A hexamethyldisilazane separation and purification process and system

Abstract

The invention discloses a hexamethyldisilazane separation and purification process and system. The process comprises: adding the solid-liquid mixed reaction material from the hexamethyldisilazane reactor into a cylindrical cone filter, and sending the extruded reaction material to a reaction material intermediate tank; injecting a saturated ammonium chloride solution into the cylindrical cone filter, and extruding the saturated ammonium chloride solution containing a small amount of hexamethyldisiloxane and hexamethyldisilazane; vacuum drying the cylindrical cone filter, and discharging ammonium chloride crystals as a by-product; the reaction material in the reaction material intermediate tank enters an alkali washing tower after enhanced mixing in a static mixer, and the residual ammonium chloride is removed by alkali washing; the liquid-liquid two-phase discharged from the alkali washing tower enters a liquid separation tank, and the water phase is separated at the bottom of the liquid separation tank, and the water phase is divided into two streams, one of which is sent for treatment as waste liquid, and the other is circulated back to the static mixer, and the organic phase is separated at the top of the separation tank, and the organic phase contains hexamethyldisiloxane and hexamethyldisilazane, and is sent to a distillation unit to purify the hexamethyldisilazane product.

Description

Technical Field

[0001] The invention relates to the technical field of chemical engineering, and in particular to a hexamethyldisilazane separation and purification process and system. Background Art

[0002] Hexamethyldisilazane (HMDS), also known as hexamethyldisilazane, hexamethyldisilazane, etc., has a CAS number of 999-97-3. It is a colorless, non-toxic, transparent liquid with a slight amine odor. It is also one of the silyl reagents.

[0003] Hexamethyldisilazane has broad application prospects in chemical analysis, synthesis, electrochemistry, membrane chemistry, hydrophobic materials, inorganic fillers, composite materials, etc.

[0004] The alkali washing process of the present invention, the reaction equation that occurs is as follows:

[0005] NH4Cl+NaOH→NH3·H2O+NaCl

[0006] The mainstream industrial production process of hexamethyldisilazane is to use trimethylchlorosilane as the raw material, react with ammonia in an inert solvent to produce hexamethyldisilazane products. Since the reaction product is ammonium chloride, the ammonium chloride will exist in the reaction material in the form of crystals. In order to prevent the ammonium chloride crystals from sinking into the downstream distillation process, the reaction material needs to be treated to remove the ammonium chloride crystals.

[0007] The existing industrial treatment method is to send the reaction material containing ammonium chloride crystals directly to the alkali washing kettle for intermittent alkali washing, so that all the ammonium chloride reacts with caustic soda to generate sodium chloride and ammonia water. After the traditional solid-liquid separation of the water phase and the oil phase, the oil phase is sent to distillation and the water phase is sent to deammoniation. The removed ammonia is compressed by a compressor and then recycled to the reactor for reuse. This process does not produce ammonium chloride, but can maximize the use of ammonia. The disadvantage is that a large amount of salt-containing wastewater will be generated.

[0008] On the other hand, with the continuous increase in market demand, the scale of hexamethyldisilazane production plants of manufacturers is also getting larger and larger. At present, hexamethyldisilazane plants are all intermittent production in the whole process, with low production efficiency and not conducive to large-scale plants.

[0009] The patent specification with publication number CN 105732688 A discloses an efficient synthesis method of hexamethyldisilazane. As the reaction in the reactor proceeds, ammonium chloride solids accumulate, and a discharge operation is performed. The material is pumped to a plate and frame filter press with a mortar pump. The ammonium chloride solids are retained in the plate and frame filter press, and the clarified liquid flows back to the reactor for reaction, and the cycle is repeated until the reaction end.

[0010] The patent specification with publication number CN 112999999 A discloses a production process of hexamethyldisilazane, including the steps of preparing materials, making ammonium chloride, washing and drying. The washing process is specifically as follows: after the ammonium chloride is completely precipitated, it is filtered, and the obtained ammonium chloride precipitate is washed several times with alkaline solution, each washing liquid is added to the filtrate, and dried with anhydrous sodium sulfate. Summary of the invention

[0011] The invention provides a hexamethyldisilazane separation and purification process, which has simple process, advanced equipment, closed separation of ammonium chloride to increase safety, continuous alkali washing to reduce operation intensity, and can realize the conversion between the intermittent operation of the reaction unit and the continuous operation of the distillation unit, and can meet the needs of continuous production after the hexamethyldisilazane device is scaled up.

[0012] A hexamethyldisilazane separation and purification process comprises the steps of:

[0013] (1) The solid-liquid mixed reaction material from the hexamethyldisilazane reactor is added to the cone filter, the nitrogen pressure of the cone filter is turned on, and the cone filter is subjected to pressure filtering operation, and the pressed reaction material is sent to the reaction material intermediate tank until the material in the cone filter is pressed dry;

[0014] (2) injecting the saturated ammonium chloride solution in the ammonium chloride circulation tank into the cylindrical cone filter, turning on the stirring of the cylindrical cone filter to uniformly re-slurry the ammonium chloride crystals and the saturated ammonium chloride solution in the cylindrical cone filter, and then turning on the nitrogen pressure of the cylindrical cone filter to press the saturated ammonium chloride solution containing a small amount of hexamethyldisiloxane and hexamethyldisilazane into the ammonium chloride circulation tank, thereby completing a full washing;

[0015] (3) introducing steam into the jacket of the cone filter, turning on the stirring, opening the vacuum tube at the top of the cone filter, and performing a vacuum drying process in the cone filter; after the drying is completed, the cone filter discharges the ammonium chloride solid in the filter as a by-product;

[0016] (4) The reaction material in the reaction material intermediate tank is pumped into a static mixer, and the fresh caustic soda solution and the circulating caustic soda solution are mixed with the reaction material from the reaction material intermediate tank before the inlet of the static mixer. After enhanced mixing in the static mixer, the mixture enters an alkali washing tower, and the residual ammonium chloride is removed by alkali washing;

[0017] (5) The liquid-liquid two-phase material discharged from the alkali washing tower enters a separator tank, and the aqueous phase is separated at the bottom of the separator tank. The aqueous phase is divided into two streams, one of which is sent for treatment as waste liquid, and the other is circulated back to the static mixer as a circulating caustic soda solution. The organic phase is separated at the top of the separator tank. The organic phase contains hexamethyldisiloxane and hexamethyldisilazane and is sent to the distillation unit to purify the hexamethyldisilazane product.

[0018] In one embodiment, in step (1), the mass fraction of solid ammonium chloride crystals in the solid-liquid mixed reaction material from the hexamethyldisilazane reactor is 5% to 40%, the mass fraction of trimethylchlorosilane is 0.05% to 0.5%, the mass fraction of hexamethyldisiloxane is 30% to 60%, and the mass fraction of hexamethyldisilazane is 10% to 25%.

[0019] The hexamethyldisilazane reactor is a batch production reactor.

[0020] Considering that the production capacity of the hexamethyldisilazane reactor may not be completely matched with the production capacity of the downstream cylindrical cone filter, an intermediate tank needs to be set between the two for buffering. Preferably, in step (1), the solid-liquid mixed reaction material from the hexamethyldisilazane reactor is first added to the cylindrical cone intermediate tank, and the agitator of the cylindrical cone intermediate tank is kept turned on after the feeding to prevent the ammonium chloride crystals from being deposited in the cylindrical cone intermediate tank, and the bottom of the cylindrical cone intermediate tank is discharged, and the solid-liquid mixed reaction material is added to the cylindrical cone filter.

[0021] Preferably, the volume of the cylindrical-conical intermediate tank is 2 to 4 times the volume of a single hexamethyldisilazane reactor.

[0022] The cylindrical cone filter used in the present invention is a shaping device which can be purchased on the market and integrates filtering (filter pressing, vacuum filtration), washing and drying functions.

[0023] Preferably, taking into account the economy of the shell pressure bearing capacity of the cone filter and the filtration speed, in step (1), the pressure of the pressurized nitrogen is 0.2-0.6 MPaG.

[0024] The ammonium chloride crystals squeezed dry in step (1) also contain inflammable and explosive media such as hexamethyldisiloxane and hexamethyldisilazane, which have the risk of explosion when exposed to air. Therefore, they cannot be directly squeezed out of the cylindrical cone filter and must be washed to remove the above-mentioned organic matter before they can be discharged.

[0025] The washing process of step (2) can be repeated 1 to 3 times.

[0026] In order to separate the organic phase brought in during the washing process, preferably, in step (2), a partition is provided in the ammonium chloride circulation tank, one side of the partition is the aqueous phase of the saturated ammonium chloride solution, and the other side is the organic phase. The organic phase in the aqueous phase can overflow from the aqueous phase side to the organic phase side through the top of the partition. The outlet for the saturated ammonium chloride solution for washing is provided at the bottom of the aqueous phase side, and the material on the organic phase side is regularly discharged into the reaction material intermediate tank.

[0027] Preferably, taking into account the cost of the vacuum pump and the drying speed and effect, in step (3), the operating pressure of the vacuum drying process is 0.2 to 30 kPaA, and the operating temperature is 90 to 140°C.

[0028] The ammonium chloride crystal byproduct of step (3) can be packaged and sold.

[0029] The filtering, washing and drying processes of the cone filter in steps (1) to (3) can be intermittent operations.

[0030] In step (4), a static mixer is used in combination with an alkali washing tower. The static mixer can be arranged on the inlet pipe of the alkali washing tower to enhance the mixing of the alkali liquid phase and the organic phase. The reaction is mainly completed in the alkali washing tower.

[0031] The alkali washing, liquid separation and distillation processes in step (4) and step (5) can be continuous operations.

[0032] The aqueous phase in step (5) contains caustic soda, sodium chloride, ammonia water and the like.

[0033] The organic phase of step (5) can be sent to the distillation unit to purify the hexamethyldisilazane product after being buffered in the organic phase intermediate tank. The water phase can be further separated from the bottom of the organic phase intermediate tank and sent for treatment as waste liquid.

[0034] Number of cone filters in steps (1) to (3) N T Number of reactors with hexamethyldisilazane N R 、The volume V of the hexamethyldisilazane reactor R , reaction time t R , preparation time t P , Volume V of the cone filter T , Filtering time t F , washing time t S , Drying time t D The following formula can be used to calculate: N T =K·N R ·(V R / V T )·(t F +t S +t D ) / (t R +t P ), where K is the design margin factor, which ranges from 1.2 to 2.

[0035] The filtering, washing and drying operation times of different cylindrical-cone filters are staggered.

[0036] Preferably, in step (4):

[0037] The fresh caustic soda solution is pre-prepared, and its concentration is between 5wt% and 25wt%, and the mass ratio of the reaction material at the outlet of the static mixer to the added fresh caustic soda solution is 0.5 to 20:1;

[0038] The mass ratio of the circulating caustic soda solution to the fresh caustic soda solution is 0 to 20:1.

[0039] In step (4), the alkali washing tower is the place where caustic soda reacts with residual ammonium chloride. The alkali washing tower can be in the form of a packed tower or a plate tower. The packing height can be 1 to 5 m or the number of plates can be 3 to 10. The empty tower liquid velocity can be 0.001 to 0.05 m / s. The tower can be provided with one inlet and one outlet, with upper inlet and lower outlet or lower inlet and upper outlet. The outer wall of the tower may have an outer jacket for cooling or may not have an outer jacket.

[0040] In step (5), the chlorine content in the organic phase separated by the separator is less than 0.1 wt%. If the chlorine (ammonium chloride) content in the organic phase exceeds 0.1 wt%, it will cause serious scaling in the distillation unit.

[0041] The present invention also provides a hexamethyldisilazane separation and purification system, comprising an ammonium chloride circulation tank and a hexamethyldisilazane reaction kettle, a cylindrical cone filter, a reaction material intermediate tank, a static mixer, an alkali washing tower, a liquid separation tank and a distillation unit connected in sequence;

[0042] A partition is arranged in the ammonium chloride circulation tank, one side of the partition is the aqueous phase of the saturated ammonium chloride solution, and the other side is the organic phase. The organic phase in the aqueous phase can overflow from the aqueous phase side to the organic phase side through the top of the partition. The aqueous phase side is connected to the cylindrical cone filter, and the organic phase side is connected to the reaction material intermediate tank.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The invention has simple process and advanced equipment, and can realize the conversion between the intermittent operation of the reaction unit and the continuous operation of the distillation unit, and can meet the demand for continuous production after the large-scale hexamethyldisilazane device is scaled up.

[0045] In order to avoid a large amount of salt-containing wastewater from the alkali washing process, the present invention sets a cone filter before alkali washing to separate most of the ammonium chloride from the reaction material, and the separated ammonium chloride is dried in the cone and sold as a by-product. The cone filter is selected because it can be operated in a closed manner throughout the process. Traditional solid-liquid separation equipment such as centrifuges and filter element filters involve open operation in the solid discharge process, and ammonium chloride crystals also carry flammable and explosive media such as hexamethyldisiloxane and hexamethyldisilazane, which are not suitable for open operation. The present invention solves the integrated solution of solid-liquid separation, washing, and drying, and avoids the escaping of flammable and explosive medium vapors into the working environment, thereby causing fire hazards.

[0046] The reaction material from which the ammonium chloride crystals are separated is further alkali washed to completely remove the ammonium chloride. Although the reaction unit for the production of hexamethyldisilazane has not yet achieved continuous operation, the continuous operation of the distillation unit is achievable as the capacity of the device is expanded. The process involved in the present invention is a key step between the reaction and the distillation, wherein the alkali washing unit is a continuous operation, and the present invention achieves an important transition from the intermittent operation of the reaction unit to the continuous operation of the distillation unit. Therefore, the present invention has a simple process, advanced equipment, closed separation of ammonium chloride to increase safety, continuous alkali washing to reduce operating intensity, and can achieve the conversion between the intermittent operation of the reaction unit and the continuous operation of the distillation unit, which is adapted to the trend of large-scale hexamethyldisilazane devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of the hexamethyldisilazane separation and purification process and system of the embodiment;

[0048] In the figure: 1- cylindrical cone intermediate tank; 2, 3- cylindrical cone filters; 4- ammonium chloride circulation tank; 5- ammonium chloride circulation pump; 6- reaction material intermediate tank; 7- reaction material pump; 8- static mixer; 9- alkali washing tower; 10- separation tank; 11- organic phase intermediate tank; 12- alkali solution circulation pump; 13- organic phase delivery pump. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0050] like Figure 1 As shown, the hexamethyldisilazane separation and purification system of the present embodiment includes a hexamethyldisilazane reactor (not shown), a cylindrical cone intermediate tank 1, a plurality of cylindrical cone filters 2, 3, an ammonium chloride circulation tank 4, an ammonium chloride circulation pump 5, a reaction material intermediate tank 6, a reaction material pump 7, a static mixer 8, an alkali washing tower 9, a liquid separator 10, an organic phase intermediate tank 11, an alkali solution circulation pump 12 and an organic phase delivery pump 13. A partition is arranged in the ammonium chloride circulation tank 4, one side of the partition is the aqueous phase of the saturated ammonium chloride solution, and the other side is the organic phase. The organic phase in the aqueous phase can overflow from the aqueous phase side to the organic phase side through the top of the partition, the aqueous phase side is connected to the cylindrical cone filters 2, 3, and the organic phase side is connected to the reaction material intermediate tank 6.

[0051] Use Figure 1 The above-mentioned hexamethyldisilazane separation and purification system shown above performs a hexamethyldisilazane separation and purification process with a production capacity of 5,000 tons per year, and comprises the following steps:

[0052] 1) The upstream hexamethyldisilazane reactor is intermittently produced. The solid-liquid mixed reaction material from the reactor is added to the cylindrical cone intermediate tank 1 for buffering. In order to prevent the ammonium chloride crystals from depositing in the cylindrical cone intermediate tank 1, the agitator of the cylindrical cone intermediate tank 1 needs to be kept turned on after the feeding. Reactor volume V R =5m 3 , total number of units is N R =13 units, single unit response time t R = 6 hours, preparation time t p = 1.5 hours; cone intermediate tank 1 volume 12m 3 , number of units: 1, operating temperature: 50℃, operating pressure: normal pressure.

[0053] 2) Add the reaction material from the bottom of the cone intermediate tank 1 to the cone filters 2 and 3 until the cone filters 2 and 3 are full, close the feed valves of the cone filters 2 and 3, open the liquid phase outlet valves of the cone filters 2 and 3, and then open the nitrogen pressure of the cone filters 2 and 3 to perform pressure filtering on the cone filters 2 and 3. The pressed reaction material is sent to the reaction material intermediate tank 6 until the material in the machine is pressed dry. Volume V of cone filters 2 and 3 T =5m 3 , cone filter 2, 3 units N T =11 units; reaction material intermediate tank 6, volume 12m 3 ; Nitrogen pressure for pressing material: 0.3MPaG, filtration time: t F = 1 hour. The design margin factor K is 1.5.

[0054] 3) The saturated ammonium chloride solution in the ammonium chloride circulation tank 4 is injected into the cylindrical cone filter 2 and 3 through the ammonium chloride circulation pump 5, and then the stirring of the cylindrical cone filter 2 and 3 is turned on to make the ammonium chloride crystals in the machine and the saturated ammonium chloride solution uniformly re-slurried, and then the pressing nitrogen of the cylindrical cone filter 2 and 3 is turned on to press the saturated ammonium chloride solution containing a small amount of hexamethyldisiloxane and hexamethyldisilazane to the water phase side of the ammonium chloride circulation tank 4 to complete a full washing. Repeat the above washing process twice. The volume of the ammonium chloride circulation tank 4 is 20m 3 , washing time t s =1.5 hours.

[0055] 4) Steam is introduced into the jackets of the cone filters 2 and 3, stirring is started, the vacuum pipes at the top of the cone filters 2 and 3 are opened, and vacuum drying is carried out in the machine. The steam pressure is 0.4MPaG saturated, the drying operating temperature is controlled at 110℃, the vacuum drying operating pressure is 5kPaA, and the drying time is t D =2 hours.

[0056] 5) After drying, the ammonium chloride crystals in the machine are discharged from the bottom by using the discharge function of the cone filter 2 and 3 and packaged and sold as a by-product.

[0057] 6) The material in the reaction material intermediate tank 6 is pumped into the static mixer 8 through the reaction material pump 7, and the fresh caustic soda solution and the circulating caustic soda solution are mixed with the reaction material before the entrance of the static mixer 8. After the static mixer 8 strengthens the mixing, the mixture enters the bottom of the alkali washing tower 9. The purpose of alkali washing is to remove the residual ammonium chloride. The continuous liquid inflow of the alkali washing tower 9 is 5100kg / h, the liquid enters from the bottom and exits from the top, the tower diameter is 700mm, the empty tower liquid velocity is 0.003m / s, the filler is a random PP ball ring, the filler is divided into 2 sections, each section is 2m high, the tower is not equipped with a jacket, the concentration of the fresh caustic soda solution is 15wt%, and the mass ratio of the reaction material to the fresh caustic soda solution is 0.88:1.

[0058] 7) The liquid-liquid two-phase of the top discharge of the alkali washing tower 9 enters the separator 10, and the aqueous phase is separated from the bottom. The aqueous phase contains caustic soda, sodium chloride, ammonia and other components. The aqueous phase does not circulate back to the alkali washing tower, and the alkali liquid circulation pump 12 does not work. The aqueous phase is sent to the wastewater treatment station for treatment as waste liquid. The organic phase is separated from the top of the separator 10. The organic phase contains hexamethyldisiloxane and hexamethyldisilazane, which are buffered by the organic phase intermediate tank 11 and sent to the downstream distillation unit to purify the hexamethyldisilazane product under the action of the organic phase delivery pump 13. The chlorine content of the organic phase outlet of the separator 10 is less than 0.02wt%. The bottom of the organic phase intermediate tank 11 can further separate the aqueous phase and send it for treatment as waste liquid.

[0059] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A process for separation and purification of hexamethyldisilazane, characterized in that: Includes steps: (1) The solid-liquid mixed reaction material from the hexamethyldisilazane reactor is added to the cone filter, the nitrogen pressure of the cone filter is turned on, and the cone filter is subjected to pressure filtering operation, and the pressed reaction material is sent to the reaction material intermediate tank until the material in the cone filter is pressed dry; (2) injecting the saturated ammonium chloride solution in the ammonium chloride circulation tank into the cylindrical cone filter, turning on the stirring of the cylindrical cone filter to uniformly re-slurry the ammonium chloride crystals and the saturated ammonium chloride solution in the cylindrical cone filter, and then turning on the nitrogen pressure of the cylindrical cone filter to press the saturated ammonium chloride solution containing a small amount of hexamethyldisiloxane and hexamethyldisilazane into the ammonium chloride circulation tank, thereby completing a full washing; (3) introducing steam into the jacket of the cone filter, turning on the stirring, opening the vacuum tube at the top of the cone filter, and performing a vacuum drying process in the cone filter; after the drying is completed, the cone filter discharges the ammonium chloride solid in the filter as a by-product; (4) The reaction material in the reaction material intermediate tank is pumped into a static mixer, and the fresh caustic soda solution and the circulating caustic soda solution are mixed with the reaction material from the reaction material intermediate tank before the inlet of the static mixer. After enhanced mixing in the static mixer, the mixture enters an alkali washing tower, and the residual ammonium chloride is removed by alkali washing; (5) The liquid-liquid two-phase material discharged from the alkali washing tower enters a separator tank, and the aqueous phase is separated at the bottom of the separator tank. The aqueous phase is divided into two streams, one of which is sent for treatment as waste liquid, and the other is circulated back to the static mixer as a circulating caustic soda solution. The organic phase is separated at the top of the separator tank. The organic phase contains hexamethyldisiloxane and hexamethyldisilazane and is sent to the distillation unit to purify the hexamethyldisilazane product.

2. The hexamethyldisilazane separation and purification process according to claim 1, characterized in that: In step (1), the solid-liquid mixed reaction material from the hexamethyldisilazane reactor is first added to the cylindrical-conical intermediate tank, and the agitator of the cylindrical-conical intermediate tank is kept turned on after the feeding, and the material is discharged from the bottom of the cylindrical-conical intermediate tank, and the solid-liquid mixed reaction material is added to the cylindrical-conical filter; The volume of the cylindrical-conical intermediate tank is 2 to 4 times the volume of a single hexamethyldisilazane reactor.

3. The hexamethyldisilazane separation and purification process according to claim 1, characterized in that: In step (1), the pressure of the nitrogen gas used for pressing the material is 0.2-0.6 MPaG.

4. The hexamethyldisilazane separation and purification process according to claim 1, characterized in that: In step (2), a partition is arranged in the ammonium chloride circulation tank, one side of the partition is the aqueous phase of the saturated ammonium chloride solution, and the other side is the organic phase. The organic phase in the aqueous phase can overflow from the aqueous phase side to the organic phase side through the top of the partition. The outlet of the saturated ammonium chloride solution for washing is arranged at the bottom of the aqueous phase side, and the material on the organic phase side is regularly discharged into the reaction material intermediate tank.

5. The hexamethyldisilazane separation and purification process according to claim 1, characterized in that: In step (3), the operating pressure of the vacuum drying process is 0.2-30 kPaA, and the operating temperature is 90-140°C.

6. The hexamethyldisilazane separation and purification process according to claim 1, characterized in that: The filtering, washing and drying processes of the cone filter in steps (1) to (3) are intermittent operations; The alkali washing, liquid separation and distillation processes in step (4) and step (5) are continuous operations.

7. The process for separation and purification of hexamethyldisilazane according to claim 1, characterized in that: Number of cone filters in steps (1) to (3) N T Number of reactors with hexamethyldisilazane N R 、The volume V of the hexamethyldisilazane reactor R , reaction time t R , preparation time t P , Volume V of the cone filter T , filtration time t F , washing time t S , Drying time t D The following formula is used to calculate: N T =K·N R ·(V R / V T )·(t F +t S +t D ) / (t R +t P ), where K is the design margin factor, which ranges from 1.2 to 2; The filtering, washing and drying operation times of different cylindrical-cone filters are staggered.

8. The process for separation and purification of hexamethyldisilazane according to claim 1, characterized in that: In step (4): The fresh caustic soda solution is pre-prepared, and its concentration is between 5wt% and 25wt%, and the mass ratio of the reaction material at the outlet of the static mixer to the added fresh caustic soda solution is 0.5 to 20:1; The mass ratio of the circulating caustic soda solution to the fresh caustic soda solution is 0 to 20:

1.

9. The process for separation and purification of hexamethyldisilazane according to claim 1, characterized in that: In step (4), the alkali washing tower is in the form of a packed tower or a plate tower, the packing height is 1 to 5 m or the number of tower plates is 3 to 10, the empty tower liquid velocity is 0.001 to 0.05 m / s, the tower is provided with one inlet and one outlet, and the tower can be inlet from the top and outlet from the bottom or inlet from the bottom and outlet from the top. The outer wall of the tower may have an outer jacket for cooling or may not have an outer jacket.

10. The process for separation and purification of hexamethyldisilazane according to claim 1, characterized in that: A hexamethyldisilazane separation and purification system is used; the hexamethyldisilazane separation and purification system comprises an ammonium chloride circulation tank and a hexamethyldisilazane reaction kettle, a cylindrical cone filter, a reaction material intermediate tank, a static mixer, an alkali washing tower, a liquid separation tank and a distillation unit connected in sequence; A partition is arranged in the ammonium chloride circulation tank, one side of the partition is the aqueous phase of the saturated ammonium chloride solution, and the other side is the organic phase. The organic phase in the aqueous phase can overflow from the aqueous phase side to the organic phase side through the top of the partition. The aqueous phase side is connected to the cylindrical cone filter, and the organic phase side is connected to the reaction material intermediate tank.

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