Process for the preparation of sodium tetrachloroaluminate

Abstract

A process for the production of sodium tetrachloroaluminate, the process comprising under anhydrous conditions and under an oxygen-free atmosphere: in a first feeding stage, providing a reactor comprising sodium tetrachloroaluminate and solid aluminum, and optionally solid sodium chloride, and heating the reactor to a temperature of from about 150°C to about 400°C, thereby providing a reaction mixture comprising liquid phase sodium tetrachloroaluminate; in a chlorine feeding stage, contacting the reaction mixture with a chlorine-containing gas; and in an optional further feeding stage, adding solid aluminum and / or solid sodium chloride to the reactor, wherein the optional further feeding stage is conducted during or alternatively to the chlorine feeding stage, and wherein solid sodium chloride is added to the process in at least one of the first feeding stage or the further feeding stage.

Description

Technical Field

[0001] This invention relates to a method for preparing sodium tetrachloroaluminate (NaAlCl4) from sodium chloride, aluminum and chlorine-containing gas, and particularly to a one-step synthetic route for preparing battery-grade NaAlCl4. Background Technology

[0002] Commercial production of sodium aluminum chloride typically involves mixing sodium chloride (NaCl) with anhydrous aluminum trichloride (AlCl3) and heating it to its melting point.

[0003] The anhydrous aluminum trichloride required for the reaction is typically prepared in a separate, prior process. Currently, most anhydrous aluminum trichloride is obtained by passing chlorine (Cl2) through molten aluminum metal in a ceramic-lined tubular reactor at 670–850 °C, while controlling the feed rates of chlorine and aluminum and cooling the reactor walls with water (e.g., see O. Helmboldt et al., AluminumCompounds, Inorganic, Ullmann's Encyclopedia of Industrial Chemistry, 2007). The anhydrous aluminum trichloride prepared by this reaction is then separated, condensed, and recovered as solid anhydrous aluminum trichloride suitable for storage and / or transportation, subsequently mixed with sodium chloride in a separate second step.

[0004] This two-step synthesis route is expensive and inefficient. Specifically, preparing the intermediate anhydrous aluminum trichloride at such high temperatures requires a significant amount of energy and time before separating, condensing, and recovering it as a solid.

[0005] To this end, several publications have been published on the preparation of sodium tetrachloroaluminate from sodium chloride, aluminum and chlorine.

[0006] For example, US 2004 / 0223902 A1 discloses a method including a first reaction step in which a melt of aluminum reacts with chlorine gas to produce gaseous aluminum trichloride. Subsequently, in a second reaction step, the gaseous aluminum trichloride reacts with solid sodium chloride to produce sodium tetrachloroaluminate, which is then separated as a melt. It is claimed that the heat generated by the gaseous aluminum trichloride is sufficient to heat the sodium chloride to the melting point of the sodium tetrachloroaluminate melt.

[0007] JPS52-129696 discloses a method for obtaining anhydrous aluminum trichloride-sodium chloride mixture (AlCl3-NaCl) from sodium chloride, metallic aluminum, and a chlorine-containing gas. In JPS52-129696... Figure 1In the method shown, chlorine-containing gas reacts with metallic aluminum in a packed bed reactor to prepare gaseous aluminum trichloride. This gaseous aluminum trichloride is absorbed into a circulating AlCl3-NaCl mixed melt at a predetermined molar ratio to obtain an aluminum trichloride-rich mixed melt as the product. The molar ratio of the circulating AlCl3-NaCl mixed melt is controlled in a separate step by adding a predetermined amount of sodium chloride to the melt in a salt dissolution tank. In each embodiment of JPS52-129696, the circulating AlCl3-NaCl mixed melt is prepared using an excess of AlCl3.

[0008] However, the preparation methods described in US 2004 / 0223902 A1 and JPS JPS52-129696 are not optimized in terms of process efficiency. For example, in US 2002004 / 0223902 A1, the first reaction step is still carried out at a temperature above the melting point of aluminum (i.e., ~660°C). Furthermore, both methods produce gaseous aluminum trichloride, which must be collected and dissolved in the sodium tetrachloroaluminate melt before further reaction with sodium chloride.

[0009] Furthermore, neither US 2004 / 0223902 A1 nor JPS52-129696 provides a one-step synthetic route for sodium tetrachloroaluminate. In fact, in both methods, the chlorination reaction is carried out in separate vessels from the sodium chloride reaction (i.e., the first and second reaction vessels of US2002 / 0223902, and the packed bed reactor and salt dissolution tank of JPS52-129696, respectively). JPS52-129696 even mentions that it is advantageous to carry out the chlorination reaction in separate reactors so that the temperature of this step can be controlled independently.

[0010] Therefore, a method is needed to solve these problems. Attached Figure Description

[0011] Figure 1 This is a flowchart of a preferred embodiment of the present disclosure. Detailed Implementation

[0012] It has now been discovered that sodium aluminum chloride can be prepared in a one-step synthesis using sodium chloride, aluminum, and a chlorine-containing gas. This new synthetic route not only avoids the lengthy separation process of the aforementioned intermediate anhydrous aluminum trichloride, but also enables the high-yield preparation of battery-grade sodium aluminum chloride.

[0013] Therefore, the present invention relates to a method for preparing sodium tetrachloroaluminate, the method comprising: under anhydrous conditions and an oxygen-free atmosphere: In the first feeding stage - A reactor containing sodium aluminum chloride and solid aluminum, and optionally solid sodium chloride; - Heat the reactor to a temperature of approximately 150°C to approximately 400°C. This provides a reaction mixture containing liquid sodium aluminum chloride; During the chlorine feeding stage, the reaction mixture is brought into contact with chlorine-containing gas; and In an optional further feeding stage, solid aluminum and / or solid sodium chloride are added to the reactor. The optional further feeding stage is carried out during or alternates with the chlorine feeding stage, and solid sodium chloride is added in at least one intermediate process during the first feeding stage or the further feeding stage.

[0014] Advantageously, by providing liquid sodium aluminum tetrachloride in the reactor during the first feeding stage, the method of the present invention has been found to provide a reaction medium that not only ensures good interaction between the solid and gaseous reactants, but also dissolves the anhydrous aluminum trichloride intermediate as it forms, thereby preventing its loss to the reactor headspace at temperatures above 160-170°C, and enabling the overall reaction to proceed in a single reactor.

[0015] Therefore, the method disclosed in this invention can be used to prepare high-quality sodium aluminum chloride, which can reduce operating costs and capital investment compared with US 2004 / 0223902 and 52-129696.

[0016] In the first feeding stage of the method, a reactor comprising sodium aluminum tetrachloroethylene and solid aluminum, and optionally solid sodium chloride, is provided and heated to a temperature of approximately 150°C to approximately 400°C. The reactor may be heated to the desired temperature range before or after containing one or more of the solid aluminum, solid sodium chloride, and sodium aluminum tetrachloroethylene.

[0017] Any suitable reactor, such as a stirred tank reactor, can be provided for this method. The reactor may include a circulation loop for cooling and / or feeding purposes. When a circulation loop for removing heat from the reaction mixture is included, a heat exchange device may be provided in that circulation loop.

[0018] In the first feeding stage of the method, two or more of solid aluminum, solid sodium chloride, and sodium aluminum tetrachloride may be premixed before being fed into the reactor. Alternatively, solid aluminum may be contacted with sodium aluminum tetrachloride and optionally solid sodium chloride in the reactor. This contact may occur before, after, or simultaneously with heating the reactor to the desired temperature range. Similarly, any or all of the solid aluminum, solid sodium chloride, and sodium aluminum tetrachloride may be at or above this temperature range before contact. Preferably, sodium aluminum tetrachloride is at this temperature range when in contact with solid aluminum and optionally solid sodium chloride.

[0019] The first feeding stage includes the following steps: When solid aluminum is contacted with sodium aluminum tetrachloride and optionally solid sodium chloride in the reactor, the first feeding stage includes... - In a reactor, solid aluminum is brought into contact with sodium aluminum tetrachloride and optionally solid sodium chloride; - Heat the reactor to a temperature of approximately 150°C to approximately 400°C. This provides a liquid reaction mixture containing liquid-phase sodium aluminum chloride.

[0020] Solid aluminum can be provided to the process in any suitable physical form, including powder, granules, needles, flakes, or mixtures thereof. Preferably, aluminum is added in powder form, with a particle size distribution of 300 to 3000 micrometers, more preferably 500 to 2000 micrometers, and more preferably 500 to 1500 micrometers, as determined by dry sieving according to ISO 4497. In the preparation of battery-grade sodium aluminum tetrachloride, the purity of the aluminum used should be above 95 wt.%, preferably above 98 wt.%, more preferably above 99 wt.% or above, or above 99.5 wt.% (based on trace metals). Aluminum can be derived from new sources or recovered from other applications or processes.

[0021] The solid sodium chloride supplied to the process should have a water content of at most 1 wt.%, preferably 0.5 wt.%, and more preferably 0.1 wt.%. This low water content can be achieved, for example, by drying the sodium chloride in any batch or continuous drying equipment known in the art before use, such as an oven, flash dryer, or fluidized bed dryer. When preparing battery-grade sodium tetrachloroaluminate, the purity of the sodium chloride used should be 98 wt.% or higher, preferably 99 wt.% or higher, and more preferably 99.5 wt.% or higher.

[0022] Sodium aluminum chloride can be supplied to the process in liquid or solid form. After initial process start-up, the sodium aluminum chloride required for the first feeding stage can be obtained by this method, with at least a portion of the sodium aluminum chloride retained in the reactor during the discharge stage (see below). When preparing battery-grade sodium aluminum chloride, the purity of the sodium aluminum chloride used for start-up should be higher than 98 wt.%, preferably higher than 99 wt.%, and more preferably higher than 99.5 wt.% (based on trace metals).

[0023] The first feeding stage may further include evacuating the reactor to an absolute pressure of approximately 5000 Pa or less, preferably less than approximately 3000 Pa, and more preferably less than approximately 2000 or 1500 Pa. Evacuating the reactor before the reaction mixture comes into contact with the chlorine-containing gas can improve the efficiency of the chlorine feeding stage.

[0024] As described above, in the first feeding stage, the reactor is heated to about 150°C to about 400°C, preferably about 200°C to about 350°C, more preferably about 220°C to about 320°C, and even more preferably about 230°C to about 300°C. At this temperature, the reaction mixture provided by the first feeding stage comprises solid aluminum (and optionally solid sodium chloride) suspended in the liquid sodium tetrachloroaluminate phase. Typically, the reaction mixture provided by the first feeding stage has a total solids concentration of at least 3 vol%, at least 5 vol%, at least 10 vol%, or at least 15 vol%, and at most 40 vol%, or at most 35 vol%. That is, the total solids concentration of the reaction mixture provided by the first feeding stage in the liquid sodium tetrachloroaluminate phase can be 3 to 40 vol%, preferably 5 to 40 vol%, and more preferably 5 to 35 vol%.

[0025] In the chlorine feeding stage of the method, the reaction mixture provided by the first feeding stage comes into contact with chlorine-containing gas to form a chlorinated reaction mixture (i.e., a reaction mixture in which chlorine has been partially absorbed or dissolved). Throughout the stage, the reactor temperature is preferably maintained at about 150°C to about 400°C, more preferably at about 200°C to about 350°C, even more preferably at about 220°C to about 320°C, and even more preferably at about 230°C to about 300°C, by heating and / or cooling the reactor as needed.

[0026] The chlorine-containing gas can be provided continuously or intermittently in at least two portions, preferably at least four portions, more preferably at least six portions, and most preferably at least ten portions. The duration of each portion and the time interval between portions can be the same or different. If many portions are added at short intervals, or if the time for each portion to be provided is long, it approaches continuous feeding.

[0027] Continuous feeding is the preferred feeding method, and it can be carried out at a constant or variable rate. The continuous feeding rate of chlorine-containing gas is preferably controlled by an automatic pressure-controlled feeding system.

[0028] Preferably, the chlorine-containing gas is supplied to the process to bring the absolute pressure of the reactor to about 0.20 to about 2 MPa, more preferably about 0.25 to about 1.5 MPa, and more preferably about 0.28 to about 1 MPa. Intermittent feeding can be achieved by adding a portion of the chlorine-containing gas when the reactor pressure is detected to drop below a predetermined threshold within this range; while continuous feeding can maintain a relatively constant reactor pressure by varying the rate of chlorine-containing gas feed.

[0029] The chlorine-containing gas stream supplied to the process can be chlorine gas (Cl2). To prevent the accumulation of inert substances during the reaction, the chlorine gas preferably contains less than 5 wt.% impurities, more preferably less than 1 wt.% impurities. Alternatively, the chlorine-containing gas can be a purified hydrogen chloride-containing gas stream, for example, containing at least 95 vol%, preferably at least 99 vol% hydrogen chloride.

[0030] Contact between the reaction mixture and the chlorine-containing gas can be carried out in a manner known in the art. Generally, the mixing conditions should be sufficient to ensure close contact and adequate mass transfer between the chlorine-containing gas and the liquid medium. Preferably, the liquid medium is stirred such that the chlorine-containing gas in the reactor headspace is drawn into the reaction mixture, for example, by a self-priming agitator, a hollow shaft impeller, or a Venturi jet mixer. Alternatively, the chlorine-containing gas can be introduced into the liquid reaction mixture in the form of bubbles. When the reactor includes a circulation loop, the reaction mixture can be contacted with the chlorine-containing gas in a liquid / gas contact device (e.g., a static mixer, a packed tower, a spray tower, or a Venturi mixer) provided in the loop, to which the chlorine-containing gas is fed.

[0031] Without being bound by theory, once absorbed into the reaction mixture, chlorine is thought to react with suspended solid aluminum to form anhydrous aluminum chloride, which dissolves in liquid sodium tetrachloroaluminate. Once dissolved in liquid sodium tetrachloroaluminate, anhydrous aluminum chloride can react with any suspended solid sodium chloride to form the product sodium tetrachloroaluminate.

[0032] Since the overall reaction is considered to proceed through the two consecutive steps described above, the method can include multiple feeding stages. Specifically, studies have found that dissolved anhydrous aluminum chloride will remain in the liquid phase of sodium tetrachloroaluminate until a sufficient level of solid sodium chloride is present for further reaction.

[0033] Therefore, the method may include a further feeding stage in which solid aluminum and / or solid sodium chloride are added to the reactor. This further feeding stage may be carried out during or alternate with the chlorine feeding stage.

[0034] In the first and / or further feeding stages, solid aluminum and / or solid sodium chloride can be supplied to the reactor in single portions, continuously, or intermittently, with the intermittent feeding stage consisting of at least two portions, preferably at least four portions, more preferably at least six portions, and most preferably at least ten portions. The duration of each portion and the time interval between two portions can be the same or different. If many portions are added at short intervals, or if the duration of each portion is long, it approaches continuous feeding.

[0035] To ensure the overall reaction is complete, solid sodium chloride must be added to the process at least in one of the first feeding stage or the subsequent feeding stage. Typically, the molar ratio of solid sodium chloride to solid aluminum used in the method is 0.8:1.2 to 1.2:0.8, preferably 0.9:1.1 to 1.1:0.9, and more preferably 0.95:1.05 to 1.05:0.95.

[0036] After sufficient chlorine is added, the sodium tetrachloroaluminate product can be recovered. Therefore, the method of the present invention may further include: In an optional purging phase, chlorine-containing gases are removed from the reactor; and During the recovery phase, at least a portion of sodium tetrachloroaluminate is discharged from the reactor.

[0037] In an optional purging stage, chlorine-containing gases can be removed from the reactor using an inert gas such as nitrogen.

[0038] During the recovery phase, at least a portion of the sodium tetrachloroaluminate can be discharged from the reactor at a temperature of about 150°C to about 400°C, preferably about 160°C to about 350°C, and more preferably about 160°C to about 250°C. At these temperatures, the sodium tetrachloroaluminate is a liquid and therefore easier to handle. The recovered sodium tetrachloroaluminate can then be sent for further processing, such as filtration or centrifugation, as needed.

[0039] During the recovery phase, preferably at least 10 wt.%, more preferably at least 25 wt.%, and more preferably at least 40 wt.%, of the total sodium tetrachloroaluminate (i.e., the sodium introduced in the first feeding phase and the sodium prepared by the method) is retained in the reactor for the first feeding phase of the next production run.

[0040] Therefore, as described above and as Figure 1 As shown, the method for preparing sodium aluminum tetrachlorodi ... In the first feeding stage - A reactor containing sodium tetrachloroaluminate and solid aluminum, and optionally solid sodium chloride; - Heat the reactor to a temperature of approximately 150°C to approximately 400°C. This provides a reaction mixture containing liquid-phase sodium tetrachloroaluminate; During the chlorine feeding stage, the reaction mixture is brought into contact with chlorine-containing gas; In an optional further feeding stage, solid aluminum and / or solid sodium chloride are added to the reactor. In an optional purging phase, chlorine-containing gases are removed from the reactor; and During the recovery phase, at least a portion of the sodium tetrachloroaluminate is discharged from the reactor. The optional further feeding stage is carried out during or alternates with the chlorine feeding stage, and solid sodium chloride is added in at least one intermediate process in the first feeding stage or the further feeding stage.

[0041] The method of the present invention can be carried out continuously, semi-continuously, or in batches, preferably semi-continuously or in batches. When carried out in batches, predetermined amounts of solid aluminum and solid sodium chloride can be added to the process in a first or further feeding stage, and the chlorine feeding stage can be run until a decrease (or cessation) in chlorine absorption is observed. Alternatively, based on calculated mass balance, predetermined amounts of solid aluminum, solid sodium chloride, and chlorine-containing gas can be used in the method. In continuous or semi-continuous operation, predetermined amounts of solid aluminum, solid sodium chloride, and chlorine-containing gas can be introduced into the process while sodium aluminum tetrachloride is continuously or intermittently withdrawn from the reactor to maintain the required liquid level inside the reactor.

[0042] This method is carried out under anhydrous and anaerobic atmosphere. For the avoidance of doubt, the term "anaerobic atmosphere" as used herein refers to an atmosphere containing less than 1 vol% oxygen. The method is operated under an anaerobic atmosphere to prevent oxidation reactions, such as the oxidation of aluminum. For the avoidance of doubt, the term "anhydrous" as used herein refers to an atmosphere containing less than 1 wt.% water, preferably less than 0.5 wt.%, more preferably less than 0.1 wt.%. Anhydrous conditions are also crucial for preventing the reaction of sodium tetrachloroaluminate and the intermediate anhydrous aluminum trichloroaluminate with water. Therefore, the solid sodium chloride should be dry (with a maximum water content of 1 wt.%, preferably a maximum of 0.5 wt.%, more preferably a maximum of 0.1 wt.%). The anhydrous conditions and anaerobic atmosphere required for this method can be obtained, for example, by purging the reactor with an inert gas (e.g., nitrogen, argon, or helium) before the first feeding stage. Water removal can be enhanced by heating the reactor to the temperature used in the first feeding stage and / or evacuating the reactor to a pressure below atmospheric pressure.

[0043] exist Figure 1A preferred embodiment of the method of the present invention is illustrated herein. Here: A is a reactor, B is a purification section, and C is a scrubber. In this method, liquid sodium tetrachloroaluminate is added via 1, solid aluminum via 2, and solid sodium chloride via 3 to reactor A. Reactor A is heated to a temperature between 240-270°C and evacuated while the resulting liquid reaction mixture is gently stirred. Chlorine gas is fed into reactor A via 5, and the stirring speed is increased so that the chlorine gas is drawn into the liquid reaction mixture. If necessary, the reactor temperature is maintained by heating and / or cooling the reactor walls and / or internal coils, or by a heat exchange device (not shown) installed in the reactor circulation loop. When no further chlorine absorption is observed, the chlorine feeding is stopped, and nitrogen gas is fed into reactor A via 4. The displaced chlorine gas is removed from reactor A and fed into scrubber C via 7. At least a portion of the molten sodium tetrachloroaluminate is discharged from reactor A and fed into purification section B via 6, where it is purified into a high-purity sodium tetrachloroaluminate product.

[0044] Sodium aluminum tetrachloroacetate produced by the method of this invention can be used in batteries. For example, as an electrolyte in melt metal halide batteries, including batteries used in zero-emission battery research activities.

[0045] It is worth noting that the various elements of the present invention, including but not limited to preferred ranges of various parameters, can be used in combination unless they are mutually exclusive.

[0046] The present invention will be illustrated by the following embodiments, but is not limited thereto or restricted thereto. Example

[0047] Example 1: Preparation of sodium tetrachloroaluminate from aluminum, sodium chloride and chlorine in one step A 0.5-liter reactor was filled with 96.3 g NaCl (>99.9%, dried at 700°C for 15 hours) and 44.5 g Al (Sigma Aldrich, granular, <1 mm, 99.7%, based on trace metals). The reactor was heated to 240°C and evacuated to 15 mbar. 242.8 g NaAlCl4 (obtained via the experimental procedure described in US 2017 / 0050860 A1) was heated to 240°C in a metering vessel and then transferred to the reactor. The reactor was heated to 260°C and evacuated while the mixture was gently stirred with a hollow-shaft impeller. After shutting off the vacuum pump circuit, the reactor was pressurized to 3 bar with chlorine gas. The impeller speed was increased to 1100 rpm, and chlorine gas was introduced into the reaction mixture via a self-priming impeller. Chlorine feed was pressure-controlled, and the flow rate was monitored throughout the reaction time. After 100 minutes, the reactor pressure was increased to 5 bar, thereby increasing the chlorine absorption. The reaction temperature was maintained between 260 and 270°C by cooling the reactor walls. After 2.5 hours, the reaction was stopped as no further chlorine absorption was observed. The molten product was discharged from the reactor, and 535.9 g of NaAlCl4 product was recovered. The amount of material remaining on the reactor walls was not quantified.

[0048] Based on mass balance, the theoretical chlorine absorption based on aluminum was calculated to be 175.4 g, and the theoretical yield of NaAlCl4 product was calculated to be 558.9 g. The actual measured product discharged from the reactor was 535.9 g, resulting in an overall yield of 96%.

[0049] The minimum Al conversion rate was calculated by attributing the difference between the theoretical and actual product weight (i.e., 23 g NaAlCl4) to incomplete chlorine absorption, using the following formula: (Theoretical chlorine absorption – Theoretical product yield + Actual measured product yield) / Theoretical chlorine absorption. In this example, the calculated minimum total Al conversion rate was 87%. This is a minimum value because it does not account for material remaining on the reactor wall or material lost through the gas phase.

[0050] This embodiment demonstrates that sodium tetrachloroaluminate can be prepared from aluminum, sodium chloride, and chlorine in a one-step process under relatively mild temperature conditions, with sufficiently high conversion and yield.

[0051] Example 2: One-step preparation of sodium tetrachloroaluminate from aluminum, sodium chloride, and chlorine (including two NaCl additions) 16.1 g of NaCl (>99.9%, dried at 700°C for 15 hours) and 15.0 g of Al (Sigma Aldrich, granular, <1 mm, 99.7%, based on trace metals) were packed into a 0.5 L reactor. The reactor was heated to 220°C and evacuated to 15 mbar. 242.8 g of NaAlCl4 (obtained via the experimental procedure described in US 2017 / 0050860 A1) was heated to 220°C in a metering vessel and then transferred to the reactor. The reactor was evacuated to 15 mbar and stirred with a hollow shaft impeller. After shutting off the vacuum pump circuit, the reactor was pressurized to 3 bar with chlorine gas. The reaction temperature was set to 250°C. After 1 hour of reaction, the chlorine feed was stopped and an additional 16.0 g of NaCl was added. The chlorine feed was restarted, and the pressure setpoint was set to 4 bar. After another hour, the reaction was stopped as no further chlorine absorption was observed. During the reaction, the cumulative chlorine absorption was determined based on the measured chlorine flow rate. The cumulative chlorine absorption was 17.5 nL, corresponding to 55.5 g of chlorine. The molten product was discharged from the reactor, and 419.1 g of the reaction product was recovered.

[0052] Based on mass balance, the theoretical chlorine absorption was calculated to be 59.1 g, and the theoretical yield of NaAlCl4 product was 424.7 g. Therefore, the overall yield of this reaction was 99%.

[0053] When calculating the minimum total Al conversion rate according to the method in Example 1, the conversion rate was found to be 91%. To use a more accurate method, the Al conversion rate was calculated directly from the cumulative chlorine absorption using the following formula: Measured cumulative chlorine absorption / Theoretical chlorine absorption. Based on the cumulative chlorine absorption, the Al conversion rate was calculated to be 94%. [Note: Some fluctuations in chlorine flow rate reduced the accuracy of the cumulative chlorine absorption.]

[0054] Another method for identifying reaction products is to determine their composition.

[0055] Here, the aluminum and sodium contents of the reaction products were measured using inductively coupled plasma optical emission spectrometry (ICP-OES, Agilent 5110). Energy-dispersive X-ray fluorescence spectrometry (EDXRF; Rigaku NEXCG) was used to measure the chlorine and sodium contents. Table 1 shows the analytical results and the corresponding molar ratios that can be calculated from normalized weight percentages.

[0056] Table 1

[0057] Table 1 shows that, within the range of analytical measurement accuracy, the molar composition of the product corresponds to the molar composition of sodium tetrachloroaluminate, confirming that the obtained reaction product is indeed sodium tetrachloroaluminate.

[0058] This embodiment demonstrates that the method according to the present invention can achieve almost complete conversion to sodium tetrachloroaluminate.

[0059] Although the invention has been described with reference to exemplary embodiments, it will be appreciated that various modifications can be made within the scope of the invention.

[0060] In this specification, unless otherwise expressly stated, the word "or" refers to the operator that returns a truth value when one or both of the stated conditions are met, not the operator "XOR" that satisfies only one of the conditions. The word "contains" is used to mean "including" and not "consisting of". All existing teachings acknowledged above are incorporated herein by reference. Any reference to any previously published document in this document should not be construed as an admission or indication that such teaching was common general knowledge in Europe or elsewhere as of the date of this document.

Claims

1. A method for preparing sodium aluminum tetrachloro, the method comprising: under anhydrous conditions and an oxygen-free atmosphere: In the first feeding stage - A reactor containing sodium tetrachloroaluminate and solid aluminum, and optionally solid sodium chloride; - Heat the reactor to a temperature of approximately 150°C to approximately 400°C. This provides a reaction mixture containing liquid-phase sodium tetrachloroaluminate; During the chlorine feeding stage, the reaction mixture is contacted with chlorine-containing gas; and In an optional further feeding stage, solid aluminum and / or solid sodium chloride are added to the reactor. in, The optional further feeding stage is carried out during or alternates with the chlorine feeding stage, and solid sodium chloride is added in at least one intermediate process in the first feeding stage or the further feeding stage.

2. The method as described in claim 1, wherein, During the chlorine feeding stage, the reaction mixture is contacted with chlorine-containing gas at an absolute pressure of about 0.20 MPa to about 2 MPa, preferably about 0.25 MPa to about 1.5 MPa, and more preferably about 0.28 MPa to about 1 MPa.

3. The method as claimed in claim 1 or claim 2, wherein, During the first feeding stage, the reactor is evacuated to an absolute pressure below about 5000 Pa, preferably below about 3000 Pa, more preferably below about 2000 Pa, and even more preferably below about 1500 Pa.

4. The method as described in any of the preceding claims, wherein, In the first feeding stage, the reactor is heated to about 200°C to about 350°C, preferably about 220°C to about 320°C, more preferably about 230°C to about 300°C.

5. The method as described in any of the preceding claims, wherein, The solid aluminum is added to the process in the form of aluminum powder, which has a particle size distribution of 300 micrometers to 3000 micrometers, preferably 500 micrometers to 2000 micrometers, and more preferably 500 micrometers to 1500 micrometers, as determined by dry sieving according to ISO 4497.

6. The method as described in any of the preceding claims, wherein, The total solids concentration of the reaction mixture provided in the first feeding stage in the liquid phase of sodium tetrachloroaluminate is 3 to 40 vol%, preferably 5 to 40 vol%, more preferably 5 to 35 vol%.

7. The method as described in any of the preceding claims, wherein, The molar ratio of the total amount of solid sodium chloride and solid aluminum used in this method is 0.8:1.2 to 1.2:0.8, preferably 0.9:1.1 to 1.1:0.9, and more preferably 0.95:1.05 to 1.05:0.

95.

8. The method as described in any of the preceding claims, further comprising: In an optional purging phase, chlorine-containing gases are removed from the reactor; and During the recovery phase, at least a portion of sodium tetrachloroaluminate is discharged from the reactor.

9. The method of claim 8, wherein, The recycling phase is carried out at a temperature of about 150°C to about 400°C, preferably about 160°C to about 350°C, and more preferably about 160°C to about 250°C.

10. The method of claim 8 or claim 9, wherein, During the recovery phase, at least 10 wt.% of the total sodium tetrachloroaluminate, preferably at least 25 wt.%, and more preferably at least 40 wt.% is retained in the reactor for the first feeding phase.

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