CN110449047B - High-flux positive nanofiltration membrane for biogas slurry purification and preparation method thereof - Google Patents
High-flux positive nanofiltration membrane for biogas slurry purification and preparation method thereof Download PDFInfo
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- CN110449047B CN110449047B CN201910669678.1A CN201910669678A CN110449047B CN 110449047 B CN110449047 B CN 110449047B CN 201910669678 A CN201910669678 A CN 201910669678A CN 110449047 B CN110449047 B CN 110449047B
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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Abstract
The invention provides a concept of purifying biogas slurry by using a high-flux positive nanofiltration membrane. In the invention, hydrophilic carbon quantum dots are used for modifying the nanofiltration membrane, so that the water flux is increased by 2.29 times while the high flux is kept. The modified nanofiltration membrane has high interception on lysine, leucine and glutamic acid in the biogas slurry, and the highest interception can reach 94.3%. Meanwhile, the separation factor of amino acid and negative ions reaches 2.45, which shows that the prepared nanofiltration membrane has great potential for purification treatment of biogas slurry.
Description
Technical Field
The invention relates to a high-flux positive nanofiltration membrane for biogas slurry purification treatment and a preparation method thereof, and belongs to the technical field of membrane separation materials.
Background
The biogas slurry is residue of various organic matters such as human and animal excreta and crop straws after anaerobic fermentation. The fertilizer contains a large amount of amino acid, and is a raw material of liquid fertilizer. The fertilizer has strong quick-acting nutrition capability and high nutrient availability, can be quickly absorbed and utilized by crops, can improve the yield and quality of the crops, has the functions of disease prevention and stress resistance, and is a high-quality organic liquid fertilizer. However, as the water content of the biogas slurry is high, the volume is large, the transportation and storage conditions are difficult, and the discharge continuity of the biogas slurry is in conflict with the seasonality of farmland fertilization, a relatively large-scale biogas slurry is directly discharged because the biogas slurry cannot be timely consumed and utilized, so that the environment and the human health are threatened, and the waste of resources is serious. But simultaneously, the biogas slurry contains a large amount of sulfate radicals and chloride ions, which can affect the purity of beneficial substances in the biogas slurry. Therefore, if the amino acid in the liquid can be purified and recovered, the harmless and resource comprehensive utilization of the biogas slurry can be effectively realized.
The membrane separation technology not only can effectively remove pollutants to obtain high-quality permeate liquid, but also can realize the concentration of nutrients to obtain concentrated liquid rich in nutrient substances. Nanofiltration (NF) is a new membrane separation technology between reverse osmosis and ultrafiltration developed in the late 80 s of the 20 th century, and the membrane has an aperture of about 0.5-2nm, and is suitable for separating dissolved components with a size of about 1nm, so the technology is called as nanofiltration. Therefore, the purification treatment of the biogas slurry by selecting the proper nanofiltration membrane has great prospect.
Disclosure of Invention
The invention provides a high-flux positively charged nanofiltration membrane for biogas slurry purification treatment. After the nanofiltration membrane is modified by utilizing the carbon quantum dots, the water flux of the membrane can be improved, and the separation of amino acid and negative ions in the biogas slurry can be achieved through the selection of the electrical property.
In a first aspect of the present invention, there is provided:
a nanofiltration membrane is formed by sequentially compounding a base membrane, a carbon quantum dot intermediate layer and a selective separation layer.
In one embodiment, the selective separation layer is made of a polyamide-based material.
In one embodiment, the selective separation layer is positively charged.
In one embodiment, the material of the base film is selected from Polyethersulfone (PES), Sulfonated Polysulfone (SPSF), Polyetherimide (PEI), and the like.
In a second aspect of the present invention, there is provided:
the preparation method of the nanofiltration membrane comprises the following steps:
and 3, preparing an interfacial polymerization layer on the carbon quantum dot intermediate layer by an interfacial polymerization method.
In one embodiment, the material of the base film is selected from Polyethersulfone (PES), Sulfonated Polysulfone (SPSF), Polyetherimide (PEI), and the like.
In one embodiment, the base film is coated by immersing the base film in a suspension containing carbon quantum dots in the step 2; the concentration of the carbon quantum dots in the suspension is 2-6 wt%, and the surfaces of the carbon quantum dots are treated by an activating agent.
In one embodiment, the activator is 2-chloro-1-methyl iodopyridine (CMPI).
In one embodiment, step 3 is prepared by an interfacial polymerization method using an amine monomer and an acid chloride monomer.
In one embodiment, the amine monomer is polyethyleneimine, and the concentration of the amine monomer in the aqueous phase is 1-3%; the acyl chloride monomer is trimesic acid chloride, and the concentration of the acyl chloride monomer in the organic phase is 0.1-3%.
In a third aspect of the present invention, there is provided:
the nanofiltration membrane is applied to separation of amino acid and inorganic salt in biogas slurry.
In one embodiment, the amino acid is selected from lysine, leucine or glutamic acid and the inorganic salt is selected from Na2SO4 or NaCl.
In one embodiment, high-flux positively charged nanofiltration membranes are used to increase the separation factor for amino acids and inorganic salts.
In one embodiment, a high flux positively charged nanofiltration membrane is used to increase the water flux during the separation of biogas slurry.
In a fourth aspect of the present invention, there is provided:
the carbon quantum dots are used as the base membrane and the intermediate layer of the selective separation layer for improving the flux in the biogas slurry filtering process.
In a fifth aspect of the present invention, there is provided:
application of 2-chloro-1-methyl iodopyridine (CMPI) in preparation of nanofiltration membrane.
In one embodiment, the 2-chloro-1-methyl iodopyridine (CMPI) is used to activate carbon quantum dots.
In one embodiment, the 2-chloro-1-methyl iodopyridine (CMPI) is used for improving the water flux of the nanofiltration membrane in the biogas slurry separation process.
Advantageous effects
The invention utilizes the mechanism that the positively charged nanofiltration membrane has high retention rate on positive ions and low retention rate on negative ions, and can effectively retain amino acid in the biogas slurry, remove sulfate radicals and chloride ions and purify the biogas slurry. In addition, after the carbon quantum dots modify the self-made nanofiltration membrane, the hydrophilicity of the membrane is changed, an ultra-fast ion channel is constructed, the water flux of the membrane is increased, and the performance of the electropositive membrane is greatly improved.
Drawings
Figure 1 is a flux comparison of nanofiltration membranes;
figure 2 is a comparison of the rejection of nanofiltration membranes;
FIG. 3 is the XPS characterization results;
FIG. 4 shows the results of molecular weight cut-off characterization;
FIG. 5 is a graph of the separation performance of amino acids and salts under different pH conditions;
FIG. 6 is a representation of the Zeta potential;
figure 7 is a comparison of the separation performance characterization of the prepared positive and commercial negative nanofiltration membranes for amino acids and salts;
figure 8 is a performance graph of the prepared positive and commercial negative nanofiltration membranes for concentration separation of amino acids and salts.
Detailed Description
The high-flux positive nanofiltration membrane provided by the invention is formed by sequentially compounding a base membrane, a carbon quantum dot intermediate layer and a selective separation layer.
The base film may be a normal polymer film material, which is present as a support layer. For example, the base film may be a nonwoven fabric or a polymer film, and the material may be Polyethersulfone (PES), Polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), or the like. In one embodiment, the polyethersulfone solution and the solvent are mixed to prepare a casting solution, then the casting solution is coated on a glass plate by blade coating, and the glass plate is immersed in water to prepare the porous asymmetric base membrane by a phase inversion method.
The carbon quantum dots are coated on the surface of the base film in an intermediate layer manner, and simultaneously, the carboxyl in the carbon quantum dots can react with the amino of the polyethyleneimine in the interfacial polymerization layer due to the action of the added activating agent, so that the crosslinking degree of the interfacial polymerization layer is reduced, and the aperture is increased. In addition, the hydrophilicity of the carbon quantum dots can also construct a channel through which ions can rapidly penetrate, and the flux of the membrane is increased.
The positively charged polyamide separating layer is after the above operation.
The prepared electropositive membrane has a higher isoelectric point and a high retention rate for positively charged ions such as lysine, leucine and glutamic acid compared with the electronegative membrane. And has a low rejection rate for negatively charged ions, such as sulfate ions and chloride ions. Therefore, the prepared electropositive membrane has good effect on separating amino acid and ions.
Example 1
1. Preparation of Flat sheet membranes
Dissolving a polyether sulfone high-molecular polymer material in an organic solvent, stirring overnight by using a stirrer, standing overnight, defoaming, then scraping and coating the casting solution on a glass plate by using a scraper, carrying out phase conversion treatment in water to form a membrane, and placing the prepared membrane in deionized water to obtain the polyether sulfone basement membrane.
2. Preparation of carbon quantum dot intermediate layer
Firstly, preparing an aqueous solution of carbon quantum dots, preparing a deionized water suspension containing 2wt% of the carbon quantum dots, adding 0.1g of sodium hydroxide to regulate the pH value, and then adding 0.1g of 2-chloro-1-methyl iodopyridine (CMPI) to activate the carbon quantum dots. And after stirring for half an hour, immersing the base film into the carbon quantum dot solution for 10min, and removing the redundant solution to obtain a uniform carbon quantum dot intermediate layer.
3. Preparation of the selection layer
Respectively preparing 1wt% of polyethyleneimine aqueous solution (the molecular weight of polyethyleneimine is 1.8K, 10K and 70K respectively) and 0.1wt% of organic phase solution of trimesoyl chloride as a water phase and an oil phase of interfacial polymerization reaction, wherein the trimesoyl chloride solution can be used after being stirred for one hour by using normal hexane as a solvent. Pouring the aqueous solution on a membrane, removing excessive aqueous phase by using wiping paper after two minutes, then pouring the aqueous solution into an organic phase, reacting for 1min, removing excessive solution on the surface, and then placing the prepared membrane in deionized water for storage.
The membrane prepared by this method was subsequently designated as a 2% CQDs/TFC membrane.
Comparative example 1
The difference from example 1 is that interfacial polymerization was directly performed on the base film without using carbon quantum dots as an intermediate layer to prepare an electropositive film. The membrane prepared in this comparative example was subsequently designated as a TFC membrane.
Comparative example 2
The difference from example 1 is that: in the preparation process of the carbon quantum dot intermediate layer, an activating agent 2-chloro-1-methyl iodopyridine and sodium hydroxide are not added. The membrane prepared in this comparative example was subsequently named Pure-2% CQDs/TFC membrane
Comparative example 3
The difference from example 1 is that after the carbon quantum dot intermediate layer is introduced, the aqueous phase is poured, and after ten minutes, the excess aqueous phase is removed, without adding trimesoyl chloride solution, and then put into water for storage. The membrane prepared in this control example was subsequently named 2% CQDs-PEI/PES membrane
Characterization experiment
The water flux characterization experiment is carried out at normal temperature, and the water flux characterization experiment needs to be conducted for half an hour before the test so that the prepared membrane can achieve stable performance;
the retention rate test is a test which is carried out by adopting a magnesium chloride solution with the concentration of 1000 mg/L under the conditions of the operating pressure of 6 bar and the temperature of 20 ℃, and half an hour of pre-feeding and stirring are also required before the test, so that the concentration polarization phenomenon is prevented.
The water flux results are shown in FIG. 1, and the maximum increase of the water flux of the membrane prepared in example 1 is 9.72L/m 2 ·h·bar -1 Wherein the water flux of the nanofiltration membrane with the molecular weight of 1.8K and 10K is respectively improved to 4.23 and 6.11L/m 2 ·h·bar -1 . It can be seen that the degree of flux increase of the nanofiltration membrane gradually decreases with the increase of the molecular weight, because the degree of cross-linking of interfacial polymerization increases and the influence of the intermediate layer of carbon quantum dots decreases with the decrease of the molecular weight. The retention rate data is shown in fig. 2, and the retention rate of magnesium chloride is not greatly reduced and is about 96%.
While the water fluxes using the nanofiltration membranes based on molecular weights of 1.8K, 10K and 70K in comparative example 2 were 4.20, 5.01 and 6.86 LMH.bar -1 Therefore, the carbon quantum dots after the activation treatment of the 2-chloro-1-methyl iodopyridine can effectively improve the water flux in the filtering process.
XPS characterization
FIG. 3 is a map of the elemental analysis of membrane surface C, N, O obtained in various examples (a) a broad spectrum scan of various base membranes, (b) 2% CQDs-PEI/PES, (c) TFC and (d) CQDs/TFC membrane. it is apparent that the membrane surface obtained in the examples successfully formed a polyamide structure.
MWCO characterization
FIG. 4 is a graphical representation of the molecular weight cut-off of different membranes. It can be seen from the figure that the pore size of CQDs/TFC-PEI 70K membrane and MWCO are observed to be larger than the pore size of TFC-PEI 70K membrane, while the pore size of CQD/TFC gradually decreases by decreasing PEI molecular weight. CQDs/TFC-PEI 1.8K MWCO is very similar to the original TFC membrane.
Testing of biogas slurry purification
According to a detection report obtained from a certain biogas slurry treatment company in Fuiyang City, a corresponding biogas slurry simulation solution is prepared in a laboratory for purification. Wherein the concentrations of lysine, leucine and glutamic acid are 200ppm, 200ppm and 400ppm, respectively. And Na 2 SO 4 And NaCl concentrations were 400ppm and 300ppm, respectively.
Model mixture filtration experiments of amino acids and inorganic ions at different pH values were first tested. As shown in fig. 5, the best separation was observed when pH was adjusted to 3, the separation factor between amino acids and mixed ions showed a maximum of 2.45 at pH =3, indicating that the main separation mechanism is the Donnan effect. At higher pH, the film surface charge becomes negative, increasing SO 4 2- And Cl - The separation factor is reduced. The filtration performance of commercial DK and DL membranes was compared by pH = 3. As shown in fig. 6, the separation factor of the commercial membrane is much lower than the CQD/TFC membrane because the DK and DL membranes are nearly electrically neutral at pH =3 (fig. 5), which is not easily passed by negatively charged ions. Commercial DK and DL membranes also have lower rejection of amino acids due to the lack of electrostatic repulsion between the amino acids and the membrane surface.
Biogas slurry concentration test
The concentration performance of the CQDs/TFC membranes and commercial membranes were compared by 10-fold enrichment of the simulated biogas slurry model solution, i.e., reducing the amino acid and salt solution volumes from 500ml to 50ml in the dead-end filtration tank. Region a of FIG. 8 shows that the high permeability of CQDs/TFC membranes is maintained and plateaued, while a decrease in permeability is clearly observed for commercial membranes. This is because the salt concentration increases the concentration polarization and increases the osmotic pressure, thereby decreasing the effective driving force, thereby decreasing the water permeability, which also demonstrates that NF membranes for methane slurry appreciation should be specially designed rather than implemented using commercial membranes. The b-region of fig. 8 shows that at the final stage of the concentration process, the rejection of ions by DL and DK commercial membranes was reduced by 6.7% and 15.2%, respectively, and the amino acid rejection was reduced by 13.4% and 13%, respectively, compared to the initial state. Meanwhile, the interception of the CQDs/TFC membrane is almost unchanged, and the prepared membrane has a good application prospect for biogas slurry purification.
Claims (2)
1. The nanofiltration membrane is formed by sequentially compounding a base membrane, a carbon quantum dot intermediate layer and a selective separation layer; the method is characterized by comprising the following steps:
step 1, providing a base film;
step 2, dipping the base film into a suspension containing carbon quantum dots for coating, and coating a carbon quantum dot intermediate layer on the surface of the base film; the concentration of the carbon quantum dots in the suspension is 2-6 wt%, the surfaces of the carbon quantum dots are treated by an activating agent, and the activating agent is 2-chloro-1-methyl iodopyridine;
step 3, preparing an interfacial polymerization layer on the carbon quantum dot intermediate layer by an interfacial polymerization method; the interfacial polymerization layer is prepared by an amine monomer and an acyl chloride monomer through an interfacial polymerization method;
the amine monomer is polyethyleneimine, and the concentration of the amine monomer in a water phase is 1-3 wt%; the acyl chloride monomer is trimesic acid chloride, and the concentration of the acyl chloride monomer in the organic phase is 0.1-3 wt%; the polyethyleneimine has a molecular weight of 70K.
2. The method for increasing the pore diameter of a nanofiltration membrane according to claim 1, wherein the material of the base membrane is selected from polyethersulfone, sulfonated polysulfone or polyetherimide.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1985000985A1 (en) * | 1983-08-26 | 1985-03-14 | Brunswick Corporation | Reverse osmosis membrane and process for making |
| CN108745002A (en) * | 2018-06-08 | 2018-11-06 | 太原理工大学 | A kind of sulfonated polyether-ether-ketone mixed substrate membrane containing nano-grade molecular sieve and its preparation method and application of doping carbon quantum dot in situ |
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| EP3377200A1 (en) * | 2015-11-16 | 2018-09-26 | Basf Se | Nanofiltration composite membranes comprising self-assembled supramolecular separation layer |
| CN108435002B (en) * | 2018-03-27 | 2021-03-19 | 东华大学 | Preparation method of functionalized carbon quantum dot modified composite nanofiltration membrane |
| CN109200823A (en) * | 2018-08-28 | 2019-01-15 | 浙江工业大学 | A kind of preparation method and application for the ecosystem positively charged nanofiltration membranes that polyethyleneimine is amine-modified |
| CN109200833A (en) * | 2018-10-17 | 2019-01-15 | 南京理工大学 | Remove the preparation method of bivalent cation and the nanofiltration membrane of lotus positive electricity PPCPs |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO1985000985A1 (en) * | 1983-08-26 | 1985-03-14 | Brunswick Corporation | Reverse osmosis membrane and process for making |
| CN108745002A (en) * | 2018-06-08 | 2018-11-06 | 太原理工大学 | A kind of sulfonated polyether-ether-ketone mixed substrate membrane containing nano-grade molecular sieve and its preparation method and application of doping carbon quantum dot in situ |
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