A process for the preparation of aluminium trichloride from hydrochloric acid

Abstract

The application discloses a method for preparing aluminum trichloride from hydrochloric acid, and relates to the technical field of chemical synthesis, and comprises the following steps: taking industrial by-product hydrochloric acid with a concentration of 31%, sequentially filtering through a microfiltration membrane and removing impurities through cation exchange resin to obtain purified hydrochloric acid; taking industrial-grade aluminum oxide powder, low-temperature calcining the aluminum oxide powder at 300-400 DEG C for 1-2 hours to obtain activated aluminum oxide powder. The method removes trace organic impurities from the industrial by-product hydrochloric acid through deep impurity removal, and also activates the industrial-grade aluminum oxide powder through low-temperature calcining, and the process scheme considers the uniformity of material mixing and the low volatility of HCl in the reaction stage, improves the reactivity of raw materials, reduces the loss of HCl volatilization, effectively improves the problem of low reaction conversion rate in the traditional process, avoids the waste of raw materials, reduces the influence of impurities on the purity of subsequent products, makes the products meet the demand of higher application scenarios, and improves the economic benefit and the synthesis quality of industrial production.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, specifically a method for producing aluminum trichloride from hydrochloric acid. Background Technology

[0002] Aluminum trichloride is an important inorganic chemical raw material, widely used in catalysts, water treatment agents, metal smelting and other fields. Currently, there are two main production processes for aluminum trichloride: one is to use aluminum ingots as raw materials and directly chlorinate them with chlorine gas. Although this process produces high-purity products, the cost of aluminum ingots is high (the market price is usually much higher than that of alumina powder), resulting in high total production costs and making it difficult to meet the demand for large-scale, low-cost production. The other process is to use hydrochloric acid and alumina as raw materials to react and produce aluminum trichloride. This process is lower in cost and is therefore the more common process.

[0003] In the existing process of producing aluminum trichloride from hydrochloric acid, the industrial by-product hydrochloric acid containing trace organic impurities is not deeply cleaned, industrial-grade alumina powder is not activated by low-temperature roasting, and the reaction stage lacks a system that takes into account both the uniformity of material mixing and the low volatility of hydrochloric acid (HCl). Solid-liquid separation relies on a high-energy-consuming evaporation process, and the waste residue after sublimation is only disposed of with low added value. As a result, the raw material has low reactivity, leading to a low reaction conversion rate. HCl is lost due to excessively high local concentrations, and more than 40% of the total energy consumption comes from the evaporation process. Ultimately, the purity of the product does not meet the standards and cannot meet the requirements of high-end catalysts. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for producing aluminum trichloride from hydrochloric acid, thus solving the problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for producing aluminum trichloride from hydrochloric acid, characterized by comprising the following steps:

[0006] Take 31% industrial by-product hydrochloric acid, filter it through a microfiltration membrane and remove impurities through a cation exchange resin to obtain purified hydrochloric acid, and take industrial grade alumina powder and calcine it at a low temperature of 300-400℃ for 1-2 hours to obtain activated alumina powder.

[0007] The purified hydrochloric acid and the activated alumina powder were added to a reaction vessel at a mass ratio of 6.8:1. Nitrogen gas was introduced into the reaction vessel to maintain the pressure inside the vessel at 0.05-0.1 MPa. An initial reaction was carried out at 50-60°C and a stirring speed of 50-80 rpm, a middle reaction was carried out at 70-80°C and a stirring speed of 100-150 rpm, and a later reaction was carried out at 60-70°C and a stirring speed of 180-220 rpm to obtain a reaction mixture containing aluminum chloride.

[0008] The reaction mixture is passed into a plate and frame filter press to obtain wet aluminum chloride and primary filtrate. The wet aluminum chloride is then fed into a vacuum rake dryer and dried at a vacuum of -0.08 to -0.09 MPa and a temperature of 80-90°C for 1 to 1.5 hours to obtain semi-dry aluminum chloride. Simultaneously, secondary condensate generated during drying is collected. The primary filtrate and secondary condensate are mixed and then passed into a nanofiltration membrane device. The retentate is returned to the reaction vessel, and the permeate is recycled.

[0009] The semi-dry aluminum chloride is fed into a sublimation furnace, the temperature of the impurity removal zone of the sublimation furnace is controlled at 130-140℃, nitrogen gas is introduced, and the temperature of the sublimation zone of the sublimation furnace is controlled at 185-195℃. Aluminum trichloride vapor enters a multi-layer gradient collector to obtain crude aluminum trichloride.

[0010] The crude aluminum trichloride is placed in a sealed dehydration furnace. Nitrogen gas is first introduced, and the free water in the crude aluminum trichloride is removed at a temperature of 100-110°C for 0.5-1 hour. Then, hydrochloric acid gas and nitrogen gas are introduced, and the product is dried at a temperature of 160-180°C for 1.5-2 hours to remove the water of crystallization, thus obtaining anhydrous aluminum trichloride.

[0011] Preferably, the organic matter removal of the by-product hydrochloric acid before pretreatment is carried out by passing the hydrochloric acid after removal by cation exchange resin into a modified activated carbon adsorption column filled with 20-50nm nano-titanium dioxide, and then irradiating it with 254nm ultraviolet light to obtain the by-product hydrochloric acid after removal.

[0012] The tail gas recovery and utilization in the pretreatment of alumina powder: the tail gas generated by the calcination of alumina powder is introduced into a catalytic combustion device at 300-350℃, and the water is condensed and recovered for rinsing of the plate and frame filter press.

[0013] Preferably, the purified hydrochloric acid and the activated alumina powder undergo a fluidized bed pre-reaction before being added to the reactor:

[0014] The activated alumina powder is fed into a horizontal dynamic fluidized bed, and the purified hydrochloric acid is atomized by a 20-30kHz ultrasonic atomizing nozzle and sprayed into the horizontal dynamic fluidized bed for pre-reaction to obtain the pre-reacted purified hydrochloric acid and the activated alumina, which are then introduced into the reaction vessel for further reaction.

[0015] Preferably, a low-temperature condensation-adsorption tower at 5-10°C is provided at the top of the reactor. The low-temperature condensation-adsorption tower is filled with an adsorbent, which is anhydrous calcium chloride. The low-temperature condensation-adsorption tower is used to recover the volatilized hydrochloric acid gas. The hydrochloric acid gas is dried and then passed into the sealed dehydration furnace for reuse.

[0016] Preferably, the waste residue remaining after sublimation treatment in the sublimation furnace is soaked in 5%–10% dilute hydrochloric acid for 1–2 hours and then filtered to obtain acid leaching filtrate, which is partially reused after treatment. The reuse specifically includes:

[0017] The acid leaching filtrate is pumped into the reactor, and 5% to 8% calcium aluminate powder with a particle size of 50-100 μm is added to adjust the pH to 3.5-4.0. The polymerization reaction is carried out at a temperature of 80-85℃ and a stirring speed of 80-100 rpm for 2-3 hours. Liquid aluminum chloride is obtained by passing the solution through the plate and frame filter press. The liquid aluminum chloride is then recovered and reused.

[0018] Preferably, the post-processing of the product during the sealed dehydration furnace process includes:

[0019] The condensate containing hydrochloric acid gas generated during the dehydration process in the sealed dehydration furnace is fed into the PDMS hollow fiber membrane enrichment system. Nitrogen gas is introduced into one side of the PDMS hollow fiber membrane enrichment system as a purging gas to obtain a mixed gas of hydrochloric acid gas and nitrogen gas, which is then recycled back to the sealed dehydration furnace. The residual condensate after treatment is reused as circulating water.

[0020] Preferably, if the final product is crystalline aluminum trichloride, then specifically:

[0021] The crude aluminum trichloride is dissolved in the permeate solution at a concentration of 45%–50%. The solution is then crystallized at 20–25°C for 8–10 hours, followed by centrifugation to obtain the crystalline aluminum trichloride.

[0022] Preferably, the preparation of the anhydrous aluminum trichloride includes anti-caking modification:

[0023] When the sealed dehydration furnace is cooled to 120-130°C, a mixture of silane coupling agent KH-550 and ethanol solution is added to the anhydrous aluminum trichloride. The concentration of silane coupling agent KH-550 in the mixture is 10%. The mixture is stirred for 10-15 minutes to obtain the modified anhydrous aluminum trichloride.

[0024] Preferably, when the vacuum rake dryer dries the semi-dry aluminum chloride, the rake rotation speed is increased from 15-20 rpm to 30-35 rpm every 30 minutes for 5 minutes, and the vacuum degree is pulsedly increased from -0.08 MPa to -0.095 MPa for 2 minutes.

[0025] Preferably, before capturing the aluminum trichloride vapor, the multi-layer gradient trap is preheated for 30 minutes at a gradient temperature of 150°C, 120°C and 90°C, and circulating hot water at 30-40°C is introduced into the inner wall of the multi-layer gradient trap during the capture process.

[0026] This invention provides a method for producing aluminum trichloride from hydrochloric acid. It has the following beneficial effects:

[0027] (1) This process deeply removes trace organic impurities from industrial by-product hydrochloric acid. At the same time, it activates industrial-grade alumina powder by low-temperature calcination. The process scheme takes into account both the uniformity of material mixing and the low volatility of HCl during the reaction stage, thereby improving the reaction activity of raw materials and reducing the loss of HCl volatilization. This effectively improves the problem of low reaction conversion rate in traditional processes, avoids waste of raw materials, and reduces the impact of impurities on the purity of subsequent products. This enables the products to meet the needs of higher application scenarios and improves the economic benefits and synthesis quality of industrial production.

[0028] (2) This process abandons the solid-liquid separation method that relies on high-energy evaporation in the traditional process and adopts a low-energy separation process that is more suitable for the characteristics of the aluminum chloride reaction mixture. This reduces the energy consumption of the solid-liquid separation process, significantly reduces the unnecessary consumption from the evaporation process in the total energy consumption, alleviates the serious energy waste problem of the traditional process, reduces the energy cost of industrial production, and at the same time reduces the environmental pressure brought by the high-energy process, further improving the economy and sustainability of the overall process.

[0029] (3) This process adopts a high-value-added treatment method to replace the traditional low-value-added treatment for the waste residue generated after sublimation. At the same time, it reduces the introduction of impurities through multi-stage process optimization in the early stage to improve product purity, enhance the utilization value of waste residue, and improve product quality. This not only reduces the high waste residue disposal cost in the traditional process, but also makes the product purity suitable for high-end catalysts and other scenarios with high purity requirements. This breaks the limitations of the application scenarios of traditional process products. At the same time, it realizes the resource utilization of waste residue, reduces the burden of solid waste on the environment, and achieves a dual improvement of process environmental protection benefits and product added value. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of a method for producing aluminum trichloride from hydrochloric acid according to the present invention;

[0031] Figure 2 This is a process flowchart of a method for producing aluminum trichloride from hydrochloric acid according to the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Please see Figure 1-2 This invention provides a method for producing aluminum trichloride from hydrochloric acid. To achieve the above objective, this invention employs the following technical solution, comprising the following steps:

[0034] Take 31% industrial by-product hydrochloric acid, filter it through a microfiltration membrane and remove impurities through a cation exchange resin to obtain purified hydrochloric acid, and take industrial grade alumina powder and calcine it at a low temperature of 300-400℃ for 1-2 hours to obtain activated alumina powder.

[0035] Purified hydrochloric acid and activated alumina powder were added to a reaction vessel at a mass ratio of 6.8:1. Nitrogen gas was introduced into the reaction vessel to maintain the pressure inside the vessel at 0.05-0.1 MPa. The reaction was carried out sequentially at 50-60℃ and 50-80 rpm for the initial reaction, 70-80℃ and 100-150 rpm for the intermediate reaction, and 60-70℃ and 180-220 rpm for the final reaction to obtain a reaction mixture containing aluminum chloride.

[0036] The reaction mixture is fed into a plate and frame filter press and filtered to obtain wet aluminum chloride and primary filtrate. The wet aluminum chloride is then fed into a vacuum rake dryer and dried at a vacuum of -0.08 to -0.09 MPa and a temperature of 80-90°C for 1 to 1.5 hours to obtain semi-dry aluminum chloride. At the same time, the secondary condensate generated during drying is collected. The primary filtrate and secondary condensate are mixed and then fed into a nanofiltration membrane device. The retentate is returned to the reaction vessel, and the permeate is recycled.

[0037] Semi-dry aluminum chloride is fed into a sublimation furnace. The temperature of the impurity removal zone of the sublimation furnace is controlled at 130-140℃. Nitrogen gas is introduced and the temperature of the sublimation zone of the sublimation furnace is controlled at 185-195℃. Aluminum trichloride vapor enters a multi-layer gradient collector to obtain crude aluminum trichloride.

[0038] Crude aluminum trichloride is placed in a sealed dehydration furnace. Nitrogen gas is first introduced, and the free water in the crude aluminum trichloride is removed at a temperature of 100-110℃ for 0.5-1h. Then, hydrochloric acid gas and nitrogen gas are introduced, and the product is dried at a temperature of 160-180℃ for 1.5-2h to remove the water of crystallization, thus obtaining anhydrous aluminum trichloride.

[0039] Organic matter removal of by-product hydrochloric acid before pretreatment: Hydrochloric acid that has been purified by cation exchange resin is passed into a modified activated carbon adsorption column filled with 20-50nm nano-titanium dioxide and then irradiated with 254nm ultraviolet light to obtain purified by-product hydrochloric acid.

[0040] Alumina powder tail gas recovery and utilization in pretreatment: The tail gas generated by alumina powder calcination is passed into a 300-350℃ loaded catalytic combustion device, and the condensed water is used for washing the plate and frame filter press.

[0041] Purified hydrochloric acid and activated alumina powder undergo a fluidized bed pre-reaction before being added to the reactor.

[0042] Activated alumina powder is fed into a horizontal dynamic fluidized bed. Purified hydrochloric acid is atomized through a 20-30kHz ultrasonic atomizing nozzle and sprayed into the horizontal dynamic fluidized bed for pre-reaction. The pre-reacted purified hydrochloric acid and activated alumina are then introduced into the reaction vessel for further reaction.

[0043] A low-temperature condensation-adsorption tower at 5-10℃ is installed at the top of the reactor. The adsorption tower is filled with an adsorbent, which is anhydrous calcium chloride. The low-temperature condensation-adsorption tower is used to recover the volatilized hydrochloric acid gas. After drying, the hydrochloric acid gas is passed into a sealed dehydration furnace for reuse.

[0044] The waste residue remaining after sublimation in the sublimation furnace is soaked in 5%–10% dilute hydrochloric acid for 1–2 hours, then filtered to obtain acid leaching filtrate. Part of this filtrate is then reused, specifically including:

[0045] The acid leaching filtrate is pumped into a reactor, and 5%–8% calcium aluminate powder with a particle size of 50–100 μm is added to adjust the pH to 3.5–4.0. The polymerization reaction is carried out at a temperature of 80–85℃ and a stirring speed of 80–100 rpm for 2–3 hours. Liquid aluminum chloride is obtained by passing the solution through a plate and frame filter press. The liquid aluminum chloride is then recovered and reused.

[0046] Post-processing of products during the sealed dehydration furnace process:

[0047] The condensate containing hydrochloric acid gas generated during the dehydration process in the sealed dehydration furnace is fed into the PDMS hollow fiber membrane enrichment system. Nitrogen gas is introduced into one side of the PDMS hollow fiber membrane enrichment system as a purging gas to obtain a mixed gas of hydrochloric acid gas and nitrogen gas, which is recycled back to the sealed dehydration furnace. The residual condensate after treatment is reused as circulating water.

[0048] If the final product is crystalline aluminum trichloride, then:

[0049] Crude aluminum trichloride was dissolved in a permeate solution at a concentration of 45%–50%. The solution was then crystallized at 20–25°C for 8–10 hours, followed by centrifugation to obtain crystalline aluminum trichloride.

[0050] The preparation of anhydrous aluminum trichloride includes anti-caking modification:

[0051] When the sealed dehydration furnace is cooled to 120-130℃, a mixture of silane coupling agent KH-550 and ethanol solution is added to anhydrous aluminum trichloride. The concentration of silane coupling agent KH-550 in the mixture is 10%. The mixture is stirred for 10-15 minutes to obtain modified anhydrous aluminum trichloride.

[0052] When drying semi-dry aluminum chloride in a vacuum rake dryer, the rake speed is increased from 15-20 rpm to 30-35 rpm every 30 minutes for 5 minutes, and the vacuum degree is simultaneously increased from -0.08 MPa to -0.095 MPa for 2 minutes.

[0053] Before capturing aluminum trichloride vapor, the multi-layer gradient trap is preheated for 30 minutes at a gradient temperature of 150℃, 120℃ and 90℃. During the capture process, circulating hot water at 30-40℃ is introduced into the inner wall of the multi-layer gradient trap.

[0054] Example 1

[0055] 2645 kg of 31% industrial by-product hydrochloric acid (HCl) was filtered through a 0.3 μm microfiltration membrane → D001 cation exchange resin column → modified activated carbon adsorption column filled with 20-50 nm nano-titanium dioxide → irradiated with 254 nm ultraviolet light (80 W) to obtain purified hydrochloric acid; 382 kg of industrial grade alumina powder was calcined at 350 °C for 1.5 h (the tail gas was passed into a Pt / Al2O3 catalytic combustion device at 320 °C, and the condensate was recovered for rinsing) to obtain activated alumina powder;

[0056] Activated alumina powder was fed into a horizontal dynamic fluidized bed (60℃, fluidizing gas velocity 0.25m / s), and purified hydrochloric acid was sprayed in through a 25kHz ultrasonic atomizing nozzle (particle size 8μm), with a pre-reaction rate of 65%.

[0057] The pre-reaction mixture was added to the reactor and pressurized with nitrogen to 0.07 MPa; the reaction was carried out at 55℃ and 70 rpm for 30 min (initial) → at 75℃ and 130 rpm for 60 min (middle) → at 65℃ and 200 rpm for 30 min (late). An 8℃ low-temperature condensation-adsorption tower was installed at the top of the reactor to recover HCl gas.

[0058] The reaction mixture was passed through a plate and frame filter press (8μm filter cloth, 0.25MPa) at 65℃ to obtain wet aluminum chloride and primary filtrate. The wet aluminum chloride was put into a vacuum rake dryer (-0.085MPa, 85℃). Every 30 min, the rake speed was increased from 18rpm to 32rpm (5min) and the vacuum degree was increased from -0.08MPa to -0.095MPa (2min). After drying for 1.2h, semi-dry aluminum chloride (moisture content 12%) was obtained. Secondary condensate was collected. The primary filtrate and secondary condensate were passed through a nanofiltration membrane (150Da cutoff, 0.5MPa). The retentate was returned to the reactor, and the permeate was recycled.

[0059] Semi-dry aluminum chloride was fed into a sublimation furnace for impurity removal in the impurity removal zone (135℃, nitrogen 8L / min) and sublimation in the sublimation zone (190℃, nitrogen 4L / min). Aluminum trichloride vapor entered a multi-layer gradient collector (preheated for 30 min, temperature 150℃→120℃→90℃, with 35℃ circulating hot water through the inner wall) to obtain crude aluminum trichloride. The waste residue was soaked in 8% dilute hydrochloric acid for 1.5 h, and the filtrate was pumped into a polymerization reactor. 6% calcium aluminate powder (80μm) was added to adjust the pH to 3.8, and polymerization was carried out at 82℃ and 90 rpm for 2.5 h. After pressure filtration, polyaluminum chloride (PAC) was obtained.

[0060] Crude aluminum trichloride is fed into a sealed dehydration furnace and dried with nitrogen at 105°C and 10 L / min for 0.7 h (to remove free water). Then, a mixture of HCl and nitrogen (mixing ratio 1:4, flow rate 7 L / min) is passed through it and dried at 170°C for 1.8 h. The dilute hydrochloric acid produced during dehydration is passed into a PDMS hollow fiber membrane system (50°C, 0.25 MPa) to enrich a mixture of 22% HCl and nitrogen (which is reused for dehydration). The residual liquid (HCl ≤ 0.5%) is recycled and reused to finally obtain anhydrous aluminum trichloride.

[0061] Example 2

[0062] The difference from Example 1 is that the calcination temperature of alumina powder is adjusted to 300℃ (holding temperature for 2 hours), while the rest of the process is the same as in Example 1. Example 3

[0063] The difference from Example 1 is that the pretreatment of by-product hydrochloric acid does not involve modified activated carbon adsorption and ultraviolet irradiation steps; the rest of the process is the same as in Example 1. Example 4

[0064] The difference from Example 1 is that the purified hydrochloric acid and activated alumina powder are directly added to the reactor without fluidized bed pre-reaction; the rest of the process is the same as in Example 1. Example 5

[0065] The difference from Example 1 is that crude aluminum trichloride was dissolved in the permeate (concentration 48%), crystallized at 22°C for 9 hours, and centrifuged at 3000 rpm for 12 minutes to obtain crystalline aluminum trichloride (AlCl3・6H2O). The rest of the process is the same as in Example 1.

[0066] Comparative Example 1

[0067] The difference from Example 1 is that the alumina powder is not calcined (the raw powder is used directly), while the rest of the process is the same as in Example 1.

[0068] Comparative Example 2

[0069] The difference from Example 1 is that the reaction vessel is at atmospheric pressure (without nitrogen gas), while the rest of the process is the same as in Example 1.

[0070] Comparative Example 3

[0071] The difference from Example 1 is that the vacuum rake dryer uses a constant rake speed of 18 rpm and a constant vacuum of -0.085 MPa for drying, while the rest of the process is the same as in Example 1.

[0072] Comparative Example 4

[0073] The difference from Example 1 is that the sublimation waste residue is not subjected to acid leaching-PAC preparation, but is directly disposed of as a hazardous material; the rest of the process is the same as in Example 1.

[0074] Test case

[0075] Test content and methods

[0076] Reaction conversion rate: According to GB / T39598-2021, the residual Al after titration of the reaction... 3+ Calculate the Al2O3 conversion rate.

[0077] HCl loss rate: The difference in total HCl mass before and after the reaction is calculated by weighing and divided by the initial HCl mass.

[0078] Product purity: Anhydrous aluminum trichloride is determined according to GB / T39598-2021 (ion chromatography), and crystalline aluminum trichloride is determined according to HG / T3541-2011 (complex titration).

[0079] Moisture content of semi-dry products: according to GB / T6284-2016 (Karl Fischer method).

[0080] Wastewater discharge: The total mass of wastewater ultimately discharged (excluding the recycled portion).

[0081] Waste residue utilization rate: Calculate the proportion of waste residue converted into PAC to the initial waste residue mass.

[0082] Table 1 shows the product test results for the process of producing aluminum trichloride from hydrochloric acid.

[0083]

[0084] Table 2 shows the test results of process waste emissions and utilization rates.

[0085]

[0086] As shown in Tables 1 and 2, the overall process advantages of Examples 1-5 are as follows:

[0087] The hydrochloric acid-to-aluminum-chloride process used in Examples 1-5 is significantly superior to traditional processes in terms of core process indicators and product quality: the reaction conversion rate reaches 95.3%–98.8%, the HCl loss rate is only 2.7%–5.2%, the product purity (anhydrous / crystalline) is 99.0%–99.8%, the semi-dry product moisture content is 11.9%–12.3%, the wastewater discharge is 775–785 kg / t of product, and the waste residue utilization rate is 100%. These data indicate that through the optimization of the entire process—including deep pretreatment of raw materials, fluidized bed pre-reaction, nitrogen pressure holding + HCl recovery, pulsed vacuum drying, and PAC resource utilization from waste residue—the problems of low raw material utilization, high HCl loss, insufficient product purity, large pollution emissions, and difficult waste residue disposal associated with traditional processes are effectively solved, achieving the production goals of low cost, high purity, low pollution, and resource utilization.

[0088] In Example 1, alumina was calcined at 350℃ for 1.5 hours, resulting in a reaction conversion rate of 98.7% and a product purity of 99.8%. In Example 2, the calcination temperature was lowered to 300℃ (held for 2 hours), resulting in a reaction conversion rate of 97.2% (a decrease of 1.5%) and a product purity of 99.7% (a decrease of 0.1%). There was no significant difference in HCl loss rate and wastewater discharge. Therefore, low-temperature calcination at 300-400℃ can remove moisture and organic impurities adsorbed on the surface of alumina and activate the crystal lattice (increasing active sites). Too low a temperature (300℃) will lead to insufficient activation, a reduction in active sites, and thus a slight decrease in reaction conversion rate. A calcination temperature of around 350℃ is the optimal calcination condition.

[0089] Example 1 describes the organic impurity removal of hydrochloric acid through modified activated carbon adsorption and ultraviolet photolysis, resulting in a product purity of 99.8%. In Example 3, this step was omitted, and the product purity decreased to 99.0% (a decrease of 0.8%). There was no significant difference in reaction conversion rate and HCl loss rate. Trace organic impurities (such as hydrocarbons and esters) in industrial by-product hydrochloric acid remain in the product during the reaction and sublimation process, leading to a decrease in purity. The organic impurity removal process of this invention can significantly reduce the content of organic impurities and is a key process for preparing high-end, high-purity aluminum trichloride (such as for catalysts).

[0090] Example 1 uses a fluidized bed pre-reaction, achieving a conversion rate of 98.7% and an HCl loss rate of 2.8%. Example 4 omits the pre-reaction step (direct feeding reaction), resulting in a conversion rate of 95.3% (a decrease of 3.4%) and an HCl loss rate of 5.2%. The fluidized bed pre-reaction achieves uniform and sufficient contact between hydrochloric acid and alumina through "atomized hydrochloric acid + fluidized contact," completing 60%–70% of the pre-reaction and reducing local concentration differences within the subsequent reactor. Without pre-reaction, alumina tends to settle, and the local concentration of hydrochloric acid is too high, leading to incomplete reaction (decreased conversion rate) and severe HCl volatilization (increased loss rate). This process is a core innovation in improving raw material utilization and reducing HCl loss.

[0091] Example 1 prepared anhydrous aluminum trichloride (purity 99.8%, conversion rate 98.7%), and Example 5 prepared crystalline aluminum trichloride (AlCl3・6H2O, purity 99.2%, conversion rate 98.5%). The HCl loss rate (2.8% and 2.7%) and wastewater discharge (780 kg / t and 775 kg / t) of the two were not significantly different. Therefore, the core process of this invention has good product adaptability. By simply switching between a dehydration step (anhydrous) or a dissolution-crystallization step (crystallization), the production of two mainstream aluminum trichloride products can be achieved without significant adjustments to the core equipment and process parameters. This greatly improves the flexibility of the production line and can meet different market demands (anhydrous for catalysts, crystalline for water treatment).

[0092] Comparative Example 1 directly used uncalcined alumina powder, with a reaction conversion rate of only 85.2% (a decrease of 13.5% compared to Example 1), a product purity of 98.5% (a decrease of 1.3%), and a wastewater discharge of 810 kg / t (an increase of 3.8%). Therefore, the surface of unactivated alumina adsorbs a large amount of water and organic impurities, which on the one hand covers the active sites, resulting in insufficient reaction and low conversion rate, and on the other hand, impurities enter the product with the reaction, resulting in a decrease in purity. At the same time, unreacted alumina needs to be discharged with the wastewater, increasing the wastewater treatment load.

[0093] In Comparative Example 2, the reactor was used for atmospheric pressure reaction (without nitrogen gas). The HCl loss rate increased to 10.5% (3.8 times higher than in Example 1), the reaction conversion rate was 98.5% (no significant difference), and the product purity was 99.7% (no significant difference). Therefore, HCl is highly volatile, and the exothermic reaction at atmospheric pressure will exacerbate HCl volatilization. Nitrogen gas pressure (0.05-0.1 MPa) can suppress HCl volatilization. Combined with the low-temperature condensation-adsorption tower at the top of the reactor, the HCl loss rate can be controlled within 3%. The high HCl loss rate in Comparative Example 2 not only increases the cost of raw materials but also leads to an increase in the HCl concentration in the tail gas, thus polluting the environment.

[0094] Comparative Example 3 uses a vacuum rake drying process with constant rake speed and constant vacuum, and no pulse mode. The moisture content of the semi-dried product increases to 15.8% (31.7% higher than in Example 1), and the wastewater discharge is 805 kg / t (3.2% higher). Therefore, the semi-dried aluminum chloride is prone to agglomeration during the drying process. The constant rake speed and vacuum cannot effectively break up the agglomeration, making it difficult to remove internal moisture (increased moisture content). The high moisture content of the semi-dried product increases the energy consumption of the subsequent sublimation process (requiring additional moisture removal), and the moisture that is not removed during the drying process will be discharged with the wastewater.

[0095] Comparative Example 4 directly treats the sublimation waste residue as hazardous materials (without acid leaching-PAC preparation), resulting in a waste residue utilization rate of 0% (100% in Example 1). Furthermore, additional hazardous material disposal costs (approximately 200 RMB / ton of waste residue) are incurred. Therefore, the traditional process of "directly discarding waste residue" not only wastes aluminum resources but also incurs high disposal costs and environmental risks. The PAC preparation process using waste residue acid leaching of this invention can convert waste residue into a high-value-added water treatment agent, achieving full resource utilization of waste residue, reducing solid waste pollution, and increasing economic benefits.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A process for the production of aluminum trichloride from hydrochloric acid, characterized by: The method comprises the following steps: The industrial by-product hydrochloric acid with a concentration of 31% is sequentially filtered by a microfiltration membrane and impurities are removed by a cation exchange resin to obtain purified hydrochloric acid, and the industrial-grade aluminum oxide powder is calcined at a low temperature of 300-400 ℃ for 1-2 h to obtain activated aluminum oxide powder; The purified hydrochloric acid and the activated aluminum oxide powder are put into a reaction kettle at a mass ratio of 6.8:1, nitrogen is introduced into the reaction kettle to maintain the pressure in the kettle at 0.05-0.1 MPa, and the initial reaction is sequentially carried out at 50-60 ℃ and a stirring speed of 50-80 rpm, the middle-stage reaction is carried out at 70-80 ℃ and a stirring speed of 100-150 rpm, and the late-stage reaction is carried out at 60-70 ℃ and a stirring speed of 180-220 rpm to obtain a reaction mixture containing aluminum chloride; The reaction mixture is introduced into a plate-and-frame filter press to obtain wet aluminum chloride and a first filtrate, the wet aluminum chloride is put into a vacuum rake dryer, dried at a vacuum degree of-0.08 to-0.09 MPa and a temperature of 80-90 ℃ for 1-1.5 h to obtain semi-dry aluminum chloride, and the secondary condensate water generated during drying is collected, the first filtrate and the secondary condensate water are mixed and introduced into a nanofiltration membrane device, the retentate is returned to the reaction kettle, and the permeate is recycled and reused; The semi-dry aluminum chloride is put into a sublimation furnace, the temperature of the impurity removal zone of the sublimation furnace is controlled at 130-140 ℃, nitrogen is introduced, the temperature of the sublimation zone of the sublimation furnace is controlled at 185-195 ℃, and aluminum chloride vapor enters a multi-layer gradient trap to obtain aluminum chloride crude product; The aluminum chloride crude product is put into a sealed dehydration furnace, the free water in the aluminum chloride crude product is removed by introducing nitrogen at a temperature of 100-110 ℃ for 0.5-1 h, and the crystal water in the aluminum chloride crude product is removed by introducing hydrochloric acid gas and nitrogen at a temperature of 160-180 ℃ for 1.5-2 h to obtain anhydrous aluminum chloride.

2. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: The organic matter in the by-product hydrochloric acid is removed before pretreatment: the hydrochloric acid after removal of impurities by a cation exchange resin is introduced into a modified activated carbon adsorption column loaded with 20-50 nm nano-titanium dioxide, and then irradiated by 254 nm ultraviolet light to obtain the by-product hydrochloric acid after removal of impurities; The tail gas generated during calcination of the aluminum oxide powder is introduced into a 300-350 ℃ catalytic combustion device loaded, and the water content is condensed and recovered for flushing of the plate-and-frame filter press.

3. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: The purified hydrochloric acid and the activated aluminum oxide powder are pre-reacted in a fluidized bed before being put into the reaction kettle: The activated aluminum oxide powder is put into a horizontal dynamic fluidized bed, the purified hydrochloric acid is atomized by a 20-30 kHz ultrasonic atomizing nozzle and then sprayed into the horizontal dynamic fluidized bed to carry out pre-reaction, and the purified hydrochloric acid and the activated aluminum oxide after pre-reaction are introduced into the reaction kettle for reaction.

4. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: The top of the reactor is provided with a low-temperature condensation-adsorption tower of 5-10 ℃, which is filled with anhydrous calcium chloride as an adsorbent. The low-temperature condensation-adsorption tower is used to recover the volatile hydrochloric acid gas, which is dried and then introduced into the sealed dehydration furnace for reuse.

5. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: The waste residue remaining after the sublimation treatment of the sublimation furnace is soaked in 5%-10% dilute hydrochloric acid for 1-2 h, filtered to obtain an acid leaching filtrate, and part of the treated acid leaching filtrate is reused, which specifically includes: The acid leaching filtrate is pumped into the reactor, 5%-8% calcium aluminate powder with a particle size of 50-100 μm is added to adjust the pH to 3.5-4.0, the polymerization reaction is carried out at a temperature of 80-85 ℃ and a stirring speed of 80-100 rpm for 2-3 h, and then liquid aluminum chloride is obtained through the plate and frame filter press. The liquid aluminum chloride is recovered and reused.

6. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: Post-treatment of the product during the process of the sealed dehydration furnace: The condensate containing hydrochloric acid gas generated during the dehydration process of the sealed dehydration furnace is introduced into a PDMS hollow fiber membrane enrichment system, one side of the PDMS hollow fiber membrane enrichment system is introduced into the nitrogen gas as a purge gas, and a mixed gas of the hydrochloric acid gas and the nitrogen gas is obtained, which is recycled to the sealed dehydration furnace, and the residual liquid of the treated condensate is reused as circulating water.

7. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: If the final product is crystalline aluminum chloride, specifically: The crude aluminum chloride is dissolved in the permeate, the concentration of the crude aluminum chloride dissolved in the permeate is 45%-50%, and the crystallization is carried out at a temperature of 20-25 ℃ for 8-10 h, and the crystalline aluminum chloride is obtained by centrifugal separation.

8. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: After preparing the anhydrous aluminum chloride, an anti-caking modification is included: When the sealed dehydration furnace is cooled to 120-130 ℃, a mixture of silane coupling agent KH-550 and ethanol solution is added to the anhydrous aluminum chloride, the concentration of the silane coupling agent KH-550 in the mixture is 10%, the mixture is stirred for 10-15 min, and the modified anhydrous aluminum chloride is obtained.

9. The process for the preparation of aluminium trichloride according to claim 1, characterized in that: When the vacuum rake dryer dries the semi-dry aluminum chloride, the rake rotation speed is increased from 15-20 rpm to 30-35 rpm every 30 min for 5 min, and the vacuum degree is pulsed from -0.08 MPa to -0.095 MPa for 2 min.

10. The process for the production of aluminum trichloride from hydrochloric acid as claimed in claim 1, wherein: Before capturing the aluminum chloride vapor, the temperature of each layer of the multi-layer gradient trap is preheated in the order of 150 ℃, 120 ℃ and 90 ℃ for 30 min, and circulating hot water at 30-40 ℃ is introduced into the inner wall of the multi-layer gradient trap during the capturing process.

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