High-stability ammonium carbamate powder, preparation method and application thereof

Abstract

The application relates to a high-stability ammonium carbamate powder and a preparation method and application thereof, in particular to a high-stability ammonium carbamate powder preparation method which comprises the following steps: under the action of a catalyst, carbon dioxide and ammonia gas are reacted in a gas reaction tower to generate ammonium carbamate powder containing beta crystal form with a proportion greater than 10%. The application not only solves the problems that the ammonium carbamate is easy to decompose and difficult to store, but also provides a reliable technical scheme and application prospect for the ammonium carbamate as a new type of efficient, stable and environment-friendly nitrogen fertilizer.

Description

Technical Field

[0001] This invention relates to the field of chemical manufacturing, specifically to a highly stable ammonium carbamate powder, its preparation method, and its application. Background Technology

[0002] Currently, food security and stable crop yield increases have become important strategic goals and directions in China. Therefore, finding a nitrogen fertilizer with application effects similar to urea has become a focus of research. Ammonium carbamate has a nitrogen content of 35.9%, lower than urea's 46.7%, but higher than ammonium sulfate (21.2%), ammonium nitrate (35%), ammonium chloride (26.1%), ammonium carbonate (29.1%), and ammonium bicarbonate (17.7%). The ammonium carbamate molecule consists of an ammonium ion and a carbamate ion bonded together, thus containing both ammonium and urea nitrogen. This makes it more easily absorbed by plants than urea, and it does not contain biuret (an impurity found in urea products that can cause seedling burn). It can replace urea in paddy fields, dry land, and vegetable and fruit cultivation.

[0003] Ammonium carbamate exhibits two crystal structures: one is the orthorhombic Pbca space group, referred to as the α-type; the other is the orthorhombic Ibam space group, referred to as the β-type. According to reports and literature (Zeitschrift für anorganische und allgemeine Chemie, 2007, 633, 653.), α-type ammonium carbamate is volatile and hydrolyzed, while β-type ammonium carbamate is more stable. α-type ammonium carbamate undergoes hydrolysis in high-humidity environments as follows: NH₂COONH₄ + 2H₂O = NH₄HCO₃ + NH₃·H₂O. Because the ammonia produced by hydrolysis is volatile, long-term storage of ammonium carbamate in a certain humidity environment leads to a decrease in the nitrogen content of the product. Considering the application scenario of ammonium carbamate as a nitrogen fertilizer, obtaining more β-type ammonium carbamate is our development goal. Summary of the Invention

[0004] Based on the above shortcomings, the present invention proposes a preparation technology for highly stable ammonium carbamate powder, which can be used as a highly efficient nitrogen fertilizer in the plant growth stage.

[0005] This invention provides a method for preparing highly stable ammonium carbamate powder, comprising the following steps: under the action of a catalyst, carbon dioxide and ammonia are reacted to generate ammonium carbamate powder containing a β-crystal form with a proportion greater than 10%.

[0006] Furthermore, the ammonium carbamate powder contains 10%-60% β-crystal form.

[0007] Furthermore, the raw materials used to prepare the ammonium carbamate powder are: 35-56 parts carbon dioxide, 25-44 parts ammonia, and 0.1-5 parts catalyst.

[0008] Furthermore, the catalyst comprises a complex of a bimetallic hydroxide and an oxide.

[0009] Furthermore, the bimetal comprises two types: a noble metal and a base metal, wherein the base metal is selected from any one of Cu, Ni, Fe, Al, Mn, and Co, and the noble metal is selected from any one of Pd, Pt, Ru, and Rh, and the molar ratio of the noble metal to the base metal is 1:(1-8).

[0010] Furthermore, the catalyst is prepared by taking hydroxides of noble metal and base metal as raw materials, grinding and mixing them, calcining them at high temperature to obtain oxide powder, then stirring the oxide powder with water at room temperature to obtain solid powder of oxide and hydroxide, and then filtering and drying the solid powder to obtain the catalyst.

[0011] Furthermore, the reaction is carried out at a temperature ranging from -5°C to 25°C.

[0012] The present invention also provides a highly stable ammonium carbamate powder prepared by the preparation method described above, wherein the proportion of β-crystal form in the ammonium carbamate powder is greater than 10%.

[0013] Furthermore, after the ammonium carbamate powder is stored at 40-50°C and 45-50% relative humidity for 12 months, the optimal nitrogen content is not less than 35.5%.

[0014] The present invention also provides a fertilizer composition comprising the above-prepared ammonium carbamate powder or the above-described ammonium carbamate powder as a nitrogen fertilizer.

[0015] The present invention also provides the application of the above-prepared ammonium carbamate powder, the above-described ammonium carbamate powder, or the above-described composition in crop growth; The present invention also provides a method for promoting plant growth, comprising applying the above-described ammonium carbamate powder or the above-described fertilizer composition to the plant.

[0016] The advantages of this invention compared to existing technologies are: This invention successfully prepared ammonium carbamate powder with a β-crystal form ratio greater than 50% by using a specific bimetallic catalyst to catalyze the reaction of CO2 and NH3 under mild conditions. The product exhibits excellent storage stability; after being stored at 40-50℃ and 45-50% humidity for 12 months, its nitrogen content remained above 35.5%, far superior to commercially available products. Furthermore, it demonstrated excellent fertilizer efficiency in Arabidopsis thaliana cultivation experiments, with seed production comparable to ammonium carbonate and significantly better than urea, while requiring a smaller dosage. This invention not only solves the problems of easy decomposition and difficult storage of ammonium carbamate but also provides a reliable technical solution and application prospect for its use as a highly efficient, stable, and environmentally friendly new nitrogen fertilizer. Attached Figure Description

[0017] Figure 1 Ammonium carbamate α crystal structure, (a) schematic diagram of a unit cell of ammonium carbamate; (b) schematic diagram of the wavy two-dimensional supramolecular layer structure in ammonium carbamate; (c) schematic diagram of the three-dimensional supramolecular structure of ammonium carbamate; Figure 2 The crystal structure of ammonium carbamate β: (a) Schematic diagram of a unit cell of ammonium carbamate (eight carbamate ions are located on the crystal face, eight on the axis, and two inside the unit cell; four ammonium ions are located on the crystal face and four inside the unit cell, so each unit cell contains eight pairs of cations and anions); (b) Schematic diagram of the planar two-dimensional supramolecular layer structure of ammonium carbamate; (c) Hydrogen bonding between carboxylate ions and ammonium ions in ammonium carbamate; (d) Schematic diagram of the three-dimensional supramolecular structure of ammonium carbamate. Figure 3 XRD patterns of α and β crystal structures of ammonium carbamate powder: 1) XRD pattern of α-crystal form of ammonium carbamate; 2) XRD pattern of β-crystal form of ammonium carbamate. Figure 4 XRD pattern of ammonium carbamate powder in Experimental Example 7 (of the present invention); Figure 5 Comparative Example 1 (commercially available product) XRD pattern of ammonium carbamate powder; Figure 6 Plant growth diagram. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, a more detailed description is provided below. However, it should be understood that the description herein is merely for explaining this application and is not intended to limit its scope.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. All reagents and instruments used herein are commercially available, and the characterization methods involved can be found in relevant descriptions in the prior art, and will not be repeated here.

[0020] To further understand this application, the following detailed description is provided in conjunction with the preferred embodiments.

[0021] Example 1 This embodiment provides a method for preparing highly stable ammonium carbamate powder, comprising the following steps: under the action of a catalyst, carbon dioxide and ammonia react to generate ammonium carbamate powder containing a β-crystal form proportion greater than 10%, with its nitrogen content maintained between 35.8% and 35.9%. The α-crystal structure of the ammonium carbamate powder is as follows: Figure 1 As shown, the β-crystal structure in the ammonium carbamate powder is as follows: Figure 2 As shown in Table 1, the cell parameters of ammonium carbamate powder are as follows.

[0022] Table 1. Cell parameters of α-ammonium carbamate and β-ammonium carbamate powders obtained by testing

[0023] The presence of a catalyst lowers the activation energy of the reaction, which not only accelerates the reaction but, more importantly, its surface properties induce the preferential formation of a more stable β-crystal form.

[0024] As a further preferred embodiment, the ammonium carbamate powder contains 10%-60% β-crystal form.

[0025] As a further preferred embodiment, the raw materials for preparing the ammonium carbamate powder are: 35-56 parts carbon dioxide, 25-44 parts ammonia, and 0.1-5 parts catalyst.

[0026] This formulation maximizes feed conversion and minimizes unreacted gas residue, thereby improving economic efficiency and product purity. The controlled catalyst dosage range ensures sufficient catalytic activity without excessively impacting product quality.

[0027] Both carbon dioxide and ammonia participate in the reaction in gaseous form, while the catalyst participates in the reaction in solid form.

[0028] First, a catalyst is added to the reactor, and a reaction gas is introduced to react directly under certain conditions to form ammonium carbamate powder. The proportion of β crystals in this ammonium carbamate powder is greater than 10%, which has high stability.

[0029] As a further preferred embodiment, the catalyst is developed and prepared by our company. The catalyst comprises a complex of a bimetallic hydroxide and an oxide, which serves to provide a catalytic center and control the crystal configuration.

[0030] Under the catalysis of bimetallic hydroxides and oxides, carbon dioxide and ammonia react in a gas reaction tower to generate ammonium carbamate powder containing more than 10% β-crystal form.

[0031] The catalyst used in this invention is a composite of a bimetallic oxide and hydroxide. In this catalyst, the electron-deficient metal center combines with and activates ammonia, while the electron-rich metal center combines with and activates carbon dioxide. After the activated ammonia and carbon dioxide combine on the catalyst surface, a rapid reaction occurs, induced by the crystal configuration formed by the bimetallic catalyst, to obtain ammonium carbamate with a high proportion of β-configuration.

[0032] The specific structure of bimetallic hydroxides and oxides provides a huge specific surface area, which makes the catalytic active sites highly dispersed; the complex of bimetallic hydroxides and oxides means that there are two metal centers with different electronegativity, which can efficiently activate NH3 and CO2 molecules respectively, promoting their contact and reaction on their surfaces.

[0033] As a further preferred embodiment, the bimetal includes two types: a noble metal and a base metal, wherein the base metal is selected from any one of Cu, Ni, Fe, Al, Mn, and Co, and the noble metal is selected from any one of Pd, Pt, Ru, and Rh, and the molar ratio of the noble metal to the base metal is 1:(1-8).

[0034] The catalyst is prepared as follows: Hydroxides of both noble and base metals are used as raw materials. These are ground and mixed, then calcined in a muffle furnace at 1000-1200℃ for 1-3 hours to obtain oxide powder. The oxide powder is then stirred with pure water at room temperature for 1-2 hours to obtain solid powders of oxide and hydroxide. The solid powders are then filtered and vacuum dried at 30-50℃ for 10-14 hours to obtain the catalyst.

[0035] In the catalyst complex, there are no restrictions on the ratio between hydroxide and oxide. As long as the catalyst is prepared by the method of this application, it will not affect the performance of this application.

[0036] Specifically, metal hydroxides (such as Al(OH)3, Rh(OH)3) are first calcined at high temperatures (1000-1200°C), resulting in a dehydration reaction that generates the corresponding metal oxides. For example: 2Al(OH)3 → Al2O3 + 3H2O↑, 2Rh(OH)3 → Rh2O3 + 3H2O↑. The resulting oxide powder is then stirred with pure water. Not all oxides rehydrate; their behavior depends on the characteristics of the metal element: For base metals (such as Al), their oxides (Al2O3) have high surface energy and hydration activity. Upon contact with water, their surface or part of the bulk phase reacts chemically with water, regenerating aluminum hydroxyl oxides or layered double hydroxide-like structures. This is a chemical reconstruction process, not a simple mixing. For noble metals (such as Rh), their oxides (Rh2O3) are relatively stable, with a very low tendency to hydrate at room temperature, and most remain in the oxide state. The final product is a complex of the catalyst "oxide" and the "regenerated hydroxide," rather than a simple return to the initial raw materials. Therefore, the composite may contain no precious metal hydroxides or may contain small amounts, neither of which affects the performance of the catalyst.

[0037] Preferably, the bimetallic combination can be Al and Rh, Mn and Pd, Fe and Pt, Cu and Ru, Co and Pt, Ni and Ru; the molar ratio of the bimetallic combination is 1:(1-8).

[0038] More preferably, the bimetallic combination is Al and Rh, with a molar ratio of 1:(3-3.5).

[0039] Different metal combinations exhibit different electronic structures and catalytic activities. Specific combinations (such as Al-Rh) may produce unique synergistic effects, enabling more effective and directional induction of β-crystalline structure formation.

[0040] As a further preferred embodiment, the reaction is carried out at a temperature of -5°C to 25°C, preferably 0-10°C.

[0041] The synthesis of ammonium carbamate is an exothermic reaction and is unstable and easily decomposes at high temperatures. Low temperature conditions (-5 to 25°C) favor shifting the reaction equilibrium towards the product formation and suppressing side reactions and product decomposition, thus ensuring high yield and high stability. 0-10°C is the optimal temperature range, balancing reaction rate and product stability.

[0042] Example 2 This embodiment provides a highly stable ammonium carbamate powder prepared by the preparation method described in Example 1, wherein the proportion of β crystal form in the ammonium carbamate powder is greater than 10%, and the ammonium carbamate is a mixture of α and β crystals.

[0043] As a further preferred embodiment, the nitrogen content of the ammonium carbamate powder is not less than 35.5% after being stored at 40-50°C and 45-50% relative humidity for 12 months.

[0044] β-crystal molecules are more tightly packed and have a more stable hydrogen bond network, making them less prone to moisture absorption (deliquescence) and decomposition to release ammonia.

[0045] This embodiment also provides a fertilizer composition comprising the ammonium carbamate powder prepared in Example 1 or the ammonium carbamate powder described above as a nitrogen fertilizer.

[0046] The highly stable ammonium carbamate powder prepared by this invention can be used as an effective ingredient (nitrogen source) alone or mixed with other fertilizer ingredients (such as phosphorus, potassium, trace elements, etc., which are not explicitly stated but are implied) to form a complete fertilizer product.

[0047] This embodiment also provides an application of the above-prepared ammonium carbamate powder, the above-described ammonium carbamate powder, or the above-described composition in crop growth; This embodiment also provides a method for promoting plant growth, including applying the above-described ammonium carbamate powder or the above-described fertilizer composition to the plant.

[0048] Example 3 Experimental Example 1 Catalyst preparation scheme: 10g of Al(OH)3 and 60g of Rh(OH)3 raw materials were ground and mixed, and then calcined in a muffle furnace at 1000℃ for 2h to obtain oxide powder. Then, the oxide powder was stirred with 200g of pure water at room temperature for 2h to obtain solid powder of oxide and hydroxide. The solid powder was then filtered and vacuum dried at 40℃ for 12h to obtain the catalyst LT-Al / Rh.

[0049] Experimental Example 2 The catalyst preparation scheme was the same as in Experiment 1, with raw materials of 10g Mn(OH)2 and 48g Pd(OH)2, and the resulting catalyst was LT-Mn / Pd.

[0050] Experimental Example 3 The catalyst preparation scheme was the same as in Experiment 1, with raw materials of 10g Fe(OH)3 and 75g Pt(OH)4, and the resulting catalyst was LT-Fe / Pt.

[0051] Test Example 4 The catalyst preparation scheme is the same as in Experiment 1, with raw materials of 10g Cu(OH)2 and 50g Ru(OH)3, and the resulting catalyst is LT-Cu / Ru.

[0052] Experimental Example 5 The catalyst preparation scheme was the same as in Experiment 1, with raw materials of 10g Co(OH)2 and 85g Pt(OH)4, and the resulting catalyst was LT-Co / Pt.

[0053] Experimental Example 6 The catalyst preparation scheme is the same as in Experiment 1, with raw materials of 10g Ni(OH)2 and 50g Ru(OH)3, and the resulting catalyst is LT-Ni / Ru.

[0054] Experimental Example 7 Preparation of ammonium carbamate powder The catalyst LT-Al / Rh obtained in Example 1 was installed in a catalyst-packed column within a 100 L gas reactor. The catalyst loading was 500 g. Carbon dioxide and ammonia were introduced at flow rates of 1.320 kg / h and 1.02 kg / h, respectively, by mass. The temperature inside the reactor was controlled between 0 and 10 °C. The reaction proceeded continuously, with solid products being discharged continuously. Each batch of catalyst was replaced after 1000 hours of operation. The product obtained from this catalytic reaction had a β-crystal structure comprising 52%. Figure 3 , Figure 4 As shown, the ratio of α crystal form to β crystal form is approximately 0.9:1.

[0055] Experimental Example 8 The ammonium carbamate powder preparation scheme is the same as in Example 7, the catalyst is LT-Mn / Pd, and the proportion of β crystal configuration in the obtained product is 10%.

[0056] Experimental Example 9 The ammonium carbamate powder preparation scheme was the same as in Example 7, with LT-Fe / Pt as the catalyst, and the proportion of β crystal configuration in the obtained product was 13%.

[0057] Experimental Example 10 The ammonium carbamate powder preparation scheme was the same as in Example 7, with LT-Cu / Ru as the catalyst, and the proportion of β crystal configuration in the obtained product was 37%.

[0058] Experimental Example 11 The ammonium carbamate powder preparation method was the same as in Example 7, with LT-Co / Pt as the catalyst. The proportion of β-crystal configuration in the obtained product was 27%.

[0059] Experimental Example 12 The ammonium carbamate powder preparation scheme was the same as in Example 7, with LT-Ni / Ru as the catalyst, and the proportion of β crystal configuration in the obtained product was 19%.

[0060] Comparative Example 1: Existing Technology The manufacturer of the ammonium carbamate powder is McLean. Figure 5 As shown, the ratio of α crystal form to β crystal form is approximately 30:1.

[0061] Comparative Example 2: No catalyst Under the same reaction conditions as in Example 7 (0-10°C, same flow rates of CO2 and NH3), but without the addition of any catalyst, the reaction could not proceed.

[0062] Comparative Example 3: Single Metal Catalyst The calcination product of a single metal hydroxide is used as a catalyst, such as Al2O3 or Rh2O3 obtained by calcining Al(OH)3 or Rh(OH)3, and other conditions are the same as in Experimental Example 7.

[0063] Using LT-Al2O3: No product was produced.

[0064] Using LT-Rh2O3: No product was produced.

[0065] Comparative Example 4: Non-preferred metal combination catalysts Using a metal combination not within the preferred range of claim 4, such as the LT-Cr / Ag catalyst with a molar ratio of 1:1 Cr-Ag, other conditions were the same as in Example 7. The β-crystal form accounted for 0.5% of the product.

[0066] Comparative Example 5 A catalyst with an Al:Rh molar ratio of 1:10 was prepared under the same conditions as in Example 7. The β-crystal form accounted for approximately 8% of the product.

[0067] Example 4 The stability of the ammonium carbamate powder obtained in Experimental Example 7 of this invention was investigated compared with that obtained in Comparative Examples 1, 4, and 5 under the same temperature and humidity conditions, with nitrogen content as the evaluation point. The temperature was controlled at 45-50℃ and the relative humidity at 45-50% in a constant temperature and humidity chamber. The nitrogen content was tested according to national standards GB / T 2440-2017 and GB 3559-2001.

[0068] Table 2 Nitrogen content of the present invention and comparative examples

[0069] Example 5 Since ammonium bicarbonate, ammonium sulfate, ammonium nitrate and ammonium chloride are rarely used in agriculture, they will not be discussed in this application. This embodiment is a comparative experiment of two widely used products with similar nitrogen content, ammonium carbamate and ammonium carbamate.

[0070] Plant cultivation comparison experiment: 1. Seed vernalization: Line a disposable petri dish with moistened filter paper, spread the Arabidopsis seeds evenly, cover the dish, and place it in a refrigerator at low temperature to stimulate vernalization. After three days, plant the seeds in nutrient soil.

[0071] 2. Sowing: Mix the potting soil and vermiculite in a 4:1 ratio, water and mix until the soil is moist enough to drip when squeezed by hand. Sow five Arabidopsis thaliana seeds per hole, filling 4 holes in 32 holes per tray. Be careful to avoid the seeds sticking together. Cover the tray to keep it moist. Uncover the tray after three days.

[0072] 3. Seedling removal: One week after sowing, when the seedlings have sprouted, retain the larger and healthier seedlings and remove the rest.

[0073] 4. Fertilization: Fertilize after budding, setting up four control groups: ① blank group (no nitrogen fertilizer) ② ammonium carbamate group (product obtained from Experiment 7) ③ ammonium carbonate group ④ urea group. Except for the nitrogen fertilizer group, other nutrients required by Arabidopsis thaliana, such as K, Ca, Mg, etc., were added in equal amounts.

[0074] 5. Observation of growth status like Figure 6 The differences were obvious after the plants had grown for 3 weeks. The leaves of the nitrogen-free group were wilted and yellow, the leaves of the urea group were narrow and long, and the ammonium carbonate group and the ammonium carbamate group were basically the same.

[0075] 6. Comparison of seed yield The total seed yield was 10.2g in the nitrogen-free group, 14.8g in the urea group, 17.1g in the ammonium carbonate group, and 17.3g in the ammonium carbamate group. The results show that ammonium carbamate was superior to urea and on par with ammonium carbonate.

[0076] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing highly stable ammonium carbamate powder, characterized in that, The process includes the following steps: under the action of a catalyst, carbon dioxide and ammonia react to generate ammonium carbamate powder containing more than 10% β-crystal form. In the reaction tower, carbon dioxide and ammonia both participate in the reaction in gaseous form, while the catalyst participates in the reaction in solid form; the reaction is carried out at a temperature of -5°C to 25°C. The raw materials for preparing the ammonium carbamate powder are: 35-56 parts carbon dioxide, 25-44 parts ammonia, and 0.1-5 parts catalyst. The catalyst comprises a complex of a bimetallic hydroxide and an oxide; the bimetal comprises a noble metal and a base metal, wherein the base metal is selected from any one of Cu, Ni, Fe, Al, Mn, and Co, and the noble metal is selected from any one of Pd, Pt, Ru, and Rh, and the molar ratio of the noble metal to the base metal is 1:(1-8). The catalyst is prepared by taking hydroxides of noble and base metals as raw materials, grinding and mixing them, calcining them at high temperature to obtain oxide powder, then stirring the oxide powder with water at room temperature to obtain solid powder of oxide and hydroxide, and finally filtering and drying the solid powder to obtain the catalyst.

2. The preparation method according to claim 1, characterized in that, The ammonium carbamate powder contains 10%-60% β-crystal form.

3. A highly stable ammonium carbamate powder prepared by the preparation method according to any one of claims 1-2, characterized in that, The proportion of β-crystal form in the ammonium carbamate powder is greater than 10%.

4. The powder according to claim 3, characterized in that, The nitrogen content of the ammonium carbamate powder is not less than 35.5% after being stored at 40-50℃ and 45-50% relative humidity for 12 months.

5. A fertilizer composition, characterized in that, The ammonium carbamate powder prepared according to any one of claims 1-2 or the ammonium carbamate powder according to any one of claims 3-4 is used as a nitrogen fertilizer.

6. The application of an ammonium carbamate powder prepared according to any one of claims 1-2, an ammonium carbamate powder according to claim 3 or 4, or a composition according to claim 5 in crop growth.

7. A method for promoting plant growth, characterized in that, This includes applying the ammonium carbamate powder according to any one of claims 3-4 or the fertilizer composition according to claim 5 to plants.

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