A method for preparing na y composite aerogel based on silicon-containing solid waste and mother liquor recycling, product and application thereof

Abstract

The present application relates to gas adsorption material preparation technical field, specifically to a kind of preparation method of NaY composite aerogel based on silicon-containing solid waste and mother liquor recycling, product and its application, the present application uses silicon-containing solid waste as raw material, prepares silicate solution by alkali solution, and synthesizes solid waste-based NaY molecular sieve;Utilize the active mother liquor containing alkali generated in the preparation process of NaY molecular sieve as cellulose dissolving medium, make molecular sieve preparation process and cellulose gel construct continuous coupling, simultaneously avoid additional introduction traditional alkali solvent system.Epoxy chloropropane is added to cellulose solution, and mixed with solid waste-based NaY molecular sieve, and NaY / cellulose composite aerogel is prepared by sol-gel process and freeze drying.Epoxy chloropropane promotes cellulose gel network formation, while forming stable covalent bridging structure between molecular sieve and cellulose aerogel, improves the interfacial bonding strength and structural stability of composite material, effectively reduces the risk of molecular sieve falling off, pulverization in use process.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and gas adsorption material preparation technology, specifically to a method for preparing NaY composite aerogel based on the recycling of silicon-containing solid waste and mother liquor, the product, and its application. Background Technology

[0002] With the advancement of the "dual-carbon" strategy, carbon dioxide capture and resource utilization technologies have become an important research direction in the fields of energy, chemical engineering, and environmental materials. Among them, CO2 separation technology based on adsorption has attracted widespread attention due to its advantages such as low energy consumption, simple process, and recyclability. Molecular sieve materials, especially NaY-type molecular sieves, are widely used in gas separation, catalysis, and environmental remediation because metal ion modification of Y molecular sieves promotes adsorption performance and they possess regular pore structure, large specific surface area, and excellent gas selective adsorption performance. However, traditional NaY molecular sieves are usually prepared using high-purity silicon and aluminum sources, and modification through methods such as metal ion exchange increases costs. At the same time, industrialization also suffers from problems such as high resource consumption and low solid waste utilization.

[0003] Fly ash, one of the largest industrial solid wastes emitted by coal-fired power plants, is rich in SiO2 and Al2O3, making it a potential low-cost raw material for molecular sieve synthesis. In recent years, the preparation of molecular sieves using fly ash has gradually become an important research direction for resource recycling, not only reducing the cost of molecular sieve preparation but also realizing the resource utilization of solid waste and reducing environmental pollution. Patent CN116812942B discloses a method for preparing sodalite-type molecular sieves using fly ash, synthesizing sodalite-type molecular sieves using fly ash as a silica-alumina source; patent CN115385356A discloses a method for preparing 13X molecular sieves using fly ash, proposing a process of preparing 13X molecular sieves via a solid-phase method after alkali fusion activation of fly ash; patent CN110330715A discloses a method for preparing hierarchical porous ZSM-5 molecular sieves using fly ash, further improving the utilization rate of solid waste and the crystallinity of the molecular sieve. All of the above technologies have achieved the resource utilization of fly ash and synthesized different types of molecular sieves. However, the synthesized molecular sieves are mostly in the form of powder, extruded strips, or spherical shapes. In the continuous flow adsorption process of a fixed bed, problems such as molecular sieve shedding, breakage, pulverization, resulting in large pressure drop, poor mechanical stability, and particle loss are prone to occur.

[0004] To improve the performance of molecular sieve materials in fixed-bed applications, existing technologies typically employ methods such as extrusion molding and binder granulation to enhance their mechanical strength. Patent CN111569827A discloses a hollow spherical molecular sieve material for gas adsorption, which improves the forming strength of the molecular sieve by adding a binder. However, such methods often lead to blockage of some pores in the molecular sieve, resulting in decreased gas mass transfer efficiency and reduced specific surface area, thus weakening adsorption performance. Furthermore, in traditional physical blending methods, the molecular sieve particles and the carrier are mainly bound by van der Waals forces or hydrogen bonds, which can easily lead to particle detachment during long-term airflow scouring and adsorption regeneration, affecting material stability and service life. Moreover, the synthesis process of the aforementioned molecular sieves often generates a large amount of alkaline waste liquid. However, existing technologies for preparing molecular sieves from fly ash mainly focus on the extraction of silicon and aluminum resources from solid waste and the control of molecular sieve crystal structure, lacking an effective way to utilize the large amount of highly alkaline mother liquor generated during molecular sieve synthesis. It usually needs to be neutralized before discharge, which not only increases post-treatment costs but also wastes alkaline resources. In addition, existing molecular sieve adsorbent preparation technologies mainly focus on improving the adsorption performance of the molecular sieve itself or improving the molding strength, and have not yet achieved synergistic coupling between the molecular sieve preparation process, the utilization of by-product waste liquid, and the adsorbent material construction process, which limits the development of green and low-cost molecular sieve materials.

[0005] Therefore, there is an urgent need to develop a method for preparing NaY composite aerogels based on the recycling of silicon-containing solid waste and mother liquor, as well as products and their applications, to solve the above problems. Summary of the Invention

[0006] This invention proposes a method, product, and application for preparing NaY composite aerogels based on the recycling of silicon-containing solid waste and mother liquor. The method first uses fly ash as a silicon-aluminum source to prepare NaY-type molecular sieves through a hydrothermal crystallization process, achieving high-value conversion of silicon-aluminum resources from industrial solid waste. Subsequently, the alkaline mother liquor generated during the NaY molecular sieve preparation process is directly used as a cellulose dissolution system, realizing the recycling of by-product wastewater. This avoids the introduction of high-cost chemical reagents and the generation of new wastewater pollution problems in traditional cellulose dissolution processes. Simultaneously, a composite aerogel material is stably loaded onto the cellulose aerogel framework through chemical bridging. This method is of great significance for improving the adsorption stability of molecular sieve fixed beds, reducing material preparation costs, and realizing the high-value utilization of industrial solid waste, effectively solving the aforementioned technical problems.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing NaY / cellulose covalently crosslinked composite aerogel, comprising the following steps:

[0008] S1: Extract silicon source from silicon-containing solid waste by alkaline dissolution, add aluminum source, synthesize NaY molecular sieve by hydrothermal crystallization, and collect the alkaline mother liquor after crystallization;

[0009] S2: Directly use the alkaline mother liquor described in S1 as an alkaline solvent to dissolve the cellulose raw material and obtain a cellulose solution;

[0010] S3: Add epichlorohydrin, which functions as both a crosslinking agent and a bridging agent, to the cellulose solution. After mixing evenly, add the NaY molecular sieve prepared in S1 to form a sol. Perform a sol-gel reaction on the sol to obtain a composite gel. After freeze-drying, obtain a NaY / cellulose composite aerogel.

[0011] In this process, epichlorohydrin promotes the cross-linking between cellulose molecular chains to form a three-dimensional gel network. At the same time, its epoxy groups form C-O-C covalent bonds and C-O-Si covalent bonds with the cellulose hydroxyl groups and the surface hydroxyl groups of NaY molecular sieve through ring-opening reactions, respectively, so that NaY molecular sieve is chemically anchored in the cellulose aerogel framework.

[0012] Preferably, in step S1, the silicon-containing solid waste is at least one of fly ash, coal gangue, molybdenum tailings, kaolin, marble powder, or diatomaceous earth; the alkali agent used for alkali dissolution is an aqueous solution of sodium hydroxide and / or sodium carbonate; and the supplemented aluminum source is at least one of aluminum sulfate, aluminum chloride, sodium aluminate, or aluminum hydroxide.

[0013] Preferably, in step S1, the conditions for alkali dissolution are: alkali solution concentration of 1-4M, mass ratio of silicon-containing solid waste to alkali solution of 1:3-5, alkali dissolution temperature of 80-150℃, and alkali dissolution time of 1-3h.

[0014] Preferably, in step S1, the molar ratio of the raw materials for synthesizing the NaY molecular sieve is: SiO2 / Al2O3 = 1.0–10; NaOH / SiO2 = 0.1–2.0; H2O / SiO2 = 5–50.

[0015] The stirring rate during the aging step is 100–500 r / min;

[0016] The crystallization temperature is 90℃~150℃, and the crystallization time is 12~96h.

[0017] Preferably, in step S2, the cellulose raw material is at least one of corrugated paper, straw, or defatted cotton; the alkaline mother liquor is a mixture of the mother liquor obtained after NaY molecular sieve crystallization and urea; and the concentration of cellulose in the cellulose solution is 1-5 wt%.

[0018] Preferably, in step S2, the dissolution temperature of the cellulose raw material is -20 to 25°C, the dissolution time is 1 to 5 minutes, and the stirring rate is 100 to 2000 r / min.

[0019] Preferably, in step S3, the crosslinking agent is one or more of epichlorohydrin, glutaraldehyde, and allyl glycidyl ether, and the amount used is 2%-15% of the cellulose solution. The mixing time is 0.5-3 hours, and the stirring rate is 100-2000 r / min.

[0020] Optionally, in step S3, the amount of molecular sieve used is 1-15 times the mass of cellulose in the cellulose solution, the mixing time is 0.5-3 hours, and the stirring rate is 100-2000 r / min.

[0021] Preferably, the sol-gelation process takes 12-72 hours, the freezing temperature is 35℃ to -80℃, the freezing time is 1 to 3.5 hours, and the freeze-drying time is 24 to 72 hours.

[0022] Preferably, a NaY composite aerogel based on the recycling of silicon-containing solid waste and mother liquor is proposed. The composite aerogel comprises a three-dimensional porous cellulose aerogel framework and NaY molecular sieve particles chemically anchored to the cellulose aerogel framework by C-O-Si covalent bonds.

[0023] Preferably, the composite aerogel is packed into a fixed-bed adsorption column and purged at 50–200°C in a pure nitrogen stream with a flow rate of 10–100 ml / min for 3–20 h. Then, an N2 / CO2 mixed gas with a CO2 concentration of 2%–60% is introduced into the adsorption column, and the CO2 adsorption amount is calculated based on the breakthrough curve.

[0024] Preferably, the amount of carbon dioxide adsorbed is calculated based on the breakthrough curve generated by the carbon dioxide analyzer.

[0025] The method of this invention realizes the resource utilization of silicon-containing solid waste; it proposes a new idea for the preparation of molecular sieve composite aerogels, solves the technical difficulties such as easy detachment of molecular sieves in practical applications and low mass transfer efficiency after secondary molding, and prepares NaY molecular sieve / cellulose bridged composite aerogels that can efficiently capture carbon dioxide.

[0026] The second technical objective of this invention is to provide an application of the molecular sieve composite cellulose aerogel prepared by the method described above in the adsorption of carbon dioxide.

[0027] This invention provides a method for preparing NaY composite aerogel based on the recycling of silicon-containing solid waste and mother liquor, the product, and its application, which has the following advantages compared with existing technologies:

[0028] This invention achieves a transformation of molecular sieves from traditional physical loading to chemical bonding. Epichlorohydrin, while promoting the formation of the cellulose gel network, allows its epoxy groups to undergo ring-opening reactions with the cellulose hydroxyl groups to form C–O–C bonds, and further react with the hydroxyl groups on the surface of the NaY molecular sieve to form C–O–Si bonds, thereby constructing a stable covalent bond structure between the molecular sieve and the cellulose aerogel. This method effectively improves the interfacial bonding strength between the molecular sieve and the carrier, avoiding the problems of easy detachment and pulverization of the molecular sieve during traditional physical mixing or binder molding processes.

[0029] This invention uses fly ash as a silicon resource to prepare NaY molecular sieves, which not only reduces the dependence on high-purity silicon and aluminum sources in the traditional molecular sieve preparation process and realizes the high-value utilization of industrial solid waste; at the same time, it uses the alkaline mother liquor generated in the synthesis of NaY molecular sieves as a cellulose dissolution system to realize the recycling of by-product waste liquid, reduce waste liquid discharge, and improve the resource utilization efficiency and environmental friendliness of the entire preparation process.

[0030] Meanwhile, the solid waste-based NaY molecular sieve prepared by this invention exhibits excellent CO2 adsorption performance, which is superior to that of commercial NaY molecular sieves. The NaY / cellulose composite aerogel constructed through ECH covalent bridging combines the microporous adsorption advantages of molecular sieves with the three-dimensional porous mass transfer network characteristics of cellulose aerogels, effectively improving the structural stability and gas transport efficiency of the material.

[0031] The NaY / cellulose-bridged composite aerogel prepared by this invention exhibits excellent mechanical stability and recyclability. In CO2 fixed-bed adsorption tests under simulated flue gas conditions, its adsorption performance surpasses that of traditional commercial extruded molecular sieve adsorbents. Because the molecular sieve particles are chemically bonded to the cellulose framework, they do not significantly detach during long-term operation, effectively reducing the pressure drop in the adsorption bed and the risk of pipeline blockage, making it more suitable for continuous fixed-bed CO2 capture applications. This invention features a simple preparation process, widely available raw materials, and eliminates the need for expensive silicon sources and organic binders, offering low cost, environmental friendliness, and potential for large-scale application. It provides a new technical solution for the resource utilization of solid waste and the development of high-performance CO2 capture materials. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0033] Figure 1 This is a flowchart of a method for preparing aerogel from fly ash in one embodiment of the present invention.

[0034] Figure 2 This is the XRD pattern of the NaY molecular sieve based on fly ash from solid waste prepared in Example 1.

[0035] Figure 3 This is a sample image of molecular sieve composite cellulose aerogel prepared from silicon-containing solid waste in Example 1.

[0036] Figure 4 These are SEM images of some samples of the silicon-containing solid waste molecular sieve composite cellulose aerogel prepared in Example 2.

[0037] Figure 5 The infrared spectra are those of the solid waste fly ash-based NaY molecular sieve prepared in Example 1, the silicon-containing solid waste molecular sieve composite cellulose aerogel (bridged composite aerogel) prepared in Example 2, and the unbridged composite aerogel prepared in Example 3.

[0038] Figure 6 XPS C1s and Si2p spectra of the pure cellulose aerogel prepared in Example 2 and the unbridged and bridged composite aerogels prepared in Example 3.

[0039] Figure 7 This is a comparison chart of the zeolite bonding strength in the commercially extruded molecular sieve purchased in Example 3, the unbridged composite aerogel prepared in Example 3, and the bridged composite aerogel material.

[0040] Figure 8 The bridging mechanism between epichlorohydrin-bridged molecular sieves and cellulose. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects of the present invention clearer, the present invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. The technical solutions of the present invention will be described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0042] Please see Figure 1 The present invention provides a technical solution:

[0043] This invention provides a method for preparing NaY composite aerogel based on the recycling of silicon-containing solid waste and mother liquor, comprising the following steps:

[0044] S1: Extract silicon source from silicon-containing solid waste by alkaline dissolution, add aluminum source, synthesize NaY molecular sieve by hydrothermal crystallization, and collect the alkaline mother liquor after crystallization;

[0045] S2: Directly use the alkaline mother liquor from S1 as an alkaline solvent to dissolve the cellulose raw material and obtain a cellulose solution;

[0046] S3: Add epichlorohydrin, which functions as both a crosslinking agent and a bridging agent, to the cellulose solution. After mixing evenly, add the NaY molecular sieve prepared in S1 to form a sol. Perform a sol-gel reaction on the sol to obtain a composite gel. After freeze-drying, obtain a NaY / cellulose composite aerogel.

[0047] In this process, epichlorohydrin promotes the cross-linking between cellulose molecular chains to form a three-dimensional gel network. At the same time, its epoxy groups form C-O-C covalent bonds and C-O-Si covalent bonds with the cellulose hydroxyl groups and the surface hydroxyl groups of NaY molecular sieve through ring-opening reactions, respectively, so that NaY molecular sieve is chemically anchored in the cellulose aerogel framework.

[0048] Example 1:

[0049] This embodiment uses NaY molecular sieve, ZSM-5 molecular sieve, and 13X molecular sieve for comparative testing:

[0050] (1) NaY molecular sieve

[0051] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of fly ash-based NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0052] (2) ZSM-5 molecular sieve

[0053] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of ZSM-5 molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0054] (3) 13X molecular sieve

[0055] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of 13X molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0056] Table 1 Comparison of different molecular sieves

[0057] In Example 1, composite aerogels were prepared using the same process with NaY, ZSM-5, and 13X molecular sieves, and their performance was tested. The results showed that different molecular sieve types significantly affected the structural properties and CO2 adsorption performance of the cellulose composite aerogels. Regarding the transmittance of the clear liquid, the NaY / cellulose composite aerogel exhibited the highest transmittance (98.82%), followed by 13X (95.38%), and ZSM-5 the lowest (80.41%). This difference may be related to the uniformity of dispersion and interfacial compatibility of the molecular sieves in the cellulose system: NaY has a higher surface hydroxyl density, which facilitates more complete covalent cross-linking with the active intermediate formed after epichlorohydrin ring-opening, thereby constructing a more uniform three-dimensional network structure and reducing light scattering; while ZSM-5, due to its fewer surface hydroxyl groups and denser structure, has relatively weaker dispersion and interfacial bonding in the system, making it more prone to local aggregation, thus leading to a decrease in transmittance.

[0058] In terms of mechanical properties, the compressive strength followed the order: NaY (13.5568 N / mm) > 13X (10.5568 N / mm) > ZSM-5 (8.6492 N / mm). This result indicates that the Si-OC covalent cross-linking between NaY and cellulose via epichlorohydrin is more complete, thus significantly enhancing the interfacial bonding strength and stress transfer efficiency. In contrast, ZSM-5 has a lower number of reactive hydroxyl groups and a limited degree of covalent cross-linking, resulting in a relatively loose composite network structure and weaker compressive strength.

[0059] In terms of CO2 adsorption performance, the order was NaY (5.58 mmol / g) > 13X (5.30 mmol / g) > ZSM-5 (4.91 mmol / g). This trend is not only related to the intrinsic pore structure and adsorption active sites of the molecular sieve, but also influenced by its dispersion state and effective exposure in the cellulose matrix. NaY, due to its higher pore volume and better interfacial immobilization effect, has more fully exposed adsorption sites, thus exhibiting the highest adsorption capacity. Overall, the NaY system shows the best performance in terms of structural compactness, mechanical properties, and CO2 adsorption capacity, indicating that it is more suitable as a molecular sieve support system for epichlorohydrin covalently crosslinked cellulose aerogels.

[0060] Example 2:

[0061] This embodiment uses different crosslinking agents for testing:

[0062] (1) Epichlorohydrin

[0063] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0064] (2) Glutaraldehyde

[0065] Ten parts of cellulose solution and one part of glutaraldehyde were mixed and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of solid waste-based NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0066] (3) Allyl glycidyl ether

[0067] Ten parts of cellulose solution and one part of cycloallylic glycidyl ether were mixed and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of solid waste-based NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0068] Table 2 Comparison of different crosslinking agents

[0069] In Example 2, composite aerogels were prepared using the same process but with different crosslinking agents, and their performance was tested. The results showed that different crosslinking agents had a significant impact on the structural construction and CO2 adsorption performance of the molecular sieve / cellulose composite aerogel. Among them, the epichlorohydrin (ECH) system exhibited the best overall performance, with significantly higher light transmittance (98.82%), compressive strength (13.5568 N / mm), and CO2 adsorption capacity (5.42 mmol / g) than the glutaraldehyde system and the allyl glycidyl ether (AGE) system. This result indicates that ECH can not only promote crosslinking between cellulose molecular chains in the system, but also react with cellulose hydroxyl groups and hydroxyl groups on the surface of the molecular sieve through the ring-opening reaction of epoxy groups, thereby constructing a stable Si-OC covalent bridge structure and achieving efficient integrated fixation of inorganic molecular sieve and organic cellulose aerogel.

[0070] In contrast, the glutaraldehyde system primarily achieves cross-linking through intermolecular acetalization of cellulose, lacking effective chemical anchoring of the molecular sieve. This results in weak interfacial bonding and a heterogeneous network structure, leading to the lowest mechanical properties and CO2 adsorption capacity. The AGE system, possessing both epoxy groups and a flexible organic structure, can improve network flexibility and pore connectivity to some extent, thus its performance falls between that of the ECH and glutaraldehyde systems. ECH achieves the simultaneous construction of molecular sieves and cellulose aerogels through a "ring-opening reaction-covalent bridging" mechanism, making it a key cross-linking agent for achieving one-step high-performance molecular sieve / cellulose composite aerogels.

[0071] Example 3:

[0072] This example uses epichlorohydrin of different concentrations for testing:

[0073] (1) 5% epichlorohydrin

[0074] 20 parts of cellulose solution were mixed with 1 part epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. 35 parts of NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0075] (2) 10% epichlorohydrin

[0076] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0077] (3) 15% epichlorohydrin

[0078] Seven parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0079] Table 3 Comparison of different crosslinking agent ratios

[0080] In Example 3, composite aerogels were prepared using the same process but with different proportions of crosslinking agent, and their performance was tested. The results showed that the proportion of crosslinking agent (epicochloropropane, ECH) significantly controlled the structure formation and CO2 adsorption performance of the NaY / cellulose covalently crosslinked composite aerogel. Regarding the transmittance of the clear liquid, when the ECH content was 5%, the transmittance was low (80.05%), indicating insufficient crosslinking and inadequate covalent bridging between NaY and cellulose, resulting in a certain degree of microphase separation and structural inhomogeneity. As the crosslinking agent proportion increased to 10%, the transmittance significantly increased to 98.82%, indicating that ECH could fully participate in the ring-opening reaction between the cellulose hydroxyl groups and the NaY surface hydroxyl groups, forming a uniform, dense, and highly continuous three-dimensional interpenetrating network structure. When the proportion was further increased to 15%, the transmittance slightly decreased to 98.77%, indicating that excessive crosslinking might lead to over-curing of local networks, slightly affecting the system's uniformity.

[0081] In terms of mechanical properties, the compressive strength was as follows: 10% (13.5568 N / mm) > 15% (13.2816 N / mm) ≤ 5% (4.7311 N / mm). When the crosslinking agent content was low (5%), the covalent bond density was insufficient, resulting in weak interfacial bonding between the cellulose network and the molecular sieve, low stress transfer efficiency, and therefore poor mechanical properties. When the crosslinking agent content was increased to 10%, the covalent bond density of Si-OC and COC in the system reached a relatively balanced state, making the network structure the most dense and uniform, thus exhibiting the highest compressive strength. However, when the crosslinking agent was further increased to 15%, although the crosslinking density was further improved, excessive crosslinking may lead to increased network rigidity and local stress concentration, thus slightly reducing the overall mechanical properties.

[0082] Regarding CO2 adsorption performance, the system showed a correlation between 5% (5.78 mmol / g) and 10% (5.58 mmol / g) and 15% (5.02 mmol / g). This trend indicates that a lower degree of crosslinking is beneficial for forming a more open hierarchical porous structure, resulting in a higher exposure of the active sites of the NaY molecular sieve and thus improving the CO2 adsorption capacity. However, as the crosslinking agent content increases, the network structure gradually becomes denser, and some pores are occupied or restricted by the crosslinking structure, leading to obstruction of gas diffusion paths and a decrease in adsorption performance.

[0083] In summary, the ECH addition ratio exhibits a significant "structure-performance balance effect" on the composite aerogel performance: 10% is the optimal level for mechanical properties, while 5% shows the best performance in CO2 adsorption. This indicates a competitive relationship between crosslinking density and pore structure openness. Reasonable control of ECH dosage is a key factor in achieving high-performance molecular sieve covalently crosslinked cellulose aerogels.

[0084] Example 4:

[0085] This example demonstrates experiments using different molecular sieve contents:

[0086] (1) The molecular sieve content is 40%.

[0087] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 17 parts of NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0088] (2) The molecular sieve content is 60%.

[0089] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Twenty-six parts of NaY molecular sieve were then added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0090] (2) (3) The molecular sieve content is 80%.

[0091] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0092] Table 4 Comparison of different molecular sieve contents in composite aerogels

[0093] In Example 4, composite aerogels were prepared using the same process but with different molecular sieve contents, and their performance was tested. Regarding the transmittance of the clear liquid, as the NaY content increased from 40% to 80%, the transmittance slightly decreased from 99.88% to 98.82%. This small change indicates that the system maintains high structural homogeneity under the action of epichlorohydrin (ECH). The slight decrease in transmittance is mainly attributed to the increased inorganic phase ratio due to the increased molecular sieve content, which slightly increases the number of light scattering centers. However, the ECH-mediated Si-OC covalent bonds effectively restrict the aggregation of NaY particles, allowing the system to maintain a good dispersion and a continuous three-dimensional network structure.

[0094] In terms of compressive strength, the material exhibits a significant enhancement trend, gradually increasing from 6.2715 N / mm at 40% NaY content to 10.4294 N / mm at 60% NaY content, and reaching 13.5568 N / mm at 80% NaY content. This result indicates that with increasing NaY content, the number of surface hydroxyl groups capable of participating in the ECH ring-opening reaction increases synchronously, leading to a higher density of covalently bridged structures (Si-OC and COC bonds) between the cellulose chains and NaY. This inorganic-organic bicontinuous network significantly improves stress transfer efficiency and skeletal rigidity, thereby enhancing overall mechanical properties.

[0095] Regarding CO2 adsorption performance, it also showed a significant increasing trend with increasing NaY content, rising from 2.61 mmol / g to 4.12 mmol / g, and reaching 5.58 mmol / g at 80%. This is mainly attributed to the molecular sieve as the main adsorption active phase, whose increased content directly increased the number of available microporous structures and adsorption sites in the material. Simultaneously, ECH covalent cross-linking effectively prevented the aggregation and pore obstruction of the molecular sieve under high loading conditions, allowing its adsorption sites to be fully exposed, thereby significantly improving CO2 adsorption capacity.

[0096] Therefore, increasing the NaY molecular sieve content can significantly enhance the mechanical properties and CO2 adsorption performance of the composite aerogel while maintaining high structural uniformity. This indicates that the ECH-mediated covalent cross-linking system can effectively coordinate the structural stability and functional performance under high molecular sieve loading conditions, providing an effective strategy for the construction of high-performance molecular sieve / cellulose composite aerogels.

[0097] Example 5:

[0098] This embodiment applies composite aerogel:

[0099] (1) Commercial extruded molecular sieves

[0100] The extruded NaY molecular sieve purchased from Liaoning Raodong Company

[0101] (2) Unbridged composite aerogel

[0102] Ten parts of cellulose solution and 35 parts of fly ash-based NaY molecular sieve were mixed and stirred at 5℃ and 1000 r / min for 1 h. The mixture was then poured into a mold and gelled for 24 h. After gelation, the mixture was demolded, washed, and the unbridged composite gel was placed in a freeze dryer and frozen at -80℃ to -35℃ for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the unbridged composite aerogel.

[0103] (3) Bridged composite aerogel

[0104] Ten parts of cellulose solution were mixed with one part of epichlorohydrin and stirred at 5°C and 1000 rpm for 1 hour. Then, 35 parts of fly ash-based NaY molecular sieve were added to the mixture and stirred at 5°C and 1000 rpm for 1 hour. The mixture was then poured into a mold and gelled for 24 hours. After gelation, the mixture was demolded, washed, and the composite gel was placed in a freeze dryer and frozen at -80°C to -35°C for 2.5 to 3.5 hours. The freeze-drying time was 24 to 48 hours to obtain the composite aerogel.

[0105] Table 5 Comparison of different adsorbent materials

[0106] Example 5 prepared commercially extruded molecular sieves, unbridged composite aerogels, and bridged composite aerogels. The three samples from Table 3 were immersed in water and then subjected to ultrasonic vibration for 5 minutes. The solutions were then analyzed using a UV-Vis spectrophotometer to measure absorbance, observe solution transparency, and assess the bonding strength between the solid components and the carrier material. These results indicate that the zeolite in the bridged composite aerogel is firmly anchored in the cellulose network, thus reducing the risk of zeolite detachment and subsequent pipe blockage. The maximum compressive strength of the three samples was also tested. The results showed that the bridged composite aerogel had the highest maximum compressive strength, reaching 13.5568 N / mm, indicating that the bridged composite aerogel possesses superior mechanical properties and can adapt to more complex adsorption environments. The three samples were subjected to adsorption in a 9.45-inch fixed-bed column with an inner diameter of 0.43 inches using a simulated flue gas environment. A specific amount of adsorbent was placed in the adsorption column and preheated at 90°C for 6 hours under a pure nitrogen flow (30 cm³ / min). The adsorption column was then cooled to the target adsorption temperature of 25°C. The carbon dioxide concentration was measured to ensure the mixed gas injected into the adsorption column contained 10% carbon dioxide and 90% nitrogen. The carbon dioxide concentration in the outlet gas was monitored in real time using an online carbon dioxide analyzer (model 906, Quintiles Instruments, Grafton, USA) connected to a computer, and the adsorption capacity was calculated based on the breakthrough curve generated by the analyzer. The results showed that the bridged composite aerogel exhibited good carbon dioxide adsorption performance, with an adsorption capacity of 4.61 mmol / g. In conclusion, the bridged composite aerogel possesses excellent comprehensive performance and is more suitable for practical carbon dioxide adsorption.

[0107] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all such deductions or substitutions should be considered as falling within the scope of patent protection determined by the submitted claims.

Claims

1. A method for preparing NaY composite aerogel based on the recycling of silicon-containing solid waste and mother liquor, comprising the following steps: S1: Extract silicon source from silicon-containing solid waste by alkaline dissolution, add aluminum source, synthesize NaY molecular sieve by hydrothermal crystallization, and collect the alkaline mother liquor after crystallization; S2: Directly use the alkaline mother liquor described in S1 as an alkaline solvent to dissolve the cellulose raw material and obtain a cellulose solution; S3: Add epichlorohydrin, which functions as both a crosslinking agent and a bridging agent, to the cellulose solution. After mixing evenly, add the NaY molecular sieve prepared in S1 to form a sol. Perform a sol-gel reaction on the sol to obtain a composite gel. After freeze-drying, obtain a NaY / cellulose composite aerogel. In this process, epichlorohydrin promotes the cross-linking between cellulose molecular chains to form a three-dimensional gel network. At the same time, its epoxy groups form C-O-C covalent bonds and C-O-Si covalent bonds with the cellulose hydroxyl groups and the surface hydroxyl groups of NaY molecular sieve through ring-opening reactions, respectively, so that NaY molecular sieve is chemically anchored in the cellulose aerogel framework.

2. The method for preparing NaY composite aerogel according to claim 1, characterized in that: In step S1, the silicon-containing solid waste is at least one of fly ash, coal gangue, molybdenum tailings, kaolin, marble powder, or diatomaceous earth; the alkali agent used for alkali dissolution is an aqueous solution of sodium hydroxide and / or sodium carbonate; and the supplemented aluminum source is at least one of aluminum sulfate, aluminum chloride, sodium aluminate, or aluminum hydroxide.

3. The method for preparing NaY composite aerogel according to claim 2, characterized in that: In S1, the conditions for alkaline dissolution are: alkaline solution concentration of 1-4M, mass ratio of silicon-containing solid waste to alkaline solution of 1:3-5, alkaline dissolution temperature of 80-150℃, and alkaline dissolution time of 1-3h.

4. The method for preparing NaY composite aerogel according to claim 3, characterized in that: In S1, the molar ratio of the raw materials for synthesizing NaY molecular sieve is: SiO2 / Al2O3 = 1.0–10; NaOH / SiO2 = 0.1–2.0; H2O / SiO2 = 5–50. The stirring rate during the aging step is 100–500 r / min; The crystallization temperature is 90℃~150℃, and the crystallization time is 12~96h.

5. The method for preparing NaY composite aerogel according to claim 1, characterized in that: In step S2, the cellulose raw material is at least one of corrugated paper, straw, or defatted cotton; the alkaline mother liquor is a mixture of the mother liquor obtained after NaY molecular sieve crystallization and urea; and the concentration of cellulose in the cellulose solution is 1-5 wt%.

6. The method for preparing NaY composite aerogel according to claim 1, characterized in that: In step S2, the dissolution temperature of the cellulose raw material is -20 to 25°C, the dissolution time is 1 to 5 minutes, and the stirring rate is 100 to 2000 r / min.

7. The method for preparing NaY composite aerogel according to claim 1, characterized in that: In step S3, the crosslinking agent is one or more of epichlorohydrin, glutaraldehyde, and allyl glycidyl ether, and the amount used is 2%-15% of the cellulose solution. The mixing time is 0.5-3 hours, and the stirring rate is 100-2000 r / min.

8. The method for preparing NaY composite aerogel according to claim 1, characterized in that: In step S3, the amount of molecular sieve used is 1-15 times the mass of cellulose in the cellulose solution, the mixing time is 0.5-3 hours, and the stirring rate is 100-2000 r / min.

9. A NaY composite aerogel based on the recycling of silicon-containing solid waste and mother liquor, characterized in that, The composite aerogel, prepared by any one of claims 1 to 8, comprises a three-dimensional porous cellulose aerogel framework and NaY molecular sieve particles chemically anchored to the cellulose aerogel framework by C-O-Si covalent bonds.

10. The application of the NaY composite aerogel according to claim 9, characterized in that: The composite aerogel was packed into a fixed-bed adsorption column and purged at 50–200°C in a pure nitrogen stream with a flow rate of 10–100 ml / min for 3–20 h. Then, an N2 / CO2 mixed gas with a CO2 concentration of 2%–60% was introduced into the adsorption column, and the CO2 adsorption capacity was calculated based on the breakthrough curve.

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