Pulse column having packing for liquid-liquid extraction

Abstract

To provide a pulse column for liquid-liquid extraction, which has as high mixing efficiency as possible and a satisfactory hydrodynamic function over as wide a range of an operation parameter values as possible.SOLUTION: A pulse column comprises a cylindrical tube 10 having a longitudinal axis Z and an inner diameter D0, and a packing 20 located inside the tube. The packing comprises a rod 30 extending along the longitudinal axis, and a plurality of truncated disks 40 that is regularly distributed and fixed at intervals E along the rod, each of the truncated disks extending in a transverse plane P perpendicular to the rod. Each truncated disk has, as the outer periphery in the transverse plane, two arcs of a circle of a radius R, which are connected by two identical and parallel linear edges 41 spaced apart by a distance D, and any two adjacent truncated disks are oriented with respect to each other in the transverse plane by a non-zero orientation angle.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present invention belongs to the field of chemical engineering, in particular to the field of liquid-liquid extraction. Among the various devices for continuous liquid-liquid extraction operations, the pulse column is known, which comprises a cylindrical tube and a set of immobile solid objects (so-called packing) that impede the movement of the liquids and are contained inside the tube. During operation, the tube is positioned vertically and two immiscible liquids circulate in the tube in opposite directions (the heavier liquid is introduced at the top and the lighter liquid at the bottom). Under the effect of pulsing (vibrational movement applied to all the liquids) and the packing, one of the liquids is dispersed in the other liquid in the form of droplets. This dispersion increases the contact surface between the two liquids, allowing one or more solutes initially contained in one of these liquids to migrate into the other liquid.

[0002] The invention therefore relates to a pulse column for liquid-liquid extraction comprising a cylindrical tube having a longitudinal axis Z and an internal diameter D0 and a packing located inside the tube. [Background technology]

[0003] Several solutions are known for the packing contained in the tube. In a first solution shown in Fig. 4A, the packing 120 consists of a rod 130 and a series of regularly spaced elements 140 attached to the rod 130 and passing through them. The rod 130 extends along a longitudinal axis Z, which is the longitudinal axis of the tube 110. The tube 110 is shown diagrammatically with dashed lines. Each element 140 is a truncated circular disc 143, i.e. the disc has a single straight edge whose length is less than the diameter of the disc, the remainder of the circumference of the disc being a part of a circle. Each truncated disc 143 extends in a transverse plane (perpendicular to the longitudinal axis Z). The truncated disks 143 are placed along the rod 130 such that any two adjacent truncated disks 143 are oriented at an angle of 180° to each other (i.e., two adjacent disks 143 are symmetrical to each other about the longitudinal axis Z if they are placed in the same transverse plane). The distance between two adjacent truncated disks 143 is constant. This packing is called "truncated disk packing".

[0004] However, in the case of small diameter tubes, for example those of the order of 15 mm, and / or when one of the liquids has a viscosity much greater than that of the other, packings with truncated disks are inefficient. Inefficient means that the mass transfer between the two liquids is too small compared to perfect theoretical mixing, and the column height is too high to obtain a given mass transfer. One cause of this low efficiency is excessive axial mixing, often along the longitudinal axis Z. This mixing is called the axial dispersion coefficient D ax The higher this coefficient, the less efficient the mass transfer within the column. Thus, for a column with a diameter of 15 cm and a liquid with a viscosity of 8 cP (centipoise) and a flow rate of 2 L / h / cm 2For a total specific flow rate of 1.5 cm (i.e., a two-phase total specific flow rate of 3.5 L / h), a pulse amplitude of 1.5 cm and a pulse frequency of 1 Hz (this test is called the standard test), a 6.9 cm diameter tube with truncated disks spaced 2 cm apart is used. 2 / s axial dispersion coefficient D ax is obtained.

[0005] To try to improve the efficiency of the column, a first solution is envisaged, which consists in reducing the distance between the elements 140. Tests carried out have shown that this configuration reduces the axial dispersion coefficient D ax The standard test above showed that it was possible to reduce the 2 / s D ax is obtained for truncated disks spaced 1 cm apart, which is 6.9 cm for truncated disks spaced 2 cm apart. 2 / s D ax Lower than.

[0006] A second solution is envisaged, as shown in Fig. 4B, in which the packing 120 consists of two parallel rods 130 and a series of regularly spaced elements 140 attached to them, through which the two rods pass. These rods 130 extend along a longitudinal axis Z, which is the longitudinal axis of the tube 110. The tube 110 is shown diagrammatically in dashed lines. A first form of the element 140 is a ring 141 (a circular disk in whose centre a hole is drilled to form a ring), and a second form of the element 140 is a circular disk 142 with a diameter larger than the diameter of the hole in the ring 141 and smaller than the outer diameter of the ring 141. Each ring 141 and each disk 142 extends in a transverse plane P (perpendicular to the longitudinal axis Z). The rings 141 and discs 142 are alternately placed along the two rods 130 such that each disc 142 is located between two rings 141, and the distance between a ring 141 and an adjacent disc 142 is constant. This packing is called "disc and ring packing". In the above standard test, the distance between a ring 142 and an adjacent disc 141 is equal to 1 cm and is 3.5 cm.2 / s D ax which is 6.9 cm for truncated disks spaced 2 cm apart. 2 / s D ax lower than the value.

[0007] However, tests carried out with the first and second solutions above have shown that the range of operating parameters (pulse amplitude, frequency of the column, and flow rate through the column) within which there is a satisfactory hydrodynamic function is narrower compared to configurations in which the elements 140 are spaced further apart. In particular, the maximum total specific flow rate before congestion of the column (i.e. when the two liquids cannot circulate in opposite directions) DST max Disk truncation (DST) max =3L / h / cm 2 ) rather than the first solution (DST max =2L / h / cm 2 ) and the second solution (DST max =1.8L / h / cm 2 ) is smaller. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to remedy these drawbacks.

[0009] The present invention aims to propose a pulse column for liquid-liquid extraction with as high a mixing efficiency as possible and a satisfactory hydrodynamic functioning over as wide a range of operating parameter values ​​as possible. [Means for solving the problem]

[0010] This object is achieved by the fact that the packing comprises a rod extending along a longitudinal axis Z and a number of truncated disks regularly distributed along and fixed to said rod, each of said truncated disks extending in a transverse plane P perpendicular to said rod with a spacing E therebetween, each truncated disk having as its periphery in the transverse plane P two arcs of a circle of radius R connected by two identical and parallel straight edges spaced a distance D apart, any two adjacent disks being oriented with respect to each other in the transverse plane by a non-zero orientation angle.

[0011] These provisions result in more efficient mixing of the two liquids in the pulse column: the hydrodynamic performance is satisfactory over a wider range of operating parameter values ​​than is the case with prior art packings.

[0012] For example, the spacing between two adjacent disks is constant.

[0013] For example, the spacing E is on the order of magnitude of the inner diameter D0 of the tube.

[0014] For example, the spacing E is smaller than the inner diameter D0 of the tube.

[0015] For example, the inner diameter D0 is smaller than 50 mm.

[0016] For example, the spacing E between two adjacent discs is equal to 10 mm and the inner diameter D0 of the tube is equal to 15 mm.

[0017] For example, the ratio of the lateral surface area of ​​the disk to the internal cross-sectional surface area of ​​the tube is between 75% and 80%.

[0018] For example, at least the surface of the disc is made from a hydrophilic material.

[0019] For example, at least the surface of the disk is made from a hydrophobic material.

[0020] For example, the straight edges are crenelated.

[0021] For example, the orientation angle is equal to 90°.

[0022] The invention will be more clearly understood and its advantages will best appear from a reading of the following detailed description of embodiments illustrated by way of non-limiting examples, the present description making reference to the accompanying drawings, in which: [Brief description of the drawings]

[0023] [Figure 1A] FIG. 1A is a side view of a pulse column for liquid-liquid extraction according to the present invention. [Figure 1B] FIG. 1B is a cross-sectional view taken along line BB of FIG. 1A, showing a truncated disk according to the present invention. [Diagram 2] FIG. 2 is a perspective view of a portion of the pulse column of FIG. 1A. [Diagram 3] FIG. 3 is a perspective view of another embodiment of a truncated disk of a pulse column in accordance with the present invention. [Figure 4A] FIG. 4A, previously described, is a perspective view of a portion of a prior art pulse column. [Figure 4B] FIG. 4B, previously described, is a perspective view of a portion of another prior art pulse column. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 1A shows a pulse column 1 positioned vertically that allows for continuous liquid-liquid extraction by circulating two immiscible liquids in opposite directions within the pulse column 1 (heavy liquid introduced at the top and light liquid introduced at the bottom) and applying pulses (vibrational motion) to the two liquids, for example, one of the liquids is aqueous (e.g., water) and the other is organic.

[0025] The pulse column 1 comprises a cylindrical tube 10 of longitudinal axis Z and inner diameter D0 and a packing 20 located inside the tube 10. The packing 20 comprises a rod 30 extending along the longitudinal axis Z and a number of truncated disks 40 regularly distributed along the rod 30. For example, the rod 30 is located at the center of the tube 10 and therefore has a longitudinal axis Z passing through the rod 30. For example, the rod 30 is cylindrical in shape. The disks 40 are provided with holes through which the rod 30 passes and are fixed to the rod 30 by any means, for example welding. Two adjacent disks 40 are spaced apart by a distance E (called the spacing) measured along the longitudinal axis Z. For example, this spacing E is constant (i.e. identical for any two adjacent disks 40). Each disk 40 extends in a transverse plane P (i.e. perpendicular to the longitudinal axis Z and therefore perpendicular to the rod 30).

[0026] FIG. 1B is a cross-sectional view along the line BB in FIG. 1A, showing the disks 40 (i.e., in their transverse plane P). Each disk 40 has as its periphery, in the transverse plane P, two arcs of a circle of radius R and centre C, the two arcs being separate and identical and connected by two identical and parallel straight edges 41 spaced apart by a distance D. Thus, the disk 40 is cut in two points and is symmetrical with respect to its centre C, through which the longitudinal axis Z passes. The orientation axis A of the disk 40 in the plane P is defined as a transverse axis passing through the centre C and parallel to the straight edges 41. Any two adjacent disks 40 (referred to as first and second disks) are oriented with respect to each other in the transverse plane P by a non-zero orientation angle θ. As shown in FIG. 2, the orientation angle θ is the angle between the orientation axis A1 of the first disk 40 and the orientation axis A2 of the second disk 40.

[0027] For example, as shown in FIG. 2, the orientation angle θ is equal to 90° (ie, any two adjacent disks 40 are at right angles with respect to each other).

[0028] For example, the spacing E between two adjacent disks 40 is of the same order of magnitude as the inner diameter D0 of the tube 10. For example, this spacing E is smaller than the inner diameter D0 of the tube 10. For example, the inner diameter D0 of the tube 10 is smaller than 50 mm, for example smaller than 15 mm. For example, the spacing E is equal to 10 mm.

[0029] The inventors carried out tests under the same operating conditions of the pulse column as described above (standard test) when used with prior art packings. Thus, a column with an internal diameter D0 of 15 cm, a spacing E of 1 cm and one liquid with a viscosity of 8 cP (centipoise), a flow rate of 2 L / h / cm 2 For a total specific flow rate of 3.5 L / h (i.e., a biphasic total specific flow rate of 3.5 L / h), a pulse amplitude of 1.5 cm and a pulse frequency of 1 Hz, the inventors 2 / s D ax The maximum total specific flow rate (TSFR) before congestion of the obtained column was obtained for the range of use. max is 3L / h / cm 2 These D ax and DST max The values ​​are superior to those obtained using prior art packing.

[0030] The permeability of Packing 20 is S L the surface area left for the free passage of liquid through the disk 40, called the surface area S T This means the ratio of the surface area of ​​the cross section of the tube 10 (in a plane perpendicular to the internal longitudinal axis Z), called S T =π(1 / 2D0) 2 The surface area S left for the liquid to pass freely is L is S L =S1+S2, where S1 is the surface area of ​​a ring with an outer diameter of 1 / 2D0 and an inner diameter of R (i.e., S1=S T -πR 2 ) and S2 is the removed surface area of ​​the disk 40. The removed surface area S2 of the disk 40 is calculated by subtracting the surface area S of the disk 40 from the surface area of ​​a circle of radius R. D(i.e., the surface area of ​​this disk 40 in a plane perpendicular to the longitudinal axis Z). Therefore, the surface area S of the disk 40 D is S D = {[α-sin(α)]·R 2}, cos(α / 2)=(D / 2R), where α is the truncated angular sector shown in FIG. 1B, and D is the distance defined above and shown in FIG. 1. Thus, the removed surface area S2 of the disk 40 is S2=πR 2 -S D Therefore, the transparency is equal to S L / S T is equal to.

[0031] For example, this transmission is between 20% and 25%. For example, an inner diameter D0 of the tube 10 equal to 15 mm, a radius R of the disk 40 equal to 7.25 mm and a distance D equal to 10.55 mm results in a transmission of 22%. A transmission between 20% and 25% corresponds to an inner cross section S of the tube 10 between 75% and 80%. T The lateral surface area S of the disk 40 D Ratio of S D / S T This is equivalent to S T =S D +S1+S2=S D +S L and therefore S D / S T = 1 - {transparency}.

[0032] For the embodiment shown in Fig. 3, the straight edge 41 of each disk 40 is crenelated (i.e., each straight edge 41 has a crenellation 415). The relief of this crenellation 415 is visible to the naked eye and is distinct from roughness, which is not visible to the naked eye. This crenellation 451 helps the formation of smaller droplets and contributes to improving the efficiency of mixing of the two liquids circulating in the tube 10.

[0033] The disk 40 can be made of any material. Advantageously, the material is hydrophilic (e.g. stainless steel) or at least the surface of the disk 40 is made of a hydrophilic material, which reduces adhesion of organic liquids to the disk 40. Alternatively, the material is hydrophobic or at least the surface of the disk 40 is made of a hydrophobic material (e.g. the disk 40 is made of stainless steel covered with a polymer or the like), which reduces adhesion of water to the disk 40 (the operation is said to be in the "continuous organic phase"). [Explanation of symbols]

[0034] 1 Pulse Column 10 Cylindrical tube 20 Packing 30 Rod 40 truncated disc 41 Straight Edge 110 Tube 120 Packing 130 Rod 140 elements 143 Truncated Disk 415 Cleaneration A orientation axis A1: Orientation axis of the first disk A2 Orientation axis of the second disk C center D0 inner diameter E interval P horizontal plane R radius S D surface area S L surface area S T surface area Z vertical axis α angle θ orientation angle

Claims

1. Vertical axis (Z) and inner diameter (D ０ ) a cylindrical tube (10); a packing (20) located inside the tube (10); A pulsed column for liquid-liquid extraction comprising: The packing (20) is a rod (30) extending along said longitudinal axis (Z); a plurality of truncated disks (40) regularly distributed at intervals (E) along said rod (30) and fixed thereto, each of said truncated disks (40) extending in a transverse plane (P) perpendicular to said rod (30); 1. A pulse column (1), characterized in that each of the truncated disks (40) has as its periphery in the transverse plane (P) two arcs of a circle of radius (R) connected by two identical and parallel straight edges (41) spaced a distance D apart, and any two adjacent truncated disks (40) are oriented with respect to each other in the transverse plane (P) by a non-zero orientation angle (θ).

2. 2. The pulse column (1) of claim 1, wherein the spacing (E) between two adjacent truncated disks (40) is constant.

3. The spacing (E) is the inner diameter (D ０ 3. The pulse column (1) of claim 2, wherein the pulse width is of the same order of magnitude as the pulse width .

4. The spacing (E) is the inner diameter (D ０） 4. The pulse column (1) according to claim 2 or 3, wherein

5. The inner diameter (D ０ 5. The pulse column (1) according to claim 1, wherein the distance between the first and second electrodes is less than 50 mm.

6. The spacing (E) is equal to 10 mm, and the inner diameter (D ０） The pulse column (1) according to claim 5, wherein is equal to 15 mm.

7. The inner cross-sectional surface area (S Ｔ ) of the lateral surface area (S Ｄ 7. The pulse column (1) according to claim 1, wherein the ratio of

8. 8. A pulse column (1) according to any one of claims 1 to 7, wherein at least a surface of the truncated disc (40) is made from a hydrophilic material.

9. 8. A pulse column (1) according to any one of claims 1 to 7, wherein at least a surface of the truncated disc (40) is made from a hydrophobic material.

10. The pulse column (1) according to any one of claims 1 to 9, wherein the straight edge (41) is cleaned.

11. 11. A pulse column (1) according to any one of the preceding claims, characterized in that the orientation angle (θ) is equal to 90°.

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