A method for synthesizing aluminum trichloride

Abstract

The application discloses a synthesis method of aluminum trichloride and relates to the technical field of aluminum trichloride synthesis. The process for preparing the aluminum trichloride is as follows: (1) pre-iron removal of bauxite; (2) preparation of mixed salt powder; (3) fluidized bed-salt bath combined chlorination; and (4) three-stage gradient condensation purification. The application adopts a three-stage full closed loop architecture of "pre-iron removal of bauxite, combined chlorination reaction, and gradient condensation purification", replaces a traditional single aluminum ingot method or a coarse aluminum oxide method process, and solves the problems of difficult impurity control and high energy consumption from the root. The obtained aluminum trichloride has the advantages of high purity and low iron content.

Description

Technical Field

[0001] This invention relates to the field of aluminum trichloride synthesis technology, specifically to a method for synthesizing aluminum trichloride. Background Technology

[0002] Aluminum trichloride is a widely used strong Lewis acid inorganic compound. It can be used as a core catalyst in organic synthesis processes such as petroleum cracking, synthetic dyes, pharmaceuticals, and fragrances. It can also be used as an inorganic flocculant for oil and fluoride removal in drinking water and industrial wastewater, showing excellent results in treating low-temperature, low-turbidity water. Furthermore, it can be used as a mold hardener in precision casting and in industries such as textiles, papermaking, and leather processing. The mainstream industrial production processes for aluminum trichloride include the aluminum ingot method, the alumina method, and the aluminum chloride hexahydrate dehydration method.

[0003] Currently, the mainstream aluminum trichloride production processes in China generally suffer from three major drawbacks: the aluminum ingot method has high raw material costs and a large proportion of high-risk manual operations; the alumina method is difficult to stably control iron impurities in the product and has high energy consumption for subsequent purification; and the aluminum chloride hexahydrate dehydration method has serious hydrolysis side reactions, poor thermal stability, and high costs. This invention, with "low iron and high purity, safety and cost reduction, and green and low carbon" as its core objectives, has developed a method for synthesizing aluminum trichloride. The aluminum trichloride synthesized by this method has the advantages of high purity and low iron content. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing aluminum trichloride to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for synthesizing aluminum trichloride, the method comprising: (1) Pre-iron removal from bauxite; (2) Preparation of mixed salt powder; (3) Fluidized bed-salt bath combined chlorination; (4) Three-stage gradient condensation purification.

[0006] Further, the process of pre-removing iron from bauxite in step (1) is as follows: the bauxite is crushed into bauxite powder of 200-300 mesh, and then the bauxite powder is fed into a closed rotary kiln. Low-concentration chlorine gas is introduced at 450℃-650℃ and kept at the temperature for 90-120 minutes to obtain low-iron bauxite.

[0007] Furthermore, the concentration of the low-concentration chlorine gas is 5% to 15% by volume.

[0008] Further, the process for preparing the mixed salt powder in step (2) is as follows: anhydrous aluminum trichloride and anhydrous sodium chloride are vacuum dried at 140~150℃ for 2~3h, the dried anhydrous aluminum trichloride and anhydrous sodium chloride are mixed at a molar ratio of 52:48, and then fed into a closed ball mill protected by argon gas for grinding and mixing for 30~40min to obtain the mixed salt powder.

[0009] Furthermore, the fluidized bed-salt bath composite chlorination in step (3) is divided into a fluidized bed stage and a salt bath stage.

[0010] Furthermore, the fluidized bed stage process is as follows: low-iron bauxite and petroleum coke with a particle size of 100-200 mesh are added into the furnace at a ratio of 100:20-28, chlorine gas is introduced at 920℃-960℃, and the reaction time is 40-55 minutes to obtain crude gas phase product.

[0011] Furthermore, the concentration of chlorine in the fluidized bed stage is 90%~95% by volume.

[0012] Furthermore, the process of the salt bath stage is as follows: the crude gas phase product is introduced into a eutectic salt bath reactor containing mixed salt powder, the amount of mixed salt powder being 3 to 4 times the mass of bauxite powder, and a rare earth catalyst being added at 0.01 to 0.02 times the mass of bauxite powder; chlorine gas is introduced, and the reaction is carried out at 720°C for 30 to 45 minutes to obtain crude aluminum chloride product.

[0013] Furthermore, the concentration of chlorine gas during the salt bath stage is 85% to 90% by volume.

[0014] Furthermore, the rare earth catalyst is a mixture of one or more of cerium chloride and lanthanum chloride.

[0015] Furthermore, the three-stage gradient condensation purification in step (4) is divided into three stages: high-temperature pre-separation, medium-temperature crystallization, and low-temperature deep collection.

[0016] Furthermore, the process of the high-temperature pre-separation stage is as follows: the crude aluminum chloride product is introduced into a jacketed cooler at 320°C and kept at that temperature for 20-30 minutes; the process of the medium-temperature crystallization stage is as follows: the gas phase obtained from the high-temperature pre-separation is introduced into a scraped-wall automatic collector at 220°C and held for 10-15 minutes to collect the crystals; the process of the low-temperature deep collection stage is as follows: the remaining tail gas is introduced into a cryogenic collector at 80°C and held for 5-8 minutes to recover the residual trace amounts of aluminum trichloride fine powder.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: The synthesis method of aluminum trichloride provided by this invention innovatively adopts a three-stage closed-loop architecture of "pre-removal of iron from bauxite → compound chlorination reaction → gradient condensation purification", which replaces the traditional single aluminum ingot method or crude alumina method process, and fundamentally solves the problems of difficult impurity control and high energy consumption.

[0018] In the pre-iron removal stage of bauxite, the traditional high-impurity route of direct chlorination of bauxite is abandoned, and a low-temperature selective iron removal unit is added. Low-concentration chlorine gas is introduced in the range of 450℃-650℃. Relying on the characteristic of preferential chlorination of iron, the iron in the raw material is volatilized separately in the form of gaseous ferric chloride.

[0019] In the complex chlorination reaction stage, the traditional single fixed bed / fluidized bed reactor is abandoned. Chlorine gas is introduced in the range of 920℃-960℃ to complete the initial chlorination. Then, it is introduced into the eutectic salt bath reactor to complete the deep reaction in a constant temperature environment of 720℃. A trace amount of rare earth catalyst is added to the salt bath to allow the unreacted alumina to fully contact with the chlorine gas.

[0020] During purification, the gaseous product from the chlorination reaction is introduced into a jacketed cooler at 320°C during the high-temperature pre-separation stage to separate out heavy impurities such as residual ferric chloride and alumina dust with higher boiling points. During the medium-temperature crystallization stage, the gaseous product is introduced into a scraped-wall automatic collector at 220°C to complete the directional crystallization and collection of aluminum trichloride. During the low-temperature deep collection stage, residual trace amounts of fine aluminum trichloride powder can be recovered. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: A method for synthesizing aluminum trichloride, the method comprising the following preparation steps: (1) The bauxite is crushed into 200 mesh bauxite powder, and then the bauxite powder is fed into a closed rotary furnace. Low concentration chlorine gas with a volume fraction of 5% is introduced at 570℃ and kept at the temperature for 90 minutes to obtain low iron bauxite. (2) Anhydrous aluminum trichloride and anhydrous sodium chloride were vacuum dried at 140℃ for 3h. The dried anhydrous aluminum trichloride and anhydrous sodium chloride were mixed at a molar ratio of 52:48 and ground and mixed in a closed ball mill protected by argon for 30min to obtain mixed salt powder. (3) Fluidized bed stage: Low-iron bauxite and petroleum coke with a particle size of 100 mesh are added into the furnace at a ratio of 100:26. Chlorine gas with a volume fraction of 90% is introduced at 950℃ and the reaction time is 40 min to obtain crude gas phase product; Salt bath stage: The crude gas phase product is introduced into a eutectic salt bath reactor containing mixed salt powder. The amount of mixed salt powder is 3 times the mass of bauxite powder. Rare earth catalyst with a mass fraction of 0.01 times that of bauxite powder is added; Chlorine gas with a volume fraction of 85% is introduced and the reaction is carried out at 720℃ for 30 min to obtain crude aluminum chloride product; The rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride at a mass ratio of 1:1. (4) High temperature pre-separation: The crude aluminum chloride product is introduced into a jacketed cooler at 320℃ and kept at that temperature for 20 min; Medium temperature crystallization: The gas phase obtained from the high temperature pre-separation is introduced into a scraped wall automatic collector at 220℃ and kept for 10 min to collect the crystals; Low temperature deep collection: The remaining tail gas is introduced into a cryogenic collector at 80℃ and kept for 5 min to recover the residual trace amounts of aluminum trichloride fine powder and obtain aluminum trichloride.

[0023] Example 2: A method for synthesizing aluminum trichloride, the method comprising the following preparation steps: (1) The bauxite is crushed into 200 mesh bauxite powder, and then the bauxite powder is fed into a closed rotary kiln. Low concentration chlorine gas with a volume fraction of 10% is introduced at 570℃ and kept at the temperature for 105 min to obtain low iron bauxite. (2) Anhydrous aluminum trichloride and anhydrous sodium chloride were vacuum dried at 145℃ for 2.5h. The dried anhydrous aluminum trichloride and anhydrous sodium chloride were mixed at a molar ratio of 52:48 and ground and mixed in a closed ball mill protected by argon for 35min to obtain mixed salt powder. (3) Fluidized bed stage: Low-iron bauxite and petroleum coke with a particle size of 100 mesh are added to the furnace at a ratio of 100:26. Chlorine gas with a volume fraction of 93% is introduced at 950℃ and the reaction time is 43 min to obtain crude gas phase product; Salt bath stage: The crude gas phase product is introduced into a low eutectic salt bath reactor containing mixed salt powder. The amount of mixed salt powder is 3.5 times the mass of bauxite powder. Rare earth catalyst with a mass fraction of 0.015 times that of bauxite powder is added. Chlorine gas with a volume fraction of 87% is introduced and the reaction is carried out at 720℃ for 40 min to obtain crude aluminum chloride product; The rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride at a mass ratio of 1:1. (4) High temperature pre-separation: The crude aluminum chloride product is introduced into a jacketed cooler at 320°C and kept at that temperature for 25 min; Medium temperature crystallization: The gas phase obtained from the high temperature pre-separation is introduced into a scraped wall automatic collector at 220°C and kept for 13 min to collect the crystals; Low temperature deep collection: The remaining tail gas is introduced into a cryogenic collector at 80°C and kept for 6 min to recover the residual trace amounts of aluminum trichloride fine powder and obtain aluminum trichloride.

[0024] Example 3: A method for synthesizing aluminum trichloride, the method comprising the following preparation steps: (1) The bauxite is crushed into 300 mesh bauxite powder, and then the bauxite powder is fed into a closed rotary kiln. Low concentration chlorine gas with a volume fraction of 15% is introduced at 570℃ and kept at the temperature for 120 min to obtain low iron bauxite. (2) Anhydrous aluminum trichloride and anhydrous sodium chloride were vacuum dried at 150°C for 3 hours. The dried anhydrous aluminum trichloride and anhydrous sodium chloride were mixed at a molar ratio of 52:48 and then ground and mixed in a closed ball mill protected by argon for 40 minutes to obtain mixed salt powder. (3) Fluidized bed stage: Low-iron bauxite and petroleum coke with a particle size of 200 mesh are added into the furnace at a ratio of 100:26. Chlorine gas with a volume fraction of 95% is introduced at 950℃ and the reaction time is 55 min to obtain crude gas phase product; Salt bath stage: The crude gas phase product is introduced into a low eutectic salt bath reactor containing mixed salt powder. The amount of mixed salt powder is 4 times the mass of bauxite powder. Rare earth catalyst with a mass fraction of 0.02 times that of bauxite powder is added. Chlorine gas with a volume fraction of 90% is introduced and the reaction is carried out at 720℃ for 45 min to obtain crude aluminum chloride product; The rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride at a mass ratio of 1:1. (4) High temperature pre-separation: The crude aluminum chloride product is introduced into a jacketed cooler at 320°C and kept at that temperature for 30 min; Medium temperature crystallization: The gas phase obtained from the high temperature pre-separation is introduced into a scraped wall automatic collector at 220°C and kept for 15 min to collect the crystals; Low temperature deep collection: The remaining tail gas is introduced into a cryogenic collector at 80°C and kept for 8 min to recover the residual trace amounts of aluminum trichloride fine powder and obtain aluminum trichloride.

[0025] Comparative Example 1: The difference between the synthesis method of aluminum trichloride in Comparative Example 1 and Example 2 is that the "introducing 10% volume fraction of low-concentration chlorine gas at 570°C" in step (1) is changed to "introducing 10% volume fraction of low-concentration chlorine gas at 450°C".

[0026] Comparative Example 2: The difference between the synthesis method of aluminum trichloride in Comparative Example 2 and Example 2 is that the step (1) of "introducing 10% volume fraction of low-concentration chlorine gas at 570°C" is changed to "introducing 10% volume fraction of low-concentration chlorine gas at 490°C".

[0027] Comparative Example 3: The method for synthesizing aluminum trichloride in Comparative Example 3 differs from that in Example 2 in that the step (1) of "introducing a low concentration of chlorine gas with a volume fraction of 10% at 570°C" is changed to "introducing a low concentration of chlorine gas with a volume fraction of 10% at 530°C".

[0028] Comparative Example 4: The difference between the synthesis method of aluminum trichloride in Comparative Example 1 and Example 2 is that the step (1) of "introducing 10% volume fraction of low-concentration chlorine gas at 570°C" is changed to "introducing 10% volume fraction of low-concentration chlorine gas at 610°C".

[0029] Comparative Example 5: The difference between the synthesis method of aluminum trichloride in Comparative Example 1 and Example 2 is that the "introducing 10% volume fraction of low-concentration chlorine gas at 570°C" in step (1) is changed to "introducing 10% volume fraction of low-concentration chlorine gas at 650°C".

[0030] Comparative Example 6: The method for synthesizing aluminum trichloride in Comparative Example 6 differs from that in Example 2 in that the step (3) of "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:26" is changed to "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:20".

[0031] Comparative Example 7: The method for synthesizing aluminum trichloride in Comparative Example 7 differs from that in Example 2 in that the step (3) of "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:26" is changed to "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:22".

[0032] Comparative Example 8: The method for synthesizing aluminum trichloride in Comparative Example 8 differs from that in Example 2 in that the step (3) of "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:26" is changed to "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:24".

[0033] Comparative Example 9: The method for synthesizing aluminum trichloride in Comparative Example 9 differs from that in Example 2 in that the step (3) of "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:26" is changed to "adding low-iron bauxite and petroleum coke with a particle size of 100 mesh into the furnace at a ratio of 100:28".

[0034] Comparative Example 10: The method for synthesizing aluminum trichloride in Comparative Example 10 differs from that in Example 2 in that the phrase "the rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride in a mass ratio of 1:1" in step (3) is changed to "the rare earth catalyst is cerium chloride".

[0035] Comparative Example 11: The method for synthesizing aluminum trichloride in Comparative Example 11 differs from that in Example 2 in that the phrase "the rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride in a mass ratio of 1:1" in step (3) is changed to "the rare earth catalyst is lanthanum chloride".

[0036] Comparative Example 12: The method for synthesizing aluminum trichloride in Comparative Example 12 differs from that in Example 2 in that the phrase "the rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride in a mass ratio of 1:1" in step (3) is changed to "the rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride in a mass ratio of 1:0.5".

[0037] Comparative Example 13: The method for synthesizing aluminum trichloride in Comparative Example 13 differs from that in Example 2 in that the phrase "the rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride in a mass ratio of 1:1" in step (3) is changed to "the rare earth catalyst is obtained by mixing cerium chloride and lanthanum chloride in a mass ratio of 1:2".

[0038] Comparative Example 14: The method for synthesizing aluminum trichloride in Comparative Example 14 differs from that in Example 2 in that the step (3) of "introducing 93% volume fraction of chlorine gas at 950°C" is changed to "introducing 93% volume fraction of chlorine gas at 920°C".

[0039] Comparative Example 15: The method for synthesizing aluminum trichloride in Comparative Example 15 differs from that in Example 2 in that the step (3) of "introducing 93% volume fraction of chlorine gas at 950°C" is changed to "introducing 93% volume fraction of chlorine gas at 930°C".

[0040] Comparative Example 16: The method for synthesizing aluminum trichloride in Comparative Example 16 differs from that in Example 2 in that the step (3) of "introducing 93% volume fraction of chlorine gas at 950°C" is changed to "introducing 93% volume fraction of chlorine gas at 940°C".

[0041] Comparative Example 17: The method for synthesizing aluminum trichloride in Comparative Example 17 differs from that in Example 2 in that the step (3) of "introducing 93% volume fraction chlorine gas at 950°C" is changed to "introducing 93% volume fraction chlorine gas at 960°C".

[0042] Test example: Test method: Aluminum trichloride purity: The main content of aluminum trichloride was determined by chemical titration. Iron content: determined by atomic absorption spectrometry to characterize the level of metallic impurities; Test groups: Examples 1-3; Examples 2 and Comparative Examples 1-5; Examples 2 and Comparative Examples 6-9; Examples 2 and Comparative Examples 10-13; Examples 2 and Comparative Examples 14-17. The test results are shown in Tables 1-5.

[0043] Table 1 - Examples 1-3:

[0044] Table 2 - Examples 2 and Comparative Examples 1-5:

[0045] As shown in Table 2, the purity of aluminum trichloride first increases and then decreases with the increase of the pre-iron removal reaction temperature of bauxite, while the iron content of impurities first decreases and then increases with the increase of the pre-iron removal reaction temperature of bauxite. Therefore, the preferred pre-iron removal reaction temperature of bauxite is 570℃.

[0046] Table 3 - Examples 2 and Comparative Examples 6-9:

[0047] As shown in Table 3, the purity of aluminum trichloride increases with the increase of petroleum coke usage. When the ratio of low-iron bauxite to petroleum coke reaches 100:26, further increasing the amount of petroleum coke has little effect on the purity of aluminum trichloride, and the purity tends to stabilize. Therefore, the preferred ratio of low-iron bauxite to petroleum coke is 100:26.

[0048] Table 4 - Examples 2 and Comparative Examples 10-13:

[0049] As shown in Table 4, the purity of aluminum trichloride is higher when cerium chloride and lanthanum chloride are used in combination than when cerium chloride and lanthanum chloride are used alone. The purity of cerium chloride and lanthanum chloride mixed in a mass ratio of 1:1 is higher than that of cerium chloride and lanthanum chloride mixed in a mass ratio of 1:0.5 or 1:2. Therefore, the rare earth catalyst is preferably a mixture of cerium chloride and lanthanum chloride in a mass ratio of 1:1.

[0050] Table 5 - Examples 2 and Comparative Examples 14-17:

[0051] As shown in Table 5, the purity of aluminum trichloride increases with the increase of the temperature in the fluidized bed stage. When the temperature reaches 950℃, the purity of aluminum trichloride decreases with further increase of the reaction temperature. Therefore, the preferred temperature for the fluidized bed stage is 950℃.

[0052] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing aluminum trichloride, characterized in that, The method for synthesizing aluminum trichloride includes: (1) Pre-iron removal from bauxite; (2) Preparation of mixed salt powder; (3) Fluidized bed-salt bath combined chlorination; (4) Three-stage gradient condensation purification; The process of pre-removing iron from bauxite in step (1) is as follows: the bauxite is crushed into bauxite powder of 200-300 mesh, and then the bauxite powder is fed into a closed rotary kiln. Low-concentration chlorine gas is introduced at 450℃-650℃ and kept at the temperature for 90-120 minutes to obtain low-iron bauxite. The process for preparing mixed salt powder in step (2) is as follows: anhydrous aluminum trichloride and anhydrous sodium chloride are vacuum dried at 140~150℃ for 2~3h, the dried anhydrous aluminum trichloride and anhydrous sodium chloride are mixed at a molar ratio of 52:48, and then ground and mixed in a closed ball mill protected by argon for 30~40min to obtain mixed salt powder. Step (3) involves a fluidized bed-salt bath composite chlorination process divided into a fluidized bed stage and a salt bath stage. The process of the salt bath stage is as follows: the crude gas phase product is introduced into a eutectic salt bath reactor containing mixed salt powder, the amount of mixed salt powder is 3 to 4 times the mass of bauxite powder, and a rare earth catalyst of 0.01 to 0.02 times the mass of bauxite powder is added; chlorine gas is introduced, and the reaction is carried out at 720°C for 30 to 45 minutes to obtain crude aluminum chloride product. The fluidized bed stage process is as follows: low iron bauxite and petroleum coke with a particle size of 100-200 mesh are added into the furnace at a ratio of 100:20-28, chlorine gas is introduced at 920℃-960℃, and the reaction time is 40-55 minutes to obtain crude gas phase product. The rare earth catalyst is one or a mixture of cerium chloride and lanthanum chloride; Step (3) involves three stages of three-stage gradient condensation purification: high-temperature pre-separation at 320℃, medium-temperature crystallization at 220℃, and low-temperature deep collection at 80℃.

2. The method for synthesizing aluminum trichloride according to claim 1, characterized in that, The process of the high-temperature pre-separation stage is as follows: the crude aluminum chloride product is introduced into a jacketed cooler at 320°C and kept at that temperature for 20-30 minutes; the process of the medium-temperature crystallization stage is as follows: the gas phase obtained from the high-temperature pre-separation is introduced into a wall-scraping automatic collector at 220°C and kept for 10-15 minutes to collect the crystals; the process of the low-temperature deep collection stage is as follows: the remaining tail gas is introduced into a cryogenic collector at 80°C and kept for 5-8 minutes to recover the residual trace amounts of aluminum trichloride fine powder.

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