A method for integrated preparation of lignin extraction-sulfonic acid modification based on eutectic solvent coupling microwave, sulfonated lignin and application

Abstract

The application provides a lignin extraction-sulfonic acid modification integrated preparation method based on a deep eutectic solvent coupled with microwaves, sulfonated lignin and application, and belongs to the technical field of oil field chemicals. The preparation method comprises the following steps: mixing choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid, heating and stirring to obtain a ternary deep eutectic solvent system; adding biomass powder into the ternary deep eutectic solvent system and performing a reaction under microwave conditions; after the reaction is completed, filtering, adjusting the pH of the obtained filtrate to neutral, and obtaining a mixed solution; then adding an organic solvent to the obtained mixed solution to perform precipitation, and performing filtering, washing and drying to complete lignin extraction-sulfonic acid modification. The application realizes in-situ grafting of sulfonic acid functional groups in the lignin separation process by means of the ternary deep eutectic solvent and microwave-assisted extraction, so that sulfonation modification of lignin is completed. After sulfonation modification, the obtained sulfonated lignin is applied to drilling fluid, and a viscosity reduction effect can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for integrated preparation of lignin extraction-sulfonic acid modification based on eutectic solvent coupling microwave, sulfonated lignin and application, belonging to the technical field of oil field chemistry. BACKGROUND

[0002] Fossil resources are consumed as bulk chemical raw materials and industrial fuels in large quantities. Due to limited reserves and non-renewable, the development and utilization of alternative resources has been a hot research field. Wood fiber, as an important biomass material, has a huge reserve and is renewable, and is considered as an effective carbon-containing resource, which can be used to alleviate the shortage of fossil resources. Among them, lignin is derived from wood fiber and is the only renewable high molecular aromatic polymer in nature. At present, lignin, a byproduct of the pulp and paper industry, is the main source of industrial lignin. However, most of the industrial lignin is used as fuel for heat recovery, and the utilization rate of high value is low, which not only increases the environmental burden, but also to some extent is not conducive to the sustainable development of resources.

[0003] Among them, sulfonated lignin as an important application field of industrial lignin is widely used in dye dispersant, pesticide dispersant, concrete water reducing agent, drilling fluid viscosity reducer and coal water slurry dispersant, and the earliest sulfonated lignin comes from the by-product of sulfite pulping process. According to the different pH values of the cooking liquor, it is divided into acid (pH value = 2-5), neutral (pH value = 5-7), and alkaline (pH value = 9-13.5) to cause lignin to be removed / dissolved in the cooking liquor. The phenolic structure units in lignin can be converted into unstable quinone intermediates, and then sulfonic acid groups are formed. However, the pH conditions of sulfite pulping are widely used, so the structure of sulfonated lignin produced has great difference. On the other hand, lignin sulfonate has high water solubility, and after cooking and pulping, sulfonated lignin will remain in the pulping waste liquid, and the waste liquid also contains hemicellulose and residual chemicals, which leads to low purity of lignin sulfonate produced by sulfite process, accounting for 50%~80% of the total mass of solids, 30% of hemicellulose, and about 10% of inorganic matter. There is also a sulfite lignin which is sulfonated by hydroxylated reaction of formaldehyde and Na2SO3 as sulfonating reagent. The hydroxypropyl sulfonation method is an environmentally friendly and efficient lignin sulfonation method, which avoids the use of formaldehyde. These traditional sulfonated lignin methods mainly use inorganic salt (Na2SO3, NaHSO3, H2SO4, etc.) sulfonating reagent to sulfonate the active sites in the side chain of lignin, and the process is relatively mature and has been widely used in the production of commercial lignin sulfonate. For example, Chinese patent document CN105601943A provides a method for preparing sulfonated lignin from sulfite papermaking waste liquid, which comprises the following steps: first, the sulfite papermaking waste liquid is treated by membrane to obtain a membrane concentrate, then the membrane concentrate is sequentially subjected to sulfonation and condensation to obtain sulfonated lignin. The membrane concentrate is subjected to sulfur dioxide sulfonation reaction, sodium bisulfite sulfonation reaction, or sodium sulfite sulfonation reaction. However, such lignin sulfonation process is faced with problems such as low purity, product structure diversification, insufficient content of sulfonic acid groups, high energy consumption, and complicated steps, which makes it difficult to apply in high-end fields.

[0004] In summary, there are great challenges in how to realize high-purity extraction of sulfonated lignin, increase the content of sulfonic acid groups, and simplify the separation and purification steps after reaction. Therefore, it is urgent to develop an efficient sulfonated lignin method to realize large-scale application of sulfonated lignin. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a lignin extraction-sulfonic acid modification integrated preparation method based on low eutectic solvent coupling microwave, sulfonated lignin and application. The present application constructs a ternary low eutectic solvent (DES) through the interaction of choline chloride (ChCl), epichlorohydrin (ECH) and 4-hydroxybenzenesulfonic acid (4-HBSA), and combines with microwave-assisted extraction to realize in-situ grafting of sulfonic acid functional groups in the lignin separation process, thereby completing the sulfonation modification of lignin. After sulfonation modification, the solubility of lignin in water is significantly improved, and the hydrogen bonds and polar forces between clay particles are weakened through adsorption, thereby destroying the spatial network structure of the clay particles. In addition, the electronegativity of the sulfonic acid group enhances the negative charge on the surface of the clay particles, further improves the electrostatic repulsion between the particles, and prevents the aggregation of the clay particles. When the clay particles are applied as a viscosity reducer in drilling fluid, excellent viscosity reduction effect can be achieved.

[0006] The technical scheme of the present application is as follows:

[0007] A lignin extraction-sulfonic acid modification integrated preparation method based on low eutectic solvent coupling microwave, comprising the following steps:

[0008] (1) Choline chloride (ChCl), epichlorohydrin (ECH) and 4-hydroxybenzenesulfonic acid (4-HBSA) are mixed and heated and stirred until a uniform transparent liquid is formed to obtain a low eutectic solvent (DES) ternary system;

[0009] (2) Biomass powder is added to the low eutectic solvent (DES) ternary system obtained in step (1), and the reaction is carried out under microwave conditions; after the reaction is completed, the obtained filtrate is filtered and the pH is adjusted to neutral to obtain a mixed solution; then ethanol is added to the obtained mixed solution for precipitation, and after filtration, washing and drying, lignin extraction-sulfonic acid modification is completed to obtain an environmentally friendly water-based drilling fluid sulfonated lignin.

[0010] According to the present application, the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH) and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) is 1: (1-4): (5-20), and further preferably 1:2:10.

[0011] According to the present application, the temperature of the heating and stirring in step (1) is 40-70℃, and further preferably 60℃.

[0012] According to the present application, the biomass powder in step (2) is wheat straw powder, corn straw powder or birch stem powder, and further preferably birch stem powder; the particle size of the biomass powder is 500-1000nm.

[0013] According to the application, preferably, the mass ratio of the biomass powder to the DES ternary system in step (2) is 1:8-15, and more preferably 1:10.

[0014] According to the application, preferably, the power of the microwave in step (2) is 800-1300 W, and more preferably 1000 W.

[0015] According to the application, preferably, the temperature of the reaction in step (2) is 60-100℃, and more preferably 80℃; and the reaction time is 1-8 h, and more preferably 4-5 h.

[0016] According to the application, preferably, in step (2), the pH is adjusted to neutral by using a 1wt% hydrochloric acid aqueous solution.

[0017] According to the application, preferably, the volume ratio of the ethanol to the mixed solution in step (2) is 1-4:1; and the precipitation time is 20-40 min.

[0018] According to the application, preferably, in step (2), the washing is performed by using anhydrous ethanol; and the drying is performed by vacuum drying at 60-70℃ for 15-20 h.

[0019] An environment-friendly sulfonated lignin for water-based drilling fluid is obtained by the above preparation method.

[0020] According to the application, the above environment-friendly sulfonated lignin for water-based drilling fluid is applied as a viscosity reducer in an environment-friendly water-based drilling fluid, and the addition amount of the environment-friendly sulfonated lignin for water-based drilling fluid in the environment-friendly water-based drilling fluid is 3-6wt%.

[0021] The technical features and advantages of the application are as follows:

[0022] 1、The application adopts a low eutectic solvent with a specific composition, choline chloride (ChCl) as a hydrogen bond acceptor, epichlorohydrin (ECH) as a hydrogen bond acceptor and crosslinking agent, and 4-hydroxybenzenesulfonic acid (4-HBSA) as a hydrogen bond donor and sulfonating agent, and realizes the integration of lignin extraction and sulfonic acid modification by combining with microwave enhanced reaction. Specifically, under the action of microwave irradiation, the ternary system of the low eutectic solvent (DES) selectively breaks the lignin-carbohydrate complex in biomass, directionally dissociates lignin, and destroys the intramolecular and intermolecular hydrogen bonds (such as phenolic hydroxyl and ether bond) of lignin, so that the lignin structure is loose, and more active sites (such as phenolic hydroxyl and aliphatic hydroxyl) are exposed. Based on the ring-opening reaction mechanism, the epichlorohydrin in the DES can react with the phenolic hydroxyl in the lignin and the hydroxyl in the 4-hydroxybenzenesulfonic acid at the same time, and the sulfonic acid functional group is grafted to the surface of the lignin, so that the sulfonation modification of the lignin is realized. The method of the application solves the problems of high pollution, high energy consumption, complicated steps and the like existing in the traditional lignin sulfonation process.

[0023] 2、The application improves the utilization rate of lignin, reduces the utilization of lignin as a byproduct of the pulp and paper industry, to a certain extent, reduces the burden on the environment, and to a certain extent, is conducive to the sustainable development of resources.

[0024] 3、The selectivity of the low eutectic solvent enables it to preferentially dissolve lignin without dissolving other components (such as cellulose and hemicellulose) other than lignin, thereby realizing effective extraction of lignin. 4-hydroxybenzenesulfonic acid (4-HBSA) is both a hydrogen bond donor in the DES system and a sulfonation reagent, and completes the sulfonation modification of lignin during the extraction of lignin, providing sulfonic acid groups (-SO3H) to directly participate in the sulfonation reaction of lignin. In addition, epichlorohydrin (ECH) acts as both a hydrogen bond acceptor and a crosslinking agent, on the one hand, it forms a hydrogen bond network with other components in the DES to enhance the stability and solubility of the system; on the other hand, through ring-opening reaction, it reacts with active hydroxyl groups in the lignin molecule and hydroxyl groups in the 4-HBSA molecule to crosslink, and effectively grafts the sulfonic acid functional group to the surface of the lignin.

[0025] 4、The lignosulfonate obtained by the application has aromatic group, phenolic hydroxyl, alcoholic hydroxyl, carbonyl, carboxyl, sulfonic acid group and other active groups, and has the advantages of being renewable, biodegradable and non-toxic. In the drilling fluid, it is mainly used as a viscosity reducer and a fluid loss additive. And the carboxyl and sulfonic acid group are strong anion groups with strong hydration characteristics, good water solubility, and can form a strong solvation layer on the polymer chain, thereby playing the role of salt resistance, temperature resistance and pollution resistance, further expanding the application environment of the viscosity reducer.

[0026] 5. The sulfonated lignin obtained by this invention, when used as a viscosity reducer in water-based drilling fluids, has the advantages of significant viscosity reduction, high temperature resistance, and salt and shear resistance. The prepared sulfonated lignin has a viscosity reduction rate of more than 86% in fresh water-based slurry at a temperature of 200-240℃; the shear stable viscosity is not higher than 37 mPa·s; and the salt resistance rate is greater than 38%, which can meet the high temperature environment of deep wells and is convenient for field application. Attached Figure Description

[0027] Figure 1 The infrared spectrum of sulfonated lignin for the environmentally friendly water-based drilling fluid prepared in Example 1. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] All raw materials used in the embodiments are conventional and commercially available; unless otherwise specified, the methods described are existing technologies. All other examples based on the embodiments of this invention, modified or refined by those skilled in the art, fall within the scope of protection of this invention.

[0030] Example 1

[0031] An integrated preparation method for lignin extraction and sulfonic acid modification based on microwave coupling with a eutectic solvent includes the following steps:

[0032] (1) Choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) were mixed in a molar ratio of 1:2:10 and heated and stirred at 60°C until a homogeneous transparent liquid was formed, thus obtaining a ternary system of eutectic solvent (DES).

[0033] (2) Birch trunk powder (particle size of 800 nm) was added to the ternary system of eutectic solvent (DES) obtained in step (1). The mass ratio of birch trunk powder to eutectic solvent (DES) ternary system was 1:10. The reaction was carried out at 80℃ and 1000W microwave assisted conditions for 4.5 h. After the reaction was completed, the mixture was filtered and the pH of the filtrate was adjusted to neutral with 1wt% hydrochloric acid aqueous solution to obtain a mixture. Ethanol was added to the mixture for precipitation for 30 min. The volume ratio of ethanol to the mixture was 2:1. After filtration, the precipitate was washed with ethanol 3 times to remove residual impurities and unreacted reactants. The precipitate was vacuum dried at 65℃ for 18 h to complete lignin extraction-sulfonic acid modification and obtain sulfonated lignin for environmentally friendly water-based drilling fluid.

[0034] The infrared spectrum of the sulfonated lignin used in the environmentally friendly water-based drilling fluid obtained in this embodiment is as follows: Figure 1 As shown, byFigure 1 The characteristic peak at 3408 cm -1 is caused by the vibration of phenolic and alcoholic hydroxyl groups in lignin and the intermolecular hydrogen bonds formed by them, the peak at 2931 cm -1 is caused by the vibration of methyl groups (-CH3) and methylene groups (-CH2-) on the side chain of lignin, the peak at 1510 cm -1 is caused by the vibration of benzene ring skeleton (C=C) in lignin, the peak at 1419 cm -1 is caused by the vibration of aromatic ring skeleton due to the coupling of C-H in-plane bending, the peak at 1132 cm -1 is caused by the vibration of aromatic ether C-O-C in lignin, the characteristic peak at 1037 cm -1 is the most fundamental difference between lignin and sulfonated lignin, which is caused by the vibration of -SO3 sulfonic acid group, which comes from the symmetric stretching vibration of S=O in sulfonic acid group, indicating that the lignin has undergone sulfonation reaction and successfully introduced hydrophilic sulfonic acid group on the lignin. The peak at 866 cm -1 is caused by the out-of-plane bending vibration of C-H in lignin.

[0035] Example 2

[0036] A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave is as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) is 1:2:5.

[0037] Example 3

[0038] A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave is as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) is 1:2:15.

[0039] Example 4

[0040] A lignin extraction-sulfonic acid modification integrated preparation method based on deep eutectic solvent coupling microwave is as described in Example 1, except that the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) in step (1) is 1:1:10.

[0041] Example 5

[0042] A method for preparing a modified lignin based on a deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that in step (1), the molar ratio of choline chloride (ChCl), epichlorohydrin (ECH), and 4-hydroxybenzenesulfonic acid (4-HBSA) is 1:3:10.

[0043] Embodiment 6

[0044] A method for preparing a modified lignin based on a deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that in step (2), the mass ratio of birch stem powder to deep eutectic solvent (DES) ternary system is 1:5.

[0045] Embodiment 7

[0046] A method for preparing a modified lignin based on a deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that in step (2), the mass ratio of birch stem powder to deep eutectic solvent (DES) ternary system is 1:15.

[0047] Embodiment 8

[0048] A method for preparing a modified lignin based on a deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that in step (2), the power of the microwave is 800 W.

[0049] Embodiment 9

[0050] A method for preparing a modified lignin based on a deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that in step (2), the power of the microwave is 1200 W.

[0051] Embodiment 10

[0052] A method for preparing a modified lignin based on a deep eutectic solvent coupled with microwave is as described in Embodiment 1, except that in step (2), the birch stem powder is replaced with corn straw powder (particle size of 800 nm).

[0053] Comparative Example 1

[0054] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that in step (1), 4-hydroxybenzenesulfonic acid (4-HBSA) is not added.

[0055] Comparative Example 2

[0056] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Embodiment 1, except that in step (1), epichlorohydrin (ECH) is not added.

[0057] Comparative Example 3

[0058] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (2), the reaction is carried out at 80°C for 4.5h under water bath conditions.

[0059] Comparative Example 4

[0060] Sulfonated lignin is prepared using a conventional sulfite pulping process, using sodium sulfite as the sulfonating agent, and a reaction temperature of 180°C. The specific steps are as follows:

[0061] (1) First, 5g of birch wood powder is mixed with 200mL of deionized water, and 0.5mg of sodium sulfite and 8g of sodium hydroxide are added to form a reaction slurry;

[0062] (2) The reaction slurry is heated to 180°C and maintained in a 1MPa pressure vessel for 6h. During this process, the sodium sulfite and the lignin in the wood undergo a chemical reaction, converting the lignin into lignosulfonate;

[0063] (3) The resulting solution is filtered to obtain a filtrate, and sodium hydroxide is added to adjust the pH of the filtrate to 10. The lignosulfonate is separated by centrifugation, and the resulting precipitate is freeze-dried (-65°C, 24h) to obtain sulfonated lignin.

[0064] Comparative Example 5

[0065] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1), the epichlorohydrin is replaced with urea.

[0066] Comparative Example 6

[0067] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1), the epichlorohydrin is replaced with lactic acid.

[0068] Comparative Example 7

[0069] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1), the 4-hydroxybenzenesulfonic acid is replaced with sulfamic acid.

[0070] Comparative Example 8

[0071] A method for preparing a modified lignin for an environmentally friendly water-based drilling fluid is as described in Example 1, except that in step (1), the 4-hydroxybenzenesulfonic acid is replaced with sodium sulfite.

[0072] Test Example 1

[0073] The sulfonate group content of the sulfonated lignin prepared in the examples and comparative examples was tested, and the content of the sulfonate group characteristic function of the obtained sulfonated lignin was determined using a two-phase titration method, and the specific steps were as follows:

[0074] The solvent used in the experiment was prepared: 1.75 g of Himin 1622 was accurately weighed, dissolved with water and diluted to a 250 mL volumetric flask to obtain a stock solution; before use, 25.00 mL of the stock solution was accurately removed, diluted with ultrapure water and diluted to a 250 mL volumetric flask to obtain a standard solution; 5.44 g of sodium sulfate and 2.52 g of anhydrous sodium sulfate were weighed and dissolved in 400 mL of ultrapure water, then 5.0 mL of concentrated sulfuric acid was added, stirred uniformly, cooled and diluted to 500 mL with ultrapure water to obtain an acidic buffer solution (pH about 3) used for testing; 0.5 g of disulfide blue VN150 and 0.25 g of acid blue-1 were dissolved and diluted to a 250 mL volumetric flask with ultrapure water to obtain an indicator solution.

[0075] Sample pretreatment: accurately weigh 0.1 g of dried sulfonated lignin (accurate to 0.0001 g) sample in a beaker, dissolve with a small amount of ultrapure water, and slightly heat or ultrasonic to assist dissolution. The solution was quantitatively transferred to a separatory funnel, washed with a small amount of chloroform 2-3 times to remove non-polar organic impurities that may be contained in the sample, the organic phase was discarded, and the aqueous phase was retained to obtain a sample solution.

[0076] Specific test method: accurately remove an appropriate amount of sample solution (or pretreated aqueous phase) into a dry 250 mL iodometric flask, add 10 mL of acidic buffer, 10 mL of chloroform, and 0.5-1.0 mL of indicator solution in turn. Titrate with the Himin 1622 standard solution, start with a faster speed, and shake the iodometric flask vigorously (note to release gas), so that the two phases are in full contact, near the end point, add dropwise or even half dropwise, and shake well, when the organic phase (lower chloroform phase) changes from pink or colorless to persistent blue-gray or blue, and the aqueous phase color becomes lighter or almost colorless, record the volume V (mL) of Himin 1622 standard solution consumed. Blank experiment: except that no sample is added, the rest of the steps are the same, perform a blank titration, and record the volume V0 (mL) of Himin 1622 standard solution consumed. The total content of sulfonate groups is calculated according to the following formula, and the test results are shown in Table 1.

[0077] (1)

[0078] In formula (1), V: the volume of Himin 1622 standard solution consumed by the sample, mL; V0: the volume of Himin 1622 standard solution consumed by the blank, mL; C: the concentration of the Himin 1622 standard solution, mol / L; m: the mass of the sample, g; 1000: unit conversion factor. The test results are shown in Table 1.

[0079] Table 1 Sulfonate group content

[0080]

[0081] The test results show that the sulfonate group content of the lignin sulfonate in Example 1 is 1.22 mmol / g. Example 2 reduces the amount of 4-hydroxybenzenesulfonic acid (4-HBSA) in the eutectic solvent ternary system. When the content of 4-HBSA is less, the sulfonating agent of the system may be insufficient, the number of sulfonate groups (-SO3H) introduced into the lignin molecule is limited, the reaction kinetics is limited, the activation energy is difficult to overcome, the sulfonation rate is slow, the overall reaction time is prolonged, and the sulfonate group content of the final product is reduced. Example 3 increases the amount of 4-hydroxybenzenesulfonic acid (4-HBSA) in the eutectic solvent ternary system. When the content of 4-HBSA is more, the system may be too acidic, which may cause self-degradation of lignin, further reducing the number of active sites on the lignin molecule. At the same time, it may also greatly increase the viscosity of the system, affecting the efficiency of lignin sulfonation modification, and reducing the content of sulfonate groups. Moreover, too much sulfonating agent may cause side reactions, such as cross-linking between sulfonic acid groups, the generation of by-products (such as low molecular weight sulfates), resulting in reduced purity of the modified lignin sulfonate, complex post-treatment, and affecting performance consistency and subsequent use. Example 4 reduces the amount of epichlorohydrin (ECH) in the eutectic solvent ternary system. When the content of ECH is less, the cross-linking degree of the system is insufficient, and the degree of sulfonation is low, so the content of sulfonate groups is reduced. Example 5 increases the amount of epichlorohydrin (ECH) in the eutectic solvent ternary system. When the content of ECH is more, the viscosity of the system is too high, and the high cross-linking degree of the DES system makes it difficult for the aromatic ring of lignin to be attacked by the sulfonating agent. In addition, the high cross-linking solvent may compete or interfere with the hydrogen bonds between lignin molecules, thereby affecting the extraction and modification efficiency of lignin, and thus reducing the content of sulfonate groups. In Example 6, the amount of DES is reduced, resulting in insufficient functional groups of DES, which cannot fully break the hydrogen bond network in biomass, and cannot effectively extract lignin, so the content of sulfonate groups in the final product is reduced. In Example 7, the amount of DES is increased, although it increases the contact area between DES and biomass, but the high concentration of DES changes the polarity of the reaction system, resulting in poor swelling of lignin, and -SO3H is difficult to contact with phenolic hydroxyl active sites, so the reaction efficiency is slightly reduced. At the same time, it increases the cost of lignin sulfonate extraction, and further increases the cost in the subsequent separation and purification process, which is not economically beneficial. Microwave heating can reduce the viscosity of DES and improve mass transfer, but a suitable microwave intensity is needed. When the microwave intensity in Example 8 is 800W, the local temperature does not reach the temperature of the lignin sulfonation reaction, so the content of sulfonate groups is reduced. The microwave intensity in Example 9 is higher, which may cause the sulfonate groups and ether bonds in the lignin sulfonate to break, and may also cause more side reactions (condensation or degradation of lignin) to occur, resulting in desulfonation or polymerization of the lignin sulfonate, affecting the molecular weight and activity of the product.Based on the analysis of the examples and comparative examples, example 1 is the best experimental condition of the lignin extraction-sulfonic acid modification integrated preparation method based on the eutectic solvent coupling microwave.

[0082] Test example 2

[0083] The sulfonated lignin prepared in the examples and comparative examples was tested in the drilling fluid, and the test results are shown in Table 2, and the test method is as follows:

[0084] (1) Preparation of fresh water base slurry: 400 mL of deionized water was added to a high-speed stirring cup, and high-speed stirring was started at a speed of 8000 r / min, and then 24.0 g of bentonite and 0.84 g of anhydrous sodium carbonate were added, and high-speed stirring was continued for 20 min, and the stirring was stopped at least twice to scrape the bentonite adhered to the wall of the high-speed stirring cup, and then 0.5 g of polyacrylamide with a molecular weight of 5 million and a hydrolysis degree of 25-30% and a solid content of ≥90% was slowly added, and high-speed stirring was continued for 20 min, and the stirring was stopped at least twice to scrape the bentonite and polyacrylamide on the wall, and the fresh water base slurry was obtained after being sealed and cured at 25±2℃ for 24 h.

[0085] The prepared fresh water base slurry was high-speed stirred at 8000 r / min for 5 min, and the 100 r / min reading was tested according to the standard GB / T16783.1-2014, and the value was required to be between 100-120, and if it did not meet the requirements, bentonite was added to meet the index requirements.

[0086] (2) Fresh water base slurry viscosity reduction rate and apparent viscosity reduction rate refer to the standard "SY / T5695-2017 Two-sex ion polymer for drilling fluid viscosity reducer": the specific detection method is as follows:

[0087] High temperature viscosity reduction rate determination: three 400 mL portions of the prepared fresh water base slurry were taken and placed in high temperature aging tanks, and were placed in a roller heating furnace set at a temperature of 200℃, 220℃ and 240℃, and were heated and rolled for 16 h, and after cooling to room temperature (25℃), high-speed stirring was carried out at 8000 r / min for 5 min, and the 100 r / min reading was tested according to the standard GB / T16783.1-2014, and was recorded as R 100 ; three 400 mL portions of the prepared fresh water base slurry were taken, and 0.4 g of sulfonated lignin prepared in the examples or comparative examples was added as a viscosity reducer at a stirring speed of 8000 r / min, and high-speed stirring was carried out at 8000 r / min for 20 min, and was placed in a high temperature aging tank, and was placed in a roller heating furnace set at a temperature of 200℃, 220℃ and 240℃, and was heated and rolled for 16 h, and after cooling to room temperature, high-speed stirring was carried out at 8000 r / min for 5 min, and the 100 r / min reading was tested according to the standard GB / T16783.1-2014, and was recorded as R 100（1） ;

[0088] The viscosity reduction rate is calculated according to formula (2):

[0089] D = [R 100 -R 100(1) ] / R 100 x 100% (2)

[0090] In formula (2): D: viscosity reduction rate, %; R 100 : reading of fresh water base slurry at 100 r / min, mPa-s; R 100(1) : reading of fresh water base slurry after adding viscosity reducer at 100 r / min, mPa-s.

[0091] The test results are shown in Table 2.

[0092] (3) Test of shear stable viscosity:

[0093] Take the prepared fresh water base slurry, add the sulfonated lignin prepared in the examples or comparative examples as a viscosity reducer to obtain a test slurry, and the concentration of the viscosity reducer in the test slurry is 3wt%. The test slurry is placed on a high-speed mixer and sheared at a speed of 12000 rpm for 30 minutes. After high-speed shearing for 30 minutes, the stirring is immediately stopped, and the slurry is poured into the sample cup of a rotary viscometer. The reading at 600 rpm after shearing is measured and recorded as Φ600, the AV (according to formula (3)) is calculated, and the shear stable viscosity (AV) is obtained. The test results are shown in Table 2.

[0094] AV = Φ600 / 2 (3)

[0095] (3) The salt tolerance is tested according to the "Water-based drilling fluid for petroleum and natural gas industry" GB / T 16783.1-2014, and the specific detection method is as follows:

[0096] (4) Test of salt tolerance:

[0097] Take 400 mL of prepared fresh water base slurry, add the sulfonated lignin prepared in the examples or comparative examples as a viscosity reducer to obtain a test slurry, and the concentration of the viscosity reducer in the test slurry is 3wt%, and place it in a roller heating furnace set at a temperature of 220°C and heat roll for 16h, test the apparent viscosity before adding salt; Take 400 mL of fresh water base slurry, add the sulfonated lignin prepared in the examples or comparative examples as a viscosity reducer to obtain a test slurry, and the concentration of the viscosity reducer in the test slurry is 3wt%, then add 60g of sodium chloride (NaCl), simulate the salt pollution of the formation, fully stir the drilling fluid at a stirring speed of 8000 r / min, so that the salt is completely dissolved and uniformly distributed, after the NaCl is completely dissolved, it is loaded into a high-temperature aging tank, and placed in a roller heating furnace set at a temperature of 220°C and heat roll for 16h, test the apparent viscosity after adding salt, calculate the salt tolerance according to formula (4), and the test results are shown in Table 2.

[0098] Salt tolerance rate = apparent viscosity before adding salt / apparent viscosity after adding salt × 100% (4).

[0099] Table 2 Viscosity reduction rate, shear stable viscosity and salt tolerance rate results

[0100]

[0101] From the above data, it can be seen that the lignin sulfonate prepared based on the method of the application has good dispersibility, can effectively disperse solid particles (such as clay and other mineral particles) in the water-based drilling fluid, prevent aggregation and precipitation, and reduce the viscosity of the liquid. The lignin sulfonate weakens the hydrogen bond and polar force between clay particles through adsorption, and destroys the spatial network structure of the clay particles. In addition, the electronegativity of the sulfonic acid group enhances the negative charge on the surface of the clay particles, further enhancing the electrostatic repulsion between the particles, preventing the aggregation of the clay particles, thereby playing a viscosity reducing role. This is the mechanism of action of the lignin sulfonate in reducing viscosity. The application of the eutectic solvent (choline chloride / 4-hydroxybenzenesulfonic acid / epichlorohydrin) as a solvent and sulfonating agent at the same time, combined with microwave enhanced reaction, realizes the integration of lignin extraction and sulfonic acid modification, and solves the problems of high pollution, high energy consumption, complicated steps and the like in the traditional lignin sulfonation process.

Claims

1. A method for integrated preparation of lignin extraction-sulfonic acid modification based on deep eutectic solvent coupling with microwave, characterized in that, The method comprises the following steps: (1) mixing choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid, and stirring and heating to form a homogeneous transparent liquid to obtain a ternary eutectic solvent system; the molar ratio of the choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid is 1:(1-4):(5-20); the temperature of the stirring and heating is 40-70°C; (2) adding biomass powder into the ternary eutectic solvent system obtained in step (1) and performing a reaction under microwave conditions; after the reaction is completed, the obtained filtrate is filtered, and the pH of the filtrate is adjusted to neutral to obtain a mixed solution; then, ethanol is added to the mixed solution to perform precipitation, and the precipitation is filtered, washed and dried to complete lignin extraction and sulfonic acid modification, and an environmentally-friendly sulfonated lignin for water-based drilling fluid is obtained; the biomass powder is wheat straw powder, corn straw powder or birch stem powder; the mass ratio of the biomass powder to the ternary eutectic solvent system is 1:8-15; the power of the microwave is 800-1300 W; the temperature of the reaction is 60-100°C; and the time of the reaction is 1-8 h.

2. The method according to claim 1, wherein the method is characterized by, In step (1), the molar ratio of the choline chloride, epichlorohydrin and 4-hydroxybenzenesulfonic acid is 1:2:

10.

3. The method according to claim 1, wherein the method is characterized by, In step (2), the particle size of the biomass powder is 500-1000 nm.

4. The method according to claim 1, wherein the method is characterized by, In step (2), the mass ratio of the biomass powder to the ternary eutectic solvent system is 1:

10.

5. The method according to claim 1, wherein the method is characterized by, In step (2), the power of the microwave is 1000 W.

6. The method according to claim 1, wherein the method is characterized by, In step (2), the pH is adjusted to neutral by using a hydrochloric acid solution with a concentration of 1 wt%; The volume ratio of the ethanol to the mixed solution is 1-4:1; the time of the precipitation is 20-40 min; the washing is performed by using anhydrous ethanol; and the drying is performed at 60-70°C under vacuum for 15-20 h.

7. An environmentally friendly sulfonated lignin for use in water-based drilling fluids, characterized in that, The environmentally-friendly sulfonated lignin for water-based drilling fluid is obtained by using the preparation method in any one of claims 1-6.

8. The use of the sulfonated lignin according to claim 7, as a viscosity reducer in the environmentally friendly water-based drilling fluid, characterized in that, The addition amount of the environmentally-friendly sulfonated lignin for water-based drilling fluid in the environmentally-friendly water-based drilling fluid is 3-6 wt%.

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