Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-08-03
2002-10-08
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06462232
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a production process for acrylic acid. More specifically, the present invention relates to a process for producing acrylic acid stably at a high yield over a long period of time in subjecting acrolein or acrolein-containing gas to vapor phase oxidation with an oxidizing catalyst to produce acrylic acid.
RELATED ART
Acrylic acid is industrially produced on a large scale by a catalytic vapor phase oxidation of acrolein. In this case, acrolein-containing gas obtained by subjecting propylene to vapor phase oxidation with an oxidizing catalyst containing molybdenum and bismuth as essential components is generally used for a reaction raw material as it is or by adding air and steam thereto. Accordingly, acrylic acid is usually produced by so-called two-step reaction comprising a former step for subjecting propylene to catalytic vapor phase oxidation to form acrolein and a latter step for subjecting acrolein-containing gas obtained in this former step to catalytic vapor phase oxidation to produce acrylic acid.
In the two-step reaction described above, however, the acrolein-containing gas obtained in the former step has a high reactivity to bring about an after-reaction at a high temperature, and not only acrolein is oxidized to carbon monooxide and carbon dioxide, but also sudden heat generation and a change in the volume are caused, so that there is a problem in terms of safety. Accordingly, the acrolein-containing gas obtained in the former step is quickly cooled down to a safe temperature at which the after-reaction does not take place.
Accordingly, the acrolein-containing gas fed to the latter step has a lower temperature than the reaction temperature or is heated up to the reaction temperature at most if heated again by pre-heating. The reasons thereof are not only to prevent, as described above, the after-reaction of acrolein but also because of the risk that an introduction of the acrolein-containing gas having a higher temperature than the reaction temperature makes it impossible to sufficiently control the reaction and therefore causes an abnormal reaction such as a run-away reaction.
Disclosed in Japanese Patent Application Laid-Open No. 229984/1993 is an improved reaction temperature program for the purpose of elevating a conversion of acrolein and a selectivity of acrylic acid. It is described therein that acrolein-containing gas is pre-heated to a temperature which is higher by 0 to 20° C. than an inlet temperature of a reaction layer and then introduced into the reaction layer. However, it is an essential requisite in this process that a temperature of the second reaction zone at an outlet side of the reaction layer is lowered than a temperature of the first reaction zone at an inlet side and the reaction temperature is lowered by 5 to 40° C.
PROBLEMS TO BE SOLVED BY THE INVENTION
With respect to a production of acrylic acid from acrolein, it has been a continuous research subject for technicians still now in the technical field concerned to enhance the yield of acrylic acid and lower the product cost thereof. The process described in Japanese Patent Application Laid-Open No. 229984/1993 described above is not yet sufficiently satisfactory.
Thus, an object of the present invention is to provide an improved process for producing acrylic acid from acrolein stably at a high yield over an extended period of time.
MEANS FOR SOLVING THE PROBLEMS
As described above, in the conventional process, the acrolein-containing gas fed to the latter step has a lower temperature than the reaction temperature or is heated up to the reaction temperature at highest if heated again by pre-heating, and therefore the catalyst in the vicinity of a gas inlet in the catalyst layer does not sufficiently display an oxidation function thereof. In other words, the above catalyst layer fulfills a function only as a preheating layer for heating the gas up to the reaction temperature. Intensive investigations continued by the present inventors paying attentions to the above matter have resulted in finding that if acrolein-containing gas is introduced into the catalyst layer at a higher temperature than the reaction temperature, the whole catalyst layer is effectively utilized and the yield of acrylic acid from acrolein is raised and that this rise in the yield of acrylic acid is more effectively obtained by controlling the temperature of the reaction layer so that it becomes higher from the inlet side of the gas to the outlet side.
Thus, according to the present invention, provided is a process for subjecting acrolein or acrolein-containing gas to catalytic vapor phase oxidation to produce acrylic acid, characterized by controlling the reaction so that the following equations (1) and (2) are satisfied:
1° C.≦T
0
−T
1
≦15° C. (1)
T
1
<T
2
(2)
wherein T
0
represents a temperature of acrolein or the acrolein-containing gas in an inlet of a catalyst layer; T
1
represents a temperature in an inlet part of the catalyst layer; and T
2
represents a temperature in an outlet part of the catalyst layer.
EMBODIMENT OF THE INVENTION
Either acrolein obtained by organic synthesis or acrolein-containing gas obtained by subjecting propylene to catalytic vapor phase oxidation in, for example, a two-step reaction may be used for a starting material used in the present invention. This acrolein-containing gas includes gas obtained by adding thereto, if necessary, oxygen (air), steam and substantially inert gas and gas obtained by separating acrolein and then adding thereto oxygen (air), steam and substantially inert gas. For the sake of convenience, they are hereinafter called generically acrolein-containing gas to explain the present invention.
FIG. 1
is a schematic diagram for explaining the temperature (T
0
) of the acrolein-containing gas in the inlet of the catalyst layer, the temperature (T
1
) in the inlet part of the catalyst layer and the temperature (T
2
) in the outlet part of the catalyst layer, wherein 1 represents a catalyst-filled layer, and 2 represents a heat transfer medium surrounding the catalyst-filled layer.
The temperature (T
1
) in the inlet part of the catalyst layer and the temperature (T
2
) in the outlet part of the catalyst layer mean respectively the temperatures of the heat transfer media adjacent to the inlet part of the catalyst layer and the outlet part of the catalyst layer. The inlet part of the catalyst layer and the outlet part of the catalyst layer mean respectively areas falling in a range of 200 mm from the inlet end of the catalyst layer and the outlet end of the catalyst layer, and the temperatures of the heat transfer media adjacent thereto mean the average temperatures of the heat transfer media in these areas.
The present invention is characterized by that the temperature (T
0
) of the acrolein-containing gas in the inlet of the catalyst layer is elevated by 1 to 15° C., preferably 2 to 10° C. higher than the temperature (T
1
) in the inlet part of the catalyst layer (T
0
−T
1
=1 to 15° C., preferably 2 to 10° C.) and that the temperature (T
2
) in the outlet part of the catalyst layer is elevated higher, preferably 1 to 10° C. higher than the temperature (T
1
) in the inlet part of the catalyst layer (T
1
<T
2
, preferably T
2
−T
1
=1 to 10° C.).
If T
0
−T
1
is lower than 1° C., the sufficiently high yield of acrylic acid is not obtained, and if it exceeds 15° C., the yield of acrylic acid is rather reduced. Further, in the case of T
1
≧T
2
, the sufficiently high yield of acrylic acid is not obtained.
A process for producing acrylic acid from propylene according to a two-step method comprises usually a former step in which propylene is subjected to vapor phase oxidation in the presence of an oxidation catalyst to produce acrolein-containing gas, a cooling step in which the acrolein-containing gas fed from the former step is quenched to prevent an after reaction of acrolein and a latter step in which the acrolein-containing gas is subjected t
Hironaka Hideyuki
Nakamura Daisuke
Tanimoto Michio
Deemie Robert W.
Geist Gary
Nippon Shokubai Co. , Ltd.
Sherman & Shalloway
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