METHOD AND TUBULAR MEMBRANE FOR PERFORMING A FORWARD OSMOSIS PROCESSING

Abstract

A method for processing a fluid with forward osmosis process includes providing one or more tubular membranes each including a tubular nonwoven base layer on the outside of the tubular membrane forming an outer shell of the tubular membrane and providing a lumen for feed flow; a polymer substrate layer on the lumen-side of the tubular membrane comprising three regions, including a region where the polymer substrate layer is partially intruded into the tubular base layer, a region with an open macrovoid structure and a region with an asymmetrical foamy layer, where the partially intruded region forms an intermediate layer; and a functional top layer on the polymer substrate layer. The tubular base layer comprises a longitudinal weld. The method includes providing the feed flow through the lumen and providing a draw solution on the outer shell side of the tubular membrane; and processing the feed flow with the membrane.

Claims

1-16. (canceled)

17. A method for processing a fluid with forward osmosis process, the method comprising: providing one or more tubular membranes, with the tubular membrane comprising: a tubular base layer of a nonwoven material on the outside of the tubular membrane and forming an outer shell of the tubular membrane and providing a lumen for the feed flow; a polymer substrate layer on the lumen-side of the tubular membrane comprising three regions, including a region where the polymer substrate layer is partially intruded into the tubular base layer, a region with an open macrovoid structure and a region with an asymmetrical foamy layer, wherein the partially intruded region forms an intermediate layer; and a functional top layer on the polymer substrate layer; wherein the tubular base layer comprises a longitudinal weld; the method further comprising: providing the feed flow through the lumen and providing a draw solution on the outer shell side of the tubular membrane; and processing the feed flow with the membrane.

18. The method according to claim 17, further comprising cleaning the membrane in a cleaning step comprising a reversal of flows and/or an adjustable and/or settable crossflow velocity and/or an osmotic backwash.

19. The method according to claim 17, further comprising: providing hydraulic pressure to the feed flow with a pressure in the range of 0-4 bar, wherein the hydraulic pressure on the feed side exceeds the pressure on the draw side.

20. A tubular membrane configured for forward osmosis processing, the tubular membrane comprising: a tubular base layer of a nonwoven material on the outside of the tubular membrane and forming an outer shell of the tubular membrane and providing a lumen for the feed flow; a polymer substrate layer on the lumen-side of the tubular membrane comprising three regions, including a region where the polymer substrate layer is partially intruded into the tubular base layer, a region with an open macrovoid structure and a region with an asymmetrical foamy layer, wherein the partially intruded region forms an intermediate layer; and a functional top layer on the polymer substrate layer; wherein the tubular base layer comprises a longitudinal weld.

21. The tubular membrane according to claim 20, wherein the functional polymer membrane layer comprises a polyamide-based layer on the polymer substrate layer.

22. The tubular membrane according to claim 20, wherein the foamy asymmetrical layer of the polymer substrate layer is integrally formed, and wherein the foamy asymmetrical layer is formed on top of the macrovoid-structured layer, wherein the macrovoid-structured layer is provided with a substantial amount of macrovoids, the macrovoids having a length that substantially extends in a radial direction of the tubular membrane.

23. The tubular membrane according to claim 20, wherein the tubular membrane is self-supporting.

24. The tubular membrane according to claim 20, wherein the nonwoven base layer has a weight between 60-120 g/m.sup.2.

25. The tubular membrane according to claim 20, wherein the nonwoven base layer has a thickness in the range of 50-200 μm.

26. The tubular membrane according to claim 20, wherein the nonwoven base layer has an air permeability, measured at a pressure difference of around 200 Pa, in the range of 25-125 L/m.sup.2/s.

27. The tubular membrane according to claim 20, wherein the polymer substrate layer has a molecular weight cut off in the range of 5-20 kDa, wherein the molecular weight cut off is determined with filtration comprising polyethylene glycols.

28. The tubular membrane according to claim 20, wherein the longitudinal weld has a width in the range of 0.5-2 mm.

29. The tubular membrane according to claim 20, wherein the inner diameter of the tubular membrane is in the range of 3-8 mm.

30. The tubular membrane according to claim 20, wherein the tubular membrane cross section is circular shaped or oval shaped.

31. Device configured for forward osmosis process of feed flow, comprising a number of tubular membranes, wherein the tubular membrane comprises: a tubular base layer of a nonwoven material on the outside of the tubular membrane and forming an outer shell of the tubular membrane and providing a lumen for the feed flow; a polymer substrate layer on the lumen-side of the tubular membrane comprising three regions, including a region where the polymer substrate layer is partially intruded into the tubular base layer, a region with an open macrovoid structure and a region with an asymmetrical foamy layer, wherein the partially intruded region forms an intermediate layer; and a functional top layer on the polymer substrate layer; wherein the tubular base layer comprises a longitudinal weld.

32. The method according to claim 17, wherein the pressure is in the range of 0-2 bar.

33. The method according to claim 17, wherein the pressure is in the range of 0-1 bar.

34. The method according to claim 18, further comprising: providing hydraulic pressure to the feed flow with a pressure in the range of 0-4 bar, wherein the hydraulic pressure on the feed side exceeds the pressure on the draw side.

35. The method according to claim 17, further comprising the step of forming the foamy asymmetrical layer of the polymer substrate layer, wherein the foamy asymmetrical layer is formed on top of the macrovoid-structured layer, wherein the macrovoid-structured layer is provided with a substantial amount of macrovoids, the macrovoids having a length that substantially extends in a radial direction of the tubular membrane, and wherein the functional polymer membrane layer comprises a polyamide-based layer on the polymer substrate layer.

Description

[0047] Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

[0048] FIG. 1A schematically shows a tubular membrane in an embodiment of the invention;

[0049] FIG. 1B schematically shows a device with a number of tubular membranes illustrated in FIG. 1A;

[0050] FIG. 2A shows a detailed and enlarged segment of the tubular membrane illustrated in FIG. 1A;

[0051] FIG. 2B shows a section of the wall segment of FIG. 2A;

[0052] FIGS. 3A and B show properties of two types of membranes respectively membrane type I8 (FIG. 3A) and membrane type I5 (FIG. 3B);

[0053] FIG. 4 shows a schematic overview of concentration gradient over the membrane; and

[0054] FIG. 5 shows some experimental results.

[0055] Tubular membrane 2 (FIG. 1A) has a length L, an inner diameter D.sub.in and an outer diameter D.sub.out. It is noted that the membrane diameter is preferably defined with respect to D.sub.in, even though it is possible to define the membrane diameter based on the outer diameter. Tubular membrane 2 has outer wall 4 and inner wall 6. Outer wall 4 is defined by outer layer 8 comprising a nonwoven material. Inner wall 6 is defined by polymer substrate layer 10 having the functional polymer layer 11 on top. The transition of nonwoven-substrate layer 12 is defined by the nonwoven region which is intruded with the polymer substrate layer 10. This transition region 12 enables attaching the substrate material to the nonwoven material. Longitudinal weld 14 has a width W and connects sides of nonwoven layer 8 to define the lumen of tubular membrane 2 along longitudinal axis 16. Feed flow F flows through the lumen in tubular membrane 2.

[0056] In the illustrated embodiment tubular membrane 2 has an inner diameter D.sub.in in the range of 5-6 mm, and width W is in the range of 0.7-1.3 mm.

[0057] Device 18 (FIG. 1B) comprises a bundle 20 of tubular membranes 2. A holder or housing 22 holds bundle 20 together such that the feed flow enters the lumen side of bundle 20 and draw flow enters the shell side of bundle 20. The feed flow and draw flow are solely in contact over the tubular membranes. It will be understood that device 18 is schematically illustrated. The skilled person could envisage different embodiments of bundle 20 in accordance to the invention.

[0058] On outer side 4 (FIG. 2A) nonwoven material 8 is very open as compared to substrate layer 10 that has a number of macrovoids 24. Macrovoids 24 have a length L.sub.1 that substantially extends in a radial direction of the tubular membrane. It will be understood that the transition of nonwoven-substrate layer 12 between polymer substrate layer 10 and nonwoven base layer 8 can be irregularly shaped. Macrovoids 24 (FIG. 2B) substantially extend parallel to each other.

[0059] In the illustrated embodiment functional layer 11 is applied onto substrate layer 8 by interfacial polymerization. Commonly, the polymerization is a polycondensation reaction between two highly reactive monomers that are dissolved in two immiscible liquids which forms an ultrathin functional layer on top of the substrate layer. The separation of monomer pre-cursors in two phases results in the localized reaction at the interface and formation of a polymer layer. In the illustrated embodiment this formation occurs between 1,3-phenylene diamine (MPD) (in water) and trimesoyl chloride (TMC) (in hexane). The crosslinked network forms with the interchain-CONH-linkage between the aromatic rings.

[0060] In the following table a composition of the two liquids for obtaining functional layer 11 is represented.

TABLE-US-00001 TABLE representation of the composition of the coating layer Reaction solution A Reaction solution B Concentration Concentration Component (w/v-%) Component (w/v-%) Water Hexan MPD (m- 0.25-4  TMC 0.05-0.5 Phenylendiamine) (Trimesoylchloride) SDS (sodium  0.2-1  dodecylsulfonate) CSA   2-6  (campher-10- sulfonic acid) TEA   1-2  (triethylamine) Glycerin   5-20 DMSO (dimethyl sulfoxide)  0.5-2 

[0061] It will be understood that many variations are possible in composition of the reactive system, i.e. variations in reactant A and reactant B, additives, solvents. Furthermore, the preparation conditions can be varied by many parameters as well: pre-treatment of the substrates, coating time, post treatment after each coating step, curing temperature and curing time amongst others.

[0062] Two membrane types have been compared relating to embodiments with longitudinal welds and spirally oriented welds, respectively. The two different membrane types also indicated by membrane type I8 (FIG. 3A) and membrane type I5 (FIG. 3B). Results show an increasing gain of membrane surface (.box-tangle-solidup.) between the longitudinal weld (□) and the spiral weld (.diamond-solid.) embodiments. This effect increases with increasing welding width. In the illustrated embodiments the welding width increases from 0.5 to 1.3 mm.

[0063] Experiments have been performed with tubular membrane 2 in the ALFS mode (active layer facing feed side). In the experiments respective media on the feed-side and draw-side of the membrane are circulated. Water is transported through the membrane from the feed-side to the draw side and the feed-side becomes more concentrated while the draw-side becomes more diluted (FIG. 4). Highest concentration difference is in top layer 11. Also shown is the effective concentration gradient that is smaller than the concentration difference between feed flow and draw solution.

[0064] Experimental results (FIG. 5) are shown for: [0065] a) 10 LPM (also defined as liters per minute or L/min) feed, 1.5 LPM draw and below 0.2 bar TMP; [0066] b) 25 LPM feed, 1.5 LPM draw and below 0.2 bar TMP; and [0067] c) 25 LPM feed, 1.5 LPM draw and 0.2-0.4 bar TMP.
In the experiments nonwoven layer 8 of membrane 2 comprises polyester, a PES substrate layer and a lumen diameter of about 5 mm. The functional layer comprises aquaporin proteins formulated into a biomimetic matrix embedded on the surface by an immobilization matrix made by interfacial polymerization. The experiments were performed in an ALFS configuration. Further conditions were membrane area is 0.4 m.sup.2, counter current configuration, draw solution concentration 1 M NaCl, duration 2-4 hrs. Water permeability of the substrate membrane is about 150-200 LMH measured at 1 bar. Results show a water flux Jw (LMH), salt flux Js (gMH) and ratio of Js/Jw. The experiments show the feasibility of using membranes according to the present invention in an FO process.

[0068] In addition, the following examples are provided to further support the present invention by providing aspects thereof as examples.

EXAMPLE 1

[0069] The first example is directed to a method for producing a tubular membrane support, and more specifically a longitudinal welded membrane support. A longitudinal welded membrane support is in this example defined as the tubular base layer with a polymeric substrate layer.

[0070] In the example, polyester nonwoven that is used has the following specifications: weight: 85 g/m.sup.2, thickness: 120 μm and air permeability measured at 200 Pa: 85 L/s/m.sup.2. The nonwoven tube is formed by bending the nonwoven tape over a mandrel with an outer diameter of 5.5 mm and the overlap is fixed by means of ultrasonic welding in a continuous process. A polymer solution is coated continuously and in situ on the tubular nonwoven tube. The polymer solution contains polyethersulfone (PES) Ultrason 6020 (BASF) between 10-25 wt. % with polyvinylpyrrolidone PVP as pore forming additive in an aprotic solvent. Polymer solution is conveyed through the mandrel and leaves the system in the casting section. The polymer solution is brought onto the tube followed by doctoring to obtain a layer thickness of 0.1 mm Subsequently, the coated tube is conveyed through a cutting section where the coated tube is cut with a defined length dependent on module type. In a following step, the coated tube is transported in a precipitation bath containing RO-water (i.e. water prepared by reverse osmosis) with a temperature of 25° C., where the phase inversion process takes place and the membrane support is formed. The longitudinal welded membrane support is produced with a velocity between 7 and 10 m/min. The membrane support is rinsed with water for at least 16 hours. The membrane support is conditioned with 20% glycerin solution for at least 5 hours, followed by air-drying, followed by drying at 60° C. for more than 12 hours.

[0071] The membrane support has an inner diameter of approx. 5.3 mm and has a bursting pressure larger 8 bar. It is found that the pure water flux measured at 1 bar TMP under crossflow conditions is between 100-250 LMH. The retention of PEG 100k (polyethylene glycol with average My of 100,000 g/mol) measured with same conditions is >90%. The molecular weight cut-off measured with PEG-mixture is 5-15 kDa.

EXAMPLE 2

[0072] The second example relates to a tubular membrane module, which in this example comprises a plurality of tubular membrane support as described in example 1. Each tubular membrane support has a membrane length of 1.1 times the module length. The plurality of tubular membrane supports, in this case comprising 118 membranes, is aligned parallel to each other for forming a membrane mat. Such a membrane mat is for example described in DE102016009914A1. DE102016009914A1 also discloses that the mat is rolled-up to a bundle. This bundle is inserted in a PVC module housing with a length of 125 cm and an outer diameter of 90 mm. The membrane bundle is fixed into the module housing by means an epoxy potting process. The epoxy block is approx. 3 cm thick. This results in an effective membrane length in the module of approx. 119 cm. The total membrane surface on the lumen side is approx. 2.3 m.sup.2. The feed and retentate connections are 3 inch pipe grooves according to standard IPS PVC groove specifications and the shell side connections are ¾ inch female thread connections.

EXAMPLE 3

[0073] The third example relates to a method for making a forward osmosis tubular membrane module.

[0074] In this example, a single-tube membrane module is provided, which module has a length of 50 cm and a lumen surface area of approx. 0.008 m.sup.2. The module furthermore has a lumen inlet and a lumen outlet as well as a shell side inlet and a shell side outlet.

[0075] In a method step, the module is wetted in a glycerin-containing solution for at least 48 hours. Before the coating procedure starts, the module is emptied on the lumen side as well as on the shell side. The aqueous phase is prepared in advance and the composition of the aqueous phase contains following components with corresponding ratios:

[0076] RO-water:glycerine:isopropanol:m-phenylenediamine: 3,5-diaminobenzoic acid:camphor-10-sulfonic acid:trimethylamine:sodium dodecylsulfonate 100:10:0:1.5:1.5:6:1:1 (AqRec1)/100:10:4:1.5:1.5:6:1:1 (AqRec2)/100:10:6:1.5:1.5:6:1:1 (AqRec3).

[0077] The aqueous phase is conveyed bottom-up to fill the lumen side completely for 30 s, the lumen side is drained followed by top-down pressurized air flushing for 1 min with 1 Nm.sup.3/h followed by deadend pressurizing the tube with pressurized air at 0.5 bar for 1 min. After these steps, the pressure is released and the module is treated with the organic phase.

[0078] The organic phase, consisting of 0.15 wt % of trimesoylchloride in n-hexane, is conveyed bottom-up to fill the lumen side completely for 120 s, after which the lumen side is drained and followed by top-down pressurized air flushing for 1 min with 1 Nm.sup.3/h. Subsequently, this is followed by dead-end pressurizing the tube with pressurized air at 0.5 bar for 1 min. The pressure is than released and the module is heat-treated on as well as the lumen as the shell side with 80° C. hot pressurized air at module entrance with 2.1 Nm.sup.3/h for 15 min.

[0079] After the module is cooled down and subsequently the module is immersed in RO-water with ambient temperature. The membrane module can be measured in wet condition after at least 16 hours. Alternatively, the membrane module is dried with the membrane conditioning and drying process as described above.

[0080] Two modules per coating recipe were prepared using the method as described in this example. These modules were tested in counter-current, active layer facing feed solution configuration at ambient temperature with RO-water in the feed side and 1 M NaCl solution in RO-water on the draw side. The linear velocity on the lumen and shell side is 30 cm/s on both sides. The duration of the measurement was 90 minutes and the water flux and reverse salt flux were determined by averaging the data of the final 45 minutes of the measurement. This tests of the modules resulted in the following results:

TABLE-US-00002 AqRec1 AqRec2 AqRec3 Water flux (LMH) 7.43 6.56 6.32 6.26 6.97 7.02 Reverse salt flux (gMH) 4.3 2.1 1.6 1.5 2.4 2.3

[0081] Results of test with modules of method according to example 3

EXAMPLE 4

[0082] In the fourth example, an alternative procedure for manufacturing a forward osmosis tubular membrane module is provided. In this example, an alternative functional layer is provided to the module. The alternative functional layer is based on aquaporin containing thin film composites. The procedure of making these functional layers is similar to the procedure as described in example 3. Vesicle forming materials are added to the aqueous phase. Modules as described in example 2 have been coated by means of this formulation with their developed coating procedure by Aquaporin Asia Pte. Ltd. The tubular forward osmosis membrane modules with Aquaporin Inside® with a lumen surface area of approx. 2.3 m.sup.2 are prepared and characterized.

[0083] The results of the membrane module with the alternative layer are provided below. It is noted that the modules were tested in co-current, active layer facing feed solution configuration at ambient temperature with RO-water in the feed side and 1 M NaCl solution in RO-water on the draw side. The linear velocity on the lumen and shell side are presented in the table below. The duration of the measurement is 2-4 h. The water flux and reverse salt flux are determined by averaging the data of the stationary part of the measurement. This tests of the modules resulted in the following results:

TABLE-US-00003 1 2 3 4 5 Linear flow velocity on: Feed side (cm/s) 1.9 3.2 25.6 25.6 25.6 Draw side (cm/s) 0.6 0.6 0.6 5.6 11.2 TMP (bar) <0.2 <0.2 <0.2 <0.2 <0.2 Water flux (LMH) 3.81 4.13 5.05 5.78 6.16 Reverse salt flux (gMH) 0.14 0.05 0.25 0.38 0.37

[0084] Results of test with modules of method according to example 3

[0085] The tests have shown that the advantage of using TFC with Aquaporin Inside® is the high salt rejection of the membrane with sufficient water flux through the membrane.

[0086] The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are described by the following claims, within the scope of which many modifications can be envisaged.