CN101817541B - Method and device for separating magnesium chloride hexammoniate during silane production by the magnesium silicide method - Google Patents

Abstract

The invention discloses a method for separating and recovering hexaammoniated magnesium chloride and liquid ammonia in the process of producing silane by the magnesium silicide method. The process steps are as follows: input the hexaammoniated magnesium chloride liquid ammonia salt mud produced in the process of producing silane by the magnesium silicide method into a filter; The liquid ammonia from the top of the filter is input into the liquid ammonia storage tank for recycling; the salt mud solid from the lower part of the filter is sent to the dryer with a salt mud feeder; the ammonia gas from the upper part of the dryer is sent to the condenser to make ammonia The gas is liquefied in the condenser whose temperature is lower than -33.5°C; the liquid ammonia is input into the liquid ammonia storage tank for recycling. The invention also discloses a device for implementing the method of the invention. The device and method of the present invention have realized large-scale industrial production, and separated and recovered hexaammoniated magnesium chloride and liquid ammonia through a continuous liquid-solid filter, the separation speed is fast, the efficiency is high, and the solid liquid holding capacity is small; Magnesium chloride is continuously dried at high temperature, with high drying efficiency and effective recovery of complexed ammonia.

Description

Separation method and device of magnesium chloride hexaammoniate in the process of producing silane by magnesium silicide method

technical field

The invention belongs to the technical field of polysilicon, and relates to the recovery of by-products of silane production, in particular to a method and a device for separating and recovering magnesium chloride hexaammoniate and liquid ammonia produced in the process of producing silane by a magnesium silicide method.

Background technique

Silane is widely used in the epitaxial deposition of monocrystalline silicon films and the production of polycrystalline silicon films, the manufacture of amorphous silicon solar cells and photosensitive parts of copiers, the replacement of traditional toner cartridges with silicon drums, and the production of brown glass in the glass industry. In addition, silane and ethylene can produce silicon carbide ultrafine powder under laser activation, and silane and ammonia can produce silicon nitride ultrafine powder under laser activation. With the rapid development of the photovoltaic industry, the domestic demand for silane has increased rapidly.

With the continuous maturity of silane preparation technology and continuous increase in output, the recycling of liquid ammonia and the by-product magnesium chloride hexaammoniate suspension in the silane preparation process has gradually attracted the attention of silane research and preparation units. In the existing silane preparation technology of magnesium silicide method, there are few reports on the recovery and utilization of liquid ammonia and magnesium chloride hexaammoniate suspension. Chinese Patent Application Publication CN101659414A (Xi'an Aerospace Huawei Chemical Bioengineering Co., Ltd. Low-temperature production of silane and comprehensive recovery process of by-products. Publication date 2010-03-03.) reports the continuous recovery of liquid ammonia in the reaction material, and at the same time six Magnesium ammonia chloride is simply dried to recover the remaining ammonia, which makes the recovery and utilization of liquid ammonia continuous and recyclable, reduces the consumption of liquid ammonia and reduces environmental pollution. But the recovery of liquefied ammonia in this method has the following deficiencies:

(1) the recovery of liquefied ammonia in liquid ammonia and magnesium chloride hexaammonia suspension is realized by the method for settling, and settling time is long, and production scale is limited;

(2) The solid content of the hexaammoniated magnesium chloride liquid ammonia turbid liquid is low (no more than 40%) after settling, and a large amount of liquid ammonia needs to be vaporized and separated in the subsequent drying process, and the energy consumption is huge;

(3) the magnesium chloride hexaammoniate after the sedimentation has only been simply dried, and the complexed ammonia in the magnesium chloride hexaammoniate has not been effectively recycled, and the ammonia consumption is large, and the ammonia therein will continue to play, causing damage to the surrounding environment and Adverse effects on human health.

(4) Large-scale industrialized production cannot be realized.

Contents of the invention

The purpose of the present invention is to provide a method for the recovery and utilization of liquid ammonia and magnesium chloride hexaammoniated suspension produced in the process of producing silane by the current magnesium silicide method, which has the disadvantages of small production scale, large energy consumption, insufficient ammonia recovery, and environmental pollution. The invention discloses a method for separating and recovering magnesium chloride hexaammoniate and liquid ammonia in the process of producing silane by the magnesium silicide method.

Another object of the present invention is to provide a separation and recovery device for magnesium chloride hexaammoniate and liquid ammonia in the process of producing silane by the magnesium silicide method, so as to meet the technological requirements of the method of the present invention.

Fig. 1 has provided the schematic block diagram of method flow and device of the present invention. The basic principle of the method of the present invention is: the hexaammoniated magnesium chloride liquid ammonia suspension (commonly known as salt mud) is sent to a filter for airtight filtration, and the clear liquid is returned to the reaction system for recycling. Hexaammoniated magnesium chloride is deposited on the surface of the filter element to a certain thickness, and the liquid slurry in the filter is exhausted; the filter cake is squeezed with gas through the filter to further recover the liquid ammonia in it, reducing the moisture content of the filter cake, and the gas It can be nitrogen, air or ammonia; then the preheated gas is fed to vaporize and recover the liquid ammonia in the filter cake, and the gas can be nitrogen, air or ammonia; finally, the filter cake is unloaded.

The separation and recovery method of magnesium chloride hexaammoniate and liquefied ammonia in the magnesium silicide method production silane process of the present invention comprises the following steps:

A, the hexaammoniated magnesium chloride liquid ammonia salt mud input filter that produces in the process of producing silane by the magnesium silicide method;

B. The liquid ammonia from the top of the filter is input into the liquid ammonia storage tank for recycling;

C. The salt mud solid from the lower part of the filter is sent to the dryer with a salt mud feeder;

D. The ammonia gas from the upper part of the dryer is sent to the condenser, so that the ammonia gas is liquefied in the condenser at a temperature lower than -33.5°C;

E. The liquid ammonia obtained by liquefaction is input into the liquid ammonia storage tank for recycling.

In the step A, a pump or a valve can be used to control the flow of the magnesium chloride hexaammoniated liquid ammonia salt mud to the filter, and a pump is preferably used.

As a preferred embodiment, in the step A, an intermediate tank for salt mud is set before the salt mud filter, and the salt mud is first sent into the middle tank for storage, and then pumped into the salt mud filter. With this method, the flow of salt mud can be better controlled to ensure stable operation during industrial implementation.

In the above filtration process, when the filter cake reaches a certain thickness, the liquid slurry in the filter is exhausted, and ammonia gas is passed into the filter to squeeze the filter cake, and the liquid ammonia in it is further recovered to reduce the moisture content of the filter cake. amount; and then feed the preheated ammonia gas to vaporize and recover the liquid ammonia in the filter cake, and the liquid holding capacity in the filter cake will further decrease.

In the step E, the liquid ammonia is put into the liquid ammonia storage tank for recycling, and the liquid ammonia can be directly sent into the liquid ammonia storage tank by a pump.

As a preferred embodiment, a liquid ammonia recovery tank is set after the condenser in the step E, and the liquid ammonia is first sent into the recovery tank for storage, and then pumped into the liquid ammonia storage tank. By adopting this method, the reliability of industrialized continuous and stable operation can be significantly improved.

A preferred separation and recovery device for magnesium chloride hexaammoniate and liquefied ammonia in the process of producing silane by the magnesium silicide method, the device includes a salt mud production pump, a salt mud intermediate tank, a filter, a salt mud feeder, a dryer, a condenser, Liquid ammonia storage tank and liquid ammonia recovery tank; among them, the outlet of the salt mud extraction pump is connected to the top inlet of the salt mud middle tank, the lower outlet of the salt mud middle tank is connected to the salt mud filter pump, and the outlet of the salt mud filter pump is connected to the filter pump. The liquid ammonia discharge pipe at the top of the filter is connected with the liquid ammonia storage tank, the salt mud solid outlet at the lower part of the filter is connected with the salt mud feeder, the outlet of the salt mud feeder is connected with the dryer, and the outlet of the dryer is At least one ammonia gas outlet in the upper part is connected to the condenser, the condenser is connected to the liquid ammonia recovery tank, and the liquid ammonia recovery tank is connected to the liquid ammonia storage tank through the liquid ammonia recovery pump.

The filter is the main equipment of the device of the present invention.

The salt mud filter is preferably a hermetic filter with a built-in filter element to ensure that the ammonia gas is sealed in the filter system during the filtration process, so as not to pollute the environment and protect the health of workers.

The filter can be operated under normal pressure, negative pressure or positive pressure; positive pressure is preferred to increase the filtration rate and reduce the moisture content of solids. The operating pressure is 0.2-2.0 MPa, preferably 1.0 MPa.

The filter element can be a filter cloth, a metal sintered tube or a ceramic sintered tube, etc.; it is preferable to cover the filter cloth with a skeleton support, and the filter cloth is selected mainly because the industrial process is convenient to implement, and at the same time, the cost is significantly lower than the metal sintered tube or ceramic sintered tube.

As a preferred solution, the filter can be connected in parallel in multiple stages to realize continuous operation, and the number of stages is at least 2, preferably 3 or 4.

The dryer used in the present invention can be a spiral dryer or an airflow dryer, etc., preferably a spiral dryer, which can be dried more thoroughly, because the spiral dryer can provide a stable heat source, and the drying temperature is selected from 400 to 600 ° C, preferably 450 to 600 ° C. 550°C.

The spiral dryer is an external heating jacket or coil, and the heat source can be steam, heat transfer oil or electric heating. The built-in screw can realize the movement of solid material.

The middle tank for salt mud is preferably equipped with a stirring device inside and/or a circulation device outside to prevent the solids in the salt mud from settling, to make the solids in the salt mud evenly distributed, and to facilitate continuous operation.

The salt mud feeder can be a screw feeder, a rotary feeder or a disc feeder, etc., preferably a screw feeder, because the magnesium chloride hexammoniate is wet and easy to stick to the wall or block, and the screw feeder can well solve the sticky wall. or clogging problems.

The condenser can be tube-and-tube, fin-cooled, shell-and-tube or fin-tube, and tube-and-tube or fin-cooled is preferred in combination with practicality and condensation requirements. The cooling temperature is -33.5 to 60°C, preferably -35°C. ~45°C.

As a preferred embodiment, the outlet of the drier is connected with the magnesium chloride packaging machine to realize the continuous packaging of the magnesium chloride.

The present invention separates and recovers the liquid ammonia and magnesium chloride hexaammoniate in the magnesium chloride hexaammoniate liquid ammonia suspension through a continuous liquid-solid filter, the separation speed is fast, the efficiency is high, and the liquid holding capacity of the solid is small; Continuous high-temperature drying is achieved, and the drying efficiency is high. At the same time, the complexed ammonia in magnesium chloride hexaammoniate is effectively recycled.

Description of drawings

Fig. 1 is a schematic block diagram of the method flow process and device of the present invention;

Fig. 2 is a schematic diagram of a preferred process flow and device of the method of the present invention.

In Figure 2: 1-liquid ammonia storage tank; 2-silane generator; 3-salt mud extraction pump; 4-salt mud middle tank; 5-salt mud filter pump; 6-salt mud filter; 7-salt mud Feeder; 8-screw dryer; 9-magnesium chloride packaging machine; 10-liquid ammonia condenser; 11-liquid ammonia recovery tank; 12-liquid ammonia recovery pump.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

The separation and recovery device of hexaammoniated magnesium chloride and liquid ammonia in the process of producing silane by the magnesium silicide method of the present invention comprises a salt mud extraction pump 3, a salt mud middle tank 4, a salt mud filtration pump 5, a filter 6, and a salt mud feeder 7 , screw dryer 8, condenser 10, liquid ammonia storage tank 1, liquid ammonia recovery tank 11, liquid ammonia recovery pump 12 and magnesium chloride packaging machine 9, the outlet of salt mud extraction pump 3 is connected with the top of salt mud middle tank 4, The salt mud middle tank 4 is equipped with a stirring device, the lower outlet of the salt mud middle tank 4 is connected with the salt mud filter pump 5, and the outlet of the salt mud filter pump 5 is connected with the salt mud filter 6, and the filter 6 is a closed filter with a built-in filter element , the filter element is supported by a skeleton and covered with filter cloth, the liquid ammonia discharge pipe at the top of the filter 6 is connected with the vertical liquid ammonia storage tank 1, the salt mud solid discharge port at the bottom of the filter 6 is connected with the screw feeder 7, and the salt The outlet of the mud feeder 7 is connected to the screw dryer 8, and at least one ammonia gas outlet on the upper part of the dryer 8 is connected to the condenser 10. The packaging machine 9 is connected, the condenser 10 is connected with the liquid ammonia recovery tank 11, the condenser 10 adopts an ethanol jacket lower than -40°C for cooling, and the liquid ammonia recovery tank 11 is connected with the liquid ammonia storage tank 1 through the liquid ammonia recovery pump 12.

As shown in accompanying drawing 2, the magnesium silicide process technology provided by the present invention produces the magnesium chloride hexaammoniated magnesium chloride separation method in the silane process, and it comprises the steps:

The liquid ammonia and hexammoniated magnesium chloride suspension in the continuous silane generator 2 are input into the middle tank 4 of the salt mud through the salt mud extraction pump 3, and the solid content of the salt mud is 20%;

After the suspension in the salt mud middle tank 4 is stirred evenly, it is input into the parallel 3-stage salt mud filter 6 through the salt mud filter pump 5 for filtration, and the filtration pressure is 1.0MPa. When the thickness of the filter cake reaches 10cm, it is drained into the filter The liquid slurry in the filter 6 is passed into ammonia gas to squeeze the filter cake, and the liquid ammonia therein is further recovered to reduce the moisture content of the filter cake. Ammonia gas at 20°C vaporizes and recovers the liquid ammonia in the filter cake, reducing the liquid holdup in the filter cake to 5%;

After the liquid ammonia and hexammoniated magnesium chloride suspension are filtered through the salt mud filter 6, the liquid ammonia is recovered to the liquid ammonia storage tank 1, and the filtered solid enters the salt mud feeder 7;

After filtering, the solids are fed into the screw dryer 8 from the salt mud feeder 7 and dried continuously at 500°C with a residence time of 1 hour. The ammonia gas enters the condenser 10 and is cooled and liquefied by an ethanol jacket lower than -40°C. The dried magnesium chloride enters the magnesium chloride packaging machine 9 and is cooled to 20° C. for packaging;

The ammonia liquefied in the condenser 10 enters the liquid ammonia recovery tank 11 and enters the liquid ammonia storage tank 1 through the liquid ammonia recovery pump 12 for use.

In the method of the invention, the total recovery rate of ammonia after two steps of filtering and drying is greater than 98%.

Claims (9)

1. a method for separating and recovering magnesium chloride hexaammoniate and liquefied ammonia in the production of silane process by a magnesium silicide method, comprising the steps: A, the hexaammoniated magnesium chloride liquid ammonia salt mud input filter that produces in the process of producing silane by the magnesium silicide method; B. The liquid ammonia from the top of the filter is input into the liquid ammonia storage tank for recycling; C. The salt mud solid from the lower part of the filter is sent to the dryer with a salt mud feeder; D. The ammonia gas from the upper part of the dryer is sent to the condenser, so that the ammonia gas is liquefied in the condenser at a temperature lower than -33.5°C; E, the liquid ammonia obtained by liquefaction is input into the liquid ammonia storage tank for recycling; Wherein, in the step A, the hexaammoniated magnesium chloride liquid ammonia salt mud is first passed through the middle tank of salt mud and then input into the filter, and the suspension in the middle tank of salt mud is stirred evenly and then input into the parallel 3-stage salt mud filter through the salt mud filter pump Filter in the filter, the filter pressure is 1.0MPa, when the filter cake thickness reaches 10cm, the liquid slurry in the filter is exhausted, and ammonia gas is passed into the filter to squeeze the filter cake, and the liquid ammonia in it is further recovered to reduce the The moisture content of the filter cake, the solid liquid hold-up is 20%, and the ammonia gas preheated to 20° C. is introduced to vaporize and recover the liquid ammonia in the filter cake, and the liquid hold-up in the filter cake is reduced to 5%. 2. The separation and recovery method according to claim 1, characterized in that, in the step E, the liquid ammonia is first loaded into a liquid ammonia recovery tank and then sent to a liquid ammonia storage tank for recycling. 3. A separation and recovery device for magnesium chloride hexaammoniate and liquefied ammonia in the production of silane by the magnesium silicide method, is characterized in that the device comprises a salt mud extraction pump (3), a salt mud intermediate tank (4), a filter (6 ), salt mud feeder (7), dryer (8), condenser (10), liquid ammonia storage tank (1), liquid ammonia recovery tank (11); wherein, the outlet of salt mud production pump (3) It is connected with the top inlet of the salt mud middle tank (4), the lower outlet of the salt mud middle tank (4) is connected with the salt mud filter pump (5), the outlet of the salt mud filter pump is connected with the filter (6), and the filter (6 ) is connected to the liquid ammonia storage tank (1), the salt mud solid discharge port at the bottom of the filter (6) is connected to the salt mud feeder (7), and the outlet of the salt mud feeder (7) Link to each other with dryer (8), the top of dryer (8) has at least one ammonia gas outlet to link to each other with condenser (10), condenser (10) links to each other with liquid ammonia recovery tank (11), and liquid ammonia recovery tank ( 11) Connect to the liquid ammonia storage tank (1) through the liquid ammonia recovery pump (12). 4. The separation and recovery device according to claim 3, characterized in that, the filter (6) is arranged in parallel with 2 to 4 filters. 5. The separation and recovery device according to claim 3 or 4, characterized in that, said filter (6) is a built-in filter core type airtight filter, and said filter core is a skeleton support outer cover filter cloth, metal sintered tube or Ceramic sintered tube. 6. The separation and recovery device according to claim 5, characterized in that, the dryer (8) is a spiral dryer. 7. The separation and recovery device according to claim 3, characterized in that, the middle tank for salt mud (4) has a stirring device inside and/or a circulation device outside. 8. The separation and recovery device according to claim 3, characterized in that, the salt mud feeder (7) is a screw feeder. 9. The separation and recovery device according to claim 3, characterized in that, the condenser (10) is a tube-and-tube type or a sheet-cooled type.

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