Catalyst – solid sorbent – or support therefor: product or process – Regenerating or rehabilitating catalyst or sorbent – Gas or vapor treating
Reexamination Certificate
2001-09-21
2003-12-16
Bos, Steven (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Regenerating or rehabilitating catalyst or sorbent
Gas or vapor treating
C502S208000, C502S209000, C502S210000, C502S211000, C502S212000, C502S213000, C502S214000, C502S055000
Reexamination Certificate
active
06664206
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
This invention relates to a method for reactivating a catalyst for methacrylic acid preparation. More particularly, the invention relates to a method for reactivating a catalyst which is used in the occasion of methacrylic acid preparation through vapor-phase oxidation of methacrolein or vapor-phase oxidative dehydrogenation of isobutyric acid and whose activity is lowered (which catalyst may hereafter be referred to as deteriorated catalyst).
PRIOR ART
Many proposals have been made in the past concerning catalysts useful for methacrylic acid preparation through vapor-phase oxidation of methacrolein or vapor-phase oxidative dehydrogenation of isobutyric acid.
However, it is invariably found difficult for all of those known catalysts to stably maintain the catalytic activity over a prolonged period. From economical standpoint, on the other hand, it is desirable to reactivate the deteriorated catalysts to allow their repetitive use.
Hence, methods of regenerating deteriorated catalysts have also been proposed: e.g., a method comprising, after withdrawing the deteriorated catalyst from reaction tubes, treating it with a nitrogen-containing heterocyclic compound (Patent Publication Hei 4 (1992)-50062B1-JP) and a method comprising, after withdrawing the deteriorated catalyst from reaction tubes, treating it with aqueous ammonia and a nitrogen-containing heterocyclic compound, (Patent Publication Hei 7 (1995)-20552B1-JP) and the like. Those methods, however, consist of many steps such as (1) withdrawing the deteriorated catalyst from reaction tubes, (2) treating it in an aqueous medium, (3) if necessary, drying the treated catalyst, (4) shaping the resultant solid and (5) calcining the same, and hence cannot be regarded as industrially advantageous methods.
On the other hand, methods of reactivating the deteriorated catalyst within the reaction tubes have also been proposed, including: a method of treating the deteriorated catalyst with ammonia and water (Patent Publication Sho 54 (1979)-11272B1-JP); a method of treating with a nitrogen-containing compound such as nitric acid and nitrous acid (Patent Publication Sho 56 (1981)-91846A-JP); a method of treating with a gas containing at least 10 vol. % of steam (Patent Publication Sho 58 (1983)-156351A-JP); and a method of treating with a gas containing at least 0.2 vol. % of oxygen (Patent Publication Hei 6 (1994)-7685A-JP). According to these methods, however, not necessarily satisfactory results are guaranteed, although the treated, deteriorated catalysts do recover their activity to a certain extent.
Problems to be Solved by the Invention
The object of the present invention is to provide a method for efficiently reactivating a catalyst which is used in the occasion of methacrylic acid preparation through catalytic vapor-phase oxidation of methacrolein or catalytic vapor-phase oxidative dehydrogenation of isobutyric acid, which contains P and Mo, and whose activity level has dropped.
Means to Solve the Problem
Our extensive studies have found that such deteriorated catalysts could be effectively regenerated by treating them with a gas containing a nitrogen-containing heterocyclic compound. We have also discovered that the deteriorated catalysts could be very effectively regenerated, when they are treated with a gas which contains a nitrogen-containing heterocyclic compound and steam; or with a gas which contains a nitrogen-containing heterocyclic compound and another gas which contains steam. That is, we have discovered that the catalysts which were reactivated (hereafter referred to as reactivated catalysts) with a gas which contained a nitrogen-containing heterocyclic compound restored the activity level approximately equivalent to the original level and furthermore maintained the restored activity level stably over a prolonged term. This invention is completed based on those discoveries.
According to the present invention, therefore, a method of reactivating a catalyst for methacrylic acid production is provided, said catalyst being used in the occasions of producing methacrylic acid through vapor-phase oxidation of methacrolein or vapor-phase oxidative dehydrogenation of isobutyric acid, containing P and Mo and exhibiting reduced catalytic activity, which method is characterized by treating the catalyst with a gas which contains a nitrogen-containing heterocyclic compound.
According to the invention, furthermore, a method for reactivating a catalyst for methacrylic acid production is provided, said catalyst being used in the occasions of producing methacrylic acid through vapor-phase oxidation of methacrolein or vapor-phase oxidative dehydrogenation of isobutyric acid, containing P and Mo and exhibiting reduced catalytic activity, which method is characterized by treating the catalyst with a gas which contains a nitrogen-containing heterocyclic compound and steam; or with a gas which contains a nitrogen-containing heterocyclic compound and another gas which contains steam.
Embodiments of the Invention
Kind of the catalysts for methacrylic acid production, which are the objects of the reactivation method of the present invention, is not critical, so long as they are useful in the occasions of producing methacrylic acid through vapor-phase oxidation of methacrolein or vapor-phase oxidative dehydrogenation of isobutyric acid, and contain P and Mo. More specifically, heteropolyacid catalysts containing heteropolyacids having P—Mo or P—Mo—V as their essential constituents, or salts thereof may be named. In particular, the method of the invention is conveniently used for reactivating the heteropolyacid catalysts which are expressed by the following general formula (1):
P
a
Mo
b
V
c
X
d
Y
e
O
f
(1)
(wherein Mo, V, P and O are molybdenum, vanadium, phosphorus and oxygen, respectively; X stands for at least one element selected from the group consisting of potassium, rubidium, cesium and thallium; Y is at least an element selected from the group consisting of alkaline earth metals, copper, silver, arsenic, antimony, bismuth, iron, cobalt, nickel, chromium, manganese, tungsten, zirconium, niobium, titanium, zinc, tin, selenium, tellurium, germanium, palladium, rhodium, rare earth elements and silicon; and suffixes a, b, c, d, e and f denote atomic ratios of the respective elements, where when b is 12, a, c, d and e each is a value not more than 3 but not including 0 (zero), and f is a value determined by valencies and atomic ratios of those elements other than oxygen).
Those heteropolyacid catalysts which are expressed by the general formula (1) are known per se, and can be prepared by themselves accepted methods.
The reactivation method of the invention is used for regenerating above-described catalysts for methacrylic acid production, which are deteriorated for various reasons. Specific examples of the deteriorated catalysts include those whose activity level dropped because of exposure to high temperatures not lower than 450° C. for many hours under temperature control failure during the reaction; because of use in the reaction for a prolonged period while oxygen or methacrolein supply is suspended; or because of temperature control failure during the catalyst calcination, in consequence exposing the catalyst under preparation to high temperatures; those whose activity level gradually dropped during the continuous reaction over a long term; or those which are given a high temperature oxidation treatment for removing polymers deposited on the catalyst surface. In particular, the reactivation method of the invention is conveniently used for regeneration of the catalysts whose activity is gradually reduced during the continuous reaction over a prolonged term.
The nitrogen-containing heterocyclic compound to be used in the invention is subject to no critical limitation, and can be suitably selected from known nitrogen-containing heterocyclic compounds. In particular, at least one compound selected from pyridine, piperidine, piperazine, quinoline and derivatives thereof is convenien
Kasuga Hiroto
Shiraishi Eiichi
Bos Steven
Nippon Shokubai Co. , Ltd.
Sherman & Shalloway
Wright, Sr. William G.
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