Method and device for preparing formic acid and hydrogen through electrolysis

Abstract

The invention relates to a method and device for preparing formic acid and hydrogen through electrolysis. According to the method, an alkaline electrolyte containing methanol is electrolyzed, a cathode electrode for electrolysis takes foamed nickel as a base material to load iron-cobalt-nickel nanoparticles, an anode electrode takes foamed nickel as a base material to load cobalt-nickel particles, and a cathode chamber generates hydrogen; and collecting the electrolyte obtained after electrolysis in the anode chamber in the electrolysis device for bipolar membrane electrodialysis, and obtaining a primary formic acid solution in the acid chamber of the bipolar membrane electrodialysis device. The device comprises an electrolysis device and a bipolar membrane electrodialysis device, a cathode electrode, a first bipolar membrane, a positive membrane, a negative membrane, a second bipolar membrane and an anode electrode are sequentially arranged in the bipolar membrane electrodialysis device, and an acid chamber, a salt chamber and an alkali chamber are sequentially divided among the first bipolar membrane, the positive membrane, the negative membrane and the second bipolar membrane. Compared with an existing methyl formate hydrolysis method for preparing formic acid, an intermediate methyl formate is toxic to a human body, formic acid and hydrogen can be safely prepared, and production safety accidents are prevented.

Description

Technical Field

[0001] The present application relates to the technical field of formic acid production, and in particular to a method and device for producing formic acid and hydrogen by electrolysis. Background Art

[0002] Formic acid is one of the important basic organic chemical raw materials, and is widely used in organic synthesis, pesticides, leather and medicine. Formic acid can be used to synthesize various pharmaceutical intermediates; it can also be used as a metal surface treatment agent, rubber additive and industrial solvent; it can also be directly used in fabric processing, leather tanning, textile printing and dyeing, and green fodder storage.

[0003] At present, most industrial countries in the world adopt the methyl formate hydrolysis method to produce formic acid. The methyl formate hydrolysis method first uses CO to carbonylate methanol to synthesize methyl formate, then hydrolyzes methyl formate into methanol and formic acid, and obtains formic acid through separation and purification, such as patent document CN101481304A. However, methyl formate, an intermediate of formic acid prepared by the methyl formate hydrolysis method, is toxic to the human body and can cause adverse reactions such as chest oppression and dyspnea.

[0004] Therefore, how to safely prepare formic acid and prevent production safety accidents has become a problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] In order to safely produce formic acid and prevent production safety accidents, the present application provides a method and apparatus for producing formic acid and hydrogen by electrolysis.

[0006] According to one aspect of the present application, a method for preparing formic acid and hydrogen by electrolysis is provided, comprising:

[0007] Electrolyzing an alkaline electrolyte containing methanol, wherein the cathode electrode structure in the electrolysis device used is a nickel foam substrate loaded with iron-cobalt-nickel nanoparticles, the anode electrode structure in the electrolysis device is a nickel foam substrate loaded with cobalt-nickel nanoparticles, and the cathode chamber in the electrolysis device generates hydrogen;

[0008] The electrolyte after electrolysis in the anode chamber of the electrolysis device is collected, and a bipolar membrane electrodialysis device is used to perform bipolar membrane electrodialysis on the collected electrolyte after electrolysis in the anode chamber, and a primary formic acid solution is obtained in the acid chamber of the bipolar membrane electrodialysis device.

[0009] According to another aspect of the present application, a device for preparing formic acid and hydrogen by electrolysis is provided, which is used to implement the method for preparing formic acid and hydrogen by electrolysis, comprising:

[0010] Electrolysis devices and bipolar membrane electrodialysis devices;

[0011] The cathode electrode of the electrolysis device is constructed with nickel foam as the substrate and loaded with iron-cobalt-nickel nanoparticles, the anode electrode of the electrolysis device is constructed with nickel foam as the substrate and loaded with cobalt-nickel nanoparticles, and the electrolysis device is provided with a gas outlet near the cathode electrode to collect hydrogen;

[0012] The bipolar membrane electrodialysis device is provided with a cathode electrode, a first bipolar membrane, a cation membrane, a cathodic membrane, a second bipolar membrane and an anode electrode in sequence, and the first bipolar membrane, the cation membrane, the cathodic membrane and the second bipolar membrane are divided into three compartments, namely, an acid chamber, a salt chamber and an alkali chamber.

[0013] The present application can always tend to electrolyze methanol aqueous solution to generate formic acid and hydrogen during the electrolysis process. Compared with the existing methyl formate hydrolysis method for producing formic acid, firstly, methanol is carbonylated by CO to synthesize methyl formate, and then methyl formate is hydrolyzed into methanol and formic acid to separate formic acid. Methyl formate is toxic to the human body and can easily cause production safety accidents. The present application uses methanol aqueous solution as raw material, produces formic acid at the anode of the electrolytic cell, and collects hydrogen at the cathode of the electrolytic cell, which can safely and effectively produce formic acid and hydrogen and prevent production safety accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic flow chart showing a method for producing formic acid and hydrogen by electrolysis according to an embodiment of the present application;

[0015] Figure 2 A schematic diagram showing the structure of a device for producing formic acid and hydrogen by electrolysis according to an embodiment of the present application;

[0016] Figure 3 A schematic diagram showing the structure of an electrolysis device according to an embodiment of the present application;

[0017] Figure 4 A schematic diagram showing the structure of a bipolar membrane electrodialysis device according to an embodiment of the present application;

[0018] Figure 5 A schematic diagram showing the structure of a diffusion dialysis device according to an embodiment of the present application;

[0019] Figure 6 A schematic diagram showing the structure of an anion exchange membrane of a diffusion dialysis device according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0020] Various exemplary embodiments, features and aspects of the present application will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0021] Among them, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention or simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0022] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0023] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0024] In addition, in order to better illustrate the present application, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present application can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present application.

[0025] Figure 1 A schematic flow chart showing a method for producing formic acid and hydrogen by electrolysis according to an embodiment of the present application; Figure 2 A schematic diagram showing the structure of a device for producing formic acid and hydrogen by electrolysis according to an embodiment of the present application is shown; Figure 3 A schematic structural diagram of an electrolysis device according to an embodiment of the present application is shown; Figure 4 A schematic structural diagram of a bipolar membrane electrodialysis device according to an embodiment of the present application is shown; Figure 5 A schematic structural diagram of a diffusion dialysis device according to an embodiment of the present application is shown; Figure 6 A schematic structural diagram of an anion exchange membrane of a diffusion dialysis device according to an embodiment of the present application is shown.

[0026] According to one aspect of the present application, a method for preparing formic acid and hydrogen by electrolysis is provided, comprising the following steps: S100, electrolyzing an alkaline electrolyte containing methanol, wherein the structure of the cathode electrode 110 in the electrolysis device 100 used is that the substrate is nickel foam and loaded with iron-cobalt-nickel nanoparticles, and the structure of the anode electrode 120 in the electrolysis device 100 is that the substrate is nickel foam and loaded with cobalt-nickel nanoparticles, the cathode chamber in the electrolysis device 100 produces hydrogen, and the anode chamber in the electrolysis device 100 produces formic acid;

[0027] S200, collecting the electrolyte after electrolysis in the anode chamber of the electrolysis device 100 and pumping it into the salt chamber 250 of the bipolar membrane electrodialysis device 200, using the bipolar membrane electrodialysis device 200 to perform bipolar membrane electrodialysis on the collected electrolyte after electrolysis in the anode chamber, and obtaining a primary formic acid solution in the acid chamber 250 of the bipolar membrane electrodialysis device 200.

[0028] The alkaline electrolyte containing methanol means that the original electrolyte added to the electrolytic cell can be a mixed solution of methanol and potassium hydroxide, or a mixed solution of methanol and sodium hydroxide. Taking the mixed solution of methanol and potassium hydroxide as the original electrolyte as an example, the present application electrolyzes the methanol aqueous solution by setting an electrolysis device, generates formic acid at the anode, collects hydrogen at the cathode, and removes potassium hydroxide impurities in the anode electrolyte by setting a bipolar membrane electrodialysis device to harvest a relatively pure primary formic acid solution. Compared with the existing CO2 carbonylation of methanol to synthesize toxic methyl formate, and then hydrolyzes methyl formate into methanol and formic acid, and obtains formic acid through separation and refining, the present application directly electrolyzes methanol aqueous solution to produce formic acid, directly obtains a mixed solution of potassium formate and potassium hydroxide at the anode, and then obtains a primary formic acid solution through bipolar membrane electrodialysis, which can safely and effectively produce formic acid and hydrogen, and prevent production safety accidents.

[0029] In addition, in the process of preparing formic acid by the traditional methyl formate hydrolysis method, it is necessary to first use CO to carbonylate methanol, and CO is one of the main raw materials. However, CO is not environmentally friendly and is a common pollutant in indoor and outdoor air. Moreover, CO is stable in the air and the process of converting to CO2 is very slow. Moreover, CO is a colorless and odorless toxic gas that mainly acts on the blood, causing tissue hypoxia, which can cause acute and chronic poisoning, and its leakage can also cause safety accidents. The present application uses methanol-water solution as raw material, directly electrolyzes to produce high-value hydrogen and non-toxic potassium formate, and then directly obtains a primary formic acid solution through bipolar membrane electrodialysis. It is environmentally friendly, clean and efficient, and can reduce and prevent the occurrence of safety accidents.

[0030] In addition, there is currently a process for producing formic acid: formamide hydrolysis method, which also first uses CO to carbonylate methanol to synthesize toxic methyl formate, and then reacts methyl formate with anhydrous ammonia: HCOOCH3+NH3→HCONH2(formamide)+CH3OH; then the formamide obtained by fractionation and purification is mixed with sulfuric acid to undergo a hydrolysis reaction: 2HCONH2+Na2SO4+2H2O→2HCOOH+(NH4)2SO4; then formic acid is obtained after drying and condensation. Methyl formate, an important intermediate for producing formic acid by formamide hydrolysis method, is toxic, and the present application can safely produce formic acid and hydrogen, reducing and preventing the occurrence of safety accidents.

[0031] This application uses methanol as a raw material to electrolyze formic acid and hydrogen. The overall reaction formula during the electrolysis process is as follows:

[0032] CH3OH+OH — →HCOO — +2H2

[0033] During the electrolysis process, hydrogen is generated at the cathode of the electrolyzer as follows:

[0034] 4H2O+4e — →2H2+4OH —

[0035] Formic acid is produced at the anode of the electrolytic cell as follows:

[0036] CH3OH+5OH — →HCOO — +4e — +4H2O

[0037] During the electrolysis process, the cathode electrode 110 is loaded with iron-cobalt-nickel nanoparticles based on nickel foam, and the thickness of the loaded particles does not exceed 100 nanometers, which is conducive to the rapid detachment of tiny hydrogen formed on the electrode surface from the material surface, thereby increasing the cathode hydrogen evolution reaction rate.

[0038] The anode electrode 120 is loaded with cobalt-nickel bimetallic nanoparticles on a nickel foam substrate, and the loaded particles have a thickness of no more than 100 nanometers. In the existing methanol-water electrolysis hydrogen production system, methanol is usually used as a raw material for electrolysis, carbon dioxide gas with no production value is produced at the anode, and hydrogen produced by electrolysis is collected at the cathode. The microstructure of the bimetallic nanoparticles of the anode electrode 120 material of the electrolysis device of the present application is conducive to promoting methanol to generate formic acid and hydrogen, rather than carbon dioxide and hydrogen.

[0039] Specifically, this composite bimetallic alloy cluster of the anode electrode 120 can improve the material's adsorption capacity for methanol molecules and prolong the adsorption time. The synergistic effect of the bimetallic atoms of the bimetallic nanomaterial exhibits excellent stability and catalytic properties for methanol oxidation that surpass single metals. At the same time, as shown below, the nickel-cobalt bimetallic nanoparticles generate NiCo-OOH intermediates in the electrochemical reaction, and methanol cannot be completely oxidized into carbon monoxide or carbon dioxide, but tends to selectively generate formate. Taking an alkaline electrolyte composed of methanol and potassium hydroxide as an example, the nickel-cobalt bimetallic nanoparticles at the anode make methanol more inclined to generate potassium formate.

[0040] Ni(OH)2+OH — →NiOOH+H2O+e —

[0041] NiOOH+RCH2OH→Ni(OH)2+RC·HOH

[0042] RC·HOH+3OH — →RCOOH+2H2O+3e —

[0043] Therefore, the present application can always tend to electrolyze methanol to produce formic acid and hydrogen during the electrolysis process. Compared with the existing electrolysis of water to produce hydrogen and oxygen, the anode and cathode produce hydrogen and oxygen at the same time, which is easy to cause safety accidents such as explosion caused by the mixture of hydrogen and oxygen. The present application uses methanol as raw material, produces formic acid at the anode of the electrolytic cell, and collects hydrogen at the cathode of the electrolytic cell. It can safely and effectively produce hydrogen and prevent safety accidents such as explosion caused by mixing with oxygen.

[0044] Furthermore, in the existing process of producing hydrogen by electrolysis of water, the oxygen evolution reaction at the anode has severe kinetic retardation due to the four-electron transfer process, requiring high energy input to overcome the energy barrier, and the overall energy consumption of producing hydrogen by electrolysis of water is high. The present application can produce high-value hydrogen with lower energy consumption using cheap methanol, while producing high-value formic acid at the anode.

[0045] The power consumption of producing one standard cubic meter of hydrogen by conventional water electrolysis is 4.8 to 5.0 kWh, while the power consumption of producing one standard cubic meter of hydrogen by methanol electrolysis and hydrogen provided in this application is 3.6 to 3.8 kWh, and the energy consumption of producing one standard cubic meter of hydrogen by electrolysis is significantly reduced. It should be noted that under this energy consumption, the anode of the electrolyzer is also producing formic acid. Even if the electricity used is fully calculated for hydrogen production, it is 10% to 24% lower than the energy consumption of conventional water electrolysis and hydrogen production.

[0046] The electrolyte after electrolysis is rich in potassium hydroxide and potassium formate. The electrolyte after electrolysis is collected and added to the salt chamber 250 for bipolar membrane electrodialysis, and a formic acid solution is obtained in the acid chamber 250 of the bipolar membrane electrodialysis device 200. The interior of the bipolar membrane electrodialysis device 200 is usually provided with a cathode side bipolar membrane, a membrane group with a plurality of anion and cation membranes spaced apart, and an anode side bipolar membrane in sequence. The compartment divided by the anion membrane and the cation membrane in the module is called the salt chamber 250. After bipolar membrane electrodialysis, the acidic solute is enriched in the compartment between the anode side bipolar membrane and the anion membrane. Therefore, the compartment divided by the anode side bipolar membrane and the anion membrane is the acid chamber 250, and a formic acid solution is collected in the acid chamber 250.

[0047] In order to perform bipolar membrane electrodialysis on the electrolyte in the anode chamber after electrolysis and conveniently and easily realize the above-mentioned separation and impurity removal function, the bipolar membrane electrodialysis device 200 used in the bipolar membrane electrodialysis process, such as Figure 4 As shown, an anode electrode, a first bipolar membrane 210, a negative membrane 220, a positive membrane 230, a second bipolar membrane 240 and a cathode electrode are sequentially arranged inside. The first bipolar membrane 210 and the negative membrane 220 form a compartment in the bipolar electrodialysis device as an acid chamber 250, the positive membrane 230 and the negative membrane 220 form a compartment in the bipolar electrodialysis device as a salt chamber 250, and the positive membrane 230 and the second bipolar membrane 240 form a compartment in the bipolar electrodialysis device as an alkali chamber 260.

[0048] The electrolyte after electrolysis is a mixture of potassium hydroxide and potassium formate. The electrolyte after electrolysis is pumped into the salt chamber 250 of the bipolar membrane electrodialysis device 200, that is, the compartment between the positive membrane 230 and the negative membrane 220. The potassium formate present in a large amount in the solution is dissociated into formate ions and potassium ions. The formate ions enter the acid chamber 250 between the negative membrane 220 and the first bipolar membrane 210 through the negative membrane 220, and form formic acid with the hydrogen ions obtained by dissociation with the first bipolar membrane 210. Therefore, in the process of bipolar membrane electrodialysis, formic acid is enriched in the acid chamber 250. The potassium ions enter the alkali chamber 260 between the positive membrane 230 and the second bipolar membrane 240 through the positive membrane 230, and potassium hydroxide is enriched in the alkali chamber 260 of the bipolar membrane electrodialysis device 200. The present application removes potassium hydroxide impurities by subjecting the electrolyzed electrolyte to bipolar membrane electrodialysis treatment, and the formate ions dissociated from potassium formate in the original solution and the hydrogen ions dissociated from the bipolar membrane are enriched into formic acid molecules in the acid chamber, thereby obtaining a primary formic acid solution with higher purity.

[0049] In a possible implementation, the electrolysis operation of the alkaline electrolyte containing methanol is performed at a first preset temperature and a preset voltage, wherein the preset voltage is 1.4V to 1.95V and the first preset temperature is 45°C to 90°C.

[0050] During the electrolysis process, the electrolysis voltage is always controlled to be lower than the voltage value of oxygen evolution by electrolysis of water, and maintained at 1.4V~1.95V. This can prevent the anode of the electrolytic cell from undergoing oxygen evolution reaction to produce oxygen, and instead tend to electrolyze methanol to produce formic acid.

[0051] Furthermore, during the electrolysis operation of the alkaline electrolyte containing methanol, the electrolyte in the electrolyte is gradually decomposed and reduced, the resistance increases, the voltage rises, and the electrolysis efficiency gradually decreases. When the voltage reaches 1.9V, the electrolysis can be stopped and the next step of bipolar membrane electrodialysis treatment can be carried out.

[0052] In a possible implementation, before electrolyzing the alkaline electrolyte at S100, the process further includes preheating the alkaline electrolyte to a first preset temperature at S400. Specifically, the alkaline electrolyte containing methanol is added to the raw material tank 400, the alkaline electrolyte is preheated to the first preset temperature by the heat exchange device 410, and the preheated alkaline electrolyte is pumped into the electrolytic tank for electrolysis.

[0053] In a possible implementation, after collecting the electrolyte after electrolysis in the anode chamber of the electrolysis device 100, before using the bipolar membrane electrodialysis device 200 to perform bipolar membrane electrodialysis on the collected electrolyte after electrolysis in the anode chamber in S200, it also includes S600, a treatment step of reverse osmosis concentration of the electrolyte in the anode chamber after electrolysis.

[0054] The electrolyte after electrolysis in the anode chamber contains a large amount of water, and the concentration of potassium formate is low. At this time, the energy consumption of bipolar membrane electrodialysis is large, and the impurity removal efficiency is low. In order to increase the concentration of formic acid, thereby reducing the workload of the bipolar membrane electrodialysis device 200 and improving the enrichment efficiency of bipolar membrane electrodialysis, the present application conducts reverse osmosis concentration to the electrolyte after electrolysis in the anode chamber after electrolysis. The effluent from the anode chamber is pumped into the high-pressure side of the membrane, the concentrated solution is collected on the high-pressure side of the membrane, and the concentrated solution is pumped into the salt chamber 250 of the bipolar electrodialysis device.

[0055] Reverse osmosis, also known as reverse osmosis, is a membrane separation operation that uses pressure difference as a driving force to separate solvents from solutions. When pressure is applied to the liquid on one side of the membrane, the solvent will penetrate in the opposite direction of natural penetration. As a result, the permeated solvent, i.e., the permeate, is obtained on the low-pressure side of the membrane; the concentrated solution, i.e., the concentrate, is obtained on the high-pressure side.

[0056] In a possible implementation, after collecting the electrolyte after electrolysis in the anode chamber of the electrolysis device 100, before using the bipolar membrane electrodialysis device 200 to perform bipolar membrane electrodialysis on the collected electrolyte after electrolysis in the anode chamber in S200, the process also includes: S300 performing a diffusion dialysis treatment step on the electrolyte after electrolysis in the anode chamber. Diffusion dialysis can effectively remove excess alkali in the electrolyte with extremely low energy consumption, thereby improving the purity of the formic acid solution and reducing energy consumption.

[0057] In a possible implementation, in order to improve the efficiency of diffusion dialysis, after collecting the electrolyte after electrolysis in the anode chamber of the electrolysis device 100, before performing diffusion dialysis on the electrolyte after electrolysis in the anode chamber in S300, it also includes an operation step of cooling the electrolyte after electrolysis in the anode chamber to below a second preset temperature, and the second preset temperature is 20° C. to 40° C. Further, the second preset temperature is 40° C.

[0058] In a possible implementation, after electrolyzing the alkaline electrolyte containing methanol in S100, before performing bipolar membrane electrodialysis in S200 / diffusion dialysis in S300 / reverse osmosis concentration in S600, an operation step of collecting the electrolyte in the anode chamber after electrolysis to the intermediate liquid tank in S500 is also included. The present application collects the electrolyte rich in formic acid obtained from one electrolysis in the intermediate liquid tank, which is convenient for quickly replacing the electrolyte for the next electrolysis and also for batch processing.

[0059] In one possible implementation, S700, the primary formic acid solution after bipolar membrane electrodialysis is distilled, and the methanol impurities remaining in the formic acid solution are removed by using the different boiling points to obtain a secondary formic acid solution. After electrolysis, the anode chamber outlet liquid is a mixture of potassium hydroxide, potassium formate and a small amount of methanol. After bipolar membrane electrodialysis removes potassium hydroxide impurities, the solution collected in the acid chamber 250 is a mixture of formic acid and a small amount of methanol. The boiling point of methanol is 64.7°C, and the boiling point of potassium formate is 100.8°C. The difference between the boiling points of the two is more than 30°C, and they can be separated and purified by distillation technology. According to the difference in boiling points, the separation operation of methanol and formic acid in the distillation tower kettle is a common technical means, and this application does not explain too much, and the effect of being able to separate methanol and formic acid is sufficient.

[0060] In one possible implementation, the distillation apparatus used in the distillation operation is a distillation tower operated at normal pressure. The above-mentioned mixed aqueous solution of formic acid and methanol is heated until the methanol is evaporated and separated for reuse. Continue heating, use 1,2-dichloroethane as an entrainer, first heat the top temperature to 74.5°C to 75.5°C, control the bottom temperature of the tower at 80°C, and continuously produce azeotropes of 1,2-dichloroethane and water. A condensing phase separator is used for phase separation. After the rising steam at the top of the tower is condensed by the condenser, the produced product is layered in the phase separator, the organic phase refluxes into the tower from the top, and the water phase is produced from the bottom of the phase separator. A 70% to 85% mixed solution of concentrated formic acid and 1,2-dichloroethane is obtained in the bottom of the tower. The formic acid content of the primary formic acid solution is 7 to 12wt%. The present application sets up a distillation apparatus and uses the different boiling points of methanol and formic acid to separate and obtain more than 70% formic acid products.

[0061] In one possible implementation, S800, the secondary formic acid solution is subjected to membrane distillation, and a tertiary formic acid solution is collected on the cold side of the membrane distillation. The primary formic acid solution is heated by a distillation device until methanol evaporates and separates to obtain a secondary formic acid solution rich in formic acid. However, formic acid and water have the same boiling point and are difficult to separate using ordinary distillation methods. Studies have found that when membrane distillation is used to treat formic acid-water solution, there is no azeotropic phenomenon, and formic acid and water can be separated by membrane distillation technology. The liquid outlet of the distillation device is connected to the liquid inlet of the membrane distillation device, and the formic acid aqueous solution at the liquid outlet of the distillation device is pumped into the membrane distillation device for concentration.

[0062] The membrane distillation device is equipped with a hydrophobic membrane as the filtration medium. The two sides of the hydrophobic membrane are the warm side and the cold side respectively. The effluent of the distillation device is pumped into the warm side and heated to 60-78°C. Most of the water and all the methanol in the formic acid aqueous solution are converted into steam state, and the steam pressure difference on both sides of the membrane is used as the driving force for mass transfer. The water and methanol vapor on the warm side pass through the hydrophobic membrane and enter the cold side. The cold side is equipped with a condensing device to condense and obtain high-purity formic acid.

[0063] Furthermore, the hydrophobic membrane material used in the membrane distillation device used in the membrane distillation step is polytetrafluoroethylene, the micropore diameter of the hydrophobic membrane is 0.2 to 0.4 microns, and the porosity is 65% to 85%.

[0064] In a possible implementation, the solubility of potassium hydroxide in water is low, and the alkali chamber 260 of the bipolar membrane electrodialysis device 200 is provided with a liquid outlet, and the potassium hydroxide solution enriched in the alkali chamber 260 is cooled, crystallized, and precipitated for reuse.

[0065] According to another aspect of the present application, the present application also provides an apparatus for electrolyzing formic acid and hydrogen, which is used to implement the above-mentioned method for electrolyzing formic acid and hydrogen. Figure 2 , the device for preparing formic acid and hydrogen by electrolysis comprises:

[0066] An electrolysis device 100 and a bipolar membrane electrodialysis device 200; the cathode electrode 110 of the electrolysis device 100 is made of nickel foam and loaded with iron-cobalt-nickel nanoparticles, the anode electrode 120 of the electrolysis device 100 is made of nickel foam and loaded with cobalt-nickel nanoparticles, and the electrolytic cell of the electrolysis device 100 is provided with a gas outlet 140 near the cathode electrode 110 to collect hydrogen; the interior of the bipolar membrane electrodialysis device 200 is provided with an anode electrode, a first bipolar membrane 210, a negative membrane 220, a positive membrane 230, a second bipolar membrane 240 and a cathode electrode in sequence, and the first bipolar membrane 210, the negative membrane 220, the positive membrane 230 and the second bipolar membrane 240 are divided into three compartments, namely, an acid chamber 250, a salt chamber 250 and an alkali chamber 260.

[0067] The present application electrolyzes an alkaline electrolyte containing methanol by setting an electrolysis device 100, and arranges anode and cathode electrodes 110 and 120 so that the electrolysis tends to produce formic acid and hydrogen. Compared with the existing electrolysis of water to generate hydrogen and oxygen, the cathode and cathode produce hydrogen and oxygen at the same time, which easily leads to safety accidents such as explosion caused by the mixture of hydrogen and oxygen. The present application uses methanol aqueous solution as raw material, produces formic acid at the anode of the electrolytic cell, and collects hydrogen at the cathode of the electrolytic cell. Formic acid and hydrogen can be produced safely and effectively, and safety accidents such as methyl formate leakage and explosion caused by the mixture of hydrogen and oxygen can be avoided.

[0068] The electrolyte after electrolysis is rich in potassium hydroxide and potassium formate. The present application sets up a bipolar membrane electrodialysis device 200 to perform bipolar membrane electrodialysis on the collected anode chamber electrolyte after electrolysis to remove impurities such as potassium hydroxide, and obtains a relatively pure primary formic acid solution in the salt chamber 250 of the bipolar membrane electrodialysis device 200.

[0069] In a possible implementation, a preset distance is provided between the cathode electrode 110 and the anode electrode 120 of the electrolysis device, and the preset distance is 0.1 to 0.5 cm. Further, the preset distance is 0.4 cm.

[0070] In one possible implementation, Figure 3 As shown, the electrolytic cell in the electrolysis device 100 is a rectangular parallelepiped as a whole, and the electrolysis device 100 includes more than two electrolytic cells, and the two or more electrolytic cells are adjacently distributed along the width direction of the electrolytic cell to form an electrolytic stack. The cathode chambers of the two or more adjacent electrolytic cells are connected, and the anode chambers of the two or more electrolytic cells are connected to each other. The cathode chamber of the electrolytic cell at the end of the electrolytic stack is provided with an electrolyte inlet and a hydrogen outlet 140, and the anode chamber of the electrolytic cell at the end of the electrolytic stack is provided with an electrolyte inlet, an electrolyte outlet and an outlet. The hydrogen outlet 140 of the cathode chamber is connected to the steam-water separator 600, the electrolyte inlet of the anode chamber is connected to the outlet of the raw material liquid tank 400, and the electrolyte outlet of the anode chamber is connected to the salt chamber 250 of the bipolar membrane electrodialysis device 200. The present application sets more than two electrolytic cells in series, which can increase the speed of electrolytic production of formic acid and hydrogen and speed up the production progress. The number of electrolytic cells in series is determined according to the required production capacity.

[0071] In a possible implementation, an ion exchange membrane 130 is provided inside the electrolytic cell, and the ion exchange membrane 130 divides the alkaline electrolytic cell into two compartments, a cathode chamber and an anode chamber, and a gas outlet 140 is provided in the cathode chamber to collect hydrogen. At this time, hydrogen is generated in the cathode chamber, and potassium formate is generated in the electrolyte of the anode chamber.

[0072] An ion exchange membrane 130 is provided to divide the cathode chamber and the anode chamber into two compartments inside the electrolyzer, and ions can flow across the chambers through the ion exchange membrane 130 to complete the basic function of electrolysis. The present application separates the cathode chamber from the anode chamber by providing an ion exchange membrane 130. Under the general trend of electrolyzing methanol to produce formic acid and hydrogen in the electrolyzer, even if a small part of the oxygen evolution reaction occurs due to operating errors such as voltage fluctuations, the present application can also physically separate the anode and cathode inside the electrolyzer to prevent safety hazards such as explosions caused by the mixing of hydrogen and oxygen. Furthermore, the anode chamber is also provided with an air outlet to prevent operating errors from causing the anode to produce oxygen or carbon dioxide and other gases that are difficult to discharge, causing pressure safety accidents.

[0073] In a possible implementation, the ion exchange membrane 130 is a cation exchange membrane, potassium ions pass through the cation exchange membrane, potassium hydroxide is enriched at the cathode, and potassium hydroxide impurities at the anode chamber outlet are reduced. Further, the ion exchange membrane 130 is a PPS ion exchange membrane.

[0074] In a possible implementation, the device for preparing formic acid and hydrogen by electrolysis further includes an electric diffusion electrodialysis device 300, wherein the diffusion electrodialysis device 300 is provided with a dialysis tank, such as Figure 5 As shown, the dialysis tank is provided with an anode electrode, two or more membrane groups arranged in sequence, and a cathode electrode. Each membrane group includes a cationic membrane and a cation membrane, that is, the dialysis tank is provided with an anionic membrane and a cation membrane at intervals. The anionic membrane and the cation membrane divide the dialysis tank into a raw liquid chamber 310 and a receiving chamber 320. The raw liquid chamber 310 and the receiving chamber 320 are arranged at intervals in the dialysis tank, and the anionic membrane of the diffusion electrodialysis device 300 is an anion exchange membrane that selectively permeates hydroxide ions. In addition to the characteristics of ordinary anionic membranes, the anionic membrane that selectively permeates hydroxide ions also has extremely high selective permeability to hydroxide ions. For other anions, such as COOH — , CI — 、SO4 2— 、NO3 — The electrolyte in the anode chamber after electrolysis is collected and pumped into the stock solution chamber 310 of the diffusion electrodialysis device 300. The diffusion electrodialysis device 300 is supplied with direct current, and the anions in the stock solution chamber 310 move toward the anode electrode, among which OH — Pass through the anastomotic membrane into the adjacent receiving chamber 320, while COOH — The cations in the original liquid chamber 310 are retained by the anion membrane and move toward the anode electrode. + The potassium hydroxide impurities in the electrolyte can be removed by electrodialysis using the diffusion electrodialysis device 300. Figure 5As shown, after the electrodialysis treatment, the potassium hydroxide solution is collected in the receiving chamber 320 for reuse, while the solution in the raw material chamber 310 is pumped into the salt chamber of the bipolar membrane electrodialysis device for further impurity removal.

[0075] In a possible implementation, the device for producing formic acid and hydrogen by electrolysis also includes a raw material liquid tank 400; the raw material liquid tank 400 is provided with a heat exchange device 410, and the raw material liquid tank 400 is also provided with an alkali pump 420, which is suitable for pumping the alkaline electrolyte containing methanol in the raw material liquid tank 400 into the electrolytic cell of the electrolysis device 100.

[0076] The electrolysis temperature can adjust the reaction rate of hydrogen production by electrolysis. Too low a temperature will result in a slow reaction speed and low production efficiency. Too high a temperature will easily produce a potassium methoxide reaction, which will affect the conductivity and consume potassium hydroxide in the electrolyte. The present application sets a raw material tank 400, adds an alkaline electrolyte containing methanol to the raw material tank 400, and the raw material tank 400 is provided with a heat exchange device 410 to preheat or cool the alkaline electrolyte containing methanol, thereby ensuring that the alkaline electrolyte containing methanol can enter the electrolytic cell for electrolysis at the first preset temperature required for electrolysis.

[0077] Furthermore, an ion exchange membrane 130 is provided inside the electrolytic cell of the electrolysis device 100, and the ion exchange membrane 130 divides the alkaline electrolytic cell into two compartments, a cathode chamber and an anode chamber. The alkali pump 420 of the raw material liquid tank 400 is suitable for pumping the alkaline electrolyte containing methanol in the raw material liquid tank 400 into the anode chamber.

[0078] In a possible implementation, the device for producing formic acid and hydrogen by electrolysis further includes an intermediate liquid tank 500; the liquid outlet of the anode chamber is communicated with the inlet of the intermediate liquid tank 500, the outlet of the intermediate liquid tank 500 is communicated with the salt chamber 250 of the bipolar membrane electrodialysis device 200, and an intermediate pump is provided at the connection between the intermediate liquid tank 500 and the bipolar membrane electrodialysis device 200, and the intermediate pump is suitable for pumping the solution in the intermediate liquid tank 500 into the salt chamber 250 of the bipolar membrane electrodialysis device 200. The present application facilitates batch processing by providing the intermediate liquid tank 500, and can cooperate with multiple electrolytic cells connected in series to improve production efficiency.

[0079] In one possible implementation, both the anode chamber and the cathode chamber are provided with gas outlets 140 and 150, the gas outlet 140 of the cathode chamber is provided with a gas-water separator 600, the gas-water separator 600 is provided with an air inlet, an air outlet and a liquid return hole, the air inlet of the gas-water separator 600 is connected with the gas outlet of the cathode chamber, and the outlet of the gas-water separator 600 is suitable for connecting with a hydrogen storage device.

[0080] In a possible implementation, a back pressure valve 700 is further provided at the outlet of the steam-water separator 600. The present application reduces pressure fluctuations by providing the back pressure valve 700, thereby maintaining a constant pressure at the outlet of the steam-water separator 600, preventing unstable pressure water from entering the hydrogen storage device; and maintaining the pressure balance inside the alkaline electrolyzer to ensure the amount of electrolyte.

[0081] In a possible implementation, the back pressure valve 700 inputs the collected hydrogen into the hydrogen storage device at a pressure of 2 kg.

[0082] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing formic acid and hydrogen by electrolysis, characterized in that: include: Electrolyzing an alkaline electrolyte containing methanol, wherein the cathode electrode structure in the electrolysis device used is a nickel foam substrate loaded with iron-cobalt-nickel nanoparticles, the anode electrode structure in the electrolysis device is a nickel foam substrate loaded with cobalt-nickel nanoparticles, and the cathode chamber in the electrolysis device generates hydrogen; The electrolyte after electrolysis in the anode chamber of the electrolysis device is collected, and a bipolar membrane electrodialysis device is used to perform bipolar membrane electrodialysis on the collected electrolyte after electrolysis in the anode chamber, and a primary formic acid solution is obtained in the acid chamber of the bipolar membrane electrodialysis device.

2. The method for preparing formic acid and hydrogen by electrolysis according to claim 1, characterized in that: Before electrolyzing the alkaline electrolyte, the method further includes preheating the alkaline electrolyte to a first preset temperature.

3. The method for preparing formic acid and hydrogen by electrolysis according to claim 1, characterized in that: After collecting the electrolyte after electrolysis in the anode chamber of the electrolysis device, the step of performing reverse osmosis concentration on the electrolyte after electrolysis is also included before using a bipolar membrane electrodialysis device to perform bipolar membrane electrodialysis on the collected electrolyte after electrolysis in the anode chamber.

4. The method for preparing formic acid and hydrogen by electrolysis according to claim 1, characterized in that: Also includes: The primary formic acid solution after bipolar membrane electrodialysis is distilled, and the methanol impurities remaining in the formic acid solution are removed by utilizing the difference in boiling points to obtain a secondary formic acid solution.

5. A device for preparing formic acid and hydrogen by electrolysis, characterized in that: The method for producing formic acid and hydrogen by electrolysis according to any one of claims 1 to 4 comprises: Electrolysis devices and bipolar membrane electrodialysis devices; The cathode electrode of the electrolysis device is constructed with nickel foam as the substrate and loaded with iron-cobalt-nickel nanoparticles, the anode electrode of the electrolysis device is constructed with nickel foam as the substrate and loaded with cobalt-nickel nanoparticles, and the electrolysis device is provided with a gas outlet near the cathode electrode to collect hydrogen; The bipolar membrane electrodialysis device is provided with a cathode electrode, a first bipolar membrane, a cation membrane, a cathodic membrane, a second bipolar membrane and an anode electrode in sequence, and the first bipolar membrane, the cation membrane, the cathodic membrane and the second bipolar membrane are divided into three compartments, namely, an acid chamber, a salt chamber and an alkali chamber.

6. The device for preparing formic acid and hydrogen by electrolysis according to claim 5, characterized in that: An ion exchange membrane is arranged inside the electrolytic cell of the electrolysis device. The ion exchange membrane divides the alkaline electrolytic cell into two compartments, a cathode chamber and an anode chamber. The cathode chamber is provided with a gas outlet to collect hydrogen.

7. The device for preparing formic acid and hydrogen by electrolysis according to claim 6, characterized in that: The ion exchange membrane is a cation exchange membrane.

8. The device for preparing formic acid and hydrogen by electrolysis according to claim 7, characterized in that: The cation exchange membrane is a PPS ion exchange membrane.

9. The device for preparing formic acid and hydrogen by electrolysis according to claim 6, characterized in that: A steam-water separator is provided at the gas outlet of the cathode chamber, and hydrogen is collected at the gas outlet of the steam-water separator.

10. The device for preparing formic acid and hydrogen by electrolysis according to claim 9, characterized in that: The gas outlet of the steam-water separator is also provided with a back pressure valve.

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