Process for producing catalyst

Details Process for producing catalyst Process for producing catalyst

2001-11-19

2004-08-17

Koslow, C. Melissa (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Phosphorus or compound containing same

C502S022000, C502S024000, C502S025000, C502S026000, C502S054000, C502S208000, C502S209000, C502S210000, C502S212000, C502S213000, C502S514000, C428S319100, C428S312800, C428S116000, C096S004000, C096S007000, C096S011000, C095S055000, C095S056000

Reexamination Certificate

active

06777369

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for producing a catalyst using a compound recovered from a used catalyst, as a material for elements constituting the catalyst to be produced.
BACKGROUND ART
A catalyst containing at least molybdenum, an A element (at least one element selected from the group consisting of phosphorus and arsenic) and an X element (at least one element selected from the group consisting of potassium, rubidium and cesium) can be used for production of methacrylic acid by gas phase catalytic oxidation of methacrolein, production of methacrylic acid by oxidative dehydration of isobutyric acid, and other purpose.
In JP-A-53-113790 and JP-A-63-130144 are described processes for producing a catalyst using, as a material, a compound obtained by treating, with ammonia solution or the like, a used catalyst having a composition such as mentioned above, which used catalyst has been used for production of methacrylic acid by gas phase catalytic oxidation of methacrolein.
However, the catalysts produced by the processes described in JP-A-53-113790 and JP-A-63-130144 are different in structure from virgin catalysts produced by an ordinary process and therefore have shown low catalytic performances in some cases.
DISCLOSURE OF THE INVENTION
Hence, in order to effectively utilize a used catalyst containing at least molybdenum, an A element (at least one element selected from the group consisting of phosphorus and arsenic) and an X element (at least one element selected from the group consisting of potassium, rubidium and cesium), the present invention aims at providing a process for producing a catalyst using, as a material, a compound containing at least molybdenum and said A element, which has been recovered from a used catalyst having a composition such as mentioned above.
The gist of the present invention lies in a process for producing a catalyst, which comprises dispersing, in water, a used catalyst containing at least molybdenum, an A element (at least one element selected from the group consisting of phosphorus and arsenic) and an X element (at least one element selected from the group consisting of potassium, rubidium and cesium), adding thereto an alkali metal compound and/or ammonia solution, then adjusting the resulting mixture to pH 6.5 or less to generate a precipitate containing at least said molybdenum and said A element, and using the precipitate as a material for catalyst-constituting elements.
According to the present invention, it is possible to produce a catalyst using, as a material, a compound which has been recovered from a used catalyst containing at least molybdenum, an A element and an X element and which contains at least molybdenum and the A element; thereby, the used catalyst can be utilized effectively.
The present invention is particularly useful in producing a catalyst of a formula (1) (shown later) for production of methacrylic acid by gas phase catalytic oxidation of methacrolein, using a material recovered from a used catalyst which was, before the use, a catalyst of the formula (1) for production of methacrylic acid by gas phase catalytic oxidation of methacrolein.
According to the present invention, in recovering the compound containing at least molybdenum and the A element, molybdenum and the A element can be recovered at high ratios; therefore, the used catalyst can be utilized effectively.
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the used catalyst containing at least molybdenum, an A element and an X element includes catalysts which have been used in, for example, production of methacrylic acid by gas phase catalytic oxidation of methacrolein or production of methacrylic acid by oxidative dehydrogenation of isobutyric acid. A catalyst for use in production of methacrylic acid preferably has a composition represented by the following formula (1):
A
a
Mo
b
V
c
Cu
d
D
e
X
f
Y
g
Z
h
O
i
  (1)
(wherein Mo, V, Cu and O are molybdenum, vanadium, copper and oxygen, respectively; A is at least one element selected from the group consisting of phosphorus and arsenic; D is at least one element selected from the group consisting of antimony, bismuth, germanium, zirconium, tellurium, silver, selenium, silicon, tungsten and boron; X is at least one element selected from the group consisting of potassium, rubidium and cesium; Y is at least one element selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum; Z is sodium and/or thallium; a, b, c, d, e, f, g, h and i are each the atomic ratio of each element; when b is 12, a=0.5 to 3, c=0.01 to 3, d=0 to 2, e=0 to 3, f=0.01 to 3, g=0 to 3, h=0 to 3, and i is the atomic ratio of oxygen necessary for satisfying the valency of each component other than oxygen).
The used catalyst containing at least molybdenum, an A element and an X element is first dispersed in water. Thereto is added an alkali metal compound and/or ammonia solution. The amount of the alkali metal compound and/or ammonia solution added may be such that the molybdenum, A element and X element are dissolved; however, the amount is preferably such that the resulting mixture has a pH of 8 or more, more preferably such that the mixture has a pH of 8.5 to 12. The alkali metal compound usable has no particular restriction as to the kind; however, there can be mentioned, for example, sodium hydroxide, potassium hydroxide, cesium hydroxide and sodium hydrogencarbonate, with sodium hydroxide being preferred particularly.
Next, to the mixture after addition of the alkali metal compound and/or ammonia solution is added an acid for pH adjustment to 6.5 or less. It is preferable that, prior to the pH adjustment, the insolubles in the mixture are removed by filtration or the like. As the acid added for pH adjustment, there can be mentioned, for example, hydrochloric acid, nitric acid and sulfuric acid, with hydrochloric acid and nitric acid being preferred particularly.
The material after pH adjustment is preferably kept for a given time for formation of a precipitate. The time of keeping is preferably about 0.5 to 24 hours, and the liquid temperature is preferably about normal temperature to 90° C. During the keeping, the material may be allowed to stand but preferably is stirred.
The precipitate formed by pH adjustment, i.e. the compound containing at least molybdenum and an A element is presumed, from the compositional analysis and X-ray diffractometry, to contain, as the main component, a Dawson type heteropolyacid salt having a central element (e.g. phosphorus) and molybdenum ratio of 2:18, or a mixture of a Keggin type heteropolyacid salt having a central element (e.g. phosphorus) and molybdenum ratio of 1:12 and a Dawson type heteropolyacid. As the adjusted pH is lower, the proportion of the Keggin type heteropolyacid salt is larger.
When the proportion of each element contained in the precipitate formed from the used catalyst, relative to the amount of each element contained in the used catalyst is defined as the recovery of each element, the recovery of each element varies depending upon the composition of the used catalyst, the amount of ammonium root in the mixture before pH adjustment, and the adjusted pH. In the case of, for example, a used catalyst having a composition of the above-mentioned formula (1), the A element recovered in the form of a heteropolyacid salt of Keggin type is mostly phosphorus. Meanwhile, the A element recovered in the form of a heteropolyacid salt of Dawson type is phosphorus and arsenic; however, when both of them are present, arsenic is recovered preferentially. Therefore, in a used catalyst having a composition containing both phosphorus and arsenic, the adjustment of pH is preferably made to 1.5 or less in order to recover phosphorus preferentially, and to 2 to 6.5 in order to recover arsenic preferentially. In determining the pH to be adjusted, it is desirable to consider the recoveries of individual elements including moly

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