Preparation of urea catalyst and process for synthesizing urea through plasma atomization absorption

Abstract

The invention provides preparation of a urea catalyst and a process for synthesizing urea through plasma atomization absorption. The urea catalyst prepared by the invention can promote two key steps of C-N coupling and hydrogenation deoxidation, reduce a hydrogen evolution competitive reaction and a side reaction of reducing nitrite into ammonia, and effectively improve the urea yield and Faraday efficiency. Meanwhile, the urea is synthesized by adopting a high-frequency pulse plasma-atomization absorption cascade reaction, and the process weakens N = N bond energy, so that the N2 dissociation reaction can be carried out at normal temperature and normal pressure, air (N2 / O2) can be efficiently converted into nitrogen oxide (NOx), the conversion efficiency of N2 is effectively improved, and the reaction energy barrier is reduced. And the atomization absorption process can selectively generate high-concentration NO2 <->, and the subsequent electro-catalysis C-N coupling reaction is improved, so that the compound process solves the huge problem of C-N coupling in the co-electrolysis process of NO2 <-> / NO3 <-> and CO2. The catalyst prepared by the method is high in Faraday efficiency and urea yield, the urea synthesis process is simple and environment-friendly, N2 and CO2 in the air are used as raw materials, and the national policy is met.

Description

Technical Field

[0001] The present invention relates to the fields of urea electrocatalyst and urea synthesis, and in particular to a process for preparing a urea electrocatalyst and synthesizing urea and its application. Background Art

[0002] Urea (CO(NH2)2), an essential chemical in agricultural fertilizers, plays a key role in promoting crop growth. To date, the traditional Bosch−Meiser process (2NH3 + CO2 → CO(NH2)2 + H2O) for industrial urea synthesis requires high temperatures (150–200°C) and high pressures (100–200 atm), resulting in significant CO2 emissions and enormous energy consumption. With the intensifying environmental and energy crises, the development of green and efficient urea synthesis processes is urgently needed.

[0003] Recent studies have reported that the co-electrolysis of N2 and CO2 in aqueous solution to synthesize urea is an effective way to synthesize urea sustainably. However, this method is limited by the high activation energy barrier (941 kJ / mol) of the strong N≡N bond in N2 and the extremely low solubility of N2 in water, resulting in very low synthesis efficiency. However, the conversion of N2 into NO2 - , using NO2 - and CO2 co-electrolysis (UENC) to convert CO2 and NO2 - The conversion of NO2 into urea is of great significance in solving environmental problems and alleviating energy crises. However, the UENC process involves a complex electron transfer process. - The CN coupling in the CO2 reaction is very difficult, resulting in a decrease in urea yield and Faradaic efficiency (FE urea ) is still lower than expected, so there is an urgent need to develop high-performance UENC catalysts for urea synthesis. For the UENC process, the required catalyst can not only catalyze CO2→*CO and NO2 - →*NH2 reaction, and can efficiently produce key *CO and *NH2 intermediates, and can promote the electrocatalytic coupling of *CO and *NH2 to produce urea. Summary of the Invention

[0004] In response to the technical problems raised above, a preparation method of a urea catalyst and a process for synthesizing urea by plasma atomization absorption are provided. The catalyst obtained by the method has excellent Faradaic efficiency and a high yield of synthesized urea. To achieve the above-mentioned objectives, the preparation method and the urea synthesis process of the present invention include the following technical solutions: A process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, wherein the preparation method of the urea catalyst comprises the following steps: Step 1: Mix copper sulfate pentahydrate (CuSO4·5H2O) and ruthenium chloride trihydrate (RuCl3·3H2O), wherein the mass fraction of copper sulfate pentahydrate is 80% to 95% and the mass fraction of ruthenium chloride trihydrate is 5% to 20%, and the mixture is mixed in an ethanol-water mixed solvent (V / V = 1:1).

[0005] Step 2: Place the mixture in an ice-water bath and stir vigorously until a uniform blue mixture is formed.

[0006] Step 3: Inject 0.02-0.04 mol of NaOH solution into the blue mixture in step 2 and continue stirring for 30 minutes.

[0007] Step 4: After cooling the mixture formed in step 3 for 20 to 30 hours, transfer it to a polytetrafluoroethylene-lined stainless steel reactor with a filling degree controlled at 50% to 70%. The reactor is sealed and placed in a forced air drying oven. The mixture is heated to 130°C at a heating rate of 5°C / min and reacted at this temperature for 15 to 20 hours, and then naturally cooled to room temperature.

[0008] Step 5: Centrifuge the mixture obtained in step 4 to collect the black precipitate, and wash it alternately with deionized water and anhydrous ethanol multiple times to remove impurities. Finally, dry the washed black precipitate in a vacuum drying oven at 50-80°C for 10-15 hours to obtain a black powder product.

[0009] Step 6: calcine the black powder obtained in step 5 at 400°C for 3-6 hours to obtain a ruthenium-doped copper oxide (Ru1 / CuO) sample.

[0010] Step 7: The Ru1 / CuO sample was treated with Ar plasma in an AX-1000 plasma system for 5-30 minutes, with the pressure maintained at 10-20 Pa and a 10-30 MHz RF power of 100-200 W applied for 10-30 minutes to obtain Ru1 / CuO. x electrocatalyst.

[0011] The present invention discloses a process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, comprising the following steps: Step 1: The present invention first uses air (N2 / O2) as a nitrogen source, and uses high-energy species (such as electrons and neutral particles) generated by high-frequency pulse plasma reaction to activate N2 molecules. Through the non-equilibrium energy transfer mechanism, the N≡N bond energy is effectively weakened, and its dissociation energy is reduced from 9.8 eV in the ground state to 2~3 eV, thereby achieving efficient activation of nitrogen under mild conditions, that is, air (N2 / O2) can be efficiently converted into nitrogen oxides (NO) at room temperature and pressure. x ), effectively improving the conversion efficiency of N2.

[0012] Step 2: Further, plasma activated nitrogen oxides (NO x ) is efficiently mixed with the alkaline absorption liquid, effectively increasing the reaction contact area in the form of atomized contact, increasing the reaction rate, and promoting NO2 - The selective generation of NO2 in the absorption liquid increases - content.

[0013] Step 3: Further, the NO2-rich - The absorption liquid is added to the electrolytic cell as the electrolyte for the electrocatalytic reaction. The synthesized high-efficiency catalyst is used as the cathode and the platinum electrode is used as the anode. CO2 gas is introduced into the electrolyte near the cathode. By applying a stable voltage at the anode and cathode, two catalytic reactions are carried out simultaneously in the electrolytic cell: CO2 → *CO and NO2 - →*NH2 reaction, which can efficiently produce key *CO and *NH2 intermediates and promote the electrocatalytic coupling of *CO and *NH2 to produce urea.

[0014] The present invention has the following advantages: 1. The urea electrocatalyst developed in the present invention can promote the two key steps of CN coupling and hydrogenation and deoxygenation, reduce the competitive reaction of hydrogen evolution and nitrite reduction reaction, and effectively improve the urea yield and Faradaic efficiency.

[0015] 2. The present invention weakens the N≡N bond energy through high-frequency pulse plasma technology, so that the N2 dissociation reaction can be carried out at room temperature and pressure, and can efficiently convert air (N2 / O2) into nitrogen oxides (NO x ), effectively improving the conversion efficiency of N2 and reducing the reaction energy efficiency.

[0016] 3. The present invention adopts atomization absorption self-buffering process to selectively generate high concentration of NO2 in the alkaline absorption liquid - Due to the subsequent electrocatalytic CN coupling reaction (CO2+NO3 - ) UE It is a 16-electron reaction, and (CO2+NO2 - ) UE Only 12 electrons are needed to generate urea and NO2 - The reaction kinetics of CN coupling with CO2 is better, so this composite process solves the problem of NO2 - / NO3 - The great difficulty of CN coupling during co-electrolysis with CO2.

[0017] 4. The catalyst prepared by the method of the present invention has high Faradaic efficiency and high urea yield. The process for synthesizing urea is simple and environmentally friendly. In addition, N2 and CO2 in the air are used as raw materials, which effectively complies with national policies. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1 Ru1 / CuO in Example 1 of the present invention x X-ray diffraction (XRD) patterns of the catalyst.

[0020] Figure 2 Ru1 / CuO in Example 1 of the present invention x Scanning electron microscopy image of the catalyst.

[0021] Figure 3 Ru1 / CuO in Example 1 of the present invention x High-resolution transmission electron microscopy image of the catalyst.

[0022] Figure 4 Ru1 / CuO in Example 1 of the present invention x Plot of urea yield and Faradaic efficiency of the catalysts. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0024] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. Example 1

[0025] A process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, wherein the preparation method of the urea catalyst comprises the following steps: Step 1. Dissolve 2 g of copper sulfate pentahydrate (CuSO4·5H2O) and 0.15 g of ruthenium chloride trihydrate (RuCl3·3H2O) in an ethanol-water mixed solvent (V / V = 1:1).

[0026] Step 2: Place the mixed solution in an ice-water bath and stir vigorously until a uniform blue solution is formed.

[0027] Step 3: Pour 20 ml of NaOH solution into the flask in step 2 and continue stirring for 30 minutes.

[0028] Step 4: After cooling the mixture in step 3 for 24 hours, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel reactor with a filling degree controlled at 70%. The reactor was sealed and placed in a forced air drying oven, heated to 130°C at a heating rate of 5°C / min and kept at this temperature for 20 hours, and then naturally cooled to room temperature.

[0029] Step 5: After the reaction is completed, the black precipitate is collected by centrifugation and washed alternately with deionized water and anhydrous ethanol for multiple times to remove impurities. Finally, the precipitate is dried in a vacuum drying oven at 60° C. for 10 hours to obtain a black powder product.

[0030] Step 6: calcining the obtained black powder at 400 °C for 3 hours to obtain a ruthenium-doped copper oxide (Ru1 / CuO) sample.

[0031] Step 7: The Ru1 / CuO sample was treated with Ar plasma in an AX-1000 plasma system for 20 minutes. The pressure was maintained at 10 Pa and a 17 MHz RF power of 150 W was applied for 20 minutes to obtain Ru1 / CuO. x Electrocatalytic materials.

[0032] The present invention discloses a process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, wherein the urea synthesis process comprises the following steps: Step 1: The present invention first uses air (N2 / O2) as a nitrogen source, and uses high-energy species (such as electrons and neutral particles) generated by high-frequency pulse plasma reaction to activate N2 molecules. Through the non-equilibrium energy transfer mechanism, the N≡N bond energy is effectively weakened, and its dissociation energy is reduced from 9.8 eV in the ground state to 2~3 eV, thereby achieving efficient activation of nitrogen under mild conditions, that is, air (N2 / O2) can be efficiently converted into nitrogen oxides (NO) at room temperature and pressure. x ), effectively improving the conversion efficiency of N2.

[0033] Step 2: Further, plasma activated nitrogen oxides (NO x ) is efficiently mixed with alkaline absorption liquid (pH 9), effectively increasing the reaction contact area in the form of atomized contact, increasing the reaction rate, and promoting NO2 - The selective generation of NO2 in the absorption liquid increases - content.

[0034] Step 3: Further, the NO2-rich - The absorption liquid was added to the electrolytic cell as the electrolyte for the electrocatalytic reaction. The synthesized high-efficiency catalyst was used as the cathode and the platinum electrode was used as the anode. CO2 gas (5-10 L / min) was introduced into the electrolyte near the cathode. By applying a stable voltage (voltage fluctuation ±0.05 V) to the anode and cathode, two-step catalytic reactions were carried out simultaneously in the electrolytic cell: CO2 → *CO and NO2 - →*NH2 reaction, which can efficiently produce key *CO and *NH2 intermediates and promote the electrocatalytic coupling of *CO and *NH2 to produce urea. Example 2

[0035] A process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, wherein the preparation method of the urea catalyst comprises the following steps: Step 1: Dissolve 2 g of copper sulfate pentahydrate (CuSO4·5H2O) and 0.2 g of ruthenium chloride trihydrate (RuCl3·3H2O) in an ethanol-water mixed solvent (V / V = 1:1).

[0036] Step 2: Place the mixed solution in an ice-water bath and stir vigorously until a uniform blue solution is formed.

[0037] Step 3: Pour 25 ml of NaOH solution into the flask in step 2 and continue stirring for 30 minutes.

[0038] Step 4: After cooling the mixture in step 3 for 24 hours, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel reactor with a filling degree controlled at 70%. The reactor was sealed and placed in a forced air drying oven, heated to 130°C at a heating rate of 5°C / min and kept at this temperature for 25 hours, and then naturally cooled to room temperature.

[0039] Step 5: After the reaction is completed, the black precipitate is collected by centrifugation and washed alternately with deionized water and anhydrous ethanol for multiple times to remove impurities. Finally, the precipitate is dried in a vacuum drying oven at 60° C. for 10 hours to obtain a black powder product.

[0040] Step 6: calcining the obtained black powder at 400 °C for 4 hours to obtain a ruthenium-doped copper oxide (Ru1 / CuO) sample.

[0041] Step 7: The Ru1 / CuO sample was treated with Ar plasma in an AX-1000 plasma system for 20 minutes, with the pressure maintained at 10 Pa and a 13 MHz RF power of 150 W applied for 30 minutes to obtain Ru1 / CuO x Electrocatalytic materials.

[0042] The present invention discloses a process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, wherein the urea synthesis process comprises the following steps: Step 1: The present invention first uses air (N2 / O2) as a nitrogen source, and uses high-energy species (such as electrons and neutral particles) generated by high-frequency pulse plasma reaction to activate N2 molecules. Through the non-equilibrium energy transfer mechanism, the N≡N bond energy is effectively weakened, and its dissociation energy is reduced from 9.8 eV in the ground state to 2~3 eV, thereby achieving efficient activation of nitrogen under mild conditions, that is, air (N2 / O2) can be efficiently converted into nitrogen oxides (NO) at room temperature and pressure. x ), effectively improving the conversion efficiency of N2.

[0043] Step 2: Further, plasma activated nitrogen oxides (NO x ) is efficiently mixed with alkaline absorption liquid (pH 9), effectively increasing the reaction contact area in the form of atomized contact, increasing the reaction rate, and promoting NO2 - The selective generation of NO2 in the absorption liquid increases - content.

[0044] Step 3: Further, the NO2-rich - The absorption liquid was added to the electrolytic cell as the electrolyte for the electrocatalytic reaction. The synthesized high-efficiency catalyst was used as the cathode and the platinum electrode was used as the anode. CO2 gas (5-10 L / min) was introduced into the electrolyte near the cathode. By applying a stable voltage (voltage fluctuation ±0.05 V) to the anode and cathode, two-step catalytic reactions were carried out simultaneously in the electrolytic cell: CO2 → *CO and NO2 - →*NH2 reaction, which can efficiently produce key *CO and *NH2 intermediates and promote the electrocatalytic coupling of *CO and *NH2 to produce urea.

Claims

1. A process for preparing a urea catalyst and synthesizing urea by plasma atomization absorption, characterized in that: The preparation method of the urea catalyst is as follows: Step 1, mixing copper sulfate pentahydrate and ruthenium chloride trihydrate, wherein the mass fraction of copper sulfate pentahydrate is 80% to 95% and the mass fraction of ruthenium chloride trihydrate is 5% to 20%, and the mixture is mixed in an ethanol-water mixed solvent (V / V = 1:1); Step 2: Place the mixture in an ice-water bath and stir vigorously until a uniform blue mixture is formed; Step 3: Inject 0.02-0.04 mol of NaOH solution into the blue mixture in step 2 and continue stirring for 30 minutes; Step 4: After cooling the mixture formed in step 3 for 20 to 30 hours, transfer it to a polytetrafluoroethylene-lined stainless steel reactor with a filling degree controlled at 50% to 70%. The reactor is sealed and placed in a forced air drying oven, heated to 130°C at a heating rate of 5°C / min and kept at this temperature for 15 to 20 hours, and then naturally cooled to room temperature. Step 5: Centrifuge the mixture obtained in step 4 to collect the black precipitate, and wash it alternately with deionized water and anhydrous ethanol multiple times to remove impurities. Finally, dry the washed black precipitate in a vacuum drying oven at 50-80°C for 10-15 hours to obtain a black powder product; Step 6: calcining the black powder obtained in step 5 at 400° C. for 3 to 6 hours to obtain a ruthenium-doped copper oxide (Ru1 / CuO) sample; Step 7: The Ru1 / CuO sample was treated with Ar plasma in an AX-1000 plasma system for 5-30 minutes, with the pressure maintained at 10-20 Pa and a 10-30 MHz RF power of 100-200 W applied for 10-30 minutes to obtain Ru1 / CuO. x electrocatalyst.

2. The plasma atomization absorption synthesis urea process according to claim 1, characterized in that: The steps include: Step 1: Using air (N2 / O2) as the nitrogen source, high-energy species (such as electrons and neutral particles) generated by high-frequency pulse plasma reaction are used to activate N2 molecules. Through the non-equilibrium energy transfer mechanism, the N≡N bond energy is effectively weakened, and its dissociation energy is reduced from 9.8 eV in the ground state to 2~3 eV, thereby achieving efficient activation of nitrogen under mild conditions, that is, air (N2 / O2) can be efficiently converted into nitrogen oxides (NO x ); Step 2: plasma activated nitrogen oxides (NO x ) is efficiently mixed with the alkaline absorption liquid, and NO2 is selectively generated during the reaction - , increasing the NO2 in the absorption liquid - content; Step 3: enrich NO2 - The absorption liquid is added to the electrolytic cell as the electrolyte for the electrocatalytic reaction, the urea electrocatalyst synthesized in claim 1 is used as the cathode, the platinum electrode is used as the anode, CO2 gas is introduced into the electrolyte near the cathode, and a stable voltage is applied to the anode and the cathode, and two-step catalytic reactions are carried out simultaneously in the electrolytic cell: CO2 → *CO and NO2 - →*NH2 reaction, which can efficiently produce key *CO and *NH2 intermediates and promote the electrocatalytic coupling of *CO and *NH2 to produce urea.

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