Process for obtaining a dry retentate without external contamination

Abstract

The present invention relates to a method for obtaining a dry retentate from a liquid to be filtered comprising solid particles. The method comprises filtering said liquid to be filtered through a filter (2) comprising a filter medium (21) to obtain a retentate, and drying said retentate to obtain a dry retentate. This drying step (13) is carried out inside said filter (2). For the abstract: Figure 2

Description

Title of the invention: Process for obtaining a dry retentate without external contamination technical field

[0001] The present invention relates to the field of filtration processes and devices, in particular filtration for obtaining a retentate.

[0002] The present invention relates more particularly to a filtration process configured to limit the oxidation of the retentate before its drying, or more generally its contamination by an external atmosphere.

[0003] The present invention will thus find many advantageous applications in many industries, in particular the chemical and hydrometallurgical industries.

[0004] The present invention will find particularly advantageous applications in the manufacture of precursors of active cathode materials. Previous art

[0005] Filtration processes commonly aim to obtain two products from a fluid to be filtered: on the one hand, the filtrate, corresponding to the fluid separated from its particles, impurities, or other matter, which have been retained by the filter; on the other hand, the retentate, corresponding to these same particles retained by the filter. Depending on the fluid considered and the purpose of the filtration process, the finished product may correspond to the filtrate, the retentate, or both separated products.

[0006] In certain industries, particularly in chemicals and hydrometallurgy, the retentate may be a relatively unstable product, which is sensitive to the external atmosphere. The retentate is, for example, sensitive to oxidation.

[0007] It is thus known to conduct chemical reactions such as filtration in a controlled atmosphere, for example a nitrogen atmosphere, so as to prevent oxidation of the retentate.

[0008] It is also known to dry the retentate after filtration. Once dry, the retentate is less sensitive to the external atmosphere and can be exposed with reduced risk. Industrial processes therefore employ drying machines configured to dry the retentate.

[0009] However, transferring the retentate to a drying machine requires its exposure to the outside atmosphere, during which the wet retentate is highly susceptible to contamination, particularly oxidation. This transfer is therefore complex, and protecting the retentate during the transfer would require placing the entire industrial installation under a controlled atmosphere, for example under nitrogen, which is impractical.

[0010] The Applicant therefore submits that there is currently no satisfactory alternative solution for obtaining a dry retentate, without the drying of this same retentate exposing it to external contamination. Summary of the invention

[0011] The present invention aims to improve the current situation described above.

[0012] The present invention is more particularly aimed at overcoming the following drawbacks: above by proposing a process for obtaining a dry retentate without contamination from the outside atmosphere.

[0013] To this end, the object of the present invention relates in a first aspect to a process for obtaining a dry retentate from a liquid to be filtered comprising solid particles, the process comprising the following steps: - filtration of the liquid to be filtered through a filter comprising a filtration medium, so as to obtain a retentate; and - drying of the retentate, so as to obtain a dry retentate.

[0014] It is understood here that the retentate corresponds to the finished product of the process. In other filtration processes, the finished product corresponds to the filtrate, that is, the liquid to be filtered, purified of solid particles. The techniques associated with such processes can therefore alter the retentate and are generally not suitable.

[0015] As stated previously, it is understood that the filtration and drying steps are, as such, known to those skilled in the art. Filtration corresponds to the use of the filter as such, with the retentate accumulating on the filter medium and the filtrate passing through the filter medium. Filtration thus comprises the passage of the liquid to be filtered through the filter, such that a filtrate passes through the filter medium and the retentate accumulates on the filter medium. This is sometimes referred to as the formation of a retentate cake. The filter comprises, for example, a chamber with a liquid inlet and a liquid outlet, arranged on either side of the filter medium, so as to allow the passage of the liquid to be filtered.

[0016] Once the retentate has been obtained by filtration, drying makes it possible to obtain a dry retentate, free of liquid, and less sensitive to contamination by the outside atmosphere, in particular to oxidation.

[0017] Advantageously, the drying step is carried out inside the filter.

[0018] In other words, drying is carried out "in situ," without removing the retentate from the filter. In particular, drying is performed by maintaining the inside of the filter under a controlled atmosphere, for example, by injecting a specific gas. This design thus avoids exposing the retentate to the outside atmosphere and preserves its purity until it is sufficiently dry to eliminate or reduce the associated risks. to its exposure. Keeping the retentate in the filter greatly simplifies environmental control, allowing the retentate to be maintained in a controlled atmosphere without interruption until it is completely dry. For example, the retentate is constantly protected from oxygen until it dries, after which the dry retentate is more resistant to oxidation.

[0019] Those skilled in the art also understand that energy consumption and logistical requirements related to drying are reduced by eliminating the transfer of the retentate between the filter and a drying machine. Since the drying of the retentate in the filter may differ from its drying inside a dedicated machine, comparing the energy consumption of the process according to the present invention with that of traditional processes remains complex.

[0020] Thanks to the present invention, it is therefore possible to obtain a dry retentate of greater purity, without requiring a complex installation between a filter and a retentate drying machine.

[0021] In an advantageous embodiment of the present invention, the dry retentate corresponds to a precursor of cathode active material.

[0022] The Applicant submits that the process according to the present invention is particularly advantageous for obtaining precursors of cathode active materials, also called pCAMs (from the English "Precursors of Cathode Active Materials"). A cathode active material, also called a CAM (from the English "Cathode Active Material"), comprises grains of transition metal oxides, for example, nickel, cobalt, and manganese. Similarly, a precursor of this active material comprises grains of mixed hydroxides of these metals, therefore, in the same example, nickel, cobalt, and manganese.

[0023] A process for manufacturing pCAM thus comprises dissolving metals, which are supplied in the form of various salts, most often sulfates, but also chlorides, carbonates, etc. The mixing of the salts, in precise proportions, forms insoluble hydroxides by coprecipitation. A mother liquor is then obtained, comprising a suspension of mixed hydroxide grains of the desired metals. The mother liquor thus corresponds to the liquid to be filtered according to the present invention. Similarly, the mixed hydroxide grains correspond to the solid particles according to the present invention.

[0024] These mixed hydroxide grains must not form metal oxides and must therefore be protected from atmospheric oxygen. The coprecipitation reaction is thus carried out under a controlled atmosphere, preferably under a nitrogen atmosphere.

[0025] It is thus known to filter the mother liquor using a filter press. Such a filter press advantageously allows in situ rinsing of the retentate after its formation, of in order to eliminate traces of the mother liquor, and as described below. Other variations employ a vacuum belt filter or a disc filter.

[0026] However, the wet retentate is particularly sensitive to oxidation, as stated above, and the transfer of the retentate to a drying machine is particularly complex.

[0027] The use of the process according to the invention thus makes it possible to obtain a dry pCAM retentate, minimizing its oxidation and without requiring complex transfer to a drying machine. Once dry, the pCAM is more resistant to oxidation and no longer needs to be protected to the same extent. Obviously, the process according to the invention can also include other finishing treatments on the dry retentate to obtain the precursor of the active cathode material. The process according to the invention can also be integrated into a larger process, for example, a process for obtaining CAM, in which the pCAM corresponds to an intermediate product.

[0028] In one embodiment, the filter corresponds to a spark plug filter.

[0029] Advantageously, the candle filter comprises a housing containing a plurality of tubes having a porous wall and forming the filtration medium, the tubes having a first end equipped with means for extracting a filtrate from the liquid and a second end sealed, the filtration and drying steps being carried out inside the housing.

[0030] Those skilled in the art understand that, in a candle filter, also called a candle filter, the tubes correspond to the candles of the filter. During filtration, the liquid to be filtered passes through the porous wall of the tubes, and the retentate accumulates around them. Drying is advantageously carried out so that the retentate remains around the tubes and is only discharged after drying.

[0031] The tubes are, for example, arranged to extend substantially vertically, with the first end corresponding to the upper end of the tubes and the second end to the lower end of the tubes. The tubes are, for example, connected to each other at their first end by a tube sheet, by tubing, or by any other means enabling the tubes to be connected to each other and the inside of the tubes to be communicated with means for extracting the filtrate. The tube sheet or the tubing correspond, for example, to the means for extracting the filtrate. The sealing of the second end serves exclusively to prevent the liquid from entering the tube without passing through the porous wall. A second end can, for example, also be porous and also form the filtration medium.

[0032] It is also understood that the enclosure of the candle filter defines the interior of the filter, forming a restricted space whose internal atmosphere can be controlled without great difficulty.

[0033] A candle filter advantageously has a compact structure, especially compared to a filter press, and requires less energy during the filtration phase, because the differential filtration pressure, and therefore the pressure under which the liquid to be filtered is put, is lower.

[0034] The Applicant further submits that, in the context of obtaining pCAM, the use of candle filters is not known in the prior art.

[0035] The conventional operation of a candle filter comprises the following steps: - filtration, by introducing the liquid to be filtered into the filter housing, outside the tubes, so that the liquid enters the tubes via the porous wall and the solid particles are retained on the external surface of the tubes, forming the retentate; - separation of the retentate, by introducing a reverse flow of liquid, i.e., by introducing liquid into the tubes so that the liquid exits via the porous wall, separating the retentate from the tubes, which collects in the lower portion of the housing by sedimentation; and - unloading of the retentate, by opening a discharge orifice in the lower portion of the filter.

[0036] A person skilled in the art will thus understand that the process according to the present invention includes, for example, the same filtration step. In particular, the candle filter has at least one inlet for the liquid to be filtered in communication with the outside of the tubes, and one outlet for the liquid to be filtered in communication with the inside of the tubes. Furthermore, before the retentate is discharged, the process according to the present invention advantageously includes a retentate drying step. As stated below, the retentate is preferably dried before its separation, so that the retentate remains on the tubes and dries more easily.

[0037] It is also understood that the fluid flow is determined so that the retentate accumulates around the tubes, in order to facilitate its separation, and that the filter is advantageously oriented so that the tubes extend vertically and the retentate separates by falling towards a bottom of the filter.

[0038] Preferably, the porous wall comprises a perforated surface covered with a polytetrafluoroethylene, or PTFE, membrane.

[0039] The Applicant submits that a PTFE membrane greatly improves filtration fineness by using a membrane with very fine porosity, and thus increases the amount of retentate obtained. Furthermore, while it is known to equip tubes with a membrane to form the candle, filtration fineness is generally improved by adding a fibrous foreign substance, such as cellulose, to the liquid to be filtered. This fibrous substance then accumulates on the membrane and forms a pre-layer, improving the filtration quality. However, when the end product of filtration is the retentate, this technique cannot be This is because the pre-coating mixes with the retentate and denatures it. Using a PTFE membrane thus makes it possible to obtain the same filtration fineness as pre-coating techniques, while preserving the retentate.

[0040] In an additional embodiment, the process further includes a step of rinsing the retentate inside the filter, so as to obtain a wet retentate, the drying step being carried out on the wet retentate.

[0041] Preferably, the rinsing step includes passing a rinsing liquid, separate from the liquid to be filtered, through the filter so that the rinsing liquid passes through the filtering medium.

[0042] It is understood here that rinsing makes it possible to eliminate all traces of the liquid to be filtered from the retentate, particularly when such a liquid is more difficult to remove by drying. The rinsing liquid corresponds, for example, to demineralized water, so as to avoid any reaction with the retentate. Furthermore, as stated previously, it is known to implement rinsing the retentate in a filter press. In a candle filter as described above, or in other filters, it is possible to implement such rinsing by providing an identical passage between the rinsing liquid and the liquid to be filtered, for example via a common inlet and outlet for the rinsing liquid and the liquid to be filtered. In particular, and as described below, it is possible to follow the filtration step with rinsing, without separating the retentate from the filter medium.

[0043] Preferably, the rinsing step includes recycling the rinsing liquid so as to circulate in a loop through the filter.

[0044] It is understood that this design allows for at least partial savings on the rinse aid. It remains necessary to recycle the rinse aid when the concentration of soluble substances in the rinse aid is too high. Such recycling can be implemented using various techniques known to those skilled in the art, for example, reverse osmosis. For instance, an assessment of the rinse aid's condition is planned before its recirculation or recycling, for example, by measuring the rinse aid's conductivity.

[0045] In an embodiment that can be combined with the previous embodiment, the drying includes the passage of a drying gas through the filter, so that the drying gas circulates through the retentate and the filtration medium and removes the moisture from the retentate.

[0046] It is understood here that the drying gas is selected so as to provide a controlled atmosphere in the filter, in order not to denature the retentate. The drying gas corresponds, for example, to dry nitrogen, preferably heated.

[0047] It is understood here that the circulation of the drying gas through the filtration medium results in its circulation through the retentate, so as to carry away the water which is there and remove it.

[0048] The Applicant submits that such a drying step can last up to an hour, or even longer depending on the thickness of the retentate. When the retentate dries, it contracts and cracks. The Applicant further submits that the thickness of the retentate, i.e., the amount of liquid to be filtered per filter operation, must be controlled, because excessive thickness results in the retentate detaching from the filter medium before or during drying, thus reducing its efficiency, since the gas can then bypass the retentate and pass through the filter medium. For example, an evaluation of the drying efficiency is planned to control its duration and proper functioning, for example, by measuring the humidity of the outgoing gas.

[0049] Preferably, the process further includes a transition step before drying, the transition including an introduction of the drying gas so as to expel any liquid from the filter.

[0050] It is understood here that this design makes it possible to maintain a constant flow against the retentate, so as to ensure that it remains against the filter medium, and so as to ensure that the retentate atmosphere remains controlled. The introduction of the drying gas also allows the liquid to be gradually removed. The liquid here corresponds alternatively to the liquid to be filtered or, if the process includes a rinsing step, to the rinsing liquid. "Removing all liquid from the filter" means removing the liquid from the filter, excluding the liquid from the retentate, the subsequent drying step then corresponding to removing the liquid from the retentate. In other words, the transition corresponds to a change from a filter atmosphere consisting of liquid to an atmosphere consisting of gas.

[0051] It is also understood that the liquid discharge depends on the filter design, particularly the outlets arranged on the filter. For example, the liquid is first discharged from below, lowering the liquid level in the filter before the filter medium, and then from above, after the filter medium. In a candle filter as described above, the liquid is thus discharged from below, for example through its initial inlet, and then from above, i.e., through the candles and above or through the filtrate extraction means, i.e., the tube sheet or the tubing. This design therefore requires a gas inlet separate from the liquid inlet, so as to allow the liquid to be discharged through this same inlet.

[0052] A person skilled in the art understands that this transition step is delicate and must be carried out with increased supervision, because the retentate must remain stuck to the filtration medium without separating, and must not be disturbed during the drop in liquid level.

[0053] In yet another embodiment, the drying includes vacuuming the filter so as to remove moisture from the retentate.

[0054] It is understood here that vacuum sealing is implemented following or replacing the introduction of the drying gas. Obviously, such vacuum sealing does not result in any contamination of the retentate, regardless of the retentate's composition. Vacuum sealing thus generates suction on and within the retentate in order to remove the moisture from the retentate.

[0055] A person skilled in the art also understands that the vacuuming must be carried out with great care to avoid separation of the retentate, in particular its falling when the retentate is suspended. The vacuuming also facilitates subsequent separation of the retentate, notably as described later, the introduction of a new fluid breaking the vacuum and causing an impulse that facilitates the separation of the retentate.

[0056] In an additional embodiment, the filtration step defines a first flow through the filtration medium and the drying step defines a third flow through the filtration medium, the first and third flows having a similar direction.

[0057] In addition, the rinsing step, if present, defines a second flow through the filtration medium, the first, second and third flows having a similar direction.

[0058] The third flow can correspond to the drying gas flow as described above and / or to a suction flow allowing the filter to be placed under vacuum.

[0059] It is understood here that maintaining a continuous flow through the filter medium helps to keep the retentate in place and prevents its premature separation from the filter medium. The flows thus have the same direction, that is, they pass through the filter medium in the same direction, so as to exert continuous pressure on the retentate. Advantageously, the flows also have similar or proportional flow rates, so as to exert a similar pressure on the retentate. It is further understood that the orientation of the first flow defines the disposition of the retentate with respect to the filter medium, the subsequent flows being constrained by this disposition.

[0060] Additionally, it is also possible for the drying gas to exit on either side of the filter. For example, it is anticipated that some of the drying gas will never pass through the filter medium and will simply flow along the retentate. Furthermore, if the retentate is suspended, the drying process naturally results in the formation of droplets that flow by gravity, which do not necessarily pass through the filter medium depending on its arrangement. The direction stated above thus corresponds to the direction of the flows through the filter medium, although other flows that do not pass through the filter medium are also possible.

[0061] In another embodiment that can be combined with the preceding embodiments, the process further includes a dry retentate unloading step configured to separate the dry retentate from the filtration medium.

[0062] It is understood here that the retentate discharge includes the separation of the retentate as described above. In particular, compared to the conventional operation of a candle filter as described above, the retentate discharge step according to the invention includes, for example, separation, corresponding to a dissociation between the retentate and the filter medium, and discharge as described above, corresponding to an extraction of the retentate from the filter. The retentate extraction is, for example, carried out via a discharge orifice in the lower portion of the filter, as described above, so that the retentate falls naturally out of the filter. The filter may, for example, have a conical lower portion so as to gather the retentate towards a discharge orifice with a narrowed section.Preferably, and particularly compared to the conventional operation of a candle filter, the discharge is carried out without the introduction of liquid, so as to avoid re-wetting the dry retentate.

[0063] Preferably, the unloading includes vibrating the filtering medium.

[0064] Preferably, the filtration step defines a first flow through the filtration medium, the discharge comprising a passage of a discharge fluid through the filter defining a fourth flow through the filtration medium, the fourth flow and the first flow having an opposite direction.

[0065] It is understood here that the unloading may include vibration and / or the passage of a fluid. Optionally, those skilled in the art may provide other additional means for separating the retentate from the filter medium, or for facilitating its extraction from the filter.

[0066] The discharge fluid is advantageously a gas, so as to ensure that the retentate remains dry, compared to a gas identical or similar to the drying gas. Since the retentate is dry, and therefore less susceptible to external contamination, the constraints on the discharge fluid are reduced, especially as the discharge of the retentate results in its exposure to the atmosphere outside the filter, which is a priori uncontrolled.

[0067] As stated previously, and particularly when the filter is a candle filter, it is advantageous to arrange the filter media and determine the first flow so that the retentate accumulates in suspension on the filter media, and the discharge of the retentate corresponds to a fall of the retentate towards the bottom of the filter. The retentate can then be easily extracted by opening a lower orifice, for example via a discharge valve.

[0068] In addition, vibrating the entire filter, and not just the filtering medium, advantageously allows the retentate, once separated, to slide to the bottom of the filter, preferably through the lower orifice, and facilitates its extraction.

[0069] According to a second aspect, the present invention relates to a precursor of cathode active material obtained at least partially by the process according to the first aspect of the present invention.

[0070] As stated above, a pCAM can be composed of a mixture of materials known to the person skilled in the art, for example a mixture of Nickel, Cobalt and Manganese, for example having a composition such as described in one of the documents EP 3693340 A2 or WO 2020175925 Al. The person skilled in the art understands of course that the composition of the pCAM depends on the active cathode material sought, which may correspond to a lithium cobalt oxide (LiCoO2), a lithium manganese oxide (LiMn2O4), a lithium iron phosphate (LiFePO4 or LFP) or a lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC).

[0071] Furthermore, the process according to the first aspect of the present invention may include additional finishing steps, on the dry retentate, so as to obtain the pCAM.

[0072] As stated previously, manufacturing a pCAM using the process according to the first aspect of the invention makes it possible to obtain a pCAM exhibiting very low oxidation, due to its protection from the external atmosphere until the end of its drying. The resulting pCAM thus exhibits superior quality.

[0073] According to a third aspect, the present invention relates to a cathode active material obtained from a cathode active material precursor according to the second aspect of the present invention.

[0074] According to a fourth aspect, the present invention relates to a battery, preferably a vehicle battery, comprising an active cathode material according to the third aspect of the present invention.

[0075] Thus, by the various functional and structural technical characteristics above, the Applicant proposes a process for obtaining a dry retentate which avoids any contamination of the retentate, in particular by the outside atmosphere, especially before its drying. Description of the figures

[0076] Other features and advantages of the present invention will become apparent from the description of the particular and non-limiting embodiments of the present invention below, with reference to the attached Figures 1 and 2, in which:

[0077] [Fig.1]

[0078] Fig. 1 illustrates a flowchart of the different stages of a process for obtaining a dry retentate, according to a particular and non-limiting embodiment of the present invention;

[0079] [Fig.2]

[0080] [Fig.2] schematically illustrates a cross-sectional view of a filter configured for the implementation of a process according to [Fig.1]. Detailed description

[0081] A process for obtaining a dry retentate will now be described in what follows with joint reference to Figures 1 and 2. The same elements are identified with the same reference symbols throughout the description that follows.

[0082] As indicated in the preamble to the description, filtration processes for obtaining a retentate encounter significant constraints when the wet retentate is vulnerable to the external atmosphere, and transport to a drying machine results in exposure and contamination of the retentate before it dries. In particular, precursors of active cathode materials, after filtration, are in the form of a wet retentate that is particularly susceptible to oxidation.

[0083] One of the objectives of the present invention is to propose a method for obtaining a dry retentate which allows the retentate to be preserved until it is dry, without requiring the entire installation to be placed under a controlled atmosphere.

[0084] This is made possible in the example described below, which considers a process for obtaining a pCAM, in particular process 1 of [Fig. 1]. It will be understood that the process according to the present invention can be applied to obtaining a plurality of other compounds, in particular compounds sought in the fields of chemistry and hydrometallurgy.

[0085] It is further understood that the process according to the present invention, which employs filtration, is specifically designed to obtain a retentate. While it is also possible to recover and use the filtrate obtained during the execution of this process, the process differs from filtration processes aimed at obtaining the filtrate in that the nature and quality of the retentate must be preserved.

[0086] Furthermore, the process according to the invention can be part of a broader process for obtaining a pCAM, which includes prior steps, in particular preparing the liquid to be filtered, for example by mixing salts in solution, and / or additional steps subsequent to obtaining the retentate so as to transform the retentate into a pCAM and / or make it suitable for use in obtaining a cathode active material. Similarly, the process according to the invention can be part of a a broader process for obtaining a CAM, or even a process using the CAM for subsequent purposes, particularly for the manufacture of batteries.

[0087] As illustrated in [Fig. 1], the process 1 comprises, in a first step 11, a filtration of a liquid to be filtered through a filter, preferably filter 2 of [Fig. 2]. The liquid to be filtered comprises solid particles, here a suspension of mixed hydroxide grains, corresponding to a mixture of the constituent hydroxides of pCAM, for example, nickel, cobalt, and manganese. The liquid to be filtered thus flows through filter 2, via a filtration medium 21, such that a retentate accumulates on the filtration medium 21 inside filter 2. Simultaneously, a filtrate passes through filter 2 and is discharged from filter 2. The retentate is formed from the solid particles of the liquid to be filtered, i.e., here, the mixed hydroxide grains.

[0088] In the example of [Fig. 2], filter 2 corresponds in particular to a candle filter. Filter 2 thus defines an enclosure 20 inside which a plurality of tubes are arranged, which form the candles of filter 2. The tubes have a porous wall, so as to form the filtration medium 21. Advantageously, the porous wall is formed of a perforated surface covered with a PTFE membrane, so as to perform very fine filtration. The PTFE membrane is an integral part of the filtration medium 21 and does not risk denaturing or mixing with the retentate.

[0089] Thus, during filtration, the liquid to be filtered is introduced into the filter 2 via a first inlet 23, located on one side of the filter medium. Preferably, the first inlet 23 is arranged so as to communicate with the external surface of the tubes. In this way, the liquid to be filtered passes through the tubes and the retentate accumulates on the external surface, i.e., around the tubes, inside the enclosure 20.

[0090] Furthermore, the tubes are also equipped with filtrate extraction means 22. The extraction means 22 allow the different tubes to be connected and the inside of the tubes to be communicated with a first outlet 24 of the filter 2. The tubes are, for example, directly connected to the first outlet 24 and / or connected to a distinct portion of the filter 2, for example an upper portion, which is separated from the filter medium 21 by the extraction means 22. Here, the extraction means 22 correspond to a tube plate, allowing the tubes to be connected to each other, delimiting an upper portion of the filter 2 from the lower portion comprising the filter medium 21, and communicating with the first outlet 24.

[0091] Consequently, the circulation of the liquid to be filtered defines a first flow, in which the liquid to be filtered enters through the first inlet 23, passes through the filtration medium 21 and exits, in the form of a filtrate, through the first outlet 24 via the extraction means 22. In particular, the use of a candle filter makes it possible to reduce the energy required for filtration, compared to other filters used for obtaining pCAM, in particular in comparison to a filter press commonly used in the prior art.

[0092] Once the retentate has accumulated on the filter medium 21, in a second step 12 of process 1, the retentate is rinsed inside the filter 2. Rinsing 12 thus comprises the passage of a rinsing liquid through the filter 2. The rinsing liquid is intended to remove any trace of the liquid to be filtered still present on or in the retentate. The rinsing liquid therefore corresponds to a separate fluid, which is selected so as not to react with the retentate. The rinsing liquid corresponds, for example, to mineralized water.

[0093] The circulation of the rinsing liquid thus defines a second flow. Advantageously, the second flow is similar or identical to the first flow; that is, the rinse fluid passes through the filter 2 in a manner similar to the fluid to be filtered. In particular, the second flow through the filter medium 21 is identical to the first flow through the filter medium 21. Since the first flow results in the accumulation of retentate on the filter medium, the second flow allows the rinse fluid to pass through or bypass the retentate and through the filter medium 21 without dislodging the retentate from the filter medium 21. On the contrary, the second flow at least partially ensures that the retentate remains against the filter medium 21. In other words, the circulation of the rinse fluid maintains pressure of the retentate against the filter medium 21.In the example described here, the rinsing liquid, like the liquid to be filtered, enters the filter 2 through the first inlet 23, in the lower portion of the filter 2, passes through the filtering medium 21, and exits the filter 2 through the first outlet 24 via the extraction means 22, in the upper portion of the filter 2.

[0094] Advantageously, the rinse 12 is provided to include a recycling of the rinse aid. In other words, the first outlet 24 is connected to the first inlet 23 so that the rinse aid circulates in a loop through the filter 2. The connection between the first outlet 24 and the first inlet 23 is, for example, controlled to regulate the recycling. In particular, it is understood that a rinse aid saturated with soluble substances can no longer perform its rinsing function, and that the recycling of the rinse aid is controlled according to the state of the rinse aid.

[0095] After filtration 11 and rinsing 12, a wet retentate is thus obtained on the filtration medium 21. This retentate is particularly sensitive to the external atmosphere, in particular to oxidation.

[0096] Thus, in a third step 13 of process 1, the wet retentate is dried to obtain a dry retentate. In particular, the drying 13 is here carried out inside filter 2. Since filter 2 has a small internal space, defined by enclosure 20, the atmosphere of filter 2 can thus be controlled throughout the entire drying process of the retentate. In particular, such a drying process 13 advantageously includes the passage of a drying gas 131 through filter 2. This drying gas is selected so as not to alter the retentate and to allow the removal of moisture from the retentate, and corresponds, for example, to heated dry nitrogen.

[0097] Prior to drying 13, a transition step 130 is thus provided. During the transition 130, the drying gas is introduced into the filter 2, progressively, in order to expel the liquid from the filter 2. In other words, the liquid from the previous step, in particular the rinsing liquid, is expelled from the filter 2 by the drying gas, so as to pass from one controlled environment to another.

[0098] Advantageously, the drying gas passage 131 and the transition 130 exhibit the same drying gas flow. The two stages correspond, for example, to the same control of the inlets and outlets of the filter 2, so that the circulation of the drying gas is the same and the two stages are distinguished only by the internal environment of the filter 2. In particular, the liquid is provided to be expelled from the filter 2 not only through the first outlet 24 in the upper portion, but also through the first inlet 23 in the lower portion. For example, the liquid is first expelled from below, lowering the liquid level in the filter 2 before the filter media 21, exiting through the first inlet 23, and then from above, after the filter media 21, in the upper portion, inside the tubes and the tube sheet, exiting through the first outlet 24.

[0099] In order to allow the liquid to be expelled from the filter 2 by the first inlet 23 and the first outlet 24, the drying gas is provided to enter the filter by a second inlet 25 separate from the first inlet 23.

[0100] Furthermore, during the drying stage 13, the circulation of the drying gas defines a third flow. Advantageously, this third flow through the filter medium 21 has the same direction as the first flow, so as to also maintain the retentate against the filter medium 21. A second inlet 25 is thus provided, also designed to communicate with the external surface of the tubes, i.e., formed along the lower portion of the filter 2 as described above.

[0101] According to the example in [Fig. 2], the second inlet 25 is provided just below the extraction means 22, so as to communicate with the external surface of the tubes while being positioned as high as possible on the filter 2, so that the liquid that has not passed through the filter medium 21 exits through the first inlet 23, driven out by the drying gas, and the liquid that has passed through the filter medium 21 exits through the first outlet 24, once the drying gas has passed through the filter medium 21. In other words, the filter medium 21 and / or the extraction means 22 delimit a lower portion of the filter 2, the first inlet 23 being arranged along a lower end of this lower portion, and the second inlet 25 being arranged along an upper end of this lower portion, so that the liquid level drops when the drying gas is introduced and the majority of the liquid in the lower portion exits through the first inlet 23. This design thus ensures a smooth transition between rinsing 12 and drying 13, so that the retentate does not separate from the filter medium 21.

[0102] In this same design, the drying gas also exits the filter 2 through the first outlet 24, after passing through the filter medium 21 and the retentate, in order to remove the moisture from the retentate. This means that the drying gas carries the liquid from the retentate with it and expels it from the filter 2. Furthermore, the drying of the retentate may result in partial dripping of the retentate, i.e., the formation of liquid at the bottom of the filter 2 that is not carried away by the drying gas. The arrangement of the first inlet 23 for the discharge of this liquid, at the lower end of the lower portion of the filter 2, thus allows the liquid that is not carried away by the drying gas to also be discharged.

[0103] Thus, the passage of the drying gas 131 corresponds to a circulation of the drying gas, from the second inlet 25 to the first outlet 24, passing through the retentate and the filtering medium 21, so as to carry away the moisture from the retentate and evacuate it out of the filter 2. Such an operation lasts for example about one hour, and is controlled according to the hygrometry of the drying gas at the outlet of the filter 2.

[0104] Optionally, the drying unit 13 also includes a vacuum 132 for the filter 2. Like the passage of the drying gas, the vacuum 132 allows for the absorption and removal of moisture from the retentate. A vacuum pump is thus provided, connected via a second outlet 26 in communication with an internal surface of the filter 2. It is understood here that the second outlet 26 is configured to generate suction of the liquid and / or gas in the filter, so as to create the vacuum. Thus, the vacuum, like the passage of the drying gas 131, generates a third flow as described previously, in the same direction as the first flow through the filter medium 21, so as to maintain the retentate against the filter medium 21, i.e., here from the external surface to the internal surface of the tubes.The second outlet 26 is thus arranged on the same side as the first outlet 24 with respect to the filtration medium 21 and the extraction means 22, that is to say here along an upper portion of the filter 2. According to another design, one can also imagine a vacuum pump connected directly to the first outlet 24.

[0105] Thus, implementing the drying 13 inside the filter 2 itself makes it possible to keep the retentate in a controlled atmosphere, without risk of oxidation or other contamination from the outside atmosphere, and in a more feasible way than a Atmospheric control outside the filter 2. Once the retentate has dried, it is less vulnerable and can be exposed to the outside atmosphere. In addition, the dry retentate tends to crack, which facilitates its separation from the filter media 21.

[0106] A fourth step 14 of process 1 then involves unloading the dry retentate. This fourth step 14 aims to separate the dry retentate from the filter medium 21 and extract it from the filter 2, either for direct use or for further processing, including finishing treatments to obtain pCAM.

[0107] It is understood here that, when the dry retentate is separated from the filter medium 21, the retentate naturally tends to fall to the bottom of the filter 2. The filter 2 has, for example, a conical lower wall, provided with a third outlet 27 at its lower end, which can be opened to discharge the retentate. This design is substantially similar to that of a conventional candle filter, in which the solids collect in the lower cone by sedimentation before being discharged.

[0108] Various means can be provided for separating the retentate from the filter medium and conveying it towards the third outlet 27. The unloading 14 includes, for example, a vibration 141 of the filter medium 21, so as to detach the retentate by the movement of the filter medium 21. This vibration 141 can also correspond to a vibration of the entire filter 2, in particular the lower part, so as to facilitate the fall of the retentate towards the bottom of the filter 2 and its passage through the third outlet 27.

[0109] In parallel or alternatively to the vibration 141, the unloading 14 here includes the passage of a discharge fluid 142, which defines a fourth flow opposite to the first flow. It is understood here that, since the first flow presses the retentate against the filter medium 21, just like the second and third flows described above, the fourth flow provides a reverse impulse that separates the retentate from the filter medium 21. The passage of the discharge fluid 142 corresponds, for example, to a gas pulse, along the fourth flow, so as to generate a strong thrust to detach the dry retentate from the filter medium 142. The discharge fluid corresponds, for example, to a gas similar to the drying gas, although the dry retentate is already more resistant to oxidation.If it is possible to implement this solution for other arrangements of filter 2, in particular when the third outlet 27 is not located at the bottom of filter 2, it is clear that the orientation as described here is the most effective for discharging the dry retentate.

[0110] Thus, it will be understood that the present invention provides a method for obtaining a dry retentate from a liquid to be filtered, which does not require the use of a drying machine separate from the filter and eliminates logistical constraints and the associated costs. The resulting dry retentate is better protected from the outside atmosphere and has a superior quality.

[0111] Such a process can thus be used for the manufacture of a variety of compounds, and most preferably for the manufacture of precursors of active cathode materials. Maintaining the retentate in a small, controlled-atmosphere chamber protects the pCAM from oxidation until it dries, and therefore results in an unoxidized pCAM, thereby ensuring the quality of the CAMs and their applications based on such pCAMs.

[0112] It should be noted that this detailed description relates to a particular embodiment of the present invention, but in no way does this description limit the scope of the invention; on the contrary, its purpose is to remove any possible inaccuracy or misinterpretation of the following claims.

[0113] It should also be noted that the reference signs in parentheses in the following claims are in no way intended to be limiting; these signs are solely intended to improve the intelligibility and understanding of the following claims and the scope of protection sought.

Claims

Demands

1. A process (1) for obtaining a dry retentate from a liquid to be filtered comprising solid particles, said process (1) comprising the following steps: - filtration (11) of said liquid to be filtered in a filter (2) comprising a filtration medium (21), so as to obtain a retentate; and - drying (13) of said retentate, so as to obtain a dry retentate, characterized in that said drying step (13) is carried out inside said filter (2).

2. Method (1) according to claim 1, wherein said dry retentate corresponds to a precursor of cathode active material.

3. A method (1) according to claim 1 or 2, wherein said filter (2) corresponds to a candle filter, said candle filter comprising a housing (20) containing a plurality of tubes having a porous wall and forming said filtration medium (21), said tubes having a first end provided with means for extracting a filtrate of said liquid and a second end sealed, said filtration (11) and drying (13) steps being carried out inside said housing (20).

4. Method (1) according to claim 3, wherein said porous wall comprises a perforated surface covered with a polytetrafluoroethylene, or PTFE, membrane.

5. A method (1) according to any one of claims 1 to 4, further comprising a step of rinsing said retentate inside said filter (2), so as to obtain a wet retentate, said drying step (13) being carried out on said wet retentate.

6. Method (1) according to claim 5, wherein said rinsing step (12) comprises passing a rinsing liquid, separate from said liquid to be filtered, through said filter (2) so that said rinsing liquid passes through said filtering medium.

7. Method (1) according to claim 6, wherein said rinsing step (12) comprises recycling said rinsing liquid so as to circulate in a loop through said filter (2).

8. A method (1) according to any one of claims 1 to 7, wherein said drying (13) comprises passing a drying gas (131) through said filter (2), such that said drying gas circulates through said retentate and said filtration medium (21) and removes moisture from said retentate.

9. A method (1) according to claim 8, further comprising a transition step (130) before said drying (13), said transition (130) comprising an introduction of said drying gas so as to expel any liquid from said filter (2).

10. A method (1) according to any one of claims 1 to 9, wherein said drying (13) comprises a vacuuming (132) of said filter (2) so as to remove moisture from said retentate.

11. A method (1) according to any one of claims 1 to 10, wherein said filtration step (11) defines a first flow through said filtration medium (21) and said drying step (13) defines a third flow through said filtration medium (21), said first and third flows having a similar direction.

12. A method (1) according to any one of claims 1 to 11, further comprising an unloading step (14) of said dry retentate configured to separate said dry retentate from said filtration medium (21).

13. Method (1) according to claim 12, wherein said unloading (14) comprises a vibration (141) of said filtering media (21).

14. Method (1) according to claim 12 or 13, wherein said filtration step (11) defines a first flow through said filtration medium (21), said discharge (14) comprising a passage of a discharge fluid (142) through said filter (2) defining a fourth flow through said filtration medium (21), said fourth flow and said first flow having an opposite direction.

15. Cathode active material precursor obtained by the process according to any one of claims 1 to 14.

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