Highly selective alicyclic polyamide nanofiltration membrane and making method thereof

Abstract

The present invention discloses a highly selective alicyclic polyamide nanofiltration membrane and a making method thereof. The method comprises the following steps: alternately and uniformly coating at least an alicyclic acid chloride solution and at least an alicyclic amine solution on a porous support membrane, using a spin coating method or a soaking method, to form at least one layer of the alicyclic polyamide nanofiltration membrane. Preferred embodiments exhibit improved ion selectivity, e.g. increased water flux, enhanced divalent/monovalent rejection selectivity, reduced fouling and improved divalent rejection rate (Ca.sup.2+, Mg.sup.2+) compared to the traditional aromatic-alicyclic mixed-structure polyamide nanofiltration membrane and/or the whole aromatic polyamide nanofiltration membrane. Therefore, the alicyclic polyamide nanofiltration membranes made in the present invention has great application prospect in the fields of zero-liquid discharge of industrial wastewater, water softening, and produce water treatment, etc.

Claims

1. A method of making a highly selective alicyclic polyamide nanofiltration membrane, comprising the steps of: alternately and uniformly coating two or more kinds of an alicyclic acid chloride solution and two or more kinds of an alicyclic amine solution on a porous support membrane using a spin coating method for interfacial polymerization, to form layers of the highly selective alicyclic polyamide nanofiltration membrane; wherein the spin coating method comprises alternately spin-coating the alicyclic acid chloride solution and alicyclic amine solution on the porous support membrane for 2-300 s at 50-10,000 rpm, to form via multi-layer interface reaction polymerization, a multi-layer alicyclic polyamide nanofiltration membrane.

2. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 1, wherein the interfacial polymerization further comprises the following steps: removing extra alicyclic acid chloride solution or extra alicyclic amine solution on the porous support membrane by the spin coating method after an interfacial reaction of the alicyclic acid chloride solution and the alicyclic amine solution, and wherein the extra alicyclic acid chloride solution or the extra alicyclic amine solution is thrown away at 3,000-10,000 rpm for 2-300 s with a soaking solvent.

3. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 1, wherein a concentration of the alicyclic acid chloride solution is 0.01-2 wt%, a concentration of the alicyclic amine solution is 0.01-4 wt%.

4. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 3, wherein the alicyclic acid chloride solution comprises an alicyclic acid chloride, an organic solvent and an additive; a mass fraction of the alicyclic acid chloride is 0.01-2 wt%, a mass fraction of the organic solvent is 96-99.98 wt% and a mass fraction of the additive is 0.01-2 wt%; the organic solvent is one or more selected from the group consisting of n-hexane, cyclohexane, cyclopentane, n-heptane, n-octane and an isoparafin of the ISO-PAR series; and the alicyclic amine solution comprises an alicyclic amine, an aqueous solvent and an additive; a mass fraction of the alicyclic amine is 0.01-4 wt%, a mass fraction of the aqueous solvent is 46-99.98 wt% and a mass fraction of the additive is 0.01-50 wt%; and the aqueous solvent is water.

5. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 4, wherein the alicyclic amine comprises a structural formula of: ##STR00003## wherein R.sub.1, R.sub.2 are respectively (CH.sub.2).sub.n or NH, n is 1-3; R.sub.3, R.sub.4, R.sub.5, R.sub.6 are respectively NH.sub.2 or CH.sub.3; a number of the NH is 1-2, and a number of the NH.sub.2 is 2-4; and when a plurality of NH.sub.2 are on a same side of a ring, both a cis conformation and a trans conformation are included.

6. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 4, wherein the alicyclic acid chloride comprises a structural formula of: ##STR00004## wherein A is an alicyclic group selected from the group consisting of four-membered ring, five-membered ring, six-membered ring, seven-membered ring and eight-membered ring; and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are respectively C(O)Cl group or H, a number of C(O)Cl group is 3-6, two C(O)Cl groups are ortho or meta to each other.

7. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 1, wherein the porous support membrane is selected from the group consisting of organic polymer ultrafiltration membrane, hollow fiber ultrafiltration membrane, inorganic ultrafiltration membrane and organic-inorganic hybrid porous membrane; the organic polymer ultrafiltration membrane is selected from the group consisting of polysulfone, polyethersulfone, polyacrylonitrile and polyimide; and the inorganic ultrafiltration membrane material is a porous alumina or a porous ceramic membrane.

8. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 2, wherein a concentration of the alicyclic acid chloride solution is 0.01-2 wt%, a concentration of the alicyclic amine solution is 0.01-4 wt%.

9. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 8, wherein the alicyclic acid chloride solution comprises an alicyclic acid chloride, an organic solvent and an additive; a mass fraction of the alicyclic acid chloride is 0.01-2 wt%, a mass fraction of the organic solvent is 96-99.98 wt% and a mass fraction of the additive is 0.01-2 wt%; the organic solvent is one or more selected from the group consisting of n-hexane, cyclohexane, cyclopentane, n-heptane, n-octane and an isoparafin of the ISO-PAR series; and the alicyclic amine solution comprises an alicyclic amine, an aqueous solvent and an additive; a mass fraction of the alicyclic amine is 0.01-4 wt%, a mass fraction of the aqueous solvent is 46-99.98 wt% and a mass fraction of the additive is 0.01-50 wt%; and the aqueous solvent is water.

10. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 1, wherein the multi-layer alicyclic polyamide nanofiltration membrane comprises 10 layers.

11. The method of making the highly selective alicyclic polyamide nanofiltration membrane according to claim 1, wherein the 2-300 s at 50-10,000 rpm comprises at least one of 10 s at 300 rpm and 10 s at 500 rpm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional morphology of the alicyclic polyamide nanofiltration membrane prepared in Embodiment 1 of the present invention;

(2) FIG. 2 is a cross-sectional morphology of the alicyclic polyamide nanofiltration membrane Embodiment 2, prepared by the conventional interfacial polymerization-plate frame method;

(3) FIG. 3 is the linear variation of the thickness of active layers varying with the number of layers, wherein the test data of thickness are from the ellipsometer;

(4) FIG. 4 shows the rejection effects of the alicyclic polyamide nanofiltration membrane prepared in Embodiment 1 of the present invention and rejection effects of the commercial semi-aromatic polyamide nanofiltration membrane for SO.sub.4.sup.2 and Cl.sup.1 with different concentrations. The test conditions are as follows: salts used are NaCl and Na.sub.2SO.sub.4, wherein the Cl.sup.1 and SO.sub.4.sup.2 are of the same molar concentration, having a total ion molar concentrations of 14.04 mol.Math.m.sup.3, 28.08 mol.Math.m.sup.3, 56.16 mol.Math.m.sup.3, 84.24 mol.Math.m.sup.3, 112.32 mol.Math.m.sup.3, 140.04 mol.Math.m.sup.3, and 168.48 mol.Math.m.sup.3, and the test pressure is 1 MPa, the temperature is 25 C., and a flow rate is 7 LPM.

DETAILED DESCRIPTION

(5) The principle and features of the present invention are described below with reference to the accompanying drawings. The illustrated embodiments are only used to explain the present invention, and are not intended to limit the scope of the present invention.

Embodiment 1

(6) A method of making a highly selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of the alicyclic amine solution on a polyethersulfone ultrafiltration membrane by spin-coating method. Specially, allowing the piperazine solution to stand on the membrane for 120 s, throwing away the alicyclic amine solution by the spin-coating method at a rotation speed of 10,000 rpm for 40 s. Wherein the alicyclic amine solution includes a piperazine, an aqueous solvent and an additive. Wherein the additive is acetone and the aqueous phase solvent is water. Wherein a mass fraction of the piperazine is 1.5 wt %, a mass fraction of the acetone is 0.1 wt % and a mass fraction of the water is 98.4 wt %. (2) Coating a layer of the alicyclic acid chloride solution on the polyethersulfone ultrafiltration membrane coated with the alicyclic amine solution obtained in step (1) by the spin-coating method for interfacial polymerization, with a spin-coating time of 10 s and a rotation speed of 300 rpm. Then throwing away the extra alicyclic acid chloride solution by the spin-coating method at a rotation speed of 10,000 rpm for 40 s. Wherein the alicyclic acid chloride solution includes a 1, 3, 5-cyclohexane tricarboxylic acid chloride and an organic solvent, wherein the organic solvent is n-hexane. A mass fraction of the 1, 3, 5-cyclohexanetricarboxylic acid chloride is 0.1 wt % by weight, and a mass fraction of the organic solvent is 99.9 wt % by weight; (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with n-hexane for 15 s, removing the n-hexane at a rotation speed of 3,000 rpm for 40 s, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 50 C. for 60 s to obtain the highly selective alicyclic polyamide nanofiltration membrane, and the cross-section thereof is shown in FIG. 1. (4) For comparison, a series of equal molar concentration of Cl.sup.1 and SO.sub.4.sup.2 were used to test the desalination performance of the above alicyclic polyamide membrane and the commercial semi-aromatic polyamide membrane. The comparison curve is shown in FIG. 4.

Embodiment 2

(7) Preparing the alicyclic polyamide nanofiltration membrane by interfacial polymerization method, including the following steps: (1) Soaking a polyethersulfone ultrafiltration membrane in an alicyclic amine solution, and taking the polyethersulfone ultrafiltration membrane out after 120 s; gas purging the surface of the ultrafiltration membrane to remove the extra alicyclic amine solution. Wherein the alicyclic amine solution is composed of piperazine, additive and aqueous phase solvent. Wherein the additive is acetone, the aqueous phase solvent is water. Wherein a mass fraction of the piperazine is 1.5 wt %, a mass fraction of the acetone is 0.1 wt %, and a mass fraction of the aqueous solvent is 98.4 wt %; (2) Soaking a 1, 3, 5-cyclohexanetricarboxylic acid chloride solution on the ultrafiltration membrane with the piperazine solution on the surface obtained in the step (1), and taking the ultrafiltration membrane out after 10 s; wherein the organic solvent is n-hexane. Wherein a mass fraction of the 1, 3, 5-cyclohexanetricarboxylic acid chloride is 0.1 wt %, and a mass fraction of organic solvent is 99.9 wt %; (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with n-hexane for 15 s, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 50 C. for 60 s, similarly to that of Embodiment 1, to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(8) The cross-sectional view of Embodiment 2 is shown in FIG. 2. It can be seen from FIG. 1 and FIG. 2 that the alicyclic polyamide nanofiltration membrane prepared by the conventional interfacial polymerization-plate frame method has a consistent cross-sectional morphology, while that of the alicyclic polyamide nanofiltration membrane prepared by the spin-coating method is composed of a porous supporting layer and an active layer. The comparison of the desalination performances of the alicyclic polyamide nanofiltration membranes prepared by the conventional interfacial polymerization-plate frame method and the spin-coating method used in Embodiment 1 of the present invention is shown in FIG. 4. Both the rejection rates of Mg.sub.2SO.sub.4 by the nanofiltration membrane prepared by the interfacial polymerization spin-coating method and the nanofiltration membrane prepared by the interfacial polymerization-plate frame method remain above 97%, within a polymerization time of 5-30 s. The nanofiltration membrane prepared by the interfacial polymerization-spin-coating method has a 20-40% increase in membrane flux compared to the nanofiltration membrane prepared by the interfacial polymerization-plate frame method, at different interfacial polymerization periods.

(9) The rejection rates of the alicyclic polyamide nanofiltration membrane prepared in Embodiment 1 and the alicyclic polyamide nanofiltration membrane prepared in Embodiment 2 for various types of salts are respectively tested. Wherein the test conditions are as follows: cross-flow test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 1 and Table 2.

(10) TABLE-US-00001 TABLE 1 Salt rejection properties of the alicyclic polyamide nanofiltration membrane prepared in Embodiment 1 for salts Na.sub.2SO.sub.4 MgSO.sub.4 CaCl.sub.2 NaCl KCl Rejection rate (%) 98.97 0.04 97.77 0.07 65.15 0.08 15.47 0.15 18.49 0.39 Membrane Flux 62.41 0.29 60.45 0.43 53.70 0.42 63.55 0.63 65.83 0.33 (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1)

(11) TABLE-US-00002 TABLE 2 Salt rejection properties of the alicyelic polyamide nanofiltration membrane prepared in Embodiment 2 for salts Na.sub.2SO.sub.4 MgSO.sub.4 CaCl.sub.2 NaCl KCl Rejection rate (%) 97.58 0.29 96.83 0.32 64.17 0.15 16.04 0.28 19.27 0.42 Membrane Flux 42.8 1.97 41.8 1.37 .sup.36 2.3 46.3 1.97 47.2 1.52 (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1)

(12) As can be seen from Table 1 and Table 2, rejection abilities of the alicyclic polyamide nanofiltration membrane for different salts are: Na.sub.2SO.sub.4>MgSO.sub.4>CaCl.sub.2>KCl>NaCl. Referring to Table 1, the rejection rate for the divalent salt Na.sub.2SO.sub.4 is more than 98.97%, while the rejection rate for monovalent salts of NaCl and KCl are respectively 15.47% and 18.49%, showing an excellent selective permeability differences between the monovalent salt and bivalent salt. As to the flux, the fluxes of the alicyclic polyamide membrane to different salts are KCl>NaCl>Na.sub.2SO.sub.4>MgSO.sub.4>CaCl.sub.2. Wherein the flux of the monovalent salt is greater than that of the divalent salt due to the different radii of hydration ions of different salt solutions, resulting in osmotic pressure difference on both sides of the diaphragm during infiltration. Comparison of Table 1 and Table 2 shows that the rejection rates of the alicyclic polyamide prepared by the interfacial polymerization spin-coating method and the interfacial polymerization-plate-frame method do not differ much. While the flux of the interfacial polymerization spin-coating method is higher than that of the latter.

Embodiment 3

(13) A method of making a highly selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of the alicyclic amine solution on a polyethersulfone ultrafiltration membrane by spin-coating method. Specially, spin-coating a mixed alicyclic amine solution including piperazine and graphene oxide on the membrane at a speed of 500 rpm for 10 s, throwing away the alicyclic amine solution by the spin-coating method at a rotation speed of 9,000 rpm for 30 s. Wherein the alicyclic amine solution is composed of piperazine, aqueous solvent and additive. Wherein a mass fraction of the graphene oxide is 0.05 wt %, a mass fraction of the piperazine is 2 wt % and a mass fraction of the aqueous solvent is 97.95 wt %. (2) Coating a layer of the alicyclic acid chloride solution on the polyethersulfone ultrafiltration membrane coated with the alicyclic amine solution obtained in step (1) by the spin-coating method for interfacial polymerization. Specially, spin-coating the alicyclic acid chloride solution on the membrane at 500 rpm for 10 s. Then throwing away the extra alicyclic acid chloride solution by the spin-coating method at a rotation speed of 3,000 rpm for 40 s. Wherein the alicyclic acid chloride solution is composed of 1, 2, 4,-cyclopentane tricarboxylic acid chloride and organic solvent, wherein the organic solvent is n-heptane. Wherein a mass fraction of the 1, 2, 4,-cyclopentane tricarboxylic acid chloride is 0.01 wt %, and a mass fraction of the n-heptane is 99.99 wt %. (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with n-hexane for 60 s, removing the n-hexane at a rotation speed of 10,000 rpm for 60 s, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 90 C. for 2 min to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(14) The desalination performance of the alicyclic polyamide nanofiltration membrane prepared using the graphene oxide as aqueous solvent in this embodiment is tested. The test conditions are as following: cross-current test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 3.

(15) TABLE-US-00003 TABLE 3 Effects of graphene oxide as an aqueous additive on the desalination performance Graphene oxide-based alicyclic alicyclic polyamide polyamide nanofiltration membrane nanoflitration membrane Rejection rate Membrane Flux Rejection rate Membrane Flux (%) (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1) (%) (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1) Na.sub.2SO.sub.4 98.90 89.615 98.95 56.56 NaCl 12.53 0.58 104.34 3.74 15.49 0.4 67.61 2.5

(16) As can be seen from Table 3, the alicyclic polyamide nanofiltration membrane added with graphene oxide shows lower monovalent salt rejection rate and higher flux than that of the non-added alicyclic polyamide nanofiltration membrane, and the rejection rate of divalent salt remains unchanged. In particular, the rejection rates of Na.sub.2SO.sub.4 and NaCl for graphene oxide-based alicyclic polyamide nanofiltration membranes are 98.90% and 12.53%, respectively; and the fluxes are 89.62 and 104.34 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1, respectively. Compared the performance of alicyclic polyamide nanofiltration membrane made without the addition of graphene oxide, the fluxes of monovalent and divalent salts increase by 55% and 58%, respectively. While the monovalent salt rejection rate dropped to 12.53% and the rejection rate of divalent salt remains unchanged.

Embodiment 4

(17) A method of making a highly selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of alicyclic amine solution on a polyacrylonitrile ultrafiltration membrane by spin-coating method. Specially, spin-coating an alicyclic amine solution on the membrane at a speed of 50 rpm for 5 s, throwing away the alicyclic amine solution at a rotation speed of 10,000 rpm for 10 s. Wherein the alicyclic amine solution is composed of trans-1, 4-cyclohexanediamine, camphorsulfonic acid and water. Wherein a mass fraction of the trans-1, 4-cyclohexanediamine is 2 wt %, a mass fraction of the camphorsulfonic acid is 0.5 wt % and a mass fraction of the water is 97.5 wt %. (2) Coating a layer of alicyclic acid chloride solution on the polyacrylonitrile ultrafiltration membrane coated with the alicyclic amine solution obtained in step (1) by spin-coating method for interfacial polymerization. Specially, spin-coating the alicyclic acid chloride solution on the membrane at 500 rpm for 20 s. Then throwing away the extra alicyclic acid chloride solution at a rotation speed of 3,000 rpm for 60 s. Wherein the alicyclic acid chloride solution is composed of 1, 2, 3, 4-cyclobutane tetracarboxylic acid chloride and organic solvent, wherein the organic solvent is n-heptane. Wherein a mass fraction of the 1, 2, 3, 4-cyclobutane tetracarboxylic acid chloride is 0.38 wt %, and a mass fraction of the n-heptane is 99.62 wt %. (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with cyclohexane for 120 s, and removing the cyclohexane at a rotation speed of 7,000 rpm for 50 s. (4) Repeating step (1), step (2) and step (3) to obtain the alicyclic polyamide nanofiltration membrane prepared by the layer by layer assembly method, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 70 C. for 5 min to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(18) The desalination performance, for Na.sub.2SO.sub.4 and NaCl, of the alicyclic polyamide nanofiltration membrane prepared by four cycles of layer by layer assemblies, using the 1, 2, 3, 4-cyclobutane tetracarboxylic acid chloride as the alicyclic acid chloride solution, in this embodiment is tested. The test conditions are as following: cross-current test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 4.

(19) TABLE-US-00004 TABLE 4 Salt rejection properties of the 1,2,3,4-cyclobutane tetracarboxylic acid chloride-based alicyclic polyamide nanofiltration membrane Na.sub.2SO.sub.4 NaCl Rejection rate Membrane Flux Rejection rate Membrane Flux (%) (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1) (%) (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1) 1 layer 86.35% 90.20 12.84% 118.41 2 layers 94.36% 82.93 13.70% 101.84 3 layers 96.27% 75.38 14.25% 91.76 4 layers 98.51% 72.40 15.01% 85.32

(20) As can be seen from Table 4, the rejection rates of Na.sub.2SO.sub.4 and NaCl for the alicyclic polyamide nanofiltration membranes prepared by layer by layer assembly method are 98% and 15%, respectively. And with the increase of the number of layers, the rejection rate of Na.sub.2SO.sub.4 increases from 86.35% to 98.51%; while the rejection rate of NaCl increases from 12.84% to 15.01%, which remains nearly unchanged. At the same time, with the increase of the number of layers, the flux of the alicyclic polyamide nanofiltration membranes prepared by the layer by layer assembly method decreases as expected. When the layers increases from 1 to 4, the flux for Na.sub.2SO.sub.4 decreased from 90.20 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1 to 72.40.Math.kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1, while the flux for NaCl decreases from 118.41 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1 to 85.32 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1. Thus, alicyclic polyamide nanofiltration membranes with different layers show controllable characteristics on the rejection rate and flux, that is, the layer by layer can be assembled to adjust and regulate the performance of the nanofiltration membrane.

Embodiment 5

(21) A method of making a highly selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of alicyclic amine solution on a polyethersulfone ultrafiltration membrane by soaking method. Specially, allowing the alicyclic amine solution to stand on the polyethersulfone membrane for 240 s, throwing away the alicyclic amine solution at a rotation speed of 3,000 rpm for 60 s. Wherein the alicyclic amine solution is composed of trans-1, 4-cyclohexanediamine and water. Wherein a mass fraction of the trans-1, 4-cyclohexanediamine is 3 wt %, a mass fraction of the water is 97 wt %. (2) Coating a layer of alicyclic acid chloride solution on the polyethersulfone ultrafiltration membrane coated with the alicyclic amine solution obtained in step (1) by spin-coating method for interfacial polymerization. Specially, allowing the alicyclic acid chloride solution to stand on the ultrafiltration membrane for 60 s, then throwing away the extra alicyclic acid chloride solution at a rotation speed of 8,000 rpm for 50 s. Wherein the alicyclic acid chloride solution is composed of a 1, 2, 4, 5-cyclohexane tetracarboxylic acid chloride, an organic solvent and an additive, wherein the additive is acetone and the organic solvent is n-heptane. Wherein a mass fraction of the 1, 2, 4, 5-cyclohexane tetracarboxylic acid chloride is 0.12 wt %, a mass fraction of the acetone is 1 wt % and a mass fraction of the n-heptane is 98.88 wt %. (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with cyclohexane for 120 s, removing the cyclohexane at a rotation speed of 10,000 rpm for 60 s. (4) Soaking the washed alicyclic polyamide nanofiltration membrane in a 3 wt % isopropanol-water solution for 3 min, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 90 C. for 5 min to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(22) The rejection rates test of the alicyclic polyamide nanofiltration membrane prepared in this embodiment are performed on various types of salts. The test conditions are as follows: cross-current test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 5.

(23) TABLE-US-00005 TABLE 5 Salt rejection properties of the alicyclic polyamide nanofiltration membrane prepared using 1,2,4,5-cyclohexane tetracarboxylic acid chloride for various types of salts Na.sub.2SO.sub.4 MgSO.sub.4 CaCl.sub.2 NaCl MgCl.sub.2 Rejection rate (%) 95.14 0.23 93.4 0.2 87.15 0.45 20.71 0.76 93.37 0.35 Membrane Flux 48.69 0.83 46.10 0.42 40.18 0.98 45.78 0.73 43.33 0.74 (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1)

(24) As can be seen from Table 5, both the flux and rejection rate of the alicyclic polyamide nanofiltration membranes prepared from 1, 2, 4, 5-cyclohexanetetracarboxylic acid chloride and trans-1, 4-cyclohexanediamine are lower than that of the alicyclic polyamide nanofiltration membranes prepared from 1, 3, 5-cyclohexane tricarboxylic acid chloride and piperazine. Specifically, the flux of the nanofiltration membrane for Na.sub.2SO.sub.4 is 48.69 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1, and the rejection rate of Na.sub.2SO.sub.4 is 95.14%; meanwhile, the flux for NaCl is 45.780.73 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1 and the rejection rate of NaCl is 20.71%. Thus, it is further demonstrated that invented alicyclic polyamide nanofiltration membranes are highly selective toward the salt separation.

Embodiment 6

(25) A method of making a highly selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of alicyclic amine solution on a polyethersulfone ultrafiltration membrane by plate frame method. Specially, soak-coating the alicyclic amine solution to stand on the polyethersulfone membrane for 120 s, removing the extra aqueous phase solution by gas purging or roller squeezing. Wherein the alicyclic amine solution is composed of piperazine and an aqueous phase solution, wherein the aqueous phase solution is water. Wherein a mass fraction of the piperazine is 3.2 wt %, a mass fraction of the water is 96.8 wt %. (2) Coating a layer of alicyclic acid chloride solution on the polyethersulfone ultrafiltration membrane containing the piperazine on the surface, obtained in step (1) for interfacial polymerization. Specially, coating the alicyclic acid chloride solution on the membrane containing piperazine molecules and standing for reaction for 30 s, then removing the extra alicyclic acid chloride solution. Wherein the alicyclic acid chloride solution is composed of a 1, 2, 3, 4-cyclobutane formic acid chloride and an organic solvent. Wherein a mass fraction of the 1, 2, 3, 4-cyclobutane formic acid chloride is 0.32 wt %. Wherein the organic solvent is n-hexane and a mass fraction of the n-hexane is 99.68 wt %. (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with n-hexane for 40 s, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 60 C. for 2 min to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(26) The rejection rates test of the alicyclic polyamide nanofiltration membrane prepared in this embodiment are performed on various types of salts. The test conditions are as following: cross-current test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 6.

(27) TABLE-US-00006 TABLE 6 Salt rejection properties of the alicyclic polyamide nanofiltration membrane prepared by interfacial polymerization method for various types of salts. Na.sub.2SO.sub.4 MgSO.sub.4 CaCl.sub.2 NaCl MgCl.sub.2 Rejection rate (%) 99.1 0.13 99.4 0.04 99.1 0.11 83.3 0.54 99.1 0.31 Membrane Flux 86.8 0.61 88.3 0.24 84.6 0.91 96.7 0.30 82.9 0.82 (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1)

(28) As can be seen from Table 6, the rejection abilities of the alicyclic polyamide nanofiltration membrane prepared from 1, 2, 3, 4-cyclobutane formic acid chloride for different salts are: Na.sub.2SO.sub.4MgSO.sub.4CaCl.sub.2MgCl.sub.2>NaCl. Wherein the rejection rate of the alicyclic polyamide nanofiltration membrane prepared from this kind of acid chloride for all divalent salts is more than 99%, and the rejection rate for the monovalent salt is 83.3%, and the flux is 82.9-96.7 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1.

Embodiment 7

(29) A method of making a highly selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of alicyclic amine solution on a polyimide ultrafiltration membrane by spin-coating method. Specially, allowing an alicyclic amine solution to stand on the membrane for 180 s, throwing away the alicyclic amine solution at a rotation speed of 5,000 rpm for 30 s. Wherein the alicyclic amine solution is composed of reduced graphene oxide, piperazine and water. Wherein a mass fraction of the reduced graphene oxide is 0.1 wt %, a mass fraction of the piperazine is 2 wt %, and a mass fraction of the water is 97.9 wt %. (2) Coating a layer of the alicyclic acid chloride solution on the polyimide ultrafiltration membrane coated with the alicyclic acid chloride solution obtained in step (1) by spin-coating method for interfacial polymerization. Specially, allowing the alicyclic acid chloride solution to stand on the membrane coated with the alicyclic amine solution for 5 s, throwing away the extra alicyclic acid chloride solution at a rotation speed of 3,000 rpm for 40 s. Wherein the alicyclic acid chloride solution includes a 1, 3, 5-cyclohexane tricarboxylic acid chloride, additive and an organic solvent. Wherein the additive is lutidine and the organic solvent is cyclohexane. Wherein a mass fraction of the 1, 3, 5-cyclohexane tricarboxylic acid chloride is 0.2 wt %, a mass fraction of the lutidine is 1 wt % and a mass fraction of cyclohexane is 98.8 wt %. (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with n-hexane for 60 s, removing the n-hexane at a rotation speed of 10,000 rpm for 60 s, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 60 C. for 2 min to obtain the highly selective alicyclic polyamide nanofiltration membrane. (4) Repeating the above steps to obtain alicyclic polyamide nanofiltration membranes with different layers.

(30) The desalination performance of the alicyclic polyamide nanofiltration membrane prepared, using the reduced graphene oxide as aqueous solvent in this embodiment is tested. The test conditions are as following: cross-current test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 7.

(31) TABLE-US-00007 TABLE 7 Rejection properties of the alicyclic polyamide nanofiltration membrane prepared from the reduced graphene oxide for Na.sub.2SO.sub.4 and NaCl Na.sub.2SO.sub.4 NaCl Rejection rate Membrane Flux Rejection rate Membrane Flux (%) (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1) (%) (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1) 1 layer 99.03% 97.23 11.15 0.17% 106.61 2.62 2 layers 99.28% 89.24 11.64 0.28% 101.29 1.75 3 layers 99.38% 81.37 12.03 0.91% 94.82 2.83 4 layers 99.71% 76.38 12.48 0.72% 90 1.39

(32) As can be seen from Table 7, as compared to Embodiment 1, the alicyclic polyamide nanofiltration membrane added with the reduced graphene oxide shows a lower monovalent salt rejection rate and a higher flux than the non-added alicyclic polyamide nanofiltration membrane. The rejection rate of the divalent salt remains unchanged. In particular, when the number of layer by layer assembly layers increases from 1 layer to 4 layers, the rejection rate of the alicyclic polyamide nanofiltration membrane for Na.sub.2SO.sub.4 does not change much, all of which are maintained at over 99%, whereas the flux decreases from 97.23 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1 to 76.38 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1. The rejection rates of NaCl are all below 12%, whereas flux for NaCl decreases from 106.61 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1 to 90 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1. Thus, the above results demonstrate that alicyclic polyamide nanofiltration membranes with different layers prepared by layer by layer assembly method exhibit controllable rejection rates and fluxes, that is, the active layer can be assembled to adjust and regulate the performance of the nanofiltration membrane.

Embodiment 8

(33) A method of making a highly-selective alicyclic polyamide nanofiltration membrane, including the steps of: (1) Coating a layer of alicyclic amine solution on a polyethersulfone ultrafiltration membrane by soaking method. Specially, allowing an alicyclic amine solution to stand on the polyethersulfone membrane for 120 s, removing the extra alicyclic amine solution by gas purging or roller squeezing. Wherein the alicyclic amine solution is composed of trans-1, 4-cyclohexanediamine and water. Wherein a mass fraction of the trans-1, 4-cyclohexanediamine is 2 wt % and a mass fraction of the water is 98 wt %. (2) Interfacial polymerizing the polyethersulfone ultrafiltration membrane coated with the alicyclic amine solution obtained in step (1) with an alicyclic acid chloride solution.

(34) Specially, allowing the alicyclic acid chloride solution to stand on the ultrafiltration membrane obtained in step (1) for 30 s, then throwing away the extra alicyclic acid chloride solution at a rotation speed of 8,000 rpm for 50 s. Wherein the alicyclic acid chloride solution is composed of a 1, 3, 5-cyclohexane tricarboxylic acid chloride and an organic solvent. Wherein the organic solvent is cyclohexane. Wherein a mass fraction of the 1, 3, 5-cyclohexane tricarboxylic acid chloride is 0.2 wt % and a mass fraction of the cyclohexane is 99.8 wt %. (3) Washing the alicyclic polyamide nanofiltration membrane obtained in step (2) with n-hexane for 120 s, removing the n-hexane at a rotation speed of 10,000 rpm for 60 s (4) Soaking the washed alicyclic polyamide nanofiltration membrane in a 3 wt % isopropanolwater solution for 3 min, then providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 70 C. for 5 min to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(35) The rejection rates, for various types of salts, of the alicyclic polyamide nanofiltration membrane prepared in this embodiment are tested. The test conditions are as following: cross-current test, a single salt concentration of 2,000 ppm, 25 C., 1 MPa, and a flow rate of 7 LPM. The details of the test are shown in Table 8.

(36) TABLE-US-00008 TABLE 8 Salt rejection properties of the alicyclic polyamide nanofiltration membrane prepared using 1,3,5-cyclohexane tricarboxylic acid chloride for various types of salts. Na.sub.2SO.sub.4 MgSO.sub.4 CaCl.sub.2 NaCl MgCl.sub.2 Rejection rate (%) 98.08 0.01 98.34 0.21 92.81 0.49 29.57 1.68 95.61 0.52 Membrane Flux 53.72 1.17 55.99 2.28 56.69 0.05 63.06 0.41 55.23 0.96 (kg .Math. m.sup.2 .Math. h.sup.1 .Math. MPa.sup.1)

(37) As can be seen from Table 8, as compared to the alicyclic polyamide nanofiltration membrane prepared from 1, 3, 5-cyclohexane tricarboxylic acid chloride and piperazine, the alicyclic polyamide nanofiltration membrane prepared from 1, 3, 5-cyclohexane tricarboxylic acid chloride and trans-1,4-cyclohexanediamine shows a lower monovalent salt rejection rate. The rejection rate of the divalent salt CaCl.sub.2) is higher than that of the alicyclic polyamide nanofiltration membrane prepared from 1, 3, 5-cyclohexane tricarboxylic acid chloride and piperazine. In particular, the flux for Na.sub.2SO.sub.4 is 53.72 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1, and the rejection rate is 98.08%. At the same time, the rejection rate for the NaCl is 29.57%, and the flux thereof is 63.06 kg.Math.m.sup.2.Math.h.sup.1.Math.MPa.sup.1. Thus, it shows that the structure of the nanofiltration membrane can be regulated by designing the molecular structures of the monomers polymerized at the interface, so as to selectively separate the divalent salt from the monovalent salt. Compared to the trimesoyl chloride and 1, 3-phenylenediamine having planar structures, the trans-1, 4-cyclohexanediamine and 1, 3, 5-cyclohexane tricarboxylic acid chloride have a twisted conformation. Thus, the nanofiltration membrane prepared therefrom shows a more developed pore structure in the internal structure, which further facilitates Cl.sup.1 going through the nanofiltration membrane, to achieve the selective screening of Cl.sup.1 and SO.sub.4.sup.2.

Embodiment 9

(38) Preparing the alicyclic polyamide nanofiltration membrane by interfacial polymerization method, including the following steps:

(39) (1) Soaking a polysulfone ultrafiltration membrane in an alicyclic amine solution and taking the polysulfone ultrafiltration membrane out after 120 s; gas purging the surface of the ultrafiltration membrane to remove the extra alicyclic amine solution. Wherein the alicyclic amine solution is composed of piperazine and aqueous phase solvent. Wherein the aqueous phase solvent is water. Wherein a mass fraction of the piperazine is 2 wt %, and a mass fraction of the aqueous solvent is 98 wt %;

(40) (2) Soaking a 1, 3, 5-cyclohexanetricarboxylic acid chloride solution on the polysulfone ultrafiltration membrane with the piperazine solution on the surface obtained in the step (1), and taking the ultrafiltration membrane out after 20 s; wherein the organic solvent is iso-Par L. Wherein a mass fraction of the 1, 3, 5-cyclohexanetricarboxylic acid chloride is 0.1 wt %, and a mass fraction of organic solvent is 99.9 wt %;

(41) (3) Providing a heat-treatment to the alicyclic polyamide nanofiltration membrane at 60 C. for 120 s, similarly to that of Embodiment 1, to obtain the highly selective alicyclic polyamide nanofiltration membrane.

(42) TABLE-US-00009 TABLE 9 Salt rejection properties of the alicyclic polyamide nanofiltration membrane prepared in Embodiment 9 for salts Na.sub.2SO.sub.4 MgSO.sub.4 CaCl.sub.2 NaCl KCl Rejection rate (%) 98.27 97.15 67.45 11.57 16.38 Water flux 93.21 90.25 83.76 97.59 95.25 (kg m.sup.2 h.sup.1 MPa.sup.1)

(43) As can be seen from Table 9, rejection abilities of the alicyclic polyamide nanofiltration membrane for different salts are: Na.sub.2SO.sub.4>MgSO.sub.4>CaCl.sub.2)>KCl>NaCl. Specifically, the rejection rate for the divalent salt Na.sub.2SO.sub.4 is more than 98.27%, while the rejection rate for monovalent salts of NaCl and KCl are respectively 11.57% and 16.38%, showing an excellent selective permeability differences between the monovalent salt and bivalent salt. As to the flux, the fluxes order of the alicyclic polyamide membrane to different salts are NaCl>KCl>Na.sub.2SO.sub.4>MgSO.sub.4>CaCl.sub.2, wherein the flux of the monovalent salt is greater than that of the divalent salt, due to the different radius of hydration ions of different salt solutions, resulting in osmotic pressure difference on both sides of the diaphragm during infiltration.

(44) The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention, should be included in the protection scope of the present invention.