A method for clean and efficient separation of components from acid-hydrolyzed fiber residue and high-value utilization of the residual liquid.

Abstract

The present invention relates to a method for cleanly and efficiently separating acid hydrolyzed fiber residue components and performing in-situ polymerization reaction of residual liquid generated in the separation process at room temperature to prepare a flocculant for sewage purification. The method comprises using a low eutectic solvent (DES) method to separate high-purity lignin and cellulose components from the acid hydrolyzed fiber residue, and making full use of the characteristics of the DES residual liquid rich in lignin degradation products after multiple cycles, establishing an autocatalytic system by adding a trace amount of initiator, and performing in-situ polymerization reaction at room temperature to prepare a high-performance flocculant. The present invention is a breakthrough in that the DES residual liquid with severely reduced pretreatment effect is used as a raw material to perform in-situ polymerization reaction at room temperature through an autocatalytic system to prepare an efficient sewage treatment agent, and the high-value utilization of the acid hydrolyzed fiber residue is achieved under the principle of no waste.

Description

Technical Field

[0001] The present invention belongs to the technical field of conversion and application of acid hydrolyzed fiber residue, and relates to a conversion method based on pretreatment of acid hydrolyzed fiber residue with a low eutectic solvent, specifically to efficiently separate the acid hydrolyzed fiber residue to obtain high-purity cellulose and lignin, and at the same time, to highly value-make use of the residual liquid generated in the separation process to prepare a flocculant for sewage purification. Background Art

[0002] With the excessive consumption of non-renewable fossil resources and the increasing global environmental deterioration, people are striving to develop renewable alternative raw materials that can produce fuels and chemicals. Lignocellulosic biomass resources are renewable, carbon neutral, and environmentally friendly. my country is rich in biomass resources. For example, the annual output of straw biomass resources alone has exceeded 700 million tons, which is the main raw material in the textile, food chemical, and biomass energy industries. However, under the current biomass refining model, a large number of by-products are produced while obtaining the target products. For example, when industries such as xylose, oligoxylose, and furfural convert hemicellulose in biomass raw materials into high-value-added chemicals, a large amount of xylose residue, oligoxylose residue, and furfural residue rich in lignin and cellulose are produced. Most of these acid hydrolyzed fiber residues are only used for combustion to generate heat, which not only causes a large amount of greenhouse gas emissions and aggravates environmental pollution, but also the main components (cellulose and lignin) are not fully utilized, resulting in serious waste of resources. Effectively separating the main components of acid hydrolyzed fiber residues and converting them into the required chemicals or materials is the only way to achieve diversified and high-value biomass refining.

[0003] In the traditional biorefining process, a large amount of strong acid, strong base, organic solvent, surfactant, etc. are usually used, which causes serious environmental and economic burdens. Exploring a set of green and efficient pretreatment systems to selectively separate the components of lignocellulosic biomass resources is the basis for realizing the high-value utilization of lignocellulosic biomass resources. In recent years, deep eutectic solvent (DES) as an efficient and easy-to-synthesize green solvent has received extensive attention in the field of lignocellulosic biomass pretreatment. It is worth noting that the recyclability of DES is the key to its becoming a hot topic in the field of biomass pretreatment. However, since some lignin degradation products are difficult to separate from DES solvent by effective means, the pretreatment capacity of DES solvent for lignocellulosic biomass resources after recycling is reduced, so its recycling efficiency and number are limited. In general, the effective recycling number of DES solvent is difficult to exceed ten times, which is also the bottleneck for DES as a green solvent for biomass pretreatment. Unfortunately, there is no report on how to deal with the DES residual liquid with seriously reduced separation effect after multiple cycles of recycling.

[0004] In addition, regardless of the pretreatment method, a large amount of lignin degradation products are produced during the acid hydrolysis fiber residue pretreatment process. They are difficult to separate, obtain and utilize, resulting in a huge waste of resources and environmental pollution. How to make full use of these lignin degradation products with unique aromatic structures and high reactivity still faces huge challenges and opportunities. Converting DES residual liquid rich in lignin degradation products into high value-added products in a highly environmentally and economically beneficial method will surely promote the industrial development of DES solvents in the field of acid hydrolysis fiber residues and even all wood fiber biomass resource pretreatment.

[0005] In addition, most of the existing technologies for preparing lignin-based flocculants are copolymerization systems initiated by thermal decomposition of initiators. This initiation method usually has the disadvantages of complex steps, long reaction time, many side reactions, and the need for heating and condensation equipment. The present invention makes full use of the characteristics of DES residual liquid, that is, it is rich in lignin degradation products and Lewis acids with aromatic structural characteristics, and only a small amount of initiator is added to establish an in-situ autocatalytic system. Lignin degradation products and metal ions can induce initiators to generate free radicals at room temperature, and then induce lignin degradation products and DES components with unsaturated structures to undergo free radical polymerization. Based on the above background, the present invention uses a low eutectic solvent to clean and efficiently separate acid hydrolyzed fiber residues, and uses DES residual liquid to prepare flocculants. After adding a certain amount of initiator, the DES residual liquid can realize in-situ polymerization at room temperature, thereby preparing a high-performance flocculant. The present invention truly realizes the concept of waste-free production, and the raw material demand and energy consumption in the flocculant production process will be greatly reduced, which will help achieve the goal of carbon neutrality as soon as possible. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a green and efficient pretreatment method for acid hydrolysis fiber residue, selectively separate the main components of the acid hydrolysis fiber residue, and specifically subject the DES residual liquid to an in situ polymerization reaction at room temperature through an autocatalytic system to prepare a high-performance flocculant, thereby achieving the full component conversion of wood fiber raw materials on a waste-free principle.

[0007] In order to achieve the above technical objectives, the present invention is specifically implemented through the following technical solutions:

[0008] A method for high-value utilization of DES residual liquid comprises the following steps:

[0009] 1) Mix unsaturated organic acid, unsaturated ammonium chloride and Lewis acid uniformly, heat to 50-120° C., and keep the temperature constant until the system becomes uniform and transparent, thereby obtaining DES;

[0010] 2) mixing the air-dried acid hydrolyzed fiber residue with DES and pre-treating at a certain temperature for a period of time; after DES pre-treatment, pouring the formed dark brown liquid into three volumes of ethanol / water solvent and stirring, vacuum filtering and washing with ethanol / water three times to obtain a cellulose-rich solid;

[0011] 3) the filtrate is rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension is centrifuged to obtain lignin;

[0012] 4) continuing to rotary evaporate the collected supernatant to remove water and obtain a recovered DES solution;

[0013] 5) repeating steps 2)-4) until the separation effect of the DES solvent on the acid hydrolyzed fiber residue is seriously reduced;

[0014] 6) taking the DES residual liquid obtained in step 5) and having a significantly reduced pretreatment effect after multiple cycles of use, directly adding an initiator and deionized water, stirring to completely dissolve it; passing nitrogen gas into the obtained solution to exclude oxygen, after 5-30 minutes, and then reacting at room temperature under a nitrogen atmosphere; after the reaction, adding the solution dropwise into an ethanol solution, standing and precipitating to obtain a precipitate; and washing the precipitate three times with a mixture of anhydrous ethanol and acetone, and freeze-drying to obtain a flocculant.

[0015] Furthermore, the acid hydrolysis fiber residue is at least one of industrial xylose residue, xylo-oligosaccharide residue and furfural residue.

[0016] Furthermore, the DES is composed of unsaturated organic acid, unsaturated ammonium chloride and Lewis acid in a molar ratio of 1-20:1-20:0.01-1.

[0017] Furthermore, the unsaturated organic acid is at least one of acrylic acid, methacrylic acid, cinnamic acid or 4-imidazole acrylic acid, and the unsaturated ammonium chloride is at least one of allyltrimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride and (meth)acryloyloxyethyldimethylbenzylammonium chloride.

[0018] Further, the solid in step 2) is mixed with DES at a mass ratio of 1:10-1:20, and the heating condition is 50-150°C for 1-6 hours. Preferably, the mass ratio of the solid to DES is 1:5-20, and the heating condition is 60-120°C for 2-4 hours.

[0019] Furthermore, the initiator is at least one of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobisisobutyramidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azoisobutylcyanoformamide.

[0020] Furthermore, the initiator accounts for 0.05-1% of the total mass of the reactants.

[0021] Furthermore, the reaction temperature is 25-40°C, and the reaction time is 1-8h.

[0022] It can be seen from the above technical solutions that compared with the prior art, the present invention has at least the following beneficial effects:

[0023] 1. The DES described in the present invention is composed of an unsaturated organic acid as a hydrogen bond donor and an unsaturated ammonium chloride as a hydrogen bond acceptor in a certain molar ratio. Since the components constituting DES all have unsaturated connecting bonds, the lignin degradation products remaining in the DES waste liquid also have high reactivity; in addition, the residual lignin degradation products and the Lewis acid in DES can form a self-catalytic system. Therefore, the DES residual liquid whose separation effect is seriously reduced after multiple cycles only needs to add a small amount of initiator to carry out in-situ polymerization at room temperature to prepare a high-performance flocculant. Compared with other documents or patents, the process of preparing flocculants in this patent does not require heating and excessive use of chemical reagents, and embodies green production in terms of raw materials, preparation process, etc.

[0024] 2. The flocculant preparation method of the present invention successfully prepares an amphoteric flocculant with a stable core skeleton by grafting unsaturated quaternary ammonium salt monomers and unsaturated organic acids in DES residual liquid onto the skeleton of rigid lignin degradation products, and fully utilizes the characteristics of each component in DES residual liquid. The rigid skeleton of lignin degradation products can enhance the bridging and sweeping effect of the flocculant when treating sewage, and the carboxyl and quaternary ammonium salt groups can promote the flocculant to flocculate and precipitate pollutants with different types of charges through charge attraction, so that the flocculant can be applied to multiple fields such as decolorization, sterilization, and turbidity removal.

[0025] 3. The preparation method of the present invention selectively separates the main components of the acid hydrolyzed fiber residue, and retains the integrity of its component structure while efficiently separating, so that the separated lignin and cellulose have high utilization value; in particular, the present invention has a breakthrough in using DES residual liquid with a severely reduced separation effect after multiple cycles of recycling as a raw material to prepare an efficient sewage treatment material, which not only realizes the full component conversion of the acid hydrolyzed fiber residue, but also solves the subsequent treatment problem of DES waste liquid. Compared with other documents or patents, this patent truly realizes the full component utilization of the acid hydrolyzed fiber residue on the principle of no waste, providing a new way for the green and high-value utilization of acid hydrolyzed fiber residue and even all plant fiber resources. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment specifically provides a method for preparing a flocculant based on DES pretreatment acid hydrolysis fiber residue and using the DES residual liquid generated during the pretreatment process, which includes the following steps:

[0030] 1) Preparation of DES solvent: Prepare acrylic acid, methacryloyloxyethyltrimethylammonium chloride and aluminum chloride DES solvent in a molar ratio of 1:1:0.05, and heat and stir the solvent at 80° C. for 1 h to form a transparent solvent.

[0031] 2) DES pretreatment: 3.0 g of xylose residue and 30.0 g of the DES prepared above were added to the reactor and reacted at 115°C for 3 h; after the reaction, the reactor was immediately cooled to room temperature. Subsequently, the dark brown slurry was poured into three times the volume of ethanol / water solvent and stirred, vacuum filtered and rinsed three times with ethanol / water to obtain a cellulose-rich solid. The filtrate was rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension was centrifuged to obtain lignin. The collected supernatant was further rotary evaporated to remove water to obtain a recovered DES solution. The lignin removal rate in this process is nearly 90%. Repeat the above steps until the separation effect of DES solvent on acid hydrolysis fiber residue is seriously reduced.

[0032] 3) Preparation of flocculant: Take 3.5g of DES residual liquid after multiple recycling in step 2), directly add 1.5wt% ammonium persulfate and 1.5mL deionized water, stir to completely dissolve; pass nitrogen gas into the obtained solution for 20min to remove oxygen, then react at 25℃ for 3h in nitrogen atmosphere to carry out in-situ polymerization reaction through autocatalytic system. After the reaction, add the solution dropwise into ethanol solution, let it stand and precipitate to obtain precipitate; wash the precipitate 3 times with a mixture of anhydrous ethanol and acetone, and obtain flocculant after freeze-drying.

[0033] 4) When the flocculant prepared in this example was used to treat a kaolin suspension (the dosage of the flocculant was 4 mg / L and the concentration of kaolin was 0.1 wt%), the removal rate exceeded 99%.

[0034] Example 2

[0035] This embodiment specifically provides a method for preparing a flocculant based on DES pretreatment acid hydrolysis fiber residue and using the DES residual liquid generated during the pretreatment process, which includes the following steps:

[0036] 1) Preparation of DES solvent: Prepare acrylic acid, allyltrimethylammonium chloride and aluminum chloride DES solvent in a molar ratio of 1:1:0.05, and heat and stir the solvent at 80° C. for 1 h to form a transparent solvent.

[0037] 2) DES pretreatment: 3.0 g furfural residue and 30.0 g DES prepared above were added to the reactor and reacted at 120°C for 3 h; after the reaction, the reactor was immediately cooled to room temperature. Subsequently, the dark brown slurry was poured into three times the volume of ethanol / water solvent and stirred, vacuum filtered and rinsed three times with ethanol / water to obtain a cellulose-rich solid. The filtrate was rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension was centrifuged to obtain lignin. The collected supernatant was further rotary evaporated to remove water to obtain a recovered DES solution. The lignin removal rate in this process was nearly 82%. Repeat the above steps until the separation effect of DES solvent on acid hydrolysis fiber residue was seriously reduced.

[0038] 3) Preparation of flocculant: Take 3.5g of DES residual liquid after multiple recycling in step 2), directly add 1.5wt% ammonium persulfate and 1.5mL deionized water, stir to completely dissolve; pass nitrogen gas into the obtained solution for 20min to remove oxygen, then react at 25℃ for 3h in nitrogen atmosphere to carry out in-situ polymerization reaction through autocatalytic system. After the reaction, add the solution dropwise into ethanol solution, let it stand and precipitate to obtain precipitate; wash the precipitate 3 times with a mixture of anhydrous ethanol and acetone, and obtain flocculant after freeze-drying.

[0039] 4) When the flocculant prepared in this example was used to treat a kaolin suspension (the dosage of the flocculant was 4 mg / L and the concentration of kaolin was 0.1 wt%), the removal rate exceeded 93%.

[0040] Example 3

[0041] This embodiment specifically provides a method for preparing a flocculant based on DES pretreatment acid hydrolysis fiber residue and using the DES residual liquid generated during the pretreatment process, which includes the following steps:

[0042] 1) Preparation of DES solvent: Prepare acrylic acid, methacryloyloxyethyltrimethylammonium chloride and ferric chloride DES solvent in a molar ratio of 1:1:0.1, and heat and stir the solvent at 80° C. for 1 h to form a transparent solvent.

[0043] 2) DES pretreatment: 3.0 g of xylose residue and 30.0 g of the DES prepared above were added to the reactor and reacted at 115°C for 3 hours; after the reaction, the reactor was immediately cooled to room temperature. Subsequently, the dark brown slurry was poured into three times the volume of ethanol / water solvent and stirred, vacuum filtered and rinsed three times with ethanol / water to obtain a cellulose-rich solid. The filtrate was rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension was centrifuged to obtain lignin. The collected supernatant was further rotary evaporated to remove water to obtain a recovered DES solution. The lignin removal rate in this process was nearly 87%. Repeat the above steps until the separation effect of the DES solvent on the acid hydrolysis fiber residue was seriously reduced.

[0044] 3) Preparation of flocculant: Take 3.5g of DES residual liquid after multiple recycling in step 2), directly add 1.5wt% ammonium persulfate and 1.5mL deionized water, stir to completely dissolve; pass nitrogen gas into the obtained solution for 20min to remove oxygen, then react at 25℃ for 3h in nitrogen atmosphere to carry out in-situ polymerization reaction through autocatalytic system. After the reaction, add the solution dropwise into ethanol solution, let it stand and precipitate to obtain precipitate; wash the precipitate 3 times with a mixture of anhydrous ethanol and acetone, and obtain flocculant after freeze-drying.

[0045] 4) The flocculant prepared in this example was used to treat the E. coli wastewater (the dosage of the flocculant was 12 mg / L and the concentration of E. coli was 1×10 8 CFU / mL), the removal rate can reach 98.4%, and it has a good sterilization effect;

[0046] Example 4

[0047] This embodiment specifically provides a method for preparing a flocculant based on DES pretreatment acid hydrolysis fiber residue and using the DES residual liquid generated during the pretreatment process, which includes the following steps:

[0048] 1) Preparation of DES solvent: Prepare acrylic acid, allyltrimethylammonium chloride and aluminum chloride DES solvent in a molar ratio of 1:1:0.05, and heat and stir the solvent at 80° C. for 1 h to form a transparent solvent.

[0049] 2) DES pretreatment: 3.0 g of xylose residue and 30.0 g of the DES prepared above were added to the reactor and reacted at 115°C for 3 h; after the reaction, the reactor was immediately cooled to room temperature. Subsequently, the dark brown slurry was poured into three times the volume of ethanol / water solvent and stirred, vacuum filtered and rinsed three times with ethanol / water to obtain a cellulose-rich solid. The filtrate was rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension was centrifuged to obtain lignin. The collected supernatant was further rotary evaporated to remove water to obtain a recovered DES solution. The lignin removal rate in this process is nearly 90%. Repeat the above steps until the separation effect of DES solvent on acid hydrolysis fiber residue is seriously reduced.

[0050] 3) Preparation of flocculant: Take 3.5g of DES residual liquid after multiple cycles in step 2), directly add 1.5wt% potassium persulfate and 1.5mL deionized water, stir to completely dissolve; pass nitrogen gas into the obtained solution for 20min to remove oxygen, then react at 40°C for 3h under nitrogen atmosphere to carry out in-situ polymerization reaction through the autocatalytic system. After the reaction, add the solution dropwise into ethanol solution, let it stand and precipitate to obtain a precipitate; wash the precipitate 3 times with a mixture of anhydrous ethanol and acetone, and obtain the flocculant after freeze-drying.

[0051] 4) When the flocculant prepared in this example was used to treat a kaolin suspension (the dosage of the flocculant was 4 mg / L and the concentration of kaolin was 0.1 wt%), the removal rate exceeded 98.3%.

[0052] Example 5

[0053] This embodiment specifically provides a method for preparing a flocculant based on DES pretreatment acid hydrolysis fiber residue and using the DES residual liquid generated during the pretreatment process, which includes the following steps:

[0054] 1) Preparation of DES solvent: Prepare acrylic acid, dimethyldiallylammonium chloride and ferric chloride DES solvent in a molar ratio of 1:1:0.05, and heat and stir the solvent at 80° C. for 1 h to form a transparent solvent.

[0055] 2) DES pretreatment: 3.0 g furfural residue and 30.0 g DES prepared above were added to the reactor and reacted at 115°C for 3 h; after the reaction, the reactor was immediately cooled to room temperature. Subsequently, the dark brown slurry was poured into three times the volume of ethanol / water solvent and stirred, vacuum filtered and rinsed three times with ethanol / water to obtain a cellulose-rich solid. The filtrate was rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension was centrifuged to obtain lignin. The collected supernatant was further rotary evaporated to remove water to obtain a recovered DES solution. The lignin removal rate in this process is nearly 80%. Repeat the above steps until the separation effect of DES solvent on acid hydrolysis fiber residue is seriously reduced.

[0056] 3) Preparation of flocculant: Take 3.5g of DES residual liquid after multiple recycling in step 2), directly add 1.5wt% azobisisobutylamidine hydrochloride and 1.5mL deionized water, stir to completely dissolve; pass nitrogen gas into the obtained solution for 20min to remove oxygen, then react at 25℃ for 3h under nitrogen atmosphere to carry out in-situ polymerization reaction through autocatalytic system. After the reaction, add the solution dropwise into ethanol solution, let it stand and precipitate to obtain precipitate; wash the precipitate 3 times with a mixture of anhydrous ethanol and acetone, and obtain flocculant after freeze-drying.

[0057] 4) When the flocculant prepared in this example was used to treat a kaolin suspension (the dosage of the flocculant was 4 mg / L and the concentration of kaolin was 0.1 wt%), the removal rate exceeded 92%.

[0058] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that numerous changes, modifications, substitutions and variations may be made to the examples without departing from the principles and spirit of the invention, the scope of the invention being defined by the appended claims and their equivalents.

Claims

1. A method for high-value utilization of DES residual liquid, characterized in that: The following steps are involved: 1) Mix unsaturated organic acid, unsaturated ammonium chloride and Lewis acid uniformly, heat to 50-120° C., and keep the temperature constant until the system becomes uniform and transparent, thereby obtaining a deep eutectic solvent (DES); 2) mixing the air-dried acid hydrolyzed fiber residue with DES and pretreating at a certain temperature for a period of time; After DES pretreatment, the formed dark brown liquid was poured into three volumes of ethanol / water solvent, stirred, vacuum filtered and washed three times with ethanol / water to obtain a cellulose-rich solid; 3) the filtrate is rotary evaporated in a vacuum rotary evaporator to remove ethanol, and the concentrated suspension is centrifuged to obtain lignin; 4) continuing to rotary evaporate the collected supernatant to remove water and obtain a recovered DES solution; 5) repeating steps 2)-4) until the separation effect of the DES solvent on the acid hydrolyzed fiber residue is seriously reduced; 6) taking the DES residual liquid obtained in step 5) and having a significantly reduced pretreatment effect after multiple cycles of use, directly adding an initiator and deionized water, stirring to completely dissolve it; passing nitrogen gas into the obtained solution to exclude oxygen, after 5-30 minutes, and then reacting at room temperature under a nitrogen atmosphere; after the reaction, adding the solution dropwise into an ethanol solution, standing and precipitating to obtain a precipitate; and washing the precipitate three times with a mixture of anhydrous ethanol and acetone, and freeze-drying to obtain a flocculant.

2. The method according to claim 1, wherein the low eutectic solvent is characterized in that the molar ratio of the unsaturated organic acid, the unsaturated ammonium chloride and the Lewis acid is 1-20:1-20:0.01-1.

3. The method according to claim 1, wherein the low eutectic solvent is characterized in that the unsaturated organic acid is at least one of acrylic acid, methacrylic acid, cinnamic acid or 4-imidazole acrylic acid, and the unsaturated ammonium chloride is at least one of allyltrimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and (meth)acryloyloxyethyldimethylbenzylammonium chloride.

4. The method according to claim 1, wherein the acid hydrolyzed fiber residue is characterized in that the acid hydrolyzed fiber residue is at least one of industrial xylose residue, oligoxylose residue, and furfural residue.

5. The method according to claim 1, wherein the preparation reaction is an in-situ autocatalytic copolymerization reaction, characterized in that: The reaction temperature is 25-40°C and the reaction time is 1-8h.

6. The method according to claim 1, wherein the initiator accounts for 0.05-1% of the total mass of the reactants; the initiator is at least one of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobisisobutyramidine hydrochloride, azobisisobutylimidazoline hydrochloride, and azoisobutylcyanoformamide.

7. A flocculant with excellent flocculation performance, characterized in that Obtained according to the preparation method according to any one of claims 1 to 6.