CN102190573A - Method for preparing formic acid through electrochemical catalytic reduction of carbon dioxide - Google Patents

Abstract

The invention relates to a method for producing formic acid by electrochemically catalytically reducing carbon dioxide, which belongs to the technical field of carbon dioxide resource utilization. The invention uses a proton exchange membrane to separate the electrolytic cell into a cathode chamber and an anode chamber, injects a mixed solution of organic solvent/ionic liquid/water dissolved in a large amount of carbon dioxide into the cathode chamber, and injects an aqueous solution containing supporting electrolyte into the anode chamber. After the electrolysis power supply is turned on, carbon dioxide undergoes an electroreduction reaction on the cathode to generate formic acid. Through this invention, an organic solvent/ionic liquid/water mixed solution with good conductivity, low viscosity, strong ability to dissolve carbon dioxide, wide electrochemical window, and low cost can be obtained. In this mixed solution, carbon dioxide is electroreduced, The current density of the carbon dioxide electroreduction reaction can be increased, and the electrocatalytic activity and long-term stability of the cathode material can be improved at the same time.

Description

A method for preparing formic acid by electrochemical catalytic reduction of carbon dioxide

technical field

The invention relates to a method for preparing formic acid by electrochemically catalytically reducing carbon dioxide, which belongs to the technical field of resource utilization of carbon dioxide.

Background technique

Carbon dioxide is the main component that causes the greenhouse gas effect, and it is also an important resource. Converting carbon dioxide into other chemical raw materials and reducing the use of fossil fuels is an important technical way to reduce carbon dioxide emissions, and it is also a practical problem that industries with high carbon dioxide emissions such as thermoelectricity, steel, and cement urgently need to solve. Vigorously researching and developing new technologies for carbon dioxide resource transformation can promote the rapid development of emerging industries for carbon dioxide resource utilization.

Formic acid is an important basic chemical raw material, widely used in medicine, dyes, leather and other fields. In the article "Research Progress in Electrochemical Reduction of Carbon Dioxide" (Tao Yingchu, Wu Shaohui, Zhang Xi. "Chemical Bulletin" 2001(5):272-277), it involves a catalytic reduction of carbon dioxide to formic acid by electrochemical method in aqueous solution. The method, the reaction principle is: water oxidizes on the anode to generate hydrogen ions and oxygen, the hydrogen ions migrate to the cathode through the mass transfer process, and participate in the electrocatalytic reduction of carbon dioxide on the cathode to generate formic acid and side reaction products.

However, the existing technology of producing formic acid by electrocatalytic reduction of carbon dioxide in aqueous solution has the following problems: first, carbon dioxide is a non-polar molecule, and its solubility in aqueous solution is very small, only 0.033mol/L in the standard state, causing the cathode reaction speed to be too high. Second, in the electroreduction of carbon dioxide in an aqueous solution, in order to improve the conductivity of the electrolyte, it is necessary to add an inorganic supporting electrolyte to the electrolyte, thus inevitably bringing some inorganic impurities into the electrolyte, some of which The electrodeposition reaction occurs on the surface of the cathode, forming surface active sites with low hydrogen evolution overpotential, which leads to the acceleration of the hydrogen evolution reaction, and also reduces the electrocatalytic activity of the electrode material for the carbon dioxide electroreduction reaction.

Contents of the invention

The object of the present invention is to overcome the deficiencies in the electrocatalytic reduction of carbon dioxide mentioned above, and provide a method for the preparation of formic acid by electrochemical catalytic reduction of carbon dioxide. Carbon dioxide is efficiently converted to formic acid.

The technical scheme of the present invention is realized in that way: the electrolytic cell is divided into a cathode chamber and an anode chamber by using a perfluorosulfonic acid type proton exchange membrane, and an organic solvent/ionic liquid/water mixed solution dissolved with carbon dioxide is used as the cathode chamber electrolyte, The aqueous solution containing the supporting electrolyte is used as the electrolyte in the anode chamber, the In, Pb, Zn or Sn electrode is used as the cathode, and the graphite, glassy carbon or IrO ₂ ·Ta ₂ O ₅ coated titanium electrode is used as the anode, and the carbon dioxide is reduced by electrolytic reduction. converted to formic acid. The specific process is as follows:

Step 1, at room temperature, the ionic liquid is dissolved in an organic solvent with a water content of 5% to 15% (mass ratio) at a liquid/agent volume ratio of 1:1 to 6 to obtain organic solvent/ionic liquid/water mixture. Then transport the mixed solution to the gas absorption tower for dissolving and absorbing carbon dioxide until the concentration of carbon dioxide reaches 0.05-0.69 mol/L, inject the solution containing carbon dioxide into the cathode chamber, and use it as the cathode chamber electrolyte; at the same time, Injecting an aqueous solution containing a supporting electrolyte into the anode chamber as an electrolyte in the anode chamber;

Step 2, turn on the electrolysis power supply at room temperature, control the electrolysis voltage to 3-4.2V, and the current density to 200-450A/m ² , and carry out the electrolysis reaction for 1.5-3 hours (the reaction time depends on the actual situation, so that the electrolyte It only needs to fully reduce the carbon dioxide in the electrolytic cell, when the amount of electrolyte in the electrolytic cell is large, it will take a long time). Water undergoes an oxidation reaction on the anode to generate hydrogen ions and oxygen. The hydrogen ions migrate to the cathode through the mass transfer process, and undergo an electroreduction reaction with carbon dioxide on the cathode to generate formic acid and dissolve in the electrolyte;

Step 3, draw out the electrolyte solution dissolved in formic acid from the cathode chamber, and evaporate the formic acid by distillation (heating to above the boiling point of formic acid) to obtain the formic acid product; the electrolyte solution after separation of formic acid is used again for dissolution and absorption Carbon dioxide (taken in the gas absorption tower), and then the solution dissolved in carbon dioxide is reinjected into the cathode chamber to form the electrolyte circulation. Oxygen, the product of the anode reaction, and hydrogen, the main by-product of the cathode reaction, can be collected in the upper part of the anode chamber and the cathode chamber, respectively.

In the present invention, the supporting electrolyte in the aqueous solution of the anode chamber is any one of sodium bicarbonate, potassium bicarbonate, potassium hydrogen phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium hydrogen sulfate, potassium hydrogen sulfate or sulfuric acid. One, its concentration in aqueous solution is 0.1-2mol/L (determined according to actual needs). The organic solvent in the cathode chamber electrolyte is one of dimethyl sulfoxide, acetonitrile, tetrahydrofuran, methanol, ethanol or propylene carbonate, or any mixture of the above-mentioned organic solvents, and the ionic liquid is an imidazole ionic liquid or a pyridine ionic liquid, Or any mixture of the above ionic liquids.

The structural formula of imidazole ionic liquid is:

Among them, R ₁ and R ₂ are C ₁ -C ₅ hydrocarbon chains; M and N are functional groups or hydrogen atoms connected to the hydrocarbon chains, and the functional groups are: -NH ₂ , -CN or -OH; X ^- is CF ₃ SO ₃ ^- , CF ₃ COO ^- , (CF ₃ SO ₂ ) ₂ N ^- , HCO ₃ ^- , H ₂ PO ₄ ^- , HSO ₄ ^- , Cl ^- , Br ^- , I ^- .

The structural formula of pyridine ionic liquid is:

Among them, R ₁ and R ₂ are C ₁ -C ₅ hydrocarbon chains; M and N are functional groups or hydrogen atoms connected to the hydrocarbon chains, and the functional groups are: -NH ₂ , -CN or -OH; X ^- is CF ₃ SO ₃ ^- , CF ₃ COO ^- , (CF ₃ SO ₂ ) ₂ N ^- , HCO ₃ ^- , H ₂ PO ₄ ^- , HSO ₄ ^- , Cl ^- , Br ^- , I ^- .

The main electrochemical reactions involved in the present invention have:

Anode reaction:

Cathode reaction:

Overall response:

Compared with the prior art, the present invention has the following beneficial effects:

(1) Organic solvents such as dimethyl sulfoxide, acetonitrile, tetrahydrofuran, methanol, ethanol, and imidazole and pyridine ionic liquids have good solubility and absorption properties for carbon dioxide, and the mixed solution obtained by dissolving ionic liquids in organic solvents has conductivity It has the advantages of good stability, low viscosity, strong ability to dissolve carbon dioxide, wide electrochemical window, and low cost of use;

(2) Using the organic solvent/ionic liquid mixed solution containing a small amount of water as the electrolyte in the cathodic chamber can make the current density of carbon dioxide electroreduction reaction reach 200-450A/m ² , and the current efficiency of formic acid can reach 61-78%. And the electrocatalytic activity and long-term stability of the cathode material can be improved.

(3) Ionic liquids have high ion mobility and electrical conductivity. Electroreduction of carbon dioxide in an organic solvent/ionic liquid mixed solution containing a small amount of water does not require adding inorganic supporting electrolytes to the electrolyte, thus avoiding some inorganic Impurities are electrodeposited on the surface of the cathode, causing the reduction of the catalytic activity of the electrode material and the intensification of the side reaction of hydrogen evolution.

Description of drawings

Figure 1 is a schematic diagram of the structural principle of the electrolytic cell of the present invention.

In the figure: 1-electrolysis power supply, 2-cathode, 3-electrolyte in cathodic chamber, 4-proton exchange membrane, 5-electrolyte in anode chamber, 6-anode.

Detailed ways

The technical scheme of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the technical content of the present invention is not limited to the scope described.

Embodiment 1: as shown in accompanying drawing 1, electrolytic cell is separated into cathode compartment and anode compartment by perfluorosulfonic acid type proton exchange membrane, adopts In electrode as cathode, adopts graphite electrode as anode, by electroreduction reaction, carbon dioxide converted to formic acid. The specific process is as follows:

Step 1. Dissolve 1-butyl-3-methylimidazolium trifluoromethanesulfonic acid ionic liquid in dihydrogen disulfide with a water content of 15% (mass percentage) at room temperature at a liquid/dose volume ratio of 1:4. In methyl sulfoxide, an organic solvent/ionic liquid/water mixed solution is obtained. The mixed solution is transported to the gas absorption tower for dissolving and absorbing carbon dioxide until the concentration of carbon dioxide reaches 0.05 mol/L, injecting the above solution dissolved in carbon dioxide into the cathode chamber as the cathode chamber electrolyte; at the same time, injecting 0.1mol/L sodium bicarbonate aqueous solution, as the anode chamber electrolyte;

Step 2, turn on the electrolysis power supply at room temperature, control the electrolysis voltage to 3.9V, and the current density to 280A/m ² , carry out the electrolysis reaction for 3 hours, and the water oxidizes on the anode to generate hydrogen ions and oxygen, and the hydrogen ions undergo mass transfer The process migrates to the cathode, and an electroreduction reaction occurs with carbon dioxide on the cathode to generate formic acid, which is dissolved in the electrolyte, and the current efficiency of generating formic acid reaches 61%;

Step 3, lead out the electrolyte solution dissolved in formic acid from the cathode chamber, heat the electrolyte solution to 100.8°C, and use distillation to make the formic acid fully volatilize and escape to obtain the formic acid product; at the same time, the electrolyte solution after separating the formic acid is used again After dissolving and absorbing carbon dioxide (into the gas absorption tower), the above-mentioned electrolyte solution dissolved in carbon dioxide is injected into the cathode chamber to form electrolyte recycling. Oxygen, a by-product of the anode reaction, and carbon monoxide, a by-product of the cathode reaction, can be collected in the upper part of the anode chamber and the cathode chamber, respectively.

Embodiment 2: as shown in accompanying drawing 1, adopt perfluorosulfonic acid type proton exchange membrane to divide electrolytic cell into cathode compartment and anode compartment, adopt Pb electrode as cathode, adopt glassy carbon electrode as anode, by electroreduction reaction, the Carbon dioxide is converted to formic acid. The specific process is as follows:

Step 1: Dissolve 1-butylpyridine trifluoromethanesulfonate ionic liquid in methanol with a water content of 10% (mass percentage) at a liquid/dose volume ratio of 1:6 at room temperature to obtain an organic solvent /ionic liquid/water mixed solution, and then transport the mixed solution to the gas absorption tower, dissolve and absorb carbon dioxide until the carbon dioxide concentration reaches 0.083 mol/L, inject the above solution dissolved in carbon dioxide into the cathode chamber, and use it as the cathode chamber Electrolyte; At the same time, inject 2mol/L sodium bisulfate aqueous solution in the anode chamber as the anode chamber electrolyte;

Step 2, turn on the electrolysis power supply at room temperature, control the electrolysis voltage to 3V, and the current density to 200A/m ² , carry out the electrolysis reaction for 2 hours, and the water will undergo oxidation reaction on the anode to generate hydrogen ions and oxygen, and the hydrogen ions will pass through the mass transfer process Migrate to the cathode, and undergo an electroreduction reaction with carbon dioxide on the cathode, the generated formic acid is dissolved in the electrolyte, and the current efficiency of generating formic acid reaches 69%;

Step 3, lead out the electrolyte solution dissolved in formic acid from the cathode chamber, heat the electrolyte solution to 108°C, use distillation to make the formic acid fully volatilize and escape, and obtain the formic acid product; the electrolyte solution after separating the formic acid is used again for dissolving Absorb carbon dioxide (into the gas absorption tower), and then inject the above electrolyte solution dissolved in carbon dioxide into the cathode chamber to form electrolyte recycling. Oxygen, a by-product of the anode reaction, and carbon monoxide, a by-product of the cathode reaction, can be collected in the upper part of the anode chamber and the cathode chamber, respectively.

Embodiment 3: as shown in accompanying drawing 1, adopt the perfluorinated sulfonic acid type proton exchange membrane to separate the electrolytic cell into cathode chamber and anode chamber, adopt Sn electrode as cathode, adopt IrO ₂ Ta ₂ O ₅ coating titanium electrode as The anode, through an electroreduction reaction, converts carbon dioxide into formic acid. The specific process is as follows:

Step 1, at room temperature, according to the liquid/dose volume ratio of 1:1, 1-butyl-3-methylimidazole bistrifluoromethanesulfonimide ionic liquid is dissolved in water content rate 5% (mass percentage ) in a mixed organic solvent of dimethyl sulfoxide/propylene carbonate (the volume ratio of dimethyl sulfoxide to propylene carbonate is 1:1) to obtain a mixed solution of organic solvent/ionic liquid/water, which is sent to the gas In the absorption tower, after dissolving and absorbing carbon dioxide until the concentration of carbon dioxide reaches 0.69 mol/L, inject the above solution dissolved in carbon dioxide into the cathode chamber as the cathode chamber electrolyte; at the same time, inject the concentration of 0.2mol/L into the anode chamber Potassium dihydrogen phosphate aqueous solution, as the anode chamber electrolyte;

Step 2, turn on the electrolysis power supply at room temperature, control the electrolysis voltage to 4.2V, and the current density to 450A/m ² , and carry out the electrolysis reaction for 1.5 hours. The oxidation reaction of water on the anode generates hydrogen ions and oxygen, and the hydrogen ions undergo mass transfer. The process migrates to the cathode, and an electroreduction reaction occurs with carbon dioxide on the cathode, and the generated formic acid is dissolved in the electrolyte, and the current efficiency of generating formic acid can reach 78%;

Step 3, draw out the electrolyte solution dissolved in formic acid from the cathode chamber, heat the electrolyte solution to 108°C, and use the method of distillation to make the formic acid fully volatilize and escape to obtain the formic acid product; at the same time, the electrolyte solution after separating the formic acid is used again After dissolving and absorbing carbon dioxide (into the gas absorption tower), the above-mentioned electrolyte solution dissolved in carbon dioxide is injected into the cathode chamber to form electrolyte recycling. Oxygen, a by-product of the anode reaction, and carbon monoxide, a by-product of the cathode reaction, can be collected in the upper part of the anode chamber and the cathode chamber, respectively.

Claims (5)

1. an electrochemical catalysis reducing carbon dioxide prepares the method for formic acid, it is characterized in that: electrolyzer is divided into cathode compartment and anolyte compartment with perfluorinated sulfonic acid type proton exchange membrane, cathode compartment electrolytic solution is the mixing solutions of the organic solvent, ionic liquid and the water that are dissolved with carbonic acid gas, anolyte compartment's electrolytic solution is the aqueous solution that contains supporting electrolyte, adopt In or Pb, Zn, Sn electrode as negative electrode, adopt Graphite Electrodes or glass-carbon electrode, IrO ₂Ta ₂O ₅Coated titanium electrode is formic acid with electrolytic method with the carbonic acid gas electroreduction as anode.

2. electrochemical catalysis reducing carbon dioxide according to claim 1 prepares the method for formic acid, it is characterized in that: concrete preparation process is as follows:

1.1 ionic liquid is dissolved in the aqueous organic solvent, obtain the mixing solutions of organic solvent, ionic liquid and water, carbonic acid gas is dissolved in this mixing solutions, the mixing solutions that will be dissolved with carbonic acid gas then is injected in the cathode compartment as electrolytic solution, simultaneously, in the anolyte compartment, inject the aqueous solution that contains supporting electrolyte;

Carry out electrolytic reaction 1.2 connect electrolysis power, make water that oxidizing reaction take place on anode, generate hydrogen ion and oxygen, hydrogen ion is moved to negative electrode through mass transfer process, with carbonic acid gas electro-reduction reaction takes place on negative electrode, generates formic acid;

Draw from cathode compartment 1.3 will be dissolved with the electrolytic solution of formic acid, the formic acid volatilization is overflowed, obtain the formic acid product with the distillatory method; The electrolytic solution that separates behind the formic acid is used to dissolve absorbing carbon dioxide once more, the electrolytic solution that is dissolved with carbonic acid gas of gained heavily is injected in the cathode compartment, form circulation of elecrolyte; The main by product hydrogen of reaction product of anode oxygen and cathodic reaction can be collected in anolyte compartment and cathode compartment top respectively.

3. the method for preparing formic acid according to claim 1,2 described electrochemical catalysis reducing carbon dioxides, it is characterized in that: the supporting electrolyte in anolyte compartment's aqueous solution is any in sodium bicarbonate, saleratus, potassium hydrogen phosphate, sodium hydrogen phosphate, SODIUM PHOSPHATE, MONOBASIC, potassium primary phosphate, sodium pyrosulfate, sal enixum or the sulfuric acid, and its concentration in water is 0.1-2mol/L; Organic solvent in the cathode compartment is a kind of in methyl-sulphoxide, acetonitrile, tetrahydrofuran (THF), methyl alcohol, ethanol or the propylene carbonate, or any mixture of above-mentioned organic solvent, and the water ratio of organic solvent is 5%～15%; Ionic liquid is imidazoles or pyridines ionic liquid, or above-mentioned ion liquid any mixture, and ionic liquid and organic solvent blended liquid/agent volume ratio are 1:1～6.

4. prepare the method for formic acid according to the described a kind of electrochemical catalysis reducing carbon dioxide of claim 3, it is characterized in that: the structural formula of glyoxaline ion liquid is:

Wherein, R ₁, R ₂Be C ₁-C ₅Hydrocarbon chain; M, N are functional group or the hydrogen atom that is connected on the hydrocarbon chain, and functional group is :-NH2 ,-CN or-OH; X ^-Be CF ₃SO ₃ ^-, CF ₃COO ^-, (CF ₃SO ₂) ₂N ^-, HCO ₃ ^-, H ₂PO ₄ ^-, HSO ₄ ^-, Cl ^-, Br ^-, I ^-

The ion liquid structural formula of pyridines is:

Wherein, R ₁, R ₂Be C ₁-C ₅Hydrocarbon chain; M, N are functional group or the hydrogen atom that is connected on the hydrocarbon chain, and functional group is :-NH2 ,-CN or-OH; X ^-Be CF ₃SO ₃ ^-, CF ₃COO ^-, (CF ₃SO ₂) ₂N ^-, HCO ₃ ^-, H ₂PO ₄ ^-, HSO ₄ ^-, Cl ^-, Br ^-, I ^-

5. the method for preparing formic acid according to claim 1,2 described electrochemical catalysis reducing carbon dioxides, it is characterized in that: with the mixing solutions dissolving absorbing carbon dioxide of organic solvent, ionic liquid and water, gas concentration lwevel reaches 0.05～0.69mol/L, and the liquid aspiration is received process and carried out in absorption column of gas.

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