CN114773531A - Modified chitosan flocculant and preparation method and application thereof - Google Patents
Modified chitosan flocculant and preparation method and application thereof Download PDFInfo
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- CN114773531A CN114773531A CN202210413278.6A CN202210413278A CN114773531A CN 114773531 A CN114773531 A CN 114773531A CN 202210413278 A CN202210413278 A CN 202210413278A CN 114773531 A CN114773531 A CN 114773531A
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- 229920001661 Chitosan Polymers 0.000 title claims abstract description 142
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- PUVAFTRIIUSGLK-UHFFFAOYSA-M trimethyl(oxiran-2-ylmethyl)azanium;chloride Chemical compound [Cl-].C[N+](C)(C)CC1CO1 PUVAFTRIIUSGLK-UHFFFAOYSA-M 0.000 claims abstract description 14
- 150000007524 organic acids Chemical class 0.000 claims description 40
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- 239000002351 wastewater Substances 0.000 claims description 28
- 239000003999 initiator Substances 0.000 claims description 19
- 239000003795 chemical substances by application Substances 0.000 claims description 17
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- 238000011282 treatment Methods 0.000 claims description 12
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- 238000007259 addition reaction Methods 0.000 claims description 11
- 238000007334 copolymerization reaction Methods 0.000 claims description 11
- 238000007142 ring opening reaction Methods 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 8
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- 230000006196 deacetylation Effects 0.000 claims description 5
- 238000003381 deacetylation reaction Methods 0.000 claims description 5
- 229910001870 ammonium persulfate Inorganic materials 0.000 claims description 3
- XMPZTFVPEKAKFH-UHFFFAOYSA-P ceric ammonium nitrate Chemical compound [NH4+].[NH4+].[Ce+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O XMPZTFVPEKAKFH-UHFFFAOYSA-P 0.000 claims description 3
- USHAGKDGDHPEEY-UHFFFAOYSA-L potassium persulfate Chemical compound [K+].[K+].[O-]S(=O)(=O)OOS([O-])(=O)=O USHAGKDGDHPEEY-UHFFFAOYSA-L 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
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- 238000001179 sorption measurement Methods 0.000 abstract description 20
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- 230000000694 effects Effects 0.000 abstract description 17
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- 230000001965 increasing effect Effects 0.000 abstract description 10
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- -1 cationic quaternary ammonium salt Chemical class 0.000 abstract description 2
- 239000000243 solution Substances 0.000 description 65
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- 239000010802 sludge Substances 0.000 description 20
- 238000000034 method Methods 0.000 description 18
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 16
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- 238000001035 drying Methods 0.000 description 14
- HMHFERXOZSZRML-UHFFFAOYSA-M trimethyl-(3-methyloxiran-2-yl)azanium;chloride Chemical compound [Cl-].CC1OC1[N+](C)(C)C HMHFERXOZSZRML-UHFFFAOYSA-M 0.000 description 13
- 239000000047 product Substances 0.000 description 12
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- RUTXIHLAWFEWGM-UHFFFAOYSA-H iron(3+) sulfate Chemical compound [Fe+3].[Fe+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O RUTXIHLAWFEWGM-UHFFFAOYSA-H 0.000 description 6
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- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
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- 125000003047 N-acetyl group Chemical group 0.000 description 1
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- MSWZFWKMSRAUBD-UHFFFAOYSA-N beta-D-galactosamine Natural products NC1C(O)OC(CO)C(O)C1O MSWZFWKMSRAUBD-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F251/00—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
-
- 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
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
- C02F1/56—Macromolecular compounds
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B37/00—Preparation of polysaccharides not provided for in groups C08B1/00 - C08B35/00; Derivatives thereof
- C08B37/0006—Homoglycans, i.e. polysaccharides having a main chain consisting of one single sugar, e.g. colominic acid
- C08B37/0024—Homoglycans, i.e. polysaccharides having a main chain consisting of one single sugar, e.g. colominic acid beta-D-Glucans; (beta-1,3)-D-Glucans, e.g. paramylon, coriolan, sclerotan, pachyman, callose, scleroglucan, schizophyllan, laminaran, lentinan or curdlan; (beta-1,6)-D-Glucans, e.g. pustulan; (beta-1,4)-D-Glucans; (beta-1,3)(beta-1,4)-D-Glucans, e.g. lichenan; Derivatives thereof
- C08B37/0027—2-Acetamido-2-deoxy-beta-glucans; Derivatives thereof
- C08B37/003—Chitin, i.e. 2-acetamido-2-deoxy-(beta-1,4)-D-glucan or N-acetyl-beta-1,4-D-glucosamine; Chitosan, i.e. deacetylated product of chitin or (beta-1,4)-D-glucosamine; Derivatives thereof
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/26—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof
- C02F2103/28—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof from the paper or cellulose industry
Abstract
The invention provides a modified chitosan flocculant, a preparation method and application thereof, and belongs to the technical field of wastewater treatment. According to the invention, 2, 3-epoxypropyl trimethyl ammonium chloride is firstly grafted into chitosan molecules to prepare CTS-ETA, ETA is cationic quaternary ammonium salt, and introduction of cationic groups can increase the solubility and enhance the cationic strength of CTS flocculant, so that the electric neutralization capacity is increased, and the flocculation effect is enhanced; then, CTS-ETA-AM is prepared by grafting co-polyacrylamide on CTS-ETA, so that the molecular weight is increased, the adsorption and bridging effects are increased, and the flocculation performance is improved. The modified chitosan flocculant prepared by the invention is loose and porous, has excellent adsorption performance, and has the characteristics of good water solubility, wide pH application range, high charge density and large molecular weight.
Description
Technical Field
The invention relates to the technical field of wastewater treatment, and particularly relates to a modified chitosan flocculant as well as a preparation method and application thereof.
Background
In various water and wastewater treatment processes, oxidation, ion exchange, adsorption, membrane separation, flocculation, and the like are commonly used in industry. Among them, flocculation is a process of aggregating finely divided or dispersed particles and forming large flocs for settling and separation from wastewater, the main purpose of which is to remove colloids and suspended substances. Compared with other common treatment methods, the flocculation method has the advantages of simple method, short treatment time, low cost, high efficiency and the like, so that the flocculation method is widely applied to primary treatment.
When the flocculation method is used for treating wastewater, the selection of a flocculant has great influence on the efficiency of purifying water quality and preventing secondary pollution. Therefore, it becomes critical to select the appropriate type of flocculant. At present, the types of flocculants are various, and flocculants are mainly classified into inorganic flocculants, organic polymeric flocculants and microbial flocculants according to the difference of chemical components of the flocculants. In past engineering practice, conventional inorganic flocculants and synthetic polymeric flocculants have been used as the most common flocculants. However, as research and application continue to progress, the disadvantages of these flocculants have also become apparent. Generally speaking, the relatively high dosage, the sludge yield and the deep chroma make the traditional inorganic flocculant unable to meet the requirement of people on water quality; in addition, the acidic conditions and residual metal ions can cause corrosion to equipment, and pose a threat to aquatic organisms and human health. Synthetic organic polymeric flocculants are the most commonly used flocculants in the industry today due to their high flocculating activity and low cost. However, their non-biodegradable or non-biodegradable nature and the toxicity of the monomers also present some serious environmental and health challenges for the application. Therefore, the biodegradable, environment-friendly, cheap and easily available natural organic polymeric flocculant with high utilization rate is more and more emphasized by comprehensively considering various factors such as effect, safety, economy and the like, and becomes a hot spot of disputed research of scholars and engineers at home and abroad. Such as chitin, starch, alginic acid, cellulose, lignin, tannin, etc. The microbial flocculant has the property of natural biological polymer flocculant, but has the defects of complex production process, long strain culture and fermentation time, high cost and the like, so that the application of the microbial flocculant in the actual water supply treatment is limited.
Chitosan (CTS) is prepared from chitin, the second most abundant natural polymer in the world next to cellulose, through a deacetylation process, and is a polycation biodegradable high-molecular copolymer of glucosamine and N-acetylglucosamine. Chitosan has been used as a natural flocculant because of its large amount of amino groups, N-acetyl groups and hydroxyl groups contained in the molecule, and its good cationic charge density and high molecular weight under acidic conditions.
The main mechanisms of removing the soluble and granular pollutants by the flocculation method are charge neutralization, adsorption bridging and net catching and sweeping actions. These mechanisms are primarily dependent on the adsorption effect of the flocculant on the particle surface, with different flocculation mechanisms being created by selecting or controlling the range of charge density and molecular weight of the polymer. It is clear that charge density and molecular weight are important factors influencing and determining the mechanism of action. However, strong hydrogen bond action exists in and among chitosan molecules, the molecular structure is in a compact crystalline state, the chitosan is insoluble in water and most organic solvents and can only be dissolved in acidic solutions such as acetic acid and formic acid, and the cationic charge density is limited due to poor solubility; in addition, the molecular weight of chitosan is relatively small, which results in light floc, poor settleability and incapability of realizing rapid settlement. These disadvantages have severely limited the use of chitosan as a flocculant.
Disclosure of Invention
The invention aims to provide a modified chitosan flocculant, a preparation method and application thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a preparation method of a modified chitosan flocculant, which comprises the following steps:
mixing organic acid solution of chitosan, 2, 3-epoxypropyl trimethyl ammonium chloride and etherifying agent, and carrying out epoxy ring-opening addition reaction to obtain modified chitosan;
and mixing the organic acid solution of the modified chitosan, acrylamide and an initiator, and carrying out graft copolymerization to obtain the modified chitosan flocculant.
Preferably, the deacetylation degree of the chitosan is more than or equal to 80 percent; the organic acid used in the organic acid solution of the chitosan is glacial acetic acid; the concentration of the organic acid is 1-5 wt%; the mass ratio of the organic acid to the chitosan is (80-120): 1.
Preferably, the mass ratio of the 2, 3-epoxypropyltrimethylammonium chloride to the chitosan is (1-5): 1.
Preferably, the etherifying agent is isopropanol; the temperature of the epoxy ring-opening addition reaction is 50-90 ℃, and the time is 4-8 h.
Preferably, the mass ratio of the acrylamide to the modified chitosan is (1-5): 1.
Preferably, the initiator is one or more of cerium ammonium nitrate, potassium persulfate and ammonium persulfate.
Preferably, the concentration of the initiator in the organic acid solution of the modified chitosan is 1-5 mmol/L.
Preferably, the temperature of the graft copolymerization is 25-85 ℃, and the time is 2.5-8.5 h.
The invention provides the modified chitosan flocculant prepared by the preparation method in the technical scheme.
The invention provides application of the modified chitosan flocculant in the technical scheme in treating papermaking wastewater.
The invention provides a preparation method of a modified chitosan flocculant, which comprises the following steps: mixing organic acid solution of chitosan, 2, 3-epoxypropyl trimethyl ammonium chloride and etherifying agent, and carrying out epoxy ring-opening addition reaction to obtain modified chitosan; and mixing the organic acid solution of the modified chitosan, acrylamide and an initiator, and carrying out graft copolymerization to obtain the modified chitosan flocculant. According to the invention, 2, 3-epoxypropyltrimethylammonium chloride (ETA) is firstly grafted into Chitosan (CTS) molecule to prepare CTS-ETA, ETA is cationic quaternary ammonium salt, and the introduction of cationic group (hydrophilic group) can increase the solubility and enhance the charge density of CTS flocculant, thereby increasing the electric neutralization capacity and further enhancing the flocculation effect; then, CTS-ETA-AM is prepared from CTS-ETA grafted co-polyacrylamide (AM), the molecular weight or molecular chain lengthening is increased, the adsorption and bridging effects of the flocculating agent on pollutants are increased, and the flocculation performance of the flocculating agent is improved. Moreover, the modified chitosan flocculant prepared by the invention is loose and porous, has excellent adsorption performance, has the characteristics of good water solubility, wide pH application range, high charge density and large molecular weight, can promote the bridging effect of the flocculant on pollutants by larger molecular weight, has higher water solubility and Zeta potential, widens the effective pH application range of the flocculant, and can enhance the electric neutralization effect, thereby improving the flocculation effect.
The modified chitosan flocculant prepared by the invention is used for papermaking wastewater, can generate larger sludge floc particle size, can promote the net catching and rolling sweeping action and shorten the settling time, shows higher flocculation efficiency, has better removal effects on turbidity and COD of the papermaking wastewater, the turbidity removal rate is 98.2%, the residual turbidity is 3NTU, the COD removal rate is 75.3%, the COD residual quantity is 201mg/L, and the flocculation effect is good.
The papermaking sludge generated when the modified chitosan flocculant treats papermaking wastewater can be used as an adsorbent for adsorbing printing and dyeing wastewater containing cationic dye methylene blue, the removal efficiency of the methylene blue reaches 98.2%, and the adsorption effect is obvious.
Drawings
FIG. 1 is a Fourier infrared spectrum of chitosan and CTS-ETA-AM prepared in example 1;
FIG. 2 is an XRD pattern of chitosan and CTS-ETA-AM prepared in example 1;
FIG. 3 is an SEM image of chitosan at 10000 times;
FIG. 4 is an SEM photograph of 10000 times CTS-ETA prepared in example 1;
FIG. 5 is an SEM photograph of CTS-ETA-AM prepared in example 1 at 10000 times;
FIG. 6 is a graph of the Zeta potential vs. pH for chitosan and CTS-ETA-AM prepared in example 1;
FIG. 7 is a graph of the viscosity change of chitosan and CTS-ETA-AM prepared in example 1;
FIG. 8 is a graph showing the comparative effect of aluminum sulfate, polyferric sulfate and polyaluminum chloride (a) and chitosan on the removal of turbidity in papermaking wastewater with CTS-ETA and CTS-ETA-AM (b) prepared in example 1;
FIG. 9 is a graph showing the comparative effect of aluminum sulfate, polymeric ferric sulfate and polymeric aluminum chloride (a) and chitosan on the removal of COD from papermaking wastewater by CTS-ETA and CTS-ETA-AM (b) prepared in example 1;
FIG. 10 is a graph showing the distribution of the particle size of sludge flocs generated in the treatment of paper-making wastewater with chitosan and CTS-ETA-AM prepared in example 1;
FIG. 11 is a graph showing the adsorption performance of methylene blue by papermaking sludge produced in the treatment of papermaking wastewater using CTS-ETA and CTS-ETA-AM prepared in example 1.
Detailed Description
The invention provides a preparation method of a modified chitosan flocculant, which comprises the following steps:
mixing organic acid solution of chitosan, 2, 3-epoxypropyl trimethyl ammonium chloride and etherifying agent, and carrying out epoxy ring-opening addition reaction to obtain modified chitosan;
and mixing the organic acid solution of the modified chitosan, acrylamide and an initiator, and carrying out graft copolymerization to obtain the modified chitosan flocculant.
In the present invention, unless otherwise specified, all the starting materials required for the preparation are commercially available products well known to those skilled in the art.
The invention mixes organic acid solution of chitosan, 2, 3-epoxypropyl trimethyl ammonium chloride and etherifying agent, and carries out epoxy ring-opening addition reaction to obtain the modified chitosan. In the invention, the deacetylation degree of the Chitosan (CTS) is preferably not less than 80%, and more preferably 80-95%.
In the invention, the organic acid used in the organic acid solution of chitosan is preferably glacial acetic acid; the concentration of the organic acid is preferably 1-5 wt%, and more preferably 2-3 wt%; the mass ratio of the organic acid to the chitosan is preferably (80-120): 1, and more preferably 100: 1. The preparation process of the organic acid solution of chitosan in the present invention is not particularly limited, and the organic acid solution of chitosan may be prepared according to the well-known process in the art.
According to the invention, the pH value of the organic acid solution of chitosan is preferably adjusted to 7 by adopting NaOH solution, so that the organic acid solution of chitosan is fully swelled and then mixed with 2, 3-epoxypropyltrimethylammonium chloride and an etherifying agent; the concentration of the NaOH solution is preferably 1 mol/L.
In the invention, the mass ratio of the 2, 3-epoxypropyltrimethylammonium chloride (ETA) to the chitosan is preferably (1-5): 1; the etherifying agent is preferably isopropanol; the dosage ratio of the etherifying agent to the 2, 3-epoxypropyltrimethylammonium chloride is preferably 50mL (1-5) g, and more preferably 50mL to 3 g.
In the present invention, the organic acid solution of chitosan, 2, 3-epoxypropyltrimethylammonium chloride and etherifying agent are preferably mixed by dissolving 2, 3-epoxypropyltrimethylammonium chloride in etherifying agent, and adding the resulting solution to the organic acid solution of chitosan whose pH is adjusted to 7.
In the invention, the temperature of the epoxy ring-opening addition reaction is preferably 50-90 ℃, more preferably 70-80 ℃, and the time is preferably 4-8 h, more preferably 6 h; the epoxy ring-opening addition reaction is preferably carried out in an inert gas atmosphere; the inert gas is preferably argon or nitrogen and meets the pure or high-purity index in the national standard (GB/T8979-.
In the invention, an etherifying agent is isopropanol, and the epoxy ring-opening addition reaction process comprises the following steps:
after the epoxy ring-opening addition reaction is completed, the obtained product is preferably cooled to room temperature, the pH value of the product is adjusted to 7 by using a NaOH solution with the concentration of 1mol/L, a precipitator is added into the obtained product, and the solid product is obtained through centrifugal separation. In the present invention, the precipitant is preferably absolute ethanol or acetone; the volume ratio of the precipitator to the etherifying agent is preferably (1-3): 1, and more preferably (2-3): 1; the rotational speed of the centrifugal separation is preferably 4500rpm, and the time is preferably 5 min.
After obtaining a solid product, preferably performing Soxhlet extraction on the solid product, and drying the obtained extract to obtain modified chitosan, marked as CTS-ETA; the Soxhlet extraction is preferably carried out in a Soxhlet extractor, and the solvent used for the Soxhlet extraction is preferably acetone; the volume ratio of the acetone to the etherifying agent is preferably (2-5) to 1, and more preferably (3-5) to 1; the extraction time is preferably 48 h. The invention removes unreacted monomers by Soxhlet extraction to realize purification.
The drying process is not particularly limited in the present invention, and may be performed according to a process well known in the art; in the embodiment of the present invention, the drying temperature is preferably 40 ℃ and the time is preferably 12 hours.
After the modified chitosan is obtained, the invention mixes the organic acid solution of the modified chitosan, acrylamide and an initiator, and carries out graft copolymerization to obtain the modified chitosan flocculant.
In the invention, the organic acid used in the organic acid solution of the modified chitosan is preferably glacial acetic acid; the concentration of the organic acid is preferably 1-5 wt%, and more preferably 3 wt%; the mass ratio of the organic acid to the modified chitosan is preferably (80-120): 1, and more preferably (100-120): 1. The preparation process of the organic acid solution of the modified chitosan is not particularly limited, and the organic acid solution of the modified chitosan can be prepared according to the well-known process in the field.
According to the invention, the pH value of the organic acid solution of the modified chitosan is preferably adjusted to 7 by adopting a NaOH solution, so that the organic acid solution of the modified chitosan is fully swelled and then mixed with acrylamide and an initiator; the concentration of the NaOH solution is preferably 1 mol/L.
In the invention, the mass ratio of the acrylamide to the modified chitosan is preferably (1-5): 1, and more preferably (1-3): 1.
In the invention, the initiator is preferably one or more of cerium ammonium nitrate, potassium persulfate and ammonium persulfate; when the initiator is more than two of the initiators, the invention has no special limitation on the proportion of different initiators and can use any proportion. In the invention, the concentration of the initiator in the organic acid solution of the modified chitosan is preferably 1-5 mmol/L, and more preferably 3 mmol/L.
The organic acid solution of the modified chitosan, the acrylamide and the initiator are not particularly limited, and the materials are uniformly mixed according to the well-known process in the field.
In the invention, the temperature of the graft copolymerization is preferably 25-85 ℃, and more preferably 35-65 ℃; the time is preferably 2.5 to 8.5 hours, and more preferably 3.5 to 6.5 hours; the graft copolymerization reaction is preferably carried out in an inert gas atmosphere; the inert gas is preferably argon or nitrogen and meets the pure or high-purity index in the national standard (GB/T8979-2008 or GB/T4842-2017).
In the invention, the reaction process of the graft copolymerization is as follows:
after the graft copolymerization is completed, the present invention preferably cools the resultant product to room temperature, adjusts the pH to 7 with a NaOH solution having a concentration of 1mol/L, adds a precipitant to the resultant product, and centrifuges to obtain a solid product. In the present invention, the precipitant is preferably absolute ethanol or acetone; the volume ratio of the precipitator to the etherifying agent is preferably (1-3) to 1, and more preferably 2 to 1; the rotational speed of the centrifugation is preferably 4500rpm, and the time is preferably 5 min.
After obtaining a solid product, preferably washing the solid product with water (removing acrylamide and a copolymer thereof), performing Soxhlet extraction, and drying the obtained extract to obtain a modified chitosan flocculant which is marked as CTS-ETA-AM; the Soxhlet extraction is preferably carried out in a Soxhlet extractor, and the solvent used for the Soxhlet extraction is preferably acetone; the volume ratio of the acetone to the etherifying agent is preferably (2-5): 1, and more preferably 3: 1; the extraction time is preferably 24 h. The invention removes unreacted AM monomer and polyacrylamide generated by homopolymerization through Soxhlet extraction.
The drying process is not particularly limited in the present invention, and may be performed according to a process well known in the art; in the embodiment of the present invention, the drying temperature is preferably 40 ℃ and the drying time is preferably 12 hours.
The invention provides the modified chitosan flocculant prepared by the preparation method in the technical scheme.
The invention provides application of the modified chitosan flocculant in the technical scheme in treatment of papermaking wastewater. The method of the present invention is not particularly limited, and the method may be applied according to a method known in the art. According to the invention, sludge floc obtained by treating papermaking wastewater by using the modified chitosan flocculant is filtered by filter paper and then fully dried to obtain papermaking sludge, and the papermaking sludge can be used for adsorbing cationic dye methylene blue printing wastewater (the concentration of methylene blue in the wastewater is 50-250 mg/L).
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It should be apparent that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the following examples, chitosan was used with a deacetylation degree of 80-95%.
Example 1
Taking 100mL of 3 wt% glacial acetic acid solution, placing the glacial acetic acid solution in a 250mL three-neck flask, stirring and dissolving 1g of CTS in the glacial acetic acid solution, adjusting the pH value to 7 by using 1mol/L NaOH solution, and fully swelling;
introducing argon gas serving as a protective gas into a three-neck flask, connecting a condensation reflux device, weighing 3g of ETA, dissolving in 50mL of isopropanol to form a solution, adding the solution into the three-neck flask, reacting with CTS at 70 ℃ for 6 hours, cooling the mixture to room temperature after the reaction is finished, adjusting the pH value to 7 by using a 1mol/LNaOH solution, adding 50mL of acetone precipitator into the obtained product, and centrifuging at 4500rpm for 5 minutes to obtain a solid product;
purifying the solid product in a Soxhlet extractor filled with 150mL of acetone solvent for 48h, and drying the obtained extract at 40 ℃ for 12h to obtain CTS-ETA;
1g of CTS-ETA is heated and stirred to be dissolved in a three-neck flask containing 100mL of glacial acetic acid solution (the concentration is 3 wt%), the pH value is adjusted to 7 by using 1mol/L of NaOH solution, and the CTS-ETA is fully swelled; introducing argon into a three-neck flask to exhaust air, and adding ammonium ceric nitrate as an initiator to ensure that the concentration of the ammonium ceric nitrate is 3 mmol/L;
adding 1g of AM into a three-neck flask, reacting with CTS-ETA at 65 ℃ for 6.5h, cooling to room temperature, adjusting the pH to 7 by using a 1mol/L NaOH solution, adding 50mL of acetone precipitator into the obtained product, centrifuging at 4500rpm for 5min to obtain a solid product, washing with deionized water, purifying in a Soxhlet extractor filled with 150mL of acetone for 24h, and drying the obtained extract at 40 ℃ for 12h to obtain CTS-ETA-AM.
Example 2
Putting 120mL of 1 wt% glacial acetic acid solution into a 250mL three-neck flask, stirring and dissolving 1g of CTS in the glacial acetic acid solution, adjusting the pH value to 7 by using 1mol/L NaOH solution, and fully swelling;
introducing argon gas serving as a protective gas into a three-neck flask, connecting a condensation reflux device, weighing 1g of ETA, dissolving in 50mL of isopropanol to form a solution, adding the solution into the three-neck flask, reacting with CTS at 90 ℃ for 8 hours, cooling the mixture to room temperature after the reaction is finished, adjusting the pH to 7 by using 1mol/LNaOH solution, adding 100mL of acetone precipitant into the obtained product, and centrifuging at 4500rpm for 5 minutes to obtain a solid product;
purifying the solid product in a Soxhlet extractor filled with 100mL of acetone solvent for 48h, and drying the obtained extract at 40 ℃ for 12h to obtain CTS-ETA;
heating and stirring 1g of CTS-ETA to dissolve the CTS-ETA in a three-neck flask containing 120mL of glacial acetic acid solution (the concentration is 3 wt%), adjusting the pH value to 7 by using 1mol/L of NaOH solution, and fully swelling; introducing argon into a three-neck flask to exhaust air, and adding ammonium ceric nitrate as an initiator to ensure that the concentration of the ammonium ceric nitrate is 1 mmol/L;
adding 3g of AM into a three-neck flask, reacting with CTS-ETA at 85 ℃ for 8.5h, cooling to room temperature, adjusting the pH to 7 by using a 1mol/L NaOH solution, adding 100mL of acetone precipitant into the obtained product, centrifuging at 4500rpm for 5min to obtain a solid product, washing by using deionized water, purifying in a Soxhlet extractor filled with 100mL of acetone for 24h, and drying the obtained extract at 40 ℃ for 12h to obtain CTS-ETA-AM.
Example 3
Putting 80mL of 5 wt% glacial acetic acid solution into a 250mL three-neck flask, stirring and dissolving 1g of CTS in the glacial acetic acid solution, adjusting the pH value to 7 by using 1mol/L NaOH solution, and fully swelling;
introducing argon into a three-neck flask as protective gas, connecting a condensation reflux device, weighing 5g of ETA, dissolving in 50mL of isopropanol to form a solution, adding the solution into the three-neck flask, reacting with CTS at 50 ℃ for 4h, cooling the mixture to room temperature after the reaction is finished, adjusting the pH to 7 by using 1mol/LNaOH solution, adding 150mL of acetone precipitator into the obtained product, and centrifuging at 4500rpm for 5min to obtain a solid product;
purifying the solid product in a Soxhlet extractor filled with 250mL of acetone solvent for 48h, and drying the obtained extract at 40 ℃ for 12h to obtain CTS-ETA;
heating and stirring 1g of CTS-ETA to dissolve the CTS-ETA in a three-neck flask containing 80mL of glacial acetic acid solution (the concentration is 3 wt%), adjusting the pH value to 7 by using 1mol/L of NaOH solution, and fully swelling; introducing argon into a three-neck flask to exhaust air, and adding ammonium ceric nitrate as an initiator to ensure that the concentration of the ammonium ceric nitrate is 5 mmol/L;
adding 5g of AM into a three-neck flask, reacting with CTS-ETA at 25 ℃ for 2.5h, cooling to room temperature, adjusting the pH to 7 by using a 1mol/L NaOH solution, adding 150mL of acetone precipitator into the obtained product, centrifuging at 4500rpm for 5min to obtain a solid product, washing with deionized water, purifying in a Soxhlet extractor filled with 250mL of acetone for 24h, and drying the obtained extract at 40 ℃ for 12h to obtain CTS-ETA-AM.
Characterization and Performance testing
1) FIG. 1 is a Fourier infrared spectrum of chitosan and CTS-ETA-AM prepared in example 1, (a) CTS, (b) CTS-ETA, and (c) CTS-ETA-AM.
FIG. 1 (a), 1597cm-1OfThe peak reflects the N-H bending vibration of the primary amine in CTS, which disappears in CTS-ETA. In FIG. 1 (b), 1479, 1557 and 3020cm-1The peaks at (A) are the C-H bending vibration and the stretching vibration of the methyl group in ETA, respectively. The characteristic peak of the isolated methyl group in ETA appeared at 1373cm-1To (3). The results show that CTS-ETA was successfully prepared by grafting ETA onto the amino group of CTS. 1653cm of FIG. 1 (c)-1And 3412cm-1The stretching vibration at (b) is respectively attributed to C ═ O and N — H of the amide group in AM. 1582cm-1The peak at (a) is the bending vibration of the primary amine in AM. Based on the above results, AM was grafted onto CTS-ETA, and CTS-ETA-AM was successfully prepared.
2) FIG. 2 is XRD patterns of chitosan with CTS-ETA and CTS-ETA-AM prepared in example 1, (a) CTS, (b) CTS-ETA, (c) CTS-ETA-AM.
In fig. 2 (a), the strong diffraction peak of CTS appears at 20.3 ° due to its strong hydrogen bonding. The results show that CTS has regular structure and stronger crystallization property. In FIG. 2 (b), the diffraction peak position of CTS-ETA is consistent with CTS, but the intensity is slightly increased. The introduction of quaternary ammonium groups in ETA increases the short-range order of CTS molecules, and the ionic interaction changes the short-range arrangement of CTS, so that CTS-ETA has better crystallization performance. The diffraction peak of CTS-ETA-AM is reduced at 20.3 compared to CTS-ETA, and several weaker diffraction peaks appear at 28.3, 47.24 and 55.64 in FIG. 2 (c), respectively. This is because AM is grafted to the hydroxyl position of CTS in CTS-ETA, and breaks the intramolecular and intermolecular hydrogen bonds, shifting the diffraction peak. This means that the crystallinity of CTS-ETA-AM is reduced, which is advantageous for improving its solubility in water or organic solvents.
3) FIGS. 3 to 5 are SEM images of chitosan, CTS-ETA prepared in example 1 and CTS-ETA-AM prepared in example 1 at 10000 times in sequence.
In FIG. 3, a smooth, less porous, dense surface appears, indicating that CTS exhibits a dense crystal structure due to intra-and intermolecular hydrogen bonding. When ETA is grafted to the amino position of CTS, intramolecular and intermolecular hydrogen bonds are broken and the crystal structure collapses, fig. 4 showing a loose, porous and rough surface of CTS-ETA. The change of the surface topography is beneficial to increasing the specific surface area and the adsorption effect of the flocculating agent and improving the flocculation performance. The introduction of AM at the hydroxyl sites of CTS further disrupts hydrogen bonding, so the surface of CTS-ETA-AM in fig. 5 is more porous, porous and rough than CTS-ETA. The results show that the specific surface area and the adsorption of the flocculant are further improved.
4) 0.1g of chitosan and CTS-ETA-AM prepared in example 1 were dissolved in 100mL of deionized water, respectively, pH was adjusted to 1-12 using 1mol/L NaOH solution and HCl solution, and the variation of the solubility of different flocculant materials with pH was tested as shown in Table 1.
TABLE 1 solubility of Chitosan at different pH values with CTS-ETA and CTS-ETA-AM prepared in example 1
Note: f-complete dissolution, S-slightly soluble, I-insoluble
It can be seen from table 1 that the change in crystal properties and the introduction of quaternary ammonium groups affect the solubility of the flocculant. Due to hydrogen bonding, the CTS only shows slight solubility or complete solubility in an acidic solution with the pH value of 1-3, which indicates that the solubility of the CTS is the worst. The hydrophilic quaternary ammonium groups in the ETA increase the solubility of CTS-ETA and show slight or complete solubility at pH < 7. The slightly soluble pH range of CTS-ETA-AM has been expanded from 3-7 to 3-9 compared to CTS-ETA. Therefore, the CTS-ETA and CTS-ETA-AM prepared in example 1 expand the applicable range of pH value and improve the practicability of the flocculant in actual wastewater.
5) FIG. 6 is a graph showing the trend of Zeta potential with pH for chitosan and CTS-ETA-AM prepared in example 1. FIG. 6 shows that the Zeta potentials of CTS-ETA and CTS-ETA-AM prepared in example 1 are higher than the value of chitosan CTS. This result indicates that grafting of ETA increases the charge density of the flocculant, thereby increasing the charge neutralization capacity at different pH values, and that CTS-ETA-AM has a stronger charge neutralization capacity than CTS-ETA. Because of the negative charge of the papermaking wastewater, the Zeta potential is increased to enhance the electric neutralization effect of the flocculating agent and improve the flocculation performance.
6) The viscosity of 0.1g of chitosan and CTS-ETA-AM prepared in example 1 was tested in 100mL of 3 wt% glacial acetic acid solution, and the results are shown in FIG. 7; as can be seen from FIG. 7, both CTS-ETA and CTS-ETA-AM have higher viscosities than CTS. As a measure of molecular weight, the higher the viscosity number, the higher the molecular weight. Thus, the CTS-ETA and CTS-ETA-AM prepared in example 1 had progressively higher molecular weights, which contributed to the bridging effect of the flocculant.
Application example
Respectively taking chitosan and CTS-ETA-AM prepared in example 1 as flocculant mother liquor to carry out papermaking water treatment application tests, and taking commercially available aluminum sulfate, polymeric ferric sulfate and polymeric aluminum chloride as comparison; respectively dissolving aluminum sulfate, polymeric ferric sulfate and polymeric aluminum chloride in deionized water to form stock solution with the concentration of 10 g/L; and respectively dissolving CTS, CTS-ETA and CTS-ETA-AM in deionized water to form stock solution with the concentration of 1 g/L.
1) The water quality parameters of the papermaking wastewater are as follows: turbidity 176NTU, COD 814 mg/L. The main pollutants in the simulated papermaking wastewater and the COD ratio provided by the main pollutants are respectively as follows: 27.02% sodium lignosulfonate, 50.49% cellulose, 14.3% hemicellulose and 8.19% others. Adding different amounts of newly prepared different flocculant stock solutions (the specific addition amount is shown in figures 8-9) into 100mL of papermaking wastewater to carry out Jar-test, wherein the experimental parameters are as follows: rapidly stirring at 120rpm for 3min, slowly stirring at 30rpm for 15min, and settling for 30 min; after the sedimentation is finished, taking a water sample at one half of the interface of the supernatant to respectively test the turbidity and the COD, and calculating the removal rate.
FIG. 8 is a graph showing the effect of removing turbidity in papermaking wastewater by using aluminum sulfate, polymeric ferric sulfate and polymeric aluminum chloride (a), chitosan and CTS-ETA-AM prepared in example 1 (b). In fig. 8, the concentrations of aluminum sulfate are: 200mg/L, 220mg/L, 240mg/L, 260mg/L, 280mg/L, 300mg/L, 320mg/L, 340mg/L and 360 mg/L; the concentrations of the polymeric ferric sulfate are respectively as follows: 100mg/L, 120mg/L, 140mg/L, 160mg/L, 180mg/L, 200mg/L, 220mg/L, 240mg/L, 260mg/L, 280mg/L and 300 mg/L; the concentrations of the polyaluminium chloride are respectively as follows: 40mg/L, 60mg/L, 80mg/L, 100mg/L, 120mg/L, 140mg/L, 160mg/L, 180mg/L, 200 mg/L.
FIG. 9 is a graph showing the comparative effect of aluminum sulfate, polyferric sulfate and polyaluminum chloride (a) and chitosan on the removal of COD from papermaking wastewater with CTS-ETA and CTS-ETA-AM (b) prepared in example 1. In fig. 9, the CTS concentrations are: 10mg/L, 12mg/L, 14mg/L, 16mg/L, 18mg/L, 20mg/L, 22mg/L and 24 mg/L; the concentration of CTS-ETA is respectively as follows: 6mg/L, 8mg/L, 10mg/L, 12mg/L, 14mg/L, 16mg/L, 18mg/L, 20mg/L, 22mg/L and 24 mg/L; the concentration of CTS-ETA-AM is respectively as follows: 6mg/L, 8mg/L, 10mg/L, 12mg/L, 14mg/L, 16mg/L, 18mg/L, 20mg/L, 22mg/L and 24 mg/L.
As shown in FIGS. 8 to 9 (a), the inorganic flocculant contains polyaluminum chloride having excellent handling properties. When the optimum dosage of polyaluminum chloride is 120mg/L, the turbidity and COD removal rate are 91% and 77.9%, respectively, and the turbidity and COD residual concentration are 18NTU and 180mg/L, respectively. When the optimal addition amount of the polymeric ferric sulfate is 160mg/L, the removal rates of turbidity and COD are 81 percent and 77.6 percent respectively, and the residual concentrations of turbidity and COD are 33NTU and 183mg/L respectively. When the optimal addition dosage of the aluminum sulfate is 300mg/L, the removal rates of turbidity and COD are respectively 90% and 78.9%, and the residual concentrations of turbidity and COD are respectively 18NTU and 172 mg/L.
As can be seen from FIGS. 8 to 9 (b), both the turbidity and the COD removal rate of CTS-ETA and CTS-ETA-AM are higher than those of CTS. Under the optimal adding condition, the turbidity removal rates of CTS-ETA and CTS-ETA-AM are respectively 7.6 percent and 8.2 percent higher than 90 percent of CTS, and the COD removal rates are respectively 2.9 percent and 5.3 percent higher than 70.4 percent of CTS. The results show that the modification of CTS in specific surface area, molecular weight and cationic strength improves the adsorption, bridging and charge neutralization overall performance of the flocculant.
The optimal amount of CTS-ETA-AM is less than that of polyaluminium chloride. The addition amount is small, and the flocculant is convenient to transport and store in a sewage treatment plant. When the optimal dosage of the CTS-ETA-AM is 14mg/L, the turbidity removal rate is 98.2 percent, and the residual turbidity is 3NTU, which is obviously superior to 91 percent and 18NTU of the polyaluminum chloride. The COD removal rate is 75.3%, the COD residual quantity is 201mg/L, and the COD removal rate is consistent with 77.9% and 180mg/L of the polyaluminium chloride. Therefore, the modified chitosan flocculant has advantages in the aspect of papermaking wastewater treatment performance compared with the comparative example and unmodified chitosan.
2) FIG. 10 is a graph showing the particle size distribution of sludge flocs generated in the treatment of papermaking wastewater with chitosan and CTS-ETA-AM prepared in example 1, (a) CTS, (b) CTS-ETA, and (c) CTS-ETA-AM;
as can be seen from FIG. 10, the average particle sizes of sludge flocs produced by CTS-ETA and CTS-ETA-AM were 1.5 μm and 5.63 μm larger than 37.26 μm in CTS, respectively. In addition, D of sludge flocs produced by CTS-ETA and CTS-ETA-AM502.16 μm and 5.83 μm higher than 27.55 μm for CTS, respectively. The larger sludge floc is beneficial to improving the flocculation effect and shortening the settling time in the flocculation process. Therefore, the modified chitosan prepared in example 1 was effective and practical for the treatment of actual wastewater.
3) Filtering and drying sludge flocs generated by treating papermaking wastewater by using CTS-ETA and CTS-ETA-AM in application example 1 to obtain papermaking sludge, and using the papermaking sludge for treating cationic dye methylene blue printing wastewater:
placing a series of conical flasks (pH is 6.58) containing 0.2-1 g of papermaking sludge and 100mL of 50mg/L methylene blue solution with plugs into a water bath oscillator to implement a static adsorption experiment, wherein the parameters of the water bath oscillator are set within the following ranges: the time is 2-10 h, and the temperature is 20-60 ℃; and (4) after the static adsorption experiment is finished, taking supernatant, testing the content of methylene blue and calculating the adsorption removal rate.
FIG. 11 is a graph showing the adsorption performance of methylene blue by paper sludge produced in the treatment of paper mill wastewater with CTS-ETA and CTS-ETA-AM prepared in example 1. (a) The influence of the adding amount of the papermaking sludge is realized when the temperature is 20 ℃ and the time is 24 hours; (b) the influence of adsorption time when the temperature is 20 ℃ and the adding amount is 6 g/L; (c) the influence of temperature when the adding amount of the paper making sludge is 6g/L and the adsorption time is 6 hours;
as can be seen from FIG. 11, when the amount of the added papermaking sludge was 6g/L, the adsorption time was 6 hours, and the adsorption temperature was 20 ℃, the removal rate of methylene blue could reach 98.2% at the maximum.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. The preparation method of the modified chitosan flocculant is characterized by comprising the following steps of:
mixing organic acid solution of chitosan, 2, 3-epoxypropyl trimethyl ammonium chloride and etherifying agent, and carrying out epoxy ring-opening addition reaction to obtain modified chitosan;
and mixing the organic acid solution of the modified chitosan, acrylamide and an initiator, and carrying out graft copolymerization to obtain the modified chitosan flocculant.
2. The preparation method according to claim 1, wherein the deacetylation degree of chitosan is more than or equal to 80%; the organic acid used in the organic acid solution of the chitosan is glacial acetic acid; the concentration of the organic acid is 1-5 wt%; the mass ratio of the organic acid to the chitosan is (80-120): 1.
3. The preparation method according to claim 1, wherein the mass ratio of the 2, 3-epoxypropyltrimethylammonium chloride to the chitosan is (1-5): 1.
4. The production method according to claim 1, wherein the etherifying agent is isopropyl alcohol; the temperature of the epoxy ring-opening addition reaction is 50-90 ℃, and the time is 4-8 h.
5. The preparation method according to claim 1, wherein the mass ratio of the acrylamide to the modified chitosan is (1-5): 1.
6. The preparation method according to claim 1, wherein the initiator is one or more of cerium ammonium nitrate, potassium persulfate and ammonium persulfate.
7. The preparation method according to claim 1 or 6, wherein the concentration of the initiator in the organic acid solution of the modified chitosan is 1 to 5 mmol/L.
8. The preparation method of claim 1, wherein the temperature of the graft copolymerization is 25-85 ℃ and the time is 2.5-8.5 h.
9. The modified chitosan flocculant prepared by the preparation method of any one of claims 1 to 8.
10. Use of the modified chitosan flocculant of claim 9 in the treatment of papermaking wastewater.
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