WO2020239012A1 - Method for preparing hydroxyethyl cellulose - Google Patents

Abstract

Disclosed is a method for preparing hydroxyethyl cellulose. The method for preparing hydroxyethyl cellulose comprises a process of subjecting a cellulose raw material to alkalization, etherification, pH adjustment, washing and desalination, and solid–liquid separation to obtain hydroxyethyl cellulose, and also comprises the step of adding a precipitant before washing and desalination, and/or also comprises the step of adding a crosslinker between pH adjustment and washing and desalination. The method for preparing hydroxyethyl cellulose inhibits the dissolution and/or delays the dissolution of hydroxyethyl cellulose in water, achieves washing and desalination, and ensures the quality of the product; in comparison with conventional production processes, the washing liquid does not use organic solvents, there is no washing solvent recovery process step, production costs are significantly reduced, and the safety hazards and occupational health risks caused by the use of organic solvents are reduced; furthermore, the washing efficiency is high, one wash can achieve the objective of washing, saving washing time and improving production efficiency.

Description

Method for preparing hydroxyethyl cellulose

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on May 30, 2019, the application number is 201910465188.X, and the invention title is "a method for preparing hydroxyethyl cellulose", the entire content of which is incorporated by reference Incorporated in this application.

Technical field

The invention belongs to the technical field of cellulose, and particularly relates to a method for preparing hydroxyethyl cellulose.

Background technique

Hydroxyethyl cellulose (HEC) is a white or light yellow, odorless, non-toxic fibrous or powdered solid, which belongs to non-ionic soluble cellulose ethers. Because HEC has good thickening, suspending, dispersing, emulsifying, bonding, filming, protecting moisture and providing protective colloids, it has been widely used in petroleum exploration, coatings, construction, medicine and food, textiles, papermaking and polymers Polymerization and other fields.

Ash content, that is, the residual amount of inorganic salts generated during the reaction process is an important parameter to measure the quality of hydroxyethyl cellulose. In order to remove the inorganic salts generated by the reaction, the product needs to be washed repeatedly with washing liquid. "Pharmaceutical and Chemical Industry" 2006 Issue 8 "Synthesis and Application of Hydroxyethyl Cellulose" mentions the use of sodium hydroxide to alkalize cotton fiber, and after etherification, acid is used to neutralize the alkali in the system, and the salt produced is ethanol. Washing 3 to 4 times to remove, the single use of ethanol is 10 times the quality of cotton fiber. With technological innovation, later production of hydroxyethyl cellulose mostly uses alcohol (or ketone, etc.)/water mixed solvents for product washing and purification, where the mass fraction of water is 10%-30%, requiring 3 to 4 washing operations. For another example, the continuous washing process disclosed in the patent application No. 201810007892.6 to produce low ash hydroxyethyl cellulose, the washing liquid used is C1～C3 alcohols with a water mass fraction of 10%-18%. The washing liquid The dosage is to adjust the solid content of the system to 5%-10%. The above washing methods have the problems of large amount of organic solvents in the washing liquid, high washing cost, long recovery period, low production efficiency, and the washing liquid is flammable, and the safety hazard is large. The use of alcohol cannot avoid the occupational health risks of acute and chronic poisoning. .

Summary of the invention

The invention provides a method for preparing hydroxyethyl cellulose with clean production, high production efficiency, low cost and high safety, and solves the problems existing in the prior art.

The technical solutions adopted by the present invention to solve the above technical problems are:

A method for preparing hydroxyethyl cellulose, the method includes the process of preparing hydroxyethyl cellulose by alkalizing, etherifying, adjusting pH, washing and desalting, and solid-liquid separation of cellulose raw materials,

Before washing and removing salt, it also includes the step of adding a precipitating agent, which is a salt that is immiscible with hydroxyethyl cellulose in water;

and / or

After adjusting the pH and washing and removing salt, a step of adding a cross-linking agent is also included, and the cross-linking agent can undergo a cross-linking reaction with the hydroxyethyl cellulose.

Precipitating agent and crosslinking agent can be added to the reaction at one time or in batches. Among them, the salt as a precipitant will weaken the hydrogen bond between water and hydroxyethyl cellulose, dehydrate the hydroxyethyl cellulose, and the molecular chain curls and twists to form a network agglomerated structure to form precipitation in water, inhibiting hydroxyethyl The base cellulose is water-soluble in the subsequent water washing and purification process, and the precipitating agent is dissolved in the washing water, and then the precipitated hydroxyethyl cellulose and the salt dissolved in the water are separated by centrifugation; the cross-linking agent makes the hydroxyethyl cellulose The molecules are bonded and cross-linked to form a water-insoluble network polymer within a certain period of time, delaying the water-soluble time of hydroxyethyl cellulose and realizing pure water washing.

Further, the cation of the water-soluble salt as a precipitating agent is one or more of sodium, iron, ammonium, magnesium, aluminum, and zinc, and the anion is chloride, phosphate, sulfate, sulfite, One or more of nitrate, carbonate and borate; preferably, the salt that is immiscible with hydroxyethyl cellulose in water is selected from disodium hydrogen phosphate, sodium sulfite, magnesium sulfate, aluminum sulfate, and sodium nitrate Any one or more of sodium sulfate, sodium carbonate, and diammonium hydrogen phosphate.

Further, the total amount of the precipitating agent is 0.8 to 1.2 times the mass of the cellulose raw material.

Further, the crosslinking agent is a dialdehyde aqueous solution, preferably a glyoxal aqueous solution with a mass fraction of 30% to 42%, preferably diluted with water to a concentration of 5% to 42%.

Further, the temperature of the cross-linking reaction is 30-35°C, the cross-linking time is 3 to 4 hours, the total amount of cross-linking agent is 0.15-0.3 times the mass of the cellulose raw material, and the time and amount of the cross-linking agent can be Make the hydroxyethyl cellulose molecules deeply cross-linked and prevent the hydroxyethyl cellulose from dissolving in water for a certain period of time.

Further, the washing method is water washing.

Furthermore, the temperature of the soft water for washing is 12-20℃, the pH is 6-7, the amount of soft water is 15-20 times the quality of the cellulose raw material, and the washing time is 5-20min, which ensures the washing efficiency without causing hydroxyethyl. The base cellulose is dissolved in water washing and cannot be separated into solid and liquid. Soft water is water that does not contain or contains less soluble calcium and magnesium compounds.

Further, the cellulose undergoes alkalization and etherification reactions in the solvent, but the solvent needs to be removed before or after the pH is adjusted. The solid-liquid separation method such as centrifugation or pressure filtration can be selected when the solvent is removed; the solvent is selected From one or more of tert-butanol, isopropanol, acetone, and ethylene glycol dimethyl ether. In actual operation, the material needs to be dried after removing the solvent to ensure that the solvent is fully removed.

Furthermore, in the pH adjustment step, the purpose is to neutralize excess alkali and adjust the pH of the reaction mixture to be neutral or weakly acidic.

Further, the precipitation agent is added before the solvent is removed, and the solvent removal method is centrifugal separation. The precipitation agent is a water-soluble salt, which destroys the hydration function of hydroxyethyl cellulose and inhibits the swelling and dissolution of hydroxyethyl cellulose. The precipitant is preferably added before the solvent is removed, because when the solvent is removed by centrifugation, a large amount of electrolyte increases the water content in the liquid phase, while the water content in the solid phase decreases. The low water content and the inhibitory effect of the precipitant make the ethyl acetate Crude cellulose-based products are not prone to material agglomeration and partial dissolution, which is beneficial to the subsequent drying process.

Because the crosslinking reaction occurs under acidic conditions, the crosslinking agent should be added after adjusting the pH. Because the crosslinking agent will form a hemiacetal structure between the alcohol solvent molecules and the hydroxyethyl cellulose molecules, the hemiacetal structure will be de-crosslinked in the subsequent washing process, and the small alcohol molecules will be separated from the hydroxyethyl cellulose molecules. And enter the wastewater; what is more serious is that the small alcohol molecules that are not removed during washing will be carried into the hydroxyethyl cellulose product, which affects the effective content of the product. In addition, if the hydroxyethyl cellulose molecule undergoes a cross-linking reaction and then the solvent is removed and dried, the cross-linked hydroxyethyl cellulose will change color and yellow due to the high temperature during drying, which will affect the product quality. Therefore, when an alcohol solvent is selected for the reaction, the crosslinking agent is preferably added after the alcohol solvent is removed, and more preferably after the alcohol solvent is removed and the temperature is dried and cooled to prevent the alcohol molecules from affecting the hydroxyethyl cellulose. The impact of the product.

The invention has the following advantages:

Some cellulose ether products, such as hydroxypropyl methyl cellulose, have high temperature gel properties and can be washed with hot water. However, hydroxyethyl cellulose does not have high-temperature gel properties. In the traditional process, pure water cannot be used to wash products. Only alcohol (or ketone)/water mixed solvents can be used for washing. The amount of organic solvents is large, solvent recovery is required, and the production cost is high. And in terms of safety, there is a risk of flammability and explosion. The present invention formulates a production process based on the properties of hydroxyethyl cellulose. By adding a precipitating agent and/or a cross-linking agent during the reaction process, and specifically adjusting the washing parameters, the hydroxyethyl cellulose inhibits dissolution and/or in water. Or delay the dissolution to achieve water washing and desalination, ensuring the quality of the product. Compared with the traditional production process, the washing liquid does not use organic solvents and there is no washing solvent recovery process, the production cost is significantly reduced, and the safety hazards caused by the use of organic solvents are reduced. And occupational hygiene risks, and the washing efficiency is high, one washing can achieve the purpose of washing, saving washing time and improving production efficiency.

Detailed ways

In order to explain the overall concept of the application more clearly, a detailed description will be given below by way of examples. In the following description, a lot of specific details are given in order to provide a more thorough understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features known in the art are not described.

Example 1:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 500kg of sodium sulfite and 160kg of flake caustic soda into the reaction kettle, mix well with the solvent, add 700kg of cotton fiber, and carry out alkalization reaction at 18℃ for 1h; add 800kg of ethylene oxide and carry out etherification reaction at 65℃ for 2.5h , Get crude hydroxyethyl cellulose. Then add 300kg of sodium sulfite into the reactor, and after mixing uniformly, add hydrochloric acid to neutralize the excess alkali, and the obtained slurry I contains 230kg of sodium chloride (theoretical calculation value);

B. Slurry I enters the centrifuge, solid-liquid separation, powder I and solvent are obtained;

C. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

D. The powder II enters the washing kettle, add 14T soft water with a temperature of 18°C and a pH value of 6.7, and stir for 20 minutes to obtain slurry II;

E. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅲ and waste water are obtained;

F. The powder Ⅲ enters the dryer for drying to obtain the finished product hydroxyethyl cellulose.

After detection and calculation, the ash content of the obtained hydroxyethyl cellulose product is 2.9%, and the product yield reaches 94%.

In this embodiment, part of the precipitating agent is added before alkalization, because the presence of electrolyte will reduce the amount of free alkali to a certain extent, improve the alkalization effect, thereby improving product quality and inhibiting side reactions. In addition, due to the relatively low water content of the materials in the alkalization and etherification stages, too much electrolyte may be partially insoluble due to oversaturation, and solids sink to the bottom of the reactor and unevenly dispersed. Therefore, the precipitation agent is divided Add in one time, that is, the remaining precipitant is added after etherification, and new water will be generated during the subsequent neutralization, which can dissolve this part of the precipitant.

Example 2:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 160kg of solvent and flake caustic soda into the reaction kettle, add 700kg of cotton fiber after mixing, and carry out alkalization reaction at 18℃ for 1h; add 800kg of ethylene oxide and carry out etherification reaction at 65℃ for 2.5h to obtain hydroxyl For crude ethyl cellulose, after adding acetic acid to neutralize excess alkali, the obtained slurry I contains 320 kg of sodium acetate (theoretical calculation value);

B. Add 600kg of disodium hydrogen phosphate to the reaction kettle and stir for 20 minutes to obtain slurry II;

C. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅰ and solvent are obtained;

D. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

E. The powder Ⅱ enters the washing kettle, add 11T of soft water with a temperature of 19°C and a pH value of 6.5, and stir for 5 minutes to obtain slurry Ⅲ;

F. Slurry Ⅲ enters the centrifuge, solid-liquid separation, powder Ⅲ and waste water are obtained;

G. The powder Ⅲ enters the dryer for drying to obtain the finished product hydroxyethyl cellulose.

After detection and calculation, the ash content of the obtained hydroxyethyl cellulose product is 4.7%, and the product yield reaches 95%.

Example 3:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 160kg of solvent and flake caustic soda into the reaction kettle, add 700kg of cotton fiber after mixing, and conduct alkalization reaction at 18°C for 1h. Add 800 kg of ethylene oxide, and carry out etherification reaction at 65° C. for 2.5 hours to obtain crude hydroxyethyl cellulose. After adding nitric acid to neutralize the excess alkali, the obtained slurry I contains 340 kg of sodium nitrate (theoretical calculation value);

B. Add 200kg of disodium hydrogen phosphate and 500kg of sodium sulfite to the reaction kettle, and stir for 30 minutes to obtain slurry II;

C. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅰ and solvent are obtained;

D. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

E. The powder Ⅱ enters the washing kettle, add 12T of soft water with a temperature of 20°C and a pH value of 6.4, and stir for 10 minutes to obtain slurry Ⅲ;

F. Slurry Ⅲ enters the centrifuge, solid-liquid separation, powder Ⅲ and waste water are obtained;

G. The powder Ⅲ enters the dryer for drying to obtain the finished product hydroxyethyl cellulose;

After detection and calculation, the ash content of the obtained hydroxyethyl cellulose product is 4.0%, and the product yield reaches 95%.

In Examples 1-3 of the application of the present invention, by adding a precipitating agent during the reaction, the water solubility of hydroxyethyl cellulose is inhibited, and the salt generated by the reaction is removed by washing with water. The comparison between the production process described in the "Synthesis and Application of Hydroxyethyl Cellulose" in "Pharmaceutical and Chemical Industry" 2006 issue 8 and the production process of Examples 1-3 of the present application is shown in Table 1.

Table 1 Comparison between the production process of Examples 1-3 of the present application and the traditional process

It can be seen from Table 1 that the production process of the present invention changes the dissolution of hydroxyethyl cellulose in water by adding a precipitant, and cooperates with the water temperature and time of the washing process to achieve complete washing and desalination.

Example 4:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 160kg of solvent and flake caustic soda into the reaction kettle, add 700kg of cotton fiber after mixing, and carry out alkalization reaction at 18℃ for 1h; add 800kg of ethylene oxide and carry out etherification reaction at 65℃ for 2.5h to obtain hydroxyl Crude ethyl cellulose. After adding hydrochloric acid to neutralize excess alkali, the obtained slurry I contains 230 kg of sodium chloride (theoretical calculation value);

B. Slurry I enters the centrifuge, solid-liquid separation, powder I and solvent are obtained;

C. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

D. Cool powder II to 35℃, mix 160kg of 42% glyoxal aqueous solution with 230kg water, spray it in atomization, stir for 4h, keep the temperature at 30～35℃, obtain powder III;

E. The powder Ⅲ enters the washing kettle, add 14T soft water with a temperature of 19℃ and a pH of 6.5, and stir for 20 minutes to obtain slurry Ⅱ;

F. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅳ and waste water are obtained, and the centrifugal operation time is 8 minutes;

G. The powder IV enters the dryer for drying to obtain the finished product hydroxyethyl cellulose.

After detection and calculation, the ash content of the obtained hydroxyethyl cellulose product is 2.8%, and the product yield reaches 95%.

Example 5:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 160kg of solvent and flake caustic soda into the reaction kettle, add 700kg of cotton fiber after mixing, and conduct alkalization reaction at 18°C for 1h. Add 800 kg of ethylene oxide, and carry out etherification reaction at 65° C. for 2.5 hours to obtain crude hydroxyethyl cellulose. After adding acetic acid to neutralize the excess alkali, add 105kg of glyoxal aqueous solution with a mass fraction of 40%, stir for 3h, and maintain the temperature at 30-35°C. The obtained slurry I contains 320kg of sodium acetate (theoretical calculation value);

B. Slurry I enters the centrifuge, solid-liquid separation, powder I and solvent are obtained;

C. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

D. The powder Ⅱ enters the washing kettle, add 11T of soft water with a temperature of 17°C and a pH value of 6.8, and stir for 5 minutes to obtain slurry Ⅱ;

E. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅲ and waste water are obtained, centrifugal operation time is 5 minutes;

F. The powder Ⅲ enters the dryer for drying to obtain the finished product hydroxyethyl cellulose.

After detection and calculation, the ash content of the obtained hydroxyethyl cellulose product is 4.9%, and the product yield reaches 96%.

Example 6:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 160kg of solvent and flake caustic soda into the reaction kettle, add 700kg of cotton fiber after mixing, and carry out alkalization reaction at 18℃ for 1h; add 800kg of ethylene oxide and carry out etherification reaction at 65℃ for 2.5h to obtain hydroxyl Crude ethyl cellulose. After adding nitric acid to neutralize the excess alkali, the obtained slurry I contains 340 kg of sodium nitrate (theoretical calculation value);

B. Slurry I enters the centrifuge, solid-liquid separation, powder I and solvent are obtained;

C. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

D. Cool powder II to 35℃, take 210kg of 30% glyoxal water solution, spray it in atomization, stir for 4h, keep the temperature at 30～35℃, obtain powder III;

E. The powder Ⅱ enters the washing kettle, add 13T of soft water with a temperature of 20°C and a pH of 6.2, and stir for 15 minutes to obtain slurry Ⅱ;

F. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅲ and waste water are obtained, centrifugal operation time is 7 minutes;

G. The powder Ⅲ enters the dryer for drying to obtain the finished product hydroxyethyl cellulose.

After detection and calculation, the ash content of the obtained hydroxyethyl cellulose product is 3.8%, and the product yield reaches 95%.

Under acidic conditions, the two aldehyde groups of glyoxal react with the two hydroxyl groups of hydroxyethyl cellulose to form two hemiacetal structures, that is, crosslinking reaction occurs. Numerous hemiacetal structures are filled between the hydroxyethyl cellulose polymer chains, so that multiple hydroxyethyl cellulose polymer chains form a cross-linked network polymer. The hydroxyethyl cellulose of this structure is not in water. Dissolve. But in water, this cross-linked structure will de-cross-link, that is, the hemiacetal structure is hydrolyzed at a certain rate, until the cross-link is destroyed, the polymer chain is de-cross-linked, and the hydroxyethyl cellulose will quickly dissolve. This phenomenon is called delayed dissolution, and the time before dissolution is the delayed dissolution time. The prolonged dissolution time is greatly affected by the pH value. The prolonged dissolution time in the present invention refers to the prolonged dissolution time under the conditions of room temperature and pH value of 6-7.

Application Examples 4-6 of the present invention prolong the dissolution time of hydroxyethyl cellulose by adding a large amount of crosslinking agent during the reaction process, and realize the removal of the salt generated by the reaction by washing with water. The patent application with application number 201810007892.6 uses waste etherification liquid or C1-C3 alcohols for desalination and washing. The comparison with the production process of Examples 4-6 of the present application is shown in Table 2.

Table 2 Comparison between the production process of Examples 4-6 of the present invention and the traditional process

It can be seen from Table 2 that the production process of the present invention makes the hydroxyethyl cellulose delayed in water-soluble time longer by reasonably designing the amount of cross-linking agent, cross-linking time, and temperature, and cooperates with the water temperature and time of the washing process to achieve complete washing. Desalting.

The method for measuring the delayed dissolution time in Table 2 is: take the crude hydroxyethyl cellulose after cross-linking reaction, remove the solvent, weigh 3g, add 100mL (pH=6, temperature 20℃) of water, use a glass rod Stir evenly and time. When the bubbles rise slowly, it is considered that the hydroxyethyl cellulose begins to dissolve, and this time is the delayed dissolution time.

Example 7:

The method for preparing hydroxyethyl cellulose provided in this embodiment includes the following steps:

A. Add 400kg of sodium nitrate and 160kg of flake caustic soda into the reaction kettle. After mixing with the solvent evenly, add 700kg of cotton fiber and carry out alkalization reaction at 18℃ for 1h; add 800kg of ethylene oxide and carry out etherification reaction at 65℃2.5 h, to obtain crude hydroxyethyl cellulose, then add 200kg of sodium sulfate to the reactor and mix evenly, add hydrochloric acid to neutralize the excess alkali, and the obtained slurry I contains 230kg of sodium chloride (theoretical calculation value);

B. Slurry I enters the centrifuge, solid-liquid separation, powder I and solvent are obtained;

C. The powder I enters the dryer, and the solvent is recovered until no distillate is steamed out to obtain powder II;

D. Cool powder II to 35℃, take 210kg of 30% glyoxal water solution, spray it in atomization, stir for 4h, keep the temperature at 30～35℃, obtain powder III;

E. The powder Ⅲ enters the washing kettle, add 14T of water with a temperature of 19°C and a pH value of 6.5, stir for 20 minutes to obtain slurry Ⅱ;

F. Slurry Ⅱ enters the centrifuge, solid-liquid separation, powder Ⅳ and waste water are obtained, and the centrifugal operation time is 8 minutes;

G. The powder IV enters the dryer for drying to obtain the finished product hydroxyethyl cellulose.

After testing, the ash content of the obtained hydroxyethyl cellulose product was 3.0%, and the product yield reached 97%.

Example 7 uses the precipitant and the crosslinking agent to treat the crude hydroxyethyl cellulose at the same time, changes the dissolution of the hydroxyethyl cellulose in water, and matches the water temperature and time of the washing process to achieve complete washing and desalination.

The product indicators in Examples 1-7 of the present application are tested in accordance with ASTM D2364, the American Society for Testing and Materials standard, and the indicators are shown in Table 3.

Table 3 Product indicators and yields of Examples 1-7 of the present invention

Serial number	Moisture%	Ash content%	1% aqueous solution viscosity cp	Yield%
1	2.4	2.9	2300	94
2	3.6	4.7	2350	95
3	3.2	4.0	2400	95
4	4.2	2.8	2250	95
5	3.6	4.9	2300	96
6	3.0	3.8	2050	95
7	2.6	3.0	2200	97

It can be seen from Table 3 that the ash content of the products in Examples 1-7 of the present application is within 5%, and a high-purity hydroxyethyl cellulose product can be obtained by one washing. The product yield is high, and the water washing does not increase the material loss.

In summary, the production process of the present invention can reduce the washing solvent loss by 50-120 kg, reduce the steam consumption by 2 to 3 tons, and reduce the production cost by producing a single ton of hydroxyethyl cellulose product. Compared with the traditional process, the total amount of washing liquid is reduced by half, and the salt in the product can be effectively removed through one washing, saving washing time by 1 to 2.5 hours, and improving production efficiency.

The above-mentioned specific implementation manners should not be regarded as a limitation to the protection scope of the present invention. For those skilled in the art, any alternative improvements or changes made to the implementation manners of the present invention fall within the protection scope of the present invention.

Anything not described in detail in the present invention is the well-known technique of those skilled in the art.

Claims (12)

1. A method for preparing hydroxyethyl cellulose, said method comprising the process of preparing hydroxyethyl cellulose by alkalization, etherification, pH adjustment, washing and desalination and solid-liquid separation steps of cellulose raw material, characterized in that :

   Before washing and removing salt, it also includes the step of adding a precipitating agent to the precipitation of hydroxyethyl cellulose, where the precipitating agent is a salt that is incompatible with hydroxyethyl cellulose in water;

   or

   Before washing and removing salt, it also includes the step of adding a precipitating agent to the precipitation of hydroxyethyl cellulose. The precipitating agent is a salt that is immiscible with hydroxyethyl cellulose in water. After adjusting the pH to washing and removing salt, it also includes The step of adding a cross-linking agent, which can undergo a cross-linking reaction with hydroxyethyl cellulose;

   In the above two schemes,

   The precipitating agent is a salt that is immiscible with hydroxyethyl cellulose in water. The cation is one or more of sodium, iron, ammonium, magnesium, aluminum, and zinc, and the anion is phosphate, sulfate, and sulfite. , One or more of carbonate and borate; or the precipitating agent is one or two of disodium hydrogen phosphate and diammonium phosphate;

   Cellulose undergoes alkalization and etherification in the solvent, and the solvent is removed before or after the pH is adjusted;

   The precipitation agent is added before the solvent is removed, and the solvent removal method is centrifugal separation.
2. The method for preparing hydroxyethyl cellulose according to claim 1, wherein the cation of the salt that is immiscible with hydroxyethyl cellulose in water is selected from the group consisting of sodium, iron, ammonium, magnesium, aluminum and zinc. One or more, the anion is one or more of phosphate, sulfate, sulfite, carbonate and borate.
3. The method for preparing hydroxyethyl cellulose according to claim 2, wherein the salt that is immiscible with hydroxyethyl cellulose in water is selected from sodium sulfite, magnesium sulfate, aluminum sulfate, sodium nitrate, sodium sulfate and Any one or more of sodium carbonate.
4. The method for preparing hydroxyethyl cellulose according to claim 1, wherein the total amount of the precipitating agent is 0.8 to 1.2 times the mass of the cellulose raw material.
5. The method for preparing hydroxyethyl cellulose according to claim 1, wherein the crosslinking agent is a dialdehyde aqueous solution.
6. The method for preparing hydroxyethyl cellulose according to claim 5, wherein the crosslinking agent is a glyoxal aqueous solution with a mass fraction of 30% to 42%.
7. The method for preparing hydroxyethyl cellulose according to claim 6, wherein the crosslinking agent is an aqueous solution of glyoxal diluted with water to a concentration of 5% to 42%.
8. The method for preparing hydroxyethyl cellulose according to claim 1, wherein the temperature of the cross-linking reaction is 30 to 35°C, the cross-linking time is 3 to 4 hours, and the total amount of cross-linking agent is based on the quality of the cellulose raw material. 0.15 to 0.3 times.
9. The method for preparing hydroxyethyl cellulose according to claim 1, wherein the washing method is water washing.
10. The method for preparing hydroxyethyl cellulose according to claim 9, wherein the temperature of the soft water for washing is 12-20°C, the pH is 6-7, and the amount of soft water is 15-20 times the mass of the cellulose raw material. The time is 5-20min.
11. The method for preparing hydroxyethyl cellulose according to claim 1, wherein the solvent is a solvent, and the crosslinking agent is added after removing the solvent.
12. The method for preparing hydroxyethyl cellulose according to claim 11, wherein the crosslinking agent is added after removing the solvent and drying and cooling.