Modified corn straw nanocellulose fluid as well as preparation method and application thereof

Abstract

The invention provides a modified corn straw nanocellulose fluid as well as a preparation method and application thereof. The modified corn straw nanocellulose fluid is prepared from the modified corn straw nanocellulose and then used as a cavity coating of a salt-cavern gas storage, and the modified corn straw nanocellulose fluid has the advantages that (1) the mechanical property is excellent, the compressive strength of the coating is larger than or equal to 20 MPa, the salt solution corrosion resistance is high, and the strength retention rate is larger than 90% after the coating is soaked in a 25% NaCl solution for 180 days; (2) intelligent response capability: closed-loop response of pressure fluctuation-fracture generation-automatic repair is realized through wettability regulation and control (a water phase contact angle is 90-110 degrees) and a self-repair mechanism; and (3) the cost economic advantage: the raw material cost is reduced by 40% compared with the synthetic polymer, frequent repair is not needed, and the whole life cycle cost is reduced by more than 35%.

Description

Technical Field

[0001] This invention belongs to the field of safety protection technology for salt cavern gas storage, specifically relating to a modified corn stalk nanocellulose fluid, its preparation method, and its application in sealing salt cavern gas storage. Background Technology

[0002] As a core infrastructure for global energy peak shaving, salt cavern gas storage facilities, with a total global storage capacity of up to 1.2 trillion cubic meters, play a crucial role in seasonal peak shaving and emergency reserves of natural gas. These facilities are formed through water-soluble mining, with naturally occurring fissures of 1-100 μm and nanopores <1 μm created by dissolution in the rock walls, forming a complex seepage network. Data from the U.S. Energy Information Administration (EIA) shows that the gas permeability of conventional salt cavern gas storage facilities is generally higher than 8 × 10⁻⁶. - 18 m 2 A 500,000-cubic-meter gas storage facility in Germany suffered an annual loss rate of 0.7% due to a leak caused by a crack, resulting in direct economic losses exceeding 3 million euros. With the surging demand for hydrogen energy storage, the permeability of hydrogen molecules is three times that of natural gas, making traditional sealing technologies insufficient to meet permeability requirements of <10%. -19 m 2 The stringent requirements necessitate nanoscale sealing solutions.

[0003] Existing sealing material systems suffer from significant technical bottlenecks: cement-based grouts experience shrinkage and cracking rates exceeding 60% within three months due to salt rock erosion; a salt cavern in Texas, USA, experienced secondary leakage six months after cement sealing; polymer gels, when soaked in a 25% salt solution for 180 days, undergo molecular chain hydrolysis leading to a 72% strength reduction, and the released acrylamide monomers are classified as Group 2A carcinogens; bentonite swells upon contact with water, reducing its compressive strength by 50%, making it unable to withstand gas storage pressures above 30 MPa. China's "Safety Specifications for Gas Storage Facilities" explicitly requires that newly built salt caverns have an annual leakage rate ≤0.05%, indicating a clear performance gap in traditional technologies.

[0004] The development of nanoscale sealing materials has become a breakthrough in the industry, but inorganic nanomaterials and synthetic polymers have inherent defects. Nanoscale silica (particle size 20-50 nm) readily reacts with Cl- in high-salt environments. - The formation of ion pairs leads to particle aggregation and sedimentation. A case study of its application in a Russian salt cavern showed that the fluid viscosity increased fourfold one month after the injection of nano-SiO2, and the construction pressure surged, causing the process to be interrupted. Although polyacrylamide (PAM) nanogels can improve the sealing efficiency, their monomer toxicity and decades-long degradation cycle have led to restrictions on their use by the EU's Nanomaterials Regulation.

[0005] Bio-based nanomaterials have become a research focus due to their environmental friendliness, but there are key obstacles in the modification technology of corn stalk nanocellulose. Existing technologies lack synergistic regulation of the surface wettability and pore matching of corn stalk nanocellulose, making it difficult to achieve precise nanoscale filling.

[0006] The unique environment of salt cavern gas storage facilities places multiple stringent requirements on sealing materials: high mineralization leads to compression of the double electric layer on the material surface, and conventional hydrophilically modified corn stalk nanocellulose is prone to agglomeration; periodic pressure fluctuations subject the sealing layer to repeated shear stress, and the fatigue life of traditional physical adsorption coatings is only 50-80 cycles; the reservoir temperature of 40-80℃ accelerates material degradation, and unmodified corn stalk nanocellulose has a half-degradation period of only 45 days in a 60℃ salt solution. In addition, the new demand for co-storage of CO2 and natural gas requires materials to also have resistance to acid gas corrosion, while the International Energy Agency (IEA) 2024 report pointed out that only 12% of the sealing materials in the current technology can simultaneously meet the requirements of high sealing performance and environmental friendliness.

[0007] Corn stalks, an agricultural waste with an annual output of over 2 billion tons, exhibit potential for biodegradability and interface regulation after modification with nanocellulose. However, key technologies for their specific application in salt cavern gas storage still need to be mastered. These technologies include how to achieve chemical bonding between corn stalk nanocellulose and salt rock through surface modification, how to regulate nanoparticle size to match fractures of different scales, and how to construct a dynamic self-healing mechanism. These are the technological gaps that the industry urgently needs to address. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a modified corn stalk nanocellulose fluid, its preparation method, and its application.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention provides a method for preparing modified corn stalk nanocellulose fluid. The method includes: treating corn stalks with alkali and enzymatically hydrolyzing them, then modifying and nano-sizing them with a silane coupling agent to obtain modified corn stalk nanocellulose with a particle size of 50-200 nm; dispersing 1-5 wt% of the modified corn stalk nanocellulose in an aqueous solution containing a stabilizer to obtain modified corn stalk nanocellulose fluid.

[0011] Furthermore, the silane coupling agent is KH-570 or KH-560, and the amount used is 2-5% of the mass of the modified corn straw nanocellulose, and the water contact angle after modification is 90°-110°.

[0012] Furthermore, the nano-sizing process employs high-pressure homogenization at 150-200 MPa combined with ultrasonic treatment at 500-800 W for 30-60 minutes.

[0013] Furthermore, based on the total amount of the modified corn stalk nanocellulose fluid, the amount of stabilizer used is 0.5-2 wt% polyacrylamide or 1-3 wt% zwitterionic polymer.

[0014] The present invention also provides a modified corn stalk nanocellulose fluid prepared by the above-mentioned method for preparing modified corn stalk nanocellulose fluid.

[0015] The present invention also provides an application of the above-mentioned modified corn stalk nanocellulose fluid in the sealing of salt cavern gas storage tanks.

[0016] The present invention provides a method for improving the safety of a salt cavern gas storage facility based on a modified corn stalk nanocellulose fluid. The method includes: cleaning the cavity of the salt cavern and optimizing the surface roughness of the cavity to Ra = 2.5-5.0 μm; injecting the modified corn stalk nanocellulose fluid as described above into the cavity at a pressure of 1-3 MPa; and forming a 50-200 nm coating on the wall surface after air lift and drainage.

[0017] Furthermore, the injection volume is 15-25% of the cavity volume, and the system is circulated for 2-4 hours after injection, with an air lift drainage rate of 0.3-0.8 m / h.

[0018] Furthermore, the method also includes: real-time monitoring of permeability and triggering self-repair via an activation solution; the self-repair activation solution contains 0.1-0.5 mol / L Ca 2+ And 0.5-1.0 mol / L urea.

[0019] This invention also provides a salt cavern gas storage system, comprising forming a modified corn stalk nanocellulose coating on the inner wall of a cavity using the modified corn stalk nanocellulose fluid as described above, wherein the permeability of the modified corn stalk nanocellulose coating is ≤5×10⁻⁶. -20 m 2 Compressive strength ≥15MPa.

[0020] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages:

[0021] This invention uses corn stalks as raw material to prepare modified corn stalk nanocellulose. The modified corn stalk nanocellulose is biodegradable, and the carbon footprint of the production process is reduced by 70% compared with traditional polymers, which meets the standards for green gas storage construction. The modified corn stalk nanocellulose is used to make modified corn stalk nanocellulose fluid, and then used as the cavity coating of salt cavern gas storage. It has the following characteristics: (1) Excellent mechanical properties: the coating compressive strength is ≥20MPa, and it has strong resistance to salt solution corrosion. After soaking in 25% NaCl solution for 180 days, the strength retention rate is >90%; (2) Intelligent response capability: through wettability regulation (water phase contact angle 90°-110°) and self-repair mechanism, a closed-loop response of "pressure fluctuation-crack generation-automatic repair" is realized; (3) Cost advantage: the raw material cost is reduced by 40% compared with synthetic polymers, and frequent repairs are not required, and the total life cycle cost is reduced by more than 35%. Detailed Implementation

[0022] This invention provides a method for improving the safety of salt cavern gas storage facilities based on modified corn stalk nanocellulose fluid, which includes the following core steps:

[0023] (1) Pretreatment of salt cavern

[0024] Impurity removal: The cavity is cleaned by circulating high-pressure brine (concentration 20-25%) to remove salt crystals and mud impurities from the inner wall;

[0025] Surface optimization: The surface roughness of the cavity is adjusted to Ra = 2.5-5.0μm by CO2 dry ice jetting technology, which enhances the adhesion of the nano-coating.

[0026] (2) Preparation of modified corn straw nanocellulose

[0027] Raw material pretreatment:

[0028] Corn stalks were crushed into 0.2-0.5 mm powder and treated with 5% NaOH solution at 70℃ for 2 hours to remove lignin.

[0029] Cellulose microfibrils were obtained by enzymatic hydrolysis at 50°C for 12 hours using cellulase (enzyme activity ≥1000 IU / g).

[0030] Surface modification:

[0031] Silane coupling modification: Add KH-570 silane coupling agent (the amount is 2-5% of the mass of corn straw nanocellulose), react in a 60℃ water bath for 3h, and adjust the water contact angle to 90°-110°.

[0032] Nanoparticle processing: Modified corn straw cellulose nanoparticles with a particle size of 50-200 nm and a specific surface area ≥200 m² are prepared by high-pressure homogenization (pressure 150-200 MPa) combined with ultrasonic treatment (power 500-800 W, time 30-60 min). 2 / g.

[0033] (3) Modified corn straw nanocellulose nanofluid configuration

[0034] Modified corn straw nanocellulose was dispersed at a concentration of 1-5 wt% in an aqueous solution containing 0.5-2 wt% polyacrylamide (PAM, molecular weight 8-12 million).

[0035] For high-salt reservoirs (mineralization > 30000 mg / L), 1-3 wt% of zwitterionic polymer is added as a salt-resistant stabilizer, and ultrasonically dispersed for 30 min to form a stable fluid.

[0036] (4) Nanofluid injection and film formation process

[0037] Pressure injection: Corn straw nanocellulose nanofluid is injected into the salt cavern cavity at a pressure of 1-3 MPa, and the injection volume is 15-25% of the cavity volume;

[0038] Dynamic circulation: Maintain fluid flow at a rate of 0.5-1.0 m. 3 Cycle at a rate of / h for 2-4h to ensure that the nanoparticles are fully adsorbed on the crack surface;

[0039] Air lift drainage: Nitrogen gas lift (pressure 2-4MPa) is used to drain the cavity solution, and the drainage rate is controlled at 0.3-0.8m / h to form a dense coating of 50-200nm thick on the wall surface.

[0040] (5) Intelligent monitoring and repair of sealing performance

[0041] Real-time monitoring: Fiber optic sensors are used to monitor cavity permeability, coating thickness, and pressure fluctuations in real time. When permeability > 10... -19 m 2 The repair mechanism is triggered at any time;

[0042] Self-healing process: Automatic injection of Ca-containing... 2+ An activation solution containing 0.1-0.5 mol / L urea and 0.5-1.0 mol / L was used to catalyze the generation of CaCO3 by the urease activity on the surface of residual corn straw nanocellulose, which then filled the newly formed cracks.

[0043] As another objective of this invention, this invention provides a method for improving the sealing performance of salt cavern gas storage facilities by using modified corn stalk cellulose, which can reduce the permeability of the salt cavern by more than 95% (from 10). -18 m2 Reduced to <5×10 -20 m 2 The annual leakage rate is less than 0.03%, meeting the stringent sealing requirements for natural gas storage.

[0044] The present invention will now be described in detail with reference to specific embodiments.

[0045] Example 1

[0046] This invention provides a method for improving the safety of salt cavern gas storage facilities based on modified corn stalk nanocellulose fluid, applying the modified corn stalk nanocellulose fluid to a salt cavern gas storage facility in North China. The method includes:

[0047] Cavity pretreatment:

[0048] The chamber was cleaned with a 25% NaCl solution (60°C) at a pressure of 10 MPa to remove salt crystal impurities.

[0049] The surface roughness was adjusted to Ra = 3.2 μm by CO2 dry ice spraying.

[0050] Preparation of modified corn straw cellulose:

[0051] Corn stalks were crushed and then treated with 8% NaOH solution to obtain cellulose microfibers through enzymatic hydrolysis.

[0052] After modification with 3% KH-570 silane coupling agent, and homogenization under 180MPa high pressure and ultrasonic treatment under 600W, particles with a diameter of 80-120nm and a specific surface area of ​​250m² were obtained. 2 / g modified corn straw cellulose.

[0053] Nanofluid preparation:

[0054] 2 wt% modified corn straw cellulose was dispersed in an aqueous solution containing 1 wt% PAM and ultrasonically dispersed for 45 min to form a stable fluid.

[0055] Injection and film formation:

[0056] A corn stalk cellulose fluid (20% of the volume of the cavity) was injected at a pressure of 2 MPa and circulated for 3 hours. The fluid was then drained using nitrogen gas at 3 MPa to form a coating 100-150 nm thick.

[0057] Effect detection:

[0058] Coating penetration rate reduced to 3×10 -20 m 2 When the working pressure is maintained at 20MPa for 72 hours, the pressure drop is <0.05MPa and the annual leakage rate is 0.02%.

[0059] Example 2

[0060] This invention provides a method for improving the safety of salt cavern gas storage facilities based on modified corn stalk nanocellulose fluid, which involves applying the modified corn stalk nanocellulose fluid to enhance the sealing of high-salinity salt caverns. The method includes:

[0061] Cavity pretreatment:

[0062] The surface was cleaned with a 30% NaCl solution, and the surface roughness was adjusted to Ra = 4.0 μm.

[0063] Preparation of modified corn straw cellulose:

[0064] Based on silane modification, a zwitterionic monomer (methacryloyloxyethyltrimethylammonium chloride) was grafted onto the cellulose to obtain salt-resistant corn straw cellulose (particle size 100-150 nm).

[0065] Nanofluid preparation:

[0066] A fluid containing 3 wt% corn stalk cellulose and 2 wt% salt-resistant stabilizer (zwitterionic polymer) was prepared.

[0067] Injection and film formation:

[0068] Supercritical CO2 (pressure 10 MPa) is injected simultaneously after injection to promote interfacial carbonation reaction.

[0069] Effect detection:

[0070] After immersion in a 35% NaCl solution for 120 days, the coating permeability stabilized at 5 × 10⁻⁶. -20 m 2 With a compressive strength of 18MPa, it enables the synergistic storage of CO2 and natural gas.

[0071] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the present invention. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing modified corn stalk nanocellulose fluid, characterized in that, The preparation method includes: treating corn stalks with alkali and enzymatically hydrolyzing them, then modifying and nano-sizing them with a silane coupling agent to obtain modified corn stalk nanocellulose with a particle size of 50-200 nm; dispersing 1-5 wt% of the modified corn stalk nanocellulose in an aqueous solution containing a stabilizer to obtain a modified corn stalk nanocellulose fluid.

2. The method for preparing modified corn straw nanocellulose fluid according to claim 1, characterized in that, The silane coupling agent is KH-570 or KH-560, and the dosage is 2-5% of the mass of the modified corn straw nanocellulose. The water contact angle after modification is 90°-110°.

3. The method for preparing modified corn straw nanocellulose fluid according to claim 1, characterized in that, The nano-sizing process employs high-pressure homogenization at 150-200 MPa combined with ultrasonic treatment at 500-800 W for 30-60 minutes.

4. The method for preparing modified corn straw nanocellulose fluid according to claim 1, characterized in that, Based on the total amount of the modified corn stalk nanocellulose fluid, the amount of the stabilizer is 0.5-2 wt% polyacrylamide or 1-3 wt% zwitterionic polymer.

5. A modified corn stalk nanocellulose fluid prepared by the method of any one of claims 1 to 4.

6. The application of the modified corn stalk nanocellulose fluid according to claim 5 in the sealing of salt cavern gas storage tanks.

7. A method for improving the safety of salt cavern gas storage facilities based on modified corn stalk nanocellulose fluid, characterized in that, The method includes: Clean the cavity of the salt cavern and optimize the surface roughness of the cavity to Ra = 2.5-5.0 μm; The modified corn stalk nanocellulose fluid as described in any one of claims 1 to 4 is injected into the cavity at a pressure of 1-3 MPa, and after air lift and drainage, a 50-200 nm coating is formed on the wall surface.

8. The method for improving the safety of salt cavern gas storage based on modified corn stalk nanocellulose fluid according to claim 7, characterized in that, The injection volume is 15-25% of the cavity volume, and the system is circulated for 2-4 hours after injection. The air lift drainage rate is 0.3-0.8 m / h.

9. The method for improving the safety of salt cavern gas storage based on modified corn stalk nanocellulose fluid according to claim 7, characterized in that, The method also includes: real-time monitoring of permeability and triggering self-repair through an activation solution; The self-healing activating solution contains 0.1-0.5 mol / L Ca 2+ And 0.5-1.0 mol / L urea.

10. A salt cavern gas storage system, characterized in that, This includes forming a modified corn stalk nanocellulose coating on the inner wall of the cavity using a modified corn stalk nanocellulose fluid as described in any one of claims 1 to 4, wherein the permeability of the modified corn stalk nanocellulose coating is ≤5×10⁻⁶. -20 m 2 Compressive strength ≥15MPa.