CA2362108C - Access valve devices, their use in separation apparatus, and corresponding methods - Google Patents

Abstract

The separation process is for separating a target component from a liquid incorporating the target component with other components. It comprises the steps of providing a bed of particulate packing medium;
flowing liquid upwardly through the bed of particulate packing medium; through a restricted-permeability element and through a process outlet, to expand the bed in the bed space and effect separation of the target component from the liquid through retention by the particulate packing medium; opening a clearing outlet communicating directly with the bed space, at or adjacent the restricted-permeability element; and forcing a clearing flow of fluid relative to the restricted permeability element to disturb the particulate matter which has accumulated against it, and causing said matter to pass out of the bed space through the clearing outlet.

Description

., v , ACCESS VALVE DEVICES, THEIR USE IN SEPARATION APPARATUS, AND CORRESPONDING METHODS
FIELD OF THE INVENTION
This specification relates to methods and apparatus for_ the control of fluid flow, e.g in chromatography, i.e.
apparatus and methods for separating substances by passing a mobile phase through a stationary or retained phase to cause separation of mobile phase components.
BACKGROUND
Chromatography is a well-established and valuable technique in both preparative and analytical work as well as in purification generally. Typical industrial chromatography apparatus has an upright housing in which a bed of packing material, usually particulate, rests against a permeable retaining layer. Fluid mobile phase enters through an inlet e.g at the top of the column, usually through a porous, perforated, mesh or other restricted-permeability layer, moves through the packing bed and is taken out at an outlet, typically below a restricted-permeability layer.
Changing the bed of packing material, because it is spent or in order to run a different process, is an arduous task particularly with big industrial columns which can be hundreds of litres in volume. The existing bed has usually become compacted and difficult to remove.
The housing must be dismantled, the compacted pac~;ing mass disrupted and then removed. Furthermore, the new bed must be very evenly packed if the column is to be effective:

the fresh material must be added carefully while maintaining a flow of liquid. Usually the apparatus must be kept clean, particularly with biological products where high system sterility may be needed for weeks or even months. One small contamination can be disastrous.
Conventionally, many hours have been needed to change the spent packing in a big column.
GB-A-2258415 describes a column which can be packed and unpacked without taking it apart, using special supply and discharge valves in the top and bottom plates of the housing. The packing supply valve has a spray nozzle which can be retracted into the top plate, with the spray openings closed by a seal on the plate, or advanced to project into the column bed space, freeing the openings for a slurry of packing material to be pumped in. The discharge valve has an advanceable nozzle with radially-directed spray openings at its enlarged head, positioned coaxially within a wider bore of the bottom plate. When retracted the head fits in the bore to seal itself and the bore. To empty the column, the nozzle is advanced and buffer liquid pumped through it. The advanced nozzle head breaks up the packed medium and the pumped-in buffer carries it out through the larger bore, now opened.
There are difficulties in maintaining long-term sanitary conditions with these valve assemblies.

THE INVENTION
The process is a separation process in which a liquid incorporating components to be separated is caused to flow upwardly through a bed of particulate stationary phase (packing medium) enclosed in a bed space of a column housing, for example at a rate which expands or fluidises the bed. After passing through the bed the liquid passes a restricted-permeability element (typically a mesh, or a porous or other perforated layer which will retain the packing medium particles) and out of the column housing through a process outlet.
Preferably, the liquid may incorporate parti culate or cohesive matter which will not pass, or not freely pass, the restricted-permeability element.
Biological culture products are an important example of this. For instance, expanded bed separation is used to remove a target protein, by adsorption onto the bed particles, from an unclarified or partially-clarified culture broth containing cells, cell debris, lipid particles and/or the like.
As separation proceeds, such materials accumulate against the restricted-permeability element used to prevent escape of packing material through the process outlet. In time, the accumulated matter prevents effective operation.
Processing must be stopped, the column housing opened and the accumulated matter cleared before restarting.

CA 02362108 2001-11-16' Our proposal is to remove such accumulated matter from the bed space, e.g. from time to time as the process proceeds, and optionally without cutting off the input of feed stock liquid.
According to the present invention, there is provided a separation process for separating a target component from a liquid incorporating the target component with other components, the separation process comprising:
providing a bed of particulate packing medium, said medium being adapted to retain the target component and said bed thereof being enclosed in a bed space defined by a column housing, said housing having a process outlet and a restricted permeability element between the process outlet and bed space to retain the particulate packing medium in the bed space;
flowing liquid upwardly through the bed of particulate packing medium, through the restricted-permeability element and through the process outlet, to expand the bed in the bed space and effect separation of the target component from the liquid through retention by the particulate packing medium said other components of the liquid comprising particulate matter, said particulate matter accumulating against the restricted-permeability element during the flowing of the liquid, and the process further comprising opening a clearing outlet communicating directly with the bed space, at or adjacent the restricted-permeability element, and forcing a clearing flow of fluid relative to the restricted permeability element to disturb the particulate matter which has accumulated against it, and causing said matter to pass out ~of the bed space through the clearing outlet.
So, the separation process may continue with reduced or eliminated interruptions for clearance of accumulated matter from the bed space.
Preferably, the clearing flow may be provided by forcing a reverse flow through the restricted-permeability element, e.g. back through the process outlet, or through other conduits penetrating the impermeable wall behind the restricted-permeability element. Additionally or alternati-vely the clearing flow may come through one or more nozzles on the bed space side of the element by pumping fluid out of them e.g. at the centre of the element, and desirably with a clearing flow radiating from a conduit penetrating the housing wall.
20 According to the present invention, there is provided a separation process for separating a target component from a liquid incorporating the target component with other components, the separation process comprising:
providing a bed of particulate packing medium, said medium being adapted to retain the target component and said bed thereof being'enclosed in a bed space defined by a column housing, said housing having a process inlet, an inlet-side restricted-permeability element separating the bed space from the process inlet, a process outlet, an outlet-side restricted-permeability element separating the bed space from the process outlet, said restricted-permeability elements retaining the~particulate packing medium in the bed space;
introducing a flow of liquid through the process inlet and upwardly through the inlet-side restricted-permeability element, through the bed of particulate packing medium to expand the bed in the bed space, through the outlet-side restricted-permeability element and through the process outlet, and introducing a mobile phase material containing the target component directly into the bed space through a valued input opening.
Preferably, introduction is through an access valve device opening through the restricted-permeability element.
In this way a mobile phase incorporating particulate matter, or other matter which might clog the restricted-permeability element, can be introduced conve-niently into the bed for processing.
By combining the above proposals, the introduced particulate or other matter can then conveniently be cleared from the bed space.

BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of our proposal are now described in detail, with reference to the accompanying drawings in which:
Figure 1 is a cross-sectional schematic side view of a chromatography column showing the basic features thereof;
Figure 2 is an axial cross-section showing an end plate construction in more detail;
Figure 3 shows enlarged, in axial cross-section, the construction of an access valve;

Figure 4 is an axial cross-section corresponding to Fig. 2 with the access valve in a part-open position;
Figure 5 is an axial cross-section corresponding to Fig. 2 but with the access valve in a fully-open position;
Figure 6 is an axial cross-section of the end plate illustrating a medium packing operation;
Figure 7 is a view corresponding to Fig. 6, with the column in operation and the access valve being cleaned;
Figure 8 is an axial cross-section corresponding to Fig. 6 illustrating the process of unpacking a packing medium f rom the column;
Figure 9 is an axial cross-section of the top end plate of a chromatography column undergoing expanded-bed chromatography, illustrating a clearing operation;
Figure 10 is an axial cross-section of a column end which is a variant of that in Figs 2 to 8; and Figure 11 is a schematic view of a second version of the access valve.
DETAILED DESCRIPTION OF EMBODIMENTS
Figure 1 shows schematically the general components of a chromatography column The column has a cylindrical fluid-impermeable side wall 11, e.g. of stainless steel or a high-strength/reinforced polymeric material which may be translucent. The open top and bottom ends of the side wall 11 are closed by top and bottom end assemblies 12,13. Each end assembly has a fluid-impermeable end plate 3 fitting sealingly to plug the opening of the cylindrical wall 11, and preferably of stainless steel or high-strength engineering plastics material, e.g polypropylene. The end plates are backed up by metal retaining plates 2 bearing against their outer surfaces and projecting radially beyond the side wall as retaining flanges 22 through which adjustable tension rods 14 are secured. These link the top and end assemblies 12,13 and help the construction to withstand high fluid pressures.
Each end plate 3 has a central through-opening 31 for communication between the exterior of the column and the packing bed space 9 defined by the side wall 11 and end assemblies 12, 13. Access through the opening 31 is sub-divided into separate conduits, connected externally through a connection manifold 8.
A filter layer 4, typically of filtered or woven plastics or steel, extends across the area of the bed space 9 at the inner surface of the end plate 3. The inner surface 35 of the end plate 3 is recessed behind the filter layer 4, e.g. conically as illustrated, and preferably with the use of support ribs (not indicated) supporting the filter layer 4 from behind, to define between them a filtration space 34. One of the conununication conduits, a mobile phase conduit 33, opens inwardly into this filtration space 34, as well as outwardly to a mobile phase connector 81 of the manifold 2~ 8.
From the manifold 8, an access valve device 5 projects inwardly through the end plate opening 31 and sealingly through a central orifice 41 of the filter layer 4. The access valve 5, embodiments of which are described in more detail below, governs the communication of one or more conduits from the manifold 8 directly to the bed space 9, i.e. bypassing the filter layer 4. Indicated here are first and second valued conduits 51, 61 governed by the valve 5, and connected externally through connectors 82 of the manifold 8.
In a typical operation of the column, a packed bed of particulate stationary phase material fills the bed space 9 between the top and bottom filter layers 4. The valve devices 5 being closed, a mobile phase is fed in through mobile phase connector 81 (arrow "A"), passes through conduit 33 into the filtration space 34 and through the filter layer 4 to elute down through the packed bed, effecting separation of its components. Liquid eluate passes thought the filter layer 4 of the bottom end assembly 13 and out through the mobile phase connector 81 thereof (arrow "B") for collection as appropriate.
Figure 1 and the above explanation are to illustrate general relationships of components and a typical mode of operation. The skilled person knows, and it will also appear from the following description, that other specific constructions and modes of operation may be appropriate for different kinds of process.
A more detailed embodiment of an end plate and valve construction is now described with reference to Figures 2 and 3.

A manifold 8 is provided as a machined metal or plastics block fired sealingly over the central opening 31 of the end plate 3 by threaded connectors 88, and recessed into a central aperture 23 of an outer metal retaining plate 2 which is fixed to the end plate 3 by bolts 21 or other suitable fasteners. The periphery of the end plate 3 seals against the column side wall 11 with an annular polymeric seal member 32 which also overlaps the filter layer 4 to retain its periphery. This seal member may have an internal rigid reinforcement. Unlike a conventional O-ring it eliminates dead space by sealing with a cylindrical surface and mounting in a shape-fitting groove of the end plate.
The manifold 8 has a central bore 91 coaxial with the plate opening 31 and having inwardly and outwardly directed threaded connection openings 83, 89. The cylindrical barrel 6 of a spool valve S is screwed into the inward connection 83, to extend coaxially inwardly through the central plate opening 31 and out through a central circular orifice 41 of the filter layer 4, terminating in an outward flange 65 which overlaps the filter layer 4. A cylindrical outer sleeve 66 fits snugly around the barrel 6, its outward edge resting against the inward face of the manifold block through a polymeric sealing ring 662 and its inner edge resting against the outer surface of the filter layer 4 through another polymeric sealing ring 661, trapping the layer 4 between the sleeve 66 and barrel flange 65. Since the barrel's outer diameter corresponds to that of the layer orifice 41, it is possible in the illustrated condition to remove the barrel by unscrewing it and withdrawing it inwardly, without disturbing the filter layer 4. This is an advantage for column maintenance.
One or more flow conduits 33 are created by clearance between the barrel assembly (barrel and sleeve) and the plate opening 31. Thus, the plate opening 31 may have a plurality of axially-extending channels distributed around it to form the conduits 33, intervening surfaces of the opening 31 fitting against the barrel assembly. Or, a full annular clearance may be provided. Or, these conduits may be provided away from the barrel assembly, defined only through the material of the plate 3. The inner ends of the conduits 33 communicate into the filtration space 34. Their outer ends align sealingly (by virtue of polymeric sealing rings 662,663) with connection conduits 811 of the manifold block, connected in common to a threaded or otherwise connectable port 81. This establishes direct fluid communication between filtration space 34 and the port 81, while communication between the bed space 9 and port 81 is necessarily through the filter layer 4. Ribs provided on the inner plate surface 35 (in known manner) assist even distribution or collection of fluid to or from the space 34.
A bore 61 extends axially through the barrel 6 from one end to the other. The bore's outward end merges sealingly (by polymeric sealing ring 664) and without change of diameter into the central manifold bore 91. The inward end of the bore 6 is on the bed space side of the filter layer 4, and constitutes a mouth opening 611. The bore 61 has a uniform cylindrical cross-section except for a radially-enlarged portion near but outward of the mouth 611. The enlarged portion 612 has a central cylindrical part bordered on either side by tapering surfaces 613.
These are angled at not more than 45" from axial.
A central probe element acts in the bore 61, to give the function of a spool valve. The probe element has an elongate tube 72 with an open internal bore 73, extending axially from adjacent the barrel mouth 611 out through the outward end of the barrel 6 and the coaxial ball 91 of the manifold 8. Outwardly of_ the outer barrel end, a tapered sealing ring 665 seals between the tube 72 and surrounding manifold bore 91: a plug collar 87 is screwed into the outer connection 89 of the manifold to hold the tapered seal 665 effectively in place.
At its inward end, the probe has a solid head 71 with a pointed tip 74, terminating the bore 73. The head 71 has a cylindrical sealing surface 711, of the same diameter as the barrel bore 61, and which as shown can seal against an inward sealing surface 64 at the mouth 611 of the barrel bore 61, assisted by a flush-recessed polymeric sealing ring 641.
The probe bore 73 opens at a set (Fig. 4) of spray openings 75 opening through and distributed circurnferentially around the tube 72. The tip sealing surface 711 stands radially proud of these openings 75.
Immediately outwardly of the openings the probe head 71 has another radially-enlarged portion or land 76 which presentsla cylindrical sealing surface 761 bordered by tapering portions 762 angled at not more than 45" from the axial.
Outwardly of this second enlargement 76 the tube exterior 72 is a plain cylinder.
The diameter of the sealing surface 761 on the second enlargement 76 is the same as that 711 on the first enlargement 71.
The tube 72 being narrower than the barrel ball 61, an annular-section clearance 51 is defined between them.
This constitutes an outer valve conduit extending out through the outer end of the barrel 6 into the manifold bore 91 up to the seal 665, where it diverts to a threaded or otherwise connectable manifold port 82.
Beyond the manifold 8, the outer end of the probe tube 72 is connected to means for advancing or retracting it axially relative to the barrel 6, with sliding through the seal 665. These means may be motor or servo activated, e.g. advancing the probe by rotating a fixed drive member which engages the tube 72 via a screw thread, e.g. as proposed in GB-A-2258415. Additionally or alternatively, a manual control is provided for. the axial adj us tmen t .
The spool valve effect of the valve 5 is as follows.
Figs 2 and 3 show a first, closed condition in which.

the head sealing land 711 seals with the mouth sealing surface 64 of the barrel, isolating both the valve conduits 51, 73 from the bed space 9. The filtration conduits 33 are not affected by the valve. The nozzle openings 75 and the second sealing land 76 register 5 axially with the radially-enlarged portion 612 of t:he barrel bore 61. This puts the nozzle openings 75 into communication with the outer valve conduit 51, creating a continuous sealingly-enclosed flow path between the probe tube bore 73 and the manifold port 82. This path has no 10 unswept areas or dead spaces. Within the valve device 5, none of its boundary surfaces deviates from the local central flow axis/layer by more than 45°, assisting effective sweeping. In the manifold the path likewise has no dead ends.
15 Consequently, when the chromatography column is running (see also Fig. 7) the valve device and its associated connections can be cleaned in place by.feeding a cleaning solution (e. g. aqueous alkali, or other suitable cleaning medium known to the art) through that fully-sweepable cleaning path. It is particularly envisaged to feed the cleaning solution in through the probe tube 72.
Figure 4 illustrates a second, partially-open condition of the valve 5. The probe tube 72 is advanced sufficiently to bring the second sealing land 76 into register with the bore mouth 611, where their respective sealing surfaces 761, 64 effect a sliding seal. This also brings the nozzle openings 75 to outside the mouth 611, communicating with the bed space 9. Accordingly the inner valve conduit constituted by the bore 73 is put into direct communication with the bed space, bypassing the filter layer 4, while the outer valve conduit 51 remains isolated from the bed space 9.
Figure 6 illustrates an application of this in creating a new bed of packing material. The packing itself can be as described in GB-A-2258415. Specifically a flowable flurry of packing material particles in carrier liquid is pumped in through the tube 72 and sprays out radially in circumferentially-distributed directions from the openings 75. As packing material accumulates in the bed space 9 excess carrier fluid escapes through the filter layer 4 and away through the filtration conduits 33 and manifold port 81, to which a connecting tube is fastened. This is continued until sufficient packing material has been introduced.
Figure 5 illustrates a third condition of the valve.
Here the probe tube 72 has been advanced further inwardly to bring the second sealing land 76 clear of the mouth seal 64, which now opposes the smaller-diameter outer surface of the tube 72 to create a clearance, opening the outer valve conduit 51 to the bed space 9 through the mouth 611.
Figure 8 shows how to exploit this third condition to unpack material from a column bed. It should be noted that, as disclosed in GB-A-2258415, the advanced pointed head 71 of the probe is apt to disrupt existing bed material, which is often a hard compacted mass, and thereby help to initiate unpacking. A carrier liquid such as a buffer is pumped in through the probe bore 73 and out through the nozzle openings 75; its high nozzle velocity helps to disrupt and entrain the packed material. The particulate packing material cannot pass the filter layer 4, but it can respond to the pumping in of liquid by escaping as a slurry through the mouth 611 of the valve and along the outer valve conduit 51 to the manifold port 82 for discharge along a connected tube.
So, for the first time a single column wall installation enables both packing and unpacking of a column. This can give much greater flexibility in column operation. Note that the packing and unpacking operations can be effected entirely from outside the column housing, without needing to dismantle or remove the end assemblies.
Furthermore the valve which can do this can itself'be cleaned in place, even when the column is running by introducing a mobile phase onto the bed through the filtration conduits 33 as shown in Fig. 7. So, even this relatively sophisticated wall installation does not introduce a risk of contaminants accumulating and leaching into a long-running process perhaps with disastrous results. In the terminology of the skilled person in this field, this valve device is a "sanitary"
installation.
Furthermore the valve is easily dismantled for maintenance because the probe can be entirely withdrawn inwardly from the barrel bore 61.
Further modes of use, in relation to expanded-bed separation processes, are explained with reference to Figs. 9 and 10. Expanded bed adsorption is a recently-developed separation technique, particularly for reducing or eliminating the need to clarify biological cultures before eluting them through a packing to separate out a desired component',. The packing bed is expanded by an upflow of liquid medium so that even particulate material in the sample can~,work its way through the bed to the outlet above the bed. For expansion the bed must rest on a permeable layer' through which the liquid up-flow is established. Introduction of the sample must therefore generally be done'. as a single pass, which sample batch then elutes through the bed. Usually desired materials are adsorbed onto. the bed particles, and in a subsequent step are recovered by stopping the liquid up-flow~
compressing the bed by moving down the upper plate and then percolating through the bed a liquid that desorbs the target substance from the bed particles.
A column for this can have top and bottom retaining assemblies which each have an impermeable plate interior filter layer and a central valve device as shown in the previous Figures. The normal filtration conduits and means for establishing up-flow of a mobile phase are also provided.
A first feature here is that a sample e.g.

unclarified broth, can conveniently be introduced into the expanded bed, bypassing the lower filter mesh, by injecting it though the inner valve conduit 73 of the lower valve in its second, partially open condition.
Where sample is injected intermittently the lower valve is returned to its fully-closed first condition in between.
Our new valve construction therefore provides a convenient way of introducing such a sample past a mesh required for maintaining an up-flow.
A second and very significant feature is explained in relation to Fig. 9, which shows in more detail a top end assembly for the expanded-bed process.
During normal running of the process the mobile phase passes through the filter layer 4', through the filtration conduits 33' and out. There is a gradual accumulation of particulate debris and other matter reluctant to pass the filter 4', e.g. lipids. This therefore accumulates in an upper bed space region 91 adjacent to filter layer 4'. In time it hinders the maintenance of proper flow.
By moving the upper valve device 5' to its third, fully-open condition for a short period of time, while creating a clearing flow of liquid adjacent the filter layer 4' to disturb the accumulated matter, this matter can be caused to follow the clearing flow out of the bed space via the outer valve conduit 51. One method of achieving a clearing flow is to provide a short blast of suitable liquid, e.g. a buffer, through the probe bore 73' and out through the nozzle openings 75' which are near the filter layer 4'. Alternatively or additionally, the normal flow direction (arrow "X") of buffer out of the system can temporarily be reversed and buffer pumped back in through the filtration conduits 33' (arrow "Y").
thereby creating a temporarily downward flow through the S filter layer 4' (arrow "Z"), disrupting the accumulated material so that it can accompany the escape of the temporary liquid pressure wave out through the valve conduit 51. This may be done either with or without cut-off of the supply of sample at the bottom of the column.
Thus, the process can be run as long as the absorption proceeds efficiently, without needing to stop for other reasons. This is a highly advantageous procedure.
Fig 10 shows a variant end plate construction for a 15 chromatography column. The differences from the previous embodiment include the following.
The filter layer 4 is formed integrally with.inner and outer annuli 41,42, in one piece in plastics material.
The inner annulus 41 forms a flush termination for the 20 barrel 6 of the central valve 5, and has an inwardly-facing surface to form the seal with the valve's central probe_ This flush one-piece construction further reduces the risk of contamination at the point of access. It also enables the filter layer's inner periphery to self-trap in 2; a groove of the valve barrel 6, enabling that barrel 6 to be one component rather than two. The end cell and valve components may be of polypropylene.

The filter layer's outer annulus 42 is used to hold the filter layer in place by trapping between the wall 11 of the column and the end plate 3 of the cell, which in this version is a one-piece polypropylene construction.
The connection manifold 8 has the mobile phase inlet/outlet port S1 and the waste slurry outlet port 82 inclined outwardly, rather than perpendicularly as in the previous embodiment, to improve flow. A further significant feature in this embodiment is that the filter layer 4 is concave, by virtue of the support ribs on the end plate 3 being formed with inclined rather than slightly radial edges. We find that this slight conicity improves drainage from the column during clearing.
Fig 11 shows schematically a different embodiment valve which however embodies similar concepts. Here the central movable probe is a simple armature rather than a fluid-carrying nozzle. Its enlarged head 171 is carried on actuating rod 272 and has a flat end surface 17J.2, a first outer sealing land 1711, a conical convergence 1613 to a narrow recess or waist 1612, and a smaller enlargement 176 with a second sealing surface 1761.
The mobile phase conduit 33 is provide outside the valve barrel 6 as before. Inside the valve barrel the central fluid conduit 173 is defined not through the probe 272,171 but rather by an inner conduit wall 172 surrounding the probe shaft 272 and having an opening with an inwardly-directed seal 174, recessed back from r_he main opening through the filter layer 4, which has its own 2z inwardly-directed seal 141 at the mouth of the.oucer conduit defined between the outer barrel wall 6 and the inner conduit wall 172.
Fig'11 shows the valve fully open, with the central probe fully advanced to open both conduits e.g for unpacking and column. Unpacking liquid is pumped in through the inner conduit 173 and squirts out around the armature head 171; waste slurry flows back and out through the outer conduit.
In the partially open position, e.g for packing a column, the armature is partially retracted so that second sealing surface 1761 seals off the inner conduit, the outer conduit remaining open. Slurry can be pumped in through the outer conduit. This shears the slurry less than the spray nozzle of the first embodiment.
Full retraction of the armature brings its front surface 1712 flush with the filter layer 4 and its first head sealing surface 1711 into sealing engagement~with the central filter opening seal 141, closing off the outer conduit. At the same time the second sealing land 176 drops below the inner conduit seal 174 which then opposes the recess 1612 to permit a circulating, clean-in-place flow through the inner and outer conduits.
Note that in the open conditions the conical portion 1613 of the head 171 can be axially adjusted to alter the direction of liquid pumped in. This embodiment illustrates how two separate seals on the fixed part of the valve can provide the same effect as previously if their spacing is different from that of the corresponding sealing portions of the movable part.

Claims (9)

CLAIMS:

1. A separation process for separating a target component from a liquid incorporating the target component with other components, the separation process comprising providing a bed of particulate packing medium, said medium being adapted to retain the target component and said bed thereof being enclosed in a bed space defined by a column housing, said housing having a process outlet and a restricted permeability element between the process outlet and bed space to retain the particulate packing medium in the bed space;
flowing liquid upwardly through the bed of particulate packing medium, through the restricted-permeability element and through the process outlet, to expand the bed in the bed space and effect separation of the target component from the liquid through retention by the particulate packing medium;
said other components of the liquid comprising particulate matter, said particulate matter accumulating against the restricted-permeability element during the flowing of the liquid, and the process further comprising opening a clearing outlet communicating directly with the bed space, at or adjacent the restricted-permeability element, and forcing a clearing flow of fluid relative to the restricted permeability element to disturb the particulate matter which has accumulated against it, and causing said matter to pass out of the bed space through the clearing outlet.

2. A separation process as claimed in claim 1, in which the liquid comprises unclarified or partially-clarified cell culture broth, and the target component is a protein product in the culture broth.

3. A separation process as claimed in claim 1 in which the clearing flow comprises a reverse flow forced back through the restricted permeability element.

4. A separation process as claimed in claim 1 in which a said clearing flow is forced through at least one nozzle at the bed space side of the restricted-permeability element.

5. A separation process as claimed in claim 4 in which a said nozzle is on a conduit at the centre of the restricted-permeability element, and the clearing flow radiates from the nozzle.

6. A separation process as claimed in claim 1 in which the column housing has a housing wall and an access valve is provided through the housing wall and restricted-permeability element to enable communication of first and second fluid flow conduits directly into the bed space, said access valve being adjustable between a closed condition in which said conduits are isolated from the bed space and an open condition in which said conduits are open to the bed space;
said access valve being adjusted in the process to the open position whereupon said second fluid flow conduit provides the clearing outlet and a said clearing flow of fluid is introduced through the first fluid flow conduit.

7. A separation process as claimed in claim 1 in which the column housing has an inlet-side restricted-permeability element and said flowing comprises pumping liquid medium through the inlet-side restricted-permeability element to expand the bed, and an inlet-side access valve movable between open and closed conditions is provided to communicate directly with the bed space, a material containing said target component being introduced directly into the bed space through said inlet-side access valve in its open condition.

8. A separation process as defined in claim 7 in which said material comprises an unclarified or partially-clarified culture broth, and the target component is a protein product in the culture broth.

9. A separation process as claimed in claim 7 in which the inlet-side access valve opens at the centre of the inlet-side restricted permeability element.