CN115873135B

CN115873135B - Polyanionic cellulose, and preparation method and application thereof

Info

Publication number: CN115873135B
Application number: CN202111144985.1A
Authority: CN
Inventors: 魏开轩; 王康; 逯贵广
Original assignee: China Petroleum and Chemical Corp; Research Institute of Sinopec Nanjing Chemical Industry Co Ltd
Current assignee: China Petroleum and Chemical Corp; Research Institute of Sinopec Nanjing Chemical Industry Co Ltd
Priority date: 2021-09-28
Filing date: 2021-09-28
Publication date: 2024-06-28
Anticipated expiration: 2041-09-28
Also published as: CN115873135A

Abstract

The invention relates to the field of oilfield chemistry, and discloses polyanionic cellulose, a preparation method and application thereof. The preparation method comprises the following steps: (1) Alkalizing the cellulose raw material to obtain an alkalized product; (2) In the presence of a solvent, carrying out etherification reaction on the alkalization product and a compound etherifying agent, and carrying out post-treatment on the reaction product to obtain polyanionic cellulose; wherein the auxiliary etherifying agent is at least one selected from 4-chlorobenzenesulfonic acid, sodium 4-chlorobenzenesulfonate, sodium 3-chloro-2-hydroxy propane sulfonate and sodium chloroethane sulfonate. The prepared polyanionic cellulose has excellent temperature resistance and filtration reducing performance as a water-based drilling fluid auxiliary agent.

Description

Polyanionic cellulose, and preparation method and application thereof

Technical Field

The invention relates to the field of oilfield chemistry, in particular to a temperature-resistant polyanion cellulose, a preparation method and application thereof.

Background

The polyanionic cellulose is used as a water-soluble ionic cellulose ether, can form viscous solution after being dissolved in water, and has the effects of thickening, dispersing, film forming, bonding, protecting colloid and the like. Based on the characteristics, the polyanionic cellulose is used as a drilling aid in a large amount, can play roles in thickening, improving mud cake quality, reducing fluid loss and the like in drilling fluid, and is an important chemical treatment agent for maintaining stability of the drilling fluid, improving rheological property of the drilling fluid, reducing fluid loss of harmful fluid to stratum, stabilizing well wall, ensuring well diameter rule and protecting hydrocarbon reservoir. The polyanionic cellulose is prepared from natural fibers, belongs to an environment-friendly drilling aid, and is expected to be used more and more in the future along with the improvement of the environment-friendly requirement of the drilling fluid.

At present, along with the reduction of shallow oil gas resources easy to be extracted, china gradually enters a deep oil gas resource extraction stage, along with the increase of drilling depth, the formation temperature is increased, the upper limit of the use temperature of common polyanion cellulose is usually about 100 ℃, and the use temperature is increased continuously to cause degradation failure of the polyanion cellulose, so that the application range of the polyanion cellulose is greatly limited.

CN105566500a discloses a preparation method of particle type polyanionic cellulose, comprising the following steps: (1) Alkalizing cellulose, etherifying, mixing with ethanol water solution, regulating pH, controlling pH to 6.5-8.5, washing, centrifuging to obtain intermediate material; (2) The intermediate material enters a stirrer, the temperature is controlled at 20-60 ℃, deionized water is sprayed onto the intermediate material while stirring, and the stirring is carried out for 40-100min, so as to obtain a primary cellulose product; (3) And drying, drying and crushing the stirred primary cellulose product to obtain the granular polyanionic cellulose. The method aims at solving the problems that polyanionic cellulose is easy to be blocked and difficult to dissolve, and a conventional chloroacetic acid etherifying agent is used.

CN104448010a discloses a process for preparing instant polyanionic cellulose, comprising: (1) Alkalizing cellulose, etherifying, mixing with ethanol water solution, regulating pH, controlling pH to 6.5-8.5, washing, centrifuging to obtain intermediate material; (2) Mixing the intermediate material with ethanol water solution I, adding mixed solution A, and performing crosslinking reaction at normal temperature for 30-80min under stirring; the mixed solution A is formed by mixing glyoxal, an acidic aqueous solution and an ethanol aqueous solution II, wherein the glyoxal dosage in the mixed solution A is 3-8% of the weight of the cellulose, the acidic aqueous solution in the mixed solution A is an acetic acid aqueous solution and/or a citric acid aqueous solution, and the dosage of the acidic aqueous solution is 0.1-1.5% of the weight of the cellulose; (3) And (3) centrifugally separating, drying, crushing and sieving the materials subjected to the crosslinking reaction to obtain the instant polyanionic cellulose. The method solves the problem that common polyanionic cellulose is easy to form fish eyes in the dissolution process, greatly shortens the dispersion dissolution time in water, reduces the on-site drilling fluid slurry preparation time, and adopts the conventional chloroacetic acid etherifying agent in the preparation process.

In conclusion, the current improvement direction of the polyanionic cellulose is mainly developed aiming at material consumption, product morphology and solubility in the production process, the molecular structure of the product is not changed, and the temperature resistance of the product is not greatly improved. Therefore, the polyanionic cellulose with higher temperature resistance is developed, so that the application range of the polyanionic cellulose is widened, and the polyanionic cellulose has important significance for deep oil and gas resource exploitation.

Disclosure of Invention

The invention aims to solve the problems of insufficient temperature resistance and unsatisfactory filtration-loss reduction effect under high temperature conditions of polyanion cellulose prepared by the prior art, and provides polyanion cellulose, a preparation method and application thereof.

In order to achieve the above object, a first aspect of the present invention provides a method for producing a polyanionic cellulose, comprising:

(1) Alkalizing the cellulose raw material to obtain an alkalized product;

(2) In the presence of a solvent, carrying out etherification reaction on the alkalization product and a compound etherifying agent, and carrying out post-treatment on the reaction product to obtain polyanionic cellulose; wherein,

The compound etherifying agent contains a main etherifying agent and an auxiliary etherifying agent, wherein the auxiliary etherifying agent is at least one selected from 4-chlorobenzenesulfonic acid, 4-chlorobenzenesulfonic acid sodium, 3-chloro-2-hydroxypropyl sodium sulfonate and chloroethane sodium sulfonate.

In a second aspect the present invention provides a polyanionic cellulose obtainable by the method of the first aspect.

A third aspect of the present invention provides the use of a polyanionic cellulose as described in the second aspect above in a water-based drilling fluid.

Through the technical scheme, the invention has the following beneficial effects:

(1) The specific compound etherifying agent is used in the etherification reaction, and under the combined action of the main etherifying agent and the auxiliary etherifying agent, the prepared polyanion cellulose has excellent temperature resistance, viscosity increasing effect and filtration reducing performance. 1% w/v of said polyanionic cellulose was added to 4% w/v sodium bentonite slurry and the resulting slurry was heated to 150℃for 16 hours The value is kept well, the viscosity retention rate is higher than 50%, and the medium-pressure filtration loss is not higher than 16mL;

(2) Multiple alkalization or etherification is not needed in the preparation process, and the process is simple and easy to control.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

The following describes specific embodiments of the present invention in detail. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.

The first aspect of the present invention provides a process for the preparation of a polyanionic cellulose comprising:

(1) Alkalizing the cellulose raw material to obtain an alkalized product;

The compound etherifying agent contains a main etherifying agent and an auxiliary etherifying agent, wherein the auxiliary etherifying agent is at least one selected from 4-chlorobenzenesulfonic acid, sodium 4-chlorobenzenesulfonate, sodium 3-chloro-2-hydroxypropyl sulfonate and sodium chloroethane sulfonate.

According to the present invention, preferably, the cellulose raw material is selected from at least one of purified cotton, absorbent cotton, cotton linters and lignocellulose. Wherein the main components of the cellulose raw material comprise 44.44wt% of carbon, 6.17wt% of hydrogen and 49.39wt% of oxygen.

According to the present invention, in order to provide the prepared polyanionic cellulose with better temperature resistance, viscosity increasing property and fluid loss reducing property, preferably, the polymerization degree of the cellulose raw material may be 400 to 3000.

According to the invention, the complex etherifying agent is a mixture containing both a main etherifying agent and an auxiliary etherifying agent. Wherein, preferably, the main etherifying agent may be selected from chloroacetic acid and/or sodium chloroacetate; preferably, the auxiliary etherifying agent may be selected from at least one of 4-chlorobenzenesulfonic acid, sodium 4-chlorobenzenesulfonate, sodium 3-chloro-2-hydroxypropylsulfonate and sodium chloroethanesulfonate, and more preferably, may be selected from at least one of sodium 4-chlorobenzenesulfonic acid, sodium 3-chloro-2-hydroxypropylsulfonate and sodium chloroethanesulfonate.

According to the present invention, among the complex etherifying agents, a main etherifying agent is preferably used: the weight ratio of the auxiliary etherifying agent is 4:1-8, more preferably 3:1-2, so that the prepared polyanionic cellulose has better temperature resistance and filtration reduction performance.

According to the present invention, in the step (1), the alkalizing treatment may employ methods and processes conventional in the art, and the present invention is not particularly limited thereto, and for example, the cellulose raw material may be soaked in an excess alkali solution at a temperature of 10 to 30 ℃ for a time of 0.5 to 4 hours. The alkali solution used for the alkalization treatment may be an aqueous solution of sodium hydroxide and/or potassium hydroxide, and the concentration of the alkali solution may be 10 to 50% by weight, more preferably 20 to 40% by weight. The alkalization product is obtained, namely alkali cellulose.

According to the statement of the invention, in the step (2), the alkalization product obtained in the step (1) is mixed with a solvent and heated, and the composite etherifying agent is added to carry out etherification reaction after the temperature is raised to the temperature required by the etherification reaction. Wherein the solvent can be at least one selected from ethanol, ethylene glycol, n-butanol, isopropanol, isobutanol, benzene and toluene; the compound etherifying agent comprises the following components: the weight ratio of the cellulose raw materials is 4-10:10, preferably 6-10:10; the solvent is as follows: the weight ratio of the cellulose raw materials is 10-20:1.

In the present invention, preferably, the conditions of the etherification reaction may include: the temperature is 50-150 ℃ and the time is 1-3h.

According to the present statement, in step (2), the post-treatment comprising neutralization, washing and drying performed sequentially can be performed in a manner and by parameters conventional in the art. For example, after the etherification reaction is completed, acetic acid diluted by an organic solvent may be added to neutralize the etherification reaction product to a pH of 6 to 8, and then the product is repeatedly washed with an aqueous alcohol solution and dried to obtain the final product of polyanionic cellulose.

A third aspect of the present invention provides the use of a polyanionic cellulose as described in the first aspect above in a water-based drilling fluid.

The present invention will be described in detail by examples. In the following examples and comparative examples,

Unless otherwise specified, all materials used are commercially available products.

Example 1

(1) Mixing 5.0g of refined cotton with a polymerization degree of about 800 with 10g of NaOH aqueous solution with a concentration of 40wt%, and soaking and alkalizing at 20 ℃ for 1h to obtain an alkalized product;

(2) Adding the alkalization product and 100g of toluene into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 75 ℃; chloroacetic acid: 4-chlorobenzenesulfonic acid = 3:1 (mass ratio) preparing 5.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 3 hours at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture until the pH value is 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S1).

Example 2

(2) Adding the alkalization product and 100g of isopropanol into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 80 ℃; chloroacetic acid: 4-chlorobenzenesulfonic acid = 3:2 (mass ratio) preparing 5.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 1 hour at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S2).

Example 3

(1) Mixing 5.0g of refined cotton with a polymerization degree of about 600 with 20g of NaOH aqueous solution with a concentration of 20wt%, and soaking and alkalizing at 20 ℃ for 1h to obtain an alkalized product;

(2) Adding the alkalization product and 50g of isopropanol into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 75 ℃; chloroacetic acid: sodium 3-chloro 2-hydroxy propane sulfonate = 2:1 (mass ratio) preparing 3.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 1 hour at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S3).

Example 4

(2) Adding the alkalization product and 50g of isopropanol into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 75 ℃; chloroacetic acid: sodium chloroethanesulfonate=2: 1 (mass ratio) preparing 3.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 3 hours at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S4).

Example 5

(2) Adding the alkalization product and 50g of isopropanol into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 80 ℃; chloroacetic acid: 4-chlorobenzenesulfonic acid = 2:1 (mass ratio) preparing 3.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 1 hour at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S5).

Example 6

(2) Adding the alkalization product and 50g of isopropanol into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 80 ℃; chloroacetic acid: 4-chlorobenzenesulfonic acid = 1:2 (mass ratio) preparing 5.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 1 hour at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S6).

Example 7

(2) Adding the alkalization product and 100g of benzene into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 75 ℃; chloroacetic acid: sodium 4-chlorobenzenesulfonate = 3:1 (mass ratio) preparing 5.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 1 hour at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S7).

Example 8

(1) Mixing 5.0g of refined cotton with the polymerization degree of 2600 and 20g of NaOH aqueous solution with the concentration of 20wt%, and soaking and alkalizing for 1h at 20 ℃ to obtain an alkalized product;

(2) Adding the alkalization product and 50g of isopropanol into a four-neck flask together for mixing, stirring and heating in a water bath, and setting the etherification reaction temperature to 75 ℃; chloroacetic acid: 4-chlorobenzenesulfonic acid = 4:1 (mass ratio) preparing 5.0g of compound etherifying agent, dripping the compound etherifying agent after reaching the reaction temperature, and carrying out etherification reaction for 1 hour at the set temperature;

(3) After the reaction is finished, acetic acid diluted by isopropanol is dripped into the mixture to neutralize the mixture to pH 6 to 8, then the product is washed by using an aqueous solution of isopropanol with the concentration of 95 weight percent, and the product is dried for 24 hours at the temperature of 75 ℃ to obtain the polyanionic cellulose (marked as S8).

Comparative example 1

The procedure of example 1 was followed, except that in step (2), the complex etherifying agent was replaced with chloroacetic acid of the same weight as it, i.e. chloroacetic acid alone was used as the etherifying agent. The other conditions were the same as in example 1 to obtain a product (designated as D1).

Comparative example 2

The procedure of example 1 was followed, except that in step (2), the complex etherifying agent was replaced with 4-chlorobenzenesulfonic acid of the same weight as it, i.e., only 4-chlorobenzenesulfonic acid was used as the etherifying agent. The other conditions were the same as in example 1 to obtain a product (designated as D2).

Comparative example 3

The procedure of example 1 was followed except that in step (2), 4-chlorobenzenesulfonic acid in the complex etherifying agent was replaced with epichlorohydrin. The other conditions were the same as in example 1 to obtain a product (designated as D3).

Comparative example 4

The procedure of example 1 is followed, except that in step (2), chloroacetic acid: 4-chlorobenzenesulfonic acid = 1:3 (mass ratio). The other conditions were the same as in example 1 to obtain a product (designated as D4).

Test case

The products prepared in examples 1-8 and comparative examples 1-4, as well as commercially available polyanionic cellulose, were added as an aid to the aqueous drilling fluid base slurry to evaluate the properties of the different polyanionic celluloses described above. In the following examples of the test that were conducted,

The rheological parameters of the drilling fluid are measured by a six-speed viscometer according to the method specified in GB/T16783.2-2012;

Medium pressure fluid loss (API, mL) was measured using a medium pressure fluid loss meter and according to the method specified in GB/T29170-2012;

the manufacturer of the six-speed rotary viscometer is Beijing prospecting engineering institute model WT-AUTO-900;

The manufacturer of the medium pressure filtration apparatus is Qingdao Shun electronic mechanical Co., ltd, model ZNS.

Preparing water-based drilling fluid base slurry: to 400mL of tap water was added 16g of sodium bentonite for drilling fluid (available from Torile slurry technologies Co., ltd.) and stirred for 30min at 10000r/min, and the mixture was allowed to stand in a sealed state for 24 hours to obtain 4% w/v sodium bentonite slurry (designated as base slurry A).

To 400mL of the above-prepared base slurry A were added 4g (i.e., 1% w/v) of the products S1 to S8 obtained in examples 1 to 8, the products D1 to D4 obtained in comparative examples 1 to 4, commercially available polyanionic cellulose (brand: LV-PAC, available from Hebei Yanxing chemical Co., ltd.) respectively, and after stirring for 20 minutes at 3000r/min, the slurry was transferred to an aging tank, the aging tank was placed in a high-temperature roller heating furnace, heated at 150℃for 16 hours, cooled to room temperature, and after stirring for 10 minutes at 3000r/min, the rheological properties, medium pressure filtrate and viscosity retention were measured before and after the heated rolling of the slurry, and the results are shown in Table 1.

Wherein the viscosity retention rate is calculated according to the formula (1),

TABLE 1

As can be seen from Table 1, the addition of 1% w/v polyanionic cellulose S1-S8 to the water-based drilling fluid base slurry A significantly increased the viscosity of the base slurry, after 16h of hot rolling at 150℃The value is well maintained, the viscosity retention rate is more than 50%, and the medium-pressure filtration loss is not higher than 16mL, which indicates that the polyanionic cellulose provided by the application has good viscosity increasing, temperature resisting and filtrate reducing agent effects.

In contrast, the composite etherifying agent in the method is not used in the preparation process of the products D1-D4, and as a result, the viscosity retention rate of the slurry is obviously reduced after the slurry is thermally rolled for 16 hours at 150 ℃, the filtration loss is higher than 20mL, and the slurry cannot resist the high temperature of 150 ℃. The viscosity retention rate of the slurry after hot rolling for 16 hours at 150 ℃ is only 11.8% by using the commercially available polyanionic cellulose LV-PAC, and the difference between the temperature resistance and the S1-S8 is remarkable.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A process for preparing a polyanionic cellulose comprising:

(1) Alkalizing the cellulose raw material to obtain an alkalized product;

The compound etherifying agent contains a main etherifying agent and an auxiliary etherifying agent, wherein the main etherifying agent is selected from chloroacetic acid and/or sodium chloroacetate; the auxiliary etherifying agent is at least one of 4-chlorobenzenesulfonic acid, sodium 4-chlorobenzenesulfonate, sodium 3-chloro-2-hydroxypropyl sulfonate and sodium chloroethane sulfonate;

the main etherifying agent: the weight ratio of the auxiliary etherifying agent is 3:1-2;

the compound etherifying agent comprises the following components: the weight ratio of the cellulose raw material is 4-10:10.

2. The method of claim 1, wherein the cellulosic feedstock is selected from at least one of purified cotton, absorbent cotton, cotton linters, and lignocellulose.

3. The method of claim 2, wherein the cellulose raw material has a degree of polymerization of 400-3000.

4. A process according to any one of claims 1 to 3, wherein the co-etherifying agent is selected from at least one of sodium 4-chlorobenzenesulphonate, sodium 3-chloro-2-hydroxypropylsulfonate and sodium chloroethanesulfonate.

5. A process according to any one of claims 1-3, wherein in step (1) the alkaline solution used for the alkalizing treatment is an aqueous solution of sodium hydroxide and/or potassium hydroxide.

6. The process according to claim 4, wherein in step (1), the alkaline solution used for the alkalizing treatment is an aqueous solution of sodium hydroxide and/or potassium hydroxide.

7. The process according to claim 5, wherein the lye is present in a concentration of 10-50wt%.

8. The process according to claim 7, wherein the lye is present in a concentration of 20-40wt%.

9. The process according to claim 6, wherein the lye is present in a concentration of 10-50wt%.

10. The process according to claim 9, wherein the lye is present in a concentration of 20-40wt%.

11. The method according to any one of claims 1 to 3, 6 to 10, wherein in step (2), the conditions of the etherification reaction include: the temperature is 50-80 ℃ and the time is 1-3h;

And/or, the complex etherifying agent: the weight ratio of the cellulose raw materials is 6-10:10;

And/or, the solvent: the weight ratio of the cellulose raw materials is 10-20:1, a step of;

And/or the solvent is at least one selected from ethanol, ethylene glycol, n-butanol, isopropanol, isobutanol, benzene and toluene.

12. The process according to claim 4, wherein in step (2), the conditions of the etherification reaction include: the temperature is 50-80 ℃ and the time is 1-3h;

13. The method according to claim 5, wherein in step (2), the conditions of the etherification reaction include: the temperature is 50-80 ℃ and the time is 1-3h;

14. The method according to any one of claims 1-3, 6-10, 12-13, wherein in step (2), the post-treatment comprises neutralization, washing and drying performed sequentially.

15. The method according to claim 4, wherein in step (2), the post-treatment comprises neutralization, washing and drying performed sequentially.

16. The method according to claim 5, wherein in step (2), the post-treatment comprises neutralization, washing and drying performed sequentially.

17. The method of claim 11, wherein in step (2), the post-treatment comprises neutralization, washing, and drying performed sequentially.

18. A polyanionic cellulose produced by the method of any one of claims 1-17.

19. Use of the polyanionic cellulose of claim 18 in a water-based drilling fluid.