Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-05-11
2002-06-04
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C502S205000, C562S532000, C562S537000, C568S471000, C568S479000
Reexamination Certificate
active
06399818
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
This invention relates to a process for producing unsaturated aldehydes and unsaturated carboxylic acids. More particularly, the invention relates to a process for vapor-phase catalytic oxidation of at least one starting compound selected from propylene, isobutylene, t-butanol and methyl-t-butyl ether (hereinafter these compounds may be referred to as “propylene and the like”) to produce corresponding unsaturated aldehydes and unsaturated carboxylic acids. When propylene is used as the starting compound, acrolein and acrylic acid are produced, and when isobutylene, t-butanol or methyl-t-butyl ether is used as the starting compound, methacrolein and methacrylic acid are formed.
CONVENTIONAL TECHNOLOGY
Many improved catalysts for producing unsaturated aldehydes and unsaturated carboxylic acids with high efficiency by vapor-phase catalytic oxidation reaction of propylene and the like were heretofore proposed. For example, Sho 50(1975)-13308A-JP (=GB 1,444,659A) and Sho 50(1975)-47915A-JP (=GB 1,444,659A) disclosed catalysts whose essential components were Mo, Bi, Fe, Sb, Ni, and at least one another element selected from K, Rb and Cs. Sho 64(1989)-56634A-JP (=EP 304,867A) taught catalysts whose essential components were Mo, Bi, Fe and at least an element selected from Ni and Co.; Sho 56(1981)-52013B-JP (=GB 1,330,074A), the catalysts essentially containing Mo, Bi and Fe and at least an additional element selected from Mg, Ca, Zn, Cd and Ba; and Sho 56(1981)-23969B-JP (=GB 1,390,271), catalysts essentially containing Mo, Bi and Fe, and at least one element selected from Group IIA compounds and Group IIB compounds of the periodic table.
Industrial scale production of unsaturated aldehydes and unsaturated carboxylic acids by vapor-phase catalytic oxidation reaction of propylene and the like is subject to a number of problems, one of which is occurrence of local abnormally high temperature spots (hot spots) in the catalyst layers. Because the vapor-phase catalytic reaction of propylene and the like is extremely exothermic, hot spots may occur in the catalyst layers to induce over-oxidation or the excessive heat generation at the hot spots may cause deterioration of the catalyst. In the worst case, a run-away reaction may be induced. In particular, where concentration of starting material or space velocity is increased to raise productivity of the object products, the excessive heat generation takes place to make stable production of the object products difficult.
Various methods have been proposed to control occurrence of such hot spots or the excessive heat generation at the hot spots. For example, methods in which the catalyst at the hot spots was diluted with inert substances [Sho 43(1968)-24403B-JP, Sho 53(1978)-30688B-JP (=U.S. Pat. No. 3,801,634) and Sho 51(1976)-127013A-JP (=GB 1,529,384A)]; methods in which ring-formed catalysts were used [Sho 62(1987)-36739B-JP (=U.S. Pat. No. 4,438,217) and Sho 62-36740B-JP (=U.S. Pat. No. 4,511,671)]; a method in which two or more reaction zones were provided in each reaction tube [Sho 51(1976)-127013A-JP (=GB 1,529,384A)]; a method in which plural catalysts, which were prepared to have different activity levels by varying the amount and/or kind of alkali metals therein, were filled in the reaction tubes in such a manner that the activity level rose from the reactant gas-inlet side toward the outlet side [Sho 63(1988)-38331B-JP (=U.S. Pat. No. 4,837,360)] were included among the proposals.
PROBLEM TO BE SOLVED BY THE INVENTION
However, those known methods have not completely solved the problems pertaining to the hot spots.
Accordingly, therefore, the object of the present invention is to provide a process for effectively inhibiting or controlling occurrence of hot spots or excessive heat generation at the hot spots to enable production of unsaturated aldehydes and unsaturated carboxylic acids at high yields.
MEANS TO SOLVE THE PROBLEMS
We have discovered, after extensive studies, that when plural shaped catalysts exhibiting different activity levels are prepared by varying: [I] content of inert component of the shaped catalysts; and [II] at least one of the factors (a) occupation volume of the shaped catalysts, (b) kind and/or amount of the alkali metal(s) in the shaped catalysts and (c) calcining temperature of the shaped catalysts; and the catalysts are filled in each of reaction tubes in such a manner that the catalytic activity level rises from the reactant gas inlet side toward the outlet side, occurrence of hot spots or excessive heat generation at the hot spots can be effectively controlled, and in consequence unsaturated aldehydes and unsaturated carboxylic acids can be produced at high yields.
Thus, according to the invention, a process for preparing unsaturated aldehydes and unsaturated carboxylic acids through vapor-phase catalytic oxidation of at least one starting compound selected from propylene, isobutylene, t-butanol and methyl-t-butyl ether with molecular oxygen or a molecular oxygen-containing gas, using a fixed bed shell-and-tube type reactor filled with shaped catalysts is provided, which is characterized in that plural shaped catalysts exhibiting different activity levels are prepared by varying at least one of the factors: [I] content of inert component of the shaped catalyst and [II] (a) occupation volume of the shaped catalyst, (b) kind and/or amount of the alkali metal(s) in the shaped catalyst, and (c) calcining temperature of the shaped catalyst; and which catalysts are filled in each of the reaction tubes in such a manner that the catalytic activity level rises from the reactant gas-inlet side of each reaction tube toward the outlet side.
The term, activity level, as used herein is determined based on the conversion of the starting compound (propylene and the like).
WORKING EMBODIMENTS OF THE INVENTION
The active components of the catalyst to be used in the present invention are not critical, so long as they are useful in vapor-phase catalytic oxidation reaction of propylene and the like, to produce the corresponding unsaturated aldehydes and unsaturated carboxylic acids. Whereas, complex oxides which are expressed by the following general formula (1) are particularly suitable:
Mo
a
W
b
Bi
c
Fe
d
A
e
B
f
C
g
D
h
O
x
(wherein Mo is molybdenum; W is tungsten; Bi is bismuth; Fe is iron; A is at least an element selected from cobalt and nickel; B is at least an element selected from phosphorus, antimony, boron, tin, cerium, niobium, lead, chromium and zinc; C is at least an element selected from alkali metal elements; D is at least an element selected from alkaline earth metal elements; and O is oxygen; a, b, c, d, e, f, g, h and x stand for atomic numbers of Mo, W, Bi, Fe, A, B, C, D and O, respectively; where a is 12, b is 0-5, c is 0.1-10, d is 0.1-10, e is 1-20, f is 0-5, g is 0.001-3, h is 0-5, and x is a numerical value determined by state of oxidation of each of the elements).
The complex oxides which are expressed by the general formula (1) are known, and can be prepared by heretofore known methods. More specifically, for example, Japanese Patent No. 2,659,839 (=U.S. Pat. No. 5,276,178) may be referred to.
The inert component to be used in the invention may be any that is inert to the reaction. For example, those generally used as inert carriers, such as silicon carbide, aluminum oxide (alumina), zirconium oxide (zorconia), titanium oxide (titania), silicon oxide-aluminium oxide (silica-alumina) and the like can be used. Of those, alumina and zirconia are conveniently used.
BET specific surface area of such inert substance desirably does not exceed 20 m
2
/g, preferably ranging 0.1-15 m
2
/g, inter alia, 0.5-10 m
2
/g. Where the specific surface area is large, CO and CO
2
formation increases to decrease yield of the object products. Average particle diameter of the inert substance desirably does not
Sento Tadashi
Tanimoto Michio
Nippon Shokubai Co. , Ltd.
Sherman & Shalloway
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