Sodium carboxymethyl cellulose and its production method, dust suppressant

Abstract

The application belongs to the field of cellulose ethers, and embodiments provide a sodium carboxymethyl cellulose and a preparation method and a dust suppressant thereof. The method comprises the following steps: mixing cellulose, a solid base and a solid etherifying agent to obtain a first mixture; adjusting the humidity of the first mixture by using a humidity adjusting medium to obtain a flowable wet powder body; mechanically activating the wet powder body to obtain a second mixture; performing a heating treatment on the second mixture to cause the second mixture to undergo an alkalization reaction and an etherification reaction; performing a neutralization treatment on the obtained heating treatment product to obtain a neutral mixture; and sequentially performing a dissolution treatment and a purification treatment on the neutral mixture to obtain the sodium carboxymethyl cellulose. The method of the embodiments of the application does not require a large amount of organic solvents such as isopropyl alcohol, thereby reducing the generation of waste liquid and significantly reducing the environmental disposal cost and production safety risk.

Description

Technical Field

[0001] This application relates to the field of cellulose ether technology, and in particular to a sodium carboxymethyl cellulose, its preparation method, and a dust suppressant. Background Technology

[0002] The particle size of dust particles in the dry beach area of ​​iron tailings is mainly distributed between 1μm and 100μm. The surface of the particles is covered with flotation reagent residues and some heavy metal ions, which results in a large specific surface area, high surface energy, and easy suspension in the air by wind disturbance.

[0003] Currently, composite dust suppressants composed of sodium carboxymethyl cellulose, polyacrylamide, and glycerol are commonly used to treat particulate dust. Sodium carboxymethyl cellulose, as a key binder, requires large amounts of organic solvents in its existing preparation methods, resulting in significant wastewater generation and increased subsequent wastewater treatment costs. This makes it difficult to meet the demands of green and large-scale applications.

[0004] It should be noted that the above content is not necessarily prior art, nor is it intended to limit the scope of protection of this application. Summary of the Invention

[0005] This application provides a sodium carboxymethyl cellulose, its preparation method, and a dust suppressant to solve or alleviate one or more of the technical problems mentioned above.

[0006] A first aspect of this application provides a method for preparing sodium carboxymethyl cellulose, comprising the following steps:

[0007] Cellulose, solid alkali and solid etherifying agent are mixed to obtain a first mixture;

[0008] The humidity of the first mixture is adjusted using a humidity-regulating medium to obtain a flowable wet powder;

[0009] The wet powder is mechanically activated to obtain a second mixture;

[0010] The second mixture is heated to cause an alkalization and etherification reaction.

[0011] The product obtained from the heat treatment is neutralized to obtain a neutral mixture;

[0012] The neutral mixture was subjected to dissolution and purification processes in sequence to obtain sodium carboxymethyl cellulose.

[0013] The method of this application first mixes cellulose, solid alkali, and solid etherifying agent in solid form to obtain a first mixture. Then, only a small amount of humidifying medium is added to maintain the humidity of the first mixture, resulting in a flowable wet powder. Next, mechanical activation is used to promote uniform dispersion of the alkali and its transfer into the cellulose, resulting in a second mixture. The second mixture is then subjected to alkalization and etherification reactions under heating conditions to obtain a reaction material containing sodium carboxymethyl cellulose and by-product salts. The heat-treated product is then neutralized, dissolved, and purified to obtain sodium carboxymethyl cellulose. This method, using a solid-state mixing-humidification-reaction (alkalization and etherification) route based on solid alkali and solid etherifying agent to prepare sodium carboxymethyl cellulose, eliminates the need for large amounts of organic solvents such as isopropanol and only requires limited dissolution and purification of the neutral mixture, thereby reducing wastewater generation and significantly lowering environmental disposal costs and production safety risks. Furthermore, the method of this application eliminates the complex unit operations of solvent recovery, distillation, and repeated washing in traditional processes. In summary, this method significantly shortens the process flow, greatly reduces equipment investment and operating energy consumption (especially thermal energy consumption), and is more in line with the requirements of green chemistry and clean production.

[0014] According to embodiments of this application, the solid alkali includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate; the solid etherifying agent includes at least one of sodium monochloroacetate, potassium monochloroacetate, methyl chloroacetate, and ethyl chloroacetate; in the first mixture, the mass ratio of the cellulose, the alkali, and the etherifying agent is 1:(0.30-0.40):(0.80-1.00). Therefore, the alkali and etherifying reactions of the cellulose, the alkali, and the etherifying agent can be fully carried out.

[0015] According to an embodiment of this application, the humidity conditioning medium includes at least one of deionized water, ethanol, and isopropanol; the mass ratio of the humidity conditioning medium to the first mixture is 1:(0.08-0.15). This ensures that the first mixture is adjusted to a flowable wet powder or wet granule state.

[0016] According to an embodiment of this application, the heat treatment temperature is 50°C-70°C, and the heat treatment time is 1.5h-4h. This further promotes the alkalization and etherification reactions, yielding a reactant containing sodium carboxymethyl cellulose.

[0017] According to an embodiment of this application, the neutralization process includes: introducing carbon dioxide or an atomized acid solution into the product obtained from the heat treatment; the acid solution includes at least one of acetic acid solution, citric acid solution, lactic acid solution, and carbonic acid solution. Therefore, after the process is completed, a small amount of neutralization should be performed by introducing carbon dioxide or atomizing a small amount of weak acid solution to adjust the pH of the system to near neutral, thereby reducing the alkalinity of the subsequent solution and avoiding excessive water and salt introduction.

[0018] According to an embodiment of this application, the dissolution process includes: mixing the neutral mixture with water to obtain a mixture; in the mixture, the concentration of sodium carboxymethyl cellulose is 3wt%-8wt%. Therefore, this process eliminates the need for organic solvents, thereby avoiding problems such as the recovery and volatilization loss of waste organic solvents.

[0019] According to an embodiment of this application, the purification process includes: microfiltration of the mixture to obtain a filtrate, with fresh water added as first dialysis water during the microfiltration process; ultrafiltration of the filtrate to obtain a retentate, with fresh water added as second dialysis water during the ultrafiltration process; concentration of the retentate to obtain a concentrate; and drying of the concentrate to obtain sodium carboxymethyl cellulose. This process eliminates the need for large amounts of washing liquid, thereby significantly reducing the generation of saline wastewater and organic wastewater.

[0020] According to embodiments of this application, the microfiltration is ceramic membrane filtration, the pressure of which is 0.1 MPa-0.5 MPa, and the pore size of the ceramic membrane is 20 nm-100 nm; the ultrafiltration is organic membrane filtration, the pressure of which is 1 MPa-3 MPa, and the molecular weight cutoff of the organic membrane is 2 kD-10 kD. This further facilitates microfiltration.

[0021] A second aspect of this application provides sodium carboxymethyl cellulose prepared using the method of the first aspect. This sodium carboxymethyl cellulose is characterized by low salt content and good solubility.

[0022] A third aspect of this application provides a dust suppressant comprising sodium carboxymethyl cellulose, glycerol, and polyacrylamide as described in the second aspect. Based on the mass of the dust suppressant, the sodium carboxymethyl cellulose has a mass fraction of 2%-3%, the glycerol has a mass fraction of 20%-24%, and the polyacrylamide has a mass fraction of 0.3%-0.4%. This dust suppressant is easy to spray and forms a stable and durable solidified shell. Attached Figure Description

[0023] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0024] Figure 1 These are schematic diagrams illustrating the process of preparing sodium carboxymethyl cellulose in some embodiments;

[0025] Figure 2 This is a graph showing the results of the dust suppressant penetration depth test conducted on Example 1b and Comparative Examples 1b-4b.

[0026] Figure 3 The results of water retention tests on the dust suppressants of Example 1b and Comparative Examples 1b-4b are shown in the figure. (a) is the result of the water retention test conducted at 25°C, and (b) is the result of the water retention test conducted at 45°C.

[0027] Figure 4 The graph shows the hardness test results of the dust suppressant crust formation in Example 1b and Comparative Examples 1b-4b.

[0028] Figure 5 The graph shows the wind erosion test results of the dust suppressants in Example 1b and Comparative Examples 1b-4b. Detailed Implementation

[0029] The embodiments of this application are described in detail below. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0030] It should be noted that the terms "first," "second," etc., used in this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a method or product comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these methods or products.

[0031] In this application, when numerical intervals (i.e., numerical ranges) are involved, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, etc.

[0032] Currently, composite dust suppressants composed of sodium carboxymethyl cellulose, polyacrylamide, and glycerol are commonly used to treat particulate dust. Sodium carboxymethyl cellulose, as a key binder, still suffers from the following problems in its existing preparation methods: First, sodium carboxymethyl cellulose is mostly prepared using the traditional isopropanol suspension method. This method results in low solid content, strong dependence on organic solvents, and large solvent consumption, leading to high energy consumption and a heavy burden on solvent recovery. Furthermore, this process easily causes uneven distribution of the degree of substitution in the dust suppressant and batch-to-batch viscosity fluctuations. Second, in the post-reaction processing stage, traditional processes typically require alternating washing of the solid phase with ethanol solution and deionized water until chloride ions are undetectable in the washing liquid and the pH is close to neutral. This reliance on repeated washing for desalination and impurity removal results in numerous washing cycles, high detergent consumption, and the generation of large amounts of high-salt washing wastewater, significantly increasing subsequent treatment costs and failing to meet the requirements of green and large-scale applications.

[0033] Accordingly, a first aspect of the embodiments of this application provides a method for preparing sodium carboxymethyl cellulose. (See reference...) Figure 1 This includes the following steps:

[0034] S100: Cellulose, solid alkali and solid etherifying agent are mixed to obtain a first mixture;

[0035] S200: Adjust the humidity of the first mixture using a humidity-regulating medium to obtain a flowable wet powder;

[0036] S300: Mechanically activate the wet powder to obtain a second mixture;

[0037] S400: The second mixture is heated to cause an alkalization and etherification reaction in the second mixture;

[0038] S500: The product obtained from the heat treatment is neutralized to obtain a neutral mixture;

[0039] S600: The neutral mixture is sequentially dissolved and purified to obtain sodium carboxymethyl cellulose.

[0040] The method of this application first mixes cellulose, solid alkali, and solid etherifying agent in solid form to obtain a first mixture. Then, only a small amount of humidifying medium is added to maintain the humidity of the first mixture, resulting in a flowable wet powder. Next, mechanical activation is used to promote uniform dispersion of the alkali and its transfer into the cellulose, resulting in a second mixture. The second mixture is then subjected to alkalization and etherification reactions under heating conditions to obtain a reaction material containing sodium carboxymethyl cellulose and by-product salts. The heat-treated product is then neutralized, dissolved, and purified to obtain sodium carboxymethyl cellulose. This method, using a solid-state mixing-humidification-reaction (alkalization and etherification) route based on solid alkali and solid etherifying agent to prepare sodium carboxymethyl cellulose, eliminates the need for large amounts of organic solvents such as isopropanol and only requires limited dissolution and purification of the neutral mixture, thereby reducing wastewater generation and significantly lowering environmental disposal costs and production safety risks. Furthermore, the method of this application eliminates the complex unit operations of solvent recovery, distillation, and repeated washing in traditional processes. In summary, this method significantly shortens the process flow, greatly reduces equipment investment and operating energy consumption (especially thermal energy consumption), and is more in line with the requirements of green chemistry and clean production.

[0041] According to an embodiment of this application, in step S100, cellulose, solid alkali, and solid etherifying agent are mixed to obtain a first mixture. This solid-solid mixing process allows the solid alkali, cellulose, and solid etherifying agent to be physically homogeneously mixed in a dry environment, thereby improving the mixing uniformity of the first mixture.

[0042] In some embodiments, the cellulose may be dried prior to mixing, thereby reducing the moisture content of the cellulose and facilitating the mixing of the cellulose, solid alkali and solid etherifying agent.

[0043] In some embodiments, the solid alkali reacts with the hydroxyl groups on the cellulose molecular chain to generate a highly reactive sodium cellulose salt, which is a chemical prerequisite for subsequent etherification reactions (e.g., the reaction of the solid alkali with sodium monochloroacetate). Optionally, the solid alkali includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate.

[0044] In some embodiments, the solid etherifying agent undergoes a nucleophilic substitution reaction with sodium cellulose in the presence of a base. Optionally, the solid etherifying agent includes at least one of sodium monochloroacetate, potassium monochloroacetate, methyl chloroacetate, and ethyl chloroacetate.

[0045] As a specific example, the solid etherifying agent is sodium monochloroacetate and the solid base is sodium hydroxide, so that sodium monochloroacetate, sodium hydroxide and cellulose can react to obtain sodium carboxymethyl cellulose.

[0046] In some embodiments, the mass ratio of the cellulose, the alkali, and the etherifying agent in the first mixture is 1:(0.30-0.40):(0.80-1.00). This allows for sufficient alkalization and etherification reactions among the cellulose, alkali, and etherifying agent.

[0047] According to an embodiment of this application, in step S200, the humidity of the first mixture is adjusted using a humidity-regulating medium to obtain a flowable wet powder. This step is crucial for the solid-phase reaction, minimizing the amount of organic solvent (humidifying medium) used from the source, thereby enabling the solid-phase reaction to proceed in an efficient and controllable wet particle state.

[0048] In some embodiments, the humidity conditioning medium includes at least one of deionized water, ethanol, and isopropanol.

[0049] In some embodiments, the mass ratio of the humidity-conditioning medium to the first mixture is 1:(0.08-0.15). As can be seen from the aforementioned ratio, the amount of humidity-conditioning medium added is trace. This is not to dissolve or disperse the first mixture in large quantities, but rather to adjust the first mixture into a flowable wet powder or wet granule state, thereby ensuring that the overall solid content of the wet powder is not less than 70%. A higher solid content means a significant increase in the effective reactant mass, while minimizing the amount of solvent (humidity-conditioning medium) introduced, thus reducing the amount of subsequent waste liquid to be treated.

[0050] According to an embodiment of this application, in step S300, the wet powder is mechanically activated to obtain a second mixture. In this step, cellulose has a highly crystalline structure and low reactivity; in the high-solids-content wet powder state, the liquid phase is minimal, and the penetration of concentrated alkali is limited. Mechanical activation (such as the intense impact and shearing of a planetary ball mill, or the squeezing and tearing of a kneader) directly and physically disrupts the crystalline structure and hydrogen bonds of cellulose through strong mechanical forces, generating numerous amorphous regions and microcracks; this greatly increases the surface area of ​​contact between the cellulose hydroxyl groups and solid reactants (e.g., NaOH and ClCH2COONa). Mechanical activation, through high-intensity shearing, grinding, and mixing, uniformly "embeds" or "coats" the solid alkali and etherifying agent onto the surface and internal cracks of the mechanically activated cellulose microfibers, thereby reducing the activation energy required for subsequent alkalization and etherification reactions.

[0051] Furthermore, the mechanical activation is carried out under planetary ball milling, kneading, or continuous twin-screw reactive extrusion conditions. Specifically, taking a planetary ball mill as an example, the mechanical activation time is 15 to 120 minutes, preferably 30 to 90 minutes; the revolution speed of the planetary ball mill is 200 to 500 rpm, preferably 300 to 400 rpm.

[0052] According to an embodiment of this application, in step S400, the second mixture is heated to induce an alkalization and etherification reaction. In this step, after mechanical activation in a "high solids content, moist powder" environment, the solid alkali and solid etherifying agent are highly dispersed and embedded within the cellulose. Heating the second mixture (e.g., to 55°C-70°C) first induces solid-state alkalization of the solid alkali with the active hydroxyl groups of cellulose, forming uniform alkali cellulose. Subsequently, the closely contacting solid etherifying agent undergoes solid-state etherification with the alkali cellulose. This sequential, spatially tightly coupled reaction in a quasi-solid phase effectively inhibits the hydrolysis of the etherifying agent (e.g., sodium monochloroacetate), improves the utilization rate of the etherifying agent, and thus makes the reaction pathway more precise and the yield of the target product higher.

[0053] In some embodiments, the temperature of the heat treatment is 50°C-70°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, etc. The heat treatment time is 1.5h-4h, for example, 1.5h, 2h, 3h, 3.5h, 4h, etc. This further promotes the curing and etherification reactions, yielding a reactant containing sodium carboxymethyl cellulose.

[0054] According to this application, in step S500, the product obtained from the heat treatment is neutralized to obtain a neutral mixture. This step, by using gas or atomized acid for neutralization, introduces almost no additional moisture, maintains the high solids state of the system, thereby significantly shortening the subsequent desalination time and reducing the subsequent dialysis water consumption, thus improving the operating efficiency and lifespan of the membrane system.

[0055] In some embodiments, the neutralization process includes: introducing carbon dioxide or an atomized acid solution into the product obtained from the heat treatment, wherein the acid solution includes at least one of acetic acid solution, citric acid solution, lactic acid solution, and carbonic acid solution. Therefore, after the process is completed, a small amount of neutralization should be performed by introducing carbon dioxide or an atomized small amount of weak acid solution to adjust the pH of the system to near neutral, thereby reducing the alkalinity of the subsequent solution and avoiding excessive water and salt introduction. The concentration of the acid solution can also be adjusted according to the actual production process.

[0056] According to this application, in step S600, the neutral mixture is sequentially dissolved and purified to obtain sodium carboxymethyl cellulose.

[0057] In some embodiments, the dissolution process includes mixing the neutral mixture with water to obtain a mixture. In the mixture, the concentration of sodium carboxymethyl cellulose is 3wt%-8wt%. Therefore, this process eliminates the need for organic solvents, thereby avoiding problems such as waste organic solvent recovery and volatilization losses.

[0058] In some embodiments, the purification process includes:

[0059] S601: The mixture is microfiltered to obtain filtrate, and fresh water is added as the first dialysis water during the microfiltration process;

[0060] S602: The filtrate is subjected to ultrafiltration to obtain a retentate, and fresh water is added during the ultrafiltration process as a second dialysis water;

[0061] S603: The retentate is concentrated to obtain a concentrated solution;

[0062] S604: The concentrate is dried to obtain sodium carboxymethyl cellulose.

[0063] Microfiltration removes insoluble mechanical impurities and unreacted substances. Online dialysis (adding the first dialysis water) is performed during microfiltration to maintain system volume and facilitate the removal of soluble small-molecule salts and impurities via the microfiltration membrane. Ultrafiltration membranes efficiently retain large-molecule sodium carboxymethyl cellulose (CMC), while allowing smaller molecules like sodium chloride, sodium glycolate, and water to pass through freely. Even after ultrafiltration, the CMC concentration in the retentate remains low. Concentration (vacuum concentration, such as evaporation) or membrane concentration (such as nanofiltration) increases the solids content to a suitable level for drying, significantly reducing the amount of water required for subsequent evaporation and saving considerable steam or electricity. Drying the desalted and concentrated solution (spray drying or fluidized bed drying) yields a highly soluble, low-salt, uniformly sized powdered sodium carboxymethyl cellulose product. Furthermore, this process eliminates the need for large amounts of washing liquid, significantly reducing the generation of saline and organic wastewater.

[0064] Furthermore, the microfiltration is a ceramic membrane filtration, the pressure of the microfiltration is 0.1MPa-0.5MPa, and the pore size of the ceramic membrane is 20nm-100nm.

[0065] Furthermore, during the microfiltration process, the amount of the first dialysis water added is 0.05 to 0.15 times the volume of the feed liquid in the microfiltration section.

[0066] Furthermore, the ultrafiltration is organic membrane filtration, the ultrafiltration pressure is 1-3 MPa, and the molecular weight cutoff of the organic membrane is 2kD-10kD.

[0067] Furthermore, during the ultrafiltration process, the amount of the second dialysis water added is 4 to 6 times the volume of the retained liquid.

[0068] Furthermore, using conductivity or chloride ion content as the desalination endpoint criterion, small ions and molecules such as sodium chloride and sodium glycolate continuously migrate to the permeate.

[0069] In some embodiments, the permeate produced during the ultrafiltration process is further subjected to evaporation crystallization or salt separation crystallization to recover salts.

[0070] A second aspect of this application provides sodium carboxymethyl cellulose prepared using the method of the first aspect. This sodium carboxymethyl cellulose is characterized by low salt content and good solubility.

[0071] A third aspect of this application provides a dust suppressant comprising sodium carboxymethyl cellulose, glycerol, and polyacrylamide as described in the second aspect. Based on the mass of the dust suppressant, the mass fraction of sodium carboxymethyl cellulose is 2%-3%, the mass fraction of glycerol is 20%-24%, and the mass fraction of polyacrylamide is 0.3%-0.4%. This dust suppressant uses sodium carboxymethyl cellulose as a binder, glycerol as a wetting agent, and polyacrylamide as a coagulant. By controlling the proportions of these three components, the viscosity of the dust suppressant solution is moderate, resulting in low surface tension, excellent wettability, and strong agglomeration and crusting ability. This dust suppressant is easy to spray and can form a stable and durable solidified crust.

[0072] Furthermore, the dust suppressant also includes water. Based on the mass of the dust suppressant, the mass fraction of sodium carboxymethyl cellulose is 2%-3%, the mass fraction of glycerol is 20%-24%, the mass fraction of polyacrylamide is 0.3%-0.4%, and the balance is water.

[0073] Furthermore, at room temperature, the viscosity of the dust suppressant is 30 mPa·s-40 mPa·s.

[0074] Furthermore, the surface tension of the dust suppressant is controlled at approximately 56 mN / m to 60 mN / m.

[0075] Exemplary embodiments according to this application will now be described in more detail with reference to the accompanying drawings. It should be understood that these exemplary embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0076] Example 1a

[0077] (1) Mix 100g of cellulose, 35g of solid sodium hydroxide and 90g of solid etherifying agent (sodium monochloroacetate) to obtain a first mixture;

[0078] (2) Adjust the humidity of the first mixture using a humidity-regulating medium (20g of deionized water) to obtain a flowable wet powder;

[0079] (3) The wet powder is mechanically activated in a planetary ductile iron mill to obtain a second mixture;

[0080] (4) The second mixture is heated to cause alkalization and etherification reactions. The heating time is 3 hours and the temperature is 65°C.

[0081] (5) Carbon dioxide is introduced into the product obtained in step (4) to obtain 239g of neutral mixture;

[0082] (6) The neutral mixture is mixed with water to obtain a mixture, wherein the concentration of sodium carboxymethyl cellulose in the mixture is controlled to be 5 wt%;

[0083] (7) The mixture is microfiltered to obtain filtrate, and fresh water is added as first dialysis water during the microfiltration process (the amount of first dialysis water added is 0.10 times the volume of the microfiltration feed liquid). The microfiltration is ceramic membrane filtration, the pressure of the microfiltration is 0.3 MPa, and the pore size of the ceramic membrane is 50 nm.

[0084] (8) The first filtrate is subjected to ultrafiltration to obtain a retentate, and fresh water is added as a second dialysis water during the ultrafiltration process (the amount of the second dialysis water added is 5 times the volume of the retentate). The pressure of the ultrafiltration is 2 MPa, and the molecular weight cutoff of the organic membrane is 2 kD.

[0085] (9) The retentate is vacuum concentrated to obtain a concentrate; the concentrate is spray dried to obtain 132g of sodium carboxymethyl cellulose powder.

[0086] Example 2a

[0087] Sodium carboxymethyl cellulose was prepared according to Example 1a, except that the humidity of the first mixture was adjusted using a humidifying medium (25g) to obtain a flowable wet powder. 130g of sodium carboxymethyl cellulose powder was obtained upon completion of the reaction.

[0088] Example 3a

[0089] Sodium carboxymethyl cellulose was prepared according to Example 1a, except that the humidity of the first mixture was adjusted using a humidifying medium (30g) to obtain a flowable wet powder. 135g of sodium carboxymethyl cellulose powder was obtained upon completion of the reaction.

[0090] Comparative Example 1a

[0091] Place 100g of cellulose in a 3000mL beaker, add about 1000mL of pure water, stir to disperse, and let stand for 30min to remove soluble impurities to obtain a slurry; vacuum filter the slurry, remove the filtrate, wash twice with pure water, 500mL each time, for a total of 1000mL, and set aside the filter residue; add 1500mL of isopropanol to a beaker and place it on a magnetic stirrer, and slowly add the cellulose filter residue while stirring to form a uniform slurry.

[0092] Measure approximately 400g of a 30wt% sodium hydroxide solution using a graduated cylinder and add it to the slurry in three portions while stirring. Stir the slurry at room temperature for 30 minutes to allow the cellulose to uniformly adsorb and disperse the alkali solution. Raise the reaction temperature to 60°C using a water bath while maintaining stirring. Gradually add 150g of sodium monochloroacetate; to prevent local overconcentration, it can be pre-dissolved in a small amount of isopropanol before adding. Control the temperature at 60°C and stir continuously for 3 hours. After the reaction is complete, cool the mixture to room temperature and separate the solid phase using vacuum filtration. Stir continuously while adding 1mol of sodium hydroxide solution. Adjust the pH to approximately 7 with 1 / L acetic acid (or dilute hydrochloric acid); wash the filter residue twice with 70% ethanol (or isopropanol), 500 mL each time, for a total of 1000 mL, to remove unreacted monochloroacetic acid and sodium chloride; then wash repeatedly with pure water five times, 500 mL each time, for a total of 2500 mL, until the filtrate is no longer alkaline (pH≈7); transfer the wet filter residue to an oven and dry at 60°C for 24 hours until constant weight; grind the dried coarse lumps into a uniform powder using a mortar and pestle; pass through an 80-mesh sieve to obtain 108 g of sodium carboxymethyl cellulose powder.

[0093] Test Case A

[0094] The degree of substitution, NaCl content, total amount of organic solvent used in the reaction stage (kg / kg product), and total amount of water / alcohol consumed in the purification stage (kg / kg product) of sodium carboxymethyl cellulose in Examples 1a, 2a, 3a and Comparative Example 1a were measured, and the results are shown in Table 1.

[0095] Degree of substitution: The sample was fully dispersed in ethanol and then acidified with dilute hydrochloric acid to convert sodium carboxymethyl salt into carboxymethyl acid. It was then repeatedly washed with an ethanol-water mixture until no chloride ions were reacted in the washing solution, and then dried at 60°C to constant weight. Approximately 0.5g of the dried sample was accurately weighed and a quantitative excess of standard sodium hydroxide solution was added to completely neutralize the carboxyl groups and allow them to swell completely. Using phenolphthalein as an indicator or a pH meter, the remaining sodium hydroxide was back-titrated with standard hydrochloric acid. The carboxyl content in the sample was calculated based on the actual amount of sodium hydroxide consumed, and then the degree of substitution was calculated.

[0096] NaCl content: Accurately weigh approximately 1.0g of sample, add deionized water to a certain volume, stir and extract for 60min to fully dissolve NaCl; filter or centrifuge to obtain the supernatant; titrate with silver nitrate standard solution to determine the chloride ion content, the indicator method can be the Mohr method with potassium chromate indicator, or potentiometric titration; convert the chloride ion content to NaCl content.

[0097] Total amount of organic solvents used in the reaction stage (kg / kg product): Record the types and masses of all organic solvents added in the reaction stage; calculate the total amount of organic solvents used in the reaction stage using the mass of the final dry basis sodium carboxymethyl cellulose product obtained in the current batch as the denominator.

[0098] Total water consumption during purification (kg / kg product): Record all fresh water entering the system during the purification stage, including water used for solution preparation and dialysis makeup water; if a small amount of alcohol is used for cleaning or maintenance, it should also be included; calculate the total water / alcohol consumption during the purification stage using the dry basis product mass as the denominator.

[0099] Table 1

[0100]

[0101] As can be seen from Table 1 above, Examples 1a to 3a prepared using the high-solids-content solid-phase reaction and membrane desalination route exhibit significant advantages in terms of degree of substitution, residual salt content, and resource consumption. Firstly, the degree of substitution in Examples 1a to 3a is all in the range of approximately 0.88 to 0.94, indicating that under conditions where isopropanol suspension and dispersion is not required, solid-phase mechanical enhancement combined with micro-humidification can still achieve a relatively complete carboxymethylation reaction. Furthermore, the degree of substitution varies little with different amounts of humidification medium, suggesting that this high-solids-content solid-phase process is robust to humidity fluctuations and conducive to obtaining a stable product structure.

[0102] Secondly, the residual NaCl content of the sample in the example was about 0.40 wt% to 0.45 wt%, which was significantly lower than that of Comparative Example 1a, which used traditional alcohol washing and water washing. Even after multiple washes with ethanol or isopropanol and pH adjusted to neutral as the endpoint, the latter two still had high salt residue in the finished product. This indicates that membrane dialysis desalination is more thorough in removing small ion by-product salts and the endpoint is easier to control, thus enabling the production of sodium carboxymethyl cellulose with lower salt content, which is more suitable for subsequent compounding and membrane formation.

[0103] Furthermore, regarding the input of organic solvents during the reaction stage, Examples 1a-3a showed better results than Comparative Example 1a, indicating that replacing repeated washing with ethanol and water with membrane desalination can significantly reduce water and alcohol consumption and waste liquid generation, and organic solvents can be omitted during the reaction stage.

[0104] In summary, the results in the table above demonstrate that the method of this application can significantly reduce NaCl residue while maintaining or improving the degree of substitution, eliminate organic solvent consumption during the reaction stage, and significantly reduce water and alcohol consumption during the purification stage, thereby achieving simultaneous improvement in product quality and green manufacturing performance.

[0105] Examples 1b-5b and Comparative Examples 1b-4b below are used to illustrate the application of sodium carboxymethyl cellulose in dust suppressants.

[0106] Example 1b

[0107] The dust suppressant is controlled based on its mass: glycerol has a mass fraction of 21.78%; sodium carboxymethyl cellulose has a mass fraction of 2.19%; polyacrylamide has a mass fraction of 0.32%; and the remainder is water.

[0108] Example 2b

[0109] The dust suppressant is controlled based on its mass: glycerol has a mass fraction of 24%; sodium carboxymethyl cellulose has a mass fraction of 2%; polyacrylamide has a mass fraction of 0.31%; and the remainder is water.

[0110] Example 3b

[0111] The dust suppressant is controlled based on its mass: glycerol has a mass fraction of 20%; sodium carboxymethyl cellulose has a mass fraction of 2.3%; polyacrylamide has a mass fraction of 0.31%; and the remainder is water.

[0112] Example 4b

[0113] The dust suppressant is controlled based on its mass: glycerol has a mass fraction of 24%; sodium carboxymethyl cellulose has a mass fraction of 2.3%; polyacrylamide has a mass fraction of 0.31%; and the remainder is water.

[0114] Example 5b

[0115] In the dust suppressant, based on the mass of the dust suppressant, the following are controlled: glycerol mass fraction 20%; sodium carboxymethyl cellulose mass fraction 2.15%; polyacrylamide mass fraction 0.3%; and the balance being water.

[0116] Comparative Example 1b

[0117] The dust suppressant is an aqueous solution of glycerol, and the mass fraction of glycerol is 20% based on the mass of the dust suppressant.

[0118] Comparative Example 2b

[0119] The dust suppressant is an aqueous solution of sodium carboxymethyl cellulose, and the mass fraction of sodium carboxymethyl cellulose is 2% based on the mass of the dust suppressant.

[0120] Comparative Example 3b

[0121] The dust suppressant is an aqueous solution of polyacrylamide, and the mass fraction of polyacrylamide is 0.3% based on the mass of the dust suppressant.

[0122] Comparative Example 4b

[0123] The dust suppressant is water.

[0124] Test Case B

[0125] The dust suppressants of Examples 1b-5b and Comparative Examples 1b-4b were tested as follows, and the results are shown in Table 2.

[0126] Dust suppression efficiency: Weigh 30g of tailings dam dust particles and place them in a petri dish. Spray 10ml of the dust suppressant solution prepared in Examples 1b-5b and Comparative Examples 1b-4b onto the surface of the dish. After the dust particles are completely wetted, place them in a constant temperature oven at 25℃ to dry to constant weight. Then, take out the sample and place it on the experimental table. Use a wind erosion test device to continuously blow the dust particles treated with the dust suppressant solution at a wind speed of 11m / s for 30min. Calculate the dust suppression rate using the following formula.

[0127]

[0128] In the formula, W —Dust suppression rate, % M —Dust particle weight, g; m 1—Total weight of dust particles and petri dishes before wind erosion, g; m 2 — Total weight of dust particles and petri dishes after wind erosion, g.

[0129] Surface tension and viscosity: Surface tension was tested according to the plate method in GB / T22237-2008 "Determination of surface tension of surfactants"; viscosity was measured according to the method specified in GB / T10247-2008 "Viscosity measurement method" at a temperature of 25℃.

[0130] Table 2

[0131]

[0132] As shown in Table 2, the viscosity of the dust suppressant solutions prepared in Examples 1b, 2b, 3b, 4b, and 5b of this invention is between 30 mPa·s and 40 mPa·s. This ensures good adhesion while facilitating spraying and prevents clogging of the nozzle due to excessive viscosity. The dust suppression rate is greater than 90%, indicating good dust suppression ability. Comparative Example 1b has too low viscosity, which is not conducive to bonding small-diameter dust particles. Comparative Examples 2b and 3b have good viscosity. The surface tension of Comparative Examples 1b, 2b, and 3b is greater than that of all examples, indicating that the wetting ability of the monomeric dust suppressant solution to dust particles is weaker than that of the composite dust suppressant solution. The dust suppression rate of Comparative Examples 1b, 2b, and 3b is much lower than that of all examples, indicating that the dust suppression effect of the monomeric dust suppressant solution is poor. Comparative Example 4b is worse than all examples and Comparative Examples 2b-3b.

[0133] Figure 2 This diagram shows the results of penetration depth tests on the dust suppressants used in Examples 1b and 1b-4b. Using tailings dam dust particles as the test matrix, the penetration depth of each dust suppressant on the dust surface over time was compared. The results show that at 130 min, the composite dust suppressant solution achieved a penetration depth of approximately 11 cm in the dust sample, significantly higher than the 1.9 cm penetration depth of water and sodium carboxymethyl cellulose solution alone, and also significantly better than the approximately 6.5 cm level of glycerol and polyacrylamide solutions alone. This indicates that the dust suppressant solution of this application achieves good depth penetration while considering viscosity.

[0134] Figure 3 The graph shows the results of water retention tests on the dust suppressants of Example 1b and Comparative Examples 1b-4b. Specifically, from the perspective of water retention, the water loss rate of dust samples after spraying the dust suppressants of Example 1b and Comparative Examples 1b-4b was measured over a certain period of time under two temperature conditions: 25°C and 45°C. Figure 3 Figure (a) shows the results of a water retention test conducted at 25°C. The results indicate that the cumulative water loss rate of the dust sample after spraying the dust suppressant of Example 1b was lower than that of the dust sample after spraying water, indicating that it can effectively slow down the evaporation of free water. Figure 3 Figure (b) shows the results of a water retention test conducted at 45°C. The cumulative water loss rate of the dust sample after spraying the dust suppressant of Example 1b within 8 hours was still lower than that of the dust samples after spraying the dust suppressants of Comparative Examples 1b-4b. This indicates that the dust suppressant of Example 1b has a stronger water retention capacity at high temperatures and can provide more durable moisture and toughness support for the crust layer under the combined action of high temperature and strong wind.

[0135] Figure 4The graph shows the hardness test results of the dust suppressant crust of Examples 1b and Comparative Examples 1b-4b. Specifically, the dust suppressant of Example 1b and the dust suppressant of Comparative Examples 1b-4b were sprayed on dust at 45°C. The five dust samples were dried to constant weight, and the surface hardness of the solidified crust was measured using a Shore hardness tester. The results show that the hardness of the crust of the dust sample obtained after spraying the dust suppressant (Example 1b) can reach more than 60HA, which is much higher than that of the dust samples after spraying glycerol (Comparative Example 1b), sodium carboxymethyl cellulose (Comparative Example 2b), polyacrylamide (Comparative Example 3b), and water (Comparative Example 4b).

[0136] Figure 5 The graph shows the wind erosion test results of the dust suppressants of Example 1b and Comparative Examples 1b-4b. Specifically, the dust suppressants of Example 1b and Comparative Examples 1b-4b were sprayed on dust at 45 ℃. The five dust samples were dried to constant weight and tested using a wind erosion test device. When the wind speed was increased to 7 m / s, 11 m / s and 15 m / s, only the dust suppressant (Example 1b) maintained a dust suppression rate of over 95%, while the dust suppression rates of the dust suppressants of Comparative Examples 1b-4b decreased significantly. This indicates that the solidified shell formed by the dust sample sprayed with the dust suppressant (Example 1b) has excellent integrity and resistance to damage under strong wind conditions and is suitable for strong wind environments in tailings ponds.

[0137] It should also be noted that the terms "some embodiments" or "embodiments" used in this application refer to specific features, structures, or characteristics described in connection with those embodiments, which are included in at least one embodiment described in the general description of this application. The appearance of the same expression in multiple places in the specification does not necessarily refer to the same embodiment. Furthermore, when a specific feature, structure, or characteristic is described in connection with any embodiment, the intention is to suggest that implementing such a feature, structure, or characteristic in conjunction with other embodiments also falls within the scope of this application.

[0138] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0139] It should also be noted that the above are merely preferred embodiments of this application and do not limit the scope of protection of this application. Any equivalent structural or procedural transformations made based on the content of this application’s specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of protection of this application.

Claims

1. A method for preparing sodium carboxymethyl cellulose, characterized in that, Includes the following steps: Cellulose, solid alkali and solid etherifying agent are mixed to obtain a first mixture; The humidity of the first mixture is adjusted using a humidity-regulating medium to obtain a flowable wet powder. The humidity-regulating medium includes deionized water, and the mass ratio of the humidity-regulating medium to the first mixture is (0.08-0.15):

1. The wet powder is mechanically activated to obtain a second mixture; The second mixture is heated to cause an alkalization and etherification reaction. The product obtained from the heat treatment is neutralized to obtain a neutral mixture; The neutral mixture was subjected to dissolution and purification processes in sequence to obtain sodium carboxymethyl cellulose; The dissolution process includes: mixing the neutral mixture with water to obtain a mixture; The purification process includes: microfiltration of the mixture to obtain filtrate, and adding fresh water as the first dialysis water during the microfiltration process; The filtrate is subjected to ultrafiltration to obtain a retentate, and fresh water is added during the ultrafiltration process as a second dialysis water.

2. The preparation method according to claim 1, characterized in that, The solid alkali includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate; The solid etherifying agent includes at least one of sodium monochloroacetate, potassium monochloroacetate, methyl chloroacetate, and ethyl chloroacetate; In the first mixture, the mass ratio of the cellulose, the alkali and the etherifying agent is 1:(0.30-0.40):(0.80-1.00).

3. The preparation method according to claim 1, characterized in that, The temperature of the heat treatment is 50℃-70℃, and the heat treatment time is 1.5h-4h.

4. The preparation method according to claim 1, characterized in that, The neutralization process includes: introducing carbon dioxide or atomized acid solution into the product obtained from the heat treatment; The acid solution includes at least one of acetic acid solution, citric acid solution, lactic acid solution, and carbonic acid solution.

5. The preparation method according to claim 1, characterized in that, In the mixture, the concentration of sodium carboxymethyl cellulose is 3wt%-8wt%.

6. The preparation method according to claim 5, characterized in that, The retentate is concentrated to obtain a concentrated solution; The concentrate was dried to obtain sodium carboxymethyl cellulose.

7. The preparation method according to claim 6, characterized in that, The microfiltration is a ceramic membrane filtration, the pressure of the microfiltration is 0.1MPa-0.5MPa, and the pore size of the ceramic membrane is 20nm-100nm; The ultrafiltration is an organic membrane filtration, the ultrafiltration pressure is 1MPa-3MPa, and the molecular weight cutoff of the organic membrane is 2kDa-10kDa.

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