Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Patent
1997-08-27
1998-09-01
McKane, Joseph
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
C07C25300
Patent
active
058012664
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP96/00402 filed Feb. 22, 1996, WO96/26917, Sep. 6, 1996.
TECHNICAL FIELD
The present invention relates to a method for producing acrylonitrile by ammoxydation, more particularly to a method for facilitating recovery of acrylonitrile by efficiently removing high boiling point compounds (heavies) and the like in the process of quenching a reacted gas.
BACKGROUND ART
The method for producing acrylonitrile by ammoxydation has been improved in various ways since its success in industrialization, and it is said that the method has technically matured. Still, efforts have been made to improve unit consumption of raw materials and utility, and to reduce production cost by achieving production efficiency.
It is well known that reacted gas obtained by reacting raw materials contains by-products such as hydrocyanic acid, acetonitrile and aldehyde in addition to acrylonitrile when acrylonitrile is produced by ammoxydation. The by-products react with acrylonitrile in the presence of unreacted ammonia or react with one another; as a result, high boiling point compounds are produced. The high boiling point compounds cause not only reduction in the yield of acrylonitrile, the target product, but also clogging at various places in towers in the subsequent processes. Consequently, the by-products must be immediately separated from the reacted gas.
Conventionally, a method has been adopted for separating unreacted ammonia in the form of a salt and simultaneously removing other impurities and the by-products mentioned above by preliminarily cooling the reacted gas produced in a reactor, then transferring the cooled reacted gas to a quenching tower immediately, and washing and quenching the reacted gas with water containing acids such as sulfuric acid. As one of the conventional methods, there is proposed a method employing a multi-stage quenching tower to divide a quenching process into two steps or more, which comprises separating most of the unreacted ammonia in the form of a salt by contacting the water containing a sufficient amount of sulfuric acid to neutralize the unreacted ammonia and simultaneously condensing a part of the water vapor contained in the reacted gas in the first chamber, and condensing most of the residual water vapor in the second chamber (U.S. Pat. No. 3,649,179).
This method has succeeded in reducing the cost for separating and treating the salt because of its higher concentration of the resultant ammonium salt than that in the conventional methods. Yet, the gas introduced from the first quenching chamber to the second quenching chamber contains unreacted ammonia, high boiling point compounds, polymers and scattered catalysts which are not removed in the first quenching chamber. A liquid containing high boiling point compounds, polymers, scattered catalysts and an ammonium salt is transferred in the form of mist together with the gas. Therefore, the liquid discharged from the second quenching chamber contains these impurities. To recover acrylonitrile contained in the discharged liquid, impurities should be removed.
Heretofore, the impurities contained in the discharged liquid was removed in an acrylonitrile recovery process or a waste water column; however, the impurities clogged a recovery column, a stripper and reboilers and pipes when the discharged liquid was transferred to the acrylonitrile recovery process. A large quantity of steam is required to transfer the discharged liquid to a waste water column for recovery of acrylonitrile from the discharged liquid. Therefore, the method was not economical.
Further, in the method of the above U.S. patent, if the liquid discharged from the second quenching chamber is sent back to the first quenching chamber in order to decrease the content of high boiling point compounds and the like in the discharged liquid, the same effect will be exhibited as in the case that a gas is treated in a one-stage quenching tower. In other words, the effect of the two-stage quenching tower cannot be obtained. Accordingly, the problem
REFERENCES:
patent: 3649179 (1972-03-01), Ikeda et al.
Asahi Kasei Kogyo Kabushiki Kaisha
McKane Joseph
Murray Joseph
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