EP1379867A1

EP1379867A1 - Protective device for the chromatographic bed in dynamic axial compression chromatographic columns

Info

Publication number: EP1379867A1
Application number: EP02761925A
Authority: EP
Inventors: Wilhelm Hauck; Harlene Marks; Jean Blehaut; Roger-Marc Nicoud
Original assignee: Novasep SAS
Current assignee: Novasep Process SAS
Priority date: 2001-04-10
Filing date: 2002-04-09
Publication date: 2004-01-14
Also published as: FR2823134B1; US20040099604A1; WO2002084275A1; US7132053B2; FR2823134A1

Abstract

The invention concerns a chromatographic device comprising: a column (12) for receiving a chromatographic bed (14) through which flows a first fluid; a piston (36) sliding inside the column (12) and exerting pressure on the bed (14), a chamber (28) containing a second fluid exerting pressure on the piston (36); a regulator (52) for the pressure exerted by the piston (36) on the bed based on the pressure inside the chamber (28), on the flow pressure of the first fluid at the intake of the column (12) and on a reference pressure on the bed (14). Said device enables to separate at least two compounds to be subjected to chromatographic analysis, while adjusting the pressure exerted on the chromatographic bed. The device efficiently uses the chromatographic bed while protecting it.

Description

CHROMATOGRAPHIC BED PROTECTION DEVICE

IN THE CHROMATOGRAPHIC COLUMNS

DYNAMIC AXIAL COMPRESSION

Field of the invention

The present invention relates to the protection of the chromatographic bed of chromatographic columns and in particular in columns with dynamic axial compression.

Technological background In a separation process by chromatography, the efficiency of the column used is a key parameter. The column is generally filled with a solid product in the form of very fine grains, usually between 5 and 100 μm in size, forming the chromatographic bed. In order to obtain high efficiency, the arrangement of the grains inside the column must be as homogeneous as possible and, moreover, empty volumes must be avoided between the chromatographic bed and the inputs-outputs of the column. It is known in the prior art to use columns with dynamic axial compression in order to ensure the existence of a compact bed, with no free space between the inlet-outlet distributors and the bed.

Thus, known from French patent application FR-A-2 219 797 is a chromatography device in the form of a column intended to contain a bed of adsorbent material. The apparatus consists of a tube comprising a cover and a body sliding in the tube for exerting pressure in the tube. The sliding body is a piston comprising at its head a porous plate permeable to fluids. To obtain the bed intended for chromatography, a suspension of particles of a material capable of constituting an adsorbent bed is introduced into the tube devoid of its cover, the piston being set back enough to allow the introduction of the suspension, without being necessarily in neutral. The cover is adapted to the tube, then pressure is exerted on said suspension by means of the piston. The liquid is discharged through the porous plates, and said particles are compressed between the piston and the cover. This device makes it possible, in an exemplary embodiment, to reach the stage of compression of the bed chosen and the settlement of the particles desired when the sliding body has traveled 2/5 of the height of the column.

However, this device has the disadvantage of achieving imprecise settlement of the bed, since it is evaluated by the sole position of the piston along the tube.

Also known from European patent application EP-A-0 145 578, under priority of applications FR-A-2 556 099 and FR-A-2 573 532, a chromatography apparatus comprising a tube of which a part is intended for contain an adsorbent bed. This tube has two end walls and a piston sliding longitudinally in the tube. The piston marks between the two end walls a separation between a chamber chromatography containing the bed and an enclosure in which a pressure prevails so as to move the piston along the tube. The particularity of this device is that the fluid contained in the enclosure is liquid to be chromatographed derived from the inlet pipe thereof. A part of the liquid is diverted towards the enclosure by an enclosure conduit and the other part of the liquid is entrained towards the chromatographic chamber by a flow conduit passing through the enclosure and the piston. At equilibrium of the piston, the force exerted on the side of the enclosure on the piston is equal to the sum of the force on the piston caused by the flow of the liquid in the chamber to be chromatographed and the mechanical force of the bed on the piston.

This device allows, in addition to performing the elution step, to define the pressure exerted on the bed.

In a first embodiment, the piston has a constant cross-section but the pressure in the flow and enclosure conduits is regulated by pressure reducing valves. Thus, the tabs can be tared so that the difference in pressures exerted by the flow of the liquid and by the liquid in the enclosure is adjusted to a set pressure on the bed. In another embodiment, the pressure in the flow and enclosure conduits is the same but the cross section of the piston varies. The piston has two sections sliding in corresponding bores, the smallest section A being located on the side of the chromatographic chamber and the largest section B on the side of the enclosure. Due to the difference in surface area of the faces A and B of the piston, the force exerted at B is greater than the force exerted at A. Thus the sections of the piston can be chosen so that the difference in pressures exerted by the flow of the liquid and by the liquid in the enclosure is adjusted to a set pressure on the bed.

In fact, the apparatus described in the above document has various drawbacks. If a pressure drop occurs in the flow conduit, the pressure exerted on the piston by the liquid in the enclosure applies directly to the bed which can cause deterioration of the bed. In addition, the movements of the chromatographic bed not being monitored and the enclosure being unable to discharge liquid during the chromatography, this device cannot adapt the pressure exerted on the bed as a function of the movements of the latter. A deterioration of the bed can again follow. On the other hand, this system cannot be used in SMB (Simulated Moving Bed) or in NARICOL. In such configurations, the chromatography devices are mounted in a loop and the liquids injected into the beds alternate. In the apparatus described in EP-A-0 145 578, the same liquid is sent into the bed and into the enclosure, the alternation of injection of liquids generates a mixture of these.

Summary of the invention

The present invention relates to an improved chromatography device which overcomes the drawbacks of known devices. This device increases the efficiency of the chromatographic bed while protecting it. The present invention relates to a chromatography device comprising:

- a column intended to receive a chromatographic bed through which a first fluid flows,

- a piston sliding in the column and exerting pressure on the bed, - a chamber containing a second fluid exerting pressure on the piston,

a regulator of the pressure exerted by the piston on the bed as a function of the pressure in the chamber, the flow pressure of the first fluid at the inlet of the column and a set pressure on the bed.

The regulator is Integral Proportional Action (PI), Differential Proportional Action (PD) or Differential Integral Proportional Action (PID).

The device further includes a first sensor which measures the flow pressure of the first fluid at the inlet of the column and a second sensor which measures the pressure in the chamber.

In one embodiment, the first fluid flows through the bed from the piston towards the end of the column.

In another embodiment the first fluid flows through the bed from the end of the column towards the piston.

The piston sliding in the column is connected to another piston sliding in the chamber by a rod. In one embodiment, the second fluid is regulated by bypass by the regulator.

The invention also provides a set of devices as described above, associated in a loop.

The invention also relates to a method for separating at least two compounds from a first fluid, comprising the chromatography of said fluid in the device described above, the method comprises the steps:

- introduction of the first fluid into the column containing the bed and measurement of the flow pressure at the inlet thereof,

- flow of the first fluid through the chromatographic bed, - collection of the first chromatography fluid.

With the device according to the invention, it is possible, during the separation process, to carry out the steps:

- introduction of a second fluid into the chamber and measurement of the pressure,

- regulation of the pressure in the chamber as a function of the pressure measured in the chamber, the flow pressure of the first fluid at the inlet of the column and a set pressure on the bed. The invention also relates to a method for adjusting the pressure on the chromatographic bed in the device described above, the method comprising the step:

- regulation of the pressure in the chamber as a function of the pressure measured in the chamber, the flow pressure of the first fluid at the inlet of the column and a set pressure on the bed.

The regulation of the pressure exerted on the bed makes it possible to draw all the efficiency while protecting it against its degradation.

Brief description of the drawings

Other characteristics and advantages of the invention will appear on reading the detailed description which follows of embodiments of the invention, given by way of example only and with reference to the drawing which represents schematically:

- Figure 1, an axial section of a chromatography device according to the invention.

Description of the invention

Reference will be made to liquid phase chromatography and this by way of illustration, which a person skilled in the art will easily transpose to gas chromatography without departing from the invention. Likewise, this device is suitable for the chromatography of supercritical fluids.

FIG. 1 schematically represents a chromatography device 10 comprising a column 12 for performing the chromatography and a part of which is intended to contain a chromatographic bed 14 resting on an end wall 16. Above the column 12, the device 10 also comprises a jack 22. The jack 22 comprises a movable piston 24 connected to one end of a rod 26. The piston 24 delimits two chambers 28 and 30 in the jack 22. The first chamber 28, or upper chamber, is delimited between the piston 24 and the upper wall 32 of the cylinder 22. The second chamber 30, or lower chamber, is delimited between the piston 24 and the lower wall 34 of the cylinder 22. The lower wall 34 marks the separation between the cylinder 22 and the column 12. The rod 26 connected to the piston 24 is located in the lower chamber 30 and opens into the column 12 passing through the lower wall 34 of the jack 22. Appropriate seals will be used. ilises to seal between the chamber 30 and the column 12. The other end of the rod 26 located in the column 12 is connected to a body 36. The body 36 slides in the column 12. The sliding body 36 is for example a piston. It comes to bear on the chromatographic bed 14. The position of the actuator 22 relative to the column 12 is not limited to that described above. It is in fact possible to envisage placing the jack under the column so that the piston 36 is pressed upwards against the bed 14.

The liquid to be chromatographed is conveyed to the bed 14 and is discharged therefrom via flexible communication lines to the outside. The piston 36 includes a conduit 20 provided with a first flow pressure sensor 45. The wall 16 also has a conduit 18. The liquid to be chromatographed reaches the bed 14 via the conduit 20 and then leaves via the of the conduit 18, after passing through the bed 14. The sensor 45 makes it possible to measure the flow pressure of the fluid at the inlet of the column 12. The liquid to be chromatographed can also circulate in the other direction. It then reaches the column 12 via the conduit 18, flows through the bed 14, then leaves the column 12 through the conduit 20. The sensor 45 is placed on the inlet conduit 18.

The jack 22 is supplied by a propellant fluid circuit. Typically, the cylinder 22 is a double-acting hydraulic cylinder. The propellant fluid is then a hydraulic liquid. A first conduit 38 connects the chamber 28 with a source of hydraulic fluid 44. The conduit 38 includes a second pressure sensor 46. A second conduit 40 connects the lower chamber 30 with the source of hydraulic fluid 44. A conduit bypass 42 connects the conduits 38 and 40. The bypass conduit 42 includes means for regulating the flow of propellant in the bypass. These means include an all or nothing valve (TOR) 48 and a regulation valve 50. The regulation valve is controlled by a regulator 52 of the type with integral proportional action (PI), with differential proportional action (PD) or with proportional action. Differential Integral (PID). The liquids used in the device are separate fluids. The first fluid, that is to say the gas or the liquid to be chromatographed, is not the same as the propellant fluid, or second fluid, used in the jack 22. In other words, there has no bypass in the conduits of the first fluid to supply the jack 22.

The operation of the device will now be explained.

The device is used in a mode of descent of the piston 36 to compact the chromatographic bed 14 in the column 12. The column 12 is previously filled with the material forming the bed 14. The hydraulic fluid is then sent to the chamber 28 of the jack 22 in order to lower the piston 36 into the column 12 until the piston 36 comes into contact with the bed 14 and ensures its compaction. In this case, the digital valve 48 and the control valve 50 are closed.

At the end of separation, the device allows the piston 36 to be raised to allow the bed 14 to be emptied from the column 12. The hydraulic fluid is sent to the chamber 30 of the jack 22 in order to reassemble the piston 36. In this case, the valve TOR 48 and the control valve 50 are also closed. The device is used for the separation of at least two compounds from a liquid to be chromatographed. The process includes the steps:

- introduction of the liquid to be chromatographed in column 12 containing the bed 14. The liquid is for example introduced through the flexible conduit 20. - flow of the liquid through the bed 14. Depending on the affinities of the compounds with the bed

14, the compounds flow with different speeds along the bed 14.

- Collection of liquid chromatography. The liquid compounds are separated and collected in the flexible conduit 18.

The separation of the compounds is accompanied by the regulation of the pressure exerted on the bed 14.

When the piston 36 is static, the different forces exerted on the piston are in equilibrium. The different forces are the hydraulic force (Fh) supplied by the hydraulic source to the piston 36 compensated by the flow force (Fe) of the liquid to be chromatographed at the inlet of the column 12 and by the mechanical force of the bed (FI) . The mechanical strength of the bed is thus given by the balance of forces

Fl ≈ Fh- Fe Eq. 1

The transformation of the balance of forces into a balance of pressures leads to

Pl = Ph. AlJA2 -Pe Eq. 2

where Al is the surface of the piston 36 in the column 12 and A2 is the surface of the piston 24 in the chamber 28.

During the use of a chromatography device, an abrupt stop of the flow of the liquid to be chromatographed can occur, for example during an emergency stop. The flow force Fe then becomes zero and all the hydraulic force Fh is exerted on the bed. We therefore have: FI = Fh. If the mechanical strength of the bed is medium (for example if the bed is made of silica with large pore diameters), it may suffer unwanted compaction or even be damaged by the piston 36. Similarly, when in use, the bed may swell to the point of being more strongly pressed against the piston. It is then necessary for the piston 36 to follow the bed in its movements.

Depending on the conditions for carrying out the chromatography (the liquid to be chromatographed, flow speed in the bed, etc.) and the characteristics of the bed used

(material used, porosity, mechanical resistance ...), it is possible to determine a pressure deposit (Pcl) exerted on the bed. The hydraulic pressure Ph must be calculated as a function of the flow pressure so as to check:

Ph = (Pcl + Pe). Al / A2 Eq. 3

When the flow pressure Pe varies, equation 3 shows that PI can be kept constant at the value of Pcl by varying Ph. To do this, it is necessary to measure the hydraulic pressure Ph and the flow pressure at entry of column 12. The use of a regulator 52 of the PI, PD, PID type allows the pressure on the bed 14 to be adjusted according to the steps:

- programming of a set pressure on the bed;

- introduction of the liquid to be chromatographed in the column 12 which contains the bed 14 and measurement of the liquid flow pressure by the sensor 45 at the inlet of the column 12; - Flow of the liquid through the bed 14;

- Introduction of the hydraulic fluid into the chamber 28 and measurement of the hydraulic pressure supplied to the jack 22 by the sensor 46;

- comparison according to an algorithm for regulating the three aforementioned pressures;

- Regulation of the pressure in the chamber 28 as a function of the pressure measured in the chamber 28, of the flow pressure of the liquid to be chromatographed at the inlet of the column 12 and of the pressure set on the bed.

The separation process can then be completed by the step of introducing the hydraulic liquid into the chamber 28 and the step of regulating the pressure in the chamber 28. By way of illustration, when a stop occurs from the flow of the liquid to be chromatographed, the flow pressure drops to zero. With equation 3, we deduce that the hydraulic pressure must be reduced to reach Ph = Pcl. A2 / A1. To achieve this, the regulator 52 derives the hydraulic fluid in the bypass duct 42 by opening the TOR valve 48 and by opening the control valve 50 at a percentage controlled by the regulator 52. The hydraulic fluid sent by the hydraulic source 44 does not enter the chamber 28 but is diverted into the bypass duct 42. It is then evacuated towards the hydraulic source 44. In this way, the pressure in the chamber 28 is reduced, generating less pressure from the piston 36 on the bed 14.

The adjustment of the pressure exerted by the piston 36 on the bed 14 makes it possible to adapt to the movements of the bed 14 when the latter inflates, for example. The increase in the volume of the bed 14 would result in an increase in the mechanical pressure of the bed PI which would become greater than the set pressure Pcl. In a classic implementation of the cylinder 22, the hydraulic fluid cannot exit from the upper chamber 28 of the cylinder 22, and an increase in the pressure PI would result in an increase in the hydraulic pressure. It is therefore necessary in this case to evacuate the hydraulic fluid from the chamber 28 in order to keep PI constant. Again, the digital valve 48 is open and the control valve 50 is open at a percentage controlled by the regulator 52, allowing the pressure PI to be kept constant and equal to Pcl.

The regulation of the pressure of the piston 36 on the bed 14 makes it possible to adapt to the operating conditions of the device. It provides all the efficiency of the bed 14 while protecting it.

The device described above is not limited to a single piston compacting the bed 14 but it is possible to envisage the action of two pistons on the bed 14. On the other hand, the skilled person will able to use other types of cylinders such as pneumatic cylinders.

The chromatography device according to the invention is advantageously used in a method of separation by SMB, Simulated Moving Bed (US 2,985,589, US 3,291,726, US 3,268,605 and US 3,268,604 belonging to UOP, US 5,578,215 and US 5,578,216 belonging to IFP and NONASEP, EP 471,082 and EP 563,388 belonging to DAICEL) or in a process by NARICOL (US 6,136,198). Such a method implements a set of these associated columns in a loop.

Claims

1. Chromatography device comprising:

- a column (12) intended to receive a chromatographic bed (14) through which 5 flows a first fluid,

- a piston (36) sliding in the column (12) and exerting pressure on the bed (14),

- a chamber (28) containing a second fluid exerting pressure on the piston (36),

- a regulator (52) of the pressure exerted by the piston (36) on the bed as a function of the pressure in the chamber (28), of the flow pressure of the first fluid at the inlet of the column (12 ) and a set pressure on the bed (14)

2. Device according to claim 1, characterized in that the regulator (52) is with integral proportional action (PI), with differential proportional action (PD) or with differential integral proportional action (PID).

15.

3. Device according to claim 1 or 2, characterized in that a first sensor (45) measures the flow pressure of the first fluid at the inlet of the column (12) and a second sensor (46) measures the pressure in the room (28).

4. Device according to one of claims 1 to 3, characterized in that the first fluid flows through the bed (14) from the piston (36) towards the end (16) of the

20 column (12).

5. Device according to one of claims 1 to 3, characterized in that the first fluid flows through the bed (14) from the end (16) of the column (12) towards the piston ( 36).

6. Device according to one of claims 1 to 5, characterized in that a piston (24) sliding in the chamber (28) is connected to a rod (26) actuating the piston (36).

7. Device according to one of claims 1 to 6, characterized in that the second fluid is regulated by bypass by the regulator (52).

8. Set of chromatography devices according to one of claims 1 to 7 wherein the devices are associated in a loop.

9. A method of separating at least two compounds from a first fluid, comprising the chromatography of said fluid in the device according to one of claims 1 to 8, the method comprising the steps:

- introduction of the first fluid into the column (12) containing the bed (14), - flow of the first fluid through the chromatographic bed,

- collection of the first chromatography fluid.

10. Method according to claim 9, characterized in that between the flow and collection steps, the method further comprises the steps of:

- introduction of a second fluid into the chamber (28) and measurement of the pressure, - regulation of the pressure in the chamber (28) as a function of the pressure measured in the chamber (28), of the flow pressure of the first fluid at the inlet of the column (12) and a set pressure on the bed (14).

11. Method for adjusting the pressure on the chromatographic bed in the device according to one of claims 1 to 8, the method comprising the step: - regulating the pressure in the chamber (28) as a function of the pressure measured in the chamber (28), the flow pressure of the first fluid at the inlet of the column (12) and a set pressure on the bed (14).