A method for green conversion of biogas sulfur paste based on biological catalysis technology

Abstract

The present application provides a kind of green conversion method of biogas sulfur paste based on biological catalysis technology, belong to solid waste resource and green chemical technology field.The green conversion method of the present application includes the following steps:S1, sulfur paste dry material is oxidized using desulfurization microbial inoculum, the product after oxidation is sequentially heated and melted, reduced pressure rectification, and the purified product is obtained;S2, the purified product is mixed with an alcohol solvent, an enzyme catalyst is added for catalytic reaction, and after the reaction is completed, carbon disulfide is obtained by separation and purification;The enzyme catalyst is lipase;Or S2 is to heat and melt the purified product, add a polymerization aid, after heat preservation, pour the molten material into excess cold water to cool, solidify and dry, and obtain insoluble sulfur.The technical scheme of the present application realizes the resource treatment of biogas sulfur paste, and the process is green and environmentally friendly, and the product has high added value.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and green chemical technology, specifically to a green conversion method for biogas sulfur paste based on biocatalysis technology. Background Technology

[0002] Biogas, as an important renewable energy source, generates a large amount of sulfur paste as a byproduct during its desulfurization and purification process. Sulfur paste is a viscous solid waste primarily composed of elemental sulfur, but also containing water, thiosulfates, sulfites, sulfates, as well as complex organic impurities and microbial cells. Improper disposal not only wastes sulfur resources but also poses environmental pollution risks.

[0003] Currently, the resource utilization of sulfur paste typically focuses on coking sulfur paste, with limited research on sulfur paste produced as a byproduct of biogas desulfurization and purification. Coking sulfur paste is a low-grade sulfur solid waste generated during the wet oxidation desulfurization process of coke oven gas in the coking industry. Its components include elemental sulfur, desulfurization byproducts (such as ammonium thiocyanate, sulfates, and thiosulfates), tar-like substances, moisture, and ash. Resource utilization of coking sulfur paste typically includes physical melting, chemical, and biological methods. While the treatment of biogas desulfurization sulfur paste can refer to the treatment of coking sulfur paste, certain challenges remain in its resource utilization.

[0004] Traditional physical melting methods require high temperatures, resulting in high energy consumption. Furthermore, the organic matter in these methods carbonizes at high temperatures, leading to a blackened product, low purity (typically ≤98%), and the potential generation of harmful gases such as SO2. For example, Chinese patent CN118458702A, entitled "A Method for Purifying Sulfur Paste to Prepare Sulfur," discloses a process where sulfur paste is dehydrated, mixed with a flocculant, and then heated in full contact with high-temperature steam. The sulfur paste melts, and the molten liquid is thoroughly heated and mixed. The resulting volatile gases and some SO2 enter a flue gas treatment system. After heating and mixing, the sulfur paste is allowed to settle and separate into layers. The supernatant is then filtered, condensed, and dried to obtain high-purity sulfur. The steam temperature is 130~360℃, and the purity of the obtained sulfur is 85%~89.6%.

[0005] Chemical methods include solvent extraction and chemical oxidation-reduction methods. Solvent extraction uses toxic solvents such as carbon disulfide and toluene, posing safety and environmental risks. For example, Chinese patent CN109704289A, entitled "A Method for Extracting High-Purity Sulfur from Sulfur Paste," discloses introducing pretreated sulfur paste and an organic solvent into a reactor equipped with a steam heating jacket, and carrying out the extraction reaction under certain temperature conditions. Specifically, the organic solvent is one or a mixture of xylene, 200# solvent oil, and heavy benzene. Chemical oxidation-reduction methods convert elemental sulfur or other sulfur-containing compounds in sulfur paste into soluble or easily recoverable sulfur, such as sulfates, sulfites, or elemental sulfur, through oxidation or reduction reactions, thereby achieving the resource utilization or harmless treatment of sulfur. Although this method avoids high temperatures, it still relies on chemical consumption, resulting in higher costs and the potential for secondary pollution.

[0006] Existing biological methods mainly focus on treating soluble sulfides (such as hydrogen sulfide) or using sulfur-oxidizing bacteria to completely oxidize sulfur into sulfuric acid. This method not only fails to recover valuable elemental sulfur, but also generates high-concentration acidic wastewater that needs to be neutralized, thus failing to achieve the original intention of resource recovery.

[0007] More importantly, most existing technological approaches end with the production of low-grade crude sulfur, resulting in limited added value. For high-value sulfur chemicals such as carbon disulfide (CS2) and insoluble sulfur (IS), industrial production still heavily relies on traditional, energy-intensive, and highly polluting processes. The industrial production of CS2 primarily employs the natural gas-sulfur method or activated carbon catalysis. For example, Chinese patent CN1919731A, entitled "A Method for Preparing Carbon Disulfide," discloses the reaction of natural gas and sulfur at temperatures of 550–800°C and pressures of 0.3–1.0 MPa to produce carbon disulfide. However, these technological solutions consume enormous amounts of energy and easily generate byproducts such as COS and CS; the preparation of insoluble sulfur also suffers from high polymerization temperatures and high energy consumption.

[0008] Therefore, there is an urgent need in this field for a novel solution that can simultaneously achieve green and efficient purification of sulfur paste at the source and its transformation into high-value-added chemicals at the end. This solution needs to organically couple environmentally friendly biotechnology with advanced green synthesis technology to overcome the limitations of existing technologies. Summary of the Invention

[0009] In view of this, the present invention provides a green conversion method for biogas sulfur paste based on biocatalysis technology, which realizes the resource utilization of biogas sulfur paste in a green and environmentally friendly process with high added value of the product.

[0010] To achieve the above objectives, this invention provides a green conversion method for biogas sulfur paste based on biocatalysis technology, comprising the following steps: S1. The sulfur paste dry material is oxidized with desulfurizing microbial agents. The oxidized products are then heated and melted, and then distilled under reduced pressure to obtain the purified product. S2. The purified product is mixed with an alcohol solvent, and an enzyme catalyst is added to carry out the catalytic reaction. After the reaction is completed, carbon disulfide is obtained by separation and purification.

[0011] The green conversion method provided by this invention carries out the core biological oxidation and enzyme catalysis steps under mild conditions, completely avoiding SO2 emissions and high-temperature energy consumption of traditional melting methods, as well as highly toxic byproducts such as COS and CS and ultra-high energy consumption of traditional CS2 synthesis methods. It conforms to the principles of green chemistry and produces carbon disulfide products with higher added value.

[0012] In this invention, the enzyme catalyst is a lipase, whose catalytic essence lies in the catalytic triplet at its active center (usually composed of serine, histidine, and aspartic acid / glutamic acid) forming a strong nucleophile. In the reaction system with excess sulfur and alcohol solvents, the active center mechanism of this enzyme undergoes an adaptive shift. The catalytic mechanism is as follows: the activated serine nucleophile attacks the sulfur atom in the sulfur (S8) ring, forming an enzyme-thiolated intermediate; the hydroxyl group of the alcohol solvent, such as methanol, then attacks this intermediate, releasing methanethiol (CH3SH); the two molecules of methanethiol further undergo a non-enzymatic dehydrogenation coupling reaction at the high temperature of the reaction system, generating the final products carbon disulfide (CS2) and hydrogen. The key to achieving the above catalytic pathway lies in: 1. Enzyme adaptability: Specific lipases possess a wide hydrophobic substrate channel capable of accommodating sulfur atoms. 2. Reaction medium: The non-aqueous environment, dominated by molten sulfur and alcohol solvents, alters the thermodynamic and kinetic behavior of the enzyme, enabling it to catalyze a synthetic reaction rather than a hydrolysis reaction. 3. Mild conditions: The temperature of the catalytic reaction must ensure the fluidity of sulfur while remaining within the thermal stability range of the immobilized enzyme.

[0013] Optionally, the lipase is Novozym435.

[0014] Optionally, water is added during oxidation in step S1, and the mass ratio of sulfur paste, water and desulfurization microbial agent is 1:(2~5):(0.08~0.15).

[0015] Optionally, the desulfurizing microbial agent is one or a combination of two or more of Thiobacillus ferrooxidans, Thiobacillus denitrificationus, and Thiobacillus acidophilus.

[0016] Optionally, the sulfur paste is obtained by dehydrating the sulfur paste produced from biogas desulfurization, and the moisture content of the sulfur paste does not exceed 10%.

[0017] Optionally, the purified product is sulfur with a purity of not less than 99.5%.

[0018] In this invention, through efficient bio-oxidation and distillation purification steps, the purity of sulfur is consistently maintained at no less than 99.5%.

[0019] Optionally, the purity of the carbon disulfide is not less than 99.0%.

[0020] The carbon disulfide synthesized via enzyme catalysis in this invention has high purity, low impurity content, and high product quality.

[0021] Optionally, the oxidation temperature is 30~40℃, the pH is 6.5~7.5, and the time is 5~7 days.

[0022] Optionally, the heating and melting temperature in step S1 is 100~120℃.

[0023] Optionally, the temperature of the vacuum distillation is 130~150℃, and the vacuum degree is -0.08~-0.10MPa.

[0024] Optionally, the alcohol solvent is methanol, and the molar ratio of methanol to sulfur atoms in the purified product is 1:(1.8~2.2).

[0025] Optionally, the lipase is an immobilized lipase preparation.

[0026] Optionally, the immobilized lipase is a lipase immobilized on an insoluble carrier by physical or chemical methods.

[0027] The advantage of using immobilized enzyme preparations in this invention is that after the reaction is complete, the catalyst can be separated from the reaction system and recycled through simple filtration or centrifugation. This greatly reduces production costs and avoids contamination of the final product, carbon disulfide, by enzyme residue, ensuring product purity. Furthermore, immobilization enhances enzyme stability, making it more suitable for industrial-scale stirred reactors.

[0028] Optionally, the mass of the enzyme catalyst is 0.5 to 2.0% of the total mass of the purified product and the alcohol solvent.

[0029] Optionally, the catalytic reaction is carried out at a temperature of 60-80°C for 4-10 hours. Preferably, the catalytic reaction is carried out at a temperature of 65-75°C.

[0030] The catalytic reaction provided by this invention has a low temperature, the reaction process does not require high energy consumption, and the temperature of 60~80℃ ensures the fluidity of sulfur while remaining within the thermal stability range of the immobilized enzyme.

[0031] Optionally, step S2 involves heating and melting the purified material, adding a polymerization aid, keeping it at a constant temperature, and then pouring the melt into excess cold water to cool, solidify, and dry it to obtain insoluble sulfur.

[0032] The green conversion method provided by this invention has low overall energy consumption, meets green environmental protection requirements, and is highly safe.

[0033] Optionally, the polymerization aid is ferric chloride or aluminum chloride, and the mass of the polymerization aid is 0.1-0.9% of the purified substance. Preferably, the mass of the polymerization aid is 0.1-0.5% of the purified substance.

[0034] In order to enable the polymerization aid to play a role in the polymerization catalysis rather than oxidation, the present invention precisely controls the amount of aid added (0.1%-0.9%), so that it only serves as a catalytic active site and is insufficient to trigger a large-scale oxidation reaction.

[0035] At high temperatures, the Fe of the present invention 3+ Or Al 3+ Ions can effectively polarize and attack sulfur atoms in the soluble sulfur ring (S8), inducing ring-opening and triggering a sulfur cationic polymerization reaction to generate a chain-like polymer—insoluble sulfur. In the molten sulfur system, sulfur is in large excess, forming a reducing environment that further inhibits the oxidizing properties of the additive itself. The aforementioned additive can significantly reduce the activation energy of the polymerization of S8 cyclic molecules into chain-like sulfur polymers, improve the reaction rate and product yield, and contribute to the formation of polymer structures with better thermal stability.

[0036] Optionally, the heating and melting temperature in step S2 is 220~250℃.

[0037] In order to ensure that the polymerization aid plays a catalytic role in the polymerization reaction rather than an oxidizing role, the present invention strictly controls the temperature, and the polymerization temperature is controlled at 220-250℃. This temperature is far below the threshold of 300℃ or above for the violent redox reaction between sulfur and ferric chloride / aluminum.

[0038] Optionally, the heat preservation time is 1 to 2 hours.

[0039] Optionally, the rapid cooling involves pouring the molten material into cold water at a temperature below 25°C.

[0040] The above-described technical solution of the present invention has at least the following beneficial effects: The green conversion method provided by this invention realizes the transformation from sulfur paste to purified product to high value-added product. It uses steps such as bio-oxidation to obtain high-purity sulfur, which is then further converted into high value-added product. The whole process has low energy consumption, no toxic by-products, high safety, and is green and environmentally friendly. Attached Figure Description

[0041] Figure 1 This is the purity detection spectrum of the carbon disulfide product in Example 1 of the present invention; Figure 2 This is a purity detection spectrum of the carbon disulfide product in Comparative Example 1 of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will be described in conjunction with the accompanying drawings of the embodiments of the present invention. Figures 1-2 The technical solutions of the embodiments of the present invention will be clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0043] The purity of the sulfur products in this application was tested using the gravimetric method described in section 6.22 of the national standard GB / T 2449.1-2021.

[0044] Example 1 100 kg of biogas sulfur paste was mechanically dehydrated using a plate and frame filter press to obtain 60 kg of dry sulfur paste with a moisture content of 8.5%. The 60 kg of dry sulfur paste was mixed with 150 kg of water (mass ratio 1:2.5), and then 6 kg (10% of the dry paste mass) of a compound bacterial agent consisting of *Thiobacillus ferrooxidans* and *Thiobacillus denitrificationus* in a 1:1 mass ratio was added for biological oxidation. The oxidation process was carried out at a temperature of 35 ± 1 °C, and the pH was maintained at 7.0 ± 0.2 by adding dilute NaOH solution dropwise. Air was introduced and the mixture was stirred for 6 days. After the oxidation reaction, solid-liquid separation was performed using a plate and frame filter press to obtain solid desulfurization products. These products were then added to a sulfur melting kettle and heated to 110 °C to melt. The mixture was then filtered while hot (using diatomaceous earth as a filter aid) to remove unmelted residue, yielding light yellow crude sulfur. The crude sulfur was transferred to a vacuum distillation unit and distilled at 145°C and a vacuum of -0.09 MPa to obtain 49.5 kg of a colorless to slightly yellow purified product (sulfur product). Chemical analysis showed that the sulfur purity reached 99.6%.

[0045] 30 kg of the above-mentioned sulfur product and 12.3 kg of methanol (sulfur to methanol molar ratio of 2:1) were added to a stirred reactor, along with 0.42 kg (1.0% of the total reactant mass) of immobilized lipase (Novozym435). The reaction was carried out at 70℃ and atmospheric pressure for 8 hours. After the reaction, 38.8 kg of carbon disulfide product was obtained by distillation. Gas chromatography analysis showed a purity of 99.94% and a thiocarbonate content of less than 0.05%. The gas chromatography detection method was based on the national standard GB / T 30431-2020, using a TCD detector.

[0046] The remaining 19.5 kg of sulfur product was heated and melted in a polymerization reactor at 240°C, with 58.5 g (0.3%) of ferric chloride added as a polymerization aid, and the mixture was kept at this temperature for 1.5 h. The melt was then rapidly poured into cold water at 15°C for rapid cooling. After filtration, the solid was dehydrated and vacuum dried at 80°C to obtain 18.2 kg of insoluble sulfur product.

[0047] Example 2 150 kg of biogas sulfur paste was mechanically dehydrated using a plate and frame filter press to obtain 88 kg of dry material with a moisture content of 9%. The 88 kg of dry sulfur paste was mixed with 220 kg of water (mass ratio 1:2.5), and then 8.8 kg (10% of the dry material mass) of *Thiobacillus acidophilus* inoculant was added. Oxidation was carried out at a controlled temperature of 38℃ and pH of 6.8, with air introduced and stirring for 5.5 days. After the oxidation reaction, solid-liquid separation was performed using a plate and frame filter press to obtain solid desulfurization product. The desulfurization product was added to a sulfur melting kettle and heated to 105℃ to melt. While hot, it was filtered (using diatomaceous earth as a filter aid) to remove infusible residue, yielding light yellow crude sulfur. The crude sulfur was transferred to a vacuum distillation unit under vacuum distillation conditions of 135℃ / -0.10 MPa. After distillation, 72.5 kg of sulfur product was obtained, with a purity of 99.7%.

[0048] 45 kg of sulfur was mixed with the corresponding amount of methanol (molar ratio 2:1), and 1.5% of a lipase catalyst (Lipozyme® 435 manufactured by Novozymes) was added. The mixture was reacted at 65 °C for 9 h. After the reaction was completed, 57.8 kg of carbon disulfide was obtained by distillation, and the purity was 99.4% as determined by gas chromatography.

[0049] 27.5 kg of sulfur was melted in a polymerization reactor at 230 °C, and 110 g of aluminum trichloride (0.4%) was added as a polymerization aid. The mixture was kept at this temperature for 1.8 h. The melt was then rapidly poured into cold water at 20 °C for rapid cooling. After filtration, a solid was obtained, which was then dehydrated and vacuum dried to yield 25.9 kg of insoluble sulfur.

[0050] Example 3 80 kg of biogas sulfur paste from kitchen waste with a high organic matter content (approximately 15%) was mechanically dehydrated using a plate and frame filter press to obtain 48 kg of dry sulfur paste with a moisture content of 9.5%. The 48 kg of dry sulfur paste was mixed with 120 kg of water (mass ratio 1:2.5), and then 4.8 kg (10% of the dry paste mass) of a bacterial agent composed of *Thiobacillus ferrooxidans*, *Thiobacillus denitrifyingus*, and *Thiobacillus acidophilus* (mass ratio of bacterial strains 1:1:1) was added for biological oxidation. The oxidation was controlled at 40°C and pH 7.2, with aeration and stirring for 7 days. Subsequent processing followed the instructions in Example 1. 38.5 kg of industrial sulfur with a purity of 99.8% was obtained.

[0051] Following Example 1, high-purity carbon disulfide and insoluble sulfur were obtained. The product properties were all superior to or equivalent to those of Example 1.

[0052] Comparative Example 1 Compared with Example 1, the difference is that the step of mixing the sulfur paste dry material with the desulfurization microbial agent for bio-oxidation is skipped, and the dehydrated sulfur paste dry material is directly subjected to subsequent processing.

[0053] 100 kg of biogas sulfur paste from the same source and batch as in Example 1 was mechanically dehydrated using a plate and frame filter press to obtain 60 kg of dry sulfur paste with a moisture content of 8.5%. Skipping the step of mixing the dry sulfur paste with desulfurizing microbial agents for bio-oxidation, the dehydrated dry sulfur paste was directly processed. The dry sulfur paste was placed in a sulfur melting kettle and heated to 110°C to melt. While hot, it was filtered (using diatomaceous earth as a filter aid) to remove unmelted residue, yielding crude sulfur. The crude sulfur was then transferred to a vacuum distillation unit and distilled at 145°C and a vacuum of -0.09 MPa to obtain the sulfur product.

[0054] The above heating and melting process produces a distinctly pungent odor of decomposing organic matter, and the melt is dark in color, appearing blackish-brown. The resulting sulfur product is dark yellow, and chemical analysis shows a purity of only 98.1%.

[0055] 30 kg of this sulfur product was added to a stirred reactor along with 12.3 kg of methanol (sulfur to methanol molar ratio of 2:1). 0.42 kg (1.0% of the total reactant mass) of immobilized lipase (Novozym435) was also added. The reaction was carried out at 70℃ and atmospheric pressure for 8 hours. After the reaction, carbon disulfide was obtained by distillation. Gas chromatography analysis showed a purity of 96.87%. The gas chromatography method followed the national standard GB / T 30431-2020, using a TCD detector.

[0056] The reaction rate of carbon disulfide synthesis catalyzed by the above lipase was significantly reduced, and the activity of the immobilized lipase catalyst decreased significantly after one cycle of repeated use, i.e., it was "poisoned" and deactivated, and the carbon disulfide yield decreased by about 30% compared with Example 1.

[0057] The comparison between Example 1 and Comparative Example 1 demonstrates that the microbial desulfurization and purification step can effectively degrade organic impurities in sulfur paste. This step is crucial for preventing the carbonization of organic matter during the melting process, ensuring the acquisition of high-purity sulfur products with a purity of ≥99%, and guaranteeing the stable and efficient operation of subsequent enzyme catalysis steps. This step is indispensable.

[0058] Comparative Example 2 The difference from Example 1 is that carbon disulfide is prepared using a traditional activated carbon catalytic method.

[0059] 30 kg of sulfur product and 18 kg of coke were thoroughly mixed and placed in a dedicated reactor. The reaction system was heated to 850°C and reacted at this high temperature for 2 hours, allowing the sulfur vapor to react with the hot coke. The resulting gaseous product was condensed to obtain crude carbon disulfide. The condensed crude carbon disulfide liquid was yellow in color, and gas chromatography analysis showed a purity of approximately 95%.

[0060] The above-mentioned process for preparing carbon disulfide is extremely energy-intensive and places stringent requirements on the reactor material, demanding high-temperature corrosion resistance. In addition to generating the target product, carbon disulfide, the reaction also produces large amounts of toxic and harmful byproducts such as carbon monoxide (CO) and carbon oxysulfide (COS). The exhaust gas treatment system is complex, posing a significant environmental risk. The resulting crude carbon disulfide contains a considerable amount of sulfide impurities such as COS, requiring multiple complex purification processes including alkali washing and distillation to reach the 99.0% industrial standard.

[0061] The comparison between Example 1 and Comparative Example 2 fully highlights the significant advantages of the enzyme-catalyzed synthesis of carbon disulfide in this invention. This invention is carried out under mild conditions of 70°C, with negligible energy consumption; using enzymes as catalysts, the reaction exhibits extremely high selectivity, produces virtually no byproducts such as COS, and achieves a direct product purity of 99.94%, eliminating the need for complex purification. This demonstrates that the enzyme-catalyzed pathway of this invention possesses unparalleled advantages over traditional methods in terms of energy saving, safety, environmental protection, and product purity.

[0062] Comparative Example 3 Compared with Example 1, the difference is that the enzyme catalyst is replaced with an equal mass of Bacillus subtilis protease or amylase.

[0063] 30 kg of the same high-purity sulfur product as in Example 1 was mixed with methanol at a sulfur to methanol molar ratio of 2:1. The immobilized lipase catalyst was replaced with an equal mass of Bacillus subtilis protease or amylase. The reaction was carried out at 70°C and atmospheric pressure for 8 hours. The results showed that the reaction hardly occurred, and the yield of carbon disulfide was <5%, which was extremely low.

[0064] As can be seen from Example 1 compared with Comparative Example 3, not all enzymes can catalyze this reaction. The lipase selected in this invention has an important influence on the synthesis of carbon disulfide.

[0065] Comparative Example 4 Compared with Example 1, the difference is that the polymerization aid is replaced with an equimolar amount of iodine or bromine.

[0066] Take 20 kg of the same high-purity sulfur product as in Example 1 and heat it to melt at 240°C. Instead of adding ferric chloride, add an equimolar amount of iodine or bromine. Maintain the temperature for 1.5 hours and then rapidly cool. The conversion rate of insoluble sulfur in the resulting product is approximately 60%, which is low. Furthermore, the product has poor thermal stability; after being placed at 105°C for 15 minutes, the insoluble sulfur content significantly decreases, indicating severe reversion.

[0067] Compared with Comparative Example 4, Example 1 shows that the present invention uses ferric chloride or aluminum chloride as a Lewis acid catalyst, achieving a conversion rate of insoluble sulfur >90%, indicating high conversion efficiency and excellent product thermal stability. This demonstrates that the Lewis acid polymerization aid selected in this invention has significant advantages in reaction efficiency and product quality.

[0068] The effect of enzyme catalyst dosage on the yield of carbon disulfide synthesis was investigated, and the results are shown in Table 1.

[0069] Experimental method: The same amount of sulfur and methanol, with a sulfur to methanol molar ratio of 1.8:1, were added to a stirred reactor, along with immobilized lipase (Novozym435) in different proportions of the total mass of the reactants. The reaction was carried out at 70℃ and atmospheric pressure for 8 hours. After the reaction was completed, carbon disulfide was obtained by distillation. The yield of carbon disulfide was calculated and shown in Table 1.

[0070] Table 1. Carbon disulfide synthesis yield at different amounts of enzyme catalyst

[0071] As shown in Table 1, when the amount of lipase used in this application is 0.5-2% of the total mass of the reactants, the carbon disulfide yield can reach more than 85%.

[0072] The effects of the amount of polymerization aid on the conversion rate and thermal stability of insoluble sulfur were investigated, and the results are shown in Table 2.

[0073] Experimental method: Sulfur was heated and melted in a polymerization reactor at 230℃, and different amounts of ferric chloride were added as polymerization aids. The mixture was kept at this temperature for 1.5 hours. Subsequently, the melt was rapidly poured into cold water at 20℃ for rapid cooling. After filtration, the solid was dehydrated and vacuum dried at 80℃ to obtain insoluble sulfur product. The yield and thermal stability of insoluble sulfur were calculated and are shown in Table 2.

[0074] Thermal stability of insoluble sulfur (%) = (mass of insoluble sulfur after heating / total sulfur mass before heating) × 100%, heating conditions: 105℃ × 15 min Table 2. Conversion rate and thermal stability of insoluble sulfur at different dosages of polymerization aids.

[0075] As shown in Table 2, when the amount of the polymerization aid of the present invention is 0.1% to 0.9% of the amount of sulfur, it has a high conversion rate of insoluble sulfur and thermal stability. When the amount of the polymerization aid ferric chloride is 0.3% to 0.5% of the mass of sulfur, the conversion rate of insoluble sulfur is even higher and the thermal stability is even better.

[0076] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A green conversion method for biogas sulfur paste based on biocatalysis technology, characterized in that, Includes the following steps: S1. The sulfur paste dry material is oxidized with desulfurizing microbial agents. The oxidized products are then heated and melted, and then distilled under reduced pressure to obtain the purified product. S2. The purified product is mixed with an alcohol solvent, and an enzyme catalyst is added to carry out a catalytic reaction. After the reaction is completed, carbon disulfide is obtained by separation and purification. The enzyme catalyst is lipase.

2. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 1, characterized in that, In step S1, water is added during oxidation. The mass ratio of sulfur paste dry material, water, and desulfurization microbial agent is 1:(2~5):(0.08~0.15).

3. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 1, characterized in that, The desulfurization microbial agent is one or a combination of two or more of the following: Thiobacillus ferrooxidans, Thiobacillus denitrificationis, and Thiobacillus acidophilus.

4. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 3, characterized in that, The alcohol solvent is methanol, and the molar ratio of methanol to sulfur atoms in the purified product is 1:(1.8~2.2).

5. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 1, characterized in that, The lipase is an immobilized lipase preparation.

6. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 1, characterized in that, The mass of the enzyme catalyst is 0.5 to 2.0% of the total mass of the purified product and the alcohol solvent.

7. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 1, characterized in that, The catalytic reaction is carried out at a temperature of 60-80°C for 4-10 hours.

8. The green conversion method for biogas sulfur paste based on biocatalysis technology according to any one of claims 1-3, characterized in that, Step S2 involves heating and melting the purified material, adding a polymerization aid, keeping it at a constant temperature, and then pouring the melt into an excess of cold water to cool, solidify, and dry, thereby obtaining insoluble sulfur.

9. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 8, characterized in that, The polymerization aid is ferric chloride or aluminum chloride, and the mass of the polymerization aid is 0.1-0.9% of the purified substance.

10. The green conversion method for biogas sulfur paste based on biocatalysis technology according to claim 8, characterized in that, The heating and melting temperature is 220~250℃.

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