Preparation method of negatively charged ceramic composite nanofiltration membrane

Abstract

The application relates to the field of membrane materials and membrane separation technology, in particular to a preparation method of a negatively charged ceramic composite nanofiltration membrane.The commercial ceramic nanofiltration membrane is cleaned and soaked first, then is subjected to a grafting reaction in an ethanol solution of 3-aminopropyltrimethoxysilane, then the grafted ceramic nanofiltration membrane is immersed in a water solution of chloroacetic acid for reaction, and finally, the ceramic nanofiltration membrane grafted with N,N-diacetic acid-3-(trimethoxysilyl)propylamine can be obtained.The membrane can effectively intercept negatively charged small-molecule organic pollutants in water and divalent or multivalent salt ions of sulfate in water; the silicon carbide-based ceramic composite nanofiltration membrane prepared by the method has the advantages of simple preparation method, mild preparation condition, and low preparation cost.

Description

Technical Field

[0001] This invention patent relates to the fields of membrane materials and membrane separation technology, specifically a method for preparing a negatively charged ceramic composite nanofiltration membrane. Background Technology

[0002] Membrane separation, as a highly efficient and energy-saving filtration technology, has been widely applied in food and pharmaceutical industries, energy and chemical industries, air pollution control, water treatment, and wastewater resource utilization. Among these, nanofiltration membranes, due to their ability to remove divalent and multivalent ions and retain organic molecules with molecular weights of approximately 150-1500 Da, are widely used in industrial desalination and zero-discharge industrial wastewater treatment. Furthermore, compared to reverse osmosis membranes, nanofiltration membranes have a higher flux and a higher removal rate of calcium and magnesium ions from water, making them widely used in the direct drinking water sector. The separation mechanism of nanofiltration membranes mainly lies in the sieving of membrane pore size and the equilibrium of surface charge. Therefore, the properties of the membrane surface charge are one of the core factors determining the selectivity and antifouling ability of nanofiltration membranes.

[0003] Compared to polymeric organic nanofiltration membranes, ceramic nanofiltration membranes possess superior characteristics such as acid and alkali resistance, high temperature resistance, high mechanical strength, large water flux, and long service life, exhibiting irreplaceable advantages in harsh environments (such as strong acids or alkalis, organic solvents, strong oxidants, and high-temperature systems). However, currently commercially available ceramic nanofiltration membranes are mainly prepared using the sol-gel method, forming a membrane layer composed of nano-sized particles (such as TiO2, ZrO2, Al2O3) with pore sizes concentrated in the range of 1-10 nanometers. Their filtration mechanism relies solely on pore size sieving, and the Dow balance is not very pronounced. While the nano-sized pores offer high retention rates for micro-pollutants, colloids, bacteria, and large organic molecules in water, they have very low removal rates for negatively charged small organic molecules, negatively charged dyes, and divalent or polyvalent ions such as magnesium sulfate and calcium sulfate. Therefore, ceramic nanofiltration membranes cannot perfectly exhibit the selective interception of pollutants and the retention rate of over 90% for divalent or polyvalent ions that organic nanofiltration membranes can. Summary of the Invention

[0004] This invention addresses the problem that ceramic nanofiltration membranes, which only have pore size sieving and lack a Dornan equilibrium separation mechanism, have poor retention effects on divalent and polyvalent ions. It proposes a method of chemical grafting to graft negatively charged molecular brushes onto the ceramic nanofiltration membrane layer, thereby endowing the ceramic nanofiltration membrane with the ability to selectively separate negatively charged organic pollutants and to achieve highly efficient retention of divalent or polyvalent sulfate salts.

[0005] The technical solution for achieving the objective of this invention is a method for preparing a negatively charged ceramic composite nanofiltration membrane, comprising the following steps: Step 1: Ultrasonically clean the ceramic nanofiltration membrane of the product for 15 minutes, and then soak it in ethanol for 1 hour to remove impurities from its surface and pores; Step 2: The ceramic nanofiltration membrane cleaned in Step 1 is immersed in an ethanol solution of 3-aminopropyltrimethoxysilane at room temperature for 12 hours. Its surface is repeatedly rinsed with anhydrous ethanol and then vacuum dried at 60°C to obtain the 3-aminopropyltrimethoxysilane-grafted ceramic nanofiltration membrane. The reaction process is as follows:

[0006] Step 3: The ceramic nanofiltration membrane grafted with 3-aminopropyltrimethoxysilane was immersed in an aqueous solution of chloroacetic acid and reacted at 60°C for 12 hours. The membrane surface was repeatedly rinsed with deionized water and dried under vacuum at 60°C to obtain the ceramic nanofiltration membrane grafted with N,N-diacetyl-3-(trimethoxysilyl)propylamine. The reaction process is as follows:

[0007] Preferably, the ceramic nanofiltration membrane support described in step one is either alumina or silicon carbide. Preferably, the membrane material of the ceramic nanofiltration membrane mentioned in step one is a composite material of one or more of alumina, zirconium oxide, silicon oxide or titanium oxide. Preferably, the concentration of 3-aminopropyltrimethoxysilane in step two is 10~30 mmol / L; Preferably, the concentration of chloroacetic acid in step three is 20~60 mmol / L; Preferably, the pH value of the chloroacetic acid aqueous solution in step three is 10-13; The present invention has the following beneficial effects: (1) On the surface of the ceramic nanofiltration membrane of the product, negatively charged molecular brushes are grafted by chemical grafting, giving the ceramic nanofiltration membrane a Daonan balance effect, which can effectively intercept negatively charged small molecule organic pollutants in water and divalent or polyvalent sulfate ions in water.

[0008] (2) The silicon carbide-based ceramic composite nanofiltration membrane prepared by this method is simple to prepare, has mild preparation conditions, and low preparation cost. Detailed Implementation

[0009] The present invention will be further illustrated below with examples, but these are not intended to limit the scope of the invention.

[0010] Example 1 The ceramic membrane was ultrasonically cleaned for 10 min, then soaked in ethanol solution for 1 h to remove impurities from its surface and pores. The treated ceramic membrane was then filtered separately with 1 g / L MgSO4 and CaSO4 aqueous solutions in a cross-flow filtration device at 25 °C and 0.5 MPa to evaluate the membrane's permeation flux and rejection rate.

[0011] Example 2 Step 1: Ultrasonically clean the silicon carbide ceramic nanofiltration membrane of the product for 10 minutes, and then soak it in ethanol solution for 1 hour to remove impurities from its surface and pores; Step 2: The cleaned silicon carbide ceramic nanofiltration membrane was immersed in an ethanol solution of 20 mmol / L 3-aminopropyltrimethoxysilane at room temperature for 12 h, and then its surface was repeatedly rinsed with anhydrous ethanol and dried under vacuum at 60 °C to obtain a 3-aminopropyltrimethoxysilane-grafted silicon carbide ceramic nanofiltration membrane. Step 3: The ceramic nanofiltration membrane grafted with 3-aminopropyltrimethoxysilane was immersed in an aqueous solution of chloroacetic acid with a concentration of 40 mmol / L, the pH was adjusted to 12 with sodium hydroxide, and the reaction was carried out at 60°C for 12 h. The membrane surface was repeatedly rinsed with deionized water and dried under vacuum at 60°C to obtain the ceramic nanofiltration membrane grafted with N,N-diacetyl-3-(trimethoxysilyl)propylamine. Step 4: The ceramic nanofiltration membrane grafted with N,N-diacetyl-3-(trimethoxysilyl)propylamine was used to filter 1 g / L aqueous solutions of MgSO4 and CaSO4 in a cross-flow filtration device at a temperature of 25 °C and a filtration pressure of 0.5 MPa. The permeation flux and rejection rate of the membrane were evaluated.

[0012] Example 3 With other conditions unchanged, a silicon carbide-based ceramic composite nanofiltration membrane was prepared with a concentration of 10 mmol / L of 3-aminopropyltrimethoxysilane, and the membrane's permeation flux and rejection rate were evaluated.

[0013] Example 4 With other conditions unchanged, a silicon carbide-based ceramic composite nanofiltration membrane was prepared with a concentration of 30 mmol / L of 3-aminopropyltrimethoxysilane, and the membrane's permeation flux and rejection rate were evaluated.

[0014] Example 5 With other conditions unchanged, a silicon carbide-based ceramic composite nanofiltration membrane was prepared at a chloroacetic acid concentration of 20 mmol / L, and the membrane's permeation flux and rejection rate were evaluated.

[0015] Example 6 With other conditions unchanged, a silicon carbide-based ceramic composite nanofiltration membrane was prepared at a chloroacetic acid concentration of 60 mmol / L, and the membrane's permeation flux and rejection rate were evaluated.

[0016] The specific formula for calculating the permeate flux of ceramic membrane is as follows:

[0017] In the formula: J represents the permeation flux, with units of L·m -2 ·h-1 ; W represents the volume or weight of the permeate, in L or Kg. A represents the effective filtration area of ​​the membrane, measured in meters (m²). 2 ; t represents the filtration time of the membrane, in hours (h).

[0018] The salt rejection rate of the nanofiltration membrane was measured using a conductivity meter to determine the salt concentration before and after rejection. The specific formula for calculating the rejection rate (R) is as follows:

[0019] In the formula: R is the rejection rate of the ceramic membrane (%); C p It is the salt concentration of the permeate (g / L); C f It is the salt concentration of the feed solution (g / L).

[0020] The test results are shown in the table below: Example <![CDATA[Permeation flux (L·m -2 ·h -1 )]]> <![CDATA[Interception rate (%) of MgSO4]]> <![CDATA[Intercept rate (%) of CaSO4]]> 1 133.6 8.7 9.5 2 42.8 91.3 94.1 3 68.4 55.4 64.8 4 29.7 93.2 95.3 5 30.6 82.9 84.9 6 24.3 93.7 94.6 Test results showed that a negatively charged silicon carbide ceramic composite nanofiltration membrane was successfully prepared.

[0021] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent variations and modifications described in accordance with the scope of the present invention and the description should fall within the scope of the present invention.

Claims

1. A method for preparing a negatively charged ceramic composite nanofiltration membrane, characterized in that... Includes the following steps: Step 1: Using the ceramic nanofiltration membrane of the product as a support, first ultrasonically clean it for 15 minutes, and then soak it in ethanol for 1 hour to remove impurities from its surface and pores. Step 2: Immerse the cleaned ceramic nanofiltration membrane in an ethanol solution of 3-aminopropyltrimethoxysilane at room temperature for 12 hours, rinse its surface repeatedly with anhydrous ethanol, and dry it under vacuum at 60°C to obtain a 3-aminopropyltrimethoxysilane-grafted ceramic nanofiltration membrane. Step 3: The ceramic nanofiltration membrane grafted with 3-aminopropyltrimethoxysilane was immersed in an aqueous solution of chloroacetic acid and reacted at 60°C for 12 hours. The membrane surface was repeatedly rinsed with deionized water and dried under vacuum at 60°C to obtain a ceramic nanofiltration membrane grafted with N,N-diacetyl-3-(trimethoxysilyl)propylamine.

2. The preparation method according to claim 1, characterized in that... The ceramic nanofiltration membrane support is either alumina or silicon carbide.

3. The preparation method according to claim 1, characterized in that... The ceramic nanofiltration membrane is made of one or more composite materials selected from alumina, zirconium oxide, silicon oxide, or titanium oxide.

4. The preparation method according to claim 1, characterized in that... The concentration of the 3-aminopropyltrimethoxysilane is 10~30 mmol / L.

5. The preparation method according to claim 1, characterized in that... The concentration of the chloroacetic acid is 20~60 mmol / L.

6. The preparation method according to claim 1, characterized in that... The pH value of the chloroacetic acid aqueous solution is 10-13.

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