Process for producing acrolein and acrylic acid

Details Process for producing acrolein and acrylic acid Process for producing acrolein and acrylic acid

2000-08-04

2003-10-14

Rotman, Alan L. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

C562S545000, C562S546000, C562S547000, C568S479000, C568S480000

Reexamination Certificate

active

06632965

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for producing acrolein and acrylic acid. More particularly, it relates to a process for producing acrolein and acrylic acid by the vapor-phase oxidation of propylene in the presence of a molybdenum-bismuth-iron-based oxide catalyst.
DESCRIPTION OF THE PRIOR ART
In producing acrolein and acrylic acid by the vapor-phase oxidation of propylene, a compound oxide catalyst containing molybdenum, bismuth and iron is usually used.
One disadvantage of this molybdenum-bismuth-iron-based compound oxide catalyst is that, when water vapor is present in the reaction system, the molybdenum component thereof tends to be sublimated and the sublimation of the molybdenum component is promoted especially at high temperatures. Moreover, in the case of exothermic reactions, such as the oxidation reaction of propylene, the catalyst bed tends to develop local areas having an abnormally high temperature (i.e., hot spots), which creates an environment in which the molybdenum component is more liable to sublimation. Furthermore, the sublimated molybdenum component tends to accumulate in areas having lower temperatures, leading to an increase in the pressure drop of the catalyst bed and hence a further rise in hot spot temperature.
In order to solve these problems, a variety of improvements in the molybdenum-bismuth-iron-based compound oxide catalyst or the process for producing acrolein and acrylic acid have been proposed. For example, Japanese Patent Laid-Open No. 113730/'80 discloses a process using two or more molybdenum-bismuth-iron-based compound oxide catalysts having different activities controlled by varying the content of an alkali metal (e.g., potassium or rubidium) wherein two or more axially disposed reaction zones of each reaction tube of a fixed-bed multitubular reactor are packed with the aforesaid catalysts in such a way that the activity increases from the gas inlet side of the reaction tube toward the gas outlet side thereof.
Problem to Be Solved by the Invention
In these conventional molybdenum-bismuth-iron-based compound oxide catalysts or processes for producing acrolein and acrylic acid, the problems have been solved to some extent. However, it is still desired to develop a more improved process for producing acrolein and acrylic acid with aid of a molybdenum-bismuth-iron-based compound oxide catalyst.
Accordingly, an object of the present invention is to provide a process for producing acrolein and acrylic acid by the vaporphase oxidation of propylene in the presence of molybdenum-bismuth-iron-based compound oxide catalysts wherein acrolein and acrylic acid can be stably produced in high yield for a long period of time.
Means for Solving the Problem
The above object of the present invention can be accomplished by a process for producing acrolein and acrylic acid by the vapor-phase catalytic oxidation of propylene with molecular oxygen or a molecular oxygen-containing gas in a flxed-bed multitubular reactor, which comprises
(a) using, as the catalysts therefor, compound oxide catalysts of the general formula
 Mo
a
W
b
Bi
c
Fe
d
A
e
B
f
C
g
D
h
O
x
  (I)
wherein Mo is molybdenum; W is tungsten, Bi is bismuth; Fe is iron; A is at least one element selected from the group consisting of cobalt and nickel; B is at least one element selected from the group consisting of phosphorus, antimony, boron, tin, cerium, niobium, lead, chromium and zinc; C is at least one element selected from the group consisting of alkali metals and thallium; D is at least one element selected from the group consisting of silicon, aluminum, titanium and zirconium; O is oxygen; a, b, c, d, e, f, g, h and x are the number of atoms of Mo, W, Bi, Fe, A, B, C, D and O, respectively; and when a is 12, b has a value of 0 to 5, c has a value of 0.1 to 10, d has a value of 0.1 to 10, e has a value of 1 to 20, f has a value of 0 to 5, g has a value of 0.001 to 3, h has a value of 0 to 30, and x has a value determined by the oxidation state of each element, and
(b) packing the catalysts in each reaction tube having two or more reaction zones disposed along its axis in such a way that the catalyst packed in the reaction zone on the gas outlet side has a lower 20 ratio of the Bi and/or Fe content to the Mo content than the catalyst packed in the reaction zone on the gas inlet side.
Detailed Description of the Preferred Embodiments
The molybdenum-bismuth-iron-based compound oxide catalysts of the general formula (I) which are used in the present invention are well known per se and may be prepared according to well-known processes.
The essential feature of the present invention lies in the fact that each of the reaction tubes of a fixed-bed multitubular reactor is packed with molybdenum-bismuth-iron-based compound oxide catalysts in a specified manner. That is, according to the present invention, each reaction tube having two or more reaction zones (usually two or three reaction zones) disposed along the axis of the tube is packed with two or more catalysts having different ratios of the bismuth and/or iron content to the Mo content (hereinafter referred to as “bismuth-iron proportion”) in such a way that the bismuth-iron proportion decreases from the gas inlet side toward the gas outlet side. For example, where each reaction tube has two reaction zones, two catalysts having different bismuth-iron proportions are prepared. Of these, the catalyst having a higher bismuth-iron proportion is packed in the reaction zone on the gas inlet side (hereinafter referred to as “the former-stage reaction zone”), and the catalyst having a lower bismuth-iron proportion is packed in the reaction zone on the gas outlet side (hereinafter referred to as “the latter-stage reaction zone”).
When the contents of constituent elements are expressed as atomic ratios, the catalysts used in the present invention may contain 0.1 to 10 of Bi and 0.1 to 10 of Fe per 12 of molybdenum, as defined by the general formula (I). Accordingly, in the practice of the present invention, it is necessary to prepare two catalysts having different bismuth-iron proportions within these limits. Of these, the catalyst having a higher bismuth-iron proportion must be packed in the former-stage reaction zone, and the catalyst having a lower bismuth-iron proportion must be packed in the latter-stage reaction zone.
When the bismuth-iron proportion (ie., the atomic ratio of bismuth and/or iron to 12 of molybdenum) for the catalyst packed in the former-stage reaction one (hereinafter referred to as “the former-stage catalyst) is denoted by M
1
, and the bismuth-iron proportion (i.e., the atomic ratio of bismuth and/or iron to 12 of molybdenum) for the catalyst packed in the latter-stage reaction zone (hereinafter referred to as “the latter-stage catalyst) is denoted by M
2
, M
1
and M
2
preferably satisfy the relationship represented by 1<M
1
/M
2
≦100, more preferably 1.1≦=M
1
,M
2
≦20, and most preferably 1.25≦M
1
/M
2
≦10.
If M
1
is equal to or less than M
2
(i.e., M
1
/M
2
≦1), it will be difficult to control the sublimation of the molybdenum component. On the other hand, if M
1
is excessively greater than M
2
(e.g., 100<M
1
/M
2
), the process will be disadvantageous in that the desired catalyst performance cannot be achieved, the reaction temperature will be raised, and the sublimation of the molybdenum component will be promoted.
Accordingly, in a preferred embodiment of the present invention, it is desirable to prepare the former-stage catalyst and the latter-stage catalyst so as to satisfy the relationship represented by 1<M
1
/M
2
≦100, and pack them in the former-stage reaction zone and the latter-stage reaction zone, respectively.
In the present invention, no particular limitation is placed on the ratio of the group A element content to the Mo content (hereinafter referred to as “the proportion of the group A elements”). However, in a preferred embodiment of the present invention, two catalysts having different proportions of the group A elements are

Affiliated with

Also associated with

Rating

Process for producing acrolein and acrylic acid does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for producing acrolein and acrylic acid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing acrolein and acrylic acid will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3160995