Cement-based porous material for online carbon sequestration in cement kilns and method for its production

Abstract

The application relates to the technical field of cement-based porous materials, and discloses a cement-based porous material for online carbon fixation of a cement kiln and a preparation method thereof. Modified nanosol formed by adding siliceous nanomaterials grafted with polyether polyols or aluminum nanomaterials grafted with polyether polyols in the process of preparing a cement-based slurry is added to the cement-based slurry, so that the cement-based slurry is quickly thickened, and the ether group in the porous material foam slurry makes the foam break, thereby rapidly forming a foam hole structure connected with each other in the porous material foam slurry; and a large number of micro-nano interconnected pore spaces can be constructed in the foam hole structure, so that the number of interconnected pores in the sample added with the modified nanosol is increased, and the average pore diameter is reduced; the prepared cement-based porous material has good carbon fixation capacity and CO2 storage capacity, the micro-nano interconnected pore spaces in the cement-based porous material are not damaged in the ordinary drying process, and the strength and other performances are improved to a certain extent.

Description

Technical Field

[0001] This invention relates to the field of cement-based porous materials technology, specifically to cement-based porous materials for online carbon fixation in cement kilns and their preparation methods. Background Technology

[0002] The massive emissions of greenhouse gases such as CO2 have led to global climate change, one of the most serious problems facing humanity today. The construction industry, as a representative of high-energy-consuming and high-polluting industries, emits large amounts of CO2 while consuming energy. Cement, as the most widely used building material, has consistently high carbon emissions during its production process, reaching a total of 1.23 billion tons in 2020, accounting for more than 12% of the country's total carbon emissions. Therefore, the development and application of carbon sequestration technologies are of paramount importance.

[0003] Cement-based materials possess a good ability to sequester CO2, and their strength and other properties are also improved after carbon fixation, which has significant practical implications for reducing carbon emissions in the cement industry. To improve the carbon fixation efficiency of cement-based materials, scholars both domestically and internationally have conducted in-depth research. Fang et al. incorporated recycled micropowder into silicate concrete to increase carbon fixation, achieving a carbon fixation rate of 19.8% in their samples. Shi Caijun et al. proposed a pre-curing technology, which can effectively improve the CO2 curing degree of concrete. Furthermore, by appropriately adjusting conditions such as CO2 partial pressure, temperature, humidity, and curing time during the carbon fixation curing process, the formation of carbonization products can be effectively promoted, thereby improving the CO2 sequestration efficiency and strength of the concrete. However, these carbon fixation technologies still fall short of the goal of mild and efficient carbon fixation.

[0004] Both domestic and international researchers have used porous concrete, such as foamed concrete, for carbon fixation, which has accelerated the carbon fixation rate. However, the dense solid phase between the pores still affects the permeation and transport of CO2 in the material, and the carbon fixation potential of foam has not been fully realized. Summary of the Invention

[0005] Based on the above problems, this invention provides a cement-based porous material for online carbon fixation in cement kilns and its preparation method. It can refine the pores in cement-based slurry, and the prepared cement-based porous material has good carbon fixation and CO2 storage capabilities. It is also suitable for online carbon fixation of flue gas. In addition, the micro-nano interconnected pore space in the cement-based porous material is not damaged by the ordinary drying process, and its strength and other properties are also improved to a certain extent.

[0006] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a cement-based porous material for online carbon fixation in a cement kiln includes:

[0008] A cement-based slurry is prepared by mixing and stirring raw materials including cement, modified nano-sol, and water evenly; the modified nano-sol is a sol-dispersion system formed by grafting polyether polyol onto silica nanomaterials or alumina nanomaterials.

[0009] Mix the foaming agent with water and stir to make foam;

[0010] According to the dry density ratio requirements of porous materials, the cement-based slurry and the foam are mixed and stirred evenly to prepare porous material foam slurry.

[0011] Cement-based porous materials are obtained by molding and curing porous material foam slurry.

[0012] Furthermore, the modified nanosol is added in a volume substitution manner to replace the foam, and the volume substitution rate of the modified nanosol is 5-90% of the foam volume.

[0013] Furthermore, the silicon nanomaterial is a nanomaterial containing silanol groups, and the aluminum nanomaterial is a nanomaterial containing aluminumol groups.

[0014] Furthermore, the foaming agent is an animal protein foaming agent, and the volume ratio of the foaming agent to water during foam preparation is 1:(5-100), resulting in a foam density of 20-100 kg / m³. 3 .

[0015] Furthermore, the designed dry density of the cement-based porous material is 80-1000 kg / m³. 3 The water-cement ratio of the cementitious slurry is 0.3 to 1.0.

[0016] Furthermore, the steps for molding and curing the porous material foam slurry include: pouring the porous material foam slurry into a mold, covering the mold with plastic wrap, placing it at room temperature for 24 hours, demolding it, and then curing it at a temperature of 20±2℃ and a relative humidity of over 90%.

[0017] Furthermore, the raw materials for preparing cement-based slurry also include fibers, and the amount of fibers used is 0.1-5% of the cement-based slurry.

[0018] To achieve the above-mentioned technical effects, the present invention also provides a cement-based porous material for online carbon fixation in cement kilns, which is prepared by the method described above for preparing the cement-based porous material for online carbon fixation in cement kilns.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention utilizes modified nanosols formed by adding silica nanomaterials grafted with polyether polyols or alumina nanomaterials grafted with polyether polyols during the preparation of cement-based slurries. On one hand, the rapid pozzolanic reaction between the solid particles and hydration products in the silica or alumina nanomaterials rapidly thickens the cement-based slurry. Simultaneously, ether groups are gradually released, causing foam rupture in the porous foam slurry and rapidly forming interconnected pore structures, thus improving the passage of kiln tail gas. On the other hand, the solid particles in the silica or alumina nanomaterials act as nucleation agents... The nucleation center induces the rapid formation of hydration products in the slurry, and becomes a spatial fulcrum, connecting and intersecting various hydration products. This further refines the pores, thereby constructing a large number of micro- and nano-interconnected pore spaces. As a result, the number of micro-pores and the average pore size of the sample with modified nano-sol increases. When CO2 passes through in the flue gas, it can increase the contact area between CO2 and the solid phase, accelerate the carbonization reaction, and thus facilitate rapid carbon fixation. The resulting cement-based porous material has good carbon fixation and CO2 storage capabilities. Moreover, the micro- and nano-interconnected pore spaces in the cement-based porous material are not destroyed by the ordinary drying process, and the strength and other properties are also improved to a certain extent. Attached Figure Description

[0021] Figure 1 The image shows the pore structure of the 5-SFC sample cross-section in Example 2. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0023] Example 1:

[0024] A method for preparing a cement-based porous material for online carbon fixation in a cement kiln includes:

[0025] A cement-based slurry is prepared by mixing and stirring raw materials including cement, modified nano-sol, and water evenly; the modified nano-sol is a sol-dispersion system formed by grafting polyether polyol onto silica nanomaterials or alumina nanomaterials.

[0026] Mix the foaming agent with water and stir to make foam;

[0027] According to the dry density ratio requirements of porous materials, the cement-based slurry and the foam are mixed and stirred evenly to prepare porous material foam slurry.

[0028] Cement-based porous materials are obtained by molding and curing porous material foam slurry.

[0029] In this embodiment, modified nanosols formed by adding silica nanomaterials grafted with polyether polyols or alumina nanomaterials grafted with polyether polyols during the preparation of cement-based slurry are initially encapsulated in the modified nanosols. During cement hydration, the solid particles in the silica or alumina nanomaterials not only react rapidly with the hydration products via a pozzolanic reaction, causing the cement-based slurry to thicken rapidly, but also the hydroxyl-containing silica and alumina solid nanomaterials possess an electric double layer. When cement hydrates, they release a large amount of alkali, causing the pH value of the system to rise, disrupting the diffusion double layer, generating aggregates, and further promoting slurry thickening. In addition, ether groups are gradually released during the rapid thickening of the slurry. These ether groups cause the foam in the porous material foam slurry to rupture, thereby creating a porous material foam slurry... The material rapidly forms an interconnected pore structure, improving the passage of kiln tail gas. On the other hand, solid particles in silica or alumina nanomaterials act as nucleation centers, inducing the rapid formation of hydration products in the slurry. These nucleation centers become spatial fulcrums, connecting and intersecting various hydration products, further refining the pores and constructing a large number of micro- and nano-interconnected pore spaces. This results in an increase in the number of micropores and a decrease in the average pore size inside the sample with modified nanosol. When CO2 passes through in the flue gas, it increases the contact area between CO2 and the solid phase, accelerating the carbonization reaction and thus facilitating rapid carbon fixation. The resulting cement-based porous material has good carbon fixation and CO2 storage capabilities, and the micro- and nano-interconnected pore spaces in the cement-based porous material are not damaged by ordinary drying processes, and its strength and other properties are also improved to a certain extent.

[0030] Example 2

[0031] A method for preparing cement-based porous materials for online carbon fixation in cement kilns. In this embodiment, the relevant raw materials for the cement-based slurry are as follows:

[0032] Cement: PO 42.5R cement.

[0033] Modified nanosol: nano-alumina grafted with polypropylene glycol, with a solid content of 16%, and the mass ratio of nano-alumina to polyvinyl ether is 20000:1.

[0034] Foaming agent: is an animal protein foaming agent;

[0035] Fiber: It is a bundle of monofilament polypropylene fiber with a diameter of 18.2μm and a length of 6mm.

[0036] In this embodiment, the mix proportion for preparing the cement-based porous material sample was designed according to JGJ / T 341-2014 "Technical Specification for Application of Cement-based Porous Materials". A volume substitution method was adopted, with modified nano-sol replacing the foam. In this embodiment, the amount of modified nano-sol was calculated based on a substitution rate of 27%. Given that the solid content of the modified nano-sol was 16% and the water-cement ratio was 0.5, the design dry density of the cement-based porous material was calculated to be 500 kg / m³. 3 and 800kg / m 3 The proportions of each raw material under the specified conditions are shown in Table 1:

[0037] Table 1. Mix proportions of cement-based porous materials (kg / m³) 3 )

[0038]

[0039]

[0040] According to the proportions of each raw material in Table 2, water, fiber, and modified nano-sol were added to the cement in sequence and stirred evenly to prepare a cement-based slurry. A foaming agent solution was also prepared, with a volume ratio of foaming agent to water of 1:20 and a foam density of 30 kg / m³. 3 Take the appropriate volume of foam and quickly stir it evenly in the cement-based slurry to make a porous foam slurry. Pour it into a mold and cover the mold with plastic wrap. Demold after 24 hours and cure for 20 days under standard curing conditions (temperature 20±2℃, relative humidity above 90%).

[0041] After curing, the prepared 5-SFC samples were hydrated with anhydrous ethanol, then dried in a vacuum drying oven at 45°C until constant weight. The cross-section was then cut, and the microstructure of the cross-section was observed using an industrial microscope. Figure 1 As shown, the sample cross-section has fewer spherical pores with small diameters, and mainly exhibits a complex intersecting pore structure.

[0042] In addition, the relevant performance tests and results of each group of samples are shown in Table 2 below:

[0043] Table 2. Relevant performance data of cement-based porous material specimens in each group.

[0044] serial number Complete carbonization time (h) Carbon sequestration (%) 5-SFC 8 28.0 5-FC 232 22.4 8-SFC 96 23.5 8-FC 320 21.0

[0045] 1) Complete carbonization time: The specimens were dried in a 60℃ drying oven for 48 hours, and then carbonized in the flue gas from a cement kiln tail. The specimen size was 100mm×100mm×100mm. Every 8 hours, one specimen was taken and the carbonization depth was measured using a 1% phenolphthalein solution. The test results are shown in Table 2. The porous material prepared using this patent significantly improved the carbon fixation rate in the flue gas from the kiln tail.

[0046] 2) Carbon fixation content: The carbon fixation content is mainly determined based on the thermal analysis curve of the sample. The weight loss above 500℃ in the thermal analysis curve is due to the decomposition of CaCO3. The mass of CO2 gas generated by decomposition divided by the mass of the specimen is the total CO2 content of 5-SFC, 5-FC, 8-SFC, and 8-FC, as shown in Table 2. The actual carbon fixation contents of each group of specimens are 28.0%, 22.4%, 23.5%, and 21.0%, respectively. The carbon fixation data show that the cement-based porous materials prepared by the method of this invention have improved carbon fixation contents at the same density level.

[0047] It should be noted that the modified nanosol used in this embodiment is nano-alumina grafted with polyether polyol. Other siliceous nanomaterials containing silanol or aluminum nanomaterials containing aluminum hydroxyl groups that promote the thickening of cement-based slurry can also be used in the nanomaterials grafted with polyether polyol in this invention.

[0048] The above are embodiments of the present invention. The above embodiments and specific parameters are only for clearly illustrating the invention verification process and are not intended to limit the patent protection scope of the present invention. The patent protection scope of the present invention shall still be determined by its claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the protection scope of the present invention.

Claims

1. A method for preparing a cement-based porous material for online carbon fixation in cement kilns, characterized in that, include: A cement-based slurry is prepared by mixing and stirring raw materials including cement, modified nano-sol, and water evenly. The modified nanosol is a sol dispersion system formed by grafting polyether polyols onto silica nanomaterials or alumina nanomaterials. Mix the foaming agent with water and stir to make foam; According to the dry density ratio requirements of porous materials, the cement-based slurry and the foam are mixed and stirred evenly to prepare porous material foam slurry. Cement-based porous materials are obtained by molding and curing porous material foam slurry.

2. The method for preparing cement-based porous materials for online carbon fixation in cement kilns according to claim 1, characterized in that: The modified nanosol is added by volume substitution to replace the foam, and the volume substitution rate of the modified nanosol is 5-90% of the foam volume.

3. The method for preparing cement-based porous materials for online carbon fixation in cement kilns according to claim 1, characterized in that: The silicon nanomaterial is a nanomaterial containing silanol groups, and the aluminum nanomaterial is a nanomaterial containing aluminumol groups.

4. The method for preparing cement-based porous materials for online carbon fixation in cement kilns according to claim 1, characterized in that: The foaming agent is an animal protein foaming agent. During foam preparation, the volume ratio of the foaming agent to water is 1:(5-100), and the resulting foam density is 20-100 kg / m³. 3 .

5. The method for preparing cement-based porous materials for online carbon fixation in cement kilns according to claim 1, characterized in that: The designed dry density of the cement-based porous material is 80-1000 kg / m³. 3 The water-cement ratio of the cementitious slurry is 0.3 to 1.

0.

6. The method for preparing cement-based porous materials for online carbon fixation in cement kilns according to claim 1, characterized in that: The steps for molding and curing porous material foam slurry include: pouring the porous material foam slurry into a mold, covering the mold with plastic wrap, placing it at room temperature for 24 hours, demolding it, and then curing it for 28 days at a temperature of 20±2℃ and a humidity of 95%RH.

7. The method for preparing cement-based porous materials for online carbon fixation in cement kilns according to claim 1, characterized in that: The raw materials for preparing cement-based slurry also include fibers, and the amount of fibers used is 0.1-5% of the cement-based slurry.

8. A cement-based porous material for online carbon fixation in cement kilns, characterized in that, The cement-based porous material is prepared by the method for preparing cement-based porous materials for online carbon fixation in cement kilns as described in any one of claims 1-7.

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