Inorganic oxide particle-containing composition with low coefficient of variation

Abstract

[Problem] There is provided an inorganic oxide particle-containing composition exhibiting excellent dispersion stability of inorganic oxide particles and excellent salt tolerance. [Solution] An inorganic oxide particle-containing composition, wherein, in image analysis of a frozen sample by cryo-transmission electron microscope observation, the sample being prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that the concentration of inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, a coefficient of variation, which is a value obtained by dividing a standard deviation of areas of Voronoi partition regions based on an inorganic oxide particle distribution in a region of interest (ROI) by the arithmetic mean of the areas, is 0.1 to 0.7.

Description

DESCRIPTIONTITLE OF THE INVENTION: INORGANIC OXIDE PARTICLE-CONTAINING COMPOSITION WITH LOW COEFFICIENT OF VARIATIONTECHNICAL FIELD

[0001] The present invention relates to an inorganic oxide particle-containing composition exhibiting excellent dispersion stability of inorganic oxide particles.BACKGROUND ART

[0002] Compositions (sols) containing inorganic oxide particles such as aqueous silica sols are used in various fields such as abrasives and functional inorganic fillers.In recent years, in the field of CO2 capture and storage (CCS: Carbon dioxide Capture and Storage) techniques, in order to improve the CO2 trapping ability in deep underground aquifers (such as porous sandstone layers), a method in which water wettability of rock surfaces is applied using an aqueous dispersion containing silica nanoparticles has been proposed (Non-Patent Document 1).In addition, silica nanoparticles have been used in enhanced oil recovery (EOR) flooding for recovering crude oil by injection of the nanoparticles into the oil reservoirs in both inland and offshore oil fields. For example, it has been proposed to improve the efficiency of removing crude oil from rock surfaces by incorporating fine particles such as an aqueous silica sol (colloidal silica dispersions) into a crude oil recovery chemical solution, thereby improving the crude oil recovery rate (Patent Document 1).

[0003] Furthermore, one technique for evaluating the degree of dispersion of particles in a composition or the like, is a technique in which particles in an object image are converted into Voronoi polygons through Voronoi tessellation, the areas of these polygons are measured, and the degree of dispersion is evaluated based on the standarddeviation or the coefficient of variation of the areas.For example, Patent Document 1 proposes, in an electrostatic image-developing toner, in a cross-sectional image of toner particles taken with a transmission electron microscope, setting predetermined values for the average value and coefficient of variation of the areas of Voronoi polygons centered on low-brightness islands (Patent Document 2).In addition, Patent Document 3 proposes, in an electrophotographic belt having an elastic layer containing silicone rubber, magnesium hydroxide and the like, in a cross section of the electrophotographic belt in a direction perpendicular to the circumferential direction, setting the coefficient of variation calculated from the area values of Voronoi polygons formed through Voronoi tessellation using magnesium hydroxide particles exposed on the cross section as base points to a predetermined value. In this proposal, it is evaluated that, when the coefficient of variation is set to 1.5 or less, the dispersed state of magnesium hydroxide is favorable and excellent flame retardancy is obtained.Prior Art DocumentsPatent Documents

[0004] Patent Document 1: WO 2019 / 054414Patent Document 2: JP 2002-287410 APatent Document 3: JP 2023-8686 ANon-Patent Documents

[0005] Non-Patent Document 1: International Journal of Greenhouse Gas Control 66 (2017) 97-105SUMMARY OF THE INVENTIONProblem to be Solved by the Invention

[0006] The present invention describes an inorganic oxide particle-containing composition in which, an image analysis in a brine environment of the inorganic oxideparticle-containing composition, a measurement of the coefficient of variation of the inorganic oxide particle-containing composition, which is a value obtained by dividing the standard deviation of areas of Voronoi partition regions based on an inorganic oxide particle distribution in a region of interest (RO I) by the arithmetic mean of the areas, results in a predetermined value, which indicates excellent dispersion stability of inorganic oxide particles and excellent salt tolerance in water.Means for Solving the Problem

[0007] A first aspect of the present invention relates to an inorganic oxide particle-containing composition, wherein, an image analysis of a frozen sample by cryo-transmission electron microscope observation is undertaken, the sample being prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that concentration of inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, a coefficient of variation, which is a value obtained by dividing a standard deviation of areas of Voronoi partition regions based on an inorganic oxide particle distribution in a region of interest (RO I) by arithmetic mean of the areas, is 0.1 to 0.7.A second aspect of the present invention relates to the inorganic oxide particle-containing composition according to the first aspect, wherein, an image analysis of a frozen sample by cryo-transmission electron microscope was performed, the sample being prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that concentration of inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, a proportion of inorganic oxide particles in the region of interest (RO I) (total area occupied by the inorganic oxide particles / ROI area) is 1 to 50%.A third aspect of the present invention relates to the inorganic oxide particle-containing composition according to the first aspect, wherein the inorganic oxide particle-containing composition is a composition containing particles having an average secondary particle diameter of 5 nm to 100 nm, which is determined by a dynamic lightscattering method, the particles being of at least one inorganic oxide selected from the group consisting of silica, alumina, tin oxide, zirconium oxide, titanium oxide, and antimony oxide.A fourth aspect of the present invention relates to the inorganic oxide particle-containing composition according to the first aspect, further comprising an organic acid or salts of the acid.A fifth aspect of the present invention relates to the inorganic oxide particle-containing composition according to the fourth aspect, wherein the organic acid has a carboxy group.A sixth aspect of the present invention relates to the inorganic oxide particle-containing composition according to the fourth aspect, wherein the organic acid includes at least one selected from the group consisting of formic acid, acetic acid, propionic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, citric acid, malic acid, tartaric acid, butyric acid, fumaric acid, maleic acid, thioglycolic acid, oxalic acid, malonic acid, succinic acid, and lactic acid.A seventh aspect of the present invention relates to the inorganic oxide particle-containing composition according to the first aspect, wherein, in a room-temperature salt tolerance test in which the inorganic oxide particle-containing composition is stored at 20°C for 24 hours in an environment with salt concentration of 4% by mass such that concentration of the inorganic oxide particles is 0.5% by mass, an average secondary particle diameter (rl) of the inorganic oxide particles measured by a dynamic light scattering method before storage and an average secondary particle diameter (r2) of the inorganic oxide particles measured by a dynamic light scattering method after storage satisfy the following relationship:0.9 < (r2 / rl) < 5.An eighth aspect of the present invention relates to the inorganic oxide particle-containing composition according to the first aspect, wherein, in a high-temperature salt tolerance test in which the inorganic oxide particle-containing composition is stored at 50°C for 7 days in an environment with salt concentration of 4%by mass such that concentration of the inorganic oxide particles is 0.5% by mass, an average secondary particle diameter (rhl) of the inorganic oxide particles measured by a dynamic light scattering method before storage and an average secondary particle diameter (rh2) of the inorganic oxide particles measured by a dynamic light scattering method after storage satisfy the following relationship:0.9 < (rh2 / rhl) < 5.A ninth aspect of the present invention relates to a method for producing the inorganic oxide particle-containing composition according to the fourth aspect, comprising a step of adding an organic acid or salts of the acid to an aqueous inorganic oxide particle sol with stirring for 0.1 to 20 hours.A tenth aspect of the present invention relates to the inorganic oxide particle-containing a composition according to the first aspect, wherein the inorganic oxide particle-containing composition is a chemical solution for carbon dioxide storage.Effects of the Invention

[0008] The inorganic oxide particle-containing composition of the present invention is a composition in which the coefficient of variation of the areas of Voronoi partition regions based on an inorganic oxide particle distribution in a region of interest (RO I) exhibits a predetermined value, and in an environment in which the dispersion stability of the inorganic oxide particles contained in the composition is not impaired, for example, in an underground environment where formation water with a high salt concentration is present, assuming that nanoparticles are injected for applications such as CCS and EOR, the inorganic oxide particle-containing composition has excellent dispersion stability, and the present invention has an effect of providing the composition with excellent salt tolerance in such an environment.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [FIG. 1] FIG. 1 is a diagram showing the coefficient of variation of the areasof partition regions based on a particle distribution (horizontal axis) versus the DLS average particle diameter (r2) of samples after room-temperature salt tolerance evaluation for chemical solutions of examples and a comparative example (vertical axis).[FIG. 2] FIG. 2 is a diagram showing the coefficient of variation of the areas of partition regions based on a particle distribution in the chemical solutions of the examples and the comparative example.[FIG. 3] FIG.3 is an image obtained by applying a TEM image of dispersed inorganic oxide particles within the region of interest (RO I) in Example 1 to a binary image conversion and a Voronoi tessellation.[FIG. 4] FIG.4 is an image obtained by applying a TEM image of dispersed inorganic oxide particles within the region of interest (RO I) in Comparative Example 1 to a binary image conversion and a Voronoi tessellation.MODES FOR CARRYING OUT THE INVENTION

[0010] In order to index the dispersed state in a system containing inorganic oxide particles, the inventors of the present invention obtained images of the inorganic oxide particles in a dispersed state, then performed Voronoi tessellation on the images using the particles present in a region of interest (RO I) as base points, and calculated the coefficient of variation of Voronoi tessellated regions (a value obtained by dividing a standard deviation of the areas by the arithmetic mean of the areas). In addition, the inventors obtained the region of inorganic oxide particles present in the region of interest (RO I) by image analysis, calculated each area of the inorganic oxide particles in the ROI from the obtained particle region data, and calculated the area proportion of the inorganic oxide particles in the ROI (value obtained by dividing the total area of inorganic oxide particles (occupancy area) in the ROI by the ROI area).The coefficient of variation, which is a value obtained by dividing a standard deviation of the areas of the partition regions by the arithmetic mean of the areas, can be regarded as a value that indicates the degree of variation in the areas of the partitionregions relative to the average value. That is, in a system in which particles are dispersed, such as the inorganic oxide particle-containing composition according to the present invention, the coefficient of variation can be used as a value for evaluating the uniformity of the dispersed state of the particles. A smaller coefficient of variation reflects less variation in the areas of the partition regions, that is, indicating that, in a system in which particles are dispersed, the particles are in a well-dispersed state.On the other hand, when the coefficient of variation is zero, it indicates a state in which there is no variation at all relative to the average area. However, such a state is extremely rare in practice, and the coefficient of variation typically shows values of 0.1 or higher. Therefore, in the inorganic oxide particle-containing composition according to the present invention, it is not essential to require a level of dispersion uniformity as strict as a coefficient of variation of zero, and a certain degree of variation can be tolerated.In addition, if the area proportion (also referred to as the occupancy area proportion) of inorganic oxide particles in the region of interest (ROI) is smaller than that of other samples prepared under the same sample preparation conditions, it can be regarded as reflecting aggregation of inorganic oxide particles.

[0011] However, in order to perform image analysis of the inorganic oxide particle-containing composition, it is necessary to observe the inorganic oxide particle-containing composition (in a salt water environment) under an electron microscope. Moreover, because electron microscope observation is performed in a vacuum, the liquid in the sample evaporates when placed in a vacuum environment, causing the dispersed particles to aggregate, and thus it is difficult to observe the actual dispersed state of the particles.The present inventors adopted an image analysis method using a cryo-transmission electron microscope to perform image analysis of the actual dispersed state and particle size of the particles in the liquid.The cryo-transmission electron microscopic method is a method of observing biological structures by freezing them in their native state without staining them, that is, a method based on a transmission electron microscope (TEM), in which an electron beamis emitted to biomolecules such as proteins under liquified ethane cooling, and the sample is observed.In the present invention, in order to evaluate the dispersion behavior of inorganic oxide particles in a liquid, the dispersed state of particles in the liquid is fixed by rapidly cooling the sample to be measured to a amorphous vitrified form, image analysis is performed on the vitrified sample using a cryo-transmission electron microscope, and thus the coefficient of variation of the areas of the partition regions can be calculated through the Voronoi tessellation and the area proportion of the particles in the region of interest can be calculated.

[0012] Thus, the inventors found that, during image analysis in a salt water environment, by selecting an inorganic oxide particle-containing composition in which the coefficient of variation of the areas of Voronoi partition regions based on the inorganic oxide particle distribution in the region of interest (ROI) exhibit a predetermined value, and preferably selecting an inorganic oxide particle-containing composition in which the occupancy area proportion of particles in the ROI (region of interest) exhibits a predetermined value, it is possible to provide a composition exhibiting excellent dispersion stability of inorganic oxide particles and excellent salt tolerance.Hereinafter, the present invention will be described in detail.

[0013] Regarding the inorganic oxide particle-containing composition according to the present invention, in image analysis of a frozen sample by cryo-transmission electron microscope observation, where the sample of the inorganic oxide particle-containing composition in 4% by mass of salt water is prepared, for example, the sample is prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that the concentration of the inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, the coefficient of variation, which is a value obtained by dividing a standard deviation of the areas of Voronoi partition regions based on an inorganic oxide particle distribution in the region of interest (ROI) by the arithmetic mean of the areas, is 0.1 to 0.7. Here, the coefficient of variation is a value that is not influenced by the area occupied by the inorganic oxide particles in the ROI anddoes not vary depending on the inorganic oxide particle concentration. In addition, the coefficient of variation may be 0.1 to 0.7, 0.1 to 0.6, 0.2 to 0.7, 0.3 to 0.7, or 0.3 to 0.6. When the coefficient of variation is 0.1 to 0.7, it is possible to provide a composition in which the dispersion stability of inorganic fine particles is excellent in an underground environment where formation water with a high salt concentration is present and the salt tolerance is excellent in such an environment.

[0014] In addition, regarding the inorganic oxide particle-containing composition according to the present invention, in image analysis of a frozen sample by cryo-transmission electron microscope observation, where the sample of the inorganic oxide particle-containing composition in 4% by mass of salt water is prepared, for example, the sample is prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that the concentration of the inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, the proportion of inorganic oxide particles in the region of interest (ROI) (occupancy area proportion: total area occupied by inorganic oxide particles / ROI area) is preferably 1 to 50%. The proportion of inorganic oxide particles in the region of interest (ROI) (occupancy area proportion: total area occupied by inorganic oxide particles / ROI area) may be 1 to 50%, 5 to 50%, 10 to 50%, 15 to 50%, 20 to 50%, 1 to 40%, 10 to 40%, or 20 to 40%. When the proportion of inorganic oxide particles in the region of interest (ROI) (occupancy area proportion: total area occupied by inorganic oxide particles / ROI area) is 1 to 50%, it is possible to provide a composition in which the dispersion stability of inorganic fine particles is excellent in an underground environment where formation water with a high salt concentration is present and the salt tolerance is excellent in such an environment.Here, in the above example, evaluation is performed when the concentration of inorganic oxide particles in the sample to be analyzed is 0.5% by mass, but the preferable occupancy area proportion varies depending on the concentration of the inorganic oxide particles in the sample to be analyzed and the particle diameter of the inorganic oxide particles.In setting the concentration of inorganic oxide particles in the sample to be analyzed, for example, an image analysis of a control vitrified sample obtained by rapidly cooling a mixture solution containing the inorganic oxide particle-containing composition and pure water, in cryo-transmission electron microscope observation, the concentration of inorganic oxide particles can be set such that the proportion of inorganic oxide particles in the region of interest (RO I) (total area of inorganic oxide particles / ROI area) is 20 to 40%.

[0015] In the cryo-transmission electron microscope observation, first, a frozen sample to be analyzed is prepared.The frozen sample is prepared by rapidly freezing a sample adjusted to a predetermined salt concentration (4% by mass) and an inorganic oxide particle concentration (0.5% by mass). When ice crystals grow during cooling, volume expansion occurs, the original dispersed state cannot be maintained and thus rapid cooling is performed to vitrify water in an amorphous state. In addition, similarly, if the vitrified sample is heated, ice crystallization will occur in the sample. Therefore, it is necessary to immerse the sample in liquid nitrogen to maintain a low-temperature state of the sample before it is inserted into a sample chamber of the electron microscope.Rapid freezing methods include a method in which a sample is instantly dropped into liquefied ethane or liquefied propane cooled with liquid nitrogen and thus vitrified and a method in which a sample is vitrified with liquid nitrogen under a high pressure. In the present invention, a sample that is rapidly vitrified in liquefied ethane at a freezing rate of 104oC or higher or 106oC or higher per second by the former method is used.The frozen sample is transported into a cryo-transmission electron microscope device without exposure to the atmosphere and while maintaining a cryogenic environment, using a dedicated tool or the like, and observed under an electron microscope.The image analysis of the obtained image is performed, for example, by specifying a region of interest (RO I) in each obtained image, removing noise in the RO I, and then identifying the particles in the ROI. When Voronoi tessellation is performed based onthe distribution of the identified particles and the particle area is obtained from the particle region data, the coefficient of variation and the area proportion of inorganic oxide particles can be calculated.

[0016] The inorganic oxide particle-containing composition of the present invention according to one aspect may contain particles having an average secondary particle diameter of 5 nm to 100 nm, which is determined by a dynamic light scattering method, the particles being of at least one inorganic oxide selected from the group consisting of silica, alumina, tin oxide, zirconium oxide, titanium oxide, and antimony oxide.For example, the inorganic oxide particle-containing composition may be in the form of an inorganic oxide particle sol containing the inorganic oxide particles and an aqueous medium. The aqueous medium is usually water, and ordinary industrial water, deionized water, distilled water or the like can be used.A specific example of the inorganic oxide particle-containing composition is an aqueous inorganic oxide particle sol containing inorganic oxide particles as a dispersoid and water as a dispersion medium, for example, an aqueous silica sol. The aqueous silica sol is a colloidal dispersion system using an aqueous solvent (aqueous medium) as a dispersion medium and colloidal silica particles as a dispersoid, and can be produced by a known method using water glass (sodium silicate aqueous solution) as a raw material.

[0017] When the inorganic oxide particle-containing composition itself or a sample obtained by mixing the composition with salt water or the like is measured by the dynamic light scattering method, the average secondary particle diameter (DLS average particle diameter: Z average particle diameter, harmonic average particle diameter) and the dispersed state (whether the inorganic oxide particles are in a dispersed state or aggregated state) of the inorganic oxide particles can be determined.The DLS average particle diameter is the average value of the secondary particle diameters (dispersed particle diameters), and the DLS average particle diameter in a completely dispersed state is said to be about twice the average primary particle diameter (which is the specific surface area diameter obtained by measurement using a nitrogenadsorption method (BET method) or Sears method, and is the average value of the primary particle diameters). Here, when the DLS average particle diameter is larger, it can be determined that the inorganic oxide particles in the medium are in a more aggregated state.In the inorganic oxide particle-containing composition of the present invention, as described above, the average particle diameter (DLS average particle diameter) of the inorganic oxide particles is, for example, 5 nm to 100 nm, or may be 10 nm to 80 nm, 10 nm to 50 nm, or 10 nm to 40 nm. By making particles have a DLS average particle diameter of more than 5 nm, the particles do not aggregate in the inorganic oxide particle-containing composition and become more stable, and by making particles have an average particle diameter of less than 100 nm, for example, it is expected that, when the composition is applied as a chemical solution for carbon dioxide storage, it will more easily penetrate the gaps in the underground layer or the pores of rocks when it is injected into the underground layer.

[0018] The value of the DLS average particle diameter is, for example, an (initial) value before various tests are performed in a salt water environment, but the inorganic oxide particles in the inorganic oxide particle-containing composition according to the present invention are particles with excellent dispersion stability, and even after various tests are performed in the salt water environment, the ratio of particle diameters before and after the test is a maximum of about 5, that is, the value of the DLS average particle diameter can be approximately within the above numerical range (range of 5 to 100 nm).

[0019] Here, as described above, when particles have a large DLS average particle diameter, it is not preferable because the particles may not penetrate into gaps and the like in the underground layer and block the gaps and the like. Therefore, it is preferable to use an inorganic oxide particle-containing composition of the present invention (aqueous inorganic oxide particle sol) that does not contain coarse particles, for example, an inorganic oxide particle-containing composition (aqueous inorganic oxide particle sol) in which the cumulative particle size distribution D90 of the average particlediameters (DLS average particle diameters) of inorganic oxide particles determined by a dynamic scattering method is 5 to 200 nm, 5 to 150 nm, 5 to 100 nm, or 5 to 70 nm. In addition, it is preferable that inorganic oxide particles contained in the inorganic oxide particle-containing composition (aqueous inorganic oxide particle sol) exhibit salt tolerance such that, upon contact with salt water contained in the underground layer or the like, the inorganic oxide particles do not aggregate to an extent exceeding the DLS average particle diameter or D90 range.The D90 represents the particle size value below which 90% dof the particles in a sample are found. The cumulative particle size distribution can be obtained, for example, by a dynamic light scattering method or image analysis, and as an example, the value of the cumulative particle size distribution can be measured by particle size distribution using a dynamic light scattering method particle diameter measurement device. The D value analysis methods include a number distribution method and a volume distribution method. In the number distribution method, particles are regarded as perfect circles having the same area as the particles, and the percentage of particles having a specific particle diameter is measured. In addition, in the volume distribution method, assuming that the volume and the weight are proportional if the density of the particles is constant, the mass percentage of particles having a specific particle diameter in a certain amount of a sample is measured. As an example, it is preferable to obtain the D value (D90) by the volume distribution method.

[0020] Here, the average primary particle diameter of the inorganic oxide particles constituting the inorganic oxide particle-containing composition of the present invention is, for example, 5 to 100 nm, and may be, for example, 5 to 70 nm, 5 to 60 nm, 5 to 50 nm, or 5 to 30 nm.Unless otherwise specified, the average primary particle diameter of the inorganic oxide particles may be the specific surface area diameter measured by the nitrogen adsorption method (BET method) or the Sears method particle diameter in the case of silica particles.The specific surface area diameter (average particle diameter (specific surface areadiameter) D (nm)) obtained by measurement by the nitrogen adsorption method (BET method) is calculated based on the specific surface area S (m / g) measured by the nitrogen adsorption method, and for example, it is obtained by the formula of D (nm) = 2720 / S in the case of silica particles.The Sears method particle diameter refers to an average particle diameter of silica particles measured based on the method with reference to G. W. Sears, Anal. Chem. 28(12) p. 1981, 1956 “a rapid method for measuring the colloidal silica particle diameter.” Specifically, it is an equivalent diameter (specific surface area diameter) calculated from the specific surface area of colloidal silica determined from the amount of 0.1 N-NaOH required to titrate colloidal silica equivalent to 1.5 g of SiOo from a pH of 4 to a pH of 9.

[0021] As the aqueous inorganic oxide particle sol, commercially available products can be used. In addition, an aqueous inorganic oxide particle sol with an inorganic oxide particle concentration of 5 to 50% by mass is generally commercially available, and is preferable because it is readily available.As an example of a commercially available aqueous inorganic oxide particle sol, commercially available aqueous silica sols may be exemplified. The aqueous silica sol includes an alkaline aqueous silica sol and an acidic aqueous silica sol, although both can be used, the acidic aqueous silica sol is preferably used. Examples of commercially available acidic aqueous silica sols include Snowtex (product name) ST-OXS, ST-OS, ST-O, ST-O-40, ST-OL, and ST-OYL (commercially available from Nissan Chemical Corporation); and ADELITE (product name) AT-series (commercially available from ADEKA). Here, the silica solid content concentration in the aqueous silica sol used is preferably 5 to 55% by mass.

[0022] The silica solid content concentration is a value determined by a baking method, specifically, a value obtained by dividing the mass of the baking residue obtained by baking an aqueous silica sol at l,000°C for 30 minutes or longer in the atmosphere by the mass of the aqueous silica sol. In addition, the mass of the baking residue is referred to as “silica solid content.Here, the concentration of inorganic oxide particles in the aqueous inorganic oxide particle sol (inorganic oxide particle solid content concentration) can also be determined by a similar procedure (baking method), and in this case, the mass of the baking residue can be referred to as “inorganic oxide particle solid content.”

[0023] The concentration of inorganic oxide particles (inorganic oxide particle solid content concentration) in the inorganic oxide particle-containing composition according to the present invention is not particularly limited, and may be, for example, 0.01% by mass to 50.0% by mass, 0.1% by mass to 50.0% by mass, 10.0% by mass to 25.0% by mass, or for example, 15.0% by mass to 25.0% by mass based on the total mass of the inorganic oxide particle-containing composition.

[0024] In the inorganic oxide particle-containing composition of the present invention, the surface of the inorganic oxide particles may be treated with a silane coupling agent.Here, “coated with a silane compound” refers to a form in which the surface of the inorganic oxide particles is coated with a silane compound and also includes any form in which a silane compound is bonded to the surface of the inorganic oxide particles.“A form in which the surface of the inorganic oxide particles is coated with a silane compound” may refer to a form in which at least a part of the surface of the inorganic oxide particles is coated with a silane compound, that is, includes a form in which the silane compound covers a part of the surface of the inorganic oxide particles and a form in which the silane compound covers the entire surface of the inorganic oxide particles. In this form, it is not important whether the silane compound is bonded to the surface of the inorganic oxide particles.In addition, “a form in which a silane compound is bonded to the surface of the inorganic oxide particles” may refer to a form in which a silane compound is bonded to at least a part of the surface of the inorganic oxide particles, that is, includes a form in which the silane compound is bonded to a part of the surface of the inorganic oxide particles, a form in which the silane compound is bonded to a part of the surface of the inorganic oxide particles and covers at least a part of the surface, and also a form inwhich the silane compound is bonded to the entire surface of the inorganic oxide particles and covers the entire surface.

[0025] The silane compound may be a silane compound having, for example, an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group. In addition, the silane compound preferably has, in addition to the hydrophilic organic group, for example, a hydrolyzable group such as an alkoxy group, an acyloxy group, or a halogen group.Specific examples of these silane compounds (c) include silane coupling agents having an epoxy group-containing organic group or an amino group-containing organic group.Examples of silane coupling agents having an epoxy group-containing organic group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)propyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)propyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4-epoxycyclohexyl)methyltrimethoxysilane,2-(3,4-epoxycyclohexyl)methyltriethoxysilane, l-(3,4-epoxycyclohexyl)methyltrimethoxysilane, and l-(3,4-epoxycyclohexyl)methyltriethoxysilane.In addition, examples of silane coupling agents having an amino group-containing organic group include 3-(2-(2-aminoethylamino)ethylamino)propyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrichlorosilane,3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(l,3-dimethyl-butylidene)propylamine,N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane.

[0026] The inorganic oxide particles whose surface is treated with a silane coupling agent, that is, the inorganic oxide particles of which at least some are coated with a silane compound having a hydrophilic organic group (also referred to as “inorganic oxide particles whose surface is treated with a silane compound”) can be obtained, for example, by adding a silane compound to an aqueous inorganic oxide particle sol and then performing a heat treatment at 50 to 100°C for about 1 hour to 20 hours. In this case, the amount of the silane compound added with respect to the inorganic oxide particles (inorganic oxide particle solid content) in the aqueous inorganic oxide particle sol can be set to, for example, a mass ratio of silane compound / inorganic oxide particle = 0.1 to 10.0.The amount of surface treated with the silane compound, that is, the amount of the silane compound bonded to the surface of the inorganic oxide particles is preferably, for example, about 0.1 to 12 molecules per 1 nm of the surface of the inorganic oxide particles.

[0027] Here, when the above surface-treated inorganic oxide particles (also referred to as surface-modified inorganic oxide particles) are used as inorganic oxide particles constituting the inorganic oxide particle-containing composition according to the present invention, unreacted silane compounds used in the surface treatment and unmodified inorganic oxide particles may remain in the inorganic oxide particle-containing composition, and a composition from which these unreacted silane compounds and unmodified inorganic oxide particles have been removed can also be used.

[0028] In addition, the inorganic oxide particles constituting the inorganic oxide particle-containing composition according to the present invention have a high absolute value of zeta potential, which induces electrical repulsion, and in consideration of dispersibility, the zeta potential (absolute value) can be increased accordingly.

[0029] In addition, the inorganic oxide particle-containing composition according to the present invention may contain an organic acid or salts of the acid. Theaddition of an organic acid or salts of the acid can be expected to improve the dispersion stability of the inorganic oxide particles in the inorganic oxide particle-containing composition in a salt water environment. The organic acid is preferably an acid having a carboxy group.Specific examples of organic acids or salts of the acids include acetic acid, lactic acid, citric acid, malic acid, succinic acid, tartaric acid, butyric acid, oxalic acid, malonic acid, fumaric acid, maleic acid, propionic acid, formic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, thioglycolic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid sodium salts, L-aspartic acid, L-aspartic acid-diacetic acid tetrasodium salts, and diethylenetriaminepentaacetic acid. Among these, at least one selected from the group consisting of formic acid, acetic acid, propionic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, citric acid, malic acid, tartaric acid, butyric acid, fumaric acid, maleic acid, thioglycolic acid, oxalic acid, malonic acid, succinic acid, and lactic acid is preferable. In addition to the salts exemplified above, alkali metal salts such as sodium salts and potassium salts of the organic acids, ammonium salts, and amine salts may be exemplified.The amount of the organic acid or salts of the acid based on the total mass of the inorganic oxide particle-containing composition according to the present invention may be, for example, 0.01% by mass to 10% by mass, 0.1% by mass to 10% by mass, or 0.5% by mass to 10% by mass.In addition, the organic acid or salts of the acid may be contained in a proportion such that the mass ratio (organic acid or salts of the acid / inorganic oxide particle) is, for example, 0.0001 to 2, 0.001 to 2, or 0.01 to 1.5, with respect to the inorganic oxide particles constituting the inorganic oxide particle-containing composition according to the present invention.In addition, the organic acid or salts of the acid may have a first acid dissociation constant pKa (at 25°C) of 10 or less, -5 to 8, -5 to 8, -1 to 8, 1 to 8, -5 to 5, or 1 to 5. The first acid dissociation constant is the acid dissociation constant itself when the organic acid or salts of the acid are a monovalent acid, and is the acid dissociationconstant for dissociation of the first proton when the organic acid or salts of the acid are a polyvalent acid. Specifically, the pKa in the aqueous solution can be actually measured by measuring the acid dissociation constant (at 25°C) using an infinitely dilute aqueous solution, and can also be calculated using the following software package 1 based on a Hammett’s substituent constant and known literature value database. Software package 1: Advanced Chemistry Development (ACD / Labs) Software V8.00 for Solaris (1994-2004 ACD / Labs). When the first acid dissociation constant pKa (at 25°C) of the organic acid or salts of the acid is set to 10 or less, it is expected that the dispersion stability of the inorganic oxide particles in the inorganic oxide particle-containing composition in a salt water environment will be improved.

[0030] In an aspect in which the inorganic oxide particle-containing composition according to the present invention contains an organic acid, the method for producing the composition is not particularly limited, and for example, a step of adding an organic acid to an aqueous inorganic oxide particle sol with stirring and stirring the mixture for 0.1 to 20 hours may be performed.

[0031] [Stability evaluation (salt tolerance evaluation)]The dispersion stability of the inorganic oxide particle-containing composition according to the present invention can be evaluated by comparing the DLS average particle diameters before and after storage under predetermined conditions.For example, when assuming use as a chemical solution for carbon dioxide storage or the like, the salt tolerance (salt water stability) of the inorganic oxide particle-containing composition can be evaluated by a salt tolerance test in which the composition is stored in a salt-containing environment. In the measurement before and after storage in the test, when a change in the DLS average particle diameter (average secondary particle diameter) of the inorganic oxide particles measured by the dynamic light scattering (DLS) method is small, it can be evaluated that the inorganic oxide particles maintain a dispersed state, and therefore the inorganic oxide particle-containing composition can be evaluated as having favorable salt tolerance. On the other hand, when the DLS average particle diameter (average secondary particle diameter) of theinorganic oxide particles before and after storage in the test increases significantly, it can be considered to reflect the aggregated state of the inorganic oxide particles, and such an inorganic oxide particle-containing composition can be evaluated as having poor salt tolerance.

[0032] For example, in order to evaluate salt tolerance at room temperature, a room-temperature salt tolerance test in which the inorganic oxide particle-containing composition is stored at 20°C for 24 hours in an environment with a salt concentration of 4% by mass such that the concentration of the inorganic oxide particles is 0.5% by mass.In the inorganic oxide particle-containing composition according to the present invention, when the DLS average particle diameter (average secondary particle diameter) of the inorganic oxide particles before storage in the room-temperature salt tolerance test is (rl), and the DLS average particle diameter (average secondary particle diameter) of the inorganic oxide particles after storage is (r2), it is preferable that 0.9 < (r2 / rl) < 5 be satisfied. When (r2 / rl) is less than 5, after the room-temperature salt tolerance test, it can be evaluated that the inorganic oxide particles do not aggregate or gel and maintain a dispersed state in a salt tolerance evaluation sample, and more preferably, (r2 / rl) may be 1.5 or less (the rate of change in DLS average particle diameter is 50% or less) or 1.1 or less (the rate of change in average particle diameter is 10% or less).

[0033] In addition, in order to evaluate high-temperature salt tolerance, a high-temperature salt tolerance test in which the inorganic oxide particle-containing composition is stored at 50°C for 7 days in an environment with a salt concentration of 4% by mass such that the concentration of the inorganic oxide particles is 0.5% by mass.In the inorganic oxide particle-containing composition according to the present invention, when the DLS average particle diameter (average secondary particle diameter) of the inorganic oxide particles before storage in the high-temperature salt tolerance test is (rhl), and the DLS average particle diameter (average secondary particle diameter) of the inorganic oxide particles after storage is (rh2), it is preferable that 0.9 < (rh2 / rhl) < 5 be satisfied. When (rh2 / rhl) is less than 5, after the high-temperature salt tolerance test, it can be evaluated that the inorganic oxide particles do not aggregate or gel and maintaina dispersed state in a salt tolerance evaluation sample, and more preferably, (rh2 / rhl) may be 1.5 or less (the rate of change in DLS average particle diameter is 50% or less) or 1.1 or less (the rate of change in average particle diameter is 10% or less).

[0034] As described above, the inorganic oxide particle-containing composition according to the present invention can be used as a chemical solution for carbon dioxide storage. The chemical solution for carbon dioxide storage is expected to be used for a variety of applications, including, but not limited to, for example, a chemical solution for increasing the amount of carbon dioxide stored in bedrock and improving storage stability by making (modifying) the surface of underground rocks water wet, for example, a rock surface wettability adjusting agent for increasing residual trapping and improving stabilization, where carbon dioxide is stored in a non-mobile state in small pores in bedrock, a mineralization promoting agent for promoting mineral trapping through carbon dioxide mineralization, and a dissolution promoting agent for promoting dissolution of basic minerals in the preliminary stage.When the composition is used as a chemical solution for carbon dioxide storage, for example, it can be injected into the underground layer after the concentration of inorganic oxide particles in an aqueous medium gas has been adjusted to about 0.001 to 30% by mass. Regarding the order of injection of carbon dioxide and the inorganic oxide particle-containing composition, for modifying the wettability of underground rocks, it is preferable to inject the inorganic oxide particle-containing composition before, or simultaneously with the injection of carbon dioxide. Here, similarly, for mineralization of carbon dioxide, it is preferable to inject the inorganic oxide particle-containing composition before, or simultaneously with injection of carbon dioxide. Alternatively, even if the inorganic oxide particle-containing composition is injected after carbon dioxide is injected, the effect is not impaired at all.

[0035] Here, in addition to being used as a chemical solution for carbon dioxide storage, the inorganic oxide particle-containing composition according to the present invention is expected to be used in a wide range of underground injection applications, including enhanced oil recovery (EOR) applications, for example, an application as acrude oil recovery chemical solution for performing injection from an injection well into an underground layer in order to recover crude oil from an underground hydrocarbon-containing layer and recovering a crude oil from a production well.[Examples]

[0036] Hereinafter, the present invention will be described in more detail with reference to examples and the comparative example, but the present invention is not limited to these examples.

[0037] (Measurement devices)In examples, CRYO ARM (registered trademark) 300 II (product name, commercially available from JEOL Ltd.) was used as a cryo-transmission electron microscope.The silica sols prepared in synthesis examples and chemical solutions prepared in preparation examples were analyzed (for the pH value, the electrical conductivity, and the DLS average particle diameter) using the following devices.•DLS average particle diameter (dynamic light scattering method particle diameter): a dynamic light scattering method particle diameter measurement device Zetasizer Nano (commercially available from Spectris, Malvern Division) was used.•pH: a pH meter (commercially available from DKK-TOA Corporation) was used. •Electrical conductivity: an electrical conductivity meter (commercially available from DKK-TOA Corporation) was used.•Viscosity: a BM II type viscometer (commercially available from Tokyo Keiki Co., Ltd.) was used (measured at 20°C).

[0038] (Cryo-transmission electron microscope observation)Each of the chemical solutions produced in the examples and the comparative example described below was diluted and mixed with 4% by mass of salt water so that the silica concentration (solid content) was 0.5% by mass to prepare a sample to be frozen.In order to prepare a sample for cryo-transmission electron microscope observation, an automatic plunge freezing device (product name LEICA EM GP2, commerciallyavailable from Leica Microsystems) was used.The sample to be frozen was dropped onto a grid in the device, and the grid was then brought into contact with filter paper for several seconds to remove an excess solution. Then, the sample to be frozen was immersed in liquefied ethane and rapidly frozen at a freezing rate of 104oC or higher per second to prepare a frozen sample. The frozen sample was transported into a cryo-transmission electron microscope device using a dedicated tool (commercially available from JEOL Ltd.) without exposure to the atmosphere and while maintaining a low temperature environment, and then observed.The frozen sample was observed under conditions of an acceleration voltage of 300 kV, an observation magnification of 30 k, and an exposure time of 4 s. In each frozen sample, 200 images were obtained under the same conditions, and image analysis was performed according to the following procedure.

[0039] (Cryo-transmission electron microscope analysis)The images obtained by cryo-transmission microscope observation were subjected to image analysis to calculate the occupancy area proportion of the (silica) particle part in the ROI (selected region (region of interest) in the image) and the coefficient of variation of Voronoi partition regions.The obtained images were analyzed using data analysis software (product name Avizo, commercially available from Thermo Fisher Scientific).An ROI was specified in the range of 3,360 x 3,292 pixels at the center of each image (564.48 x 553.056 (nm ) in this measurement field of view), and denoising processing was performed in the ROI. Here, a machine learning model that was trained and constructed for Poisson noise processing in backscattered electron (BSE) images under a scanning electron microscope (SEM) was applied.The denoised image was subjected to adaptive binarization to obtain binary data, and closing processing was then performed to exclude small regions caused by noise. At the same time, the watershed algorithm was used to separate regions of particles that were in contact or overlapping. Then, filtering was performed based on the circle-equivalent diameter and the value of shape anisotropy (the value obtained bysubtracting the ratio of the minimal eigenvalue and the maximum eigenvalue of the covariance matrix from 1) of each region in the binary data, and regions caused by ice crystals or impurities that were slightly mixed in the measurement range were excluded.According to the above treatment, only the region in the TEM image where particles were present was obtained.The area of particles in the ROI was calculated from the binary data of the obtained particle regions, and the total value thereof was divided by the area of the ROI to calculate the occupancy area proportion of particles. The same processing was performed on 200 images obtained from the same sample, and the average value thereof was calculated as the occupancy area proportion of particles in the ROI.In addition, Voronoi tessellation was performed based on the distribution of the identified particles. The coefficient of variation was calculated from the area of the obtained partition regions.

[0040] (Room-temperature salt tolerance evaluation)A stirring bar was placed in a 200 ml polystyrene bottle, 0.56 g of each of the chemical solutions produced in the examples and the comparative example described below was then added, and the mixture was stirred with a magnetic stirrer. While stirring with a magnetic stirrer, 10.56 g of pure water and 88.89 g of a brine solution containing sodium chloride, calcium chloride, and magnesium chloride and having a salt concentration of 4.5% by mass were added, and the mixture was stirred for 1 hour. This was used as a brine test sample (salt tolerance evaluation sample) for evaluating the salt tolerance of a chemical solution (a silica particle concentration of 0.5% by mass) under a salt concentration of 4% by mass. In the obtained brine test sample (salt tolerance evaluation sample), the pH, the electrical conductivity, and the DLS average particle diameter (rl) of the aqueous silica sol (silica particles) in the sample were evaluated.

[0041] 100 g of the brine test sample was placed in a 200 mL sealable polystyrene container, the container was sealed, the polystyrene container was then left at 20°C and maintained for 24 hours to perform a room-temperature salt tolerance test, and for the brine test sample (salt tolerance evaluation sample) after the test, the appearance,the pH, the electrical conductivity, and the DLS average particle diameter (r2) of the aqueous silica sol (silica particles) in the sample were evaluated.Here, the salt tolerance was evaluated according to the determination of salt tolerance (refer to determination of salt tolerance> below) based on the measurement results of the DLS average particle diameter of the aqueous silica sol (silica particles) in the sample after storage (24 hours) at 20°C for a predetermined time, and evaluation of the appearance.

[0042] determination of room-temperature salt tolerance>A: room-temperature salt tolerance test: the ratio of the DLS average particle diameter (r2) after storage to the DLS average particle diameter (rl) before storage was more than 0.9 and 1.1 or less.B: room-temperature salt tolerance test: the ratio of the DLS average particle diameter (r2) after storage to the DLS average particle diameter (rl) before storage was more than 1.1 and 1.5 or less.C: room-temperature salt tolerance test: the ratio of the DLS average particle diameter (r2) after storage to the DLS average particle diameter (rl) before storage was more than 1.5 and less than 5.0.D: room-temperature salt tolerance test: the ratio of the DLS average particle diameter (r2) after storage to the DLS average particle diameter (rl) before storage was 5.0 or more and 20.0 or less.E: room-temperature salt tolerance test: the ratio of the DLS average particle diameter (r2) after storage to the DLS average particle diameter (rl) before storage was more than 20.0 or the sample became cloudy and separated into a solid and a liquid.The room-temperature salt tolerance test results indicate that A is most preferable, followed by B, C, D, and E in descending order of preference, and in the present invention, ratings down to the evaluation C are considered acceptable.

[0043] (High-temperature salt tolerance evaluation)A stirring bar was placed in a 200 mL polystyrene bottle, 0.56 g of each of the chemical solutions produced in the examples and the comparative example describedbelow was then added, and the mixture was stirred with a magnetic stirrer. While stirring with a magnetic stirrer, 10.56 g of pure water and 88.89 g of a brine solution containing sodium chloride, calcium chloride, and magnesium chloride and having a salt concentration of 4.5% by mass were added, and the mixture was stirred for 1 hour. This was used as a brine test sample (high-temperature salt tolerance evaluation sample) for evaluating the high-temperature salt tolerance of a chemical solution (a silica particle concentration of 0.5% by mass) under a salt concentration of 4% by mass. In the obtained brine test sample (high-temperature salt tolerance evaluation sample), the pH, the electrical conductivity, and the DLS average particle diameter (rhl) of the aqueous silica sol (silica particles) in the sample were evaluated.

[0044] 100 g of the brine test sample was put into a 200 mL sealable polystyrene container, the container was sealed, the polystyrene container was then left at 50°C and maintained for 7 days to perform a high-temperature salt tolerance test, and for the brine test sample (high-temperature salt tolerance evaluation sample) after the test, the appearance, the pH, the electrical conductivity, and the DLS average particle diameter (rh2) of the aqueous silica sol (silica particles) in the sample were evaluated.Here, the salt tolerance was evaluated according to the determination of high-temperature salt tolerance (refer to determination of salt tolerance> below) based on the measurement results of the DLS average particle diameter of the aqueous silica sol (silica particles) in the sample after storage (after 7 days) at 50°C for a predetermined time and evaluation of the appearance.

[0045] determination of high-temperature salt tolerance>A: high-temperature salt tolerance test: the ratio of the DLS average particle diameter (rh2) after storage to the DLS average particle diameter (rhl) before storage was more than 0.9 and 1.3 or less.B: high-temperature salt tolerance test: the ratio of the DLS average particle diameter (rh2) after storage to the DLS average particle diameter (rhl) before storage was more than 1.3 and 2.0 or less.C: high-temperature salt tolerance test: the ratio of the DLS average particle diameter1(rh2) after storage to the DLS average particle diameter (rhl) before storage was more than 2.0 and less than 5.0.D: high-temperature salt tolerance test: the ratio of the DLS average particle diameter (rh2) after storage to the DLS average particle diameter (rhl) before storage was 5.0 or more and 20.0 or less.E: high-temperature salt tolerance test: the ratio of the DLS average particle diameter (rh2) after storage to the DLS average particle diameter (rhl) before storage was more than 20.0 or the sample became cloudy and separated into a solid and a liquid.The high-temperature salt tolerance test results indicate that A is most preferable, followed by B, C, D, and E in descending order of preference, and in the present invention, ratings down to the evaluation C are considered acceptable.

[0046] (Measurement of binding amount of organic components bonded to silica particles (organic acid, silane compound, etc.))<Removal of organic components not bonded to silica particles>2 g of each of the chemical solutions produced in the examples and the comparative example described below and 4 g of pure water were put into a 15 mL centrifugation cell with a filter (commercially available from Merck, product name Amicon Ultra- 15, a molecular cutoff of 100,000, centrifugal ultrafiltration filter unit), and centrifuged at a centrifugal force of 2770 G for 20 minutes. After centrifugation, the liquid discharged from the bottom of the unit was discarded, the same mass of pure water as the discarded liquid was added to each chemical solution concentrated on the filter, and the mixture was re-dispersed and then centrifuged again at a centrifugal force of 2770 G for 20 minutes. The above procedure was repeated a total of four times to obtain a binding amount measurement sample (aqueous silica sol) from which organic components not bonded to silica particles contained in each chemical solution were removed. <Measurement of carbon content>The binding amount measurement sample (aqueous silica sol) from which organic components not bonded to silica particles were removed was heated and dried at 100°C and crushed in a mortar to obtain a binding amount measurement sample powder (silicasol powder). The carbon content in the obtained powder was measured using an organic trace element analyzing device (2400 II series CHNS / O analyzer, commercially available from PerkinElmer Japan Co., Ltd.), and the amount of surface treatment (organic acid or silane binding amount (organic acid in the case of Examples 1 to 5) of silica particles was calculated from the obtained carbon content according to the following formula.Amount of surface treatment (organic acid binding amount: molecules / nm ) = (Cm - Cn - Sc x A) / (Ct x Cs)In the formula, Cm is the carbon content (% by mass), Cn is the carbon molecular weight, Sc is the number of carbon atoms in the organic acid, A is the Avogadro’s number, Ct is the silica particle mass, and Cs is the silica specific surface area.

[0047] (Example 1)400 g of an aqueous silica sol (Snowtex (product name) ST-O, commercially available from Nissan Chemical Corporation, a silica concentration = 20.5% by mass, an average particle diameter of 11.0 nm, determined by the BET method, and an average particle diameter of 17.2 nm, determined by the DLS method) and a magnetic stirring bar were placed in a 500 mL polystyrene bottle, 8.2 g of malonic acid (with an active component concentration of 99.0% by mass, commercially available from Junsei Chemical Co., Ltd.) was then added while stirring with a magnetic stirrer, and the mixture was stirred for 1 hour to obtain 408 g of a chemical solution according to Example 1.The obtained chemical solution had a silica solid content of 20.1% by mass, a pH of 1.8, an electrical conductivity of 6,110 pS / cm, a viscosity of 4.6 mPa-s, and a DLS average particle diameter of 20.9 nm.

[0048] (Example 2)409 g of a chemical solution according to Example 2 was obtained in the same manner as in Example 1 except that 9.4 g of succinic acid (with an active component concentration of 99.9% by mass, commercially available from Junsei Chemical Co., Ltd.) was used in place of 8.2 g of malonic acid.The obtained chemical solution had a silica solid content of 20.0% by mass, a pH of2.4, an electrical conductivity of 1,492 pS / cm, a viscosity of 4.4 mPa-s, and a DLS average particle diameter of 20.4 nm.

[0049] (Example 3)409 g of a chemical solution according to Example 3 was obtained in the same manner as in Example 1 except that 9.4 g of maleic acid (with an active component concentration of 99.0% by mass, commercially available from Kanto Chemical Co., Inc.) was used in place of 8.2 g of malonic acid.The obtained chemical solution had a silica solid content of 20.0% by mass, a pH of 1.5, an electrical conductivity of 1,558 pS / cm, a viscosity of 4.6 mPa-s, and a DLS average particle diameter of 21.7 nm.

[0050] (Example 4)411 g of a chemical solution according to Example 4 was obtained in the same manner as in Example 1 except that 10.9 g of DL-malic acid (with an active component concentration of 99% by mass, commercially available from Kanto Chemical Co., Inc.) was used in place of 8.2 g of malonic acid.The obtained chemical solution had a silica solid content of 20.0% by mass, a pH of 2.0, an electrical conductivity of 3,130 pS / cm, a viscosity of 4.9 mPa-s, and a DLS average particle diameter of 21.6 nm.

[0051] (Example 5)416 g of a chemical solution according to Example 5 was obtained in the same manner as in Example 1 except that 15.7 g of citric acid monohydrate (with an active component concentration of 99.5% by mass, commercially available from Kanto Chemical Co., Inc.) was used in place of 8.2 g of malonic acid.The obtained chemical solution had a silica solid content of 19.7% by mass, a pH of 1.8, an electrical conductivity of 4,170 pS / cm, a viscosity of 4.4 mPa-s, and a DLS average particle diameter of 20.2 nm.

[0052] (Comparative Example 1)412 g of a chemical solution according to Comparative Example 1 was obtained in the same manner as in Example 1 except that 11.9 g of L- Arabinose (with an activecomponent concentration of 99.9% by mass, commercially available from FUJIFILMWako Pure Chemical Corporation) was used in place of 8.2 g of malonic acid.The obtained chemical solution had a silica solid content of 19.9% by mass, a pH of 2.8, an electrical conductivity of 550 pS / cm, a viscosity of 5.6 mPa-s, and a DLS average particle diameter of 21.0 nm.

[0053] The chemical solutions of Examples 1 to 5 and Comparative Example 1 were evaluated for the room temperature / high-temperature salt tolerance according to (room-temperature salt tolerance evaluation) and (high-temperature salt tolerance evaluation). In addition, the occupancy area proportion of particles in the ROI was calculated according to (cryo-transmission electron microscope analysis) and the coefficient of variation of the areas of the partition regions was calculated based on the particle distribution. In addition, for the chemical solutions of Examples 1 to 5, according to (Measurement of binding amount of organic components bonded to silica particles (organic acid, silane compound, etc.)), the carbon content (C amount: % by mass) and the amount of surface treatment (organic acid binding amount: molecules / nm ) were calculated.

[0054] Table 1 shows physical properties of chemical solutions of the examples and the comparative example, physical properties of room-temperature salt tolerance evaluation samples, the physical properties and appearances of the samples after the room-temperature salt tolerance test, the room-temperature salt tolerance test results (rl / r2 ratio, the determination results of the salt tolerance test), the occupancy area proportion of particles in the ROI and the calculation results of the coefficient of variations of the areas of the partition regions based on the particle distribution. In addition, Table 2 shows the first acid dissociation constants at 25°C calculated using the software package 1 based on a database of Hammett’s substituent constants and known literature values for the organic acids used in the examples and the comparative example, the physical properties and appearances of the samples after the high-temperature salt tolerance test in the examples and the comparative example, and the high-temperature salt tolerance test results (rhl / rh2 ratio, the determination results of the high-temperature salttolerance test). In addition, Table 3 shows the carbon content (C amount: % by mass) and the amount of surface treatment (organic acid binding amount: molecules / nm ) of the examples and the comparative example.In addition, FIG. 1 is a diagram showing the coefficient of variation of the areas of the partition regions based on the particle distribution (horizontal axis) with respect to the DLS average particle diameter (r2) (vertical axis) of the samples after room-temperature salt tolerance evaluation in the chemical solutions of the examples and the comparative example, and FIG. 2 is a diagram showing the coefficient of variation of the areas of the partition regions based on the particle distribution in the chemical solutions of the examples and the comparative example.

[0055] [Table 1]Table 1

[0056] [Table 2]Table 2

[0057] [Table 3]Table 3

[0058] As shown in Table 1, the chemical solutions (inorganic oxide particle-containing compositions) of Example 1 to Example 5 were compositions in which the coefficient of variation of the areas of the partition regions based on the particle distribution was 0.36 to 0.57, the occupancy area proportion of particles in the region of interest (ROI) was 20.2% to 36.5%, with both numerical values falling within predetermined ranges (coefficient of variation: 0.1 to 0.7, occupancy area proportion: 1% to 50%). For these compositions, the ratio (r2 / rl) of the DLS average particle diameters before and after the room-temperature salt tolerance test was performed was less than 5, and as shown in Table 2, the ratio (rh2 / rhl) of the DLS average particle diameters before and after the high-temperature salt tolerance test was performed was less than 5, and even after both salt tolerance tests, the compositions remained as a colloidal-colored transparent liquid, and could be evaluated as having inorganic oxide particles that maintained the dispersed state without aggregation or gelling. In addition, as shown in Table 3, it was confirmed that the chemical solutions (inorganic oxide particle-containing compositions) of Example 1 to Example 5 were formed by bonding an organic acid contained in the chemical solution to inorganic oxide particle (silica particles). On the other hand, in the case of the chemical solution (inorganic oxide particle-containing composition) of Comparative Example 1 in which L- Arabinose (sugar) was added in place of an organic acid, the coefficient of variation was 0.6 and the occupancy area proportion was 0.8%, both of which were outside the predetermined ranges, the ratio (r2 / rl) of the DLS average particle diameters before and after the room- temperature salt tolerance test was performed was 6.1, the ratio (rh2 / rhl) of the DLS average particle diameters before and after the high-temperature salt tolerance test was performed was88.8, and even after both salt tolerance tests, it was confirmed that the sample became cloudy and the inorganic oxide particles aggregated.In addition, as shown in FIG. 1, in the results, although the samples (the examples) with a coefficient of variation in a range of 0.1 to 0.7 maintained a DLS average particle diameter (r2) of less than 100 nm after the room-temperature salt tolerance test, it was found that the sample (the comparative example) with a coefficient of variation of more than 0.7 had a DLS average particle diameter (r2) that was significantly larger than 100 nm, that is, the obtained results suggest that, for a target composition, it was also possible to evaluate the salt tolerance of the composition by evaluating the coefficient of variation of the areas of the partition regions based on the particle distribution.

Claims

CLAIMS

1. An inorganic oxide particle-containing composition, wherein, in image analysis of a frozen sample by cryo-transmission electron microscope observation, the sample being prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that the concentration of inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, a coefficient of variation, which is a value obtained by dividing a standard deviation of areas of Voronoi partition regions based on an inorganic oxide particle distribution in a region of interest (ROI) by the arithmetic mean of the areas, is 0.1 to 0.7.

2. The inorganic oxide particle-containing composition according to claim 1, wherein, in image analysis of a frozen sample by cryo-transmission electron microscope observation, the sample being prepared by adding the inorganic oxide particle-containing composition to 4% by mass of salt water such that concentration of inorganic oxide particles is 0.5% by mass, and rapidly freezing with liquefied ethane, a proportion of inorganic oxide particles in the region of interest (ROI) (total area occupied by the inorganic oxide particles / ROI area) is 1 to 50%.

3. The inorganic oxide particle-containing composition according to claim 1, wherein the inorganic oxide particle-containing composition is a composition containing particles having an average secondary particle diameter of 5 nm to 100 nm, which is determined by a dynamic light scattering method, the particles being of at least one inorganic oxide selected from the group consisting of silica, alumina, tin oxide, zirconium oxide, titanium oxide, and antimony oxide.

4. The inorganic oxide particle-containing composition according to claim 1, further comprising an organic acid or salts of the acid.

5. The inorganic oxide particle-containing composition according to claim 4, wherein the organic acid has a carboxy group.

6. The inorganic oxide particle-containing composition according to claim 4, wherein the organic acid includes at least one selected from the group consisting of formic acid, acetic acid, propionic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, citric acid, malic acid, tartaric acid, butyric acid, fumaric acid, maleic acid, thioglycolic acid, oxalic acid, malonic acid, succinic acid, and lactic acid.

7. The inorganic oxide particle-containing composition according to claim 1, wherein, in a room-temperature salt tolerance test in which the inorganic oxide particle-containing composition is stored at 20°C for 24 hours in an environment with salt concentration of 4% by mass such that concentration of the inorganic oxide particles is 0.5% by mass, an average secondary particle diameter (rl) of the inorganic oxide particles measured by a dynamic light scattering method before storage and an average secondary particle diameter (r2) of the inorganic oxide particles measured by a dynamic light scattering method after storage satisfy the following relationship:0.9 < (r2 / rl) < 5.

8. The inorganic oxide particle-containing composition according to claim 1, wherein, in a high-temperature salt tolerance test in which the inorganic oxide particle-containing composition is stored at 50°C for 7 days in an environment with salt concentration of 4% by mass such that concentration of the inorganic oxide particles is 0.5% by mass, an average secondary particle diameter (rhl) of the inorganic oxide particles measured by a dynamic light scattering method before storage and an average secondary particle diameter (rh2) of the inorganic oxide particles measured by a dynamic light scattering method after storage satisfy the following relationship:0.9 < (rh2 / rhl) < 5.

9. A method for producing the inorganic oxide particle-containing composition according to claim 4, comprising a step of adding an organic acid or salts of the acid to an aqueous inorganic oxide particle sol with stirring and performing stirring for 0.1 to 20 hours.

10. The inorganic oxide particle-containing composition according to claim 1, wherein the inorganic oxide particle-containing composition is a chemical solution for carbon dioxide storage.

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