Polyamide composite membrane modified by PDA solution, preparation method of polyamide composite membrane and method for extracting m-cresol from phenol-containing wastewater

Abstract

The invention discloses a PDA solution modified polyamide composite membrane, a preparation method and a method for extracting m-cresol from phenol-containing wastewater, the polyamide composite membrane comprises a separation layer and a support layer, the support layer is a polytetrafluoroethylene (PTFE) base membrane, the separation layer is subjected to surface modification through a PDA solution to improve the hydrophilicity of the PTFE base membrane, and the PDA solution modified polyamide composite membrane is prepared from the PDA solution modified polyamide composite membrane. The surface of the polyamide film prepared by two interfacial polymerization methods contains a large number of amide groups, and the amide groups and hydroxyl groups in m-cresol form hydrogen bonds, so that the adsorption effect of the m-cresol on the surface of the polyamide film is enhanced. The polyamide composite membrane prepared by the invention shows excellent nanofiltration performance in an organic solution, the rejection rate of m-cresol can reach 52.5-65.5%, and the permeability of an organic solvent can reach 20-30L. M <-2 >. Bar <-1 >. S <-1 >. In addition, the polyamide composite membrane is relatively high in stability, can keep stable interception performance under continuous operation for 30 days, and has a very good industrial application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, and in particular to a polyamide composite membrane modified with a PDA solution, a preparation method and a method for extracting meta-cresol from phenol-containing wastewater. Background Art

[0002] Phenolic wastewater is a common pollutant in industrial wastewater, mainly from the petrochemical, pharmaceutical, dye and other industries. Phenolic substances (such as m-cresol) are highly toxic and difficult to degrade, which is extremely harmful to the environment and human health. Traditional treatment methods (such as adsorption, extraction, and biodegradation) have problems such as low efficiency, high cost, and secondary pollution.

[0003] Polyamide composite membranes have been widely used in membrane separation technology due to their excellent separation performance, chemical stability and mechanical strength. Traditional polyamide composite membranes are usually prepared by interfacial polymerization, that is, forming an ultra-thin polyamide separation layer on the surface of a porous support layer.

[0004] However, the traditional interfacial polymerization method has the following problems: Defective separation layer: Single interfacial polymerization can easily lead to uneven or defective separation layer, affecting the separation performance of the membrane. Insufficient hydrophilicity: The interfacial compatibility between the polyamide layer and the hydrophobic support layer (such as PTFE) is poor, making it difficult to balance the membrane flux and retention rate. Application limitations: Traditional polyamide membranes are prone to swelling or degradation in organic solvents or high-concentration wastewater treatment, limiting their scope of application. Summary of the invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a polyamide composite membrane modified with a PDA solution, a preparation method and a method for extracting meta-cresol from phenol-containing wastewater. The polyamide composite membrane modified with a PDA solution of the present invention improves the permeation flux and the retention rate.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A polyamide composite membrane modified with a PDA solution comprises a support layer and a separation layer formed on the surface of the support layer; the support layer is a polytetrafluoroethylene (PTFE) base membrane with a molecular weight cutoff of 200-2000 Da1; the separation layer is a polyamide film prepared by modifying the polydopamine (PDA) to improve the hydrophilicity of the surface of the PTFE base membrane and undergoing two interfacial polymerization reactions, and the surface of the polyamide film contains a large number of amide groups; the separation layer has a thickness of 20-200 nm and an effective separation area of ​​5-100 cm 2 .

[0008] The polyamide composite membrane has a molecular weight cutoff of 50-300 Da1, and can intercept small molecular weight substances such as m-cresol, thereby separating them from phenol-containing wastewater.

[0009] The method for preparing a polyamide composite membrane modified with a PDA solution comprises the following steps:

[0010] Step (1): immersing the PTFE base membrane as a support layer in a PDA solution with a concentration of 1-5 mg / mL for 2-6 minutes to complete the hydrophilic modification and then rinsing with deionized water;

[0011] Step (2): immersing the modified PTFE base membrane in an aqueous solution containing polyethyleneimine PEI and piperazine PIP and an organic solution containing trimesoyl chloride TMC in sequence to perform a first interfacial polymerization reaction;

[0012] Step (3): repeating step (2) to complete the second interfacial polymerization reaction, generating a separation layer on the surface of the support layer, and forming a polyamide composite membrane;

[0013] Step (4): Dry the polyamide composite membrane at 60-80° C. for 10-30 min, and store it in deionized water after washing.

[0014] In step (1), the PDA solution is prepared by dopamine hydrochloride and tris(hydroxymethyl)aminomethane Tris in a mass ratio of 1:1-1:10. The advantage is that PDA (polydopamine) has strong adhesion and abundant functional groups, and the preparation using this mass ratio can effectively adsorb m-cresol.

[0015] In step (2), the mass concentration ratio of PEI to PIP is 1:0.1-1:0.3. The advantage is that PEI is rich in amino groups and PIP has amide groups. The synergistic effect of the two at this mass concentration ratio can significantly improve the adsorption capacity of m-cresol.

[0016] The method for extracting m-cresol from phenol-containing wastewater using a polyamide composite membrane modified with a PDA solution comprises the following steps:

[0017] (1) The polyamide composite membrane was soaked with isopropanol and loaded into the nanofiltration device, and the system temperature was adjusted to 20-30° C.;

[0018] (2) inputting a model oil containing m-cresol as phenol-containing wastewater into a nanofiltration device, controlling the operating pressure to 0.1-4 bar, and setting the permeation time to a preset value;

[0019] (3) The permeate was collected and the concentration of m-cresol was determined. The permeate flux and the retention rate of the polyamide composite membrane were calculated. The two important parameters for evaluating the adsorption of m-cresol by the polyamide composite membrane are the permeate flux and the retention rate. The calculation formula is:

[0020] Permeation flux: P = V / (A × Δp × t)

[0021] Retention rate: R = (1-CP / C f )×100%

[0022] V is the volume of permeate, L

[0023] ΔP represents the osmotic pressure, bar

[0024] T is the penetration time, s

[0025] A represents the effective area of ​​the polyamide composite membrane, m 2

[0026] C p Indicates the concentration of cresols in the model oil, g / L

[0027] C f Indicates the concentration of cresols in the permeate, g / L.

[0028] The model oil has an intermediate cresol concentration of 50-200 g / L, which has the advantage of high separation efficiency and is convenient for subsequent treatment or recovery.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1) The polyamide composite membrane separation layer modified with PDA solution in the present invention is a polyamide film prepared by surface modification with PDA solution to improve the hydrophilicity of the PTFE-based membrane and by two interfacial polymerization methods. The surface of the polyamide film contains a large number of amide groups, which form hydrogen bonds with the hydroxyl groups in m-cresol, thereby enhancing the adsorption of m-cresol on the surface of the polyamide film.

[0031] 2) The preparation method of the present invention is stable and reliable. The polyamide composite membrane prepared by the above method exhibits excellent nanofiltration performance in organic solutions, with a retention rate of 52.5-65.5% for m-cresol and an organic solvent permeability of 20-30 L·m -2 bar -1 ·s -1 In addition, the polyamide composite membrane has high stability and can maintain its interception performance under 30 days of continuous operation, which has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a long-term stability test of the polyamide composite membrane modified with PDA solution in the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0034] The invention provides a polyamide composite membrane modified with a PDA solution, a preparation method and a method for extracting meta-cresol from phenol-containing wastewater. The polyamide composite membrane comprises a separation layer and a support layer, wherein the separation layer is a polyamide membrane and the support layer is a PTFE-based membrane.

[0035] Implementation Cases

[0036] Example 1

[0037] The preparation method of the polyamide composite membrane modified with PDA solution is as follows:

[0038] First, the surface of the PTFE base membrane was modified by PDA coating to improve the hydrophilicity of the PTFE base membrane: the PDA solution containing 1g / L dopamine hydrochloride and 6g / L tris(hydroxymethyl)aminomethane was soaked in the PTFE base membrane for 5min, and then the modified PTFE base membrane was rinsed with deionized water. Then, a polyamide film layer was synthesized on the inner surface of the modified PTFE base membrane by interfacial polymerization: an aqueous phase solution containing 12.5g / L polyethyleneimine PEI, 0.625g / L piperazine and an organic phase solution containing 1.25g / L trimesoyl chloride TMC were prepared and poured on the surface of the modified PTFE base membrane to form a polyamide film layer on its surface to obtain a polyamide composite membrane for 30min, and the excess aqueous solution was rinsed off with a cyclohexane solution, and then heat-treated in an oven at 60°C for 10min. In order to obtain a defect-free polyamide layer, the interfacial polymerization step was performed a second time: an aqueous solution containing 12.5 g / L polyethyleneimine PEI, 0.625 g / L piperazine and an organic solution containing 1.25 g / L trimesoyl chloride TMC were immersed on the surface of the modified PTFE base membrane for 10 minutes, and the excess aqueous solution was rinsed off with a cyclohexane solution, and then heat-treated in an oven at 60°C for 15 minutes. The prepared polyamide composite membrane was washed with deionized water several times and stored in deionized water to maintain a sterile environment.

[0039] Example 2

[0040] Method for extracting m-cresol from phenol-containing wastewater using polyamide composite membrane:

[0041] First, the polyamide composite membrane is soaked in an isopropanol solution to remove the air in the polyamide composite membrane; the polyamide composite membrane is loaded into a permeation pool of an organic solvent-resistant nanofiltration membrane evaluation device with a cold trap circulation pump, and the effective area of ​​the polyamide composite membrane is recorded as A: the stock solution bottle is loaded with a prepared concentration of meta-cresol model oil, and the model oil is stirred evenly and the temperature is stabilized at 25°C before being used to simulate phenol-containing wastewater, and the intermediate cresol concentration of the model oil is marked as Cp; the stock solution bottle is connected to the permeation pool of the nanofiltration membrane evaluation device and its sealing is checked; the cold trap circulation pump is turned on, the nanofiltration membrane evaluation device is operated to stabilize the permeation pressure of the polyamide composite membrane at 0.1 bar, and the permeation time of the model oil in the stock solution bottle in the polyamide composite membrane is recorded as T; after running for a period of time, the nanofiltration membrane evaluation device and the cold trap circulation pump are turned off, and the liquid that permeates through the polyamide composite membrane in the permeation pool, that is, the permeate, is recorded as V, and the intermediate cresol concentration of the permeate is recorded as C f Repeat steps (3) and (4) for multiple times, and take the average value of the obtained data; use gas chromatograph to analyze the concentration of intermediate cresol in the permeate, and calculate the permeation flux and retention rate of the polyamide composite membrane.

[0042] Example 3

[0043] The difference from Example 1 is that the mass concentration ratio of dopamine hydrochloride to tris(hydroxymethyl)aminomethane during the preparation of the polyamide composite membrane is 1:10, and the retention rate of m-cresol is measured to be 54.23%, and the permeation flux is 12.30 m -2 bar -1 ·s -1 .

[0044] Example 4

[0045] The difference from Example 1 is that the mass concentration ratio of polyethyleneimine to piperazine in the preparation process of the polyamide composite membrane is 1:0.5, and the measured retention rate of m-cresol is 56.48%, and the permeation flux is 16.45 m -2 bar -1 ·s -1 .

[0046] Example 5

[0047] The difference from Example 2 is that the temperature of the raw material liquid was stabilized at 20°C during the evaluation of the polyamide composite membrane. The retention rate of m-cresol was 55.28% and the permeation flux was 17.61 m -2 bar -1 ·s -1 .

[0048] Example 6

[0049] During the evaluation of the polyamide composite membrane, the raw material liquid temperature was stabilized at 25°C before evaluation. The retention rate of m-cresol was 64.36% and the permeation flux was 16.12 m -2 bar -1 ·s -1 .

[0050] Example 7

[0051] During the evaluation of the polyamide composite membrane, the raw material liquid temperature was stabilized at 30°C before evaluation. The retention rate of m-cresol was 54.16% and the permeation flux was 17.22 m -2 bar -1 ·s -1 .

[0052] Example 8

[0053] The difference from Example 2 is that during the evaluation of the polyamide composite membrane, the concentration of meta-cresol in the model oil was prepared to be 50 g / L and then evaluated. The retention rate of meta-cresol was measured to be 52.48% and the permeation flux was 18.2 m -2 bar -1 ·s -1 .

[0054] Example 9

[0055] The difference from Example 2 is that during the evaluation of the polyamide composite membrane, the concentration of meta-cresol in the model oil was prepared to be 100 g / L and then evaluated. The retention rate of meta-cresol was measured to be 64.51% and the permeation flux was 16.7 m / s. -2 bar -1 ·s -1 .

[0056] Example 10

[0057] The difference from Example 2 is that during the evaluation of the polyamide composite membrane, the concentration of meta-cresol in the model oil was prepared to be 150 g / L and then the evaluation was performed. The retention rate of meta-cresol was measured to be 55.48% and the permeation flux was 17.8 m -2 bar -1 ·s -1 .

[0058] Embodiment 11

[0059] as follows Figure 1 As shown, the membrane was subjected to OSN test using 100 g / L phenol model oil to evaluate its long-term stability. Figure 1 The membrane performance remained stable throughout the test period with negligible fluctuations, and the average toluene permeate flux was 18.5 m -2 h- 1 bar -1, with a m-cresol rejection of 65.6%. The membrane demonstrated excellent stability, maintaining consistent performance over an extended period of time. During testing, the membrane showed no signs of defects or breakage, indicating that the PTFE-based membrane remained stable at this pressure despite its large and irregular surface pore size.

Claims

1. A polyamide composite membrane modified with a PDA solution, characterized in that: The invention comprises a support layer and a separation layer formed on the surface of the support layer; the support layer is a polytetrafluoroethylene (PTFE) base membrane with a molecular weight cutoff of 200-2000 Da1; the separation layer is a polyamide film prepared by polydopamine (PDA) modification to improve the hydrophilicity of the surface of the PTFE base membrane and two interfacial polymerization reactions, and the surface of the polyamide film contains a large number of amide groups; the thickness of the separation layer is 20-200 nm, and the effective separation area is 5-100 cm 2 .

2. The polyamide composite membrane modified with a PDA solution according to claim 1, characterized in that: The molecular weight cut-off of the polyamide composite membrane is 50-300 Da1.

3. The method for preparing a polyamide composite membrane modified with a PDA solution according to claim 1 or 2, characterized in that: The steps include: Step (1): immersing the PTFE base membrane as a support layer in a PDA solution with a concentration of 1-5 mg / mL for 2-6 minutes to complete the hydrophilic modification and then rinsing with deionized water; Step (2): immersing the modified PTFE base membrane in an aqueous solution containing polyethyleneimine PEI and piperazine PIP and an organic solution containing trimesoyl chloride TMC in sequence to perform a first interfacial polymerization reaction; Step (3): repeating step (2) to complete the second interfacial polymerization reaction, generating a separation layer on the surface of the support layer, and forming a polyamide composite membrane; Step (4): Dry the polyamide composite membrane at 60-80° C. for 10-30 min, and store it in deionized water after washing.

4. The preparation method according to claim 3, characterized in that: In step (1), the PDA solution is prepared by mixing dopamine hydrochloride with tris(hydroxymethyl)aminomethane Tris in a mass ratio of 1:1-1:

10.

5. The preparation method according to claim 3, characterized in that: In step (2), the mass concentration ratio of PEI to PIP is 1:0.1-1:0.

3.

6. A method for extracting m-cresol from phenol-containing wastewater using a polyamide composite membrane modified with a PDA solution as claimed in claim 1 or 2, characterized in that: The steps include: (1) The polyamide composite membrane was soaked with isopropanol and loaded into the nanofiltration device, and the system temperature was adjusted to 20-30° C.; (2) inputting a model oil containing m-cresol as phenol-containing wastewater into a nanofiltration device, controlling the operating pressure to 0.1-4 bar, and setting the permeation time to a preset value; (3) The permeate was collected and the concentration of m-cresol was determined. The permeate flux and the retention rate of the polyamide composite membrane were calculated. The two important parameters for evaluating the adsorption of m-cresol by the polyamide composite membrane are the permeate flux and the retention rate. The calculation formula is: Permeation flux: P = V / (A × Δp × t) Retention rate: R = (1-C P / C f )×100% V is the volume of permeate, L ΔP represents the osmotic pressure, bar T is the penetration time, s A represents the effective area of ​​the polyamide composite membrane, m 2 C p Indicates the concentration of cresols in the model oil, g / L C f Indicates the concentration of cresols in the permeate, g / L.

7. The method for extracting m-cresol from phenol-containing wastewater using a polyamide composite membrane modified with a PDA solution as claimed in claim 6, characterized in that: The concentration of cresol in the model oil is 50-200 g / L.

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