Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-03-09
2001-09-18
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S312000, C502S313000, C502S315000, C502S316000, C502S317000, C502S318000, C502S319000, C502S321000
Reexamination Certificate
active
06291393
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a metal oxide catalyst for use in the production of acrylic acid by a vapor phase catalytic oxidation of a hydrocarbon having three carbon atoms such as propane and propylene.
BACKGROUND OF THE INVENTION
In general, acrylic acid is produced through a two-stage oxidation process comprising a step of catalytic reaction of propylene with oxygen to acrolein and a step of catalytic reaction of acrolein with oxygen to acrylic acid.
In recent years, on the other hand, for the reason that there is a difference in price between propane and propylene or the two-stage oxidation of propylene requires complicated steps, the production of acrylic acid using propane as a starting material through a one-stage process has been studied. Many proposals have been made on the catalyst for use in such a process. Representative examples of proposed catalysts include [V, P, Te]-based catalyst [as disclosed in “Catalysis Today”, 13, 679 (1992)], AgBiVMoO (as disclosed in JP-A-2-83348 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”)), BiMo
12
V
5
Nb
0.5
SbKO
n
(as disclosed in U.S. Pat. No. 5,198,580), [Mo, Te, V, Nb]-based catalyst (as disclosed in JP-A-6-279351), and [Mo, Sb, V, Nb]-based catalyst (as disclosed in JP-A-9-316023 and JP-A-10-137585).
Furthermore, JP-A-10-230164 discloses an improvement in the catalyst for the production of acrylic acid disclosed in the above cited JP-A-9-316023 and JP-A-10-137585, i.e., process for the production of [Mo, Sb, V, Nb]-based oxide catalyst involving a first step of reacting V
+5
and Sb
+3
at a temperature of 70° C. or higher in the presence of Mo
+6
in an aqueous medium and bubbling molecular oxygen or a gas containing molecular oxygen through the reaction solution during or after the reaction and a second step of mixing an Nb compound with the reaction mixture and then calcining the mixture.
However, the above proposed catalyst is disadvantageous in that the yield of acrylic acid as the desired product is insufficient or life of the catalyst itself is short. For example, the [Mo, Te, V, Nb]-based catalyst proposed in the above cited JP-A-6-279351 allows the production of acrylic acid in a high yield but is liable to evaporate Te, thereby causing deterioration of catalytic activity with the lapse of time. Further, the [Mo, Sb, V, Nb]-based catalyst disclosed in JP-A-9-316023 and JP-A-10-230164 still has further improvement in the yield of acrylic acid or the reproducibility of production of catalyst. Further, where those catalysts are used for fluidized bed reaction, it is required for the catalysts to exhibit excellent catalytic properties as well as excellent abrasion resistance. Those catalysts are still insufficient in this respect.
SUMMARY OF THE INVENTION
As a result of extensive studies to overcome the above-described problems, it has been found that a catalyst which exhibits an excellent abrasion resistance and gives a high yield of acrylic acid can be obtained by adding an aqueous solution of nitric acid or ammonium nitrate together with an Nb compound or a Ta compound at the second step in the process for the production of a metal oxide catalyst for the production of acrylic acid disclosed in the above cited JP-A-10-230164. The present invention has been completed based on this finding.
It is therefore an object of the present invention to provide a metal oxide catalyst which can give a high yield and exhibits an excellent abrasion resistance in the production of acrylic acid by a vapor phase catalytic oxidation of propane.
A first embodiment of the present invention is to provide a metal oxide catalyst comprising Mo, V, Sb, A (A represents Nb or Ta) and optionally other metals for the production of acrylic acid by a vapor phase catalytic reaction of propane, which is prepared through the following steps (1) and (2):
(1) Step of reacting V
+5
and Sb
+3
at a temperature of 70° C. or higher in the presence of Mo
+6
in an aqueous medium, and bubbling an oxygen-containing gas into the reaction mixture during or after the reaction; and
(2) Step of adding to the reaction product obtained in step (1) a solution containing a compound comprising A and an aqueous solution of nitric acid or ammonium nitrate, uniformly stirring these components, and then calcining the resulting mixture.
A second embodiment of the present invention is to provide the above-described metal oxide catalyst wherein bubbling the oxygen-containing gas into the reaction solution obtained in step (1) is replaced by addition of hydrogen peroxide to the reaction solution obtained in step (1).
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in more detail below.
In the step (1) of the present invention, the three reactants Sb
+3
, V
+5
and Mo
+6
undergo oxidation-reduction reaction at a temperature of 70° C. or higher in an aqueous medium. This reaction does not proceed unless heated at a temperature of 70° C. or higher. The reaction temperature is preferably in the vicinity of the boiling point of the aqueous medium. The reaction time is preferably from about 5 to 15 hours.
The main elementary reaction in the above reaction is represented by the following formulae (a) and (b):
V
+5
+Sb
+3
→V
+3
+Sb
+5
(a)
V
+3
+Mo
+6
→V
+4
+Mo
+5
(b)
When the oxygen-containing gas is blown into the reaction solution or hydrogen peroxide is added to the reaction solution during or after the reaction, Mo
+5
produced by the reaction (b) is reconverted to Mo
+5
, making it possible to appropriately control the concentration of Mo
+5
. This makes it possible to produce a catalyst giving a high yield of acrylic acid.
The V
+5
compound comprising V
+5
used in the above reaction is preferably ammonium metavanadate or vanadium pentaoxide. The Sb
+3
compound comprising Sb
+3
is preferably antimony trioxide or antimony acetate. The Mo
+6
compound comprising Mo
+6
is ammonium molybdate, molybdenum oxide or molybdic acid, and ammonium molybdate is preferably from the standpoint that it is water-soluble.
The preferred proportion of Mo
+6
compound, V
+5
compound and Sb
+3
compound used in the oxidation-reduction reaction is such that the atomic ratio of Mo, V and Sb constituting the desired catalyst corresponds to the following empirical formula:
MoV
i
Sb
j
wherein i and j each represent a number of from 0.01 to 1.5.
The suffixes i and j each preferably represent a number of from 0.1 to 1. If i and j in the above compositional formula each are below 0.01 or exceed 1.5, the conversion of propane and the selectivity of acrylic acid in the reaction for the production of acrylic acid are decreased.
The preferred proportion of V
+5
compound and Sb
+3
compound used in the oxidation-reduction reaction is from 0.3 to 1:1 in terms of atomic ratio of Sb
+3
to V
+5
. If the proportion of Sb
+3
is below 0.3, the selectivity of acrylic acid is lowered. On the other hand, if the proportion of Sb
+3
exceeds 1, the conversion of propane is lowered.
The preferred charged amount of the metal compound in the aqueous medium is from 3 to 30 parts by weight per 100 parts by weight of water as calculated in terms of total amount of three metal compounds. When the total amount of the three metal compounds exceeds 30 parts by weight, the V compound or Mo compound partly becomes insoluble, possibly making the oxidation-reduction reaction incomplete.
The progress of the reaction can be known by quantitatively analyzing pentavalent Sb in the reaction mixture, and then comparing the analysis with the initially charged amount of trivalent Sb. In some detail, a 1 N aqueous solution of oxalic acid in an amount of 10 times or more than that of the reaction solution was added to the reaction solution th
Furuta Madoka
Niizuma Hiroshi
Takahashi Mamoru
Tu Xinlin
Bell Mark L.
Hailey Patricia L.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Toagosei Co. Ltd.
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