Preparation, regeneration and application of a chelating microfiltration membrane

Abstract

A polyvinylidene fluoride (PVDF) casting membrane solution is shaped as a flat sheet membrane by thermally induced phase separation (TIPS), the PVDF membrane is defluorinated with an alkaline potassium permanganate solution, and then the carbon chain is extended with glycidyl methacrylate (GMA) as the graft monomer, and finally the nucleophilic substitution is carried out between melamine and GMA to produce a chelating microfiltration membrane for capturing and enriching heavy metals with high flux and high capacity.

Claims

1. A preparation method of a chelating microfiltration membrane, comprising: A. preparing a polyvinylidene fluoride flat sheet membrane: adding 70-90 parts of a solvent into a reactor, then adding 4-22 parts of a pore-forming agent and 6-16 parts of polyvinylidene fluoride, then dissolving completely to form a casting membrane solution; stirring and reacting the casting membrane solution for 1-44 h in the reactor, wherein the reaction temperature is controlled at 50-100 C.; wherein the casting membrane solution, after being settled and defoamed, is shaped as a diaphragm by employing a thermally induced phase separation process; soaking the diaphragm in distilled water for 1-3 h, and finally drying to produce a polyvinylidene fluoride PVDF flat sheet membrane; B. defluorination: adding the polyvinylidene fluoride flat sheet membrane obtained in step A and a low concentration alkaline potassium permanganate solution to the reactor, wherein a mass ratio of the flat sheet membrane and the alkaline potassium permanganate solution is 1:20-1:50, with a temperature controlled at 10-100 C., performing the reaction for 1-25 h, and then washing and drying to obtain a defluorinated flat sheet membrane; C. grafting glycidyl methacrylate: adding the deflourinated flat sheet membrane obtained in step B and a solution of glycidyl methacrylate at a concentration of 0.5-5% to the reactor, wherein a mass ratio of the deflourinated flat sheet membrane and the solution of glycidyl methacrylate is 1:20-1:50, then adding an initiator and a polymerization inhibitor, wherein the temperature is controlled at 10-120 C., and the reaction is performed for 1-25 h, and then washing and drying to obtain a grafted flat sheet membrane; D. melamine modification: adding the grafted flat sheet membrane obtained in step C and a solution of melamine at a concentration of 0.1-5.0% to the reactor, wherein a mass ratio of the grafted flat sheet membrane and the solution of melamine is 1:20-1:50, with the temperature controlled at 10-120 C., performing the reaction for 1-36 h, and then washing and drying.

2. The preparation method of a chelating microfiltration membrane according to claim 1, wherein the solvent in step A is one selected from the group consisting of N-methyl pyrrolidone, N,N-dimethyl acetamide, trimethylolpropane, dimethyl phthalate, and triethyl phosphate.

3. The preparation method of a chelating microfiltration membrane according to claim 2, wherein the pore-forming agent in step A is one selected from the group consisting of polyethylene glycol and polyvinyl pyrrolidone.

4. The preparation method of a chelating microfiltration membrane according to claim 3, wherein a mass fraction of the alkaline potassium permanganate solution in step B is 0.5-5%.

5. The preparation method of a chelating microfiltration membrane according to claim 4, wherein the solvent in the solution of glycidyl methacrylate in step C is one selected from the group consisting of methanol, ethanol, n-propanol, isopropanol and toluene.

6. The preparation method of a chelating microfiltration membrane according to claim 5, wherein the initiator in step C is one selected from the group consisting of 2,2-azoisobutyronitrile, ammonium persulfate, potassium persulfate, and benzoyl peroxide, with a concentration of 0.01-0.05%.

7. The preparation method of a chelating microfiltration membrane according to claim 6, wherein the polymerization inhibitor in step C is one selected from the group consisting of methylhydroquinone, p-hydroxyanisole, and 2-tert-butylhydroquinone, with a concentration of 0.01-0.05%.

8. The preparation method of a chelating microfiltration membrane according to claim 1, further comprising a regeneration process including soaking the chelating microfiltration membrane in a solution of hydrochloric acid, nitric acid or sulfuric acid at 0.001-1.0 M for 1-72 h and then soaking and washing in deionized water for 1-72 h.

Description

DETAILED DESCRIPTION

(1) To further illustrate the content of the present invention, the present invention will be described in detail in combination with the following examples, which was only used to illustrate the present invention, without limiting the application ranges of the present invention.

EXAMPLE 1

(2) (1) Preparation of PVDF flat sheet membrane: to a reactor was first added 76 g N,N-dimethylacetamide, then added 9 g polyethylene glycol with a molecular weight of 400 and 15 g polyvinylidene fluoride PVDF, which were stirred to be dissolved completely to give a casting membrane solution; the casting membrane solution was stirred and reacted for 12 h in the reactor, with the temperature controlled at 80 C., after being settled and defoamed, which was shaped as a diaphragm by employing TIPS phase inversion process, after then the diaphragm was soaked in distilled water for 1 h, and finally was dried to produce a polyvinylidene fluoride PVDF flat sheet membrane;

(3) (2) Defluorination: to the reactor were added the PVDF membrane produced in step (1) and the alkaline potassium permanganate solution of 1%, wherein the mass ratio of the flat sheet membrane and the solution was 1:20, with the temperature controlled at 80 C., the reaction was performed for 4 h, and then washed and dried;

(4) (3) Grafting glycidyl methacrylate: to the reactor were added the membrane produced in step (2) and the solution of glycidyl methacrylate in methanol at a concentration of 2%, wherein the mass ratio of the flat sheet membrane and the solution was 1:50, into which were then added 2,2-azoisobutyronitrile and p-hydroxyanisole, the concentrations of which were respectively controlled at 0.01% and 0.05% , with the temperature controlled at 65 C., the reaction was performed for 5 h, and then washed and dried;

(5) (4) Melamine ammoniation: to the reactor was added the solution of melamine at a concentration of 0.25%, wherein the mass ratio of the flat sheet membrane and the solution was 1:25, the membrane produced in step (3) was added into the reactor, with the temperature controlled at 70 C., the reaction was performed for 8 h, and then washed and dried;

(6) (5) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 25 C., the flux of pure water was detected as 646 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 30 min at a differential pressure of 0.2 MPa.

EXAMPLE 2

(7) (1) Preparation of PVDF flat sheet membrane: to a reactor was first added 80 g triethyl phosphate, then added 4 g polyvinyl pyrrolidone with a molecular weight of 8000 and 16 g polyvinylidene fluoride PVDF, which were stirred to be dissolved completely to give a casting membrane solution; the casting membrane solution was stirred and reacted for 44 h in the reactor, with the temperature controlled at 100 C., after being settled and defoamed, which was shaped as a diaphragm by employing TIPS phase inversion process, after then the diaphragm was soaked in distilled water for 3 h, and finally was dried to produce a polyvinylidene fluoride PVDF flat sheet membrane;

(8) (2) Defluorination: to the reactor were added the PVDF membrane produced in step (1) and the alkaline potassium permanganate solution of 0.5%, wherein the mass ratio of the flat sheet membrane and the solution was 1:35, with the temperature controlled at 10 C., the reaction was performed for 1 h, and then washed and dried;

(9) (3) Grafting glycidyl methacrylate: to the reactor were added the membrane produced in step (2) and the solution of glycidyl methacrylate in toluene at a concentration of 0.5%, wherein the mass ratio of the flat sheet membrane and the solution was 1:25, into which were then added potassium persulfate and methylhydroquinone, the concentrations of which were respectively controlled at 0.02% and 0.01%, with the temperature controlled at 80 C., the reaction was performed for 1 h, and then washed and dried in air;

(10) (4) Melamine ammoniation: to the reactor was added the solution of melamine at a concentration of 0.1%, wherein the mass ratio of the flat sheet membrane and the solution was 1:50, the membrane produced in step (3) was added into the reactor, with the temperature controlled at 100 C., the reaction was performed for 36 h, and then washed and dried;

(11) (5) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 25 C., the flux of pure water was detected as 597 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 30 min at a differential pressure of 0.1 MPa.

EXAMPLE 3

(12) (1) Preparation of PVDF flat sheet membrane: to a reactor was first added 70 g trimethylol propane, then added 22 g polyethylene glycol with a molecular weight of 500 and 8 g polyvinylidene fluoride PVDF, which were stirred to be dissolved completely to give a casting membrane solution; the casting membrane solution was stirred and reacted for 1 h in the reactor, with the temperature controlled at 50 C., after being settled and defoamed, which was shaped as a diaphragm by employing TIPS phase inversion process, after then the diaphragm was soaked in distilled water for 2 h, and finally was dried in air to produce a polyvinylidene fluoride PVDF flat sheet membrane;

(13) (2) Defluorination: to the reactor were added the PVDF membrane produced in step (1) and the alkaline potassium permanganate solution of 5.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:40, with the temperature controlled at 75 C., the reaction was performed for 25 h, and then washed and dried;

(14) (3) Grafting glycidyl methacrylate: to the reactor were added the membrane produced in step (2) and the solution of glycidyl methacrylate in isopropanol at a concentration of 5.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:20, into which were then added ammonium persulfate and 2-tert-butyl hydroquinone, the concentrations of which were respectively controlled at 0.03% and 0.02%, with the temperature controlled at 30 C., the reaction was performed for 15 h, and then washed and dried;

(15) (4) Melamine ammoniation: to the reactor was added the solution of melamine at a concentration of 5.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:35, the membrane produced in step (3) was added into the reactor, with the temperature controlled at 40 C., the reaction was performed for 16 h, and then washed and dried;

(16) (5) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 25 C., the flux of pure water was detected as 597 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 1 h at a differential pressure of 0.15 MPa.

EXAMPLE 4

(17) (1) Preparation of PVDF flat sheet membrane: to a reactor was first added 90 g N-methylpyrrolidone, then added 4 g polyvinyl pyrrolidone with a molecular weight of 24000 and 6 g polyvinylidene fluoride PVDF, which were stirred to be dissolved completely to give a casting membrane solution; the casting membrane solution was stirred and reacted for 30 h in the reactor, with the temperature controlled at 75 C., after being settled and defoamed, which was shaped as a diaphragm by employing TIPS phase inversion process, after then the diaphragm was soaked in distilled water for 2 h, and finally was dried to produce a polyvinylidene fluoride PVDF flat sheet membrane;

(18) (2) Defluorination: to the reactor were added the PVDF membrane produced in step (1) and the alkaline potassium permanganate solution of 3.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:50, with the temperature controlled at 100 C., the reaction was performed for 15 h, and then washed and dried;

(19) (3) Grafting glycidyl methacrylate: to the reactor were added the membrane produced in step (2) and the solution of glycidyl methacrylate in ethanol at a concentration of 3.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:45, into which were then added benzoyl peroxide and p-hydroxyanisole, the concentrations of which were respectively controlled at 0.04% and 0.04%, with the temperature controlled at 40 C., the reaction was performed for 20 h, and then washed and dried;

(20) (4) Melamine ammoniation: to the reactor was added the solution of melamine at a concentration of 5.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:20, the membrane produced in step (3) was added into the reactor, with the temperature controlled at 120 C., the reaction was performed for 1 h, and then washed and dried;

(21) (5) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 35 C., the flux of pure water was detected as 651 L.Math.m.sup.2.Math..sup.1 after being pre-pressed for 30 min at a differential pressure of 0.15 MPa.

EXAMPLE 5

(22) (1) Preparation of PVDF flat sheet membrane: to a reactor was first added 85 g dimethyl phthalate, then added 5 g polyethylene glycol with a molecular weight of 400 and 10 g polyvinylidene fluoride PVDF, which were stirred to be dissolved completely to give a casting membrane solution; the casting membrane solution was stirred and reacted for 24 h in the reactor, with the temperature controlled at 85 C., after being settled and defoamed, which was shaped as a diaphragm by employing TIPS phase inversion process, after then the diaphragm was soaked in distilled water for 90 min, and finally was dried to produce a polyvinylidene fluoride PVDF flat sheet membrane;

(23) (2) Defluorination: to the reactor were added the PVDF membrane produced in step (1) and the alkaline potassium permanganate solution of 4.5%, wherein the mass ratio of the flat sheet membrane and the solution was 1:30, with the temperature controlled at 50 C., the reaction was performed for 8 h, and then washed and dried;

(24) (3) Grafting glycidyl methacrylate: to the reactor were added the membrane produced in step (2) and the solution of glycidyl methacrylate in n-propanol at a concentration of 1.8%, wherein the mass ratio of the flat sheet membrane and the solution was 1:45, into which were then added 2,2-azoisobutyronitrile and methyl hydroquinone, the concentrations of which were respectively controlled at 0.02% and 0.03%, with the temperature controlled at 10 C., the reaction was performed for 8 h, and then washed and dried;

(25) (4) Melamine ammoniation: to the reactor was added the solution of melamine at a concentration of 3.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:40, the membrane produced in step (3) was added into the reactor, with the temperature controlled at 60 C., the reaction was performed for 4 h, and then washed and dried;

(26) (5) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 25 C., the flux of pure water was detected as 574 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 1 h at a differential pressure of 0.2 MPa.

EXAMPLE 6

(27) (1) Preparation of PVDF flat sheet membrane: to a reactor was first added 75 g N,N-dimethylacetamide, then added 15 g polyvinyl pyrrolidone with a molecular weight of 10000 and 10 g polyvinylidene fluoride PVDF, which were stirred to be dissolved completely to give a casting membrane solution; the casting membrane solution was stirred and reacted for 10 h in the reactor, with the temperature controlled at 90 C., after being settled and defoamed, which was shaped as a diaphragm by employing TIPS phase inversion process, after then the diaphragm was soaked in distilled water for 150 min, and finally was dried to produce a polyvinylidene fluoride PVDF flat sheet membrane;

(28) (2) Defluorination: to the reactor were added the PVDF membrane produced in step (1) and the alkaline potassium permanganate solution of 2.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:25, with the temperature controlled at 65 C., the reaction was performed for 12 h, and then washed and dried;

(29) (3) Grafting glycidyl methacrylate: to the reactor were added the membrane produced in step (2) and the solution of glycidyl methacrylate in methanol at a concentration of 4.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:35, into which were then added potassium persulfate and 2-tert-butyl hydroquinone, the concentrations of which were respectively controlled at 0.05% and 0.01%, with the temperature controlled at 75 C., the reaction was performed for 25 h, and then washed and dried;

(30) (4) Melamine ammoniation: to the reactor was added the solution of melamine at a concentration of 2.0%, wherein the mass ratio of the flat sheet membrane and the solution was 1:25, the membrane produced in step (3) was added into the reactor, with the temperature controlled at 10 C., the reaction was performed for 24 h, and then washed and dried;

(31) (5) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 20 C., the flux of pure water was detected as 678 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 30 min at a differential pressure of 0.1 MPa.

EXAMPLE 7

Regeneration of the Chelating Microfiltration Membrane

(32) The chelating microfiltration membrane obtained in Example 1, after dynamic absorption and entrapment of heavy metal ions, was soaked in a solution of hydrochloric acid at a concentration of 0.5M for 36 h, then soaked in deionized water for 12 h and washed to neutral, thus recovering the heavy metal ion-absorbing capacity of the adsorption membrane.

(33) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 20 C., the flux of pure water was detected as 589 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 30 min at a differential pressure of 0.1 MPa.

EXAMPLE 8

Regeneration of the Chelating Microfiltration Membrane

(34) The chelating microfiltration membrane obtained in Example 3, after dynamic absorption and entrapment of heavy metal ions, was soaked in a solution of nitric acid at a concentration of 0.001M for 72 h, then soaked in deionized water for 1 h and washed to neutral, thus recovering the heavy metal ion-absorbing capacity of the adsorption membrane.

(35) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 25 C., the flux of pure water was detected as 601 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 1 h at a differential pressure of 0.2 MPa.

EXAMPLE 9

Regeneration of the Chelating Microfiltration Membrane

(36) The chelating microfiltration membrane obtained in Example 5, after dynamic absorption and entrapment of heavy metal ions, was soaked in a solution of sulfuric acid at a concentration of 1.0M for 1 h, then soaked in deionized water for 20 h and washed to neutral, thus recovering the heavy metal ion-absorbing capacity of the adsorption membrane.

(37) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 30 C., the flux of pure water was detected as 558 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 30min at a differential pressure of 0.15 MPa.

EXAMPLE 10

Regeneration of the Chelating Microfiltration Membrane

(38) The chelating microfiltration membrane obtained in Example 6, after dynamic absorption and entrapment of heavy metal ions, was soaked in a solution of nitric acid at a concentration of 0.1M for 12 h, then soaked in deionized water for 72 h and washed to neutral, thus recovering the heavy metal ion-absorbing capacity of the adsorption membrane.

(39) The above described chelating microfiltration membrane was placed in a cross flow membrane filtration system, the temperature of which was controlled at 25 C., the flux of pure water was detected as 659 L.Math.m.sup.2.Math.h.sup.1 after being pre-pressed for 30 min at a differential pressure of 0.2 MPa.

(40) The absorption and entrapment effects on heavy metals of the heavy metal chelating microfiltration membrane produced in Examples 1-6 were presented in Table 1, it can be seen that the heavy metal chelating microfiltration membrane produced in the present invention possess excellent treatment effects on heavy metal containing waster water.

(41) TABLE-US-00001 TABLE 1 The absorption and entrapment effects on heavy metals of the heavy metal chelating microfiltration membrane produced in Examples 1-6 Type of Initial Type of Initial the heavy Concentration, Removing the heavy Concentration, Removing metal mg/L rate % metal mg/L rate % Example 1 copper 6.3 100 zinc 8.4 99.8 Example 2 cadmium 10.2 98.6 lead 19.5 97.3 Example 3 nickle 5.8 99.7 chromium 5.2 98.9 Example 4 cobalt 5.9 99.6 nickle 5.5 99.9 Example 5 copper 6.7 99.7 iron 5.5 99.1 Example 6 chromium 4.9 98.2 lead 21.3 98.8

(42) The absorption and entrapment performances on heavy metals of the same chelating microfiltration membrane before and after regeneration were presented in Table 2, it can be seen that the heavy metal chelating microfiltration membrane produced in the present invention possess excellent regeneration ability, with a simple regeneration process, and allowing for the industrial application.

(43) TABLE-US-00002 TABLE 2 The absorption and entrapment performances on heavy metals of the same chelating microfiltration membrane before and after regeneration Type of Initial Type of Initial the heavy Concentration, Removing the heavy Concentration, Removing metal mg/L rate % metal mg/L rate % Example 1 lead 15.4 98.6 copper 5.7 99.1 Example 2 nickle 6.3 99.8 cadmium 9.8 98.4 Example 3 chromium 4.9 98.9 zinc 6.3 98.7 Example 4 cobalt 5.4 99.5 lead 16.1 97.5 Example 5 copper 6.5 98.8 nickle 5.4 97.8 Example 6 iron 5.5 97.6 chromium 5.2 99.2

(44) It is needed to illustrate that the above examples are only the preferred examples of the present invention, which are not used to confine the scope of the present invention, and the equivalent exchanges or substitutions on the basis of which are all in the scope of the present invention.