Chromatography system with tilt-prevention structure and associated process

Abstract

Chromatography apparatus and methods are described, especially for expanded bed adsorption. A column tube has a process fluid input device at the bottom and a movable piston in the top. The piston is enclosed in the column by a cover plate. The piston body has an inflatable seal, and is connected by a frame to a contact ring which carries another inflatable member to contact the tube wall. Process fluid leaves the operating volume through an opening of the piston and flexible hose, through the enclosed space and out through the cover plate. The space above the piston can be pressurised to control piston movement. The contact ring maintains piston alignment. The inflatable seals are used to fix the piston in position, allow it to slide or allow washing. The piston outlet may include a vortex-inhibitor. Bed and piston levels may be monitored by ultrasound sensors.

Claims

1. A chromatography apparatus for expanded bed adsorption, comprising a column tube, and top and bottom end cells which close off the column tube, defining between them an operating volume configured to contain a bed of adsorbent medium particles as stationary phase material; first and second process liquid conduits communicating into the operating volume for liquid to enter and leave the operating volume, including a process liquid inlet injection arrangement, and a top outlet opening in the top end cell as a process liquid outlet, wherein the column tube is configured to flow a process liquid up through the bed of particles in an expanded state thereof, characterised in that an outlet structure at the top outlet opening includes a vortex-inhibiting structure beneath the top outlet opening, the vortex-inhibiting structure comprising one or more divider, partition or slot-defining elements to divide flow entering the outlet opening and inhibit rotational movements around an outlet axis.

2. The chromatography apparatus of claim 1 wherein said one or more elements of the vortex-inhibiting structure are disposed in the outlet opening and/or projecting down below the entrance of the outlet opening.

3. The chromatography apparatus of claim 1 wherein said one or more elements of the vortex-inhibiting structure project radially out beyond the entrance of the outlet opening.

4. The chromatography apparatus of claim 1 wherein said one or more elements of the vortex-inhibiting structure extend substantially radially, e.g. in radial planes, relative to the outlet axis.

5. The chromatography apparatus of claim 4 wherein said one or more elements of the vortex-inhibiting structure extend in radial planes relative to the outlet axis.

6. The chromatography apparatus of claim 1 wherein said vortex-inhibiting structure comprises two or more upright radial vanes projecting downwardly and outwardly relative to the outlet opening so as to reduce or inhibit rotational flow.

7. The chromatography apparatus of claim 1 wherein said vortex-inhibiting structure also comprises a downwardly-facing baffle.

8. The chromatography apparatus of claim 7 wherein said downwardly-facing baffle is below the level of vanes or partitions comprised in said elements of the vortex-inhibiting structure.

9. The chromatography apparatus of claim 1 wherein said process liquid inlet injection arrangement comprises a distribution rotor with an array of process liquid injection holes.

10. The chromatography apparatus of claim 1 wherein said top end cell is a top piston slidably axially movable inside the column tube.

11. The chromatography apparatus of claim 10 wherein the top piston has an inner face directed onto and directly exposed to the operating volume, which inner face is convergent towards the entrance of the outlet opening.

12. The chromatography apparatus of claim 11 wherein the convergent inner face is conical and its cone angle relative to the radial plane is between 4° and 25°.

13. The chromatography apparatus of claim 10 wherein the vortex-inhibiting structure has a lower extremity which projects down axially below the periphery of the top piston.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Having described the general concepts proposed, we now describe examples with reference to the accompanying drawings in which:

(2) FIG. 1 is an axial cross-section of an EBA column embodying the invention.

(3) FIG. 2 is a plan view of the column, showing a line A-A for the section of FIG. 1.

(4) FIG. 3 is a radial cross-section at B-B of FIG. 1.

(5) FIG. 4 is a radial cross-section showing details of the piston and top cover of the column.

(6) FIG. 5 is an oblique view of the piston separate from the column.

(7) FIGS. 6(a) and 6(b) are oblique schematic views of piston designs showing conceptual alternatives for tilt-preventing structures.

(8) FIG. 7 is a plan view of a bottom plate with the column tube removed.

(9) FIG. 8 is a fragmentary sectional view through the top cover showing sealed fitting of an air input to an air chamber.

(10) FIG. 9 is a schematic side view of the column indicating an array of sensors and elements of the column tube contents for EBA to be detected thereby.

(11) FIG. 10 is a fragmentary sectional view through a segment of tube wall showing a way of mounting an ultrasonic transceiver.

(12) FIG. 11 is a schematic diagram showing more details of an air supply system.

(13) FIG. 12 shows schematically a column of packed-bed type with a movable piston according to our proposals.

DESCRIPTION OF THE SELECTED EMBODIMENTS

(14) For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features that are not relevant to the present invention may not be shown for the sake of clarity.

(15) With reference to FIGS. 1 to 3, an expanded bed adsorption (EBA) apparatus comprises a vertical column tube 1 clamped between a top plate or cover 3 and a bottom plate 4 by a set of tie bars 11. In this embodiment the column tube 1 is of transparent polymer, e.g. acrylic. The column shown is 300 mm in internal diameter, 25 mm wall thickness. The tube may be e.g. from 1 to 2 m in height.

(16) The bottom plate—see FIG. 7—carries a rotational process fluid input device 41, in the form of a circular rotor with radially-projecting arms 43 and a hub 42. Each arm has a series of downwardly-directed holes. The rotor 41 is drivable in rotation by a motor 44, and a process liquid inlet 45 is connected to feed process liquid up into the hub 42 of the rotor and along the arms 43, to be injected into the operating volume 13 of the column tube at positions distributed across the base plate 4. Rotors of this kind are known to the skilled person, and exist in various forms. In addition to feeding process liquid for separation, such as a cell broth homogenate, the rotor can be used to feed plain buffer for establishing a bed, or for washing media out of the column through a slurry inlet/drain hole 46 in the base plate 4. Preferably the drain hole 46 is also used as an inlet for feeding slurry of media particles into the column, being often preferable to loading the media from the top.

(17) A self-aligning piston 2 operates in the column, dividing it into an operating volume 13 between the piston and base plate 4 and a pneumatic control space or chamber 77 between the piston 2 and top cover 3. The piston 2 consists of a closed circular piston plate 21 connected by an open upwardly-extending frame (in this case a set of four vertical struts 85) to a contact ring 81 which constitutes a stabilising or tilt-preventing part of the piston.

(18) In more detail, with reference to FIGS. 4 and 5, the piston body or piston plate 21 carries a peripheral elastomeric sealing member 23, held in place by a clamping flange 212. In this embodiment the seal 23, whose function is to form a fluid-tight separation between the pneumatic space 77 and the operating volume 13, is a dynamic seal which can be energised with compressed air, by means of a compressed air line 71 connecting between a working space 881 defined inside the hollow seal member 23 via a connector 871 on the piston body 21. This air line 71 (see FIG. 1) passes in a sealed mode through the cover plate 3 and to a pressurised air control unit 6, connected in turn to a pressurised air supply 7. These are shown schematically in FIG. 1, and may use per se conventional technology. FIG. 4 shows the piston seal 23 in its non-energised condition, in which there is some clearance between seal and tube wall to enable cleaning. Desirably for this purpose the clearance is substantially larger than the largest diameter particles to be used in the process, so that particles can be reliably washed away from the sealing faces. When the pressurised air is fed to the seal's working space 881, e.g. at excess (gauge) pressure up to 6 bar, the seal is forced out against the column tube wall to make a fluid-tight seal and also prevent movement of the piston 2 up or down the tube. By reducing or relieving the pressure supply, e.g. to 2-3 barg, sliding of the piston may be allowed.

(19) The piston 2 is not guided by any axial rod or tube extending out through the top of the column, unlike some known constructions. To preserve its axial alignment, i.e. to stop it from tilting as it moves, it comprises an inbuilt tilt-prevention structure in the form of a contact ring 81 which, by virtue of being axially spaced from the annular locus of the piston seal 23, contacting around the interior of the tube, prevents the piston from tilting. The axial spread or span of the piston seal and contact engagements (“X” in FIG. 5) is determined relative to the piston diameter (“D” in FIG. 5) so as to inhibit tilting sufficiently that the piston seal remains fully in contact with the tube wall, and hard piston material cannot contact the tube wall.

(20) In this version the stabilising contact ring 81 consists of a rigid steel support ring 810 carrying an inflatable annular elastomeric seal element 83, similar in structure and operation to the piston seal itself, which contacts the tube wall. However this contact seal 83 has no intrinsic sealing function, because the support ring 81 is open; its purpose is only to make an even and controllable contact around the tube interior. This contact can be controlled by the supply of pressurised gas along a stabiliser contact air line 72 connecting to the corresponding stabiliser seal working space 882 through a connector 872 on the support ring 810. Again, this air line 72 passes in a sealing manner through the cover plate 3 of the column and to the above-mentioned air control unit and air supply.

(21) The piston 2 defines the top of the operating volume for the EBA process, including an outlet for the process liquid. The piston has a conically-recessed underside converging towards the central outlet. This embodiment cone has an angle of about 18°, and this steep angle helps escape of any air bubbles. At the centre, an outlet flow connector or union 24 is fixed through a central orifice of the piston plate 21, and has a top clamp fitting 241 e.g. a triclamp fitting for connection of a flexible outlet hose 9 above the piston. With reference to FIGS. 1 and 4, the outlet hose 9 connects at its other end to a fixed connector or union 33 (triclamp to triclamp through the top plate) communicating in a sealing fashion through the cover plate 3 to an external outlet conduit. The outlet hose 9, desirably of wire-reinforced silicone tubing, is flexible to accommodate movement of the piston 2 up and down inside the column tube 1, strong enough to support the weight of the piston, and short enough to hold the piston off the bottom plate.

(22) On the underside of the outlet connector 24 a vortex-inhibitor device 25 is fitted, in this case by screws on a flange which is part of the anti-vortex device, which passes down (FIG. 4) through the piston and is stopped by the flange, having holes for bolts screwing into the piston body 21 (stainless steel). The vortex inhibitor in this embodiment comprises a unit with a set of three flat radial vanes at 120° to one another and meeting along the axis. These inhibit rotational flow (vortex formation) as liquid leaves the operating volume 13 through the outlet and into the conduit 9. This inhibition of rotational flow at the outlet helps to prevent undesired disruption of the media bed in the region adjacent the outlet. Additionally, approach to the outlet from directly beneath is blocked by a baffle portion 26 of the vortex-inhibiting fitting 25, so that liquid approaches primarily radially rather than axially. In this embodiment the baffle portion is extended to form a nose or bump stop 26 which projects axially below the piston body. The bump stop/vortex-inhibitor fitting is made of a single piece of engineering plastics, such as PEEK. Should the piston 2 by accident be dropped down the column with the sealing rings 23,83 released and the hose 9 not in place to stop it, the bump stop 26 will strike the central hub of the input rotor at the bottom (or other strong central structure, according to the design) avoiding damage caused by the peripheral sealing parts of the piston hitting the bottom plate or rotor.

(23) In this embodiment the top stabilising contact ring 83 can be pressurised in the same way and to the same pressure as the sealing ring 23 proper. However this is just one option. It is also possible to use ordinary elastomeric seals, without pneumatic actuation. Or, different mechanisms may be provided, actuated either pneumatically or by other means, for urging the seals or contact structures either out against the tube wall, or in away from the tube wall to allow movement of the piston and/or passage of cleaning liquid. One suitable construction uses an inflatable seal for the piston seal 23 and a simple elastomer ring for the top contact, so that some frictional restraint is always imposed on movement of the piston 2.

(24) The illustrated piston is based on a primarily steel structure apart from the vortex-controlling outlet, but the skilled person will appreciate that other material types may advantageously be used as discussed earlier.

(25) A pneumatic space 77 is defined above the piston, the outlet hose 9 and any energising air lines 71,72 for the piston components extending in isolated fashion through the pneumatic space 77. The pneumatic space 77 is connected also to a pressurised air supply via the air chamber air line 73, also connecting to the air supply 7 via the air control unit 6. By adjusting the air pressure supplied to line 73, the pressure in the air chamber 77 can be controlled to move the piston 2 up or down, or to maintain its position against changing pressures beneath from the up-flowing process liquid in the operating volume 13. In practice we find that this can readily be achieved with air gauge pressures less than 3 bar against seal pressures of 2-3 bar. The air line 73 may optionally incorporate an air filter, such as a submicron disposable filter, enabling the pneumatic space 77 to be kept sterile which is not possible in previous movable-piston EBA columns.

(26) A circular access hatch 311,312 is provided in the top cover plate 3 so that routine operations such as cleaning (e.g. spraying in liquid) and visual inspection can be done without removing the top plate from the column tube. In this embodiment the hatch opening 312 is 100 mm diameter so that a hand can pass through. The removable (bolted) hatch cover 311 makes a fluid-tight seal, sealing out sideways with a sealing ring against the edge of the hatch opening 312. The construction shown has the air hose union 33 offset from the centre to maximise space for the hatch, but depending on overall dimensions it may be preferable to have the union central.

(27) FIG. 8 shows how the air chamber air line 73 may be connected fluid-tightly and securely into the cover plate 3, using a swaged connector of the “Swagelok” type, comprising a main fitting 731 that screws into a threaded bore in the plate 3 with a bottom shoulder, a metal-supported seal (“Dowty seal”) beneath the flange of this, and a top swaging nut 732 to clamp the end of the air line 73 by means of an entrapment washer 733 and a tapered wedge washer 734 of soft material to seal against the air line tube 73. The air supply lines 71,72 to the piston may pass through similar fittings, except that because these air lines pass right through they have an identical sealing clamp on the underside too.

(28) FIG. 11 shows details of an air supply arrangement. In this arrangement air supply lines 71,72,73 for the top seal, bottom seal and pneumatic chamber are taken from a main supply line 700 e.g. from a 7 bar air cylinder. Each of the individual supply lines has, in sequence, a precision air regulator 705, a unidirectional valve 706 (e.g. a ball valve) to prevent back flow, a relief valve 708 for venting air in case of excessive pressurisation, and a pressure gauge 707. The regulator 705 for the pneumatic chamber line 73 provides for a smaller pressure range up to 4 bar whereas the inflatable seal lines 71,72 regulate up to 7 bar. The pneumatic chamber pressure acts on the outsides of the seals, so they need to be able to be pressurised to a higher pressure to guarantee the necessary outward mechanical force again the column wall.

(29) It will be understood that the stabilising function of the top ring 81 seen in FIG. 5 does not intrinsically require a seal. A variety of alternative structures may be used to provide adequate tilt-prevention, therefore. Some such structures are illustrated schematically in FIGS. 6(a) and 6(b). FIG. 6(a) shows a tilt-preventing structure supported through a frame as in the previous embodiment, but having a contact ring 8′ which contacts the column tube interior intermittently at circumferentially-spaced positions, through a plurality of projecting slider contact portions. These might be of hard plastics. In FIG. 6(b), a similar effect is achieved by vertical fins 8″ distributed around the top of the piston 2, and projecting high enough to stabilise it against tilting. The skilled person will readily conceive other possibilities, depending on the dimensions of the column, the type of piston seal and the materials to be used.

(30) FIG. 1 shows the air control unit 6 only schematically. Generally it comprises for each air line 71,72,73 a respective shut-off valve, enabling the air chamber or seal components to be isolated while in a pressurised state, or opened to the pressure supply or to vent. It also incorporates respective pressure gauges to monitor the line pressures. It may have a manual-precision air regulator control for adjusting the individual line pressures. Most preferably it also provides for automated control in dependence on certain sensed conditions in the column tube, as indicated schematically in FIG. 1 by reference numeral 5 to indicate inputs from sensors which monitor conditions in the column at various positions.

(31) To illustrate the possible roles and operation of sensors, see FIG. 9 which shows schematically the contents of the column tube 1. The piston 2 is shown at a primary position, also at alternative positions 2′ and 2″. FIG. 9 also shows characteristic conditions in the operating volume 13 during expanded bed operation, namely a bed region 14 consisting of the dense media particles, a top “headspace” of clear liquid immediately beneath the piston 2, and a turbid band or layer 15 between the headspace 16 and bed proper 14. This turbid layer contains fines from the mass of media. It is desirable to run the process with an appreciable headspace so that fines are not washed out of the operating volume 13 through the outlet. FIG. 9 also shows an array of six sensors 5, here numbered as 1 to 6, distributed down the wall of the column tube 1. These are desirably ultrasonic transceivers, which emit into the tube interior and detect characteristic echoes which differ according to whether they encounter empty space, the presence of the solid piston, headspace liquid, expanded bed 14, fine particles in the turbid region 15, raised solute concentration etc. The deployment of ultrasonic transceivers on vessels of this kind, and control circuitry for them, are known in themselves. However in this apparatus they are used in a distinctive way to facilitate control—either manual or automated—of the piston position, by means of adjusting the pressure in the pneumatic air space 77.

(32) The skilled person will be able to conceive various modes in which the sensors can be used to control the piston position to achieve suitable EBA operating conditions.

(33) In one possibility (“Aspect A”) the sensors monitor the elements of the column bed. For example Sensor 1 monitors the headspace, Sensor 2 is positioned to align with the turbid band 15 in the correct operational position, Sensors 3 and 4 are to monitor the boundary between the turbid band 15 and the EBA bed proper 14, and Sensors 5 and 6 operate when the bed is allowed to settle (e.g. for elution of product), to monitor the top of the bed.

(34) Another possible operational mode (“Aspect B”) is as follows.

(35) Sensors 1 and 2 define between them a range of appropriate positions for the piston 2. Initially, a piston may be positioned somewhat above the intended piston height during operation in expanded bed mode. Liquid on the column side, e.g. plain buffer, is flowed upwards to fill the lines and fill the column. By closing off a valve in the outlet conduit above the connector 33 (not shown) liquid pressure will rise in the operating volume 13 and push the piston up, starting to compress air in the air chamber 77. When the piston 2 reaches Sensor 2, Sensor 2 sends a signal and the air control unit 6 responds by initialising a routine to stop further piston movement, by e.g. pressurising the inflatable seals 23,83 to stop the piston, by opening the process liquid valve to allow process liquid to flow out again, by increasing air supply into the top chamber 77 to give the desired pressure differential between the air above and the liquid below the piston, or by some combination of these steps. This can maintain the piston in the desired operating height zone without passing Sensor 1 (which, if actuated, indicates a problem and may automatically trigger a halt in process liquid flow).

(36) In Aspect B, Sensors 3 and 4 can monitor the position of the interface between the clear supernatant 16 and the turbid zone 15, to ensure that the fines in the turbid zone do not leave the column and foul downstream equipment. In combination with the pressurised air control unit 6 and suitable operating software or program control, they can prevent the piston being pushed down into the turbid region. Sensors 5 and 6 can indicate a position for the top of the particle bed 14 and define desired tolerances for the bed height: if Sensor 6 detects the boundary, the air chamber pressure can be dropped or the liquid pressure increased to move the piston up. It stops when Sensor 5 detects the boundary. Conversely, if the piston were too high, Sensor 5 would fire and the opposite routine would operate. The piston can then be maintained between Sensors 5 and 6.

(37) A further possibility (“Aspect C”) is to operate with three sensors above the piston (or the interface between the turbid zone and the clear headspace) and three below. In relation to the selected element (piston or interface) the three sensors in each direction could indicate degrees of deviation from a target position, e.g. Sensors 3 and 4 indicating respectively the upper and lower boundaries of the desired position band, Sensor 2 indicating “high” and Sensor 1 indicating “very high”. Similarly for “low” and “very low” positions with Sensors 5 and 6. The control unit 6 can be programmed to initiate, for each detected position (fired sensor) an appropriate routine of events such as opening and closing valves, operating pumps, increasing or decreasing air pressure and the like to adjust the conditions on the column so the piston (or interface) remained in the target area.

(38) Finally, we show a way of mounting an ultrasonic transceiver 51 so that it can conveniently be brought into good operating contact with the surface of the tube wall 1. See FIG. 10. A horizontal elongate mounting member 52 is clamped so that it can pivot around one of the upright tie bars 11. The ultrasonic transceiver 51 is mounted at one end of the mounting member 52. At the other end a threaded adjuster 53 is provided, aligned substantially radially with the column tube. Desirably the adjuster 53 is of plastics material, so as not to scratch the tube. Clamping screws are provided (not shown) so that the transceiver mounting 52 can be positioned and held at any desired position up or down the tie bar 11. Further sensors may be positioned on the same or other tie bars. A visual length scale may be provided as well, to facilitate positioning. When the threaded fastener 53 is tightened through the corresponding threaded hole in the mounting member 52, by a lever effect the face of the transceiver 51 is brought gradually into contact with the outside surface of the tube wall 1. By this means the transceivers can easily be brought into an appropriate pressure contact against the tube surface, which is important for effective operation. The transceiver device likewise is then radially-oriented relative to the tube.

(39) FIG. 12 shows schematically the application of the present “balanced piston” concept in a packed bed column, in which the bottom end cell 104 (which may be a conventional packed-column design) and the top end cell incorporated in the present piston 102 are provided with media-retaining mesh layers 1041,1021 mounted over per se conventional convergent collection surfaces leading to and from process liquid conduits 1042,1022. To obviate the conventional support rods projecting up out of the top of the column in a conventional column, a top piston 102 embodying the present proposals is used and comprises a stabiliser ring 181 carrying a peripheral contact member 183 (formed here as a rubber seal ring, although without sealing function) spaced by an open frame 185 above the main piston seal to prevent it from tilting. A top cover plate 103 defines a pneumatic space 177 above the piston 102 to receive pressurised air or other gas via gas supply 173. An array of ultrasound sensors 151 is provided up the wall 101 of the column. These are useful to control the processes and/or the movement of the piston 102. They may be used to control the piston movement on detecting the correct position, or other parameters in the bed. If inflatable seals are used, as in the earlier embodiment, additional air inlets to supply these may be provided through the cover plate 103. In this embodiment a steel column wall 101 is envisaged. The column may be e.g. about 2 m in diameter.

(40) Packing of the column and chromatographic processing may be by conventional methods. Slurry may be injected into the column bed space 113 through a central multi-functional packing valve of known type, or through a simple valve with slurry lines, communicating through the base and mesh as indicated at 146. The bed can then be packed by driving the piston down and this may be by pneumatic pressure rather than the conventional mechanical or hydraulic drives

(41) The present balanced piston in a packed bed column can avoid the presence of moving parts and complex mechanisms such as hydraulic or pneumatic drives extending above the envelope of the column. Being relatively mobile under controllable conditions, the top piston may easily be position-adjusted during use, e.g. to accommodate the swelling or shrinking of a packed bed according to changes in the ionic strength or nature of the buffer or other process liquid in which it is immersed.

(42) While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.