Polyurethane type high molecular chelating flocculant and its preparation and application

Abstract

The application discloses a polyurethane type high-molecular chelation flocculant and a preparation method thereof. The polyurethane type high-molecular chelation flocculant is prepared by a two-step method. In the first step, a polyurethane prepolymer terminated by isocyanate groups is prepared by a solution polymerization method with diisocyanate, di(multi)alcohol and hydrophilic monomer dimethylol propionic acid as main raw materials, dibutyltin dilaurate as a catalyst and ethyl acetate as a solvent, and then neutralized into a salt by a NaOH aqueous solution; after vacuum removal of the solvent, polyurethane macromolecules containing primary (secondary) amine in the molecular chain are obtained by chain extension with polyamine at 5-15 0 C. In the second step, the polyurethane type high-molecular chelation flocculant is obtained by reacting CS2 with amine (primary amine or secondary amine) under alkaline conditions. The polyurethane type high-molecular chelation flocculant prepared by the application contains multiple sodium aminodithiocarbamate soft base structures in the molecular chain, can effectively form stable chelate macromolecules with soft acid heavy metal ions, and the formed flocs have a large volume and are easy to separate. The high-molecular chelation flocculant can be used for treating industrial wastewater containing low-concentration heavy metals, protects the environment and people's health, and brings good social and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of polymeric flocculant preparation and wastewater treatment technology, and more specifically, to a polyurethane-type polymeric chelating agent and its preparation method. Background Technology

[0002] Water is an essential ecological resource for human survival and development. With the rapid development of modern industry and agriculture, the amount and scope of water use are constantly expanding, resulting in a continuous increase in wastewater with increasingly complex compositions. Broadly speaking, wastewater can be divided into organic and inorganic pollutant wastewater, with inorganic pollutant wastewater containing heavy metals accounting for a significant proportion. Heavy metals typically refer to metallic elements with atomic weights between 63 and 200. Besides harming the ecological environment, heavy metals accumulate in the human body through water, food, and other pathways, seriously affecting health and endangering life. While organic pollutants can usually be degraded or structurally destroyed through environmental factors or chemical treatments, eliminating their toxicity, heavy metal pollution cannot have its atomic number altered or its toxicity eliminated through environmental factors or chemical means. Instead, it can only be addressed through physicochemical methods such as enrichment, separation, storage, or resource reuse. The main toxic heavy metal ions in wastewater include copper, nickel, mercury, cadmium, lead, chromium, and zinc. Although copper plays a vital role in the metabolism of organisms, excessive copper intake can lead to cumulative poisoning symptoms such as vomiting, muscle spasms, convulsions, and even death. Cadmium and chromium are even listed as possible carcinogens for humans. Cadmium poses a serious threat to human health; long-term exposure can lead to kidney dysfunction and ultimately death. With social development and the continuous improvement of people's living standards, there is a growing awareness of ecological environmental protection and public health and safety, and water resource protection has received significant attention. Strict standards have been established for the discharge of heavy metal wastewater. Removing heavy metals from wastewater, protecting the ecological environment and public health and safety, and conserving water resources are essential requirements for the sustainable development of society as a whole.

[0003] Continuous theoretical and practical research and exploration have gradually led to the development of specific methods and comprehensive treatment systems for heavy metal removal from wastewater. Heavy metal treatment methods include chemical precipitation, adsorption, membrane separation, ion exchange, and chelation sedimentation. Each method has its own characteristics. For example, chemical precipitation is relatively simple and inexpensive, and is currently the most widely used industrial method for treating heavy metal wastewater. However, it is not effective for treating low concentrations of trace heavy metals, and it generates a large amount of solid waste sludge containing high concentrations of metal elements. This sludge is difficult to treat and requires appropriate storage facilities. Membrane separation, on the other hand, has a significant separation effect, achieving a heavy metal removal rate of 99%, and is suitable for separating trace heavy metals. However, its biggest drawback is its high cost. Furthermore, membrane fouling leads to membrane pore blockage, reducing water flux, and this process is irreversible. Chelation sedimentation is a relatively simple and inexpensive method for removing heavy metal ions. Heavy metal ions form relatively stable 5-membered and 6-membered ring structures through chelating agents. According to the hard-soft acid-base pairing rule, sulfur-containing soft acid ligands have a high coordination ability with heavy metal soft bases. Among sulfur-containing chelating agents, aminodithiocarbamates have a broad-spectrum chelating ability for heavy metals, including small molecules with monofunctional and multifunctional groups, as well as polymers containing multiple dithiocarbamate groups. Although monoaminodithiocarbamate small molecule chelating agents have strong chelating ability, the resulting flocs are small, with poor sedimentation performance, and a suitable excess is required to achieve good results. Small molecules containing multifunctional groups can combine with chelating groups from different chelating agent molecules to form large molecular chelates through the combination of the same heavy metal ion with chelating groups, thereby forming large flocs and improving sedimentation efficiency. High molecular weight chelating agents not only have good chelating ability but also good flocculation performance, and have become one of the research hotspots in recent years. Polyurethane-type polymeric chelating flocculants use di(poly)ols, diisocyanates, hydrophilic components, polyamines, and carbon disulfide as main raw materials. A polyurethane prepolymer is prepared through a polyaddition reaction, and active amines are introduced into the molecular chain via chain extension using polyamines. Then, a nucleophilic addition reaction with carbon disulfide is conducted to prepare a polymeric chelating flocculant containing aminodithiocarbamate in the molecular chain. The synthesis process is simple, and the raw materials are abundant. The molecular weight, water solubility, and chelating capacity of the resin can be adjusted through formulation and preparation process, demonstrating unique advantages in application fields and offering good economic and social benefits. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings and defects of current small molecule flocculants, such as small floc particle size, incomplete precipitation and separation, and complex synthesis of polymeric flocculants, as well as the limited availability or high price of monomers. The present invention provides a polyurethane-type polymeric chelating flocculant.

[0005] Another technical problem to be solved by the present invention is to provide a method for preparing polyurethane-type polymeric chelating flocculants.

[0006] The objective of this invention is achieved through the following methods: A polyurethane-type polymeric chelating flocculant, characterized in that: the molecular structure of the polyurethane ester-type polymeric chelating flocculant is a block structure, consisting of polymer soft segments composed of oligomeric diols and polymer hard segments composed of urethane esters, while the molecular chain contains an adjustable number of hydrophilic functional groups and amino dithiocarbamate chelating functional groups.

[0007] Furthermore, the polyurethane-type polymeric chelating flocculant is a polyurethane-type polymeric chelating flocculant obtained by preparing polyurethane prepolymer through a polyaddition reaction using di(poly)ol, diisocyanate, hydrophilic monomer, polyamine, etc. as the main raw materials, and then introducing amino dithiocarbamate through chain extension and nucleophilic addition with carbon disulfide.

[0008] Furthermore, the raw materials for the polyurethane-type polymeric chelating flocculant include: the di(poly)ols, which can be small molecule diols such as ethylene glycol, butanediol, 1,3-pentanediol, hexanediol, and trimethylolpropionic acid; or oligomeric diols with a molecular weight between 500 and 2000, including polyether diols and polyester diols; the diisocyanates refer to toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, etc.; the polyamines refer to ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and melamine; and the hydrophilic component is dimethylolpropionic acid. Furthermore, the method for preparing the polyurethane-type polymeric chelating flocculant is solution polymerization, and the solvent used is low-toxicity ethyl acetate. Furthermore, the polyurethane-type polymeric chelating flocculant is a solvent-free aqueous dispersion that is environmentally friendly and safe. The dispersion has a light brownish-yellow appearance, and its appearance varies from opaque to translucent to transparent liquid depending on the amount of hydrophilic monomers.

[0009] Furthermore, the raw materials and formulation of the polyurethane-type polymeric chelating flocculant are as follows: the molar ratio of isocyanate to hydroxyl group R = 1.25~1.80, dimethylolpropionic acid 4.5~12.0 wt.% by weight, and dithiocarbamate functional groups (chelating groups) 10~15 wt.% according to CS2.

[0010] 7. A polyurethane-type polymeric chelating flocculant according to claims 1-5, comprising the following steps: S1. Add the specified amounts of oligomeric diol, small molecule polyol, and hydrophilic monomer to the reaction vessel, and add an appropriate amount of solvent to stir and dissolve (or disperse). S2. Add the specified amount of diisocyanate to the reaction vessel through a constant pressure funnel at room temperature and with constant stirring. After the addition is complete, wash the constant pressure funnel with an appropriate amount of solvent and combine the washing liquid into the reaction vessel. S3. Turn on the reflux condenser, add the catalyst in the specified amount, heat and control the temperature at a certain T1, react for a certain time H1, then raise the temperature to T2, continue to react for a certain time H2, and cool to room temperature; S4. Neutralize with NaOH aqueous solution to form salt and hydrate, cool to T3, and add the appropriate amount of polyamine for chain extension and end capping; S5. Remove the solvent by vacuuming; S6. Add the appropriate amounts of CS2 and NaOH, heat to T4, and react for H3 hours to obtain polyester-type sodium aminodithiocarbamate.

[0011] Furthermore, the solvent used in step S1 is low-toxicity ethyl acetate; in step S3, the temperature T1 is 35~500°C, the time H1 is 0.5~1.0 hours, the temperature T2 is 65~800°C, and the time H2 is 3.5~6.5 hours; in step S4, the neutralization degree is pH 7.5~8.5, and the temperature T3 is 10~250°C; in step S6, NaOH can be added all at once or in steps, but the pH must be 7.5~8.5, the temperature T4 must be 35~500°C, and the reaction time H3 must be 5~7 hours.

[0012] 8. A polyurethane-type polymeric chelating flocculant according to claims 1-5 is provided for its application in wastewater treatment, the treatment method comprising the following steps: Y1. Take a certain proportion of wastewater components into a wastewater treatment tank, and adjust the pH value of the wastewater in the treatment tank with stirring; Y2. Take a certain amount of polyurethane ester-type polymer chelating flocculant and add it to the treatment tank under gentle stirring, and continue to stir gently for 30 minutes; Y3. Allow to stand and settle for 8-12 hours, then remove the supernatant. Y4. Centrifugation and precipitation yields a mixed precipitate containing heavy metals; Furthermore, in step Y1, the pH value should ideally be near neutral to suit the discharge of treated water and to facilitate more effective removal of heavy metal ions; in step Y2, a certain amount of polyurethane-type polymeric chelating flocculant refers to a molar ratio of aminodithiocarbamate to heavy metal ions between 1.05 and 1.2:1; the gentle stirring mentioned refers to preventing the flocs from being dispersed into tiny particles that are difficult to precipitate and separate during vigorous stirring; the mixed precipitate containing heavy metals obtained in step 4 can be separated from the heavy metals and flocculant by adding acid, thus enabling resource reuse.

[0013] Compared with existing technologies, the beneficial effects are: Removing heavy metals from wastewater is a crucial issue for ecological security and public health. Heavy metal ions, which are soft acids, can form stable six-membered ring chelates with sodium aminodithiocarbamate, a soft base. When the heavy metal chelate is electrically neutral, it will form flocs that precipitate or suspend in the water. Currently, the flocs produced by using small-molecule sodium aminodithiocarbamate to form chelates with heavy metals are small and fragile, making effective separation difficult. Furthermore, high dosages are required; otherwise, water-soluble chelates may form. Although polymeric flocculants have some applications and good effects, their synthesis typically involves synthesizing functional monomers, resulting in complex production processes, high prices, and limited widespread application. The polymeric flocculant prepared in this invention uses commercially available raw materials, is readily available, and has a simple preparation process, making it easy to industrialize and offering significant application value and economic benefits. Attached Figure Description

[0014] Figure 1 These are photos of homemade wastewater. Figure 2 This is a photograph of the water treatment at pH=6.8 in Example 7; Figure 3 This is a photograph of the treatment results at pH=7.0 in Example 7. Detailed Implementation

[0015] The following examples further explain and clarify the invention, but the specific examples do not constitute any limitation on the invention. Unless otherwise specified, the methods and equipment used in this example are conventional methods and equipment in the art, and the raw materials used are commercial raw materials. Example 1

[0016] This embodiment provides the formulation composition of a polyurethane ester-type polymeric chelating flocculant. Example 2

[0017] This embodiment provides the formulation composition of a polyurethane ester-type polymeric chelating flocculant. Example 3

[0018] This embodiment provides the formulation composition of a polyurethane ester-type polymeric chelating flocculant. Example 4

[0019] This embodiment provides the formulation composition of a polyurethane ester-type polymeric chelating flocculant. Example 5

[0020] This embodiment provides the formulation composition of a polyurethane ester-type polymeric chelating flocculant.

[0021] Note: The amount of chelating agent added is based on a molar ratio of heavy metal ions to sodium aminodithiocarbamate of 1:1.05~1.2. Example 6

[0022] This embodiment provides the application of polyurethane ester-type polymeric chelating flocculants in the treatment of heavy metal-containing wastewater.

[0023] Note: The amount of chelating agent added is based on a molar ratio of heavy metal ions to sodium aminodithiocarbamate of 1:1.05~1.2. Example 7

[0024] This embodiment provides the application of polyurethane ester-type polymeric chelating flocculants in wastewater treatment at different pH levels.

[0025] Note: The amount of chelating agent added is based on a molar ratio of heavy metal ions to sodium aminodithiocarbamate of 1:1.05~1.2. Example 8

[0026] This embodiment provides a method for preparing polyurethane ester-type polymeric chelating flocculants (Examples 1-5). The specific steps are as follows: S1. Add the specified amounts of oligomeric diol, small molecule polyol, and hydrophilic monomer to the reaction vessel, and add an appropriate amount of solvent to stir and dissolve (or disperse). S2. Add the specified amount of diisocyanate to the reaction vessel through a constant pressure funnel at room temperature and with constant stirring. After the addition is complete, wash the constant pressure funnel with an appropriate amount of solvent and combine the washing liquid into the reaction vessel. S3. Turn on the reflux condenser, add the catalyst in the specified amount, heat and control the temperature at a certain T1, react for a certain time H1, then raise the temperature to T2, continue to react for a certain time H2, and cool to room temperature; S4. Neutralize with NaOH aqueous solution to form salt and hydrate, cool to T3, and add the appropriate amount of polyamine for chain extension and end capping; S5. Remove the solvent by vacuuming; S6. Add the appropriate amounts of CS2 and NaOH, heat to T4, and react for H3 hours to obtain polyester-type sodium aminodithiocarbamate.

[0027] Furthermore, the solvent used in step S1 is low-toxicity ethyl acetate; in step S3, the temperature T1 is 35~500°C, the time H1 is 0.5~1.0 hours, the temperature T2 is 65~800°C, and the time H2 is 3.5~6.5 hours; in step S4, the neutralization degree is pH 7.5~8.5, and the T3 is 10~250°C; in step S6, NaOH can be added all at once or in steps, but the pH must be 7.5~8.5, the temperature T4 must be 35~500°C, and the reaction time H3 must be 5~7 hours. Example 9

[0028] This embodiment provides the application of polyurethane ester-type polymeric chelating flocculants (Examples 6-7). The specific steps are as follows: Y1. Take a certain proportion of wastewater components into a wastewater treatment tank, and adjust the pH value of the wastewater in the treatment tank with stirring; Y2. Take a certain amount of polyurethane ester-type polymer chelating flocculant and add it to the treatment tank under gentle stirring, and continue to stir gently for 30 minutes; Y3. Allow to stand and settle for 8-12 hours, then remove the supernatant. Y4. Centrifugation and precipitation yields a mixed precipitate containing heavy metals; Furthermore, in step Y1, the pH value should ideally be near neutral to suit the discharge of treated water and to facilitate more effective removal of heavy metal ions; in step Y2, a certain amount of polyurethane-type polymeric chelating flocculant refers to a molar ratio of aminodithiocarbamate to heavy metal ions between 1.05 and 1.2:1; the gentle stirring mentioned refers to preventing the flocs from being dispersed into tiny particles that are difficult to precipitate and separate during vigorous stirring; the mixed precipitate containing heavy metals obtained in step 4 can be separated from the heavy metals and flocculant by adding acid, thus enabling resource reuse. Example 10

[0029] This embodiment provides some photographs showing the treatment effect of wastewater with polyurethane-type polymeric flocculant (Example 7), see the attached instruction manual. Figures 1-3 .

Claims

1. A polyurethane-type polymeric chelating flocculant, characterized in that, The polyurethane ester-type polymeric chelating flocculant is composed of hydrophilic groups, amino dithiocarbamate, soft segment oligomer diol, and urethane hard segment.

2. The polyurethane-type polymeric chelating flocculant according to claim 1, characterized in that, The polyurethane-type polymeric chelating flocculant is prepared by polyaddition reaction of diols (poly)ols, diisocyanates, hydrophilic monomers, polyamines, etc., as the main raw materials, to form a polyurethane prepolymer, which is then chain-extended with polyamines to form a polymer containing secondary (primary) amines, and then introduced into the form of amino dithiocarbamate by nucleophilic addition with carbon disulfide.

3. The polyurethane-type polymeric chelating flocculant according to claims 1-2, characterized in that, The formulation of the polyurethane-type polymeric chelating flocculant includes the following molar ratio of isocyanate to hydroxyl groups. R =1.25~1.80, dimethylolpropionic acid 4.5~12.0 wt.% by weight, dithiocarbamate functional groups (chelating groups) 10~15 wt.% by CS2.

4. The polyurethane-type polymeric chelating flocculant according to claim 1 or 2, characterized in that, The di(poly)ol can be a small molecule diol, such as ethylene glycol, butanediol, 1,3-pentanediol, hexanediol, or trimethylolpropionic acid, or an oligomeric diol with a molecular weight between 500 and 2000, including polyether diols and polyester diols; the diisocyanate refers to toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, etc.; the polyamine refers to ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and melamine; the hydrophilic component is dimethylolpropionic acid.

5. A polyurethane-type polymeric chelating flocculant according to claim 1 or 2, characterized in that, The preparation of polyurethane-type polymeric chelating flocculants involves two steps. Step 1: Diisocyanate undergoes a polyaddition reaction with bis(polyol), the hydrophilic monomer dimethylolpropionic acid, and a small amount of catalyst. The polymerization method is solution polymerization, generating an isocyanate-terminated prepolymer, which is then cooled to 5-15°C. 0 C, and neutralize with sodium hydroxide to form a salt and aqueous solution. Then, add polyamine for chain extension, remove solvent by vacuum to obtain polyurethane containing primary (secondary) amine; Second step: add the specified amount of NaOH aqueous solution, add CS2 dropwise at a certain temperature, and after the addition is complete, continue the reaction for a certain time to obtain polyurethane-type polymeric chelating flocculant.

6. The polyurethane-type polymeric chelating flocculant according to claims 1 and 4, characterized in that, The solvent is ethyl acetate, which is of low toxicity, and the catalyst is dibutyltin dilaurate.

7. A polyurethane-type polymeric chelating flocculant according to claims 1-5, comprising the following steps: S1. Add the specified amounts of oligomeric diol, small molecule polyol, and hydrophilic monomer to the reaction vessel, and add an appropriate amount of solvent and stir to dissolve (or disperse). S2. Add the specified amount of diisocyanate to the reaction vessel through a constant pressure funnel at room temperature and with constant stirring. After the addition is complete, wash the constant pressure funnel with an appropriate amount of solvent and combine the washing liquid into the reaction vessel. S3. Turn on the reflux condenser, add the appropriate amount of catalyst, heat and control the temperature at a certain T1, react for a certain time H1, then raise the temperature to T2, continue to react for a certain time H2, and cool to room temperature; S4. Neutralize with NaOH aqueous solution to form salt and hydrate, cool to T3, and add the appropriate amount of polyamine for chain extension and end capping; S5. Remove the solvent by vacuuming; S6. Add the appropriate amounts of CS2 and NaOH, heat to T4, and react for H3 hours to obtain polyester-type sodium aminodithiocarbamate.

8. The method for preparing a polyurethane-type polymeric chelating flocculant according to claim 7, characterized in that, The solvent used in step S1 is low-toxicity ethyl acetate; in step S3, the temperature T1 is 35~50°C. 0 C. Time H1 is 0.5~1.0 hours, temperature T2 is 65~80 degrees Celsius. 0 C. Time H2 is 3.5~6.5 hours; the degree of neutralization in step S4 is pH 7.5~8.5, and the temperature T3 is 10-25 degrees Celsius. 0 C; In step S6, NaOH can be added all at once or in stages, but the pH must be 7.5~8.5 and the temperature T4 must be 35~50°C. 0 C, the reaction time H3 is 5~7 hours.

9. A polyurethane-type polymeric chelating flocculant according to claims 1-5 is provided for its application in wastewater treatment, the treatment method comprising the following steps: Y1. Take the wastewater with the determined proportions of the components into the wastewater treatment tank, and adjust the pH value of the wastewater in the treatment tank with stirring; Y2. Take a certain amount of polyurethane-type polymeric chelating flocculant and add it to the treatment tank under gentle stirring, and continue to stir gently for 30 minutes; Y3. Allow to stand and settle for 8-12 hours, then remove the supernatant. Y4. Centrifugation and precipitation yields a mixed precipitate containing heavy metals; Furthermore, in step Y1, the pH value should ideally be near neutral to facilitate the discharge of treated water and to promote more effective removal of heavy metal ions. In step Y2, the specified amount of polyurethane-type polymeric chelating flocculant refers to a molar ratio of aminodithiocarbamate to heavy metal ions between 1.05 and 1.2:

1. The gentle stirring mentioned above is to prevent the flocs from being dispersed into tiny particles that are difficult to precipitate and separate during vigorous stirring. The mixed precipitate containing heavy metals obtained in step 4 can be separated from the heavy metals and flocculant by adding acid, thus enabling resource reuse.

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