Conductive cement admixture, conductive cement composition, and conductive hydraulic composition

Abstract

To provide a material, in which conductivity of a composite of carbon and triiron tetraoxide is effectively utilized.SOLUTION: The invention provides a conductive cement admixture containing at least a composite of carbon and triiron tetraoxide. Preferably, the conductive cement admixture comprises, as the composite of carbon and triiron tetraoxide: at least 60 to 90 mass% of graphite; 0 to 5.0 mass% of Fe2O3; 0 to 5.0 mass% of Fe3O4; 0.1 to 5.0 mass% of Fe; and 0.1 to 30 mass% of iron carbide. The invention also provides a conductive cement composition comprising at least 5 to 60 vol.% of the conductive cement admixture, based on a total of 100 vol.% of the conductive cement admixture and cement.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a conductive cement admixture containing solid carbon produced by reducing carbon dioxide, a conductive cement composition containing the admixture, and a conductive hydraulic composition using the composition. [Background technology]

[0002] According to a report by the Ministry of Economy, Trade and Industry (Agency for Natural Resources and Energy), the amount of carbon dioxide emitted during cement production in 2022 was approximately 40 million tons, accounting for approximately 3.5% of Japan's total greenhouse gas emissions. Of this amount of carbon dioxide (approximately 40 million tons), approximately 25 million tons came from raw materials such as limestone, and approximately 15 million tons came from fossil fuels used to burn cement clinker (Non-Patent Document 1). Given this situation, the cement industry has recently been working diligently to develop carbon recycling technology, which is one form of carbon neutrality that suppresses carbon dioxide emissions. Here, carbon recycling is a technology that reduces carbon dioxide emissions during cement production by repeating the following steps (a) to (c), and also treats carbon dioxide as a resource and utilizes the fixed carbon dioxide products (calcium carbonate, etc.) (Non-Patent Document 1). (a) A process for separating and recovering carbon dioxide from exhaust gas generated during the production of cement clinker. (b) A step in which the recovered carbon dioxide reacts with calcium sources such as calcium hydroxide and cement hydrate in the concrete during the production of concrete to fix the carbon dioxide. (c) A process of fixing carbon dioxide to calcium sources in hardened concrete or waste concrete.

[0003] Furthermore, in Patent Documents 1 and 2, the present inventors have proposed a three-stage catalytic reaction system in which methane is produced by the reaction of carbon dioxide and hydrogen according to the following formula (1), and this methane further reacts with carbon dioxide according to the following formula (2) to produce carbon monoxide, and then carbon is produced by the disproportionation of the carbon monoxide according to the following formula (3): Methanation reaction: CO2 + 4H2 → CH4 + 2H2O (1) Dry reforming reaction: CH4 + CO2 → 2CO + 2H2 (2) Carbon capture reaction: 2CO → C+CO2 (3) However, the carbon generated through the above formulas (1) to (3) has low crystallinity, and carbon ( C ) and the catalyst of formula (3), iron tetraoxide ( F Because it is difficult to isolate carbon from CF composites (hereinafter referred to as "CF composites"), the CF composites have been discarded until now. Therefore, in order to keep the above three-stage catalytic reaction system operating smoothly, it is necessary to develop applications for CF composites.

[0004] Incidentally, several cement mortars containing conductive materials have been known for some time. For example, Patent Documents 3 to 6 propose a cement admixture for cathodic protection containing a conductive polymer, etc., a cement composition containing the admixture, and a cement mortar using the composition. These materials are used for cathodic protection of concrete structures, and are said to allow current to flow more uniformly because the conductive polymer is more uniformly dispersed within the mortar than conventional cathodic protection mortars that use carbon fibers. However, since conductive polymers are expensive, the above-mentioned cement admixtures containing conductive polymers lack versatility. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Ministry of Economy, Trade and Industry, Bureau of Economy, Trade and Industry, Agency for Natural Resources and Energy, "Domestic and international trends toward carbon neutral concrete and cement," p. 21, published October 18, 2024 [Non-patent document 2] David L. Chandler, “MIT engineers create an energy-storing supercapacitor from ancient materials,” MIT News, July 31, 2023, Internet <URL:https: / / news.mit.edu / 2023 / mit-engineers-create-supercapacitor-ancient-materials-0731> [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-141702 [Patent Document 2] Japanese Patent Publication No. 2023-141707 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-265038 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-265040 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-273603 [Patent Document 6] Japanese Patent Application Laid-Open No. 2006-273605 Summary of the Invention [Problem to be solved by the invention]

[0007] Furthermore, in recent years, with the spread of electric vehicles, conductive hydraulic compositions such as conductive concrete that can be powered from the road while the electric vehicle is running have been attracting attention (see Non-Patent Document 2 above). This conductive hydraulic composition uses carbon black as a carbon-based material to impart conductivity to the hydraulic composition, and the hydraulic composition itself also contains a conductive iron component (ferrite phase) derived from cement. Therefore, if the CF composite can be used as a material for imparting electrical conductivity to a hydraulic composition in place of the above-mentioned carbon-based material or in place of part of the above-mentioned carbon-based material, it could be a useful application of the CF composite. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into the use of CF composites in place of carbon-based materials or in place of part of the carbon-based materials, and have found that conductive cement admixtures, conductive cement compositions, and conductive hydraulic compositions containing CF composites have excellent electrical conductivity, leading to the completion of the following inventions [1] to [6].

[0009] [1] An electrically conductive cement admixture containing at least a CF compound. [2] The conductive cement admixture according to [1] above, wherein the CF composite contains at least 60 to 90 mass% graphite, 0 to 5.0 mass% Fe2O3, 0 to 5.0 mass% Fe3O4, 0.1 to 5.0 mass% Fe, and 0.1 to 30 mass% iron carbide. [3] A conductive cement composition comprising at least 5 to 60% by volume of the conductive cement admixture according to [1] or [2] above, with the total of the conductive cement admixture and cement being 100% by volume. [4] A conductive hydraulic composition which is a cement paste containing at least 10 to 90% by volume of the conductive cement composition described in [3] above, with the total of the conductive cement composition and water being 100% by volume. [5] A conductive coating material, wherein the conductive hydraulic composition is a coating material that imparts conductivity to concrete or mortar. [6] An electrically conductive hydraulic composition comprising at least the electrically conductive cement composition according to [3] above, aggregate, and water, If the conductive hydraulic composition is concrete, 1 m of the conductive hydraulic composition 3 per unit weight, the conductive cement composition is 230 to 1400 kg, the coarse aggregate is 500 to 1200 kg, the fine aggregate is 300 to 1100 kg, and the water is 100 to 230 kg, If the conductive hydraulic composition is mortar, 1 m of the conductive hydraulic composition 3 per unit weight, the conductive cement composition is 280 to 2000 kg, the fine aggregate is 350 to 2000 kg, and the water is 200 to 300 kg. Conductive hydraulic composition. [Effects of the Invention]

[0010] The conductive cement admixture of the present invention can effectively utilize the CF composite as an excellent conductive material, and therefore can smoothly operate the above-mentioned three-stage catalytic reaction system, thereby contributing to carbon neutrality. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a conceptual diagram showing a three-stage catalytic reaction system in which a CF composite is produced (reproduced from FIG. 1 of Patent Document 1). [Figure 2] FIG. 1 is a schematic diagram showing the shape (spiral shape) of a catalyst used in a three-stage catalytic reaction system (reproduced from FIG. 3 of Patent Document 1). [Figure 3] 1 is a photograph showing a CF composite. [Figure 4] FIG. 1 is a diagram showing an example of an X-ray diffraction chart of a CF composite. DETAILED DESCRIPTION OF THE INVENTION

[0012] As described above, the conductive cement admixture of the present invention is an admixture for cement that contains at least a CF composite, and the CF composite contains at least 60 to 90 mass% of graphite, 0 to 5.0 mass% of Fe2O3, 0 to 5.0 mass% of Fe3O4, 0.1 to 5.0 mass% of Fe, and 0.1 to 30 mass% of iron carbide. The present invention will be described in detail below, dividing it into a conductive cement admixture, a conductive cement composition, and a conductive hydraulic composition.

[0013] 1.Conductive cement admixture The conductive cement admixture contains at least a CF composite, which contains at least 60 to 90 mass% graphite, 0 to 5.0 mass% Fe2O3, 0 to 5.0 mass% Fe3O4, 0.1 to 5.0 mass% Fe, and 0.1 to 30 mass% iron carbide. To mix the conductive cement admixture with cement, the CF composite is preferably ground into a powder or granular form.

[0014] The CF composite is a composite of carbon produced through the reactions (1) to (3) below using a three-stage catalytic reaction system shown in Figure 1, and triiron tetroxide, which is a catalyst of the following formula (3). As an example of the CF composite, an X-ray diffraction chart of the composite is shown in Figure 4. Methanation reaction: CO2 + 4H2 → CH4 + 2H2O (1) Dry reforming reaction: CH4 + CO2 → 2CO + 2H2 (2) Carbon capture reaction: 2CO → C+CO2 (3)

[0015] The carbon dioxide may be carbon dioxide contained in exhaust gas from a cement factory or a concrete product factory, or carbon dioxide recovered from one or more exhaust gases selected from exhaust gas from a cement factory, a concrete product factory, etc. Here, the carbon dioxide recovered from the exhaust gas is, for example, carbon dioxide recovered by a carbon dioxide separation and recovery method such as an amine method, and is preferred because it has a higher concentration and purity than carbon dioxide in exhaust gas, thereby improving the reaction efficiency of the carbon dioxide. The exhaust gases from cement plants mainly consist of final exhaust gases, boiler exhaust gases, and heavy machinery exhaust gases, while the exhaust gases from concrete product plants mainly consist of boiler exhaust gases and heavy machinery exhaust gases.

[0016] 2. Conductive cement composition The conductive cement composition is a cement composition containing at least 5 to 60% by volume of the conductive cement admixture, with the total of the conductive cement admixture and cement being 100% by volume. Here, the cement is not particularly limited, and examples thereof include one or more types selected from ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, sulfate-resistant Portland cement, blast-furnace cement, fly ash cement, silica cement, coal ash-containing cement, and ecocement.

[0017] 3. Conductive hydraulic composition. One embodiment of the conductive hydraulic composition is a cement paste containing at least 10 to 90% by volume of the conductive cement composition, with the total of the conductive cement composition and water being 100% by volume. One application of the conductive hydraulic composition is as a conductive coating material that imparts conductivity to concrete or mortar.

[0018] Another aspect of the conductive hydraulic composition is a conductive hydraulic composition containing at least the conductive cement composition, aggregate, and water, If the conductive hydraulic composition is concrete, 1 m of the conductive hydraulic composition 3 The conductive cement composition contains at least 230 to 1400 kg, coarse aggregate 500 to 1200 kg, fine aggregate 300 to 1100 kg, and water 100 to 230 kg per 10 ... If the conductive hydraulic composition is mortar, 1 m of the conductive hydraulic composition 3 The amount of the conductive cement composition is 280 to 2000 kg, the amount of the fine aggregate is 350 to 2000 kg, and the amount of water is 200 to 300 kg. The fine aggregate may be one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, lightweight fine aggregate, etc. The coarse aggregate may be one or more selected from river gravel, mountain gravel, crushed stone, slag coarse aggregate, lightweight coarse aggregate, etc. Furthermore, the fine aggregate and coarse aggregate may be natural aggregate, artificial aggregate, or recycled aggregate. [Example]

[0019] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. 1. Reactor Preparation (1) Preparation of the first reactor (methanation reactor) The heating furnace constituting the first reactor was a temperature-controllable one-zone electric furnace (a ceramic electric tubular furnace with an effective length of 300 mm, manufactured by Asahi Rika Seisakusho Co., Ltd.), and the atmospheric pressure flow-type reaction tube was a quartz tube with an inner diameter of 8 mm and a length of 600 mm. Two catalysts with a spiral structure as shown in Figure 2 coated with 10 mass% Ni / CeO2 were installed as catalysts for the methanation reaction at the positions of the thermocouples used to control the temperature of the heating furnace inside the atmospheric pressure flow-type reaction tube, to prepare the first reactor.

[0020] The catalyst for the methanation reaction was prepared by using CeO2 (reagent, manufactured by Kanto Chemical Co., Ltd.) as a support and loading 10 mass% of Ni (Ni(NO3)2·6H2O with a purity of 98%, manufactured by Wako Pure Chemical Industries, Ltd.) by evaporation to dryness. The support was then calcined in air at 500°C for 2 hours to separate the nitric acid component. Next, the fired product was cooled, and then distilled water was added thereto, followed by grinding in a mortar to prepare a paste of Ni / CeO2 catalyst. Furthermore, a spiral aluminum plate (JIS A1100 H14, width 7 mm, length 50 mm, thickness 1.5 mm) shown in Figure 2 was surface treated using a 0.8 mol sodium hydroxide aqueous solution and a 3.0 mol hydrochloric acid aqueous solution. The spirally twisted aluminum plate was then repeatedly dried with cold air and immersed until a sufficient amount of Ni / CeO2 catalyst was supported on it to promote the methanation reaction, thereby producing a catalyst for the methanation reaction.

[0021] (2) Preparation of the second reactor (dry reforming reactor) The second reactor was prepared in the same manner as the methanation reactor, except that the dry reforming catalyst was used instead of the methanation catalyst. The catalyst for the dry reforming reaction described above was a commercially available γ-Al2O3 (C20, manufactured by Nippon Light Metal Co., Ltd.) support loaded with 10 mass% Ni (98% pure Ni(NO3)2·6H2O, manufactured by Wako Pure Chemical Industries, Ltd.) by evaporation to dryness. It was prepared in the same manner as the catalyst for the methanation reaction described above, except that the Ni / γ-Al2O3 paste was applied to a spirally twisted stainless steel plate (SUS304, width 7 mm, length 50 mm, thickness 0.5 mm) as shown in Figure 2.

[0022] (3) Preparation of the third reactor (carbon capture reactor) The third reactor was prepared in the same manner as the methanation reactor, except that a quartz tube with an inner diameter of 21 mm and a length of 600 mm was used as the atmospheric flow-type reaction tube, and eight catalysts for the carbon capture reaction were placed inside the atmospheric flow-type reaction tube instead of the catalyst for the methanation reaction (two bundles of four catalysts were arranged in series). The catalyst for the carbon capture reaction was magnetite (FeO reagent with 98% purity, manufactured by Wako Pure Chemical Industries, Ltd.), which was made into a paste by adding distilled water to the magnetite. The catalyst was prepared in the same manner as the catalyst for the methanation reaction, except that the magnetite paste was applied to a spirally twisted stainless steel plate (SUS304, width 7 mm, length 50 mm, thickness 0.5 mm) as shown in Figure 2.

[0023] (4) Carbonization of carbon dioxide After preparing each reactor, the catalyst was reduced by holding it at 500°C for 1 hour while flowing hydrogen at 200 ml / min. Next, the control temperatures of the first reactor were set to 450°C, the second reactor to 800°C, and the third reactor to 450°C. After all reactors had reached the predetermined temperatures, a standard hydrogen gas cylinder was used as the hydrogen supply equipment, and a standard carbon dioxide gas cylinder was used instead of the process exhaust gas. A raw material gas consisting of hydrogen and carbon dioxide was supplied to the methanation reactor via a mass flow controller and the first gas mixer.

[0024] The H2 / CO2 molar ratio in the raw material gas was 2.57, and the reaction was carried out for 4 hours, after which the produced carbon was recovered. Specifically, the mass flow controllers were used to set the hydrogen flow rate to 180 ml / min and the carbon dioxide flow rate to 70 ml / min, resulting in a total raw material gas flow rate of 250 ml / min, which was then supplied to the methanation reactor.

[0025] In addition, a water vapor removal device and a sampling hole were installed at the outlet of each reactor. 30 minutes after the temperature of each reactor reached the set temperature, samples were taken from the sampling hole using a syringe, and the amounts of hydrogen, nitrogen, oxygen, methane, carbon monoxide, and carbon dioxide were quantified using a gas chromatograph GC-2014 (Shimadzu Corporation).

[0026] A wet gas meter was installed at the outlet of the third reactor to measure the gas flow rate. The mixed gas discharged from the third reactor was not recycled but discharged to an outdoor removal facility. After the third reactor was sufficiently cooled, the CF composite was removed from the atmospheric pressure flow-type reactor tube. Next, the CF composite was collected from the carrier and catalyst using a brush, and the solidified portion was ground in an agate mortar to obtain a powder with a particle size of 1 mm or less and a density of 2.78 g / cm. 3 A powder of the CF composite (the conductive cement admixture of the present invention) was produced. The X-ray diffraction chart of the conductive cement admixture is shown in FIG. The chemical composition (contents) of the CF composite used was 78.6 mass % graphite, 0.5 mass % Fe2O3, 0.2 mass % Fe3O4, 1.0 mass % Fe, and 19.7 mass % iron carbide.

[0027] 2. Preparation of conductive hydraulic composition (hardened cement paste) and measurement of its electrical resistivity Using the above conductive cement admixture, ordinary Portland cement, and tap water, conductive hydraulic compositions were prepared according to the formulations in Table 1, following the steps (i) to (iii) below, and their electrical resistivity was measured. 3, and ordinary Portland cement is 3.16g / cm 3 , and tap water is 1.00 g / cm 3 It was.

[0028] [Table 1]

[0029] (i) 150 g of water and 272 g of cement were placed in the mixing bowl of a Hobart mixer and mixed for 30 seconds at a rotation speed of 140±5 rpm and an orbital speed of 62±5 rpm, after which 102.6 g of conductive cement admixture was added and mixed for another 30 seconds. (ii) Next, the cement paste adhering to the inside of the mixing bowl and the paddle was scraped off, and then the mixture was mixed for another 2 minutes. The resulting cement paste was placed in a formwork and sealed and cured at room temperature for 1 day, after which hardened cement paste specimens (4 cm long, 4 cm wide, 16 cm long) were produced at ages of 3, 7, 14, and 28 days. (iii) The electrical resistivity of the hardened cement paste at each of the above ages was measured in accordance with the four-electrode method B described in JSCE-G 581-2018 "Test method for electrical resistivity of concrete by the four-electrode method (draft)" by measuring the voltage (V) and current (I), and the electrical resistivity (R, unit: Ωm) was calculated using the following formula (A). The results are shown in Table 1. R=2πaV / I (A) However, a in equation (A) is the distance between the electrodes.

[0030] As shown in Table 1, the electrical resistivity of the comparative example was 170 Ωm at 3 days, 313 Ωm at 7 days, 472 Ωm at 14 days, and 733 Ωm at 28 days, showing a significant increase as the material ages (i.e., conductivity decreases significantly). This is because the electrical resistivity according to JSCE-G 581-2018 is affected by the moisture content inside the specimen at the time of measurement, and it is presumed that as the material ages, the moisture content decreases due to hydration and drying, causing the electrical resistivity to increase. In contrast, the electrical resistivity of Example 1 was 47 to 50 Ωm at ages of 3 days, 7 days, and 14 days, which remained almost unchanged with increasing age, and was significantly lower at 1 / 4 to 1 / 20 of that of the comparative example (i.e., high conductivity). Furthermore, the electrical resistivity of Example 2 remained unchanged at 30 Ωm at ages of 3 days, 7 days, and 14 days, and was significantly lower than that of the comparative example, 1 / 5 to 1 / 30. Furthermore, the electrical resistivity of Example 3 remained unchanged at 16 Ωm at ages of 3 days, 7 days, 14 days, and 28 days, and was significantly lower than that of the comparative example, at 1 / 10 to 1 / 40. Furthermore, the electrical resistivity of Example 4 remained unchanged at 9 Ωm at ages of 3 days, 7 days, 14 days, and 28 days, and was significantly lower than that of the comparative example, at 1 / 20 to 1 / 80. From these facts, it can be said that the conductive hydraulic composition of the present invention exhibits constant electrical resistivity (conductivity) without being affected by the water content state inside the test specimen. Therefore, the conductive cement admixture etc. of the present invention can effectively utilize the CF compound as an excellent conductive material, allowing the above-mentioned three-stage catalytic reaction system to operate smoothly, contributing to carbon neutrality. [Explanation of symbols]

[0031] 1 Carbon deposition device 3 Hydrogen supply equipment 4 Hydrogen flow meter 5. First gas mixer 6 Second gas mixer 7. Third gas mixer 8. First Gas Separator 9 Second gas separator 10 First reactor (methanation reactor) 20 Second reactor (dry reforming reactor) 30 Third reactor (carbon capture reactor) 41 First Water Vapor Removal Facility 42 Second water vapor removal facility 43 Third Water Vapor Removal Facility 50 flow meter 61 Sulfur oxide removal equipment 62 Carbon dioxide concentration equipment 70 Equipment for recycling mixed gases

Claims

1. An electrically conductive cement admixture containing at least a composite of carbon and triiron tetroxide.

2. The carbon and triiron tetroxide composite contains 60 to 90 mass % of graphite and Fe. ２ O ３ 0 to 5.0 mass % of Fe ３ O ４ 2. The conductive cement admixture according to claim 1, comprising at least 0 to 5.0 mass% of ZnO, 0.1 to 5.0 mass% of Fe, and 0.1 to 30 mass% of iron carbide.

3. 3. A conductive cement composition comprising at least 5 to 60% by volume of the conductive cement admixture according to claim 1 or 2, with the total of the conductive cement admixture and cement being 100% by volume.

4. 4. A conductive hydraulic composition, which is a cement paste containing at least 10 to 90% by volume of the conductive cement composition according to claim 3, with the total of the conductive cement composition and water being 100% by volume.

5. 5. A conductive coating material, wherein the conductive hydraulic composition according to claim 4 is a coating material that imparts conductivity to concrete or mortar.

6. An electrically conductive hydraulic composition comprising at least the electrically conductive cement composition according to claim 3, aggregate, and water, If the conductive hydraulic composition is concrete, 1 m of the conductive hydraulic composition ３ per unit weight, the conductive cement composition is 230 to 1400 kg, the coarse aggregate is 500 to 1200 kg, the fine aggregate is 300 to 1100 kg, and the water is 100 to 230 kg, If the conductive hydraulic composition is mortar, 1 m of the conductive hydraulic composition ３ The conductive cement composition contains at least 280 to 2000 kg, 350 to 2000 kg of fine aggregate, and 200 to 300 kg of water per 1000 sieve. Conductive hydraulic composition.

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