Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-05-17
2001-03-20
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S675000, C210S679000, C210S688000, C204S166000, C521S028000, C423S139000, C423S024000, C423S029000, C075S728000, C525S107000, C525S128000, C525S438000, C525S440030, C525S129000, C525S100000
Reexamination Certificate
active
06203708
ABSTRACT:
This invention relates to ion exchange resins comprising an ion exchange material dispersed or distributed throughout a polyurethane matrix and methods of producing the same.
Various polymeric materials have been developed and shown to be useful in ion exchange or deionising systems for removing soluble electrolytes from an ionising solvent (typically aqueous solutions). Commercially available ion exchange resins are produced from polymers such as phenol-formaldehyde, styrene-divinyl benzene, acrylonitrile, acrylates and polyamines. These polymers may subsequently be modified, for example, by halomethylation, sulphonation, phosphorylation, carboxylation, etc. Further modification of the resin so produced may be achieved by a further chemical reaction to attach particular ligands to the benzene ring present in the resin or to the halomethyl, sulphonic acid, carboxylic acid, amide, amine, nitrile, or other reactive site. This further reaction enables the production of an ion exchange resin with specific reactive sites thereby exhibiting greater selectively towards particular metal ions or other anions or cations. In conventional practice, the ion exchange resins are produced in bead or granular form, the bead size generally varying from 40 microns to in excess of 1 mm in diameter.
Known ion exchange resins, suffer from a number of disadvantages however. To increase the available surface area of ion exchange resins which are produced in bead or granular form, the polymers may be produced in a macroporous form. It has been reported that these beads can suffer from osmotic shock, poor regeneration efficiencies, often lower sorption capacities and higher regeneration costs. In order to achieve a rapid removal of cations or anions from solution it is necessary to reduce the size of the beads to maximise the surface to volume ratio.
In a typical hydrometallurgical process, the ion exchange beads may be added to a clarified lixiviant, a process solution partly clarified by removal of the larger ore solids, or alternatively the ion exchange beads may be mixed with the ore solids in the form of a pulp, the granular ion exchange resin then being recovered by screening. Alternatively, the polymer may be manufactured containing a magnetic material, in which case, the ion-exchange beads may be recovered by magnetic separation. It has been suggested that particularly high values for absorption are obtained if the resins are finely ground. However, fine grinding of the ion exchange resin or the use of ion exchange resin beads of diameters similar to that of the ore pulp in which it is dispersed, make the resin difficult to recover by simple screening.
It has been proposed to disperse known ion exchange resins into a polyurethane polymer. It has been found, however, that a chemical reaction may occur between the liquid isocyanate compound of a polyurethane system and the reactive ligand present on the surface of the ion exchange bead. The catalysts used in the production of the polyurethane foam or the highly reactive isocyanate component can also react with the ligands on the ion exchange resin, destroying their ion exchange properties. Such a reaction may become one of a number of competing chemical reactions which occur during the production of a cured polyurethane resin from liquid components. If the ion exchange resin has an active hydrogen ion, the acidic property will be neutralized by the alkaline catalyst, destroying both the urethane foam reaction and the ion exchange property of the resin. It has also been proposed to add finely ground ion exchange beads to a flexible polyurethane foam prior to foaming. It has been reported, however, that the presence of the ion exchange bead in the foaming system adversely affected the foaming reaction and the physical properties of the cured foam.
It is an object of the present invention to produce an ion exchange resin which overcomes or alleviates one or more of the difficulties associated with the prior art.
According to the present invention there is provided an ion exchange resin comprising a polymer containing ion exchanging sites which is dispersed or distributed throughout a polyurethane matrix wherein said ion exchanging sites are introduced subsequent to the formation of said polyurethane matrix.
The term “ion exchange resin” when used herein includes any polymeric material capable of removing anions and/or cations from solution by sorption irrespective of the mechanism.
The term “dispersed or distributed” when used herein includes a dispersion of discrete particles as well as networks of polymers which are intimately mixed throughout or incorporated within the polyurethane matrix such in interpenetrating polymer systems.
The ion exchange resin comprises a urethane polymer as a matrix or continuous phase. The ion exchange material typically takes the form of a modified second polymer dispersed or distributed throughout the polyurethane matrix. The ion exchanging sites are introduced subsequent to the formation of the polyurethane matrix. This may be done in a number of different ways. A polymer having no ion exchanging sites may be introduced into urethane raw materials, a polyurethane polymerisation reaction may then be conducted to form a polyurethane matrix having the polymer dispersed or distributed therein. The introduced polymer may then be chemically modified to provide ion exchanging sites. In an alternative embodiment, a polyurethane foam may be interpenetrated with one or more monomers, at least one of which has one or more ion exchanging ligands attached. The one or more monomers may then be polymerised to provide a polymer containing ion exchanging sites. In yet another embodiment, a polyurethane matrix may be provided, the matrix may be interpenetrated with one or more monomers none of which have ion exchange ligands attached. The monomers may be polymerised to provide a polymer and the polymer may then be chemically modified to provide ion exchanging sites. In each of these embodiments, the ion exchanging sites are introduced subsequent to the formation of the polyurethane matrix, thereby overcoming the problems associated with the prior art.
Polyurethane formulation and manufacture in many forms is well known. Polyurethane resins can be produced in a range of shapes and forms for example beads including microcontroller beads and expanded beads, foams including elastomeric foams, films, fibres and membranes.
Therefore the ion exchange resin of the present invention can be produced in a form best suited to a particular application or process. For example, larger particles of open cell polyurethane having a suitable ion exchange material dispersed therein, when incorporated into a resin-in-pulp based metals recovery process can easily be removed from the pulp by screening. Standard ion exchange resins are difficult to separate from pulps by simple screening procedures. Polyurethanes particularly those based on polyether polyols have the further advantage that they exhibit excellent resistance to both acidic and alkaline solutions, have good abrasion resistance and good flexibility over a wide range of temperatures and may be formulated to obtain a controlled degree of hydrophilicity.
the dispersed or distributed phase polymer typically may be a polymer formed from monomers of styrene, acrylonitrile, vinyl chloride, vinylidene chloride, divinyl benzene, butadiene, epichlorohydrin, caprolactone, thiodiglycol, thiodianiline, diallylamine, methylacrylonitrile, hydrazides, dicyclopentadiene, vinyl butyral, succinic anhydride, allyl halides, allyl malonic acid, acryloyl chloride, polyacetal, vinyl alcohol, aminosalicylic acid, dimethylolpropionic acid, &agr;-methyl styrene, p-methyl styrene, acrylates such as methylmethacrylatek, acrylamide, methylacrylamide, acrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, glycidyl methacrylate, ethylene dimethacrylate, methylacrylic acid, hydroxyethyl methacrylate, ethylene glycol dimethacrylate, ethyl acrylate, acrylimido salicylic acid, acrylimido diacetic acid, acrylimido malonic a
Jay William Harold
Lawson Frank
Barry Chester T.
Foley & Lardner
Monash University
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