CN117604542A - Electrolysis system and electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid - Google Patents

Abstract

The invention discloses an electrolysis system and electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid, which includes a flue gas treatment module, an electrolysis module and a product purification module connected in sequence; the flue gas treatment module is used to treat the flue gas. The carbon dioxide is purified; the electrolysis module includes at least one electrolytic cell. The electrolytic cell includes a carbon dioxide reduction chamber, a methanol oxidation chamber and an ion exchange membrane between the two. The carbon dioxide reduction chamber is equipped with a cathode, and the carbon dioxide reduction chamber and the flue gas treatment module are The electrolyte source is connected, an anode is provided in the methanol oxidation chamber, and the methanol oxidation chamber is connected to the methanol source and the electrolyte source; the product purification module is used to purify the formic acid obtained by electrolysis in the carbon dioxide reduction chamber and the methanol oxidation chamber. By coupling carbon dioxide reduction and methanol oxidation, the required voltage of the electrolytic cell and the amount of carbon dioxide emissions are reduced, and the efficient preparation of formic acid is achieved.

Description

Electrolysis system and electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid

Technical field

The invention relates to the field of carbon dioxide recycling, and in particular to an electrolysis system and electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid.

Background technique

The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

Carbon dioxide electrocatalytic reduction technology is a commonly used technology to reduce emissions of carbon dioxide and other greenhouse gases and develop a carbon recycling economy. However, in the current common carbon dioxide electrocatalytic reduction reaction, the anode usually produces oxygen. There are usually two problems: First, the currently used The oxygen evolution reaction at the anode is a complex four-electron process. Compared with the two-electron process at the cathode, it is very slow, which seriously limits the efficiency of the electrolytic cell. Second, the added value of oxygen is not high, and due to the crossover of cathode and anode gas products, The anode product is mixed with impurity gases such as carbon dioxide and requires secondary purification. Problems such as high electrode potential, slow rate, low added value of the product, and the need for secondary purification in the oxygen evolution reaction have restricted the industrialization and industrial application of carbon dioxide electrolysis. It is necessary to explore a method with low electrode potential, fast reaction rate, and high added value of the product. Anodic reaction.

Formic Acid is a colorless liquid with the chemical formula HCOOH. It has important value and uses in many aspects, such as being used as a solvent, catalyst, bleach, dehydrating agent and feed additive.

In traditional formic acid preparation methods, thermal methods are usually used, including one-step method, two-step method and three-step method. Among them, the one-step method is that methanol and carbon dioxide directly react under the action of a catalyst to generate formic acid; the two-step method: first, methanol is oxidized to generate formaldehyde, and then formaldehyde reacts with water to generate formic acid; the three-step method: first, methanol is oxidized to generate formaldehyde, and then formaldehyde It is reduced with hydrogen to produce methanol, and finally methanol reacts with carbon dioxide to produce formic acid. These thermochemical methods have certain shortcomings, such as complex operations, high energy consumption, and difficulty in ensuring product quality.

The electrochemical method is to obtain formic acid through simultaneous oxidation and reduction through electrolysis. The preparation process of formic acid needs to be completed through methanol oxidation reaction (MOR) and anodizing oxidation reaction (OER). MOR is the oxidation of methanol to formic acid on the anode, while OER refers to the oxidation of water to oxygen on the anode. In the traditional method, these two reactions are independent, that is, methanol undergoes the MOR reaction on the anode, and water undergoes the OER reaction on the anode. However, this independent reaction method has some disadvantages, such as low reaction efficiency and high energy consumption.

Contents of the invention

In view of the shortcomings of the existing technology, the purpose of the present invention is to provide an electrolysis system and electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid.

In order to achieve the above objects, the present invention is achieved through the following technical solutions:

In a first aspect, the present invention provides an electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid, including a flue gas treatment module, an electrolysis module and a product purification module connected in sequence;

Flue gas treatment module, used to purify carbon dioxide in flue gas;

The electrolysis module includes at least one electrolytic cell. The electrolytic cell includes a carbon dioxide reduction chamber, a methanol oxidation chamber and an ion exchange membrane between the two. The carbon dioxide reduction chamber is provided with a cathode, and the carbon dioxide reduction chamber is connected to the flue gas treatment module and the electrolyte source. An anode is provided in the methanol oxidation chamber, and the methanol oxidation chamber is connected to the methanol source and the electrolyte source;

The product purification module is used to purify formic acid obtained by electrolysis in the carbon dioxide reduction chamber and the methanol oxidation chamber.

The voltage required for the operation of an electrolytic cell consists of four parts: theoretical potential, activation loss, concentration loss, and ohmic loss. The theoretical potential is the theoretical voltage required for the cathode and anode reactions to occur. Different reaction combinations can reduce the theoretical voltage required; the activation loss is the overpotential required for the activation of the cathode and anode reactions (and the additional energy required to drive the reaction). This loss can be reduced by improving the catalyst; concentration loss is the energy loss caused by the decrease in the concentration of cathode and anode reactants and insufficient reactant supply. This loss can be reduced through flow field design and reactant ratio design; ohmic loss is the internal resistance of the electrolytic cell The energy loss caused by Joule heat. The internal resistance of the electrolytic cell is composed of catholyte resistance, cathode resistance, ion exchange membrane resistance, anode resistance, and anolyte resistance. The solid resistance is much smaller than the liquid resistance, so the improvement of the structure and solution concentration is reduced. Key measure of ohmic losses. The anode reaction of traditional carbon dioxide reduction is an oxygen evolution reaction. The theoretical electrode potential is 1.23V. The potential of methanol oxidation to formic acid is: 0.103, which is much lower than the oxygen evolution reaction. Therefore, by coupling carbon dioxide reduction and methanol oxidation, the required voltage of the electrolytic cell and the amount of carbon dioxide emissions are reduced, and the efficient preparation of formic acid is achieved. Secondly, compared with the traditional thermal method for preparing formic acid, the electrolysis method does not require high temperature and high pressure conditions, has higher reaction efficiency, is more environmentally friendly, meets economic efficiency requirements, achieves comprehensive utilization of resources, and reduces environmental pollution.

Formic acid is generated in both the carbon dioxide reduction chamber and the methanol oxidation chamber through electrolysis. Through the reaction conditions and process settings, the formic acid in the reduction chamber and the oxidation chamber is mixed, separated and purified in a unified manner, effectively improving the preparation efficiency and separation cost of formic acid, and effectively reducing the cost of formic acid preparation. energy consumption.

An ion exchange membrane is installed between the carbon dioxide reduction chamber and the methanol oxidation chamber to isolate the materials in the carbon dioxide reduction chamber and the methanol oxidation chamber to avoid the crossover of materials in the reduction chamber and the oxidation chamber, causing electrode side reactions and affecting the difficulty of purifying formic acid. .

In some embodiments, an anolyte liquid phase flow channel is also included. The anolyte liquid phase flow channel is located in the methanol oxidation chamber, and the inlet and outlet of the anolyte liquid phase flow channel are connected for circulating the electrolyte in the methanol oxidation chamber. Because the reaction that occurs at the anode is the oxidation of methanol to formic acid, the electrolyte is a carrier and does not directly participate in the reaction. There is no reaction loss. Its function is to improve the conductivity of the anolyte and reduce the overall ohmic loss. Circulating electrolyte can save costs and reduce chemical emissions.

In some embodiments, a catholyte liquid phase flow channel is further included, and the catholyte liquid phase flow channel is connected to the inlet end and the outlet end of the formic acid reduction chamber. Used to circulate the electrolyte in the formic acid reduction chamber.

In some embodiments, the cathode catalytic material is selected from one of lead, mercury, indium, tin, cadmium, thallium, bismuth, copper or alloys thereof.

Preferably, the cathode is a self-supporting structure or includes a support body and cathode material sprayed on it.

In some embodiments, the anode catalytic material is selected from one of iron, cobalt, nickel, copper, or alloys thereof.

Preferably, the anode is a self-supporting structure or includes a support body and anode material sprayed on it.

The cathode and anode catalytic materials are designed and selected for the electrode reaction, and their purpose is to improve the selectivity and reaction rate of the target cathode and anode reactions.

In some embodiments, a heat exchanger is further included for maintaining a constant operating temperature within the electrolytic cell.

In some embodiments, the product purification module includes a first electrolyte gas-liquid phase separation chamber and a second electrolyte gas-liquid phase separation chamber, the inlet of the first electrolyte gas-liquid phase separation chamber is connected to the carbon dioxide reduction chamber, and the gas outlet The carbon dioxide separation chamber, the carbon dioxide purification chamber and the carbon dioxide reduction chamber are connected; the inlet of the second electrolyte gas-liquid phase separation chamber is connected to the methanol oxidation chamber.

Preferably, the carbon dioxide separation chamber is provided with an oxidation chamber and a drying chamber connected in sequence, the oxidation chamber is filled with metal oxide, and the drying chamber is filled with desiccant. The mixed gas separated in the first electrolyte gas-liquid phase separation chamber is passed through the carbon dioxide separation chamber to remove mixed CO and hydrogen from the unreacted carbon dioxide to purify the carbon dioxide and recycle the carbon dioxide. Carbon monoxide and hydrogen are highly reducing gases that can react with metal oxides such as copper oxide and iron oxide to generate carbon dioxide and water vapor. Therefore, there is an oxidation chamber and a drying chamber in the carbon dioxide separation chamber. The oxidation chamber is filled with metal oxides, such as copper oxide, iron oxide, etc., and the drying chamber is filled with desiccant. The gas passes through the oxidation chamber and drying chamber in sequence to remove the carbon monoxide and hydrogen involved in the gas.

Preferably, the product purification module also includes a methanol distillation chamber, a formic acid crude distillation chamber and a formic acid rectification chamber connected in sequence. The inlet of the methanol distillation chamber is respectively connected with the first electrolyte gas-liquid phase separation chamber and the second electrolyte gas-liquid phase separation chamber. The liquid outlet connection of the phase separation chamber.

Further preferably, the methanol distillation chamber is connected to a methanol storage tank. In the process of purifying the product formic acid, a methanol distillation chamber is used to distill and remove unreacted methanol in the mixed liquid. The distilled methanol is stored in a methanol storage tank for easy recycling.

In a second aspect, the present invention provides an electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid, which includes the following steps:

After dust removal, desulfurization and denitrification of the flue gas, a mixed aqueous solution of hot K ₂ CO ₃ and KOH is used to absorb the carbon dioxide in the flue gas to form an enriched liquid. The enriched liquid is passed into the desorption tower for decomposition and purification, and the Decompose and purify carbon dioxide for drying;

Mix the electrolyte and methanol at a volume ratio of 1:1-3 and then pass them into the methanol oxidation chamber, and pass the electrolyte and CO ₂ into the carbon dioxide reduction chamber. The electrolyte is a mixture of alkali metal sulfate and sulfuric acid, and the alkali metal The ion concentration is not less than 0.5mol/L, and the solution pH is 0.5-2;

Pass the purified carbon dioxide into the carbon dioxide reduction chamber to perform an electrolysis reaction. Carbon dioxide is reduced to generate formic acid, and methanol is oxidized to generate formic acid;

Just purify the formic acid in the electrolysis product.

The electrolyte and methanol are mixed at a volume ratio of 1:1-3 and then passed into the methanol oxidation chamber. If the methanol concentration is too high, the conductivity of the anolyte is too small, the overall ohmic resistance of the electrolytic cell increases, and the efficiency decreases. The methanol concentration is too small, the anode reactant concentration is too low, the reaction concentration loss increases, and the efficiency decreases.

Alkali metal ions can promote carbon dioxide reduction reaction and cathode reaction. Therefore, it is necessary to limit the concentration of alkali metal ions. If it is too small, it will cause excessive cathode activation loss and reduce the efficiency of the electrolytic cell.

In some embodiments, in the mixed aqueous solution of K ₂ CO ₃ and KOH, the mass concentration of KOH is 5%-30%.

Preferably, the temperature of the mixed aqueous solution of K ₂ CO ₃ and KOH is 40-80°C. The reaction rate of KOH and CO ₂ increases at high temperature, which can promote the progress of the reaction. It can also increase the solubility of KHCO ₃ and K ₂ CO ₃ to avoid precipitation.

In some embodiments, the purification includes the step of separating gas and liquid of the electrolysis product, and purifying the separated gas mixture to remove CO and hydrogen.

Further preferably, the separated carbon dioxide is recycled into the carbon dioxide reduction chamber.

Preferably, the liquid obtained by gas-liquid separation is subjected to methanol distillation, formic acid crude distillation and formic acid rectification to obtain a formic acid product.

Preferably, when performing crude distillation of formic acid, sulfuric acid is added to the solution to adjust the pH value of the solution to 1-4.

In some embodiments, during the electrolysis reaction, the temperature of the electrolytic cell is no higher than 60°C.

In some embodiments, the electricity used for electrolysis is green electricity. The main sources of green electricity are solar energy, wind energy, biomass energy and geothermal energy. my country mainly relies on solar energy and wind energy.

The beneficial effects achieved by one or more embodiments of the present invention are:

The invention uses green electricity to electrolyze methanol and carbon dioxide to prepare formic acid. The green electricity can be stored in the formic acid in the form of chemical energy, effectively utilizing and storing the green electricity, and solving the problem of renewable energy consumption to a certain extent. .

Dust, nitrogen oxides, sulfur oxides, carbon dioxide, etc. in the flue gas are targeted and utilized, and the carbon dioxide is utilized through the carbon dioxide reduction chamber, and clean energy is stored in formic acid in the form of stable chemical energy. ; At the same time, the industrial by-product methanol is effectively utilized to efficiently co-produce formic acid, an important chemical raw material; in addition, throughout the electrolysis production process, the reduction chamber and oxidation chamber electrolytes realize mixing, separation and distillation, reducing the need for alkaline electrolyte reduction chambers The high cost of separation and distillation caused by separation from the oxidation chamber, and most of the raw materials and electrolytes of the system can be recycled, which is economical and environmentally friendly.

Description of drawings

The description and drawings that constitute a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

Figure 1 is a schematic diagram of the overall structure of an electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to an embodiment of the present invention;

Figure 2 is a schematic diagram of the overall structure of an electrolytic cell for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to an embodiment of the present invention.

Among them, 1-primary flue gas pretreatment chamber; 2-secondary flue gas pretreatment chamber; 3-carbon dioxide purification chamber; 4-carbon dioxide separation chamber; 5-carbon dioxide reduction chamber; 6-methanol oxidation chamber; 7-electrolyte Storage room; 8-First electrolyte gas-liquid phase separation chamber; 9-Second electrolyte gas-liquid phase separation chamber; 10-Methanol distillation chamber; 11-Formic acid crude distillation chamber; 12-Heat exchanger; 13-Formic acid essence Distillation chamber; 14-methanol storage tank; 15-anode liquid phase flow channel; 16-anode; 17-ion exchange membrane; 18-cathode liquid phase flow channel; 19-cathode; 20-cathode gas phase channel.

Detailed ways

It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings commonly understood by one of ordinary skill in the art to which this invention belongs.

Example

As shown in Figure 1, an electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid includes a flue gas treatment module, an electrolysis module, a product purification module and a storage module, where,

The flue gas treatment module includes:

The primary flue gas pretreatment room 1 is connected to the flue gas pipeline of the power plant to remove dust and sulfides in the flue gas. For example, a cyclone separator is used to remove dust in the flue gas, and the flue gas is desulfurized to remove sulfide.

The secondary flue gas pretreatment chamber 2 denitrates the flue gas and removes impurities such as nitrogen oxides;

Carbon dioxide purification chamber 3 uses chemical absorption purification method to absorb the carbon dioxide in the flue gas with hot K ₂ CO ₃ /KOH aqueous solution to form a rich liquid, which enters the analysis tower to add decomposed and purified carbon dioxide, and undergoes further dehydration and drying, etc. Treatment, the mass concentration of KOH in the hot solution is 5%-30%;

The carbon dioxide separation chamber 4 is connected to the gas phase outlet of the electrolyte gas-liquid phase separation chamber, and removes a small amount of carbon monoxide and hydrogen in the gas phase of the gas-liquid mixture after electrolysis.

The electrolysis module consists of multiple repeating modules, each of which includes:

The carbon dioxide reduction chamber 5 is connected to the outlet of the carbon dioxide purification chamber, and under a certain voltage and current, reduces carbon dioxide to formic acid in an acidic solution; the methanol oxidation chamber 6 is connected to the outlet of the methanol storage chamber, and under a certain voltage and current, oxidizes methanol into formic acid; An ion exchange membrane is passed between the carbon dioxide reduction chamber 5 and the methanol oxidation chamber 6;

Heat exchanger 12 maintains a constant operating temperature of the electrolytic cell;

Product purification module and storage module include:

The electrolyte storage chamber 7 is connected to the liquid phase outlet of the formic acid distillation chamber to provide electrolyte for the electrolysis module;

The first electrolyte gas-liquid phase separation chamber 8 is connected to the carbon dioxide reduction chamber, and the second electrolyte gas-liquid phase separation chamber 9 is connected to the product outlet of the methanol oxidation chamber 6 to separate the gas-liquid phase products;

The methanol distillation chamber 10 is connected to the liquid phase outlet of the first electrolyte gas-liquid phase separation chamber 8 and the second electrolyte gas-liquid phase separation chamber 9 to distill the methanol in the solution for recycling;

The formic acid crude distillation chamber 11 is connected to the liquid phase outlet of the methanol distillation chamber 10. After adding sulfuric acid to adjust the solution to a suitable pH value, the formic acid in the solution is distilled.

The formic acid distillation chamber 13 is connected to the gas phase outlet of the formic acid crude distillation chamber 11, and performs secondary purification of formic acid based on secondary distillation.

The methanol storage tank 14 is connected to the outlet of the formic acid distillation chamber 13 to store formic acid.

The electrolytic cell is an electrocatalytic reduction device composed of multiple single electrolytic cells. The single electrolytic cells are shown in Figure 2 and include,

Ion exchange membrane 17 isolates the methanol oxidation chamber and the carbon dioxide reduction chamber to avoid product crossover;

Anode 16, which is located on the side of the ion exchange membrane close to the methanol oxidation chamber;

Cathode 19, which is located on the side of the ion exchange membrane close to the carbon dioxide reduction chamber;

Anolyte liquid phase flow channel 15, which is located on the side of the anode away from the ion exchange membrane to circulate the anolyte;

The cathode liquid phase flow channel 18 is located on the side of the cathode away from the ion exchange membrane to circulate the catholyte;

The cathode gas phase channel 20 is located on the side of the cathode away from the ion exchange membrane to circulate carbon dioxide gas. The cathode gas phase channel and the liquid phase channel are separated by a hydrophobic porous cathode.

The cathode catalytic material is composed of a single metal material or alloy such as lead, mercury, indium, tin, cadmium, thallium, bismuth, copper, etc. The anode catalytic material is composed of iron, cobalt, nickel, copper and other metal materials and their oxides or alloys. The catalyst microstructure includes but is not limited to nanoparticles, nanowires, single atoms and other forms.

An electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid includes the following steps:

Circuit: Clean energy generates green electricity, part of which is supplied to the carbon dioxide electrolytic cell for electrolysis; the other part is converted into alternating current through the inverter and rectified by the distribution box and distributed to the power supply line of the system. The circuit controller controls the operation of the circuit and the power storage group Store excess electrical energy and replenish electrical energy to power supply lines;

Gas path: The power plant flue gas passes through the flue gas pretreatment chamber. Impurities such as dust, sulfur and nitrogen oxides in the flue gas then enter the carbon dioxide purification chamber. The purer carbon dioxide is obtained and enters the carbon dioxide reduction chamber to be reduced. The product is separated by gas and liquid. , the gas passes through the carbon dioxide separation chamber, and the unreacted carbon dioxide is separated and continues to enter the reduction chamber, forming a gas phase material cycle of carbon dioxide;

Liquid path: After part of the electrolyte and methanol solution are mixed in a certain ratio (1:1-1:3), they enter the methanol oxidation chamber for oxidation to generate formic acid. The remaining electrolyte enters the carbon dioxide reduction chamber to provide a liquid environment to promote the carbon dioxide reduction reaction. And take away the formic acid products. After the products in the carbon dioxide reduction chamber and the methanol anode chamber are separated by gas and liquid, the solutions are mixed and enter the methanol distillation chamber together. The separated methanol enters the oxidation chamber again to be oxidized, forming a circulation of methanol materials. The obtained solution enters the formic acid and distillation chamber for purification of formic acid. The obtained high-purity formic acid is stored in the formic acid storage tank, while the separated impurities are transported to the electrolyte storage chamber to form a circulation of electrolyte materials.

The cathode liquid phase flow channel and the anode liquid phase flow channel are serpentine, cross-shaped or bionic flow channels, and the flow rate of the liquid phase flow channel does not exceed 100 sccm.

The electrolyte is a mixture of alkali metal sulfate and sulfuric acid, the alkali metal concentration is not less than 0.5mol/L, and the solution pH range is 0.5-2.

The solution temperature in the methanol distillation chamber is 72-75°C, the steam temperature is 65-70°C, and the pressure is less than 0.2MPa. In the formic acid crude distillation chamber, formic acid can be crudely distilled by azeotropic distillation, dry distillation or extraction.

The temperature of the electrolysis module should not be higher than 60℃.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. An electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid, which is characterized by: including a flue gas treatment module, an electrolysis module and a product purification module connected in sequence; Flue gas treatment module, used to purify carbon dioxide in flue gas; The electrolysis module includes at least one electrolytic cell. The electrolytic cell includes a carbon dioxide reduction chamber, a methanol oxidation chamber and an ion exchange membrane between the two. The carbon dioxide reduction chamber is provided with a cathode, and the carbon dioxide reduction chamber is connected to the flue gas treatment module and the electrolyte source. An anode is provided in the methanol oxidation chamber, and the methanol oxidation chamber is connected to the methanol source and the electrolyte source; The product purification module is used to purify formic acid obtained by electrolysis in the carbon dioxide reduction chamber and the methanol oxidation chamber. 2. The electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 1, characterized in that: it also includes an anolyte liquid phase flow channel, the anode liquid phase flow channel is located in the methanol oxidation chamber, and the anolyte liquid phase flows The inlet and outlet of the channel are connected and used to circulate the electrolyte in the methanol oxidation chamber; Or, it also includes a cathode liquid phase flow channel, and the cathode liquid phase flow channel is connected with the inlet end and the outlet end of the formic acid reduction chamber. 3. The electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 1, characterized in that: the cathode catalytic material is selected from one of lead, mercury, indium, tin, cadmium, thallium, bismuth, and copper. species or alloys thereof; Or, the cathode is a self-supporting structure or includes a support body and cathode material sprayed on it; Or, the anode catalytic material is selected from one of iron, cobalt, nickel, copper or their alloys; Or, the anode is a self-supporting structure or includes a support body and anode material sprayed on it. 4. The electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 1, characterized in that: the product purification module includes a first electrolyte gas-liquid phase separation chamber and a second electrolyte gas-liquid phase. In the separation chamber, the inlet of the first electrolyte gas-liquid phase separation chamber is connected to the carbon dioxide reduction chamber, the gas outlet is connected to the carbon dioxide reduction chamber through the carbon dioxide separation chamber, the carbon dioxide purification chamber, and the second electrolyte gas-liquid phase separation chamber inlet is connected to the methanol oxidation chamber. . 5. The electrolysis system for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 1, characterized in that: the carbon dioxide separation chamber is provided with an oxidation chamber and a drying chamber that are connected in sequence, and the oxidation chamber is filled with metal oxides. , the drying chamber is filled with desiccant; Preferably, the product purification module also includes a methanol distillation chamber, a formic acid crude distillation chamber and a formic acid rectification chamber connected in sequence. The inlet of the methanol distillation chamber is respectively connected with the first electrolyte gas-liquid phase separation chamber and the second electrolyte gas-liquid phase separation chamber. liquid outlet connection of the phase separation chamber; Further preferably, the methanol distillation chamber is connected to a methanol storage tank. 6. An electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid, which is characterized by: including the following steps: After dust removal, desulfurization and denitrification of the flue gas, a mixed aqueous solution of hot K ₂ CO ₃ and KOH is used to absorb the carbon dioxide in the flue gas to form an enriched liquid. The enriched liquid is passed into the desorption tower for decomposition and purification, and the Decompose and purify carbon dioxide for drying; Mix the electrolyte and methanol at a volume ratio of 1:1-3 and then pass it into the methanol oxidation chamber, and pass the electrolyte into the carbon dioxide reduction chamber. The electrolyte is a mixture of alkali metal sulfate and sulfuric acid, and the concentration of alkali metal ions does not vary. Below 0.5mol/L, the pH value of the solution is 0.5-2; Pass the purified carbon dioxide into the carbon dioxide reduction chamber to perform an electrolysis reaction. Carbon dioxide is reduced to generate formic acid, and methanol is oxidized to generate formic acid; Just purify the formic acid in the electrolysis product. 7. The electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 6, characterized in that: in the mixed aqueous solution of K ₂ CO ₃ and KOH, the mass concentration of KOH is 5%-30%; Preferably, the temperature of the mixed aqueous solution of K ₂ CO ₃ and KOH is 40-80°C. 8. The electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 6, characterized in that: the purification includes the step of gas-liquid separation of the electrolysis product, and the separated mixed gas is subjected to carbon dioxide Purification to remove CO and hydrogen; Further preferably, the separated carbon dioxide is recycled into a carbon dioxide reduction chamber; Preferably, the liquid obtained by gas-liquid separation is subjected to methanol distillation, formic acid crude distillation and formic acid rectification to obtain a formic acid product; Preferably, when performing crude distillation of formic acid, sulfuric acid is added to the solution to adjust the pH value of the solution to 1-4. 9. The electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 6, characterized in that: during the electrolysis reaction, the temperature of the electrolytic cell is not higher than 60°C. 10. The electrolysis method for power plant flue gas treatment coupled with methanol oxidation to produce formic acid according to claim 6, characterized in that: the electricity used for electrolysis is green electricity.