A method for preparing a carbon dioxide adsorbent, a carbon dioxide adsorbent and its application

Abstract

The present invention discloses a method for preparing a carbon dioxide adsorbent, comprising treating waste lithium iron phosphate batteries to obtain a lithium iron phosphate positive electrode material; adding the lithium iron phosphate positive electrode material to a mixed solution of CH3COOH and H2O2, reacting in a water bath to obtain a lithium-containing filtrate; adding Na2CO3, (NH3)2CO3 and silicon dioxide, stirring and evaporating, and then calcining, grinding and sieving the calcined product to obtain the carbon dioxide adsorbent. The present invention also discloses a carbon dioxide adsorbent prepared by the method described. The present invention also discloses an application of a carbon dioxide adsorbent. The present invention can recycle waste lithium batteries, has the advantages of simple process, and the prepared carbon dioxide adsorbent has high adsorption capacity and stable adsorption performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery recycling, and in particular to a method for preparing a carbon dioxide adsorbent, the carbon dioxide adsorbent and applications thereof. Background Art

[0002] Lithium iron phosphate batteries (LiFePO4) are the most widely used in power batteries due to their low toxicity, high safety, excellent cycle performance and low cost. With the explosive growth of new energy vehicles, it is estimated that by 2024, lithium iron phosphate batteries will account for more than 60% of the installed capacity of the global power battery market. The theoretical life of lithium iron phosphate batteries is 7 to 8 years. Currently, more and more lithium iron phosphate batteries are discarded because they have reached the retirement age. If the huge amount of discarded lithium batteries is not handled, it will not only cause great pollution to the environment, but also cause a waste of energy.

[0003] The recycling of waste lithium iron phosphate batteries mainly adopts the wet recycling process, which dissolves the metal ions in the lithium iron phosphate battery by acid and alkali solution, and further extracts the dissolved metal ions in the form of oxides, salts, etc. by precipitation, adsorption, etc. In the reaction process, most reagents such as H2SO4, NaOH and H2O2 are used. The wet recycling process is simple, the equipment requirements are not high, the cost is relatively low, and it is suitable for industrial-scale production.

[0004] At present, there are also reports on the preparation of carbon dioxide adsorbent by converting lithium ions in waste batteries into lithium orthosilicate in a CH3COOH+H2O2 leaching system. However, when the adsorbent is prepared by this system, lithium needs to be precipitated first and then purified, and the steps are repeated many times, which is cumbersome. In addition, the adsorption capacity of carbon dioxide prepared by this method is low, and the effect of adsorbing carbon dioxide is poor. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to solve the problems of complex process, high energy consumption and low adsorption capacity of CO2 adsorbent prepared by using waste lithium iron phosphate batteries in the existing CH3COOH+H2O2 leaching system, and to provide a method for preparing carbon dioxide adsorbent, carbon dioxide adsorbent and application thereof. The method has a simple process and the prepared CO2 adsorbent has a high adsorption capacity.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a carbon dioxide adsorbent comprises the following steps:

[0008] Processing waste lithium iron phosphate batteries to obtain lithium iron phosphate positive electrode materials;

[0009] Adding lithium iron phosphate positive electrode material to a mixed solution of CH3COOH and 6 vol.% H2O2, reacting in a 50-70°C water bath for 30-60 minutes, adjusting the pH value to 8-10, and then filtering to obtain a lithium-containing filtrate;

[0010] At a constant temperature of 95°C, Na2CO3, (NH3)2CO3 and silicon dioxide were added to the lithium-containing filtrate, stirred and evaporated for 2-3 hours to obtain a slurry;

[0011] The slurry is calcined at 750-800° C. for 6-8 hours, and the calcined product is ground and sieved to obtain the carbon dioxide adsorbent.

[0012] Preferably, the waste lithium iron phosphate battery is discharged, reacted in a 2-4 mol / L NaOH solution at 30-40° C. for 2-4 h, and dried and filtered to obtain the lithium iron phosphate positive electrode material.

[0013] Preferably, the mass volume ratio of the lithium iron phosphate positive electrode material to the mixed solution is 1-2g:10-20mL; wherein the mixed solution is a mixture of 0.05mol / L CH3COOH and H2O2 in a volume ratio of 94:6.

[0014] Preferably, the amount of Na2CO3 added is 10-12% of the molar number of lithium ions; the amount of (NH3)2CO3 added is sufficient to convert all lithium ions into Li2CO3. The purpose of adding Na2CO3 and (NH3)2CO3 is to convert CO3 2- Reacts with Li to form Li2CO3 precipitate. 1 mol CO3 2- and 2 mol Li + Li2CO3 precipitate is generated, and the amount of Na2CO3 added is 10-12% of the molar number of Li, CO3 2- The amount is obviously not enough, and the rest is balanced by (NH3)2CO3, so as to achieve the purpose of converting all Li into Li2CO3.

[0015] Preferably, the silicon dioxide is hydrophilic fumed silicon dioxide, and the molar ratio of Li + :SiO2=(4-4.2):1 added.

[0016] Preferably, during calcination, the material is heated to the calcination temperature at a heating rate of 2.5-10° C. / min.

[0017] The invention also discloses a carbon dioxide adsorbent, which is prepared by the method described above; the main components of the carbon dioxide adsorbent are Li4SiO4 and Na2CO3, and the Na2CO3 is doped in Li4SiO4.

[0018] The invention also discloses an application of a carbon dioxide adsorbent, wherein the carbon dioxide adsorbent is used to adsorb carbon dioxide.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The preparation method provided by the present invention comprises the following steps: + In the process of converting to Li2CO3, the impurity Na2CO3 is introduced and the amount of Na2CO3 introduced is controlled so that Na2CO3 is evenly dispersed in Li4SiO4 to obtain a Na2CO3-doped lithium orthosilicate carbon dioxide adsorbent. In the entire preparation process, not only are the steps of stirring when adding Na2CO3, (NH3)2CO3 and silica in the traditional recovery process omitted, but there is no need for lithium precipitation and purification crystallization. At the same time, the "impurities" that should have taken extra steps and costs to remove are cleverly made into dopants in the adsorbent preparation process, so that the precipitation process, preparation process and doping process are combined into one step, while simplifying the steps and improving the performance of the adsorbent, and at the same time greatly reducing the preparation cost of the adsorbent. This method provides preliminary theoretical guidance for the simplification and performance improvement of the preparation of adsorbents in other recovery systems.

[0021] 2. The carbon dioxide adsorbent prepared by the present invention has good adsorption performance, and its CO2 adsorption capacity can reach 0.24g / g.

[0022] 3. The carbon dioxide adsorbent provided by the present invention is used to adsorb carbon dioxide, which has the advantages of large adsorption capacity, stable adsorption performance after 80 cycles, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a graph showing the CO2 adsorption capacity of the carbon dioxide adsorbent prepared in Examples 1-3 of the present invention after 20 cycles.

[0024] Figure 2 This is a comparison chart of the heating rate and the adsorption capacity of the carbon dioxide adsorbent prepared in Examples 2, 4, 5 and 6.

[0025] Figure 3 This is a comparison chart of the effect of the Na2CO3 ratio on the adsorption capacity of the carbon dioxide adsorbent prepared in Examples 5, 7, and 8.

[0026] Figure 4 Graph showing the sodium content in the carbon dioxide adsorbents prepared in Examples 2, 5 and 7 of the present invention.

[0027] Figure 5 Specific surface area and pore volume diagram of the carbon dioxide adsorbent prepared in Examples 2, 5 and 7 of the present invention.

[0028] Figure 6Graph showing the pore sizes of the carbon dioxide adsorbents prepared in Examples 2, 5 and 7 of the present invention.

[0029] Figure 7 The SEM-EDS images of the carbon dioxide adsorbents prepared in Examples 2, 5 and 7 of the present invention.

[0030] Figure 8 This is a graph showing the CO2 adsorption capacity of the carbon dioxide adsorbent prepared in Example 7 of the present invention after 80 cycles.

[0031] Fig. 9 This is a graph showing the CO2 adsorption capacity of the carbon dioxide adsorbent prepared in Comparative Example 1 after 80 cycles.

[0032] Fig.10 This is a cost comparison chart of the carbon dioxide adsorbent prepared in Example 1 of the present invention and the commercially available lithium orthosilicate adsorbent. DETAILED DESCRIPTION

[0033] The embodiment of the present invention discloses a method for preparing a carbon dioxide adsorbent, comprising the following steps:

[0034] Processing waste lithium iron phosphate batteries to obtain lithium iron phosphate positive electrode materials;

[0035] Adding lithium iron phosphate positive electrode material to a mixed solution of CH3COOH and 6 vol.% H2O2, reacting in a 50-70°C water bath for 30-60 minutes, adjusting the pH value to 8-10, and then filtering to obtain a lithium-containing filtrate;

[0036] At a constant temperature of 95°C, Na2CO3, (NH3)2CO3 and silicon dioxide were added to the lithium-containing filtrate, stirred and evaporated to obtain a slurry;

[0037] The slurry is calcined at 750-800° C. for 6-8 hours, and the calcined product is ground and sieved to obtain the carbon dioxide adsorbent.

[0038] The embodiment of the present invention further discloses a carbon dioxide adsorbent, which is prepared by the method described above; the main components of the carbon dioxide adsorbent are Li4SiO4 and Na2CO3, and the Na2CO3 is doped in Li4SiO4.

[0039] The embodiment of the present invention further discloses a carbon dioxide adsorbent, which is used to adsorb carbon dioxide.

[0040] Example 1

[0041] A method for preparing a carbon dioxide adsorbent comprises the following steps:

[0042] The waste lithium iron phosphate battery was discharged (soaked in a 10% by mass NaCl solution for 24 hours) and disassembled to obtain the positive electrode material, which was then reacted in a 2 mol / L NaOH solution at 30°C for 2 hours. After filtration and drying, the lithium iron phosphate positive electrode material was obtained.

[0043] 10 g of the positive electrode material was added to 100 mL of a mixed solution of 0.05 mol / L CH3COOH and 6 vol.% H2O2, and reacted in a 50°C water bath for 30 minutes. The pH was adjusted to 8 using NH3·H2O, and then filtered to obtain a lithium-containing filtrate.

[0044] At a constant temperature of 95°C, 10 wt.% Na2CO3 of the molar number of lithium ions was added to the lithium-containing filtrate, and the corresponding (NH3)2CO3 was added to ensure sufficient CO3 2- Combined with Li, at the same time according to Li + The mixture was mixed with hydrophilic fumed silica in a molar ratio of 4.2:1, stirred and evaporated, and stirred in a water bath until it could hardly be stirred to obtain a slurry.

[0045] The slurry was placed in a muffle furnace and calcined at 750° C. for 6 hours, with a heating rate of 7.5° C. / min during the heating process. The calcined product was ground and sieved to obtain the carbon dioxide adsorbent.

[0046] Embodiment 2-8

[0047] The control conditions in Examples 2-8 that are different from those in Example 1 are shown in Table 1, and the rest are the same as in Example 1.

[0048] Table 1 Preparation and recovery conditions in Examples 1-8

[0049]

[0050] The carbon dioxide adsorbent prepared in the embodiment was subjected to an adsorption test. The adsorbent performance test was mainly performed by adjusting the working procedure of a thermogravimetric analyzer (TGA) to complete a variety of tests. TGA is a German NETZSCH TG-209F3 thermogravimetric analyzer with a balance accuracy of 0.0001 mg, a test temperature range of room temperature-1000°C, and a heating rate range of 0-50°C / min. During the specific test, 10 mg of the adsorbent prepared in each embodiment was placed in an empty crucible, and the heating rate was maintained at 10°C / min from room temperature to a predetermined adsorption temperature, the atmosphere was switched to 85 ml / min of N2 and 15 ml / min of CO2, the adsorption time was 30 min, and after the adsorption was completed, the temperature was raised to 700°C at a rate of 40°C / min, and desorbed under pure N2 conditions for 10 min. Subsequently, it was cooled to the initial adsorption temperature at a rate of -30°C / min, and an atmosphere of 85 ml / min of N2 and 15 ml / min of CO2 was introduced, and the adsorption reaction was carried out again. The above process is a complete adsorption / desorption performance, and the number of cycles required to complete the experiment is set by the program at different times.

[0051] After testing, the results of the CO2 adsorption capacity of the carbon dioxide adsorbent prepared in Examples 1-3 under 20 cycles are as follows: Figure 1 As shown. Figure 1 It can be seen that when pH = 8 (Example 1), the initial adsorption capacity of the adsorbent is 0.134g / g. During the first five cycles, the adsorption capacity of the adsorbent decreases to a certain extent, slowly drops to 0.128g / g, and finally stabilizes at 0.127g / g during 20 cycles. The initial adsorption performance of the adsorbent prepared at pH = 10 (Example 3) is lower than that of pH = 8 (Example 1), and its initial adsorption capacity is 0.112g / g. As the cycle proceeds, its change trend is close to that at pH = 8, and there is also a certain decrease during the first five cycles, and finally stabilizes at 0.107g / g during 20 cycles. The sample prepared at pH = 9 (Example 2) increases from 0.155g / g to 0.162g / g, and maintains a relatively stable adsorption performance during 20 cycles.

[0052] The effect of the heating rate on the adsorption capacity of the carbon dioxide adsorbent prepared by Examples 2, 4, 5 and 6 was studied. Figure 2 As shown. Figure 2It can be seen that the adsorption capacity of the Li4SiO4 adsorbent prepared at a heating rate of 10°C / min (Example 6) is significantly the lowest, at only 0.079g / g. The experimental groups with heating rates of 5°C / min (Example 5) and 7.5°C / min (Example 2) performed better, reaching 0.206g / g and 0.155g / g respectively in the initial stage. Although there were no obvious fluctuations in subsequent cycle tests, the adsorption performance of these two adsorbents eventually stabilized at 0.205g / g and 0.156g / g. When the heating rate was 2.5°C / min (Example 4), its adsorption performance decreased, and the final stabilized adsorption performance was 0.123g / g.

[0053] The carbon dioxide adsorbents prepared in Examples 5, 7 and 8 were used to study the effect of the doping ratio of Na2CO3 on the adsorption capacity of the carbon dioxide adsorbents. Figure 3 As shown. Figure 3 It can be seen that the initial adsorption performance of the three groups of Li4SiO4 adsorbents is above 0.2g / g. When the proportion of Na2CO3 is 10% (Example 5) and 12% (Example 8), the adsorption capacity is maintained at 0.204g / g and 0.21g / g respectively. In particular, when the proportion of Na2CO3 is 11% (Example 7), the initial adsorption capacity reaches 0.241g / g. Although there is a slight trend of first rising and then falling during the cycle, its adsorption performance is still at the highest level in the end, stabilizing at 0.245g / g.

[0054] As an impurity introduced during the recovery process and an effective dopant during the adsorbent preparation process, Na element needs to be paid special attention to. The sodium content of the carbon dioxide adsorbents prepared in Examples 2, 5 and 7 was determined by ICP test. Figure 4 As shown, from the comparison between Example 2 and Example 5, it is found that when the introduction ratio of Na2CO3 is unchanged, the content of the prepared adsorbent is 5.8wt.% and 5.9wt.%, respectively. In Example 7, when the introduction ratio of Na2CO3 is 11%, the final sodium content of the Li4SiO4 adsorbent is 6.8wt.%. This indicates that the final sodium content of 6.8wt.% is the ideal sodium content for synthesizing the Li4SiO4 adsorbent using waste lithium iron phosphate batteries.

[0055] The above three groups of adsorbents (Examples 2, 5 and 7) were further tested for specific surface area and pore volume. Under the premise of determining the pH, the specific surface area and pore volume of the prepared adsorbent can be increased by appropriately extending the heating time during the calcination process, and the appropriate amount of sodium introduced is more obvious. Figure 5 As shown in the figure, the heating time of the calcination process of Example 5 was prolonged compared with that of Example 2, and its specific surface area and pore volume increased from 1.5m2 / g, 0.0059cm 3 / g increased to 2.2m 2 / g, 0.0069cm 3 / g. Compared with Example 5, Example 7 increases the proportion of Na2CO3, and its specific surface area and pore volume increase from 2.2m 2 / g, 0.0069cm 3 / g increased to 2.8m 2 / g, 0.0094cm 3 / g. Figure 6 As shown in the figure, the adsorbents have certain similarities in pore distribution, and the pore range is mainly concentrated between 1-3nm. The difference is that with the continuous improvement of conditions, the number of pores in this range has increased significantly, which is also an important reason why the final adsorption capacity can be kept stable at a higher level.

[0056] Figure 7 The SEM-EDS test of three groups of adsorbents (Examples 2, 5, and 7) shows that the morphologies of the three groups of adsorbents are relatively similar. However, with the increase in the heating time and the Na2CO3 ratio, the pores of the adsorbents become significantly richer, which is considered to be conducive to the adsorbents maintaining efficient, stable and continuous adsorption, which is consistent with the previous BET-BJH test results. Through EDS scanning, it was found that the main impurities of the adsorbents were still Na and P. Na was evenly distributed in the adsorbent, playing a reinforcing role as a dopant, so the best adsorption performance was achieved after the Na2CO3 ratio was optimized.

[0057] The carbon dioxide adsorbent prepared in Example 7 (pH = 9, heating rate of 5 ° C / min, Na2CO3 ratio of 11%) was tested for up to 80 cycles in a 15% CO2 atmosphere under N2 balance. The results are as follows: Figure 8 As shown. It was found that the initial adsorption capacity of the adsorbent was 0.24 g / g, and then increased to 0.25 g / g in the second cycle. Although there were certain fluctuations and decreases during the continuous adsorption / desorption process, the final adsorption capacity was still able to maintain a high level, and finally stabilized at about 0.24 g / g. It can be seen that the adsorption capacity of the carbon dioxide adsorbent prepared in Example 7 has long-term stability.

[0058] Comparative Example 1

[0059] The waste lithium iron phosphate battery was discharged (soaked in a 10% by mass NaCl solution for 24 hours) and disassembled to obtain the positive electrode material, which was then reacted in a 2 mol / L NaOH solution at 30°C for 2 hours. After filtration and drying, the lithium iron phosphate positive electrode material was obtained.

[0060] 10 g of the positive electrode material was added to 100 mL of a mixed solution of 0.05 mol / L CH3COOH and 6 vol.% H2O2, reacted in a 50°C water bath for 30 minutes, and filtered to obtain a filtrate. Then, NaOH was added to adjust the pH to 7.5-8, and the lithium-containing filtrate was obtained by filtering.

[0061] Na2CO3 was added to the lithium-containing filtrate at a constant temperature of 95°C in a molar ratio of lithium to sodium of 2:1, precipitated for 2 hours, filtered three times with the addition of distilled water, and then dried at 120°C for 24 hours to obtain Li2CO3.

[0062] After extracting Li2CO3 from waste lithium iron phosphate batteries, the Li4SiO4 adsorbent was synthesized by a solid phase method. Li2CO3 and SiO2 were mixed at a molar ratio of 2.05:1 and calcined in a muffle furnace at 750°C for 6 hours with a heating rate of 10°C / min. The calcined product was then ground and sieved to obtain Li4SiO4 powder.

[0063] After testing, the CO2 adsorption capacity of the adsorbent prepared in the comparative example is 0.13 g / g. Fig. 9 As shown. The CO2 adsorption capacity of the adsorbent prepared in Example 7 of the present invention is 0.24 g / g. It can be seen that the CO2 adsorption capacity of the adsorbent prepared in Example 7 is increased by 184.6%.

[0064] At the same time, the cost of the carbon dioxide adsorbent prepared in the embodiment of the present invention is similar to the cost of directly using commercially available Li2CO3 to prepare the adsorbent. Fig.10 As shown in the figure, it can be seen that the cost of the new process proposed by the present invention is only 1 / 5-1 / 3 of the cost of the traditional preparation method. The cost of the carbon dioxide adsorbent is greatly reduced, which is conducive to the application of Li4SiO4 adsorbent in the adsorption of carbon dioxide.

[0065] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a carbon dioxide adsorbent, characterized in that: The following steps are included: Processing waste lithium iron phosphate batteries to obtain lithium iron phosphate positive electrode materials; Adding lithium iron phosphate positive electrode material to a mixed solution of CH3COOH and 6 vol.% H2O2, reacting in a 50-70°C water bath for 30-60 minutes, adjusting the pH value to 8-10, and then filtering to obtain a lithium-containing filtrate; At a constant temperature of 95°C, Na2CO3, (NH4)2CO3 and silicon dioxide were added to the lithium-containing filtrate, stirred and evaporated for 2-3 hours to obtain a slurry; calcining the slurry at 750-800° C. for 6-8 hours, grinding and sieving the calcined product to obtain the carbon dioxide adsorbent; The carbon dioxide adsorbent has stable adsorption performance after 80 cycles.

2. The method for preparing a carbon dioxide adsorbent according to claim 1, characterized in that: The waste lithium iron phosphate battery is discharged, reacted in a 2-4 mol / L NaOH solution at 30-40° C. for 2-4 hours, and dried and filtered to obtain a lithium iron phosphate positive electrode material.

3. The method for preparing a carbon dioxide adsorbent according to claim 1, characterized in that: The mass volume ratio of the lithium iron phosphate positive electrode material to the mixed solution is 1-2g:10-20mL; wherein the mixed solution is a mixture of 0.05mol / L CH3COOH and H2O2 in a volume ratio of 94:

6.

4. The method for preparing a carbon dioxide adsorbent according to claim 1, characterized in that: The amount of Na2CO3 added is 10-12% of the molar number of lithium ions; the amount of (NH4)2CO3 added is sufficient to convert all lithium ions into Li2CO3.

5. The method for preparing a carbon dioxide adsorbent according to claim 1, characterized in that: The silicon dioxide is a hydrophilic fumed silicon dioxide, and the molar ratio of Li + :SiO2=(4-4.2):1 added.

6. The method for preparing a carbon dioxide adsorbent according to claim 1, characterized in that: During calcination, the material is heated to the calcination temperature at a heating rate of 2.5-10°C / min.

7. A carbon dioxide adsorbent, characterized in that: The carbon dioxide adsorbent is prepared by the method described in any one of claims 1 to 6; the main components of the carbon dioxide adsorbent are Li4SiO4 and Na2CO3, and the Na2CO3 is doped in Li4SiO4.

8. An application of a carbon dioxide adsorbent, characterized in that: The carbon dioxide adsorbent according to claim 7 is used for adsorbing carbon dioxide.

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