An anode non-metallic molecular catalyst for chlor-alkali industry and a preparation method thereof

Abstract

The application discloses a chlor-alkali industry anode nonmetallic molecular catalyst and a preparation method thereof. The catalyst contains a compound with a structure of formula I, formula II or formula III, the catalyst does not contain any metal, the preparation process is simple, and the cost is low. The catalyst uses recyclable carbon dioxide as an activator, shows higher catalytic activity than an industrial size stable anode in an anode chlorine evolution reaction, and has comparable selectivity and durability.

Description

Technical Field

[0001] This invention belongs to the field of chlor-alkali chemical technology, and particularly relates to a non-metallic molecular catalyst for chlor-alkali industry anodes and its preparation method. Background Technology

[0002] The chlor-alkali industry plays a vital role in the chemical industry, producing hundreds of millions of tons of chlorine, hydrogen, sodium hydroxide, sodium chlorate, and sodium hypochlorite annually. These are fundamental chemicals for industrial applications, water treatment, and many others. The key reaction in the chlor-alkali industry is the electrolysis of saturated brine to produce chlorine and hydrogen. The total electricity consumption of the electrolysis step in the chlor-alkali industry is approximately 150 TWh, accounting for about 3% of global electricity consumption. A large portion of this electricity is wasted on overpotential. Reducing the overpotential of the anode and the amount of precious metals used are crucial for the chlor-alkali industry, which depends on an effective anode catalyst. Currently, the size-stabilized anode (DSA) is mainly used industrially, consisting of a RuO2 / IrO2 / TiO2 metal solid solution catalyst and a Ti plate support. DSA electrodes have high catalytic activity and long lifespan; however, they rely heavily on precious metals.

[0003] Recently, researchers have developed some new catalysts, but they are still mainly composed of precious metals. Further development of the chlor-alkali industry requires the development of new catalysts, especially non-precious metal catalysts. Summary of the Invention

[0004] This application discloses a non-metallic molecular catalyst, characterized in that the catalyst contains a compound having the structure of formula I, formula II, or formula III.

[0005]

[0006] Among them, R1 is selected from H and C. 1-6 Alkanes; R2 is selected from H, halogenated groups, C 1-6 Alkanes, C 1-6 Alkoxy or C 1-6 Haloalkanes; R3 is selected from H, halogenated groups, C 1-6 Alkanes, C 1-6 Alkoxy or C 1-6 Haloalkanes; R4 and R5 are independently selected from H, halogenated groups, and C. 1-6 Alkanes, C 1-6 Alkoxy or C 1-6 Halogenated alkanes.

[0007] Furthermore, R1 is selected from H and C. 1-6 Alkanes; R2 is selected from H, halogroups, or C. 1-6 Halogenated alkanes; R3 is selected from H, halogenated groups, or C. 1-6 Haloalkanes; R4 and R5 are independently selected from H, halogenated groups, and C. 1-6 Alkanes.

[0008] Furthermore, R1 is selected from H, methyl, ethyl, or tert-butyl ( t Bu); R2 is selected from H, Cl, I or CF3; R3 is selected from H, Cl, I or CF3; R4 and R5 are independently selected from H, halogenated groups, C 1-6 Alkanes.

[0009] Furthermore, this application discloses a non-metallic molecular catalyst, characterized in that the catalyst contains a compound having the structure of Formula I, with the substituents defined as described above.

[0010] Preferably, the non-metallic molecule is a compound having the following structure:

[0011]

[0012] The catalyst is an anode catalyst used in electrolyzers, particularly an anode catalyst for electrolyzers used in the chlor-alkali industry. Chlor-alkali electrolyzers (or chlor-alkali electrolyzers) are used to electrolyze saturated brine to produce chlorine, hydrogen, and sodium hydroxide.

[0013] This application discloses a non-metallic molecular catalyst using small organic molecules as the active component. This is the first report of this type of small organic molecule material as an anode catalyst in a chlor-alkali electrolyzer. Test results show that this type of non-metallic molecular catalyst exhibits an overpotential of 89 mV (10 kA·m) in the chlorine evolution reaction (CER). -2 With 99.6% selectivity, it has great commercial value.

[0014] This application also discloses the use of the catalyst in chlor-alkali chemical industry, chlorate production, chlorine production, hydrogen production, and seawater desalination.

[0015] This application also discloses a method for preparing chlorine, hydrogen and sodium hydroxide by electrolyzing sodium chloride solution, characterized in that the method uses the aforementioned non-metallic molecular catalyst, including compounds of formula I, II or III, and obtains chlorine, hydrogen and sodium hydroxide by separation.

[0016] Furthermore, this application discloses a method for preparing chlorine, hydrogen, and sodium hydroxide by electrolyzing a sodium chloride solution, wherein CO2 is used as an auxiliary agent; that is, carbon dioxide gas is used as an auxiliary agent during the electrolysis of the sodium chloride solution to generate chlorine, hydrogen, and sodium hydroxide, and then the carbon dioxide is separated to obtain chlorine, hydrogen, and sodium hydroxide.

[0017] The separated carbon dioxide is either recovered or recycled back into the electrolysis system.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. A novel non-metallic molecule, especially organic small molecule catalyst, for the chlor-alkali industry is provided, which realizes the high efficiency of non-metallic catalysis of chlor-alkali reaction. This is also the first time that organic small molecules have been used in CER reaction, which expands the design system of traditional CER catalysts.

[0020] 2. This application employs a type of non-metallic organic molecular catalyst with a simple production process and low cost, enabling the production of chlor-alkali industry catalysts free of any precious metals, thus significantly reducing the cost of precious metal catalysts. The non-metallic molecular electrode prepared by this method achieves a 10 kA·m ionization rate in the chlorine evolution reaction. -2 With an overpotential of only 89mV and a selectivity of up to 99.6%, it demonstrates enormous commercial value and potential.

[0021] 3. This application demonstrates the potential applications of small organic molecule catalysts in the electrochemical field, providing a highly efficient heterogeneous organic catalyst for the chlor-alkali industry, and showing great potential in chlorine batteries, organic synthesis, and other fields. Compared with industrially sized, size-stable anodes, this catalyst reduces power consumption per ton of alkali by 14.6%, which is of great significance for energy-saving upgrades of high-energy-consuming anodes in the existing chlor-alkali industry. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below. Referring to the accompanying drawings will provide a clearer understanding of the features and advantages of the present invention. The drawings are illustrative and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort. Wherein:

[0023] Figure 1 The 1H NMR spectrum (Figure a) and 1C NMR spectrum (Figure b) of compound 1a are shown.

[0024] Figure 2 Figure 1 shows the electrolysis test results of compound 1a. Figure 1a shows the polarization curves of compound 1a and DSA at 5M NaCl (pH=2) and 90℃. Figure 1b shows the selectivity and Faraday efficiency of compound 1a at 5M NaCl (pH=2) and 90℃.

[0025] Figure 3 The stability of compound Ia was tested under constant current (800 mA) and constant voltage (1.5-1.7 V) conditions, respectively, when CO2 was introduced (at a rate of 10 sccm), 5 M NaCl (pH=2), and at 90 °C.

[0026] Figure 4 This is a comparison of the performance of control samples from 1a to 1h.

[0027] Figure 5This is a schematic diagram of the catalytic process. Detailed Implementation

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0029] Preparation Example 1: Preparation of Heterogeneous Catalysts

[0030] a) At 30°C and under a nitrogen atmosphere, 10 g of vinyltriphenylphosphine ligand and 100 mg of azobisisobutyronitrile were added to 100 mL of tetrahydrofuran. After mixing, the mixture was stirred for 20 minutes.

[0031] b) Transfer the mixed solution obtained in step a) to a high-pressure reactor for synthesis. Under an inert gas atmosphere at 100°C, use a solvothermal polymerization method and let it stand for 48 hours to carry out the polymerization reaction to obtain triphenylphosphine organic polymer.

[0032] c) The polymer obtained in step b) is filtered at room temperature and the tetrahydrofuran solvent is removed under vacuum to obtain the triphenylphosphine polymer, which is the support for the heterogeneous catalyst.

[0033] d) At 30 degrees Celsius under an argon atmosphere, 10 mg of palladium acetate was dissolved in 50 mL of methanol, and 0.5 g of the organic polymer support obtained in step c) was added. After stirring for 2 hours, the mixture was filtered and the organic solvent was removed under vacuum to obtain a heterogeneous catalyst.

[0034]

[0035] Example 1 Compound 1a

[0036] Compound 1a was prepared by adding 2-iodo-5-trifluoromethylaniline (1 mmol, 287.02 mg), tert-butyl isocyanate (1.2 mmol, 99.76 mg), a heterogeneous catalyst (20 mg), and 1,8-diazabicyclo[5.4.0]undec-7-ene (2 mmol, 304.48 mg) to a 35 mL Schlenk reaction tube. After purging the air from the reaction vessel with carbon dioxide, 7 mL of acetonitrile was injected. The mixture was heated at 100 °C for 12 hours and then cooled to room temperature. The reaction mixture was filtered and the reaction solvent was evaporated under reduced pressure. The residue was purified by column chromatography using ethyl acetate and petroleum ether as eluents (ethyl acetate to petroleum ether volume ratio 1:3) to give pure compound 1a in 78% yield.

[0037]

[0038] Example 2: Preparation of compound 1b-1h

[0039] In Example 2, the catalyst synthesis process was the same as in Example 1, except that iodo-5-trifluoromethylaniline was replaced with iodo-arylamines with different substituents.

[0040] Compound 1b was prepared by replacing 2-iodine-5-trifluoromethylaniline with 4-amino-3-iodotrifluorotoluene as a raw material.

[0041] Compound 1c was prepared using 2-iodo-5-methylaniline as a starting material.

[0042] Compound 1d was prepared from 2-iodo-5-methoxyaniline.

[0043] Compound 1e was prepared from 5-chloro-2-iodoaniline.

[0044] Commercially available compounds including 6-chloroindole (1f), 6-iodoindole (1g), and 3-acetamidotrifluorotoluene (1h).

[0045]

[0046] Example 3: Electrode Preparation

[0047] After synthesizing the above compounds, the compounds are coated onto an electrode (carrier). The electrode is a commonly used electrode, such as a titanium electrode or a carbon electrode, to prepare an anode with a non-metallic molecule load.

[0048] To prepare the electrode paste (sometimes also called ink), compound 1a-1h, isopropanol, deionized water, and 5% Electrode slurry was prepared by ultrasonically mixing the suspension at a weight ratio of 1:12:11:11 for 4 hours. Ink was then brushed onto the anode plate until approximately 4.0 mg / cm³ was reached on the anode. -2 Non-metallic molecule loading. Dispersed ink droplets (electrostatic spraying) are applied to carbon paper (gas diffusion layer) or a titanium plate, and then dried in a vacuum oven at room temperature. The dried electrode requires heat treatment. The heat treatment environment is Ar atmosphere, temperature is 190-200℃, and duration is 10-20 seconds. Electrodes prepared using this method showed an organic small molecule loading of 3-4 mg / cm³. 2 .

[0049] Example 4: Electrolysis Experiment Test

[0050] Test Environment: The prepared electrode was placed under electrochemical test conditions. The required test conditions were: electrolyte was a 5M NaCl solution, pH adjusted to 1-2 with hydrochloric acid; counter electrode was a Pt mesh; reference electrode was an Ag / AgCl electrode; and test temperature was 85-95 degrees Celsius. Throughout the test, CO2 was introduced and removed along with the electrolyte at a rate of 10 sccm.

[0051] Activation method: Multi-voltage activation is used, the process alternating between -2V and 1.3V to achieve -10 and 10mA·cm. -2 The current density is [specified]. The duration of each specific voltage is 0.2–2 seconds. The entire activation test lasts 3000 s (7500 cycles) or longer to fully activate the catalyst on the anode. The anode is further activated during the reaction, and the catalytic efficiency of some catalysts is improved.

[0052] Test methods: Polarization curves were tested after activation at a scan rate of 10 mV / s and a scan range of 0-1.7 V. Stability tests were performed after activity evaluation, using a constant voltage of 1.55 V and a constant current of 800 mA·cm⁻¹. -2 The test was conducted under the specified conditions. The gas produced after the test was then passed into a gas chromatograph for selectivity evaluation. The selectivity curves for the anolyte chlorine evolution (CER) and anolyte oxygen evolution (OER) reactions were obtained from the same sample.

[0053] Experimental Results and Analysis

[0054] Figure 1 The 1H and 1C spectra of compound 1a are shown.

[0055] Figure 2 The performance of the non-metallic organocatalyst obtained in this process is as follows: at 1000 mA·cm -2 The overpotential was only 89 mV. No OER performance was observed in the 1.3-1.9 V range, indicating high catalyst selectivity. The catalyst 1a after activation with CO2 gas is denoted as NCOOH, and the catalyst 1a before activation (without CO2 gas) is denoted as RCON-H. NCOOH is the active intermediate generated after the reaction of catalyst 1a with the introduced CO2 gas (based on a hypothesized mechanism).

[0056] Figure 3 In the diagram, the spherical markings represent the stability test of compound 1a under constant current (800 mA) conditions at 5 M NaCl (pH=2) and 90 °C; the quadrilateral markings represent the stability test of 1a under constant voltage (1.4 V) conditions at 5 M NaCl (pH=2) and 90 °C. No significant performance degradation was observed during the 10-day stability test. Figure 3 ).

[0057] Following the above testing method, a series of synthesized control samples were tested, and the test results are as follows: Figure 4 As shown, the tested compounds generally exhibited good performance, with compounds 1c and 1d showing slightly worse performance. A lower charge transfer resistance (Rct) indicates lower electron transfer resistance and a faster CER reaction rate. The closer the overpotential is to 0V, the better the catalyst performance, the lower the actual voltage required to reach the relative current density, the less energy consumed, and the higher the catalytic activity.

[0058] Figure 4 The diagram illustrates the reaction mechanism proposed by the applicant. Catalyst 1a is substituted with a small amount of hypochlorous acid in the electrolyte to generate the key intermediate N-Cl. Subsequently, N-Cl is oxidized on the electrode surface to generate RCON. - Intermediate. RCON - It combines with carbon dioxide gas to form nitrogen-carboxyl compounds NCOO - Following NCOO - Oxidation occurs on the electrode surface, resulting in the loss of one electron and the formation of an amide radical cation (N). + radical). N + The chlorine radical undergoes a single-electron transfer process with the chloride ion, oxidizing the chloride ion into a chlorine radical, which then reduces itself to 1a. After quenching, the chlorine radical directly generates chlorine gas.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The use of a compound having the structure of Formula I, Formula II, or Formula III as an anode catalyst in an electrolyzer for use in the chlor-alkali industry. ， in, In this compound, R1 is selected from H and C. 1-6 Alkyl group; R2 is selected from H, halogroup, C 1-6 Alkyl, C 1-6 Alkoxy or C 1-6 Halogenated alkyl group; R3 is selected from H, halogenated group or C 1-6 Haloalkyl; R4 and R5 are independently selected from H, halogenated groups, and C. 1-6 alkyl.

2. The use as described in claim 1, wherein, In the compound, R1 is selected from H, methyl, ethyl, or tert-butyl; R2 is selected from H, Cl, I, or CF3; R3 is selected from H, Cl, I, or CF3; R4 and R5 are independently selected from H, halogenated groups, C... 1-6 alkyl.

3. The use as described in claim 1, characterized in that, The compound contains compounds having the structure of Formula I.

4. The use as described in claim 1, wherein, The compound is a compound having the following structure. 。 5. The use as described in any one of claims 1-4, wherein, The catalyst is used in chlor-alkali chemical industry, chlorate production or chlorine production.

6. A method for preparing chlorine gas, hydrogen gas, and sodium hydroxide by electrolyzing sodium chloride solution, characterized in that, The method uses the compound as described in any one of claims 1-4 as the anode catalyst and CO2 as an auxiliary agent. After separating carbon dioxide, chlorine, hydrogen and sodium hydroxide products are obtained.

7. The method of claim 6, wherein, The separated carbon dioxide is either recovered or recycled back into the electrolysis system.

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