阅读说明：本技术 一种以二氧化钛为引发剂制备壳聚糖基絮凝剂的方法 (Method for preparing chitosan-based flocculant by using titanium dioxide as initiator ) 是由 黄静 唐晓旻 张世欣 王韬 向靖 于 2020-06-30 设计创作，主要内容包括：本发明公开了一种以二氧化钛为引发剂制备壳聚糖基絮凝剂的方法。该方法是以壳聚糖、马来酸酐、3-(2-噻吩基)丙烯酸为原料,尿素为助溶剂；先制备马来酰化壳聚糖,再将马来酰化壳聚糖和3-(2-噻吩基)丙烯酸溶解于纯水中,充分搅拌至其完全溶解；通氮驱氧,并加入二氧化钛引发剂后；然后在低压紫外汞灯照射下反应6~8h；待产物陈化后,对产物进行提取和纯化,即得改性壳聚糖絮凝剂。本发明制备方法工艺简单、反应平稳、易于控制、能耗低,所得改性壳聚糖絮凝剂稳定性好,易于溶解；且对含重金属的地表水、垃圾渗滤液有较好的处理效果,有良好的社会效益和经济效益。(The invention discloses a method for preparing a chitosan-based flocculant by using titanium dioxide as an initiator. The method takes chitosan, maleic anhydride and 3- (2-thienyl) acrylic acid as raw materials, and urea as a cosolvent; firstly, preparing maleylation chitosan, then dissolving the maleylation chitosan and 3- (2-thienyl) acrylic acid in pure water, and fully stirring until the maleylation chitosan and the 3- (2-thienyl) acrylic acid are completely dissolved; introducing nitrogen to drive out oxygen, and adding a titanium dioxide initiator; then reacting for 6-8 h under the irradiation of a low-pressure ultraviolet mercury lamp; and after the product is aged, extracting and purifying the product to obtain the modified chitosan flocculant. The preparation method has the advantages of simple process, stable reaction, easy control and low energy consumption, and the obtained modified chitosan flocculant has good stability and is easy to dissolve; and the method has better treatment effect on surface water and landfill leachate containing heavy metals, and has good social benefit and economic benefit.)

1. A method for preparing chitosan-based flocculant by taking titanium dioxide as an initiator is characterized in that the titanium dioxide is taken as the initiator, chitosan, maleic anhydride and 3- (2-thienyl) acrylic acid are taken as raw materials, and urea is taken as a cosolvent. Weighing a certain amount of chitosan and maleic anhydride, placing the chitosan and maleic anhydride into pure water, slowly dropwise adding glacial acetic acid, and continuously and rapidly stirring in a water bath at the temperature of 30-40 ℃; after 4-5h of reaction, drying in vacuo to obtain maleylated chitosan. The maleylation chitosan and the 3- (2-thienyl) acrylic acid are completely dissolved in pure water, and the urea is added into the reactor to be rapidly stirred until the two are completely dissolved. Introducing nitrogen to expel oxygen, adding a titanium dioxide initiator, and uniformly stirring; the initiator is anatase hydrophilic titanium dioxide, the particle size of the titanium dioxide is 5-10 nm, and the mass ratio of the titanium dioxide to the maleylation chitosan is 0.03-0.06: 1. And (3) reacting for 6-8 h under the irradiation of a low-pressure ultraviolet mercury lamp, and extracting and purifying a product after the reaction is finished and aging to obtain the modified chitosan-based flocculant.

2. The method for preparing the chitosan-based flocculant by using titanium dioxide as the initiator according to claim 1, wherein the mass ratio of the chitosan to the maleic anhydride is 1.5-2: 1; the total concentration of the chitosan and the maleic anhydride in the solution is 15-20%; the mass ratio of the chitosan to the glacial acetic acid is 1.5-2: 1; the vacuum drying temperature is 50-60 ℃.

3. The method for preparing the chitosan-based flocculant by using titanium dioxide as the initiator according to claim 1, wherein the mass ratio of the 3- (2-thienyl) acrylic acid to the maleylated chitosan is 3-4: 1; the total concentration of the 3- (2-thienyl) acrylic acid and the maleylation chitosan in the reaction solution is 20-30 percent; the mass ratio of urea to the maleylation chitosan is 2-2.5: 1; the ultraviolet light irradiation wavelength range is 300-380 nm, and the ultraviolet light intensity range is 0.02-0.39 mW/cm²。

Technical Field

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for preparing a chitosan-based flocculant by using titanium dioxide as an initiator.

Background

With the development of society and economy, China pays more and more attention to the protection of water environment. There are numerous water treatment methods. Compared with other water treatment methods, the coagulation method has the advantages of simplicity, high efficiency and small investment, and is widely regarded and applied. With the development of scientific technology, the variety of the flocculating agent is increased day by day. For sewage treatment, it is critical whether the treatment requirements can be met or not to be able to properly select and use the flocculating agent with excellent performance. The flocculating agent is mainly divided into an inorganic flocculating agent, an organic flocculating agent and a microbial flocculating agent. Compared with inorganic flocculant, the organic polymer flocculant has the advantages of small dosage, high flocculation speed, little influence of coexisting salts, medium pH and environmental temperature, less sludge generation and the like. It is widely applied to the waste water treatment of petroleum, printing and dyeing, chemical industry, paper making and the like. Although the organic flocculant makes up the defects of the inorganic flocculant, the residual acrylamide and ethylene imine monomers in the commonly adopted polyacrylamide flocculant have the risks of carcinogenesis, teratogenesis and mutation on human health, and are easy to cause secondary pollution. Therefore, the preparation of the non-toxic, safe and environment-friendly flocculating agent is important for environmental protection and human development.

The chitosan is well developed as a natural polymeric flocculant which is safe, nontoxic and easy to biodegrade. Free amino groups on a chitosan molecular chain can be protonated in an acidic medium, so that the chitosan molecular chain presents the characteristic of cationic polyelectrolyte, and the removal efficiency of pollutants in a water body is effectively improved. However, the molecular structure of chitosan contains a large amount of-OH and-NH₂The groups are interacted, so that a large amount of hydrogen bond interaction exists between chitosan molecules and in the chitosan molecules, the solubility of the chitosan in alkaline and neutral aqueous solutions is not enough, and the application range of the chitosan in the field of water pollution treatment is influenced. Therefore, in order to improve the performance of chitosan, chemical modification of chitosan is required to obtain a modified chitosan flocculant with a significant flocculation effect on water.

Chinese patent application No. CN201910473988.6 discloses a preparation method of a modified chitosan flocculant, a product and application thereof. The invention relates to a preparation method of a modified chitosan flocculant, which comprises carboxymethylation modification of chitosan, quaternization modification of carboxymethyl chitosan and purification of carboxymethyl chitosan quaternary ammonium salt. The chitosan used in the invention has wide source and low price, and the product can be completely biodegraded, thereby causing no secondary pollution to the environment. Carboxymethyl chitosan is obtained by carboxymethylation of chitosan, so that the water solubility of the carboxymethyl chitosan is obviously improved compared with that of chitosan, and carboxyl of the carboxymethyl chitosan has strong chelating capacity on metal ions such as cadmium, lead, mercury, arsenic and the like. The carboxymethyl chitosan is quaternized, the quaternary ammonium salt has positive charges, and the flocculation capacity of colloid particles with negative charges is enhanced, so that the flocculation sedimentation speed is accelerated. The flocculant prepared by the method has the advantages of enhanced flocculation capability on negatively charged colloidal particles and weaker flocculation capability on positively charged colloidal particles.

Chinese patent application No. CN201611128064.5 discloses a polymeric titanium salt modified chitosan flocculant, a preparation method and application thereof. Mixing a titanium-containing compound and a strong acid aqueous solution for reaction to obtain an acidic titanium salt aqueous solution, cooling, diluting the cooled acidic titanium salt aqueous solution, adding an organic base for reaction to adjust the alkalization degree of a reaction system, then adding a zinc salt, an aluminum salt, a calcium salt or an iron salt for stirring reaction, stirring for reaction for 1-60 min, adding an organic chitosan monomer, an olefin functional organic monomer and a stabilizer into the reaction solution, continuing the reaction for 1-3 h, and aging for 1-48 h under the water bath condition of 20-60 ℃ after the reaction is finished to obtain the polymerized titanium salt chitosan-based flocculant. The preparation method is complex to operate and needs strong acid.

Titanium dioxide is one of the most commonly used photocatalysts, has the advantages of high catalytic activity, no toxicity, no pollution, low cost and the like, and thus has great potential in the fields of atmospheric treatment and the like. Titanium dioxide has not been used as an initiator in the preparation of flocculants. Therefore, the development of a novel and efficient chitosan-based flocculant by using titanium dioxide as an initiator is necessary.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides the preparation method of the chitosan-based flocculant, which takes titanium dioxide as an initiator, and has the advantages of low energy consumption, simple process, good water solubility and good product stability.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

taking chitosan, 3- (2-thienyl) acrylic acid and maleic anhydride as raw materials, and urea as a cosolvent; weighing a certain amount of chitosan and maleic anhydride, placing the chitosan and maleic anhydride into pure water, slowly dropwise adding glacial acetic acid, and continuously and rapidly stirring in a water bath; after a certain period of reaction, it was dried in vacuo to obtain maleylated chitosan. The maleylation chitosan and the 3- (2-thienyl) acrylic acid are completely dissolved in pure water, and the urea is added into the reactor to be rapidly stirred until the two are completely dissolved. Introducing nitrogen to expel oxygen, adding a titanium dioxide initiator, and uniformly stirring; finally, the reactor is placed under a low-pressure ultraviolet mercury lamp for reaction; and after the reaction is finished and the product is aged, extracting and purifying the product to obtain the modified chitosan-based flocculant.

The method specifically comprises the following steps:

1) synthesis of maleylated chitosan: weighing a certain amount of chitosan and maleic anhydride in pure water according to the mass ratio of 1.5-2: 1 to prepare a solution with the total concentration of 15-20%, slowly dropwise adding glacial acetic acid, and continuously and rapidly stirring in a water bath at 30-40 ℃. Reacting for 4-5h, and drying in vacuum at 50-60 ℃ to obtain the maleylation chitosan.

2) Preparing a solution: weighing a certain amount of 3- (2-thienyl) acrylic acid and maleylation chitosan according to the mass ratio of 3-4: 1 of the 3- (2-thienyl) acrylic acid to the maleylation chitosan, completely dissolving the 3- (2-thienyl) acrylic acid and the maleylation chitosan in pure water to prepare a solution with the total concentration of 20-30%, and then adding a certain amount of urea into a reactor according to the mass ratio of the urea to the maleylation chitosan of 2-2.5: 1, and rapidly stirring until the two are completely dissolved.

3) Adding an initiator: after nitrogen is introduced to drive out oxygen, adding initiator titanium dioxide into the reactor according to the mass ratio of the titanium dioxide to the maleylation chitosan of 0.03-0.06: 1, and uniformly stirring; the initiator titanium dioxide is anatase 5-10 nm hydrophilic titanium dioxide.

4) Ultraviolet irradiation and reaction: in the wavelength range of 300 to 380nm andthe illumination intensity is 0.02-0.39 mW/cm²And irradiating under an ultraviolet lamp for 6-8 h. And (3) aging, and then extracting and purifying the product to obtain the modified chitosan-based flocculant.

Wherein: step 1), adding the chitosan and the maleic anhydride at a mass ratio of 1.5-2: 1, wherein the total concentration of the chitosan and the maleic anhydride in the solution is 15-20%. When the adding proportion is less than 1.5:1, the adding amount of the maleic anhydride is too large, and the graft copolymerization efficiency of the reaction is reduced under the condition of the same solid content. When the adding proportion is more than 2:1, the adding amount of the maleic anhydride is too small, and the grafting copolymerization efficiency of a large amount of chitosan is reduced. When the total concentration of the chitosan and the maleic anhydride in the solution is lower than 15%, the maleylation efficiency of the chitosan is lower, and a large amount of solvent needs to be evaporated; when the total concentration of chitosan and maleic anhydride in the solution is more than 15%, the chitosan needs a longer time to dissolve. Among various chemical modification methods, graft modification and acylation modification are the simplest strategies to increase the solubility of chitosan in a large pH range, and chitosan with good water solubility can be obtained by introducing aliphatic and aromatic acyl groups of different molecular weights to amino and hydroxyl groups on the chitosan molecule for chitosan acylation. The maleylation chitosan has good performances of moisture retention, moisture absorption, drug relief and the like, and has good application prospect in the aspect of water treatment.

The mass ratio of the chitosan to the glacial acetic acid in the step 1) is 1.5-2: 1. Wherein, the dropwise adding of the glacial acetic acid mainly plays a role in protonation, so that the chitosan is dissolved in water after being protonated. When the mass ratio is more than 2:1, it is difficult to completely protonate and dissolve chitosan, and when the mass ratio is less than 1.5:1, glacial acetic acid is too much to be economical and may have an influence on the subsequent reaction. When glacial acetic acid is dripped, chitosan is dripped after being uniformly dispersed.

The maleylation temperature of the chitosan in the step 1) is 30-40 ℃, and the reaction time is 4-5 h. When the reaction temperature is lower than 30 ℃, the maleylation rate of the chitosan is too slow, the required reaction time is greatly prolonged, and the amount of maleic anhydride grafted to the molecular weight of the chitosan is small. And when the temperature is higher than 40 ℃, the grafting rate of the obtained maleylation chitosan is increased slightly, and the energy consumption is higher. When the reaction time is less than 4 hours, the reaction can not be completely carried out; after more than 5 hours, the graft ratio is not increased and is uneconomical.

Step 2) the adding ratio of the 3- (2-thienyl) acrylic acid to the maleylation chitosan is 3-4: 1, and the total concentration of the 3- (2-thienyl) acrylic acid and the maleylation chitosan in the reaction solution is 20-30%. When the adding proportion is less than 3:1, the amount of 3- (2-thienyl) acrylic acid is less, and less 3- (2-thienyl) acrylic acid and the molecular chain of the maleylation chitosan are subjected to graft copolymerization. When the adding proportion is higher than 4:1, self-polymerization crosslinking easily occurs between the 3- (2-thienyl) acrylic acid monomers, so that the 3- (2-thienyl) acrylic acid cannot be well grafted and copolymerized with a molecular chain of the maleylation chitosan, and the water solubility of a prepared polymer sample is poor. When the total concentration of the 3- (2-thienyl) acrylic acid and the maleylation chitosan in the reaction solution is lower than 20 percent, the molecular weight of the obtained product is lower; when the total concentration of the 3- (2-thienyl) acrylic acid and the maleylation chitosan in the reaction solution is higher than 30 percent, the molecular weight of the product is high, but the solubility is poor.

In the step 2), under the condition of appropriate dosage of the cosolvent urea, the generation of hydrogen bonds can be prevented, so that the crosslinking probability is reduced, and the aim of increasing the product solubility is fulfilled. The urea is uneconomically used in an excessive amount and may affect the flocculation property if the urea acts as a chain transfer agent to lower the intrinsic viscosity of the product.

The initiator added in the step 3) is hydrophilic titanium dioxide with 5-10 nm of anatase titanium; the catalytic effect of the nano anatase titanium dioxide is better than that of the common nano gold red titanium dioxide. Because anatase titanium dioxide has higher activity and less impurity content, the crystal form is not stable like a golden red crystal, the forbidden band width is larger, and active electrons are more easily generated by photocatalysis; the anatase type photocatalytic initiation efficiency is better. The photocatalytic activity of titanium dioxide is closely related to the particle size, and the smaller the titanium dioxide particle in solution, the more the number of particles per unit mass, and the larger the specific surface area, which is more favorable for the photocatalytic reaction to proceed on the surface, so the reaction rate and efficiency are higher. Therefore, the particle size of the initiator titanium dioxide is selected to be 5-10 nm. The hydrophilic type titanium dioxide enables it to react better with monomers and the like dissolved in water. When the mass ratio of the initiator titanium dioxide to the maleylation chitosan is less than 0.03:1, the polymerization can not be effectively initiated to obtain the 3- (2-thienyl) acrylic acid modified chitosan-based flocculant. When the mass ratio of the initiator to the maleylated chitosan is more than 0.06:1, the initiator is too large to be economical and may generate a large amount of radicals in a short time, the collision probability of the radicals increases, chain growth terminates early, and the intrinsic viscosity of the product is affected.

In the step 4), the ultraviolet illumination time is 6-8 h, the ultraviolet wavelength is 300-380 nm, and the illumination intensity is 0.02-0.39 mW/cm²(ii) a The titanium dioxide generates electron holes under the ultraviolet irradiation, and generates free radicals to initiate the grafting copolymerization modification of the maleylation chitosan and the monomer. The low ultraviolet light illumination intensity provided by the low-pressure mercury lamp can greatly reduce energy consumption. But when the illumination intensity is lower than 0.02mW/cm²In time, the time required for initiating the copolymerization reaction increases, and the reaction efficiency decreases; when the illumination intensity is higher than 0.39mW/cm²In the low light intensity range, the molecular weight of the product is not obviously increased, and the energy consumption is increased. And the narrower wavelength range of the ultraviolet light is more favorable for exciting the titanium dioxide to generate free radicals. When the illumination time is less than 6 hours, the reaction is not completed; and after the reaction time is more than 8 hours, the molecular weight and the performance of the product cannot be obviously improved, and the energy consumption is higher.

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

1. the preparation method has the advantages of simple process, low energy consumption, high production efficiency, lower production cost and easy operation and control.

2. The preparation method provided by the invention has the advantages of stable reaction, easiness in control and few side reactions, and the obtained modified chitosan-based flocculant has good stability and easiness in dissolution and has a good treatment effect on surface water and landfill leachate containing heavy metals.

3. According to the invention, common titanium dioxide initiator is used for replacing photoinitiator for graft copolymerization of maleylation chitosan and 3- (2-thienyl) acrylic acid under the irradiation of ultraviolet light, so that the physicochemical property of chitosan is improved, some defects of the chitosan are made up, the flocculation performance of the chitosan is improved, and the chitosan can be better applied to the field of water treatment. Therefore, the chitosan-based flocculant synthesized by using titanium dioxide as an initiator has good social and economic benefits in practical application.

Detailed Description

The present invention will be described in further detail with reference to specific examples, wherein the raw materials used are common commercial products unless otherwise specified.