Pulsed column for liquid-liquid extraction with packing

Abstract

The invention relates to a pulsed column (1) for liquid-liquid extraction comprising a cylindrical tube (10) with a longitudinal axis (Z) and an internal 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 plurality of truncated discs (40) fixed and distributed regularly along the rod (30) with a spacing (E) and each extending in a transverse plane (P) perpendicular to the rod (30), each of the truncated discs (40) having as its perimeter in the transverse plane (P) two arcs of a circle of radius (R) connected by two identical parallel rectilinear edges (41) spaced apart by a distance (D), any two of the adjacent truncated discs (40) being oriented relative to each other in the transverse plane (P) by a non-zero orientation angle (θ). Abstract figure: Figure 1A

Description

Title of the invention: Pulsed column for liquid-liquid extraction with packing

[0001] The present invention lies in the field of chemical engineering and more particularly in liquid-liquid extraction. Among the various devices for carrying out a continuous liquid-liquid extraction operation, the pulsed column is known, which comprises a cylindrical tube and a set of immobile solid parts constituting an obstacle to the movement of the liquids, called packing and housed inside this tube. In operation, this tube is placed vertically and two immiscible liquids circulate in this tube in opposite directions (the heavier liquid being introduced at the top and the lighter liquid being introduced at the bottom). Under the effect of the pulsation (oscillating movement applied to all the liquids) and the packing, one of the liquids is dispersed in the other in the form of drops.This dispersion increases the contact surface between the two liquids, which allows one or more solutes initially contained in one of these liquids to be transferred to the other liquid.

[0002] Thus, the invention relates to a pulsed column for liquid-liquid extraction comprising a cylindrical tube with longitudinal axis Z and internal diameter Do and a packing located inside the tube.

[0003] Several solutions are known concerning the packing housed in the tube. In a first solution illustrated in [Fig.4A], the packing 120 consists of a rod 130 and a series of regularly spaced elements 140 mounted on this rod 130 which passes through these elements 140. This rod 130 extends along the longitudinal axis Z which is the longitudinal axis of the tube 110. The tube 110 is shown schematically in dotted lines. Each element 140 is a truncated circular disc 143, that is to say that the disc has a single rectilinear edge whose length is less than the diameter of the disc, the remainder of the circumference of the disc being a portion of a circle. Each truncated disc 143 extends in a transverse plane (perpendicular to the longitudinal axis Z).The truncated discs 143 are arranged along the rod 130 such that any two adjacent truncated discs 143 are oriented 180° to each other (i.e., two adjacent discs 143, if arranged in the same transverse plane, would be symmetrical to each other about the longitudinal axis X). The distance between two adjacent truncated discs 143 is constant. This packing is called "truncated disc packing".

[0004] However, the truncated disc packing has insufficient efficiency in the case of small diameter tubes, for example diameters of the order of 15 mm, and / or in the case where one of the liquids has a viscosity much higher than the viscosity of the other liquid. Insufficient efficiency means a mass transfer between the two liquids that is too low compared to a theoretically perfect mixer, and a column height that is too great to obtain a given mass transfer. One cause of this low efficiency is often excessive axial mixing (along the longitudinal axis Z). This mixing is characterized by an axial dispersion coefficient Dax. The higher this coefficient, the lower the efficiency of the mass transfer achieved in the column.Thus, for a column with a diameter of 15 cm and one of the liquids with a viscosity of 8 cP (centipoise), a total specific flow rate (TSF) of 2 L / h / cm2 (i.e. a total flow rate of the two phases of 3.5 L / h), a pulsation amplitude of 1.5 cm and a pulsation frequency of 1 Hz (this test is called the standard test), we obtain an axial dispersion coefficient Dax of 6.9 cm2 / s for truncated discs spaced 2 cm apart.

[0005] In an attempt to improve the efficiency of the column, a first solution was considered which consists of reducing the distance between the elements 140. The tests carried out showed that this configuration allowed a reduction in the axial dispersion coefficient Dax of the column. For the standard test above, a Dax of 2.1 cm2 / s is obtained for truncated discs spaced 1 cm apart, which is lower than the Dax value of 6.9 cm2 / s for truncated discs spaced 2 cm apart.

[0006] A second solution has also been considered, illustrated in [Fig.4B], in which the lining 120 is made up of two parallel rods 130 and a series of regularly spaced elements 140 mounted on these two rods which pass through these elements 140. These rods 130 extend along the longitudinal axis Z which is the longitudinal axis of the tube 110. The tube 110 is shown schematically in dotted lines. A first type of element 140 is a crown 141 (circular disc pierced in its center with a hole to form a ring) and a second type of element 140 is a circular disc 142 whose diameter is greater than the diameter of the hole in the crown 141 and less than the outside diameter of the crown 141. Each crown 141 and each disc 142 extends in a transverse plane P (perpendicular to the longitudinal axis Z).The rings 141 and the discs 142 are arranged alternately along the two rods 130 so that each disc 142 is located between two rings 141, and the distance between a ring 142 and an adjacent disc 141 is constant. This packing is called "disc and ring packing". For the standard test above, and with a distance between a ring 142 and an adjacent disc 141 equal to 1 cm, a Dax of 3.5 cm2 / s is obtained, which is lower than the Dax value of 6.9 cm2 / s for truncated discs spaced 2 cm apart.

[0007] However, the tests carried out with the first solution and with the second solution above have shown that the ranges of values ​​of the operating parameters (amplitude and pulsation frequency in the column, flow rate through the column) for which satisfactory hydrodynamic operation exists were reduced compared to the configuration where the elements 140 were more spaced apart. In particular, the maximum total specific flow rate (TSF) before clogging of the column (i.e. the impossibility of circulation of the two liquids in countercurrent) TSFmax is lower for the first solution (TSFmax = 2 L / h / cm2) and for the second solution (TSFmax = 1.8 L / h / cm2) than for more spaced truncated discs (TSFmax = 3 L / h / cm2). Description of the invention

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

[0009] The invention aims to propose a pulsed column for liquid-liquid extraction which has the highest possible mixing efficiency, and satisfactory hydrodynamic operation over the widest possible range of operating parameter values.

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

[0011] Thanks to these arrangements, the mixing of the two liquids within the pulsed column is carried out more efficiently. The hydrodynamic operation is satisfactory over a range of operating parameter values ​​which is wider than in the case of the packings of the prior art.

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

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

[0014] For example, the spacing E is less than the diameter Do of the tube.

[0015] For example, the diameter Do of the tube is less than 50 mm.

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

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

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

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

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

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

[0022] The invention will be well understood and its advantages will appear better, on reading the detailed description which follows, of embodiments shown as non-limiting examples. The description refers to the appended drawings in which:

[0023] [Fig. 1] [Fig. 1] is, in (A) a side view of a pulsed column for liquid-liquid extraction according to the invention; in (B) a section along line BB of [Fig.lA] which shows a truncated disc according to the invention.

[0024] [Fig.2] [Fig.2] is a perspective view of a portion of the pulsed column of the [Fig.lA],

[0025] [Fig.3] [Fig.3] is a perspective view of another embodiment of a truncated disk of the pulsed column according to the invention.

[0026] [Fig. 4] [Fig. 4], already described, is, in (A), a perspective view of a portion of a pulsed column according to the prior art; in (B) a perspective view of a portion of another pulsed column according to the prior art. Detailed description of the invention

[0027] [Fig.1A] illustrates a pulsed column 1 which allows continuous liquid-liquid extraction by vertically positioning this pulsed column 1 and circulating two immiscible liquids in opposite directions in this pulsed column 1 (the heavier liquid being introduced at the top and the lighter liquid being introduced at the bottom) and then applying a pulsation (oscillating movement) to these two liquids. For example, one of these liquids is aqueous (e.g. water) and the other liquid is organic.

[0028] The pulsed column 1 comprises a cylindrical tube 10 with a longitudinal axis Z and an internal diameter Do and a packing 20 located inside this tube 10. The packing 20 comprises a rod 30 which extends along the longitudinal axis Z and a plurality of truncated discs 40 distributed regularly along the rod 30. For example, the rod 30 is located in the center of the tube 10 and is therefore crossed by the longitudinal axis Z. For example, the rod 30 is cylindrical. The discs 40 are provided with a hole through which the rod 30 passes and are fixed to the rod 30 by any means, for example by welding. Two adjacent discs 40 are spaced apart by a distance E (called spacing) measured along the longitudinal axis Z. For example, this spacing E is constant, that is to say, is identical for any two adjacent discs 40. Each of the discs 40 extends in a transverse plane P, that is to say perpendicular to the longitudinal axis Z and thus to the rod 30.

[0029] [Fig.lB] is a section along line BB of [Fig.lA] which shows a disc 40, that is to say in its transverse plane P. Each of the discs 40 has as its perimeter in the transverse plane P two arcs of a circle of radius R and center C which are disjoint and identical and which are connected by two identical parallel rectilinear edges 41 spaced apart by a distance D. The disc 40 is therefore truncated in two places, and is symmetrical by relative to its center C through which the longitudinal axis Z passes. The orientation axis A of a disc 40 in the plane P is defined as the transverse axis which passes through the center C and which is parallel to the rectilinear edges 41. Any two adjacent discs 40 (called first and second discs) are oriented relative to each other in the transverse plane P by a non-zero orientation angle 0. As illustrated in [Fig.2], the orientation angle 0 is the angle between the orientation axis A1 of the first disc 40 and the orientation axis A2 of the second disc 40.

[0030] For example, the orientation angle 0 is equal to 90°, as illustrated in [Fig.2], that is to say that any two adjacent discs 40 are at right angles to each other.

[0031] For example, the spacing E between two adjacent discs 40 is of the order of magnitude of the diameter Do of the tube 10. For example, this spacing E is less than the diameter Do of the tube 10. For example, the diameter Do of the tube 10 is less than 50 mm, for example less than 15 mm. For example, the spacing E is equal to 10 mm.

[0032] The inventors carried out tests under the same operating conditions of the pulsed column as described above (standard test) in the case of using the packings of the prior art. Thus, for a column with an internal diameter Do = 15 cm, a spacing E = 1 cm and one of the liquids with a viscosity of 8 cP (centipoise), a total specific flow rate (DST) of 2 L / h / cm2 (i.e. a total flow rate of the two phases of 3.5 L / h), a pulsation amplitude of 1.5 cm and a pulsation frequency of 1 Hz, the inventors obtained a Dax of 3.6 cm2 / s. Concerning the range of use, the maximum total specific flow rate (DST) before clogging of the column DSTmax obtained was equal to 3 L / h / cm2. These values ​​of Dax and DSTmax are better than those obtained with the use of the packings of the prior art.

[0033] The transparency of the lining 20 is the ratio of the surface area left free for the passage of liquids at the level of a disc 40, called SL, to the surface area of ​​the internal cross-section (in a plane perpendicular to the longitudinal axis Z) of the tube 10, called ST, and which is therefore ST = ir-^ / zDo)2. The surface area left free for the passage of liquids SL is SL = S1+S2 where SI is the surface area of ​​a ring of external radius / zDq and internal radius R, i.e. SI = (ST - jtR2) and S2 is the surface area removed from a disc 40. The surface area S2 removed from a disc 40 is equal to the surface area of ​​a circle of radius R minus the surface area SD of the disc 40 (i.e. the surface area of ​​this disc 40 in a plane perpendicular to the longitudinal axis Z). The surface SD of the disk 40 is therefore SD = {[a -sin(a)]-R2} with cos(a / 2) = D / (2R) where a is the angle of the truncated angular sectors, illustrated in [Fig.lB] and D is the distance defined above and illustrated in [Fig. 1].The removed surface S2 of a 40 disc is therefore equal to S2 = irR2 - SD. The transparency is thus equal to SL / ST.

[0034] For example, this transparency is between 20% and 25%. For example, the diameter Do of tube 10 is equal to 15 mm, radius R of disc 40 is equal to 7.25 mm and distance D is equal to 10.55 mm, which gives a transparency of 22%. A transparency of between 20% and 25% corresponds to a ratio SD / ST of the cross-sectional area SD of disc 40 to the surface of the internal cross-section ST of tube 10 of between 75% and 80%. Indeed, ST = SD + SI + S2 = SD + SL and therefore SD / ST = 1 - {transparency}

[0035] According to an embodiment illustrated in [Fig. 3], the rectilinear edges 41 of each disc 40 are notched, that is to say that each rectilinear edge 41 has a notch 415. The reliefs of this notch 415 are visible to the naked eye and are distinct from a roughness, a roughness not being visible to the naked eye. This notch 415 promotes the formation of smaller drops and contributes to increasing the efficiency of the mixing of the two liquids which circulate in the tube 10.

[0036] The discs 40 can be made of any material. Advantageously, this material is hydrophilic (for example stainless steel), or at least the surface of the discs 40 is made of a hydrophilic material, which minimizes the adhesion of the organic liquid to the discs 40 (operation called in “continuous aqueous phase”). Alternatively, this material is hydrophobic (for example a polymer such as PTFE), or at least the surface of the discs 40 is made of a hydrophobic material (for example the disc 40 is made of stainless steel covered with such a polymer), which minimizes the adhesion of water to the discs 40 (operation called in “continuous organic phase”).

Claims

Claims

1. Pulsed column (1) for liquid-liquid extraction comprising a cylindrical tube (10) with longitudinal axis (Z) and internal diameter (Do) and a packing (20) located inside said tube (10), said packing (20) being characterized in that it comprises a rod (30) extending along said longitudinal axis (Z) and a plurality of truncated discs (40) fixed and distributed regularly along said rod (30) with a spacing (E) and each extending in a transverse plane (P) perpendicular to said rod (30), each of said truncated discs (40) having as its perimeter in said transverse plane (P) two arcs of a circle of radius (R) connected by two identical parallel rectilinear edges (41) spaced apart by a distance (D), any two of said adjacent truncated discs (40) being oriented relative to each other in said transverse plane (P) by a non-zero orientation angle (0).

2. Pulsed column (1) according to claim 1 such that said spacing (E) between two adjacent discs (40) is constant.

3. Pulsed column (1) according to claim 2 such that said spacing (E) is of the order of magnitude of said diameter (Do) of the tube (10).

4. Pulsed column (1) according to claim 2 or 3 such that said spacing (E) is less than said diameter (Do) of the tube (10).

5. Pulsed column (1) according to any one of claims 1 to 4 such that said diameter (Do) of the tube (10) is less than 50 mm.

6. Pulsed column (1) according to claim 5 such that said spacing (E) is equal to 10 mm and said diameter (Do) of the tube (10) is equal to 15

7. mm. Pulsed column (1) according to any one of claims 1 to 6 such that the ratio of the cross-sectional area (SD) of said disc (40) to the internal cross-sectional area (ST) of said tube (10) is between 75% and 80%.

8. Pulsed column (1) according to any one of claims 1 to 7 such that at least the surface of said discs (40) is made of a hydrophilic material.

9. Pulsed column (1) according to any one of claims 1 to 7 such that at least the surface of said discs (40) is made of a hydrophobic material.

10. Pulsed column (1) according to any one of claims 1 to 9 such that said rectilinear edges (41) are crenellated.

11. Pulsed column (1) according to any one of claims 1 to 10 characterized in that said orientation angle (0) is equal to 90°.

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