JP4889866B2 - Method for producing acrylonitrile - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to the production of acrylonitrile by ammoxidation of propylene using a fluidized bed reactor. More specifically, the present invention relates to a method for obtaining a stable acrylonitrile yield at a high level for a long period of time immediately after the start of the reaction by pretreating the catalyst in a fluidized bed reactor when starting the acrylonitrile production.
[0002]
[Prior art]
There is no specific proposal of a method for pretreating the catalyst in the reactor in advance at the start of acrylonitrile production by ammoxidation reaction of propylene. As a similar technique, a heat treatment for producing a catalyst and a heat treatment method for regenerating and activating a catalyst with reduced performance are known.
[0003]
Many catalysts for ammoxidizing propylene to produce acrylonitrile have been proposed. For example, Japanese Patent Publication No. 38-17967 proposes an oxide catalyst containing molybdenum, bismuth and iron, and Japanese Patent Publication No. 38-19111 proposes an oxide catalyst containing antimony and iron. Numerous improvement proposals have been made. Examples of these improvements include JP-A-49-101335, JP-B-51-33888, JP-A-52-125124, JP-B-53-18014, JP-A-57-180431, 58-38424, JP-A-59-204163, JP-B-61-43094, JP-B-61-26419, JP-A-4-118051, JP-A-7-289901, JP-A-7 JP-A-328441 and JP-A-10-43595 have been proposed. Although the specific manufacturing method of these catalysts differs individually, it manufactures through the following processes. A step of preparing a raw material slurry comprising various metal components which are catalyst constituents, a catalyst carrier component such as silica, a step of spray-drying the raw material slurry to obtain a spherical powder, a step of drying the powder, the drying It consists of the process of finally firing the powder. The final calcination process is usually performed at a high temperature in an air atmosphere at 500 ° C. to 950 ° C. for 1 hour to 50 hours, although the optimum conditions vary depending on the catalyst.
[0004]
As another similar technique, there is a method for regenerating a catalyst whose performance has deteriorated due to long-term use. As a method for regenerating the catalyst used for the ammoxidation reaction of propylene, there are a method of calcining the catalyst at a high temperature, a method of adding an active component in the catalyst, a method of adding a new component to the catalyst, and a combination of these methods. is there. As examples of specific proposals, Japanese Patent Laid-Open No. 54-62193 discloses a method of calcining a deteriorated iron / antimony catalyst in a temperature range of 600 ° C. to 950 ° C., and Japanese Patent Publication No. 63-33903 discloses a deteriorated molybdenum. Japanese Patent Publication No. 55-49541, Japanese Patent Application Laid-Open No. 7-289901 and Japanese Patent Application Laid-Open No. 11-319562 show a method of adding molybdenum to a deteriorated molybdenum-containing catalyst and finally calcination. ing. All of these finally calcinate the catalyst at a high temperature of 500 ° C. to 1000 ° C.
[0005]
According to the above-described conventional technology, the produced or regenerated catalyst is packed with a packaging material and packed in a drum can, or stored in a state of being directly packed in a metal container such as a hopper. The storage period can be as long as several months or more, although it cannot be generally stated. When such a catalyst is charged into a reactor and used for acrylonitrile production, the acrylonitrile yield is lower than expected for several months from the start of the reaction, Nevertheless, it may remain at a low level. Conventionally, no disclosure has been made regarding the solution of such problems.
[0006]
[Problems to be solved by the invention]
The present invention proposes a method for producing acrylonitrile for obtaining an acrylonitrile yield that is high immediately after the start of the reaction and is stable over time when producing acrylonitrile by ammoxidizing propylene in a fluidized bed reactor. .
[0007]
[Means for Solving the Problems]
As a result of diligent investigations to solve the problems, the present inventors have found that when starting acrylonitrile production by propylene ammoxidation reaction using a fluidized bed reactor, the fluidized bed reactor is used under specific conditions prior to the start of the reaction. By carrying out catalyst pretreatment, a high acrylonitrile yield was obtained immediately after the start of the reaction, and an industrially easy-to-implement method capable of obtaining stable reaction results over a long period of time was found and the present invention was achieved.
[0008]
That is, the present invention is a method for producing acrylonitrile by propylene ammoxidation reaction using a fluidized bed reactor, and the fluidized bed reactor is filled with a catalyst before starting the ammoxidation reaction, so that the oxygen concentration is 5 % to 30 %. The gist is a method for producing acrylonitrile in which the catalyst is heated in a temperature range of 300 ° C. to 450 ° C. for 1 hour to 100 hours in a% gas atmosphere.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The present invention is characterized in that a pretreatment is performed in which the catalyst is heated under specific conditions in the fluidized bed reactor before the start of the ammoxidation reaction, that is, before the raw material is supplied. In general, although the catalyst is subjected to a high-temperature calcination treatment in the final step of the production or regeneration / activation process, the cause of the remarkable effect obtained by the relatively low-temperature pretreatment of the present invention is unknown. However, it is considered that the catalyst was poisoned by the influence of moisture and atmospheric gas during storage, and the poisoning was removed by the method of the present invention.
[0010]
The heat treatment in the present invention is performed in an oxygen-containing atmosphere and gas flow with an oxygen concentration of 5 % to 30%. If the oxygen concentration is too low or too high, the effect is insufficient. The use of air is convenient as the oxygen-containing gas, but oxygen or air can be diluted with an inert gas or oxygen-enriched air can be used.
[0011]
The heat treatment temperature in the present invention is set to 300 ° C. to 450 ° C. When the temperature is 300 ° C. or lower, the effect is insufficient, and when the temperature exceeds 450 ° C., the effect is not particularly promoted, and it is difficult to carry out in a normal reactor and is not practical. The heat treatment time is 1 hour to 100 hours. If the heating time is 1 hour or less, the effect is insufficient, and if the heating is performed for a long time of 100 hours or more, there is a case where the effect does not increase and a bad influence such as a decrease in the catalyst surface area may occur. The heat treatment method is not particularly limited, a method of heating with a heater on the outer wall of the reactor, a method of introducing a gas heated through a heat exchanger into the reactor, an oxygen-containing gas in a high-temperature combustion gas Various methods such as a method of directly introducing a high-temperature gas mixed with an inert gas into the reactor, a method of introducing a combustible gas such as oxygen-containing gas and ammonia into the reactor, and burning the combustible gas in the catalyst layer Can be selected arbitrarily.
[0012]
In the method of the present invention, in order to efficiently perform the heat treatment, it is effective to consider the gas superficial velocity, and it is preferable that the range is 0.1 m / s to 1 m / s. When the gas superficial velocity is 0.1 m / s or less, the fluidization of the catalyst becomes poor in an industrial scale apparatus, so that a sufficient heat treatment effect may not be obtained. Further, when the gas flow rate is excessive, the amount of catalyst entrained and transported with the gas increases, so that the scattering loss of the catalyst tends to increase. The pressure in the heat treatment is not particularly limited, but a range of atmospheric pressure to 2 × 10 ⁵ Pa is preferably used.
[0013]
The catalyst used in the method of the present invention is not particularly limited, but is particularly effective for a catalyst system containing iron and antimony, or molybdenum and bismuth as essential components. Specific examples of these catalyst systems include those listed in the conventional literature described in the section “Prior Art”.
[0014]
In order to fully demonstrate the effects of the present invention, it is desirable to start the reaction by feeding raw material propylene and ammonia as soon as possible following the heat treatment. As a manufacturing method after the start of the reaction, a normal method conventionally used by the operator may be adopted. At the start of the reaction, for safety reasons, it is important to sufficiently reduce the oxygen concentration in order to prevent the formation of squealing gas at the inlet and outlet of the reactor. Specifically, US Pat. No. 4,386,228 and Ordinary methods disclosed in Kozoki Keizo, “Process System Design (Part 1)”, pp. 68-71 (Maruzen 1974) and the like can be used.
[0015]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The propylene conversion rate and acrylonitrile yield in the examples are defined by the following formulas.
Propylene conversion rate (%) = (number of moles of reacted propylene) / (number of moles of supplied propylene) × 100
Acrylonitrile yield (%) = (Mole number of acrylonitrile produced) / (Mole number of supplied propylene) × 100
[0016]
Example 1
The experimental formula shown in Example 1 of Japanese Patent Laid-Open No. 4-118051 is Fe ₁₀ Sb ₁₀ Mo _8.5 Bi _1.5 K _0.2 Ni _5.0 B _0.75 P _0.55 O _{75. A} catalyst of ₂₅ (SiO ₂ ) ₄₅ was prepared by the disclosed method. This catalyst is put in a polyethylene bag and stored in an air atmosphere at room temperature for 3 months. Then, 2.93 kg of this catalyst is collected and filled into a stainless steel fluidized bed reactor having a height of 3 inches and a height of 2 m. did. While introducing air heated to about 400 ° C. in the heat exchanger to the catalyst layer, the catalyst layer was heated by an electric heater provided on the outer wall of the reactor. At this time, after the catalyst layer temperature reached 300 ° C., the gas superficial velocity was maintained at about 0.15 m / s to 0.18 m / s, and the temperature was raised to 400 ° C. while performing heat treatment for 2 hours. After the catalyst layer temperature reached 400 ° C., propylene and ammonia were supplied to the catalyst layer. The reaction conditions were such that the temperature was 430 ° C., the molar ratio was air: ammonia: propylene = 9.5: 1.2: 1.0, the apparent contact time was 3.5 seconds, and the pressure was adjusted so that the reactor outlet was at atmospheric pressure. .
The reaction results were as follows: 10 hours after the start of the reaction, propylene conversion 98.5%, acrylonitrile yield 85.0%, 700 hours after the start of the reaction, propylene conversion 98.0%, acrylonitrile yield 84.8% there were.
[0017]
(Example 2)
Using the same catalyst and the same reactor as in Example 1, the heat treatment method of the catalyst layer is from 300 ° C. to 400 ° C. for 1 hour, and the gas superficial velocity is about 0.15 m / s to 0.18 m / s. The temperature was raised, and subsequently at 80 ° C. air 80 vol. %, Water vapor 20 vol. The ammoxidation reaction of propylene was carried out in the same manner as in Example 1 except that 1% of the mixed gas was circulated at a gas superficial velocity of 0.18 m / s.
The reaction results were: propylene conversion rate 98.3%, acrylonitrile yield 85.2% 10 hours after the start of the reaction, propylene conversion rate 97.7%, acrylonitrile yield 84.9% 700 hours after the start of the reaction. there were.
[0018]
(Comparative Example 1)
Using the same catalyst and the same reactor as in Example 1, the ammoxidation of propylene was carried out in the same manner as in Example 1 except that the temperature of the catalyst layer was increased from 300 ° C. to 400 ° C. in 0.5 hours. Reaction was performed.
The reaction results were as follows: 10 hours after the start of the reaction, propylene conversion 96.5%, acrylonitrile yield 83.0%, 700 hours after the start of the reaction, propylene conversion 96.8%, acrylonitrile yield 83.5% there were.
[0019]
(Comparative Example 2)
Using the same catalyst and the same reactor as in Example 1, the heat treatment method of the catalyst layer was maintained at a temperature of 300 ° C. to 400 ° C., and the gas superficial velocity was maintained at about 0.05 m / s to 0.06 m / s. However, the ammoxidation reaction of propylene was performed in the same manner as in Example 1 except that the temperature was raised in 2 hours.
The reaction results were as follows: 10 hours after the start of the reaction, propylene conversion 97.0%, acrylonitrile yield 83.3%, 700 hours after the reaction started, propylene conversion 97.8%, acrylonitrile yield 84.2% there were.
[0020]
【Effect of the invention】
According to the present invention, a high acrylonitrile yield can be obtained immediately after the start of the reaction, and a stable acrylonitrile yield can be easily achieved over time.

Claims (2)

A method for producing acrylonitrile by ammoxidation of propylene using a fluidized bed reactor, before the start ammoxidation, the oxygen concentration is 5% to 30% of the atmosphere by filling the catalyst into the fluidized bed reactor A process for producing acrylonitrile in which the gas superficial velocity is maintained in the range of 0.1 m / s to 1 m / s and the catalyst is heated while fluidizing in the temperature range of 300 ° C. to 450 ° C. for 1 hour to 100 hours . .   2. The process of claim 1, wherein the catalyst comprises iron and antimony or molybdenum and bismuth as essential components.