A method for preparing sulfur by using an amide-modified guanidine-based aqueous deep eutectic solvent

Abstract

The present application belongs to the field of valuable resource recovery, and discloses a method for preparing sulfur by using acrylamide modified guanidine-based aqueous deep eutectic solvent: acrylamide modified guanidine-based ionic liquid and water are mixed to prepare an aqueous deep eutectic solvent absorbent; the aqueous deep eutectic solvent absorbent is used to absorb sulfur dioxide gas to obtain an aqueous absorbent rich in SO2; H2S gas is introduced into the aqueous absorbent rich in SO2 while stirring, so that the Claus reaction occurs; the reaction product is heated to above the melting point of sulfur, and then cooled and separated to obtain separated sulfur and regenerated absorbent. The present application can overcome the low conversion rate of the Claus reaction in the traditional aqueous absorbent system, and the method for preparing sulfur by using acrylamide modified guanidine-based aqueous deep eutectic solvent can increase the conversion rate of SO2 to 95.37%, greatly improving the conversion rate of sulfur.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of valuable resource recovery, and particularly relates to a method for preparing sulfur by using an acetoamide modified guanidino-containing aqueous eutectic solvent. BACKGROUND

[0002] A large amount of sulfur dioxide (SO2) flue gas is generated in the high-temperature smelting process of non-ferrous metal sulfide minerals, and excessive emission of SO2 will cause a large amount of acid rain, which will harm buildings and trees, and endanger human health. At the same time, SO2 is also an important raw material for chemical production, which can be used to produce common chemical products such as sulfuric acid and sulfur. Therefore, the green and efficient treatment of SO2 in non-ferrous smelting flue gas has become the focus of flue gas purification.

[0003] Traditional flue gas desulfurization methods include calcium method, ammonia method, seawater desulfurization, etc. Although they are widely used, they still have problems such as low utilization rate of by-products, difficulty in regenerating absorbents, and serious secondary pollution. Therefore, it is urgent to develop a new desulfurization method of SO2 adsorbent and realize cyclic regeneration. Ionic liquids (ILs) are composed of organic cations and organic (inorganic) anions, and are a kind of salt in a molten state near room temperature. They have the characteristics of being able to be constructed by anions and cations, being green and pollution-free, having low vapor pressure, and being able to be recycled after desorption. They are an extremely efficient desulfurizer. The main desulfurization principle of ILs is to use their functional groups and chemical bonds to physically and chemically absorb SO2 gas, thereby capturing SO2.

[0004] At present, after the recovery of SO2 by ionic liquids, the main use is to prepare sulfuric acid. However, sulfuric acid inevitably has a high maintenance cost and is highly dangerous during storage and transportation. Therefore, converting SO2 into stable substances can effectively solve such problems. With the aid of liquid-phase Claus reaction, converting SO2 into elemental sulfur is an innovative research to realize the conversion and recovery of SO2. It not only solves the problem of low utilization rate of SO2 after absorption, but also reduces the difficulty of storing and transporting acid or gas prepared from desorbed SO2. Moreover, the desorbed ILs can be recycled, which maximizes the cost input from a macro perspective. Most ionic liquids have high viscosity. Adding water to the absorbent not only improves the flowability of ionic liquids and accelerates the mass transfer of the reaction, but also reduces the use cost of the absorbent. However, in the current research, the participation of water will greatly reduce the conversion rate of the liquid-phase Claus reaction. Traditional aqueous absorbents are not suitable for preparing sulfur. The patent document with the publication number CN109876601A discloses a method for converting SO2 into sulfur by coupling the Claus reaction in ionic liquids. The SO2 conversion rate can reach 96% in a system without water by using ethanolamine lactate. However, the SO2 conversion rate is not high in a system containing 30-50wt% water. Therefore, it is urgent to find a method to improve the Claus conversion rate of aqueous ionic liquids. SUMMARY

[0005] The technical problem solved by the present application is to overcome the deficiencies and defects mentioned in the above background art, and to provide a method for preparing sulfur by using acetamide modified guanidine-based aqueous deep eutectic solvent.

[0006] To solve the above technical problems, the technical solution provided by the present application is:

[0007] A method for preparing sulfur by using acetamide modified guanidine-based aqueous deep eutectic solvent, comprising the following steps:

[0008] (1) mixing acetamide modified guanidine-based ionic liquid and water to prepare an aqueous deep eutectic solvent absorbent;

[0009] (2) using the aqueous deep eutectic solvent absorbent obtained in step (1) to absorb sulfur dioxide gas to obtain an SO2-rich aqueous absorbent;

[0010] (3) passing H2S gas into the SO2-rich aqueous absorbent obtained in step (2) while stirring to make it undergo the Claus reaction;

[0011] (4) heating the reaction product obtained after step (3) to above the sulfur melting point, then cooling and separating to obtain separated sulfur and regenerated absorbent. In this step, the sulfur is liquefied and agglomerated by heating to the sulfur melting point, and after cooling, the sulfur is separated from the absorbent, and the regenerated absorbent is obtained again.

[0012] The above method for preparing sulfur by using acetamide modified guanidine-based aqueous deep eutectic solvent, preferably, the mass content of water in the aqueous deep eutectic solvent absorbent is 30-70%.

[0013] The above method for preparing sulfur by using acetamide modified guanidine-based aqueous deep eutectic solvent, preferably, in step (3), the pressure of the H2S gas is 0.05-0.25 MPa.

[0014] The above method for preparing sulfur by using acetamide modified guanidine-based aqueous deep eutectic solvent, preferably, in step (3), the reaction temperature is 30-80℃, and the time is 10-90 min.

[0015] The above method for preparing sulfur by using acetamide modified guanidine-based aqueous deep eutectic solvent, preferably, the aqueous deep eutectic solvent absorbent is prepared by the following preparation method:

[0016] At 50-80℃, add acetamide (AA) to tetramethyl guanidine acetate ([TMG]Ac), heat and stir for more than 0.5h, then prepare an aqueous deep eutectic solvent absorbent ([TMG]Ac-AA) with water.

[0017] Preferably, the molar ratio of the tetramethyl guanidine acetate and the acetamide is 3: (1-9).

[0018] Preferably, the tetramethyl guanidine acetate is prepared by the following preparation method: taking equal molar amounts of 1, 1, 3, 3-tetramethyl guanidine and acetic acid respectively dissolved in anhydrous ethanol, the obtained solutions are respectively added to a three-necked flask and a constant pressure funnel, the constant pressure funnel is opened to make the 1, 1, 3, 3-tetramethyl guanidine and acetic acid react, after the reaction is completed, water and organic solvents are removed by a rotary evaporator, and the product is dried to obtain the tetramethyl guanidine acetate.

[0019] Preferably, the reaction is carried out under a cold water bath condition, and the temperature of the cold water bath is 10-20 DEG C.

[0020] The main principle of the present application is that after the absorbent captures SO2, a certain pressure of H2S is injected into the absorbent containing SO2 to make the SO2 converted into valuable resource sulfur by the Claus reaction, realizing the high-value recycling of SO2, and the Claus reaction equation is: SO2+2H2S=3S+2H2O. When the absorbent contains a large amount of water, the SO2 exists in three substances (H2SO3>HSO3 - >SO3 2- ) in the aqueous solution, and the SO3 2- does not react with H2S. The lower the pH of the absorbent, the closer the S (IV) species and proportion to the left, which is beneficial to the conversion rate. The SO2 conversion rate increases with the decrease of the pH in the system, but the increase of the acidity of the system will reduce the SO2 absorption amount. In order to keep the SO2 absorption amount and conversion rate of the aqueous system at a high level, the tetramethyl guanidine acetate is modified by adding acetamide, so as to achieve the purpose of high absorption and high conversion. The deep eutectic solvent obtained by mixing the acetamide and the tetramethyl guanidine acetate makes the absorbed SO2 mainly exist in the form of hydrogen bond in the aqueous absorbent due to the strong hydrogen bond effect between the deep eutectic solvent and SO2, the acetamide modified absorbent has low viscosity and is suitable for reaction mass transfer, and the SO2 captured by the aqueous absorbent can be efficiently converted into sulfur, and the absorbed SO2 will not be reduced after the modification.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The present application can overcome the low Claus conversion rate of the traditional absorbent aqueous system, and the method for preparing sulfur by modifying the guanidine-based aqueous deep eutectic solvent with acetamide can increase the SO2 conversion rate to 95.37%, which greatly improves the conversion rate of sulfur.

[0023] (2) The acetamide modified guanidine group containing aqueous deep eutectic solvent adopted by the present application is an ideal solvent for capturing acid gas, which is similar to the properties of ionic liquid and is obtained by simply mixing two components; the synthesis steps are simple, the cost is low, and most of them are biodegradable, and have a high SO2 absorption amount for SO2.

[0024] (3) The acetamide modified guanidine group containing aqueous deep eutectic solvent adopted by the present application can be reused, realizing the green recycling use of the absorbent. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the influence of different water contents of tetramethyl guanidine acetate in Comparative Example 1 on the SO2 conversion efficiency.

[0026] Figure 2 It is the influence of different molar mixing ratios of tetramethyl guanidine acetate and acetamide in Example 1 on the SO2 conversion efficiency of the aqueous absorbent.

[0027] Figure 3 It is the influence of different H2S pressures on the SO2 conversion efficiency in Example 2.

[0028] Figure 4 It is the influence of different water contents on the SO2 conversion efficiency in Example 3.

[0029] Figure 5 It is the influence of different Claus reaction temperatures on the SO2 conversion efficiency in Example 4.

[0030] Figure 6 It is the influence of different Claus reaction times on the SO2 conversion efficiency in Example 5. DETAILED DESCRIPTION

[0031] In order to facilitate the understanding of the present application, the present application will be described in more detail and in a more comprehensive and detailed manner below in combination with the drawings of the specification and the preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all the professional terms used below have the same meaning as generally understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing the specific embodiments and are not intended to limit the protection scope of the present application.

[0033] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0034] Comparative Example 1:

[0035] The comparative example mainly investigates the influence of water content of ordinary different tetramethyl guanidine acetate on SO2 conversion efficiency, and the specific steps are as follows:

[0036] (1) Take tetramethyl guanidine acetate to prepare water-containing absorbent with water content of 0%, 30%, 50% and 70wt%, respectively, and carry out subsequent parallel test. Then take 5g of the water-containing absorbent into a 25ml glass pressure-resistant tube, place it in a 30℃ water bath, and pass 50ml·min -1 of pure SO2 gas stream into the absorbent, and continue for 1h to obtain the absorbent after absorbing SO2, and record the change of mass before and after the absorption of the absorbent with an electronic balance.

[0037] (2) Add a stirring rotor to the glass pressure-resistant tube containing the absorbent after absorbing SO2 obtained in step (1), place the pressure-resistant tube in a water bath, and set the water bath temperature to 30℃. In order to ensure sufficient reaction, the H2S pressure needs to be excessive, and the H2S pressure is controlled to be 0.2MPa through a pressure gauge, the valve is opened to let H2S contact the absorbent after absorbing SO2, and the speed of the rotor is controlled to be 200rpm, and the reaction is carried out for 1.5h.

[0038] (3) Because sulfur has the characteristics of stickiness and loose porosity, it is easy to block in industrial production process, and it is difficult to separate by flushing, so it is urgent to develop a separation method suitable for industrial application. Based on the physical properties of low melting point (119℃) of sulfur and high stability of ionic liquid, combined with the huge heat released by Claus reaction, the method of heating separation is adopted, the mixture obtained in step (2) is heated to 120℃, the sulfur is melted into liquid droplets and precipitated at the bottom of the reactor, and after cooling, the sulfur and ionic liquid are directly separated, the SO2 conversion rate is calculated according to the change of SO2 and the actual weight of sulfur, and the influence of ordinary water-containing tetramethyl guanidine acetate on SO2 conversion efficiency is shown in Figure 1 .

[0039] From Figure 1 it can be seen that when the water content of ordinary tetramethyl guanidine acetate absorbent system is 0%, 30%, 50% and 70wt%, the SO2 conversion rate is 94.58%, 78.64%, 74.51% and 73.81% respectively. From the experimental results, it can be seen that when the water content of ordinary tetramethyl guanidine acetate absorbent increases, the SO2 conversion rate will gradually decrease. The water content of tetramethyl guanidine acetate absorbent is not conducive to the Claus reaction, which leads to the decrease of SO2 conversion rate.

[0040] Example 1:

[0041] This example mainly investigates the influence of different molar mixing ratio of tetramethyl guanidine acetate and acetamide modification on SO2 conversion efficiency, and the specific steps are as follows:

[0042] (1) Take equal molar amounts of tetramethyl guanidine and acetic acid and dissolve them in an appropriate amount of anhydrous ethanol, respectively. Add the obtained tetramethyl guanidine solution and acetic acid solution to a three-necked flask and a constant pressure funnel, respectively. Open the constant pressure funnel to make it react. The reaction is carried out under the condition of a cold water bath (15℃). After the reaction, remove water and organic solvents by a rotary evaporator. Dry the final product at 60℃ under vacuum for 48h to remove water, and obtain tetramethyl guanidine acetate ([TMG]Ac). Then, at 80℃, add different molar amounts of acetamide (AA) (molar ratios are 3:0, 3:1, 2:1, 1:1, 1:2, 1:3) to [TMG]Ac to carry out parallel tests. Heat and stir for 1h to obtain [TMG]Ac-AA absorbent. Then, prepare the absorbent with a water content of 50wt% by mixing with water. Take 5g of the water-containing absorbent into a 25mL glass pressure-resistant tube, and place it in a 30℃ water bath. Pass a 50ml·min -1 of pure SO2 gas stream into the absorbent for 1h to obtain the absorbent after SO2 adsorption. Record the change in mass of the absorbent before and after absorption by an electronic balance.

[0043] (2) Add a stirring rotor to the glass pressure-resistant tube containing the SO2-containing absorbent, and place the pressure-resistant tube in a water bath. Set the water bath temperature to 30℃. To ensure sufficient reaction, the H2S pressure needs to be excessive. Control the H2S pressure to be 0.2MPa by a pressure gauge, open the valve to let H2S contact the SO2-absorbed absorbent, and control the stirring rotor speed to be 200rpm. React for 1.5h.

[0044] (3) Heat the mixture obtained in step (2) to 120℃ to make sulfur melt into liquid droplets and precipitate at the bottom of the reactor. After cooling, separate the sulfur and ionic liquid directly. According to the change in SO2 and the actual weight of the obtained sulfur, calculate the SO2 conversion rate. The effect of different molar mixing ratios of tetramethyl guanidine and acetamide on SO2 conversion efficiency is shown in Figure 2 .

[0045] From Figure 2It can be seen that the Claus conversion rates of the synthesized deep eutectic water absorbent [TMG]Ac-AA are significantly higher than those of the [TMG]Ac water absorbent. With increasing acetamide content, the SO2 conversion rate increases significantly, and the highest SO2 conversion rate (95.37%) is achieved when the molar ratio of [TMG]Ac to AA is 1:1. In contrast, the original [TMG]Ac water absorbent has a conversion rate of only 74.51%. The addition of acetamide increases the Claus conversion rate of the [TMG]Ac water absorbent by nearly 20%, possibly because the synthesized deep eutectic solvent [TMG]Ac-AA forms strong intramolecular hydrogen bonds with SO2, resulting in a higher interaction energy between DES and SO2 than that of the [TMG]Ac absorption process. When the molar ratio of tetramethylguanidine acetate to acetamide exceeds 1:1, the SO2 conversion rate decreases with further increases in acetamide content. This may be because the increased alkalinity of the system with the addition of large amounts of acetamide leads to a portion of the absorbed sulfur dioxide being converted to SO3. 2- It exists in the form of SO3. 2- It is difficult for SO2 to react with H2S to form elemental sulfur, thus reducing the SO2 conversion rate.

[0046] Example 2:

[0047] This embodiment mainly examines the effect of different H2S pressures on SO2 conversion efficiency. The specific process is as follows:

[0048] (1) Weigh 5g of the acetamide-modified absorbent [TMG]Ac-AA prepared in Example 1 with the optimal molar ratio of [TMG]Ac and AA of 1:1 and 5g of H2O into a beaker to prepare an absorbent with a water content of 50wt%. Take 5 portions of 5g of the water-containing absorbent and conduct parallel tests in 25mL glass pressure-resistant tubes, place them in a 30℃ water bath, and add 50ml·min -1 Pure SO2 gas was introduced into the absorbent, and after 1 hour, the absorbent with SO2 adsorbed was obtained. The change in mass of the absorbent before and after absorption was recorded using an electronic balance.

[0049] (2) Add a stirring rotor to a glass pressure-resistant tube containing SO2 absorbent, place the tube in a water bath, and set the water temperature to 30℃. Control the H2S pressure to 0.05, 0.10, 0.15, 0.20, and 0.25 MPa using a pressure gauge, open the valve to allow H2S to contact the SO2-absorbing absorbent, and control the stirring speed to 200 rpm to allow the reaction to proceed for 1.5 hours. The effect of different H2S pressures on SO2 conversion efficiency is shown in the figure. Figure 3 As shown.

[0050] from Figure 3It can be seen that when the hydrogen sulfide pressure is 0.05, 0.10, 0.15, 0.20, 0.25 MPa, the SO2 conversion rates are 64.12%, 78.53%, 97.95%, 97.36%, and 95.87%, respectively. The experimental results show that when the hydrogen sulfide pressure is less than 0.15 MPa, the conversion rate increases significantly with the increase of the pressure; when the hydrogen sulfide pressure is greater than 0.15 MPa, the conversion rate hardly changes with the increase of the pressure, and then decreases slightly. This is because when the pressure is too low, the hydrogen sulfide does not reach the stoichiometric ratio, and the reaction is not complete. When the hydrogen sulfide pressure is excessive, a small amount of sulfur is dissolved in the absorbent, reducing the actual sulfur yield.

[0051] Example 3

[0052] This example mainly investigates the effect of different water content in the absorbent on the SO2 conversion efficiency, and the specific steps are as follows:

[0053] (1) Different amounts of H2O and acetylamide modified absorbent [TMG]Ac-AA were mixed to prepare acetylamide modified absorbent with different mass percentages, and the water content was 30%, 40%, 50%, 60%, and 70%. Among them, [TMG]Ac-AA (1:1) was prepared according to the optimal molar ratio of [TMG]Ac and AA in Example 1, which was 1:1. 5 g of absorbent with different water content was taken in a 25 mL glass pressure-resistant tube, placed in a 30°C water bath, and 50 ml·min -1 of pure SO2 gas stream was passed into the absorbent, and the mass change of the absorbent before and after absorption was recorded by an electronic balance.

[0054] (2) A stirring rotor was added to the glass pressure-resistant tube containing the SO2-containing absorbent, and the pressure-resistant tube was placed in a water bath, with the water temperature set to 30°C. The hydrogen sulfide pressure was set to 0.15 MPa, the valve was opened to allow H2S to contact the SO2-absorbed absorbent, and the stirring rotor of the water bath was set to 200 rpm for 1.5 h. The effect of different water content in the absorbent on the SO2 conversion efficiency is shown in Figure 4

[0055] From Figure 4 it can be seen that when the water content in the absorbent is 30%, 40%, 50%, 60%, and 70%, the SO2 conversion rates are 98.46%, 98.17%, 97.95%, 92.13%, and 87.34%, respectively. The experimental results show that the conversion rate of SO2 decreases with the increase of water content in the absorbent. This is because the more water in the system, the lower the SO2 content in the absorbent, and the absorbed SO2 will dissolve in water to generate SO3 2- , and SO3 2- ​It is difficult to react with H2S to generate elemental sulfur, thereby resulting in a decrease in SO2 conversion rate.

[0056] Example 4:

[0057] This example mainly investigates the influence of different Claus reaction temperatures on SO2 conversion efficiency, and the specific process is as follows:

[0058] (1) Six 5g H2O and 5g acetylamide modified absorbent [TMG]Ac-AA were weighed and mixed to prepare 50% acetylamide modified absorbent with water content for parallel experiments, wherein [TMG]Ac-AA (1:1) was prepared according to the optimal molar ratio of [TMG]Ac and AA of 1:1 in Example 1. 5g of the water-containing absorbent was taken in a 25mL glass pressure-resistant tube. It was placed in a water bath, and the water bath temperature was set to 30℃, 40℃, 50℃, 60℃, 70℃ and 80℃ respectively. 50ml·min -1 of pure SO2 gas stream was passed into the absorbent, and after 1h of continuous passing, the SO2 adsorbed absorbent was obtained, and the mass change of the absorbent before and after absorption was recorded by an electronic balance.

[0059] (2) A stirring rotor was added to the glass pressure-resistant tube containing the SO2-containing absorbent, and the pressure-resistant tube was placed in a water bath, and the water temperature was set to 30℃, 40℃, 50℃, 60℃, 70℃, 80℃ respectively. The hydrogen sulfide pressure was set to 0.15MPa, the valve was opened to allow H2S to contact the SO2-absorbed absorbent, and the stirring rotor was controlled at 200rpm to allow the reaction to proceed for 1.5h. The influence of different Claus reaction temperatures on SO2 conversion efficiency is shown in Figure 5

[0060] As can be seen from Figure 5 , when the temperature is 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, the SO2 conversion rate is 97.95%, 98.54%, 98.77%, 98.3%, 97.45%, 97.02% respectively. When the temperature is in the range of 30~50℃, with the increase of temperature, the SO2 conversion rate shows a slight upward trend. When the temperature is greater than 50℃, the SO2 conversion rate gradually begins to decrease. This is because when the temperature begins to rise, the SO2 captured by the absorbent is desorbed, which improves the reaction mass transfer effect. However, the Claus reaction is an exothermic reaction, and a large amount of heat will be released when SO2 and H2S come into contact, and high temperature of the system will inhibit the forward reaction. According to the experimental results, the optimal reaction temperature of the absorbent is 30℃ in terms of economy.

[0061] Example 5:

[0062] This example mainly investigates the influence of different Claus reaction times on SO2 conversion efficiency, and the specific steps are as follows: ​

[0063] (1) Weigh 5g H2O and 5g acetamide-modified absorbent [TMG]Ac-AA (1:1) to prepare an acetamide-modified absorbent with a water content of 50%. Take 5g of the water-containing absorbent into a 25mL glass pressure-resistant tube, place it in a water bath, and set the water bath temperature to 30℃. 50ml·min -1 Pure SO2 gas was passed into the absorbent and continuously passed through for 1 hour. The absorbent after adsorbing SO2 was obtained, and the mass change of the absorbent before and after absorption was recorded using an electronic balance.

[0064] (2) Add a stirring rotor to a glass pressure-resistant tube containing SO2 absorbent, place the pressure-resistant tube in a water bath, control the water bath temperature at 30℃, set the hydrogen sulfide pressure to 0.15MPa, open the valve to allow H2S to contact the absorbent that has absorbed SO2, control the water bath speed at 200rpm, and allow the reaction to proceed for different times. The effect of different Claus reaction times on SO2 conversion efficiency is shown in the figure. Figure 6 As shown.

[0065] from Figure 6 It can be seen that when the Claus reaction time is 10 min, 30 min, 60 min, 90 min, and 120 min, the SO2 conversion rates are 66.64%, 74.16%, 84.36%, 97.95%, and 98.11%, respectively. In the entire Claus reaction, the SO2 conversion rate is fastest in the first ten minutes, reaching 66.64%. Afterward, the SO2 conversion rate increases slowly with time, reaching near completion at 90 min. Based on the experimental results, considering overall economic factors, the optimal reaction time for the absorbent is 90 min.

Claims

1. A method for preparing sulfur using an aqueous deep eutectic solvent of guanidinium modified with acetamide, characterized by, The method comprises the following steps: (1) mixing acetamide modified guanidine-based ionic liquid and water to prepare an aqueous deep eutectic solvent absorbent; the aqueous deep eutectic solvent absorbent is prepared by the following method: adding acetamide to tetramethyl guanidine acetate at 50-80 DEG C, stirring and heating for more than 0.5 h, and then mixing with water to prepare the aqueous deep eutectic solvent absorbent; (2) using the aqueous deep eutectic solvent absorbent obtained in step (1) to absorb sulfur dioxide gas to obtain an SO2-rich aqueous absorbent; (3) introducing H2S gas into the SO2-rich aqueous absorbent obtained in step (2) while stirring to make it undergo a Claus reaction; (4) heating the reaction product obtained in step (3) to above the sulfur melting point, then cooling and separating to obtain separated sulfur and regenerated absorbent.

2. The method for preparing sulfur using an aqueous deep eutectic solvent modified with acetamide according to claim 1, wherein the aqueous deep eutectic solvent modified with acetamide is prepared by mixing the guanidine-based deep eutectic solvent and the acetamide in a ratio of 1:0.1 to 1:

10. The mass content of water in the aqueous deep eutectic solvent absorbent is 30-70%.

3. The method of claim 1, wherein the guanidine-based aqueous deep eutectic solvent is modified with acetamide. In step (3), the pressure of the introduced H2S gas is 0.05-0.25 MPa.

4. The method for preparing sulfur using an aqueous deep eutectic solvent modified with acetamide according to claim 1, wherein the aqueous deep eutectic solvent modified with acetamide is prepared by mixing 1 mol of guanidine with 1 mol of acetamide in 2 mol of water. In step (3), the reaction temperature is 30-80 DEG C and the reaction time is 10-90 min.

5. The method of claim 1, wherein the guanidine-based aqueous deep eutectic solvent is modified with acetamide. The molar ratio of the tetramethyl guanidine acetate to the acetamide is 3: (1-9).

6. The method of claim 1, wherein the guanidine-based aqueous deep eutectic solvent is modified with acetamide. The tetramethyl guanidine acetate is prepared by the following method: dissolving equal molar amounts of 1, 1, 3, 3-tetramethyl guanidine and acetic acid in anhydrous ethanol, respectively, adding the obtained solutions into a three-necked flask and a constant pressure funnel, respectively, opening the constant pressure funnel to make the 1, 1, 3, 3-tetramethyl guanidine and acetic acid react, removing water and organic solvent after the reaction is completed, and drying to obtain the tetramethyl guanidine acetate.

7. The method of claim 6, wherein the guanidine-based aqueous deep eutectic solvent is modified with acetamide. The reaction is carried out under a cold water bath condition, and the temperature of the cold water bath is 10-20 DEG C.

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