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
2001-04-03
2004-01-06
Silverman, Stanley S. (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,...
C502S027000, C502S029000, C502S211000, C562S535000
Reexamination Certificate
active
06673733
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
This invention relates to a method for regenerating heteropolyacid catalyst and method for producing methacrylic acid. More particularly, the invention relates to a method for regenerating heteropolyacid catalyst whose activity has been deteriorated due to, for example, prolonged use for catalytic vapor phase oxidation reaction; and also to a method for producing methacrylic acid through vapor phase oxidation or vapor phase oxidative dehydrogenation of methacrolein, isobutyl aldehyde and/or isobutyric acid in the presence of the regenerated heteropolyacid catalyst.
PRIOR ART
Heretofore, heteropolyacid catalyst whose chief component is a heteropolyacid composed of molybdophosphoric acid (phosphorus-molybdenum) or molybdovanadophosphoric acid (phosphorus-molybdenum-vanadium), or a salt thereof has been used for producing methacrylic acid through vapor phase oxidation of methacrolein, isobutyl aldehyde or isobutyric acid and the like.
It is normal for industrial scale vapor phase oxidation reaction to be conducted continuously over a prolonged period, and during which the catalyst used in the reaction is subject to severe thermal load. This induces undesirable physical and chemical changes in the catalyst and consequently deterioration of the catalyst progresses to gradually render continuation of the reaction difficult. Hence the deteriorated catalyst must be taken out of the reaction tube after a prescribed period of time and a newly prepared catalyst, be re-filled. The cost of the catalyst in that occasion incurs a heavy economical burden. This situation is same for production of methacrylic acid through vapor phase oxidation of methacrolein, isobutylaldehyde or isobutyric acid and the like, using a heteropolyacid catalyst.
It is therefore generally important from economical standpoint to regenerate the catalyst whose activity is reduced, and various proposals have been made for regeneration of deteriorated heteropolyacid catalyst. For example, Official Gazette of Patent Publication Hei 4(1992)-50062B1-JP describes a method for regenerating deteriorated catalyst by a treatment with a nitrogen-containing heterocyclic compound such as pyridine. Also Official Gazette of Patent Publication Hei 7(1995)-20552B1-JP (=U.S. Pat. No. 4,814,305) teaches a method of regenerating the deteriorated catalyst which contains phosphorus, molybdenum and alkali metal, by a treatment with an aqueous solution containing aqueous ammonia, amine and the like, followed by drying and calcination.
However, the cause of deterioration of heteropolyacid catalyst has not yet been made clear. Above-referenced Official Gazettes also contain no concrete disclosure about the cause of the deterioration. The invention of Hei 4-50062B1-JP, therefore, judges the end of its regeneration treatment by conducting the following three measurements of the regenerated catalyst: (1) X-ray diffraction measurement—as for deteriorated catalyst, diffraction lines attributable to molybdenum trioxide are found, which are not found with the same catalyst before deterioration (fresh catalyst). The regeneration is judged to be complete, when such diffraction lines disappear as the result of the regeneration treatment and the X-ray diffraction chart which is the same to that of the fresh catalyst is obtained; (2) BET specific surface area measurement—a deteriorated catalyst has a specific surface area reduced to about 60% of that of the fresh catalyst. When it recovers to approximately the same level to that of the fresh catalyst as the result of the regeneration treatment, the treatment is judged to have been completed; and (3) activity level measurement—when a deteriorated catalyst comes to show equivalent performance in the reaction to that of the fresh catalyst in consequence of the regeneration treatment, the treatment is deemed to be complete. The invention of Hei 7-20552B1-JP (=U.S. Pat. No. 4,814,305) also confirms completion of the regeneration based on similar measurements as above.
PROBLEMS TO BE SOLVED BY THE INVENTION
As above, reduction in the costs for catalyst notably contributes to cut down the production costs, and development of a new regeneration method which can substantially improve those heretofore known methods is in demand. Thus, as to heteropolyacid catalyst also a method for regenerating deteriorated catalyst with high efficiency is desired, which enables the deteriorated catalyst to exhibit approximately equivalent activity to that of the fresh catalyst and furthermore to maintain that activity for a long period.
Accordingly, therefore, one of the objects of the present invention is to provide a method for regenerating a deteriorated heteropolyacid catalyst to one having the same composition with that of the fresh catalyst.
Another object of the invention is to provide a method for regenerating a deteriorated heteropolyacid catalyst to one having a different composition from that of the starting fresh catalyst, i.e., a method for preparing a new heteropolyacid catalyst, using the deteriorated heteropolyacid catalyst as the starting material.
Still other object of the invention is to provide a method for preparing methacrylic acid through catalytic vapor phase oxidation of methacrolein, isobutylaldehyde and/or isobutyric acid, using the catalyst which is regenerated by either of the above methods.
MEANS TO SOLVE THE PROBLEMS
We have found that the causes for deterioration of heteropolyacid catalysts after prolonged use are: (1) of the components constituting them, particularly those heteropolyacid-constituting components such as phosphorus, molybdenum and vanadium scatter and are lost, and in consequence composition notably changes from that of the fresh catalyst; (2) specific surface area is reduced; and (3) a part of the heteropolyacid structure is collapsed. We have accordingly pursued studies on replenishment of the scattered and lost heteropolyacid-constituting elements into the deteriorated catalyst, to discover that the disappeared heteropolyacid-constituting elements can be effectively replenished by treating the deteriorated catalyst in the presence of a nitrogen-containing heterocyclic compound under the conditions wherein ammonium ions and nitrate anions are present at a specific ratio; that the so obtained regenerated heteropolyacid catalyst has approximately the same specific surface area to that of the fresh catalyst; that X-ray diffraction chart of the regenerated heteropolyacid catalyst is approximately the same to that of the fresh catalyst, indicating recovery of the collapsed heteropolyacid structure; and that a catalyst, which is deteriorated because of partial collapse of its heteropolyacid structure under excessive thermal load although retaining its composition unaffected, can also exhibit the catalytic performance and have the structure regenerated by a similar treatment. The present invention is completed based on these discoveries.
Thus, according to the invention, as a method for regenerating a deteriorated catalyst whose activity attributable to a heteropolyacid catalyst containing heteropolyacid composed of molybdophosphoric acid and/or molybdovanadophosphoric acid or salt(s) thereof is reduced, a method is provided which is characterized by mixing the deteriorated catalyst with a nitrogen-containing heterocyclic compound under such conditions that ammonium ions and nitrate anions are present at such a ratio that the total amount of the ammonium ions present per mol of the total amount of the nitrate anions does not exceed 1.7 mols, drying the mixture and calcining the same.
According to the invention, furthermore, a method for preparation of methacrylic acid through catalytic vapor phase oxidation of methacrolein, isobutyl aldehyde and/or isobutyric acid is provided, said method being characterized by use of a catalyst which is regenerated by the above-described method.
The regeneration method of the invention is useful for regenerating heteropolyacid catalysts whose activity has been deteriorated for various reasons.
Fukumoto Naohiro
Kasuga Hiroto
Kimura Naomasa
Shiraishi Eiichi
Nippon Shokubai Co. , Ltd.
Sherman & Shalloway
Silverman Stanley S.
Strickland Jonas N.
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