Agitated extraction column and process to separate substances

Abstract

An agitated extraction column is proposed for extracting a substance from a first liquid into a second liquid, or from the second liquid into the first liquid by means of liquid-liquid extraction wherein both liquids are immiscible, and the first liquid exhibits a higher density than the second liquid, wherein the agitated extraction column is radially delimited by a column wall, wherein a plurality of compartments is separated by partition trays, wherein each partition tray comprises at least one flow passage through which at least one of the liquids can flow from one compartment into another adjacent compartment, further comprising a drive shaft for rotating about an axial direction, an agitator connected to the drive shaft and configured for stirring the liquids, wherein one of the compartments is configured as a settling compartment for separating the first and the second liquid through gravitational forces. Further, one of the compartments is configured as an isolation compartment arranged adjacent to the settling compartment in the axial direction, wherein the isolation compartment is configured and arranged to supply the first liquid from the isolation compartment into the settling compartment, wherein the second liquid is routed past the isolation compartment into a merging compartment, and wherein the isolation compartment comprises at least one opening in the column wall for exchange of liquids between the isolation compartment and the outside of the column. Further, a process for separating substances is proposed, using the agitated extraction column.

Description

[0001] Sulzer Management AG, CH-8401 Winterthur (Schweiz) S13774PEP

[0002] Agitated extraction column and process to separate substances

[0003] The invention relates to an agitated extraction column and process for liquid-liquid extraction, according to the preambles of the independent claims.

[0004] Liquid-liquid extraction (LLE) is a widespread method to separate specific substances or complexes based on their differing solubilities in two immiscible, often but not limited to polar and non-polar liquids, such as water and an organic solvent. This separation involves transferring one or more substances, i.e. , the one or more solutes, from a first liquid phase, typically referred to as feed solution, to a second liquid phase, typically referred to as solvent, driven by chemical potential. The solvent which is enriched in solutes after liquidliquid extraction is called extract, while the correspondingly solute-depleted feed solution is termed raffinate.

[0005] Particularly widespread use of liquid-liquid extraction is found in hydrometallurgy for separating and purifying various metals, including uranium, plutonium, zirconium, hafnium, cobalt, nickel, and rare earth elements. Therein, the primary advantage of LLE lies in its ability to selectively separate specific substances from complex mixtures, yielding individual streams containing the corresponding high-purity extracts. In addition, since LLE can be performed under relatively mild conditions (close to ambient temperature and pressure), it offers an effective, easy, and safe method for purifying substances that might decompose under high temperatures used in distillation. LLE is also widely used in industries such as fine organic compound production, perfume processing, drug purification, flavor and aroma extraction, and vegetable oil and biodiesel production, and often serves as initial separation technique.

[0006] Next to batchwise single stage liquid-liquid extractions, commonly used for lab scale applications, technical implementations of continuous LLE for example comprise devices such as columns, in which two or more immiscible phases are contacted in countercurrent direction in vertical orientation, where the specific heavier liquid or liquids are fed from the top and the specific lighter liquid or liquids are fed from the bottom. Such an arrangement is often denoted as vertical liquid-liquid extraction column. Within a typical vertical liquid-liquid extraction column, horizontal dividers, such as perforated plates exhibiting holes for liquids to pass through the plate, or any other tray-like structures provide compartments of the column, which are permeable to the feed solution, raffinate, solvent and extract. These compartments act as individual stages of extraction, improving the overall efficiency of the column because each compartment allows for the two phases to reach a corresponding near-equilibrium state in each compartment, in turn creating a stepwise equilibrium configuration between the two phases along the column. This stagewise approach is akin to the concept of theoretical plates in distillation, where each compartment represents a step towards achieving complete separation, and more compartments typically enable closer approximation to ideal equilibrium conditions.

[0007] To further enhance the contact between the feed solution and the solvent with the aim of enhancing the mass transfer from the first to the second liquid phase in each compartment, i.e., increasing the stage extraction efficiency and thus decrease the amount of solvent necessary, agitators in form of blades, paddles, impellers, or other stirring structures connected to a rotating shaft in vertical direction, are often placed in each compartment, creating more intimate contact between the phases. In particular, these agitators are usually configured to create a minimal vertical conveying effect and instead provide flow patterns within the compartments dominated by oval or circular motion of the liquid mixture. This in turn increases the residence time and contact of the specific fluids and therefore the extraction efficiency in each compartment. However, since liquid-liquid extraction is a process driven by chemical potential, once an equilibrium is approached, prolonging the residence time does not significantly increase the degree of extraction anymore, which is why mass transfer between the compartments is essential.

[0008] At the ends of the vertical liquid-liquid extraction column in flow direction, the solute depleted raffinate and the solute enriched extract can be removed, often realized by using a separator which separates the specific lighter fluid through gravitational forces in an overflow-type compartment from the specific heavier fluid at the top of the column, and a separator which separates the specific heavier fluid through gravitational forces in a settlertype compartment from the specific lighter fluid at the bottom of the column.

[0009] In a multitude of applications, such as hydrometallurgy, treatment of the feed solution, for example the aqueous phase, is necessary during the extraction process, not before or after, in order to shift the solubility equilibrium of the solute towards the solvent, for example an organic phase, thus ensuring efficient extraction. However, this treatment is often detrimental to the solvent, for example when dosing an acid or base to an aqueous feed solution to adjust its pH, where contact of a concentrated acid or base with, for example, an organic solvent can cause undesired reactions, which can lead to precipitation or destruction of the desired properties of the organic solvent, in turn resulting in loss of extraction efficiency or even blocking of the column. While contact of diluted treatment agents, such as acids or bases, with the solvent might theoretically be tolerable, using diluted acids or bases renders impossible in technical implementations due to the resulting large volumetric changes of the column contents. To mitigate such issues current liquid-liquid extraction technology often relies on external phase separators, wherein the liquid mixture is supplied to the phase separator from any compartment of the column before one liquid can be subjected to external treatment independently prior to being reinjected into the column.

[0010] For example, when using an aqueous feed solution, of which one solute, which can be a metal, shall be extracted using an organic solvent, the pH of the feed solution changes during the extraction process. However, to maintain a large enough chemical potential between the feed solution and the solvent for reaching high extraction efficiencies, i.e. , reaching a high solute concentration in the extract and low solute concentration in the raffinate, the pH of the feed solution must be adjusted somewhere between two stages, i.e., compartments of the liquid-liquid extraction column. Therefore, one of the stages, i.e, the compartments of the liquid-liquid extraction column, can be configured as a withdrawal compartment, from which the mixtures is fed to a settling device to create two separate streams of the feed solution and the solvent. Prior to re-injection of both liquids into the next stage, the feed solution is treated with a concentrated acid or base, whereas the solvent is protected from any detrimental influence of this treatment. However, this approach requires extensive additional equipment, such as external settling devices, pumps, and controls, as well as additional footprint, consequently leading to significant cost.

[0011] Starting from this state of the art, it is therefore an object of the invention to propose an effective and cost-efficient agitated extraction column and process for continuous liquidliquid extraction, particularly suitable for liquid-liquid extractions, wherein the liquid with higher density must be treated during the process to maintain desired liquid properties, whereas a negative impact to the liquid with lower density during the treatment is prevented. In addition, it is an object of the invention to propose a process to separate substances with such an extraction column.

[0012] The subject matter of the invention satisfying this object is characterized by the features of the independent claims.

[0013] Thus, according to the invention, an agitated extraction column for extracting a substance from a first liquid into a second liquid, or from the second liquid into the first liquid by means of liquid-liquid extraction is proposed, wherein both liquids are immiscible, and the first liquid exhibits a higher density than the second liquid. The agitated extraction column is radially delimited by a column wall and comprises a plurality of compartments is separated by partition trays, wherein each partition tray comprises at least one flow passage through which at least one of the liquids can flow from one compartment into another adjacent compartment. These flow passages can be formed as simple holes, meshes, tubes, channels, or any other form that allows a liquid to flow from one side of a partition tray to the other side of the partition tray. Further, the agitated extraction column comprises a drive shaft for rotating about an axial direction and an agitator connected to the drive shaft and configured for stirring the liquids. One of the compartments of the agitated extraction column is configured as a settling compartment for separating the first and the second liquid through gravitational forces, wherein the agitator is arranged outside the settling compartment, and one of the compartments is configured as an isolation compartment arranged adjacent to the settling compartment in the axial direction. The isolation compartment is configured and arranged to supply the first liquid from the isolation compartment into the settling compartment, wherein the second liquid is routed past the isolation compartment into a merging compartment, and wherein the isolation compartment comprises at least one opening in the column wall for exchange of liquids between the isolation compartment and the outside of the column. Thus, the present invention enables operando treatment, for example adjustment of pH, of the first liquid, often the feed solution, within an agitated extraction column while preventing potentially detrimental contact of concentrated treatment solutions and the second liquid, such as the solvent inside the column. In turn risks of precipitation or any chemical reaction between treatment agents and solvents can be mitigated in a cost-efficient way, as alternative to costly external treatment devices.

[0014] In a preferred embodiment of the agitated extraction column, the isolation compartment is arranged between the settling compartment and the merging compartment regarding the axial direction, wherein at least one flow channel is provided for guiding the second liquid from the settling compartment into the merging compartment. Therein, the flow channel is configured to prevent the second liquid from entering the isolation compartment. According to the invention, this arrangement of the compartments and flow channels allows for a compact and simple design of the agitated extraction column with minimized footprint and external piping.

[0015] Furthermore, it is preferred that the settling compartment comprises a top partition tray and a bottom partition tray, wherein the top partition tray comprises a centrally arranged tube extending into the settling compartment and surrounding the drive shaft at a distance to the drive shaft for enabling the first liquid to flow downwards along the drive shaft.

[0016] A further preferred configuration is that a sealing element is provided for sealing between the bottom partition tray and the drive shaft.

[0017] The centrally arranged tube primarily acts as a flow direction device, so that the first liquid is guided to flow into the settling compartment, without disturbing the flow of the second fluid, which settles, due to the lower density with respect to the first fluid and the immiscibility of the two fluids, in the upper part of the settling compartment. It must be noted that the word tube in this context does not limit the flow direction device to a certain geometry, and merely describes a flow direction device extending from the top partition tray. In addition, the sealing device helps to prevent upwards flow of the second liquid along the drive shaft, and thus inhibits intrusion of the second liquid into the isolation compartment through the centrally arranged tube. Instead, other flow passages in the bottom partition tray, preferably arranged at a distance to the drive shaft, can be used to enable liquid exchange between the settling compartment and any compartment arranged below.

[0018] Furthermore, it is preferred that the agitated extraction column comprises an inlet chamber within the settling compartment, wherein a partition wall is arranged coaxially with respect to the centrally arranged tube, wherein a partition wall end is spaced from the bottom partition tray in axial direction, providing a gap between the bottom partition tray and the partition wall end. This optional arrangement further enhances the separation performance of the settling compartment, as it provides an additional barrier between regions where predominantly the first liquid is present, such as the inlet chamber, and the rest of the settling compartment, in particular the upper part of the settling compartment, where predominantly the second fluid is present. By using at least two wall segments, in particular the partition wall and the partition wall end, to delimit the inlet chamber, optimal flow geometries can be realized, wherein the first liquid flows from the inlet chamber through a gap towards other flow passages in the bottom partition tray, further preventing intrusion of the second liquid into the inlet chamber, and consequently the isolation compartment.

[0019] In a further preferred embodiment, each isolation compartment comprises at most eight hundred flow channels, wherein the total cross section with regard to the axial direction of said flow channels within each isolation compartment is between one half and eighty percent of the cross section with regard to the axial direction of the agitated extraction column, preferably between one and fifty percent, and most preferably between one and a half and twelve percent. Notably, any number of flow channels equal to or larger than one can be used for routing the second liquid past the isolation compartment, however, care must be taken to select the number and size, i.e. cross section, such that a reasonable balance is achieved between minimizing the pressure drop across the flow channels and ensuring the separation performance of the settling compartment. Further, the cross section with regard to the axial direction is to be understood such that if a flow channel is for example formed as a cylindrical tube, the cross section with regard to the axial direction would exhibit the form of a circle. A preferred configuration is that the vertical dimension of the centrally arranged tube in the settling compartment is between two and ninety eight percent of the vertical dimension of the settling compartment, preferably between five and eighty percent, and most preferably between fifteen and seventy percent, wherein the free cross section with regard to the axial direction of the centrally arranged tube around the drive shaft is between one half and eighty percent of the cross section with regard to the axial direction of the agitated extraction column, preferably between one and fifty percent, and most preferably between two and thirteen percent. Similar to the flow channels, according to the invention, any combination of vertical dimension and free cross section of the centrally arranged tube in the settling compartment can be chosen, yet the above-described combinations have shown to achieve best performance in guiding the first liquid, such that the separation performance of the settling compartment is optimal. Further, the free cross section is to be understood as the cross section delimited by the centrally arranged tube and the drive shaft.

[0020] Preferably, the agitated extraction column has a circular cross section, and all partition trays have a circular form or are otherwise sealed or connected to the column wall.

[0021] Further, a preferred configuration of the agitated extraction column according to the invention comprises three to five hundred subsequent compartments in the axial direction, preferably four to three hundred, and most preferably five to one hundred. Depending on the solubility of the substance to be extracted from the first liquid into the second liquid, or from the second liquid into the first liquid, and the chemical potential driving the process, the number of compartments should be adapted to reach a desired degree of extraction. Notably, according to the invention, any number of compartments equal to or larger than three, is advantageous to achieve high extraction yields.

[0022] In a preferred embodiment of the agitated extraction column, a first plurality of openings in the column wall is distributed along the circumference of the isolation compartment.

[0023] Further, a second plurality of injection openings in the column wall is distributed along the circumference of the settling compartment or along the circumference of any other compartment below the settling compartment. With respect to only one opening in the column wall, this arrangement of the openings or the injection openings enables more uniform liquid withdrawal and injection leading to optimized flow patterns within the column. In another preferred configuration of the agitated extraction column, a plurality of compartments comprises agitators, wherein preferably each compartment of the plurality of compartments comprises one agitator, wherein the agitators are configured to transport the liquids predominantly in horizontal radial and tangential direction, while minimizing vertical conveying effects. Agitation of compartments other than the settling compartment and isolation compartment, increases the contact and residence time of the first liquid and the second liquid, which enhances the extraction performance per compartment. The agitators preferably create oval flow patterns within each compartment of the plurality of compartments, while minimizing vertical transport of the liquids through agitation between compartments. To this end, one agitator per agitated compartment renders optimal, however alternatively a plurality of agitators per compartment can be beneficial in certain circumstances.

[0024] It is particularly preferred that the number of isolation compartments in the agitated extraction column is between one and three hundred, preferably one and one hundred, and most preferably between one and eighty. It must be noted that the optimal number of isolation compartments is determined by the need for treatment of the first liquid.

[0025] A further preferred configuration of the agitated extraction column is that the first, bottommost, and last, upper-most compartment each comprise an inlet and an outlet. If these inlets and outlets are used for admittance of the first liquid and the second liquid, as well as discharge of the extract and raffinate, this configuration enables most efficient use of the size and capital cost of the extraction column.

[0026] In addition, according to the invention, a process to separate substances is proposed, wherein one or more substances are extracted from a first liquid into a second liquid, or from the second liquid into the first liquid by means of liquid-liquid extraction, wherein both liquids are immiscible, wherein both liquids are brought into intimate contact, wherein the first liquid exhibits a higher density than the second liquid, wherein the extraction is based on differing solubilities of the substances in the immiscible liquids, wherein a feed solution containing the substances to be extracted and a solvent are admitted into an agitated extraction column according to the invention in countercurrent direction. Therein, the agitated extraction column is oriented vertically, and the first liquid is admitted to the agitated extraction column from the top and the second liquid is admitted to the agitated extraction column from the bottom. Further, a treatment of the first liquid is required during the extraction process, wherein the treatment of the first liquid requires separation of the first liquid from the second liquid. According to the invention, the separation of the first liquid and the second liquid is performed inside the agitated extraction column in a settling compartment, wherein the second liquid is routed past an isolation compartment, enabling operando treatment of the first liquid in the isolation compartment through injection of treatment agents through an opening in the column wall, or extraction of the first liquid from the isolation compartment through an opening in the column wall for treatment outside of the agitated extraction column before reinjection of the treated first liquid into the agitated extraction column in any compartment, preferably below the isolation compartment, through an injection opening in the column wall.

[0027] This invention represents a prime example of process intensification, as it significantly reduces the capital cost and operational expenses of a traditional vertical extraction column, wherein the first liquid would need to be treated during the process, while enabling high extraction efficiency.

[0028] Further advantageous measures and embodiments of the invention will become apparent from the dependent claims.

[0029] The invention will be explained in more detail hereinafter with reference to embodiments of the invention and with reference to the drawings.

[0030] In the schematic drawing is shown:

[0031] Fig. 1 : a cross-sectional view of a section of a first embodiment of an agitated extraction column according to the invention,

[0032] Fig. 2: a cross-sectional view of a section of a second embodiment of an agitated extraction column according to the invention,

[0033] Fig. 3 a cross-sectional view of a section of a third embodiment of an agitated extraction column according to the invention,

[0034] Fig. 4: as Fig. 1 , however with an illustration of the internal liquid flows in the agitated extraction column, and Fig. 5: as Fig. 4, but with a more detailed illustration of the internal liquid flows.

[0035] Fig. 1 shows a section of a first embodiment of an agitated extraction column for extracting a substance from a first liquid H (see Fig. 5) into a second liquid L (see Fig. 5), or from the second liquid L into the first liquid H by means of liquid-liquid extraction wherein both liquids are immiscible, and the first liquid H exhibits a higher density than the second liquid L according to the invention. The agitated extraction column is designated in its entirety by the reference numeral 1. The center line of the agitated extraction column 1 defines the axial direction A and the agitated extraction column extends further in the axial direction A than shown in Fig. 1, as indicated by the break lines on the top and the bottom of the Fig. 1. In this embodiment, the agitated extraction column comprises a column wall 10, which radially delimits the agitated extraction column 1 , and a plurality of compartments, which are separated by partition trays 11. In the first embodiment, the agitated extraction column 1 has a circular cross section, and all partition trays 11 have a circular form or are otherwise sealed or connected to the column wall 10. Further, each partition tray 11 comprises at least one flow passage 12 through which at least one of the liquids can flow from one compartment into another adjacent compartment. Notably, flowing into another adjacent compartment does not entail that the liquid or liquids entering the adjacent compartment encounter the liquid or liquids in the adjacent compartment, yet solely indicates that the liquids or liquid can pass through the partition tray in specific places. For example, in this embodiment, the flow passages 12 can be holes in the partition trays 11 , or tube or flow channel inlets or outlets, wherein the partition tray 11 is arranged at an end of the tube or flow channel, or tube or flow channel lead-throughs in the partition trays 11. Alternatively, the flow passages 12 can be implemented as meshes or valves. In this embodiment, the agitated extraction column comprises a vertical drive shaft 13 with agitators 14 configured for stirring the liquids, arranged in compartments designated for mixing the liquids admitted to the column, i.e., outside a settling compartment 15 and outside an isolation compartment 16. The settling compartment 15 is configured for separating the first and the second liquid L through gravitational forces, and an isolation compartment 16 is arranged adjacent to the settling compartment 15 in the axial direction A. The settling compartment 15 comprises a top partition tray 30 and a bottom partition tray 31, wherein the top partition tray 30 comprises a flow passage 12, configured as the inlet of a centrally arranged tube 32. The isolation compartment 16 is configured and arranged to supply the first liquid H from the isolation compartment 16 into the settling compartment 15 through the flow passage 12 and the centrally arranged tube 32 surrounding the drive shaft 13 at a distance to the drive shaft 13 for enabling the first liquid H to flow downwards along the drive shaft 13. In other embodiments, other flow passages 12, such as described above, can be used to supply the first liquid H from the isolation compartment 16 into the settling compartment 15, wherein the flow passage should be arranged such, that the probability for the second liquid L to enter the isolation compartment 16 in counter-flow direction through this flow passage is minimized. Instead, in the first embodiment of an agitated extraction column, the second liquid L is routed past the isolation compartment 16 into a merging compartment 17, which is arranged adjacent to the isolation compartment 16 in the axial direction A. Further, in this embodiment, the isolation compartment 16 comprises an opening 18 in the column wall 10 for exchange of liquids between the isolation 16 compartment and the outside of the column 1. In other embodiments, this opening 18 in the column wall 10 can be replaced by a first plurality of openings 18 in the column wall 10, wherein the first plurality of openings 18 in the column wall 10 is distributed along the circumference of the isolation compartment 16.

[0036] In the first embodiment, the isolation compartment 16 is arranged between the settling compartment 15 and the merging compartment 17 regarding the axial direction A and one flow channel 20 is provided for guiding the second liquid L from the settling compartment 15 into the merging compartment 17, wherein the flow channel 20 is configured to prevent the second liquid L from entering the isolation compartment 16.

[0037] In other embodiments, this one flow channel 20 can be replaced by a plurality of flow channels 20 in the isolation compartment 16, wherein the isolation compartment 16 can comprise at most five hundred flow channels 20, preferably between two and two hundred flow channels 20, and most preferably between four and fifty flow channels 20.

[0038] Fig. 1 shows only a section of the first embodiment of an agitated extraction column 1 according to the invention, wherein the agitated extraction column 1 comprises more than five subsequent compartments in the axial direction. Other embodiments preferably comprise three to five hundred subsequent compartments in the axial direction A, preferably four to three hundred, and most preferably five to one hundred.

[0039] Further, in other embodiments the number of isolation compartments 16 is, depending on the total number of compartments, between one and three hundred, preferably one and one hundred, and most preferably between one and eighty.

[0040] In the first embodiment of an agitated extraction column 1 one injection opening 100 in the column wall 10 is provided in the settling compartment 15 for re-injection of treated liquids, in particular of the treated first liquid H. Alternatively, this injection opening 100 can also be arranged in any other compartment, including the settling compartment 15 and the isolation compartment 16. Optionally, the injection opening 100 can be omitted in other embodiments, if the opening 18 in the column wall 10 is used for injection instead of withdrawal of liquids, i.e., if the first liquid H is treated within the isolation compartment 16.

[0041] In other embodiments, one injection opening 100 in the column wall 10 can be replaced by a second plurality of injection openings 100 in the column wall 10, wherein the second plurality of injection openings 100 in the column wall 10 is distributed along the circumference of the settling compartment 15 or along the circumference of any other compartment below the settling compartment 15.

[0042] Notably, each agitated extraction column comprises inlets and outlets for admitting and discharging process liquids, wherein one advantageous configuration is that the agitated extraction column 1 comprises each an inlet and an outlet in the first, bottom-most, and last, upper-most compartment.

[0043] Fig. 2 shows a cross-sectional view of a section of a second embodiment of an agitated extraction column 1 , wherein in addition to the first embodiment shown in Fig. 1 , a sealing element 33 is provided for sealing between the bottom partition tray 31 and the drive shaft 13. This sealing 33 helps to prevent the second liquid L to enter the centrally arranged tube 32 in a counterflow direction, so that the performance of the isolation compartment 16 is enhanced.

[0044] Fig. 3 shows a cross-sectional view of a section of a third embodiment of an agitated extraction column 1, wherein in addition to the second embodiment shown in Fig. 2, an inlet chamber 40 is provided within the settling compartment 15, wherein a partition wall 41 is arranged coaxially with respect to the centrally arranged tube 32, wherein a partition wall end 42 is spaced from the bottom partition tray 31 in axial direction A for providing a gap between the bottom partition tray 31 and the partition wall end 42. This gap enables enhanced flow direction, guiding the first liquid H towards the flow passages 12 in the bottom partition tray, wherein the second liquid L is hindered from entering the inlet chamber 40 and thus further hindered to enter the centrally arranged tube 32.

[0045] In other embodiments, the settling compartment 15 can comprise an inlet chamber 40, even if no sealing element 33 is provided. Fig. 4 shows an illustration of the internal liquid flows within the section of the agitated extraction column shown in Fig. 1. It has to be understood that the reference to the first embodiment is exemplary, only. The illustration shown in Fig. 4 is also applicable to the other embodiments. In addition, Fig. 5 provides a more detailed illustration of the flows within the section of the same agitated extraction column shown in Fig. 4. The first liquid H (see Fig. 5) and the second liquid F (see Fig. 5) are immiscible, and the first liquid H exhibits a higher density than the second liquid L. The flows of the two immiscible liquids H, L are indicated by arrows, wherein the arrows with reference numeral HF represent the flow of the first liquid H and the arrows with the reference numeral LF represent the flow of the second liquid L. In Fig. 4, only the flows HF and LF are indicated, wherein Fig. 5 additionally shows the two liquids H, L.

[0046] In Fig. 5, all compartments are filled with the first liquid H, wherein the first liquid H is admitted to the agitated extraction column 1 from the top and leaves the agitated extraction column 1 at the bottom, and the second liquid L is admitted to the agitated extraction column 1 from the bottom and leaves the agitated extraction column 1 at the top. Thus, within the agitated extraction column 1 , the first liquid H flows from the top to the bottom and the second liquid L rises from the bottom to the top in form of bubbles. The opening 18 in the column wall 10 is used to withdraw the first liquid H from the isolation compartment 16 for external treatment, after which the treated first liquid H is re-injected through the injection opening 100 into the settling compartment 15 below the settling zone LS in the settling compartment 15. From the settling zone LS, the second liquid L is routed through the flow channels 20 into the merging compartment 17.

Claims

CLAIMS1. An agitated extraction column (1) for extracting a substance from a first liquid (H) into a second liquid (L), or from the second liquid (L) into the first liquid (H) by means of liquid-liquid extraction wherein both liquids are immiscible, and the first liquid (H) exhibits a higher density than the second liquid (L), wherein the agitated extraction column (1) is radially delimited by a column wall (10) and comprises a plurality of compartments is separated by partition trays (11), wherein each partition tray comprises at least one flow passage (12) through which at least one of the liquids can flow from one compartment into another adjacent compartment, further comprising a drive shaft (13) for rotating about an axial direction (A), an agitator (14) connected to the drive shaft (13) and configured for stirring the liquids, wherein one of the compartments is configured as a settling compartment (15) for separating the first and the second liquid (L) through gravitational forces, wherein the agitator (14) is arranged outside the settling compartment (15), characterized in that one of the compartments is configured as an isolation compartment (16) arranged adjacent to the settling compartment (15) in the axial direction (A), wherein the isolation compartment (16) is configured and arranged to supply the first liquid (H) from the isolation compartment (16) into the settling compartment (15), wherein the second liquid (L) is routed past the isolation compartment (16) into a merging compartment (17), and wherein the isolation compartment (16) comprises at least one opening (18) in the column wall (10) for exchange of liquids between the isolation (16) compartment and the outside of the column (1).

2. An agitated extraction column (1) in accordance with claim 1, wherein the isolation compartment (16) is arranged between the settling compartment (15) and the merging compartment (17) regarding the axial direction (A), wherein at least one flow channel (20) is provided for guiding the second liquid (L) from the settling compartment (15) into the merging compartment (17), wherein the flow channel (20) is configured to prevent the second liquid (L) from entering the isolation compartment (16).

3. An agitated extraction column (1) in accordance with anyone of the preceding claims, wherein the settling compartment (15) comprises a top partition tray (30) and a bottom partition tray (31), wherein the top partition tray (30) comprises a centrally arranged tube (32) extending into the settling compartment (15) and surrounding the drive shaft (13) at a distance to the drive shaft (13) for enabling the first liquid (H) to flow downwards along the drive shaft (13).

4. An agitated extraction column (1) in accordance with claim 3, wherein a sealing element (33) is provided for sealing between the bottom partition tray (31) and the drive shaft (13).

5. An agitated extraction column (1) in accordance with claim 3 or 4, wherein an inlet chamber (40) is provided within the settling compartment (15), wherein a partition wall (41) is arranged coaxially with respect to the centrally arranged tube (32), wherein a partition wall end (42) is spaced from the bottom partition tray (31) in axial direction (A) providing a gap between the bottom partition tray (31) and the partition wall end (42).

6. An agitated extraction column (1) in accordance with anyone of claims 2 - 5, wherein each isolation compartment (16) comprises at most eight hundred flow channels (20), wherein the total cross section with regard to the axial direction (A) of said flow channels (20) within each isolation compartment (16) is between one half and eighty percent of the cross section with regard to the axial direction (A) of the agitated extraction column (1), preferably between one and fifty percent, and most preferably between one and a half and twelve percent.

7. An agitated extraction column (1) in accordance with anyone of claims 3 - 6, wherein the vertical dimension of the centrally arranged tube (32) in the settling compartment (15) is between two and ninety eight percent of the vertical dimension of the settling compartment (15), preferably between five and eighty percent, and most preferably between fifteen and seventy percent, wherein the free cross section with regard to the axial direction (A) of the centrally arranged tube (32) around the drive shaft (13) is between one half and eighty percent of the cross section with regard to the axial direction (A) of the agitated extractioncolumn (1), preferably between one and fifty percent, and most preferably between two and thirteen percent.

8. An agitated extraction column (1) in accordance with anyone of the preceding claims, wherein the agitated extraction column (1) has a circular cross section, and all partition trays (11) have a circular form or are otherwise sealed or connected to the column wall (10).

9. An agitated extraction column (1) in accordance with anyone of the preceding claims comprising three to five hundred subsequent compartments in the axial direction (A), preferably four to three hundred, and most preferably five to one hundred.

10. An agitated extraction column (1) in accordance with anyone of the preceding claims wherein a first plurality of openings (18) in the column wall (10) is distributed along the circumference of the isolation compartment (16).

11. An agitated extraction column (1) in accordance with anyone of the preceding claims wherein a second plurality of injection openings (100) in the column wall (10) is distributed along the circumference of the settling compartment (15) or along the circumference of any other compartment below the settling compartment (15).

12. An agitated extraction column (1) in accordance with anyone of the preceding claims, wherein a plurality of compartments comprises agitators (14), wherein preferably each compartment of the plurality of compartments comprises one agitator (14), wherein the agitators (14) are configured to transport the liquids predominantly in horizontal radial and tangential direction, while minimizing vertical conveying effects.

13. An agitated extraction column (1) in accordance with anyone of the preceding claims, wherein the number of isolation compartments (16) is between one and three hundred, preferably one and one hundred, and most preferably between one and eighty.

14. An agitated extraction column (1) in accordance with any of the preceding claims, wherein the first, bottom-most, and last, upper-most compartment each comprise an inlet and an outlet.

15. A process to separate substances, wherein one or more substances are extracted from a first liquid (H) into a second liquid (L), or from the second liquid (L) into the first liquid (H) by means of liquid-liquid extraction, wherein both liquids are immiscible, wherein both liquids are brought into intimate contact, wherein the first liquid (H) exhibits a higher density than the second liquid (L), wherein the extraction is based on differing solubilities of the substances in the immiscible liquids, wherein a feed solution containing the substances to be extracted and a solvent are admitted into an agitated extraction column (1) in accordance with anyone of the claims 1-13 in countercurrent direction, wherein the agitated extraction column (1) is oriented vertically, wherein the first liquid (H) is admitted to the agitated extraction column (1) from the top and the second liquid (L) is admitted to the agitated extraction column (1) from the bottom, wherein a treatment of the first liquid (H) is required during the extraction process, wherein the treatment of the first liquid (H) requires separation of the first liquid (H) from the second liquid (L), characterized in that the separation of the first liquid (H) and the second liquid (L) is performed inside the agitated extraction column (1) in a settling compartment (15), wherein the second liquid (L) is routed past an isolation compartment (16), enabling operando treatment of the first liquid (H) in the isolation compartment (16) through injection of treatment agents through an opening (18) in the column wall (10), or extraction of the first liquid (H) from the isolation compartment through an opening (18) in the column wall (10) for treatment outside of the agitated extraction column (1) before reinjection of the treated first liquid (H) into the agitated extraction column (1) in any compartment, preferably below the isolation compartment (15), through an injection opening (100) in the column wall (10).

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