Highly selective absorbent for sulfur dioxide in industrial mixed waste gas

Abstract

This invention relates to a highly selective absorbent for sulfur dioxide in industrial mixed waste gas, comprising: a metal ion and an organic ligand connected together; wherein the metal ion is a four-coordinate metal ion or a six-coordinate metal ion; and wherein the organic ligand contains a zimidazole group. The beneficial effects of this invention are: it can reduce the lower limit of SO2 absorption to the ppb level, achieving ultra-low emissions; and it can efficiently absorb SO2 with a wide SO2 / CO2 ratio range, making it more suitable for the constantly changing operating conditions in actual industrial applications.

Description

Technical Field

[0001] This invention relates to the field of industrial hazardous waste treatment, and more specifically, to a highly selective absorbent for sulfur dioxide in mixed industrial waste gas. Background Technology

[0002] As an air pollutant, excessive SO2 emissions can easily lead to acid rain and acid fog that corrodes buildings, and can also cause physical and mental harm to humans. Therefore, strictly controlling sulfur dioxide emissions is an urgent issue that concerns the vital interests of humankind.

[0003] Currently, the main desulfurization methods commonly used in industry include limestone / gypsum desulfurization, magnesium desulfurization, ammonia desulfurization, and seawater desulfurization. While these desulfurization processes are all applied industrially, they each suffer from problems such as insufficient absorption efficiency, solid waste generation, and high energy consumption. Furthermore, all of these methods use alkaline absorbents, and industrial gas mixtures containing SO2 typically contain competing CO2 molecules. Traditional absorbent solvents struggle to achieve high-capacity and high-selectivity absorption and separation of SO2 / CO2.

[0004] Patent CN101274204B discloses an absorbent for absorbing sulfur dioxide in mixed industrial waste gas with an absorption efficiency of over 99%. However, the absorbent formulation contains organic compounds such as amines, which pose pollution and corrosion risks. In addition, it is insufficient for absorbing mixed waste gas with SO2 concentrations below 35 ppm. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a highly selective absorbent for sulfur dioxide in industrial mixed waste gas.

[0006] In a first aspect, a highly selective absorbent for sulfur dioxide in industrial mixed waste gas is provided, comprising: a metal ion and an organic ligand connected together; wherein the metal ion is a tetracoordinate metal ion or a hexacoordinate metal ion; and wherein the organic ligand is provided with a zimidazole group.

[0007] Preferably, the metal ion is Al. 3+ Fe 3+ Cu 2+ Co 3+ Pt 2+ Ni 4+ Zn 2+ and Cr 3+ Any one of them.

[0008] Preferably, the metal ion is Al. 3+ .

[0009] Preferably, the highly selective sulfur dioxide absorbent is a metal-organic framework material with a pore size of 3-10 nm.

[0010] In a second aspect, a method for synthesizing the organic ligand as described in the first aspect is provided, for synthesizing the organic ligand as claimed in claim 1, comprising: introducing a zimidazole group into biphenyl dicarboxylic acid via a Suzuki coupling reaction; the general structural formula of the organic ligand is:

[0011]

[0012] Wherein, groups R1, R2, R3, R4, R5, R6, R7 and R8 may be the same or different, and each is independently selected from the following substituents: H, saturated or unsaturated C1-C4 alkyl, C1-C4 alkoxy, halogen, carboxyl, hydroxymethyl, amino, cyano, halo-C1-C4 alkyl, halo-C1-C4 alkoxy, nitro, unsubstituted or substituted furan, thiophene, phenyl, pyridine.

[0013] Thirdly, a method for synthesizing a highly selective absorbent for sulfur dioxide in industrial mixed waste gas as described in the first aspect is provided, comprising:

[0014] S1. Thoroughly mix the dissolved organic ligand with the aqueous solution of the metal ion salt;

[0015] S2. Construct a highly selective sulfur dioxide absorbent using a hydrothermal method with the mixture.

[0016] Preferably, in S1, the molar ratio of organic ligand to metal ion is 1:(1-5).

[0017] Preferably, in S1, the molar ratio of organic ligand to metal ion is 1:(2-3).

[0018] Preferably, in S2, the hydrothermal temperature is 150-350℃.

[0019] Preferably, in S2, the hydrothermal temperature is 200-300℃.

[0020] Fourthly, an application of a highly selective absorbent for sulfur dioxide in industrial mixed waste gas as described in the first aspect is provided, wherein the composition of the industrial mixed waste gas ranges from 35 to 12,000 ppm SO2, CO2 accounts for 0.1% to 12%, NO accounts for 1% to 5%, and the remainder is N2.

[0021] The beneficial effects of this invention are:

[0022] (1) The highly selective absorbent for sulfur dioxide in industrial mixed waste gas provided by the present invention is adsorbed at low temperature and desorbed at high temperature. It is regenerable and has low energy consumption.

[0023] (2) The highly selective absorbent for sulfur dioxide in industrial mixed waste gas provided by the present invention can efficiently absorb SO2 with a wide SO2 / CO2 ratio range, and is more suitable for the constantly changing working conditions in actual industrial applications.

[0024] (3) The high-selectivity absorbent for sulfur dioxide in industrial mixed waste gas provided by the present invention can achieve a selectivity and absorption rate of over 99%, thus avoiding waste of absorbent.

[0025] (4) The highly selective absorbent for sulfur dioxide in industrial mixed waste gas provided by the present invention can reduce the lower limit of SO2 absorption to the ppb level, thereby achieving ultra-low emissions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the molecular structures of the zimidazole group, SO2, and CO2.

[0027] Figure 2 A schematic diagram illustrating the construction of metal-organic framework materials;

[0028] Figure 3 A schematic diagram for separating high-purity CO2;

[0029] Figure 4 A schematic diagram for separating high-purity SO2;

[0030] Figure 5 This is a schematic diagram of the synthesis of compounds S1 and S2;

[0031] Figure 6 This is a schematic diagram of the proton NMR spectrum of compound S2.

[0032] Figure 7 This is a schematic diagram of the absorption rate curves of BYIMD-Al-MOFs at different times.

[0033] Figure 8 This is a schematic diagram of another absorption rate curve of BYIMD-Al-MOFs at different times;

[0034] Figure 9 A schematic diagram of the pilot-scale experimental platform for sulfur dioxide absorbent;

[0035] Explanation of reference numerals in the attached diagram: Absorption tower 1, Desorption tower 2, Vacuum pump 3. Detailed Implementation

[0036] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0037] Example 1:

[0038] With the increasing severity of environmental problems, global emission standards for sulfur dioxide are becoming more stringent. Therefore, focusing on the absorption limit of absorbents is extremely important. Researching and developing novel green and efficient absorbents to achieve efficient SO2 / CO2 separation and sulfur resource recovery is of great significance. To this end, this invention provides a highly selective absorbent for sulfur dioxide in industrial mixed waste gas, which, compared to existing sulfur dioxide absorbents, can reduce the absorption limit of SO2 to the ppb level.

[0039] Metal-organic frameworks (MOFs) are porous materials with unique topological structures formed through self-assembly, using metal ions as central or connecting points and organic ligands as bridging structures. Compared to more mature technologies like molecular sieves, MOFs, as an emerging porous material, offer advantages such as large specific surface area, high porosity, diverse structures, and more regular pores, thus possessing excellent gas adsorption and storage potential. This invention, based on a selected metal ion, artificially selects the configuration and functional groups of the organic ligands according to different adsorption target molecules. It also allows for the use of metal ions with different coordination numbers and coordination forms, provided the organic ligands are selected. Existing experimental results show that the adsorption capacity of MOFs without the introduction of functional groups mainly depends on the pore size. Smaller pore sizes are suitable for gas adsorption but lack selectivity, relying primarily on physisorption. Larger pore sizes make it almost impossible to capture gas molecules through simple physisorption. Therefore, this invention introduces functional groups that can selectively adsorb polar gases onto a larger pore structure to achieve highly efficient and selective absorption of SO2 gas.

[0040] The combination of large-pore structure with specific functional groups can ensure sufficient gas molecule throughput and improve gas adsorption efficiency per unit time. On the other hand, the introduction of specific groups can ensure the gas throughput while also taking into account the directional adsorption of target components. In addition, this strategy can also enable a unit adsorbent material to have a larger SO2 saturation adsorption capacity, reduce the material regeneration frequency, and obtain higher economic benefits.

[0041] like Figure 1As shown, sulfur atoms possess unpaired lone pairs of electrons, giving SO2 a "V"-shaped molecular structure. This structure exhibits high polarity, making it readily approach electron-deficient conjugated systems. Other common gases, such as CO2 and N2, are nonpolar molecules with a linear structure. The presence of polar "C=N" bonds makes imidazole a strong electron-withdrawing group with significant electron deficiency. Furthermore, the conjugated structure of gemiimidazole has four polar "C=N" bonds, making it even easier to adsorb nearby polar molecules with lone pairs of electrons through dipole-dipole interactions. When this structure forms a metal-organic framework (MOF), desorption can be rapidly achieved through heating to obtain pure SO2. Therefore, this invention introduces the gemiimidazole group into organic ligands to form MOF absorbents with large pore sizes and the ability to efficiently and selectively adsorb sulfur dioxide.

[0042] Specifically, such as Figure 2 As shown, this invention introduces a zimidazole group into the middle of biphenyl dicarboxylic acid via a Suzuki coupling reaction, and then uses a six-coordinate metal ion (Al) 3+ or Fe 3+ By connecting the pores, the metal-organic framework material BYIMD-Al-MOFs with a pore size of 4-5 nm can be constructed in high yield using a hydrothermal method.

[0043] After synthesis, the material is cooled to room temperature, followed by filtration, washing, and vacuum activation. XRD powder diffraction is then performed to confirm its structure before use. Next, as... Figure 3 As shown, a mixture of SO2 and CO2 was used as the experimental subject. The prepared absorbent was used in the experiment in the form of solid powder or slurry. First, the mixed gas was allowed to pass through the inlet of the absorption tower and come into full contact with the absorbent for a certain period of time. When the gas mixture passed through the pores, SO2 was fully adsorbed while CO2 was not adsorbed and passed through the pores smoothly. The exhaust gas was collected at the outlet to obtain high-purity CO2.

[0044] like Figure 4 As shown, the absorbent circulates back and forth between the absorption tower and the desorption tower to ensure continuous absorption and separation through reuse of the absorbent. The absorbent enters the desorption tower via a circulation pump and pipeline, and is then evenly sprayed through a spray device at the top of the desorption tower. The desorption tower is equipped with a heater to heat the absorbent sprayed from top to bottom (85℃~120℃). The SO2 gas desorbed due to the increased temperature enters the top gas pipeline, is cooled and pressurized by a heat exchanger, and then enters the SO2 storage tank. The regenerated absorbent is then returned to the top of the absorption tower by the circulation pump and evenly sprayed again by the spray device to complete the adsorption of SO2 in the intake gas.

[0045] The above-mentioned sulfur dioxide absorbent has the following characteristics:

[0046] 1) First, an organic ligand is obtained by introducing an imidazole group into the middle of biphenyl dicarboxylic acid using the Suzuki coupling reaction. Then, the organic ligand solution and the metal ion solution are mixed, and the sulfur dioxide absorbent material is obtained by hydrothermal synthesis.

[0047] 2) Sulfur dioxide molecules with lone pairs of electrons adsorbed nearby through dipole-dipole interactions.

[0048] 3) The synthesized sulfur dioxide absorbent material has a pore size of 3-10 nm and a specific surface area of ​​600-1000 m². 3 / g.

[0049] 4) It has advantages such as high selectivity, large absorption capacity, low regeneration energy consumption, and applicability to industrial waste gas mixtures with trace amounts of SO2.

[0050] In summary, the sulfur dioxide absorbent provided by this invention establishes a pilot-scale experimental platform for treating mixed waste gases of different concentrations. It selectively absorbs SO2 while simultaneously recovering high-purity SO2, thus achieving waste gas utilization. It achieves a separation efficiency of over 99% under varying SO2 concentrations and a wide SO2 / CO2 mixing ratio, further reducing the lower limit of SO2 absorption to the ppb level.

[0051] Example 2:

[0052] like Figure 5 As shown, the preparation of BYIMD-Al-MOFs includes the following steps:

[0053] Step 1) Synthesis of compound S1: 4-Bromobenzoic acid (4.4 g, 22.5 mmol), pinacol diboronic acid ester (6.9 g, 27 mmol), K2CO3 (6.6 g, 47.5 mmol), and Pd(PPh3)4 (650 mg) were weighed and dissolved in 80 mL of DMF in a 250 mL round-bottom flask. Nitrogen gas was purged for 30 minutes, the system was sealed, and the mixture was vigorously stirred at 358 K for 24 h. After cooling to room temperature, the mixture was poured into 250 mL of deionized water. Approximately 100 mL of dichloromethane was used for extraction three times consecutively. The organic phase was collected and dried over anhydrous sodium sulfate. The solvent was then removed by rotary evaporation, and the mixture was purified by column chromatography (EA / PE = 1:6) to obtain S1 (5.13 g, 92%). 1 HNMR (400MHz, CDCl3): δ=7.84 (d, J=7.6Hz, 2H), 7.35 (d, J=7.6Hz, 2H), 1.56 (s, 12H).

[0054] Step 2) Synthesis of compound S2: S1 (4.2 g, 17 mmol), p-bromoimidazole (1.9 g, 7 mmol), K2CO3 (3.1 g, 36.5 mmol), and Pd(PPh3)4 (330 mg) were weighed and dissolved in 50 mL of THF. 10 mL of water was added, and the mixture was placed in a 150 mL round-bottom flask. Nitrogen gas was purged for 30 minutes, the system was sealed, and the mixture was vigorously stirred at 353 K for 24 h. After cooling to room temperature, the mixture was poured into 250 mL of deionized water. Approximately 100 mL of dichloromethane was used for extraction three times consecutively. The organic phase was collected and dried over anhydrous sodium sulfate. The solvent was then removed by rotary evaporation, and the mixture was purified by column chromatography (EA / PE = 1:3) to obtain the desired product. Figure 6 S2 (1.35g, 56%) is shown. 1 HNMR (400MHz, CDCl3): δ=7.92 (d, J=8.4Hz, 4H), 7.66 (d, J=8.4Hz, 4H).

[0055] Step 3) Synthesis of BYIMD-Al-MOFs: Weigh 2.2g S2 into 15ml ethanol and stir until completely dissolved; weigh 1.4g Al2(SO4)3·18H2O and dissolve in 15ml deionized water and stir until completely dissolved; mix the two solutions and stir for 30min until homogeneous, then transfer to a 50ml stainless steel reactor and react at 160℃ for 24h. After the reaction is complete, cool naturally to room temperature and filter. Wash three times each with distilled water and anhydrous ethanol. After drying the sample, place it in a 150℃ vacuum drying oven for 12h to obtain BYIMD-Al-MOFs.

[0056] Example 3:

[0057] In the preparation of BYIMD-Cu-MOFs, the preparation steps of the organic ligands are the same as in Example 2, and will not be repeated here. In addition, 1.8 g of S2 was weighed into 15 ml of ethanol and stirred until completely dissolved; 6.3 g of Cu(NO3)2·3H2O was weighed into 15 ml of deionized water and stirred until completely dissolved; the two solutions were mixed and stirred for 30 min until homogeneous, and then transferred to a 50 ml stainless steel reactor and reacted at 160 °C for 24 h. After the reaction was complete, the mixture was naturally cooled to room temperature and filtered. The sample was washed three times each with distilled water and anhydrous ethanol. After drying, the sample was placed in a vacuum drying oven at 150 °C for 12 h to obtain BYIMD-Cu-MOFs.

[0058] Example 4:

[0059] In the preparation of BYIMD-Fe-MOFs, the preparation steps of the organic ligands are the same as in Example 2, and will not be repeated here. In addition, 1.9 g of S2 was weighed into 15 ml of ethanol and stirred until completely dissolved; 0.5 g of FeCl3·6H2O was weighed and dissolved in 15 ml of deionized water and stirred until completely dissolved; the two solutions were mixed and stirred for 30 min until homogeneous, then transferred to a 50 ml stainless steel reactor and reacted at 160 °C for 24 h. After the reaction was complete, the mixture was naturally cooled to room temperature and filtered. The samples were washed three times each with distilled water and anhydrous ethanol. After drying, the samples were activated in a vacuum drying oven at 150 °C for 12 h to obtain BYIMD-Fe-MOFs.

[0060] Example 5:

[0061] This invention provides, for example Figure 9 The pilot-scale experimental platform for sulfur dioxide absorbent shown consists of an absorption tower 1 and a desorption tower 2.

[0062] The operation process of the pilot-scale experimental platform is as follows: After the raw gas is pressure regulated and stabilized, the flow rate is controlled by a mass flow meter or float flow meter. It is heated to a certain temperature by a preheater and then enters absorption tower 1. Adsorbent (slurry or solid adsorption bed) is added to absorption tower 1. The raw gas is fully mixed with the adsorbent in absorption tower 1 by bubbling or a gas distributor to absorb SO2 in the mixed flue gas. The slurry is discharged from the top of the tower or sent to a flue gas analyzer. The collected adsorbent slurry is sent to the desorption tower by a plunger metering pump at a certain flow rate. It is desorbed by heating and / or depressurization. The desorbed adsorbent slurry is circulated to the top of the absorption tower by a plunger metering pump and participates in SO2 absorption in absorption tower 1 again by spraying. The exhaust gas discharged from desorption tower 2 is vented or sent to a flue gas analyzer for analysis. The venting and detection of absorption tower 1 and desorption tower 2 are switched by a four-way valve. Vent valves are set at the bottom of absorption tower 1 and desorption tower 2 respectively for venting adsorbent slurry and venting bubbles.

[0063] The performance of the absorbent was evaluated using the pilot-scale platform provided by this invention. The specific calculation formula is as follows:

[0064]

[0065] The absorbent formulation used in this embodiment is as follows: the prepared BYIMD-Al-MOFs powder to be used is mixed with deionized water at a mass ratio of 1:10, and then the pH of the system is adjusted to 4-5 with dilute hydrochloric acid.

[0066] The simulated industrial mixed waste gas composition was: 12% SO2, CO2 percentages of 12% / 8% / 4% / 1% / 0.1%, and the remainder N2. The absorption rate curves of BYIMD-Al-MOFs at different time points were tested, as shown below. Figure 7 As shown.

[0067] The absorbent absorbs sulfur dioxide very quickly, reaching over 90% within five minutes. The final absorption test data are shown in Table 1.

[0068] Table 1

[0069] <![CDATA[CO2 volume fraction]]> <![CDATA[Final SO2 content ppm]]> Selective 12% 0.91 99.0 8% 0.87 99.1 4% 0.75 99.3 1% 0.56 99.4 0.1% 0.49 99.9

[0070] After passing through the absorbent of this invention, the SO2 content is reduced to below 1 ppm. Under different carbon dioxide partial pressure conditions, the absorption selectivity is above 99%, indicating that the absorbent has a wide range of operating conditions and can reduce the SO2 concentration in the mixed waste gas to a low level.

[0071] Example 6:

[0072] Using the same pilot-scale experimental platform as in Example 5 above, the composition of the simulated industrial mixed waste gas was: 12% SO2, 12% CO2, and the remainder N2. The SO2 absorption rate and selectivity of three absorbents—BYIMD-Al-MOFs, BYIMD-Cu-MOFs, and BYIMD-Fe-MOFs—were tested at an eight-minute absorption time. The results are shown in Table 2.

[0073] Table 2

[0074] Types of absorbents <![CDATA[SO2 absorption rate %]]> Selective BYIMD-Al-MOFs 95.5 99.0 BYIMD-Cu-MOFs 84.3 88.1 BYIMD-Fe-MOFs 73.5 76.5

[0075] Example 7:

[0076] The absorbent formulation used in this embodiment is the same as that in Example 5, and will not be described again.

[0077] The simulated industrial mixed waste gas composition is as follows: flow velocity is 3 Nm. 3 / h, 500 ppm SO2, CO2 percentages of 12% / 8% / 4% / 1% / 0.1%, and the remainder N2. The absorption rate curves of BYIMD-Al-MOFs at different times were tested as follows: Figure 8 As shown.

[0078] The absorbent absorbs sulfur dioxide very quickly, reaching over 90% within five minutes. The final absorption test data are shown in Table 3.

[0079] Table 3

[0080] <![CDATA[CO2 volume fraction]]> <![CDATA[Final SO2 content in ppm]]> Selective 12% 0.75 99.4 8% 0.67 99.6 4% 0.55 99.5 1% 0.47 99.8 0.1% 0.32 99.9

[0081] After passing through the absorbent of this invention, the SO2 content is reduced to below 1 ppm. Under different carbon dioxide partial pressure conditions, the absorption selectivity is above 99%, indicating that the absorbent has a wide range of operating conditions and can reduce the SO2 concentration in the mixed waste gas to a low level.

[0082] Example 8:

[0083] To further illustrate the high selectivity of the absorbent designed in this invention for SO2, the following experimental conditions were designed:

[0084] The absorbent formulation used in this embodiment is the same as that in Example 5, and will not be described again.

[0085] The simulated industrial mixed waste gas composition is as follows: flow velocity is 3 Nm. 3 / h, 500 / 250 / 50 / 35 ppm SO2, CO2 accounts for 12%, NO accounts for 1%, and the remainder is N2.

[0086] Similarly, the experimental data obtained through the pilot-scale platform are shown in Table 4:

[0087] Table 4

[0088] <![CDATA[SO2 volume fraction ppm]]> <![CDATA[Final SO2 content ppm]]> Selective 500 0.67 99.3 250 0.43 99.4 50 0.35 99.5 35 0.21 99.9

[0089] The results show that the absorbent designed in this invention can still maintain a high SO2 absorption rate, a low absorption limit, and high selectivity in the presence of NO.

Claims

1. A highly selective absorbent for sulfur dioxide in industrial mixed waste gas, characterized in that, include: A metal ion and an organic ligand connected together; the metal ion is a four-coordinate metal ion or a six-coordinate metal ion; The organic ligand contains a zimidazole group; A method for synthesizing organic ligands includes: introducing a zimidazole group into biphenyl dicarboxylic acid via a suzuki coupling reaction; the general structural formula of the organic ligand is: Wherein, groups R1, R2, R3, R4, R5, R6, R7, and R8 are H; the metal ion is Al. 3+ Fe 3+ Cu 2+ The highly selective sulfur dioxide absorbent is a metal-organic framework material with a pore size of 3-10 nm.

2. A method for synthesizing a highly selective absorbent for sulfur dioxide in industrial mixed waste gas as described in claim 1, characterized in that, include: S1. Thoroughly mix the dissolved organic ligand with the aqueous solution of the metal ion salt; S2. Construct a highly selective sulfur dioxide absorbent using a hydrothermal method with the mixture.

3. The method for synthesizing a highly selective absorbent for sulfur dioxide in industrial mixed waste gas according to claim 2, characterized in that, In S1, the molar ratio of organic ligands to metal ions is 1:(1-5).

4. The method for synthesizing a highly selective absorbent for sulfur dioxide in industrial mixed waste gas according to claim 3, characterized in that, In S2, the hydrothermal temperature is 150-350℃.

5. The application of a highly selective absorbent for sulfur dioxide in industrial mixed waste gas as described in claim 1, characterized in that, The composition range of industrial mixed waste gas is: 35-12000 ppm SO2, CO2 accounting for 0.1%-12%, NO accounting for 1%-5%, and the remainder being N2.

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