cyclohexadiene, ethoxy, acteylactenonato, diethylamide, tert-butylimido, N, ' -diisopropyl-acetamidinato,
triethylphosphine, dimethylamino-2-propoxy, and combinations thereof .
In an exemplary embodiment of the present process as second reactant precursor oxygen, peroxide, water, ammonia, a fluoride, a chloride, ozone, hydrogen, nitrogen, nitrogen oxide, phosphohydride, ethoxy, methoxy, and combinations thereof, is used. It is preferred to use an oxygen source precursor, such as deionized water.
In an exemplary embodiment of the present process an oxygen source precursor is deionized water. Therewith oxide comprising layers can be deposited.
In an exemplary embodiment of the present process deposition is carried out at a temperature between 373 °K and 573 °K and/or at a (partial) pressure of 1-105 Pa. So at an elevated temperature and/or at a wide range of pressures atomic layers are deposited. These boundary conditions give the best results in terms of homogeneity, control of layer thickness, completion of deposition, etc. In an example, When the deposition takes place under atmospheric pressure, i.e. 105 Pa, the vapour pressure of the metal source precursor that conveyed to the reactor is typically lower than 4000 Pa (about 30 Torr) , preferably 650-1300 Pa (about 5-10 Torr) .
In an exemplary embodiment of the present process a pore size is reduced by 0.04-0.4 ran.
In an exemplary embodiment of the present process (i) first a top-layer of the substrate and a support layer of the substrate are provided with a metal source precursory during a period of 0.1-30 s, preferably 0.2-10 s, more preferably 1- 5 s .
In an exemplary embodiment of the present process wherein (iv) an oxygen source precursor is provided to the surface of the top layer only, such as deionized water, during a period of 0.1-120 sec, preferably 1-60 sec, more preferably 2-30 sec.
In an exemplary embodiment of the present process in steps (ii and v) the membrane is purged with an inert gas, such as nitrogen, preferably during a period of 1-10 min, more preferably 2-8 min, even more preferably 5-7 min.
In an exemplary embodiment of the present process in between steps (iii) a rest period of 0.05-120 min is
provided, preferably during a period of 2-20 min, more preferably 5-15 min, even more preferably 8-10 min.
In an exemplary embodiment of the present process steps (i)-{v) are repeated 1-30 times, preferably 2-10 times, such as 3, 4 or 5 times.
In an exemplary embodiment of the present process an MWCO is tailored by a number of deposition layers to a value of 10-450 Da, preferably 20-300 Da, more preferably 30-200 Da, such as 50-100 Da.
In an exemplary embodiment of the present process a variety of metal oxide layers is provided therewith forming a stack of layers, the metal oxides being selected from Al oxides, Ti oxides, and W oxides, such as AI2O3, Ti02, and WOx. When the above-mentioned tungsten-containing metal source precursors are used to coat tungsten oxide (WOx) on
substrates, an extra benefit is that the produced inorganic tight nanofiltration membranes are negatively charged. The negatively charged tight nanofiltration membrane can reject ions more effectively from water or wastewater compared to a non-charged membrane, thanks to an electrostatic repulsion effect .
In a second aspect the present invention relates to an inorganic NF membrane obtainable by the present process. As has been identified in the description the present process provides certain advantages. The present membrane may therefore be characterized in a molecular weight cut-off size of <450 Da, preferably < 400 Da, more preferably < 300 Da, even more preferably < 250 Da, such as < 200 Da or < 150 Da, and having a water permeability of more than 1.39 *10~8 l/(m2*s*Pa) (5 1/ (m2*h*bar) , preferably more than 2.78 *10~8 l/(m2*s*Pa), such as more than 5.56 *10~8 1/ (m2*s*Pa) . In addition well defined pore sizes are obtained. These values are confirmed by experiments. Such differentiates the present membrane over the above cited prior art. Typically the membranes with smaller pore sizes have a somewhat lower water permeability compared to membranes with relatively large pore sizes .
In an exemplary embodiment of the present membrane a pore size is smaller than 1 nm.
In an exemplary embodiment the present membrane has a (negative) layer for rejecting divalent or trivalent ions, typically rejecting cations, such as metal ions. In an exemplary embodiment the present membrane
comprises a homogeneous metal oxide filtration layer and a tubular membrane.
In an exemplary embodiment of the present membrane the surface of the membrane has an increased negative charge, preferably by coating with an oxide, such as tungsten oxide. Therewith ion rejection is enhanced.
In a third aspect the present invention relates to a use of a membrane according to the invention in fluid treatment, such as water or waste-water treatment, drinking water production, and industrial water production.
In a fourth aspect the present invention relates to a reactor 100 for performing a process according to the
invention, comprising a reactor chamber 50, at least two temperature resistant insulators 31 spaced apart and provided at an inside of the reaction chamber, a first insulator located at a first part of the reactor chamber and a second insulator located at a second part of the reactor chamber, wherein the insulator preferably is an o-ring, at least one inlet 41 for a precursor purge comprising a first valve 11, at least one outlet 42 for a precursor purge comprising a second valve 12, at least one outlet 43 for a precursor purge comprising a third valve 13, wherein the second valve and third valve, respectively, are located to direct a precursor to both the top-layer and support-layer part of a membrane or to the top layer thereof only, and wherein the insulators position the membrane. For performing the present process prior art reactor designs may not suffice, and hence the present improved reactor is provided, intended especially for carrying out the present process.
The invention will hereafter be further elucidated through the following examples which are exemplary and explanatory of nature and are not intended to be considered limiting of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims.
SUMMARY OF THE FIGURES
Figures 1 shows certain aspects of the present reactor. Figures 2a, b show flow types.
Figs. 2c, d show schematics of ALD.
Figure 3a, c show a monolithic ceramic membrane (fig. 3a prior art} with supply channels of 0.5-2 mm.
Figure 4 shows a working principle of a nanofilter.
In the figures:
100 reactor
11 valve 1
12 valve 2
13 valve 3
20 substrate
21 support layers
22 top layers
23 intermediate layer
24 ALD layer (s)
31 o-ring
41 precursor purge inlet
42 precursor purge outlet 1
43 precursor purge outlet 2
50 reactor chamber
60 monolithic membrane
70 supply channel
72 pore
Figure 1 is detailed in the examples and description .
Figures 2a, show flow types. Figures 2a (Prior Art) and
2b both show schematics of a filtration layer 22 located at an outward side of a ceramic nanofiltration membrane. In addition a support layer 21 of the NF membrane is shown. In fig. 2a arrows indicate a flow of precursor chemicals. In a typical flow type ALD reactor, the precursor chemicals pass by and come in contact with only the outer surface of the substrate, including filtration layer (top layer) and the outer surface of the support layer. In fig. 2b the flow of precursor chemicals penetrates the top layer of the NF- membrane. Therewith the diffusion of precursor chemicals into the top layer, i.e. the membrane pores, is facilitated and the coating in the membrane pore can be conducted in a reproducible and controllable manner. In addition to the top layer 22 and support layer 22 an intermediate layer 23 may be present .
Fig. 2c shows a schematic representation of the present membrane with a small number of atomic layers deposited (e.g. 3) represented by a thin black line 24.
Fig. 2d shows a schematic representation of the present membrane with a somewhat larger number of atomic layers deposited (e.g. 6) represented by a thicker black line 24.
Figure 3a shows an example of a monolithic ceramic membrane 60 (prior art) with supply channels 70 of 0.5-2 mm. The supply channels are provided in three circular band (19 in total) . It is noted that a number of supply channels could be smaller than 19, but coals also easily exceed a few hundred. The channels are ordered in a hexagonal fashion with respect to a top surface of the membrane. In between bands a free space of 1-10 mm is provided, having no channels. A diameter of the cylindrical membrane filter is from 1-10 cm.
Fig. 3b shows an enlargement of a channel section of the pore in fig. 3a. The electron microscope image shows a top Ti02 layer 22 of about 0.1 nm, an intermediate AI2O3 layer 23 of about 0.5 nm, and a ceramic support layer 21. In the very top a channel is still visible.
Fig. 3c shows an actual cross-section of a membrane, such as that of fig. 3a.
Figure 4 shows a working principle of a nanofilter 60. Supply channel 70 are provided through which a contaminated fluid flows, in the example water comprising oil
schematically represented in the top right container. The water passes through pores 72, whereas the oil flows through the supply channels 70. As a result clean water (middle right container) and contaminate (oil) (lift container) are
obtained .
EXAMPLES
Example 1.
The present invention includes a method to fabricate inorganic tight nanofiltration membranes which can be used e.g. for water and wastewater treatment. This type of
inorganic nanofiltration membranes meets the followed
criteria: a MWCO less than 450 Da and good water permeability larger than 1.39*10"8 1/ (m2*s*Pa) (5 1/ (m2*h*bar) , such as 8.3*10"Θ l/(m2*s*Pa). In the present process a coating of 1-10 layers of metal oxide molecules is homogeneously deposited on a pore wall of a porous substrate, which is an inorganic nanofiltration membrane with MWCO of 450-1000 Da (pore size of 0.8-1.0 nm) , using atomic layer deposition. In the atomic layer deposition method, the metal oxide is formed by a metal source precursor and an oxygen source precursor. Herein, the metal source precursor is Titanium Tetrachloride (TiCl¾) or titanium isopropoxide (Ti (OCH (CH3) 2) ) or trimethylaluminum
(Al2 e6) ; the oxygen source precursor is deionized water. The coating is carried out at a temperature of 373 °K, 473 °K, and 573 °K, respectively. During this process, the diameter of the original pores in the inorganic nanofiltration
membranes is narrowed by 0.04 to 0.4 nm, and an inorganic tight nanofiltration membrane with MWCO < 450 Da is produced. The atomic layer deposition to the proposed inorganic
nanofiltration membrane (substrate) could be carried out in traditional ALD reactors. However, in order to form the deposited layers only in the top layer of the substrate, a novel reactor (Figure 1) and novel processes are developed to fabricate the inorganic tight nanofiltration membranes.
The substrate is loaded in the reactor 50. Two high temperature resistant O-rings 31 are placed to separate the reaction chamber into two parts: a top-layer 22 exposed chamber (connected with valves 11 and 13) and support layer 21 exposed chamber (connected with the valve 12) . By
controlling of the valves, the vapours (precursors 41) can either be conveyed through the top layer and support layers
(43) , or be introduced to merely the surface of the top layer
(42) .
Example 2
The present invention also includes a new operation procedure of atomic layer deposition for fabrication of the above mentioned inorganic tight nanofiltration membranes. The procedures are described as followed (Figure 1):
Step 1: open valves 11 and 12; close valve 13; the vapour of the metal source precursor (precursor 41) is penetrated through the substrate 20 from the top-layer 21 to the support layer 20; the exposure time is between 0.1s and 30 s, e.g. depending on a thickness of a layer to be
deposited .
Step 2 (optional) : close valves 11, 12 and 13; wait for 0.5 to 120 min.
Step 3: open valves 11, 12; and close valve 13; purge with inert gas (such as nitrogen gas) for 1 to 10 min.
Step 4: open valves 11 and 13; close valve 12; the vapour of the oxygen source precursor (precursor 2) is conveyed via the channels to the surface of the top layer 22; the exposure time is between 1 and 30 min.
Step 5: open valves 11 and 12; close valve 13; purge with inert gas (such as nitrogen gas) for 1 to 10 min.
Step 6: to coat another atomic layer of metal oxide, repeat the Steps 1 to 5.
Advantages of using the reaction chamber illustrated in
Figure 1 and of using the above operation procedure are:
- The metal precursor is introduced to the membrane substrate using a flow-through approach (Fig. 2b). The metal precursors can react with the entire surface and the pore walls more rapidly compared to the sweep-flow approach (fig. 2a).
- The purging gas is applied using the flow-through approach as well. The purging can be much more complete within a shorter time, compared to the sweep-flow approach, to avoid overgrowth deep-inside of the membrane support layer.
- The oxygen source precursor is introduced to the membrane substrate using the sweep-flow approach. The metal oxide layer can be more located in the filtration layer to reduce the pore size in the filtration layer of the ceramic NF membrane. The support layer can still remain with a
relatively high porosity, which is found crucial to reduce the filtration resistance of the produced membrane.

Claims

1. Process for producing an inorganic nanofiltration membrane comprising
providing a porous substrate having micropores with an initial pore size smaller than 5 nm, preferably a ceramic substrate, such as a monolithic membrane with feed channels, providing at least one precursor of a layer material to be deposited, the layer comprising a metal,
(i) depositing 1-30 metal comprising layers by atomic layer deposition on pore walls of the substrate by flowing the at least one precursor through the porous substrate,
wherein first a top-layer of the substrate and a support layer of the substrate are provided with a metal source precursor,
(ii) optionally purging with an inert gas,
(iii) optionally providing a rest period,
(iv) providing an oxygen source precursor to the surface of the top layer only, and
(v) optionally purging with an inert gas.
2. Process according to claim 1, wherein the substrate is an inorganic nanofiltration membrane with a molecular weight cut-off (MWCO) (as determined by using a series of non- charged polymers with each a specific molecular weight (Da) ) of 450-1000 Da or with a pore size of 0.7-1.0 nm (as
determined by electron microscopy) .
3. Process according to any of the preceding claims, wherein as a metal source an organic or inorganic precursor is used, wherein the metal is selected from Li, B, C, Mg, Ca, V, Cr, Fe, Co, Ni, Cu, Mo, Al, Si, Ti, Zr, Zn, W, and
combinations thereof, preferably an Al, Ti, Zr or W metal source .
4. Process according to any of the preceding claims, wherein the at least one metal precursor comprises a further moiety, wherein the further moiety is selected from halides, alkyls, cyclopentadienyls , alkoxides, β-diketonates, amides, imides, sylils, amidinates, and heterocyclic moieties.
5. Process according to any of the preceding claims, wherein as second reactant precursor oxygen, peroxide, water, ammonia, a fluoride, a chloride, ozone, hydrogen, nitrogen, nitrogen oxide, phosphohydride , ethoxy, methoxy, and
combinations thereof, is used.
6. Process according to any of the preceding claims, wherein deposition is carried out at a temperature between 373 °K and 573 °K and/or at a (partial) pressure of 1-105 Pa.
7. Process according to any of the preceding claims, wherein a pore size is reduced by 0.04-0.4 nm.
8. Process according to any of the preceding claims, wherein (i) the top-layer of the substrate and a support layer of the substrate are provided with a metal source precursor during a period of 0.1-30 s.
9. Process according to claim 8, wherein (iv) the oxygen source precursor is provided to the surface of the top layer only during a period of 0.1-120 sec.
10. Process according to any of the claims 8-9, wherein in steps (ii and v) the membrane is purged with an inert gas, such as nitrogen, preferably during a period of 1-10 min.
11. Process according to any of claims 8-10, wherein a rest period of 0.05-120 min is provided.
12. Process according to any of claims 8-11, wherein steps (i)-(v) are repeated 1-30 times.
13. Process according to any of the preceding claims, wherein an M CO is tailored by a number of deposition layers to a value of 10-450 Da.
14. Process according to any of the preceding claims, wherein a variety of metal oxide layers is provided therewith forming a stack of layers, the metal oxides being selected from Al oxides, Ti oxides, and oxides, such as AI2O3, Ti02, and WOx.
15. Inorganic nanofiltration membrane obtainable by a process according to any of the preceding claims
characterized in a molecular weight cut-off size of <450 Da and having a water permeability of more than 1.39*10~8 l/(m2*s*Pa) {5 1/ (m2*h*bar) .
16. Membrane according to claim 15, wherein a pore size is smaller than 1 nm.
17. Membrane according to any of claims 15-16, having a layer for rejecting divalent or trivalent ions.
18. Membrane according to any of claims 15-17,
comprising a homogeneous metal oxide filtration layer and a tubular membrane.
19. Membrane according to any of claims 15-17, wherein the surface of the membrane has an increased negative charge, preferably by coating with tungsten oxide.
20. Use of a membrane according to any of claims 15-19 in fluid treatment, such as water or waste-water treatment, drinking water production, and industrial water production.
21. Reactor (100) for performing a process according to any of claims 1-14, comprising
a reactor chamber (50) ,
at least two temperature resistant insulators (31) spaced apart and provided at an inside of the reaction chamber, a first insulator located at a first part of the reactor chamber and a second insulator located at a second part of the reactor chamber, wherein the insulator preferably is an o-ring,
at least one inlet (41) for a precursor purge comprising a first valve (11),
at least one outlet (42) for a precursor purge comprising a second valve (12) ,
at least one outlet (43) for a precursor purge
comprising a third valve (13),
wherein the second valve and third valve, respectively, are located to direct a precursor to both the top-layer and support-layer part of a membrane or to the top layer thereof only, and
wherein the insulators position the membrane.
PCT/NL2017/050069 2016-02-04 2017-02-02 Preparation of inorganic tight nanofiltration membranes WO2017135822A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL2016222A NL2016222B1 (en) 2016-02-04 2016-02-04 Preparation of inorganic tight nanofiltration membranes.
NL2016222 2016-02-04

Publications (1)

Publication Number Publication Date
WO2017135822A1 true WO2017135822A1 (en) 2017-08-10

Family

ID=55802432

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NL2017/050069 WO2017135822A1 (en) 2016-02-04 2017-02-02 Preparation of inorganic tight nanofiltration membranes

Country Status (2)

Country Link
NL (1) NL2016222B1 (en)
WO (1) WO2017135822A1 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5503873A (en) * 1994-06-30 1996-04-02 California Institute Of Technology Method for forming improved H2 -permselective oxide membranes using temporary carbon barriers
US6649255B1 (en) * 1999-03-04 2003-11-18 Douglas E. Fain, Sr. Article and method for producing extremely small pore inorganic membranes
EP2138222A1 (en) * 2008-06-27 2009-12-30 George P. Sakellaropoulos Method for pore size modification of an inorganic membrane by chemical vapor infiltration

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5503873A (en) * 1994-06-30 1996-04-02 California Institute Of Technology Method for forming improved H2 -permselective oxide membranes using temporary carbon barriers
US6649255B1 (en) * 1999-03-04 2003-11-18 Douglas E. Fain, Sr. Article and method for producing extremely small pore inorganic membranes
EP2138222A1 (en) * 2008-06-27 2009-12-30 George P. Sakellaropoulos Method for pore size modification of an inorganic membrane by chemical vapor infiltration

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
KEMELL M ET AL: "Coating of highly porous fiber matrices by atomic layer deposition", CHEMICAL VAPOR DEPOSITION, WILEY-VCH VERLAG, WEINHEIM, DE, vol. 14, no. 11/12, 1 November 2008 (2008-11-01), pages 347 - 352, XP001517316, ISSN: 0948-1907, DOI: 10.1002/CVDE.200800710 *

Also Published As

Publication number Publication date
NL2016222B1 (en) 2017-08-14

Similar Documents

Publication Publication Date Title
JP5681192B2 (en) Method for applying atomic layer deposition coatings on porous non-ceramic substrates
US6854602B2 (en) Hydrogen-selective silica-based membrane
EP2061597B1 (en) Method and apparatus for membrane deposition
US20090000475A1 (en) Zeolite membrane structures and methods of making zeolite membrane structures
US20150044130A1 (en) Metal doped zeolite membrane for gas separation
EP2915578B1 (en) Ceramic separation membrane structure, and repair method thereof
EP2258465B1 (en) Ceramic filter
WO2009102363A2 (en) Ultra-thin microporous/hybrid materials
CA2555926A1 (en) Hydrogen-selective silica-based membrane
CA2666279A1 (en) Method of manufacturing ceramic porous membrane and method of manufacturing ceramic filter
US11554359B2 (en) Supported zeolite films and methods for preparing
US6649255B1 (en) Article and method for producing extremely small pore inorganic membranes
US10537858B2 (en) Hydrophilic, light active coating for membranes
US20050065028A1 (en) Catalytic nanoporous membranes
JP2006239663A (en) Production method of hydrogen gas separation membrane
JP2009536916A (en) Nanoporous carbonaceous membrane and method related thereto
US8216342B2 (en) Membrane production method
TWI600796B (en) Nanoporous thin film and method for fabricating the same
WO2017135822A1 (en) Preparation of inorganic tight nanofiltration membranes
JP4605920B2 (en) Gas separation filter
AHMADIAN et al. An optimum routine for surface modification of ceramic supports to facilitate deposition of defect-free overlaying micro and meso (nano) porous membrane
WO2021192454A1 (en) Zeolite membrane composite, separating device, separation method, and method for producing zeolite membrane composite
KR20230106404A (en) Composite membrane with improved chemical resistance to organic solvent and fabrication method thereof
JP2008119566A (en) Gas separation apparatus
So et al. Preparation of Silica-Based Membrane for H 2 Separation by Multi-Step Pore Modification

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 17706596

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 17706596

Country of ref document: EP

Kind code of ref document: A1