Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs
Reexamination Certificate
1999-06-18
2001-04-17
Dunn, Tom (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
C502S011000, C502S079000, C502S400000
Reexamination Certificate
active
06218327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of cation-exchanged adsorbents. More particularly, the present invention relates to a single-step continuous ion exchange process for the production of cation-exchanged zeolite adsorbents.
2. Description of Related Art
Many techniques are known for making mixed-cation zeolites, such as calcium-lithium zeolites, by ion-exchange of existing sodium and/or potassium zeolites. At present, the processes for producing mixed cation zeolites require a complex and expensive sequence of successive ion-exchange steps in which ions present in the “raw” (i.e. untreated) zeolite are exchanged with other ions to produce a mixed cation zeolite product with the desired adsorbent properties. The prior art utilizes two basic methods for producing ion exchange materials containing mixed cations.
In a first method, the batches of raw (untreated) zeolite are exchanged with an aqueous solution containing the 35 ions which are to be introduced into the product zeolite. The ion composition of the aqueous solution, which is referred to in the art as “brine”, is adjusted to be in equilibrium with the ion concentration desired in the mixed-cation zeolite product.
In a second method, the slow and inefficient batch exchange steps are replaced with fast and continuous counterflow steps in which untreated zeolite is continuously countercurrently exchanged with a brine containing the mixed cations to be introduced into the product zeolite. The ion composition of the brine is again in equilibrium with the ion concentration desired in the mixed-cation zeolite product.
The prior art methods either require a multi-step procedure which utilizes extra equipment and is time consuming, or require large amounts of brine which wastes valuable cations. The prior art methods are illustrated in Chao U.S. Pat. No. 5,174,979 and Milton U.S. Pat No. 2,882,244.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a single step ion-exchange process for producing adsorbents, such 20 as mixed cation zeolites, which does not suffer from,one or more of the drawbacks of the above prior art processes.
Another object of the present invention is to provide an ion exchange process which permits reduced amounts of expensive cations to be utilized and reduces the loss of valuable cations in the spent brine solutions.
Yet another object of the invention is to provide a process for making mixed cation-exchanged zeolites having an improved (more uniform) cation distribution compared to those provided by prior art processes.
Another object of the present invention is to provide an ion exchange process which reduces both costs and processing time compared to the processes of the prior art.
These and other objects will be apparent to those skilled in the art in light of the following description, claims, and drawings.
SUMMARY OF THE INVENTION
The process of the present invention removes one or more ions from an ion-exchangeable adsorbent material, such as a zeolite, and replaces these ions with two or more desired ions in a single, continuous countercurrent ion-exchange step. A “raw” zeolite in which substantially all of the ion-exchangeable sites are occupied by one or more undesirable cations is thus converted to a product zeolite in which two or more desired cations have replaced most or practically all the undesirable cations. This is accomplished by ion exchange in a continuous counterflow contactor using a feed brine containing the desired cations at predetermined concentrations wherein the ion composition of the brine is not in equilibrium with the-product zeolite. The brine contains essentially stoichiometric amounts of the more strongly held cation(s) whereas the least strongly held cation is provided at an excess sufficient to overcome the unfavorable equilibrium and mass transfer resistance with respect to that cation.
An equilibrating step (and process stage) may optionally be provided to insure uniform cation distribution in the product zeolite. In addition, a washing step may optionally be provided to wash the zeolite following the equilibrating step (or following the exchange step, if there is no equilibration).
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Gomez-Vaillard et al, “Performance of Continuous Cyclic Ion-Exchange Reactors”, Chem. Eng. Sci., v36, n2, 1981, pp. 307-317 (abstract).
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Dunn Tom
Follett Robert J.
Praxair Technology Inc.
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