A sulfur-tolerant co2 adsorbent and method of making same

Abstract

The present application relates to the field of solid waste resource utilization, and particularly relates to a sulfur-resistant CO2 adsorbent and a preparation method thereof; the method comprises the following steps: (1) fly ash pretreatment; (2) silicon-aluminum precursor extraction, adding hydrochloric acid to the calcination product obtained in step (1); (3) forming a wet gel; (4) ultra-low temperature vacuum drying, obtaining an aerogel carrier; (5) sulfur-resistant doping modification, simultaneously adding a modifier K2CO3 and a dopant manganese acetate; (6) drying and sieving, selecting a sample with a certain particle size, and obtaining the sulfur-resistant CO2 adsorbent; (1) the sulfur-resistant CO2 adsorbent prepared by the present application has superior performance, even under the condition that the atmosphere contains SO2, the cumulative adsorption amount is still as high as 1.75 mmol / g, and the sulfur-resistant adsorption performance is maintained well, which exceeds most CO2 adsorbents. The modified adsorbent prepared by the present application has sulfur-resistant performance, improves the service life of the adsorbent, and saves cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid waste resource utilization, and particularly relates to a sulfur-resistant CO2 adsorbent and a preparation method thereof. BACKGROUND

[0002] Fly ash is a by-product of power plant combustion, accounting for 60%-88% of total solid waste of coal-fired power plants, and the global annual output is estimated at about 1 billion tons. Although the utilization of fly ash has gradually increased over the years, the global average utilization rate is still very low.

[0003] The surface of fly ash is mainly composed of dense irregular block structure, and the microstructure is poor, which is not conducive to chemical reaction. The most important chemical elements in fly ash are Si and Al, and the main crystalline mineral in fly ash is mullite Al6Si2O 13 In addition, there are crystalline SiO2, Al2O3, CaO and amorphous glass, which are suitable for preparing mesoporous silicon-aluminum composite aerogel. The prepared silicon-aluminum composite aerogel has developed microstructure, uniform and rough surface, rich pores and loose overall structure. The large pore size and open pore structure are used to load active components on the surface to realize CO2 adsorption. This structure is conducive to the loading of active components, facilitates the diffusion of gas in the pores, and is beneficial to the CO2 adsorption reaction.

[0004] Using cheap fly ash, a solid waste of power plant, in the CO2 capture link of CCUS can greatly reduce the cost of carbon capture, reduce fly ash emissions, reduce the demand for waste landfill of power plant waste, and save natural resources. In addition, using fly ash generated on site directly in coal-fired power plants does not need to be transported, which reduces the transportation cost. Therefore, using fly ash, a solid waste of coal-fired power plant, for CO2 adsorption can not only reduce CO2 emissions and reduce the damage of power plant to the environment, but also reduce the demand for waste landfill of fly ash and save resources.

[0005] However, due to the presence of a small amount of SO2 in the flue gas of the power plant, the CO2 adsorbent will be deactivated, and the adsorption performance will be greatly reduced. SUMMARY

[0006] The present application provides a sulfur-resistant CO2 adsorbent and a preparation method thereof to solve the problems of deactivation of conventional adsorbents in SO2 atmosphere and high cost of conventional sol-gel method for preparing CO2 adsorbents. The sulfur-resistant CO2 adsorbent prepared by the method has a high specific surface area and can still maintain good CO2 adsorption performance in SO2-containing flue gas. Manganese acetate is used as a precursor to promote the distribution of the dopant on the surface of the aerogel carrier. At the same time, the present application uses cheap fly ash as the precursor of the adsorbent, which overcomes the disadvantage of high cost of conventional sol-gel method for preparing CO2 adsorbents.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a preparation method of a sulfur-resistant CO2 adsorbent, comprising the following steps:

[0008] (1) fly ash pretreatment, using sodium carbonate as a pretreatment agent, mixing and calcining with fly ash at high temperature;

[0009] (2) extraction of silicon-aluminum precursor, adding hydrochloric acid to the calcined product obtained in step (1) while stirring for 1 hour, filtering and taking the filtrate;

[0010] (3) forming a wet gel, adding propylene oxide to the filtrate obtained in step (2) while adjusting the pH value of the filtrate, and forming a wet gel after standing;

[0011] (4) ultra-low temperature vacuum drying, placing the sample obtained in step (3) into an ultra-low temperature refrigerator for freezing and then drying by a vacuum freeze dryer to obtain an aerogel carrier;

[0012] (5) sulfur-resistant doping modification, adding the aerogel carrier obtained in step (4) into deionized water for stirring, and adding a modifier K2CO3 and a dopant precursor manganese acetate;

[0013] (6) drying and sieving, selecting a sample with a certain particle size to obtain a sulfur-resistant CO2 adsorbent.

[0014] Since the aerogel prepared from fly ash has a high specific surface area and a large pore volume, the manganese acetate dissolved in water can be loaded into the internal voids of the aerogel, and a thin layer of MnO2 is formed during the subsequent drying process, so that the MnO2 is uniformly distributed on the surface of the adsorbent and in the internal voids without crystallization, and a large number of mesopores are beneficial to the passage and reaction of gas molecules.

[0015] Further, the mass ratio of sodium carbonate to fly ash in step (1) is 0.7:1.

[0016] Further, the calcination temperature in step (1) is 850℃, and the calcination time is 3 hours.

[0017] Further, the concentration of hydrochloric acid added in step (2) is 3 mol / L, and the mass-volume ratio of the calcined product to hydrochloric acid is 1g:10mL.

[0018] Further, the volume ratio of propylene oxide to the filtrate in step (3) is 1:2, and the pH value of the filtrate is 9-10.

[0019] Preferably, the freezing temperature in step (4) is -80℃.

[0020] Preferably, the K2CO3 content in step (5) is 30% of the mass of the aerogel carrier, and the MnO2 content generated by the manganese acetate is 2% of the mass of the aerogel carrier.

[0021] Preferably, the anti-sulfur CO2 adsorbent particle size in step (6) is 150 microns.

[0022] In addition, the application also provides an anti-sulfur CO2 adsorbent prepared by the above preparation method.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] (1) The anti-sulfur CO2 adsorbent prepared by the application has superior performance, and even under the condition that the atmosphere contains SO2, the cumulative adsorption capacity is still as high as 1.75 mmol / g, maintaining good anti-sulfur adsorption performance, which exceeds most CO2 adsorbents.

[0025] (2) The aerogel prepared by the application has good microstructure, a BET specific surface area as high as 873.9 m 2 / g, an average pore size of 2.5 nm, a mesopore ratio of 80.4%, a micropore ratio of 19.5%, and a macropore ratio of only 0.1%; while the specific surface area of fly ash itself is only 6.92 m 2 / g, the mesopore ratio is 39.6%, the macropore ratio is as high as 60.4%, and there is no micropore. The application realizes high-value utilization of the coal-fired solid waste fly ash.

[0026] (3) The cost of the precursor material of the anti-sulfur CO2 adsorbent is estimated. According to the market price of the raw materials inquired from the chemical material procurement wholesale website (chem.1688.com), the price of sodium carbonate is 1100 yuan / t, and the price of 31% industrial hydrochloric acid is 600 yuan / t. The adsorption capacity of the CO2 adsorbent prepared by the application is 1.75 mmol / g, and according to the theoretical loading of K2CO3 of 30% and the doping amount of 2%, 12.99 kg of adsorbent and 8.703 kg of aerogel carrier are needed to adsorb 1 kg of CO2. According to the experimental results, 3 mol / L hydrochloric acid of 10 mL is needed to prepare 1 g of aluminum aerogel, which is equivalent to 3.8 g of 31% industrial hydrochloric acid. Therefore, 4.35 kg of sodium carbonate and 33.07 kg of 31% industrial hydrochloric acid are needed to adsorb 1 kg of CO2. The raw material cost is roughly estimated to be 25 yuan / kg of CO2. If tetraethyl orthosilicate is used as the precursor to prepare the aerogel, the price of tetraethyl orthosilicate is 16 yuan / kg, and according to the same loading and adsorption capacity, the rough cost of the raw materials is 437 yuan / kg of CO2. The manufacturing cost is greatly reduced.

[0027] (4) The modified adsorbent prepared by the application has anti-sulfur performance, improves the service life of the adsorbent, and saves costs.

[0028] (5) The use of cheap power plant solid waste fly ash in the CO2 capture link of CCUS can greatly reduce the cost of carbon capture, reduce fly ash emissions, reduce the demand for power plant waste landfill, and save natural resources.

[0029] (6) Direct use of on-site generated fly ash in coal-fired power plants does not require logistics transportation, reducing transportation costs. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the X-ray diffraction pattern of the coal-fired solid waste fly ash.

[0031] Figure 2 is a fly ash pretreatment result graph under different calcination temperatures and proportions according to the embodiments of the present application.

[0032] Figure 3 is a loss on ignition calculation result graph under different calcination temperatures and proportions according to the embodiments of the present application.

[0033] Figure 4 is a fly ash pretreatment result graph under different calcination temperatures and proportions according to the embodiments of the present application.

[0034] Figure 5 is an aerogel photo obtained after low-temperature freezing and vacuum drying according to the embodiments of the present application.

[0035] Figure 6 is a low-temperature N2 adsorption-desorption curve graph of the aerogel prepared according to the embodiments of the present application and the sulfur-resistant CO2 adsorbent.

[0036] Figure 7 is a pore size distribution graph of the aerogel prepared according to the embodiments of the present application and the sulfur-resistant CO2 adsorbent.

[0037] Figure 8 is an X-ray diffraction pattern of the aerogel prepared according to the embodiments of the present application and the sulfur-resistant CO2 adsorbent before and after reaction.

[0038] Figure 9 is a cumulative adsorption amount curve graph of the fly ash-based sulfur-resistant CO2 adsorbent prepared according to the embodiments of the present application. DETAILED DESCRIPTION

[0039] The present application will be further described below in conjunction with specific embodiments.

[0040] The fly ash raw material in the following examples is from a power plant in North China, and the chemical composition analysis of the fly ash is shown in Table 1, and the crystal structure analysis of the fly ash by XRD is shown in Figure 1 .

[0041] Table 1 Fly ash chemical composition table

[0042]

[0043] Example

[0044] (1) Fly ash pretreatment. 20g of Na₂CO₃ with mass ratios of 0.4, 0.5, 0.6, 0.7, and 0.8 were weighed using a balance and thoroughly ground and mixed with fly ash. The uniformly mixed samples were placed in a muffle furnace and calcined for 3 hours at 700℃, 800℃, 850℃, 900℃, and 1000℃, respectively. The product results at different temperatures and ratios are shown below. Figure 2 As shown in the figure. According to the experimental results, at a calcination temperature of 1000℃, the alkali fusion products of all proportions of Na2CO3 and fly ash mixtures were brownish-yellow in color and had a hard and dense structure. This substance adhered tightly to the inner wall of the magnetic boat, making it difficult to remove and dissolve in hydrochloric acid, thus preventing further acid leaching. When the calcination temperature was 900℃, the alkali fusion product of the Na2CO3:fly ash mixture (0.8:1) was relatively dense and adhered to the magnetic boat; when the Na2CO3:fly ash ratio was less than 0.7, the alkali fusion product could be detached from the magnetic boat, and the structure became more brittle as the ratio decreased. Under these temperature conditions, all alkali fusion products were dark yellow lumps. At a calcination temperature of 850℃, the alkali fusion product was a fine and uniform powder. As the ratio of Na2CO3 to fly ash increased, the color gradually lightened from light red, becoming white at a ratio of 0.8. At a calcination temperature of 800℃, all proportions of the alkali fusion products are whitish, loosely structured, and uniformly powdery samples, easily recovered for further processing. The whitest color is observed when the Na₂CO₃:fly ash ratio is 0.6 and 0.7. At a calcination temperature of 700℃, the product is a brownish-red, lumpy substance that is easily crushed into powder. At this temperature, when the Na₂CO₃:fly ash ratio is greater than 0.7, a whitish, bubbly structure can be observed on the surface.

[0045] To quantitatively analyze the degree of completion of the alkali-fusion reaction, the loss on ignition of the mixture after calcination was calculated under all conditions, using the formula (1). The quantitative analysis results of the loss on ignition under all conditions are shown in [reference needed]. Figure 3 .

[0046]

[0047] In the formula, η is the loss on ignition rate;

[0048] m1—Total mass of the mixture before reaction, in g;

[0049] m2 — the total mass of the mixture after the reaction, in grams.

[0050] Under high-temperature calcination conditions, fly ash reacts with Na₂CO₃. A high loss on ignition rate indicates that the reaction releases a large amount of gas, suggesting a relatively complete reaction. At a calcination temperature of 1000℃, the product is hard and dense, and not easily soluble in hydrochloric acid, indicating that the alkali-fused product at this temperature is unsuitable for the next step. Figure 3 It can be concluded that under all temperature conditions, the highest ignition loss rate of the mixture is achieved when the Na2CO3:fly ash ratio is 0.7, indicating that the alkali fusion reaction is most complete at this ratio. Therefore, 0.7 can be determined as the optimal ratio of Na2CO3 to fly ash for alkali fusion. At a calcination temperature of 700℃, the ignition loss rate is between 12.08% and 13.53%, which is generally low, indicating that the reaction between fly ash and Na2CO3 is not sufficient at 700℃, suggesting that this calcination temperature is too low. At calcination temperatures of 800-900℃, the ignition loss rate is generally higher, and under the same mixing ratio, the ignition loss rates at different temperatures are relatively similar. The ignition loss rate obtained under the calcination conditions of 900℃ and a Na2CO3:fly ash mixing ratio of 0.8 is 15.71%. In this group, the mixed sample product agglomerated and adhered to the magnetic boat, making complete recovery impossible, resulting in an inaccurate ignition loss rate calculated from this data set. Figure 2 Based on the experimental results, the sample with this structure is not suitable for the next step of acid leaching; therefore, this condition was not selected as the optimal alkali fusion condition, and the experiment was not repeated. At temperatures of 800-900℃, excluding the aforementioned special group, the loss on ignition rates of other samples ranged from 15.36% to 21.50%. When the calcination temperature was 850℃ and the Na₂CO₃:fly ash ratio was 0.7, the highest loss on ignition rate of 21.50% was obtained under these conditions.

[0051] (2) Extraction of silicon-aluminum precursors. 2 mol / L, 3 mol / L, and 4 mol / L hydrochloric acid were added to the samples obtained in step (1) at a calcination temperature of 850℃ and a Na2CO3:fly ash ratio of 0.7, respectively. The mixture was stirred with a magnetic stirrer for 1 hour, then filtered, and the filtrate was collected. The results are as follows: Figure 4 As shown. When the hydrochloric acid concentration is 2 mol / L, the solution is lighter in color, and there is a lot of mud-like precipitate at the bottom of the beaker that cannot dissolve in hydrochloric acid. When the hydrochloric acid concentration is 3 mol / L and 4 mol / L, the solution in the beaker is homogeneous, and there is no visible precipitate. As the hydrochloric acid concentration increases, the color of the solution changes from white to yellow. This is because the hydrochloric acid causes the Fe in the solid sample to... 3+ It dissolves in hydrochloric acid; the higher the concentration of hydrochloric acid, the more Fe can be dissolved and released. 3+The more, the solution color is more yellow. At the same time, it can be observed in the experiment that high concentration of hydrochloric acid can make the alkali fusion product react faster and the precipitate disappear. When the concentration of hydrochloric acid is 4 mol / L, the solution has begun to form gel during the process of acid immersion and filtration. The silica sol can form gel under acidic or basic conditions, while the aluminum gel needs to be formed under basic conditions, so the gel at this time is silica gel. The silica gel forms too fast under acidic conditions, which makes the aluminum sol fixed in the skeleton of the silica gel, which is not conducive to the formation of aluminum gel. After stirring with a magnetic stirrer and filtering, there is more precipitate on the filter paper when the concentration of hydrochloric acid is 2 mol / L, and there is almost no precipitate on the filter paper when the concentration of hydrochloric acid is 3 mol / L. Because the concentration of 2 mol / L hydrochloric acid cannot make the reaction completely, the concentration of 4 mol / L hydrochloric acid reacts too fast, and when the concentration of hydrochloric acid is 3 mol / L, the acid immersion reaction can be fully carried out, and a uniform and easy-to-filter solution can be formed.

[0052] (3) Form a wet gel. Add propylene oxide to the filtrate obtained by adding 3 mol / L hydrochloric acid in step (2), and adjust the pH of the filtrate to 9-10, and stand for 1 hour. The beaker is tilted at 45° and no liquid flows out, indicating that a wet gel has been formed.

[0053] (4) Ultra-low temperature vacuum drying. Put the sample obtained in step (3) into an ultra-low temperature refrigerator, freeze at -80℃, and then dry it with a vacuum freeze dryer to obtain a loose and porous aerogel carrier, such as Figure 5 . The low temperature N2 adsorption-desorption experiment curve, pore size distribution graph and X-ray diffraction graph of the aerogel are shown in Figure 6 , Figure 7 , Figure 8 . The BET specific surface area of the aerogel prepared by this method is as high as 873.9 m 2 / g, the BJH cumulative pore volume is 0.35 cm 3 / g, the average pore size is 2.5 nm, the mesopore ratio is 80.4%, the micropore ratio is 19.5%, and the macropore ratio is only 0.1%.

[0054] (5) Sulfur-doping modification. Add the aerogel carrier obtained in step (4) to deionized water with modifier K2CO3 and doping agent precursor manganese acetate and stir for 12 h. The theoretical loading amount of K2CO3 is selected as 30%, and 2% Mn is doped with manganese acetate as the precursor.

[0055] (6) Dry and sieve the sample obtained in step (5), and select the sample with a particle size of 150 μm to obtain a sulfur-resistant CO2 adsorbent. The low temperature N2 adsorption-desorption experiment curve, pore size distribution graph and X-ray diffraction graph of the adsorbent are shown in Figure 6 , Figure 7 , Figure 8 , and the performance test of the adsorbent is shown in Figure 9(200 mg / Nm3of SO2) in the atmosphere. The CO2adsorbent prepared by the present method has a cumulative adsorption capacity of up to 1.75 mmol / g under the optimal adsorption conditions. 3 SO2) in the atmosphere. The CO2adsorbent prepared by the present method has a cumulative adsorption capacity of up to 1.75 mmol / g under the optimal adsorption conditions.

[0056] Comparative Example

[0057] The present comparative example provides an undoped CO2adsorbent, which is prepared by the same method as in the example except that Mn is not doped in step (5). The other methods and steps are the same as in the example and will not be repeated here. The CO2cumulative adsorption capacity of the comparative adsorbent is 1.36 mmol / g.

Claims

1. A method for preparing a sulfur-tolerant CO2 adsorbent, characterized by, The method comprises the following steps: (1) fly ash pretreatment, using sodium carbonate as a pretreatment agent, mixing and calcining with fly ash at high temperature; (2) extracting silicon-aluminum precursor, adding hydrochloric acid to the calcination product obtained in step (1), stirring for 1 hour, filtering and taking the filtrate; (3) forming a wet gel, adding propylene oxide to the filtrate obtained in step (2) while adjusting the pH value of the filtrate, and forming a wet gel after standing; (4) ultra-low temperature vacuum drying, placing the sample obtained in step (3) into an ultra-low temperature refrigerator for freezing, and then drying by using a vacuum freeze dryer to obtain an aerogel carrier; (5) sulfur-doping resistance modification, adding the aerogel carrier obtained in step (4) into deionized water for stirring, and adding a modifier K2CO3 and a doping agent precursor manganese acetate; the K2CO3 content is 30% of the mass of the aerogel carrier, and the MnO2 content obtained from the precursor is 2% of the mass of the aerogel carrier; (6) drying and screening, selecting a sample with a certain particle size to obtain a sulfur-resistant CO2 adsorbent.

2. The method of claim 1, wherein the anti-sulfur CO2 adsorbent is prepared by the steps of: The mass ratio of sodium carbonate to fly ash in step (1) is 0.7:

1.

3. The method for preparing a sulfur-resistant CO2 adsorbent according to claim 1, characterized in that, The calcination temperature in step (1) is 850°C, and the calcination time is 3 hours.

4. The method for preparing a sulfur-resistant CO2 adsorbent according to claim 1, characterized in that, The concentration of hydrochloric acid added in step (2) is 3 mol / L, and the mass-volume ratio of the calcination product to hydrochloric acid is 1 g:10 mL.

5. The method for preparing a sulfur-resistant CO2 adsorbent according to claim 1, characterized in that, The mass ratio of propylene oxide to the filtrate in step (3) is 1:2, and the pH value of the filtrate is 9-10.

6. The method of claim 1, wherein the anti-sulfur CO2 adsorbent is prepared by the steps of: The freezing temperature in step (4) is -80°C.

7. The method for preparing a sulfur-resistant CO2 adsorbent according to claim 1, characterized in that, The particle size of the sulfur-resistant CO2 adsorbent in step (6) is 150 microns.

8. The sulfur-resistant CO2 adsorbent prepared by the preparation method according to any one of claims 1-7.

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