Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2000-06-06
2001-08-28
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C525S361000, C525S362000, C525S366000, C525S367000
Reexamination Certificate
active
06281255
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed generally to the regeneration of weakly basic anion exchange resins with a combination of an alkali metal carbonate and an alkali metal bicarbonate. Preferably, the alkali metal is sodium. The combination can be naturally available sodium sesquicarbonate.
BACKGROUND OF THE INVENTION
Resin-type ion exchange devices have many uses such as the residential or industrial softening of water, deionization of sugar compounds, treatment of industrial waste or process waters and processing of protein complexes. As the fluid to be processed is passed through a vessel containing an ion exchange resin, ions in the fluid to be processed are exchanged with ions found in the resin, thereby removing objectionable ions from the fluid and exchanging them for less objectionable ions found in the resin. As this process progresses, the ability of the resin to exchange ions is gradually reduced. That is, as the resin captures the objectionable ions and releases the less objectionable ions, its capacity to continue this exchange process is gradually exhausted. Eventually, a steady state is reached in which no further objectionable ions in the fluid to be processed can be exchanged for the less objectionable ions found in the resin.
At this point, the ion exchange resin may be regenerated by chemically removing the objectionable ions from the resin and replacing these with the less objectionable ions. This regeneration process requires the suspension of the ion exchange exhaustion process (often referred to as the service cycle). During regeneration, a substance having a high concentration of the less objectionable ions is applied to the ion exchange resin. Because this produces a new balance of concentrations between the respective ions, the ion exchange resin now exchanges the objectionable ions captured during the service cycle for the less objectionable ions applied during regeneration. As a result of this process, the ability of the ion exchange resin to remove objectionable ions from the fluid to be processed is restored.
Weakly basic anion exchange resins, useful for neutralization of acidic aqueous streams, are conventionally regenerated with solutions of sodium hydroxide. For example, anion exchange resins may be regenerated by alkali metal hydroxides as disclosed in U.S. Pat. Re 29,680 or U.S. Pat. No. 4,151,079. However, use of such regenerants in the regeneration cycle may lead to a variation in pH for the solution eluted from the resin over time during the service cycle. If neutralization is incomplete, and the effluent is of low pH, corrosion of pipes further in the system may occur, while if the neutralization is incomplete and the pH of the effluent is high, precipitation may occur further in the system. Moreover, it may be undesirable to discard such regenerants once they have been used for regeneration, so they must be recycled for reuse, such as by electrodialysis as disclosed in U.S. Pat. No. 5,352,345. This recycling will undesirably increase the cost of the neutralization system.
Alternatively, if the ion exchange resin is thermally regenerable, countercurrent thermal regeneration may be utilized to regenerate the resin as disclosed in U.S. Pat. No. 4,184,948, avoiding use of chemical regenerants, but at greater cost.
Therefore, there is a need for an alternative method which allows efficient regeneration without increasing cost, or producing spent regenerants which cannot easily be discarded.
It is an object of this invention to provide a method for regenerating weakly basic anionic resins without increasing cost, or producing spent regenerants which cannot easily be discarded.
BRIEF SUMMARY OF THE INVENTION
The invention is directed to a method for regenerating a spent weakly basic anion exchange resin comprising the step of contacting said resin with a regenerant dosage of a combination of an alkali metal carbonate and an alkali metal bicarbonate, to obtain a regenerated weakly basic anion exchange resin.
For the practice of this aspect of the invention, an aqueous fluid influent may pass through the regenerated weakly basic anion exchange resin, the fluid influent having a pH of from about 3.0 to about 6.5. Moreover, an aqueous fluid effluent may elute from said regenerated weakly basic anion exchange resin, the fluid effluent having a pH of from about 6.5 to about 7.5. The influent may be industrial water or residential water.
The invention is also directed to a method for partial deionization of and neutralization of an impure fluid to remove calcium ions, magnesium ions and bicarbonate ions from said fluid with a weakly acidic cation exchange resin and neutralization of said fluid with a weakly basic anion exchange resin comprising the steps of:
a) passing said impure fluid through said weakly acidic cation exchange resin to remove said calcium ions, said magnesium ions and said bicarbonate ions, eluting a partially deionized acidic fluid;
b) passing said partially deionized acidic fluid continuously through said weakly basic anion exchange resin, eluting a deacidified fluid;
c) recovering said deacidified fluid;
d) regenerating said weakly basic anion exchange resin periodically by contacting said resin with a regenerant dosage of a combination of an alkali metal carbonate and an alkali metal bicarbonate, and regenerating said weakly acidic cation exchange resin periodically by contacting said resin with a regenerant dosage of citric acid; and then, e) repeating steps a) through d).
The partially deionized acidic fluid may have a pH of from about 3.0 to about 6.5; and the deacidified fluid may have a pH of from about 6.5 to about 7.5. The impure fluid may be industrial water or residential water. Moreover, in the method, the weakly acidic cation exchange resin and the weakly basic anion exchange resin may be layered in a single column, or each resin may be in a separate column.
For the practice of either method, the alkali metal carbonate may be sodium carbonate and said alkali metal bicarbonate may be sodium bicarbonate; a presently preferred combination is an alkali metal sesquicarbonate, such as sodium sesquicarbonate, potassium sesquicarbonate or a combination thereof; a presently preferred weakly basic anion exchange resin is an acrylate resin, although a styrenic weakly basic anion resin may also be utilized; and the resin may also be contacted said with a co-regenerant, a surfactant or a sequestering agent.
DETAILED DESCRIPTION OF THE INVENTION
Weakly Basic Anion Exchange Resins
A general description of ion exchange is found in
The Encyclopedia of Chemical Technology,
3rd Edition, John Wiley & Sons, New York, 1981, vol. 13, pages 678-705. Weakly basic anion exchange resins possess a primary, secondary, or most commonly, a tertiary amine functionality. Acrylic weakly basic resins constitute a subgroup of this type of ion exchange resin. Instead of the more common aromatic benzene ring linkage between the polymer backbone and the functionality, acrylic weakly basic resins utilize aliphatic amide linkages. These aliphatic linkages confer unique properties to the acrylic weakly basic resins. One such key property is pK
b
(the ionization constant). As the pK
b
increases, the basic strength of the anion exchange resin decreases, pK
b
values for the acrylic weakly basic resins measure 5.5 to 6.0, whereas values for styrenic and other weakly basic resins exceed 7.0. Thus, the acrylic weakly basic anion exchangers are sufficiently basic to form a salt with carbon dioxide (present in water as carbonic acid) but not with silica (present as silicic acid). Other weakly basic resins do not form salts with either common weak acid. In addition, the relatively higher basicity aids in the removal of humic acids during the deionization process as well as elution of same during the regeneration process.
The anionic exchange resins used for the practice of the methods disclosed herein are gel type AMBERLITE Acrylic Anion Exchange resins such as AMBERLITE IRA 67, available from Rohm & Haas, referred to as acrylate resins herein. St
Kunin Robert
Pennisi Nichole L.
Yarnell Peter A.
Graver Technologies, Inc.
Rockey, Milnamow & Katz L.t.d.
Zitomer Fred
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