process

Abstract

Metal carbonate (M(CO3) x ) to metal bicarbonate (M(HCO3) y A continuous process for at least partially converting to ), comprising supplying a composition containing a metal carbonate and a composition containing water to a reactor to form a mixture of water and metal carbonate, and optionally adding a water / metal salt solution, wherein the reactor is supplied with a gas containing carbon dioxide (CO2) under high pressure.

Description

[Technical Field]

[0001] This invention relates to a process for the continuous bicarbonation of metal salts. This process is particularly useful for the production of lithium bicarbonate. [Background technology]

[0002] Lithium salts (such as LiPF6) are used in batteries, such as commercial rechargeable batteries, where their high solubility in non-aqueous polar solvents is a key application.

[0003] Lithium salts are used as precursors for lithium compounds (such as LiPF6) used in lithium-ion batteries. Lithium bicarbonate (LiHCO3) is typically used as a precursor compound because it has higher solubility in water than other salts such as lithium carbonate (Li2CO3) and can be safely transported in aqueous solutions. Other salts with lower solubility require larger transport containers, making their transport less economical.

[0004] Currently, lithium bicarbonate is generally produced by carbonation using CO2 in an aqueous environment within a reactor.

[0005] The following reactions: [ka] This process generates a solution of lithium bicarbonate.

[0006] The bicarbonation reaction is slightly exothermic.

[0007] The process may be batch-based. These batch processes are often inefficient because they are operated at low CO2 pressures.

[0008] There are also continuous manufacturing processes. In the continuous manufacturing processes currently in use, a mixture of water and lithium carbonate is typically introduced into the reactor along with a carbon dioxide source (often aerated by passing a lithium carbonate solution through it).

[0009] This can be difficult because lithium carbonate's initial solubility in water is lower than that of other lithium salts. Lithium carbonate is more solubility in water at low temperatures.

[0010] Since lithium carbonate is more soluble at lower temperatures, the reactor is usually cooled. Carbon dioxide can be recycled.

[0011] Current continuous manufacturing processes do not achieve rapid CO2 dissolution. This has negative consequences because the slow dissolution of CO2 limits the conversion from lithium carbonate to lithium bicarbonate. The utilization efficiency of carbon dioxide can be as low as 30% to 40%. To solve the problem of low conversion rates, large-scale batch reactors are required for industrial-scale production. However, even these large reactors (and associated equipment) are typically complex and have high system operating costs.

[0012] Therefore, an improved method for producing lithium bicarbonate is needed. [Overview of the Initiative]

[0013] According to the present invention, metal carbonate (M(CO3) x ) to metal bicarbonate (M(HCO3) y A sequence of processes is provided to convert at least partially to ), and this process is A composition containing a metal carbonate and a composition containing water are supplied to a reactor to form a mixture of water and metal carbonate. This includes optionally adding a water / metal salt solution. Here, the reactor is supplied with a gas containing carbon dioxide (CO2) under high pressure.

[0014] The process of the present invention has been found to achieve a high conversion rate of metal carbonates. The conversion has also been found to occur rapidly. This is thought to be (at least in part) due to improved CO2 dissolution in the process of the present invention. These factors contribute to the advantage that a smaller reactor (compared to the prior art) is required to carry out the process of the present invention.

[0015] Generally, metal carbonates are either lithium carbonate or contain lithium carbonate.

[0016] Preferably, the reactor includes a plug flow reactor (PFR).

[0017] Preferably, the process of the present invention uses parallel flow through a reactor. Since the reaction in the process of the present invention has been found to proceed rapidly and with a high conversion rate, it has been found that the bicarbonation reaction can occur in piping. This eliminates the need for reaction vessels with the pressure ratings required for existing batch / continuous processes.

[0018] The reactor is preferably lined with an elastic material (such as PTFE). The lining is used to avoid (or at least mitigate) metallic contamination of the metal (lithium) bicarbonate and downstream products (e.g., from the reactor). In this regard, avoiding contamination is important not only for the purity of the product but also to ensure that downstream steps (e.g., further processing such as fluorination of the metal bicarbonate) proceed as intended. Further processing such as fluorination of the metal bicarbonate has been found to be adversely affected by metallic contamination.

[0019] Either a single reactor or multiple reactors can be used. When using multiple reactors, they may be connected in series, in which case the output from one reactor is fed to subsequent reactors in the series. When using multiple reactors, it is possible to introduce process steps between two (or more) reactors. As an example, there may be a heating / cooling mechanism such as a heat exchanger (referenced below to provide cooling) between the reactors. (Alternatively and / or additionally, one or more of the multiple reactors may have their own cooling mechanism).

[0020] The total residence time through the reactor / series of reactors is from about 5 seconds to about 5 minutes, for example from about 1 minute to about 4 minutes, for example about 3 minutes. Here, it can be seen that the residence time depends on several factors such as the concentration of the reactants, sparging, scale of the reaction, shear rate, etc. For example, a longer residence time may be required for the formation of large bubbles.

[0021] Normally, the product metal bicarbonate is in the form of a salt solution.

[0022] The metal bicarbonate solution is preferably withdrawn from the final reactor and transferred to a storage tank.

[0023] Optionally, there may be a purification step. As an example, unwanted metal ions (e.g., Mg 2+ and / or Ca 2+ ) and their salts may be removed. A preferred form of ion removal is ion exchange. The bicarbonate solution has been found to maintain a stable state. (Compared to the bicarbonation step, even though the pressure is usually reduced), unreacted metal carbonate (M(CO3) x / Li2CO3) remains in solution and has been found not to precipitate for several days. Furthermore, it has been found that there is little or no decarbonation / back reaction with respect to the metal carbonate.

[0024] The addition of any metal salt solution functions as a dilution step for diluting the mixture of water and metal carbonate. The diluting salt preferably does not participate in the metal bicarbonate formation reaction. In other words, the diluting salt is preferably inert insofar as the metal bicarbonate formation reaction is concerned. To minimize the size of the slurry tank / continuous slurry mixer, a high initial metal carbonate (M(CO3) x ) concentration is used, so it is preferable to use a diluting salt. This high initial metal carbonate (M(CO3) x ) concentration may result in the formation of metal bicarbonate (M(HCO3) y ) that exceeds the solubility limit of metal bicarbonate (M(HCO3) y ). The diluting salt is used to dilute the slurry to the desired (maximum) bicarbonate concentration.

[0025] As an alternative, pure water may be used to achieve the required metal (lithium) bicarbonate concentration. Thus, in an alternative method, instead of optionally adding a solution of a metal salt, water may be optionally added.

[0026] The diluting salt preferably contains a metal salt similar / identical to the metal carbonate. For example, when the metal carbonate contains lithium carbonate, the diluting salt contains a lithium salt. Preferably, the metal diluting salt contains a metal halide such as a metal fluoride salt. In fact, the diluting salt solution is preferably obtained from a downstream step (such as further treatment such as fluorination of metal bicarbonate). Thus, the diluting salt preferably contains lithium fluoride (LiF). The diluting salt solution can also have the advantage of precipitating unwanted ions such as Ca 2+ and / or Mg 2+ . These can be removed by filtration before ion exchange. In this regard, in a preferred embodiment where the diluting salt contains lithium fluoride, it has been found that unwanted ions such as Ca 2+ and / or Mg 2+ precipitate as their respective fluorides.

[0027] The initial (pre-dilution) concentration of the metal carbonate is preferably in the range of 0.1 to 500 g / L, more preferably in the range of 120 to 240 g / L (1.6 to 3.3 moles). The (post-dilution) concentration of the metal bicarbonate is a maximum of 75 g / L (maximum of 1.2 moles). The concentration of the metal diluent is preferably about 0.1 to 2 g / L, more preferably about 1.5 g / L (about 0.06 moles).

[0028] A gas preferably containing carbon dioxide (CO2) (preferably substantially containing CO2) is applied at a pressure of 0.1 to 100 barg, more preferably 5 to 10 barg.

[0029] Metal carbonate (M(CO3) x To achieve carbonation, the amount of carbon dioxide (CO2)-containing gas supplied to the reactor is preferably at least stoichiometric / equomolar, and more preferably an excess of carbon dioxide (CO2). At least a portion of the carbon dioxide (CO2)-containing gas is preferably recovered from and / or recycled back into the reactor.

[0030] Generally, gases containing carbon dioxide are supplied to the reactor by injection via a gas injector. The gas injector is preferably positioned below the expected level of liquid in the reactor so that the gas containing carbon dioxide is introduced into the reaction mixture in the form of bubbles / microbubbles. Each reactor may have a single gas injector or multiple gas injectors. If there are multiple reactors, each reactor may have a different number of injectors and / or different injector properties. Excessive gas diffusion may be mitigated / prevented by using an appropriate mixer, such as an in-line mixer.

[0031] If there are multiple gas injectors, these injectors / each injector may be different from one another. For example, each injector may have its own mass flow control to optimize the gas / liquid ratio.

[0032] The gas injector is preferably in the form of a gas spagger. A preferred example of a gas spagger is a sintered metal gas spagger. These may be optimized to generate the required outlet velocity of fine gas bubbles.

[0033] Since the bicarbonation reaction is slightly exothermic, the reactor is preferably cooled. The reactor is preferably cooled to below 30°C, more preferably below 20°C. If the temperature is higher, the metal carbonate (M(CO3) x Problems may arise with the precipitation of ). Cooling is preferably carried out by standard cooling methods such as the use of a heat exchanger. In addition, by employing pressurized CO2 injection, this process benefits from the Joule-Thomson effect of cooling.

[0034] Generally, the conversion of metal carbonates is at least partial. Preferably, the conversion of metal carbonates is carried out so that all of the metal carbonate supplied to the reactor is converted to at least a soluble form (i.e., not in the form of a suspension / slurry). If complete dissolution (confirmed by means such as turbidity analysis) is not achieved, the product solution can be returned to the reactor for further carbonation steps. [Examples]

[0035] Example 1 - Lithium bicarbonate (LiHCO) 3 Preparation of ) - Laboratory-scale example Lithium carbonate powder was added to 25 L of demineralized water (or mother liquor from the LiF process, saturated with LiF at a concentration of approximately 1.3 g / L) in a plastic container to create a slurry containing 40-60 g / L of Li2CO3.

[0036] The slurry was mixed using a standard overhead stirrer with a coated impeller to dissolve Li2CO3 to its solubility limit (approximately 13 g / L).

[0037] Next, the Li2CO3 slurry was pumped by a diaphragm pump at a discharge pressure of 8 barg and delivered to the plug flow reactor (PFR) at a flow rate of 1 L / min, as measured by an in-line rotometer.

[0038] There were three PFRs connected in series. Each PFR contained a 30m long PFA tube with an ID of 1 / 4 inch.

[0039] At the beginning of each PFR, there was a CO2 injection point containing a T-piece and a sintered nozzle with a pore size of 2 microns.

[0040] CO2 was supplied from a compressed gas cylinder adjusted to 8.5-9 barg. The minimum total CO2 addition rate was 16 g / min at 40 g / L and 28 g / min at 60 g / L, controlled by in-line mass flow control. The CO2 addition rate at each injection point could be controlled independently.

[0041] The total residence time was approximately 3 minutes, after which complete dissolution of Li2CO3 was observed. This was visually apparent. The concentration was measured by conductivity and IC.

[0042] After passing through multiple PFRs, the solution passed through a back pressure controller that maintained the system back pressure at 6 barg. The pressure drop throughout the entire process was approximately 2 bar.

[0043] The bicarbonate solution was then collected in 25L bottles and stored.

[0044] Because the level of impurities in the Li2CO3 powder was very low, no precipitated impurities were observed. To evaluate the IX performance, another experiment was performed using the administered impurities.

[0045] The bicarbonate solution (up to 60 g / L) was found to remain stable. Residual Li2CO3 remained in the solution and did not precipitate for several days despite a decrease in pressure. This allows the bicarbonate solution to be stored in atmospheric pressure storage tanks for downstream processing steps, eliminating the need for more expensive pressure vessels.

Claims

1. Metal carbonate (M(CO) ３ ) ｘ ) and metal bicarbonate (M(HCO) ３ ) ｙ A sequential process that converts to at least partially ) A composition containing a metal carbonate and a composition containing water are supplied to a reactor to form a mixture of water and metal carbonate, This includes optionally adding a water / metal salt solution. The reactor contains carbon dioxide (CO2) under high pressure. ２ A continuous process supplied with a gas containing ).

2. The process according to claim 1, wherein the metal carbonate is lithium carbonate or comprises lithium carbonate.

3. The process according to claim 1 or 2, wherein the reactor includes a plug flow reactor (PFR).

4. The process according to any one of claims 1, 2, or 3, wherein a single reactor is used or a plurality of reactors are used.

5. The process according to claim 4, wherein if multiple reactors are used, they are connected in series.

6. The process according to any one of claims 1 to 5, wherein the total residence time through the reactor / series of reactors is approximately 3 minutes.

7. The process according to any one of claims 1 to 6, wherein the metal bicarbonate solution is withdrawn from the final reactor and transferred to a storage tank.

8. The process according to any one of claims 1 to 7, wherein the initial (pre-dilution) concentration of the metal carbonate is in the range of 120 to 240 g / L (1.6 to 3.3 moles).

9. The aforementioned carbon dioxide (CO2) ２ The process according to any one of claims 1 to 8, wherein the gas containing ) is applied at a pressure of 5 to 10 barg.

10. The process according to any one of claims 1 to 9, wherein the gas containing carbon dioxide is applied to the reactor by injection via a gas injector.

11. The process according to any one of claims 1 to 10, wherein the reactor is cooled to below 20°C.

12. A metal bicarbonate produced by the process described in any one of claims 1 to 11.

Images