Method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing ardealite

Abstract

This invention relates to the field of phosphogypsum resource utilization, specifically disclosing a method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum. The method includes the following steps: adding a deagglomerating agent to phosphogypsum, followed by flotation and water washing to obtain purified phosphogypsum; drying and heating the purified phosphogypsum in a preheating furnace; mixing the dried phosphogypsum with carbon sulfide and adding it to a first-stage airlift circulating reactor, while introducing sulfur gas; conveying the reacted material to a second-stage airlift circulating reactor, where the reaction yields calcium oxide and a mixture of sulfur dioxide and carbon dioxide; catalytically oxidizing and absorbing the carbon dioxide mixture to obtain sulfuric acid and carbon dioxide gas; dissolving calcium oxide in water and introducing carbon dioxide gas to obtain a calcium carbonate suspension; filtering and drying the calcium carbonate suspension to obtain light calcium carbonate. This invention solves the problems of low purity and high decomposition temperature of calcium oxide products in existing technologies, achieving closed-loop material circulation and full component utilization.

Description

Technical Field

[0001] This invention relates to the field of phosphogypsum utilization, and specifically to a method for decomposing phosphogypsum to prepare light calcium carbonate and co-produce sulfuric acid. Background Technology

[0002] my country's phosphate fertilizer industry discharges approximately 80 million tons of phosphogypsum annually, with historical stockpiles exceeding 900 million tons, posing risks of land occupation and phosphorus and fluorine pollution. Currently, its resource utilization is concentrated in building materials and cement retarders, but this is unsustainable due to application scenarios and regional limitations. Phosphogypsum's main component is calcium sulfate dihydrate, rich in sulfur and calcium resources. By utilizing chemical decomposition technology to achieve the recycling of sulfur within the phosphate chemical system and the efficient conversion of calcium as a chemical raw material, a large-scale, sustainable phosphogypsum resource utilization pathway can be constructed, possessing significant circular economy value and enormous disposal potential.

[0003] Existing technologies for the decomposition of phosphogypsum mainly use carbon as a reducing agent, but this results in high decomposition temperatures, reaching 1250-1450℃, typically above 1400℃, and producing large amounts of carbon dioxide. In terms of products, the calcium oxide produced has low purity or produces cement clinker with lower output value, leading to higher overall production costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum, thereby solving the problems of low purity of calcium oxide and high decomposition temperature in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum includes the following steps: Step S1: Add phosphogypsum to a deagglomerating agent, and then proceed with flotation and water washing to obtain purified phosphogypsum; Step S2: Drying and heating the purified phosphogypsum in a preheating furnace; Step S3: After the dried phosphogypsum is mixed with carbon sulfide, it is added to the first-stage airlift circulating reactor and sulfur gas is introduced; the reacted material is transported to the second-stage airlift circulating reactor, and after the reaction, calcium oxide and a mixture of sulfur dioxide and carbon dioxide are obtained. In step S4, the mixture of sulfur dioxide and carbon dioxide is catalytically oxidized and absorbed to obtain sulfuric acid and carbon dioxide gas; after calcium oxide is dissolved in water, the generated carbon dioxide gas is passed through to obtain a calcium carbonate suspension; after the calcium carbonate suspension is filtered and dried, light calcium carbonate is obtained.

[0006] As a preferred embodiment, in step S1, the deagglomerating agent includes one or more of tartaric acid, citric acid, sulfuric acid, phosphoric acid, hydrochloric acid, sodium dodecylbenzenesulfonate, polyethylene glycol, and aluminum sulfate.

[0007] As a preferred embodiment, in step S1, the amount of depolymerizing agent added is 1.0%~2.3%, the concentration of the depolymerizing agent is 10%~40%, and the reaction time is 0.5h~3.0h.

[0008] As a preferred embodiment, the temperature of the preheating furnace in step S2 is 280℃~450℃, and the preheating time is 0.5h~2h.

[0009] As a preferred embodiment, in step S3, the mass ratio of phosphogypsum to carbon sulfide is 100:5~50, the mass ratio of phosphogypsum to sulfur is 100:8~40, and the ratio of carbon sulfide to sulfur is 10~50:100.

[0010] As a preferred embodiment, in step S3, the reaction temperature in the first-stage airlift circulating reactor is 400~800℃, the back pressure is controlled at -0.1~-1.5MPa, the sulfur gas velocity is controlled at 0.3~5.0m / s, and the reaction time is 0.5h~1.5h.

[0011] As a preferred embodiment, in step S3, the reaction temperature in the second-stage airlift circulating reactor is 1050~1300℃, the back pressure is controlled at -0.1~-1.5MPa, and the reaction time is 1.0h~2.5h. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of one embodiment of the present invention. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0014] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0015] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0016] Regarding the decomposition of phosphogypsum, existing technologies disclose a method for decomposing phosphogypsum using phosphogypsum and carbon as raw materials. After reacting carbon with oxygen to produce carbon monoxide, the prepared calcium oxide molar fraction reaches 80%. Other existing technologies disclose a preheating and pre-decomposition method for co-producing sulfuric acid and cement using phosphogypsum. This method involves mixing pretreated phosphogypsum with reducing agents, mineralizing agents, siliceous raw materials, and aluminous raw materials, then preheating it in a counter-current suspension with hot flue gas in an oxidizing atmosphere with low oxygen content. Next, it undergoes co-current suspension pre-reduction decomposition with hot flue gas with high CO content, yielding hot raw material with high calcium oxide content. This material enters a rotary kiln for further heating and mineralization to produce cement clinker. After heat exchange and cooling, the flue gas is purified by oxygenation, sublimation, sulfur reduction, carbon reduction, and dust removal before being used to produce sulfuric acid.

[0017] Existing cement production facilities that decompose phosphogypsum have achieved large-scale processing of phosphogypsum, but due to high investment costs and low cement market prices, the actual operating costs are too high, limiting the feasibility of long-term operation.

[0018] In summary, carbon is currently the main reducing agent used in the decomposition of phosphogypsum, but this method has drawbacks such as high decomposition temperature and the generation of large amounts of carbon dioxide. In terms of products, the products are low-purity calcium oxide and cement clinker. The low purity of the calcium oxide products or the production of cement clinker with lower output value result in high overall production costs.

[0019] Furthermore, this invention provides a method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum, comprising the following steps: Step S1: Add phosphogypsum to a deagglomerating agent, and then proceed with flotation and water washing to obtain purified phosphogypsum; Step S2: Drying and heating the purified phosphogypsum in a preheating furnace; Step S3: After the dried phosphogypsum is mixed with carbon sulfide, it is added to the first-stage airlift circulating reactor and sulfur gas is introduced; the reacted material is transported to the second-stage airlift circulating reactor, and after the reaction, calcium oxide and a mixture of sulfur dioxide and carbon dioxide are obtained. In step S4, the mixture of sulfur dioxide and carbon dioxide is catalytically oxidized and absorbed to obtain sulfuric acid and carbon dioxide gas. Calcium oxide is dissolved in water, and the generated carbon dioxide gas is passed through to obtain a calcium carbonate suspension. The calcium carbonate suspension is filtered and dried to obtain light calcium carbonate. Flotation washing is a standard procedure. Sulfur gas can be generated using existing technology.

[0020] This invention provides a clean production method for the resource utilization of phosphogypsum, with light calcium carbonate and industrial sulfuric acid as the core products. First, through efficient thermal decomposition and deep purification, a highly active calcium oxide intermediate with a purity exceeding 99.0% is obtained. The purity and quality of this intermediate directly affect the efficiency of subsequent synthesis. This calcium oxide, after carbonation treatment, yields high-quality light calcium carbonate with a purity exceeding 98.0% and controllable particle size and crystal form. The entire process achieves closed-loop material recycling and full component utilization, with no new solid waste emissions, meeting the technical requirements of green chemistry and a circular economy.

[0021] Thermodynamic calculations for calcium sulfate and carbon sulfide are shown in Tables 1 and 2: CaSO4+CS(s)=CaS+CO2(g)+SO2(g) (1) CaS+ CaSO4 = CaO + SO2(g) (2) Table 1. Thermodynamic calculation data for Formula 1 Calculations show that the reaction is exothermic and spontaneous. The heat generated during the reaction provides some energy to the system, effectively reducing the need for external heating and thus lowering the actual reaction temperature. This not only reduces energy consumption and improves the thermal efficiency of the process but also simplifies operation and temperature control, demonstrating both good economic efficiency and technical feasibility.

[0022] In one implementation method, in step S1, the deagglomerating agent includes one or more of tartaric acid, citric acid, sulfuric acid, phosphoric acid, hydrochloric acid, sodium dodecylbenzenesulfonate, polyethylene glycol, and aluminum sulfate. Using only a single deagglomerating agent will reduce the effectiveness of phosphogypsum of different qualities; therefore, it is necessary to change the agent or combine agents to achieve the purpose of deagglomeration.

[0023] This invention employs a deagglomerating agent to disperse phosphogypsum particles, effectively breaking down their inherent agglomerated structure and deagglomerating the originally tightly bound secondary particles. This significantly reduces particle size and increases specific surface area. This process helps to fully expose soluble phosphorus, fluorine, and silicon impurities that are trapped or adsorbed between phosphogypsum crystals, while simultaneously releasing small amounts of phosphates, fluorides, and silicates doped into the crystal lattice. This process improves interfacial contact of impurities and subsequent leaching efficiency, laying the foundation for the next step of phosphogypsum decomposition.

[0024] In one embodiment, in step S1, the amount of depolymerizing agent added is 1.0% to 2.3%, the concentration of the depolymerizing agent is 30% to 50%, and the reaction time is 0.5 h to 3.0 h.

[0025] This invention utilizes a deagglomerating agent to produce smaller phosphogypsum particles, resulting in a larger contact area between materials and significantly improving reaction efficiency. By dispersing the phosphogypsum particles, their particle size is significantly reduced and their size distribution improved. This optimization substantially increases the specific surface area of ​​the particles, significantly expanding the contact interface in the reaction system, thereby enhancing mass and heat transfer processes. This structural characteristic effectively promotes molecular diffusion and chemical interaction at the solid-gas phase reaction interface, significantly improving the overall reaction rate and conversion efficiency from a physical perspective.

[0026] In one implementation, the preheating furnace temperature in step S2 is 280℃~450℃, and the preheating time is 0.5h~1.0h. This temperature is suitable for treating free water and crystal water in phosphogypsum, reducing the impact of moisture on the system, such as its effect on corrosion equipment.

[0027] In one embodiment, in step S3, the ratio of phosphogypsum to carbon sulfide is 100:5~50, the ratio of phosphogypsum to sulfur is 100:8~40, and the ratio of carbon sulfide to sulfur is 10~50:100. The output materials can be adjusted within these ranges.

[0028] In one embodiment, in step S3, the reaction temperature in the first-stage airlift circulating reactor is 400~800℃, the back pressure is controlled at -0.1~-1.5MPa, the gas velocity of sulfur gas is controlled at 0.3~5.0m / s, and the reaction time is 0.5h~1.5h.

[0029] The two-stage reaction of this invention requires different conditions. The first stage reaction only requires the vaporization of CS at a certain temperature to react with calcium sulfate, while the second stage requires a higher reaction temperature. The two-stage reaction is easier to control, resulting in more stable product quality.

[0030] In one implementation method, in step S3, the reaction temperature in the second-stage airlift circulating reactor is 1050~1300℃, the back pressure is controlled at -0.1~-1.5MPa, and the reaction time is 1.0h~2.5h. This stage requires a higher processing temperature to further stabilize the product quality.

[0031] The airlift circulating reactor in this embodiment of the invention can be a conventional structure, such as the LG-QSHL type.

[0032] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to the present invention.

[0033] The composition of phosphogypsum raw materials in the embodiments is shown in Table 3: Table 3 Composition of phosphogypsum raw materials Example 1

[0034] like Figure 1 As shown, the method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum in this embodiment is carried out as follows: Step S1: Add sulfuric acid (w=15%) to phosphogypsum, the amount added is 1.0%, mix and react for 4 hours, and then obtain purified phosphogypsum by flotation and water washing.

[0035] Step S2: The purified phosphogypsum is sent into a preheating furnace and preheated at 300°C for 1.5 hours.

[0036] Step S3: After mixing phosphogypsum and carbon sulfide, the phosphogypsum is fed into the first-stage airlift circulating reactor, and sulfur gas is introduced. The ratio of phosphogypsum, sulfur, and carbon sulfide is 100:25:12.5. The reaction temperature is 700℃, the reaction time is 1 hour, the reactor back pressure is controlled at -0.1 MPa, and the sulfur gas velocity is controlled at 0.4 m / s. The reacted material is then transported to the second-stage airlift circulating reactor via a hot gas flow. The reaction temperature is 1100℃, the reaction time is 1 hour, and the reactor back pressure is controlled at -0.1 MPa. The gas produced during the reaction is fed into a sulfuric acid unit to obtain sulfuric acid and carbon dioxide gas. In this embodiment, the sulfur gas can be generated by heating sulfur to 104℃ to become liquid sulfur, and then using high-pressure gas to send the liquid sulfur out of the nozzle to form sulfur gas.

[0037] Step S4: After the reaction is complete, the solid is calcium oxide, which is added to water to form calcium hydroxide solid. Then, the generated carbon dioxide gas is passed through to obtain a calcium carbonate suspension. After filtration and drying, high-purity light calcium carbonate is obtained. The purity of calcium oxide is 99.54%, the purity of calcium carbonate is 98.65%, and the purity of sulfuric acid is 97.82%. Example 2

[0038] The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum in this embodiment is carried out as follows: Step S1: Add polyethylene glycol (w=10%) and hydrochloric acid (w=20%) to phosphogypsum at amounts of 1.5% and 2.5% respectively, mix and react for 3 hours, and then obtain purified phosphogypsum through flotation and water washing. Step S2: The purified phosphogypsum is sent to a preheating furnace and preheated at 450°C for 1.5 hours.

[0039] Step S3: After mixing phosphogypsum and carbon sulfide, the phosphogypsum is fed into the first-stage airlift circulating reactor, and sulfur gas is introduced. The ratio of phosphogypsum, sulfur, and carbon sulfide is 100:12.5:25. The reaction temperature is 650℃, the reaction time is 1.5 hours, the reactor back pressure is controlled at -0.12 MPa, and the sulfur gas velocity is controlled at 0.8 m / s. The reacted material is then transported via hot gas to the second-stage airlift circulating reactor, where the reaction temperature is 1200℃, the reaction time is 1.5 hours, and the reactor back pressure is controlled at -0.15 MPa. The gas produced during the reaction is fed into the sulfuric acid unit to obtain sulfuric acid and carbon dioxide gas.

[0040] Step S4: After the reaction is complete, the solid is calcium oxide, which is added to water to form calcium hydroxide solid. The generated carbon dioxide gas is then introduced to obtain a calcium carbonate suspension. After filtration and drying, high-purity light calcium carbonate is obtained. The purity of calcium oxide is 99.67%, the purity of calcium carbonate is 98.84%, and the purity of sulfuric acid is 97.31%. Example 3

[0041] The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum in this embodiment is carried out as follows: Step S1: Add sulfuric acid (w=20%) to phosphogypsum at a rate of 1.5%, mix and react for 2 hours, then obtain purified phosphogypsum through flotation and water washing.

[0042] Step S2: The purified phosphogypsum is sent to a preheating furnace and preheated at 400°C for 1 hour.

[0043] Step S3: After mixing phosphogypsum and carbon sulfide, the phosphogypsum is fed into the first-stage airlift circulating reactor, and sulfur gas is introduced. The ratio of phosphogypsum, sulfur, and carbon sulfide is 100:10:35. The reaction temperature is 500℃, the reaction time is 1.5 hours, the reactor back pressure is controlled at -0.18 MPa, and the sulfur gas velocity is controlled at 0.35 m / s. The reacted material is then transported via hot gas to the second-stage airlift circulating reactor, where the reaction temperature is 1100℃, the reaction time is 2 hours, and the reactor back pressure is controlled at -0.12 MPa. The gas produced during the reaction is fed into the sulfuric acid unit to obtain sulfuric acid and carbon dioxide gas.

[0044] After the reaction is complete, the solid is calcium oxide, which is added to water to form calcium hydroxide solid. Then, the generated carbon dioxide gas is passed through to obtain a calcium carbonate suspension. After filtration and drying, high-purity light calcium carbonate is obtained. The purity of calcium oxide is 99.71%, the purity of calcium carbonate is 99.21%, and the purity of sulfuric acid is 97.69%.

[0045] Comparative Example 1 Unlike Example 1, no deagglomeration agent was added, and step S1 was performed as follows: Purified phosphogypsum is obtained by flotation and washing.

[0046] The remaining steps are the same as in Example 1.

[0047] Comparative Example 2 Unlike Example 2, a second-stage airlift circulating reactor is not introduced, and step S3 is performed as follows: After mixing phosphogypsum with carbon sulfide, the phosphogypsum is fed into a first-stage airlift circulating reactor, and sulfur gas is introduced. The ratio of phosphogypsum, sulfur, and carbon sulfide is 100:12.5:25. The reaction temperature is 650℃, the reaction time is 1.5h, the back pressure of the reactor is controlled at -0.12MPa, and the gas velocity of sulfur gas is controlled at 0.8m / s. The gas produced during the reaction is fed into a sulfuric acid unit to obtain sulfuric acid and carbon dioxide gas.

[0048] The remaining steps are the same as in Example 2.

[0049] Comparative Example 3 Unlike Example 3, only carbon sulfide was used as the reducing agent, and step S3 was performed as follows: Step S3: After mixing phosphogypsum and carbon sulfide, the phosphogypsum is fed into the first-stage airlift circulating reactor. The ratio of phosphogypsum, sulfur, and carbon sulfide is 100:0:35. The reaction temperature is 500℃, the reaction time is 1.5 hours, the reactor back pressure is controlled at -0.18 MPa, and the sulfur gas velocity is controlled at 0.35 m / s. The reacted material is then transported via hot gas to the second-stage airlift circulating reactor. The reaction temperature is 1100℃, the reaction time is 2 hours, and the reactor back pressure is controlled at -0.12 MPa. The gas produced during the reaction is fed into the sulfuric acid unit to obtain sulfuric acid and carbon dioxide gas. The remaining steps are the same as in Example 3.

[0050] After the reaction is complete, the solid calcium oxide is added to water to form calcium hydroxide solid. Then carbon dioxide gas is introduced to obtain a calcium carbonate suspension. After filtration and drying, high-purity light calcium carbonate is obtained.

[0051] The purity of calcium oxide, calcium carbonate, and sulfuric acid were determined in accordance with GB 30614-2014 National Food Safety Standard for Food Additives Calcium Oxide, GB / T 19281-2014 Analytical Methods for Calcium Carbonate, and GB / T 534-2024 Industrial Sulfuric Acid.

[0052] Table 4 Comparison of results between the examples and comparative examples As can be seen from Table 4, in Comparative Example 1, because the phosphogypsum was not deagglomerated before water washing and flotation, the phosphogypsum particles were wrapped together, resulting in a large amount of impurities. Since water washing and flotation could not completely remove the impurities, these impurities migrated into calcium oxide, calcium carbonate, and sulfuric acid along with the material.

[0053] In Comparative Example 2, the material was not introduced into the second-stage airlift circulating reactor during the decomposition of phosphogypsum. Firstly, this resulted in a significant decrease in the overall reaction temperature, and secondly, a significant reduction in the reaction time. Reaction (2) could not proceed, and the final product could not be effectively converted into calcium oxide and calcium carbonate. At the same time, a large amount of impurities would also enter the sulfuric acid along with the gaseous material, reducing the purity of the sulfuric acid.

[0054] In Comparative Example 3, the lack of sulfur during the decomposition of phosphogypsum resulted in insufficient reducing agent, preventing a complete reaction. Consequently, a large amount of calcium sulfate entered the calcium oxide and calcium carbonate products, leading to a decrease in product purity.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum, characterized in that, Includes the following steps: Step S1: Add phosphogypsum to a deagglomerating agent, and then proceed with flotation and water washing to obtain purified phosphogypsum; Step S2: Drying and heating the purified phosphogypsum in a preheating furnace; Step S3: After the dried phosphogypsum is mixed with carbon sulfide, it is added to the first-stage airlift circulating reactor and sulfur gas is introduced; the reacted material is transported to the second-stage airlift circulating reactor, and after the reaction, calcium oxide and a mixture of sulfur dioxide and carbon dioxide are obtained. In step S4, the mixture of sulfur dioxide and carbon dioxide is catalytically oxidized and absorbed to obtain sulfuric acid and carbon dioxide gas; after calcium oxide is dissolved in water, the generated carbon dioxide gas is passed through to obtain a calcium carbonate suspension; after the calcium carbonate suspension is filtered and dried, light calcium carbonate is obtained.

2. The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In step S1, the deagglomerating agent includes one or more of tartaric acid, citric acid, sulfuric acid, phosphoric acid, hydrochloric acid, sodium dodecylbenzenesulfonate, polyethylene glycol, and aluminum sulfate.

3. The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In step S1, the amount of depolymerizing agent added is 1.0%~2.3%, the concentration of depolymerizing agent is 10%~40%, and the reaction time is 0.5h~3.0h.

4. The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: The temperature of the preheating furnace mentioned in step S2 is 280℃~450℃, and the preheating time is 0.5h~2h.

5. The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In step S3, the mass ratio of phosphogypsum to carbon sulfide is 100:5~50, the mass ratio of phosphogypsum to sulfur is 100:8~40, and the ratio of carbon sulfide to sulfur is 10~50:

100.

6. The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In step S3, in the first-stage airlift circulating reactor, the reaction temperature is 400~800℃, the back pressure is controlled at -0.1~-1.5MPa, the sulfur gas velocity is controlled at 0.3~5.0m / s, and the reaction time is 0.5h~1.5h.

7. The method for preparing light calcium carbonate and co-producing sulfuric acid by decomposing phosphogypsum according to claim 1, characterized in that: In step S3, in the second-stage airlift circulating reactor, the reaction temperature is 1050~1300℃, the back pressure is controlled at -0.1~-1.5MPa, and the reaction time is 1.0h~2.5h.

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