Method for reducing spontaneous combustion of sodium aluminum hydride and sodium aluminum hydride tablet

Abstract

The invention belongs to the field of preparation of sodium aluminum hydride, and particularly relates to a method for reducing spontaneous combustion of sodium aluminum hydride and a sodium aluminum hydride tablet. The method comprises the following steps: pressing powdery sodium aluminum hydride into tablets to obtain the sodium aluminum hydride tablets. The powdery sodium aluminum hydride is pressed into the compact sheet shape, the spontaneous combustion property of the sodium aluminum hydride in the air can be effectively reduced through verification, the spontaneous combustion time of the sodium aluminum hydride in the air is prolonged from several minutes to 1 h or above, and safe storage, transportation and use of the sodium aluminum hydride solid are facilitated; and the reaction activity of the sodium aluminum hydride solid is not influenced due to compression molding by a physical means.

Description

Technical Field

[0001] The invention belongs to the field of preparation of sodium aluminum hydride, and particularly relates to a method for reducing the spontaneous combustion of sodium aluminum hydride and a sodium aluminum hydride tablet. Background Art

[0002] Sodium aluminum hydride (LiAlH4) is a strong reducing agent and is widely used in organic synthesis reactions. At the same time, sodium aluminum hydride is also an excellent solid hydrogen storage medium, which is used for efficient and safe storage and transportation of hydrogen.

[0003] The Chinese invention patent with authorization announcement number CN 116573613 B, which was authorized on September 19, 2023, discloses a method for synthesizing sodium aluminum hydride using a single substance, which is to introduce hydrogen into a mechanical mixture of metallic aluminum, metallic sodium and a solvent in an autoclave for high-temperature and high-pressure reaction, and the obtained sodium aluminum hydride solution or sodium aluminum hydride suspension is filtered to remove large particles, and the solvent is removed from the filtrate to obtain powdered sodium aluminum hydride.

[0004] A Chinese invention patent with an authorization announcement number of CN 101531338 B and an authorization announcement dated December 1, 2010 discloses a method for preparing sodium aluminum hydride, which uses liquid sodium, solid aluminum and hydrogen as reaction raw materials, triethylaluminum and titanium as catalysts, and toluene as solvent, and obtains a sodium aluminum hydride suspension through a high temperature and high pressure reaction, and then obtains a powdered sodium aluminum hydride solid through sedimentation, discharge of the supernatant, and drying.

[0005] The properties of powdered sodium aluminum hydride solid are extremely unstable and will quickly self-ignite after contact with air. At present, sealed bags or sealed barrels filled with nitrogen are often used for the storage and transportation of powdered sodium aluminum hydride. However, due to the easy self-ignition of powdered sodium aluminum hydride, there are great safety risks in the storage and transportation process; in the subsequent use process, the operating window given to operators by powdered sodium aluminum hydride is also very short, and production accidents caused by the self-ignition of sodium aluminum hydride also occur from time to time. Summary of the invention

[0006] The purpose of the present invention is to provide a method for reducing the spontaneous combustion of sodium aluminum hydride, so as to solve the problem that powdered sodium aluminum hydride is easy to spontaneously combust after contacting air.

[0007] The second object of the present invention is to provide sodium aluminum hydride tablets prepared by the above method, so as to solve the problem that the existing powdered sodium aluminum hydride has great safety risks during storage, transportation and use.

[0008] In order to achieve the above first purpose, the technical solution adopted by the present invention is:

[0009] A method for reducing the spontaneous combustion of sodium aluminum hydride comprises the following steps: pressing powdered sodium aluminum hydride into sheets to obtain sodium aluminum hydride tablets.

[0010] The present invention is a pioneering invention. By pressing powdered sodium aluminum hydride into dense flakes, it has been verified that the spontaneous combustion of sodium aluminum hydride in the air can be effectively reduced, and the spontaneous combustion time of sodium aluminum hydride in the air is extended from about 1 minute to more than 1 hour, which is very beneficial to the safe storage, transportation and use of sodium aluminum hydride solid. Moreover, since the sodium aluminum hydride is pressed and formed by physical means, the reaction activity of the sodium aluminum hydride solid will not be affected.

[0011] Preferably, the sodium aluminum hydride tablet has a thickness of 5 to 10 mm and a maximum planar dimension of 10 to 15 mm. Further preferably, the planar shape of the sodium aluminum hydride tablet is circular, elliptical or polygonal.

[0012] Preferably, the pressing pressure is 10-20 MPa. More preferably, the holding time at 10-20 MPa is more than 5 seconds, for example, the holding time is 5 seconds to 10 seconds.

[0013] Preferably, the powdered sodium aluminum hydride is obtained by subjecting a sodium aluminum hydride suspension to solid-liquid separation, washing, and drying.

[0014] Further preferably, the drying includes introducing hot heat transfer oil into the jacket of the drying device and using hot gas for purging and drying, and the temperature of the hot gas and the hot heat transfer oil is 90-95° C. More preferably, after drying, cold heat transfer oil is introduced into the jacket of the drying device and the temperature is lowered to below 40° C. The hot gas and the cold gas can be non-oxygen-containing drying gas, such as nitrogen, argon, etc.

[0015] Preferably, the solid-liquid separation, washing and drying are carried out in the same equipment.

[0016] In order to achieve the above second purpose, the technical solution adopted by the present invention is:

[0017] Sodium aluminum hydride tablets prepared by the above method.

[0018] The stability of the sodium aluminum hydride tablets in the air is significantly improved compared with that of powdered sodium aluminum hydride. The characteristics of the tablets match the chemical properties of sodium aluminum hydride, which can effectively reduce the spontaneous combustion of sodium aluminum hydride powder and improve the safety of sodium aluminum hydride solid during storage, transportation and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the sodium aluminum hydride production system used in the embodiment of the present invention;

[0020] Among them, 1-integrated equipment; 2-powder silo; 3-tablet press; 4-sodium aluminum hydride slurry injection port; 5-solvent injection port; 6-gas injection port; 7-gas discharge port; 8-gas-solid separation port; 9-liquid discharge port; 10-solid material outlet; 11-sodium aluminum hydride slurry injection pipeline; 12-solvent injection pipeline; 13-flushing pipeline; 14-first gas injection pipeline; 15-second gas injection pipeline; 16-gas-solid separation device; 17-solvent recovery pipeline; 18-condenser; 19-solvent collection tank; 20-first backflush pipeline; 21-second backflush pipeline; 22-tail gas outlet pipeline; 23-nitrogen inlet pipeline; 24-solvent outflow pipeline; 25-mother liquor outflow pipeline; 26-drying tail gas pipeline; 27-heat transfer oil feed pipeline; 28-heat transfer oil discharge pipeline. DETAILED DESCRIPTION

[0021] The technical concept of the present invention is to compress powdered sodium aluminum hydride into tablets to prevent the sodium aluminum hydride with a large specific surface area from directly contacting the air, thereby suppressing its easy spontaneous combustion characteristics. Not all easy spontaneous combustion substances can reduce their spontaneous combustion after being compressed into tablets. The powdered sodium aluminum hydride is compressed into tablets to suit its chemical reaction activity, so the purpose of the present invention can be well achieved.

[0022] Furthermore, the sodium aluminum hydride suspension is subjected to solid-liquid separation, washing, and drying in the same equipment, and then directly subjected to feeding, pressing, discharging, and packaging, so that the efficiency and safety of the entire production process of sodium aluminum hydride can be improved. The sodium aluminum hydride tablets are also convenient for subsequent storage and transportation. When the sodium aluminum hydride solid is used in the subsequent process, the safe operation window period of the operator is extended, the safety of use is improved, and production accidents caused by spontaneous combustion of sodium aluminum hydride are reduced or even avoided.

[0023] First, the sodium aluminum hydride production system is described below.

[0024] like Figure 1 As shown, the sodium aluminum hydride production system includes an integrated device 1 for achieving solid-liquid separation, washing and drying, a powder silo 2 and a tablet press 3.

[0025] The integrated equipment 1 is used to achieve solid-liquid separation, washing and drying of sodium aluminum hydride slurry, including a tank body with a sealed inner cavity, wherein the upper end of the tank body is provided with a sodium aluminum hydride slurry injection port 4, a solvent injection port 5, a gas injection port 6 for hot gas or cold gas injection, a gas discharge port 7, and a gas-solid separation port 8, and the lower end of the tank body is provided with a liquid discharge port 9 and a solid material outlet 10. The sodium aluminum hydride slurry injection port 4 is connected to the sodium aluminum hydride slurry injection pipeline 11, which is used to pass the sodium aluminum hydride slurry into the sealed inner cavity of the tank body. The solvent injection port 5 is connected to the solvent injection pipeline 12, which is used to pass the cleaning solvent into the sealed inner cavity of the tank body; a flushing pipeline 13 is also connected between the solvent injection pipeline 12 and the sodium aluminum hydride slurry injection pipeline 11, and the flushing pipeline 13 can flush the sodium aluminum hydride slurry remaining in the sodium aluminum hydride slurry injection pipeline 11 to ensure that the sodium aluminum hydride slurry injection pipeline 11 is clean.

[0026] The gas injection port 6 is connected to a first gas injection pipeline 14, and the first gas injection pipeline 14 is also connected to a second gas injection pipeline 15. One of the first gas injection pipeline 14 and the second gas injection pipeline 15 is used to pass hot gas for drying, and the other is used to pass cold gas for cooling. The gas outlet 7 is used to discharge the gas in the sealed inner cavity and discharge it as tail gas.

[0027] The gas-solid separation port 8 is connected to a gas-solid separation device 16, which includes a filter membrane for separating gas and powdered sodium aluminum hydride. The outlet of the gas-solid separation device 16 is connected to a solvent recovery pipeline 17, on which a condenser 18 and a solvent collection tank 19 are sequentially arranged. During the hot gas drying process, the organic solvent therein will volatilize, and the powdered sodium aluminum hydride will fly around. The gas-solid separation device 16 prevents the powdered sodium aluminum hydride from entering the solvent recovery pipeline 17. After the organic solvent gas enters the solvent recovery pipeline 17, it is condensed by the condenser 18 and flows into the solvent collection tank 19. The gas-solid separation device 16 is also connected to a backflush pipeline, which is used to backflush the filter membrane of the gas-solid separation device 16 with hot gas or cold gas, and blow the powdered sodium aluminum hydride adsorbed on the filter membrane back into the sealed inner cavity of the integrated device 1. The backflush pipeline includes a first backflush pipeline 20 and a second backflush pipeline 21 connected to the first backflush pipeline 20. One of the first backflush pipeline 20 and the second backflush pipeline 21 is used to introduce hot gas, which can be used when the integrated equipment 1 is in the hot gas drying stage; the other is used to introduce cold gas, which can be used when the integrated equipment 1 is in the cold gas cooling stage.

[0028] The upper end of the solvent collection tank 19 is provided with an exhaust gas outlet pipeline 22 and a nitrogen inlet pipeline 23. The exhaust gas outlet pipeline 22 discharges the gas components in the solvent collection tank 19, and the nitrogen inlet pipeline 23 introduces nitrogen into the solvent collection tank 19, so that the solvent collection tank 19 is in a slightly positive pressure state to prevent the outside air from entering. The lower end of the solvent collection tank 19 is connected to a solvent outflow pipeline 24.

[0029] The drain port 9 of the integrated device 1 is connected to a mother liquor outflow pipeline 25, and a drying tail gas pipeline 26 is also connected between the mother liquor outflow pipeline 25 and the solvent recovery pipeline 17. The initial liquid phase separation components of the sodium aluminum hydride slurry and the liquid phase separation components after washing can be discharged as mother liquor through the mother liquor outflow pipeline 25. The impurities contained in the mother liquor are mainly catalysts, which can be directly reused in the synthesis step. The drying tail gas pipeline 26 is used during drying (and cooling), so that hot nitrogen (or cold nitrogen) passes through the filter cake and filter plate, and then flows into the solvent collection tank 19 through the drying tail gas pipeline 26 and the solvent recovery pipeline 17.

[0030] The tank body is also provided with a heat transfer oil feed pipe 27 and a heat transfer oil discharge pipe 28 for feeding heat transfer oil into the tank body jacket. In the hot gas drying stage, hot heat transfer oil is fed through the heat transfer oil feed pipe 27 and the heat transfer oil discharge pipe 28 to assist in drying; in the cooling stage, cold heat transfer oil is fed through the heat transfer oil feed pipe 27 and the heat transfer oil discharge pipe 28 to assist in cooling.

[0031] The solid material outlet 10 of the integrated equipment 1 is connected to the powder silo 2 through a connecting pipeline, and the powdered sodium aluminum hydride after washing and drying enters the powder silo 2 through the connecting pipeline. The powder silo 2 is connected to the tablet press 3, and the powdered sodium aluminum hydride in the powder silo 2 enters the tablet press 3 to be pressed into sodium aluminum hydride tablets, which are then bagged (or barreled) and sealed by a packaging machine, and can be stored or transported as finished products.

[0032] The production process of the above-mentioned sodium aluminum hydride production system is as follows:

[0033] Nitrogen is injected into the integrated device 1 through the gas injection port 6 for gas replacement, and the replaced gas is discharged from the gas discharge port 7. Sodium aluminum hydride slurry enters the integrated device 1 through the sodium aluminum hydride slurry injection pipeline 11 for filtration, and the filtrate flows out through the mother liquid outflow pipeline 25, and then the solvent is injected into the integrated device 1 through the solvent injection pipeline 12 for washing, and the filtrate flows out through the mother liquid outflow pipeline 25; washing can be performed more than twice.

[0034] After washing is completed, hot nitrogen is introduced into the integrated equipment 1 for purging and drying, and the heat transfer oil inlet and outlet pipelines of the jacket are opened at the same time. The airflow generated during the purging and drying process is divided into two paths. One path is used for gas-solid separation at the gas-solid separation port 8. The gas components are condensed by the condenser 18 and enter the solvent collection tank 19. The non-condensable gas in the solvent collection tank 19 is discharged through the tail gas outlet pipeline 22; the other path passes through the filter cake and filter plate from below, and then flows into the solvent collection tank 19 through the drying tail gas pipeline 26 and the solvent recovery pipeline 17. During the purging and drying period, the powdered sodium aluminum hydride will block the filter membrane of the gas-solid separation device 16, causing the gas-solid separation efficiency to decrease. Hot nitrogen is introduced into the backflush pipeline for backflush, and the powdered sodium aluminum hydride is blown back into the integrated equipment 1 to ensure the separation efficiency of the gas-solid separation device 16. After purging and drying, cold nitrogen is introduced into the integrated equipment 1 to cool it down, and at the same time, the jacket is switched to cold heat transfer oil. During the cooling process of the cold nitrogen, the backflush pipeline can also be used to introduce cold nitrogen for backflush, so as to achieve the purpose of cleaning the filter membrane of the gas-solid separation device 16 and improving the gas-solid separation efficiency.

[0035] After the cooling is completed, the powdered sodium aluminum hydride is transported to the feed hopper of the tablet press 3, and then tableted into a dense sheet of about φ10*5mm, and then transported to the packaging machine for bagging (or barreling) and sealing.

[0036] The implementation process of the present invention is described in detail below in conjunction with specific embodiments.

[0037] 1. Specific embodiments of the method for reducing the spontaneous combustion of sodium aluminum hydride and the sodium aluminum hydride tablets of the present invention

[0038] Example 1

[0039] The method for reducing the spontaneous combustion of sodium aluminum hydride in this embodiment adopts the above-mentioned sodium aluminum hydride production system, and is specifically described as follows:

[0040] (1) Under a nitrogen atmosphere, the sodium aluminum hydride suspension is filtered to remove the solvent, and then a solvent is added to stir, mix and wash, and filter; the above solvent addition and washing process is performed twice to fully dissolve and wash the soluble impurities on the surface of the sodium aluminum hydride solid.

[0041] The above sodium aluminum hydride suspension is obtained by high temperature and high pressure reaction with liquid sodium, solid aluminum and hydrogen as reaction raw materials, triethylaluminum as catalyst and toluene as solvent. The solvent used for cleaning is toluene. In other implementation situations, tetrahydrofuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and the like can be used.

[0042] In this step, the filtration and washing of the sodium aluminum hydride suspension are both carried out in an integrated device, thereby reducing the possibility of the sodium aluminum hydride contacting the air.

[0043] (2) Use hot nitrogen to purge and dry the filtered sodium aluminum hydride. At the same time, hot heat transfer oil is introduced into the jacket to control the drying temperature to 90-95°C. After the material is dried, cold nitrogen is introduced, and the jacket is switched to cold heat transfer oil to cool down to 40°C.

[0044] Hot nitrogen drying and subsequent cooling are carried out in an integrated device, which can be used in conjunction with a condenser and a solvent collection tank to recover the organic solvent volatilized during the hot nitrogen drying process. The backflush system can be used to backflush the gas-solid separation device to reduce the adhesion and blockage of powdered sodium aluminum hydride.

[0045] (3) The processed material in step (2) is conveyed to the feed hopper of the tablet press, and then tabletted into a dense sheet of about φ10*5mm to obtain sodium aluminum hydride tablets. Nitrogen protection is carried out during the material transfer and tableting process to prevent the sodium aluminum hydride powder from contacting the air. The tableting pressure is 10MPa and the holding time is 5s. The sodium aluminum hydride tablets obtained in this embodiment are cylindrical, with a height of 5mm, a circular tablet plane shape, and the maximum dimension of the plane is the diameter of the circle, specifically 10mm. In other implementation situations, the tableting pressure can also be 20MPa, and the holding time is 5s.

[0046] Sodium aluminum hydride tablets are packaged in two layers of PE bags (filled with nitrogen) and packaged in aluminum barrels on the outside, thus obtaining a finished product that is convenient for storage and transportation.

[0047] Example 2

[0048] The method for reducing the spontaneous combustion of sodium aluminum hydride in this embodiment is different from that in Example 1 in that the specification of the obtained sodium aluminum hydride tablets is a hexagon with a side length of 5 mm and a thickness of 5 mm.

[0049] In other implementation situations, the planar shape of the sodium aluminum hydride tablets may also be elliptical, rhombic, etc., which also has the same effect of reducing spontaneous combustion as in Example 1.

[0050] Example 3

[0051] The method for reducing the spontaneous combustion of sodium aluminum hydride in this embodiment is different from that in Embodiment 1 in that the tableting pressure is 5 MPa.

[0052] 2. Experimental Examples

[0053] Experimental Example 1 Spontaneous Combustion Test

[0054] This experimental example conducts a spontaneous combustion experiment of different solid forms of sodium aluminum hydride. The experimental process is as follows:

[0055] 1.1 Spontaneous combustion performance of sodium aluminum hydride tablets and powdered sodium aluminum hydride in Example 1

[0056] The same mass (10g) of sodium aluminum hydride tablets and powdered sodium aluminum hydride were exposed to the same air environment with a humidity of 40%, and the spontaneous combustion time of the sodium aluminum hydride tablets and powdered sodium aluminum hydride was observed. The results showed that after being placed for 1 minute, the powdered sodium aluminum hydride released heat and then burned, while the sodium aluminum hydride tablets remained stable after being placed for 1 hour without burning.

[0057] 1.2 Spontaneous combustion performance of sodium aluminum hydride tablets of different shapes in Example 1 and Example 2

[0058] The same mass (10g) of sodium aluminum hydride round tablets and hexagonal tablets were exposed to the same air environment with a humidity of 70%, and the spontaneous combustion time of the two was observed. The results showed that the sodium aluminum hydride tablets of both shapes were still stable after being placed for 1 hour, and no combustion occurred.

[0059] 1.3 Spontaneous combustion performance of sodium aluminum hydride tablets in Example 3 (spontaneous combustion performance of tablets under different compression pressures)

[0060] Tablets of the same mass (10g) with a compression pressure of 10MPa and 5MPa were exposed to the same air environment with a temperature and humidity of 40%, and the spontaneous combustion time of the two was observed. The results showed that the sodium aluminum hydride tablets with a compression pressure of 5MPa spontaneously combusted after being left for another 10 minutes. However, the sodium aluminum hydride tablets with a pressure of 10MPa remained stable after being left for 1 hour, and no combustion occurred. Therefore, the compression pressure is recommended to be in the range of 10 to 20MPa.

[0061] It can be seen from the above spontaneous combustion experimental process that the sodium aluminum hydride tablets prepared by the method of the present invention can ensure that the sodium aluminum hydride solid does not spontaneously combust when placed in the air within 1 hour, which is very beneficial to the storage and transportation of the sodium aluminum hydride solid, and greatly broadens the application scenarios of the sodium aluminum hydride solid.

[0062] Experimental Example 2 Reactivity Experiment

[0063] This experimental example compares the reactivity of sodium aluminum hydride tablets and powdered sodium aluminum hydride as reducing agents.

[0064] Powdered sodium aluminum hydride is prone to material scattering during feeding. If the scattered material overflows from the reaction container, it will not only cause dust pollution, but also may cause spontaneous combustion. Sodium aluminum hydride tablets can be directly put into the reaction solvent (such as ethylene glycol dimethyl ether) during feeding. It is not only easy to break up and disperse, but also because no other substances are added during tableting, and only physical compression molding is used, which does not affect the reaction activity and does not introduce impurities into the reaction system.

Claims

1. A method for reducing the spontaneous combustion of sodium aluminum hydride, characterized in that: The following steps are involved: The powdered sodium aluminum hydride is pressed into sheets to obtain sodium aluminum hydride tablets.

2. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 1, characterized in that: The sodium aluminum hydride tablet has a thickness of 5 to 10 mm and a maximum plane dimension of 10 to 15 mm.

3. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 2, characterized in that: The planar shape of the sodium aluminum hydride tablet is circular, elliptical or polygonal.

4. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 1, characterized in that: The pressing pressure is 10-20 MPa.

5. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 4, characterized in that: The holding time at 10-20MPa is more than 5s.

6. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 1, characterized in that: The powdered sodium aluminum hydride is prepared by subjecting a sodium aluminum hydride suspension to solid-liquid separation, washing and drying.

7. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 6, characterized in that: The drying comprises introducing heat transfer oil into the jacket of the drying equipment and using hot gas for purging and drying, wherein the temperature of the hot gas and the heat transfer oil is 90-95°C.

8. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 7, characterized in that: After drying, cold heat transfer oil is introduced into the jacket of the drying equipment and cold gas is used to cool the temperature to below 40°C.

9. The method for reducing the spontaneous combustion of sodium aluminum hydride as claimed in claim 6, characterized in that: The solid-liquid separation, washing and drying are carried out in the same equipment.

10. A sodium aluminum hydride tablet prepared by the method according to any one of claims 1 to 9.

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