Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-10-10
2004-06-08
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C502S208000, C502S209000, C502S210000, C502S211000
Reexamination Certificate
active
06747172
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION PERTAINS
This invention relates to a method for preparing methacrylic acid. More detailedly, this invention relates to a method for preparing methacrylic acid by catalytically vapor phase oxidizing isobutane.
PRIOR ART
As to a method for preparing methacrylic acid via methacrolein by catalytically vapor phase oxidizing an unsaturated hydrocarbon or tertiary alcohol such as isobutene or tertiary butanol, various methods have been proposed and some of them are industrially adopted.
Also as to a method for preparing methacrylic acid directly by catalytic vapor phase oxidation of isobutane as a saturated hydrocarbon, reports have been made in several publications including Japanese Laid-open Patent Publication No. 55-62041. Many of the methods use a hetero poly acid catalyst containing silicon, phosphorus or arsenic as the hetero atom and molybdenum and/or vanadium as the poly atom as disclosed in Japanese Laid-open Patent Publication No. 62-132832, Japanese Laid-open Patent Publication No. 63-145249, etc. As catalysts other than hetero poly acid catalysts, Mo—V—Sb—Te—O catalysts (Japanese Laid-open Patent Publication No. 9-278680 and Japanese Laid-open Patent Publication No. 10-128112), P—V—Au and/or Ag catalysts (Japanese Laid-open Patent Publication No. 5-178774), etc. have been reported.
However, such prior catalysts have the disadvantage that when the conversion of isobutane is fixed at a low level, the selectivities of methacrylic acid and methacrolein are high to some degree, but when the conversion of isobutane is fixed at a high level, the selectivities of methacrylic acid and methacrolein are lowered, and by-products such as acetic acid and acrylic acid and combustion products such as carbon monoxide and carbon dioxide increase.
Problem to be Solved by the Invention
The object of the invention lies in providing a method for preparing methacrylic acid in high selectivity and high yields by vapor phase oxidizing isobutane in the presence of a catalyst using molecular oxygen or a molecular oxygen-containing gas.
Means for Solving the Problem
The present inventors have found that when, in preparing methacrylic acid by catalytic vapor phase oxidation of isobutane, a catalyst comprising a sparingly water-soluble salt of a hetero poly acid and a composite oxide containing phosphorus, molybdenum and vanadium is used, the above object can be accomplished, and have completed the invention based on the finding.
Thus, according to the invention is provided a method for preparing methacrylic acid which comprises, in preparing methacrylic acid by vapor phase oxidizing isobutane in the presence of a catalyst using molecular oxygen or a molecular oxygen-containing gas, using as the catalyst a catalyst comprising
(i) a sparingly water-soluble salt of a hetero poly acid and
(ii) a composite oxide containing phosphorus, molybdenum and vanadium.
MODE FOR CARRYING OUT THE INVENTION
The sparingly water-soluble of a hetero poly acid as component (i) of the catalyst of the invention means a salt of a hetero poly acid with at least one element selected from potassium, rubidium, cesium and thallium. The hetero poly acid is a generic term including typical hetero poly acids such as 12-molybdophosphoric acid, 12-tungstophosphoric acid, 12-molybdosilicic acid, 12-tungstosilicic acid, 12-molybdoarsenic acid and 12-tungstoarsenic acid; these hetero poly acids wherein part of molybdenum and/or tungsten is replaced with vanadium; or these hetero poly acids wherein molybdenum, tungsten or vanadium is coordinated in a mixed state. Such a sparingly water-soluble salt of a hetero poly acid can readily be prepared by adding to an aqueous solution of a hetero poly acid an aqueous solution containing at least one element selected from potassium, rubidium, cesium and thallium. In the invention, the thus obtained sparingly water-soluble salt of a hetero poly acid can be used in a slurry state as the obtained form or in a solid state after the separation of water from the slurry by a treatment such as filtration or centrifugation.
As the hetero poly acids, ones on the market can be used as such or after purification by a known method such as ether extraction, drying or recrystallization. It is also possible to use a hetero poly acid prepared by a known method, for example by acidifying with hydrochloric acid or the like an aqueous solution containing a sodium salt of a metallic acid such as molybdic acid or tungstic acid and sodium phosphate or sodium silicate or the like, heating the solution to make reaction occur, separating the reaction product with an ether as an etherified product from the resulting aqueous solution, and drying the product.
Among the sparingly water-soluble salts of hetero poly acids, preferably used are those having the element composition (but excluding oxygen) represented by the general formula (1), namely
A
a
B
b
MO
c
W
d
V
e
(1)
(wherein A represents a counter cation and is at least one element selected from potassium, rubidium, cesium and thallium, B represents a hetero atom of the hetero poly acid and is at least one selected from silicon, phosphorus and arsenic, Mo, W and V represent molybdenum, tungsten and vanadium respectively which are poly atoms of the hetero poly acid, a, b, c, d and e represent an atomic ratio of the respective elements and when b is 1, a is 3 to 4, c is 0 to 12, d is 0 to 12 and e is 0 to 3, and the total of c, d and e is 12.).
The other component (ii) of the catalyst of the invention is a composite oxide containing phosphorus, molybdenum and vanadium as indispensable components, and it can further contain as other optional components potassium, rubidium, cesium, thallium, magnesium, calcium, strontium, barium, manganese, chromium, iron, cobalt, nickel, copper, zinc, aluminum, tin, lead, antimony, bismuth, yttrium, zirconium, titanium, niobium, tantalum, rhodium, palladium, platinum, silver, lanthanum, cerium, praseodymium, neodymium, etc.
Among them, preferably used are composite oxides represented by the following general formula (2)
P
p
Mo
q
V
r
X
s
O
t
(2)
(wherein P, Mo, V and O represent phosphorus, molybdenum, vanadium and oxygen, respectively, X represents at least one element selected from potassium, rubidium, cesium, thallium, magnesium, calcium, strontium, barium, manganese, chromium, iron, cobalt, nickel, copper, zinc, aluminum, tin, lead, antimony, bismuth, yttrium, zirconium, titanium, niobium, tantalum, rhodium, palladium, platinum, silver, lanthanum, cerium, praseodymium and neodymium, and p, q, r, s and t represent an atomic ratio of the respective elements and when q is 12, p is 1 to 2, r is a number of 2 or less not including 0, s is 0 to 2 and t represents a number of oxygen atoms necessary for satisfying the valences of the respective elements.).
Preparation methods of the composite oxide are not particularly limited, and it can be prepared according to a conventional method. For example, it can be prepared by a method which comprises dissolving or dispersing such raw materials as mentioned below, heating the solution or dispersion to concentrate it to dryness. As phosphorus sources as a raw material, there can be mentioned orthophosphoric acid, pyrophosphoric acid, phosphorous acid, polyphosphoric acid, phosphorus pentoxide, phosphorus pentachloride, sodium phosphate, etc. As molybdenum sources, there can be mentioned molybdenum trioxide, molybdic acid, ammonium paramolybdate, sodium molybdate, etc. As vanadium sources, there can be mentioned, besides vanadium oxide, pentavalent, tetravalent or trivalent vanadium-containing compounds such as metavanadic acid or its salts, pyrovanadic acid or its salts, and vanadium oxyhalides. Hetero poly acids comprising phosphorus, molybdenum and/or vanadium such as molybdophosphoric acid and molybdovanadophosphoric acid can also be used as raw materials.
As raw materials of potassium, rubidium, cesium, thallium, magnesium, calcium, strontium, barium, manganese, chromium, iron, cobalt, nickel, copper, zinc, aluminum, tin, lead, antimony,
Motoyama Atsushi
Nakamura Isao
Nippon Shokubai Co. , Ltd.
Richter Johann
Sherman & Shalloway
Zucker Paul A.
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