Multicomponent ion exchange resins

Details Multicomponent ion exchange resins Multicomponent ion exchange resins

2000-05-30

2003-03-18

Zitomer, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Ion-exchange polymer or process of preparing

C521S025000, C521S029000, C521S032000, C521S033000

Reexamination Certificate

active

06534554

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to multicomponent ion exchange resins comprising granules comprising at least one crosslinked acidic resin and at least one crosslinked basic resin. Each superabsorbent ion exchange granule has at least one microdomain of the acidic resin in contact with or in close proximity to, at least one microdomain of the basic resin. The ion exchange resins can be used, for example, in the purification of water, sugar refining, recovery of transition metals, recovery of proteins from fermentation broths and agricultural by-products, and in pharmaceutical separations technology.
BACKGROUND OF THE INVENTION
Ion exchange generally is defined as a reversible chemical interaction between a solid and a fluid, wherein selected ions are interchanged between the solid and fluid. An exemplary ion exchange process includes a exchange process wherein a fluid passes through a bed of porous resin beads having charged mobile cations or anions, such as hydrogen or hydroxide ions, which are available for exchange with metal ions or anions present in the fluid. The ion exchange resin readily exchanges hydrogen ions for the metal ions, or hydroxide ions for other anions, present in the fluid as the fluid passes through the bed.
In time, the number of hydrogen or hydroxide ions available for exchange with metal ions or other anions diminishes. Eventually, the resin becomes exhausted and cannot perform any further ion exchange (i.e., all available exchange sites are occupied). However, the resin can be regenerated. Regeneration is accomplished using a regenerant solution, which, in the case of a cation exchange resin, comprises an acid, i.e., a large excess of hydrogen ions, that is passed over the ion exchange beads and drives the collected ions from the resin, thereby converting the ion exchange resin back to its original form.
A specific example of a cation exchange process is the purification/softening of tap water. In this process, weak acid ion exchange resins use carboxyl radicals, in the sodium form, as the cation exchange site. The sodium ions are the charged mobile cations. Alkaline earth metals, such as calcium and magnesium, present in the tap water are exchanged for the sodium cations of the resin as the water passes through a bed of the ion exchange resin beads. Removal of calcium and magnesium ions from water in exchange for sodium ions via weak acid cation exchange resins is not limited to the water purification/softening applications, but also includes the softening of fluids, such as clay suspensions, sugar syrups, and blood, thereby rendering the fluids more amenable to further processing. When the exchange capabilities of the ion exchange resin are exhausted, a weak acid can be used to regenerate the acid form of the resin, followed by conversion of the acid form of the resin to the sodium form with dilute sodium hydroxide.
Similarly, an anion exchange resin containing anionic radicals removes anions, like nitrate and sulfate, from solution. Anion exchange resins also can be regenerated with a sodium hydroxide solution, for example.
The reversibility of the ion exchange process permits repeated and extended use of an ion exchange resin before replacement of the resin is necessary. The useful life of an ion exchange resin is related to several factors including, but not limited to, the amount of swelling and shrinkage experienced during the ion exchange and regeneration processes, and the amount of oxidizers present in a fluid passed through the resin bed.
Cation exchange resins typically are highly crosslinked polymers containing carboxylic, phenolic, phosphonic, and/or sulfonic groups, and roughly an equivalent amount of mobile exchangeable cations. Anion exchange resins similarly are highly crosslinked polymers containing amino groups, and roughly an equivalent amount of mobile exchangeable anions. Suitable exchange resins, preferably, (a) possess a sufficient degree of crosslinking to render the resin insoluble and low swelling; (b) possess sufficient hydrophilicity to permit diffusion of ions throughout its structure; (c) contain sufficient accessible mobile cation or anion exchange groups; (d) are chemically stable and resist degradation during normal use; and (e) are denser than water when swollen.
Hatch U.S. Pat. No. 3,957,698 discloses production of weak acid ion exchange resins by the suspension copolymerization of methacrylic or acrylic acid, in a low molecular weight hydrocarbon diluent, with 0.5 to 10 wt. % of divinylbenzene, based on the weight of initial monomers, to achieve the proper degree of crosslinking. In order to prepare high purity ion exchange resins by this process, the resin is heated at a high temperature or is extensively washed with solvents to remove the diluent. The resin particles were in the size range of 2 to 5 microns.
Meitzner et al. U.S. Pat. No. 4,224,415 discloses the preparation of ion exchange particles prepared by suspension copolymerization of water-insoluble monomers, such as methyl acrylate and methyl methacrylate, with a crosslinking agent, such as divinylbenzene. In addition, a precipitant is added to the monomer phase to impart a reticular nature to the resulting particles. This process requires a divinylbenzene content in the range from 8 to 25 wt. % to prepare the desired materials. The particles must be hydrolyzed with a strong base in order to prepare a material with exchangeable functionalities.
Therefore, conventional weak acid cation exchange resins typically are produced using a multistep process. The first step is a batch, aqueous suspension polymerization of methyl acrylate monomer, in the presence of divinylbenzene, to provide crosslinked beads of methyl acrylate. The poly(methyl acrylate) beads then are reacted with sodium hydroxide to hydrolyze the ester groups of the poly(methyl acrylate), and thereby introduce carboxylate (i.e., weak acid) functionality into the beads. Due to solubility of the acrylic acid in the aqueous phase of the suspension polymerization, acrylic acid is not wholly substituted for the methyl acrylate monomer in the foregoing process. Therefore, conventional manufacturing processes preferably utilize methyl acrylate, which is a relatively expensive monomer, in the syntheses of the ion exchange resin. Acrylic acid, however, can be copolymerized in a batch process with methyl acrylate monomer utilizing a divinylbenzene cross-linker.
The essentially total removal of ions from electrolyte-containing solutions is often accomplished using two ion exchange resins. In this process, deionization is performed by contacting an electrolyte-containing solution with two different types of ion exchange resins, i.e., an anion exchange resin and a cation exchange resin. The most common deionization procedure uses an acid resin (i.e., cation exchange) and a base resin (i.e., anion exchange). The two-step reaction for deionization is illustrated with respect to the desalinization of water as follows:
NaCl+R—SO
3
H→R—SO
3
Na+HCl
HCl+R—N(CH
3
)
3
OH→R—N(CH
3
)
3
Cl+H
2
O.
The acid resin (R—SO
3
H) removes the sodium ion; and the base resin (R—N(CH
3
)
3
OH) removes the chloride ions. This ion exchange reaction, therefore, produces water as sodium chloride is adsorbed onto the resins. The resins used in ion exchange do not absorb significant amounts of water.
The most efficient ion exchange occurs when strong acid and strong base resins are employed. However, weak acid and weak base resins also can be used to deionize saline solutions. The efficiency of various combinations of acid and base exchange resins are as follows:
Strong acid—strong base (most efficient)
Weak acid—strong base
Strong acid—weak base
Weak acid—weak base (least efficient).
The weak acid/weak base resin combination requires that a “mixed bed” configuration be used to obtain deionization. The strong acid/strong base resin combination does not necessarily require a mixed bed configuration to deionize water. Deionization also can be achieved by sequentially passing th

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