U.S. patent application number 14/825198 was filed with the patent office on 2015-12-17 for chromatography system with tilt-prevention structure and associated process.
The applicant listed for this patent is Biotechflow Limited. Invention is credited to Martin John Hofmann.
Application Number | 20150360145 14/825198 |
Document ID | / |
Family ID | 48048477 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150360145 |
Kind Code |
A1 |
Hofmann; Martin John |
December 17, 2015 |
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.
Inventors: |
Hofmann; Martin John;
(Stroud, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Biotechflow Limited |
Stroud |
|
GB |
|
|
Family ID: |
48048477 |
Appl. No.: |
14/825198 |
Filed: |
August 13, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/GB2014/050456 |
Feb 17, 2014 |
|
|
|
14825198 |
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Current U.S.
Class: |
210/656 ;
210/198.2 |
Current CPC
Class: |
G01N 30/6021 20130101;
B01D 15/206 20130101; B01D 15/22 20130101; G01N 30/6026 20130101;
G01N 30/603 20130101; G01N 30/58 20130101; G01N 30/56 20130101 |
International
Class: |
B01D 15/22 20060101
B01D015/22 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2013 |
GB |
1302714.9 |
Claims
1. A chromatography apparatus comprising: a column tube having a
tube axis defining an axial direction of the apparatus; first and
second end cells which close off the column tube, defining between
them an operating volume in the column tube; at least one of the
end cells is a movable piston, slidably movable inside the column
tube in the axial direction thereof and comprising a peripheral
operating seal to seal against the inside of the column tube; said
movable piston comprising a piston body comprising the operating
seal; and a tilt-prevention structure projecting axially from the
piston body and connected to be rigidly axially aligned therewith,
wherein the tilt-prevention structure comprising a
circumferentially-distributed contact structure which engages
around the interior of the column tube at an axial spacing from the
operating seal.
2. The chromatography apparatus of claim 1 in which said movable
piston is free of rigid structure passing through any fixed column
end structure of the apparatus.
3. The chromatography apparatus of claim 1 in which said contact
structure is annular and engages continuously around the column
tube interior.
4. The chromatography apparatus of claim 1 in which the contact
structure is radially movable relative to the tilt-prevention
structure; and the movable piston comprises a contact structure
actuating mechanism operable to urge the contact structure radially
outwardly against the column tube interior and/or to retract it to
a radially retracted condition or position.
5. The chromatography apparatus of claim 1 comprising an outer
closure of the column tube, and in which the movable piston, column
tube and outer closure define a pneumatic space outside the movable
piston, separated from the operating column, and a pressured gas
supply for supplying pressurised gas into the pneumatic space to
act on the movable piston.
6. The chromatography apparatus of claim 1 in which the contact
structure comprises an elastomeric ring.
7. The chromatography apparatus of claim 1 in which the engagement
of the contact structure with the column tube interior is around a
single annulus at a constant axial spacing from the operating
seal.
8. The chromatography apparatus of claim 1 in which the
tilt-prevention structure is an open structure comprising any of
rods, legs and struts with intervening spacing.
9. The chromatography apparatus of claim 1 in which an axial extent
of the contact structure, said axial extent being the maximum axial
distance reached by the contact structure from the axial position
of the operating seal, is at least 25% of a diameter of the movable
piston.
10. The chromatography apparatus of claim 1 in which the operating
seal comprises an elastomer ring in a peripheral channel of a
piston body.
11. The chromatography apparatus of claim 1 comprising a pneumatic
mechanism for the radial advance or retraction of the operating
seal.
12. The chromatography apparatus of claim 1 comprising sensors to
detect the axial position of the movable piston in the column
tube.
13. The chromatography apparatus of claim 1 in which the movable
piston has a central process fluid outlet and comprises a
vortex-inhibiting structure at said process fluid outlet, the
vortex-inhibiting structure comprising one or more divider,
partition or slot-defining elements.
14. A chromatography apparatus comprising: a column tube having an
inside surface and a tube axis defining an axial direction of the
apparatus; a movable piston, slidably movable inside the column
tube in the axial direction and comprising a peripheral operating
seal to seal against the inside surface of the column tube; said
movable piston having a diameter and comprising a piston comprising
the peripheral operating seal; a tilt-prevention structure
projecting axially from the piston body, the tilt-prevention
structure comprising an annular contact structure which engages
around the inside surface of the column tube at an axial spacing
from the operating seal which is at least 25 percent of the
diameter of the movable piston; and an open frame structure
connecting the annular contact structure rigidly to the piston
body.
15. The chromatography apparatus of claim 14 in which the movable
piston has a central process fluid outlet.
16. The chromatography apparatus of claim 14 comprising a
pneumatically-actuated mechanism to urge the contact structure
radially outwardly against the inside surface of the column
tube.
17. The chromatography apparatus of claim 14 in which the contact
structure comprises a polymeric ring to contact the inside surface
of the column tube.
18. A chromatography apparatus comprising: a column tube having a
tube axis defining an axial direction of the apparatus; a fixed
outer end closure of the column tube; an end cell comprising a
piston slidably movable inside the column tube in the axial
direction thereof and comprising a peripheral operating seal to
seal against the inside of the column tube, said movable piston
being free of rigid structure passing through the fixed outer end
closure, and whereby the movable piston, column, tube and outer end
closure define a pneumatic space in the column tube; and a
pressurised gas supply inlet for the supply of pressurised gas into
the pneumatic space to act on the movable piston.
19. The chromatography apparatus of claim 18 in which the movable
piston has a process fluid outlet, a sealed connector is provided
extending through the column tube or through said outer end
closure, and a flexible conduit is connected at one end to the
process fluid outlet and at the other end to the sealed
connector.
20. The chromatography apparatus of claim 18 in which the operating
seal comprises an elastomer ring and the apparatus comprises a
pneumatic mechanism operable to advance or retract the operating
seal radially relative to the piston, so as either to urge the
operating seal outwardly against the inside of the column tube or
to retract it to a radially retracted condition.
21. A chromatography process carried out with the chromatography
apparatus of claim 1, the process comprising: providing a bed of
particulate medium in the operating volume; adjusting the position
of the movable piston in the axial direction towards the bed of
particulate medium; and passing a process fluid through the bed of
particulate medium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of PCT/GB2014/050456
filed Feb. 17, 2014, which claims priority to GB1302714.9 filed
Feb. 15, 2013, both of which are hereby incorporated by
reference.
BACKGROUND
[0002] This invention has to do with apparatus, systems and
processes for chromatography. Aspects of the invention have
particular relevance for expanded bed (fluidised bed) processes.
These are processes in which a process liquid is contacted with a
bed of solid particulate medium in a column, by passing the liquid
through the column. Contact with the solid medium allows treatment
of the liquid, in most cases the treatment constituting or
comprising separation of a component of the process liquid by
retention thereof on the medium.
[0003] Chromatography has traditionally used packed beds of
particulate medium, retained between end retaining structures of
the column tube which keep the bed of medium in place while
allowing passage of the liquid components. The end retaining
structures (sometimes called "cells") have a mesh through which
liquid but not media particles can pass. The cells may be fixed to
the column tube, or one or both of them may be operationally
slidable within it, with a piston seal, for adjustment of bed
height.
[0004] In recent years the industrial-scale production of
biologically-produced molecules, e.g. for drugs, vaccines or
diagnostic agents, has become of great technical and economic
importance. Many such products are produced in cell cultures and
they (or their precursors) must be separated from a culture product
(e.g. homogenised broth or slurry) which typically contains
insoluble solids such as cell debris as well as contaminants; it
cannot be passed as mobile phase through a packed bed to adsorb the
product chromatographically (preparative chromatography) because
the solids would block the system. Rather, the culture product must
first be processed to remove the solid matter and make a process
liquid able to pass through stationary phase beds.
[0005] Expanded Bed Adsorption (EBA) enables separation of target
components from such process liquids without preliminary
centrifugation or filtration. In EBA the process liquid runs up
through a bed of adsorbent medium particles in expanded (fluidised)
state. Solid material in the process liquid passes up right through
the bed to the outlet; the inlet and outlet are without meshes.
Target product is adsorbed onto the particulate medium and is
subsequently eluted (washed) from it, either downwardly with the
bed packed or upwardly with the bed fluidised.
[0006] EBA therefore offers important efficiencies. For example,
because it can directly process liquids containing high proportions
of solids or of target substance, such as high cell density broths
from a bioreactor, it enables the high productivity of such
bioreactor processes to be carried through the later
processing.
[0007] However EBA also presents major technical challenges. It is
difficult to maintain the expanded bed in a stable and effective
state, e.g. maintaining the vertical gradation of reducing particle
size, and avoiding direct channeling of process liquid through the
bed.
[0008] Measures taken to control bed behaviour include special
process liquid injection arrangements at the bottom of the column,
to produce plug-like flow e.g. by injecting the liquid through an
array of holes distributed over the bottom cell, optionally
stirring with a rotating stirrer. Or, an array of process liquid
injection holes is in a motor-driven distribution rotor. At the top
of the bed a movable piston or float may lie on the liquid surface
to mount the process liquid outlet, or the outlet tube may simply
dip into the clear liquid ("headspace" or supernatant) above the
particle bed.
[0009] EBA columns are relatively tall, because of the bed
expansion. Expanded bed height--which may be about twice the rest
height--is controlled by adjustment of the liquid flow rate,
optionally in conjunction with a top piston or float as mentioned.
Top pistons are problematic because the mounting and control
structure connecting them through the end of the column (usually a
pipe incorporating the outlet conduit and/or guide rods) needs
large vertical clearance.
[0010] Solids passing through the column may accumulate and foul
the apparatus--cell materials are often sticky--which is then
difficult to disassemble for cleaning. As the apparatus is scaled
up, bed diameter increases, components become larger and heavier
and serious operational difficulties may arise.
[0011] As a consequence of these various technical challenges,
scale-up of EBA for industrial application has scarcely progressed
despite the intrinsic merits of the EBA method in itself.
SUMMARY
[0012] We propose new kinds of chromatography apparatus and
chromatography processes with a view to enhancing and facilitating
the operation of apparatus and processes of the kind described,
especially but not exclusively EBA. One particular aspect addressed
is construction, operation and control of a movable end cell or
piston.
[0013] Particular advantages are envisaged for scale-up of EBA and
also other movable-cell apparatus and methods
[0014] General Context
[0015] The apparatus aspects of the invention relate in general to
chromatography apparatus comprising a column tube and first and
second end retainer structures (end cells) which close off the
column tube at respective axially-spaced first and second positions
to define between them an operating volume which in use contains a
stationary phase material, typically a bed of particles. The
apparatus has first and second process fluid conduits communicating
into the operating volume at the first and second positions,
preferably through the end cells, for liquid e.g process fluid or
mobile phase liquid such as buffer (equilibration, elution, wash)
to enter and leave the operating volume in use.
[0016] Movable Piston Proposals
[0017] In a first aspect, at least one of the end cells is a
movable piston, slidably axially movable inside the tube over a
range of operational positions and comprising a peripheral
fluid-tight operating seal which seals against the inside of the
column tube in operation to prevent the passage of liquid. It may
be the top cell of an upright column.
[0018] One proposal in this aspect is that the piston comprises a
piston body, which mounts or comprises the operating seal and
closes off the tube (except for any said process fluid conduit
therein, which is desirably present, preferably at the centre) and
additionally a tilt-prevention structure, connected to and rigidly
axially-aligned with the piston body, the tilt-prevention structure
having a circumferentially-distributed contact structure which
engages around the interior of the column tube at an axial spacing
from the operating seal to maintain axial alignment of the piston
in the column tube. The contact structure may slide against the
tube interior surface.
[0019] Preferred features of the piston are as follows, which
(insofar as they are compatible) are desirably combined.
[0020] The contact structure may be annular and engage continuously
around the tube interior. If however it has plural
circumferentially-spaced contact elements these are preferably
spaced by angular circumferential gaps not more than 90.degree.,
preferably not more than 70.degree., more preferably not more than
45.degree. or not more than 30.degree., to assure adequate
tilt-prevention. It may be non-metallic, e.g. polymeric or
elastomeric. It may be an elastomeric ring, although it does not
have a sealing function. The contact structure may be radially
movable in the tilt-prevention structure and the piston may
comprise a contact structure actuating mechanism such as a
pneumatically-actuated mechanism for urging the contact structure
radially outwardly against the tube interior and/or for retracting
it to a radially retracted condition or position. A preferred
contact structure is or comprises an elastomeric ring, e.g. a
hollow ring, with a pneumatically-actuated mechanism for urging it
outwards. A pneumatic gas line may connect between this mechanism
and the exterior of the apparatus, e.g. out through an end of the
tube, such as through an end plate or cover.
[0021] Desirably the contact structure of the tilt-prevention
structure and the operating seal are the only piston parts engaging
the column, so that the piston can travel along the column without
tilting or jamming, without having a rigid connection (such as the
axial piston rod pipes or guide rods of the prior art) engaging
(passing) through a fixed column end structure of the apparatus.
That is, the piston may be entirely inside the column tube, and be
self-aligning with the column tube axis by its axially-distributed
engagements with the column wall.
[0022] The engaged locus of the contact structure may be at a
constant axial spacing from the operating seal, around the tube.
Preferably it contacts the tube interior at a single annular locus
spaced from the operating seal (e.g. a circle parallel to that of
the seal), contacting either continuously or intermittently around
the circle.
[0023] Preferably the tilt-prevention (or stabilising) structure
does not contact the column wall between the operating seal and the
contact structure. Desirably the tilt-prevention structure is open,
in the sense that the column wall behind the operating seal, i.e.
between the operating seal and the contact structure, is open or
exposed to the column tube interior space behind the piston (i.e.
outside the operating volume). This can facilitate access and
cleaning. Of course in principle however tilt-prevention may be
provided simply by sufficient axial length of a piston body.
[0024] The tilt-prevention structure may comprise an open frame
e.g. comprising or consisting of rods, legs or struts with
intervening spacing. The frame can connect an annular body
supporting the operating seal to the contact structure, which may
itself be, comprise or be mounted on an annular body.
[0025] Alternatively, if the contact structure has plural
circumferentially-spaced contact elements these may be provided on
respective axially projecting legs or struts, e.g. extending from
the outside of the piston body. The piston body is closed, e.g. as
a plate or disc, except for any process fluid inlet through it,
whereas the contact structure or support body for it may be an open
ring. The back (outer side) of the piston body may be exposed
through the contact structure, so a connector or union comprised in
or fixed to the piston body, for a fluid conduit, may be exposed
and operable on the outer side of the piston body. The same may be
true of one or more other connectors, e.g. for actuation of dynamic
elements as discussed below.
[0026] The degree of axial spacing needed between the
tilt-preventing contact structure (or the axially-extreme part
thereof) and the operating seal will depend on the dimensions of
the column, the piston and on the structure at the operating seal.
Axial alignment needs to be maintained sufficiently to maintain the
seal and to prevent jamming of the piston. This may take into
account the extent to which the operating seal projects relative to
its surrounding mounting, which may be of a hard material e.g.
metal which to avoid damage should not contact the tube interior
especially if the latter is of plastics material. Typically the
axial extent (the maximum distance reached by the contact structure
away from the operating seal axial position) is at least 20%, at
least 25% or at least 30% of the diameter of the piston (or of the
corresponding internal diameter of the column tube).
[0027] The operating seal of the piston body may be of any suitable
kind, for example an elastomer ring (single or multiple). The
piston body may have a peripheral groove or channel in which it is
mounted or housed. A mechanism or means may be provided for
advancing or retracting the operating seal radially, e.g. to urge
it outwardly against the tube interior to enhance the seal at a
selected position, and/or to retract it to loosen or release the
seal and facilitate or allow movement of the piston along the tube,
or the passage of liquid around it e.g. for cleaning. A pneumatic
mechanism is preferred for this radial drive or actuation of the
seal, being easily actuated from outside the column tube. A
pneumatic gas line for this purpose may connect to the piston body
and extend through an interior gas space which when pressurised
expands the operating seal. Depending on the structure, material
and dimensions of the seal either of the retraction or the
expansion movement/urge may be under elastic recovery or under
forced actuation by a mechanism as mentioned. The seal may be
radially retractable sufficiently to form an annular clearance
between the seal and the column tube wall. For process purposes,
this clearance is desirably larger than the largest media particles
used in the column. When engaged with the tube wall, e.g. under
radially outward actuation as proposed, the operating seal may
function to grip the tube to hold the piston in position e.g.
against its own weight and/or against positive fluid pressure from
above or below. Or, the contact structure or a combination of the
contact structure and seal may serve this function.
[0028] The piston body desirably has a central opening as (or for)
the process fluid/mobile phase conduit. This opening may receive or
form a union or connector, for connecting to a flexible process
fluid/mobile phase conduit outside the piston body. A conventional
releasable liquid-tight connector such as a triclamp is suitable.
Preferably the inner face of the piston body, directed onto to the
operating volume, is convergent towards the conduit entrance, to
facilitate smooth flow and escape of liquid and gas through the
opening. If it is an expanded bed apparatus, this inner face may be
directly exposed to the operating volume. If it is a packed bed,
there may be an overlying mesh layer to prevent the passage of
particles. The form of a converging inner surface may be conical or
dished. If conical, the cone angle relative to the radial plane is
preferably between 4.degree. and 25.degree..
[0029] The materials used for the piston and tilt-prevention
structure thereof will depend on the size of the apparatus and the
chosen structure, but typically metal and/or engineering plastic
materials are suitable. The piston is preferred not to be a buoyant
or floatable component. Steel is generally good, but heavy and
expensive. Engineering plastics such as PEEK are very good but
expensive. Large shaped components subject to primarily general
pressures and stresses, such as a piston body, may be made from
standard plastics such as polypropylene which are much cheaper,
easier to form and have adequate strength.
[0030] A second proposal concerning the moveable piston, which may
have any of the features proposed above in the first proposal, is
apparatus and methods providing for the use of pressurised gas in a
pneumatic space behind (outside) the movable piston to control the
piston's position, i.e. to hold or change its axial position in the
column tube. For this purpose, apparatus has a gas-tight pneumatic
space defined outside the movable piston, preferably by the column
tube and an outer closure (e.g. an end plate) thereof. Means are
provided for supplying pressurised gas into this pneumatic space to
act on the movable piston, e.g. directly on the outer surface of
the piston body of a self-aligning piston as described in the first
proposal above. A gas supply line may connect into the pneumatic
space through the column tube wall or, more preferably, through an
end plate constituting the outer closure and which can be removed
from the column tube. A gas supply is connected to the gas supply
line. A gas pressure control for the gas supply line can be
provided, preferably as part of the apparatus (i.e. as distinct
from a control on the supply itself), and desirably provide both a
shut-off condition and a range of maintainable operating pressures.
The operating pressures need not be high for most processes, e.g.
in a range of 0 to 5 bar (gauge pressure). However higher pressures
e.g. up to 10 barg may be used if supported by the apparatus. The
gas supply may be sterile or via a sterilising filter in the supply
line, enabling sterile conditions in the space outside the piston
during operation.
[0031] Usually, at various stages of a chromatography process, the
operating volume is at raised pressure and this must be contained
by the end cells (i.e. retaining structures or closures). Where a
movable piston provides an end cell, the structure and material of
the piston and the means by which the piston is held and moved must
all be able to withstand this bed pressure or operating fluid
pressure, which for large columns means heavy and awkward
components. By applying pneumatic pressure on the outside of a
movable piston to counter-balance all or part of the liquid
pressure on the other side, the strength demands on the piston are
reduced and it can be made lighter and easier to handle.
[0032] Thus it can be arranged that the piston and its components
(including the operating seal) may need to withstand only the
difference between the pressures in the pneumatic space and the
operating volume, both of which pressures are controllable,
together with any frictional resistance during position change, the
weight of the piston itself and the structural forces involved in
alignment via the contact structure and in urging the seal and
contact structure out against the tube wall. The difference in
pressures is usually/typically less than 0.5 bar, and may be
controlled or controllable to such low differential pressures, e.g.
less than 0.5 bar in an EBA process. The general balancing of axial
forces also facilitates the radial actions/movements of the piston
with operating seal and contact structure.
[0033] Where the piston engages the piston wall by means of an
inflatable element e.g. a seal, and the column interior is
pressurised, it is necessary to provide adequate excess inflation
pressure to enable the inflatable element to expand against the
surrounding pressure in the column.
[0034] The fluid pressure in the operating volume may be sufficient
to move the movable piston outwardly (usually upwardly). So, both
inward and outward piston movements may be available by adjustment
of the gas pressure (e.g. air pressure) in the pneumatic space,
without necessarily needing to adjust the liquid flow pressure in
the operating volume as well, although of course that is also a
possibility but usually the process fluid flow is adjusted
primarily or only with the bed behaviour in mind. In some other
kinds of chromatography processes the piston may be allowed to move
to accommodate volume changes of a packed media bed, e.g. swelling
or shrinking of the medium as the ionic composition of the
surrounding liquid changes.
[0035] One particular desirable context for such apparatus and
procedures is expanded bed or fluidised bed chromatography, in
which the movable piston is the top cell of an upright column. A
central process fluid outlet of the movable piston may connect to
the exterior of the column via a flexible conduit e.g. a polymeric
hose, which may extend through the pneumatic space and through the
column tube (or an end closure thereof) via a sealed isolated
connector to maintain the gas-tight condition of the space. The
flexible conduit can flex or contract/extend to accommodate the
necessary operational range of axial movement of the piston and so
that it can fit in the pneumatic chamber at less than full
extension.
[0036] An expanded bed or fluidized bed chromatography process, or
separation or purification process, in which the height of the
movable piston is adjusted by controlling gas pressure in the
pneumatic space, is an aspect of the present proposal. Most
preferably it uses a self-aligning piston as described in the first
aspect above. Thus, unlike the proposal in U.S. Pat. No. 5,366,621
to use gas pressure behind a piston to help move the piston, this
proposal would then not involve rigid piston support structures
extending out through the end of the column. The piston can
therefore be both lighter in weight and vertically compact, and
correspondingly better suited for scaling-up. Thus, while column
dimensions are not especially critical for operational
effectiveness, we envisage greatest benefit in application of our
proposals in larger preparative-scale apparatus e.g. column
diameters of at least 100 mm, or at least 200 mm, or preferably at
least 300 mm for expanded fluidised bed apparatus and processes, or
at least 750 mm or at least 1000 mm in diameter for packed bed
apparatus and processes (including ion-exchange) which may be as
large as e.g. 4 m diameter, although these too may be smaller e.g.
down to 300 or 100 mm diameter and still have advantages. Column
height is important insofar as conventional larger columns have
used long piston guides which, with a stand, greatly increased
height e.g. so that a 1 m column tube has needed more than 2 m
available operating height.
[0037] Nevertheless the principles described are also effective
with smaller columns, e.g. laboratory-scale columns such as from 5
to 50 mm diameter, and columns less than 1 m long (high).
[0038] The column tube may be of any suitable material, e.g.
conventional materials such as transparent plastics (e.g. acrylic)
or metal e.g. steel. Transparent column tubes are preferred in some
processes for visual monitoring. In expanded/fluidised bed
apparatus a transparent tube is preferred.
[0039] In packed bed apparatus and processes, the need to move a
top piston through large distances can be less than in expanded bed
processes. However there will be a need for substantial movement,
because the bed is usually packed from slurry filled into the
column, and the distance moved by the piston to the packed
condition will correspond to the dilution % of the slurry. With
some packed processes (such as ion exchange) there may be
significant expansion or contraction of the bed during processing.
The pistons may be very large and cumbersome. The present proposals
for the use of pneumatic pressure-balancing drive with a
self-aligning piston are valuable, therefore. Conventional large
columns with top pistons often use a set of hydraulic rams
positioned around or above the column tube to support and move the
piston. These are bulky structures, and control of the rams so that
they act together to slide the piston without tilting and jamming
is difficult and requires sophisticated apparatus. By deploying gas
pressure in an enclosed pneumatic space behind the piston, as
proposed herein, the piston can be made lighter in structure and
more easily handleable and controllable. A set of hydraulic rams
can be omitted.
[0040] A third aspect of our proposals relating to movable pistons
is about the axial positioning and control of the movable piston in
the column tube.
[0041] In combination with either or both of the previous proposals
about the structure and control of the movable piston, we prefer
that the apparatus comprises sensing means for detecting the axial
position in the column tube of the movable piston and/or of
features of a media particle bed or particle distribution
(especially in the context of EBA in which there is usually a
liquid-filled headspace or supernatant, which in turn may have a
clear upper part and a cloudy/turbid lower part, between the top of
the bed and the underside of the piston). Firstly, such sensing
means may determine and may also indicate any operational position
taken by the piston in the tube. Additionally or alternatively, a
sensing means may comprise means for determining whether the axial
position of the piston registers with one or more predetermined
axial positions relative to the column, e.g. a predetermined lower
position (perhaps corresponding to a packed bed state, e.g. for
eluting an EBA column) and a predetermined upper position (e.g.
corresponding to a predetermined adsorption stage position of an
expanded bed column with the bed expanded, a stable expanded bed
height position with a predetermined height of supernatant e.g.
clear supernatant, or corresponding to a position for cleaning or
servicing the apparatus). For that purpose, position-specific
sensing means may be provided mounted at the side of the column
tube at the corresponding positions, and able to detect the
presence of the piston by any means appropriate to the nature of
the piston and column tube wall, e.g. optically or by
ultrasound.
[0042] Secondly, sensing means such as ultrasound may operate/be
operable to detect position or condition of features of the medium
particles, the bed thereof, or materials passing through or in the
bed. Potentially useful detectable and/or measurable features
include any one or more of the top of a bed (or expanded bed), the
position of an interface between an expanded bed and clear
supernatant, the height of a bed or expanded bed, the height of a
supernatant liquid layer, the presence or height of a cloudy or
turbid (low medium concentration) supernatant region or layer, the
presence/position of an interface between cloudy and clear
supernatant regions, the presence/position of an interface between
a cloudy supernatant region and an expanded bad regions. The
packed, expanded, stable or unstable conditions of a bed, regions
of clear supernatant, cloudy regions or regions of lower medium
concentration may be detected, e.g. using density-dependent
detection such as ultrasound. Concentrations or concentration
variations of other (non-medium) substances in the bed may also be
detected, such as solutes of interest e.g. target molecules, or
non-medium particles.
[0043] In relation to the apparatus and process proposals above for
driving the movement of the piston, preferably by pneumatic means,
the apparatus may comprise and the process may use a control system
to control the gas pressure in the pneumatic space (to adjust,
change or maintain the axial position of the piston) in dependence
on signals received from the position/condition-sensing means,
which in turn depend on the position of the piston or on the
position or condition of or in the particle bed or of the top of
the bed, or on the detection of media particles or other particles
or substances in general. This control system may enable or provide
automated control of the piston position or bed condition (although
visual/manual intervention may be used instead or additionally) in
dependence on column or process conditions (of any of the
detectable kinds set out above) in real time, e.g. as a mode of
Process Analytical Technology whereby process and product quality
are designed, analysed or controlled with measurement of critical
process parameters.
[0044] For monitoring such positions over a range, the apparatus
may comprise a set or array of sensors or detectors distributed
axially (usually vertically) on or at the side of the column tube
and acting laterally (e.g. detection path in a radial plane).
Additionally or alternatively the system may have a sensor acting
axially (axially-extending detection path) which can measure the
axial position of the piston e.g. as a distance relative to an end
plate or end closure of the column.
[0045] Position-specific sensors may be e.g. ultrasound, optical,
capacitive or inductive detectors (often with a combination of
transmitter and receiver, preferably combined in a single
transceiver) mounted on or adjacent the column tube wall,
preferably with axial position adjustability relative to the column
tube. A position-specific detector may include an indicator that
any of the piston, bed front, media particles or clear liquid is
present at the predetermined position, on the detection path. One
or more supplementary detectors or sensors may be provided axially
adjacent any mentioned predetermined position to indicate approach,
overshoot or undershoot of the corresponding entity/condition to be
detected (piston, bed front, liquid, media particles etc. as
described above) relative to the predetermined position.
[0046] In preferred apparatus, desirably for expanded bed or
fluidised bed columns but not limited to these, piston position
detection is by means of an ultrasound transceiver mounted
vertically adjustably, e.g. slidably, adjacent the tube wall, e.g.
on a vertical support element of the apparatus, and securable at
any of a range of axial positions. A set of such transceivers may
be used to provide detection of adjacent positions as mentioned
above, e.g. a set of at least two or at least three axially
adjacent sensors.
[0047] Transceiver Mounting
[0048] An independent proposal herein is for the mounting of an
ultrasound transmitter, receiver or transceiver. Ultrasound
transducers generally need to make close contact at a suitable
pressure against the surface of the tube to operate effectively. It
is desirable, but difficult, to reach this condition by advancing
the transducer gradually against the tube surface, to a controlled
extent and pressure. To this end, we propose mounting an ultrasound
transducer (e.g. a transceiver) on or in a pivoted mounting element
adjacent to the column tube. The transducer face is to one side of
the pivot. To the other side of the pivot, the mounting element
carries a rotatable threaded adjuster element with an end
positioned to bear against the column tube wall. The end that bears
against the tube wall may be of a plastics material, if necessary,
to avoid damage to the tube surface. Turning the adjuster with its
end against the tube wall controllably and gradually pushes that
end of the mounting element away from the tube wall, by threaded
engagement with the mounting element, bringing the face of the
ultrasound transducer correspondingly progressively towards and
into operational contact with the tube wall. Desirably the pivot
axis is vertical, e.g. provided on an upright structural element
adjacent the column wall. This proposal enables rapid deployment of
ultrasound sensing at newly-determined operating positions. For
best results the axis of the threaded adjuster is preferably
perpendicular to the tube wall, i.e. radial relative to the
tube.
[0049] Flow Control
[0050] Another aspect herein (preferably combined with any one or
more or all of the aspects above) is particularly concerned with
expanded bed or fluidised bed processes, in which process liquid
flows out of the column through a top outlet opening, preferably in
a top end cell or top piston, but optionally in a free outlet
conduit end that does not close off the column tube interior.
[0051] As mentioned above, the maintenance of a stable and
effective expanded bed is challenging. One challenge is to avoid
the formation of vortices in the liquid upflow. In the expanded bed
apparatus and processes described herein, we prefer to use a
process liquid inlet injection arrangement having an array of
process liquid injection holes in a distribution rotor. These
rotors have significant advantages, but their rotation naturally
tends to initiate vortex formation in the bed volume. It is known
to reverse the rotation direction from time to time to reduce this
tendency, but it can still be a problem. Moreover, even without a
rotational structure at the process liquid input, liquids have a
tendency to form vortices where they flow out from a larger volume
through a restricted conduit, such as from the bed volume out
through the process liquid outlet of an expanded bed process.
[0052] Noting this, we have found that vortex formation can be
usefully reduced by providing a vortex-inhibiting structure beneath
the outlet opening, preferably as part of the outlet structure or
as part of a piston or end cell structure which incorporates the
outlet structure. The vortex-inhibiting structure comprises one or
more divider, partition or slot-defining elements. These may be
disposed in the opening and/or projecting down below the opening
entrance, and/or projecting radially out beyond it. The one or more
elements desirably extend(s) substantially radially, e.g. in radial
planes, relative to the outlet axis. This structure divides the
flow entering the outlet, and inhibits rotational movements around
the outlet axis.
[0053] Preferably it comprises two or more upright radial vanes
projecting downwardly and outwardly relative to the outlet opening,
so as to reduce or inhibit rotational flow.
[0054] The structure may also comprise a downwardly-facing baffle,
desirably at or below the level of the vanes or partitions, to
promote approach of liquid to the outlet in a radially inward
rather than axial direction.
[0055] Preferably the vortex-inhibiting structure for the outlet is
incorporated in a fitting which is attached at or to the underside
(inside face) of a movable top piston. Additionally or
alternatively it or part of it (e.g. vanes) may be incorporated in
the structure of the piston face. As mentioned, it may also be used
in a column with a non-movable end cell, especially top cell, such
as in a fixed wall or a non-moving or non-adjustable piston.
[0056] A preferred embodiment combines the above vortex inhibitor
with a feature of a movable piston which is itself another new and
independent proposal herein, namely a piston component or fitting
with a lower extremity or structure which projects down axially
below the periphery of the piston (which desirably has a dished or
coned lower surface) to form a bump stop, so that if for any reason
the piston should fall down inside the column, this (preferably
central) lower extremity meets the structure at the bottom of the
column first. The centre is typically a strong point, e.g. the hub
of a rotary process liquid injection rotor, the outer parts of
which would be vulnerable to damage if the piston fell on them. In
the preferred embodiment the bump stop extremity and optionally
also the vortex-inhibiting structure themselves are formed of
polymeric or plastics materials to reduce the impact, and may be
formed as a single unit e.g. in one piece. Preferably the extremity
is downwardly convex to avoid trapping e.g. of air.
[0057] It is also a proposal herein to provide a vortex-inhibiting
structure as described above at the inlet to the operating volume,
such as at the bottom of a column tube. The options above are all
applicable, but the other way up. Vortex-inhibiting structure may
be provided at both ends.
Preferred Embodiments
Expanded Bed Adsorption Column
[0058] Drawing together the proposals above, preferred embodiments
of our proposals are EBA columns and processes having a movable top
piston, pneumatically-operable as discussed above, and preferably
with sensor means for detecting or monitoring one or more positions
of piston, liquid, bed front, particles, bed conditions or solute
concentrations etc. as mentioned above, desirably also with
feedback or dependency for the pneumatic actuation to control the
piston in dependence on the position(s) or condition(s) detected by
the sensor means. A top plate of the column may define the top of
the pneumatic gas space. The process fluid exit conduit (piston
exit conduit) is a flexible conduit or hose which may pass
sealingly right through the top plate, or may connect to a fixed
union in the top plate which connects the interior flexible conduit
section with an exterior conduit section. One or more actuating
lines, e.g. one or more pneumatic actuating lines, for any of
dynamic operating seal(s) and/or piston tilt-preventing contact
structure elements, may also pass sealingly through the top plate,
or be connected through it via a fixed union. Since the top plate
should make an airtight seal, it is preferred to leave it in place
without disturbing its main peripheral seal. It may be for example
bolted onto a top flange of the column tube. In this proposal and
in the movable piston proposals in general it is preferred to
provide a removable access hatch in the top plate 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. Thus, the hatch opening is desirably at least 50 mm,
more preferably at least 100 mm across, e.g. a circular opening, so
that e.g. a hand can pass through. The removable hatch cover makes
a fluid-tight seal, desirably sealing out sideways with a sliding
(plug) seal against the edge of the hatch opening.
[0059] At the bottom of the column, the apparatus preferably has a
process liquid injection rotor with an array of injection holes,
and a drive to rotate it. These are known, and a skilled person can
choose a suitable one for the purpose in hand. Usually the bottom
of the column is closed off by a fixed end plate, which may have a
separate hole for the draining and optionally injection of the
column contents (media particles). This can be a sanitary valved
hole.
[0060] The underside of the top piston preferably has an
anti-vortex structure as described above, which also preferably
includes a lower bump stop extremity which is a lowermost part of
the piston, so as to limit impact in case the piston falls.
[0061] Desirably the flexible outlet conduit is able to take the
weight of the piston. Optionally a supplementary tether is
provided, e.g. a wire whip check, that connects between the piston
and the top plate to absorb initial energy should the piston fall,
protecting the flexible conduit against shock loads. The flexible
conduit may be made e.g. of wire-reinforced polymeric hose.
[0062] The column may be mounted on or connected to a mobile
platform ("skid"), in a generally known way. A programmed control
unit may be provided for operating the pneumatic drive, and may be
integrated into the skid (programmable control platform).
[0063] The apparatus preferably comprises a gas filter to clean
(sterilise) the gas, typically air, which is pumped into the
pneumatic space above the piston.
[0064] Conventional or known media may be used for the EBA,
according to the skilled person's knowledge. As is well known,
preferred media particles for EBA are density-controlled, usually
having a high-density core e.g. of quartz, tungsten carbide,
zirconia or steel, and an active coat, e.g. of agarose gel,
carrying selective binding groups for the target substance, e.g.
Protein A for antibodies.
[0065] The apparatus and processes herein may be used for the
production or purification of drugs, biopharmaceuticals, hormones,
vaccines, or diagnostic agents, or biologically-produced precursors
of these.
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] Having described the general concepts proposed, we now
describe examples with reference to the accompanying drawings in
which:
[0067] FIG. 1 is an axial cross-section of an EBA column embodying
the invention.
[0068] FIG. 2 is a plan view of the column, showing a line A-A for
the section of FIG. 1.
[0069] FIG. 3 is a radial cross-section at B-B of FIG. 1.
[0070] FIG. 4 is a radial cross-section showing details of the
piston and top cover of the column.
[0071] FIG. 5 is an oblique view of the piston separate from the
column.
[0072] FIGS. 6(a) and 6(b) are oblique schematic views of piston
designs showing conceptual alternatives for tilt-preventing
structures.
[0073] FIG. 7 is a plan view of a bottom plate with the column tube
removed.
[0074] FIG. 8 is a fragmentary sectional view through the top cover
showing sealed fitting of an air input to an air chamber.
[0075] 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.
[0076] FIG. 10 is a fragmentary sectional view through a segment of
tube wall showing a way of mounting an ultrasonic transceiver.
[0077] FIG. 11 is a schematic diagram showing more details of an
air supply system.
[0078] FIG. 12 shows schematically a column of packed-bed type with
a movable piston according to our proposals.
DESCRIPTION OF THE SELECTED EMBODIMENTS
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.degree., 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.
[0087] 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.degree. 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] Another possible operational mode ("Aspect B") is as
follows.
[0100] 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).
[0101] 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.
[0102] 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.
[0103] 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.
[0104] 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.
[0105] 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
[0106] 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.
[0107] 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.
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