Method for removing water from particulate matter

Abstract

1. A method for removing water from a particulate material selected from (oxy)hydroxides and carbonates containing at least one of nickel or cobalt and at least one metal other than nickel, comprising: 1. A process comprising the steps of introducing at least one granular material having a moisture content in the range of 1-30% by weight, based on said granular material, into a rotary kiln equipped with an external heating element and moving said granular material through the rotary kiln together with a gas flow, wherein the residual moisture of the resulting product is in the range of 50 ppm to 1.5% by weight.

Description

[Technical field]

[0001] The present invention relates to a process for removing water from a granular material selected from (oxy)hydroxides and carbonates comprising at least one transition metal of nickel or cobalt and at least one metal other than nickel, comprising the steps of introducing at least one granular material having a moisture content in the range of 1 to 30% by weight, based on said granular material, into a rotary kiln equipped with an external heating element and moving said granular material through the rotary kiln together with a gas flow, the residual moisture of the resulting product being in the range of 50 ppm to 1.5% by weight. [Background technology]

[0002] Moisture removal from particulate solid materials is a subject of great interest. Drying of wet materials is a fundamental operation in pre-industrial and industrial process technologies. Several challenges must be addressed: in many cases the morphology of the particulate matter needs to be preserved, neither dusting nor clumping or ring formation is desired; heat transfer needs to be efficient: due to the high energy of evaporation a lot of energy has to be transferred to the wet material and high energy losses are undesirable, regardless of how the energy is produced.

[0003] In continuous processes, water removal poses even more challenges since reaction times are averaging times in many continuous reactors: both short cuts and very long residence times for particle groups must be avoided due to incomplete reactions and undesirable agglomeration of secondary particles, respectively.

[0004] In the production of cathode active materials for lithium-ion batteries, the topic of water removal is of increasing interest. The corresponding composite oxides are generally produced using a two-stage process. In the first stage, sparingly soluble compounds of transition metals are made by precipitating them from a solution, e.g. carbonates or hydroxides. This sparingly soluble salt is often also called precursor. Such precursors are expected to meet stringent specifications regarding their particle size distribution and internal physical structure, characterized for example by their sphericity or specific surface area (BET surface). In the second stage, the precursors are complexed with lithium compounds, e.g. Li2CO3, LiOH or Li2O, and calcined at high temperatures, e.g. 600-1100 °C. Water removal is therefore of great importance between the two stages. Homogeneous precursors, both in composition, including water content, and in morphology, including particle size distribution, are highly desirable. Summary of the Invention [Problem to be solved by the invention]

[0005] In many cases, after coprecipitation, the precursor is separated from the mother liquor by solid-liquid separation methods, in particular filtration. The resulting filter cake may contain up to 30% by weight of water. Removal of said water requires a lot of energy. At the same time, it is desirable not to adversely affect the morphology of the precursor.

[0006] It was therefore an object of the present invention to provide a process by which water can be removed from granular material in an economical manner whilst maintaining the morphology of the granular material, and further to provide a reactor for carrying out such a process. [Means for solving the problem]

[0007] Thus, a process as defined at the outset is found, which process is hereinafter also called "process of the invention" or "process according to the invention". The process of the invention is a continuous process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The process of the invention starts with a particulate material, also called particulate solid, in particular a filter cake. The particulate material introduced in the process of the invention is wet. This is taken to mean in the present invention that the wet particulate material has a moisture content in the range of 1-30% by weight. The moisture content may be determined by drying in a vacuum at a temperature of 100° C. until the mass does not change. In the course of the process of the invention, the wet particulate material is introduced as a paste, a slurry or a wet powder or an agglomerated wet powder. In a preferred embodiment, the wet particulate material is provided as a filter cake.

[0009] The granules have an average diameter (d 50 ), but preferably between 2 μm and 100 μm. The average diameter is advantageously determined by laser diffraction and in the present invention represents the mass median. The granular material may have an irregular shape, but in a preferred embodiment, the granular material has a regular shape, for example a spheroid or even a sphere. The aspect ratio may range from 1 to 10, preferably from 1 to 3, more preferably from 1 to 1.1. The aspect ratio is defined as the ratio of the width to the length, or more specifically the ratio of the particle diameter of the longest dimension to the particle diameter of the shortest dimension. A perfectly spherical particle has an aspect ratio of 1.

[0010] In a preferred embodiment of the invention, the wet particulate material is provided as a filter cake from the precipitation, or preferably co-precipitation, of a precursor for a positive electrode active material for a lithium ion battery. In such an embodiment, the particulate solid preferably has an average particle size (d 50 ), even more preferably in the range of 3 to 15 μm. For example, the wet granular material may be provided as a filter cake from precipitation of nickel or cobalt hydroxide, or from nickel or cobalt carbonate, or from coprecipitation.

[0011] The particulate material is selected from oxides, (oxy)hydroxides and carbonates of transition metals, preferably carbonates and more preferably (oxy)hydroxides. The term oxyhydroxide not only denotes compounds with the same stoichiometric share of oxide and hydroxide ions, but also non-stoichiometric compounds.

[0012] The particulate material is selected from (oxy)hydroxides and carbonates containing at least one transition metal selected from nickel or cobalt and at least one metal other than nickel, and may therefore be cobalt oxyhydroxide or cobalt hydroxide or cobalt carbonate or nickel carbonate or (oxy)hydroxide.

[0013] In one embodiment of the invention, the granular material is selected from mixed (oxy)hydroxides of nickel and at least one transition metal selected from cobalt and manganese, and optionally containing at least one further metal selected from Mg, Al, Ba, Ti, Zr, Nb, Ta, W, Mo, Sb and Y.

[0014] In one embodiment of the invention, the particulate material is selected from complex carbonates of nickel and at least one transition metal selected from cobalt and manganese, and optionally containing at least one further metal selected from Mg, Al, Ba, Ti, Zr, Nb, Ta, W, Mo, Sb and Y, preferably the particulate material is selected from complex carbonates of nickel and manganese. Carbonate in this context also includes basic carbonates, which are carbonates which also contain an oxide or a counterion of the oxide.

[0015] The moist granular material may contain small amounts of lithium, for example 1.5 to 3 mol % relative to the sum of the cobalt or possibly nickel, cobalt and other transition metals present in said (oxy)hydroxide or carbonate.

[0016] In a preferred embodiment of the invention, the moist granular material is lithium-free, where "lithium-free" refers to a lithium content of less than 1 mol % relative to the total of cobalt or possibly nickel, cobalt and other transition metals present in said (oxy)hydroxide or carbonate.

[0017] Some elements are ubiquitous. In the present invention, trace amounts of ubiquitous metals such as sodium, calcium, iron or zinc as impurities may not be considered in the description of the present invention. Trace amounts here may mean amounts of 0.02 mol % or less based on the total metal content of the starting material. Furthermore, residual sulfate anions from sulfate starting materials may also be ignored.

[0018] In one embodiment of the present invention, the metal portion of the mixed carbonate or mixed hydroxide of nickel and at least one transition metal selected from cobalt and manganese is represented by the general formula (I): Ni a M 1 b Mn c (I) and the variables are defined as follows: M 1 is Co or a combination of Co and at least one metal selected from Ti, Zr, Al, and Mg; a is in the range of 0.15 to 0.95, preferably in the range of 0.6 to 0.92 or 0.15 to 0.3; b is in the range of 0 to 0.35, preferably in the range of 0.05 to 0.2; c is in the range of 0 to 0.8, preferably in the range of 0.05 to 0.2, and a+b+c=1.0, and at least one of b and c is greater than 0.

[0019] In one embodiment of the present invention, the average residence time of the particulate solid is in the range of 30 minutes to 5 hours, preferably in the range of 1 to 3 hours, where average residence time refers to the average residence time of the particulate material in the rotary kiln.

[0020] In one embodiment of the invention the moist granular solid is introduced into the rotary kiln at ambient temperature, in another embodiment of the invention the moist granular solid is introduced into the rotary kiln at a temperature between 50°C and 100°C.

[0021] In one embodiment of the invention, the moist granular solid is introduced into the rotary kiln by a chute or a vibrating chute, by a spiral or screw conveyor, preferably by a screw conveyor with a single screw or multiple screws.

[0022] The moist granular solid is then moved through a rotary kiln. As the moist granular solid moves the moisture content decreases. Preferably, at the end of the process of the invention the residual moisture content is in the range 50 ppm to 1.5% by weight, preferably in the range 100 to 300 ppm. ppm is parts per million and is based on weight. The residual moisture content may be determined by Karl Fischer titration or by thermogravimetry.

[0023] In one embodiment of the present invention, the retort length of the rotary kiln is 1 to 50 m, preferably 5 to 25 m.

[0024] In one embodiment of the present invention, the retort diameter of the rotary kiln is in the range of 0.2 to 4 m, and preferably 1 to 2 m.

[0025] In one embodiment of the present invention, the ratio of the retort length to the retort diameter is in the range of 5-50, and preferably 10-25.

[0026] In one embodiment of the invention the rotary kiln is precisely horizontal, in another embodiment the rotary kiln is inclined, for example at an inclination angle of 0.2-7°C, and movement of the particulate solids through the rotary kiln is by gravity.

[0027] In one embodiment of the present invention, the rotary kiln is operated at 0.01 to 20 revolutions per minute, preferably 0.5 to 5 revolutions per minute, and in each case continuously or at intervals. If operation in interval mode is desired, it is possible to stop the rotation for 1 to 60 minutes after 1 to 5 revolutions, then again perform 1 to 5 revolutions and again stop for 1 to 60 minutes, and so on.

[0028] In one embodiment of the present invention, the rotary kiln may comprise an internal section. The internal section may comprise a number of machine units such as vertical baffles or dams, spiral vanes, straight or inclined blades, L-lifters, ploughshares, chain curtains or shovels. The internal section may cover the entire cross section from the wall to the centre of the rotary kiln or may extend partially from the wall to the centre of the rotary kiln. Preferably, the internal section is arranged in sections of 0.2-5 m length along the axis of the rotary tube, each section comprising 1-24 individual machine units regularly distributed along the circumference of the rotary tube.

[0029] The rotary kiln may have one or more external heating elements, such as an external furnace. Heat from such an external furnace may be generated via gas combustion, electrical resistance heating, induction heating, or microwave heating.

[0030] The particulate material is moved through the rotary kiln with a flow of gas, which may be air, an inert gas such as nitrogen, or oxygen-depleted or oxygen-enriched air or flue gas, with air and flue gas being preferred.

[0031] In one embodiment of the invention, the gas stream has an inlet temperature in the range of 0-1400° C., preferably 100 or 200-1000° C. In embodiments where the gas inlet temperature is 100° C. or higher, a pre-heating system is required. In embodiments where a pre-heating system is not desired, the inlet temperature corresponds to ambient temperature.

[0032] In one embodiment of the invention, the particulate material is moved through the rotary kiln with a co-current flow of gas. In another embodiment of the invention, the gas flow and the particulate solid are moved counter-currently through the rotary kiln. Co-current flow has the disadvantage that most finished precursors are in contact with gases that are relatively rich in moisture and carbon dioxide. This disadvantage is avoided when the gas flow and the movement of the particulate solid are counter-current.

[0033] In one embodiment of the invention, at the discharge end of the rotary kiln, an inlet flow of inert gas, air, oxygen-enriched or oxygen-depleted air or flue gas is introduced into the rotary kiln. In one embodiment of the invention, the rotary kiln has at least two distinguishable zones, for example 2 to 6 temperature zones, in which the granular material is treated at different temperature levels. The distinguishable zones are pre-established by providing different temperature levels by a strongly endothermic process step - evaporation of water and chemical decomposition of hydroxides or carbonates as water or carbon dioxide, or via separate external heating zones.

[0034] In a preferred embodiment, in the first temperature zone the temperature of the granular material is in the range of 80-130° C. and in the second temperature zone the temperature is in the range of 200-500° C., preferably 200-450° C., more preferably 220-300° C. The temperatures may be determined using sensors.

[0035] By carrying out the process of the present invention, removal of water and, where applicable, carbonates from granular material may be carried out in an economical manner whilst maintaining the morphology of the granular material. In particular, carrying out water evaporation and hydroxide / carbonate decomposition according to the process of the present invention not only reduces the equipment footprint and complexity, but also improves overall energy efficiency by making more efficient use of the sensible heat of the material and reducing heat losses.

[0036] The present invention is further illustrated by the following examples. EXAMPLES

[0037] General:d 10 , d 50 , and d 90 represent particle sizes at 10, 50, and 90% of the cumulative volume distribution.

[0038] I. Coprecipitation of precursors A continuous stirred tank reactor was charged with deionized water and 49 g of ammonium sulfate per kg of water. The solution was moderated to 55° C. and the pH was adjusted to 12 by the addition of aqueous sodium hydroxide.

[0039] The coprecipitation reaction was started by simultaneously feeding the aqueous transition metal sulfate and sodium hydroxide solutions, and the total flow rate gave an average residence time of 8 hours. The transition metal sulfate solution contained sulfates of Ni, Co, and Mn in a molar ratio of 88:7:5, and the total transition metal concentration was 1.65 mol / kg. The aqueous sodium hydroxide solution was a 25% by weight aqueous sodium hydroxide and 25% by weight aqueous ammonia solution in a mass ratio of 6. The pH value was kept at 12 by separately feeding the aqueous sodium hydroxide solution. Beginning with the start-up of all feeds, the resulting slurry was continuously removed.

[0040] The slurry was then filtered using a filter press. The resulting filter cake was washed with deionized water and then with an aqueous solution of sodium hydroxide. The resulting wet filter cake of the precursor was obtained, which had a residual moisture content of 9.5% by mass relative to the entire filter cake and an average particle size (d 50 ) is 11 μm, and the span [(d 90 )-(d 10 ) to (d 50 ) was 1.4.

[0041] II. Drying of Filter Cake II.1 Drying and dehydration in a rotary kiln with five heating zones The moist filter cake obtained from Example I was then fed into a continuously operated electrically heated rotary kiln with a mass flow rate of 20 kg / h. The rotary kiln had a heating length of 6 m and an internal diameter of 0.3 m and was heated over the length of 6 m by an external electric resistance furnace with five heating zones evenly distributed. The set temperatures were set at 200 and 240°C in the first two zones (drying zone) and 320, 440, 490°C in the last heating three zones (hydroxide decomposition zone), measured from the solids feed side. The average residence time of the particulate material reached 90 minutes in the heating section of the kiln. The volumetric flow rate of the countercurrent gas flow (air) was 20 m 3 / h, which was measured at standard conditions. The air inlet temperature was ambient.

[0042] The result was a fine powder of dehydroxylated metal oxide with a residual moisture content of 500 ppm as determined by Karl Fischer titration and a phase pattern characteristic of nickel oxide (bunsenite) as determined by powder X-ray diffraction measurements.

[0043] II.2 Drying and dehydration in rotary kilns The moist filter cake obtained in Example I. was then fed into a continuously operated electrically heated rotary kiln with a mass flow rate of 20 kg / h. The rotary kiln had a heating length of 2.3 m and an internal diameter of 0.26 m, with heating over a length of 6 m by means of an external electric resistance furnace. The set temperature was 475°C. The mean residence time of the particulate matter amounted to 45 minutes in the heating section of the kiln. The volumetric flow rate of the countercurrent gas stream (air) was 3 m3, determined at standard conditions. 3 / h. The air inlet temperature was ambient.

[0044] As a result, the residual moisture content measured by Karl Fischer titration was 0.45% by mass, and the BET specific surface area was 60 m 2 / g (as measured by N2 adsorption) and a fine powder of the dehydroxylated metal oxide was obtained with a phase pattern characteristic of nickel oxide (bundenite) as determined by powder X-ray diffraction measurements.

[0045] II.3 Drying in a rotary kiln without removing hydroxyl groups (comparison) The moist filter cake obtained in Example I. was then fed at a mass flow rate of 1.5 kg / h into a continuously operated electrically heated rotary kiln. The rotary kiln had a heating length of 1 m and an internal diameter of 0.1 m. The kiln was operated at a furnace temperature of about 150° C. The average residence time of the particulate matter in the heating section of the kiln amounted to 50 minutes. The volumetric flow rate of the countercurrent gas flow (air) was 1 Nm 3 As a result, the BET specific surface area was 33 m 2 A fine powder of dehydroxylated metal oxide was obtained with a .05% .OMEGA. / g, a residual moisture content of 1 wt.%, and a total LOI (loss on ignition) of 21.2 wt.%. The comparative precursor thus obtained showed a crystalline phase pattern characteristic of nickel hydroxide (theophrastite). [Brief description of the drawings]

[0046] [Figure 1] 1 shows SEM images of precursors made according to inventive examples II.1 and II.2, and of precursors made according to comparative example II.3.

Claims

1. 1. A method for removing water from a particulate material selected from (oxy)hydroxides and carbonates containing at least one transition metal selected from nickel or cobalt and at least one metal other than nickel, comprising:

1. A process comprising the steps of introducing at least one granular material having a moisture content in the range of 1 to 30% by weight, based on said granular material, into a rotary kiln equipped with an external heating element and moving said granular material through the rotary kiln with a gas flow, wherein the average residence time of said granular material is in the range of 30 minutes to 5 hours and the residual moisture of the resulting product is in the range of 50 ppm to 1.5% by weight.

2. 2. The method of claim 1, wherein the gas flow is countercurrent to the movement of the particulate matter.

3. 3. The method according to claim 1 or 2, wherein the particulate material is selected from (oxy)hydroxide composites of nickel and at least one transition metal selected from cobalt and manganese, and optionally comprising at least one further metal selected from Mg, Al, Ba, Ti, Zr, Nb, Ta, W, Mo, Sb, and Y.

4. A method according to any one of claims 1 to 3, wherein the gas stream has an inlet temperature in the range of from zero to 1400°C.

5. A method according to any one of claims 1 to 4, wherein the particulate material is lithium-free.

6. A method according to any one of the preceding claims, wherein the rotary kiln has at least two distinct zones in which the particulate material is treated at different temperature levels.

7. 6. The method of claim 5, wherein in a first temperature zone, the temperature of the particulate material is in the range of 80-130°C, and in a second temperature zone, the temperature is in the range of 200-500°C.

8. 8. A method according to any one of claims 1 to 7, wherein, on the discharge end of the rotary kiln, an inlet flow of inert gas, air, oxygen-enriched or oxygen-depleted air or flue gas is introduced into the rotary kiln.

9. 9. The method according to any one of claims 1 to 8, wherein the particulate material is selected from complex carbonates of nickel and at least one transition metal selected from cobalt and manganese, and optionally contains at least one further metal selected from Mg, Al, Ba, Ti, Zr, Nb, Ta, W, Mo, Sb, and Y, and the carbonate is at least partially removed as carbon dioxide.

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