A method for synthesizing urea using dry ice

Abstract

The present invention discloses a method for synthesizing urea using dry ice. A self-made atmospheric pressure corona discharge ionization device is used to efficiently ionize water molecules in the air to form water radical cation dimers. The resulting dimers first react with nitrogen in the air to produce hydroxylamine radical cations, which then react with carbon dioxide formed by sublimation of dry ice to further produce urea radical cations. The urea radical cations are then captured using mass spectrometry to produce urea. This method solves the problem of harsh reaction conditions and the need for high temperature and high pressure in the prior art of preparing urea using carbon dioxide. Furthermore, the method is green, mild, and catalyst-free, meeting carbon reduction requirements.

Description

Technical Field

[0001] The present invention relates to the field of carbon reduction, and in particular to a method for synthesizing urea using dry ice. Background Art

[0002] Urea is a neutral fertilizer suitable for a variety of soils and plants. It's easy to store, convenient to use, and minimally destructive to the soil. It's a widely used chemical nitrogen fertilizer and also the one with the highest nitrogen content. Currently, the mainstream process for industrial urea production is the direct synthesis process of ammonia and carbon dioxide (CO2), with the reaction equations being 2NH3+CO2=NH4COONH2; NH3COONH2=NH2CONH2+H2O. This process can be categorized as a full-circulation aqueous solution method, a CO2 stripping method, and an ammonia stripping method. However, all three methods require high temperatures and high pressures. The efficient conversion of CO2 to urea under mild conditions has become a hot topic for researchers.

[0003] Nitrogen is widely present in the atmosphere, with a volume fraction of 78%. It is an abundant, cheap and easily available nitrogen source. However, due to its strong triple bond, nitrogen cannot be directly absorbed and utilized by organisms. Only by converting free nitrogen in the air into nitrogen-containing compounds can it be used by humans in food or other industrial production. Therefore, research on nitrogen fixation and conversion is of great significance to the development of human society. Nitrogen fixation methods mainly include biological nitrogen fixation, industrial nitrogen fixation, and high-energy nitrogen fixation (i.e., nitrogen fixation through ionization). Among the existing nitrogen fixation methods, only artificial chemical nitrogen fixation can be used on a large scale in industrial production, and its main product is ammonia-containing compounds, such as urea.

[0004] CO2 is a cheap and renewable C1 resource, yet it is also a major contributor to global warming. Against this backdrop, CO2 reuse has become a growing global concern. Humans can readily convert CO2 captured from the environment into high-value-added chemicals, currently primarily derived from petroleum, such as urea, methanol, and oxalic acid, through chemical conversion. However, CO2's extremely stable chemical properties make efficient conversion a challenging technological challenge. Dry ice is solid carbon dioxide, obtained by liquefying CO2 into a colorless liquid at a pressure of 6250.5498 kPa and then rapidly solidifying it at low temperatures. Dry ice easily sublimates into gaseous CO2, which has a surface area 1,000 times greater than that of the solid. Dry ice is now widely used in many fields, primarily for freezing; its application in synthetic processes is still under development. Summary of the Invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a novel reaction for rapidly synthesizing urea by reacting water with dry ice and air based on corona discharge technology. This reaction not only meets the requirements of new energy, but is also atom-economical, green and pollution-free, and does not require a catalyst, making it a model of green synthetic chemistry.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for synthesizing urea using dry ice comprises: using a normal pressure corona discharge device to ionize water molecules in the air to generate water radical cation dimers; the formed water radical cation dimers first react with a nitrogen source to generate hydroxylamine radical cations; the hydroxylamine radical cations then react with a carbon source to generate urea; and the urea radical cations are captured by a mass spectrometer to produce urea.

[0008] The reaction principle is as follows:

[0009]

[0010] Furthermore, the nitrogen is nitrogen in the air, and there is no need to provide a separate nitrogen source.

[0011] Furthermore, the dry ice is 1 to 2 g.

[0012] Furthermore, the voltage applied to the atmospheric pressure corona discharge ion source is 2-3 kV.

[0013] The working principle of the homemade atmospheric pressure corona discharge device described in this invention: This device, a representative technology for the application of two-dimensional ionization theoretical models, is an improvement on the surface desorption atmospheric pressure chemical ionization (DAPCI) method previously proposed by the research team. DAPCI uses a discharge needle to ionize water vapor to generate energy and charge carriers, which are transferred through gas-solid-gas or liquid-solid-gas phases, achieving efficient ionization of molecules on solid surfaces. Based on this, the homemade atmospheric pressure corona discharge device has been improved with improvements in the discharge needle material, discharge needle tip diameter, and simplified device, enabling the production of water radical cation dimers with high signal intensity.

[0014] Furthermore, the model of the mass spectrometer is LTQ-XL, Thermo.

[0015] Furthermore, the atmospheric pressure corona discharge device includes a capillary tube and a discharge needle connected to a high voltage source, the discharge needle being located in the capillary tube, and the discharge needle tip being exposed 0.2 mm from the capillary tube outlet. Preferably, the discharge needle is made of a stainless steel acupuncture needle or a tungsten needle, but is not limited thereto.

[0016] The present invention has the beneficial effects of utilizing a normal-pressure corona discharge device to ionize moist water molecules in the air to produce water radical cation dimers. The resulting water radical cation dimers preferentially come into contact with nitrogen in the air and react to produce hydroxylamine radical cations. The hydroxylamine radical cations then react with CO₂ generated by sublimation of dry ice to produce urea radical cations, which are detected by a mass spectrometer. The present invention addresses the problem of harsh reaction conditions and the need for high temperature and high pressure in the prior art of using CO₂ to prepare urea. Furthermore, the proposed method is green, mild, catalyst-free, and meets carbon reduction requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0018] Figure 1 Schematic diagram of the structure of a urea preparation device according to an embodiment of the present invention;

[0019] Figure 2 This is the primary mass spectrum of the ionization of standard urea;

[0020] Figure 3 This is the secondary mass spectrum of the protonated ion m / z 61 formed by the ionization of standard urea;

[0021] Figure 4 This is the secondary mass spectrum of the characteristic ion m / z 121 formed by the ionization of standard urea;

[0022] Figure 5 This is the standard curve of urea.

[0023] Figure 6 The primary mass spectrum of urea was prepared for the reaction of water radical cation with nitrogen and dry ice;

[0024] Figure 7 The secondary mass spectrum of urea generated by the reaction of water radical cation with nitrogen and dry ice was prepared with a signal of m / z 61;

[0025] Figure 8 The secondary mass spectrum of urea generated by the reaction of water radical cation with nitrogen and dry ice was prepared with a signal of m / z 121;

[0026] Figure 9 The mass spectrum of water radical cation dimer (m / z 36) formed by regulating low energy (voltage 2kV) ionization of air.

[0027] Figure 10 The mass spectrum of protonated water dimer (m / z 37) was formed by controlling high energy (voltage 4kV) ionization of air.

[0028] In the figure, 1-capillary, 2-discharge needle, 3-sample plate, 4-mass spectrometer negative pressure inlet, and m / z is the ratio of mass / charge number. DETAILED DESCRIPTION

[0029] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it should not be understood as a limitation on the scope of protection of the present invention.

[0030] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the present invention.

[0031] In the description of the present invention, "several" means one or more, "many" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0032] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0033] See also Figure 1 One embodiment of the present invention provides a urea preparation device used in a urea synthesis method. Specifically, the urea device comprises a sample plate 3, an atmospheric pressure corona discharge device, and a mass spectrometer. The homemade atmospheric pressure corona discharge device comprises a capillary 1 and a discharge needle 2 connected to a high-voltage source. The discharge needle 2 is located within the capillary 1. The sample plate is positioned between the negative pressure inlet 4 of the mass spectrometer and the discharge needle 2, and is positioned toward the bottom, facilitating the input of reaction products to the mass spectrometer's negative pressure inlet 4.

[0034] See also Figure 6 , water radical cation reacts with nitrogen in nitrogen air and dry ice to prepare urea, primary mass spectrum.

[0035] See also Figure 7 and 8 , water radical cation reacts with nitrogen in the air and dry ice to prepare urea, secondary mass spectrum.

[0036] Based on the above device, the urea preparation method includes:

[0037] Place dry ice on the surface of sample plate 3 (in front of the ion source generated by corona discharge);

[0038] Turn on the high voltage source and apply high voltage to the discharge needle 1, so that the water in the air in front of the discharge needle 1 generates water radical cation dimer (m / z 36, reference Figure 9 ), the formed water radical cation dimer (m / z 36) reacts with nitrogen in the air and dry ice to produce urea radical cation, which is passed into the mass spectrometer through the negative pressure inlet 4 to capture the urea radical cation to produce urea;

[0039] The signal after dry ice injection was analyzed by tandem mass spectrometry (refer to Figure 6 ), and obtained its primary spectrum, m / z 61([urea+H] + ), m / z 78([urea+H2O] + ) and m / z 121 ([2-urea+H] + These ion signals can be used as characteristic ion signals for the formation of urea. Further, the characteristic signal m / z 61 is subjected to tandem mass spectrometry analysis to generate the main fragment ion m / z 44 ( Figure 7 ), the fragment ion is formed by the loss of NH3 from the parent ion m / z 61 and is a characteristic fragment ion of urea.

[0040] Specifically, a high voltage (2 to 3 kV) is applied to a discharge needle to generate a corona discharge at the tip of the discharge needle. At room temperature and pressure (e.g., 25°C, one atmosphere), air with a certain humidity is used as a nitrogen source (preferably with a moisture content of at least 60%) and dry ice is used as a carbon source. Water radical cation dimers are generated through corona discharge. The water radical cation dimers first react with nitrogen in the air to generate hydroxylamine radical cations, and then react with dry ice to generate urea radical cations. The urea radical cations are then detected by a mass spectrometer under vacuum conditions at the mass spectrometer port.

[0041] The following are several examples to verify the preparation results of the above urea preparation method:

[0042] Example 1

[0043] use Figure 1 The device is operated at room temperature and pressure, with the power supply voltage adjusted to 4 kV. The discharge needle ionizes the water molecules in the air, mainly producing protonated water dimer ions (m / z 37, reference Figure 10), and different concentrations of urea aqueous solution (10ppm, 25ppm, 50ppm, 100ppm, 250ppm) were dripped onto the sample plate in turn, so that it could undergo proton exchange with the protonated water dimer ions and ionize to form protonated urea signal ions.

[0044] Test 1: Set the positive ion detection mode, the mass spectrometry scan range is m / z 15-200; the applied voltage is 4kV; and the capillary temperature is 150°C. Under these conditions, the mass spectrometry signal ion m / z 61 ([urea + H] + ) and m / z 121 ([2-urea+H] + )(like Figure 2 shown).

[0045] Test 2: When performing tandem mass spectrometry analysis, the parent ion isolation width was 1.4, the collision time was 30ms, the collision energy was 20%, and the Act.Q was 0.35. Other parameters were automatically optimized by the LTQ-MS system. Tandem mass spectrometry analysis was performed on the urea characteristic signal m / z 61 generated after the addition of urea solution, and the characteristic fragment ion m / z 44 (such as the missing neutral ammonia molecule) was obtained. Figure 3 shown).

[0046] Test 3: When performing tandem mass spectrometry analysis, the parent ion isolation width is 2, the collision time is 30ms, the collision energy is 15%, the Act.Q is 0.35, and other parameters are automatically optimized by the LTQ-MS system. Tandem mass spectrometry analysis is performed on the urea characteristic signal m / z 121 generated after the addition of urea solution, and the characteristic fragment ion m / z 61 (such as the missing neutral urea molecule) is obtained. Figure 4 shown).

[0047] Test 4: Set the positive ion detection mode, the mass spectrometer scan range is m / z 15-200; the applied voltage is 4kV; the capillary temperature is 150℃. Under these conditions, Figure 1 The device is used to drip urea solutions of different concentrations (10ppm, 25ppm, 50ppm, 100ppm, 250ppm) on the surface of the sample plate, and the relationship between different concentrations of urea and signal intensity can be obtained, that is, the standard curve (such as Figure 5 shown).

[0048] Example 2

[0049] At room temperature and pressure, a small piece of dry ice weighing 1 to 2 grams is placed on the sample plate. The voltage of the atmospheric power supply discharge device is adjusted to 2.5 kV to ionize the water molecules in the air to produce water radical cation dimers (m / z 36). The formed water radical cation dimers quickly react with the surrounding nitrogen molecules to produce hydroxylamine radical cations. The hydroxylamine radical cations continue to fully react with the CO2 gas formed by the sublimation of 1 gram of dry ice on the surface of the sample plate to form urea radical cations. The urea radical cations are then passed into a mass spectrometer to capture the urea radical cations and produce urea. The results are compared and analyzed with those of Example 1.

[0050] Test 1: Set the positive ion detection mode, the mass spectrometer scan range is m / z 15-200; the applied voltage is 2.5kV; the capillary temperature is 150℃. Under these conditions, Figure 1 The device was placed in dry ice to obtain the mass spectrometry signal ion m / z 61 ([urea + H] + ), m / z 78([urea+H2O] + ) and m / z 121 ([2-urea+H] + )(like Figure 6 This result is consistent with the result of test 1 in Example 1, indicating that urea was successfully synthesized using this method.

[0051] Test 2: When performing tandem mass spectrometry analysis, the parent ion isolation width was 1.4, the collision time was 30 ms, the collision energy was 20%, and the Act.Q was 0.35. Other parameters were automatically optimized by the LTQ-MS system. Tandem mass spectrometry analysis of the urea characteristic signal m / z 61 generated after dry ice injection can obtain the characteristic fragment ion m / z 44 (such as the missing neutral ammonia molecule) Figure 7 This result is consistent with the result of Test 2 in Example 1, indicating that the structure of the m / z 61 ion is protonated urea.

[0052] Test 3: When performing tandem mass spectrometry analysis, the parent ion isolation width was 2, the collision time was 30ms, the collision energy was 15%, and the Act.Q was 0.35. Other parameters were automatically optimized by the LTQ-MS system. Tandem mass spectrometry analysis of the urea characteristic signal m / z 121 generated after dry ice injection can obtain the characteristic fragment ion m / z 61 (such as the missing neutral urea molecule) Figure 8 This result is consistent with the result of test 3 in Example 1, indicating that the structure of the m / z 121 ion is a protonated urea dimer.

[0053] In summary, the method of the present invention does produce urea, that is, urea is successfully synthesized using this method. Moreover, according to the urea synthesis method proposed in this embodiment, the entire synthesis process can be carried out at room temperature and pressure (referring to pressure), and only requires an air source as a raw material, without the need for an additional nitrogen source or a catalyst, thus saving energy, being green and pollution-free, and meeting carbon reduction requirements.

[0054] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0055] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for synthesizing urea using dry ice, characterized in that: A normal pressure corona discharge ionization device is used to ionize water molecules in the air to generate water radical cation dimers. The formed water radical cation dimers first react with a nitrogen source to generate hydroxylamine radical cations. The hydroxylamine radical cations further react with a carbon source to generate urea radical cations. The urea radical cations are then passed into a mass spectrometer to capture the urea radical cations, thereby producing urea. The nitrogen source is nitrogen in the air. The carbon source is dry ice with a mass of 1-2 g; the additional voltage of the atmospheric pressure corona discharge ionization device is 2-3 kV; The atmospheric pressure corona discharge device comprises a capillary (1) and a discharge needle (2) connected to a high voltage source, wherein the discharge needle (2) is located in the capillary (1), and the discharge needle tip is exposed 0.2 mm from the capillary outlet; the discharge needle is made of a stainless steel acupuncture needle or a tungsten needle.

2. The method for synthesizing urea using dry ice according to claim 1, wherein: The model of the mass spectrometer is LTQ-XL, Thermo.

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