Method for synthesizing carboxymethyl cellulose by slurry method based on novel etherifying agent and application

Abstract

The invention provides a method for synthesizing carboxymethyl cellulose by a slurry method based on a novel etherifying agent and an application, the method comprises the following steps: adding crushed cellulose into a reaction container filled with an organic solvent, stirring, continuously introducing nitrogen into the reaction container, and when the temperature of the reaction container reaches 25-35 DEG C, stirring for 2-3 hours; slowly dropwise adding a sodium hydroxide aqueous solution into the reaction container, keeping the temperature for a period of time, rapidly raising the temperature of the reaction container to 55 DEG C, slowly adding a novel etherifying agent into the reaction container, controlling the temperature of the reaction container to be kept at 55-75 DEG C, placing the reaction container at 65 DEG C after dropwise adding, and keeping the temperature for a period of time; wherein the novel etherifying agent is low-carbon alcohol chloroacetate or chloroacetamide, an acidic material is added into a reaction container to adjust the pH value of a reaction system to 6.5-7.5, washing liquid is used for multiple times to obtain carboxymethyl cellulose, and the novel etherifying agent is adopted to solve the problems of a traditional etherifying agent. And the high-quality and high-substitution-degree carboxymethyl cellulose is prepared.

Description

Technical Field

[0001] The invention relates to a method for synthesizing carboxymethyl cellulose, and in particular to a method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent and application thereof. Background Art

[0002] Cellulose is the most widely distributed and abundant polysaccharide in nature. It has abundant sources and has a long history of processing and utilization by humans. Chemical modification of cellulose is one of the important forms of utilizing cellulose in modern times. At present, chemical modification of cellulose mainly focuses on cellulose etherification and cellulose esterification. Carboxymethylation reaction is a kind of cellulose etherification. The so-called cellulose carboxymethylation generally refers to the sodium carboxymethyl cellulose obtained by alkalization, etherification, neutralization and washing of cellulose. It is a water-soluble salt, usually referred to as carboxymethyl cellulose (CMC). CMC aqueous solution has the functions of thickening, emulsification and suspension. It is widely used in the petroleum, food, medicine, textile and papermaking industries. It is one of the most important cellulose ethers. There are two processes for producing CMC: water-based method and solvent-based method. The water-based method uses water as the reaction medium and is a common technology for producing CMC in the early stage. It is generally used to produce medium and low-end products. The solvent method, also known as the organic solvent method, uses solvent as the reaction medium. According to the amount of solvent used, it can be divided into kneading method and slurry method. The slurry method uses a larger amount of solvent than the kneading method, but the reaction is more uniform and the product performance is better. It is the key synthetic process to be developed.

[0003] The slurry method refers to dispersing the fiber in an organic solvent (generally a low-carbon monohydric alcohol) for alkalization and etherification reactions. The slurry method has high efficiency, few side reactions, and the stability, high degree of substitution and uniform distribution of carboxymethyl groups of the obtained CMC are good. At present, the alkalizing agent used in the alkalization process is mainly a high-concentration aqueous solution of sodium hydroxide, and the etherifying agent used in the etherification reaction is chloroacetic acid or sodium chloroacetate. However, in the actual production process, it is found that when chloroacetic acid is used as the etherifying agent, the temperature of the entire reaction system rises violently during the etherification drop stage, and it is difficult to control the reaction smoothly. At the same time, the viscosity of the reaction system after the etherifying agent is added is large, which is not conducive to effective heat and mass transfer, and it is easy to cause problems such as product gelation, decreased degree of substitution and uneven distribution of carboxymethyl groups. In addition, since chloroacetic acid is a solid, it is necessary to add another solvent to dissolve the chloroacetic acid before it can be easily added to the reaction system. Another etherifying agent, sodium chloroacetate, is insoluble or difficult to dissolve in the organic solvent used in the conventional process, and needs to be dissolved in water. The addition of water will promote the occurrence of side reactions and the decrease in degree of substitution. Therefore, when synthesizing CMC with a degree of substitution of more than 1.0, sodium chloroacetate aqueous solution is generally not used as an etherifying agent, and chloroacetic acid organic solvent solution is often used as an etherifying agent. However, when chloroacetic acid is used as an etherifying agent, there are many disadvantages mentioned above. Therefore, it is extremely necessary to find a new etherifying agent when synthesizing CMC with a degree of substitution of more than 1.0. Summary of the invention

[0004] The purpose of the present invention is to provide a method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent and its application, wherein the novel etherifying agent is used to replace chloroacetic acid to overcome the problems existing in the chloroacetic acid etherifying agent, and high-quality CMC with a degree of substitution of more than 1.0 is synthesized.

[0005] To achieve the above objectives, the present technical solution provides a method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent, comprising the following steps: Dispersing cellulose: adding crushed cellulose into a reaction vessel containing an organic solvent and stirring, and continuously introducing nitrogen into the reaction vessel; Alkalization treatment: When the temperature of the reaction container reaches 25-35°C, slowly add sodium hydroxide aqueous solution into the reaction container and keep it warm for a while; Etherification treatment: quickly raise the temperature of the reaction container to 55°C, then slowly add the new etherifying agent into the reaction container, and control the temperature of the reaction container to be maintained at 55-75°C. After the addition is completed, place the reaction container at 65°C for a period of time, wherein the new etherifying agent is low-carbon alcohol chloroacetate or chloroacetamide; Neutralization washing: Acidic substances are added to the reaction vessel to adjust the pH value of the reaction system to 6.5-7.5, and carboxymethyl cellulose is obtained after multiple washings with washing liquid.

[0006] It should be noted that this scheme uses low-carbon alcohol chloroacetate or chloroacetamide as a new etherifying agent, aiming to solve the problem of intense heat generation of traditional chloroacetic acid etherifying agents during etherification reaction, so as to ensure that the etherification process can be carried out efficiently and smoothly during industrial production. The alkaline hydrolysis reaction of low-carbon alcohol chloroacetate and chloroacetamide in high-concentration alkali solution is relatively mild in exothermicity and can effectively reduce the viscosity of the reaction system, thereby solving a series of problems caused by intense heat generation of chloroacetic acid etherifying agents during etherification reaction, and facilitating the efficient preparation of high-quality carboxymethyl cellulose with a high degree of substitution (greater than 1.0).

[0007] Specifically, in the step of "dispersing cellulose": an organic solvent is used to disperse the cellulose and provide a medium environment for the subsequent alkalization reaction and etherification reaction. Although the particle size of the cellulose after crushing becomes smaller, agglomeration may still occur. In this solution, the crushed cellulose is added to the organic solvent, which can make the cellulose evenly dispersed and avoid agglomeration, thereby ensuring that the subsequent alkalization reaction and etherification reaction can proceed evenly and smoothly.

[0008] In an embodiment of the present scheme, an organic solvent is selected to react chemically with different novel etherifying agents, to not dissolve carboxymethyl cellulose and to be miscible with water to be used as a washing liquid. In some embodiments, the organic solvent is selected from any one of methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, acetone and toluene, or a mixture of several of them.

[0009] Since low-carbon alcohol chloroacetate will undergo alkaline hydrolysis in a high-concentration alkaline solution to generate the corresponding low-carbon alcohol, in order to facilitate the subsequent recovery of the organic solvent, when the new etherifying agent is selected as low-carbon alcohol chloroacetate, the organic solvent is selected from the same low-carbon alcohol as the organic solvent, for example, when the new etherifying agent is selected as ethyl chloroacetate, the corresponding low-carbon alcohol is ethanol, and the organic solvent is selected as ethanol. When the new etherifying agent is selected as chloroacetamide, the organic solvent is selected as methanol or ethanol or a mixture thereof.

[0010] It should be noted that the amount of organic solvent used will affect the viscosity of the entire reaction system. Under the premise that the sodium hydroxide solubility and dosage are determined, the amount of organic solvent used will affect the distribution of sodium hydroxide in the fiber and the degree of fiber crystallization damage, thereby affecting the alkalization reaction efficiency, and ultimately affecting the degree of substitution and other properties of the product. In general, the greater the amount of organic solvent used, the more evenly the carboxymethyl is distributed on the fiber, but the degree of substitution will decrease, and the utilization rate of the alkali is low, which leads to high product cost; on the contrary, the smaller the amount of organic solvent used, the degree of substitution will rise, the utilization rate of the alkali is high, and the product cost will be low, but it will cause the reaction system to have a large viscosity, easy gel, and uneven distribution of carboxymethyl on the cellulose chain during the entire reaction process. Therefore, too much or too little organic solvent will affect the progress of the reaction system. In order to obtain a carboxymethyl cellulose product with good performance and suitable cost, the amount of organic solvent used has a certain suitable range. After experimental exploration by the application team, it is preferred that the weight is used as the calculation standard, and the amount of sodium hydroxide aqueous solution is 180%~250% of the dry weight of cellulose, and the amount of organic solvent is 450%~600% of the dry weight of cellulose.

[0011] In the step of "dispersing cellulose", the crushed cellulose is added to a reaction vessel filled with an organic solvent and stirred. The stirring speed is set to 200-600 rpm and the stirring speed is kept constant until the end of the reaction. Nitrogen is introduced into the reaction vessel for 10-20 minutes and the nitrogen is kept introduced until the end of the reaction. At the same time, the temperature of the reaction vessel is raised to 25-35°C.

[0012] In this scheme, raising the temperature of the reaction vessel to 25-35°C helps improve the dispersibility of cellulose in the organic solvent. The increase in temperature will accelerate the molecular movement of the organic solvent, increase the organic solvent's ability to wet cellulose, make the cellulose particles more easily dispersed, avoid agglomeration, ensure that the subsequent reaction proceeds evenly, and thus improve product quality.

[0013] In the "alkalization reaction" step, when the temperature of the reaction container reaches 25-35°C, slowly drop a 35-60% sodium hydroxide aqueous solution into the reaction container and keep it warm for a period of time, wherein the dropping time is 20-40 minutes and the heat preservation time is 40-80 minutes.

[0014] It should be noted that there is also an appropriate range for the concentration of the alkali solution. A low concentration of the alkali solution will aggravate the side reactions, while a high concentration of the alkali solution will result in undissolved sodium hydroxide existing in the alkali solution, affecting the utilization rate of the alkali.

[0015] In some preferred embodiments, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution of the present solution is preferably 50-60%. Within this range, the viscosity of the reaction system during the reaction can be moderate, which is beneficial for rapid and uniform stirring, effective heat and mass transfer, and can save the amount of organic solvent used.

[0016] In the "etherification reaction" step, the reaction container is heated to 55°C within 10 minutes, and then the new etherifying agent is slowly added into the reaction container. The addition time is 20 to 40 minutes, during which the temperature of the reaction container is controlled to be maintained at 55 to 75°C. After the addition is completed, the reaction container is placed at 65°C for insulation reaction for 2.5 to 4 hours.

[0017] In this scheme, the temperature of the reaction container is quickly raised to 55°C during the etherification reaction stage to provide sufficient energy for the etherification reaction to promote the smooth progress of the etherification reaction. At this temperature, the reaction activity of the new etherification agent and the alkalized cellulose is enhanced, so that the reactant molecules have a higher movement rate and collision frequency at a higher temperature, and the chance of effective collision is increased, thereby accelerating the reaction process and making the carboxymethylation reaction more complete, which is beneficial to increasing the degree of substitution of the product and obtaining a carboxymethyl cellulose product with better performance.

[0018] In addition, the low-carbon alcohol chloroacetate of the present scheme is selected from one or more mixtures such as methyl chloroacetate, ethyl chloroacetate, propyl chloroacetate, isopropyl chloroacetate, butyl chloroacetate, isobutyl chloroacetate, tert-butyl chloroacetate, chloroacetamide, etc., and low-carbon alcohol chloroacetate and chloroacetamide undergo alkaline hydrolysis reaction under high concentration of sodium hydroxide aqueous solution to generate corresponding sodium chloroacetate and corresponding low-carbon alcohol, and this process is carried out step by step, and will not release a large amount of heat as quickly and concentratedly as when chloroacetic acid solution directly participates in the reaction, and chloroacetic acid solution is in the reaction, because its acidity is stronger, hydrogen ions are released quickly when reacting with sodium hydroxide, and a violent exothermic reaction will be caused. And in the alkaline hydrolysis reaction of low-carbon alcohol chloroacetate, energy release is relatively dispersed in multiple steps of ester bond rupture and new substance generation, so that the heating of the overall reaction is relatively mild. At the same time, the low-carbon alcohols (such as methanol, ethanol, etc.) generated by the alkaline hydrolysis reaction play a certain role in dilution and heat dissipation in the reaction system. These alcohols have a high specific heat capacity and can absorb part of the heat generated by the reaction, thereby reducing the temperature rise of the reaction system. The generated sodium chloroacetate can also proceed relatively smoothly in the subsequent etherification reaction with alkalized cellulose, and will not cause drastic temperature changes like the direct reaction of chloroacetic acid.

[0019] It should be noted that appropriately increasing the dosage of the new etherifying agent can increase the number of reactive groups near the alkalized cellulose to promote carboxymethylation. However, excessive new etherifying agent will react with sodium hydroxide to generate a by-product, sodium glycolate, which will not only reduce the carboxymethylation reaction rate but also make subsequent purification of the product difficult. The theoretical dosage of the new etherifying agent is half of the dosage of the alkalizing agent.

[0020] Preferably, the ratio of the amount of the novel etherifying agent to the amount of sodium hydroxide in the scheme of the present invention is 0.43-0.50 (molar ratio). In this scheme, the amount of alkali is set to be slightly excessive to improve the penetration of the alkali in cellulose, and the amount of alkali can be appropriately increased. Taking the novel etherifying agent as isopropyl chloroacetate as an example, the amount of isopropyl chloroacetate is 1.5-1.8 (by weight). Within this preferred range, the degree of substitution of carboxymethyl cellulose sodium salt can be obtained to be 1.0-1.5.

[0021] In the "neutralization washing" step, glacial acetic acid is added to the reaction container to adjust the pH value of the reaction system to 6.5-7.5, and then the washing liquid is used for multiple washings to obtain carboxymethyl cellulose.

[0022] In some embodiments, the washing liquid is a mixed solution of an organic solvent and water, and the organic solvent is the same as the lower alcohol of the lower alcohol chloroacetate.

[0023] It should be noted that the degree of substitution of the carboxymethyl cellulose synthesized by the slurry method based on the new etherifying agent in this scheme is 1.0-1.5, the heat release is mild in the whole synthesis process, the viscosity is small, and it is easy to control, which effectively alleviates the occurrence of gel caused by rapid temperature rise.

[0024] The reaction process of the method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent provided in this scheme is as follows: Cell-OH + NaOH→Cell-ONa + H2O; alkalization reaction ClCH2COOR + NaOH → ClCH2COONa + HOR; ester alkaline hydrolysis reaction (R is a low carbon alkyl group such as methyl, ethyl, isopropyl, etc.) ClCH2CONH2 + NaOH → ClCH2COONa + NH3; amide alkaline hydrolysis reaction C6H7O2(OH)2ONa] n + nClCH2COONa → [C6H7O2(OH)2OCH2COONa] n + nNaCl; etherification reaction.

[0025] Compared with the prior art, this technical solution has the following characteristics and beneficial effects: This scheme replaces the traditional etherifying agent with a new etherifying agent in the slurry process, which can overcome the problem of intense heat release of the traditional etherifying agent during the etherification reaction, and successfully synthesize carboxymethyl cellulose with a degree of substitution of 1.0-1.5, and the carboxymethyl group is more evenly distributed on the cellulose.

[0026] In the slurry method, the alkaline hydrolysis reaction of the new etherifying agent (low-carbon alcohol chloroacetate or chloroacetamide) in high-concentration alkali solution is relatively mild in heat release. Compared with the traditional chloroacetic acid etherifying agent, it avoids the violent heat release during the etherification reaction. In the slurry method, this mild heat release characteristic makes the reaction temperature easier to control, which is beneficial to maintain the stability of the reaction system and reduce product quality problems caused by excessive temperature fluctuations.

[0027] At the same time, the viscosity of the reaction system after using the new etherifying agent is significantly reduced. In the slurry method, moderate viscosity is conducive to the dispersion of cellulose in the organic solvent, ensuring the full mixing and contact of the materials during the reaction, and promoting the heat and mass transfer process. This makes the alkalization and etherification reactions more complete, improves the reaction efficiency, and reduces the risk of gelation caused by high viscosity, ensuring the smooth progress of the reaction and reducing the scrap rate in the production process.

[0028] The reaction process of the new etherification agent reduces the occurrence of side reactions and improves the utilization rate of raw materials (such as cellulose, sodium hydroxide, etc.) in the slurry process system. On the one hand, it reduces production costs, and on the other hand, it reduces the generation of waste, which is in line with the concept of green chemistry and sustainable development. At the same time, reducing side reactions also helps to simplify the subsequent separation and purification steps and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the infrared spectrum of the product of Example 1.

[0030] Figure 2 It is the infrared spectrum of the product of Example 2.

[0031] Figure 3 It is the infrared spectrum of the product of Example 3.

[0032] Figure 4 It is the infrared spectrum of the product of Example 4.

[0033] Figure 5 It is the infrared spectrum of the product of Example 5. DETAILED DESCRIPTION

[0034] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0035] Reagent selection: Cellulose raw material: Cellulose powder purchased from Merck (extracted from woody plant spruce, product number 22182, purity>99.5%, size<150 um). Other reagents were purchased from chemical reagent companies. Sodium hydroxide solution is an aqueous solution of chemically pure sodium hydroxide dissolved in deionized water. Chloroacetic acid alcohol solution refers to a solution of chemically pure chloroacetic acid dissolved in alcohol. For example, chloroacetic acid ethanol solution refers to an ethanol solution of chloroacetic acid dissolved in ethanol.

[0036] Performance Test: Evaluation of the severity of heat release: The volume of the reaction vessel immersed in the water bath and the volume of water in the water bath heating device were strictly controlled each time the experiment was repeated. The temperature at the beginning of the addition of the etherifying agent was taken as the starting temperature, and the temperature at the end of the addition of the etherifying agent was taken as the ending temperature. The temperature difference between the two was used as a simple basis for evaluating the severity of the reaction exotherm.

[0037] Evaluation of important physical and chemical indicators: 2% aqueous solution rotational viscosity, degree of substitution, 1% aqueous solution pH value according to the relevant items of the National Standard of the People's Republic of China GB1886.232-2016, among which the rotational viscosity 3 minutes after the start of the dripping of the etherifying agent is used as the comparison standard.

[0038] The infrared spectrum of the product was obtained by the potassium bromide tablet test using a PerkerElmer Spectrum Two infrared spectrometer. The infrared spectrum shows that the product has no ester bond (no important characteristic absorption peak of methyl group) or amino group (no important characteristic absorption peak of nitrogen-hydrogen bond).

[0039] Embodiment 1: 1. Add 100 parts of the crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent methanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a stirring speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and at the same time raise the temperature in the reaction bottle to within 25°C.

[0040] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0041] 3. Heat the reaction flask to 50°C within 10 minutes, then add 127 parts of the new etherifying agent methyl chloroacetate and 93 parts of methanol to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0042] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0043] Embodiment 2: 1. Add 100 parts of crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent ethanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and heat the reaction bottle to within 25°C.

[0044] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0045] 3. Heat the reaction flask to 50°C within 10 minutes, then add 144 parts of the new etherifying agent chloroacetic acid ethyl ester and 76 parts of ethanol to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0046] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0047] Embodiment three: 1. Add 100 parts of the crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent isopropanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and at the same time raise the temperature in the reaction bottle to within 25°C.

[0048] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0049] 3. Heat the reaction flask to 50°C within 10 minutes, then add 160 parts of a new etherifying agent, isopropyl chloroacetate, and 60 parts of isopropyl alcohol to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0050] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0051] Embodiment 4: 1. Add 100 parts of the crushed fiber into a reaction bottle with a thermometer containing 550 parts of the organic solvent n-butanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a stirring speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and at the same time raise the temperature in the reaction bottle to within 25°C.

[0052] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0053] 3. Heat the reaction flask to 50°C within 10 minutes, then add 176 parts of a new etherifying agent, n-butyl chloroacetate, and 44 parts of n-butyl alcohol to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0054] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0055] Embodiment five: 1. Add 100 parts of crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent ethanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and heat the reaction bottle to within 25°C.

[0056] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0057] 3. Heat the reaction flask to 50°C within 10 minutes, and then add 220 parts of a new etherifying agent 50% chloroacetamide ethanol solution into the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 240 minutes.

[0058] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0059] In order to evaluate the reaction heat of the conventional etherifying agent chloroacetic acid synthesis process and the performance of the synthetic product, a comparative experiment was arranged. Based on the constant molar ratios between the reactants, the amount of chloroacetic acid in the comparative group was adjusted by weight. Comparative Example 1 was compared with Example 1, Comparative Example 2 was compared with Example 2, and so on. The specific comparison scheme is as follows: Comparative Example 1: 1. Add 100 parts of the crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent methanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a stirring speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and at the same time raise the temperature in the reaction bottle to within 25°C.

[0060] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0061] 3. Heat the reaction flask to 50°C within 10 minutes, and then add 220 parts of 50% chloroacetic acid in methanol solution to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0062] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0063] Comparative Example 2: 1. Add 100 parts of crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent ethanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and heat the reaction bottle to within 25°C.

[0064] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0065] 3. Heat the reaction flask to 50°C within 10 minutes, and then add 220 parts of 50% chloroacetic acid ethanol solution to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0066] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0067] Comparative Example 3: 1. Add 100 parts of the crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent isopropanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and at the same time raise the temperature in the reaction bottle to within 25°C.

[0068] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0069] 3. Heat the reaction flask to 50°C within 10 minutes, and then add 220 parts of 50% chloroacetic acid in isopropanol solution to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0070] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0071] Comparative Example 4: 1. Add 100 parts of the crushed fiber into a reaction bottle with a thermometer containing 550 parts of the organic solvent n-butanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a stirring speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and at the same time raise the temperature in the reaction bottle to within 25°C.

[0072] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0073] 3. Heat the reaction flask to 50°C within 10 minutes, and then add 220 parts of 50% chloroacetic acid in n-butanol solution to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 180 minutes.

[0074] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0075] Comparative Example 5 1. Add 100 parts of crushed fiber into a reaction bottle with a thermometer containing 550 parts of organic solvent ethanol, and pass nitrogen into the reaction bottle for 10 minutes, and keep passing nitrogen until the reaction is completed. Start stirring at a speed of 500 rpm, and keep the stirring speed unchanged before the end of the reaction, and heat the reaction bottle to within 25°C.

[0076] 2. When the temperature in the reaction bottle reaches the set range, start to drip 200 parts of 50% sodium hydroxide solution. The dripping time is 20 minutes. After the dripping is completed, keep the temperature at this temperature for another 80 minutes.

[0077] 3. Heat the reaction flask to 50°C within 10 minutes, and then add 220 parts of 50% chloroacetic acid ethanol solution to the reaction flask. The etherifying agent is added for 40 minutes, during which the system is allowed to heat up automatically. After the addition is completed, record the system temperature and keep the reaction at 65°C for 240 minutes.

[0078] 4. After the etherification reaction is completed, add 8 parts of glacial acetic acid to the reaction bottle to adjust the pH value to 6.5-7.5. Discharge the material and wash it several times with 80% ethanol and water mixture to obtain the primary product. Then carry out various physical and chemical index tests.

[0079] Test result analysis: The carboxymethyl cellulose prepared in Examples 1 to 5 was subjected to infrared spectroscopy test, and the infrared spectrum was as follows: Figures 1 to 5 As shown, it can be seen that Examples 1 to 5 all successfully synthesized carboxymethyl cellulose.

[0080] The reaction temperature rise conditions and system viscosities of Examples 1 to 5 and Comparative Examples 1 to 5 are summarized as shown in Table 1 below: Table 1 Reaction temperature rise conditions and system viscosity of different embodiments and comparative examples .

[0081] From the data in Table 1, it can be seen that in the etherification stage, the heat release intensity of chloroacetic acid alcohol ester as etherifying agent is significantly better than that of chloroacetic acid solution as etherifying agent, and the longer the carbon chain of chloroacetic acid alcohol ester, the milder the alkaline release heat of the etherifying agent. This is in line with the law of difficulty of ester alkaline hydrolysis. Compared with short-chain alcohol chloroacetate, chloroacetamide is difficult to alkaline hydrolyze, but the heat release is milder. After adding the new etherifying agent, the viscosity of the reaction system is significantly lower than that of chloroacetic acid as etherifying agent. The reduction in viscosity is conducive to heat transfer and prevents the local temperature from being too high and causing gel to appear; it is conducive to faster dispersion and uniform distribution of the etherifying agent, and more uniform substitution of carboxylmethyl in the cellulose molecular chain.

[0082] The physical and chemical indicators of Examples 1 to 5 and Comparative Examples 1 to 5 are summarized as shown in Table 2 below: Table 2 Physical and chemical indexes of different embodiments and comparative examples .

[0083] The above data show that the main physical and chemical indicators of carboxymethyl cellulose synthesized using the new etherifying agent are basically equivalent to those using chloroacetic acid as the etherifying agent.

[0084] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent, characterized in that: The following steps are involved: Dispersing cellulose: adding crushed cellulose into a reaction vessel containing an organic solvent and stirring, and continuously introducing nitrogen into the reaction vessel; Alkalization treatment: When the temperature of the reaction container reaches 25-35°C, slowly add sodium hydroxide aqueous solution into the reaction container and keep it warm for a while; Etherification treatment: quickly raise the temperature of the reaction container to 55°C, then slowly add the new etherifying agent into the reaction container, and control the temperature of the reaction container to be maintained at 55-75°C. After the addition is completed, place the reaction container at 65°C for a period of time, wherein the new etherifying agent is low-carbon alcohol chloroacetate or chloroacetamide; Neutralization washing: Acidic substances are added to the reaction vessel to adjust the pH value of the reaction system to 6.5-7.5, and carboxymethyl cellulose is obtained after multiple washings with washing liquid.

2. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: The organic solvent is selected from any one of methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, acetone and toluene, or a mixture of several of them.

3. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: When the novel etherifying agent is low-carbon alcohol chloroacetate, the organic solvent is the same low-carbon alcohol; when the novel etherifying agent is chloroacetamide, the organic solvent is methanol or ethanol or a mixture thereof.

4. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: Based on weight, the amount of sodium hydroxide aqueous solution used is 180% to 250% of the dry weight of cellulose, and the amount of organic solvent used is 450% to 600% of the dry weight of cellulose.

5. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: When the temperature of the reaction container reaches 25-35° C., slowly drop a 35-60% sodium hydroxide aqueous solution into the reaction container and keep the temperature for a period of time, wherein the dropping time is 20-40 minutes and the temperature is kept for 40-80 minutes.

6. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: After the reaction container is heated to 55°C within 10 minutes, the new etherifying agent is slowly added into the reaction container, wherein the dropwise addition time is 20 to 40 minutes, during which the temperature of the reaction container is controlled to be maintained at 55 to 75°C. After the dropwise addition is completed, the reaction container is placed at 65°C for insulation reaction for 2.5 to 4 hours.

7. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: The low-carbon alcohol chloroacetate is selected from one or a mixture of methyl chloroacetate, ethyl chloroacetate, propyl chloroacetate, isopropyl chloroacetate, butyl chloroacetate, isobutyl chloroacetate, tert-butyl chloroacetate, chloroacetamide and the like.

8. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: The ratio of the dosage of the novel etherifying agent to that of the sodium hydroxide is 0.43-0.

50.

9. The method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: The degree of substitution of carboxymethyl cellulose is 1.0-1.

5.

10. The use of carboxymethyl cellulose prepared by the method for synthesizing carboxymethyl cellulose by a slurry process based on a novel etherifying agent according to claim 1, characterized in that: Used to synthesize carboxymethyl cellulose with a degree of substitution of 1.0-1.5.

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