A hydrogen-bonded molecular crystal material for ammonia capture and a preparation method and application thereof

Abstract

The application discloses a hydrogen bond molecular crystal material for ammonia capture and a preparation method and application thereof. The hydrogen bond molecular crystal material for ammonia capture is characterized by the following steps: a compact non-porous soft molecular crystal skeleton is formed by constructing a benzene-1,2,4,5-tetracarboxylic acid (PMA) molecule through carboxylic acid dimers and pi-pi interaction; the material is reversibly expanded when ammonia gas is encountered, a stoichiometric intercalation phase xNH3@ material is formed, and the material is stabilized through charge-assisted -COOH···NH3 and NH3···NH3 hydrogen bonds; and x in the stoichiometric intercalation phase xNH3@ material is equal to 2 or 4 or 6. The hydrogen bond molecular crystal material for ammonia capture is reversibly expanded and phase changed when ammonia gas is encountered, a stoichiometric intercalation phase xNH3@FDU-HOF-4 material (wherein, x=2 or 4 or 6) is formed, the material is stabilized through charge-assisted -COOH···NH3 and NH3···NH3 hydrogen bonds, and the material realizes sponge-like step adsorption and high capacity of ammonia.

Description

Technical Field

[0001] This invention relates to the field of gas separation and storage technology, and in particular to a hydrogen-bonded molecular crystal material for ammonia capture, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is the world's second-largest chemical product by production, with an annual output of 170 million tons. Demand is projected to grow by 22% by 2030. In agriculture, ammonia is a core raw material for fertilizer production. It also serves as a highly promising storage and transportation medium for renewable energy, and is a raw material for the synthesis of various high-value-added chemicals such as nitric acid, polyimide, and nylon, thus supporting the global chemical industry network.

[0003] Currently, over 96% of the world's ammonia is produced via the Haber-Bosch (HB) loop. This process requires operation at temperatures above 400°C and pressures of 150 bar. Furthermore, due to a single-pass conversion rate of less than 20%, a -25°C condensing chiller is needed to separate ammonia and recover unreacted N2 and H2. This refrigeration and condensation cycle is extremely energy-intensive. With the development of the green ammonia industry, developing more efficient and sustainable ammonia separation methods has become an urgent industry need.

[0004] Existing ammonia capture materials generally suffer from insufficient low-pressure adsorption capacity, selective decay under humid conditions, high regeneration energy consumption, or low purity of desorbed ammonia, making it difficult to meet the requirements of large-scale industrial applications. Therefore, developing a capture material that is low-pressure, high-capacity, resistant to water interference, low-energy regeneration, and capable of producing high-purity ammonia is of great significance for reducing energy consumption in ammonia production and promoting the development of green chemical industry. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrogen-bonded molecular crystal material for ammonia capture, its preparation method, and its applications, thereby solving the problems mentioned in the background art. To achieve the above objective, this invention provides the following technical solution: The first aspect of the present invention provides a hydrogen-bonded molecular crystal material for ammonia capture, the material being a dense, non-porous soft molecular crystal framework formed by the interaction of benzene-1,2,4,5-tetracarboxylic acid (PMA) molecules through carboxylic acid dimers and π-π interactions.

[0006] The hydrogen-bonded molecular crystal material for ammonia capture provided by the present invention undergoes reversible lattice expansion upon contact with ammonia gas to form a stoichiometric intercalation phase xNH3@ material, which is stabilized by charge-assisted -COOH···NH3 and NH3···NH3 hydrogen bonds; x = 2, 4 or 6 in the stoichiometric intercalation phase xNH3@ material.

[0007] The hydrogen-bonded molecular crystal material for ammonia capture provided by the present invention exhibits reversible stepwise adsorption of ammonia at 298 K.

[0008] The hydrogen-bonded molecular crystal material for ammonia capture provided by the present invention preferentially adsorbs NH3 in a low partial pressure of 0.001-0.2 bar or in a mixed gas containing N2, H2, CH4, Ar and NH3.

[0009] According to the hydrogen-bonded molecular crystal material for ammonia capture provided by the present invention, the material is completely regenerated at 80-200°C under inert gas or reduced pressure conditions, and ammonia with a purity ≥99.9996% is obtained by desorption.

[0010] The second aspect of the present invention provides a method for preparing a hydrogen-bonded molecular crystal material for ammonia capture as described above, characterized by comprising the following steps: dissolving PMA raw material in water or a water / alcohol solvent, crystallizing, filtering, and recrystallizing with pure water to obtain the target crystal powder.

[0011] According to the preparation method of hydrogen-bonded molecular crystal material for ammonia capture provided by the present invention, when dissolving PMA raw material in water or water / alcohol solvent, an acid regulator is also added.

[0012] According to the method for preparing hydrogen-bonded molecular crystal materials for ammonia capture provided by the present invention, the acid modifier includes HCl.

[0013] According to the method for preparing hydrogen-bonded molecular crystal materials for ammonia capture provided by the present invention, the crystallization step is carried out at room temperature or under heating conditions.

[0014] A third aspect of the present invention provides a method for selectively capturing ammonia from HB synthesis cycle gas or a mixed gas using a hydrogen-bonded molecular crystal material for ammonia capture as described above, wherein the mixed gas contains N2, H2, CH4, Ar and NH3, characterized by comprising the following steps: introducing the HB synthesis cycle gas or mixed gas into a fixed bed packed with the material at an ammonia partial pressure of 0.001-1 bar and a temperature of 273-423 K, stopping the gas intake after the outlet ammonia has penetrated; subsequently desorbing and recovering high-purity ammonia at 80-200°C and regenerating the adsorption bed.

[0015] The beneficial effects of this invention are as follows: When the hydrogen-bonded molecular crystal material for ammonia capture of this invention encounters ammonia gas, it undergoes reversible lattice expansion and phase transition to form a stoichiometric intercalation phase xNH3@FDU-HOF-4 material (where x = 2, 4, or 6). Through charge-assisted -COOH···NH3 hydrogen bonds and NH3···NH3 hydrogen bonds, it achieves sponge-like step adsorption of ammonia with high capacity. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the adaptive adsorption mechanism of the FDU-HOF-4 material of the present invention.

[0017] Figure 2 The image shows a scanning electron microscope (SEM) image of the FDU-HOF-4 material prepared in Example 1.

[0018] Figure 3 The PXRD test results are for the FDU-HOF-4 material prepared in Example 1.

[0019] Figure 4 The results are the ammonia adsorption isotherm test results of the FDU-HOF-4 material prepared in Example 1.

[0020] Figure 5 The results are the ammonia adsorption kinetics test results of the FDU-HOF-4 material prepared in Example 1.

[0021] Figure 6 The PXRD results are for the FDU-HOF-4 material prepared in Example 1 after adsorbing ammonia.

[0022] Figure 7 The results of the ammonia cycle penetration test of the FDU-HOF-4 material prepared in Example 1 are shown.

[0023] Figure 8 The PXRD results of the cyclic experiment of the FDU-HOF-4 material prepared in Example 1 are shown. Detailed Implementation

[0024] This invention aims to provide a flexible hydrogen-bonded molecular crystal material formed by the self-assembly of benzene-1,2,4,5-tetracarboxylic acid, and its application in the high-capacity, reversible, and water-resistant adsorption of ammonia under low-pressure or trace conditions, achieving high-purity desorption. This material exhibits excellent ammonia capture performance, is simple to prepare, low in cost, and can be applied on a large scale. It is particularly suitable for ammonia separation and recovery in Haber-Bosch (HB) cycles and other industrial gas streams, solving problems such as high energy consumption, poor low-pressure adsorption effect, and insufficient moisture resistance in existing ammonia separation technologies, thus achieving efficient ammonia capture and high-purity recovery.

[0025] The hydrogen-bonded molecular crystal material for ammonia capture provided by this invention is constructed from benzene-1,2,4,5-tetracarboxylic acid (PMA, also known as pyromellitic acid) molecules through weak interactions such as carboxylic acid dimers and π–π stacking, forming a densely packed, non-porous soft molecular crystal framework (named "FDU-HOF-4"). When FDU-HOF-4 encounters ammonia gas, it undergoes reversible lattice expansion and phase transition, forming a stoichiometric intercalation phase xNH3@FDU-HOF-4 material (where x = 2, 4, or 6). This phase is stabilized by charge-assisted -COOH···NH3 hydrogen bonds and NH3···NH3 hydrogen bonds, achieving sponge-like stepwise adsorption of ammonia with high capacity. Its adaptive adsorption mechanism can be found in [reference needed]. Figure 1This figure clearly illustrates the two adsorption states of the material under low and high pressure conditions, intuitively demonstrating the structural response characteristics of the flexible molecular crystal to changes in ammonia partial pressure. The FDU-HOF-4 material exhibits preferential adsorption of NH3 under low partial pressure (0.001–0.2 bar) or mixed gas (N2 / H2 / CH4 / Ar / NH3), with a NH3 retention time of approximately 508 min•g in the breakthrough experiment. -1 (dry gas) and approximately 504 min•g -1 (Moisture); NH3 with a purity of ≥99.9996–99.9998% can be recovered by thermal desorption at 120°C.

[0026] The hydrogen-bonded molecular crystal material for ammonia capture provided by this invention has the following performance characteristics: The FDU-HOF-4 material exhibits an ammonia adsorption capacity ≥15.0 mmol•g at 298 K and 10 mbar pressure. -1 ≥20.0 mmol•g at 0.2 bar -1 ≥25.0 mmol•g at 1 bar (normal pressure) -1 It is far superior to existing conventional materials, and can efficiently capture trace amounts or low partial pressure ammonia; and it still maintains step adsorption characteristics and reversibility in the temperature range of 313–343 K.

[0027] The FDU-HOF-4 material maintains high selectivity and adsorption capacity in a water-containing atmosphere with a relative humidity ≥5%, and the ammonia breakthrough retention time is ≥500 min•g. -1 It is suitable for complex industrial water-containing airflow scenarios; the adsorption half-capacity time is no more than 15 minutes under low partial pressure (about 10 mbar), the adsorption rate is fast, and the selectivity and capacity are basically not reduced under humid conditions.

[0028] FDU-HOF-4 material can be fully regenerated under inert gas or reduced pressure conditions at 80–200°C (preferably about 120°C), with energy consumption significantly lower than traditional condensation processes; the ammonia obtained by desorption has a purity of 99.9996%-99.9998% and can be directly recycled.

[0029] The FDU-HOF-4 material maintains a stable crystal form after multiple adsorption / desorption cycles, exhibits no capacity loss after being stored in air for one year, and has a long service life.

[0030] The preparation method of the hydrogen-bonded molecular crystal material for ammonia capture provided by this invention is as follows: Using benzene-1,2,4,5-tetracarboxylic acid (PMA) as a raw material, PMA is dissolved in deionized water or a water / alcohol mixture. A small amount of acid regulator (such as HCl) can be added to adjust the acidity of the system. Crystallization is carried out at room temperature or under slight heating. After filtration and collection of crystals, they are purified by recrystallization with pure water. The purified crystals are then ground and sieved using a ball mill, retaining powder with a size of 25-30 μm, thus obtaining the target hydrogen-bonded molecular crystal material. This preparation method uses an aqueous reaction system, the raw materials are inexpensive and readily available, the process is simple and mild, no complex equipment is required, and large-scale production is possible.

[0031] The ammonia capture application method of the hydrogen-bonded molecular crystal material for ammonia capture provided by this invention is as follows: The method for selectively capturing ammonia from HB synthesis cycle gas or a mixture containing N2 / H2 / CH4 / Ar / NH3 includes the following steps: The gas to be treated is introduced into a fixed bed filled with the hydrogen-bonded molecular crystal material of this invention, under conditions of an ammonia partial pressure of 0.001–1 bar and a temperature of 273–423 K; after ammonia penetration through the fixed bed outlet, the gas inlet is stopped; the adsorption bed is heated to 80–200°C (preferably about 120°C); desorption is performed by purging with an inert gas or by depressurization to recover high-purity ammonia and regenerate the adsorption bed, which can then be recycled.

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0033] Example 1: Preparation of hydrogen-bonded molecular crystal materials

[0034] A certain amount of phenyl-1,2,4,5-tetracarboxylic acid (PMA) was added to deionized water and stirred to disperse. A small amount of concentrated HCl was added dropwise to adjust the pH of the system to ensure complete dissolution of the PMA. The solution was placed in a beaker and allowed to crystallize at room temperature (or with slight heating) for 24 hours, resulting in the precipitation of white crystals. The crude product was collected by filtration. The crude product was recrystallized from pure water to obtain rod-shaped crystals. The refined crystals were ground using a ball mill, and the powder with a diameter of 25-30 μm was collected after sieving. This powder is the FDU-HOF-4 material. See [link to relevant documentation]. Figure 2 .

[0035] Characterization and validation: Detected by PXRD, see [link to relevant documentation]. Figure 3 Product spectrum and simulated spectrum Figure 1 Thermogravimetric analysis showed that the material has good thermal stability up to about 220°C; the N2 isotherms at 77K and CO2 isotherms at 195K confirmed that the material is non-porous.

[0036] Example 2: Ammonia Adsorption Isotherm and Kinetic Test of Materials

[0037] The ammonia adsorption isotherm of the FDU-HOF-4 material prepared in Example 1 was measured at 298K using a gas adsorption instrument.

[0038] See Figure 4 The ammonia adsorption isotherm test results showed that an adsorption gradient appeared at pressures of 10 mbar, 200 mbar, and 1000 mbar, with adsorption capacities reaching approximately 15.1 mmol•g. -1 20.9 mmol•g -1 25.2 mmol•g -1 The isotherms exhibit a distinct stepped shape, corresponding to the stoichiometric intercalation phase formation processes at x=2, 4, and 6.

[0039] See Figure 5 Kinetic test results show that under a low partial pressure of 10 mbar, the half-capacity time for ammonia adsorption by the material is less than 15 min, indicating a fast adsorption rate and the ability to quickly respond to industrial airflow treatment needs.

[0040] Example 3: In-situ structural characterization

[0041] The structural changes of the FDU-HOF-4 material prepared in Example 1 under different ammonia partial pressures were tracked using single-crystal X-ray diffraction and in-situ PXRD techniques.

[0042] See Figure 6 PXRD analysis of the material after ammonia adsorption showed that as the partial pressure of ammonia increased, the material successively formed 2NH3@FDU-HOF-4, 4NH3@FDU-HOF-4, and 6NH3@FDU-HOF-4 insertion phases, corresponding to cell volume expansion and the appearance of new diffraction peaks, confirming the reversibility of lattice expansion.

[0043] Infrared spectroscopy (IR) tests showed that the C=O and O–H vibration peaks of the material decreased after ammonia adsorption, while N–H stretching peaks appeared, verifying the formation of -COOH···NH3 hydrogen bonds; DFT calculations further confirmed that charge-assisted hydrogen bonds are the main driving force for ammonia adsorption.

[0044] Example 4: Dynamic Penetration and Regeneration Performance Test

[0045] A fixed-bed adsorption device was constructed to simulate the HB synthesis cycle gas components (N2 / H2 / CH4 / Ar / NH3) and filled with the FDU-HOF-4 material prepared in Example 1. The ammonia partial pressure was controlled at 0.001–0.01 bar and the temperature at 298 K. The simulated gas was introduced into the fixed bed, and the non-ammonia components permeated rapidly while ammonia was selectively retained.

[0046] See Figure 7 The test results showed that the ammonia breakthrough retention time under dry gas conditions was approximately 508 min•g.-1 Approximately 504 min•g under humid conditions (5% relative humidity) -1 It has excellent moisture resistance.

[0047] After adsorption saturation, the fixed bed is heated to 120°C and purged with inert gas for desorption. The purity of the recovered ammonia is ≥99.9998% under dry gas conditions and ≥99.9996% under humid gas conditions.

[0048] See Figure 8 After ten rounds of adsorption-desorption cycle tests, the adsorption capacity of the material did not decrease significantly, and the PXRD spectrum was basically consistent with the initial state, confirming that the material has good cycle stability.

[0049] Example 5: Industrial Process Integration Application A multi-bed switching adsorption system was constructed, filled with the FDU-HOF-4 material prepared in Example 1, and the adsorption unit and desorption regeneration unit were set to operate alternately.

[0050] Adsorption stage: HB synthesis gas is introduced into the adsorption unit at an ammonia partial pressure of 0.001–0.01 bar and a temperature of 298 K to continuously capture ammonia until breakthrough.

[0051] Desorption stage: After penetration, the adsorption unit is switched to regeneration mode, heated to 120°C and depressurized to collect the desorbed high-purity ammonia, and the material regeneration is completed at the same time.

[0052] This process can achieve efficient capture and high-purity recovery of ammonia under low pressure or trace conditions. It reduces energy consumption compared to traditional condensation processes, and the purity of desorbed ammonia is stable at over 99.9996%. It solves the problems of high energy consumption, poor low-pressure adsorption effect, and insufficient moisture resistance of existing ammonia separation technologies. It is suitable for industrial-scale applications, especially for ammonia separation and recovery in Haber-Bosch (HB) cycles and other industrial gas streams.

[0053] Regarding the embodiments of the present invention, it should also be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to obtain new embodiments.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. The scope of protection of the present invention should be determined by the scope of the claims. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A hydrogen-bonded molecular crystal material for ammonia capture, characterized in that: The material is a dense, non-porous soft molecular crystal framework formed by the interaction of carboxylic acid dimers and π–π of benzene-1,2,4,5-tetracarboxylic acid (PMA) molecules. The material is prepared by the following method: dissolving benzene-1,2,4,5-tetracarboxylic acid (PMA) raw material in water or water / alcohol solvent, crystallizing, filtering, and purifying by recrystallization with pure water. The purified crystal is then ground and sieved using a ball mill to retain powder with a size of 25-30 μm, thus obtaining the target hydrogen-bonded molecular crystal material.

2. The material according to claim 1, wherein the material undergoes reversible lattice expansion upon contact with ammonia to form a stoichiometric intercalation phase xNH3@ material, which is stabilized by charge-assisted -COOH···NH3 and NH3···NH3 hydrogen bonds; wherein x = 2, 4, or 6 in the stoichiometric intercalation phase xNH3@ material.

3. The material according to claim 1, wherein the material exhibits reversible stepwise adsorption of ammonia at 298 K.

4. The material according to claim 1, in a low partial pressure of 0.001–0.2 bar or in a mixed gas, wherein the material preferentially adsorbs NH3, and the mixed gas contains N2, H2, CH4, Ar and NH3.

5. The material according to claim 1, wherein the material is completely regenerated at 80–200°C under inert gas or reduced pressure conditions, and desorption yields ammonia with a purity ≥99.9996%.

6. A method for preparing the material according to any one of claims 1 to 5, characterized in that, Includes the following steps: The PMA raw material is dissolved in water or water / alcohol solvent, crystallized, filtered, and purified by recrystallization with pure water. The purified crystals are then ground and sieved using a ball mill to retain powder with a size of 25-30 μm, thus obtaining the target hydrogen bond molecular crystal material.

7. The preparation method according to claim 6, characterized in that, When dissolving PMA raw materials in water or water / alcohol solvents, an acid regulator is also added.

8. The preparation method according to claim 7, characterized in that, The acid regulator includes HCl.

9. The preparation method according to claim 6, characterized in that, The crystallization step is carried out at room temperature or under heating conditions.

10. A method for selectively capturing ammonia from HB synthesis cycle gas or a mixture of gases using the material as described in any one of claims 1 to 5, wherein the mixture of gases comprises N2, H2, CH4, Ar, and NH3, characterized in that, Includes the following steps: The HB synthesis circulating gas or mixed gas is introduced into a fixed bed filled with the material at an ammonia partial pressure of 0.001–1 bar and a temperature of 273–423 K. The gas intake is stopped after the ammonia has penetrated through the outlet. Then, high-purity ammonia is desorbed and recovered at 80–200°C and the adsorption bed is regenerated.

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