Liquid purification or separation – With means to add treating material – Chromatography
Reexamination Certificate
1998-06-05
2001-05-01
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
With means to add treating material
Chromatography
C210S456000, C210S656000, C096S107000
Reexamination Certificate
active
06224760
ABSTRACT:
The invention relates co apparatus for the separation of substances by chromatography, in particular to the end constructions of chromatography columns.
Chromatography is widely used for the separation of substances held in fluid media. A typical column has an upright housing filled in use with packing material. The packing material is retained in the column by end arrangements, each having an end plate, fluid inlet/outlet opening(s) communicating through the end plate to an internal flow surface thereof, and a filter layer covering the internal flow surface. The end plate may be axially movable relative to the column housing.
The filter layer allows fluid medium to pass over the cross-section of the column while retaining the packing material.
The end plate's internal flow surface is typically recessed towards the centre of the plate e.g. as a generally conical surface, with one or more central through-passages for the fluid inlet/outlet. The recessed end plate surface provides the rear surface of a flow zone which is defined between the end plate and the filter layer and is of importance in ensuring distribution of flow over the filter's flow area: without uniform flow there can be no satisfactory chromatography. To this end the conventional end plate flow surface has a centrosymmetric array of upstanding radial ribs. These also support the rear surface of the filter layer to maintain the flow zone and protect the filter layer against flow forces and packing weight. The maxima of the ribs may themselves provide a conical contour so that the installed filter layer takes a conical form.
The filter layer itself is typically a disc, secured against the end plate around its outer edge and usually also at its centre which may have a central opening for a packing nozzle, e.g. as disclosed in our WO-A-96/10451.
The conventional manufacture of a ribbed end plate is by machining, followed by laborious grinding, polishing and electropolishing steps to get the, desired smoothness of finish. A smooth finish is important in chromatography because the smoother the finish, the more uniform the flow and (especially important in the pharmaceutical field) the less the likelihood of contamination. With plastics end plates the best obtainable smoothness is only that which can be got by careful machining.
What we now propose is to provide a liner layer between the end plate and the surface layer, the liner layer having an obverse surface which provides a rear surface for the flow zone and is formed with a surface relief pattern to support the filter layer from behind and/or direct flow distribution in the flow zone.
Because a relatively thin liner layer need not serve the structural function of the relatively thick end plate its use brings substantial manufacturing flexibility
Furthermore a particular preference is to shape the liner from prefabricated uniform sheet material, e.g. metal or plastics sheet, creating the surface relief pattern by permanent deformation of the sheet material. This can be done against a shaped former e.g. urging the sheet by pressing or vacuum-forming, so as to produce reliefs on one side corresponding to recesses on the other.
An excellent surface finish may then be achieved by comparison with conventional machining, because sheet materials are routinely available with a high degree of surface smoothness which can be substantially retained when the relief pattern is formed. This is particularly advantageous for plastics components, which are not susceptible to smoothing after machining.
It is possible to make the liner layer by other methods such as casting or moulding. These can give a surface finish better than machining but usually less good than by deforming sheet material as mentioned above. All of these techniques however provide an excellent alternative to making and finishing surface reliefs on the structural end plate itself.
The liner may be formed in one piece or as a plurality of segments according to choice; a one-piece liner is simpler to install but a segmented liner can be made with smaller forming apparatus; significant when the end plate is larger.
The surface relief pattern preferably defines a set, of channels extending side-by-side away from an opening for fluid medium. Note that this “opening” may be a set of openings. An array of ribs is suitable. The usual arrangement has a circular liner with one or more central openings for fluid medium and an array of elongate ribs extending wholly or partly radially. The favoured arrangement, as on conventional machined end plates, has a set of major radial ribs—extending substantially from the inner to the outer periphery of the flow zone—and one or more sets of minor radial ribs positioned between the main ribs towards the outer periphery to sub-divide what would otherwise be larger rib spacing in that region.
The liner's obverse reliefs may provide mechanical support for the filter layer, in that the filter layer lies against them and desirably is fixed to them. The maxima of the relief pattern may define a flat or conically recessed support contour against which the filter layer lies to assume a corresponding form.
The reverse of the liner lies against an internal surface of the end plate. For purposes of mechanical support it is preferred that these surfaces are substantially complementary. Usually at least the inner and outer peripheries and preferably also those zones not corresponding to the shaped reliefs are formed to complement the end plate's internal surface. The end plate's internal surface is preferably recessed with a generally conical internal form, and provided with an opening (usually a central opening or centrosymmetric arrangement of central openings) for the passage of fluid medium. Since relief patterning and surface finish are provided by the liner, the end plate's internal surface can be plain. For additional mechanical support, however, it is possible to machine the end plate with reliefs corresponding to all or some of those of the liner and fitting into recesses on the liner's reverse. Benefit is still obtained because the liner cad provide an excellent surface finish and the machined end plate surfaces do not need to be finished.
The liner is preferably an impermeable arrangement secured to the end plate with its reverse side sealed from the flow zone. For this purpose the liner (or its segments) can have a continuous reverse surface region e.g. a perimeter margin region, which complements the end plate internal surface and is sealed to it e.g. by welding or clamping.
The filter layer itself may be conventional. Either metal or plastics filter layers can be used, usually selecting a material corresponding to that of the adjacent parts of the apparatus, and may be fitted onto or adjacent the liner by means well-known to a skilled person, e.g. welding or clamping.
The liner and filter may be assembled together to form an integrated fuzer-liner unit before fitting this onto the end plate. By combining these two components before final assembly, on-site operations can be simplified.
The end plate may have one or more through-channels to the region between the liner and end plate, for leak testing a seal between them e.g. by applying gas pressure.
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patent: 2085614 (1982-04-01), None
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patent: WO 96/10451 (1996-04-01), None
patent: WO 96/26436 (1996-08-01), None
Davies John
Persson Owe
Spencer Gerald James
Ronning, Jr. Royal N.
Therkorn Ernest G.
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