CN111548432A - Method for preparing dechlorination agent by graft reaction of chitosan oligosaccharide and benzotriazole compound and prepared dechlorination agent - Google Patents
Method for preparing dechlorination agent by graft reaction of chitosan oligosaccharide and benzotriazole compound and prepared dechlorination agent Download PDFInfo
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- CN111548432A CN111548432A CN202010433158.3A CN202010433158A CN111548432A CN 111548432 A CN111548432 A CN 111548432A CN 202010433158 A CN202010433158 A CN 202010433158A CN 111548432 A CN111548432 A CN 111548432A
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- chitosan
- benzotriazole compound
- chitosan oligosaccharide
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- 239000003795 chemical substances by application Substances 0.000 title claims abstract description 36
- 238000006243 chemical reaction Methods 0.000 title claims abstract description 30
- 239000012964 benzotriazole Substances 0.000 title claims abstract description 28
- RQFQJYYMBWVMQG-IXDPLRRUSA-N chitotriose Chemical compound O[C@@H]1[C@@H](N)[C@H](O)O[C@H](CO)[C@H]1O[C@H]1[C@H](N)[C@@H](O)[C@H](O[C@H]2[C@@H]([C@@H](O)[C@H](O)[C@@H](CO)O2)N)[C@@H](CO)O1 RQFQJYYMBWVMQG-IXDPLRRUSA-N 0.000 title claims abstract description 26
- 238000000034 method Methods 0.000 title claims abstract description 26
- -1 benzotriazole compound Chemical class 0.000 title claims abstract description 25
- 238000006298 dechlorination reaction Methods 0.000 title claims description 22
- 229920001661 Chitosan Polymers 0.000 claims abstract description 28
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 26
- 230000000382 dechlorinating effect Effects 0.000 claims abstract description 23
- 239000003963 antioxidant agent Substances 0.000 claims abstract description 17
- 230000003078 antioxidant effect Effects 0.000 claims abstract description 17
- 238000006460 hydrolysis reaction Methods 0.000 claims abstract description 17
- 239000002253 acid Substances 0.000 claims abstract description 9
- 238000007599 discharging Methods 0.000 claims abstract description 7
- 239000011261 inert gas Substances 0.000 claims abstract description 5
- 238000003756 stirring Methods 0.000 claims description 19
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 18
- 239000008367 deionised water Substances 0.000 claims description 10
- 229910021641 deionized water Inorganic materials 0.000 claims description 10
- 230000002378 acidificating effect Effects 0.000 claims description 9
- 230000007062 hydrolysis Effects 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 7
- ASOKPJOREAFHNY-UHFFFAOYSA-N 1-Hydroxybenzotriazole Chemical compound C1=CC=C2N(O)N=NC2=C1 ASOKPJOREAFHNY-UHFFFAOYSA-N 0.000 claims description 6
- MXJIHEXYGRXHGP-UHFFFAOYSA-N benzotriazol-1-ylmethanol Chemical compound C1=CC=C2N(CO)N=NC2=C1 MXJIHEXYGRXHGP-UHFFFAOYSA-N 0.000 claims description 4
- QRUDEWIWKLJBPS-UHFFFAOYSA-N benzotriazole Chemical compound C1=CC=C2N[N][N]C2=C1 QRUDEWIWKLJBPS-UHFFFAOYSA-N 0.000 claims description 4
- 238000002360 preparation method Methods 0.000 claims description 4
- KEAYESYHFKHZAL-UHFFFAOYSA-N Sodium Chemical class [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 claims description 3
- 230000006196 deacetylation Effects 0.000 claims description 3
- 238000003381 deacetylation reaction Methods 0.000 claims description 3
- 159000000001 potassium salts Chemical class 0.000 claims description 3
- 239000000460 chlorine Substances 0.000 abstract description 6
- 229910052801 chlorine Inorganic materials 0.000 abstract description 6
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 abstract description 5
- 230000000694 effects Effects 0.000 abstract description 3
- 239000000498 cooling water Substances 0.000 abstract description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 12
- 238000001816 cooling Methods 0.000 description 8
- 238000000137 annealing Methods 0.000 description 4
- 230000007797 corrosion Effects 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 238000005530 etching Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 125000002091 cationic group Chemical group 0.000 description 2
- 238000007334 copolymerization reaction Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 2
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 1
- 239000005751 Copper oxide Substances 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical group Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 1
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 1
- 229920002472 Starch Polymers 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 229910000431 copper oxide Inorganic materials 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- RXPAJWPEYBDXOG-UHFFFAOYSA-N hydron;methyl 4-methoxypyridine-2-carboxylate;chloride Chemical compound Cl.COC(=O)C1=CC(OC)=CC=N1 RXPAJWPEYBDXOG-UHFFFAOYSA-N 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229920005610 lignin Polymers 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 229920001542 oligosaccharide Polymers 0.000 description 1
- 150000002482 oligosaccharides Chemical class 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 229920000768 polyamine Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000001223 reverse osmosis Methods 0.000 description 1
- 239000010865 sewage Substances 0.000 description 1
- 229910001961 silver nitrate Inorganic materials 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 235000019698 starch Nutrition 0.000 description 1
- 239000008107 starch Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Images
Classifications
-
- 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
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/58—Treatment of water, waste water, or sewage by removing specified dissolved compounds
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/12—Halogens or halogen-containing compounds
Abstract
The invention discloses a method for preparing a dechlorinating agent by graft reaction of chitosan oligosaccharide and a benzotriazole compound and the dechlorinating agent prepared by the method, wherein chitosan is added with an acid antioxidant under the protection of inert gas to carry out hydrolysis reaction for 1 h-1.5 h at 35-40 ℃ to generate chitosan oligosaccharide M (4000-5000 Da). And n is 40-50, then the obtained product is subjected to grafting reaction with a benzotriazole compound for 2 hours under the conditions that the pH is 8-9 and the temperature is 70-80 ℃, the temperature is reduced to 25 ℃ by controlling for 2-3 hours, and a colorless or light yellow viscous finished product is obtained after discharging, and the product is a high-efficiency dechlorinating agent which can be applied to industrial boiler water treatment and industrial circulating cooling water systems. The average removing rate of the chlorine root of the boiler can reach more than 90 percent after years of actual operation, and the chlorine removing effect is obvious.
Description
Technical Field
The invention relates to a preparation method of a dechlorinating agent, in particular to a method for preparing the dechlorinating agent by graft reaction of chitosan oligosaccharide and a benzotriazole compound and the prepared dechlorinating agent.
Background
During the operation of equipment using water as a heat-conducting medium, such as a thermal boiler, a thermal pipe network system and a cooling circulating water system, due to the use and operation loss of the water medium, the operating water of the cooling circulating water system, the boiler and the thermal pipe network system is subjected to a concentration process, a large amount of water is required to be supplemented, the chloride ions in the water are continuously concentrated due to long-term operation, the concentration of the chloride ions is continuously increased, and the strong corrosiveness of the chloride ions becomes one of the hidden troubles of the operation of the boiler and other equipment.
The destruction by chloride ions is primarily manifested in the transition of the metal surface from a passive state to an active state. The chloride forms with the metal, the adsorption of the chloride to the metal surface is unstable, and soluble substances are formed, so that small etching pits with the aperture of 20-30 mu m are generated on the base metal, and the small etching pits are hole etching nuclei. Under the condition of external anode polarization, as long as a certain amount of chloride ions are contained in the medium, corrosion nuclei can develop into corrosion pores, so that the corrosion is accelerated, the service life of equipment is seriously influenced, and particularly, the corrosion to stainless steel equipment is more serious.
The removal of chloride ions is difficult because most of its compounds are water soluble and thus difficult to remove. The concentration of chlorine radicals can be reduced only by means of a large amount of sewage discharge, which causes a large amount of waste of energy and water resources and is not beneficial to energy conservation and emission reduction, and the problem is always a big problem which puzzles the safe and stable operation of equipment. The existing dechlorination method has three limitations:
1. the equipment for dechlorination, such as reverse osmosis, ion exchangers, electro-adsorption dechlorination and the like, is difficult to realize dechlorination with large water level, and has huge investment and high operation and maintenance cost.
2. Some medicaments such as silver nitrate, bismuth nitrate, copper oxide and other noble metals are too expensive to realize large-scale industrial use. Some adsorption type dechlorinating substances such as lignin, cationic starch and the like have low efficiency and cannot be used under the condition of high chloride ion concentration, and the application range of the substances is limited, so that the chemical substances are not used for preparing a real product dechlorinating product.
3. The secondary pollution can not be eliminated in the using process, and the environmental pressure is increased. The elimination of secondary pollution still requires a large investment.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for preparing a dechlorination agent by graft reaction of chitosan oligosaccharide and a benzotriazole compound, which has obvious dechlorination effect and no pollution, and the prepared dechlorination agent.
In order to solve the technical problems, the invention adopts the technical scheme that: a method for preparing a dechlorinating agent by graft reaction of chitosan oligosaccharide and a benzotriazole compound comprises the following steps:
1) preparation of chitosan oligosaccharide: stirring chitosan, deionized water and an acidic antioxidant at a low speed under the protection of inert gas, and carrying out hydrolysis reaction for 1-1.5 h at 35-40 ℃ to generate chitosan oligosaccharide with M being 4000-5000Da and n being 40-50 repeating units, wherein the mass ratio of the deionized water to the chitosan to the acidic antioxidant is 8-10: 1-2: 0.2-0.3;
2) immediately adjusting the pH value to 8-9 by NaOH after hydrolysis, adding a benzotriazole compound accounting for 40% of the mass of chitosan, stirring at medium speed, heating to 70-80 ℃ for grafting reaction, keeping the temperature for 2h, controlling the temperature to be reduced to 25 ℃ after the reaction is finished for 2 h-2.5 h, and discharging to obtain a colorless or light yellow viscous finished product serving as a dechlorinating agent.
The acid antioxidant is C6H8O6、C6H8O6Sodium salt and C6H8O6One or more of potassium salts.
The benzotriazole compound is one of 1-hydroxybenzotriazole, benzotriazole and 1-hydroxymethyl benzotriazole.
The chitosan has a deacetylation degree of more than 95% and a relative molecular mass of 2 × 105～5×105。
In the step 1), the low-speed stirring speed is 35-40rpm/min, and in the step 2), the medium-speed stirring speed is 80-85 rpm/min.
The dechlorination agent is prepared by the method for preparing the dechlorination agent by the grafting reaction of the chitosan oligosaccharide and the benzotriazole compound.
The invention has the beneficial effects that: the dechlorinating agent can be applied to industrial boiler water treatment and industrial circulating cooling water systems. The average removing rate of the chlorine root of the boiler can reach more than 90 percent after years of actual operation, and the chlorine removing effect is obvious.
Drawings
FIG. 1 is a flow chart of the method for preparing a dechlorinating agent by graft copolymerization of chitosan oligosaccharide and a benzotriazole compound.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention; it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art without any inventive work are within the scope of the present invention.
The method for preparing the dechlorinating agent by the graft reaction of the chitosan oligosaccharide and the benzotriazole compound comprises the following steps:
1) preparation of chitosan oligosaccharide: stirring chitosan, deionized water and an acidic antioxidant at a low speed under the protection of inert gas, carrying out hydrolysis reaction for 1-1.5 h at 35-40 ℃ to generate chitosan oligosaccharide with M being 4000-5000Da and n being 4-50 repeating units, wherein the mass ratio of the deionized water to the chitosan to the acidic antioxidant is 8-10: 1-2: 0.2-0.3,
2) immediately adjusting the pH value to 8-9 by NaOH after hydrolysis, adding a benzotriazole compound accounting for 40% of the mass of chitosan, stirring at medium speed, heating to 70-80 ℃ for grafting reaction, keeping the temperature for 2h, controlling the temperature to be reduced to 25 ℃ for 2 h-2.5 h, and discharging to obtain a colorless or light yellow viscous finished product which is a dechlorinating agent.
The acid antioxidant is C6H8O6、C6H8O6Sodium salt and C6H8O6One or more of potassium salts.
The benzotriazole compound is one of 1-hydroxybenzotriazole, benzotriazole and 1-hydroxymethyl benzotriazole.
The chitosan has a deacetylation degree of more than 95% and a relative molecular mass of 2 × 105-5×105。
In the step 1), the low-speed stirring speed is 35-40rpm/min, and in the step 2), the medium-speed stirring speed is 80-85 rpm/min.
The dechlorination agent is prepared by the method for preparing the dechlorination agent by graft copolymerization of the chitosan oligosaccharide and the benzotriazole compound.
As shown in FIG. 1, the chitosan oligosaccharide of the present invention is derived from the hydrolysis of chitosan, but chitosan is insoluble in water and soluble only in strong acid due to its layered structure, but it is very easily oxidized in strong acid, loses the property of cationic polyamine and loses its ability to bind to negatively charged particles, and thus cannot adsorb chloride ions. The invention hydrolyzes chitosan in acidic antioxidant to form oligomeric chitosan which is soluble in water, the antioxidant can provide acidic medium, and the antioxidant can protect the side group of chitosan.
The method comprises the steps of carrying out low-temperature reaction, protecting by inert gas, completing hydrolysis reaction at a low temperature of 35-40 ℃, carrying out the whole process under the protection of nitrogen, and stirring at a low speed of 35-40 rpm/min.
After the hydrolysis reaction is finished, the pH value is adjusted to be 8-9, 1-hydroxy benzotriazole is added, the temperature is raised to 70-80 ℃, the temperature is kept for 2-2.5 h, the grafting reaction of the benzotriazole compound can increase the steric hindrance of oligosaccharide molecular chains, the chains are not easy to gather and approach to form a layered structure, and each chain is naturally curled into a porous spherical structure in the process of cooling and annealing. And cooling for 2-2.5 hours, and cooling from 80 ℃ to below 25 ℃ to complete the grafting reaction. The stirring speed is increased to 80rpm/min in the whole reaction process, and the mixture is discharged to obtain light yellow viscous liquid which is a high-efficiency dechlorinating agent.
Example 1
(1) N was passed through a 250ml reactor2Adding 88ml of deionized water and acid antioxidant C into the mixture for five minutes6H8O62 g of chitosan and 10 g of chitosan, stirring at a low speed of 35rpm/min, starting a condenser, heating to 35-40 ℃, and carrying out heat preservation reaction for 1h to complete hydrolysis reaction. At the moment, the chitosan is hydrolyzed into the chitosan oligosaccharide, the molecular weight measured by a viscosity method is 4000-5000Da, and n is 40-50 repeating units. The reaction formula is as follows:
(2) immediately adjusting the pH value to 8-9 by using NaOH after hydrolysis, adding 4 g (40% of chitosan mass) of 1-hydroxy benzotriazole, stirring and increasing the speed to 80rpm/min, heating to 70-80 ℃, and reacting for 2h to complete the hydrolysis. And controlling annealing within 2-2.5 h, cooling to 25 ℃ and discharging.
The reaction formula is as follows:
example 2
(1) N is introduced into a 500ml reactor2Adding deionized water 175ml and acid antioxidant C after 10 min6H8O6、C6H8O62.5 g of sodium salt and 20 g of chitosan are stirred at low speed, the stirring speed is 35rpm/min, a condenser is started, the temperature is raised to 40 ℃, the temperature is kept for reaction for 1.5h, and the hydrolysis reaction is finished. At the moment, the chitosan is hydrolyzed into the chitosan oligosaccharide, the molecular weight measured by a viscosity method is 4000-5000Da, and n is 40-50 repeating units.
(2) Immediately adjusting the pH value to 8-9 by using NaOH after hydrolysis, adding 3g of benzotriazole and 5 g of 1-hydroxymethyl benzotriazole, stirring and increasing to 80rpm/min, heating to 75-80 ℃, keeping the temperature for reaction for 2h, annealing for 2 h-2.5 h after the reaction is finished, cooling to 25 ℃, and discharging.
Example 3
(1) N is introduced into a 500ml reactor2Adding 176ml of deionized water and acid antioxidant C after 10 minutes6H8O63g of C6H8O62 g of sylvite and 20 g of chitosan are stirred at a low speed of 35rpm/min, a condenser is started, the temperature is raised to 35-40 ℃, the temperature is kept for 1.5h, and the hydrolysis reaction is finished. At this time, the chitosan is hydrolyzed into oligo-chitosan, and the molecular weight measured by a viscosity method should be 4000-5000Da, wherein n is 40-50 repeating units.
(2) Immediately adjusting the pH value to 8-9 by using NaOH after hydrolysis, adding 8 g of 1-hydroxy benzotriazole, stirring and increasing the speed to 80rpm/min, heating to 80 ℃, preserving heat and reacting for 3h to finish the reaction. Annealing for 2-2.5 h, cooling to 25 ℃, and discharging.
Testing the dechlorinating effect of the dechlorinating agent:
1. taking 10L of deionized water, adding sodium chloride to prepare test sample water with the chloride ion content of 100-150 mg/L, taking 5 parts of 1000ml of each part, taking one part as a control,
2. the detection technical standard is as follows: the chloride ion detection method was performed by reference to GB/T15453-2008.
3. The test results are as follows: when 1.2 per mill is added into the chlorine-containing sample water with the chloride ion content of 147mg/L, the dechlorination efficiency can reach more than 90 percent.
Table 1: test report table of dechlorinating agent
At present, the dechlorinating agent is produced industrially, and after more than 6 years of use, the dechlorinating agent is used in a plurality of fields in China and is widely commented, and the dechlorinating agent plays an important role in saving energy and reducing emission for the country and ensuring the safe and stable operation of equipment.
The above-mentioned embodiments are only for illustrating the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and to carry out the same, and the present invention shall not be limited to the embodiments, i.e. the equivalent changes or modifications made within the spirit of the present invention shall fall within the scope of the present invention.
Claims (6)
1. A method for preparing a dechlorinating agent by graft reaction of chitosan oligosaccharide and a benzotriazole compound is characterized by comprising the following steps:
1) preparation of chitosan oligosaccharide: under the protection of inert gas, stirring chitosan, deionized water and an acidic antioxidant at a low speed, and carrying out hydrolysis reaction at 35-40 ℃ for 1-1.5 h to generate chitosan oligosaccharide with M being 4000-5000Da and n being 40-50 repeating units, wherein the mass ratio of the deionized water to the chitosan to the acidic antioxidant is as follows: and (3) chitosan: the acid antioxidant is 8-10: 1-2: 0.2-0.3;
2) immediately adjusting the pH value to 8-9 by NaOH after hydrolysis, adding a benzotriazole compound accounting for 40% of the mass of chitosan, stirring at medium speed, heating to 70-80 ℃ for grafting reaction, keeping the temperature for 2h, controlling the temperature to be reduced to 25 ℃ for 2 h-2.5 h after the reaction is finished, and discharging to obtain a colorless or light yellow viscous finished product serving as a dechlorinating agent.
2. The method for preparing the dechlorination agent by the grafting reaction of the chitosan oligosaccharide and the benzotriazole compound according to claim 1, wherein the acidic antioxidant is C6H8O6、C6H8O6Sodium salt and C6H8O6One or more of potassium salts.
3. The method for preparing the dechlorination agent by the graft reaction of the chitosan oligosaccharide and the benzotriazole compound according to claim 1, wherein the benzotriazole compound is one of 1-hydroxybenzotriazole, benzotriazole and 1-hydroxy-methylbenzotriazole.
4. The method for preparing the dechlorination agent by grafting the chitosan oligosaccharide and the benzotriazole compound according to claim 1, wherein the chitosan has a deacetylation degree of more than 95% and a relative molecular mass of 2 × 105～5×105。
5. The method for preparing the dechlorination agent by the graft reaction of the chitosan oligosaccharide and the benzotriazole compound according to claim 1, wherein the low-speed stirring speed in the step 1) is 35-40rpm/min, and the medium-speed stirring speed in the step 2) is 80-85 rpm/min.
6. The dechlorination agent prepared by the method for preparing the dechlorination agent by the graft reaction of the chitosan oligosaccharide and the benzotriazole compound as defined in any one of claims 1 to 5.
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