Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-05-23
2003-05-13
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S532000, C562S535000, C562S546000, C502S302000, C502S309000, C502S318000, C502S321000, C502S345000, C502S350000
Reexamination Certificate
active
06563000
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
This invention relates to a process for producing acrylic acid by vapor-phase catalytic oxidation of acrolein or an acrolein-containing gas with molecular oxygen or a molecular oxygen-containing gas, using a fixed bed shell-and-tube reactor.
CONVENTIONAL TECHNOLOGY
A large number of proposals have been made in the past concerning the catalysts to be used in the occasions of preparing acrylic acid through vapor-phase catalytic oxidation of acrolein or acrolein-containing gas. For example, Official Gazettes of Patent Publications, Sho 41 (1966)-1775B1 disclosed catalysts comprising molybdenum and vanadium; Sho 44 (1969)-26287B1 disclosed those comprising molybdenum, vanadium and aluminium; Sho 50 (1975)-25914B1, those comprising molybdenum and vanadium, which are prepared by a process characterized in that vanadyl oxalate is caused to be present at the time of the catalyst preparation; and Sho 57 (1982)-54172B1, those comprising molybdenum, vanadium, titanium and optionally at least an element selected from the group consisting of iron, copper, cobalt, chromium and manganese. Of these catalysts, some do attain considerably high level of acrylic acid yield from industrial standpoint, but industrial production of acrylic acid using these catalysts is still subject to a number of problems.
One of the problems is occurrence of localized abnormally high temperature zone (hot spot) in the catalyst layer. For example, in industrial scale production, productivity of the object product, i.e., acrylic acid, must be raised, and generally such means as increasing concentration of starting acrolein or space velocity are adopted to achieve this purpose. When such means is adopted, however, the reaction conditions come to be considerably restricted, because the involved vapor-phase catalytic reaction is extremely exothermic and under the heavy-load operative condition, the temperature at the hot spot rises with increase in the reaction amount of acrolein. In consequence, over-oxidation takes place to reduce the yield and accelerate thermal deterioration of the catalyst, in the worst case even causing run-away reaction.
For controlling formation of a hot spot or abnormal accumulation of heat at the hot spot, acrolein concentration in the starting material may be dropped or the space velocity may be decreased. However, such means lower the productivity and are economically disadvantageous. Also as another means diameter of reaction tubes may be made small to improve heat-removing efficiency, but such is subject to limitations incurred in industrial production and to the disadvantage of high reactor cost.
As to means for keeping hot spot temperature low, a number of proposals have been made besides those stated above. For example, Official Gazettes of Patent Publications, Sho 53 (1978) 30688B1 disclosed a method of diluting the catalyst layer at the gas-inlet side of the reactor with an inert substance; and Hei 7 (1995)-10802A1 proposed a method of sequentially increasing the carried ratio of catalytically active substance, from the gas-inlet side toward the gas-outlet side of the reactor. However, in the former method, it requires strenuous effort to uniformly mix the inert substance for dilution with catalyst, and it is not always possible to fill the mixture in the reaction tubes, maintaining the uniformly mixed state, which render the method still unsatisfactory. In the latter method, it is not necessarily easy per se to control the carried ratios of catalytically active substance. Furthermore, the catalysts useful therefor are limited to those carrier-supported type, i.e., to those in which catalytically active components are carried on inert carriers, and the catalytically active component by itself, as compression-molded or tabletted, cannot be used. A still further problem common between the two methods is that the gas-inlet side catalyst deteriorates faster than the catalyst at the gas-outlet side because the amount of the catalytically active substance at the gas-inlet side is less than that at the gas-outlet side, and in consequence continuation of the reaction over prolonged period while maintaining a high yield may become impossible.
Therefore, to control the heat accumulation at the hot spot is very important for industrial production of acrylic acid at high yields as well as for enabling stable operation over prolonged periods, inhibiting catalyst deterioration. It is of particular importance to prevent accumulation of heat at the hot spot where molybdenum-containing catalysts are used, because molybdenum component readily sublimes.
Accordingly, therefore, the object of present invention is to provide a means for solving this problem.
MEANS FOR SOLVING THE PROBLEM
We have made concentrative studies with the view to solve the above problem and discovered that the above object can be accomplished by filling the reaction tubes in a fixed bed shell-and-tube reactor to be used for the reaction with catalyst following a specific design, i.e., by using plural kinds of catalysts having different activity levels and filling the reaction tubes with them as arranged in such a manner that the catalytic activity should increase from the gas-inlet side of the reaction tubes toward the gas-outlet side. Thus the present invention is completed.
Thus, according to the present invention, a process for producing acrylic acid by vapor-phase catalytic oxidation of acrolein or an acrolein-containing gas with molecular oxygen or a molecular oxygen-containing gas using a catalyst-filled fixed bed shell-and-tube reactor is provided, which process is characterized by providing plural reaction zones in each reaction tube in said fixed bed shell-and-tube reactor, by dividing inside of each of said tubes in the axial direction thereof, and filling the plural reaction zones with plural catalysts of different activity levels in such a manner that the activity level rises from the gas-inlet side of each reaction tube toward the gas-outlet side thereof.
WORKING EMBODIMENT OF THE INVENTION
The starting material used in the present invention is acrolein or acrolein-containing gas. As such, acrolein-containing gas produced upon catalytic vapor-phase oxidation of propylene can be used as it is, or the acrolein isolated therefrom may be used upon optional addition of oxygen, steam and other gas(es).
The catalysts used in the present invention are complex oxides whose essential components are molybdenum and vanadium and which are expressed by the following general formula (1)
Mo
a
V
b
W
c
Cu
d
A
e
Q
f
R
g
D
h
O
i
(I)
(wherein Mo is molybdenum; V is vanadium; W is tungsten; Cu is copper; A is at least an element selected from the group consisting of zirconium, titanium and cerium; Q is at least an element selected from a group consisting of magnesium, calcium, strontium and barium; R is at least an element selected from the group consisting of niobium, antimony, tin, tellurium, phosphorus, cobalt, nickel, chromium, manganese, zinc and bismuth; D is at least an element selected from alkali metals; and O is oxygen; and a, b, c, d, e, f, g, h and i represent atomic ratios of Mo, V, W, Cu, A, Q, R, D and O, respectively, in which where a is 12, 1≦b≦14, 0<c≦12, 0<d≦6, 0≦e≦10, 0≦f≦3, 0≦g≦10 and 0≦h≦5, and i is a numerical value determined by degree of oxidation of each of the elements).
These catalysts can be prepared by any methods which are generally practiced for preparing this type of catalysts. Starting materials to be used for preparing those catalysts are subject to no critical limitation, and ammonium salts, nitrates, carbonates, sulfates, hydroxides, oxides and the like of those metal elements, which have been generally used are useful. Compounds each containing plural metal elements may also be used.
Plural catalysts which are represented by general formula (I) and have different activity levels can be easily prepared by varying kind(s) and/or amount(s) of the D group elements in said general formula (I). More specifi
Nakamura Daisuke
Tanimoto Michio
Yunoki Hiromi
Nippon Shokubai Co. , Ltd.
Price Elvis O.
Richter Johann
Sherman & Shalloway
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