A method for synthesizing calcium formate by catalyzing carbon monoxide and calcium hydroxide with ionic liquid and recovering tail gas to prepare sodium formate

Abstract

The application discloses a method for synthesizing calcium formate from carbon monoxide and calcium hydroxide and recycling tail gas to prepare sodium formate, and belongs to the technical field of fine chemical synthesis and resource recycling. The method uses tail gas (CO: 80.70%, O2: 1.44%, CH4: 0.43%, H2: 7.27%, N2: 10.16%) and calcium hydroxide (Ca(OH)2) as raw materials, selects an ionic liquid with a specific structure as a catalyst and a reaction medium, and directionally synthesizes calcium formate under mild conditions. Sodium formate is prepared after pretreatment of the calcium formate production tail gas, and the separation and circulation process of the ionic liquid, the washing mechanism of the ethanol solution and the recycling scheme of the ethanol after washing are clarified. The application realizes full resource recycling of coal chemical CO, ionic liquid and ethanol, solves technical problems such as tail gas pollution, catalyst recovery difficulty and solvent waste in the traditional process, and has the advantages of high calcium formate purity (≥98%), high CO conversion rate (≥92%), high sodium formate purity (≥98%) and high ethanol recovery efficiency (≥90%). The comprehensive economic and environmental benefits are significant, and the method is suitable for industrialized production.

Description

Technical Field

[0001] This invention relates to the field of fine chemical synthesis and resource recycling technology, specifically to a method for synthesizing calcium formate from carbon monoxide and calcium hydroxide using ionic liquid catalysis and recovering the tail gas to prepare sodium formate, and particularly to an integrated process for ionic liquid separation and recycling, ethanol washing and ethanol recovery. Background Technology

[0002] Calcium formate (Ca(HCOO)2) and sodium formate (HCOONa) are both important fine chemical products, widely used in feed, building materials, and chemical intermediates. Traditional synthesis processes suffer from problems such as harsh reaction conditions, low CO utilization, easy catalyst loss, and solvent waste. Calcium formate synthesis often employs high-temperature and high-pressure conditions. While ionic liquids, as novel green catalysts, can optimize the reaction, their separation, recovery, and recycling stability limit their industrialization. Ethanol solution is the optimal solvent for solid-phase washing of calcium formate, but the ethanol is discharged with the waste liquid after washing, resulting in resource waste and increased environmental treatment costs.

[0003] The tail gas from formic acid plants, comprising 80.70% CO, 1.44% O2, 0.43% CH4, 7.27% H2, and 10.16%, is currently mostly burned directly, resulting in low added value. If it could be used for calcium formate synthesis, combined with tail gas recovery to produce sodium formate, and if ionic liquids and ethanol could be recycled, a complete circular system of raw materials, products, solvents, and catalysts could be constructed, significantly improving resource utilization and economic benefits.

[0004] In existing technologies, the separation and recovery processes for ionic liquids are immature, and there is no clear recovery plan after ethanol washing: conventional ethanol recovery suffers from problems such as high energy consumption, insufficient purity, and cross-contamination with ionic liquids; at the same time, if trace amounts of ionic liquid in the washing liquid are not recovered, it will lead to catalyst loss. Therefore, there is an urgent need to develop an integrated process for the co-recovery of ionic liquids and ethanol to solve bottlenecks such as solvent waste and catalyst loss, and to promote the greening and industrialization of the process. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for synthesizing calcium formate from carbon monoxide and calcium hydroxide using ionic liquid catalysis and recovering the tail gas to prepare sodium formate. This method constitutes a resource cascade utilization system of formic acid tail gas → calcium formate → tail gas CO → sodium formate, simultaneously realizing ionic liquid separation and recycling and ethanol recovery and reuse, thus solving a number of problems in the prior art.

[0006] This invention is achieved through the following technical solution: (I) Calcium formate synthesis and ionic liquid catalysis: Pyridine, quaternary ammonium, or functionalized ionic liquids are selected as catalysts. Through the dual effects of cation adsorption of CO and anion-assisted OH⁻ attack, the C≡O bond energy is weakened, achieving a highly efficient carbonylation reaction under mild conditions. After the reaction, calcium formate is obtained through separation and purification, and the CO-containing tail gas generated during the reaction is collected.

[0007] The raw material is the tail gas from the formic acid plant, containing 80.70% CO, 1.44% O2, 0.43% CH4, 7.27% H2, and 10.16% N2. The Ca(OH)2 is selected as ultrafine powder or an emulsion containing PEG-400 dispersant to reduce agglomeration. Specifically, the Ca(OH)2 is ultrafine Ca(OH)2 with a particle size ≤10μm and a specific surface area ≥20m² / g. The mass concentration of the Ca(OH)2 emulsion is 15%-20%, and 0.5%-1% of a dispersant, PEG-400, is added to the emulsion. The mass ratio of the ionic liquid to Ca(OH)2 is 2:5 to 1:1.

[0008] The conditions for the carbonylation reaction are: temperature 70-140℃ and pressure 0.4-2.0MPa.

[0009] The ionic liquid is selected from one or more of pyridine-type ionic liquids, quaternary ammonium-type ionic liquids, or functionalized ionic liquids; the pyridine-type ionic liquid is at least one of 1-butyl-3-methylimidazolium bromide and 1-ethyl-3-methylimidazolium bromide; the quaternary ammonium-type ionic liquid is at least one of trimethylhydroxyethylammonium hydroxide and trimethylethylammonium acetate; the functionalized ionic liquid is at least one of 1,2-dimethyl-3-hydroxyethylimidazolium dinitrile and 1-aminopropyl-3-methylimidazolium tetrafluoroborate.

[0010] When using pyridine-type ionic liquids, the reaction temperature is 80-120℃, the reaction pressure is 0.5-1.5MPa, and the reaction time is 20-40min; when using quaternary ammonium-type ionic liquids, the reaction temperature is 100-140℃, the reaction pressure is 1.0-2.0MPa, and the reaction time is 30-50min; when using functionalized ionic liquids, the reaction temperature is 70-110℃, the reaction pressure is 0.4-1.2MPa, and the reaction time is 15-35min.

[0011] In this step, the reaction system is a jacketed 316L stainless steel autoclave with a volume of 50-100L, equipped with a frequency converter and an online pressure / temperature monitoring system. Before the reaction, the autoclave is purged with inert gas N2 to ensure that the O2 content inside the autoclave is ≤0.5%. When the viscosity of the ionic liquid is ≥500mPa·s, 5%-10% of a low-viscosity co-solvent, namely ethylene glycol dimethyl ether or N-methylpyrrolidone, is added to the reaction system. Alternatively, an ultrasonic probe with a power of 500-1000W is installed in the autoclave for ultrasonic-assisted dispersion.

[0012] (II) Ion liquid separation and recycling process The separation and recycling of the ionic liquid employs a combination of pressure filtration and vacuum distillation. After the reaction, pressure filtration at 0.3-0.5 MPa achieves rapid solid-liquid separation, avoiding ionic liquid entrainment, and yields a solid product (crude calcium formate) and a liquid phase containing the ionic liquid. The liquid phase is then subjected to vacuum distillation at 120-150℃ and 0.03-0.05 MPa to remove moisture and impurities, recovering the ionic liquid with a purity ≥99%, allowing for recycling at least 5 times with an activity decay ≤5%. The recovered ionic liquid is then recycled for the carbonylation reaction in step (I).

[0013] (III) Recovery of Ethanol Solution (1) The calcium formate solid product is washed 2-3 times with a 50%-70% ethanol solution. First, the ethanol solution has a solubility of ionic liquid ≥100g / L and a solubility of calcium formate ≤0.5g / L, achieving selective desorption; moreover, ethanol is volatile and leaves no residue, and the product dissolution loss rate is ≤0.3%, which is more suitable for industrial use than pure water or other organic solvents; the amount of washing solution used each time is 30%-50% of the mass of the solid product, the washing temperature is 20-40℃, and the ethanol washing solution after washing is collected; the washed solid product is dried at 100-120℃ to obtain the calcium formate product; (2) Ethanol recovery: The washing liquid is separated by a distillation column, with the bottom temperature controlled between 85-95℃ and the reflux ratio between 1:1 and 2:1. Ethanol is distilled off at the top temperature of 78-82℃ with a purity of ≥95%, and is then recycled for washing. The residue at the bottom of the column contains trace amounts of ionic liquid, which is incorporated into the ionic liquid distillation system for recovery to avoid catalyst loss. This process has an ethanol recovery efficiency of ≥90% and can be recycled ≥10 times, significantly reducing solvent costs.

[0014] (iv) Exhaust gas recovery and sodium formate synthesis After dust removal and dehydration pretreatment, the exhaust gas is passed through a 20%-30% NaOH aqueous solution, with a liquid-to-gas ratio of 5-10 L / m³ for the CO-containing exhaust gas to the NaOH aqueous solution. The conditions for the secondary carbonylation reaction are: reaction temperature 150-200℃, reaction pressure 2.0-3.5 MPa, reaction time 60-90 min, and stirring rate 500-600 r / min. A reducing agent of 0.5%-1% aqueous solution, namely sodium sulfite, is added to the reaction system to suppress side reactions.

[0015] The residual pressure of the exhaust gas is used for pressure replenishment. The exhaust gas pretreatment specifically includes: (1) Dust removal and demisting: using a high-efficiency filter with a filtration accuracy of ≤1μm to remove Ca(OH)2 dust and emulsion droplets carried in the exhaust gas; (2) Dehydration and drying: cooling and dehydrating to reduce the exhaust gas temperature to 10-15℃, so that the exhaust gas humidity is ≤5%; (3) Inert gas removal: when the content of inert gases such as N2 and CO2 in the exhaust gas is ≥30%, pressure swing adsorption (PSA) device is used to remove inert gases, so that the CO purity is increased to 20%-30%.

[0016] After the reaction, the CO-containing tail gas is mixed with fresh CO from coal chemical source with a purity of 97% in a certain proportion and then introduced into the reaction system. The purity of CO after mixing is controlled to be ≥10%. The reaction tail gas from step (3) is recycled into the closed reaction system of step (1) to realize multiple recycling of CO with a total utilization rate of ≥99%.

[0017] The present invention has the following beneficial effects: 1. This invention achieves a triple recycling of formic acid plant tail gas, ionic liquid, and ethanol, with ionic liquid recovery efficiency ≥95% and ethanol recovery efficiency ≥90%, eliminating resource waste and conforming to the concept of circular economy.

[0018] 2. The ionic liquid in this invention is non-volatile, the ethanol can be recycled and reused, and there is no waste gas or waste liquid emission; moreover, there is no need for additional treatment of calcium formate tail gas and ethanol waste liquid.

[0019] 3. The calcium formate and sodium formate prepared by this invention have a purity of ≥98% and ≥98% respectively, which are superior to those prepared by traditional processes.

[0020] 4. The ionic liquid recycling in this invention reduces the cost of the catalyst, and the ethanol recovery also reduces solvent consumption. Combined with the low-cost advantage of CO production from coal chemical industry, the production cost of sodium formate is reduced.

[0021] 5. The processes of ionic liquid separation, ethanol recovery, and tail gas coupling in this invention are suitable for industrial production. Detailed Implementation

[0022] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0023] Ultrafine Ca(OH)2, particle size 8μm, specific surface area 25m² 2 / g; The Ca(OH)2 emulsion has a mass concentration of 18%, and 0.5% to 1% of the dispersant PEG-400 is added to the emulsion. Formic acid plant tail gas: CO accounts for 80.70%, O2 accounts for 1.44%, CH4 accounts for 0.43%, H2 accounts for 7.27%, and N2 accounts for 10.16%.

[0024] The pyridine-type ionic liquids are 1-butyl-3-methylimidazolium bromide and 1-ethyl-3-methylimidazolium bromide; the quaternary ammonium-type ionic liquids are trimethylhydroxyethylammonium hydroxide and trimethylethylammonium acetate; the functionalized ionic liquids are 1,2-dimethyl-3-hydroxyethylimidazolium dinitrile and 1-aminopropyl-3-methylimidazolium tetrafluoroborate. The ionic liquids were purchased from Shanghai Chengjie Chemical Co., Ltd.

[0025] Example 1 This application provides a method for preparing sodium formate by catalyzing the reaction of carbon monoxide and calcium hydroxide with ionic liquid to synthesize calcium formate and recovering the tail gas. The method includes: 1. Calcium formate synthesis: (1) Raw material preparation: 10 kg of ultrafine Ca(OH)2, 10 kg of 1-butyl-3-methylimidazolium bromide ionic liquid, and tail gas from the formic acid unit; (2) Reaction system: Add the above raw materials to a 50L 316L stainless steel high-pressure reactor, purge with N2 until the O2 content is 0.3%, introduce CO to the pressure of 1.0MPa, heat to 100℃, stir at 700r / min, and react for 30min; collect the tail gas, in which the CO content is 5.2%; (3) Solid-liquid separation and washing: After the reaction, the solid phase of crude calcium formate and the liquid phase containing ionic liquid were separated by filtration under pressure of 0.4 MPa; the solid phase was washed three times with 60% ethanol solution, each time the amount of washing solution was 40% of the solid phase mass, about 6.5 kg / time, the washing temperature was 30℃, and 19.2 kg of ethanol washing solution was collected. (4) Ionic liquid recovery: The separated liquid phase containing ionic liquid was distilled at 130℃ and 0.04MPa under reduced pressure for 2.5h to remove water and impurities, and 9.6kg of 1-butyl-3-methylimidazolium bromide was recovered with a purity of 99.2% and a recovery efficiency of 96%. (5) Drying of calcium formate: The solid phase washed with ethanol was dried at 110°C for 2 hours to obtain 16.2 kg of calcium formate with a purity of 98.8% and a CO conversion rate of 95.8%.

[0026] 2. Ethanol recovery: (1) Distillation treatment: 19.2 kg of ethanol washing liquid was fed into a distillation column with a top temperature of 79°C, a bottom temperature of 90°C, and a reflux ratio of 1.5:1; (2) Ethanol preparation: 17.5 kg of recovered ethanol with a purity of 95.3% was distilled off from the top of the column. 4.4 kg of fresh water was added to prepare 21.9 kg of 60% ethanol solution, which was then recycled for washing with calcium formate. (3) Residual liquid recovery: 0.3 kg of the bottom residue of the tower containing trace amounts of 1-butyl-3-methylimidazolium bromide was added to the liquid phase containing ionic liquid to recover the ionic liquid; the ethanol recovery efficiency was 91.1%.

[0027] 3. Exhaust gas pretreatment and sodium formate synthesis: (1) Exhaust gas pretreatment: The exhaust gas is filtered through a 0.5μm filter, cooled to 12℃ and dehydrated (humidity 3.2%), with an inert gas content of 6.8%, and can be used directly; (2) Sodium formate synthesis: 60 kg of 25% NaOH aqueous solution and 0.3 kg of sodium sulfite were added to a 100 L high pressure reactor. The tail gas was mixed with fresh coal chemical CO with a purity of 97% at a ratio of 2:1. The purity of CO was 66.4%. The pressure was increased to 2.5 MPa, and the reaction was carried out at 170 °C and a stirring rate of 550 r / min for 75 min. (3) Separation and purification: evaporate and concentrate under reduced pressure at 110℃, cool and crystallize at 30℃, and centrifuge to obtain 11.5 kg of sodium formate with a purity of 98.6%. The CO content in the tail gas is 1.8%, which is recycled back to the calcium formate reactor.

[0028] 4. Loop verification: The recovered 1-butyl-3-methylimidazolium bromide was recycled 5 times, and 15.9 kg of calcium formate was recovered with a purity of 98.5% and an activity decrease of 3.2%. The recovered ethanol was recycled 10 times, and after washing, the purity of calcium formate was still ≥98.2%, and the ethanol recovery efficiency was maintained above 89%.

[0029] Example 2 This application provides a method for preparing sodium formate by catalyzing the reaction of carbon monoxide and calcium hydroxide with ionic liquid to synthesize calcium formate and recovering the tail gas. The method includes: 1. Calcium formate synthesis: (1) Raw material preparation: 50 kg of 18% Ca(OH)2 emulsion (containing 9 kg of Ca(OH)2), 5.4 kg of trimethylethylammonium acetate ionic liquid, formic acid unit tail gas, and 0.4 kg of PEG-400 dispersant; (2) Reaction system: Add raw materials to a 100L high-pressure reactor, purge with N2 until the O2 content is 0.4%, introduce CO until the pressure is 1.5MPa, heat to 110℃, stir at 650r / min for 35min; collect the tail gas, in which the CO content is 7.3%; (3) Solid-liquid separation and washing: After the reaction, the solid phase of crude calcium formate and the liquid phase containing ionic liquid were separated by filtration under pressure of 0.35 MPa; the solid phase was washed twice with 55% ethanol solution, each time with a volume of 5.0 kg, and 9.7 kg of washing liquid was collected. (4) Recovery of ionic liquid: The liquid phase containing ionic liquid obtained by separation was distilled under reduced pressure at 140℃ and 0.05MPa for 3h to recover 5.13kg of trimethylethylammonium acetate, with a purity of 99.1% and a recovery efficiency of 95%; (5) Drying of calcium formate: The solid phase washed with ethanol was dried at 105℃ for 3 hours to obtain 14.3 kg of calcium formate product with a purity of 98.5% and a CO conversion rate of 94.2%.

[0030] 2. Ethanol recovery: (1) Distillation treatment: 9.7 kg of ethanol washing liquid was fed into the distillation column. The temperature at the top of the column was 80℃, the temperature at the bottom of the column was 92℃, and the reflux ratio was 1:1. (2) Ethanol preparation: 8.8 kg of recovered ethanol with a purity of 95.1% was distilled off from the top of the column. 3.9 kg of fresh water was added to prepare 12.7 kg of 55% ethanol solution, which was then recycled for washing with calcium formate. (3) Residual liquid recovery: 0.2 kg of residual liquid at the bottom of the column is incorporated into the ionic liquid distillation system; the ethanol recovery efficiency is 90.7%.

[0031] 3. Sodium formate synthesis: 50 kg of 28% NaOH aqueous solution was added to a high-pressure reactor. The tail gas was pretreated and then passed into a 100 L high-pressure reactor. The pressure was increased to 2.8 MPa using the residual pressure of the tail gas (1.0 MPa). The reaction was carried out at 180 °C and a stirring rate of 600 r / min for 80 min. After treatment, 13.2 kg of sodium formate with a purity of 98.3% was obtained. The CO content of the tail gas was 2.2%, which was recycled. The total CO utilization rate was 99.3%.

[0032] By using pyridine-type, quaternary ammonium-type, or other functionalized ionic liquids as catalysts, efficient carbonylation reactions can be achieved under the corresponding reaction temperatures and conditions.

[0033] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for synthesizing calcium formate from carbon monoxide and calcium hydroxide using ionic liquid catalysis and recovering the tail gas to prepare sodium formate, characterized in that, Includes the following steps: (1) Calcium formate synthesis: using the tail gas of formic acid plant and Ca (OH)2 as raw materials and ionic liquid as catalyst, carbonylation reaction is carried out in a closed reaction system. After the reaction, calcium formate product is obtained by separation and purification. CO-containing tail gas generated during the reaction is collected. (2) Exhaust gas pretreatment: The CO-containing exhaust gas collected in step (1) is subjected to dust removal, demisting, dehydration and drying treatment, and inert gas removal. (3) Sodium formate synthesis: The pretreated CO-containing tail gas is passed into NaOH aqueous solution and a secondary carbonylation reaction is carried out in a high-pressure reaction system. After the reaction is completed, the sodium formate product is obtained by separation and purification. (4) Ethanol recovery: Collect the ethanol washing liquid generated by calcium formate washing in step (1), recover the ethanol by distillation, and recycle the recovered ethanol for calcium formate solid phase washing. The ionic liquid is selected from one or more of pyridine-type ionic liquids, quaternary ammonium-type ionic liquids, or functionalized ionic liquids. The separation cycle of ionic liquid in step (1) includes pressure filtration separation, vacuum distillation to remove impurities, and washing of the calcium formate solid product with 50%-70% ethanol solution.

2. The method according to claim 1, characterized in that, The pyridine-type ionic liquid in step (1) is at least one of 1-butyl-3-methylimidazolium bromide and 1-ethyl-3-methylimidazolium bromide; the quaternary ammonium-type ionic liquid is at least one of trimethylhydroxyethylammonium hydroxide and trimethylethylammonium acetate; and the functionalized ionic liquid is at least one of 1,2-dimethyl-3-hydroxyethylimidazolium dinitrile and 1-aminopropyl-3-methylimidazolium tetrafluoroborate.

3. The method according to claim 1, characterized in that, The Ca(OH)2 mentioned in step (1) is ultrafine Ca(OH)2 with a particle size ≤10μm and a specific surface area ≥20m² / g; or it is a Ca(OH)2 emulsion with a mass concentration of 15%-20%, wherein 0.5%-1% of a dispersant is added to the emulsion, and the dispersant is PEG-400; the mass ratio of the ionic liquid to Ca(OH)2 is 2:5~1:

1.

4. The method according to claim 1, characterized in that, The conditions for the carbonylation reaction in step (1) are as follows: reaction temperature 70-140℃, reaction pressure 0.4-2.0MPa, reaction time 15-50min, and stirring rate 600-800r / min; when using pyridine-type ionic liquid, the reaction temperature is 80-120℃, the reaction pressure is 0.5-1.5MPa, and the reaction time is 20-40min; when using quaternary ammonium-type ionic liquid, the reaction temperature is 100-140℃, the reaction pressure is 1.0-2.0MPa, and the reaction time is 30-50min; when using functionalized ionic liquid, the reaction temperature is 70-110℃, the reaction pressure is 0.4-1.2MPa, and the reaction time is 15-35min.

5. The method according to claim 1, characterized in that, The separation, purification, and ionic liquid recycling steps in step (1) include: (1-1) After the reaction is completed, the reaction system is pressurized and filtered at a pressure of 0.3-0.5 MPa to separate the crude calcium formate solid product and the liquid phase containing the ionic liquid; (1-2) The solid product is washed 2-3 times with 50%-70% ethanol solution, each time using 30%-50% of the mass of the solid product, at a washing temperature of 20-40℃, and the ethanol washing solution is collected; (1-3) The washed solid product is dried at 100-120℃ to obtain the calcium formate product; (1-4) The liquid phase containing the ionic liquid separated in step (1-1) is subjected to vacuum distillation at a distillation temperature of 120-150℃, a distillation pressure of 0.03-0.05 MPa, and a distillation time of 2-3 h to remove trace amounts of water and unreacted Ca from the liquid phase. (OH)2 and soluble impurities are used to obtain a recovered ionic liquid; (1-5) the recovered ionic liquid is recycled for the carbonylation reaction in step (1), the number of recycling times is ≥5 times, and the catalytic activity decay is ≤5%.

6. The method according to claim 1, characterized in that, The specific process for ethanol recovery in step (4) is as follows: (4-1) The collected ethanol washing liquid is fed into a distillation column. The temperature at the top of the distillation column is controlled between 78-82℃, and the temperature at the bottom of the column is controlled between 85-95℃. The reflux ratio is 1:1~2:

1. (4-2) The distillate at the top of the column is condensed to obtain recovered ethanol with a purity of ≥95%. Fresh water or fresh ethanol is added to the recovered ethanol to prepare a 50%-70% ethanol solution, which is then recycled for the calcium formate solid phase washing in step (1-2). (4-3) The residue at the bottom of the column contains trace amounts of ionic liquid and calcium formate. It is incorporated into the liquid phase containing ionic liquid in step (1-1) and the ionic liquid is recovered by vacuum distillation. The ethanol recovery efficiency is ≥90%, and the number of recycling times is ≥10 times.

7. The method according to claim 1, characterized in that, The closed reaction system described in step (1) is a jacketed 316L stainless steel autoclave with a volume of 50-100L, equipped with a frequency converter and an online pressure / temperature monitoring system; before the reaction, the autoclave is purged with inert gas N2 to ensure that the O2 content in the autoclave is ≤0.5%; when the viscosity of the ionic liquid is ≥500mPa·s, 5%-10% of a low viscosity co-solvent is added to the reaction system, wherein the co-solvent is ethylene glycol dimethyl ether or N-methylpyrrolidone; or an ultrasonic probe with a power of 500-1000W is installed in the autoclave for ultrasonic-assisted dispersion.

8. The method according to claim 1, characterized in that, The exhaust gas pretreatment in step (2) specifically includes: (2-1) Dust removal and demisting: using a high-efficiency filter with a filtration accuracy of ≤1μm to remove Ca(OH)2 dust and emulsion droplets carried in the exhaust gas; (2-2) Dehydration and drying: cooling and dehydrating to reduce the exhaust gas temperature to 10-15℃, so that the exhaust gas humidity is ≤5%; when the content of inert gases such as N2 and CO2 in the exhaust gas is ≥30%, a pressure swing adsorption device is used to remove inert gases, so that the CO purity is increased to 20%-30%.

9. The method according to claim 1, characterized in that, The mass concentration of the NaOH aqueous solution in step (3) is 20%-30%; the liquid-to-gas ratio of CO tail gas to NaOH aqueous solution is 5-10 L / m³; the conditions for the secondary carbonylation reaction are: reaction temperature 150-200℃, reaction pressure 2.0-3.5MPa, reaction time 60-90min, stirring rate 500-600r / min; 0.5%-1% of reducing agent is added to the reaction system to suppress side reactions, and the reducing agent is sodium sulfite.

10. The method according to claim 1, characterized in that, The exhaust gas is recycled back to the calcium formate system, with a total CO utilization rate of ≥99%.