A method for preparing sulfur by using phosphomolybdic heteropoly acid salt modified ionic liquid

Abstract

A method for preparing sulfur by using phosphomolybdic heteropoly acid salt modified ionic liquid, comprising the following steps: (1) dissolving phosphomolybdic heteropoly acid salt in tetramethyl guanidine amino acid ionic liquid, and adding solvent to prepare phosphomolybdic heteropoly acid salt modified ionic liquid mixed absorption solution; (2) passing SO2-containing flue gas to obtain SO2-saturated adsorbed ionic liquid mixed absorption solution; (3) continuously passing H2S gas until saturated, heating the solution and keeping warm, then cooling to room temperature, and separating and filtering the obtained solid to obtain sulfur, and the liquid is phosphomolybdic heteropoly acid salt modified ionic liquid mixed absorption waste liquid. The application selects tetramethyl guanidine amino acid ionic liquid, which not only has high adsorption capacity for SO2, but also has high thermal stability, can reduce the decomposition rate of ionic liquid in the subsequent heating process, and is beneficial to the recovery of sulfur and the regeneration of ionic liquid.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling, and particularly relates to a method for preparing sulfur using phosphomolybdate heteropolyacid salt modified ionic liquid. Background Technology

[0002] Elemental sulfur is a raw material with extremely high industrial value, widely used in key manufacturing industries such as dyes, pesticides, sulfuric acid, and rubber. my country is a major consumer of elemental sulfur, consuming over ten million tons annually, but its sulfur supply is severely insufficient, resulting in a high dependence on imports. Simultaneously, during coal combustion and metal smelting, sulfur from coal or minerals primarily enters flue gas as SO2 and is emitted into the environment. my country's coal-fired power generation and metallurgical industries alone emit over five million tons of SO2 annually. Capturing SO2 from industrial flue gas and producing sulfur can not only reduce SO2 pollution emissions but also achieve the recovery and utilization of sulfur resources. Therefore, as an important raw material for sulfur production and a typical environmental pollutant, developing technologies for capturing SO2 and producing sulfur is of great significance.

[0003] Currently, SO2 treatment in flue gas mainly focuses on two directions: harmless treatment and resource utilization. For harmless treatment, dry, semi-dry, or wet technologies are mainly used to convert gaseous SO2 into solid or liquid sulfates, thereby purifying the SO2 in the flue gas, but this does not enable the resource utilization of sulfur. For resource utilization, catalytic oxidation or reduction methods are mainly used to prepare sulfuric acid or sulfur from SO2, but these methods require high SO2 concentrations in the flue gas. Therefore, the resource utilization of low-concentration SO2 has become an urgent problem to be solved.

[0004] Ionic liquids, due to their excellent chemical stability, thermal stability, and structural tunability, are widely used in gas separation, particularly suitable for the separation and enrichment of SO2. Currently, commonly used ionic liquids for capturing SO2 can be divided into two categories: conventional ionic liquids and functionalized ionic liquids. The cations in conventional ionic liquids generally do not contain functionalized groups, while the anions are mostly tetrafluoroborate anions, hexafluorophosphate anions, and halogens. The adsorption of SO2 by conventional ionic liquids is physisorption, showing a significant positive correlation with the partial pressure of SO2, thus making them unsuitable for treating low concentrations of SO2. Functionalized ionic liquids refer to ionic liquids containing specific functional groups; their cations or anions typically incorporate various functional groups such as amine and carboxyl groups, thereby giving them special properties. Among functionalized ionic liquids for SO2 absorption, guanidine ionic liquids synthesized using guanidine organic bases as cations have attracted considerable attention. Tetramethylguanidine lactate ionic liquid is the most widely studied guanidine ionic liquid. It can achieve efficient capture of low concentrations of SO2, and then enrich SO2 through heating desorption. However, there are still problems such as high energy consumption and poor stability of ionic liquid during the regeneration process. At the same time, sulfur products cannot be obtained directly.

[0005] Therefore, there is still a lack of an efficient and stable method for sulfur regeneration in low-concentration SO2 flue gas, which would provide important technical support for the high-value utilization of low-concentration SO2. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that existing regeneration methods cannot stably obtain sulfur products from low-concentration SO2 flue gas. In order to overcome the shortcomings and defects mentioned in the background art, a method for preparing sulfur using heteropoly acid salt modified ionic liquid is provided.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0008] A method for preparing sulfur using heteropolyacid salts modified ionic liquids mainly includes the following steps:

[0009] (1) Dissolve phosphomolybdic acid salt in tetramethylguanidine amino acid ionic liquid and add solvent to prepare phosphomolybdic acid salt modified ionic liquid mixed absorption solution;

[0010] (2) Pass SO2-containing flue gas into the phosphomolybdate-modified ionic liquid mixed absorbent solution described in step (1) to obtain an ionic liquid mixed absorbent solution with SO2 saturated adsorption.

[0011] (3) H2S gas is continuously introduced into the SO2-saturated adsorption phosphomolybdate-modified ionic liquid mixed absorption liquid obtained in step (2) until saturation. The solution is heated and kept warm, then cooled to room temperature. The solid obtained by separation and filtration is sulfur, and the liquid is the mixed absorption waste liquid of the polyacid salt modified ionic liquid.

[0012] Existing ionic liquids still have shortcomings in terms of absorption rate and absorption stability for SO2 in low-concentration SO2 flue gas. This application selects tetramethylguanidine amino acid ionic liquids, in which the amino acid groups can promote the absorption of acidic gases, and further modifies the tetramethylguanidine amino acid ionic liquids to improve their absorption rate of SO2 in low-concentration SO2 flue gas.

[0013] In step (1), phosphomolybdic acid heteropoly acid salt is dissolved in tetramethylguanidine amino acid ionic liquid to modify the ionic liquid system and prepare a mixed absorbent. In the composite system of the mixed absorbent, phosphomolybdic acid heteropoly acid plays a catalytic role, and tetramethylguanidine amino acid ionic liquid plays a role in absorbing acidic gases, which can better absorb SO2 in flue gas with low concentration of SO2.

[0014] The purpose of heating and maintaining the temperature in step (3) is to remove excess water from the mixed ionic liquid and to melt and precipitate the sulfur product. In the sulfur preparation process of this application, low concentration SO2 in the flue gas is absorbed by the ionic liquid. Then, under the catalytic condition of phosphomolybdic heteropolyacid, the absorbed SO2 and the introduced H2S rapidly form fine sulfur particles, which undergo a Claus reaction. By heating, the sulfur melts, agglomerates, and precipitates at the bottom of the mixed liquid. After condensation and separation, blocky sulfur products can be obtained.

[0015] Simultaneously, the heating process can volatilize the moisture and residual H2S produced by the Claus reaction, resulting in a pure phosphomolybdate heteropoly acid salt modified ionic liquid that can be used to absorb waste liquid. After air oxidation of the heteropoly acid, the heteropoly acid modified ionic liquid can be regenerated.

[0016] Preferably, the phosphomolybdate heteropolyacid salt is tetramethylguanidine phosphomolybdate, the tetramethylguanidine amino acid ionic liquid is tetramethylguanidine glutamic acid or tetramethylguanidine glycine ionic liquid, the solvent is dimethylformamide, and the mass ratio of the tetramethylguanidine amino acid ionic liquid, the phosphomolybdate heteropolyacid salt and the solvent is 1:0.03~0.08:0.8~1.6.

[0017] Tetramethylguanidine phosphomolybdate exhibits better system compatibility with tetramethylguanidine amino acid ionic liquids. In the heteropolyacid-modified ionic liquid mixed absorbent of the present invention, tetramethylguanidine glutamic acid or tetramethylguanidine glycine ionic liquids serve as SO2 absorbents, primarily capturing SO2. The amino acid groups and guanidine groups in the ionic liquids synergistically promote SO2 absorption, enhancing the SO2 capture effect. Tetramethylguanidine phosphomolybdate acts as a modifier catalyzing the Claus reaction between SO2 and H2S, primarily accelerating the rate of the liquid-phase Claus reaction at room temperature. Dimethylformamide solvent acts as a viscosity modifier for the ionic liquid, mainly reducing its viscosity and increasing the gas-liquid mass transfer rate.

[0018] Preferably, the modification of tetramethylguanidine amino acid ionic liquid with phosphomolybdic heteropoly acid in step (1) is specifically as follows: tetramethylguanidine phosphomolybdic acid is prepared by neutralization reaction of phosphomolybdic heteropoly acid with tetramethylguanidine, and then tetramethylguanidine phosphomolybdic acid is dissolved in tetramethylguanidine amino acid ionic liquid to form a modified tetramethylguanidine heteropoly acid mixed solution.

[0019] In the modification process, the heteropolyacid is first neutralized with tetramethylguanidine to form tetramethylguanidine heteropolyacid salt. Then, the tetramethylguanidine heteropolyacid salt is dissolved in tetramethylguanidine amino ionic liquid to form a mixed solution of tetramethylguanidine heteropolyacid salt.

[0020] Preferably, in step (2), the volume concentration of SO2 in the flue gas containing SO2 is 0.8-30%; and in step (3), the volume concentration of H2S gas is above 50%.

[0021] In existing technologies, the volume concentration of SO2 in flue gas absorbed by ionic liquids is mostly above 5%. However, the modified ionic liquid in this application can achieve the absorption of low-concentration SO2 due to the synergistic effect of guanidine and amino groups, as well as the system modification and catalytic effect of phosphomolybdate heteropolyacid salt.

[0022] Preferably, the heating temperature in step (3) is 120~180℃ and the holding time is 20~60min.

[0023] Preferably, air is introduced into the phosphomolybdate heteropolyacid salt modified ionic liquid mixed absorption waste liquid obtained in step (3), and the mixture is stirred to obtain a regenerated phosphomolybdate heteropolyacid salt modified ionic liquid mixed absorption liquid, which is then returned to step (2) for recycling.

[0024] This application directly introduces air to oxidize and regenerate the waste liquid of phosphomolybdic heteropolyacid. The air oxidizes the molybdenum in the phosphomolybdic heteropolyacid waste liquid to a higher valence state, thereby improving the catalytic activity of the phosphomolybdic heteropolyacid and achieving its regeneration. This regeneration scheme is low-cost, simple to operate, and the regenerated liquid can be reused, making it highly practical.

[0025] Preferably, the air flow rate is 0.6~1.5L / min, and the ventilation time is 10~45min.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) This application selects tetramethylguanidine amino acid ionic liquid. Due to the synergistic effect of guanidine and amino groups, it not only has a high adsorption capacity for SO2, enabling the regeneration of sulfur in low-concentration SO2 flue gas, but also has high thermal stability, which can reduce the decomposition rate of ionic liquid during subsequent heating, thus facilitating the recovery of sulfur and the regeneration of ionic liquid.

[0028] (2) The tetramethylguanidine amino acid ionic liquid is modified with phosphomolybdic heteropolyacid salt. The solid phosphomolybdic heteropolyacid salt is dissolved in the tetramethylguanidine amino acid ionic liquid to form a modified ionic liquid absorbent system. In this system, it plays a catalytic role in the Claus reaction, which can greatly promote the conversion efficiency of SO2 to sulfur. The conversion efficiency of the tetramethylguanidine amino acid ionic liquid alone is not high, only about 53%. However, the conversion rate of SO2 to sulfur by the phosphomolybdic heteropolyacid salt modified tetramethylguanidine amino acid ionic liquid of this application can reach more than 95% at room temperature and pressure, realizing the efficient and low-cost preparation of sulfur. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 For example, [TMG][PMo] are different in Example 1 12 O 40 [Figure showing the effect of modifier addition amount on SO2 conversion efficiency in tetramethylguanidinylglycine (a) ionic liquid system;]

[0031] Figure 2 For example, [TMG][PMo] are different in Example 1 12 O 40 [Figure showing the effect of modifier addition amount on SO2 conversion efficiency in tetramethylguanidine glutamic acid (b) ionic liquid system;]

[0032] Figure 3 This is a graph showing the effect of different solvent addition amounts on SO2 conversion efficiency in Example 2;

[0033] Figure 4-7 The graph shows the effect of different sulfur separation temperatures on the recycling performance of ionic liquids in Example 3. Detailed Implementation

[0034] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0037] The flue gas components used in the embodiments and comparative examples of this application are shown in Table 1 below:

[0038] Table 1. Main components of low-concentration SO2 flue gas (volume fraction %)

[0039]

[0040] Example 1:

[0041] This embodiment mainly examines different [TMG][PMo] 12 O 40 The effect of modifier addition amount on SO2 conversion efficiency.

[0042] A method for preparing sulfur using heteropolyacid salts modified ionic liquids, with ([TMG][PMo) 12 O 40 Heteropolyacid salts were used as modifiers, and tetramethylguanidinyl glycinate ([TMG][Ala]) and tetramethylguanidinyl glutamate ([TMG][Gla]) were used as ionic liquid absorbents, respectively.

[0043] (1) In each experiment, weigh 2.5 g of [TMG][Ala] or [TMG][Gla] ionic liquid, add 3 g of dimethylformamide (DMF), and then add different masses of [TMG][PMo 12 O 40 ], [TMG][PMo 12 O 40 Adding amount as follows Figure 1 As shown, the mixture is homogeneous to form a heteropolyacid salt modified ionic liquid mixed absorption solution;

[0044] (2) Add different amounts of [TMG][PMo] as configured 12 O 40 The mixed absorbent of heteropolyacid salt modified ionic liquid was placed in a glass reaction tube and placed in a water bath at 30°C. Simulated flue gas was then introduced until the weight of the absorbent remained constant.

[0045] (3) H2S gas with a volume fraction of 60% was introduced into the adsorption-saturated heteropolyacid acid modified ionic liquid mixed absorption solution at a flow rate of 0.05 L / min for 30 min; after the reaction, the heteropolyacid acid modified ionic liquid mixed absorption solution was heated to 150℃ and kept at that temperature for 30 min, then naturally cooled to room temperature, filtered to obtain sulfur product, washed, dried and weighed, and the conversion rate of SO2 was calculated based on the SO2 absorption amount and sulfur mass, and the results are as follows. Figure 1 As shown.

[0046] from Figure 1 As can be seen from [TMG][PMo] 12 O 40 With increasing modifier dosage, the SO2 conversion efficiency in the [TMG][Ala] ionic liquid system gradually increases. When the modifier dosage reaches 0.075g (ionic liquid to modifier mass ratio of 1:0.03), the SO2 conversion efficiency can reach over 94%. Further increasing the modifier dosage does not significantly change the SO2 conversion rate. When the modifier dosage exceeds 0.2g (ionic liquid to modifier mass ratio of 1:0.08), the SO2 conversion efficiency shows a slight decreasing trend, which may be due to excessive modifier reducing SO2 absorption. Figure 2 As can be seen from the data, for the [TMG][Gla] ionic liquid system, the change in SO2 conversion efficiency due to the amount of modifier added follows a similar pattern. Taking all factors into consideration, the mass ratio of ionic liquid to modifier is determined to be 1:(0.03~0.08).

[0047] Example 2:

[0048] This embodiment mainly examines the effect of different solvent addition amounts on SO2 conversion efficiency.

[0049] A method for preparing sulfur using heteropolyacid salts modified ionic liquids, with ([TMG][PMo) 12 O 40 Heteropolyacid salts were used as modifiers, and tetramethylguanidinyl glycinate ([TMG][Ala]) was used as ionic liquid absorbent.

[0050] Weigh 2.5g of [TMG][Ala] ionic liquid and add [TMG][PMo] 12 O 40 0.15g of modifier was added, and then the above mixture was added to a certain amount of DMF solution to prepare a heteropolyacid salt modified ionic liquid mixed absorbent. The heteropolyacid salt modified ionic liquid mixed absorbent was used as the SO2 absorbent, and H2S was introduced to prepare sulfur. The entire reaction process was the same as in Example 1. The effect of solvent addition on SO2 conversion efficiency is shown in [the table below]. Figure 3 .

[0051] As the amount of DMF solvent added increases, the viscosity of the mixed ionic liquid gradually decreases, while the SO2 conversion rate gradually increases. This indicates that the addition of solvent is beneficial for promoting the gas-liquid mass transfer rate, thereby promoting the conversion of SO2 to sulfur. When the amount of solvent added exceeds 4g (the mass ratio of ionic liquid to solvent is 1:1.6), the SO2 conversion efficiency shows a slight decreasing trend with the increase of DMF addition, which may be due to the decrease in the concentration of effective components in the mixed solution, thus reducing the reaction rate. Taking all factors into consideration, the mass ratio of ionic liquid to solvent is determined to be 1:(0.8~1.6).

[0052] Example 3:

[0053] This embodiment mainly investigates the effect of sulfur separation temperature on the recycling performance of ionic liquids.

[0054] A method for preparing sulfur using heteropolyacid salts modified ionic liquids, with ([TMG][PMo) 12 O 40 Heteropolyacid salts were used as modifiers, and tetramethylguanidinyl glycinate ([TMG][Ala]) was used as ionic liquid absorbent.

[0055] Weigh 2.5g of [TMG][Ala] ionic liquid and add [TMG][PMo] 12 O 40 0.15g of modifier was added to the above mixture, which was then dissolved in 3g of DMF to prepare a heteropolyacid salt modified ionic liquid mixed absorbent. This heteropolyacid salt modified ionic liquid mixed absorbent was used as the SO2 absorbent, and H2S was introduced to prepare sulfur. The reaction conditions for saturated adsorption and H2S introduction were the same as in Example 1. After the reaction was complete, the ionic liquid was heated to 120℃, 150℃, 180℃, and 210℃ respectively, held at these temperatures for 30 min, and then naturally cooled to room temperature. The sulfur product was obtained by filtration, washing, drying, and weighing. The SO2 conversion rate for the first utilization was calculated based on the SO2 absorption amount and the sulfur mass. The ionic liquid obtained after sulfur separation was stirred at a rate of 100 r / min, and air was introduced into it at a flow rate of 1 L / min for 30 min. After the aeration was completed, regenerated ionic liquid was obtained, and the process of SO2 absorption and sulfur preparation was repeated four times. The SO2 conversion rate during the second to fifth cycles was obtained, and the results are shown in [Figure number missing]. Figure 4-7 .

[0056] Figure 4 This is a schematic diagram illustrating the recycling performance of ionic liquids at 120℃. Figure 5 This is a schematic diagram illustrating the recycling performance of ionic liquids at 150℃. Figure 6 This is a schematic diagram illustrating the recycling performance of ionic liquids at 180℃. Figure 7 This is a schematic diagram of the recycling performance of ionic liquids at 210℃.

[0057] from Figure 4-7 The results show that [TMG][Ala]+ [TMG][PMo] 12 O 40 The DMF ionic liquid system, within a relatively wide heating temperature range (120~180℃), maintained an SO2 to sulfur conversion efficiency of over 90% after 5 cycles. However, when the heating temperature increased to 210℃, the ionic liquid's recycling performance decreased significantly with the number of cycles; after 5 cycles, the SO2 conversion rate remained at only around 53%, indicating that excessively high heating temperatures are detrimental to the recycling of the ionic liquid. While high temperatures promote the volatilization of residual H2S and H2O and the precipitation of sulfur in the ionic liquid, they also lead to the decomposition of the ionic liquid, thus reducing the conversion efficiency. Therefore, the sulfur separation temperature range of 120~180℃ was selected.

[0058] Comparative Example 1:

[0059] This comparative example shows the performance of preparing sulfur using conventional ionic liquids alone.

[0060] Preparation of ionic liquid absorbents: Four ions were selected as absorbents: 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Hmim][Tf2N]), tetramethylguanidine lactate ([TMG][Lac]), and tetramethylguanidine glycinate ([TMG][Ala]). In each experiment, 2.5 g of the ionic liquid was weighed and 3 g of dimethylformamide (DMF) was added, and the mixture was thoroughly mixed to form the ionic liquid absorbent.

[0061] The process of SO2 conversion to sulfur preparation: The prepared absorbent was placed in a glass reaction tube and placed in a water bath at 30°C. Simulated flue gas was then introduced into the absorbent at a rate of 0.1 L / min until the weight of the absorbent remained constant, and the amount of SO2 absorbed was calculated. H2S (H2S volume fraction of 60% and N2 volume fraction of 40%) was introduced into the SO2-saturated ionic liquid at a flow rate of 0.05 L / min for 30 min. After the reaction, the ionic liquid was heated to 150°C and held at that temperature for 30 min, then allowed to cool naturally to room temperature. The sulfur product was obtained by filtration, washed, dried, and weighed. The conversion rate of SO2 was calculated based on the amount of SO2 absorbed and the mass of sulfur. The results are shown in Table 2.

[0062] Table 2 SO2 conversion rate of sulfur prepared by different ionic liquids

[0063]

[0064] As shown in Table 2, the conventional [Bmim][BF4] and [Hmim][Tf2N] ionic liquids are basically unable to convert SO2 to sulfur. However, the amino-functionalized tetramethylguanidine ionic liquids ([TMG][Lac] and [TMG][Ala]) have a conversion efficiency of approximately 46-53% for SO2 to sulfur. This indicates that functionalized ionic liquids can achieve sulfur preparation, possibly because the amino or carboxyl groups in the cations and anions promote the Claus reaction. However, the tetramethylguanidine ionic liquids alone have low conversion efficiency for SO2 and cannot achieve efficient utilization of SO2.

[0065] Comparative Example 2:

[0066] This comparative example shows the performance of conventional ionic liquid recycling alone.

[0067] Preparation of ionic liquid absorbents: Four ions were selected as absorbents: 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Hmim][Tf2N]), tetramethylguanidine lactate ([TMG][Lac]), and tetramethylguanidine glycinate ([TMG][Ala]). In each experiment, 2.5 g of the ionic liquid was weighed and 3 g of dimethylformamide (DMF) was added, and the mixture was thoroughly mixed to form the ionic liquid absorbent.

[0068] SO2 conversion to sulfur recycling process: The prepared absorbent is placed in a glass reaction tube and then placed in a water bath at 30°C. Simulated flue gas is then introduced into the absorbent at a rate of 0.1 L / min until the weight of the absorbent remains constant, and the amount of SO2 absorbed is calculated. H2S (H2S volume fraction of 60% and N2 volume fraction of 40%) is introduced into the SO2-saturated ionic liquid at a flow rate of 0.05 L / min for 30 min. After the reaction, the ionic liquid is heated to 150°C and held at that temperature for 30 min, then allowed to cool naturally to room temperature. The sulfur product is obtained by filtration, washing, drying, and weighing. The conversion rate of SO2 used in the first application is calculated based on the amount of SO2 absorbed and the mass of sulfur. The ionic liquid obtained after sulfur separation was stirred at a rate of 100 r / min, and air was introduced into it at a flow rate of 1 L / min for 30 min. After the aeration was completed, the regenerated ionic liquid was obtained, and the process of SO2 absorption and sulfur preparation was repeated 4 times. The conversion rate of SO2 during the second to fifth cycles was obtained, and the results are shown in Table 3.

[0069] Table 3. SO2 conversion rate of sulfur prepared by different ionic liquids as a function of the number of recycling cycles.

[0070]

[0071] As shown in Table 3, the [Bmim][BF4] ionic liquids were not investigated for their recycling performance because they cannot convert SO2 to sulfur. The [Hmim][Tf2N] ionic liquids showed SO2 conversion rates not exceeding 1% during recycling, indicating that sulfur production was essentially impossible. The [TMG][Lac] ionic liquid showed a significant decreasing trend in SO2 conversion rate with recycling, while the [TMG][Ala] ionic liquid showed almost no significant decrease in SO2 conversion rate after 5 cycles. These results indicate that the [TMG][Ala] ionic liquids have good recycling performance, which may be due to their high structural stability.

[0072] Comparative Example 3:

[0073] This comparative example compares the performance of different ionic liquid absorbents modified with tetramethylguanidine phosphomolybdate on SO2 conversion efficiency.

[0074] Preparation of ionic liquid absorbents: Four ions were selected as absorbents: 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Hmim][Tf2N]), tetramethylguanidine lactate ([TMG][Lac]), and tetramethylguanidine glycinate ([TMG][Ala]). In each experiment, 2.5 g of the ionic liquid was weighed, and 3 g of dimethylformamide (DMF) and 0.01 g of [TMG][PMo] were added. 12 O 40 ]), mix evenly to form an ionic liquid absorbent.

[0075] The process of SO2 conversion to sulfur preparation: The prepared absorbent is placed in a glass reaction tube and placed in a water bath at 30°C. Then, simulated flue gas is passed into the absorbent at a rate of 0.1 L / min until the weight of the absorbent remains constant, and the amount of SO2 absorbed is calculated. H2S (H2S volume fraction of 60% and N2 volume fraction of 40%) is passed into the SO2-saturated ionic liquid at a flow rate of 0.05 L / min for 30 min. After the reaction, the ionic liquid is heated to 150°C and kept at that temperature for 30 min, then naturally cooled to room temperature. The sulfur product is obtained by filtration, washing, drying, and weighing. The conversion rate of SO2 is calculated based on the amount of SO2 absorbed and the mass of sulfur. The results are shown in Table 4.

[0076] Table 4. SO2 Conversion Rate of Different Ionic Liquid Absorbents in Sulfur Preparation

[0077]

[0078] As shown in Table 4, among the four selected ionic liquids, methylguanidinyl glycinate ([TMG][Ala]) has the best SO2 conversion rate, which indicates that the amino acid groups and phosphomolybdic heteropolyacids in the ionic liquid have a synergistic promoting effect on SO2 conversion.

[0079] Comparative Example 4:

[0080] This comparative example shows the performance of different modifiers on SO2 conversion rate in tetramethylguanidine ionic liquids.

[0081] Preparation of ionic liquid absorbents: Sodium sulfonate, sodium salicylate, diethylene glycol ether, and tetramethylguanidine phosphomolybdic acid ([TMG][PMo)) were selected respectively. 12 O 40 Four materials were used as modifiers, with tetramethylguanidinyl glycinate ([TMG][Ala]) as the ionic liquid absorbent. In each experiment, 2.5g of [TMG][Ala] ionic liquid was weighed, 3g of dimethylformamide (DMF) was added, followed by 0.15g of the modifier. The mixture was then thoroughly mixed to form the ionic liquid absorbent.

[0082] The process of SO2 conversion to sulfur preparation: The prepared absorbent was placed in a glass reaction tube and placed in a water bath at 30°C. Simulated flue gas was then introduced into the absorbent at a rate of 0.1 L / min until the weight of the absorbent remained constant, and the amount of SO2 absorbed was calculated. H2S (H2S volume fraction of 60% and N2 volume fraction of 40%) was introduced into the SO2-saturated ionic liquid at a flow rate of 0.05 L / min for 30 min. After the reaction, the ionic liquid was heated to 150°C and kept at that temperature for 30 min, then allowed to cool naturally to room temperature. The sulfur product was obtained by filtration, washed, dried, and weighed. The conversion rate of SO2 was calculated based on the amount of SO2 absorbed and the mass of sulfur. The results are shown in Table 5.

[0083] Table 5. Effect of different modifiers added to tetramethylguanidine glycidate ionic liquid on SO2 conversion rate.

[0084]

[0085] As shown in Table 5, adding modifiers is beneficial to improving the conversion rate of SO2. In comparison, sodium sulfonate, sodium salicylate, and ethylene diether, tetramethylguanidine phosphomolybdic acid showed the most significant improvement in the reaction of SO2 and H2S to produce sulfur, reaching approximately 94.2%. This indicates that tetramethylguanidine phosphomolybdic acid is an excellent liquid-phase Claus reaction modifier.

Claims

1. A method for preparing sulfur using phosphomolybdic acid molybdenum heteropolyacid salt-modified ionic liquid, characterized in that, It mainly includes the following steps: (1) Dissolve phosphomolybdate heteropolyacid salt in tetramethylguanidine amino acid ionic liquid and add solvent to prepare phosphomolybdate heteropolyacid salt modified ionic liquid mixed absorption solution; wherein, the phosphomolybdate heteropolyacid salt is tetramethylguanidine phosphomolybdate salt; (2) Pass SO2-containing flue gas into the phosphomolybdate-modified ionic liquid mixed absorbent solution described in step (1) to obtain an ionic liquid mixed absorbent solution with SO2 saturated adsorption. (3) H2S gas is continuously introduced into the SO2 saturated adsorption phosphomolybdate modified ionic liquid mixed absorption liquid obtained in step (2) until saturation, the solution is heated and kept warm, and then cooled to room temperature. The solid obtained by separation and filtration is sulfur, and the liquid is phosphomolybdate modified ionic liquid mixed absorption waste liquid.

2. The method as described in claim 1, characterized in that, The tetramethylguanidine amino acid ionic liquid is a tetramethylguanidine glutamic acid or a tetramethylguanidine glycine ionic liquid, the solvent is dimethylformamide, and the mass ratio of the tetramethylguanidine amino acid ionic liquid, phosphomolybdate heteropolyacid salt and solvent is 1:0.03~0.08:0.8~1.

6.

3. The method as described in claim 2, characterized in that, In step (1), the modification of tetramethylguanidine amino acid ionic liquid with phosphomolybdic heteropoly acid is specifically carried out by: preparing tetramethylguanidine phosphomolybdic acid by neutralization reaction of phosphomolybdic acid with tetramethylguanidine, and then dissolving tetramethylguanidine phosphomolybdic acid in tetramethylguanidine amino acid ionic liquid to form a modified tetramethylguanidine heteropoly acid mixed solution.

4. The method as described in claim 1 or 2, characterized in that, In step (2), the volume concentration of SO2 in the flue gas containing SO2 is 0.8-30%; in step (3), the volume concentration of H2S gas is above 50%.

5. The method as described in claim 4, characterized in that, The step (3) of continuously introducing H2S gas until saturation specifically means: continuously introducing H2S gas until the mass of the solution no longer increases, and then stopping the introduction of H2S gas.

6. The method as described in claim 1 or 2, characterized in that, The heating temperature in step (3) is 120~180℃ and the holding time is 20~60min.

7. The method as described in claim 1 or 2, characterized in that, Air is introduced into the phosphomolybdenum heteropoly acid salt modified ionic liquid mixed absorption waste liquid obtained in step (3), and stirred to obtain a regenerated phosphomolybdenum heteropoly acid salt modified ionic liquid mixed absorption liquid. The regenerated phosphomolybdenum heteropoly acid salt modified ionic liquid mixed absorption liquid is returned to step (2) for recycling.

8. The method as described in claim 7, characterized in that, The air flow rate is 0.6~1.5L / min, and the ventilation time is 10~45min.

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