Microwave-assisted deep-eutectic solvent extraction-in-situ carboxymethylation modified cellulose integrated preparation method, modified cellulose and application

Abstract

The invention provides an integrated preparation method of microwave-assisted deep-eutectic solvent extraction-in-situ carboxymethylation modified cellulose, the modified cellulose and application. The preparation method comprises the following steps: (1) mixing choline chloride, urea and a modifier sodium chloroacetate, heating and stirring to form a uniform transparent liquid, and cooling to room temperature to obtain a deep eutectic solvent ternary system; (2) adding a biomass raw material into the eutectic solvent ternary system, and carrying out microwave treatment; and precipitating, centrifuging, washing and drying the obtained reaction liquid to obtain the modified cellulose. According to the method, raw material pretreatment, cellulose extraction and carboxymethylation reaction are integrated in a single reaction system, the technological process is remarkably simplified, the production cost is reduced, meanwhile, the product performance and environmental friendliness are improved, excellent performance is shown in the fields of oil field drilling fluid and the like, and the well wall instability risk is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for integrated preparation of microwave-assisted eutectic solvent extraction-in-situ carboxymethylation modified cellulose, modified cellulose and application, belonging to the field of oil field chemistry. BACKGROUND

[0002] In oil and gas drilling operations, drilling fluid is an essential part of the drilling system, and its rheological properties, filtration control and wellbore stability directly affect drilling efficiency and safety. Cellulose derivatives have become one of the core treatment agents for water-based drilling fluid systems due to their unique viscosity enhancement, filtration reduction and environmental protection properties. In the application of drilling fluid, unmodified cellulose has many problems: insufficient temperature and salt resistance, difficulty in maintaining rheological stability of drilling fluid; weak resistance to high valence ions, leading to colloid gelation, blocking of formation pores and aggravation of filter cake thickening; high shear sensitivity, reduced suspended cuttings capacity, and easy to cause sand sticking accidents. Therefore, through carboxymethylation modification, the temperature resistance limit, salt concentration and shear stability of CMC can be significantly improved to meet the drilling needs of deep, ultra-deep and complex formations. This technology upgrade is not only a necessary requirement for the development of drilling technology, but also a key path to break through the traditional preparation bottleneck.

[0003] However, the traditional CMC preparation process has significant defects: although the water medium method is low in cost, it has low reaction efficiency, uneven substitution degree, wide molecular weight distribution and other problems, resulting in insufficient product purity and poor batch stability; although the solvent method can improve the uniformity of substitution, it relies on a large amount of organic solvents (such as isopropyl alcohol), and the solvent recovery energy consumption is high, and residual solvents can easily cause environmental problems. In addition, the traditional process has strict requirements for raw material pretreatment, and wood pulp or cotton pulp needs to be alkalized in multiple stages, generating a large amount of high-salt wastewater and increasing environmental governance costs. The traditional preparation process of carboxymethyl cellulose (CMC) generally has problems such as complex process, high energy consumption, harsh reaction conditions, etc., which seriously restricts its large-scale application in the oil industry.

[0004] For cellulose modification, the traditional industrial production adopts a four-step method of "alkali activation-etherification-secondary alkalization-purification". For example, Chinese patent document CN104877033A discloses a preparation method of carboxymethyl modified cellulose, which synthesizes a CMC with a particle size of 30-50 nm, a viscosity of less than 28 mPa·s, and a purity of greater than 95.5% through a four-step method: alkali activation-etherification-secondary alkalization-purification. However, this synthesis method involves multiple independent steps and does not solve the fundamental problems of complex preparation steps and long production cycle. Moreover, the intermediate product needs to be frequently transferred, which easily introduces impurities and reduces product uniformity. The cellulose molecular chain is prone to degradation in multi-step reactions, resulting in uneven product substitution degree (DS), affecting the solubility, thermal stability and salt resistance of CMC, and being difficult to meet the mud performance requirements in deep well high temperature and high pressure environment. Moreover, a large amount of waste liquid is generated in the process. Chinese patent document CN119177578A discloses a lignocellulose based on waste biomass material and a preparation method thereof, which prepares a cellulose with a slurry viscosity (copper ammonia viscosity method) of less than 25 mPa·s, a reaction performance (viscose filtration method) of less than 500 s, and a polyvalent sugar content of less than 4.0%, but does not modify the carboxymethyl substitution of hydroxyl groups, resulting in that its application is difficult to meet the performance requirements of drilling fluid.

[0005] Therefore, the high cost and complex problems of the synthesis process of carboxymethyl modified cellulose have not been solved, and there is an urgent need for process innovation for simple synthesis of carboxymethyl modified cellulose. SUMMARY

[0006] In view of the deficiencies of the prior art, especially in view of the problems of complicated steps, high energy consumption, low reaction efficiency, uneven product substitution degree and serious environmental pollution existing in the preparation process of existing carboxymethyl cellulose (CMC), the present application provides an integrated preparation method of microwave-assisted low eutectic solvent extraction-in-situ carboxymethylation modified cellulose, modified cellulose and application. The method of the present application integrates raw material pretreatment, cellulose extraction and carboxymethylation reaction in a single reaction system, significantly simplifies the process flow, reduces production cost, and improves product performance and environmental friendliness.

[0007] The technical scheme of the present application is as follows: An integrated preparation method of microwave-assisted low eutectic solvent extraction-in-situ carboxymethylation modified cellulose, comprising the following steps: (1) mixing choline chloride (ChCl), urea and a modifier sodium chloroacetate, heating and stirring until a uniform transparent liquid is formed, cooling to room temperature to obtain a low eutectic solvent (DES) ternary system; (2) adding biomass raw material into the low eutectic solvent (DES) ternary system and performing microwave treatment; the obtained reaction liquid is subjected to precipitation, centrifugation, washing and drying to obtain modified cellulose.

[0008] According to the application, preferably, the molar ratio of the choline chloride (ChCl), urea and the modifier sodium chloroacetate in step (1) is 1:1.5-3:1-2, and more preferably 1:2.5:1. In the application, the urea and the choline chloride (ChCl) break the lignin-hemicellulose bond, the sodium chloroacetate and the exposed cellulose hydroxyl group undergo substitution reaction, and at the same time, the sodium chloroacetate provides a carboxymethylation reagent and an alkaline environment for the system; the molar ratio of the choline chloride (ChCl), urea and the CMC modifier sodium chloroacetate in the application has a great influence on the extraction and modification of cellulose, and if the ratio is not appropriate, the lignin-hemicellulose bond breaking efficiency will be reduced, the side reaction will be increased, the product performance will be deteriorated, the degree of substitution will be low, and the purity and performance of the prepared cellulose will be directly affected.

[0009] According to the application, preferably, the heating in step (1) is heating to 70-90℃.

[0010] According to the application, preferably, the biomass raw material in step (2) is corn straw powder, wheat straw powder, eucalyptus powder or palm trunk powder, and the particle size of the biomass raw material is 60-80 mesh.

[0011] According to the application, preferably, the mass ratio of the biomass raw material to the DES ternary system in step (2) is 1:15-30; the ratio of the DES ternary system to the biomass raw material in the application has an important influence on the extraction and modification of cellulose, and if the ratio is not appropriate, the mass transfer resistance will be increased, the solid-liquid ratio will be increased, the solvent cannot fully penetrate the biomass particles, the viscosity of the DES will be increased, the reaction will be affected, the degree of substitution (DS) will be reduced, or the yield will be too low and the viscosity of the finished product will be insufficient.

[0012] According to the application, preferably, the microwave treatment in step (2) is carried out in a microwave reactor, the power of the microwave treatment is 400-600W, the temperature is 80-100℃, and the microwave treatment time is 35-50min.

[0013] According to the application, preferably, the precipitation step in step (2) is adding anhydrous ethanol to the obtained reaction solution for precipitation, and the volume ratio of the anhydrous ethanol to the reaction solution is 2-2.5:1.

[0014] According to the application, preferably, the washing in step (2) is centrifugal washing of the obtained product with water until the pH of the supernatant is 7; and the drying is vacuum drying at 50-60℃ until the weight is constant.

[0015] According to the application, preferably, after step (2) is completed, a DES recovery step is further included, and the specific steps are as follows: the waste liquid obtained by centrifugation is recovered by rotary evaporation.

[0016] The application further provides a modified cellulose prepared by the preparation method.

[0017] According to the application, the modified cellulose is applied in a water-based drilling fluid as a thickening agent.

[0018] The technical features and advantages of the application are as follows: 1. The application is innovative in using a choline chloride-urea-sodium chloroacetate ternary DES system in combination with microwave heating technology to realize one-step extraction and carboxymethylation of cellulose in biomass raw materials. The application first uses choline chloride (ChCl) as a hydrogen bond acceptor, urea as a hydrogen bond donor, and sodium chloroacetate as a carboxyl modification agent to construct a ternary eutectic solvent (DES) system, uses biomass materials as raw materials, and uses microwave-DES to synergistically strengthen the extraction and modification of cellulose. The non-thermal effect of microwave accelerates the penetration of DES into cellulose, and the reaction time is significantly shortened. The DES solvent in the application has the functions of lignin removal and hydroxyl etherification, microwave radiation significantly accelerates the mass transfer reaction, the yield is high, and excellent performance is shown in the field of oilfield drilling fluid.

[0019] 2. The application realizes a high substitution degree DS=1.25-1.4 by regulating the molar ratio of sodium chloroacetate and the microwave power. The dense carboxymethyl enhances the hydration layer and chain rigidity, resists high-temperature and saturated salt water environment, forms a dense filter cake, and significantly improves the stability and safety of drilling fluid in complex formations.

[0020] 3. The application constructs a ternary system, integrates extraction, purification and modification in a single reaction system, has fewer reaction steps (less than 5 steps) Figure 1 , saves the alkaline activation, secondary alkalization and multi-step purification procedures in the traditional process, integrates extraction and modification in a single step, is more convenient and efficient than the traditional CMC preparation method (more than 10 steps) Figure 2 , has less equipment investment, and is low in energy consumption. The biomass raw material utilization rate of the method of the application is higher than that of the acid-alkali method, meets the green chemistry standard, and has the advantages of high efficiency, environmental protection and economy. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a flowchart of the integrated preparation method of the microwave-assisted eutectic solvent extraction-in-situ carboxymethylation modified cellulose of the application.

[0022] Figure 2 The figure is a flowchart of the preparation method of the traditional carboxymethyl modified cellulose.

[0023] Figure 3 The figure is an infrared spectrum of the carboxymethyl modified cellulose prepared in Example 1.

[0024] Figure 4 Scanning electron microscope image of carboxymethylated modified cellulose prepared in Example 1. DETAILED DESCRIPTION

[0025] The application will be further described in conjunction with specific examples, but is not limited thereto.

[0026] Meanwhile, the experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0027] The biomass raw material used in the examples is corn straw powder obtained by washing, drying, crushing and sieving corn straw with deionized water, and the particle size is 80 mesh.

[0028] Example 1 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose includes the following steps: (1) In a three-necked flask equipped with a mechanical stirring device, mix choline chloride (ChCl), urea and sodium chloroacetate according to a molar ratio of 1:2.5:1, place in a 80℃ constant temperature water bath, stir at 500rpm under the condition of mechanical stirring for 1 hour, form a uniform transparent solution, naturally cool to room temperature, and obtain a deep eutectic solvent (DES) ternary system.

[0029] (2) Mix the biomass raw material with the deep eutectic solvent (DES) ternary system obtained in step (1) according to a mass ratio of 1:25, stir uniformly, then place in a microwave reactor, treat at a power of 500W and a temperature of 90℃ for 45min, and obtain a reaction liquid.

[0030] (3) Naturally cool the obtained reaction liquid to room temperature, add 2 times the volume of anhydrous ethanol to the reaction liquid to precipitate for 30min, then centrifuge (8000rpm, 5min) to collect the precipitate; wash the centrifuged precipitate with water until the pH of the supernatant is 7 to remove unreacted reagents and DES residues; vacuum dry the washed precipitate at 55℃ to a constant weight to obtain a white powder product, which is carboxymethylated modified cellulose.

[0031] (4) Add the centrifuged waste liquid to a round-bottom flask, fix the flask on a rotating shaft, connect a condenser tube, a receiving bottle and a vacuum pipeline, start the rotating motor, adjust the speed to 120rpm, make the solution form a uniform thin film to accelerate evaporation, evaporate at 80℃ until the liquid volume no longer decreases, remove the flask, and the remaining material in the flask is the recovered deep eutectic solvent (DES).

[0032] The chemical structure of the carboxymethylated modified cellulose (CMC) synthesized in Example 1 was characterized using Fourier transform infrared spectroscopy (FT-IR), and its infrared spectrum is shown below. Figure 3 As shown. By Figure 3 It can be seen that at 2897cm -1 The absorption peak at 1426 cm⁻¹ is attributed to the stretching vibration of the CH bond, originating from the methylene (-CH₂-) functional group in the pyranose ring of the cellulose skeleton and the carboxymethyl substituent (-CH₂-COOH). -1 The characteristic absorption peak appearing at this point is due to the carboxylate group (-COO). - The symmetric stretching vibrations of 1320 cm⁻¹ indicate that carboxymethyl groups have been successfully introduced into the cellulose molecular chain. -1 The absorption peak at 1092 cm⁻¹ corresponds to the in-plane bending vibration of the OH bond. It is noteworthy that the absorption peak at 1092 cm⁻¹ corresponds to this in-plane bending vibration. -1 The strong absorption peak observed is the stretching vibration peak of the COC ether bond, which is attributed to both the β-1,4-glycosidic bond in the cellulose backbone and the ether bond formed by the etherification reaction of the carboxymethyl group with the cellulose hydroxyl group. In the above results, the characteristic peak of the carboxylate group (1426 cm⁻¹) is also significant. -1 ) and ether bond characteristic peak (1092 cm⁻¹) -1 The presence of these peaks directly proves that sodium chloroacetate underwent an etherification reaction with the hydroxyl groups of cellulose, producing carboxymethyl cellulose. Simultaneously, the characteristic peaks of cellulose itself (such as the OH vibration peak and the CH vibration peak) remain, indicating that the carboxymethylation reaction did not destroy the basic skeletal structure of cellulose. These characteristic peaks collectively verify the successful synthesis of carboxymethyl cellulose.

[0033] The scanning electron microscope image of the carboxymethylated modified cellulose prepared in this embodiment is shown below. Figure 4 As shown, by Figure 4 It can be seen that the carboxymethylated modified cellulose prepared in this embodiment is mainly in the form of strips with a loose surface structure, and some of them are cross-linked to form a network aggregate. The longitudinal dimensions of the strips are mainly in the range of 25-50 μm, and the width is about 5-8 μm. The surface structure of the carboxymethylated modified cellulose obtained by this invention is even more loose. The carboxymethylated modified nanocellulose prepared by this invention replaces some of the hydroxyl groups on the surface of nanocellulose with carboxymethyl groups. By increasing the electrostatic repulsion between molecules, it reduces the irreversible keratinization of cellulose caused by hydrogen bond lock during the drying process, thereby improving the redispersion of crystals. When added to a dispersion system containing polar groups, it can be used to prepare high-performance nanocomposites that meet specific requirements.

[0034] Example 2 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modified cellulose was as described in Example 1, except that the molar ratio of choline chloride (ChCl), urea, and sodium chloroacetate in step (1) was 1:1.5:1, and the other steps and conditions were the same as in Example 1.

[0035] Example 3 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modified cellulose was as described in Example 1, except that the molar ratio of choline chloride (ChCl), urea, and sodium chloroacetate in step (1) was 1:3:1, and the other steps and conditions were the same as in Example 1.

[0036] Example 4 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modified cellulose was as described in Example 1, except that the molar ratio of choline chloride (ChCl), urea, and sodium chloroacetate in step (1) was 1:2.5:2, and the other steps and conditions were the same as in Example 1.

[0037] Example 5 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modified cellulose was as described in Example 1, except that the mass ratio of the deep eutectic solvent (DES) ternary system to the biomass raw material powder in step (2) was 15:1, and the other steps and conditions were the same as in Example 1.

[0038] Comparative Example 1 An oil bath heating assisted deep eutectic solvent extraction method for cellulose, comprising the following steps: (1) In a three-necked flask equipped with a mechanical stirring device, choline chloride (ChCl), urea, and sodium chloroacetate were mixed according to a molar ratio of 1:2.5:1, and placed in an 80°C constant temperature oil bath. The mixture was stirred at a speed of 500 rpm for 1 hour to form a homogeneous transparent solution. The solution was cooled to room temperature to obtain a deep eutectic solvent (DES) ternary system; (2) The biomass raw material was mixed with the deep eutectic solvent (DES) ternary system obtained in step (1) according to a mass ratio of 1:25, and placed in a three-necked flask heated in a water bath. The mixture was stirred at a temperature of 80°C and a speed of 500 rpm for 90 minutes; (3) The obtained reaction solution was naturally cooled to room temperature, and 2 times the volume of anhydrous ethanol was added for precipitation for 30 minutes. Then the precipitate was collected by centrifugation (8000 rpm, 5 minutes). The precipitate obtained by centrifugation was washed with water until the pH of the supernatant was 7, and the unreacted reagents and DES residues were removed. The washed precipitate was dried under vacuum at 55°C until the weight was constant, and a white powder product was obtained, which was carboxymethylated modified cellulose.

[0039] Comparative Example 2 A method for microwave-assisted deep eutectic solvent extraction of cellulose, comprising the following steps: (1) mixing choline chloride and urea at a molar ratio of 1:2, placing in a 80℃ constant temperature water bath, stirring at 500 rpm for 1 hour, becoming a uniform transparent liquid, cooling to room temperature, obtaining a deep eutectic solvent (DES) binary system; (2) mixing the biomass raw material with the deep eutectic solvent (DES) ternary system obtained in step (1) at a mass ratio of 1:25, stirring uniformly and then placing in a microwave reactor, treating at a power of 500 W and a temperature of 90℃ for 45 min, obtaining a reaction liquid; (3) naturally cooling the obtained reaction liquid to room temperature, adding 2 times the volume of anhydrous ethanol to precipitate for 30 min, then centrifuging (8000 rpm, 5 min) to collect the precipitate; washing the precipitate obtained by centrifugation with water until the pH of the supernatant is 7 to remove unreacted reagents and DES residues; drying the washed precipitate at 55℃ under vacuum to constant weight to obtain a white powder product, which is cellulose.

[0040] Comparative Example 3 A method for preparing carboxymethyl modified cellulose, comprising the following steps: (1) adding 1 part by weight of cellulose and 35 parts by weight of isopropyl alcohol into a three-necked flask, stirring uniformly, then placing the whole system in a constant temperature water bath device, adding 1.05 parts by weight of 50wt% sodium hydroxide solution at 25℃ constant temperature, stirring for 60 min for the first alkalization.

[0041] (2) adding 15 parts by weight of isopropyl alcohol-monochloroethanol mixed solution dropwise into the reaction liquid after alkalization, adjusting the temperature to 50℃ for etherification reaction, reacting for 50 min, the mass ratio of isopropyl alcohol to monochloroethanol in the isopropyl alcohol-monochloroethanol mixed solution is 5:1, then adding 0.35 parts by weight of 50wt% sodium hydroxide solution dropwise into the above reaction system for the second alkalization process, increasing the constant temperature water bath device to 60℃, reacting for 90 min to complete the second alkalization.

[0042] (3) after the alkalization is completed, the obtained product is filtered, the filtered product is dispersed in 80wt% methanol aqueous solution, neutralized to pH 7.5 with 90wt% acetic acid aqueous solution, washed with 70wt% ethanol aqueous solution for 3 times, washed with methanol once, and dried under vacuum and low temperature conditions to obtain carboxymethyl modified cellulose.

[0043] Comparative Example 4 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose was as described in Example 1, except that equimolar amount of lactic acid was used instead of urea in step (1), and other steps and conditions were the same as in Example 1.

[0044] Comparative Example 5 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose was as described in Example 1, except that the treatment time in step (2) was changed to 90 min in the microwave reactor, and other steps and conditions were the same as in Example 1.

[0045] Comparative Example 6 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose was as described in Example 1, except that the treatment time in step (2) was changed to 20 min in the microwave reactor, and other steps and conditions were the same as in Example 1.

[0046] Comparative Example 7 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose was as described in Example 1, except that the microwave power in step (2) was set to 300 W, and other steps and conditions were the same as in Example 1.

[0047] Comparative Example 8 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose was as described in Example 1, except that the microwave power in step (2) was set to 700 W, and other steps and conditions were the same as in Example 1.

[0048] Comparative Example 9 An integrated preparation method of microwave-assisted deep eutectic solvent extraction-in-situ carboxymethylation modified cellulose was as described in Example 1, except that the mass ratio of the deep eutectic solvent (DES) ternary system to biomass raw material powder in step (2) was 35:1, and other steps and conditions were the same as in Example 1.

[0049] Test Example 1 The carboxymethylated modified cellulose or cellulose in the examples and comparative examples was tested for particle size, viscosity, degree of substitution (DS), and purity, and the results are shown in Table 1. The yield of the product obtained is also shown in Table 1.

[0050] The particle size was prepared into a 5wt% aqueous solution, and tested using a Malvern Mastersizer 2000 laser particle size instrument; The viscosity was the viscosity of a 1wt% aqueous solution of carboxymethylated modified cellulose at 25°C, which was tested using a six-speed rotational viscometer.

[0051] The degree of substitution was tested using acid-base titration.

[0052] Table 1 Particle size, viscosity, degree of substitution, purity, yield and reaction time of modified cellulose As can be seen from Table 1, the carboxymethyl-modified cellulose obtained in Example 1 has the best performance. In Example 2, the proportion of urea is reduced, which causes the hydrogen bond network of DES to be loose, the viscosity to be reduced, and the alkalization ability to be insufficient. At this time, the cellulose is not fully activated, the carboxymethylation reaction is limited, and the degree of substitution (DS) is reduced. In Example 3, the content of urea is increased, the intermolecular force of urea is enhanced, and the hydrogen bond combination with chloride ions tends to be saturated, which causes the viscosity of DES to increase. Excessive urea can increase the pH of the system, inhibit the etherification reaction, and result in a low degree of substitution. In Example 4, the content of sodium chloroacetate is increased. Although the increase in the concentration of etherifying agent can improve the DS, the side reactions (such as self-polymerization of sodium chloroacetate) are intensified, the purity of the product is reduced, and the yield is also reduced. In Example 5, the mass of the ternary system of the deep eutectic solvent (DES) is reduced. The high solid-liquid ratio causes the solvent to be insufficient for the aggregation of biomass particles, the contact area between cellulose and DES is reduced, and the high concentration of reactants can cause local overheating (when the microwave power is unchanged), which causes the degradation of cellulose and a reduction in the degree of substitution.

[0053] In Comparative Example 1, only a water bath heating method is used, and the uneven temperature distribution caused by the heat conduction from the outside to the inside results in insufficient reaction in the inner layer. At the same time, the slow heating rate causes part of the urea to undergo alkaline decomposition, which reduces the degree of substitution. In Comparative Example 3, the method for carboxymethyl-modification of ordinary cellulose has a long reaction time and a low degree of substitution. In Comparative Example 4, the type of deep eutectic solvent is replaced, and the degree of substitution of the obtained cellulose is reduced. In Comparative Example 5, the microwave treatment time is long, and long-time microwave heating causes part of the cellulose to carbonize or degrade, resulting in the aggregation of particles and loose structure, and a reduction in the degree of substitution. In Comparative Example 6, the microwave treatment time is short, which causes insufficient activation of cellulose and the hydrogen bond to be unable to be fully broken. The sodium chloroacetate does not fully penetrate into the cellulose microfibril, and the etherification reaction is limited to the surface, which reduces the degree of substitution. In Comparative Example 7, the microwave power is low, the microwave penetration depth is insufficient, the temperature distribution of the reaction system is uneven, the activation of cellulose and the etherification reaction are insufficient, and the degree of substitution is low. In Comparative Example 8, the microwave power is high, which can cause rapid heating and cause the β-1,4 glycosidic bond of the cellulose main chain to break, the molecular weight to decrease, the viscosity to decrease to 800 mPa·s, the side reactions to intensify, and the purity of the product to decrease. In Comparative Example 9, the mass of the ternary system of the deep eutectic solvent (DES) is increased, and the low solid-liquid ratio causes the solvent to be excessive, which reduces the degree of substitution.

[0054] Test Example 2 The influence of the modified cellulose prepared in the examples and comparative examples on the rheological properties and environmental performance of drilling fluid was tested.

[0055] (1) Rheological properties 20 parts by weight of bentonite was added to 400 parts by weight of deionized water, and after high-speed stirring at 6000 rpm for 20 min, 8 parts by weight of modified cellulose and 144 parts by weight of NaCl were added, and stirring was continued for 20 min to obtain a drilling fluid. The drilling fluid was loaded into a stainless steel aging tank, and constant temperature rolling was carried out at 180℃ for 16 hours. After aging, it was cooled to room temperature and taken out, and stirred at 6000 rpm for 20 min; at the same time, the base slurry without adding modified cellulose was used as a comparison.

[0056] According to the oil and gas industry standard GB / T 29170-2012 "Oil and gas industry-Drilling fluid laboratory test", the apparent viscosity (AV, mPa·s), plastic viscosity (PV, mPa·s), API filtration loss FL API of the drilling fluid before and after high temperature aging were determined, and the results are shown in Tables 2-3; and the chemical oxygen demand (COD) before aging was determined by dichromate reflux method, the five-day biochemical oxygen demand (BOD5) was determined by dilution inoculation method, and the half effective concentration (EC 50 ) was determined by micronucleus test method to evaluate the biological toxicity, and the results are shown in Table 4.

[0057] Table 2 Performance of drilling fluid after adding modified cellulose of different examples Table 3 Performance of drilling fluid after adding modified cellulose of different comparative examples Table 4 Biological toxicity of drilling fluid after thickening by modified cellulose of examples The most commonly used method to evaluate biodegradability at present is the BOD5 / COD ratio method. COD represents the chemical oxygen demand, which is the amount of oxidizing agent consumed when treating water samples under certain conditions, and it is an index representing the amount of reducing substances in water. BOD5 represents the biological oxygen demand, which is the amount of oxygen required for microbial degradation of organic matter in water under aerobic conditions within a specified temperature and time period. The biodegradability standards of water-soluble oilfield chemicals are shown in Table 5.

[0058] Table 5 Biodegradability index of water-soluble oilfield chemicals As shown in Table 2-3, when the amount of modified cellulose in the saturated salt water drilling fluid is 2%, the AV of the drilling fluid added with the modified cellulose of the examples is maintained in the range of 50.5 mPa·s to 63.5 mPa·s, the AV after aging at 180℃ is maintained in the range of 40.5 mPa·s to 48.5 mPa·s, and the AV retention rate before and after aging is more than 70%. The PV of the drilling fluid added with the modified cellulose of the examples before aging is maintained in the range of 30.5 mPa·s to 43.0 mPa·s, the PV after aging at 180℃ is maintained in the range of 23 mPa·s to 32.5 mPa·s, and the PV retention rate before and after aging is more than 66%. It is shown that the modified cellulose of the application has good temperature resistance, salt resistance, viscosity increasing and shear thinning properties as a viscosity increasing agent of the drilling fluid.

[0059] The apparent viscosity (AV) and plastic viscosity (PV) retention rates of the CMC with high degree of substitution (Examples 1-9) after aging at 180℃ are high, and the core mechanism is that the dense carboxymethyl groups enhance the rigidity of the molecular chain through electrostatic repulsion, inhibit high temperature degradation, and form a stable three-dimensional network structure. The rheological properties of the low degree of substitution or unmodified cellulose at high temperature are significantly deteriorated due to the molecular chain curling and hydrogen bond breaking, which indicates that the low degree of substitution leads to insufficient density of carboxymethyl groups, the molecular chain curls due to weak electrostatic repulsion, the hydrogen bond network is easily broken and cannot be regenerated at high temperature, and it is difficult to form a stable three-dimensional structure. In contrast, the CMC with high degree of substitution (Examples 1-5) can maintain AV and PV retention rates of more than 66% after aging due to the dense carboxymethyl groups, the enhanced rigidity of the molecular chain, and the inhibition of high temperature chain segment disentanglement by electrostatic repulsion. It can be found that the degree of substitution (DS) is the key to determine the temperature resistance and salt resistance of the CMC, and the DS needs to be more than 1.2 to stabilize the high temperature rheological properties by enhancing the rigidity of the molecular chain and the electrostatic repulsion. Optimizing the degree of substitution and molecular structure design is the core strategy to improve the temperature resistance of the CMC, and the traditional process is prone to performance defects due to uneven or insufficient degree of substitution.

[0060] In addition, the microwave-assisted DES ternary system (choline chloride-urea-sodium chloroacetate) realizes the preparation of carboxymethylated modified cellulose with high purity (more than 95.5%) and high yield (more than 90%) within 45 minutes through synchronous extraction and etherification reaction. Sodium chloroacetate acts as an etherification agent and regulates the alkaline environment, and combined with uniform heating by microwave to avoid local degradation, the side reactions are significantly reduced. In summary, the process solves the problems of complex preparation process and insufficient performance of traditional CMC through structure optimization and process intensification, and provides an efficient and environmentally friendly thickening and fluid loss reduction solution for deep well high temperature and high pressure drilling fluid.

[0061] Finally, as shown in Table 4, the modified cellulose prepared by the application has very low toxicity, good BOD5 / COD biodegradability, and good biodegradability.

[0062] The above is only a specific embodiment of the present application, but the design concept of the present application is not limited thereto, and any non-essential modification of the present application using the concept shall be deemed to be an act of infringing the protection scope of the present application. Any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application, which does not deviate from the content of the technical scheme of the present application, still belongs to the protection scope of the technical scheme of the present application.

Claims

1. A method for integrated preparation of microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modified cellulose, characterized by, The method comprises the following steps: (1) mixing choline chloride, urea and a modifier sodium chloroacetate, heating and stirring until a homogeneous transparent liquid is formed, cooling to room temperature to obtain a eutectic solvent ternary system; (2) adding a biomass raw material into the eutectic solvent ternary system and performing microwave treatment; The obtained reaction liquid is precipitated, centrifuged, washed and dried to obtain modified cellulose.

2. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (1), the molar ratio of choline chloride, urea and the modifier sodium chloroacetate is 1:1.5-3:1-2, preferably 1:2.5:

1.

3. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (1), the heating is heating to 70-90℃.

4. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (2), the biomass raw material is corn straw powder, wheat straw powder, eucalyptus powder or palm tree stem powder, and the particle size of the biomass raw material is 60-80 mesh.

5. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (2), the mass ratio of the biomass raw material to the eutectic solvent ternary system is 1:15-30.

6. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (2), the microwave treatment is performed in a microwave reactor, the power of the microwave treatment is 400-600W, the temperature is 80-100℃, and the microwave treatment time is 35-50min.

7. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (2), the precipitation step is adding anhydrous ethanol to the obtained reaction liquid for precipitation, and the volume ratio of the anhydrous ethanol to the reaction liquid is 2-2.5:

1.

8. The integrated process for the microwave-assisted deep eutectic solvent extraction-in situ carboxymethylation modification of cellulose according to claim 1, characterized in that, In step (2), the washing is centrifugal washing of the centrifuged product with water until the pH of the supernatant is 7; the drying is vacuum drying at 50-60℃ until the weight is constant; after step (2) is completed, a eutectic solvent recovery step is further included, which is as follows: the waste liquid obtained by centrifugation is recovered by rotary evaporation.

9. A modified cellulose, characterized by, Prepared by the preparation method of any one of claims 1-8.

10. Use of the modified cellulose according to claim 9, characterized in that Applied as a thickening agent in a water-based drilling fluid.

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