Adsorbent medium

Details Adsorbent medium Adsorbent medium

1992-11-02

1996-02-20

Dudash, Diana

Coating processes

Foraminous product produced

Filter, sponge, or foam

427339, B05D 500

Patent

active

054927234

DESCRIPTION:

BRIEF SUMMARY
The present invention is concerned with sponge adsorbent media having functional groups chemically bonded thereto.
There are two broad ways of making cellulosic materials in the form of flexible sponge and having functional groups (such as ion-exchange groups) chemically bonded to the cellulose. In one method, as described in GB 914421, a pre-formed flexible cellulosic sponge is modified by reaction with a reagent which introduces ion-exchange groups (such as orthophosphoric acid or sodium chloroacetate). GB 1387265 discloses ion-exchange cellulosic material prepared by reaction of cellulose with a reagent which introduces ion-exchange groups, followed by regeneration into the desired physical form, among which is sponge.
GB 1226448 discloses a method of making an ion exchanger, which comprises the introduction of cross-linking residues into regenerated cellulose together with or followed by introduction of cation or anion exchange groups into the cellulose. The cellulose is typically obtained from viscose; no preferred physical form for the cellulose is specified (i.e. the cellulose may be used in a variety of physical forms such as rod, filament, yarn, woven cloth, flakes, beads, granules, powder, sponge, tube or sheet).
The present invention is concerned with a method of preparing sponge adsorbent media having a pre-determined porous structure and which method involves modification of a flexible sponge.
Hydrophilic cellulosic chromatographic media have been widely used for the isolation or separation of macromolecules, such as proteins, both in the laboratory and on a commercial scale. However, sponge adsorbent media have not been used greatly in commercial chemical separation operations (such as ion-exchange separation techniques), probably because of the absence of any sponge adsorbent media possessing the required porous structure and the resulting difficulties of ensuring adequate contact between the liquid being treated and the sponge. For this reason, particulate and granular media are generally used, despite the disadvantages associated with the use thereof such as slow flow rates, plugging of the bed, and maldistribution of flow and also the need for considerable skill in filling a column to avoid channelling.
The mass transfer rate of substances being treated by means of adsorbent media is generally diffusion limited. The adsorption reaction at the surface of adsorbent media is fast, whilst limiting processes for adsorption and elution are the film diffusion resistance around the matrix and the pore diffusion resistance within it. Higher flow rates will reduce the resistance of film diffusion and hence increase productivity by decreasing process time. The resolution of ion-exchange chromatography requires the column to have a certain length, the flow rate being inversely proportional to column length. When recovering a biological molecule present in very low concentration in a large volume of feedstream, flow rate and capture efficiency are the major factors to be optimised.
We have now devised a method of producing cellulosic sponge adsorbent media having superior flow properties and adsorption and desorption kinetics, and which are also specifically modified so as to be suitable for use as chromatographic adsorbents.
According to the invention, there is provided a method of preparing a sponge adsorbent medium, which method comprises: preparing a cross-linked flexible sponge containing substantially uniformly distributed fibrous reinforcement, under such conditions that swelling of said sponge is controlled to a water retention value of 2 to 6; and, simultaneously or subsequently, reacting the resulting cross-linked sponge with a reagent which introduces functional groups into the modified cross-linked sponge.
The fibrous reinforcement preferably comprises cotton linters, typically present in an amount of about 2 to 50% by weight; materials such as jute, cotton fibres, flax or other hydrophilic fibres may alternatively be used. Such hydrophilic fibres preferably contain free hydroxy which are

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