A method for capturing a fluorine-containing greenhouse gas

Abstract

This invention discloses a method for capturing fluorine-containing greenhouse gases, comprising the following steps: using 100–3000 h ‑1 Industrial exhaust gas containing fluorinated greenhouse gases, including at least carbon tetrafluoride, is introduced at space velocity into a trap containing a modified adsorbent. The modified adsorbent adsorbs the fluorinated greenhouse gases in the incoming industrial exhaust gas at an adsorption temperature of 10–90°C. Adsorption stops when the concentration of carbon tetrafluoride in the outgoing industrial exhaust gas drops to 0.1–1000 ppm. The modified adsorbent is a metal cation-modified molecular sieve. The trapping method of this invention is simple in process, has low energy consumption, and can achieve efficient trapping of fluorinated greenhouse gases at room temperature and pressure.

Description

Technical Field

[0001] This invention relates to the field of greenhouse gas emission reduction materials technology, and in particular to a method for capturing fluorine-containing greenhouse gases. Background Technology

[0002] Fluorinated greenhouse gases (F-gases) include hydrofluorocarbons (HFCs), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), and perfluorinated carbon (PFCs). Their global warming potential can reach thousands or even tens of thousands, and they are known as super greenhouse gases. All F-gases are greenhouse gases regulated under the Kyoto Protocol.

[0003] Perfluorinated carbon (PFCs) are among the key greenhouse gases that need to be controlled under the Kyoto Protocol, with carbon tetrafluoride (CF4) being the most significant emitter. Compared to CO2, CF4 is chemically stable, has a long atmospheric lifetime, and exhibits a very strong greenhouse effect, with a 100-year global warming potential (GWP). 100 The value is as high as 7380. In the aluminum smelting process, due to the presence of the "anodic effect", the flux cryolite (Na3AlF6) reacts with the carbon anode to generate CF4 and is emitted; in the semiconductor manufacturing process, CF4 is an important dry etching gas and cleaning gas, and unreacted CF4 is released into the atmosphere.

[0004] Developing efficient fluorinated greenhouse gas capture technologies is of significant strategic importance. This technology can effectively reduce greenhouse gas emissions from various industries and also enable the recycling of fluorine resources.

[0005] There are few reports on existing technologies for capturing fluorinated greenhouse gases.

[0006] Chinese patent CN106241800B discloses an activated carbon specifically designed for adsorbing carbon tetrafluoride, prepared from anthracite powder and bituminous coal-based activated carbon powder. This material has high strength and high bulk density, but its CF4 adsorption capacity is relatively low.

[0007] Chinese patent CN100503005C discloses a method for refining nitrogen trifluoride using zeolite after alkaline earth metal ion exchange as an adsorbent. This material can selectively adsorb NF. 3， This method can recover excluded impurities such as CF4, but the molecular sieve desorption energy consumption is high and the NF3 adsorption capacity is low.

[0008] Chinese patent CN114789045A discloses an organic porous material for the separation and purification of electronic specialty gases. This material possesses an adjustable pore structure and good chemical and hydrothermal stability; however, the solvothermal synthesis method requires harsh conditions, and the adsorption capacity and selectivity for CF4 are low, making it unsuitable for capturing large quantities of CF4 gas. Summary of the Invention

[0009] To address the shortcomings and defects of existing technologies, this invention proposes a method for capturing fluorine-containing greenhouse gases. This method is simple in process, has low energy consumption, and uses an adsorbent with high adsorption capacity and strong stability, enabling efficient capture of fluorine-containing greenhouse gases at room temperature and pressure.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for capturing fluorine-containing greenhouse gases includes the following steps: using 100–3000 h -1 Industrial exhaust gas containing fluorinated greenhouse gases is introduced at air velocity into a trap containing a modified adsorbent, wherein the fluorinated greenhouse gases include at least carbon tetrafluoride gas; the modified adsorbent adsorbs the fluorinated greenhouse gases in the incoming industrial exhaust gas at an adsorption temperature of 10–90°C, and adsorption stops when the concentration of carbon tetrafluoride in the outgoing industrial exhaust gas drops to 0.1–1000 ppm; the modified adsorbent is a metal cation modified molecular sieve.

[0012] In addition to carbon tetrafluoride, the fluorinated greenhouse gases also include at least one of C2F6, SF6, C3F8, CHF3, CH2F2, C4F6, C4F8, and NF3.

[0013] The industrial exhaust gas described in this invention can contain carbon tetrafluoride gas. Preferably, the industrial exhaust gas described in this invention is industrial exhaust gas containing fluorine-containing greenhouse gases emitted during the aluminum smelting process when the anode effect occurs, and also includes at least one of N2, O2, CO, CO2, HF, and SO2.

[0014] This invention can reduce the concentration of fluorine-containing greenhouse gases in industrial exhaust gases to 0.1–1000 ppm.

[0015] Specifically, online mass spectrometry is used to monitor the concentration of fluorinated greenhouse gases such as carbon tetrafluoride in the effluent industrial exhaust gas in real time. Adsorption is stopped when the concentration of fluorinated greenhouse gases such as carbon tetrafluoride decreases to a target value. The target value for the concentration of fluorinated greenhouse gases such as carbon tetrafluoride is typically 0.1–1000 ppm; preferably, adsorption is stopped when the concentration of fluorinated greenhouse gases such as carbon tetrafluoride is 0.1–100 ppm; more preferably, adsorption is stopped when the concentration of fluorinated greenhouse gases such as carbon tetrafluoride is 0.1–10 ppm.

[0016] In the method for capturing fluorinated greenhouse gases described in this invention, it is necessary to reasonably control the initial concentration of fluorinated greenhouse gases flowing into the industrial exhaust gas. If the initial concentration of fluorinated greenhouse gases is too high, it will cause the adsorbent to be overloaded, reducing the capture efficiency of the adsorbent for fluorinated greenhouse gases. If the initial concentration of fluorinated greenhouse gases is too low, it will result in a lower contact area between the fluorinated greenhouse gases and the adsorbent, which will also reduce the capture efficiency of the adsorbent for fluorinated greenhouse gases.

[0017] In the capture method of the present invention, the concentration of fluorinated greenhouse gas in the industrial exhaust gas is 0.01% to 5%. When the concentration of fluorinated greenhouse gas is greater than 5%, it can be diluted with an inert gas to reduce the concentration of fluorinated greenhouse gas to 0.01% to 5%; preferably, the concentration of fluorinated greenhouse gas is reduced to 0.1% to 0.5%.

[0018] Preferably, the adsorption temperature is 20–50°C, the adsorption pressure is 0.05–0.15 MPa, and the space velocity is 1000–2500 h⁻¹. -1 .

[0019] In the capture method of the present invention, the modified adsorbent is a molecular sieve modified with metal cations, wherein the metal cations are selected from Li + K + Cs + Cu 2+ Co 2+ Zn 2+ Ce 3+ Fe 3+ La 3+ At least one of the following: the molecular sieve is ZSM-5 molecular sieve with a silica-to-alumina ratio of 2.3 to 1000; preferably, the metal cation is selected from Li. + La 3+ At least one of the following, wherein the molecular sieve is a ZSM-5 molecular sieve with a silica-alumina ratio of 5 to 200.

[0020] The ZSM-5 molecular sieve is selected from at least one of Na-ZSM-5 molecular sieve and H-ZSM-5.

[0021] Unlike greenhouse gases such as CO2, fluorinated greenhouse gases such as carbon tetrafluoride have very stable CF bonds, resulting in weak interaction with the adsorbent surface. They are not prone to electron transfer to form chemical adsorption, and the adsorption process is mainly physical adsorption, with weak van der Waals forces playing a dominant role.

[0022] This invention reveals that the entry of metal cations into the molecular sieve framework introduces point charges, thereby enhancing electrostatic quadrupole and charge-induced dipole interactions within the framework. This is beneficial for separating gases with significant differences in quadrupole or dipole moments. The hydroxyl groups in the molecular sieve framework stabilize the metal cations, preventing their aggregation and forming metal-oxygen groups within the framework. The presence of these metal-oxygen groups induces a non-uniform electric field distribution around the group, resulting in strong quadrupole interactions with perfluorinated carbon (PFCC) gas molecules. Since PFCC gas molecules exhibit a negative surface potential, the high-charge-density metal cations entering the molecular sieve framework and forming metal-oxygen groups readily polarize PFCC gas molecules, enhancing the electrostatic interaction between the material and gas molecules. This strengthens the adsorption energy of PFCC and improves the adsorption performance of the molecular sieve material for PFCC gas molecules.

[0023] This invention has revealed an optimal value for the amount of metal cation doping in molecular sieves. Excessive metal cation doping leads to aggregation on the surface and within the framework of the molecular sieve, significantly reducing the activity of the metal cations compared to the monodisperse state, thereby affecting the adsorption performance of perfluorocarbons. Specifically, the metal cation content in the modified adsorbent is 0.01% to 5%; preferably, the metal cation content in the modified adsorbent is 0.5% to 2%.

[0024] Therefore, this invention enhances the adsorption capacity of perfluorinated carbon gas molecules by increasing the surface polarity of the molecular sieve and constructing a pore structure close to the size of perfluorinated carbon molecules, thereby enhancing the physical adsorption of perfluorinated carbon gas molecules on the adsorbent surface.

[0025] In the capture of fluorine-containing greenhouse gases, a modified adsorbent can be placed on a fixed bed. The fluorine-containing greenhouse gases diffuse slowly within the pores of the modified adsorbent, exhibit strong interaction forces, and are adsorbed in large quantities, thus becoming enriched in the fixed bed. Gases such as air have weak interaction forces with the adsorbent and diffuse quickly within the pores, resulting in low adsorption amounts.

[0026] The present invention also provides a method for preparing the modified adsorbent, the method comprising: activating ZSM-5 molecular sieve at 300-600℃ for 1-5 h, then adding it to a metal cation solution for cation exchange at an exchange temperature of 20-100℃ for 0.5-6 h, exchanging 1-15 times, followed by drying and calcination at an drying temperature of 100-180℃ for 1-30 h; calcination at an calcination temperature of 400-600℃ for 2-8 h; wherein the concentration of the metal cation solution is 0.01-10 mol / L, and the solid-liquid ratio during the exchange process is 1:5-1:50.

[0027] Preferably, the concentration of the metal cation solution is 0.5–2 mol / L, and the solid-liquid ratio during the exchange process is 1:10–1:20.

[0028] Preferably, the activation temperature is 450–550°C, the activation time is 2–4 h, the exchange temperature is 70–90°C, the exchange time is 1–3 h, the number of exchanges is 10–15, the drying temperature is 100–150°C, and the drying time is 5–15 h.

[0029] The modified adsorbent of this invention can be vacuum activated before use to further improve its performance in capturing fluorine-containing greenhouse gases. Specifically, the modified adsorbent is used in a 10-100 mesh form, and the activation treatment includes the following steps: the activation temperature is 100-400℃, the activation pressure is -0.01--0.1 MPa, the activation heating rate is 2-10℃ / min, and the activation time is 2-20 h.

[0030] Under normal circumstances, the modified adsorbent described in this invention can be desorbed by vacuuming and can be recycled after regeneration. Specifically, in the capture method described in this invention, when the concentration of fluorinated greenhouse gases such as carbon tetrafluoride in the outflowing industrial exhaust gas cannot be reduced to the target value, adsorption is stopped, and the pipeline is switched to a standby capture device containing the modified adsorbent. The adsorbent bed in the original capture device is then regenerated. The regeneration process includes the following steps: regeneration temperature of 100–400°C, regeneration pressure of -0.01–-0.1 MPa, and regeneration time of 0.5–3 hours.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. The capture method described in this invention has a simple process, low operating energy consumption, and can efficiently capture fluorinated greenhouse gases such as carbon tetrafluoride in industrial exhaust gas. It can be widely used for the capture and recovery of fluorinated greenhouse gases in industrial exhaust gas.

[0033] 2. The modified molecular sieve material of the present invention has a simple preparation process, is green and environmentally friendly, has a high adsorption capacity for fluorine-containing greenhouse gases such as carbon tetrafluoride, is chemically stable, is easy to regenerate, has good cycle stability, and is suitable for industrial application.

[0034] 3. The capture method described in this invention has wide applications and can be used under normal temperature and pressure conditions. Attached Figure Description

[0035] Appendix Figure 1 The adsorption breakthrough results of the modified adsorbent prepared for Example 1 on a 1% CF4 / N2 mixed gas. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0037] Preparation Example 1

[0038] First, a certain amount of Na-ZSM-5 molecular sieve was activated in a muffle furnace at 550℃ for 3 hours. Then, a 1 mol / L lithium chloride solution was prepared, and 2.12 g of lithium chloride was added to 50 g of deionized water. After the lithium chloride was completely dissolved, 5 g of Na-ZSM-5 molecular sieve (silicon-to-aluminum ratio = 25) was added to the lithium chloride solution for ion exchange. The stirring rate was 700 r / min, the exchange temperature was 80℃, and the exchange time was 4 hours. After the exchange was completed, the molecular sieve was filtered, washed, and dried at 120℃. The above operation was repeated 10 times. After the last exchange, the molecular sieve was filtered, washed, dried, and calcined at 550℃ for 3 hours with a heating rate of 5℃ / min. After calcination, the modified molecular sieve material for capturing fluorine-containing greenhouse gases was obtained, denoted as modified adsorbent 1.

[0039] The adsorption capacity of modified adsorbent 1 can be calculated using the following formula:

[0040]

[0041] Where V is the adsorption breakthrough capacity (mL / g), F is the gas flow rate (mL / min), t is the adsorption time (min), c is the concentration of carbon tetrafluoride (%), and m is the mass of adsorbent used (g).

[0042] During the capture process, online mass spectrometry was used to detect the concentration of carbon tetrafluoride in the effluent industrial exhaust gas in real time, and the adsorption breakthrough curve of carbon tetrafluoride was obtained, as shown in the figure. Figure 1 As shown, the carbon tetrafluoride adsorption breakthrough capacity of modified adsorbent 1 was calculated to be 0.6 mL / g.

[0043] Preparation Example 2

[0044] The preparation of Example 2 was carried out in the same manner as that of Example 1, except that the metal salt was lanthanum chloride. All other operations remained the same, and modified adsorbent 2 was obtained.

[0045] Preparation Example 3

[0046] The preparation of Example 3 was carried out in the same manner as that of Example 1, except that the concentration of the lithium chloride solution was 2 mol / L. All other operations remained unchanged, and the modified adsorbent 3 was obtained.

[0047] Preparation Example 4

[0048] The preparation of Example 4 was carried out in the same manner as that of Example 1, except that the silica-alumina ratio of the Na-ZSM-5 molecular sieve was 200. All other operations remained unchanged, and the modified adsorbent 4 was prepared.

[0049] Comparative Preparation Example 1

[0050] The operation of Comparative Preparation Example 1 is the same as that of Preparation Example 1, except that the metal salt is calcium chloride. All other operations remain unchanged, and Comparative Adsorbent 1 is prepared.

[0051] Example 1

[0052] Modified adsorbent 1 was compressed into tablets and sieved to obtain an adsorbent with a mesh size of 16-25. 2g of adsorbent was filled into the middle of a stainless steel tube with an inner diameter of 6mm and a length of 400mm. The adsorbent was activated at 300℃ and -0.1MPa for 5 hours. After the adsorbent bed temperature dropped to 25℃, it was activated at atmospheric pressure for 1800 hours. -1 Industrial exhaust gas, consisting of 0.3% carbon tetrafluoride, 0.1% hexafluoroethane, 0.3% carbon dioxide, 0.8% carbon monoxide, 77.9% nitrogen, and 20.6% oxygen, was introduced from the top of the fixed-bed trap at an air velocity of 25°C. After 2 minutes of adsorption, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas was analyzed by online mass spectrometry. The capture rate of modified adsorbent 1 on various gases in the inflowing industrial exhaust gas was calculated.

[0053] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 100-150 ppm. The capture rate of carbon tetrafluoride is 97.63%, the capture rate of hexafluoroethane is 95.83%, the capture rate of carbon dioxide is 85.01%, the capture rate of carbon monoxide is 73.74%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0054] Example 2

[0055] The operation of Example 2 is the same as that of Example 1, except that the adsorption temperature is 20°C, and other operations remain unchanged.

[0056] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 50-100 ppm. The capture rate of carbon tetrafluoride is 98.68%, the capture rate of hexafluoroethane is 97.55%, the capture rate of carbon dioxide is 86.74%, the capture rate of carbon monoxide is 74.63%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0057] Example 3

[0058] The operation of Example 3 is the same as that of Example 1, except that the adsorption temperature is 40°C, and other operations remain unchanged.

[0059] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 200-250 ppm. The capture rate of carbon tetrafluoride is 95.44%, the capture rate of hexafluoroethane is 92.32%, the capture rate of carbon dioxide is 81.43%, the capture rate of carbon monoxide is 70.11%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0060] Example 4

[0061] The operation of Example 4 is the same as that of Example 1, except that the airspeed is 1200 h. -1 Other operations remain unchanged.

[0062] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 50-100 ppm. The capture rate of carbon tetrafluoride is 98.29%, the capture rate of hexafluoroethane is 97.17%, the capture rate of carbon dioxide is 86.56%, the capture rate of carbon monoxide is 74.38%, the capture rate of nitrogen is 1.83%, and the capture rate of oxygen is 0.15%.

[0063] Example 5

[0064] The operation of Example 5 is the same as that of Example 1, except that the airspeed is 2500 h. -1 Other operations remain unchanged.

[0065] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 300-350 ppm. The capture rate of carbon tetrafluoride is 92.43%, the capture rate of hexafluoroethane is 90.48%, the capture rate of carbon dioxide is 80.33%, the capture rate of carbon monoxide is 69.42%, the capture rate of nitrogen is 1.81%, and the capture rate of oxygen is 0.14%.

[0066] Example 6

[0067] The operation of Example 6 is the same as that of Example 1, except that the composition of the industrial exhaust gas is 1.3% carbon tetrafluoride, 0.1% hexafluoroethane, 0.3% carbon dioxide, 0.8% carbon monoxide, 77.4% nitrogen, and 20.1% oxygen. All other operations remain unchanged.

[0068] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 100-150 ppm. The capture rate of carbon tetrafluoride is 96.84%, the capture rate of hexafluoroethane is 94.81%, the capture rate of carbon dioxide is 84.37%, the capture rate of carbon monoxide is 72.35%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0069] Example 7

[0070] The operation of Example 7 is the same as that of Example 1, except that the composition of the industrial exhaust gas is 3.3% carbon tetrafluoride, 0.1% hexafluoroethane, 0.3% carbon dioxide, 0.8% carbon monoxide, 76.9% nitrogen, and 19.6% oxygen. All other operations remain unchanged.

[0071] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 250-300 ppm. The capture rate of carbon tetrafluoride is 93.49%, the capture rate of hexafluoroethane is 92.58%, the capture rate of carbon dioxide is 83.89%, the capture rate of carbon monoxide is 72.07%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0072] Example 8

[0073] The operation of Example 8 is the same as that of Example 1, except that the composition of the industrial exhaust gas is 4.3% carbon tetrafluoride, 0.1% hexafluoroethane, 0.3% carbon dioxide, 0.8% carbon monoxide, 76.4% nitrogen, and 19.1% oxygen. All other operations remain unchanged.

[0074] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 350-400 ppm. The capture rate of carbon tetrafluoride is 90.76%, the capture rate of hexafluoroethane is 91.94%, the capture rate of carbon dioxide is 82.65%, the capture rate of carbon monoxide is 71.57%, the capture rate of nitrogen is 1.81%, and the capture rate of oxygen is 0.13%.

[0075] Example 9

[0076] The operation of Example 9 is the same as that of Example 1, except that the composition of the industrial exhaust gas is 0.3% carbon tetrafluoride, 1.1% hexafluoroethane, 0.3% carbon dioxide, 0.8% carbon monoxide, 77.4% nitrogen, and 20.1% oxygen. All other operations remain unchanged.

[0077] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 100-150 ppm. The capture rate of carbon tetrafluoride is 97.27%, the capture rate of hexafluoroethane is 95.46%, the capture rate of carbon dioxide is 84.89%, the capture rate of carbon monoxide is 73.22%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0078] Example 10

[0079] The operation of Example 10 is the same as that of Example 1, except that the adsorbent material used is modified adsorbent 2, and the other operations remain unchanged.

[0080] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 350-400 ppm. The capture rate of carbon tetrafluoride is 91.47%, the capture rate of hexafluoroethane is 88.35%, the capture rate of carbon dioxide is 75.54%, the capture rate of carbon monoxide is 64.79%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0081] Example 11

[0082] The operation of Example 11 is the same as that of Example 1, except that the adsorbent material used is modified adsorbent 3, and the other operations remain unchanged.

[0083] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 150-200 ppm. The capture rate of carbon tetrafluoride is 95.45%, the capture rate of hexafluoroethane is 94.67%, the capture rate of carbon dioxide is 83.97%, the capture rate of carbon monoxide is 71.44%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0084] Example 12

[0085] The operation of Example 12 is the same as that of Example 1, except that the adsorbent material used is modified adsorbent 4, and the other operations remain unchanged.

[0086] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 600-650 ppm, the capture rate of carbon tetrafluoride is 85.37%, the capture rate of hexafluoroethane is 80.98%, the capture rate of carbon dioxide is 70.86%, the capture rate of carbon monoxide is 62.61%, the capture rate of nitrogen is 1.80%, and the capture rate of oxygen is 0.11%.

[0087] Example 13

[0088] The operation of Example 13 is the same as that of Example 1, except that the analysis is performed 1 minute after adsorption, and all other operations remain the same.

[0089] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 1-50 ppm. The capture rate of carbon tetrafluoride is 99.86%, the capture rate of hexafluoroethane is 99.11%, the capture rate of carbon dioxide is 95.63%, the capture rate of carbon monoxide is 88.76%, the capture rate of nitrogen is 1.90%, and the capture rate of oxygen is 0.17%.

[0090] Example 14

[0091] The operation of Example 14 is the same as that of Example 1, except that: the adsorbent after adsorption saturation in Example 1 is regenerated and adsorbed a second time. The regeneration conditions are: regeneration temperature 300℃, regeneration pressure -0.1Mpa, regeneration time 1h, and other conditions remain unchanged.

[0092] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 100-150 ppm. The capture rate of carbon tetrafluoride is 97.32%, the capture rate of hexafluoroethane is 95.13%, the capture rate of carbon dioxide is 85.03%, the capture rate of carbon monoxide is 73.55%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0093] Comparative Example 1

[0094] The operation of Comparative Example 1 is the same as that of Example 1, except that the adsorbent material used is commercial ZSM-5 molecular sieve, and other operations remain unchanged.

[0095] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 1100-1150 ppm. The capture rate of carbon tetrafluoride is 71.89%, the capture rate of hexafluoroethane is 70.64%, the capture rate of carbon dioxide is 81.45%, the capture rate of carbon monoxide is 69.96%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0096] Comparative Example 2

[0097] The operation of Comparative Example 2 is the same as that of Example 1, except that the adsorbent material used is the commercial MIL-53(Al) metal-organic framework material, and all other operations remain unchanged.

[0098] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 2250-2300 ppm. The capture rate of carbon tetrafluoride is 43.91%, the capture rate of hexafluoroethane is 41.79%, the capture rate of carbon dioxide is 56.26%, the capture rate of carbon monoxide is 50.39%, the capture rate of nitrogen is 1.55%, and the capture rate of oxygen is 0.09%.

[0099] Comparative Example 3

[0100] The operation of Comparative Example 3 is the same as that of Example 1, except that the adsorption material used is commercial activated carbon, and other operations remain unchanged.

[0101] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 2150-2200 ppm. The capture rate of carbon tetrafluoride is 45.28%, the capture rate of hexafluoroethane is 44.36%, the capture rate of carbon dioxide is 57.44%, the capture rate of carbon monoxide is 55.61%, the capture rate of nitrogen is 1.62%, and the capture rate of oxygen is 0.13%.

[0102] Comparative Example 4

[0103] The operation of Comparative Example 4 is the same as that of Example 1, except that the adsorbent used is the control adsorbent 1, and all other operations remain unchanged.

[0104] According to the test and calculation, the content of fluorinated greenhouse gases in the outflowing industrial exhaust gas is 1400-1450 ppm. The capture rate of carbon tetrafluoride is 65.38%, the capture rate of hexafluoroethane is 63.24%, the capture rate of carbon dioxide is 80.13%, the capture rate of carbon monoxide is 65.34%, the capture rate of nitrogen is 1.82%, and the capture rate of oxygen is 0.14%.

[0105] As can be seen from Examples 1 to 14, the modified adsorbent described in this invention can achieve efficient capture of fluorine-containing greenhouse gases, especially carbon tetrafluoride, at room temperature and pressure. The modified adsorbent exhibits strong chemical stability, high adsorption capacity, high selectivity for carbon tetrafluoride, and stable regeneration performance, effectively removing fluorine-containing greenhouse gases from the exhaust gas emitted during aluminum smelting.

[0106] Comparative Examples 1 to 4 tested the adsorption performance of commercial ZSM-5 molecular sieve samples, commercial MIL-53(Al) samples, commercial activated carbon samples, and modified adsorbent 5 on fluorine-containing greenhouse gases under the above test conditions. The results showed that the above materials had poor adsorption effect on fluorine-containing greenhouse gases, and the concentration of fluorine-containing greenhouse gases in the gas after adsorption was greater than 1000 ppm.

Claims

1. A method for capturing fluorine-containing greenhouse gases, characterized in that: 100-3000h -1 Industrial exhaust gas containing fluorinated greenhouse gases, including at least carbon tetrafluoride, is introduced at air velocity into a trap containing a modified adsorbent. The modified adsorbent adsorbs the fluorinated greenhouse gases in the incoming industrial exhaust gas at an adsorption temperature of 10–90°C. Adsorption stops when the concentration of carbon tetrafluoride in the outgoing industrial exhaust gas drops to 0.1–1000 ppm. The modified adsorbent is a molecular sieve modified with metal cations selected from Li. + K + Cs + Cu 2+ Co 2+ Zn 2+ Ce 3+ Fe 3 + La 3+ At least one of the following, wherein the molecular sieve is a ZSM-5 molecular sieve with a silica-alumina ratio of 2.3 to 1000.

2. The capture method according to claim 1, characterized in that: The fluorinated greenhouse gas also includes at least one of C2F6, SF6, C3F8, CHF3, CH2F2, C4F6, C4F8, and NF3.

3. The capture method according to claim 1, characterized in that: The industrial exhaust gas also includes at least one of N2, O2, CO, CO2, HF, and SO2.

4. The capture method according to claim 1, characterized in that: The concentration of fluorinated greenhouse gases in the industrial exhaust gas is 0.01% to 5%; when the concentration of fluorinated greenhouse gases is greater than 5%, it can be diluted with an inert gas.

5. The capture method according to claim 1, characterized in that: The adsorption temperature is 20–50℃, the adsorption pressure is 0.05–0.15 MPa, and the space velocity is 1000–2500 h⁻¹. -1 .

6. The capture method according to claim 1, characterized in that: The modified adsorbent contains 0.01% to 5% metal cations.

7. The capture method according to claim 1, characterized in that: The preparation method of the modified adsorbent specifically includes the following steps: activating the ZSM-5 molecular sieve at 300-600℃ for 1-5 hours, then adding it to a metal cation solution for cation exchange at an exchange temperature of 20-100℃ and an exchange time of 5-480 minutes, repeating the exchange 1-15 times, followed by drying and calcination at an drying temperature of 100-180℃ and a drying time of 1-30 hours; calcination at an calcination temperature of 400-600℃ and a calcination time of 2-8 hours; the concentration of the metal cation solution is 0.01-10 mol / L, and the solid-liquid ratio during the exchange process is 1:5-1:50.

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