High-stability ammonium carbamate powder as well as preparation method and application thereof

Abstract

The invention relates to high-stability ammonium carbamate powder as well as a preparation method and application thereof, in particular to the preparation method of the high-stability ammonium carbamate powder, which comprises the following steps: under the action of a catalyst, enabling carbon dioxide and ammonia gas to react in a gas reaction tower to generate the ammonium carbamate powder containing more than 10% of beta crystal form. The problems that ammonium carbamate is easy to decompose and difficult to store are solved, and a reliable technical scheme and application prospects are provided for the ammonium carbamate serving as an efficient, stable and environment-friendly novel nitrogen fertilizer.

Description

TECHNICAL FIELD

[0001] The application relates to the chemical manufacturing field, in particular to a high-stability ammonium carbamate powder and a preparation method and application thereof. BACKGROUND

[0002] At present, grain safety and stable yield of crops have become important strategic targets and directions in China. Therefore, finding a nitrogen fertilizer which can achieve an application effect close to that of urea has become the exploration direction of people. The nitrogen content of ammonium carbamate is 35.9%, which is lower than that of urea (46.7%), but higher than that of ammonium sulfate (21.2%), ammonium nitrate (35%), ammonium chloride (26.1%) and ammonium carbonate (29.1%) and ammonium bicarbonate (17.7%). The molecular structure of ammonium carbamate is formed by the combination of an ammonium ion and an ammonium carbonate ion, so there are both ammonium nitrogen and urea nitrogen in the molecular structure, which is more easily absorbed by plants than urea, and does not contain biuret (a kind of impurity in urea products which can cause 'burning seedlings'). Ammonium carbamate can be applied to paddy fields, dry lands and vegetable and fruit planting instead of urea.

[0003] There are two crystal structures in the crystal structure of ammonium carbamate. One is the Pbca space group of the orthorhombic system, which is called alpha crystal form, and the other is the Ibam space group of the orthorhombic system, which is called beta crystal form. According to the reports (Zeitschrift fur anorganische und allgemeine Chemie, 2007, 633, 653.) in the data and documents, ammonium carbamate with alpha crystal form is easy to volatilize and hydrolyze, and ammonium carbamate with beta crystal form is more stable. The alpha crystal form of ammonium carbamate undergoes the following hydrolysis process in a humid environment: NH2COONH4+2H2O=NH4HCO3+NH3·H2O. Since the ammonia water produced by hydrolysis is volatile, the nitrogen content in the product will decrease after long-term storage of ammonium carbamate in a certain humidity environment. Starting from the application scene of ammonium carbamate as a nitrogen fertilizer, obtaining more ammonium carbamate with beta crystal form is the development goal. SUMMARY

[0004] Based on the above-mentioned deficiencies, the preparation technology of the high-stability ammonium carbamate powder provided by the application can be applied to the plant growth stage as a high-efficiency nitrogen fertilizer.

[0005] The application provides a preparation method of high-stability ammonium carbamate powder, which comprises the following steps: under the action of a catalyst, carbon dioxide and ammonia gas are reacted to generate ammonium carbamate powder containing more than 10% of beta crystal form.

[0006] Further, the ammonium carbamate powder contains 10%-60% of the beta crystal form.

[0007] Further, the raw material for preparing the ammonium carbamate powder contains 35-56 parts of carbon dioxide, 25-44 parts of ammonia gas and 0.1-5 parts of the catalyst.

[0008] Further, the catalyst comprises a composite of double metal hydroxide and oxide.

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

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

[0011] Further, the reaction is carried out at a temperature of-5℃ to 25℃.

[0012] The application further provides a high-stability ammonium carbamate powder prepared by the above preparation method, wherein the proportion of the beta crystal form in the ammonium carbamate powder is greater than 10%.

[0013] Further, the optimal 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.

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

[0015] The application further provides application of the above-prepared ammonium carbamate powder, the above-described ammonium carbamate powder or the above-described composition in crop growth. The application further provides a method for promoting plant growth, which comprises applying the above-described ammonium carbamate powder or the above-described fertilizer composition to the plant.

[0016] Compared with the prior art, the application has the following advantages: The present application successfully prepares the ammonium carbamate powder with the beta crystal form accounting for more than 50% by catalyzing the reaction of CO2 and NH3 under mild conditions by using a specific bimetallic catalyst. The product shows excellent storage stability, and the nitrogen content is still maintained at more than 35.5% after being stored at 40-50 DEG C and 45-50% humidity for 12 months, which is much better than the commercially available product. In addition, it shows excellent fertilizer efficiency in the Arabidopsis planting experiment, and the seed yield is flat with ammonium carbonate, and is significantly better than urea, while the dosage is relatively small. The present application not only solves the problems of easy decomposition and difficult storage of ammonium carbamate, but also provides a reliable technical scheme and application prospect for ammonium carbamate as a new type of efficient, stable and environmentally friendly nitrogen fertilizer. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Ammonium carbamate alpha crystal structure, (a) schematic diagram of the unit cell of ammonium carbamate; (b) schematic diagram of the wave-shaped two-dimensional supramolecular layer structure of ammonium carbamate; (c) schematic diagram of the three-dimensional supramolecular structure of ammonium carbamate; Figure 2 Ammonium carbamate beta crystal structure, (a) schematic diagram of the unit cell of beta-ammonium carbamate (ammonium carbamate has eight on the crystal surface, eight on the axis, and two in the unit cell; the ammonium ion part is four on the crystal surface and four in the unit cell, so each unit cell contains 8 pairs of cations and anions); (b) schematic diagram of the planar two-dimensional supramolecular layer structure of beta-ammonium carbamate; (c) hydrogen bond interaction between carboxylate and ammonium ion in beta-ammonium carbamate; (d) schematic diagram of the three-dimensional supramolecular structure of beta-ammonium carbamate; Figure 3 XRD patterns of ammonium carbamate powder alpha and beta crystal structures, 1) XRD pattern of alpha crystal form of ammonium carbamate, 2) XRD pattern of beta crystal form of ammonium carbamate; Figure 4 XRD pattern of ammonium carbamate powder in test example 7 (the present application); Figure 5 XRD pattern of ammonium carbamate powder in comparative example 1 (commercial product); Figure 6 Plant growth chart. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below. However, it should be understood that the description here is only used to explain the present application, and is not used to limit the scope of the present application.

[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 in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0020] For further understanding of the present application, the following further describes the present application in conjunction with the best mode.

[0021] Embodiment 1 The present embodiment provides a method for preparing a high-stability ammonium carbamate powder, comprising the following steps: reacting carbon dioxide and ammonia gas under the action of a catalyst to generate an ammonium carbamate powder containing a β crystal form with a proportion greater than 10%, and the nitrogen content of which is maintained between 35.8% and 35.9%. The α crystal structure of the ammonium carbamate powder is as shown in Figure 1 The β crystal structure of the ammonium carbamate powder is as shown in Figure 2 The cell parameters of the ammonium carbamate powder are as shown in Table 1.

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

[0023] The presence of the catalyst reduces the reaction activation energy, not only accelerating the reaction, but more importantly, the surface properties of the catalyst induce the preferential generation of a more stable β crystal form.

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

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

[0026] This ratio maximizes the conversion rate of raw materials, reduces the residue of unreacted gas, and thus improves economic benefits and product purity. The use range of the catalyst ensures sufficient catalytic activity and does not excessively affect the product quality.

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

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

[0029] As a further preferred embodiment, the catalyst is a composite of double metal hydroxide and oxide, which provides catalytic center and controls crystal configuration.

[0030] Under the action of the double metal hydroxide and oxide catalyst, carbon dioxide and ammonia gas are reacted in a gas reaction tower to generate ammonium carbamate powder containing more than 10% of β crystal form.

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

[0032] The specific structure of the double metal hydroxide and oxide provides a large specific surface area, and the catalytically active sites are highly dispersed. The composite of double metal hydroxide and oxide means that there are two metal centers with different electronegativities, which can efficiently activate NH3 and CO2 molecules, respectively, and promote their contact and reaction on the surface.

[0033] As a further preferred embodiment, the double metal includes 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 preparation method of the catalyst is as follows: taking the hydroxides of the noble metal and the base metal as raw materials, grinding and mixing them, and then placing them in a muffle furnace for calcination at 1000-1200℃ for 1-3h to obtain oxide powder. Then the oxide powder is stirred with pure water at room temperature for 1-2h to obtain a solid powder of oxide and hydroxide. The solid powder is filtered and vacuum dried at 30-50℃ for 10-14h to obtain the catalyst.

[0035] In the catalyst composite, the ratio between the hydroxide and the oxide is not restricted, as long as the catalyst prepared by the method of the application has the performance of the application.

[0036] Specifically, first, the metal hydroxide (such as Al(OH)3, Rh(OH)3) is calcined at high temperature (1000-1200°C), a dehydration reaction occurs, and the corresponding metal oxide is generated. For example: 2Al(OH)3→ Al2O3+ 3H2O↑, 2Rh(OH)3→ Rh2O3+ 3H2O↑. Then the obtained oxide powder is stirred with pure water, and not all oxides will re-hydrate, and its behavior depends on the characteristics of the metal element: for base metals (such as Al): its oxide (Al2O3) has high surface energy and hydration activity. When in contact with water, its surface or part of the phase will chemically react with water to re-generate aluminum oxyhydroxide or layered double hydroxide-like structures. This is a chemical reconstruction process, not a simple mixing. For noble metals (such as Rh): its oxide (Rh2O3) is relatively stable, and has a low tendency to hydrate at room temperature, and most of it remains in the oxide state. The final catalyst "oxide" and "re-hydrated hydroxide" complex is obtained, not a simple return of the initial raw material. Therefore, there may be no noble metal hydroxide in the complex, or there may be a small amount, which does not affect 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, and the molar ratio is 1:(3-3.5).

[0039] Different metal combinations have different electronic structures and catalytic activities. A specific combination (such as Al-Rh) can produce a unique synergistic effect, which can more effectively direct the formation of β crystal structure.

[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 it is unstable and easy to decompose at high temperature. Low temperature conditions (-5 to 25°C) are beneficial to the movement of the reaction equilibrium to the direction of generating products, and can inhibit side reactions and product decomposition, thereby ensuring high yield and high stability. 0-10°C is the best temperature range, which can balance the reaction rate and product stability.

[0042] Example 2 This embodiment provides a high-stability ammonium carbamate powder prepared by the preparation method of Example 1, wherein the proportion of β crystal 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 ammonium carbamate powder has a nitrogen content of not less than 35.5% after being stored at 40-50℃ and 45-50% relative humidity for 12 months.

[0044] The β crystal form has a more compact molecular packing and a more stable hydrogen bond network, making it less likely to absorb moisture (deliquesce) and release ammonia gas.

[0045] The present 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 high-stability ammonium carbamate powder prepared in the present application can be used alone or mixed with other fertilizer components (such as phosphorus, potassium, trace elements, etc., although not explicitly stated but implied) to form a complete fertilizer product.

[0047] The present embodiment also provides the use of the ammonium carbamate powder prepared above, the ammonium carbamate powder described above, or the composition described above in the growth of crops. The present embodiment additionally provides a method for promoting plant growth, comprising applying the ammonium carbamate powder described above or the fertilizer composition described above to the plants.

[0048] Example 3 Test Example 1 Preparation scheme of the catalyst: Take 10g Al(OH)3 and 60g Rh(OH)3 raw materials, mix them by grinding, and then calcine them in a muffle furnace at 1000℃ for 2h to obtain an oxide powder. Then stir the oxide powder with 200g of pure water at room temperature for 2h to obtain a solid powder of oxides and hydroxides, filter the solid powder, and then vacuum dry it at 40℃ for 12h to obtain the catalyst LT-Al / Rh.

[0049] Test Example 2 The preparation scheme of the catalyst is the same as in Test Example 1, and the raw materials are 10g Mn(OH)2 and 48g Pd(OH)2, and the obtained catalyst is LT-Mn / Pd.

[0050] Test Example 3 The preparation scheme of the catalyst is the same as in Test Example 1, and the raw materials are 10g Fe(OH)3 and 75g Pt(OH)4, and the obtained catalyst is LT-Fe / Pt.

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

[0052] Test Example 5 The catalyst preparation scheme was the same as that of Test Example 1, and the raw materials were 10 g of Co(OH)2and 85 g of Pt(OH)4, respectively, and the obtained catalyst was LT-Co / Pt.

[0053] Test Example 6 The catalyst preparation scheme was the same as that of Test Example 1, and the raw materials were 10 g of Ni(OH)2and 50 g of Ru(OH)3, respectively, and the obtained catalyst was LT-Ni / Ru.

[0054] Test Example 7 Preparation of ammonium carbamate powder The catalyst LT-Al / Rh obtained in Test Example 1 was installed in a catalyst filling column in a 100 L gas reaction tower, and the catalyst loading amount was 500 g. Carbon dioxide gas and ammonia gas were introduced, and the flow rates were 1.320 Kg / h and 1.02 Kg / h, respectively, in terms of mass. The temperature in the reaction tower was controlled between 0-10 ℃. The reaction was continuously carried out, and the solid product was continuously discharged, and the catalyst was replaced after 1000 hours of single batch operation. The product obtained in the reaction was analyzed, and the results are shown in Table 1. Figure 3 、 Figure 4 As shown in Table 1, the ratio of α crystal form:β crystal form was approximately 0.9:1.

[0055] Test Example 8 The preparation scheme of ammonium carbamate powder was the same as that of Test Example 7, and the catalyst was LT-Mn / Pd, and the ratio of β crystal form in the obtained product was 10%, respectively.

[0056] Test Example 9 The preparation scheme of ammonium carbamate powder was the same as that of Test Example 7, and the catalyst was LT-Fe / Pt, and the ratio of β crystal form in the obtained product was 13%, respectively.

[0057] Test Example 10 The preparation scheme of ammonium carbamate powder was the same as that of Test Example 7, and the catalyst was LT-Cu / Ru, and the ratio of β crystal form in the obtained product was 37%, respectively.

[0058] Test Example 11 The preparation scheme of ammonium carbamate powder was the same as that of Test Example 7, and the catalyst was LT-Co / Pt, and the ratio of β crystal form in the obtained product was 27%, respectively.

[0059] Test Example 12 The preparation scheme of ammonium carbamate powder was the same as that of Test Example 7, and the catalyst was LT-Ni / Ru, and the ratio of β crystal form in the obtained product was 19%, respectively.

[0060] Comparative Example 1 Prior Art The ammonium carbamate powder was purchased from Macklin, and the product wasFigure 5 As shown, the ratio of the alpha crystal form to the beta crystal form is approximately 30:1.

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

[0062] Comparative Example 3 Single metal catalyst The calcined product of a single metal hydroxide, such as Al(OH)3 or Rh(OH)3, was used as the catalyst, after calcination to obtain Al2O3 or Rh2O3, and other conditions were the same as in Test Example 7.

[0063] LT-Al2O3 was used: no product.

[0064] LT-Rh2O3 was used: no product.

[0065] Comparative Example 4 Non-preferred metal combination catalyst A catalyst LT-Cr / Ag of a non-preferred metal combination according to claim 4, such as Cr-Ag in a molar ratio of 1:1, was used, and other conditions were the same as in Test Example 7. The beta crystal form accounted for 0.5% in the product.

[0066] Comparative Example 5 A catalyst of Al:Rh in a molar ratio of 1:10 was prepared, and other conditions were the same as in Test Example 7. The beta crystal form accounted for about 8% in the product.

[0067] Example 4 The stability of the ammonium carbamate powder obtained in Test Example 7 of the application and the ammonium carbamate powder obtained in Comparative Examples 1, 4 and 5 was respectively investigated under the same temperature and humidity, with nitrogen content as the investigation point. The temperature was controlled at 45-50°C and the relative humidity was controlled at 45-50% in a constant temperature and humidity box. The testing method of nitrogen content referred to the national standards GB / T 2440-2017 and GB 3559-2001.

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

[0069] Example 5 Since ammonium bicarbonate, ammonium sulfate, ammonium nitrate and ammonium chloride are less used in planting, they are not discussed in the present application. The present example is a comparative experiment of two widely used products with similar nitrogen content of ammonium carbamate.

[0070] Plant cultivation comparative experiment: 1. Seed vernalization: filter paper was placed on a petri dish and wetted, Arabidopsis seeds were evenly spread on the filter paper, the petri dish was covered and placed in a refrigerator for low temperature stimulation for vernalization, and after three days, the seeds were planted 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 method comprises the following steps: reacting carbon dioxide and ammonia gas under the action of a catalyst to generate ammonium carbamate powder containing more than 10% of beta crystal form.

2. The production method according to claim 1, characterized by, The ammonium carbamate powder contains 10%-60% of beta crystal form.

3. The preparation method according to claim 1, characterized in that, The raw materials for preparing the ammonium carbamate powder are as follows: 35-56 parts of carbon dioxide, 25-44 parts of ammonia gas, and 0.1-5 parts of catalyst.

4. The production method according to claim 1, characterized by, The catalyst comprises a composite of double-metal hydroxide and oxide.

5. The production method according to claim 4, characterized by, The double metal comprises noble metal and base metal, wherein the base metal is selected from any one of Cu, Ni, Fe, Al, Mn and Co, the noble metal is selected from any one of Pd, Pt and Rh, and the molar ratio of the noble metal to the base metal is 1:(1-8).

6. The production method according to claim 5, wherein The catalyst is prepared by taking hydroxides of the noble metal and the base metal as raw materials, grinding and mixing them, calcining at high temperature to obtain oxide powder, stirring the oxide powder with water at room temperature to obtain solid powder of oxide and hydroxide, filtering and drying the solid powder to obtain the catalyst.

7. The preparation method according to claim 1, characterized in that, The reaction is carried out at a temperature of-5-25℃.

8. The high-stability ammonium carbamate powder prepared by the method of any one of claims 1 to 7, characterized in that, The ammonium carbamate powder contains more than 10% of beta crystal form.

9. The powder according to claim 8, characterized in that, The nitrogen content of the ammonium carbamate powder is not less than 35.5% after being stored at 40-50℃ and relative humidity of 45-50% for 12 months.

10. A fertilizer composition characterized in that, The ammonium carbamate powder prepared according to any one of claims 1-7 or the ammonium carbamate powder according to any one of claims 8-9 is used as nitrogen fertilizer.

11. Use of the ammonium carbamate powder prepared according to any one of claims 1-7, the ammonium carbamate powder according to claim 8 or 9, or the composition according to claim 10 in the growth of crops.

12. A method of promoting plant growth, characterized by, The method comprises applying the ammonium carbamate powder according to any one of claims 8-9 or the fertilizer composition according to claim 10 to plants.

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