A high-purity diborane and its production method, industrial equipment, and application

Abstract

The present invention belongs to the field of chemical engineering, and specifically relates to a high-purity diborane and its production method, industrial equipment, and application. It includes the production stage and purification stage of diborane. The production stage of diborane includes: the first BCl3 feeding: keeping the temperature of the reaction kettle at 20-22 °C, and uniformly adding BCl3 into the reaction kettle at a feeding rate of BCl3 controlled at 50-60 g / min, so that sodium borohydride reacts with boron trichloride; the second BCl3 feeding: controlling the temperature of the reaction kettle at 35-45 °C, starting to feed after the temperature reaches, and controlling the feeding rate at 35-45 g / min to react to produce diborane; the purification stage of diborane includes purifying the crude diborane by rectification. The production method of high-purity diborane of the present invention has the advantages of high yield, high purity, safety, and low cost.

Description

Technical Field

[0001] The present invention belongs to the chemical industry field, and particularly relates to a high-purity diborane and its production method, industrial equipment, and applications. Background Art

[0002] Diborane is an important chemical raw material, widely used in fields such as semiconductor manufacturing and organic synthesis. Diborane is a gas with a boiling point of -92.5 °C, highly flammable and toxic, and can be used as a fuel or rocket propellant. Its molecular formula B2H6 is a doping source gas in the semiconductor manufacturing process, that is, a P-type source in the PN junction process, and has extremely strict requirements for product quality. Due to its flammable, explosive, and toxic characteristics, currently, the production methods of diborane mainly include chemical reduction method, thermal decomposition method, etc., but these methods have problems such as low efficiency, high cost, poor safety, and low product purity. Therefore, it is of great significance to develop a diborane production method that can be applied to large-scale industrial production, with high product yield, high purity, safety, and low cost.

[0003] In the semiconductor industry, diborane is often used to introduce boron atoms into silicon wafers to adjust the conduction type (P-type doping). Even trace impurities (such as oxygen, water, metal ions, etc.) will cause the following problems: (1) abnormal electrical properties (2) lattice defects, reducing the chip yield rate (3) chemical vapor deposition, affecting its insulation, thermal conductivity, or mechanical strength. The 99.9999% purity of diborane is a rigid requirement of the semiconductor industry for material properties, process safety, and yield control. Any trace impurity may trigger a domino effect, resulting in huge economic losses. Therefore, from synthesis, purification to packaging, it is necessary to carry out in a strictly oxygen-free and water-free environment. Summary of the Invention

[0004] One of the objectives of the present invention is to provide a production method of high-purity diborane, including the production stage and purification stage of diborane. The production stage of diborane includes:

[0005] First BCl3 feeding: Keep the temperature of the reaction kettle at 20 - 22 °C, and uniformly add BCl3 into the reaction kettle. Control the BCl3 feeding speed at 50 - 60 g / min, so that sodium borohydride reacts with boron trichloride;

[0006] Second BCl3 feeding: Control the temperature of the reaction kettle at 35 - 45 °C. After the temperature reaches, start feeding, and control the feeding speed at 35 - 45 g / min to react to generate diborane;

[0007] The purification stage of diborane includes purifying the crude diborane through rectification.

[0008] The synthesis of diborane is divided into two stages, and the reaction formulas are as follows:

[0009] (1) 7NaBH4 + BCl3 = 4NaB2H7 + 3NaCl;

[0010] (2) 6NaB2H7 + 2BCl3 = 7B2H6 + 6NaCl.

[0011] The production stage includes the following steps:

[0012] (1) Add a solvent and sodium borohydride and stir.

[0013] (2) Evacuate the reaction kettle and displace it with helium.

[0014] (3) First BCl3 feeding: Keep the temperature of the reaction kettle at 20 - 22 °C, open the helium bypass valve, adjust the flow rate to 0.5 L / min, uniformly add BCl3 into the kettle, control the BCl3 feeding speed at 50 - 60 g / min, and finish feeding in about 1 - 1.5 h.

[0015] (4) After the first BCl3 feeding is completed, purge with helium.

[0016] (5) Check before the second BCl3 feeding to ensure that there is a pressure of 0.5 MPa in the freezer. Before the second BCl3 feeding, the freezer should be displaced with helium for more than 3 times. Fill dry ice in the cold trap, place the freezer in the cold trap, add liquid nitrogen to the cold trap to the half - height of the freezer, open the valve between the freezers, open the connection valve between the freezer and the manifold, and evacuate the freezer to atmospheric pressure.

[0017] (6) Second BCl3 feeding: Control the temperature of the reaction kettle at 35 - 45 °C. After the temperature reaches, start feeding, control the feeding speed at 35 - 45 g / min, the mercury gauge pressure difference < 700 mmHg, and finish feeding in about 2 h.

[0018] (7) After the second BCl3 feeding is completed, adjust the helium flow rate and purge.

[0019] (8) Fill the manifold with helium to a pressure of 1.0 MPa and then release it to atmospheric pressure. Repeat this several times. Evacuate the freezer to 700 - 760 mmHg, close the vacuum pump, close the mercury gauge, remove the Dewar flask, heat the freezer to room temperature with circulating water, open the valve of the pre - cooled steel cylinder, and collect diborane.

[0020] (9) Drain the residual liquid, rinse the remaining substances in the reaction kettle with waste solvent until the drained liquid is clear, discharge the solvents in the reaction kettle and the cold trap. After draining the residual liquid, keep the pressure of the reaction kettle at 0.4 MPa, and keep the pressure of the manifold and the freezer at 1.0 MPa.

[0021] Before step (1) of the production stage, leak detection of the production equipment is also included.

[0022] Before step (1) of the production stage, taking material from the BCl3 feeder is also included: First, connect the BCl3 cylinder and the feeder, lower the BCl3 feeder to 0 °C using a water bath, evacuate it to 700 - 750 mmHg with a vacuum pump, fill it with helium to positive pressure, then evacuate it to 700 - 750 mmHg again, repeat multiple times, close the vacuum valve, open the cylinder valve, observe the electronic scale, take the required amount of BCl3, close the cylinder valve, and cut off the BCl3 pipeline.

[0023] In the production stage, 7.5 kg of sodium borohydride is taken, and 100 L of diethylene glycol dimethyl ether is taken; for the first BCl3 feeding, 3.34 kg is fed, and for the second BCl3 feeding, 4.46 kg is fed.

[0024] In step (1) of the production stage, use a stirrer to stir, and the stirring frequency is about 12 Hz.

[0025] Preferably, step (2) of the production stage includes: closing the mercury seal valve, opening the valves between the cold traps, the product inlet valve, the vacuum pump valve, and the mercury meter valve, evacuating to 700 - 750 mmHg, closing the vacuum pump valve and the mercury meter valve, filling with helium at a pressure of 0.2 MPa, opening the exhaust valve, discharging to atmospheric pressure, and closing the exhaust valve; repeat the above operations multiple times.

[0026] Preferably, step (7) of the production stage is specifically: after the second BCl3 feeding is completed, adjust the helium flow rate to 1.5 - 2.5 L / min and purge for 6 - 10 h.

[0027] The rectification includes the following steps:

[0028] (1) Leak detection of the rectification tower and the manifold;

[0029] (2) Replace the rectification tower and the manifold with high-purity helium;

[0030] (3) Refrigeration: Make the temperature of the alcohol in the bottom kettle insulation tank reach -70 °C, then supply liquid nitrogen from the upper kettle to make the temperature of the upper kettle lower than that of the lower kettle, and check whether there is leakage in the rectification tower at low temperature;

[0031] (4) Feeding: Open the valve at the top of the tower for discharging, close the fine adjustment valve and the manifold valve, evacuate the system, then feed diborane from the middle feed port of the tower column, observe the pressure indication in the tower, and control the pressure in the bottom kettle and the top of the tower to be lower than 0.5 MPa by controlling the supply speeds of liquid nitrogen and diborane;

[0032] (5) Total reflux: Control the temperature of the bottom of the column at -75°C to -65°C and the pressure below 0.5 MPa, the temperature of the top of the column at -155°C to -135°C and the pressure below 0.5 MPa, and reflux for 12 hours;

[0033] (6) Removing the head: Converge the product to the sampling valve and evacuate it. Adjust the sampling valve to allow the gas phase in the column to slowly enter the sampling valve at a flow rate controlled at 250 - 350 ml / min. When the pressure in the sampling valve and the sample bottle is close to the pressure inside the column, sample and analyze the contents of methane and methyl chloride. Collect the remaining gas in an aluminum bottle frozen with liquid nitrogen. Close the sampling valve, purge the system with helium, remove the sample bottle, then open the sampling valve to continuously remove the head. When the pressure inside the column is less than 0.1 MPa, a small amount of helium can be filled to continue removing the head, and sample and analyze once every 3 - 5 hours; As the methane content in the column decreases, the temperature at the top of the column gradually rises to -110°C to -90°C. When the analyzed methane content is less than 100 ppm, change the receiving bottle to receive the finished product;

[0034] (7) Receiving the finished product: Control the temperature at the top of the column at -110°C to -90°C and the pressure at 0.15 MPa - 0.2 MPa to receive the finished product. Analyze the contents of methane and methyl chloride every 1.5 - 2.5 hours until the methane content is less than 5 ppm and the methyl chloride content is less than 10 ppm, then change the bottle to receive high-purity diborane.

[0035] After step (7) of the rectification, there is also step (8) collecting the residual liquid: When the distillate gas components exceed the limit value, stop receiving the finished product, change the bottle to collect the residual liquid, stop refrigeration, and stop collecting when the temperature of the bottom of the column reaches -40°C and the pressure is normal pressure.

[0036] Preferably, after step (8) of the rectification, there is also step (9) treating the rectification column: Flush the system with high-purity nitrogen, discharge the waste gas through an alkali solution, and after the system is replaced completely, fill it with high-purity nitrogen at 0.3 MPa for future use.

[0037] Another object of the present invention is to provide an industrial equipment for producing high-purity diborane, including a reaction kettle, a cold trap, a sampling valve, a freezer, and a BCl3 feeder. The freezer includes a first freezer and a second freezer; the reaction kettle has inlets for sodium borohydride and solvent, an inlet for BCl3, and a gas outlet; the reaction kettle is connected to the cold trap and also to a mercury seal device; the cold trap is connected to the sampling valve; the sampling valve is also respectively connected to the freezer, a vacuum pump, a mercury meter, and a wide-mouth Dewar flask.

[0038] Another object of the present invention is to provide high-purity diborane obtained by the aforementioned production method.

[0039] Another object of the present invention is to provide the application of the aforementioned high-purity diborane in semiconductor preparation and organic synthesis.

[0040] Beneficial effects:

[0041] The production method of high-purity diborane applicable to industrial applications according to the present invention is safe, low-cost, and has a high yield, and high-purity diborane can be obtained.

[0042] In the present invention, sodium borohydride and boron trichloride react in stages, and diborane can be synthesized with high efficiency.

[0043] This method uses diethylene glycol dimethyl ether as a solvent. It has a high solubility for sodium borohydride and low solubility and reactivity with boron trichloride, so good results can be obtained.

[0044] The by-product of this method is NaCl, which is insoluble in diethylene glycol dimethyl ether. The used solvent can be reused after removing the insoluble matter by filtration.

[0045] This method does not use fluorine compounds with strong toxicity and difficult-to-treat waste, but adds boron trichloride in two stages and reacts under different conditions. The device is simple and easy to operate, and the produced diborane has a higher purity and a greatly increased yield compared with other methods at home and abroad. Description of the drawings

[0046] Figure 1 It is a schematic diagram of the device for diborane production.

[0047] Among them, 1, reaction kettle; 2, cold trap; 3, manifold; 4, freezer; 4.1, first freezer; 4.2, second freezer; 4.3, third freezer; 4.4, fourth freezer; 5, BCl3 feeder; 6, stirrer; 7, mercury seal device; 8, vacuum pump; 9, mercury meter; 10, wide-mouth Dewar flask. Detailed implementation manners

[0048] Next, the detailed implementation manners of the present invention will be described in detail with reference to the drawings.

[0049] The term "displacement" means replacing the air in the container with helium. The displacement of the reaction kettle or the freezer means replacing the air in the reaction kettle or the freezer with helium.

[0050] The term "decapitation" means removing the non-condensable gas accumulated at the highest point (i.e., the tower head) of the top of the distillation column.

[0051] The method of the present invention uses the boron trichloride reduction method to prepare diborane, and the characteristics are as follows:

[0052] 1) The reaction proceeds in stages. The first stage is an exothermic reaction, and the reaction temperature is 20°C to 22°C; the second stage is an endothermic reaction, and its temperature is 35°C to 45°C. High-purity diborane can be produced with high efficiency.

[0053] 2) This method uses diethylene glycol dimethyl ether as the solvent. It has a high solubility for sodium borohydride and a low solubility and reactivity with boron trichloride, so better results can be obtained.

[0054] 3) The by-product of this method is NaCl, which is insoluble in diethylene glycol dimethyl ether. The used solvent can be reused after removing the insoluble substances by filtration.

[0055] 4) This method does not use fluorine compounds with high toxicity and difficult-to-treat waste. Instead, boron trichloride is added in two steps and the reaction is carried out under different conditions. The device is simple and easy to operate. The diborane produced has a higher purity and a greatly increased yield compared with other domestic and foreign methods. The yield can reach 98%.

[0056] Production principle of diborane:

[0057] The preparation of diborane is divided into two stages, and the reaction equations are as follows:

[0058] (1) 7NaBH4 + BCl3 = 4NaB2H7 + 3NaCl;

[0059] (2) 6NaB2H7 + 2BCl3 = 7B2H6 + 6NaCl.

[0060] The first stage listed in reaction equation (1) is an exothermic reaction and the second stage listed in reaction equation (2) is an endothermic reaction. The synthesis reaction is divided into two stages.

[0061] Dissolve sodium borohydride in diethylene glycol dimethyl ether, carry BCl3 to the solution by helium gas, and carry out the synthesis of diborane. The product is collected in a freezer under liquid nitrogen freezing through three cold traps and a manifold. After the reaction is completed, the diborane is volatilized into a steel cylinder and stored at low temperature.

[0062] The raw material boron trichloride is a colorless gas with a pungent odor at normal temperature and pressure, and its boiling point is about 12.5°C. This characteristic means that at a slightly lower temperature (for example, 0°C), boron trichloride is easily converted from a gaseous state to a liquid state.

[0063] Currently, the domestic and foreign diborane purification methods include adsorption method, distillation method, and the method combining adsorption and distillation.

[0064] 1) The adsorption method uses low-temperature adsorption and temperature-raising desorption to remove most of CH4, CO2, etc. However, due to its boiling point (-88°C) and molecular weight (30), which are very close to those of diborane, the effect of removing C2H6 by the adsorption method is very poor.

[0065] 2) Combine distillation and adsorption to produce high-purity diborane.

[0066] This method involves adsorbing while distilling crude diborane containing low-boiling components such as H2, N2, O2, Ar, CO, CH4, and high-boiling components such as CH3Cl, C2H5Cl, B4H 10 , B5H9, especially impurities such as CO2 and C2H6 that are difficult to separate by distillation and are close to the boiling point of B2H6. An adsorbent that can adsorb and remove these impurities is selected, that is, distillation and adsorption are combined to make the total impurities less than 1×10 -6 , and 99.995% high-purity B2H6 is produced. However, the equipment is complex and the process is long.

[0067] 3) The batch low-temperature pressurized distillation method separates impurities under pressure. First, impurities with boiling points lower than the product are separated, and the temperature is raised to receive the product. Impurities with high boiling points remain at the bottom of the tower. This method has a simple process, a short process flow, and is easy to control. This method is adopted in this process to produce 99.9999% high-purity diborane.

[0068] Example 1

[0069] (I) Synthesis of Diborane

[0070] Raw materials: Sodium borohydride, boron trichloride.

[0071] Auxiliary materials: Solvent diethylene glycol dimethyl ether, liquid nitrogen, dry ice, helium, ice cubes.

[0072] Equipment: Helium cylinder, BCl3 feeder, reaction kettle, dry ice cold trap, wide-mouth Dewar flask, manifold, spare cylinder.

[0073] As Figure 1 shown, the production equipment includes a reaction kettle 1, a cold trap 2, a manifold 3, a freezer 4, and a BCl3 feeder 5. The freezer 4 has a first freezer 4.1, a second freezer 4.2, a third freezer 4.3, and a fourth freezer 4.4. A stirrer 6 is provided inside the reaction kettle 1. The reaction kettle 1 is fixed, and the cold trap 2, the manifold 3, the freezer 4, etc. connected by hoses are movable. The reaction kettle 1 has an inlet for sodium borohydride and a solvent, and also has an inlet for BCl3. The reaction kettle 1 is connected to the cold trap 2 and also to a mercury seal device 7. The cold trap 2 is connected to the manifold 3. The manifold 3 is respectively connected to the freezer 4, a vacuum pump 8, a mercury meter 9, and a wide-mouth Dewar flask 10.

[0074] 1. Leak detection of production equipment

[0075] For the first synthesis of each batch, there is no obvious change in the manifold and the freezer under a helium pressure of 5 MPa for 12 h, and there is no obvious change in the reactor under a helium pressure of 0.4 MPa for 12 h, indicating that the leak detection is qualified; for the subsequent synthesis of the same batch, there is no obvious change in the manifold and the freezer under an ammonia pressure of 5 MPa for 5 - 8 h, and there is no obvious change in the reactor under a helium pressure of 0.4 MPa for 5 - 8 h, indicating that the leak detection is qualified. Note that the change in pressure should be observed at the same temperature.

[0076] 2. Preparation before production

[0077] 7.5 kg of sodium borohydride is reserved for use.

[0078] 100 L of diethylene glycol dimethyl ether is taken on-site.

[0079] Feeding of BCl3: First, connect the BCl3 cylinder and the feeder. Lower the BCl3 feeder to 0 °C using a water bath, and evacuate it to 700 - 750 mmHg using a vacuum pump; fill it with helium to positive pressure, then evacuate it to 700 - 750 mmHg again, and repeat this 3 times. Close the vacuum valve. Open the cylinder valve, observe the electronic scale, take 7.8 kg of BCl3, close the cylinder valve, and cut off the BCl3 pipeline.

[0080] 3. Production process

[0081] 3.1 Adding solvent and sodium borohydride

[0082] Add the solvent and sodium borohydride, turn on the stirrer, and the stirring frequency is about 12 Hz (30 - 40 revolutions per minute).

[0083] 3.2 Evacuating and replacing the reactor

[0084] Close the mercury seal valve, open the valves between the cold traps, the product inlet valve, the vacuum pump valve, and the mercury meter valve, evacuate to 700 - 750 mmHg, close the vacuum pump valve and the mercury meter valve, fill it with helium to a pressure of 0.2 MPa, open the exhaust valve, and vent it to atmospheric pressure. Close the exhaust valve. Repeat the above operations 4 times.

[0085] 3.3 First BCl3 feeding

[0086] Heat BCl3 with a water bath, control the temperature at 25 °C, the temperature inside the reactor is 20 - 22 °C, and the water bath of the reactor jacket circulates with a set temperature of 20 °C. Start feeding, open the helium bypass valve, and adjust the flow rate to 0.5 L / min. First open the outlet of the BCl3 feeder, then open the inlet, and uniformly add BCl3 into the reactor. Control the BCl3 feeding speed at about 55 g / min, feed 3.34 kg, and finish feeding at about 1 - 1.5 kg / h. Observe the mercury seal bubble situation.

[0087] 3.4 Helium purging

[0088] After the first BCl3 feeding is completed, close the mercury seal valve, open the valves between the cold traps, the product inlet valve, the vacuum pump valve, and the mercury meter valve, evacuate to 700 - 760 mmHg, close the vacuum pump valve and the mercury meter valve, fill with helium at a pressure of 0.2 MPa, open the vent valve, vent to atmospheric pressure, and then close the vent valve. Repeat the above operations 4 times.

[0089] 3.5 Inspection

[0090] Before the second feeding, make sure there is a pressure of 0.5 MPa in the freezer. Before feeding, the freezer should be purged with helium 4 times. Fill dry ice in the cold trap.

[0091] 3.6 Place the freezer in the cold trap, add liquid nitrogen to the cold trap to reach half of the height of the freezer, open the valves between the freezers, open the connection valve between the freezer and the drain, and evacuate the freezer to atmospheric pressure.

[0092] 3.7 Second BCl3 Feeding

[0093] Before feeding, close the connection valve of the upper and lower manifolds. On the upper row, open the product inlet valve, the mercury meter valve, and the connection valve to the freezer inlet; on the lower row, open the connection valve to the freezer outlet, the connection valve to the bubbler (not shown), the freezer inlet valve, and the freezer outlet valve. Control the temperature of the reaction kettle at 40 °C. After the temperature reaches, start feeding, control the feeding speed at 40 g / min, the mercury meter pressure difference < 700 mmHg, and feed 4.46 kg, which takes about 2 h to complete the feeding. During the production process, often observe the liquid nitrogen level, and it is required to always maintain at half of the height of the freezer.

[0094] 3.8 Purge

[0095] After the feeding is completed, adjust the helium flow rate to 2 L / min and purge for 8 h.

[0096] 3.9 Volatilization and Collection

[0097] Before volatilization, fill the manifold with helium at a pressure of 1.0 MPa, vent to atmospheric pressure, and repeat 10 times. Open the inlet valves of the serially connected freezers 4.1 and 4.2, the connection valves between the freezers, and the drain connection valve. Open the vacuum pump valve and the mercury meter valve, evacuate to 700 - 760 mmHg, close the vacuum pump, close the mercury meter, and remove the Dewar flask. Heat the freezer to room temperature with circulating water, open the valve of the pre-cooled steel cylinder, and collect diborane. Repeat the above operations for the serially connected freezers 4.3 and 4.4.

[0098] 3.10 Drain Residual Liquid and Maintain Pressure

[0099] Open the lower ball valve of the reactor to discharge the residual liquid. Flush the remaining substances in the reactor with 15 L of waste solvent until the discharged liquid is clear. Drain the solvents in the reactor and the cold trap. After draining the residual liquid, maintain a pressure of 0.4 MPa in the reactor, and 1.0 MPa in the manifold and the freezer.

[0100] At this time, the yield of the crude diborane obtained is 98%, and the purity is 96%.

[0101] 3.11 Post-production treatment

[0102] After producing one batch, remove the BCl3 injection pipeline, purge it with nitrogen, and observe the inner wall condition for timely replacement if necessary. Check the plug at the sodium borohydride feed port, check the gasket condition, and replace it if necessary. Evacuate and replace the production system with helium 5 times and maintain a pressure of 0.4 MPa.

[0103] 4. Safety precautions

[0104] (1) Diborane is a flammable, explosive and highly toxic gas that decomposes in the presence of water. Therefore, the system requires high airtightness, and it should be clean and dry. The production should be carried out in a fume hood.

[0105] (2) The -50 °C cold trap of the reactor is used to prevent the volatilization of diethylene glycol dimethyl ether, and the -78 °C glass cold trap is used to remove high-boiling impurities. The feeding rate should be relatively stable. If the feeding is too fast, a large amount of gas will be generated, and the impurity removal effect of the cold trap will be reduced.

[0106] (3) To accelerate the feeding rate of boron trichloride, the cold trap can be placed in warm water at 25 °C - 30 °C to make it slightly boil, but the rate should be controlled and not too fast. The mercury seal connected to the reactor is provided to prevent pipeline blockage and excessive reactor pressure, and it is appropriate that no bubbles come out.

[0107] (4) When adding liquid nitrogen to the liquid nitrogen tank of the freezer, a negative pressure may be formed in the freezer. The exhaust gas valve should be closed in time to prevent backflow.

[0108] (5) The freezing liquid of the cold trap can be prepared with alcohol plus dry ice or liquid nitrogen. Both dry ice and liquid nitrogen are extremely cold substances. Avoid contact with the skin to cause frostbite, and wear protective gloves.

[0109] (6) When volatilizing diborane, it takes a long time to heat up. Water can be poured on the surface of the freezer to accelerate the heating and volatilization, but do not pour water into the internal small holes at the beginning because the ice formed melts relatively slowly.

[0110] (7) When diborane is stored at room temperature, it will partially decompose to form higher boranes and hydrogen. Therefore, it should be stored in a freezer or diluted with nitrogen to reduce decomposition.

[0111] (II) Rectification of diborane

[0112] The purity of diborane produced by the aforementioned method is generally 96%. Diborane produced by the reaction of boron trichloride and sodium borohydride in a solvent contains 1.5% methane, 1.5% chloromethane, and trace amounts of impurities such as CO2, H2, N2, and O2. To meet the requirements of ultra-large scale and extra-large scale integrated circuits, diborane must be purified to remove various impurities and achieve a purity of 99.9999%.

[0113] 1. Principle

[0114] Rectification utilizes the different distributions of different substances in the gas-liquid two-phase. When distilling, the steam generated and the liquid formed during steam condensation interact with each other. The high-boiling components in the gas phase and the low-boiling components in the liquid phase undergo multiple condensations and vaporizations in opposite directions to achieve the separation of the mixture. The boiling points of methane and chloromethane in diborane differ greatly from that of diborane. In rectification, methane and low-boiling impurities such as nitrogen, hydrogen, and oxygen are removed in the overhead cut at the top of the column, and high-boiling impurities such as chloromethane remain in the residue. The middle fraction can obtain high-purity diborane.

[0115] 2. Raw Materials and Equipment

[0116] Table 1: Raw Materials and Equipment

[0117]

[0118] The rectification column is divided into three parts: the reboiler, the column body, and the top of the column. The highest part at the top of the column is called the overhead. There are cooling pipes outside the rectification column and also inside the bottom of the column.

[0119] 3. Operating Procedures

[0120] 3.1 Leak test of the rectification column and the manifold. Connect the feed inlet of the rectification column to the raw material manifold with a stainless steel hose, and connect the discharge outlet to the product manifold through a needle valve with a stainless steel hose. Fill the system with nitrogen at 5.0 MPa, and if the pressure does not drop within 2 hours, the leak test is qualified.

[0121] 3.2 Purge. Clamp the raw material gas cylinder, the sample bottle, and the product receiving bottle on the manifold respectively, and purge the rectification column and the manifold three times with high-purity helium, and fill with helium at 0.5 MPa.

[0122] 3.3 Refrigeration. Add industrial alcohol to the reboiler insulation tank and the overhead. Connect and insulate the cooling pipes of the overhead, the column, and the reboiler insulation tank with a vacuum hose. Connect the liquid nitrogen tank outlet to the cooling pipe of the reboiler insulation tank with a vacuum hose, and let the liquid nitrogen flow through the cooling pipes from the reboiler insulation tank through the column to the overhead. When the alcohol temperature in the reboiler insulation tank reaches -70 °C, switch to supplying liquid nitrogen from the upper reboiler to make the temperature of the upper reboiler lower than that of the lower reboiler, and check for leaks in the rectification column at low temperature. If there are leak points, deal with them in time.

[0123] 3.4 Feeding. Open the valve at the top of the tower for discharging, close the fine-tuning valve and the manifold valve. After evacuating the system, feed diborane through the middle feed port of the tower column. Observe the pressure indication in the tower and control the pressures at the bottom and the top of the tower to be below 0.5 MPa, allowing fluctuations between 0.3 and 0.5 MPa. When the pressure is high, speed up the supply of liquid nitrogen; when the pressure is low, increase the feeding speed of diborane.

[0124] 3.5 Total reflux. Control the temperature at the bottom of the tower at -70 °C ± 5 °C and the pressure below 0.5 MPa, and control the temperature at the top of the tower at -145 ± 10 °C and the pressure below 0.5 MPa. Conduct reflux for 12 hours.

[0125] 3.6 Head removal. Evacuate the product manifold to the fine-tuning valve. Adjust the fine-tuning valve to slowly introduce the gas phase in the tower into the manifold, controlling the flow rate at 300 ml / min. When the pressures in the manifold and the sample bottle are close to the pressure inside the tower, sample and analyze the methane and chloromethane contents. Collect the remaining gas in an aluminum bottle frozen with liquid nitrogen. Close the fine-tuning valve, purge the system with helium, remove the sample bottle, then open the fine-tuning valve to continuously remove the head. When the pressure inside the tower is less than 0.1 MPa, a small amount of helium (pressure 0.3 MPa) can be filled in to continue head removal, and sample and analyze every 4 hours. As the methane content in the tower decreases, the temperature at the top of the tower gradually rises to -100 °C ± 10 °C. When the analyzed methane content is less than 100 ppm, change the receiving bottle to receive the finished product.

[0126] 3.7 Receiving the finished product. Control the temperature at the top of the tower at -100 ± 10 °C and the pressure at 0.15 MPa - 0.2 MPa to receive the finished product. Analyze methane and chloromethane every 2 hours. When the methane content is less than 5 ppm and the chloromethane content is less than 10 ppm, change the bottle to receive high-purity diborane.

[0127] 3.8 Collecting the residual liquid. When the distilled gas components exceed 1500 grams (1200 - 1300 liters), stop receiving the finished product, change the bottle to collect the residual liquid, and stop refrigeration. When the temperature at the bottom of the tower reaches -40 °C and the pressure is at atmospheric pressure, stop collecting.

[0128] 3.9 Treating the distillation column. Purge the system with high-purity nitrogen, discharge the waste gas through an alkaline solution, and after the system is thoroughly replaced, fill it with high-purity nitrogen at 0.3 MPa for future use.

[0129] 4. Safety precautions

[0130] 4.1 Although only 2 kg of diborane is used in cryogenic distillation, considering its flammable, explosive, and highly toxic nature, and it becomes more than 1700 liters after gasification, great care must be taken during operation. The distillation column system must not leak, and the pressure must not be too high. To prevent air from entering the distillation column and causing serious consequences, pressurized distillation is adopted, and the pressure is always maintained higher than atmospheric pressure throughout the distillation process.

[0131] 4.2 Use liquid nitrogen as the cold source for cryogenic distillation, and the liquid nitrogen must be sufficient. When the liquid nitrogen is insufficient, stop distillation and recycle the raw materials.

[0132] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of patent protection of the present invention.

Claims

1. A production method of high-purity diborane, characterized in that, The production method includes a production stage of diborane and a purification stage of diborane. The production stage of diborane includes: The first BCl3 feeding: Keep the temperature of the reaction kettle at 20 - 22 °C, and uniformly add BCl3 into the reaction kettle. Control the BCl3 feeding rate at 50 - 60 g / min to make sodium borohydride react with boron trichloride; The second BCl3 feeding: Control the temperature of the reaction kettle at 35 - 45 °C. After the temperature reaches, start feeding, control the feeding rate at 35 - 45 g / min, and react to generate the diborane; The purification stage of the diborane includes purification by rectifying the crude diborane, wherein the rectification includes the following steps: (1) Leak detection of the rectification tower and the manifold; (2) Replace the rectification tower and the manifold with high-purity helium; (3) Refrigeration: Make the temperature of the alcohol in the bottom kettle insulation tank reach -70 °C, and then supply liquid nitrogen from the upper kettle to make the temperature of the upper kettle lower than that of the lower kettle, and check whether there is leakage in the rectification tower at low temperature; (4) Feeding: Open the valve of the top outlet of the tower, close the fine adjustment valve and the manifold valve. After evacuating the system, feed diborane from the middle feed port of the tower column, observe the pressure indication in the tower, and control the pressure in the bottom kettle and the tower head to be below 0.5 MPa by controlling the supply rates of liquid nitrogen and diborane; (5) Total reflux: Control the temperature of the bottom kettle at -75 °C to -65 °C, the pressure below 0.5 MPa, the temperature of the tower head at -155 °C to -135 °C, the pressure below 0.5 MPa, and reflux for 12 hours; (6) Removing the head: Evacuate the product manifold to the fine adjustment valve, adjust the fine adjustment valve to make the gas phase in the tower slowly enter the manifold, control the flow rate at 250 - 350 ml / min. When the pressure in the manifold and the sample bottle is close to the pressure in the tower, sample and analyze the methane and chloromethane contents. Collect the remaining gas in an aluminum bottle frozen with liquid nitrogen, close the fine adjustment valve, purge the system with helium, then remove the sample bottle, and then open the fine adjustment valve to continuously remove the head. When the pressure in the tower is less than 0.1 MPa, a small amount of helium can be filled in to continue removing the head, and sample and analyze once every 3 - 5 hours; As the methane content in the tower decreases, the temperature of the tower head gradually rises to -110 °C to -90 °C. When the analyzed methane content is less than 100 PPm, replace the receiving bottle to receive the finished product; (7) Receiving the finished product: Control the temperature of the tower head at -110 °C to -90 °C, the pressure at 0.15 MPa - 0.2 MPa to receive the finished product. Analyze the methane and chloromethane contents every 1.5 - 2.5 hours until the methane content is less than 5 PPm and the chloromethane content is less than 10 PPm, and replace the bottle to receive high-purity diborane with a purity of 99.9999%; 2. The production method according to claim 1, characterized in that, The synthesis of the diborane is divided into two stages, and the reaction formulas are as follows: (1) 7NaBH4 + BCl3 = 4NaB2H7 + 3NaCl; (2) 6NaB2H7 + 2BCl3 = 7B2H6 + 6NaCl.

3. The production method according to claim 1, wherein The production stage includes the following steps: (1) Add a solvent and sodium borohydride into the reaction kettle and stir. The solvent is diethylene glycol dimethyl ether; (2) Evacuate the reaction kettle and replace it with helium; (3)First BCl3 feeding: Keep the temperature of the reactor at 20 - 22 °C, open the helium bypass valve, adjust the flow rate to 0.5 L / min, and uniformly add BCl3 into the reactor at a feeding rate of BCl3 controlled at 50 - 60 g / min, and complete the feeding in 1 - 1.5 h. (4)After the first BCl3 feeding is completed, purge with helium. (5)Before the second BCl3 feeding, check to ensure that there is a pressure of 0.5 MPa in the freezer. Before the second BCl3 feeding, the freezer should be purged with helium for more than 3 times. Fill dry ice in the cold trap, place the freezer in the cold trap, add liquid nitrogen to the cold trap to the half position of the freezer, open the valve between the freezers, open the connection valve between the freezer and the manifold, and evacuate the freezer to atmospheric pressure. (6)Second BCl3 feeding: Control the temperature of the reactor at 35 - 45 °C. After the temperature reaches, start feeding, control the feeding rate at 35 - 45 g / min, and the mercury gauge pressure difference < 700 mmHg, and complete the feeding in about 2 h. (7)After the second BCl3 feeding is completed, adjust the helium flow rate and conduct purging. (8)Charge the manifold with helium to a pressure of 1.0 MPa, then discharge to atmospheric pressure, repeat multiple times, evacuate the freezer to 700 - 760 mmHg, close the vacuum pump, close the mercury gauge, remove the Dewar flask, heat the freezer to room temperature with circulating water, open the valve of the pre - frozen cylinder, and collect diborane. (9)Discharge the residual liquid, rinse the residues in the reactor with waste solvent until the discharged liquid is clear, discharge the solvents in the reactor and the cold trap. After discharging the residual liquid, maintain a pressure of 0.4 MPa in the reactor, and maintain a pressure of 1.0 MPa in the manifold and the freezer. Among them, before step (1) of the production stage, it also includes taking materials from the BCl3 feeder: First, connect the BCl3 cylinder and the feeder, lower the BCl3 feeder to 0 °C with a water bath, evacuate to 700 - 750 mmHg with a vacuum pump, fill with helium to positive pressure, then evacuate to 700 - 750 mmHg again, repeat multiple times, close the vacuum valve, open the cylinder valve, observe the electronic scale, take the required amount of BCl3, close the cylinder valve, and cut off the BCl3 pipeline.

4. The production method according to claim 1, characterized in that, Before step (1) of the production stage, it also includes leak detection of production equipment. In step (1) of the production stage, stir with a stirrer. In step (2) of the production stage, it includes: Close the mercury seal valve, open the valve between the cold traps, the product inlet valve, the vacuum pump valve, and the mercury gauge valve, evacuate to 700 - 750 mmHg, close the vacuum pump valve and the mercury gauge valve, fill with helium to a pressure of 0.2 MPa, open the vent valve, discharge to atmospheric pressure, and close the vent valve; Repeat the above operations multiple times. In step (7) of the production stage, specifically: After the second BCl3 feeding is completed, adjust the helium flow rate to 1.5 - 2.5 L / min and purge for 6 - 10 h.

5. The production method according to claim 1, characterized in that, In the production stage, 7.5 kg of sodium borohydride is taken, and 100 L of diethylene glycol dimethyl ether is taken; for the first BCl3 feeding, 3.34 kg is used, and for the second BCl3 feeding, 4.46 kg is used.

6. The production method according to claim 1, characterized in that, After the step (7) of rectification, step (8) of collecting residual liquid is further included: when the distilled gas components exceed the limit value, stop receiving the finished product, change the bottle to collect the residual liquid, stop refrigerating, when the temperature of the bottom of the column reaches -40 °C and the pressure is normal pressure, stop collecting. After the step (8) of rectification, step (9) of treating the rectification column is further included: purging the system with high-purity nitrogen, discharging the waste gas through the alkali solution, and filling 0.3 MPa of high-purity nitrogen into the system after the system is replaced cleanly for future use.

7. The production method according to claim 1, characterized in that, The industrial equipment used in the production method includes a reaction kettle, a cold trap, a manifold, a freezer and a BCl3 feeder, and the freezer includes a first freezer and a second freezer; the reaction kettle has inlets for sodium borohydride and a solvent, an inlet for BCl3 and a gas outlet; the reaction kettle is connected to the cold trap and is also connected to a mercury seal device; the cold trap is connected to the manifold; the manifold is also respectively connected to the freezer, a vacuum pump, a mercury meter and a wide-mouth Dewar flask.

8. High-purity diborane obtained by the production method according to any one of claims 1-6.

9. Application of the high-purity diborane according to claim 8 in semiconductor preparation and organic synthesis.

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