Temperature-resistant and salt-resistant polyanionic cellulose and preparation method thereof

Abstract

The invention discloses temperature-resistant and salt-resistant polyanionic cellulose and a preparation method thereof, and belongs to the technical field of polyanionic cellulose preparation. The method comprises the following steps: activating bleached wood pulp or cotton pulp cellulose by using low-concentration NaOH, and grafting in an alcohol-water system by using gamma-aminoethyl-gamma-aminopropyl trimethoxy silane (KH-792), so as to obtain aminated cellulose; then adding the aminated cellulose into the UiO-66-NH2 precursor sol, and carrying out microwave in-situ growth of an MOF crystal shell to form a core-shell structure; and finally, freeze-drying to construct the hierarchical porous aerogel, and crushing to obtain the finished product. Furthermore, ion exchange can be further carried out through a CaCl solution, so that Ca-UiO-66-NH2 (at) Cellulose is obtained. The apparent viscosity of 1 wt% of the product in saturated salt water is greater than or equal to 65 mPa.s, the viscosity retention rate after aging at 180 DEG C for 16 h is greater than or equal to 90%, the API filter loss is less than or equal to 6 mL, and the product is suitable for filtrate loss reduction and viscosity improvement of the deep well high-calcium drilling fluid, and has temperature resistance, salt resistance and environmental protection performance comprehensively superior to those of commercially available PAC.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyanionic cellulose preparation, and particularly relates to a temperature-resistant and salt-resistant polyanionic cellulose and a preparation method thereof. BACKGROUND

[0002] As a water-soluble cellulose ether derivative, polyanionic cellulose (PAC) is widely used in drilling fluid systems to increase viscosity, reduce filtration loss and stabilize the well wall. However, the traditional PAC is prone to molecular chain degradation, conformation collapse and insufficient ion exchange capacity in high-temperature (> 150℃) and high-salt (especially high calcium and magnesium ions) environments, resulting in significant viscosity attenuation and rapid filtration loss, which is difficult to meet the requirements of deep wells, ultra-deep wells and complex formations. This is mainly due to the lack of temperature-resistant skeleton, underdeveloped pore structure and weak anti-ion interference ability of the single polymer structure. Although the existing technology attempts to improve the performance of PAC by introducing inorganic nanomaterials or cross-linking modification, it often faces problems such as complex preparation process, uneven loading and poor controllability of pore structure, making it difficult to achieve long-term stability in high-temperature and high-salt environments. Therefore, it is an urgent need in the field of drilling fluid materials to develop a polyanionic cellulose with high specific surface area, multi-level pore structure, high ion exchange capacity and excellent thermal stability.

[0003] Metal-organic framework (MOF) is a kind of crystalline porous material formed by self-assembly of metal ions or clusters and organic ligands through coordination bonds, which has the advantages of high specific surface area, adjustable pore size and designable structure. Among them, UiO-66-NH2 has attracted much attention due to its excellent thermal and chemical stability. If it can be introduced into the PAC system to build a stable organic-inorganic hybrid structure, it is expected to utilize the rigid pore and thermal stability of MOF to protect the PAC molecular chain, thereby significantly improving its temperature and salt resistance. However, how to achieve the firm and uniform growth of MOF on the cellulose substrate and build a multi-level pore structure that can synergistically enhance the performance is still a technical problem to be solved in the field. SUMMARY

[0004] In view of the common technical problem that the performance of polyanionic cellulose in the prior art rapidly deteriorates in high-temperature and high-salt environments, the purpose of the present application is to provide a temperature-resistant and salt-resistant polyanionic cellulose and a preparation method thereof. The method uses innovative MOF (UiO-66-NH2) in-situ hybridization and aerogel construction technology to significantly improve the viscosity stability and filtration loss control ability of the product in harsh conditions such as high temperature above 180℃ and saturated brine. To solve the above technical problems, the following technical solutions are adopted: The present application provides a preparation method of a temperature-resistant and salt-resistant polyanionic cellulose, which comprises the following steps in sequence: S1: bleached wood pulp or cotton pulp cellulose is activated by 1-3 wt% NaOH at room temperature for 1-3 h, and then acid neutralization, alcohol replacement, and drying to obtain activated cellulose; S2: the activated cellulose is dispersed in an alcohol-water mixed solvent with an alcohol-to-water mass ratio of 85:15, and the pH is adjusted to 4.5-5.5 by acetic acid. Under the protection of nitrogen, γ-aminoethyl-γ-aminopropyltrimethoxysilane KH-792 is added dropwise in an amount of 25-35% of the dry weight of the cellulose, and refluxing is performed at 45-55°C for 3-5 h to obtain aminated cellulose; S3: the aminated cellulose is immediately added to a MOF precursor sol, and the sol composition is: 0.05-0.15 mol / L ZrCl4, 0.05-0.15 mol / L 2-amino terephthalic acid, 0.5-1.0 mol / L acetic acid, and DMF / H2O in a volume ratio of 7:3. The mass ratio of cellulose to sol is 1:20-1:30; S4: in a sealed microwave reaction kettle, the temperature is raised to 120°C at 2.45 GHz and 400-600 W, and the temperature is kept constant for 15-30 min. After cooling, filtration, DMF recovery, and ethanol washing, a UiO-66-NH2@Cellulose wet gel is obtained; S5: the wet gel is pre-frozen at -40°C for 12 h, and then freeze-dried for 48 h to obtain a hierarchical porous UiO-66-NH2@Cellulose aerogel; S6: the aerogel is crushed to ≤0.15 mm to obtain a finished product of temperature-resistant and salt-resistant polyanionic cellulose.

[0005] Further, after step S5 freeze-drying, the specific surface area is increased to 700-1000 m² / g, the pore volume is 0.25-0.35 cm³ / g, and the loading amount is 15-30 wt%.

[0006] Further, after step S5 freeze-drying, a three-dimensional hierarchical porous structure is formed, and the pore size distribution is 2-50 nm.

[0007] Further, after step S6, 0.3-0.8 mol / L CaCl2 solution is used for ion exchange at 25-50°C for 30-120 min to obtain a Ca-UiO-66-NH2@Cellulose aerogel.

[0008] Further, the apparent viscosity of 1 wt% of the finished product of temperature-resistant and salt-resistant polyanionic cellulose in saturated salt solution is ≥65 mPa·s (170 s-1, 25°C); The viscosity retention rate after aging at 180°C for 16 h is ≥90%; The API fluid loss is ≤6 mL (180°C, 3.5 MPa, 1 wt% addition).

[0009] Further, the temperature-resistant and salt-resistant polyanionic cellulose is suitable for being used as a filtration loss reducer and a viscosity increasing agent in a deep well drilling fluid.

[0010] The temperature-resistant and salt-resistant polyanionic cellulose prepared by the application is prepared by a multi-step continuous interface engineering, and a metal organic framework (MOF) reinforcing phase is constructed on a cellulose matrix by covalent bonding, so that an organic-inorganic hybrid aerogel structure with stable multi-level pores is formed. The process starts from the hydrolysis and condensation reaction of the methoxy group of silane coupling agent KH-792 with the hydroxyl group on the surface of cellulose under acidic catalysis, and this step successfully introduces primary amino functional groups with strong coordination ability on the cellulose chain. These amino groups not only change the surface properties of cellulose, but also act as nucleation sites for subsequent MOF growth. When the aminoated cellulose is placed in a precursor sol containing zirconium ions and 2-amino terephthalic acid ligands, the amino groups on the surface of the cellulose can effectively reduce the nucleation potential barrier of MOF (UiO-66-NH2) through interaction with zirconium clusters or organic ligands, guiding the in-situ and uniform epitaxial growth of MOF crystals on the surface and gaps of cellulose fibers, rather than spontaneous homogeneous nucleation in the solution. In this process, acetic acid acts as a modulator to control the formation rate of zirconium clusters by competitive coordination, thereby controlling the crystal size and defect density of MOF. Finally, through the freeze-drying technology, the solvent in the wet gel system is directly sublimed, so that the three-dimensional multi-level pore structure composed of cellulose fiber network and MOF crystal accumulation, containing micropores (from MOF itself) and mesopores (from the interface of the two), can be maximally retained, rather than the collapse of the pores caused by the liquid surface tension.

[0011] The unique hybrid structure and reaction path together determine the excellent temperature-resistant and salt-resistant performance of the product. The mechanism of action can be attributed to the synergistic effect of "interface stabilization" and "pore confinement". In a high-temperature environment, the firmly covalently grafted UiO-66-NH2 MOF, as a rigid, high-thermal-stability nano-reinforcing body, plays the role of a physical crosslinking point, effectively inhibiting the thermal motion, curling and degradation of the cellulose molecular chain, and thus macroscopically exhibiting a very high high-temperature viscosity retention rate. In a high-salt environment, the traditional polyanionic cellulose fails due to the compression of the double electric layer, while the hybrid aerogel of the product relies on its rich microporous and mesoporous structure to produce a strong "confinement" and "anchoring" effect on free water through capillary force and surface tension, forming a stable bound water layer; at the same time, the negative electric interface generated by the MOF skeleton and the anionic properties of cellulose itself forms a dynamic balance with the cations in the salt water, which together maintains the hydrated lubricating film of the system under high pressure. This mechanism of physical screening and chemical stabilization enables the material to maintain excellent viscosity increasing performance and extremely low filtration loss even under the extremely harsh conditions of 180℃ high temperature and saturated salt water.

[0012] Advantages of the present application: 1. By silane grafting and microwave in-situ growth of MOF, a uniform UiO-66-NH2 core-shell structure is constructed on the surface of cellulose, and a stable hierarchical pore is formed by using the rigid channel of MOF and the three-dimensional network of cellulose, which significantly improves the specific surface area and thermal stability; 2. The freeze-drying process avoids pore collapse, giving the material high pore volume and narrow distribution of mesopores, enhancing the ion buffering capacity and polymer chain anchoring effect; 3. Ca 2+ Ion exchange further optimizes the performance in high calcium environment, with lower filtration loss; 4. The product has high viscosity retention rate and low filtration loss under high temperature and high salt conditions, and its performance is significantly better than that of commercially available PAC, meeting the requirements of deep well drilling. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 77K nitrogen adsorption-desorption isotherm of the product of Example 1; Figure 2 BJH pore size distribution graph of the product of Example 1 DETAILED DESCRIPTION

[0014] To make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0015] The following will specifically illustrate the temperature-resistant and salt-resistant polyanionic cellulose and its preparation method provided by the present application through examples.

[0016] Example 1: (1) Cellulose activation Take 20g of bleached conifer pulp and immerse it in 400mL of 2wt% NaOH solution, and stir magnetically at 25℃ for 2h to remove hemicellulose and residual lignin; then filter and wash with deionized water until neutral. Then acidify with 0.1mol / L HCl for 10min to protonate the surface hydroxyl groups, continue to wash with water until pH≈6, replace water with ethanol for 3 times, and dry at 60℃ under vacuum for 12h to obtain activated cellulose (AC) 18.3g.

[0017] (2) Silane grafting covalent anchoring AC 10 g was dispersed in a mixed solvent of ethanol / water (85:15, w / w) 200 mL, and the pH was adjusted to 5.0 with acetic acid. The dissolved oxygen was removed by bubbling nitrogen for 30 min. Under the protection of N2, γ-aminopropyltrimethoxysilane (KH-792) 3 g (30% of the dry weight of AC) was added dropwise at 50°C, and the reaction was refluxed for 4 h. After the reaction was completed, the mixture was cooled, filtered, washed with ethanol three times, and dried at 80°C under vacuum for 8 h to obtain aminated cellulose (Cell-NH2) 11.4 g, with a nitrogen content of 2.2 wt% (elemental analysis), indicating that the silane was successfully grafted.

[0018] (3) Microwave in-situ growth of UiO-66-NH2 core-shell structure The MOF precursor sol was prepared by dissolving ZrCl4 3.5 g, 2-amino terephthalic acid 2.7 g, and acetic acid 6.0 g in a mixed solvent of DMF 70 mL and deionized water 30 mL in sequence, and stirring at 25°C until clear (molar ratio Zr:ligand:acetic acid ≈ 1:1:10). Cell-NH2 2.0 g was added to 40 mL of the above sol, and after pre-adsorption for 30 min, it was transferred to a 100 mL PTFE-lined microwave reactor. The microwave power was 500 W, and the temperature was raised to 120°C in 5 min, and kept constant for 20 min, and then naturally cooled. The product was filtered, and the DMF was recovered and recycled. The ethanol was washed until it was colorless, and the wet gel of UiO-66-NH2@Cellulose was obtained.

[0019] (4) Freeze-drying to construct hierarchical porous aerogel The wet gel was pre-frozen in a -40°C refrigerator for 12 h, and then transferred to a freeze dryer (cold trap -40°C, vacuum <10 Pa) for drying for 48 h, to obtain white fluffy aerogel 2.60 g with a loading of 25 wt%.

[0020] (5) Grinding and product preparation The UiO-66-NH2@Cellulose aerogel obtained in step (4) was placed in a high-speed grinder and run at 15 000 r / min for 30 s, and then sieved through a 100-mesh sieve to obtain white fluffy powder with a particle size ≤0.15 mm, which was the finished product of the temperature-resistant and salt-resistant polyanionic cellulose. The powder can be directly used in deep well high-calcium drilling fluid systems without pre-swelling.

[0021] As Figure 1As shown, the sample presents a typical H3-type hysteresis loop: the adsorption branch rises steeply in the low pressure region (p / p0<0.1), indicating the presence of abundant micropores; the middle-high pressure region (0.1-0.8) keeps rising without plateau, corresponding to the slit mesopores formed by the stacking of flaky particles. The desorption branch is above the adsorption branch throughout, the hysteresis loop opens to the high pressure end (p / p0≈0.45-0.85) and closes at p / p0=1, with a total pore volume of 0.38 cm3 / g (STP). The BET specific surface area is 905 m2 / g, calculated from the linear segment of 0.05-0.30, and the BJH peak pore size is about 4 nm, confirming the introduction of hierarchical pore structure.

[0022] Figure 2 The BJH pore size distribution (desorption branch) of UiO-66-NH2@Cellulose is given. The curve presents a sharp main peak at 4.0 nm, corresponding to the UiO-66 lattice pores and the secondary pores at the interface of cellulose-MOF; the tail signal extends to 50 nm, reflecting the slit mesopores formed by freeze-drying. The main peak has a half-height width of about 1.2 nm, and the peak area accounts for more than 50% of the cumulative pore volume, confirming that the sample has a narrow-distributed, high-capacity mesoporous structure, which is beneficial to ion buffering and polymer chain anchoring.

[0023] The saturated brine-based slurry (26 wt% NaCl) was prepared according to API 13A standard, and the determination was made at a 1 wt% sample addition: Apparent viscosity: 65 mPa·s (25℃, 170 s⁻¹); Viscosity after hot rolling at 180℃ for 16 h: 59 mPa·s, retention rate 91%; API fluid loss: 5.8 mL (180℃, 3.5 MPa); All indicators are significantly better than the commercially available high-viscosity PAC.

[0024] Example 2: (1) Preparation of precursor The 2.0 g of UiO-66-NH2@Cellulose aerogel obtained in steps (1)-(4) of Example 1 was used as prepared.

[0025] (2) Ca²⁺ ion exchange The aerogel was immersed in 50 mL of 0.5 mol / L CaCl2 solution and stirred in a constant temperature water bath at 30℃ for 1 h; then vacuum filtration was performed, and repeated washing with deionized water was performed until there was no Cl⁻ in the filtrate (no white precipitate was formed by AgNO3 titration). The obtained wet material was again pre-frozen at -40℃ for 12 h, and freeze-dried at -40℃ for 48 h (<10 Pa) to obtain a light gray fluffy solid 1.95 g, which was the final product Ca-UiO-66-NH2@Cellulose. Ca 2+ Exchange capacity: 450 mg / g (EDTA titration).

[0026] (3) Pulverization and finished product preparation The Ca-UiO-66-NH2@Cellulose aerogel obtained in step (2) was placed in a high-speed pulverizer, which was operated at 15 000 r / min for 30 s, and passed through a 100-mesh sieve to obtain a white fluffy powder with a particle size of ≤0.15 mm, which was a finished product of temperature-resistant and salt-resistant polyanionic cellulose.

[0027] Saturated salt water-based mud (26 wt% NaCl) was prepared according to API 13A, and the viscosity was measured at a dosage of 1 wt%: 25℃ apparent viscosity: 68 mPa·s (170 s⁻¹); 180℃, 16h hot rolling viscosity: 62 mPa·s, retention rate 91%; API fluid loss: 5.5 mL (180℃, 3.5 MPa), reduced by 0.3 mL compared with the Na⁺ type final product; High calcium environment (25 wt% CaCl2) apparent viscosity: 72 mPa·s, fluid loss 6.0 mL.

[0028] Conclusion: Ca-UiO-66-NH2@Cellulose has high specific surface area, high Ca²⁺ exchange capacity and excellent temperature-resistant and salt-resistant performance, and is particularly suitable for deep well high calcium drilling fluid system.

[0029] Comparative Example 1: According to API 13A standard, commercially available high-viscosity polyanionic cellulose (PAC-HV, not hybridized) was directly selected as a blank control without further treatment. The same base mud formulation (26 wt% NaCl saturated salt water) and dosage (1 wt%) as in Example 1 were used for performance testing, and the results were as follows: 25℃ apparent viscosity: 35 mPa·s (170 s⁻¹); 180℃, 16h hot rolling viscosity: 19 mPa·s, retention rate 54%; API fluid loss: 14 mL (180℃, 3.5 MPa); High calcium environment (25 wt% CaCl2) apparent viscosity: 28 mPa·s, fluid loss 12 mL.

[0030] Compared with Example 1, the viscosity of pure PAC-HV significantly decreased under high temperature and high salt conditions, and the fluid loss was high, which did not have the temperature-resistant and salt-resistant performance required for deep well application.

[0031] Finally, it should be noted that the above detailed description is merely illustrative of the technical solutions of the present application and is not limiting, and although the present application has been described in detail with reference to the examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application, and all should be covered in the scope of the claims of the present application.

Claims

1. A process for the preparation of a heat- and salt-resistant polyanionic cellulose, characterized in that, Comprise in turn: S1: bleached wood pulp or cotton pulp cellulose is activated at room temperature for 1-3 h with 1-3 wt % NaOH, and then acid neutralization, alcohol replacement, and drying to obtain activated cellulose; S2: the activated cellulose is dispersed in an alcohol-water mixed solvent with an alcohol to water mass ratio of 85:15, the pH is adjusted to 4.5-5.5 with acetic acid, and γ-aminoethyl-γ-aminopropyl trimethoxysilane KH-792 is added dropwise under nitrogen protection, the amount is 25-35% of the dry weight of the cellulose, and refluxing is carried out at 45-55 ℃ for 3-5 h to obtain aminated cellulose; S3: the aminated cellulose is immediately added to a MOF precursor sol, the sol composition is: 0.05-0.15 mol / L ZrCl4, 0.05-0.15 mol / L 2-amino terephthalic acid, 0.5-1.0 mol / L acetic acid, DMF / H2O volume ratio 7:3, and the mass ratio of cellulose to sol is 1:20-1:30; S4: in a sealed microwave reaction kettle, heating to 120 ℃ at 2.45 GHz and 400-600 W, constant temperature for 15-30 min, cooling, filtering, DMF recovery, and ethanol washing to obtain a UiO-66-NH2@Cellulose wet gel; S5: the wet gel is pre-frozen at -40 ℃ for 12 h, and then freeze-dried for 48 h to obtain a hierarchical pore UiO-66-NH2@Cellulose aerogel; S6: the aerogel is crushed to ≤0.15 mm to obtain a finished product of a temperature-resistant and salt-resistant polyanionic cellulose.

2. The method for preparing a temperature- and salt-resistant polyanionic cellulose according to claim 1, characterized in that, The specific surface area of the product after step S5 is increased to 700-1000 m² / g, the pore volume is 0.25-0.35 cm³ / g, and the loading amount is 15-30 wt %.

3. The method for preparing a temperature- and salt-resistant polyanionic cellulose according to claim 1, characterized in that, The product after step S5 forms a three-dimensional hierarchical pore structure, and the pore size distribution is 2-50 nm.

4. The method for preparing a temperature- and salt-resistant polyanionic cellulose according to claim 1, characterized in that, The product after step S6 further comprises ion exchange in a 0.3-0.8 mol / L CaCl2 solution at 25-50 ℃ for 30-120 min to obtain a Ca-UiO-66-NH2@Cellulose aerogel.

5. A temperature-resistant and salt-resistant polyanionic cellulose prepared by any one of the methods of claims 1-4, characterized in that, 1 wt % of the finished product of the temperature-resistant and salt-resistant polyanionic cellulose has an apparent viscosity ≥65 mPa·s (170 s-1, 25 ℃) in a saturated salt water solution; The viscosity retention rate after aging at 180 ℃ for 16 h is ≥90 %; The API fluid loss is ≤6 mL (180 ℃, 3.5 MPa, 1 wt % addition amount).

6. The heat- and salt-resistant polyanionic cellulose according to claim 5, characterized in that, The temperature-resistant and salt-resistant polyanionic cellulose is suitable for use as a fluid loss additive and viscosity enhancer in deep well drilling fluids.

Images