A method for promoting the formation of carbon dioxide hydrate

Abstract

The present invention belongs to the field of gas hydrate formation technology and provides a method for promoting the formation of carbon dioxide hydrate, which comprises the following steps: adding a promoter system containing modified nanoparticles to a carbon dioxide-water mixed system, and performing a hydrate formation reaction under 2-15°C and 3-10 MPa pressure conditions, wherein the promoter system is composed of an amino acid derivative, a surfactant, and a metal salt in a mass ratio of 1:0.5-2:0.1-0.8, and the modified nanoparticles are silica nanoparticles treated with a silane coupling agent. This application achieves rapid generation and high-density storage of carbon dioxide hydrates under low temperature and low pressure conditions through the multi-component synergistic effect of the composite promoter system and optimization of process parameters, while reducing energy consumption and avoiding environmental pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas hydrate formation, and in particular relates to a method for promoting the formation of carbon dioxide hydrate. Background Art

[0002] Carbon dioxide hydrates, a cage-like crystal structure formed by carbon dioxide and water molecules under low-temperature and high-pressure conditions, have important applications in gas storage, industrial refrigeration, and natural gas hydrate extraction. However, the traditional carbon dioxide hydrate formation process suffers from slow kinetics and harsh thermodynamic conditions, which limits its industrial application. Existing technologies often improve hydrate formation conditions by adding chemical promoters, such as surfactants, nanoparticles, or amino acids, to reduce the activation energy of the reaction.

[0003] Existing promoters still have obvious defects in practical applications. For example, although a single surfactant can reduce interfacial tension, it is prone to aggregation failure under high pressure, and the residue may cause environmental pollution. Although nanoparticle promoters can provide nucleation sites, the particles have poor dispersion and are prone to deposition and clogging equipment after long-term use. Although amino acid promoters are more environmentally friendly, their promotion effect is unstable under low temperature conditions. In addition, the existing technology mostly uses a single type of promoter, and the synergistic effect between different types of substances is not fully utilized, resulting in limited promotion efficiency.

[0004] Some studies have attempted to improve performance by compounding multiple promoters, but there are problems such as unreasonable ratios and unclear mechanisms of action. For example, when surfactants are simply mixed with nanoparticles, the system may become unstable due to charge repulsion. Another scheme proposes to modify the promoter structure by metal ions, but the matching relationship between ion concentration and temperature parameters is not optimized, and uneven crystal growth is prone to occur in actual applications. In terms of process parameters, existing methods mostly use fixed temperature or pressure conditions, and do not consider the differentiated requirements of different promoter systems for thermodynamic conditions, resulting in excessive energy consumption.

[0005] Therefore, it is necessary to design a method to promote the formation of carbon dioxide hydrate. Summary of the Invention

[0006] In order to overcome the defects in the prior art, a method for promoting the formation of carbon dioxide hydrate is provided.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for promoting carbon dioxide hydrate formation, comprising the following steps: adding a promoter system comprising modified nanoparticles to a carbon dioxide-water mixture, and conducting a hydrate formation reaction under conditions of 2-15°C and 3-10 MPa pressure, wherein the promoter system is composed of an amino acid derivative, a surfactant, and a metal salt in a mass ratio of 1:0.5-2:0.1-0.8, and the modified nanoparticles are silica nanoparticles treated with a silane coupling agent;

[0009] The amino acid derivative is a condensate of L-arginine and maleic anhydride, with a degree of substitution of 60-85% and a molecular weight of 800-2000 Da; the metal salt is a mixture of magnesium chloride and copper nitrate, wherein the molar ratio of magnesium ion to copper ion is 1:0.05-0.2.

[0010] The surfactant includes sodium lauryl sulfate and polyoxyethylene lauryl ether, and the mass ratio of sodium lauryl sulfate to polyoxyethylene lauryl ether is 1:0.3-1.2.

[0011] The preparation method of the modified nanoparticles comprises: dispersing silicon dioxide with a particle size of 50-100 nm in an ethanol-water mixed solvent, adding γ-aminopropyltriethoxysilane, refluxing at 60-80° C. for 3-6 hours, centrifuging, washing, and then drying to obtain silicon dioxide nanoparticles with surface grafted amino groups, namely the modified nanoparticles.

[0012] The volume fraction of ethanol in the ethanol-water mixed solvent is 70-90%, and the amount of silane coupling agent added is 10-25% of the mass of silicon dioxide.

[0013] The amount of the accelerator system added is 0.5-3% of the mass of the carbon dioxide-water mixture system, and is added in two steps: 60-80% is added in the pre-cooling stage for the first time, and the remaining part is added after the pressure rises to 5 MPa;

[0014] The accelerator system further comprises a polysaccharide thickener, the polysaccharide thickener accounts for 0.01-0.1% of the total mass of the accelerator system, and the polysaccharide thickener is a mixture of xanthan gum and gellan gum in a mass ratio of 1:0.5-1.5.

[0015] The polysaccharide thickener is modified by carboxymethylation, with a substitution degree of 0.3-0.7. The modification method comprises: dispersing the polysaccharide in an alkaline solution, adding sodium chloroacetate, and reacting at 40-60° C. for 4-8 hours. The obtained product is the polysaccharide thickener.

[0016] The hydrate formation reaction is carried out in a vertical jacketed reactor, the temperature of the circulating coolant in the jacket interlayer is 2-5°C lower than the reaction temperature, and the flow rate is 0.5-1.2 m / s; during the hydrate formation reaction, ultrasonic waves with a frequency of 20-50 kHz are applied, and the ultrasonic power density is 50-150 W / m³.

[0017] 0.05-0.3 mol / L of an organic amine buffer is added to the carbon dioxide-water mixed system, wherein the organic amine buffer is a mixture of triethanolamine and diethanolamine in a molar ratio of 1:0.8-1.5.

[0018] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0019] 1. The technical solution of the present application significantly improves the efficiency of carbon dioxide hydrate formation through multi-component synergy. Amino acid derivatives and surfactants form a composite micelle structure, in which L-arginine derivatives form zwitterionic properties through the amino group in the molecule and the carboxyl group of maleic anhydride, forming a directional arrangement at the gas-liquid interface, effectively reducing interfacial tension. Sodium lauryl sulfate and polyoxyethylene lauryl ether in the surfactant form mixed micelles. The former stabilizes the bubble surface through electrostatic action, and the latter extends the bubble life through the steric hindrance of the polyoxyethylene chain. The synergistic effect of the two makes the carbon dioxide solubility and interfacial contact area increase synchronously.

[0020] 2. The introduction of metal salts in this application enhances the ionic strength of the system, magnesium chloride changes the dielectric constant of the solution through hydration, and the trace addition of copper nitrate forms metal coordination sites on the surface of the nanoparticles. These dual effects encourage the arrangement of water molecules into a cage-like structure. The amino-functionalized surface of the modified nanoparticles forms a hydrogen bond network, which not only acts as a physical nucleation site to accelerate the formation of crystal nuclei, but also fixes carbon dioxide molecules through chemical adsorption, solving the problem of easy agglomeration and failure of traditional nanoparticles. The organic-inorganic hybrid interface formed by the silane coupling agent treatment significantly improves the dispersion stability of the particles under high pressure conditions.

[0021] 3. This application's phased addition strategy achieves dynamic regulation. A high concentration of accelerator in the pre-cooling phase rapidly establishes a nucleation environment, while additional additions after the pressure increases are tailored to the needs of the crystal growth phase, replenishing the consumed active components. The carboxymethylated polysaccharide thickener constructs a three-dimensional network structure through the entanglement of its molecular chains. This not only inhibits the excessive aggregation of surfactant micelles, but also prolongs crystal growth time through spatial confinement, resulting in a denser and more stable hydrate structure.

[0022] 4. The enhanced heat transfer design of the vertical tube-in-tube reactor, combined with the ultrasonic cavitation effect, creates micro-scale turbulence, effectively eliminating local concentration gradients. Precise temperature control of the circulating coolant maintains the system in a metastable state. The ultrasonically generated microjets not only accelerate gas-liquid mass transfer but also break up oversized crystals to maintain a uniform particle size distribution.

[0023] 5. Organic amine buffers maintain a weakly alkaline environment in the system through a proton transfer mechanism, which not only protects the active groups of amino acid derivatives but also promotes the existence of metal ions in an appropriate valence state, thereby preventing hydroxide precipitation from interfering with the reaction process.

[0024] 6. This composite promotion system, through the synergistic optimization of intermolecular forces and macro-processing, reduces energy consumption while breaking through the efficiency bottleneck of traditional methods. The multi-level synergy of various components at the gas-liquid interface, the bulk of the solution, and the crystal growth interface simultaneously enhances nucleation site density, molecular diffusion rate, and crystal growth kinetics, achieving a comprehensive optimization chain from microscopic molecular arrangement to macro-process parameters.

[0025] 7. This method significantly improves the formation rate and stability of carbon dioxide hydrates under optimized temperature and pressure conditions by combining a promoter system of amino acid derivatives, surfactants, and metal salts with modified nanoparticles and polysaccharide thickeners. Ultrasonic wave enhancement of mass transfer and organic amine buffers for pH control enable efficient and controllable hydrate formation. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] In this application, the sources of various raw materials are briefly described as follows:

[0028] Carbon dioxide: supplied by Shenzhen Changdali Welding Materials Co., Ltd., CAS number is 124-38-9, purity grade is SFC grade.

[0029] L-Arginine and maleic anhydride condensate: purchased from J&K Scientific Corporation.

[0030] Sodium lauryl sulfate: Sangon Biotech Co., Ltd., CAS number 151-21-3, molecular biology grade, purity ≥99%, product number A100227.

[0031] Polyoxyethylene lauryl ether: purchased from Tokyo Chemical Industry, Japan.

[0032] Magnesium chloride: J&K Technologies, CAS number may be 7786-30-3, please consult its inorganic reagent series for specific models.

[0033] Copper nitrate: Strem Chemicals, CAS number 10031-43-3, purity 99.9%, product number 44-1200.

[0034] Silica nanoparticles: Xi'an Ruixi Biotechnology Co., Ltd., particle size 50-100nm, product form is white powder, specific surface area is about 800m² / g.

[0035] γ-Aminopropyltriethoxysilane: Xi'an Ruixi Biotechnology Co., Ltd., CAS No. 919-30-2, used for surface modification, purity ≥98%.

[0036] Xanthan gum: purchased from Zhejiang Ocean Development Research Institute, AS number is 11138-66-2.

[0037] Gellan gum: purchased from Zhejiang Ocean Development Research Institute, CAS No. 71010-52-1.

[0038] Triethanolamine: Dow Chemical Company, CAS number 102-71-6, purity ≥99%.

[0039] Diethanolamine: Dow Chemical Company, CAS No. 111-42-2, purity ≥99%.

[0040] Sodium chloroacetate: Amethyst brand of J&K Technologies, CAS No. 3926-62-3, analytical grade.

[0041] Anhydrous ethanol: SuperDry series from J&K Technologies, CAS number 64-17-5, purity 99.9%, product number 954403.

[0042] A method for promoting carbon dioxide hydrate formation comprises the following steps: adding a promoter system comprising modified nanoparticles to a carbon dioxide-water mixture, and conducting a hydrate formation reaction under conditions of 2-15°C and 3-10 MPa pressure, wherein the promoter system is composed of an amino acid derivative, a surfactant, and a metal salt in a mass ratio of 1:0.5-2:0.1-0.8, and the modified nanoparticles are silicon dioxide nanoparticles treated with a silane coupling agent.

[0043] The amino acid derivative is a condensation product of L-arginine and maleic anhydride, has a substitution degree of 60-85%, and a molecular weight of 800-2000 Da.

[0044] The surfactant includes sodium lauryl sulfate and polyoxyethylene lauryl ether, and the mass ratio of sodium lauryl sulfate to polyoxyethylene lauryl ether is 1:0.3-1.2.

[0045] The metal salt is a mixture of magnesium chloride and copper nitrate, wherein the molar ratio of magnesium ion to copper ion is 1:0.05-0.2.

[0046] The preparation method of the modified nanoparticles comprises: dispersing silicon dioxide with a particle size of 50-100 nm in an ethanol-water mixed solvent, adding γ-aminopropyltriethoxysilane, refluxing at 60-80° C. for 3-6 hours, centrifuging, washing, and then drying to obtain silicon dioxide nanoparticles with surface grafted amino groups, namely the modified nanoparticles.

[0047] The volume fraction of ethanol in the ethanol-water mixed solvent is 70-90%, and the amount of silane coupling agent added is 10-25% of the mass of silicon dioxide.

[0048] The amount of the accelerator system added is 0.5-3% of the mass of the carbon dioxide-water mixture system, and is added in two steps: 60-80% is added in the pre-cooling stage for the first time, and the remaining part is added after the pressure rises to 5 MPa;

[0049] The accelerator system further comprises a polysaccharide thickener, the polysaccharide thickener accounts for 0.01-0.1% of the total mass of the accelerator system, and the polysaccharide thickener is a mixture of xanthan gum and gellan gum in a mass ratio of 1:0.5-1.5.

[0050] The polysaccharide thickener is modified by carboxymethylation, with a substitution degree of 0.3-0.7. The modification method comprises: dispersing the polysaccharide in an alkaline solution, adding sodium chloroacetate, and reacting at 40-60° C. for 4-8 hours. The obtained product is the polysaccharide thickener.

[0051] The hydrate formation reaction is carried out in a vertical jacketed reactor, the temperature of the circulating coolant in the jacket interlayer is 2-5°C lower than the reaction temperature, and the flow rate is 0.5-1.2 m / s; during the hydrate formation reaction, ultrasonic waves with a frequency of 20-50 kHz are applied, and the ultrasonic power density is 50-150 W / m³.

[0052] 0.05-0.3 mol / L of an organic amine buffer is added to the carbon dioxide-water mixed system, wherein the organic amine buffer is a mixture of triethanolamine and diethanolamine in a molar ratio of 1:0.8-1.5.

[0053] This application achieves rapid generation and high-density storage of carbon dioxide hydrate under low temperature and low pressure conditions through the multi-component synergistic effect of the composite promoter system and optimization of process parameters, while reducing energy consumption and avoiding environmental pollution.

[0054] The technical solution of the present invention is further illustrated by the following examples and comparative examples, but the protection scope of the present invention is not limited thereto.

[0055] Example 1

[0056] Silica nanoparticles with a particle size of 100 nm were dispersed in an ethanol-water mixture containing 90% ethanol by volume. γ-Aminopropyltriethoxysilane (25% by weight of the silica) was added, and the mixture was refluxed at 80°C for 6 hours. The mixture was then centrifuged, washed, and dried to yield amino-modified nanoparticles. The accelerator system consisted of L-arginine-maleic anhydride condensate (85% substitution, 2000 Da molecular weight), sodium lauryl sulfate and polyoxyethylene lauryl ether (mass ratio of 1:1.2), and magnesium chloride and copper nitrate (magnesium ion: copper ion molar ratio of 1:0.2) in a mass ratio of 1:2:0.8. The accelerator system, at a concentration of 3% by weight of the carbon dioxide-water mixture, was added in two separate additions: 80% of the accelerator was added during the initial pre-cooling phase, and the remaining 20% ​​was added after the pressure reached 10 MPa. A carboxymethylated xanthan gum-gellan gum mixture (mass ratio 1:1.5, degree of substitution 0.7) was added as a thickener, at a level of 0.1% based on the total weight of the accelerator. The reaction was conducted in a vertical double-tube reactor, with the interlayer coolant temperature 5°C lower than the reaction temperature, at a flow rate of 1.2 m / s, and with 50 kHz ultrasonic waves (power density 150 W / m³). A 0.3 mol / L triethanolamine-diethanolamine buffer (molar ratio 1:1.5) was added to the carbon dioxide-water mixture. The reaction temperature was maintained at 2°C and the pressure at 10 MPa.

[0057] Example 2

[0058] In this embodiment, the same points as in Example 1 are not described in detail, and the differences are as follows:

[0059] Modified particles were prepared using 50 nm silica nanoparticles in a 70% ethanol solvent with a silane coupling agent (10% by weight of the silica) added. The reaction was refluxed at 60°C for 3 hours. The accelerator system consisted of an amino acid derivative with a 60% degree of substitution and a molecular weight of 800 Da, a surfactant (sodium lauryl sulfate to polyoxyethylene lauryl ether in a 1:0.3 weight ratio), and a metal salt (magnesium and copper ions in a 1:0.05 weight ratio) in a 1:0.5:0.1 weight ratio. The total addition amount was 0.5% of the system weight, with staged additions of 60% during the initial pre-cooling phase and the remaining 40% added after the pressure reached 3 MPa. A carboxymethylated polysaccharide with a degree of substitution of 0.3 (xanthan gum to gellan gum in a 1:0.5 weight ratio) was used as the thickener at a level of 0.01%. The reactor coolant temperature gradient was set at 2°C, the flow rate was 0.5 m / s, and the ultrasonic frequency was 20 kHz (power density 50 W / m³). The buffer concentration was 0.05 mol / L (molar ratio of triethanolamine to diethanolamine 1:0.8), the reaction temperature was 15°C, and the pressure was 3 MPa.

[0060] Example 3

[0061] In this embodiment, the same points as in Example 1 are not described in detail, and the differences are as follows:

[0062] Modified silica particles with an intermediate particle size of 75 nm were prepared by adding 15% silane coupling agent to an 80% ethanol solvent at 70°C for 4.5 hours. An amino acid derivative with a degree of substitution of 72% and a molecular weight of 1400 Da was compounded with a surfactant (mass ratio of 1:0.75) and a metal salt (magnesium and copper ions ratio of 1:0.12) at a mass ratio of 1:1.25:0.45. The total accelerator addition amount was 1.75%, added in two batches: 70% during the pre-cooling phase and the remaining 30% after the pressure reached 6.5 MPa. A carboxymethylated polysaccharide with a degree of substitution of 0.5 (mass ratio of 1:1) was used as the thickener, at a dosage of 0.055%. The reactor cooling temperature gradient was 3.5°C, the flow rate was 0.85 m / s, and the ultrasonic parameters were 35 kHz / 100 W / m³. The buffer concentration was 0.175 mol / L (molar ratio of 1:1.15), the reaction temperature was 8.5°C, and the pressure was 6.5 MPa.

[0063] Comparative Example 1

[0064] In this comparative example, the same points as in Example 1 are not repeated here, and the differences are as follows:

[0065] No carboxymethylated polysaccharide thickener is used.

[0066] Comparative Example 2

[0067] In this comparative example, the same points as Example 2 are not repeated here, and the differences are as follows:

[0068] The phased addition strategy was cancelled and all accelerators were added at once during the pre-cooling stage.

[0069] Comparative Example 3

[0070] In this comparative example, the same points as in Example 3 are not repeated here, and the differences are as follows:

[0071] The metal salt was replaced with magnesium chloride alone.

[0072] Comparative Example 4

[0073] In this comparative example, the same points as in Example 1 are not repeated here, and the differences are as follows:

[0074] Remove ultrasonic treatment from the system.

[0075] Comparative Example 5

[0076] In this comparative example, the same points as in Example 1 are not repeated here, and the differences are as follows:

[0077] Unmodified silica particles were used instead of the amino-modified particles of Example 1.

[0078] Performance test results and analysis

[0079] The carbon dioxide hydrate formation promotion was carried out according to the parameters of the embodiment and the comparative example, and the results were tested. The test results are specifically shown in Table 1.

[0080] As can be seen from Table 1, the ultra-short induction time of 8.2 minutes in Example 1 is due to the synergistic effect of amino-modified nanoparticles and zwitterionic amino acid derivatives. The hydrogen bond network formed by the amino groups on the surface of the modified particles accelerates the induction time. The amphiphilic structure of the amino acid derivative forms a directional arrangement at the gas-liquid interface, reducing the nucleation energy barrier. Compared with the 27.6 minutes of the unmodified particles in Comparative Example 5, it is confirmed that the silane coupling treatment improves the dispersibility of the particles.

[0081] The 143 v / v gas storage density of Example 1 breaks through the upper limit of traditional systems, mainly due to the synergistic effect of the phased addition strategy and the polysaccharide thickener. The high concentration of promoter in the pre-cooling stage establishes dense nucleation points, and the supplementary addition after the pressure is increased maintains the concentration gradient required for crystal growth. The three-dimensional network structure constructed by the carboxymethylated polysaccharide delays excessive crystal growth and makes the cage structure more complete. Compared with the 117 v / v added in Comparative Example 2, the effectiveness of the dynamic control strategy is demonstrated.

[0082] The uniform particle size distribution (D90) of 85 μm achieved in Example 1 relies on the coupling of ultrasonic cavitation and the vertical reactor design. The microjets generated by 50 kHz ultrasound break up large crystals, while the tube-in-tube design enhances heat transfer and prevents localized overheating. In Comparative Example 4, the D90 increased to 210 μm after the ultrasound was eliminated, and significant crystal agglomeration was observed.

[0083] The 18.5 kW·h / m³ energy consumption achieved in Example 1 represents a reduction of over 40% compared to conventional methods. This is due to the synergistic effect of the metal salt ion strength control and the buffer. Magnesium chloride modifies the solution's dielectric constant, reducing the phase transition enthalpy, while copper nitrate stabilizes the nanoparticles through coordination, synergistically reducing system energy loss. In Comparative Example 3, using a single metal salt, energy consumption rises to 25.9 kW·h / m³, demonstrating the complementary effect of the two metal ions.

[0084] No accumulation of accelerator degradation products was detected in all example systems after 200 hours of continuous operation, demonstrating the environmental friendliness of the combination of an organic amine buffer and bio-based polysaccharide. However, the lack of a thickener in Comparative Example 1 resulted in excessive residual surfactant, confirming the necessity of carboxymethylation for micelle stabilization.

[0085] Table 1 Analysis and test results

[0086]

[0087] The test results show that ethanol and specific amino acid promoters can significantly shorten the induction time of carbon dioxide hydrate, increase the generation rate and gas storage density at appropriate concentrations, while the synergistic effects of staged pressurization, low temperature (below freezing point) and polysaccharide thickeners can further optimize crystal stability.

[0088] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for promoting the formation of carbon dioxide hydrate, characterized in that: The method comprises the following steps: adding a promoter system containing modified nanoparticles to a carbon dioxide-water mixture system, and performing a hydrate formation reaction under the conditions of 2-15°C and 3-10 MPa pressure, wherein the promoter system is compounded by amino acid derivatives, surfactants and metal salts in a mass ratio of 1:0.5-2:0.1-0.8; the modified nanoparticles are amino-modified silica nanoparticles treated with a silane coupling agent; the amino acid derivatives are condensates of L-arginine and maleic anhydride, with a degree of substitution of 60-85% and a molecular weight of 800-2000 Da; and the metal salt is a mixture of magnesium chloride and copper nitrate, wherein the molar ratio of magnesium ions to copper ions is 1:0.05-0.

2.

2. The method for promoting carbon dioxide hydrate formation according to claim 1, wherein: The surfactant includes sodium lauryl sulfate and polyoxyethylene lauryl ether, and the mass ratio of sodium lauryl sulfate to polyoxyethylene lauryl ether is 1:0.3-1.

2.

3. The method for promoting carbon dioxide hydrate formation according to claim 1, wherein: The preparation method of the modified nanoparticles comprises: dispersing silicon dioxide with a particle size of 50-100 nm in an ethanol-water mixed solvent, adding γ-aminopropyltriethoxysilane, refluxing at 60-80° C. for 3-6 hours, centrifuging, washing, and then drying to obtain silicon dioxide nanoparticles with surface grafted amino groups, namely the modified nanoparticles.

4. The method for promoting carbon dioxide hydrate formation according to claim 3, wherein: The volume fraction of ethanol in the ethanol-water mixed solvent is 70-90%, and the amount of silane coupling agent added is 10-25% of the mass of silicon dioxide.

5. The method for promoting carbon dioxide hydrate formation according to claim 1, wherein: The amount of the accelerator system added is 0.5-3% of the mass of the carbon dioxide-water mixture system, and is added in two steps: 60-80% is added in the pre-cooling stage for the first time, and the remaining part is added after the pressure rises to 5 MPa; The accelerator system further comprises a polysaccharide thickener, the polysaccharide thickener accounts for 0.01-0.1% of the total mass of the accelerator system, and the polysaccharide thickener is a mixture of xanthan gum and gellan gum in a mass ratio of 1:0.5-1.

5.

6. The method for promoting carbon dioxide hydrate formation according to claim 5, characterized in that: The polysaccharide thickener is modified by carboxymethylation, with a substitution degree of 0.3-0.

7. The modification method comprises: dispersing the polysaccharide in an alkaline solution, adding sodium chloroacetate, and reacting at 40-60° C. for 4-8 hours. The obtained product is the polysaccharide thickener.

7. The method for promoting carbon dioxide hydrate formation according to claim 1, wherein: The hydrate formation reaction is carried out in a vertical jacketed reactor, the temperature of the circulating coolant in the jacket interlayer is 2-5°C lower than the reaction temperature, and the flow rate is 0.5-1.2 m / s; during the hydrate formation reaction, ultrasonic waves with a frequency of 20-50 kHz are applied, and the ultrasonic power density is 50-150 W / m³.

8. The method for promoting carbon dioxide hydrate formation according to claim 1, wherein: 0.05-0.3 mol / L of an organic amine buffer is added to the carbon dioxide-water mixed system, wherein the organic amine buffer is a mixture of triethanolamine and diethanolamine in a molar ratio of 1:0.8-1.5.

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