Method, system for continuous production of formic acid by electrochemical reduction of carbon dioxide

Abstract

This invention discloses a method and system for the continuous electrochemical reduction of carbon dioxide to formic acid. The method includes: using sodium bicarbonate solution as the cathode liquid and sodium sulfate solution as the anolyte, with a cation exchange membrane separating the anolyte and cathode liquid; introducing carbon dioxide gas into the cathode liquid, where it is reduced to formic acid, and water is converted into oxygen and hydrogen ions at the anode; during the reaction, sodium ions in the anolyte pass through the cation exchange membrane into the cathode liquid; circulating the cathode liquid in an external circulation pipeline, condensing and precipitating sodium bicarbonate solid at low temperature, and then the precipitated sodium bicarbonate cathode liquid enters the cathode zone; circulating the anolyte in an external circulation pipeline, and then entering the anode zone; once the formate concentration in the cathode liquid reaches a set value, the circulation between the cathode liquid and the anolyte stops, and the cathode liquid and anolyte are output to a post-processing stage for treatment to obtain formic acid; and replenishing the anode zone and cathode zone with sodium sulfate solution and sodium bicarbonate solution respectively to restart the circulation between the cathode liquid and the anolyte.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide resource utilization technology, specifically relating to a method and system for the continuous preparation of formic acid by electrochemical reduction of carbon dioxide. Background Technology

[0002] CO2 capture and resource conversion have become important ways to mitigate the greenhouse effect. Among these methods, electrocatalytic CO2 reduction to formic acid has become a research hotspot due to its high product selectivity and wide range of applications (pharmaceuticals, pesticides, fuel cells, etc.). The formic acid market is experiencing strong demand, with domestic demand reaching 800,000 tons in 2024, with an average annual growth rate of over 5%. The production capacity gap in North China and Northwest China exceeds 300,000 tons per year.

[0003] However, existing CO2 reduction to formic acid technology faces a core bottleneck: electrolyte salting-out. Hydroxide ions generated in the cathode reaction readily react with CO2 to form carbonate (bi) salt solids, which deposit on the catalyst surface and block active sites, leading to catalyst deactivation. This necessitates frequent replacement of the electrolyte and catalyst, significantly increasing industrial operating costs.

[0004] Meanwhile, my country's industrial sector generates hundreds of thousands of tons of sodium sulfate waste salt annually. This waste salt has low market value, and traditional disposal methods mainly involve landfilling and stockpiling. This not only occupies approximately 20 acres of land per 10,000 tons of sodium sulfate but also poses environmental risks such as soil salinization and groundwater pollution due to rainwater leaching. In contrast, sodium bicarbonate, as an important chemical raw material, is widely used in the food, pharmaceutical, and environmental protection fields, and its market price is significantly higher than that of sodium sulfate, representing a substantial value difference.

[0005] Existing CO2 reduction formic acid technologies often focus solely on product yield, failing to utilize industrial waste salt as a sodium source. This results in high sodium source costs and insufficient utilization of the electroosmosis effect to enhance ion migration, leading to low product separation efficiency.

[0006] In summary, existing formic acid preparation processes are costly and cannot meet market demand. Summary of the Invention

[0007] In view of this, the present invention discloses a method for the continuous preparation of formic acid by electrochemical reduction of carbon dioxide, which simultaneously solves the problems of CO2 reduction and salting out, resource utilization of sodium sulfate solid waste, and low-cost preparation of formic acid, and has good industrial application prospects and environmental protection significance.

[0008] Some embodiments disclose a method for the continuous electrochemical reduction of carbon dioxide to prepare formic acid, including:

[0009] Sodium bicarbonate solution is used as the cathode liquid, and an electrode with a carbon dioxide electrocatalyst is used as the cathode; sodium sulfate solution is used as the anolyte, and an electrode with a water electrolysis catalyst is used as the anode; a cation exchange membrane is set between the anolyte and the cathode liquid to isolate them from each other;

[0010] The temperature of the catholyte is controlled between 35 and 45°C. A set flow rate of carbon dioxide gas is introduced into the catholyte, and an electrochemical reaction is carried out at a set current density. In this process, carbon dioxide gas is reduced to formic acid at the cathode, and water is converted into oxygen and hydrogen ions at the anode.

[0011] During the reaction, sodium ions in the anolyte pass through the cation exchange membrane into the catholyte; the catholyte circulates through the external catholyte circulation pipeline, and the catholyte condenses at low temperature to precipitate sodium bicarbonate solid, which then enters the cathode region; the anolyte circulates through the external anolyte circulation pipeline and then enters the anode region.

[0012] Once the formate concentration in the catholyte reaches a set value, the circulation between the catholyte and anolyte stops, and the catholyte and anolyte are output to the post-processing stage according to a set ratio and quantity to obtain formic acid.

[0013] Based on the output quantities of anolyte and catholyte, corresponding quantities of sodium sulfate solution and sodium bicarbonate solution are added to the anode and cathode areas respectively, and the catholyte and anolyte circulation is initiated.

[0014] Furthermore, in some embodiments of the method for the continuous preparation of formic acid by electrochemical reduction of carbon dioxide, the concentration of sodium bicarbonate solution used as the cathode is 0.1~1.0 mol / L, and the concentration of sodium sulfate used as the anolyte is 1.5~2.0 mol / L.

[0015] Some embodiments disclose a method for the continuous electrochemical reduction of carbon dioxide to formic acid, wherein the current density in the electrochemical reaction is 0~50 mA / cm². 2 CO2 flow rate is 0~20 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 1~3 sccm / cm 2 catalyst.

[0016] Some embodiments disclose a method for the continuous electrochemical reduction of carbon dioxide to formic acid, wherein the current density in the electrochemical reaction is 50~100 mA / cm². 2 The CO2 flow rate is 20~30 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 3~6 sccm / cm 2 catalyst.

[0017] Some embodiments disclose a method for the continuous electrochemical reduction of carbon dioxide to formic acid, wherein the current density in the electrochemical reaction is 100~200 mA / cm². 2 The CO2 flow rate is 30~50 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 6~9 sccm / cm. 2catalyst.

[0018] Some embodiments disclose a method for the continuous preparation of formic acid by electrochemical reduction of carbon dioxide, in which the cathode liquid condenses and precipitates sodium bicarbonate solid at 0-5°C.

[0019] Some embodiments disclose a method for the continuous electrochemical reduction of carbon dioxide to prepare formic acid, wherein during the reaction, the cathode liquid is stirred at a speed of 400-500 rpm and the anolyte is stirred at a speed of 200-400 rpm.

[0020] In some embodiments of the method for continuous electrochemical reduction of carbon dioxide to prepare formic acid, when the formic acid concentration in the cathode solution is set to 4~6 mol / L, the cathode solution in the external circulation pipeline and the anolyte in the external circulation pipeline are stopped from circulating.

[0021] Some embodiments disclose a method for the continuous electrochemical reduction of carbon dioxide to produce formic acid, wherein the cathode liquid and anolyte are output to the post-processing process at a ratio of 1:0.5~0.7.

[0022] On the other hand, some embodiments disclose a system for the continuous electrochemical reduction of carbon dioxide to formic acid, used to perform the method for the continuous electrochemical reduction of carbon dioxide to formic acid disclosed in the embodiments of the present invention, including:

[0023] H-type electrolytic cells are equipped with cation exchange membranes to divide the H-type electrolytic cells into an anode region and a cathode region;

[0024] The anode area is equipped with an external anolyte circulation tank and an anolyte circulation pump to enable the circulation of anolyte inside and outside the anode area;

[0025] The cathode area is equipped with a sodium bicarbonate condenser, an external cathode liquid circulation tank, and a cathode liquid circulation pump to enable the circulation of cathode liquid inside and outside the cathode area.

[0026] The anolyte external circulation tank and the catholyte external circulation tank are connected to a post-processing component, which is used to receive the output anolyte and catholyte for post-processing to generate formic acid.

[0027] The method and system for the continuous electrochemical reduction of carbon dioxide to formic acid disclosed in the embodiments of the present invention have at least the following beneficial technical effects:

[0028] Process coupling innovation: For the first time, a deep coupling of electrocatalytic CO2 reduction to produce formic acid and sodium sulfate waste salt conversion has been achieved. The sulfuric acid generated from the anolyte is directly used to convert the formate ions in the cathode liquid into formic acid, forming a closed-loop system of "solid waste resource utilization - CO2 emission reduction - high-value product preparation".

[0029] Breakthrough in addressing salting-out issues: By employing an external circulation filtration system for the cathode liquid and a real-time separation design for NaHCO3, the deposition of carbonates (hydrocarbonates) on the catalyst surface is avoided, thus resolving the catalyst deactivation problem caused by electrolyte salting-out in traditional CO2 reduction processes. The electrolyte replacement cycle is extended to over 30 days, which is 4 to 10 times longer than the traditional process cycle of 3 to 7 days.

[0030] Economic efficiency and adaptability optimization: Using industrial waste salt as raw material, the treatment cost of sodium sulfate waste salt is reduced to below 500 yuan / ton, which is more than 40% lower than the landfill process; the production cost of formic acid is controlled within 3,000 yuan / ton, lower than the industry average (4,000~5,000 yuan / ton); it can treat Na + Various types of sodium sulfate waste salt with a content of 60-90% can be processed. The scale of the equipment can be flexibly adjusted according to the production capacity requirements (10-1000 tons / year), making it suitable for industrial applications of small and medium-sized enterprises.

[0031] Reaction selectivity enhancement: By precisely matching the current density, CO2 flow rate, and circulation pump flow rate, combined with high Na content in the cathode chamber... + Concentration control effectively suppresses hydrogen evolution side reactions, CO2 conversion rate ≥80%, formic acid Faraday efficiency ≥90%, and product purity and yield are improved simultaneously. Attached Figure Description

[0032] Figure 1 The system composition diagram for the continuous electrochemical reduction of carbon dioxide to formic acid disclosed in Example 1;

[0033] Figure 2 Flowchart of the method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide disclosed in Example 2;

[0034] Figure 3 Example 3 discloses a schematic diagram of the catalyst Faraday efficiency.

[0035] Figure Labels

[0036] Detailed Implementation

[0037] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in these embodiments of the invention, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in these embodiments is merely for describing particular implementations and is not intended to limit the scope of the disclosure of these embodiments.

[0038] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain; other experimental methods and technical means not specifically noted in the embodiments of this invention refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0039] The terms “basic” and “approximately” as used herein are used to describe small fluctuations. For example, they can mean less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. Numerical data presented or expressed in range format herein are used for convenience and brevity only, and should therefore be interpreted flexibly to include not only the explicitly listed values ​​that define the range, but also all independent values ​​or subranges contained within that range. For example, a numerical range of “1–5%” should be interpreted to include not only the explicitly listed values ​​from 1% to 5%, but also the independent values ​​and subranges within the indicated range. Thus, this numerical range includes independent values ​​such as 2%, 3.5%, and 4%, and subranges such as 1%–3%, 2%–4%, and 3%–5%, etc. This principle also applies to ranges that list only one value. Furthermore, this interpretation applies regardless of the width of the range or the characteristics described.

[0040] In this document, including in the claims, conjunctions such as "comprising," "including," "with," "having," "containing," "involving," and "accommodating" are understood to be open-ended, meaning "including but not limited to." Only the conjunctions "consisting of" and "composed of" are closed conjunctions.

[0041] To better illustrate the content of this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the invention can be practiced even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail, in order to highlight the main points of the invention.

[0042] Without conflict, the technical features disclosed in the embodiments of the present invention can be combined arbitrarily, and the resulting technical solutions belong to the content disclosed in the embodiments of the present invention.

[0043] In some embodiments, the method for the continuous electrochemical reduction of carbon dioxide to prepare formic acid includes:

[0044] Sodium bicarbonate solution is used as the cathode liquid, and an electrode with a carbon dioxide electrocatalyst is used as the cathode; sodium sulfate solution is used as the anolyte, and an electrode with a water electrolysis catalyst is used as the anode; a cation exchange membrane is set between the anolyte and the cathode liquid to isolate them from each other;

[0045] In some embodiments, the cathode employs a SnBi catalyst with high selectivity for the reduction of CO2 to formic acid, and the effective catalyst area is 100~500 cm². 2 The Faraday efficiency for CO2 reduction to formic acid is ≥ 90%, and the activity decay rate is ≤ 10% after more than 1000 hours of continuous operation; the anode is a Pt sheet or an IrTa-plated titanium mesh, with an effective area consistent with the effective area of ​​the cathode catalyst; Na... + Using industrial waste sodium sulfate with a content ≥ 60% as raw material, a 1.5~2.0 mol / L saturated sodium sulfate solution is prepared as the anolyte; using industrial grade sodium bicarbonate as raw material, a 0.1~1.0 mol / L sodium bicarbonate solution is prepared as the catholyte, which is beneficial for obtaining sodium bicarbonate solid with a purity of over 95% in the subsequent process.

[0046] The cathode liquid temperature is controlled between 35 and 45°C. Carbon dioxide gas at a set flow rate is introduced into the cathode liquid, and an electrochemical reaction is carried out at a set current density. During the reaction, carbon dioxide gas is reduced to formic acid at the cathode, and water is converted into oxygen and hydrogen ions at the anode. Sodium ions in the anolyte enter the cathode liquid through the cation exchange membrane. The cathode liquid circulates in the external cathode liquid circulation pipeline. The cathode liquid condenses at low temperature to precipitate sodium bicarbonate solid, and the cathode liquid with precipitated sodium bicarbonate solid enters the cathode area. The anolyte circulates in the external anolyte circulation pipeline and then enters the anode area.

[0047] Typically, the reaction mechanisms and ion migration processes involved in the continuous electrochemical reduction of carbon dioxide to formic acid include:

[0048] (1) Cathode reaction:

[0049] CO2 accepts electrons on the surface of the cathode catalyst and undergoes a reduction reaction to generate formate ions (HCOO⁻), along with the formation of OH⁻. The reaction equation is as follows:

[0050] CO2 + H2O - 2e⁻ → HCOO⁻ + OH⁻

[0051] The generated OH⁻ reacts rapidly with excess CO₂ to form bicarbonate ions HCO₃⁻:

[0052] OH⁻ + CO2 → HCO3⁻

[0053] (2) Anode reaction:

[0054] H2O is oxidized on the surface of the anode catalyst to produce O2. The reaction equation is as follows:

[0055] 2H₂O - 4e⁻ → O₂↑ + 4H+

[0056] (3) Electroosmotic migration of sodium ions: Under the action of an electric field, Na⁺ in the anolyte passes through the cation exchange membrane / sodium ion exchange membrane through the electroosmotic effect and migrates directionally into the catholyte, where it combines with HCO⁻ to form sodium bicarbonate NaHCO₃, as shown in the following reaction:

[0057] Na + + HCO3⁻ → NaHCO3;

[0058] In some embodiments, the electrolysis reaction process is powered by a DC regulated power supply, and the electrolysis process control parameters include:

[0059] (1) Temperature control: The cathode liquid temperature is controlled at 35~45℃. The condenser used for condensing and precipitating sodium bicarbonate in the external circulation pipeline of the cathode liquid is placed in an ice-water bath to maintain the external circulation liquid at a temperature of 0~5℃. This allows the sodium bicarbonate in the cathode liquid to be rapidly saturated and precipitated in the low-temperature condenser, ensuring that the cathode liquid is always in a state of unsaturated sodium bicarbonate, and avoiding the deposition of carbonate (hydrocarbonate) on the surface of the cathode catalyst, which would cause the active sites of the catalyst to be covered and deactivated. At the same time, the Na in the cathode chamber + The concentration is always kept at a relatively high level, which effectively inhibits the hydrogen evolution reaction (HER) at the cathode and ensures the selectivity of CO2 reduction to formic acid;

[0060] (2) Matching of gas introduction and flow rate: When continuously introducing CO2 gas into the cathode chamber, it is usually necessary to consider the strict matching of the gas introduction rate, the external circulation flow rate of the cathode liquid, and the current density. These three factors should work together to ensure that CO2 is fully dissolved in the cathode liquid, providing sufficient raw materials for the reaction, while avoiding a decrease in reaction efficiency due to excessive or insufficient gas. Typically, the CO2 gas can be industrial grade or industrial tail gas with a volume concentration ≥50% and a dust content ≤10mg / m³. 3 , moisture ≤ 5%;

[0061] In some embodiments, the current density is 0~50 mA / cm². 2 CO2 flow rate is 0~20 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 1~3 sccm / cm 2 catalyst;

[0062] In some embodiments, the current density is 50~100 mA / cm². 2 The CO2 flow rate is 20~30 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 3~6 sccm / cm 2 catalyst;

[0063] In some embodiments, the current density is 100~200 mA / cm². 2 CO2 flow rate is 30~50 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 6~9 sccm / cm. 2 catalyst;

[0064] (3) Stirring and monitoring control: The stirring speed of the catholy liquid is 400~500 rpm to ensure that CO2 is fully dissolved, and the stirring speed of the anoly liquid is 200~400 rpm to promote the dissolution of sodium sulfate solid; the turbidity of the cathode chamber can usually be monitored in real time by an online turbidity meter. When the turbidity is ≥50 NTU, the circulation flow rate is increased to avoid pipe blockage.

[0065] Once the formate concentration in the catholyte reaches a set value, the circulation between the catholyte and anolyte stops, and the catholyte and anolyte are output to the post-processing stage according to a set ratio and quantity to obtain formic acid.

[0066] According to the output quantities of anolyte and catholyte, the corresponding quantities of sodium sulfate solution and sodium bicarbonate solution are added to the anode and cathode areas respectively, and the catholyte and anolyte circulation is started.

[0067] The above reaction process is carried out continuously, enabling continuous production of formic acid.

[0068] Typically, to achieve continuous formic acid production, a continuous circulation system is required. This involves constructing external circulation pipelines based on the circulating liquids in the cathode and anode chambers, enabling continuous discharge and replenishment of the cathode and anode liquids respectively. Specific control methods include:

[0069] Real-time concentration monitoring and discharge triggering: The concentration of formate ions in the cathode circulating liquid is monitored in real time by an online ion chromatograph. When the concentration reaches 4~6 mol / L, the external circulation pumps of the cathode and anode are shut off first, and the cathode circulating liquid discharge valve and anode circulating liquid discharge valve are opened simultaneously. The cathode liquid and anode liquid are discharged at a volume ratio of 1:0.5~0.7 and merged into the subsequent formate synthesis and separation system for post-processing to prepare formic acid.

[0070] Precise liquid replenishment to maintain system stability: After discharging the catholyte and anolyte, continuously replenish the catholyte circulation line with 0.1~1.0 mol / L sodium bicarbonate solution and start the catholyte circulation pump; continuously replenish the anolyte circulation line with saturated sodium sulfate solution and solid sodium sulfate and start the anolyte circulation pump to ensure the Na+ in the anolyte chamber is maintained. + The concentration always meets the requirements for electroosmotic migration, thus enabling the replenishment of anolyte and catholyte without stopping the electrolysis process.

[0071] In some embodiments, the condensed sodium bicarbonate solid is processed in subsequent processes to obtain a high-purity sodium bicarbonate product. These post-processing steps include:

[0072] The sodium bicarbonate solid product precipitated by the circulating condensation of the cathode liquid is washed 2-3 times with ice water at 0-5℃, and the amount of washing liquid is 3-5 times the mass of the solid. After removing HCOONa impurities from the surface, it is dried at 80-100℃ and -0.05--0.08MPa for 2-4 hours to obtain sodium bicarbonate product with a purity ≥95%. The washing liquid is returned to the cathode chamber for recycling.

[0073] In some embodiments, the catholyte and anolyte output from the circulation pipeline enter a post-treatment process to obtain formic acid, specifically including:

[0074] Neutralization reaction: The catholyte (mainly containing HCOONa solution) and the anolyte (mainly containing sulfuric acid and sodium sulfate, with a sulfuric acid concentration of 0.5~1.0 mol / L) are mixed at a stoichiometric ratio of 1:0.5~0.6. Simultaneously, 98% concentrated sulfuric acid is slowly added dropwise to the mixture at a controlled rate of 5~10 mL / min. The mixture is continuously stirred at 300~400 rpm, and the pH value is monitored in real-time using an online pH meter to ensure that the final system pH is <7, preferably 3~5, to fully promote the following neutralization reaction:

[0075] H2SO4 + 2HCOONa → Na2SO4+2HCOOH;

[0076] H2SO4 + 2NaHCO3 → Na2SO4 + 2CO2↑ + 2H2O;

[0077] Vacuum distillation separation: The mixed solution after neutralization reaction is transferred to a vacuum distillation apparatus. The optimized distillation parameters are as follows: distillation pressure 0.02~0.05MPa, distillation temperature controlled in stages: 60~65℃ in the early stage to remove free water, 70~75℃ in the middle stage to enrich formic acid, and 75~80℃ in the later stage for deep purification, with a distillation time of 2~4h. Typically, the residual mixture after distillation (containing sodium sulfate and a small amount of sulfuric acid) is returned to the anode chamber as a supplement to the anode electrolyte, realizing the closed-loop utilization of sodium sulfate resources. The raw material recycling rate is ≥80%, reducing the cost of raw material consumption.

[0078] Refining and Purification: The crude formic acid product obtained by distillation with a purity of approximately 95-97% is further refined using a second purification method via vacuum distillation. The vacuum level is controlled at 0.01-0.02 MPa, and the distillation temperature is 65-70°C. Components with a purity ≥ 99% are collected from the distillate. For trace sulfate impurities with a mass fraction ≤ 0.1%, they are removed by adsorption using an ion exchange resin (e.g., model D301) to ensure that the sulfate content in the final formic acid product is ≤ 0.005%.

[0079] Purity testing and assurance: High performance liquid chromatography (HPLC) is used to monitor the purity of formic acid in real time, ensuring that the final purity of formic acid products is ≥ 99%, which meets the standards of the pharmaceutical and pesticide industries.

[0080] In some embodiments, a pretreatment process for the catholyte is also included, specifically including: pre-filtering the output catholyte with a precision filter with a pore size of 0.22 μm to remove trace suspended impurities in the solution, such as incompletely separated sodium bicarbonate crystals and catalyst detachment particles, so as to avoid impurities affecting the subsequent reaction and purification effect.

[0081] Some embodiments disclose a system for the continuous electrochemical reduction of carbon dioxide to formic acid, used to perform the method for the continuous electrochemical reduction of carbon dioxide to formic acid disclosed in the embodiments of the present invention, including:

[0082] H-type electrolytic cells are equipped with cation exchange membranes to divide the H-type electrolytic cells into an anode region and a cathode region;

[0083] The anode area is equipped with an external anolyte circulation tank and an anolyte circulation pump to enable the circulation of anolyte inside and outside the anode area;

[0084] The cathode area is equipped with a sodium bicarbonate condenser, an external cathode liquid circulation tank, and a cathode liquid circulation pump to enable the circulation of cathode liquid inside and outside the cathode area.

[0085] The anolyte external circulation tank and the catholyte external circulation tank are connected to a post-processing component, which is used to receive the output anolyte and catholyte for post-processing to generate formic acid.

[0086] The technical details are further illustrated below with reference to the embodiments.

[0087] Example 1

[0088] The system for the continuous electrochemical reduction of carbon dioxide to formic acid disclosed in Example 1, such as Figure 1 As shown, it specifically includes:

[0089] H-type electrolytic cell 1 is equipped with a cation exchange membrane 5 to divide the H-type electrolytic cell into an anode area and a cathode area. The anode area is equipped with an anode 2, and the anode electrode solution is a sodium sulfate solution. The cathode area is equipped with a cathode 3, and the cathode electrolyte is a sodium bicarbonate solution. The cathode area is equipped with a carbon dioxide input pipe 4 to introduce carbon dioxide gas into the cathode solution.

[0090] The anode area is equipped with an external anolyte circulation tank 12 and an anolyte circulation pump 11. The external anolyte circulation tank 12 is connected to the lower part of the anode area, and the anolyte circulation pump 11 is further connected to the upper part of the anode area to realize the circulation of anolyte inside and outside the anode area.

[0091] The cathode region is equipped with a sodium bicarbonate condenser 32, a cathode liquid external circulation tank 33, and a cathode liquid circulation pump 31. The cathode liquid circulation pump 31 is connected to the upper part of the cathode region, and the cathode liquid external circulation tank 33 is connected to the lower part of the cathode region to realize the circulation of the cathode liquid inside and outside the cathode region. During the circulation process, the cathode liquid condenses and precipitates sodium bicarbonate in the sodium bicarbonate condenser 32 outside the cathode region.

[0092] The anolyte external circulation tank 12 and the catholyte external circulation tank 33 are connected to a post-processing component 6, which is used to receive the output anolyte and catholyte for post-processing to generate formic acid.

[0093] Example 2

[0094] In Example 2, formic acid is continuously prepared using the system for the continuous electrochemical reduction of carbon dioxide disclosed in Example 1, such as... Figure 2 As shown, the preparation method includes:

[0095] Carbon dioxide is reduced by the cathode catalyst in the cathode region to produce formate ions and hydroxide ions. The hydroxide ions react with carbon dioxide to produce bicarbonate ions.

[0096] Sodium ions in the anode region enter the cathode region through the cation exchange membrane, where they form sodium bicarbonate and sodium formate.

[0097] Water generates oxygen and hydrogen ions under the action of the anodic catalyst in the anode region, and forms sulfuric acid in the anode region;

[0098] During the circulation process outside the cathode region, the catholyte in the cathode region condenses and precipitates sodium bicarbonate solid. The catholyte with reduced sodium bicarbonate concentration enters the external circulation tank of the catholyte and then returns to the cathode region to participate in the cathode electrode process.

[0099] The anolyte in the anode zone circulates inside and outside the anode zone. After entering the external circulation tank of the anolyte, it returns to the anode zone to participate in the anode electrode process.

[0100] Once the sodium formate concentration in the catholyte reaches the set concentration, the circulation of both the catholyte and anolyte is stopped; the catholyte is discharged from the external circulation tank, and the anolyte is discharged from the external circulation tank.

[0101] The output catholy and anolyte are fed into the post-processing unit according to a set ratio for post-processing to obtain formic acid product; the by-product sulfuric acid obtained from the processing is fed into the anode as anolyte for recycling; the post-processing unit is usually a formate synthesis and separation system; the process of obtaining formic acid by performing post-processing in the formate synthesis and separation system usually includes neutralization reaction, vacuum distillation separation, purification, and purity detection, etc.

[0102] Add cathodic liquid and anodic liquid to the external circulation tank of cathodic liquid and the external circulation tank of anodic liquid respectively, and start the circulation of cathodic liquid and anodic liquid;

[0103] The above process continues, enabling the continuous production of formic acid.

[0104] Example 3

[0105] In Example 3, referring to the system for the continuous electrochemical reduction of carbon dioxide to prepare formic acid disclosed in Example 1, the method for preparing formic acid includes:

[0106] Using an effective area of ​​100cm² 2 The SnBi catalyst electrode is used as the cathode, with an effective area of ​​100 cm². 2 The anode was an IrTa-plated titanium mesh electrode, and the cation exchange membrane was a Nafion 117 membrane. 3L of a 0.5mol / L sodium bicarbonate solution was prepared using industrial-grade sodium bicarbonate (99% purity) as the raw material, and the cathode solution was industrial sodium sulfate waste salt (Na... + Using 75% sodium sulfate as raw material, prepare 3L of 1.8mol / L sodium sulfate solution as anolyte;

[0107] The catholyte reaction temperature is set at 40℃, and the external circulating condenser for the catholyte is maintained at 1℃ to precipitate sodium bicarbonate solids. The current density is 200 mA / cm². 2 The carbon dioxide gas flow rate is 40 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 7 sccm / cm. 2 Catalyst, start DC power supply and circulation pump, system runs continuously;

[0108] The concentration of formate ions in the catholyte is monitored in real time using an online ion chromatograph. When the formate concentration reaches 5 mol / L, the system automatically triggers the discharge program, outputting the catholyte and anolyte from the external circulation tanks of the catholyte and anolyte at a volume ratio of 1:0.6, until all the solution in the external circulation tank is discharged. At the same time, equal amounts of 0.5 mol / L sodium bicarbonate solution and saturated sodium sulfate solution are added to the cathode and anode areas respectively, and the system continues to circulate.

[0109] The solid precipitated in the condenser was washed and dried with ice water at 3°C ​​to obtain sodium bicarbonate with a purity of 96%.

[0110] After the output catholy liquid is mixed with the anoly liquid, it is neutralized by adding concentrated sulfuric acid dropwise, and then purified by two-step vacuum distillation and ion exchange resin to finally obtain a formic acid product with a purity of 99.2%.

[0111] The electrolysis system did not experience blockage or catalyst deactivation due to salt precipitation and operated stably for 30 days, far exceeding the 3-7 day replacement cycle of traditional processes;

[0112] The average single-pass conversion rate of carbon dioxide is 82%, and the average Faraday efficiency of formic acid is 93%. Figure 3 As shown, the cost of treating sodium sulfate waste salt is 480 yuan / ton, and the comprehensive production cost of formic acid is 2850 yuan / ton.

[0113] The technical solutions and technical details disclosed in the embodiments of this invention are merely illustrative of the inventive concept of this invention and do not constitute a limitation on the technical solutions of the embodiments of this invention. Any conventional changes, substitutions, or combinations made to the technical details disclosed in the embodiments of this invention have the same inventive concept as this invention and are within the protection scope of the claims of this invention.

Claims

1. A method for the continuous preparation of formic acid by electrochemical reduction of carbon dioxide, characterized in that, include: Sodium bicarbonate solution was used as the cathode liquid, and an electrode with a carbon dioxide electrocatalyst was used as the cathode. Sodium sulfate solution is used as the anolyte, and an electrode with a water electrolysis catalyst is used as the anode; a cation exchange membrane is set between the anolyte and the catholyte to isolate them from each other; The temperature of the catholyte is controlled between 35 and 45°C. A set flow rate of carbon dioxide gas is introduced into the catholyte, and an electrochemical reaction is carried out at a set current density. In this process, carbon dioxide gas is reduced to formate at the cathode, and water is converted into oxygen and hydrogen ions at the anode. During the reaction, sodium ions in the anolyte pass through the cation exchange membrane into the catholyte; the catholyte circulates through the external catholyte circulation pipeline, and the catholyte condenses at low temperature to precipitate sodium bicarbonate solid, which then enters the cathode region; the anolyte circulates through the external anolyte circulation pipeline and then enters the anode region. Once the formate concentration in the catholyte reaches a set value, the circulation between the catholyte and anolyte stops, and the catholyte and anolyte are output to the post-processing stage according to a set ratio and quantity to obtain formic acid. Based on the output quantities of anolyte and catholyte, corresponding quantities of sodium sulfate solution and sodium bicarbonate solution are added to the anode and cathode areas respectively, and the catholyte and anolyte circulation is initiated.

2. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, The concentration of sodium bicarbonate solution used as the cathode is 0.1~1.0 mol / L, and the concentration of sodium sulfate used as the anolyte is 1.5~2.0 mol / L.

3. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, In electrochemical reactions, the current density is 0~50 mA / cm². 2 CO2 flow rate is 0~20 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 1~3 sccm / cm 2 catalyst.

4. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, In electrochemical reactions, the current density is 50~100 mA / cm². 2 The CO2 flow rate is 20~30 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 3~6 sccm / cm 2 catalyst.

5. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, In electrochemical reactions, the current density is 100~200 mA / cm². 2 The CO2 flow rate is 30~50 sccm / cm 2 The catalyst and the cathode liquid circulation rate are 6~9 sccm / cm. 2 catalyst.

6. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, Sodium bicarbonate solid is precipitated from the catholyte at 0–5°C.

7. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, During the reaction, the catholyte is stirred at a speed of 400-500 rpm, and the anolyte is stirred at a speed of 200-400 rpm.

8. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, When the formic acid concentration in the catholyte is set to 4~6 mol / L, the catholyte in the external circulation pipeline and the anolyte in the external circulation pipeline stop circulating.

9. The method for continuous preparation of formic acid by electrochemical reduction of carbon dioxide according to claim 1, characterized in that, The catholy and anolyte are fed into the post-processing stage at a ratio of 1:0.5~0.

7.

10. A system for the continuous electrochemical reduction of carbon dioxide to formic acid, used to perform the method for the continuous electrochemical reduction of carbon dioxide to formic acid according to any one of claims 1 to 9, characterized in that, include: H-type electrolytic cells are equipped with cation exchange membranes to divide the H-type electrolytic cells into an anode region and a cathode region; The anode area is equipped with an external anolyte circulation tank and an anolyte circulation pump, which are used to realize the circulation of anolyte inside and outside the anode area; The cathode area is equipped with a sodium bicarbonate condenser, a cathode liquid external circulation tank, and a cathode liquid circulation pump to realize the circulation of cathode liquid inside and outside the cathode area; The anolyte external circulation tank and the catholyte external circulation tank are connected to a post-processing component for receiving the output anolyte and catholyte for post-processing to generate formic acid.

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