Method for increasing melting temperature of ice in frozen saline solution and application thereof

Abstract

The invention belongs to the technical field of chemical engineering and energy materials, and particularly relates to a method for improving the freezing point of a saline solution and application thereof. According to the method, a saline solution and hydrophobic fumed silica are mixed, so that the saline solution enters gaps of nano-scale particles, and a solid ice phase is formed and stabilized under normal pressure and at the temperature higher than 273 K. The hydrophobic fumed silica is preferably modified with an alkylsilane compound, and an organic additive can also be added to fill gaps among particles. The method breaks through the limitation that the ice phase melts at 0 DEG C, the melting temperature of the ice can be remarkably increased, the metastable state ice content is greatly increased, the process is simple, and operation is convenient. The composite system formed by the method can be used for preparing gas hydrates, realizes high-efficiency storage of gas under the conditions of normal pressure and temperature above zero, and provides a brand-new technical solution for storage and transportation of clean energy such as natural gas and the like.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering and energy materials technology, specifically relating to a method for increasing the melting temperature of ice in frozen salt water solutions and its application. Background Technology

[0002] With the accelerated global energy transition to cleaner energy, the demand for natural gas, as a key transitional energy source, continues to grow. However, its storage and transportation still heavily rely on traditional technologies such as high-pressure cryogenic liquefaction, which suffers from problems such as complex equipment, high costs, low safety, and high energy consumption. Therefore, developing a new generation of technologies that can achieve efficient and stable gas storage at normal pressure and relatively high temperatures has become an urgent need for the industry. Against this backdrop, gas hydrate technology has shown significant potential. This technology utilizes the cage-like crystal structure formed by water molecules to encapsulate gas molecules (such as methane), forming a solid compound with advantages such as high gas storage density (approximately 160–180 cubic meters of natural gas can be stored per cubic meter of hydrate) and good safety. However, its commercial application is limited by harsh formation conditions, typically requiring high pressure (above several megapascals) and low temperature (below 0°C) to form and remain stable.

[0003] To improve hydrate formation conditions, the industry has explored various technological approaches. Early systems, such as RU2270053 and RU2277121, relied on high-pressure, low-temperature environments to force hydrate formation. While this achieved gas fixation, it required continuous external energy input, resulting in high energy consumption. Subsequent "dry water" technologies (such as RU2704971) utilized hydrophobic silica to disperse water into micron-sized droplets, increasing the gas-water contact area and enabling hydrate formation under static conditions, thus improving energy efficiency. To further enhance system stability and cycleability, systems like RU2843183C1 introduced polymer networks such as PVA gel to fix the aqueous phase. While this improved cycle performance, the addition of polymer components increased system complexity and cost.

[0004] In-depth analysis reveals that existing technologies are all limited by the physical law that ice melts at 0°C. Whether it's the high-pressure cryogenic method, the "dry water" system, or the gel composite system, all require maintaining the system in a sub-freezing environment, making it impossible to escape dependence on continuous refrigeration equipment. This leads to core challenges such as high energy consumption and system complexity. Furthermore, the structure of "dry water" materials is destroyed after a single vaporization, making them difficult to reuse; gel systems sacrifice system simplicity and economy.

[0005] Therefore, the current technological field urgently needs an innovative solution that can fundamentally overcome the aforementioned thermodynamic limitations, developing a gas hydrate storage technology that does not rely on continuous deep refrigeration, can operate at atmospheric pressure and temperatures above zero degrees Celsius, and possesses good cycle stability. This is not only key to solving the problems of high energy consumption, poor cycle performance, and system complexity of existing technologies, but will also open up a new low-energy, low-cost path for natural gas storage and transportation, and even the energy and chemical industry, possessing significant social and economic value. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes an innovative method for increasing the melting temperature of ice in frozen brine solutions and its application. This invention mixes a brine solution with hydrophobic fumed silica, allowing it to penetrate the nanoscale interparticles of the silica. This provides an innovative solution and a novel technological pathway for the efficient generation and long-term stable storage of gas hydrates, enabling the construction of a stable "metastable ice" phase without deep freezing.

[0007] The first objective of this invention is achieved through the following technical solution:

[0008] A method for increasing the melting temperature of ice in a frozen brine solution, the method comprising: mixing the brine solution with hydrophobic fumed silica, allowing the brine solution to enter the interparticle spaces of the hydrophobic fumed silica, thereby forming and stabilizing a solid ice phase at atmospheric pressure and a temperature above 273 K.

[0009] Preferably, the hydrophobic fumed silica is hydrophobic fumed silica modified with an alkylsilane compound.

[0010] More preferably, the alkylsilane compound is dimethyldichlorosilane.

[0011] Preferably, the specific surface area of ​​the hydrophobic fumed silica is 100-300 m². 2 / g.

[0012] More preferably, the specific surface area of ​​the hydrophobic fumed silica is 150-200 m². 2 / g.

[0013] Preferably, the hydrophobic fumed silica has a particle size of 7-40 nm.

[0014] Preferably, the ratio of the total mass of the salt solution to the mass of the hydrophobic fumed silica is from 0.15:1 to 5.0:1.

[0015] Preferably, the brine solution is formed by dissolving salt in water, and the salt is one or more of a halide salt.

[0016] More preferably, the halide salt is sodium chloride.

[0017] Preferably, the salt solution contains 20% to 60% salt by mass.

[0018] More preferably, the salt solution is a saturated or supersaturated salt solution containing undissolved salt crystals.

[0019] Preferably, the mixing step further includes adding an organic additive to the system, the organic additive filling the volume of the interparticle spaces that is not occupied by water.

[0020] More preferably, the amount of the organic additive is 0.05-1.0g per gram of silicon dioxide.

[0021] More preferably, the amount of the organic additive is 0.1-0.9g per gram of silicon dioxide.

[0022] More preferably, the organic additive is a non-polar organic solvent.

[0023] More preferably, the organic additive is one or more of tetrachlorosilane, tetrachloroethane, carbon tetrachloride, and hexachloroethane.

[0024] Preferably, the mixing is achieved by mechanical grinding, and the specific steps are as follows:

[0025] 1. Dry hydrophobic fumed silica is mechanically ground until a bulk density of approximately 0.1-0.3 g / cm³ is achieved. 3 Compacting materials;

[0026] 2. Weigh out salt (such as NaCl) and deionized water according to the preset mass ratio, mix them at room temperature (5-40℃), stir and equilibrate for 1 hour to form a salt water mixture containing undissolved salt crystals;

[0027] 3. Place the pretreated silica and the brine mixture prepared in step 2 together in a mortar in proportion, and mechanically grind for 5-10 minutes until a primary composite system with a uniform appearance is formed;

[0028] 4. For systems that require the addition of organic additives, after the primary composite system is formed, add the organic additives in proportion, and continue grinding for 3-5 minutes until the additives are dispersed and fill the gaps between the silica particles to form the final composite system.

[0029] Preferably, the mass ratio of the salt solution to the hydrophobic fumed silica is in the range of 0.1:1 to 5:1.

[0030] More preferably, the mass ratio of the salt solution to the hydrophobic fumed silica is in the range of 1:1 to 4:1.

[0031] More preferably, the salt in the brine solution has a salt mass fraction of 10% to 50%.

[0032] More preferably, the salt solution contains 50% salt by mass.

[0033] This method achieves stable solid ice phases at ambient pressure and temperatures above zero degrees Celsius by mixing a salt solution with hydrophobic fumed silica and utilizing the unique physicochemical environment created by the interparticle gaps in the nanoscale particles. The core principle lies in the synergistic effect of multiple levels: First, the interaction between the hydrophobic silica surface (such as the =Si(CH3)2 "umbrella-like" structure formed after modification with dimethyldichlorosilane) and water significantly enhances the clustering of water molecules between particles, forming more ordered "bound water." This bound water, depending on the strength of its interaction with the surface, can be divided into strongly correlated water and weakly correlated water, with its Gibbs free energy (ΔG) tending towards a negative value, providing favorable conditions for the stability of the ice phase from a thermodynamic perspective. Second, the nanoscale interparticle gaps (typically in the range of 0.3-50 nanometers) exert a strong spatial confinement effect on the water phase. This confinement alters the phase transition behavior of water, allowing ice to exist stably at higher temperatures or melt at lower temperatures at smaller scales, according to the Gibbs-Thomson effect. Third, the hydrophobic silica surface can maintain the solid-state stability of water or salt solutions at temperatures T>273K. Finally, the introduced organic additives fill the free volume not occupied by water in the interparticle spaces, further regulating the state of bound water and the ice / water phase transition equilibrium by altering the polarity and interfacial properties of the dispersion medium. Non-polar additives (such as CDCl3) mainly promote the formation and stabilization of metastable ice by changing the interfacial energy, synergistically with the hydrophobic surface, resulting in a significant increase in metastable ice content. Conversely, the introduction of polar additives (such as DMSO) severely disrupts the stability of metastable ice in the nano-confined environment due to its strong freezing point lowering effect and interference with the water structure, leading to a significant decrease in its content. In summary, the stabilizing effect of the hydrophobic surface, the nano-confining effect, the alteration of salt behavior, and the regulation by organic additives work synergistically to enable a portion of water to exist as "metastable ice" at temperatures above 273K, thereby achieving the technical effect of increasing the ice melting temperature.

[0034] The second objective of this invention is achieved through the following technical solution:

[0035] A brine composite system is prepared by the method described above for increasing the melting temperature of ice in a frozen brine solution.

[0036] The third objective of this invention is achieved through the following technical solution:

[0037] Use of a brine complex system in the preparation of gas hydrates or for gas storage.

[0038] Preferably, the gas is methane.

[0039] More preferably, the gas hydrate is methane hydrate.

[0040] Preferably, the application is carried out under normal pressure conditions and in a temperature range above 273K.

[0041] More preferably, the temperature range is >273K and <290K.

[0042] Preferably, when the composite system comes into contact with the gas, hydrates are generated under static conditions, without the need for external energy input to maintain high pressure or continuous low temperature.

[0043] This scheme utilizes a composite system prepared by the aforementioned method, which has been stabilized in a metastable ice phase at atmospheric pressure and above-zero temperatures, as an innovative platform for the generation and storage of gas hydrates. Its working principle lies in the fact that the "metastable ice" in this composite system acts as a pre-organized structure and efficient nucleation sites for gas hydrate formation. When the target gas (such as methane) comes into contact with the composite system rich in this metastable ice, gas molecules can be more directly and rapidly captured and embedded into the cage-like structure pre-built by the ice lattice, thereby significantly accelerating the crystal formation kinetics of gas hydrates (such as methane hydrates). Compared to the need to overcome a high nucleation energy barrier to form hydrates from liquid water, this process bypasses some kinetic obstacles. Simultaneously, the nanoporous matrix composed of hydrophobic silica not only stabilizes the ice precursor, but its huge specific surface area and complex pore structure also provide ample contact interfaces for the gas-water-solid three phases, greatly promoting the mass transfer process. Furthermore, when nonpolar organic additives are introduced into high-load systems, they not only act as thermodynamic promoters for hydrate formation but also increase the quantity of metastable ice precursors through the aforementioned synergistic effect, thereby doubly optimizing the formation efficiency and storage capacity of gas hydrates. Therefore, this application makes it possible to achieve gas hydrate fixation and stable storage under mild atmospheric pressure and above-freezing temperatures, fundamentally eliminating dependence on energy-intensive external conditions such as traditional high pressure or continuous deep refrigeration, and providing a completely new path for achieving low-energy, high-efficiency gas storage technology.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] 1. This invention overcomes the absolute dependence of ice phase formation on low-temperature environments. By utilizing the nano-confined space between hydrophobic fumed silica particles, a salt solution can form and maintain a stable solid ice phase under ambient pressure and conditions above 273 K. This characteristic provides new possibilities for realizing gas-liquid-solid phase transition processes under mild conditions.

[0046] 2. This invention provides a solution with a simple system structure, convenient operation, and no need for continuous external energy input. Compared to traditional methods that rely on complex high-pressure vessels and continuous refrigeration systems, and the "dry water" technology, which, while improving energy efficiency, suffers from insufficient structural stability, this invention only requires simple mechanical mixing and grinding steps to form a stable composite system. This system can operate under static conditions, greatly reducing equipment complexity, infrastructure construction costs, and system maintenance difficulty.

[0047] 3. The composite system constructed in this invention exhibits excellent phase stability and potential recyclability. The metastable ice phase, stabilized by the hydrophobic silica surface, has a significantly higher content than the hydrophilic silica system, providing a sufficient and stable reaction precursor for the subsequent formation of gas hydrates. The stability of this solid ice phase at above-zero temperatures effectively avoids the structural damage of "dry water" materials after a single vaporization. Furthermore, compared to solutions that introduce polymers such as PVA gel, this system has a simpler composition, avoiding the increased cost and system complexity associated with adding polymer components.

[0048] 4. This invention achieves synergistic enhancement of technical effects through optimized design of components and processes. Hydrophobic fumed silica modified with specific alkylsilanes (such as dimethyldichlorosilane) is selected, and its specific surface area is controlled within an optimal range to maximize its ability to stabilize water clusters on its surface. Simultaneously, non-polar organic additives in specific dosage ranges are introduced to fill the interparticle gaps, further suppressing the freezing point depression effect by adjusting interfacial energy and local microenvironment, thereby maximizing the increase in the melting temperature of ice. Experiments have shown that this can be achieved by up to 10⁻¹⁷ K.

[0049] 5. This invention provides a new research direction for gas storage technology. The technical approach based on the nanoconfinement effect to stabilize metastable ice phases lays a theoretical foundation for developing gas storage systems under ambient pressure and near-ambient temperature conditions, demonstrating its application potential in the field of energy storage. Attached Figure Description

[0050] Figure 1 X-ray diffraction patterns and NaCl grain size distribution functions of samples from Examples 3, 6, 9, Comparative Example 1, and Comparative Example 3;

[0051] Figure 2Examples 1-9 were tested under different dispersion media and different degrees of hydration. 1 H NMR spectrum;

[0052] Figure 3 The curves showing the relationship between the amount of unfrozen water and temperature, and the change curves of Gibbs free energy for samples of Examples 1-9 and Comparative Examples 1-3 are provided. Detailed Implementation

[0053] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0054] The materials used in the embodiments and comparative examples of this invention are described below:

[0055] Hydrophilic fumed silica: Fumed silica A-300 purchased from Wacker Chemie AG, with a specific surface area of ​​294 m². 2 / g, bulk density approximately 0.05g / cm³ 3 .

[0056] Hydrophobic fumed silica: HDK®AM1 (methyl silica) purchased from Wacker Chemie AG, modified with dimethyldichlorosilane, with a specific surface area of ​​178 m². 2 / g, bulk density approximately 0.05g / cm³ 3 .

[0057] Deuterated dimethyl sulfoxide (DMSO-d6): purchased from Sigma-Aldrich, molecular weight 84.17 g / mol, density 1.190 g / ml.

[0058] Deuterated chloroform (CDCl3): purchased from Sigma-Aldrich, molecular weight 120.38 g / mol, purity 99.8%.

[0059] Deuterated carbon tetrachloride (CCl4): purchased from Sigma-Aldrich, molecular weight 104.17 g / mol, purity 96%.

[0060] Sodium chloride (NaCl) and other conventional chemical reagents were all of analytical grade.

[0061] The present invention will be further illustrated by specific embodiments below, but the scope of protection of the present invention is not limited thereto.

[0062] I. Preparation process of composite system

[0063] The composite system described in this invention is prepared by mechanical grinding and mixing. The specific steps are as follows: First, dry hydrophobic fumed silica AM1 or hydrophilic fumed silica A-300 is pretreated by mechanical grinding until a bulk density of approximately 0.20 g / cm³ is achieved. 3 The compacted material was then prepared. Sodium chloride and deionized water were mixed in a specific ratio at room temperature (25±2℃) and stirred for 1 hour to form a brine mixture containing undissolved salt crystals. The pretreated silica and brine mixture were then placed together in a mortar and mechanically ground for several minutes until a uniform primary composite system was formed. For systems requiring organic additives, the organic additives were added in proportion after the primary composite system was formed, and grinding continued for 3-5 minutes until the additives dispersed and filled the gaps between the silica particles, forming the final composite system. The composition ratios of each embodiment and comparative example are detailed in Table 1.

[0064] Table 1. Composition ratios of the examples and comparative samples

[0065]

[0066] *Composition of mixed additives: CDCl3:CCl4:DMSO-d6 = 70%:15%:15% (volume ratio)

[0067] II. Characterization Methods for Composite Systems

[0068] The composite systems obtained in the above embodiments and comparative examples were characterized as follows:

[0069] (1) X-ray diffraction analysis

[0070] The X-ray diffraction was performed using a DRON-3M diffractometer (Burevestnik, St. Petersburg, Russia) with CuKα radiation (λ = 0.15418 nm) and a Ni filter. Reflections were recorded within the range of 2θ = 5–70° at a scan rate of 2° / min. The size distribution function of the NaCl microcrystals was analyzed by processing the X-ray diffraction patterns to determine the size of the salt nanocrystals formed in the interparticle spaces (i.e., the coherent scattering region).

[0071] (2) Low-temperature nuclear magnetic resonance analysis

[0072] Low temperature 1 HNMR was used to study the phase state of bound water. Approximately 0.1–0.2 g of the composite system sample was placed in a specific dispersion medium (air, CDCl3, or a mixture of CDCl3 + CCl4 + DMSO-d6), with an average sample volume of approximately 0.5 mL. Recordings were performed as the temperature increased from 215 K to 287 K. 1HNMR spectra were used to observe the signal intensity changes of proton chemical shift (δH) in the ranges of 4-6 ppm (strongly correlated water) and 0-2 ppm (weakly correlated water), as well as any additional signals that may appear in different dispersion media.

[0073] III. Performance Testing Methods for Composite Systems

[0074] By analyzing low temperature 1 The performance of the composite system was evaluated using the following methods based on H NMR data. It is important to note that this invention employs variable-temperature NMR technology to study the stability of the solid ice phase through an indirect yet precise method. The principle is that NMR spectrometers can sensitively detect the highly mobile signals of liquid water, while the signals of solid ice, whose molecules are fixed in a crystal lattice and move extremely slowly, cannot be detected in conventional spectra. Based on this principle, approximately 0.1-0.2 g of the composite system sample was placed in specific NMR test dispersion media, including air (i.e., no additional solvent), CDCl3, or a mixture of CDCl3 + CCl4 + DMSO-d6, with an average sample volume of approximately 0.5 mL. By monitoring the change in the intensity of the liquid water signal from 215 K to 287 K, the unfrozen water content at each temperature was calculated, and the unfrozen water content as a function of temperature, Cuw(T), was plotted.

[0075] Specific evaluation methods include:

[0076] (1) Determination of unfrozen water content: The unfrozen water content (Cuw) of the composite system at different temperatures was calculated by integrating the 1H NMR signal intensity at different temperatures, and the curve of Cuw as a function of temperature T was plotted.

[0077] (2) Water State and Quantitative Analysis of Metastable Ice: Based on the Cuw(T) curve, unfrozen water is further classified into strongly bound water (Cuws) and weakly bound water (Cuww). The metastable ice content (Cuwm) is defined and calculated, which is the newly added unfrozen water content represented by the Cuw(T) curve in the temperature range of T>273K. This parameter is obtained by analyzing the increment of the Cuw(T) curve above 273K and separating it through curve fitting, and is a quantitative evidence that directly proves the core effect of the present invention.

[0078] (3) Calculation of thermodynamic parameters: The change of Gibbs free energy (ΔG) was calculated based on the Cuw(T) curve, and the interaction strength between bound water and the silica surface was analyzed.

[0079] (4) Determination of average melting temperature: The average melting temperature is calculated by analyzing the characteristics of the Cuw(T) curve. <T m This parameter reflects the melting behavior of the main ice phase within the system.

[0080] IV. Specific Preparation Examples

[0081] Example 1

[0082] Example 1: The preparation steps of the AM1 / NaCl / water composite system containing mixed additives are as follows:

[0083] (1) Weigh 1.0 g of dry hydrophobic fumed silica HDK®AM1, place it in a mortar, and grind it mechanically for about 5 minutes until a bulk density of about 0.20 g / cm³ is formed. 3 Uniformly compacted powder.

[0084] (2) Weigh 2.0g of sodium chloride and 2.0g of deionized water, mix them in a beaker at room temperature, and stir magnetically for 1 hour to form a saturated brine mixture containing undissolved NaCl salt crystals.

[0085] (3) Place the AM1 silica powder from step (1) and the entire salt water mixture from step (2) together in a mortar and grind mechanically for 10 minutes to form a primary composite system with a uniform appearance.

[0086] (4) Add 0.8g of mixed additive to the primary composite system in step (3) and continue grinding for 5 minutes until evenly dispersed to obtain the final composite system.

[0087] Example 2

[0088] The preparation steps (1)-(3) of the AM1 / NaCl / water composite system containing CDCl3 in Example 2 are the same as those in Example 1, except for step (4). Step (4) is: add 0.8g CDCl3 to the primary composite system in step (3) and continue grinding for 5 minutes until it is evenly dispersed to obtain the final composite system.

[0089] Example 3

[0090] The preparation steps (1)-(3) of the AM1 / NaCl / water composite system in Example 3 are the same as those in Example 1, except that step (4) is not included.

[0091] Example 4

[0092] Example 4 Preparation steps (1), (3), and (4) of AM1 / NaCl / water composite system with mixed additives are the same as in Example 1, except for step (2). Step (2) is: weigh 0.0864 g of sodium chloride and 0.24 g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0093] Example 5

[0094] The preparation steps (1), (3), and (4) of the AM1 / NaCl / water composite system containing CDCl3 in Example 5 are the same as those in Example 2, except for step (2). Step (2) is as follows: Weigh 0.0864 g of sodium chloride and 0.24 g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0095] Example 6

[0096] The preparation steps (1) and (3) of the AM1 / NaCl / water composite system in Example 6 are the same as those in Example 3, except for step (2). Step (2) is as follows: Weigh 0.0864 g of sodium chloride and 0.24 g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0097] Example 7

[0098] Example 7 The preparation steps (1), (3), and (4) of the AM1 / NaCl / water composite system containing mixed additives are the same as those in Example 1, except for step (2). Step (2) is as follows: Weigh 0.0432 g of sodium chloride and 0.12 g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0099] Example 8

[0100] The preparation steps (1), (3), and (4) of the AM1 / NaCl / water composite system containing CDCl3 in Example 8 are the same as those in Example 2, except for step (2). Step (2) is as follows: Weigh 0.0432 g of sodium chloride and 0.12 g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0101] Example 9

[0102] The preparation steps (1) and (3) of the AM1 / NaCl / water composite system in Example 9 are the same as those in Example 3, except for step (2). Step (2) is as follows: Weigh 0.0432 g of sodium chloride and 0.12 g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0103] Comparative Example 1

[0104] The preparation steps (3) of the A-300 / NaCl / water composite system in Comparative Example 1 are the same as those in Example 2, except for steps (1)-(2). Step (1) is: weigh 1.0g of dry hydrophilic fumed silica A-300, place it in a mortar, and treat it by mechanical grinding for 5 minutes until a uniform compacted powder with a bulk density of about 0.20g / cm3 is formed. Step (2) is: weigh 0.15g of sodium chloride and 0.15g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0105] Comparative Example 2

[0106] The preparation steps (3)-(4) of the CDCl3-containing A-300 / NaCl / water composite system in Comparative Example 2 are the same as those in Example 3, except for steps (1)-(2). Step (1) is as follows: Weigh 1.0 g of dry hydrophilic fumed silica A-300, place it in a mortar, and mechanically grind it for 5 minutes until a bulk density of approximately 0.20 g / cm³ is formed. 3 The uniformly compacted powder; Step (2) is: weigh 0.15g sodium chloride and 0.15g deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a brine mixture containing undissolved salt crystals.

[0107] Comparative Example 3

[0108] The preparation steps (1) and (3) of the A-300 / NaCl / water composite system of Comparative Example 3 are the same as those of Comparative Example 1, except for step (2). Step (2) is as follows: Weigh 1.0g of sodium chloride and 1.0g of deionized water, mix them at room temperature, and magnetically stir to balance for 1 hour to form a salt water mixture containing undissolved salt crystals.

[0109] V. Performance Test Results and Analysis

[0110] The composite systems were systematically characterized and their performance tested. The results are as follows:

[0111] (1) X-ray diffraction analysis confirmed the formation of salt nanocrystals

[0112] X-ray diffraction analysis confirmed the formation of salt nanocrystals. Figure 1 X-ray diffraction patterns and corresponding NaCl grain size distribution functions of representative samples from Examples 3, 6, 9, Comparative Example 1, and Comparative Example 3 are presented. All composite systems exhibit distinct NaCl crystal diffraction peaks. By processing the diffraction patterns to obtain the size distribution functions, it can be found that the NaCl grain size distribution exhibits complex changes when the degree of hydration and salt content differ. This indicates that mechanical treatment of the brine mixture with nano-silica does indeed lead to the formation of salt nanocrystals in the interparticle spaces.

[0113] (2) Nuclear magnetic resonance reveals the existence of water in different states.

[0114] Figure 2 This paper presents the 1H NMR spectra of nine composite systems (Examples 1-9) using hydrophobic silica AM1 under different dispersion media and different degrees of hydration. Specifically, Figure 2 a, 2d, and 2g illustrate the AM1 composite system in air medium, corresponding to Examples 9, 6, and 3, respectively; Figure 2 b, 2e, and 2h illustrate the AM1 composite system in CDCl3 medium, corresponding to Example 8, Example 5, and Example 2, respectively. Figure 2 c, 2f, and 2i illustrate the AM1 composite system in a mixed medium of CDCl3 + CCl4 + DMSO-d6, corresponding to Examples 7, 4, and 1, respectively. These spectra clearly show the signal characteristics of water under different conditions. Only a strongly correlated water signal (chemical shift 4-6 ppm) was observed in the air environment. In the CDCl3 environment, in addition to the strongly correlated water signal, a weakly correlated water signal (chemical shift 0-2 ppm) also appeared. In the mixed additive environment, an additional HOH···OS(Me)2 structure signal (chemical shift 3 ppm) appeared. Of particular note is that no obvious weakly correlated water signal was observed in the silica A-300 / NaCl / water systems of Comparative Examples 1 to 3. This comparative result indicates that the "umbrella-like" structure = Si(CH3)2 on the hydrophobic silica surface significantly enhances the clustering of water molecules.

[0115] (3) Analysis of the thermodynamic behavior of metastable ice

[0116] Cuw(T) curves plotted based on low-temperature 1H NMR data ( Figure 3 (As shown) This provides an in-depth understanding of the thermodynamic behavior of metastable ice. Figure 3 a, 3b, and 3c respectively demonstrate the comprehensive influence of the test medium on the relationship between the unfreezing water content and temperature under different hydration levels of the hydrophobic AM1 silica composite system: Figure 3 Examples 9 (air medium), 8 (CDCl3 medium), and 7 (mixed additive medium) correspond to low hydration levels (h=0.12). Figure 3 b corresponds to the degree of hydration (h=0.24) in Examples 6 (air medium), 5 (CDCl3 medium), and 4 (mixed additive medium); Figure 3 c corresponds to high hydration levels (h=2.0) in Examples 3 (air medium), 2 (CDCl3 medium), and 1 (mixed additive medium). Figure 3Figure d shows the comparative results of the hydrophilic A-300 silica composite system, corresponding to Comparative Example 1 (air medium), Comparative Example 2 (CDCl3 medium), and Comparative Example 3 (air medium, h=1.0).

[0117] analyze Figure 3 As can be seen from ac, for the hydrophobic AM1 system, under any fixed degree of hydration, the Cuw(T) curves in different media show significant differentiation in the high-temperature region (>273K), directly demonstrating the significant regulatory effect of the medium environment on the stability of metastable ice. Especially under high hydration conditions ( Figure 3 c) The curve in the CDCl3 medium shows the largest increase in the high-temperature region, indicating its strongest metastable ice-stabilizing ability. Furthermore, compared to... Figure 3 As can be seen from a, b, and c, as the degree of hydration h increases from 0.12 to 2.0, the increment and differentiation of Cuw(T) curves in the high-temperature region of each medium are significantly enhanced, indicating that sufficient hydration is the basis for the formation of a large amount of metastable ice and the full manifestation of the medium regulation effect.

[0118] Comparison of hydrophobic systems ( Figure 3 ac) and hydrophilic systems ( Figure 3 As can be seen from the overall curve shape of d), the Cuw(T) value of the former is generally higher in the high-temperature region and the difference between the media is more significant, which conclusively proves that the hydrophobic interface has an essential advantage over the hydrophilic interface in inducing and stabilizing metastable ice.

[0119] The test results of the key performance parameters of each composite system are shown in Table 2.

[0120] Table 2 Performance test results of the examples and comparative samples

[0121]

[0122] Average melting temperature of all samples in the table <tm>All values ​​are below 273 K, a phenomenon with a clear physical cause: the NaCl salt solution in the system itself has a freezing point below 0°C, and the nanoscale interparticle gaps create a strong confinement effect, which, according to the Gibbs-Thomson theory, further lowers the freezing point of the liquid within the pores. These values ​​below 273 K... <T m The data proves that the experimental system was constructed correctly and the measurement results are reliable, providing a reliable baseline for comparison of the observed anomalous phenomena.

[0123] Against the backdrop of a general decrease in the basic freezing point, all examples in Table 2 exhibited significant Cuwm values ​​(i.e., the additional unfreezing water content above 273 K). This phenomenon transcends the classical freezing point reduction theory framework, proving the existence of metastable ice dominated by interface effects. Example 3 (hydrophobic AM1, air medium) showed a Cuwm as high as 1261 mg / g, while Comparative Example 3 (hydrophilic A-300, air medium) had a Cuwm of only 180 mg / g. This order-of-magnitude difference irrefutably demonstrates that hydrophobic surfaces are the key matrix for achieving high-temperature stable ice phases.

[0124] The degree of hydration is the decisive factor in regulating the amount of metastable ice. In air, the CuWm values ​​for Example 9 (h=0.12), Example 6 (h=0.24), and Example 3 (h=2.0) were 34, 105, and 1261 mg / g, respectively. This conforms to the basic principle of the nanoconfinement effect—sufficient hydration is required to fill the nanospace in order to fully stimulate the stabilizing ability of the hydrophobic surface for metastable ice.

[0125] The medium environment has a significant modulating effect on the stability of metastable ice. Under high hydration conditions (h=2.0), the CuWm of Example 2 (CDCl3 medium) reached the highest at 1517 mg / g, a further increase compared to 1261 mg / g of Example 3 (air medium). This indicates that in a sufficiently moist hydrophobic nanospace, the nonpolar medium CDCl3 generates a synergistic stabilizing effect with the hydrophobic surface by altering the interfacial environment. However, the CuWm of Example 1 (mixed additive medium) decreased to 458 mg / g. This is because the introduction of DMSO, a highly polar solvent with high hydration capacity, in the mixed additive has a complex impact on the hydrogen bond network and freezing point of the system, partially offsetting the stabilizing effect of the nanoconfined environment. Under low and medium hydration conditions, the difference in CuWm between the media was relatively small, further illustrating that sufficient moisture is the basis for the effective regulatory effect of the medium.

[0126] The numerical distributions of ΔGs and γS provide a deeper perspective for understanding the stabilization mechanism of metastable ice. The γS value of the hydrophilic surface in Comparative Example 3 (37.40 J / g) is significantly higher than that of the hydrophobic surface in Example 3 (20.91 J / g), reflecting different interfacial bonding modes—the hydrophilic surface tightly adsorbs water molecules through strong hydrogen bonds, while the special interfacial environment of the hydrophobic surface is more conducive to the formation of metastable ice structures with high thermal stability. The unusually high γS value (101.24 J / g) in Example 1 confirms that in the mixed medium containing DMSO, the interfacial water molecules are in a special confined state with extremely high energy.

[0127] In summary, the core discovery of this invention lies in the creation and stabilization of a portion of "metastable ice" with exceptionally high thermal stability within a saltwater nanocomposite system that inevitably melts below 0°C, utilizing the unique surface properties of hydrophobic fumed silica AM1. All experimental data consistently demonstrate that hydrophobic silica AM1 is the key matrix for the formation of metastable ice, with effects far superior to the hydrophilic material A-300; a sufficiently high degree of hydration (h≥2.0 g / g) is a necessary condition for the generation of large quantities of metastable ice; and the external medium environment can serve as an effective regulating factor, with CDCl3 further synergistically enhancing the stability of the metastable ice. This discovery makes the stable existence of solid ice phases under ambient pressure and above-zero temperatures possible, providing a novel technical pathway for the storage or transport of substances using ice phases under mild conditions.

[0128] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them without departing from the spirit of the invention or exceeding the scope defined by the appended claims.< / tm>

Claims

1. A method for increasing the melting temperature of ice in a frozen brine solution, characterized in that, The method includes: mixing a salt solution with hydrophobic fumed silica, allowing the salt solution to enter the interparticle spaces of the hydrophobic fumed silica, thereby forming and stabilizing a solid ice phase at atmospheric pressure and a temperature above 273K.

2. The method according to claim 1, characterized in that, The ratio of the total mass of the salt solution to the mass of the hydrophobic fumed silica is from 0.15:1 to 5.0:

1.

3. The method according to claim 1, characterized in that, A salt solution is formed by dissolving salt in water, wherein the salt is one or more of a halide salt.

4. The method according to claim 1 or 2, characterized in that, The salt solution contains 20% to 60% salt by mass.

5. The method according to claim 1 or 2, characterized in that, The brine solution is a saturated or supersaturated brine solution containing undissolved salt crystals.

6. The method according to claim 1, characterized in that, The mixing step further includes adding a nonpolar organic additive to the system, the nonpolar organic additive filling the unoccupied volume in the interparticle spaces.

7. The method according to claim 6, characterized in that, The amount of the organic additive is 0.05-1.0g per gram of silicon dioxide.

8. The method according to claim 1 or 6, wherein the mixing is mechanical grinding mixing, comprising the following steps: (1) The dry hydrophobic fumed silica was subjected to preliminary mechanical grinding to form a bulk density of 0.1-0.3 g / cm³. 3 Compacting materials; (2) The pretreated silica obtained in step (1) is mechanically ground with a salt solution for 5-10 minutes to form a primary composite system.

9. The method according to claim 8, wherein the mechanical grinding and mixing further comprises the following step: Add organic additives to the primary composite system and continue mechanical grinding for 3-5 minutes.

10. Use of a composite system formed by any one of the methods of claims 1-9 in the preparation of gas hydrates or for gas storage.

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