阅读说明：本技术 一种纳米纤维素络合物复合聚酰胺膜及其制备方法 (Nano cellulose complex compound polyamide membrane and preparation method thereof ) 是由 王章慧 夏道伟 于 2021-07-20 设计创作，主要内容包括：本发明属于膜分离技术领域,涉及一种纳米纤维素络合物复合聚酰胺膜及其制备方法。本发明具有多孔结构的纳米纤维素络合物利用内部的超亲水纳米通道实现兼具高通量、高分离精度聚酰胺复合膜的制备,且超亲水特征赋予复合膜优异的抗污性,其对于高性能分离膜的构筑具有重要的科学指导意义和实际应用价值。(The invention belongs to the technical field of membrane separation, and relates to a nano-cellulose complex compound polyamide membrane and a preparation method thereof. The nano cellulose complex with the porous structure realizes the preparation of the polyamide composite membrane with high flux and high separation precision by utilizing the internal super-hydrophilic nano channel, and the super-hydrophilic characteristic endows the composite membrane with excellent dirt resistance, thereby having important scientific guiding significance and practical application value for the construction of a high-performance separation membrane.)

1. The composite polyamide membrane is characterized by being obtained by carrying out interfacial polymerization reaction on an aqueous solution containing a nano cellulose complex/amine monomer and an organic solution containing a polybasic acyl chloride monomer on the surface of an ultrafiltration membrane.

2. A method for preparing a nanocellulose complex composite polyamide membrane as claimed in claim 1, characterized in that said method comprises the steps of:

s1, dripping the nano-cellulose aqueous solution with positive charge or negative charge into the nano-cellulose aqueous solution with opposite charge, centrifuging and washing to obtain nano-cellulose complex aqueous dispersion;

and S2, immersing the ultrafiltration membrane into an aqueous phase solution containing the nano-cellulose complex and the amine monomer, removing the excessive aqueous solution on the surface of the membrane, pouring the polyatomic acid chloride organic solution on the surface of the membrane for standing, removing the excessive organic solution on the surface of the membrane, carrying out heat treatment on the membrane, and washing with deionized water to obtain the nano-cellulose complex composite polyamide membrane.

3. The method for preparing a nanocellulose complex composite polyamide membrane according to claim 2, characterized in that, step S1 positively charged nanocellulose is quaternary ammonium cellulose nanofiber.

4. The method of claim 2, wherein the negatively charged nanocellulose of step S1 is any one of TEMPO-cellulose nanofibers, phosphocellulose nanofibers, carboxymethyl cellulose nanofibers, cellulose sulfonate nanofibers, or cellulose nanocrystals.

5. The method of claim 2, wherein the concentration of the positively or negatively charged nanocellulose aqueous solution of step S1 is 0.01-0.5%, and the pH is 2-12.

6. The method of claim 2, wherein the concentration of the nanocellulose complex in the aqueous solution of step S2 is 0.01-3%.

7. The method of claim 2, wherein the amine monomer concentration in the aqueous solution of step S2 is 0.1-5%.

8. The method for preparing a nanocellulose complex composite polyamide membrane as claimed in claim 2, wherein the concentration of polyacyl chloride organic solution is 0.01-3%.

9. The method for preparing a nanocellulose complex composite polyamide membrane as claimed in claim 2 or 8, wherein said polybasic acid chloride is trimesoyl chloride or terephthaloyl chloride.

10. The method for preparing the nano-cellulose complex compound polyamide membrane as claimed in claim 2, wherein the nano-cellulose complex compound polyamide membrane has a pore diameter of 0.5-20nm, a water contact angle of 2-40 ° and a water permeation flux of 35-100L/m²h, the inorganic salt rejection rate is 5-100%.

Technical Field

The invention belongs to the technical field of membrane separation, and relates to a nano-cellulose complex compound polyamide membrane and a preparation method thereof.

Background

With the rapid development of industry and agriculture, the problem of water pollution is increased, the world health organization calls that three adults (21 hundred million) in the world lack safe drinking water, and more than 340 million people die of diseases related to water sources every year. As a high-efficiency, environment-friendly and energy-saving separation technology, a membrane separation method can realize selective permeation separation of substances on a molecular level, and is widely applied to the fields of biological medicine, battery diaphragms, food processing, gas separation, water treatment, chemical engineering and the like. The Polyamide (PA) membrane is an important branch of a separation membrane and is obtained by the polycondensation reaction of polyamine and polyacyl chloride monomers at the interface of water and an organic solvent. Because the interfacial polymerization method has the advantages of simple operation, rapidness, high efficiency, self-inhibition and the like, the prepared PA membrane becomes a mainstream product of commercial nanofiltration membranes and reverse osmosis membranes. However, PA membranes have a common problem of mutual restriction of permeability and selectivity and easy contamination, and are a bottleneck that restricts separation efficiency. Therefore, there is a need to develop a high performance composite PA membrane to promote its further development and popularization.

With the rapid development of nanotechnology, the in-situ introduction of nanomaterials into PA matrices to construct thin-layer nanocomposite (TFN) films has gradually attracted the research interest of broad scholars. The method can realize the synchronous regulation and control of the bulk structure and the surface structure of the membrane, and only needs to add the nano material in situ in the water phase/organic phase, thereby being a simple and convenient method suitable for industrial application. There are a large number of existing inorganic nanomaterials (e.g., SiO)₂CNT, GO, Mxene, etc.) TFN membranes, studies have found that the introduction of inorganic nanomaterials improves the permeation flux of composite membranes to varying degrees (Water res, 2020,173: 115557; adv. mater. interfaces, 2021, 8: 2001671). However, the dispersibility of the inorganic nano material and the compatibility with the organic PA matrix are poor, and interface defects are easy to generate, so that the permselectivity of the composite membrane is limited.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a nano cellulose complex compound polyamide membrane with high water permeation flux and separation precision and a preparation method thereof.

The purpose of the invention can be realized by the following technical scheme: the composite polyamide membrane is obtained by performing interfacial polymerization reaction on an aqueous solution containing a nano cellulose complex/amine monomer and an organic solution containing a polybasic acyl chloride monomer on the surface of an ultrafiltration membrane.

The invention also provides a preparation method of the nano-cellulose complex compound polyamide membrane, which comprises the following steps:

s1, dripping the nano-cellulose aqueous solution with positive charge or negative charge into the nano-cellulose aqueous solution with opposite charge, centrifuging and washing to obtain nano-cellulose complex aqueous dispersion;

and S2, immersing the ultrafiltration membrane into an aqueous phase solution containing the nano-cellulose complex and the amine monomer, removing the excessive aqueous solution on the surface of the membrane, pouring the polyatomic acid chloride organic solution on the surface of the membrane for standing, removing the excessive organic solution on the surface of the membrane, carrying out heat treatment on the membrane, and washing with deionized water to obtain the nano-cellulose complex composite polyamide membrane.

According to the invention, a nanocellulose complex is formed by utilizing electrostatic acting force between positively charged nanocellulose and negatively charged nanocellulose in an aqueous solution, and an interfacial polymerization reaction between the aqueous solution containing the nanocellulose complex/amine monomer and an organic solution containing a polybasic acyl chloride monomer is carried out on the surface of an ultrafiltration membrane to obtain the nanocellulose complex composite polyamide membrane. The nano cellulose complex has the characteristics of super-hydrophilicity and hierarchical pores, and can provide a super-hydrophilic nano channel and a super-hydrophilic surface, so that the water permeation flux, the separation precision and the pollution resistance are obviously improved, and the high performance of the polyamide membrane is realized.

In the above nanocellulose complex composite polyamide membrane, the positively charged nanocellulose of step S1 is a quaternary ammonium cellulose nanofiber.

In the above nanocellulose complex composite polyamide membrane, the negatively charged nanocellulose of step S1 is any one of TEMPO-cellulose nanofibers, phosphocellulose nanofibers, carboxymethyl cellulose nanofibers, cellulose sulfonate nanofibers, and cellulose nanocrystals.

In the above nanocellulose complex composite polyamide membrane, the concentration of the nanocellulose aqueous solution charged positively or negatively in step S1 is 0.01-0.5%, and the pH is 2-12.

Preferably, the charge amount of the charged nanocellulose obtained in the step S1 is 0.1 to 4.0 mmol/g.

Preferably, the ultrafiltration membrane is any one of polysulfone, polyethersulfone, polyacrylonitrile and polyvinylidene fluoride ultrafiltration membranes.

In the above one of the nanocellulose complex composite polyamide membranes, the concentration of the nanocellulose complex in the aqueous phase solution of step S2 is 0.01 to 3%.

In the above nanocellulose complex composite polyamide membrane, the concentration of the amine monomer in the aqueous phase solution in step S2 is 0.1-5%.

Preferably, the amine monomer is any one of piperazine, m-phenylenediamine and polyethyleneimine.

In the nano-cellulose complex compound polyamide membrane, the concentration of the polyacyl chloride organic solution is 0.01-3%.

In the nanocellulose complex composite polyamide membrane, the polybasic acyl chloride is any one of trimesoyl chloride and terephthaloyl chloride.

Preferably, the solvent of the organic solution of the polybasic acid chloride is any one of n-hexane, cyclohexane and heptane.

Preferably, the ultrafiltration membrane is immersed in the aqueous phase solution of the nano cellulose complex and the amine monomer for 1-10min, then the excessive aqueous solution on the membrane surface is removed, and the polyacyl chloride organic solution is poured on the membrane surface and stands for 1-10 min.

Preferably, the heat treatment temperature of step S2 is 50-80 deg.C, and the time is 5-20 min.

Preferably, the nano-cellulose complex compound polyamide membrane has the pore diameter of 0.5-20nm, the water contact angle of 2-40 degrees and the water permeation flux of 35-100L/m²h, inorganicThe salt rejection is 5-100%.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the invention, the preparation of the polyamide composite membrane with high flux and high separation precision is realized by utilizing the internal super-hydrophilic nanochannel through the nano-cellulose complex with the porous structure, and the super-hydrophilic characteristic endows the composite membrane with excellent stain resistance, so that the polyamide composite membrane has important scientific guiding significance and practical application value for the construction of a high-performance separation membrane.

2. The process for preparing the nano-cellulose complex compound polyamide membrane is simple, efficient, rapid and convenient, is a simple and convenient method suitable for industrial application, and can be widely applied to the separation fields of water treatment, chemical industry, pharmacy, food and the like.

Detailed Description

The following are specific examples of the present invention and further describe the technical solutions of the present invention, but the present invention is not limited to these examples.

Example 1:

10ml of an aqueous solution of quaternary ammonium cellulose nanofibers (charge amount 1.0mmol/g) having a concentration of 0.01% and a pH of 7.0 was added dropwise at a rate of 5 drops/sec to an aqueous solution of TEMPO-cellulose nanofibers (charge amount 1.0mmol/g) having a concentration of 0.01% and a pH of 7.0 under stirring, and uncomplexed nanocellulose was removed by centrifugation and washing to obtain an aqueous nanocellulose complex solution.

Immersing a polysulfone ultrafiltration membrane into 25mL of aqueous phase solution of a nano cellulose complex and a piperazine monomer for 1 minute, wherein the concentration of the nano cellulose complex in the aqueous phase solution is 0.1%, the concentration of the piperazine monomer is 0.3%, then removing excessive aqueous solution on the surface of the membrane, pouring 25mL of 0.05% trimesoyl chloride n-hexane solution on the surface of the membrane, standing for 1 minute, then removing excessive organic solution on the surface of the membrane, placing the membrane in a 60 ℃ oven for heat treatment for 10 minutes, and washing with deionized water to obtain the nano cellulose complex composite polyamide membrane.

Example 2:

10ml of an aqueous solution of quaternary ammonium cellulose nanofibers (charge amount 1.0mmol/g) having a concentration of 0.01% and a pH of 7.0 was added dropwise at a rate of 5 drops/sec to 10ml of an aqueous solution of TEMPO-cellulose nanofibers (charge amount 1.0mmol/g) having a concentration of 0.01% and a pH of 7.0 under stirring, and uncomplexed nanocellulose was removed by centrifugation and washing to obtain an aqueous nanocellulose complex solution.

Immersing a polysulfone ultrafiltration membrane into 25mL of aqueous phase solution of a nano cellulose complex and a piperazine monomer for 1 minute, wherein the concentration of the nano cellulose complex in the aqueous phase solution is 0.01% and the concentration of the piperazine monomer is 0.2%, then removing excessive aqueous solution on the surface of the membrane, pouring 25mL of 0.05% trimesoyl chloride n-hexane solution on the surface of the membrane, standing for 1 minute, then removing excessive organic solution on the surface of the membrane, placing the membrane in a 60 ℃ oven for heat treatment for 100 minutes, and washing with deionized water to obtain the nano cellulose complex composite polyamide membrane.

Example 3:

10ml of an aqueous solution of quaternary ammonium cellulose nanofibers (charge amount 1.0mmol/g) having a concentration of 0.01% and a pH of 7.0 was added dropwise at a rate of 5 drops/sec to an aqueous solution of TEMPO-cellulose nanofibers (charge amount 1.0mmol/g) having a concentration of 0.01% and a pH of 7.0 under stirring, and uncomplexed nanocellulose was removed by centrifugation and washing to obtain an aqueous nanocellulose complex solution.

Immersing a polysulfone ultrafiltration membrane into 25mL of aqueous phase solution of a nano cellulose complex and a piperazine monomer for 1 minute, wherein the concentration of the nano cellulose complex in the aqueous phase solution is 3 percent, the concentration of the piperazine monomer is 3 percent, then removing excessive aqueous solution on the surface of the membrane, pouring 25mL of 0.05 percent trimesoyl chloride n-hexane solution on the surface of the membrane, standing for 1 minute, then removing excessive organic solution on the surface of the membrane, placing the membrane in a 60 ℃ oven for heat treatment for 10 minutes, and washing with deionized water to obtain the nano cellulose complex composite polyamide membrane.

Comparative example 1:

the difference from example 1 is only that comparative example 1, which does not prepare the nanocellulose complex, directly uses piperazine as an aqueous phase monomer and prepares the polyamide membrane through interfacial polymerization with trimesoyl chloride n-hexane solution.

Comparative example 2:

the difference from example 1 is only that comparative example 2, without preparing the nanocellulose complex, directly uses the quaternary ammonium cellulose nanofiber and piperazine as water phase monomers, and prepares the quaternary ammonium cellulose nanofiber composite polyamide membrane through interfacial polymerization with trimesoyl chloride n-hexane solution

Comparative example 3:

the difference from example 1 is only that comparative example 3, without preparing the nanocellulose complex, directly uses TEMPO-cellulose nanofibers and piperazine as aqueous phase monomers, and prepares a TEMPO-cellulose nanofiber composite polyamide membrane through interfacial polymerization with trimesoyl chloride n-hexane solution.

Table 1: results of physical Properties measurements of nanocellulose complex composite Polyamide membranes prepared in examples 1 to 4 and comparative examples 1 to 3

Examples	Pore diameter of membrane (nm)	Water contact Angle (°)
			Example 1	0.66	25
Example 2	0.50	40
			Example 3	1.02	15
Comparative example 1	0.45	65
			Comparative example 2	0.40	40
Comparative example 3	0.55	37

And (3) flux testing: cutting standard size membrane (area A: m)²) Fixing in an ultrafiltration cup, pre-pressing with deionized water at 0.4MPa for 30min, collecting deionized water under the same pressure for t (h), measuring its volume V (L), and calculating water flux J (L/m)²h)。

Separating inorganic salt: fixing the membrane in an ultrafiltration cup at 0.4MPa and with a certain concentration c_f(mg/L) of an aqueous solution of inorganic salt (sodium sulfate, sodium chloride) was preliminarily pressed for 30min, and then 10mL of the filtrate was collected under the same pressure, and its concentration c was measured with a conductivity meter_p(mg/L), the inorganic salt rejection R (%) was calculated.

Stain resistance: fixing the membrane in an ultrafiltration cup, prepressing with deionized water at 0.4MPa for 30min, and recording water permeation flux J of the membrane after continuously running for 2h₀(L/m²h) Then, using contaminant (BSA, LYZ, HA, NaAlg) water solution with certain concentration as feed solution, operating at 0.4MPa for 6h, recording permeation flux every 1h, and collecting the contaminantThe lowest flux of the dyed membrane is recorded as J_s(L/m²h) In that respect The 2h aqueous solution test and the 6h contaminant test were taken as a cycle, and after 2.5 cycles, the permeation flux J of the membrane was again recorded_r(L/m²h) In that respect The fouling resistance can be expressed in terms of the flux reduction rate (FDR), Flux Recovery Rate (FRR) of the membrane:

table 2: performance test results of the polyamide membranes prepared in examples 1 to 2 and comparative examples 1 to 3

From the above results, it can be seen that the polyamide membranes can be obtained by the four methods of the polyamide membranes prepared in example 1 and comparative examples 1 to 3, but the water permeation flux, the inorganic salt rejection rate and the anti-fouling performance are obviously different due to the difference of the physicochemical structures of the polyamide membranes.

In comparative example 1, the nanocellulose complex was not prepared, piperazine was directly used as the aqueous monomer, and the obtained polyamide membrane consisted of a compact polyamide chain, exhibiting low water permeation flux and anti-fouling performance;

in the comparative example 2, a nano cellulose complex is not prepared, the quaternary ammonium cellulose nano fiber and piperazine are directly used as water phase monomers, and as the quaternary ammonium cellulose nano fiber and carboxyl generated by hydrolysis of trimesoyl chloride form electrostatic interaction force, the structure of the obtained quaternary ammonium cellulose nano fiber composite polyamide membrane becomes more compact and is easy to generate defects, so that the water permeation flux and the rejection rate are reduced, but the introduction of the super-hydrophilic quaternary ammonium cellulose nano fiber improves the surface hydrophilicity of the membrane, so that the anti-fouling performance of the composite polyamide membrane is improved;

in comparative example 3, a nano-cellulose complex is not prepared, TEMPO-cellulose nano-fiber and piperazine are directly used as water phase monomers, the introduction of hydrophilic TEMPO-cellulose nano-fiber is beneficial to forming a low mass transfer resistance interface channel, and the surface charge negative electricity of the composite membrane is enhanced, so that the pure water permeation flux, the inorganic salt rejection rate and the stain resistance of the obtained TEMPO-cellulose nano-fiber composite polyamide membrane are all improved, but are still obviously lower than those of example 1.

In conclusion, the porous structure in the hydrophilic nanocellulose complex can provide a super-hydrophilic nanochannel with low mass transfer resistance for permeation of water molecules, so that the water permeation flux, the inorganic salt retention rate and the anti-fouling capability of the composite polyamide membrane are remarkably improved.

The technical scope of the invention claimed by the embodiments of the present application is not exhaustive, and new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope of the invention claimed by the present application; in all the embodiments of the present invention, which are listed or not listed, each parameter in the same embodiment only represents an example (i.e., a feasible embodiment) of the technical solution, and there is no strict matching and limiting relationship between the parameters, wherein the parameters may be replaced with each other without departing from the axiom and the requirements of the present invention, unless otherwise specified.

The technical means disclosed by the scheme of the invention are not limited to the technical means disclosed by the technical means, and the technical scheme also comprises the technical scheme formed by any combination of the technical characteristics. While the foregoing is directed to embodiments of the present invention, it will be appreciated by those skilled in the art that various changes may be made in the embodiments without departing from the principles of the invention, and that such changes and modifications are intended to be included within the scope of the invention.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.