Catalyst – solid sorbent – or support therefor: product or process – Regenerating or rehabilitating catalyst or sorbent – Treating with a liquid or treating in a liquid phase,...
Reexamination Certificate
1999-03-22
2002-01-29
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Regenerating or rehabilitating catalyst or sorbent
Treating with a liquid or treating in a liquid phase,...
C502S022000, C502S028000
Reexamination Certificate
active
06342462
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel process for regenerating an adsorbent which is at least partially spent, the adsorbent comprising a solid carrier, preferably a resin or a molecular sieve, a reactive metal dispersed thereon, and a reaction product. The regeneration process comprises a) contacting the absorbent with a stripping solution at stripping conditions, thereby removing at least a portion of the reaction product and yielding a stripped adsorbent, and b) reactivating the stripped adsorbent at reactivation conditions with a solution containing a compound of the reactive metal.
BACKGROUND OF THE INVENTION
The economic attractiveness, or sometimes even the utter viability, of many adsorptive industrial chemical and petroleum refining processes depends greatly on the existence of a practical adsorbent regeneration process. Regenerative techniques are desirable because expenses associated with exchanging a spent adsorbent for a new charge, particularly when several thousands of pounds of material are involved, often far outweigh those associated with regeneration. In general, then, the major objective of regeneration processes is to prolong the useful life of an adsorbent through restoration of its activity. The steps to achieve such performance revival vary significantly and are usually developed only through careful research and experimentation.
For solid adsorbents having a reactive metal to selectively remove feed contaminants, the effectiveness of the reactive metal rests on its ability to form stable complexes with the undesired species. These complexes, or reaction products of the reactive metal and feed contaminants, remain fixed to the solid, accumulate during adsorptive service, and eventually interfere with adsorbent performance. Therefore, the regeneration of reactive metal-containing adsorbents requires, at least as an initial step, the removal or stripping of accumulated reaction products. In U.S. Pat. No. 4,088,737, this removal is achieved through subjecting the adsorbent to a high-temperature, hydrogen-rich gas stream. The adsorbent to which this procedure applies is a silver-exchanged zeolite used for the selective removal of iodine-containing contaminants from gas streams.
In further prior-art teachings related to iodine-containing compound adsorption using a solid adsorbent having a reactive metal dispersed thereon, a major subject of interest is in the purification of corrosive liquid feed streams. Most notable are iodine-compound contaminated commercial carboxylic acid products, primarily acetic acid streams, resulting from modern methanol carbonylation manufacturing methods. Considerable development efforts in acetic acid purification technology have focused on different types of solid adsorbents containing iodine-reactive metals such as silver, mercury, copper, lead, thallium, palladium or combinations of these metals known to react with iodine-containing compounds to form insoluble reactive metal compounds.
For example, in U.S. Pat. No. 4,615,806, the removal of iodine-containing impurities is achieved with a macroreticulated strong acid cation-exchange resin which is stable in the organic medium and has at least one percent of its active sites converted to the silver or mercury form, presumably by cation-exchange. Later disclosures point to the utility of several other types of resins, all of which require a reactive metal to achieve the required adsorption efficiency. Overall, therefore, the prior art teachings related to adsorbents suitable for iodine-containing compound removal from gas and liquid streams specify metal-exchanged zeolites and resins.
As noted in the aforementioned '737 patent, metal-exchanged zeolites used as adsorbents in iodine-containing compound removal processes can be stripped of accumulated reaction products using high-temperature gas streams. In contrast, the application of metal-exchanged resins for iodine-containing compound adsorption greatly restricts the range of acceptable stripping temperatures. This is due to decomposition, softening, loss of strength, or other detrimental structural changes resulting from thermal effects on resins.
The present invention provides a novel solution to address the regeneration of a wide variety of spent or partially spent metal-loaded solid adsorbents which overcomes detrimental effects of prior art techniques associated with high temperature exposure. The condition of an adsorbent being at least partially spent is characterized by its having, in addition to a solid carrier and a reactive metal dispersed thereon, a compound of the reactive metal, which is understood as the reaction product of the reactive metal and the adsorbed species. The regeneration process involves contacting the adsorbent with a stripping solution capable of removing reaction products formed during the adsorption step, followed by dispersing an additional amount of metal onto the adsorbent. The latter procedure is a reactivation step, which involves contacting the adsorbent, which has been stripped or depleted in at least some reactive metal following exposure to the stripping solution, with an aqueous reactivation solution of the reactive metal cation.
Applicant has found that stripping solutions such as sodium thiosulfate can be used to remove reaction products from an adsorbent without the need for elevated temperatures. More surprising is the fact that such solutions can remove these reaction products even though such compounds are insoluble in corrosive liquid media (e.g. acetic acid) with which they are in continual contact during adsorptive service. Furthermore, the stripping of these accumulated reaction products occurs without any corresponding deleterious effects on the solid carriers, whether they be resins containing functional groups, molecular sieves having ion-exchange sites within a microporous channel network, or other suitable materials known in the art.
Applicant has further found that, subsequent to stripping accumulated reaction compounds of the reactive metal from the partially spent adsorbent, a simple reactivation procedure is beneficial for restoring the reactive metal content of the adsorbent. This reactivation can be performed at conditions similar to those used when originally dispersing reactive metal onto the adsorbent during its preparation. Contacting the stripped adsorbent with an ion-exchange solution is therefore appropriate when the adsorbent is first prepared using ion-exchange to disperse the reactive metal.
Both steps of the regeneration process (stripping and reactivating) can be performed under mild temperatures and pressures. This two-step regeneration technique of the present invention provides essentially complete restoration of adsorbent performance.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a process for regenerating an adsorbent which is at least partially spent, the adsorbent comprising a solid carrier, a reactive metal dispersed thereon, and a reaction product of the reactive metal and a contaminant, the process comprising:
(a) stripping the adsorbent with a stripping solution at stripping conditions, thereby removing at least a portion of the reaction product and yielding a stripped adsorbent and an effluent stream containing the reaction product; and
(b) reactivating the stripped adsorbent with a reactivation solution of a compound of the reactive metal at reactivation conditions, thereby dispersing an amount of reactive metal onto the adsorbent.
In a particular embodiment the present invention is a process for regenerating an adsorbent which is at least partially spent, the adsorbent comprising a resin or a molecular sieve, a reactive metal selected from the group consisting of silver, mercury, copper, lead, thallium, palladium and mixtures thereof dispersed thereon, and a metal iodide reaction product of the reactive metal and a contaminant, the process comprising:
(a) stripping the adsorbent with an aqueous solution of an alkali metal compound of an anion selected from the group consis
Griffin Steven P.
Ildebrando Christina
Molinaro Frank S.
Tolomei John G.
UOP LLC
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