Polysaccharide-based flocculant and method for producing this flocculant

Abstract

FIELD: polymer chemistry.SUBSTANCE: polysaccharide-based flocculant, method for producing the same, and the use of a block copolymer as a biodegradable flocculant. Polysaccharide-based flocculant comprises a block copolymer containing at least two covalently linked polymer blocks, one of which is a graft polymer block and the other is a linear polymer block. The graft polymer block includes a polysaccharide chain and chains grafted to it based on acrylic acid or its derivatives. The linear polymer block is obtained by polymerization of at least one monomer capable of free-radical polymerization.EFFECT: implementation of a block copolymer based on a polysaccharide for the purpose of a biodegradable flocculant, ensuring the binding of dispersed particles to form floccules, as well as in providing a combination of high flocculating capacity and biodegradability of the developed flocculant based on a polysaccharide.21 cl, 2 dwg, 9 ex

Description

[0001] Technical field of the invention group

[0002] The group of inventions relates to the field of high-molecular chemistry, in particular to compositions of biodegradable polymer flocculants intended for use in water purification and water treatment processes, in particular for the clarification of natural and waste water, dewatering of sludge, as well as in other industrial processes requiring efficient separation of liquid and solid phases, for example, in the mining, pulp and paper and oil production industries.

[0003] Level of technology of the group of inventions

[0004] The problem of removing suspended colloidal particles from water is a key one in modern industry and ecology. Coagulation and flocculation processes are widely used to address this issue. High-molecular-weight polymers are used as flocculants, the most common of which are synthetic polymers based on acrylamide and acrylic acid. These polymers demonstrate high efficiency due to their long chains, which can form bridges between particles. However, their main drawback is their slow biodegradation rate, which leads to the accumulation of persistent synthetic products in the environment. Recently, there has been a steady trend toward creating natural reagents by incorporating biodegradable fragments into the polymer structure, particularly those based on natural polysaccharides such as starch, dextrin, cellulose, and their derivatives.

[0005] A water-soluble graft copolymer [US 5075401 A, publication date: 24.12.1991] consisting of a polysaccharide backbone (in particular dextran or starch) and polyacrylamide side chains grafted to it was selected as a prototype. It is obtained by free-radical polymerization in an aqueous medium. The process involves the simultaneous presence in the reaction system of a polysaccharide, an acrylamide monomer, and a redox initiating system in the form of cerium (IV) and persulfate ions. The initiator generates active radical centers directly on the polysaccharide macromolecule, from which the growth of grafted polyacrylamide chains begins.

[0006] The significant advantage of the prototype is its biodegradability and environmental safety, but its disadvantage is its structure, which prevents its effective use as a flocculant.

[0007] This is due to the fact that in the graft copolymer structure, relatively short polyacrylamide chains are randomly distributed along a more compact polysaccharide macromolecule. It should be noted that the primary action of highly effective flocculants is through bridging, which requires very long, flexible, and linear polymer chains capable of extending over significant distances in solution and simultaneously linking several distant colloidal particles. However, the prototype architecture creates obstacles that prevent the grafted chains from fully unfolding and effectively capturing adjacent particles. Consequently, the effectiveness of the bridging mechanism is reduced, and achieving a high degree of flocculation requires the use of a higher dosage of this polymer, which leads to increased operating costs and a higher concentration of residual polymer in the purified water.In this case, the resulting floccules may be less dense and durable.

[0008] It should also be noted that in the prototype molecule, the same structure simultaneously performs two different functions: the polysaccharide backbone is responsible for biodegradability and partial particle attachment, while the grafted chains are responsible for bridging. However, in a single-step synthesis, it is impossible to independently control the parameters of these functional parts. The length and number of grafted chains are a statistical result of the reaction, preventing the polymer from maximally performing both functions, leading to an overall decrease in its performance as a flocculant.

[0009] Thus, the resulting prototype architecture is inherently suboptimal for the key flocculation mechanism - bridging, which poses a technical challenge in creating a biodegradable polymer that would overcome this structural drawback and combine the advantages of both natural and synthetic polymers without compromising their functions.

[0010] Disclosure of the essence of the invention

[0011] The technical result, which the group of inventions is aimed at achieving, consists in the implementation of a block copolymer based on a polysaccharide for the purpose of a biodegradable flocculant, which ensures the binding of dispersed particles with the formation of floccules.

[0012] An additional technical result, which the group of inventions is aimed at achieving, is to ensure a combination of high flocculating capacity and biodegradability of the developed polysaccharide-based flocculant.

[0013] The essence of the first invention from the group of inventions is as follows.

[0014] The polysaccharide-based flocculant, unlike the prototype, is presented in the form of a block copolymer containing at least two covalently linked polymer blocks, wherein:

[0015] - at least one of the said blocks is a graft polymer block (A) comprising a polysaccharide chain and chains grafted to it based on acrylic acid derivatives.

[0016] - at least one other block is a linear polymer block (B) obtained by polymerization of at least one monomer capable of free-radical polymerization.

[0017] The essence of the second invention from the group of inventions is as follows.

[0018] The method for producing a flocculant involves free-radical polymerization of at least one monomer in the presence of a macromolecular compound. Unlike the prototype, said macromolecular compound is a graft polymer comprising a polysaccharide chain and grafted acrylic acid-based chains, forming a linear polymer block (B) covalently bonded to said graft polymer block (A).

[0019] The essence of the third invention from the group of inventions is as follows.

[0020] Use of block copolymer in accordance with paragraph 1 as a biodegradable flocculant.

[0021] The graft polymer block (A) is a macromolecule consisting of a polysaccharide chain grafted with chains obtained by polymerization of monomers. The polysaccharide chain serves a dual function: it serves as a biodegradable scaffold and ensures primary adsorption on colloidal particles through polar interactions.

[0022] Various readily available natural polymers can be used as the polysaccharide chain, including dextrin, partially hydrolyzed starch, dextran, hemicellulose, or natural gums (e.g., guar). This variability provides process flexibility, allowing the selection of raw materials based on availability and the specific requirements of the final product.

[0023] Graft chains obtained by polymerization of monomers such as acrylic acid, acrylamide, their salts and / or esters form a layer with a high charge density and / or polar groups on the surface of the block (A), intensifying electrostatic and hydrogen interactions with the substrate surface. The mass fraction of the polysaccharide chain in the block (A) varies in the range from 20 to 60%, which ensures an optimal balance between biodegradability and adsorption capacity. Going beyond this range may lead to a decrease in the efficiency of the flocculant. When the polysaccharide content is below 20%, the biodegradable function weakens. When the content is above 60%, the proportion of active grafted chains becomes insufficient to ensure strong and rapid binding to colloids. Preferably, the content of the polysaccharide chain in the graft polymer block (A) is from 30 to 50 mass%. %, and chains grafted to it based on acrylic acid derivatives - from 50 to 70 mass%.

[0024] The linear polymer block (B) is a high-molecular, predominantly linear chain obtained by polymerizing monomers selected from the group consisting of at least acrylic acid, acrylates, acrylamides, styrene, and its derivatives. This block facilitates the bridging flocculation mechanism, effectively linking particles located at a significant distance from one another into voluminous floccules. The introduction of hydrophobic comonomers, such as styrene, in an amount not exceeding 1 mol% into the block (B) allows for modification of its properties for effective interaction with hydrophobic contaminants, such as emulsified petroleum products and others.

[0025] The overall structure of the block copolymer is determined by the weight ratio of blocks (A) and (B). The content of the graft polymer block (A) in the final macromolecule is from 10 to 50%, and the content of the linear polymer block (B) is from 50 to 90 wt. %. This is due to the fact that when the content of block (A) is below 10%, the adsorption function weakens, and when the content is above 50%, the spatial conformation of the block copolymer begins to approach the conformation of a simple graft copolymer, which leads to a decrease in the efficiency of block (B) in bridging. Preferably, the content of the graft polymer block (A) is from 20 to 40 wt. %, and the content of the linear polymer block (B) is from 60 to 80 wt. %.

[0026] The block copolymer architecture can be represented by a diblock (A-B) or triblock (B-A-B) structure, depending on whether the graft polymer block (A) is linked to one or two linear blocks. This allows for further tuning of the polymer properties: the diblock structure provides maximum tail length for bridging, while the triblock structure can form more complex spatial networks.

[0027] For industrial use, the flocculant can be presented in three main commercial forms. The first is an aqueous solution or gel, where the block copolymer content is 30-50% by weight. The remainder (50-70%) is predominantly water, as well as associated inorganic salts and residual monomers, which are synthesis products. The second form is a low-viscosity invert emulsion of the "water-in-oil" type with a similar polymer concentration of 30-50% by weight. In it, the dispersed aqueous phase with dissolved flocculant is stabilized in hydrocarbon oil using emulsifiers. The third, most concentrated form is a dry powder or granules. In this product, the content of the main substance (block copolymer) is at least 90% by weight. The remaining components of the powder (up to 10%) include residual moisture and inorganic salts. The choice of a specific form is determined by the requirements for logistics, storage and the consumer’s available dosing equipment.The active component, a block copolymer, maintains its high effectiveness in all available forms. Each provides ease of use in a variety of production environments.

[0028] The method for producing a flocculant involves free-radical polymerization of monomers for block (B) in the presence of a pre-synthesized graft polymer (block A), which acts as a macromolecular substrate (macroinitiator or macrochain transfer agent). This two-stage approach enables the targeted creation and combination of blocks with predetermined and optimized characteristics, which is impossible in single-stage processes.

[0029] The polymerization process can be carried out in an aqueous solution with a solids content of 30 to 50% by weight. Lower concentrations reduce productivity, while higher concentrations can lead to uncontrolled gelation and difficult heat dissipation. The polymerization temperature can be selected from 55 to 75°C, ensuring a high reaction rate and sufficient initiator efficiency without the risk of thermal degradation of the polysaccharide component.

[0030] The process can be implemented in isothermal or adiabatic mode, which allows the reaction to be carried out without external heating, thereby saving energy during the derivative process.

[0031] The graft polymer block (A) can be added before or during polymerization, allowing for control of the architecture and molecular weight distribution of the final product. Adding the block (A) before polymerization promotes the formation of more homogeneous structures, while adding it directly during the polymerization process can lead to the creation of more complex polydisperse systems.

[0032] The group of inventions is characterized by a previously unknown set of essential features from the prior art, distinguished in that:

[0033] - The flocculant is presented as a block copolymer containing at least two covalently linked polymer blocks, allowing for spatial and functional separation of the elements responsible for adsorption / biodegradability and bridging. This eliminates steric hindrance and eliminates functional conflict, allowing each block to operate at maximum efficiency.

[0034] - at least one of the blocks is a graft polymer block (A), comprising a polysaccharide chain and chains grafted to it. The presence of the polysaccharide chain is essential for the biodegradability of the entire macromolecule, as it serves as a substrate for enzymatic degradation. At the same time, its high polarity ensures strong primary adsorption on particles. At the same time, the grafted synthetic chains create a high charge density and / or polar groups on the surface of block (A), which greatly enhances and accelerates the adsorption process, making it virtually irreversible. This ensures strong fixation of the flocculant on the particles and high bridging efficiency;

[0035] —at least one other block is a linear polymer block (B), which determines the structure of the bridging domain. The long, flexible, and unbranched structure of this block allows it to assume an unfolded conformation in solution with maximum volume. This facilitates the formation of large, stable, and rapidly settling floccules.

[0036] The combination of essential features of the developed group of inventions makes it possible to achieve a synergistic effect, which consists in the fact that the covalent connection of functionally different blocks (A and B) leads to a multiple increase in flocculating capacity, which cannot be achieved either by using these blocks separately or by simply physically mixing them.

[0037] The observed non-additive increase in flocculating activity is a direct consequence of the block copolymer architecture, which provides a new mechanism for interaction between the polymer and the colloidal system. Unlike a simple physical mixture of its components or a graft copolymer (prototype), the proposed block copolymer implements an effective intramolecular mechanism.

[0038] In the developed block copolymer, due to the presence of a covalent bond, the flocculation mechanism occurs as a two-stage process. Upon contact with the suspension, the graft polymer block (A), which has a high affinity for the particle surface, is firmly adsorbed onto the colloidal particle. At the same time, the covalently attached linear block (B), due to its flexibility and high molecular weight, is forced to unfold into the solution. This leads to a maximum increase in its hydrodynamic volume. The fully unfolded linear block (B) adsorbs onto another, distant particle, forming an extremely strong and stable bridge. Thus, the function of block (A) is not only to ensure biodegradability but also to create the most favorable conditions for the operation of block (B). It provides an optimal conformation for bridge formation, which the linear polymer would not occupy in a simple mixture.

[0039] This ensures the achievement of a technical result consisting in the implementation of a block copolymer based on a polysaccharide for the purpose of a biodegradable flocculant, which ensures the binding of dispersed particles to form floccules.

[0040] The group of inventions has a set of essential features previously unknown in the prior art, which indicates its compliance with the patentability criterion of “novelty”.

[0041] The group of inventions is unknown in the prior art and does not clearly follow from it. Therefore, the group of inventions meets the patentability criterion of "inventive step."

[0042] The inventions from a group of inventions are interconnected and form a single inventive concept, which indicates that the group of inventions meets the patentability criterion of “unity of invention”.

[0043] Implementation of a group of inventions

[0044] The group of inventions is explained by the following figures.

[0045] Fig. 1 - Conditions for obtaining flocculant, where the following are indicated:

[0046] - polysaccharide type:

[0047] D - dextrin;

[0048] Kr - partially hydrolyzed starch;

[0049] GK - guar gum.

[0050] -monomer type:

[0051] AK - acrylic acid (neutralized);

[0052] AAm - acrylamide;

[0053] METAS - 2-(methacryloyloxy)ethyltrimethylammonium chloride;

[0054] AMPS - 2-acrylamido-2-methylpropanesulfonic acid;

[0055] St - styrene (1 mol.%).

[0056] - method of introducing the block (A):

[0057] In process - introduction after the start of block polymerization (B);

[0058] Before initiator - introduction before the start of polymerization.

[0059] - Polymerization type:

[0060] BP - in aqueous solution;

[0061] IE - invert emulsion.

[0062] - Polymerization mode:

[0063] Iso - isothermal;

[0064] Hell - adiabatic.

[0065] Fig. 2 - Test results of the obtained flocculant.

[0066] To illustrate the possibility of implementation and a more complete understanding of the essence of the group of inventions, an embodiment of it is presented below, which can be changed or supplemented in any way, while the present group of inventions is in no way limited to the presented embodiment.

[0067] The flocculant was obtained in two main stages:

[0068] - a graft polymer block (A) was obtained, which is a graft copolymer based on a polysaccharide;

[0069] - free-radical polymerization of monomers was carried out to form a linear block (B) in the presence of a pre-obtained graft polymer block (A).

[0070] The flocculant production process was carried out using standard chemical synthesis equipment, including a reactor equipped with a stirrer, a heating / cooling system, an inert gas supply system, a reflux condenser and a thermometer.

[0071] Specific examples of the implementation of a group of inventions.

[0072] Below are examples of obtaining flocculant (Fig. 1).

[0073] Example 1.

[0074] Stage 1. Obtaining anionic type graft-polymer block (A).

[0075] The following raw materials were placed in the reactor: a polysaccharide represented by water-soluble dextrin (D), a monomer represented by acrylic acid (AA), a neutralizing agent represented by a 50% aqueous NaOH solution, an initiator represented by ammonium persulfate (APS), and a solvent represented by deionized water. The raw materials were taken in the following quantities: 200 g of dextrin was dissolved in 300 g of water. Separately, 200 ml of acrylic acid was neutralized with an aqueous NaOH solution to a pH of 6.5-7.0.

[0076] Then the dextrin solution and neutralized monomer solution were mixed, bringing the total volume of the reaction mixture to 1.0 L with water. The mixture was heated to 65°C. The reaction mixture was degassed by bubbling with an inert gas (nitrogen) for 15 minutes. After this, an aqueous solution of the initiator (0.10 g APS in 5 ml of water) was added. The polymerization process was carried out at 65°C for 120 minutes with constant stirring. Upon completion, the reaction was stopped by cooling to 25°C and adding 0.20 g of anhydrous sodium sulfite. This resulted in an aqueous solution of the graft polymer block (A).

[0077] Step 2. Obtaining a flocculant. 200 ml of the monomer for the linear block (B), a 40% aqueous solution of acrylamide (AAm), was placed in the reactor vessel. The solution was heated to 65°C and degassed with an inert gas for 15 minutes. Polymerization was then initiated by adding an aqueous solution of ammonium persulfate (0.10 g in 5 ml of water). 5-10 minutes after adding the initiator, when signs of reaction (increased viscosity) appeared, 200 ml of the graft polymer block (A) solution obtained in Step 1 was added to the reaction mixture. The mixture was vigorously stirred for 5 minutes to homogenize, after which polymerization was continued at 65°C for another 120 minutes. At the end of the process, the reaction mass was cooled to 25°C and stabilized by adding anhydrous sodium sulfite.

[0078] Examples 2-9 of flocculant production were carried out similarly to Example 1 in accordance with the data summarized in the table (Fig. 1). The production process for each of Examples 2-9 was accompanied by the following changes.

[0079] At stage 1 of obtaining the graft-polymer block (A), the type and ratio of raw materials, as well as the process conditions, were changed.

[0080] In addition to dextrin (D), partially hydrolyzed starch (Kr), guar gum (GK) were also used as a polysaccharide, while it is possible to use dextran, hemicellulose and other polysaccharides.

[0081] In addition to acrylic acid (AA), acrylamide (AAm), 2-(methacryloyloxy)ethyltrimethylammonium chloride (METAC), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) were also used as the grafting monomer.

[0082] The mass ratio of the polysaccharide to the monomer was changed so that the content of the polysaccharide chain in the graft polymer block was from 20 to 60 mass%.

[0083] The reaction temperature was varied in the range from 55 to 75°C, and the reaction time was varied in the range from 90 to 180 minutes.

[0084] In step 2 of obtaining the block copolymer, the type and ratio of components, as well as the method of carrying out the process, were changed.

[0085] In addition to acrylamide (AAm), acrylic acid (AA) or its salts, styrene (in an amount of no more than 1 mol%), and (methacryloyloxy)ethyltrimethylammonium chloride (METAC) were also used as a monomer for the linear block (B).

[0086] The ratio of the graft polymer block (A) to the monomer for the linear block (B) was changed so that the content of the block (A) in the final flocculant was from 10 to 50 mass%.

[0087] The method of introducing block (A) was varied: in some examples, it was introduced during polymerization (as in Example 1), while in others, it was added to the reaction mixture before the initiator. Depending on the reaction conditions and the mechanism of chain transfer to the macromolecule, the resulting flocculant can have different architectures. In particular, the graft polymer block (A) can be covalently linked to one linear block (B), forming a diblock structure of the A-B type, or to two linear blocks (B) growing from different sections of block (A), which leads to the formation of a triblock structure of the B-A-B type.

[0088] In addition to polymerization in an aqueous solution, the process was also carried out using the invert emulsion polymerization (IE) method, where the aqueous phase containing monomers and block (A) was dispersed in a hydrocarbon medium (mineral oil, isoparaffin) in the presence of emulsifiers (for example, sorbitan esters).

[0089] The polymerization process was also carried out in the adiabatic mode (Ad) with a solids content of 30-45 wt.%, which was accompanied by self-heating of the reaction mass by 10-40°C.

[0090] The flocculants obtained in Examples 1-9 had the following physicochemical characteristics:

[0091] - appearance: viscous homogeneous aqueous solution from colorless to light yellow, or milky white invert emulsion.

[0092] - dry matter content, %: 30-50.

[0093] - viscosity in 1 M NaCl, dl / g: 4-20.

[0094] The flocculant obtained in any of the above examples 1-9 can be presented in various commercial forms convenient for transportation, storage, and use. The main ones are described below.

[0095] 1. Commodity form in the form of an aqueous solution

[0096] This form is a product obtained directly by polymerization in an aqueous solution (as in Examples 1-4, 6, 7, 9). It is a viscous, homogeneous aqueous solution (gel) containing 30 to 50% by weight of the developed block copolymer. This form is ready for use after preliminary dilution with water at the site of use to a working concentration (typically 0.05-0.5%). The advantage of this commercial form is ease of dosing and the elimination of the dry product dissolution step.

[0097] 2. Commodity form: invert emulsion

[0098] This form is a product obtained directly by invert emulsion polymerization (as in Examples 5 and 8). The flocculant is a low-viscosity, milky-white liquid, where the dispersed phase (aqueous polymer solution) is stabilized in a continuous hydrocarbon phase (oil). The content of the developed block copolymer in this emulsion is 30-50% by weight. Before use, the emulsion is "activated" (inverted) by rapidly mixing it with a large volume of water in the presence of a special surfactant activator. This releases the polymer and forms a working solution. The advantages of this commercial form include a high polymer concentration and low product viscosity, which facilitates transportation and dosing.

[0099] 3. Commodity form: dry powder

[0100] To obtain the most concentrated commercial form, the aqueous polymer solution or gel, obtained, for example, according to Examples 1-4, is dried using various methods, such as a drum dryer, a fluidized bed, or spray drying. The resulting product is a dry powder or granule, white or light yellow, with a block copolymer content of at least 88-90% by weight. Before use, the dry flocculant is dissolved in water using specialized solution preparation equipment, ensuring uniform wetting of the particles and preventing the formation of gel lumps. The advantages of this commercial form include maximum concentration and a long shelf life.

[0101] The choice of a specific product form is determined by the customer’s requirements and storage conditions, as well as the equipment available at the facility for preparing working solutions.

[0102] Confirmation of achievement of the technical result by the developed flocculant

[0103] The flocculants obtained in Examples 1-9 were tested to evaluate their technical performance in comparison with a control sample (prototype), which was a graft copolymer. To obtain the control sample, 40 g of dextrin and 800 ml of deionized water were placed in a reactor, heated to 40°C, and degassed with nitrogen for 30 minutes. Then, 60 g of acrylamide were added to the reactor. After the monomer was completely dissolved, 20 ml of a 0.1 M solution of cerium (IV) nitrate in 1 M nitric acid were added to the reaction mixture. The reaction was carried out at 40°C for 3 hours. As a result, a viscous solution of the graft copolymer of dextrin and polyacrylamide was obtained. A distinctive feature of this method is that the resulting product is final and does not undergo a second polymerization stage to form a linear block.

[0104] Experiment Description

[0105] 1. Evaluation of flocculation efficiency.

[0106] The performance was evaluated on three different model systems to demonstrate the versatility and superiority of the developed flocculants.

[0107] 1.1 Test on inorganic suspension (kaolin).

[0108] A model kaolin suspension with a concentration of 5 g / L was prepared. A working flocculant solution was added to the suspension at a dosage of 2 mg / L. Efficiency was assessed by the residual turbidity of the supernatant (NTU) after 5 minutes of sedimentation.

[0109] 1.2. Organic Slurry (Coal Sludge) Test:

[0110] A model coal slurry suspension with a concentration of 10 g / L was prepared. A working flocculant solution was added to the suspension at a dosage of 2 mg / L. Efficiency was assessed by the residual turbidity of the supernatant (NTU) after 5 minutes of sedimentation.

[0111] 1.3. Test on model oil-containing water:

[0112] An oil-in-water emulsion simulating industrial wastewater was prepared. Mineral oil (100 mg / L) and bentonite (50 mg / L) were added to 1 liter of water containing 5 g / L NaCl. The mixture was dispersed until a stable emulsion was obtained. A working flocculant solution (5 mg / L) was added to the emulsion. Efficiency was assessed using two parameters: residual turbidity (NTU) and residual oil content (mg / L).

[0113] 2. Biodegradability assessment

[0114] The evaluation was carried out based on the decrease in viscosity of a 0.5% flocculant solution after its treatment with the corresponding enzyme (α-amylase or cellulase) for 24 hours at 37°C.

[0115] The results of comparative tests of flocculants obtained according to Examples 1-9 and control sample K1 are presented in the table in Fig. 2.

[0116] Result Analysis and Conclusion

[0117] The analysis of the data presented in Fig. 2 clearly confirms the achievement of the technical result.

[0118] In particular, on classical models of inorganic (kaolin) and organic (coal sludge) suspensions, the flocculants in Examples 1–9 demonstrate significantly higher efficiency. Residual turbidity with their use is lower than with the prototype polymer (Example K1). This confirms that the proposed block copolymer architecture of the developed flocculant significantly improves the mechanism of bridging and particle capture.

[0119] The results of tests on a complex oil-containing emulsion are particularly revealing. Here, the developed flocculant demonstrates not just flocculation, but a comprehensive effect, including concentration and the formation of a layer of oil product on the surface of the purified emulsion. The result is both profound water clarification and effective removal of the oil products themselves, as the prototype structure proves virtually ineffective for such a complex task.

[0120] It should be noted that despite the improved functional characteristics, the developed flocculants fully maintain a high level of biodegradability comparable to the prototype (within statistical error). This demonstrates that the developed flocculant is both highly effective and environmentally safe.

[0121] Thus, it has been experimentally confirmed that the developed group of inventions makes it possible to obtain a new class of polymer flocculants, which, thanks to their block copolymer structure, make it possible to repeatedly improve flocculating capacity while maintaining biodegradability due to the resulting molecular architecture.

Claims

1. A polysaccharide-based flocculant characterized in that it contains a block copolymer containing at least two covalently linked polymer blocks, wherein: - at least one of the said blocks is a graft-polymer block (A) comprising a polysaccharide chain and chains grafted to it based on acrylic acid or its derivatives; - at least one other block is a linear polymer block (B) obtained by polymerization of at least one monomer capable of free-radical polymerization.

2. The flocculant according to claim 1, characterized in that the polysaccharide chain is selected from a group comprising at least: dextrin, partially hydrolyzed starch, dextran, hemicellulose, natural gums.

3. The flocculant according to claim 1, characterized in that the grafted chains are obtained by polymerization of monomers selected from the group comprising at least: acrylic acid, acrylamide, their salts and / or esters.

4. The flocculant according to claim 1, characterized in that the linear polymer block (B) is obtained by polymerization of monomers selected from the group comprising at least: acrylic acid, acrylates, acrylamides, styrene and its derivatives.

5. A flocculant according to claim 4, characterized in that the content of styrene and / or its derivatives does not exceed 1 mol.% of the content of block monomers (B).

6. A flocculant according to claim 1, characterized in that the content of the polysaccharide chain in the graft-polymer block (A) is from 20 to 60 mass%, and the content of chains grafted to it based on acrylic acid derivatives is from 40 to 80 mass%.

7. The flocculant according to claim 6, characterized in that the content of the polysaccharide chain in the graft-polymer block (A) is from 30 to 50 mass%, and the content of chains grafted to it based on acrylic acid derivatives is from 50 to 70 mass%.

8. The flocculant according to claim 1, characterized in that the content of the graft polymer block (A) is from 10 to 50 mass%, and the content of the linear polymer block (B) is from 50 to 90 mass%.

9. The flocculant according to claim 8, characterized in that the content of the graft polymer block (A) is from 20 to 40 mass%, and the content of the linear polymer block (B) is from 60 to 80 mass%.

10. The flocculant according to claim 1, characterized in that the graft-polymer block (A) is covalently linked to one or two linear blocks (B).

11. A flocculant according to claim 1, characterized in that it is presented in the form of an aqueous solution or gel, in which the content of the said block copolymer is from 30 to 50% by weight.

12. The flocculant according to claim 1, characterized in that it is made in the form of an invert emulsion, in which the content of the said block copolymer is from 30 to 50% by weight.

13. The flocculant according to claim 1, characterized in that it is made in the form of a dry powder or granules with a content of the said block copolymer in an amount of at least 90% by weight.

14. A method for producing a flocculant, which includes carrying out free-radical polymerization of at least one monomer in the presence of a macromolecular compound, characterized in that said macromolecular compound is a graft polymer comprising a polysaccharide chain and chains grafted to it based on acrylic acid or its derivatives, and a linear polymer block (B) is formed, covalently bonded to said graft polymer block (A).

15. The method according to paragraph 14, characterized in that the free-radical polymerization is carried out in an adiabatic mode.

16. The method according to claim 14, characterized in that the graft polymer block (A) is introduced into the reaction mixture before the introduction of the free-radical polymerization initiator.

17. The method according to claim 14, characterized in that the graft-polymer block (A) is introduced into the reaction mixture during the polymerization process.

18. The method according to paragraph 14, characterized in that the polymerization is carried out by the invert emulsion polymerization method.

19. The method according to claim 14, characterized in that the polymerization is carried out in an aqueous solution with a solids content of 30 to 50% by weight.

20. The method according to paragraph 14, characterized in that the polymerization is carried out at a temperature of 55 to 75°C.

21. Use of a block copolymer in accordance with paragraph 1 as a biodegradable flocculant.

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