Lignin particles, methods of making and use thereof

Abstract

The present application provides a kind of lignin particles, preparation method and its application, including S1.Provide basic lignin sulfonate solution, 1~10 parts by weight of lignin sulfonate is mixed with 30~100 parts by weight of water, obtain lignin sulfonate solution, and the solution pH value is adjusted to be ≥11 with basic reagent;S2.The solution obtained in step S1 is subjected to hydrothermal reaction in a closed reactor, the formation process of particles of different levels is controlled by controlling the hydrothermal reaction temperature, so as to realize the controllable preparation of product particle size;Wherein, when the reaction temperature is controlled in the first temperature interval of 180 DEG C to 210 DEG C, the hydrothermal reaction forms primary particles;When the reaction temperature is controlled in the second temperature interval of 210 DEG C to 250 DEG C, the hydrothermal reaction promotes the aggregation and crosslinking between primary particles, forms secondary aggregation particles, and the particle size of secondary aggregation particles is greater than the particle size of primary particles.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, and particularly relates to a lignin particle, its preparation method, and its application. Background Technology

[0002] Following waterflooding and polymer flooding in oil extraction, water-dominant channels (high-permeability zones) emerge in the reservoir. Injected water preferentially flows away through these channels, failing to reach low-permeability reservoirs, thus reducing the effectiveness of waterflooding. To block these water-dominant channels, numerous technologies and products have been developed, such as bulked particles, polymer microspheres, and microgels. These particulate polymers, once introduced into the reservoir, effectively block these channels, diverting injected water towards low-permeability reservoirs, thereby expanding the swept volume and improving recovery efficiency. While these polymers have achieved good results, they are prepared from petroleum-derived chemical raw materials, typically using acrylamide as the main monomer with the addition of auxiliary components. Their performance has several shortcomings, such as poor temperature and salt resistance, making them unsuitable for high-temperature, high-salinity reservoirs. Using biomass to prepare bio-based particles can overcome these performance limitations, and biomass is a renewable and environmentally friendly material, aligning with the requirements of green chemistry.

[0003] Lignosulfonates are a byproduct of papermaking and have been widely used in oilfield drilling mud, oil well fracturing, and enhanced oil recovery. In the field of oil recovery, they are mainly used as surfactants, but their performance is monotonous. If lignin sulfonates are prepared into particles, their application in the field of enhanced oil recovery will be greatly expanded. Summary of the Invention

[0004] This invention provides a method for preparing lignin particles, which can at least solve the technical problem of low recovery rate in oil extraction.

[0005] The technical solution provided by this invention is as follows: On the one hand, a method for preparing lignin particles is provided, comprising: S1. Provide an alkaline lignin sulfonate solution by mixing 1-10 parts by weight of lignin sulfonate with 30-100 parts by weight of water to obtain a lignin sulfonate solution, and adjusting the pH of the solution to ≥11 with an alkaline reagent; S2. The solution obtained in step S1 is subjected to hydrothermal reaction in a closed reactor. The formation process of particles of different sizes is controlled by adjusting the hydrothermal reaction temperature, thereby achieving controllable preparation of product particle size. When the reaction temperature is controlled within the first temperature range of 180°C to 210°C, the hydrothermal reaction forms primary particles. When the reaction temperature is controlled in the second temperature range of 210°C to 250°C, the hydrothermal reaction promotes aggregation and cross-linking between the primary particles to form secondary aggregated particles, and the particle size of the secondary aggregated particles is larger than that of the primary particles.

[0006] In an optional embodiment, in step S1, the alkaline lignosulfonate solution is obtained by the following method: after dissolving lignosulfonate in water, an alkaline reagent is added to adjust the pH value of the solution to 12.

[0007] In an optional embodiment, step S1 further includes: after adjusting the pH value, 0.1 to 5 parts by weight of a quaternization reagent is added to the alkaline lignosulfonate solution, and the quaternization reagent is 3-chloro-2-hydroxypropyltrimethylammonium chloride.

[0008] In an optional embodiment, the lignosulfonate is selected from any one or more of sodium lignosulfonate, calcium lignosulfonate, and magnesium lignosulfonate.

[0009] In an optional embodiment, when the hydrothermal reaction temperature is controlled in the first temperature range, the average particle size of the prepared primary particles is 1 nm to 200 nm.

[0010] In an optional embodiment, when the hydrothermal reaction temperature is controlled in the second temperature range, the average particle size of the prepared secondary aggregated particles is 10 μm to 1000 μm.

[0011] In an optional embodiment, the secondary aggregated particles are formed by aggregation and cross-linking of primary particles with an average particle size of 0.5 μm to 2 μm.

[0012] In an optional embodiment, in step S2, the time of the hydrothermal reaction is 5 to 20 hours.

[0013] On the other hand, a lignin-based particle is provided, which is prepared by the lignin particle preparation method described in any one of the above; And the average particle size D of the lignin particles and the hydrothermal reaction temperature T (°C) satisfy a functional relationship: when 180 ≤ T ≤ 210, 1 nm ≤ D ≤ 200 nm; when 210 < T ≤ 250, 10 μm ≤ D ≤ 1000 μm.

[0014] On yet another hand, an application of the lignin-based particle is provided, and the above lignin-based particle or the lignin-based particle prepared by the lignin particle preparation method described above is applied as a displacement and injection agent or a plugging agent in oil exploitation The method provided by the embodiments of the present invention has at least the following beneficial effects: This invention enables the directional synthesis of particles at both the nanometer and micrometer scales by adjusting temperature parameters, providing a material basis for meeting the plugging needs of oil reservoirs with different pore sizes in oil extraction. This temperature-graded particle size control method has the advantages of simple process, precise control, and good repeatability. Attached Figure Description

[0015] The above and other objects, features and advantages of this disclosure will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0016] Figure 1 A schematic diagram of a method for preparing lignin particles is shown. Detailed Implementation

[0017] Embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0018] The term "comprising" and its variations as used herein signify open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "at least partially based on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0019] Please see Figure 1 On the one hand, a method for preparing lignin particles is provided, comprising: S1. Provide an alkaline lignin sulfonate solution: Mix 1-10 parts by weight of lignin sulfonate with 30-100 parts by weight of water to obtain a lignin sulfonate solution, and adjust the pH of the solution to ≥11 with an alkaline reagent; S2. The solution obtained in step S1 is subjected to hydrothermal reaction in a closed reactor. The formation process of particles of different sizes is controlled by adjusting the hydrothermal reaction temperature, thereby achieving controllable preparation of product particle size. When the reaction temperature is controlled within the first temperature range of 180℃ to 210℃, the hydrothermal reaction forms primary particles. When the reaction temperature is controlled in the second temperature range of 210℃ to 250℃, the hydrothermal reaction promotes the aggregation and cross-linking of primary particles to form secondary aggregated particles, and the particle size of the secondary aggregated particles is larger than that of the primary particles.

[0020] This invention enables the directional synthesis of particles at both the nanometer and micrometer scales by adjusting temperature parameters, providing a material basis for meeting the plugging needs of oil reservoirs with different pore sizes in oil extraction. This temperature-graded particle size control method has the advantages of simple process, precise control, and good repeatability.

[0021] In the first temperature range (180-210℃), the high-temperature and high-pressure alkaline hydrothermal environment activates the active groups such as phenolic and alcoholic hydroxyl groups on the lignin sulfonate molecular chains, mainly resulting in intramolecular or short-range intermolecular dehydration condensation and free radical coupling cross-linking reactions. These reactions lead to the folding, entanglement, and cross-linking of lignin molecular chains, forming dense, small nanoscale primary particles. The reactions in this stage are mainly characterized by "nucleation" and "primary growth".

[0022] In the second temperature range (210-250℃): higher temperatures provide stronger reaction driving forces and molecular / particle kinetic energy. At this point, unreacted active sites on the surface of the formed primary particles (such as phenolic hydroxyl groups and quinone groups) are further activated, or particles first approach and aggregate through physical forces such as hydrogen bonds, π-π stacking, and hydrophobic interactions. Under continuous humid and hot conditions, the active groups at the aggregation interface undergo further secondary cross-linking reactions, forming stable, larger micron-sized secondary aggregated particles. The reactions at this stage are mainly characterized by "particle aggregation" and "interface fusion."

[0023] For example, the weight parts of lignin sulfonate can be 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc.

[0024] The water can be in parts by weight of 30, 40, 50, 60, 70, 90 or 100 parts, etc.

[0025] In one optional embodiment, in step S1, the alkaline lignin sulfonate solution is obtained by dissolving lignin sulfonate in water and then adding an alkaline reagent to adjust the pH of the solution to 12.

[0026] The solution pH was precisely adjusted to 12 using an alkaline reagent (such as NaOH), creating a strongly alkaline reaction environment. Under alkaline conditions, lignin sulfonate molecules undergo more complete deprotonation, resulting in phenol-oxygen anions. With increasing concentration, its nucleophilic reactivity and ability to participate in oxidative coupling reactions are significantly enhanced. An alkaline environment is conducive to the partial cleavage of ether bonds such as β-O-4 in lignin, generating new active sites.

[0027] Furthermore, strongly basic conditions are essential for subsequent nucleophilic substitution reactions of quaternizing reagents (such as CHPTAC).

[0028] Setting the pH value to 12 ensures that lignin molecules have the highest and most stable reactivity in the subsequent hydrothermal reaction, which is an important prerequisite for achieving efficient and uniform cross-linking, thereby obtaining particles with regular structure and narrow particle size distribution. This avoids incomplete reaction due to insufficient alkalinity or excessive hydrolysis that may be caused by excessive alkalinity.

[0029] In an optional embodiment, step S1 further includes: after adjusting the pH value, adding 0.1 to 5 parts by weight of a quaternizing agent to the alkaline lignin sulfonate solution, wherein the quaternizing agent is 3-chloro-2-hydroxypropyltrimethylammonium chloride.

[0030] For example, the weight parts of the quaternizing agent can be 0.1 parts, 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, 1 part, 2 parts, 3 parts, 4 parts or 5 parts, etc.

[0031] The introduction of quaternary ammonium salt groups in this invention can enhance hydrophilicity and dispersion stability. Quaternary ammonium salts are strong hydrophilic groups, which improve the solubility and dispersibility of particles in aqueous solutions and prevent agglomeration during storage or injection.

[0032] Introducing positive charge makes the originally negatively charged lignin sulfonate particles amphoteric or even positively charged, which is beneficial for their adsorption onto the negatively charged sandstone surface through electrostatic interactions, thereby improving their retention capacity and plugging effect in the reservoir. In addition, the introduced hydroxyl groups may also serve as new reaction sites to participate in hydrothermal crosslinking.

[0033] In one alternative embodiment, the lignin sulfonate is selected from any one or more of sodium lignin sulfonate, calcium lignin sulfonate, and magnesium lignin sulfonate.

[0034] Calcium, magnesium, and sodium lignosulfonates are byproducts of the papermaking industry. Their molecular structures incorporate sulfonic acid groups, giving them good water solubility, which is fundamental for homogeneous hydrothermal reactions. Different counter cations (Ca...) 2+ Mg 2+ Na + It may have a slight effect on the ionic strength of the solution and the extension state of the molecular chains, but the core lignin aromatic skeleton structure and reactive functional groups are similar.

[0035] In one alternative embodiment, when the hydrothermal reaction temperature is controlled within a first temperature range, the average particle size of the prepared primary particles is 1 nanometer to 200 nanometers.

[0036] This particle size range is a result of the hydrothermal reaction kinetics at temperatures of 180-210℃. Within this temperature range, the cross-linking reaction rate is moderate enough to form a stable cross-linked network (particles), but the energy is insufficient to drive large-scale Brownian motion and collisional aggregation of the particles. Therefore, particle growth is limited to the nanoscale.

[0037] For example, the average particle size of the primary particles can be 1 nanometer, 2 nanometer, 4 nanometer, 6 nanometer, 10 nanometer, 11 nanometer, 14 nanometer, 16 nanometer, 19 nanometer, 20 nanometer, 25 nanometer, 27 nanometer, 28 nanometer, 30 nanometer, 31 nanometer, 35 nanometer, 36 nanometer, 38 nanometer, 40 nanometer, 50 nanometer, 60 nanometer, 70 nanometer, 80 nanometer, 90 nanometer, 100 nanometer, 110 nanometer, 120 nanometer, 130 nanometer, 140 nanometer, 150 nanometer, 160 nanometer, 170 nanometer, 180 nanometer, 190 nanometer, or 200 nanometer, etc.

[0038] In one alternative embodiment, when the hydrothermal reaction temperature is controlled in the second temperature range, the average particle size of the secondary aggregated particles prepared is 10 micrometers to 1000 micrometers.

[0039] The high-temperature and high-pressure environment of 210-250℃ greatly accelerates the Brownian motion of primary particles, increasing the collision frequency. At the same time, the surface activity of particles is enhanced, making particle aggregation and interfacial cross-linking reactions dominant, ultimately forming micron-sized secondary aggregates.

[0040] For example, the average particle size of the primary particles can be 1 micrometer, 2 micrometers, 4 micrometers, 6 micrometers, 10 micrometers, 11 micrometers, 14 micrometers, 16 micrometers, 19 micrometers, 20 micrometers, 25 micrometers, 27 micrometers, 28 micrometers, 30 micrometers, 31 micrometers, 35 micrometers, 36 micrometers, 38 micrometers, 40 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, 100 micrometers, 110 micrometers, 120 micrometers, 130 micrometers, 140 micrometers, 150 micrometers, 160 micrometers, 170 micrometers, 180 micrometers, 190 micrometers, 200 micrometers, 300 micrometers, 400 micrometers, 500 micrometers, 600 micrometers, 700 micrometers, 800 micrometers, 900 micrometers, 1000 micrometers, etc.

[0041] In one alternative embodiment, the secondary aggregated particles are formed by the cross-linking of primary particles with an average particle size of 0.5 micrometers to 2 micrometers.

[0042] In this embodiment of the invention, the reaction in the second temperature range is not a direct "stacking" of molecules into giant particles, but rather a multi-level assembly process. First, submicron-sized primary particles are formed (possibly instantaneously before the temperature reaches the target range, or through the further growth of smaller primary particles). These primary particles then aggregate and cross-link as "building units" to form the final large particles. The 0.5-2 μm size represents an equilibrium result where primary particles can stably exist and effectively aggregate. This multi-level structure often endows the material with a certain degree of elasticity and deformation capability (e.g., ...). Figure 1 The particle shape shown gives it the intelligent regulating characteristic of "deforming and blocking in place" when passing through the pore throat, which is superior to homogeneous solid particles.

[0043] In one alternative implementation, the hydrothermal reaction time in step S2 is 5-20 hours.

[0044] A reaction time of 5-20 hours ensures that the crosslinking or aggregation reaction can proceed completely, resulting in a final product with stable structure and consistent properties. Too short a time will lead to incomplete reaction; too long a time may result in over-reaction or energy waste.

[0045] For example, the hydrothermal reaction time can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 14 hours, 15 hours, 16 hours, 18 hours, or 20 hours, etc.

[0046] In another aspect, a lignin-based particle is provided, which is prepared by any of the above-mentioned lignin particle preparation methods; Lignin particles consist of primary particles and secondary aggregates, with the secondary aggregates having a larger particle size than the primary particles.

[0047] On the other hand, an application of lignin-based particles is provided, in which the above-mentioned lignin-based particles or lignin-based particles prepared by the above-mentioned lignin particle preparation method are used in oil extraction as a moderating agent or a plugging agent.

[0048] To facilitate understanding of the methods provided in the embodiments of the present invention, a detailed description is given below in conjunction with specific embodiments.

[0049] Example 1 Mix 3g of sodium lignosulfonate and 100g of deionized water, and stir on a magnetic stirrer until the sodium lignosulfonate is completely dissolved. Transfer the solution to a hydrothermal reactor and place the hydrothermal reactor in a constant temperature oven at 207℃ for 8 hours to obtain lignin particles with a particle size of 50 nanometers, denoted as LS-Na-207.

[0050] Example 2 Mix 10g of calcium lignosulfonate and 100g of deionized water, and stir on a magnetic stirrer until the calcium lignosulfonate is completely dissolved. Transfer the solution to a hydrothermal reactor and place the hydrothermal reactor in a constant temperature oven at 250℃ for 7 hours to obtain lignin particles with a particle size of 50 micrometers, denoted as LS-Ca-250.

[0051] Example 3 1g of calcium lignosulfonate and 100g of deionized water were mixed and stirred on a magnetic stirrer until the calcium lignosulfonate was completely dissolved. The pH of the calcium lignosulfonate was adjusted to 12 with sodium hydroxide solution. 0.1g of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added and stirred evenly. The solution was transferred to a hydrothermal reactor and placed in a constant temperature oven at 180℃ for 9 hours to obtain lignin particles with a particle size of 100 nanometers, denoted as LS-Ca-180-Q, where Q represents quaternization.

[0052] Example 4 Mix 3g of magnesium lignosulfonate and 30g of deionized water, and stir on a magnetic stirrer until the magnesium lignosulfonate is completely dissolved. Transfer the solution to a hydrothermal reactor and place the hydrothermal reactor in a constant temperature oven at 200℃ for 9 hours to obtain lignin particles with a particle size of 100 nanometers, denoted as LS-Mg-200.

[0053] Example 5 Mix 2g of calcium lignosulfonate and 50g of deionized water under a magnetic stirrer until the calcium lignosulfonate is completely dissolved. Adjust the pH of the calcium lignosulfonate to 12 with sodium hydroxide solution, add 1g of 3-chloro-2-hydroxypropyltrimethylammonium chloride and stir well. Transfer the solution to a hydrothermal reactor and place the hydrothermal reactor in a constant temperature oven at 250℃ for 9 hours to obtain lignin particles with a particle size of 200 micrometers, denoted as LS-Ca-250-Q.

[0054] It should be noted that, under alkaline and hydrothermal conditions, the quaternizing agent can react with the lignin phenolic hydroxyl groups at their adjacent positions to stably attach the quaternary ammonium groups to the lignin skeleton in the form of ether bonds or the like.

[0055] LS-Na-207 (Example 1): Sodium lignosulfonate, 207°C, nanoparticles (20-100nm). Represents basic nanoparticles.

[0056] LS-Ca-250 (Example 2): Calcium lignosulfonate, 250°C, micron particles (10-50 μm). Represents basic micron particles.

[0057] LS-Ca-180-Q (Example 3): Calcium lignosulfonate, quaternized at 180°C, nanoparticles (15-100nm). Represents surface-modified (hydrophilic / charged) nanoparticles.

[0058] LS-Mg-200 (Example 4): Magnesium lignosulfonate, 200°C, nanoparticles (50-150 nm). Represents basic nanoparticles of different salt types.

[0059] LS-Ca-250-Q (Example 5): Calcium lignosulfonate, quaternized at 250°C, micron-sized particles (50-250 μm). Represents surface-modified large-size blocking particles.

[0060] Comparative Example 1 (Comp-1): Partially hydrolyzed polyacrylamide (HPAM) was obtained by hydrothermal reaction at temperatures below 180°C (e.g., 150°C). A commercial product with a molecular weight of ~15 million, prepared at a concentration of 2000 mg / L. It represents a conventional polymer-based oil displacement agent.

[0061] Comparative Example 2 (Comp-2): HPAM / surfactant physical compound system. 2000 mg / L HPAM + 500 mg / L petroleum sulfonate. Represents existing "polymer + surfactant" compounding technology.

[0062] Comparative Example 3 (Comp-3): Unquaternized control particles. The basic formulation of Example 5 was followed without the addition of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC), and the reaction was carried out at 250°C. This verifies the necessity of the quaternization modification in this application.

[0063] Comparative Example 4 (Comp-4): Low pH control particles. Formulation as in Example 3, but without pH adjustment (pH ~6-7), reaction at 180°C.

[0064] Comparative Example 5 (Comp-5): Commercially available polymer microspheres. Commercially available polyacrylamide-based pre-crosslinked gel microspheres with a particle size range of 50-100 μm.

[0065] Solution performance and long-term stability test (90℃, 10wt% NaCl brine, aged for 30 days).

[0066] Table 1: Basic properties and temperature and salt resistance of the solution

[0067] As can be seen from Table 1, all particles of the present invention achieved an EOR of over 12.5%, which is significantly better than the 8.9% of the traditional HPAM drive.

[0068] Surface quaternization modification is the key to performance enhancement: compared with LS-Ca-250-Q (EOR+22.3%) and LS-Ca-250 (EOR+15.1%), and LS-Ca-180-Q (EOR+18.6%) and LS-Na-207 (EOR+12.5%), the improved interfacial activity and enhanced dispersion stability brought about by quaternization significantly improve oil displacement efficiency.

[0069] Controllable particle size enables differentiated plugging: nanoparticles (Examples 1, 3) are suitable for deep wellbore regulation, while micron particles (Examples 2, 5) are suitable for near-wellbore plugging. They can be precisely designed and applied according to reservoir requirements.

[0070] The lignin particles of this invention possess the ability to physically block (rigid particles), redirect deep fluid flow (nanoscale transport), and reduce interfacial tension (quaternary ammonium salt groups), especially LS-Ca-180-Q and LS-Ca-250-Q, which achieve synergistic effects.

[0071] During the 90°C high-temperature displacement process, the lignin particles showed stable performance and a robust pressure curve; while HPAM and commercial microspheres both showed signs of performance degradation.

[0072] The lignin particles provided in this invention have an aromatic network structure that gives them extreme environmental stability. All sample samples retain more than 90% of their performance at 90°C and high salt conditions, which is higher than that of traditional polymers (35%) and commercial microspheres (85%), thus broadening the application limits of modulated drive technology in high-demand reservoirs.

[0073] Achieving "controllable particle size" to meet differentiated plugging needs, particles suitable for reservoirs with different pore sizes can be directionally prepared by precisely controlling hydrothermal temperatures (e.g., 207℃ for nanoparticles, 250℃ for microparticles). Nanoparticles are used for deep-sea regulation and displacement, while microparticles are used to plug dominant channels, offering flexible application strategies.

[0074] Significant and reliable "enhanced oil recovery" effect: Core experiments confirm that the lignin particles of this invention, especially those modified with quaternization, can achieve a significant increase in oil recovery of 18.6%-22.3% under high temperature and high salinity conditions through a synergistic mechanism of "blocking, adjusting, and washing". The effect is comprehensively superior to various existing comparative technologies.

[0075] Comparative Example A (lower temperature limit comparison) further verifies whether stable primary particles with regular morphology can be formed when the hydrothermal reaction temperature is lower than the lower limit of the first temperature range of the present invention (180°C).

[0076] Weigh 3g of sodium lignosulfonate and mix it with 100g of deionized water. Stir the mixture on a magnetic stirrer until completely dissolved to obtain a lignosulfonate solution. Transfer the solution to a hydrothermal reactor, seal it, and place it in a constant temperature oven at 150℃ for 8 hours. After the reaction, allow it to cool naturally to room temperature and open the reactor to observe the product state. The material in the reactor is a dark brown turbid liquid. After standing, there is no obvious solid sedimentation, or only a small amount of flocculent, amorphous precipitate. Only a small amount of loose aggregates can be collected by high-speed centrifugation (e.g., 12000 rpm, 15 min). These aggregates redisperse easily in deionized water with slight shaking, and it is impossible to obtain "particles" with a clear solid morphology as described in Example 1. The dispersion was tested using a dynamic light scattering (DLS) instrument, and the results showed that the particle size distribution was extremely wide (polydispersity index PDI > 0.5), and there were a large number of dissolved or colloidal components ranging from several nanometers to tens of nanometers, making it impossible to define a clear average particle size.

[0077] Comparative Example A demonstrates that the energy provided by the reaction temperature of 150°C is insufficient to drive lignin sulfonate molecules to undergo sufficient and directional intramolecular / intermolecular crosslinking reactions, thus failing to complete the morphological transformation from linear / branched macromolecules to ordered nanoparticles. This conversely proves that the first temperature range (180°C to 210°C) claimed in this invention is the necessary temperature threshold for the controllable assembly of lignin sulfonate into primary nanoparticles; below this threshold, the objective of this invention cannot be achieved.

[0078] Comparative Example B (critical temperature comparison) compares the changes in product particle size when there are slight fluctuations around the critical temperature of 210℃, to demonstrate the decisive influence of this temperature point on the product structure.

[0079] Preparation process B1: Weigh 3g of sodium lignosulfonate and mix it with 100g of deionized water, stirring to dissolve. Transfer the solution to a hydrothermal reactor, seal it, and place it in a constant temperature oven at 205℃ for 8 hours. Post-reaction treatment is the same as in Example 1.

[0080] Preparation process B2: Except for the hydrothermal reaction temperature being set to 215℃, the other steps are exactly the same as in B1.

[0081] Comparative Example B1 (205℃) Product: A solid product was obtained. Laser particle size analysis showed that the average particle size (D50) was approximately 180 nm, and the particle size distribution was relatively concentrated (span of approximately 1.5). Scanning electron microscopy (SEM) observation showed that the particles were spherical or nearly spherical with relatively smooth surfaces, which is typical of primary particle morphology.

[0082] Comparative Example B2 (215℃) Product: A solid product was obtained. Its average particle size (D50) significantly increased to 2.5 μm, entering the micrometer scale, and the particle size distribution broadened (spanning approximately 2.0). SEM observation showed that the particles were secondary aggregated structures formed by the tight aggregation and fusion of a large number of smaller nanounits (approximately 100-300 nm), with a rough surface and hierarchical pores.

[0083] The results of Comparative Examples B1 and B2 clearly show that around 210℃, the particle size and structure of the products undergo a leap in magnitude. A temperature difference of only 10℃ (from 205℃ to 215℃) causes the dominant reaction mechanism to switch from "primary particle formation" to "aggregation and cross-linking of primary particles." This strongly confirms that 210℃ is a critical and unexpected critical temperature. This invention explicitly divides the temperature ranges into "180-210℃" and "210-250℃".

[0084] Comparative Example C (temperature upper limit comparison) was used to verify the negative impact on the product structure and performance when the hydrothermal reaction temperature exceeds the upper limit of the second temperature range of the present invention (250°C).

[0085] Weigh 10g of calcium lignosulfonate and mix it with 100g of deionized water, stirring until dissolved. Transfer the solution to a hydrothermal reactor, seal it, and place it in a constant temperature oven at 280℃ for 7 hours.

[0086] After the reaction, the product was a hard, black, blocky solid that adhered firmly to the inner wall of the reactor vessel, making it difficult to remove completely using conventional scraping methods. After grinding some of the fragments, SEM observation revealed a dense, non-porous structure, exhibiting sintering or over-carbonization characteristics, completely losing the porous, fluffy, near-spherical structure of the secondary aggregated particles in Example 2. When placed in simulated formation water, the material barely expanded and was difficult to disperse. When injected into the core as a plugging agent, its inability to deform and pass through the pore throat would cause a sudden increase in injection pressure and potentially lead to core blockage, rendering it unfeasible for field application.

[0087] This comparative example demonstrates that excessively high temperatures lead to violent pyrolysis and carbonization reactions in lignin, destroying its multi-level structure and physicochemical properties (such as expansion and dispersibility) required for its functional properties. Therefore, 250°C is the upper limit temperature for maintaining the ideal micro / nano structure and application performance of lignin particles. The second temperature range of this invention (210°C to 250°C) is a carefully optimized process window; exceeding this window results in product failure, reflecting the precision and boundary significance of the process conditions in this invention.

[0088] Comparative Example D (pH comparison) can verify whether the target particles can be formed under non-alkaline conditions, even if the reaction is within the temperature range of this invention.

[0089] Weigh 1g of calcium lignosulfonate and mix it with 100g of deionized water, stirring to dissolve. Do not use sodium hydroxide solution to adjust the pH; the pH of the solution at this point is approximately 6-7 (the natural pH of lignosulfonate). Transfer the solution to a hydrothermal reactor, seal it, and place it in a constant temperature oven at 180℃ for 9 hours.

[0090] The product is a dark brown viscous gel or flocculent precipitate, and cannot be obtained as a dry powder by filtration. When dispersed in water, it forms an unstable, easily settling suspension. Laser particle size analysis shows an extremely wide hydrated particle size distribution (from hundreds of nanometers to tens of micrometers), with poor data repeatability. SEM observation reveals few uniformly shaped discrete particles; the product is mainly composed of irregular aggregates. Compared to Example 3 (LS-Ca-180-Q), the stability, dispersibility, and subsequent oil displacement effect of this product are significantly reduced.

[0091] This comparative example demonstrates that a strongly alkaline environment (pH ≥ 11) is a key chemical condition driving lignin sulfonate molecules to undergo specific condensation / crosslinking reactions, thereby oriented assembling into structurally regular and stable particles. Under neutral conditions, molecular activity is insufficient, the reaction pathway changes, and mainly amorphous polymers or gels are generated. This indicates that step S1 of this invention, "adjusting the pH value to ≥ 11," is not an optional step, but an indispensable part of the entire technical solution, working synergistically with temperature control to achieve the controllable preparation of the product.

[0092] Comparative Example E (insufficient reaction time comparison) can verify the degree of reaction completeness and product stability when the reaction time is shorter than the lower limit required by this invention (5 hours).

[0093] Referring to Example 1, 3g of sodium lignosulfonate was weighed and dissolved in 100g of water, and placed in a hydrothermal reactor. The reaction was carried out at 207°C for 2 hours, and then the reaction was terminated.

[0094] Some solids could be collected, but the yield was significantly lower than in Example 1. When the solid particles were dispersed in water and aged in a 90°C, 10wt% NaCl aqueous solution, the particle size decreased significantly or the material partially dissolved, indicating an imperfect internal cross-linking network and low structural strength. In core displacement experiments, its plugging performance deteriorated rapidly, failing to achieve a long-term stable displacement effect.

[0095] This comparative example demonstrates that sufficient reaction time (5-20 hours) is essential to ensure the full progress of the cross-linking reaction between lignin molecules, forming a stable and robust three-dimensional network structure. Insufficient time will result in "semi-finished" particles whose application performance, especially their long-term stability in harsh oil reservoir environments with high temperature and high salinity, will fail to meet the requirements of this invention.

[0096] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing lignin particles, characterized in that, Comprising: S1. Provide an alkaline lignosulfonate solution. Mix 1 to 10 parts by weight of lignosulfonate with 30 to 100 parts by weight of water to obtain a lignosulfonate solution, and adjust the pH value of the solution to ≥11 with an alkaline reagent. S2. Carry out a hydrothermal reaction on the solution obtained in step S1 in a closed reactor. Control the hydrothermal reaction temperature to regulate the formation process of particles with different hierarchical sizes, thereby achieving the controllable preparation of the product particle size. Among them, when the reaction temperature is controlled in the first temperature range of 180°C to 210°C, the primary particles are formed by the hydrothermal reaction. When the reaction temperature is controlled in the second temperature range of 210°C to 250°C, the hydrothermal reaction promotes the aggregation and crosslinking between the primary particles to form secondary aggregated particles, and the particle size of the secondary aggregated particles is larger than that of the primary particles.

2. The method for preparing lignin particles according to claim 1, characterized in that, In step S1, the alkaline lignosulfonate solution is obtained by the following method: dissolve lignosulfonate in water, and then add an alkaline reagent to adjust the pH value of the solution to 12.

3. The method for preparing lignin particles according to claim 1, characterized in that, Step S1 further includes: after adjusting the pH value, add 0.1 to 5 parts by weight of a quaternization reagent to the alkaline lignosulfonate solution, and the quaternization reagent is 3-chloro-2-hydroxypropyltrimethylammonium chloride.

4. The method for preparing lignin particles according to claim 1, characterized in that, The lignosulfonate is selected from any one or more of sodium lignosulfonate, calcium lignosulfonate, and magnesium lignosulfonate.

5. The method for preparing lignin particles according to claim 1, characterized in that, When the hydrothermal reaction temperature is controlled in the first temperature range, the average particle size of the prepared primary particles is 1 nm to 200 nm.

6. The method for preparing lignin particles according to claim 1, characterized in that, When the hydrothermal reaction temperature is controlled in the second temperature range, the average particle size of the prepared secondary aggregated particles is 10 μm to 1000 μm.

7. The method for preparing lignin particles according to claim 6, characterized in that, The secondary aggregated particles are formed by the aggregation and crosslinking of primary particles with an average particle size of 0.5 μm to 2 μm.

8. The method for preparing lignin particles according to claim 1, characterized in that, In step S2, the time of the hydrothermal reaction is 5 to 20 hours.

9. A lignin-based particle, characterized in that, Prepared by the method for preparing lignin particles according to any one of claims 1-8; And the average particle size D of the lignin particles and the hydrothermal reaction temperature T (°C) satisfy a functional relationship: when 180 ≤ T ≤ 210, 1 nm ≤ D ≤ 200 nm; when 210 < T ≤ 250, 10 μm ≤ D ≤ 1000 μm.

10. An application of lignin-based particles, characterized in that, Apply the lignin-based particles according to claim 9 or the lignin-based particles prepared by the method for preparing lignin particles according to any one of claims 1-8 in oil exploitation as a displacement and injection agent or a plugging agent.

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