Curable Compositions and Membranes

Abstract

A curable composition comprising the components (i) 0 to 60 wt % non-ionic crosslinker(s); (ii) 20 to 85 wt % curable ionic compound(s) comprising an anionic group and at least one ethylenically unsaturated group; (iii) 15 to 45 wt % solvent(s); (iv) 0 to 10 wt % of photoinitiator(s); and (v) 2 to 45 wt % of structure modifier(s); wherein the molar ratio of component (v):(ii) is 0.25 to 0.65. The compositions are useful for preparing membranes for (reverse) electrodialysis.

Claims

1.26. (canceled)

27. A process for preparing a membrane comprising the following steps: (i) applying a curable composition to a support; and (ii) curing the composition to form a membrane; wherein the curable composition comprises the components: (i) 0 to 60 wt % non-ionic crosslinker(s); (ii) 20 to 85 wt % curable ionic compound(s) comprising an anionic group and at least one ethylenically unsaturated group; (iii) 15 to 45 wt % solvent(s); (iv) 0 to 10 wt % of photoinitiator(s); and (v) 2 to 45 wt % of structure modifier(s) selected from the group consisting of polyvalent metal salts and organic compounds comprising at least two groups selected from amino and quaternary ammonium groups; wherein the molar ratio of component (v):(ii) is 0.25 to 0.65.

28. The process according to claim 27 wherein the curing step (ii) is performed such that the curable composition forms a layer on top of the support, or the curable composition permeates wholly or partially into the pores of the support thereby forming an impregnated composite membrane.

29. The process according to claim 27 wherein the composition comprises the components: (i) 2 to 40 wt % non-ionic crosslinker(s); (ii) (a) 20 to 60 wt % curable ionic compound(s) comprising an anionic group and one ethylenically unsaturated group; and (b) 0 to 60 wt % curable ionic compound(s) comprising an anionic group and at least two ethylenically unsaturated groups; (iii) 15 to 45 wt % solvent(s); (iv) 0 to 5 wt % of photoinitiator(s); and (v) 4 to 35 wt % of structure modifier(s) capable of forming ionic bonds with at least two of said anionic group(s); wherein the molar ratio of component (v):(ii) is 0.25 to 0.65.

30. The process according to claim 27 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499.

31. The process according to claim 27 wherein the curing is performed using electron beam or UV radiation.

32. The process according to claim 27 wherein the composition is cured by irradiation with an electron beam or UV light for a period of less than 30 seconds.

33. The process according to claim 27 which further comprises the step of removing at least some of the structure modifier from the membrane.

34. The process according to claim 27 wherein component (v) has a solubility in water of pH 1 at 25° C. of at least 20 g per kg of water.

35. The process according to claim 27 wherein the structure modifier is or comprises a polyvalent metal salt and some or all of the structure modifier is removed from the membrane by ion exchange and/or washing.

36. The process according to claim 27 wherein the structure modifier is selected from the group consisting of salts comprising calcium, magnesium or strontium cations and hydroxide, acetate, citrate, oxalate, carbonate, bicarbonate, phosphate, monohydrogen phosphate or dihydrogen phosphate anions, and/or organic amines selected from the group consisting of ethylene diamine and triethylene diamine.

37. The process according to claim 27 wherein the curable composition is applied continuously to a moving support by means of a manufacturing unit comprising a curable composition application station, an irradiation source for curing the composition, a membrane collecting station and a means for moving the support from the curable composition application station to the irradiation source and to the membrane collecting station.

38. The process according to claim 27 wherein the ethylenically unsaturated group(s) is or are acrylic groups.

39. The process according to claim 27 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499 and wherein the composition is cured by irradiation with an electron beam or UV light.

40. The process according to claim 27 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499, the composition is cured by irradiation with an electron beam or UV light and the curing step (ii) is performed such that the curable composition forms a layer on top of the support, or the curable composition permeates wholly or partially into the pores of the support thereby forming an impregnated composite membrane.

41. The process according to claim 27 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499, the composition is cured by irradiation with an electron beam or UV light and the structure modifier is selected from the group consisting of salts comprising calcium, magnesium or strontium cations and hydroxide, acetate, citrate, oxalate, carbonate, bicarbonate, phosphate, monohydrogen phosphate or dihydrogen phosphate anions, and/or organic amines selected from the group consisting of ethylene diamine and triethylene diamine.

42. The process according to claim 27 wherein the molar ratio of components (v):(ii) is 0.25 to 0.499, the composition is cured by irradiation with an electron beam or UV light, the curing step (ii) is performed such that the curable composition forms a layer on top of the support, or the curable composition permeates wholly or partially into the pores of the support thereby forming an impregnated composite membrane and the structure modifier is selected from the group consisting of salts comprising calcium, magnesium or strontium cations and hydroxide, acetate, citrate, oxalate, carbonate, bicarbonate, phosphate, monohydrogen phosphate or dihydrogen phosphate anions, and/or organic amines selected from the group consisting of ethylene diamine and triethylene diamine.

43. The process according to claim 41 wherein component (v) has a solubility in water of pH 1 at 25° C. of at least 20 g per kg of water.

44. The process according to claim 42 wherein component (v) has a solubility in water of pH 1 at 25° C. of at least 20 g per kg of water.

45. The process according to claim 27 wherein the support is a porous support.

46. A membrane obtained by performing the process of claim 27.

47. The membrane according to claim 46 which has a ratio of the electrical resistance of the membrane for magnesium ions to that of sodium ions of less than 3, when measured at an ion concentration of 0.5 M.

48. The membrane according to claim 46 which has an electrical resistance for sodium ions of less than 3 ohm.cm.sup.2 and for magnesium ions of less than 7 ohm.cm.sup.2, when measured at an ion concentration of 0.5 M.

Description

EXAMPLES

[0157] The following ingredients were used to prepare the composite membranes: [0158] MBA is N,N′-methylene bisacrylamide from Sigma Aldrich. [0159] AMPS is 2-Acryloylamido-2-methylpropanesulfonic acid from Hang-Zhou (China). [0160] BAMPS is the ammonium salt of 1,1-bis(acryloylamido)-2-methylpropane-2-sulphonic acid, synthesized as described in U.S. Pat. No. 4,034,001. [0161] DABCO is 1,4-diazabicyclo[2.2.2]octane (triethylenediamine) from Sigma Aldrich. [0162] Darocur™ 1173 is 2-hydroxy-2-methyl-1-phenyl-propan-1-one, a photoinitiator from BASF Resins, Paint & Coatings. [0163] Genorad is a polymerisation inhibitor from Rahn. [0164] IPA is 2-propanol from Shell (an inert organic solvent). [0165] MeOH is methanol [0166] LiOH.H.sub.2O is lithium hydroxide monohydrate from Chemetall. [0167] Ca(OH).sub.2 is calcium hydroxide from Sigma Aldrich. [0168] Mg(OH).sub.2 is magnesium hydroxide from Sigma Aldrich. [0169] CaHPO.sub.4. 2H.sub.2O is calcium hydrogenphosphate dihydrate from Sigma Aldrich. [0170] Sr(OAc).sub.2 is strontium acetate from Sigma Aldrich. [0171] Viledon® Novatexx 2223-10 is a nonwoven polyolefin porous support from Freudenberg Filtration Technologies. [0172] PW is pure water (an inert solvent). [0173] Surfactant is a polyether siloxane from Evonik.

Examples 1 to 9

[0174] The curable compositions of Examples Ex.1 to Ex.9 were prepared by mixing the indicated ingredients indicated in Table 1, wherein all amounts are the wt % of the relevant component.

TABLE-US-00001 TABLE 1 Curable Compositions Examples Component Identity Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 (iii) PW 23.1 20.9 21.4 22.6 17.4 25.4 20.4 23.1 21.5 IPA 7.7 10.5 10.7 7.5 8.8 19.7 10.2 11.5 7.2 MeOH 3.8 5.2 0 3.8 0 0 5.1 5.8 3.6 other Genorad 0.4 0.4 0.4 0.4 0.5 0.7 0.4 0.4 0.4 (ii) AMPS 38.1 34.9 35.6 37.1 43.1 33.9 34.0 38.5 35.9 other LiOH•H.sub.2O 1.9 0 0 0.9 1.1 0 0 0 1.8 (v) CaHPO.sub.4•2H.sub.2O 9.5 14.0 14.3 12.6 0 0 0 0 10.8 Ca(OH).sub.2 0 0 0 0 0 5.9 0 0 0 Mg(OH).sub.2 0 0 0 0 0 0 0 5.2 0 Sr(OAc).sub.2 0 0 0 0 0 0 16.2 0 0 DABCO 0 0 0 0 11.6 0 0 0 0 (i) MBA 14.2 12.9 7.8 13.8 16.0 12.4 12.5 14.2 6.8 (ii) BAMPS 0 0 8.6 0 0 0 0 0 10.8 (iv) Darocur ™ 0.4 0.4 0.4 0.4 0.5 0.7 0.4 0.4 0.4 1173 other Surfactant 0.9 0.8 0.8 0.9 1.0 1.3 0.8 0.9 0.8 Total (wt %) 100 100 100 100 100 100 100 100 100 pH 0.6 0.8 0.7 2.6 0.6 0.8 Molar ratio of 0.300 0.483 0.403 0.409 0.497 0.487 0.480 0.480 0.290 component (v):(ii) Note: The wt % figures in Table 1 are calculated relative to the total weight of the composition.

Preparation of Membranes M1 to M9

[0175] Each of the curable compositions described in Table 1 was applied by hand to an aluminum underground carrier using a 100 μm wire wound bar, at a speed of approximately 5 m/min, followed by application to a Viledon® Novatexx 2223-10 non-woven support. Excess composition was scraped-off using a wire bar (Standard K bar No.0 with 0.05mm diameter wire, by RK Print Coat Instruments Ltd) and the impregnated support was cured by irradiation with UV light with a dose of 0.21J/cm.sup.2 at one side using a Light Hammer LH6 from Fusion UV Systems fitted with a D-bulb working at 100% intensity with a speed of 30 m/min (single pass). The curable compositions of Ex.1 to Ex.9 resulted in membranes

[0176] M1 to M9 respectively.

Test Results on Membranes M1 and M2 and Comparative Membrane CM1

(A) Permselectivity and Electrical Resistance Results

[0177] As comparative membrane CM1 there was used a Type 1 cation exchange membrane from Fujifilm obtained from a curable composition lacking component (v).

Results

[0178]

TABLE-US-00002 TABLE 2 Electrical resistance and permselectivity data Test (ER or α Membrane (%)) M1 M2 M3 M4 M5 M6 M7 M8 M9 CM1 ER using 0.5M 2.0 2.0 1.4 2.3 3.8 4.0 1.7 1.7 1.6 2.6 NaCl ER using 0.5M 4.9 3.8 2.8 4.8 5.4 6.9 3.2 3.5 2.6 9.0 MgCl.sub.2 ER using 0.5M — 3.4 — — — — 2.4 2.8 — 8.0 CaCl.sub.2 Ratio ER Mg/ER 2.4 1.9 2.0 2.1 1.4 1.7 1.9 2.1 2.6 3.5 Na α (%) 95 89 85 90 84 84 87 89 89 89

[0179] In Table 2 “ER” means electrical resistance when tested with the indicated 0.5 M solution of NaCl, MgCl.sub.2 or CaCl.sub.2. “a (%)” means permselectivity, measured as described above.

[0180] The ratio of ER Mg/ER Na was much lower for Examples Ex.1 to Ex.9 than for Comparative Example CEx.1 made from a composition lacking component (v). This indicates the relative permeability of the membrane for multivalent ions compared to monovalent ions.

(B) Power Density Results

Preparation of Membrane Stacks

[0181] First the ion exchange membranes M1, M2 and CM1 were equilibrated over a minimum period of two hours in a 0.5 M NaCl solution prior to building membrane stacks containing them. The membrane stacks were then constructed by fitting 10 cell pairs into an 11×11 cm crossflow stack, purchased from RedStack B.V. Each cell pair comprised a cation exchange (one of membranes M1, M2 and CM1 described above) and an anion exchange membrane (Type 1 anion exchange membrane, obtained from Fujifilm) and the outermost membranes in all three of the stacks were membrane CM1. The resultant membrane stacks therefore comprised concentrate channels through which concentrated ionic solutions were passed and diluate channels through which dilute ionic solutions were passed.

[0182] The membrane stacks further comprised non-woven spacers (220 μm thick from Deukum GmbH) in both the concentrate and diluate channels to keep the membranes apart and allow the solutions to pass between the membranes. Ionic solutions were fed into the concentrate and diluate channels using Masterflex peristaltic pump from Cole-Parmer equipped with pulsation dampeners. As the power source for the stack there was used an Autolab PGSTAT302N with NOVA software from Metrohm.

[0183] The net membrane area of each membrane was 6.4×6.4 cm.sup.2.

[0184] The electrolyte in the electrode compartments of the stack was 0.1 M K.sub.3Fe(III)(CN).sub.6 and 0.1 M K.sub.4Fe(II)(CN).sub.6 in 0.25 M NaCl.

Measurement procedure

[0185] The stacks prepared above were used in a reverse electrodialysis setup to generate electrical energy. The generated net power density (in W/m.sup.2) of the abovementioned stacks comprising membranes M1, M2 or CM1 were measured as follows:

[0186] Four concentrate solutions (CSA to CSD) and four diluate solutions (DSA to DSD) indicated in Table 3 were passed through the concentrate and diluate channels respectively of each of the three stacks, each solution flowing at a rate of 53 ml/min (velocity 0.95 cm/s), temperature of 21° C. and using an average pumping energy of 0.27 W/m.sup.2. In Table 3 below the amounts indicate the concentration of the relevant ions in millimoles per litre ([mM]).

TABLE-US-00003 TABLE 3 Concentrate and Diluate solutions used to test the Membranes M1, M2 and CM1 Concentrate Channel [mM] Diluate Channel [mM] Cation CSA CSB CSC CSD DSA DSB DSC DSD Na.sup.+ 0.5 0.45 0.45 0.402 0.0171 0.0154 0.0154 0.0035 Mg.sup.2+ 0 0.05 0 0.042 0 0.0017 0 0.0005 Ca.sup.2+ 0 0 0.05 0.039 0 0 0.0017 0.0015 K.sup.+ 0 0 0 0 0 0 0 0.0007 Conductivity 47.9 49.7 50.5 50.2 1.9 2.2 2.2 1.0 [mS/cm]

[0187] The conductivity figures in Table 3 indicate the conductivity of the relevant solutions as they entered the stacks. Solutions CSA and DSA contained only water and NaCl. For Solutions CSB/DSB and CSC/DSC 10mol% of the NaCl was replaced with either MgCl.sub.2 or CaCl.sub.2 respectively. Solutions CSD and DSD were designed to resemble the composition of seawater and river water respectively.

[0188] To determine the net power density of a stack, the stack was fed with NaCl solutions CSA (through the concentrate channels) and DSA (through the diluate channels) and a current of 10 A/m.sup.2 was applied during a period of 20 minutes to finalize equilibration. For each stack the DC resistance, the average current and the open circuit potential were measured for 11 current steps from 0 to 20 A/m.sup.2 and back to 0 A/m.sup.2. If the two corresponding data points differed too much the equilibration was repeated. If the measurements were reasonably consistent then the feed solutions CSA and DSB were replaced by the test solutions CSB and DSB, first CSB in the concentrate channel and then DSB in the diluate channel. After the measurement of the DC resistance, the average current and the open circuit potential for solutions CSB and DSB the feed solutions were changed back to solutions CSA and DSA. Subsequently the DC resistance, the average current and the open circuit potential for solutions CSC and DSC were measured in the same way. Analogously the feed solutions were changed back to solutions CSA and DSA and then the DC resistance, the average current and the open circuit potential for solutions CSD and DSD were measured in the same way. The stack resistance was corrected for the electrode compartments (blank).

[0189] From a plot of gross power density against current density the maximum power density was determined for each stack and this value was used to calculate the net power density. To calculate the net power density the pumping energy was subtracted from the measured gross power density. The results are given in Table 4.

TABLE-US-00004 TABLE 4 Net power density measurement (W/m.sup.2) for stacks comprising membranes M1, M2 or CM1 Concentrate and Diluate Solutions Used Net Power Net Power Net Power Net Power Density when Density when Density when Density when CSA/DSA are CSB/DSB are CSC/DSB are CSD/DSD are Membrane Stack used used used used Stack containing 0.60 0.42 0.37 0.28 membrane M1 Stack containing 0.70 0.45 0.39 0.34 membrane M2 Stack containing 0.58 0.23 0.28 0.18 membrane CM1

[0190] The results in Table 4 indicate that with membranes M1 and M2 of the invention a much higher net power density was obtained than for Comparative Membrane CM1, especially for feed flows containing magnesium and/or calcium ions.

[0191] FIG. 1 shows the effect of feed composition and membrane type on the gross power density in a reverse electrodialysis unit according to the present invention.

[0192] In FIG. 1 it can be seen that an RED unit comprising membrane M2 fed with solutions CSA and DSA (solid round dots) had higher current density values than when the same solutions were passed through an RED unit which was identical except that the membranes M2 according to the invention were replaced with comparative membrane CM1 (hollow round dots).

[0193] FIG. 1 also shows that an RED unit comprising membrane M2 fed with solutions CSD and DSD to mimic sea water and stream water (solid triangles) had higher current density values than when the same solutions were passed through an RED unit which was identical except that the membranes M2 according to the invention were replaced with comparative membrane CM1 (hollow triangles).