Preparation method and application of polyamino nano-alumina adsorbent

Abstract

The invention relates to the field of adsorbent preparation, and particularly discloses a preparation method and application of a polyamino nano-alumina adsorbent, and the preparation method comprises the following steps: S1, preparing a 1.2 mol / L composite aluminum salt solution from aluminum nitrate and aluminum sulfate according to a molar ratio of 3: 1, mixing the composite aluminum salt solution with a 1.5 mol / L ammonium carbonate-urea solution according to a volume ratio of 1: 1.5, and stirring to obtain a mixture A; then aging for 3 hours under a water bath condition of 80 + / -1 DEG C; s2, transferring a product obtained in the step S1 into a magnetically stirred high-pressure reaction kettle, reacting for 8 hours at the temperature of 180 + / -2 DEG C, and performing tubular centrifugation after the reaction is finished; according to the invention, through molecular bridging of the silane coupling agent and hierarchical assembly of carboxyl-terminated polyethyleneimine, a chemically bonded amino-carboxyl synergistic active center is formed on the surface of alumina, so that the chemical adsorption selectivity to CO2 is remarkably enhanced, and meanwhile, the problem that active components are easy to fall off in a traditional physical impregnation method is avoided.

Description

Technical Field

[0001] The invention belongs to the field of adsorbent preparation, in particular to a preparation method and application of a polyamine-based nano-alumina adsorbent. Background Art

[0002] Amine-based adsorbents are important functional materials in the field of carbon dioxide capture. Their core principle is to undergo reversible chemical adsorption reaction between surface-loaded amino functional groups (such as primary amines and secondary amines) and CO2 molecules.

[0003] Among the traditional preparation methods, the physical impregnation method is widely used because of its simple operation and low cost. In this method, amino polymers such as polyethyleneimine (PEI) are loaded on the surface of a porous carrier (such as alumina, silica gel) by impregnation.

[0004] However, this process relies on physical adsorption interactions (such as van der Waals forces and hydrogen bonds) between the amino material and the support, resulting in weak interfacial bonding between the active component and the support. In actual operation, repeated adsorption-desorption cycles can trigger thermal migration of the amino segments or solvent swelling, causing the active sites to agglomerate and detach, significantly reducing adsorption capacity and cycle life. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a polyamine-based nano-alumina adsorbent to solve the problem in the prior art that when the physical impregnation method is used to load the amino-based material, repeated adsorption-desorption cycles will trigger thermal migration or solvent swelling effect of the amino-based chain segments, causing the active sites to agglomerate and fall off, significantly reducing the adsorption capacity and cycle life.

[0006] A method for preparing a polyamine-based nano-alumina adsorbent comprises the following steps:

[0007] S1, aluminum nitrate and aluminum sulfate were prepared into a composite aluminum salt solution with a concentration of 1.2 mol / L in a molar ratio of 3:1, the composite aluminum salt solution was mixed with a 1.5 mol / L ammonium carbonate-urea solution in a volume ratio of 1:1.5, and then aged in a water bath at 80±1°C for 3 hours;

[0008] S2. The product obtained in step S1 was transferred to a magnetically stirred autoclave, and the reaction was carried out at a temperature of 180±2°C for 8 hours. After the reaction, the product was centrifuged and washed with 60°C water until the pH value was 7.0±0.5.

[0009] S3, mixing the γ-Al2O3 precursor obtained in step S2 with 3-aminopropyltriethoxysilane in anhydrous ethanol at a mass ratio of 10:1, refluxing at a temperature of 70±1°C for 6 hours, and adjusting the pH value of the reaction system to 8.0-8.5 with triethylamine;

[0010] S4. Add 8% by mass of an aqueous solution of carboxyl-terminated polyethyleneimine to the product obtained in step S3, and carry out ultrasonic reaction at a temperature of 50±1° C. under nitrogen protection for 4 hours until the conductivity change rate of the reaction system is ≤5 μS / min;

[0011] S5. The product obtained in step S4 is subjected to vacuum freeze drying at a drying temperature of -45±2° C. for 12 hours to obtain the polyamine-based nano-alumina adsorbent.

[0012] Preferably, in step S1, the molar ratio of ammonium carbonate to urea is 1:0.3, and the composite aluminum salt solution and the ammonium carbonate-urea solution are mechanically stirred during the mixing process at a stirring speed of 150-200 rpm.

[0013] Preferably, in step S2, the rotation speed of the magnetic stirring is 200-250 rpm, the filling degree of the high-pressure reactor is 60%-70%, and the G value of the tubular centrifuge is 2000-2500.

[0014] Preferably, in step S3, the reflux device adopts a round-bottom flask with a condenser reflux tube. During the reflux process, the temperature is controlled by a constant temperature water bath, and the triethylamine is added dropwise until the pH value of the reaction system is stabilized in the range of 8.0-8.5.

[0015] Preferably, in step S4, the molecular weight of the carboxyl-terminated polyethyleneimine is 2000, the carboxyl content is 5-8%, the ultrasonic frequency of the ultrasonic reaction is 40 kHz, the ultrasonic power is 300 W, a pulse mode is adopted, and nitrogen is continuously introduced during the reaction to exclude air.

[0016] The invention discloses an application of a polyamine-based nano-alumina adsorbent in wastewater treatment. The polyamine-based nano-alumina adsorbent is used for removing carbon dioxide from gas.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] By bridging silane coupling agents and hierarchical assembly of carboxyl-terminated polyethyleneimine, chemically bonded amino-carboxyl synergistic active centers are formed on the alumina surface, significantly enhancing the chemical adsorption selectivity for CO2 while avoiding the problem of easy detachment of active components in traditional physical impregnation methods.

[0019] The ultrasound-assisted grafting process promotes the uniform distribution of functional molecules on the surface of the nanocarrier. Combined with the three-dimensional through-hole structure retained by freeze drying, the CO2 diffusion path is greatly shortened, and the mass transfer efficiency of low-concentration gas inside the adsorbent is improved.

[0020] The mechanical strength of the γ-Al2O3 matrix is enhanced through the synergistic effect of hydrothermal synthesis and surface modification, so that the adsorbent maintains skeleton integrity during multiple adsorption-desorption cycles and avoids performance degradation caused by pore collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] like Figure 1 As shown:

[0024] Example 1: Preparation method of polyamine-based nano-alumina adsorbent

[0025] Step S1:

[0026] Weigh 192 g of aluminum nitrate and 103 g of aluminum sulfate, dissolve them in an appropriate amount of deionized water, and prepare 1 L of a composite aluminum salt solution with a concentration of 1.2 mol / L.

[0027] Weigh 119 g of ammonium carbonate and 22 g of urea, dissolve them in an appropriate amount of deionized water, and prepare 1.5 L of ammonium carbonate-urea solution with a concentration of 1.5 mol / L.

[0028] The composite aluminum salt solution and the ammonium carbonate-urea solution were mixed under mechanical stirring (stirring speed 150 r / min), and then aged in a water bath at 79° C. for 3 hours.

[0029] Step S2:

[0030] The product obtained in step S1 was transferred to a magnetically stirred autoclave, the magnetic stirring speed was set to 200 r / min, the filling degree of the autoclave was 60%, and the reaction was carried out at a temperature of 178° C. for 8 hours.

[0031] After the reaction, the tube was centrifuged at a G value of 2000, and then washed with 60° C. water until the pH value was 6.5.

[0032] Step S3:

[0033] Weigh 10 g of the γ-Al2O3 precursor obtained in step S2 and 1 g of 3-aminopropyltriethoxysilane, mix them in anhydrous ethanol, use a round-bottom flask with a condenser reflux tube as a reflux device, and reflux at 69°C in a constant temperature water bath for 6 hours.

[0034] Triethylamine was added dropwise into the reaction system to adjust the pH value of the reaction system to 8.0.

[0035] Step S4:

[0036] To the product obtained in step S3, an 8% mass fraction of an aqueous solution of carboxyl-terminated polyethyleneimine (carboxyl-terminated polyethyleneimine molecular weight 2000, carboxyl content 5%) was added, and an ultrasonic reaction was carried out under nitrogen protection at a temperature of 49° C. in a pulse mode with an ultrasonic frequency of 40 kHz and an ultrasonic power of 300 W for 4 hours until the conductivity change rate of the reaction system was ≤5 μS / min.

[0037] Step S5:

[0038] The product obtained in step S4 was subjected to vacuum freeze drying at a drying temperature of -47°C for 12 hours to obtain a polyamine-based nano-alumina adsorbent.

[0039] Example 2: Preparation method of polyamine-based nano-alumina adsorbent

[0040] Step S1:

[0041] Weigh 192 g of aluminum nitrate and 103 g of aluminum sulfate to prepare 1 L of a composite aluminum salt solution with a concentration of 1.2 mol / L.

[0042] Weigh 149 g of ammonium carbonate and 32 g of urea to prepare 1.5 L of an ammonium carbonate-urea solution with a concentration of 1.5 mol / L.

[0043] The composite aluminum salt solution and the ammonium carbonate-urea solution were mixed under mechanical stirring (stirring speed 175 r / min), and then aged in a water bath at 80° C. for 3 hours.

[0044] Step S2:

[0045] The product was transferred to a magnetically stirred autoclave, the magnetic stirring speed was set to 225 r / min, the filling degree of the autoclave was 65%, and the reaction was carried out at a temperature of 180° C. for 8 hours.

[0046] After the reaction, the mixture was centrifuged in a tube with a G value of 2250 and washed with 60° C. water until the pH value reached 7.0.

[0047] Step S3:

[0048] Weigh 10 g of γ-Al2O3 precursor and 1 g of 3-aminopropyltriethoxysilane, mix them in anhydrous ethanol, reflux them in a round-bottom flask with a condenser reflux tube, and reflux them at 70°C in a constant temperature water bath for 6 hours.

[0049] Triethylamine was added dropwise into the reaction system to adjust the pH value of the reaction system to 8.2.

[0050] Step S4:

[0051] An 8% by mass fraction of an aqueous solution of carboxyl-terminated polyethyleneimine (molecular weight of carboxyl-terminated polyethyleneimine: 2000, carboxyl content: 6.5%) was added to the product. Under nitrogen protection, an ultrasonic reaction was carried out at 50°C in a pulse mode with an ultrasonic frequency of 40 kHz and an ultrasonic power of 300 W for 4 hours until the conductivity change rate of the reaction system was ≤5 μS / min.

[0052] Step S5:

[0053] The product was vacuum freeze-dried at a drying temperature of -45°C for 12 hours to obtain a polyamine-based nano-alumina adsorbent.

[0054] Example 3: Preparation method of polyamine-based nano-alumina adsorbent

[0055] Step S1:

[0056] Weigh 192 g of aluminum nitrate and 103 g of aluminum sulfate to prepare 1 L of a composite aluminum salt solution with a concentration of 1.2 mol / L.

[0057] Weigh 178 g of ammonium carbonate and 43 g of urea to prepare 1.5 L of an ammonium carbonate-urea solution with a concentration of 1.5 mol / L.

[0058] The composite aluminum salt solution and the ammonium carbonate-urea solution were mixed under mechanical stirring (stirring speed 200 r / min), and then aged in a water bath at 81° C. for 3 hours.

[0059] Step S2:

[0060] The product was transferred to a magnetically stirred autoclave with a speed of 250 r / min and a filling degree of 70% for reaction at 182° C. for 8 hours.

[0061] After the reaction, the tube was centrifuged at a G value of 2500, and then washed with 60° C. water until the pH value was 7.5.

[0062] Step S3:

[0063] Weigh 10 g of γ-Al2O3 precursor and 1 g of 3-aminopropyltriethoxysilane, mix them in anhydrous ethanol, reflux them in a round-bottom flask with a condenser reflux tube, and reflux them at 71°C in a constant temperature water bath for 6 hours.

[0064] Triethylamine was added dropwise into the reaction system to adjust the pH value of the reaction system to 8.5.

[0065] Step S4:

[0066] An 8% by mass fraction of an aqueous solution of carboxyl-terminated polyethyleneimine (molecular weight of carboxyl-terminated polyethyleneimine: 2000, carboxyl content: 8%) was added to the product. Under nitrogen protection, an ultrasonic reaction was carried out at a temperature of 51°C using a pulse mode with an ultrasonic frequency of 40 kHz and an ultrasonic power of 300 W for 4 hours until the conductivity change rate of the reaction system was ≤5 μS / min.

[0067] Step S5:

[0068] The product was freeze-dried in vacuum at a drying temperature of -43°C for 12 hours to obtain a polyamine-based nano-alumina adsorbent.

[0069] Experimental example: Performance verification of polyamine-based nano-alumina adsorbent in the DAC field

[0070] Purpose of the experiment

[0071] The adsorption performance of the polyamine-based nano-alumina adsorbent prepared in Example 2 for low-concentration CO2 (simulating direct air carbon capture) was verified, and the effects of key process parameters on the adsorption performance were analyzed through comparative experiments.

[0072] Experimental design

[0073] 1. Sample Grouping

[0074]

[0075] 2. Test Method

[0076] Dynamic adsorption test:

[0077] Equipment: Fixed bed reactor (inner diameter 10 mm, bed height 50 mm)

[0078] Gas composition: simulated air (CO2 concentration 400ppm, N2 balance, humidity 60%RH) flow rate: 200mL / min, temperature 25℃

[0079] Detection: Online infrared CO2 analyzer (accuracy ±1ppm)

[0080] Cyclic stability test:

[0081] Adsorption conditions: 25°C, 60% RH, CO2 concentration 400 ppm

[0082] Desorption conditions: 100 ° C, N2 purge (flow rate 300 mL / min, time 30 min) number of cycles: 10 times

[0083] Characterization analysis:

[0084] Specific surface area (BET): N2 adsorption-desorption isotherm (77K)

[0085] Surface amino group density: acid-base titration method

[0086] Micromorphology: SEM

[0087] Experimental results and data analysis

[0088] Table 1. Comparison of CO2 adsorption performance of different samples

[0089]

[0090] Table 2. Performance comparison of Example 2 and commercial adsorbents

[0091]

[0092] Key Results Analysis

[0093] Effect of surface modification on adsorption performance (Comparative Example 1 vs Example 2)

[0094] Since Comparative Example 1 was not modified with a silane coupling agent, the surface amino density was only 0.1 mmol / g, resulting in a CO2 adsorption capacity (0.32 mmol / g) that was significantly lower than that of Example 2 (1.25 mmol / g).

[0095] Conclusion: The introduction of 3-aminopropyltriethoxysilane is the key to improving the CO2 chemical adsorption capacity.

[0096] Effect of ultrasonic reaction on uniformity (Comparative Example 2 vs. Example 2)

[0097] In Comparative Example 2, after the ultrasonic reaction was canceled, the surface amino group density dropped to 1.9 mmol / g, and SEM showed that the polyethyleneimine was unevenly distributed (agglomeration phenomenon), and the adsorption capacity decreased by 30%.

[0098] Conclusion: Ultrasonic reaction promotes the uniform grafting of carboxyl-terminated polyethyleneimine onto the surface of γ-Al2O3 through cavitation effect.

[0099] Effect of Drying Method on Pore Structure (Comparative Example 3 vs. Example 2)

[0100] Comparative Example 3 uses ordinary vacuum drying, and the specific surface area is reduced to 210m2 / g (Example 2 is 320m 2 / g), the adsorption capacity decreased by 48% due to pore collapse caused by ice crystal growth.

[0101] Conclusion: Vacuum freeze drying (-45℃) can effectively preserve the mesoporous structure and improve the CO2 diffusion efficiency.

[0102] DAC application advantages (Example 2 vs. commercial adsorbents)

[0103] The adsorption capacity of Example 2 at low CO2 concentration (400 ppm) (1.25 mmol / g) is better than that of commercial amino silica gel (1.10 mmol / g), and the regeneration energy consumption is reduced by 18%.

[0104] Mechanism: High specific surface area of nano-alumina (320m 2 / g) and carboxyl-terminated polyethyleneimine, which enhances the physical adsorption and chemical capture efficiency of CO2.

[0105] Experimental Conclusion

[0106] The polyamine-based nano-alumina adsorbent of Example 2 exhibits significant advantages in the DAC field:

[0107] High adsorption capacity: 1.25mmol / g (400ppmCO2, 25℃)

[0108] Excellent cycle stability: capacity retention rate of 95% after 10 cycles

[0109] Low regeneration energy consumption: 45kJ / mol (15-25% lower than commercial adsorbents)

[0110] Technical core:

[0111] Silane coupling agent modification provides high-density amino active sites;

[0112] Ultrasonic-assisted grafting ensures functionalization uniformity;

[0113] Vacuum freeze drying maintains the nanoporous structure.

[0114] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0115] In the drawings of the embodiments disclosed in the present invention, only the structures related to the embodiments disclosed in the present invention are involved. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other.

[0116] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polyamine-based nano-alumina adsorbent, characterized in that: The following steps are involved: S1, aluminum nitrate and aluminum sulfate were prepared into a composite aluminum salt solution with a concentration of 1.2 mol / L in a molar ratio of 3:1, the composite aluminum salt solution was mixed with a 1.5 mol / L ammonium carbonate-urea solution in a volume ratio of 1:1.5, and then aged in a water bath at 80±1°C for 3 hours; S2. The product obtained in step S1 was transferred to a magnetically stirred autoclave, and the reaction was carried out at a temperature of 180±2°C for 8 hours. After the reaction, the product was centrifuged and washed with 60°C water until the pH value was 7.0±0.

5. S3, mixing the γ-Al2O3 precursor obtained in step S2 with 3-aminopropyltriethoxysilane in anhydrous ethanol at a mass ratio of 10:1, refluxing at a temperature of 70±1°C for 6 hours, and adjusting the pH value of the reaction system to 8.0-8.5 with triethylamine; S4. Add 8% by mass of an aqueous solution of carboxyl-terminated polyethyleneimine to the product obtained in step S3, and carry out ultrasonic reaction at a temperature of 50±1° C. under nitrogen protection for 4 hours until the conductivity change rate of the reaction system is ≤5 μS / min; S5. The product obtained in step S4 is subjected to vacuum freeze drying at a drying temperature of -45±2° C. for 12 hours to obtain the polyamine-based nano-alumina adsorbent.

2. The method for preparing a polyamine-based nano-alumina adsorbent according to claim 1, wherein: In step S1, the molar ratio of ammonium carbonate to urea is 1:0.3, and the composite aluminum salt solution and the ammonium carbonate-urea solution are mechanically stirred during the mixing process at a stirring speed of 150-200 rpm.

3. The method for preparing a polyamine-based nano-alumina adsorbent according to claim 1, wherein: In step S2, the rotation speed of the magnetic stirring is 200-250 rpm, the filling degree of the high-pressure reactor is 60%-70%, and the G value of the tubular centrifuge is 2000-2500.

4. The method for preparing a polyamine-based nano-alumina adsorbent according to claim 1, wherein: In step S3, the reflux device uses a round-bottom flask with a condenser reflux tube. During the reflux process, the temperature is controlled by a constant temperature water bath, and the triethylamine is added dropwise until the pH value of the reaction system is stabilized in the range of 8.0-8.

5.

5. The method for preparing a polyamine-based nano-alumina adsorbent according to claim 1, wherein: In step S4, the molecular weight of the carboxyl-terminated polyethyleneimine is 2000, the carboxyl content is 5-8%, the ultrasonic frequency of the ultrasonic reaction is 40 kHz, the ultrasonic power is 300 W, a pulse mode is adopted, and nitrogen is continuously introduced during the reaction to exclude air.

6. Use of the polyamine-based nano-alumina adsorbent prepared by the method according to any one of claims 1 to 5 in gas treatment, characterized in that: The polyamine-based nano-alumina adsorbent is used for removing carbon dioxide from gas.

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